April 1, 2019 - Intermediate-Term Weather Report - April Update

Written by Sig Silber

This is not an April Fools joke but might just as well be as NOAA has significantly changed their forecast for April just 10 days after they made their Early Outlook forecast. The level of change is somewhat disturbing. Perhaps “April is the Cruelest Month” for Meteorologists. If you choose to believe the forecast, April will be warm and mostly wet with large areas that have normal precipitation.

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Some Housekeeping: On March 23, 2019 we published our 15 Month Four-Season Outlook which you can access here. This report updates the Early April Outlook from that report. We published our now weekly Weather Impacts on the Economy formerly called the Drought and Agriculture Report March 28, 2019 and that can be accessed here. We also publish a Severe Weather Live Report which can be accessed here. If we forget to update the link to the most recent issue of any of our weather articles, you can find it in the Weather Directory. Remember if you leave this page to go to links or if you have clicked to enlarge a graphic, in order to get back you need to hit the return arrow usually located on the left of your URL box on the upper left of the screen. Also most of the small graphics are designed to become full size when you click on them. If that does not work, an alternative way to view the larger graphics is to right click and then hit “view image”. That should always work if I set it up correctly.

Now let us address the NOAA Update of the April, 2019 Forecast.

A note about terminology; the deviations from climatology/normal are color coded but also labeled “A” for more than (above) normal and “B” for less than (below) normal. The area designated EC means Equal Chances of being more or less than normal. In the Short Term forecasts, NOAA has switched from using EC to N for Normal. For most purposes, EC and N can be considered to mean about the same thing. “N” implies a bit more certainty that the variation from Normal/Climatology will be small compared to “EC”.

We will compare the NOAA Early Outlook for April, 2019 with the newly issued update.

First Temperature:

Early Outlook Temperature

Updated Temperature Outlook

This is a pretty big change for 10 days. Where did the cool anomaly go?

That is why I am also showing the Week 3 – 4 Forecast Issued last Friday.

This pretty much explains the change of mind by NOAA about April. It was in the cards last Friday.

To make it easier for the reader, I have also shown the Week 3 – 4 and full month forecasts side by side.

You can see how the Week 3 – 4 Forecast has impacted the full month forecast.

Now switching our focus to precipitation:

Early Outlook Precipitation

Updated Precipitation

Any resemblance to the prior forecast is totally coincidental.

I will also show the Week 3 – 4 Precipitation forecast that was issued last Friday.

You can see the westward shift here.

Here I show them side by side.

We will address this again later but I have questions about the location of the dry anomaly in the full month forecast.

Here is the full NOAA discussion released with the April Update. It is worth reading. I am also showing the discussion released last Friday with the update of Weeks 3 and 4.

Discussion Released March 31 with the Updated April Forecast

Slightly Earlier March 29 discussion of the Week 3 – 4 Forecast

30-DAY OUTLOOK DISCUSSION FOR APRIL 2019

The updated April 2019 outlook takes into account the latest numerical weather prediction guidance for the first one to two weeks of the month, as well as the subseasonal climate guidance for the Weeks 3-4 period. The overall climate background state is largely unchanged from the midmonth outlook. Conditions over the tropical Pacific continue to reflect El Nino conditions, with the various subseasonal to seasonal climate model forecasts depicting an extratropical response over the North Pacific and North America. [Editor’s Note: The impact is the same but both this and the Friday discussion indicate it is related to El Nino not to the MJO]. The MJO continues to be weak and does not play a significant role, while soils over much of the central and eastern CONUS continue to be remarkably wet relative to normal.

Experimental guidance that calibrates by subperiods of the month (1-3, 4-7, 8-14, and 15-30 day periods), and then generates an aggregate monthly forecast, is used heavily in constructing the current outlook. [Editor’s Note: We have been doing that for years to validate the forecast] The latest CFS monthly forecast guidance is also considered. The updated outlook is intended to reflect the seamless suite of official forecast guidance from Week-1 (including WPC forecast guidance) through the Week 3-4 forecast period.

The spatial structure of the updated temperature outlook is very similar to the midmonth outlook, except it is notably warmer.[Editor’s Note: OK] The latest guidance from WPC as well as the 6-10 day, Week-2, and Weeks 3-4 outlooks from CPC, do not feature any areas over the central U.S. where below-normal temperatures are favored with any confidence. Therefore we can no longer favor below-normal temperatures over parts of the central CONUS. A weakness in the above-normal temperature probabilities is depicted over parts of the central and southern Plains, consistent with the latest forecast guidance and continued above-normal soil moisture. Other key areas of forecast uncertainty exist over parts of the Great Basin, the Rockies, and parts of the northern Plains. The latest 6-10 day and Week-2 guidance further increases the uncertainty over the Great Basin extending westward to parts of northern California. The 0Z ECMWF ensemble mean has trended toward an anomalous trough centered over the interior West during Week-2, leading to only a weak tilt toward above-normal temperatures for the month as a whole. The temperature forecast over New England is less confident than in the original outlook due to the increased potential for backdoor cold fronts associated with the anomalous baroclinic zone forecast over eastern Canada.

There are some large changes in the precipitation outlook due to shorter-term weather forecasts. The first ten days or so of April are forecast to bring periods of heavy rain to parts of the West Coast associated with the eastward extension of a deep, anomalous trough over the Northeast Pacific. This leads to a two-category forecast change for parts of the Pacific Northwest. Above-normal precipitation remains favored over much of the central and southeastern CONUS, with the highest probabilities centered over Southeast Texas. For parts of the Northeast, there is some tendency toward above-normal sea-level pressure during the first part of the month, though a slight tilt toward above-normal precipitation during the 6-14 day period leads to an equal-chances forecast for the month. One exception is a slight tilt toward above-normal precipitation along the immediate coast. A forecast dry start to the month leads to modest probabilities of below-normal precipitation over the far northern Plains. There is a large degree of uncertainty over the southern part of the Alaska, though some tilt toward above-normal precipitation is still indicated for the far southern portions of the state. A dry-wet dipole over central and northern Alaska is favored, consistent with retrogression of a rex block over the North Pacific/Bering Strait region.

Week 3-4 Forecast Discussion Valid Sat Apr 13 2019-Fri Apr 26 2019

The MJO has remained weak during the past two weeks, and therefore no extratropical response to the tropical intraseasonal signal is anticipated. El Nino conditions persist over the equatorial Pacific, however, and the circulation pattern favored by dynamical model guidance is fairly consistent with the canonical response to El Nino, albeit shifted slightly to the west. Anomalous troughing is forecast southwest of the Aleutians, with positive height anomalies downstream across Canada and the northern CONUS. Near- to below-normal heights are favored over the Southwest and south-central U.S., and model guidance becomes less consistent over the East. Above-normal heights are favored across Hawaii, which is consistent with ENSO, while the upstream trough and downstream ridge depicted by the model guidance would favor southeasterly flow across Alaska.

Given the height anomaly forecast, enhanced chances for above-normal temperatures extend across much of Alaska, except along the North Slope where sea ice has not begun to break up. Above-normal temperatures are also favored across the northern tier of the CONUS from Washington to the Great Lakes, while equal chances for below- or above-normal temperatures are maintained for the Southwest and southern High Plains due to weakness in the height field and a potential for enhanced precipitation. Across the East, near to above-normal temperatures are favored, with the greatest chances for above-normal temperatures across the Southeast. With troughing possible over the North Atlantic, equal chances are maintained for the Northeast due to the potential for backdoor cold front activity. Snowpack levels are currently above normal across interior New England, but chances for heavy rainfall in Week-2 and the ever increasing sun-angle may promote rapid melting.

Given the forecast for ridging across Canada and the northern tier of the CONUS, which should preclude widespread intrusions of Canadian air, substantial northward and westward penetration of Gulf moisture may help promote above-normal precipitation from the Four Corners region through the lower Mississippi Valley. Dynamical models favor above-normal precipitation extending as far west as the Great Basin. A consensus of the dynamical and statistical guidance favors below-normal precipitation across the upper Midwest, Great Lakes, and New England. Several models also indicate a potential for enhanced rainfall across parts of the Deep South and southern Appalachians, although probabilities are generally weak. Below-normal precipitation is also favored for the northwestern two-thirds of Alaska, with equal chances for below- or above-normal precipitation maintained elsewhere.

SSTs remain slightly below normal across northwestern Hawaii, favoring a slight tilt towards below-normal temperatures. Anomalous ridging consistent with the ENSO response favors below-normal precipitation.

Summary of the Forecast and Visual Consistency Testing.

It is useful to see how the month forecast fits with the set of shorter forecasts that we have. To accomplish both purposes, we now provide our usual summary first for temperature and then for precipitation of small images of the four short-term maps. You can click on these maps to see larger versions. The easiest way to return to this report is by using the “Back Arrow” usually found top left corner of your screen to the left of the URL Box. This allows us to see the evolution of the forecasts from the 1 – 5 Day, 6 – 10 Day (which NOAA considers to be Week-1 of their intermediate forecast) , 8 – 14 Day (which NOAA considers to be Week-2) and Week 3 and 4 (which after being issued overlap with Week-2). I do not have comparable maps for the Day 1 – 5 forecast in the same format as the three maps we generally work with. What I am showing for temperature is the Day 3 Maximum Temperature and for precipitation the five-day precipitation: the latter being fairly similar in format to the subsequent set of the maps I present each week but showing absolute QPF (inches of precipitation) not QPF deviation from Normal.

First Temperature

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →

Udated Temp for April issued on March 31, 2019

↑

← The Week 3 – 4 forecast was updated last Friday so we do not need to update the forecast when the update is issued.

It looks pretty consistant other than for the Northwest.

And Precipitation

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →

April 2019 Precipitation Outlook Updated on March 31, 2019

↑

← The current Week 3 – 4 forecast was updated last Friday so we do not have to wait for when that update is issued.

It looks pretty consistant except for the location of the dry anomaly which is shown for Montana and North Dakota but the concatenation of the short-term forecasts would place it further east a bit and have it be EC rather than a dry anomaly.

Sometimes it is useful to compare the three-month outlook to the forecast for the first of the three months. It shows how much the pattern changes over the three-month period.

One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.

For both temperature and precipitation if you assume the colors in the maps are assigned correctly, it is a simple algebra equation to solve the month two/three forecast probability for a given location = (3XThree-Month Probability – Month One Probability)/2*. So you can derive the month two/three forecast this way. You can do that calculation easily for where you live or for the entire map.

It would appear that May and June 2019 will need to be a lot different than the three-month temperature maps to make the three-month forecast work. It is important to remember that here we are comparing a one month forecast issued today with a three-month forecast issued on March 21, ten days days ago. The April temperature and precipitation forecasts have changed dramatically so we have to ask the question whether or not the three-month forecast shown would be as shown if issued today. I think not. Thus it is hard to draw conclusions relative to how to think about May and June by comparing the updated April forecast with the prior three-month forecast.

*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two and Three forecast that one derives must average out to the probabilities shown in the three-month maps.

And with respect to drought. This was issued today.

This map` shows the newly revised forecast for April. Other than Western Hawaii it looks pretty good. There are a few recalcitant dry areas.

For reference Purposes it is is useful to look back at March Weather. (As of today I have data through March 30 so it is missing one day)

First Temperature

One could compare this to the forecast for April. The format is different. But you can see that it is very different and more like the forecast from 10 days ago which might explain the prior forecast.

Then Precipitation

One could compare this to the forecast precipitation for April. The format is different but I can see the pattern is very different.

Recent CONUS Weather

This is provided mainly to see the pattern in the weather that has occurred recently.

Here is the recent history of the overall atmospheric pattern for North America and the North Pacific.

Ridging and warming continue over Western Canada which is consistent with Spring. It is about time. Remember, this shows four 15 Day Periods i.e. it is history.

nd now looking at the recent weather.

And the 30 Days ending March 23, 2019	And the 30 Days ending March 30, 2019

An overall moderation of anomalies.	It is slightly less wet and slightly colder also
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

A. Now we will begin with our regular approach and focus on Alaska and CONUS (all U.S.. except Hawaii).

Water Vapor.

This view of the past 24 hours provides a lot of insight as to what is happening.

You can see from this animation that there is a Pacific Storm arriving that will impact most of the West Coast.

Tonight, Monday April 1, 2019, as I am looking at the above graphic, you see moisture impacting impacting all of the West Coast.

We now discuss Atmospheric Rivers i.e. thick concentrated movements of water moisture. More explanation on Atmospheric Rivers can be found by clicking here or if you want more theoretical information by clicking here. The idea is that we have now concluded that moisture often moves via narrow but deep channels in the atmosphere (especially when the source of the moisture is over water) rather than being very spread out. This raises the potential for extreme precipitation events. You can convert this graphic into a flexible forecasting tool by clicking here. One can obtain views of different geographical areas by clicking here.

The graphic we had been using was not updating so for the time being we added another version which is updating. It does not cover all of CONUS but it does provide a very good view of what is happening in the Pacific and the North American West Coast. But the original graphic we were using is not working so we are using both.

The moisture source is moving closer. Basiclly when I factor in the fact that there is hardly an atmospheric river currently impacting the West Coast with the Water Vapor Imagery, I conclude that these will not be very wet storms. The further out storm may be more significant but it is too soon to tell.

And this graphic provides a better view of all of CONUS.

You can see moisture impacting the West Coast and Florida. The atmospheric rivers are not very intense.

I have decided to include the IWT information for Europe.

This is not only useful for Europe but it puts the East Coast and the Antilles into better perspective. Some of the forecasts see this activity moving closer to the East Coast and having impacts.

And Now the Day One and Two CONUS Forecasts (These graphics have recently been revised by NOAA and I think greatly improved).

Day One CONUS Forecast	Day Two CONUS Forecast

These graphics update and can be clicked on to enlarge but my brief comments are only applicable to what I see on Monday night prior to publishing.

We still see snow. We also see cold fronts dominating.

Additional useful forecasts are available from our Severe Weather Report which this week can be found here and always can be located via this directory.

60 Hour Forecast Animation

Here is a national animation of weather fronts and precipitation forecasts with four 6-hour projections of the conditions that will apply covering the next 24 hours and a second day of two 12-hour projections the second of which is the forecast for 48 hours out and to the extent it applies for 12 hours, this animation is intended to provide coverage out to 60 hours. Beyond 60 hours, additional maps are available at links provided below. The explanation for the coding used in these maps, i.e. the full legend, can be found here although it includes some symbols that are no longer shown in the graphic because they are implemented by color coding.

The below makes it easier to focus on a particular day. The best way to read them is from left to right on the first row and then from left to right in the row below it.

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What is Behind the Forecasts? Let us try to understand what NOAA is looking at when they issue these forecasts.

Below is a graphic which highlights the forecast surface Highs and the Lows re air pressure on Day 7. The Day 3 forecast can be found here. the Day 6 Forecast can be found here.

The fairly weak Aleutian Low with surface central pressure of 984 hPa is forecast on Day 7 to be getting ready to impact the West Coast. The Hawaiian High is present with surface central pressure of 1024 hPa and it extends inland. To the east and north there is a Low near the Great Lakes with surface central pressure of 1008 hPa. It is impacting a large part of the NE Quadrant of CONUS. This forecasted pattern for Day 7 has changed a lot in the last 24 hours.

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Looking at the current activity of the Jet Stream. The below graphics and the above graphics are very related.

Not all weather is controlled by the Jet Stream (which is a high altitude phenomenon) but it does play a major role in steering storm systems especially in the winter The sub-Jet Stream level intensity winds shown by the vectors in this graphic are also very important in understanding the impacts north and south of the Jet Stream which is the higher-speed part of the wind circulation and is shown in gray on this map. In some cases however a Low-Pressure System becomes separated or “cut off” from the Jet Stream. In that case it’s movements may be more difficult to predict until that disturbance is again recaptured by the Jet Stream. This usually is more significant for the lower half of CONUS with the cutoff lows being further south than the Jet Stream. Some basic information on how to interpret the impact of jet streams on weather can be found here and here. I have not provided the ability to click to get larger images as I believe the smaller images shown are easy to read.

Current	Day 5

You can see the current pattern here. It is a meridional pattern for the moment.	The pattern is shifting to the north and becoming more zonal.

Putting the Jet Stream into Motion and Looking Forward a Few Days Also

To see how the pattern is projected to evolve, please click here. In addition to the shaded areas which show an interpretation of the Jet Stream, one can also see the wind vectors (arrows) at the 300 Mb level.

This longer animation shows how the jet stream is crossing the Pacific and when it reaches the U.S. West Coast is going every which way.

Click here to gain access to a very flexible computer graphic. You can adjust what is being displayed by clicking on “earth” adjusting the parameters and then clicking again on “earth” to remove the menu. Right now it is set up to show the 500 hPa wind patterns which is the main way of looking at synoptic weather patterns. This amazing graphic covers North and South America. It could be included in the Worldwide weather forecast section of this report but it is useful here re understanding the wind circulation patterns.

500 MB Mid-Atmosphere View

The map below is the mid-atmosphere 7-Day chart rather than the surface highs and lows and weather features. In some cases it provides a clearer less confusing picture as it shows only the major pressure gradients. This graphic auto-updates so when you look at it you will see NOAA’s latest thinking. The speed at which these troughs and ridges travel across the nation will determine the timing of weather impacts. This graphic auto-updates I think every six hours and it changes a lot. Thinking about clockwise movements around High Pressure Systems and counter- clockwise movements around Low Pressure Systems provides a lot of information.

As of this evening, we see for Day 7 a somewhat zonal pattern that is moving very slowly. There is a trough moving past the Great Lakes and the Mississippi River Valley. The 540 Line which is a best guess of where the chances of snow versus rain at sea level are about equal is no longer impacting CONUS. We can now see for Day 7 another Pacific Storm. The information presented on the PNA may be helpful in guessing at the track of that storm.

Here is the whole suite of similar maps for Days 3, 4, 5, 6 and repeated for Day 7. It is quite complicated. Read from left to right first row and then left to right on the second row.

You can see how this trough is expected to move across CONUS. It pretty well determines all the weather in CONUS. It is not moving very quickly.

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For Day 7 the surface and 500 millibar views are in fair agreement. It is a vertical alignment related to the very slow speed of the atmosphere moving east. But you can see that the Eastern Trough will not be reflected immediately to the ground which is an indicator of greater potential for severe weather.

Here is the seven-day cumulative precipitation forecast. More information on how to interpret this graphic is available here.

We see some moisture entering the Northwest. And there is moisture coming in from the Gulf of Mexico. The most intense Eastern precipitation is offshore and the most intense Western Precipitation does not extend inland very far.

Four – Week Outlook: Looking Beyond Days 1 to 5, What is the Forecast for the Following Three + Weeks?

I use “EC” in my discussions although NOAA sometimes uses “EC” (Equal Chances) and sometimes uses “N” (Normal) to pretty much indicate the same thing although “N” may be more definitive.

First – Temperature

6 – 10 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on April 1, 2019 was 3 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on April 1, 2019 was 3 out of 5).

–

Looking further out.

This is not a traditional El Nino Pattern.

Now – Precipitation

6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on April 1, 2019 was 3 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on April 1, 2019 was 3 out of 5)

Looking further out.

This looks more like an El Nino Pattern.

Here is the 6 – 14 Day NOAA discussion released today April 1, 2019

6-10 DAY OUTLOOK FOR APR 07 – 11 2019
Today’s ensemble means are in fairly good agreement with the 500-hPa pattern throughout the forecast domain. A trough is forecast over the western Aleutians, while a ridge continues to be predicted over mainland Alaska. Another broad trough is anticipated over eastern Canada extending to the Atlantic. The manual 500-hPa height blend is based primarily on the ensemble means from the GFS and Canadian models. The resultant manual blend features above normal heights across most of the CONUS, mainland Alaska, and Alaska Panhandle. Below normal heights are favored for the Aleutians.
Ridging favors above normal temperatures across Alaska with probabilities exceeding 70 percent for parts of the southwestern mainland. Probabilities of below normal temperatures are elevated for parts of the northern Rockies due to low level northerly flow forecast over the northwestern CONUS. Above normal 500-hPa heights favor near to above normal temperatures across much of the rest of the CONUS consistent with the reforecast-calibrated GFS and ECMWF tools.
The potential for enhanced Pacific flow leads to elevated probabilities of above normal precipitation across much of the northwestern CONUS. The highest probabilities of above normal precipitation (grater than 60 percent) are indicated for the Pacific Northwest. Above normal precipitation is favored for much of the central and eastern CONUS, while below normal precipitation is most likely for parts of the southern Rockies, consistent with the consolidation forecast tool. Above normal precipitation probabilities remain elevated for much of western and central mainland Alaska and the Aleutians under the influence of the Aleutian trough. Below normal precipitation probabilities are favored for parts of eastern interior Basin.
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Near average, 3 out of 5, due to fair model agreement on the overall upper level pattern.
8-14 DAY OUTLOOK FOR APR 09 – 15 2019
For week-2, the 500-hPa height pattern features a ridge over mainland Alaska and a weak trough over the western CONUS. Downstream zonal flow is forecast over the central and eastern CONUS. Near to weakly above normal heights are forecast over the southeastern CONUS, while weak negative height anomalies are forecast over parts of the western CONUS. Positive height anomalies are favored for mainland Alaska and the Panhandle with negative height anomalies favored for the Aleutians due to troughing.
Above normal temperatures are favored for Alaska underneath ridging with probabilities continuing to exceed 70 percent across parts of southwestern mainland Alaska. Near to above normal temperatures are favored for much of the south-central CONUS and most of the eastern CONUS underneath predicted near to above normal heights. Below normal temperatures are favored for much of the western and north-central CONUS consistent with the consolidation forecast tool.
Troughing in the southwestern CONUS and enhanced Pacific flow favor increased odds of above normal precipitation for much of the western CONUS except for the extreme northwest. Due to the relatively zonal flow, shortwave impulses are anticipated to move across the country bringing heightened precipitation chances across much of the CONUS, consistent with the consolidation forecast tool. Predicted southerly flow and low pressure near western the Aleutians favor elevated chances for above precipitation over western Alaska.
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Near average, 3 out of 5, due to good model agreement in terms of the pattern, offset by uncertainty resulting from lack of amplification.
The next set of long-lead monthly and seasonal outlooks will be released on April 18.

Analogs to the NOAA 6 – 14 Day Outlook.

Now let us take a detailed look at the “Analogs”.

NOAA normally provides two sets of Analogs.

A. Analogs related to the 5 day period centered on 3 days ago and the 7 day period centered on 4 days ago. “Analog” means that the weather pattern then resembles the recent weather pattern and the recent pattern is used to initialize the models to predict the 6 – 14 day Outlook.

B. There is a second set of analogs associated with the Outlook. It compares the forecast (rather than the prior period) to past weather patterns. I have not been regularly analyzing this second set of information. The first set applies to the 5 and 7 day observed pattern prior to today. The second set relates to the correlation of the forecasted outlook 6 – 10 days out and 8 – 14 days out with similar patterns that have occurred in the past during a longer period that includes the dates covered by the 6 – 10 Day and 8 – 14 Day Outlook. The second set of analogs also has useful information as it indicates that the forecast is feasible in the sense that something like it has happened before. I am not very impressed with that approach. But in some ways both Approach A and B are somewhat similar. I conclude that if the Ocean Condition now are different then the analogs and if the state of ENSO now is different than the analogs that is a reason to have increased lack of confidence in the forecasts and vice versa.

They put the first set of analogs in the discussion with the second set available by a link so I am assuming that the first set of analogs is the most meaningful and I find it so. But NOAA prefers the first set (A) as it helps them (or at least they think it does) assess the quality of the forecast.

Here are today’s analogs in chronological order although this information is also available with the analog dates listed by the level of correlation. I find the chronological order easier for me to work with. It also helps the reader see the impact of the phases of the PDO and AMO which are shown. The first set (A) which is what I am using today applies to the 5 and 7 day observed pattern prior to today.

Date	ENSO Phase	PDO*	AMO*	Other Comments
Mar 26, 1954	El Nino	–	+	Tail End
Mar 27, 1954	El Nino	–	+	Tail End
Apr 14, 1965	El Nino	–	–
Apr 15, 1965	El Nino	–	–
Mar 20, 1990	Neutral	– (t)	–
Mar 21, 1990	Neutral	– (t)	–
Apr 7, 1990	Neutral	+(t)	–
Apr 9, 1990	Neutral	+(t)	–
Apr 15, 1990	Neutral	+(t)	–
Mar 27, 1996	El Nino	+	–	Tail End

* I assign values that are consistent with the trend so I am doing some subjective smoothing with respect to the Phases of the AMO and PDO shown in this table. (t) = a month where the Ocean Cycle Index has just changed from a consistent pattern or does change the following month to a consistent pattern.

The spread among the analogs from March 20 to April 15 is 26 days which is very much tighter than last week and may suggest a pattern that is easier to forecast. I have not calculated the centroid of this distribution which would be the better way to look at things but the midpoint, which is a lot easier to calculate, and fairly accurate if the dates are reasonably evenly distributed, is about April 2, 2019. These analogs are describing historical weather that was centered on 3 days and 4 days ago (March 28 or March 29). So the analogs could be considered to be slightly out of sync with respect to weather that we would normally be getting right now but almost a half a week early.

For more information on Analogs see discussion in the GEI Weather Page Glossary. For sure it is a rough measure as there are so many historical patterns but not enough to be a perfect match with current conditions. I use it mainly to see how our current conditions match against somewhat similar patterns and the ocean phases that prevailed during those prior patterns. If everything lines up I have my own measure of confidence in the NOAA forecast. Similar initial conditions should lead to similar weather. I am a mathematician so that is how I think about models.

Including duplicates, there are four Neutral analogs, five El Nino Analogs, and one La Nina Analog. This suggests that El Nino may have begun to have a significant impact on the weather pattern for CONUS and Alaska. The pre-forecast analogs this week are mostly non-supportive of McCabe C which is “Northern Tier and Mid-Atlantic Drought”. By being non-supportive of McCabe C, the analogs are supporting the NOAA 6 – 14 Day Forecast.

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Historical Anomaly Analysis

When I see the same dates showing up often I find it interesting to consult this list.

A Useful Read

Some might find this analysis which you need to click to read interesting as the organization which prepares it focuses on the Pacific Ocean and looks at things from a very detailed perspective and their analysis provides a lot of information on the history and evolution of ENSO events.

Some Indices of Possible Interest: We should always remember that the forecast is driven by many factors some of which are conflicting in terms of their impacts. Please pay more attention to the graphics than my commentary which does not update on a regular basis once the article is published. The indices will continue to update. I provide these indices as they are important guidelines to the weather. It is in a way looking at the factors that are impacting the weather. There were developed because weather forecasters found them to be useful.

Looks like the AO will start Positive and then be Negative. AO Positive normally limits the potential for cold air entering CONUS from Canada. We might expect some intrusions of cooler air from Canada.

It is not a surprise when the AO and NAO are positively correlated. It looks like the AO and NAO will be mostly positively correlated.

They both have to do with Polar versus Sub-Polar pressure gradients but the AO is over CONUS and the NAO is over the Atlantic with the impacts of the NAO felt on both sides of the Atlantic. Some look at the AO as simply being the western end of the NAO but the AO is based on conditions over land and the NAO is based on conditions over the Atlantic so they are related but not the same thing. As the NAO become Negative this could impact both East Coast weather and Western Europe weather.

Eastern Pacific Oscillation. Here is a pretty good explanation. It is a bit like an extension further west of the AO. Here is some history and five forecasts ranging from 4 days to 14 days. As you can see, we have been in the Negative or Cool Phase almost all winter. We may now be trending towards EPO positive.

The forecast Phase of the PNA pattern is Neutral early and later Positive. You can see the impact of the different phases in the schematics below (Source: N.C. State Climatologist). PNA Positive in on the left and PNA Negative on the right. PNA Negative is a pattern that is more westerly located than PNA Positive. This has to do with storms entering CONUS in the Northwest and then moving south either closer to the coast or further inland.

It looks like conditions favor troughs first entering the West Coast head on but later entering the Northwest and dropping down beyond the Rocky Mountains.

………………………..PNA Positive…………………………….. PNA Negative……………..

Here is another way of integrating all forecasts into a single graphic. These forecasts extend out further into the future than the forecasts presented earlier. But they do not show the recent history. Also the set of four does not include the AO but instead the WPO so it is not the same but may be useful.

You can see a change in the pattern after about April 10.

Madden Julian Oscillation (MJO)

The MJO is an area of convective activity along the Equator which circles the globe generally in 30 to 60 days. The location of the convective activity not only impacts the Equator but also the middle latitudes. Most people are not familiar with the MJO but at certain times it plays an important role Worldwide re weather and for CONUS.

This is the Summary from the weekly NOAA analysis of the MJO.

We will continue with this part of the presentation even though the MJO is forecast to be a nonfactor for CONUS but a major factor for Northwest Australia.

It is sometimes useful to look at the recent history of the MJO.

The MJO Index (more information can be found here) indicates where the MJO has been and this Hovmoeller Graphic shows this. The Index is show for the parts of the Equator where the MJO is most usually found.

Blue is Active Phase. This week we see more tan. But the Blue is moving to the east a bit. Notice the lighter shade of the blue area.

Forecast Models.

There are a lot of models and I try to read the results from all of them. For access to a variety of models, I refer readers here. This weekly report summarizes things. Here is another useful source of information.

Now the first of the two graphics we typically present which shows where the MJO is now and how it got there.

This shows the recent history. MJO is now in Phase 6. What next?

And then a forecast. On this GFS graphic, the light gray shading shows the tracks which fit with 90% of the forecasts and the dark gray shading shows a smaller area that fits with 50% of the forecasts The large dot is the current location.

Imperceptical change in the forecast from last week.

* Remember when clicking on an image to enlarge does not work, usually it will work to right click with your mouse and click on “view image”. Sometimes it just does not work when I set it up to enlarge by simply clicking on the image.

You can see the movement of the MJO (red) and changes elsewhere which may or may not be related to the MJO. We no longer see the circled areas by NOAA to focus on. I do not really see El Nino here. But you can see the westerlies impact the West Coast of CONUS. This is a new format by NOAA with two graphics per frame. Click to enlarge.

Always a difficult graphic to describe. We see that this week was a bit different from last week. This is the new NOAA format with two graphics per frame. Click to enlarge. You can see that very important WWB about a month ago. The discussion appears to be out of date…best to look at the graphic.

Here is a larger version of the graphic on the left

You can see the WWB which triggered Kelvin Wave #3 So far there has not been another one but there could be soon.

Remember that the MJO is one of many influences on weather. What I am normally showing here is the most reliable impacts but NOAA goes into much more depth in their analysis than I could show in this report. But the goal is to demystify weather forecasting.

B. Beyond Alaska and CONUS Let’s Look at the World which of course also includes Alaska and CONUS

It is Useful to Understand the Semipermanent Pattern that Control our Weather and Consider how These Change from Winter to Summer. These two graphics (click on each one to enlarge) are from a much larger set available from the Weather Channel. They highlight the position of the Bermuda High which they are calling the Azores High in the January graphic and is often called NASH and it has a very big impact on CONUS Southeast weather and also the Southwest. You also see the north/south migration of the Pacific High which also has many names and which is extremely important for CONUS weather and it also shows the change of location of the ITCZ which I think is key to understanding the Indian Monsoon. A lot of things become much clearer when you understand these semi-permanent features some of which have cycles within the year, longer period cycles and may be impacted by Global Warming. We are now moving into Early/Mid-April. We should be returning from the set of positions shown below for the Winter Pattern to the Summer Pattern. For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant.

World Forecasts

1. Today (Source: University of Maine)

2. Short-term set for day six but can be adjusted (BOM – Australia)

3. 8 – 14 Day (NOAA/Canada/Mexico Experimental NAEFS))

4 Tropical Activity

1. Forecast for Today (you can click on the maps to enlarge them)

Australia again looks hot. So does Equatorial Africa.

And now precipitation

It is still the general pattern of a wet Equator and dry North Africa extending to the Eastern Asia and even Southern Asia. You also see a wet Eastern Brazil and a dry Australia and a wet Maritime Continent which is not supposed to happen during an El Nino.

Additional Maps showing different weather variables can be found here.

2. Forecast for Day 6 (Currently Set for Day 6 but the reader can change that)

World Weather Forecast produced by the Australian Bureau of Meteorology. Unfortunately I do not know how to extract the control panel and embed it into my report so that you could use the tool within my report. But if you visit it Click Here and you will be able to use the tool to view temperature or many other things for THE WORLD. It can forecast out for a week. Pretty cool. Return to this report by using the “Back Arrow” usually found top left corner of your screen to the left of the URL Box. It may require hitting it a few times depending on how deep you are into the BOM tool. Below are the current worldwide precipitation and temperature forecasts for six days out. They will auto-update and be current for Day 6 whenever you view them. If you want the forecast for a different day Click Here

Australia is no longer forecast to be excessively warm. But parts of South America are. These graphics change a lot as they update I think every six hours so the time of day that you look at them matters and these graphics show absolute temperatures, not anomalies.

Again, please remember this graphic updates every six hours so the diurnal pattern can confuse the reader.

Now Precipitation

This is a forecast for one particular day (Day 6). But it shows the surface Highs and the Lows which is useful information.

3. And now we have experimental 8 – 14 Day World forecasts from the NAEFS Model.

First Temperature

The Northern Tier of CONUS look cool. Southern Asia is cool. Europe other than Northern Europe is warm.

Then Precipitation

I mostly rely on the reader to interpret world maps that update frequently.

4. Tropical Hazards.

This graphic updates on Tuesdays and I usually post on Monday which is almost a week later than when this graphic was last updated. So normally Week 2 applies at the time I write this article on Monday. Mostly, as I review this now on April 1, 2019 for what is shown as Week – 2, the period April 3, 2019 to April 9, 2019, there is a wet* and cyclonic risk* anomaly impacting Northwest Australia. A wet** anomaly is approaching the Maritime Continent and norther South America is slightly affect by a wet** anomalyon the east side and a dry* anomaly on the west side. Other than Australia there is not very much going on.

* means moderate confidence and ** means high confidence.

C. ENSO SUMMARY of Current Status.

This section is organized into three parts.

1. Current Sea Surface Temperatures (SST)

2. Current Nino 3.4 Readings

3. The Surface Air Pressure Pattern that confirms the state of ENSO.

1. Current and Recent Sea Surface Temperatures (SST)

A major driver of weather is Surface Ocean Temperatures. Evaporation only occurs from the Surface of Water. So we are very interested in the temperatures of water especially when these temperatures deviate from seasonal norms thus creating an anomaly. The geographical distribution of the anomalies is very important. To a substantial extent, the temperature anomalies along the Equator have disproportionate impact on weather so we study them intensely and that is what the ENSO (El Nino – Southern Oscillation) cycle is all about. Subsurface water can be thought of as the future surface temperatures. They may have only indirect impacts on current weather but they have major impacts on future weather by changing the temperature of the water surface. Winds and Convection (evaporation forming clouds) is weather and is a result of the Phases of ENSO and also a feedback loop that perpetuates the current Phase of ENSO or changes it. That is why we monitor winds and convection along or near the Equator especially the Equator in the Eastern Pacific.

My focus here is sea surface temperature anomalies as they are one of the two largest factors determining weather around the World. If we want to have a good feel for future weather we need to look at the oceans as our weather mostly comes from oceans and we need to look at surface temperature anomalies (weather develops from the ocean surface

It is the ocean surface that interacts with the atmosphere and causes convection and also the warming and cooling of the atmosphere. So we are interested in the actual ocean surface temperatures and the departure from seasonal normal temperatures which is called “departures” or “anomalies”. Since warm water facilitates evaporation which results in cloud convection, the pattern of SST anomalies suggests how the weather pattern east of the anomalies will be different than normal.

Current Sea Surface Temperature (SST) Departures from Normal for this Time of the Year i.e. Anomalies

We have our daily map which updates back.

First the categorization of the current Monthly Average SST anomalies.
The Mediterranean, Black Sea and Caspian Sea	Western Pacific	West of North America	North and East of North America	North Atlantic
The Mediterranean and the Black Sea are neutral and the Caspian Sea is slightly warm.	Slightly warm	Waters around Alaska are warm Cool way offshore of CONUS Northwest Warm off Baja and out to sea.	Great Lakes cool Waters offshore of East Coast warm. Davis Strait slightly warm. Cool offshore south of Greenland.	North Sea warm
Equator	Eastern Pacific Moderately Warm.Pacific Coast strangely cool

Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Warm southwest of Africa Warm east of Madagascar	Cool way out to sea	Warm East and SE to and beyond New Zealand Cool offshore to the SW	Cool north and south of the Equator. Cool 30S to 40S and out to sea	Warm off shore at 20S Warm 40S

Then we look at the change in the anomalies. The SST anomaly is sort of like the first derivative and the change in the anomaly is somewhat like a second derivative. It tells us if the anomaly is becoming more or less intense.

Here it gets a little tricky as for this graphic red does not mean a warm anomaly but a warming of the anomaly which could mean more warm or less cool and blue does not mean cool but more cool or less warm. I used to interpret this graphic but really my interpretation was no more than characterizing the graphic by geographical region as per the above graphic and the reader can do this for themselves.

But I can not help mentioning that the strange cool anomaly off Columbia is BACK! Actually, it is not a cool anomaly but a four-week change in the anomaly.

I am only showing the currently issued version of the NINO SST Index Table as the prior values are shown in the small graphics on the right with this graphic. The same data in graphic form but going back a couple of more years can be found here. The full table of values can be found here. NOAA considers Nino 3.4 shown in the graphic as the best indicator of Equatorial Surface Temperature Anomalies associated with different phases of ENSO. There is a duration requirement to be a recorded El Nino or La Nina but to have El Nino Conditions the Nino 3.4 index needs to be +0.5C or warmer and to have La Nina Conditions the Nino 3.4 Index needs to be -0.5C or cooler.

Nino 3.4 remains at El Nino levels.

This graphic brings the Nino 3.4 up to date and is easy to read.

Recently has become warmer than the 0.5C NOAA threshold for El Nino. But for the moment it looks like it has peaked.

Here is a daily version

Definitely in El Nino Territory but with a slight downward trend.

Here is the NOAA proprietary Nino 3.4 forecast model. The forecast spread is enormous. The blue lines are the most recent model runs.

Starting with Surface Conditions.

TAO/TRITON GRAPHIC (a good way of viewing data related to the part of the Equator and the waters close to the Equator in the Eastern Pacific where we monitor to determining the current phase of ENSO. It is probably not necessary to follow the discussion below, but here is a link to TAO/TRITON terminology.

And here is the current version of the TAO/TRITON Graphic. The top part shows the actual temperatures, the bottom part shows the anomalies i.e. the deviation from normal.

Notice in the bottom graphic the big difference between temperature anomalies south of the Equator and north of the Equator. This creates a dynamic situation.

*Location Bar for Nino 3.4 Area Above and Below*
————————————————	A	B	C	D	E	—————–

Looks a bit like a Modok.

We may be seeing a bit less tan.

This is a Hovmoeller Diagram so we read it from the bottom (current situation) up (prior times as per the Y-Axis. Notice the slope of the downwelling phase of the Kelvin Waves has been steeping over time indicating slowing. Somewhere I think I show that the Easterlies have picked up. So the warm water is being collected at about 140W. It was becoming more intense. It now looks like this Kelvin Wave is playing out.

This may help put the above graphics in focus.

You can see the large warm anomaly which is mostly subsurface but which also is impacting the surface to some extent. You also see the cold water coming up from below further east. On the right, you see the history.

The following graphic is some similar to the above but it updates every five days not once per week. The date shown is the midpoint for the five-day average. It shows a lot more detail than the above graphic. You can see some water at depth that is very anomalously warm.

The top graphic is of most interest. There used to be two warm anomalies. One has played out. The other has not yet reached the area where it is forced to surface. It will but is not there yet. It may be sufficient to generate true El Nino Conditions which do not exist now to a point that it is clear cut. But it is getting to look more clear cut. It looks to be somewhat consistent with the JAMSTEC forecast of a peak and rapid decline but most likely will happen later than in the JAMSTEC forecast. So a blend of the two forecasts might not be such a bad forecast.

The bottom graphic shows the “thermocline” is not yet of an El Nino nature but getting there. The warm water is to the west not the east. With El Nino, this thermocline flattens out. We should not be seeing cool anomalies so close to the surface in the Eastern Pacific. This may be why the precipitation pattern has been shifted to the west.

One can imagine that the thermocline will flatten out but only for a very short time.

3. The Surface Air Pressure that Confirms the Nino 3.4 Index

And of course, Queensland Australia is the official keeper of the SOI measurements.

The SOI Index was in El Nino territory but has backed off to marginal. This graphic is a 30-day average so it changes slowly.

SOI = 10 X [ Pdiff – Pdiffav ]/ SD(Pdiff) where Pdiff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question. So really it is comparing the extent to which Tahiti is more cloudy than Darwin, Australia. During El Nino we expect Darwin Australia to have lower air pressure and more convection than Tahiti (Negative SOI especially lower than -7 correlates with El Nino Conditions). During La Nina we expect the Warm Pool to be further east resulting in Positive SOI values greater than +7).

D. Putting it all Together.

At this time, La Nina Conditions along the Equator have come to an end and we are slowly entering into weak El Nino Conditions.

There is some thought now that we might have a marginal El Nino situation that extends into next Winter. JAMSTEC ruled that out but there are some signs that this could happen. All El Nino forecasting right now runs up against the Spring Prediction Barrier (SPB) and forecasts in May are far more reliable.

E. Relevant Recent Articles and Reports

Weather in the News

Nothing to report

Global Warming in the News

Nothing to report

Useful Reference Information

Understand How the Jet Stream Impacts Weather

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This is particularly useful for locations at the base of the trough but it works wherever the jet stream is involved and when one can forecast where the jet stream will be. This is the general model but local offices of the NWS will be interpreting this very specifically for the various part of their County Warning Area (CWA). Do not be intimidated by the graphics. It is not that complicated. The idea is that if you are facing the Jet Stream (on the ground of course) and are more or less below the center of the Jet Stream, there will be different impacts to your right than to your left and it makes a difference if you are where the jet stream is dis

charging the wind (Exit Region) or where the wind is converging into the Jet stream (Entrance Region). This terminology is a bit confusing until you get used to it.

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Standard Pressure Levels

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April 1, 2019 – Intermediate-Term Weather Report – April Update

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