October 1, 2018 Weather and Climate Report – Fall and El Nino Arriving

Written by Sig Silber

Of course seasons change from south to north and often from west to east so the changeover does not occur everywhere at exactly the same time. But for many areas, the changeover will begin late this week. Tonight we combine the October update from the early outlook issued 10  days ago with our usual weather and climate report. It looks like we will also still be tracking tropical events for which if they are significant we will issue updates to this article. We are now looking ahead to October 11 when NOAA may declare that El Nino Conditions are present. The detailed discussion of the El Nino will be in a separate report published tomorrow. In this report we focus on October.

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This is part of the end of month update. It might be a bit pessimistic. The improvement might be better than shown here. We will discuss in more detail in our Thursday Night Drought and Agriculture Report.

A hint about what we will discuss tomorrow which suggests this El Nino may be stronger than currently forecast.

And this provides a good overview of the current situation.

Now let us first address the NOAA Update of the October, 2018 Forecast.

First, I present a summary showing the prior and the new October forecast and the previously issued three-month forecast. Larger graphics follow but these smaller graphics can be enlarged.

	Temperature	Precipitation
Prior Issued on September 20, 2018
Updated on September 30, 2018
Three Month Forecast Issued on September 20, 2018

Prior October Temperature Forecast Issued on September 20, 2018

New October Temperature Forecast Issued on September 30, 2018

Turning to Precipitation

Prior October Precipitation Forecast issued on September 20, 2018

New October Precipitation Forecast Issued on September 30, 2018

Here is the NOAA Discussion released on September 30, 2018 with the October Update and also the discussion released on September 28, 2018 with the Week 3 – 4 Forecast

30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2018  

THE UPDATE TO THE MID-MONTH OCTOBER TEMPERATURE AND PRECIPITATION OUTLOOK PRIMARILY UTILIZES INFORMATION FROM SHORT-RANGE, MEDIUM-RANGE, EXTENDED-RANGE MODEL GUIDANCE AND CHANGES IN INTEGRATED MONTHLY DYNAMICAL MODEL GUIDANCE INFORMATION FROM MID-MONTH. THE UPDATED OUTLOOKS DEPICTS SOME SUBSTANTIAL CHANGES IN SOME AREAS AS MODEL GUIDANCE HAS BEEN QUITE VARIABLE AT TIMES OVER THE PAST SEVERAL DAYS.

THE TEMPERATURE OUTLOOK UPDATE MAINTAINS HIGH PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES FOR MOST OF ALASKA AND FACTORS LISTED AT MID-MONTH HAVE NOT CHANGED AND MODEL GUIDANCE HAS REMAINED CONSISTENT. ANTICIPATION OF ROBUST TROUGHING IMPACTING NORTH AMERICA DESCRIBED EARLIER THIS MONTH CONTINUES TO BE A MAJOR FACTOR IN THE OUTLOOK AS THE ENTRY OF COLDER AIR INTO THE INTERIOR PORTION OF THE CONUS REMAINS FAVORED. THE LATEST GUIDANCE, HOWEVER, NOW INDICATES MORE AMPLIFIED, FULL LATITUDE TROUGHING SHIFTED TO THE WEST-CENTRAL CONUS FOR MUCH OF THE FIRST HALF OF THE MONTH. AREAS NOW MOST FAVORED FOR BELOW-NORMAL TEMPERATURES HAVE INCREASED IN COVERAGE AND SHIFTED WESTWARD TO FOCUS ON THE NORTHERN ROCKIES AND NORTHERN GREAT PLAINS AND TO LESSER CONFIDENCE FOR AN AREA CENTERED ACROSS CALIFORNIA. THIS IS TWO CATEGORY CHANGE IN SOME AREAS OF THE WESTERN CONUS FROM THE PREVIOUS OUTLOOK WHERE RIDGING WAS INITIALLY FAVORED.

MIXED SIGNALS OVER THE COURSE OF THE MONTH FROM DYNAMICAL MODEL GUIDANCE MAKES A FORECAST OF EQUAL CHANCES (EC) THE MOST PRUDENT OUTLOOK AT THIS TIME IN THE REMAINING AREAS OF THE WESTERN CONUS. ABOVE-NORMAL TEMPERATURES REMAIN FAVORED FROM THE PREVIOUS OUTLOOK IN THE SOUTHEAST, BUT HAVE BEEN EXPANDED IN COVERAGE AND PROBABILITIES INCREASED SUBSTANTIALLY AS THE ANTICIPATED 500-HPA FLOW PATTERN DURING THE FIRST HALF OF OCTOBER FAVORS STRONGLY AMPLIFIED RIDGING FOR THE EASTERN CONUS. A PARTICULAR CHALLENGE IN THE TEMPERATURE OUTLOOK IS ACROSS THE EASTERN GREAT LAKES REGION AND NORTHEAST WHERE THERE REMAINS UNCERTAINTY FOR HOW MUCH COLDER AIR IS ABLE TO ENTER THIS REGION AFTER MID-MONTH AS INDICATED BY SOME WEEK 3-4 FORECAST MODEL GUIDANCE AND TO THE EXTENT THAT THE EXTENDED-RANGE STRONGLY FAVORED ABOVE-NORMAL TEMPERATURE FORECAST IS EVENTUALLY REALIZED.

THE UPDATED OCTOBER PRECIPITATION OUTLOOK CONTINUES TO DEPICT AN ENHANCED LIKELIHOOD FOR ABOVE-NORMAL PRECIPITATION FOR SOUTHWEST ALASKA AND MUCH OF THE SOUTHERN TIER OF THE CONUS, AS WELL AS ENHANCED ODDS FOR BELOW-NORMAL PRECIPITATION FOR THE PACIFIC NORTHWEST, CONSISTENT IN MOST PLACES WITH INFORMATION LISTED AT MID-MONTH. ONE ADDITION IS AN ENHANCED LIKELIHOOD FOR BELOW-NORMAL PRECIPITATION FOR NORTHEAST ALASKA AS A RESULT OF SOME RIDGING IN THIS AREA. HIGH ODDS FOR TROPICAL CYCLONE ROSA AND/OR ITS REMAINING MOISTURE TO IMPACT MUCH OF THE SOUTHWEST CONUS HAVE DRAMATICALLY INCREASED PROBABILITIES , FOR ABOVE-NORMAL PRECIPITATION FOR OCTOBER IN THIS AREA AS WELL AS WARRANTING AN EXPANSION OF COVERAGE FOR PARTS OF CALIFORNIA, NEVADA AND THE CENTRAL ROCKIES AS IT INTERACTS WITH A SHORTWAVE TROUGH ENTERING THE PACIFIC COAST EARLY IN THE MONTH.

THE ANTICIPATED HIGHLY AMPLIFIED 500-HPA FLOW PATTERN OF A TROUGH – RIDGE PATTERN FROM THE WESTERN CONUS TO THE EASTERN CONUS FAVORS A VERY ACTIVE PATTERN DURING THE FIRST HALF OF OCTOBER WITH A CONSIDERABLY ENHANCED LIKELIHOOD OF STRONG CYCLONES, PRECIPITATION AND ASSOCIATED IMPACTS FOR A RATHER LARGE REGION STRETCHING FROM THE CENTRAL CONUS TO THE GREAT LAKES AND POTENTIALLY NEW ENGLAND AND THE OHIO VALLEY. THIS IS A CONCERN AS THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION ARE ANTICIPATED TO BE OVER SOME REGIONS IN THE MIDWEST THAT HAVE SEEN RECENT FLASH FLOODING AND CONSIDERABLY ABOVE-NORMAL STREAMFLOWS. A GENERALLY DRY START TO THE MONTH IN PARTS OF THE MID-ATLANTIC AND SOUTHEAST CONUS ARE OFFSET BY A SHIFT TO POTENTIALLY ELEVATED ODDS OF ENHANCED WETNESS AFTER MID-MONTH SO EC IS FORECAST.

Week 3-4 Forecast Discussion Valid Sat Oct 13 2018-Fri Oct 26 2018

ENSO-neutral conditions are present across the equatorial Pacific Ocean. Equatorial sea surface temperatures (SSTs) are near to above average across most of the Pacific Ocean, though the spatial distribution of convective anomalies is not particularly coherent. An MJO signal has emerged over the Western Hemisphere within the past week or so as monitored by the both the RMM and CPC indices. Some eastward propagation of the MJO signal is favored over the next couple of weeks. The Week 3-4 temperature and precipitation outlooks rely primarily on dynamical model forecasts that depict a high-amplitude wave pattern over the Pacific-North America region. The statistical guidance from both the MLR and constructed analog depicts a pattern nearly opposite that of the dynamical model consensus, which serves to limit the magnitude of forecast probabilities. The final forecast is derived from the NCEP CFS, the ECMWF, and the JMA operational ensemble prediction systems, as well as forecasts from the Subseasonal Experiment (SubX), a multi-model ensemble (MME) of experimental ensemble prediction systems. Consideration is also given to the possible evolution of the predicted circulation pattern during Week-2.

Dynamical model guidance from the various models is broadly consistent, depicting a trough south of the Aleutians, while a strong ridge is forecast over the Gulf of Alaska. Downstream a deep trough extends from central Canada eastward across the far North Atlantic, while anomalous ridging is forecast over the mid-latitude Atlantic stretching back toward the Southeast Coast. The forecast circulation pattern strongly favors above-normal temperatures over Alaska and anomalous cold air advection over the north-central CONUS. A mean frontal zone is forecast over the interior eastern CONUS, with the forecast circulation over the North Atlantic (+NAO structure) favoring a warmer solution over the Southeast compared to most of the dynamical model guidance.

The various model guidance is in fairly good agreement on the precipitation outlook for the Week 3-4 period. Forecast ridging across the Northeast Pacific supports increased chances of anomalously dry conditions for the northwestern CONUS. Above-normal precipitation is favored across much of the south-central and southeastern CONUS, consistent with dynamical model guidance and the aforementioned baroclinic zone over the interior Southeast. Above-normal precipitation is likely in southern Alaska just west of the anomalous ridge axis.

Persistent positive SST anomalies continue to surround Hawaii, supporting increased chances of above-normal temperatures and precipitation across the island chain. Dynamical model precipitation forecasts generally favor increasing odds of above-normal precipitation moving from northwest to southeast across the state.

Visual Consistency Testing.

Sometimes it is useful to see how the Monthly forecast fits with the 1 – 5 Day,  6 – 10 Day , 8 – 14 Day and Week 3 and 4 forecasts. Since we are combining the end of month October Update with the regular weekly Weather and Climate Report, this consistency testing also serves as a summary of the forecast for the next 25 days. 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

This shows magnitude rather than probability of  being higher or lower than Normal and shows the middle day of the five day period.	It is a fairly stagnant pattern but moving east		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 forecast seems feasible
The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts?        →			↑ ←  The full month forecast seems to fit with the concatenation of the partial month forecasts.

And then Precipitation

The five day QPF is shown to the right. The units are different than the other maps i.e. in units of precipitation (inches) not probabilities of exceeding or being less than climatology.	It is mostly wet but as the wet anomaly moves east a dry anomaly is appearing along the West Coast.		↑ ←  The transition from the 8 -14 day forecast shown above to the week 3/4 seems to be  feasible.
The new monthly forecast is to the right. Does it appear to be reflective of the three parts of the month for which we have forecasts?      →			↑ ← The full month forecast seems to fit fairly well with the concatenated partial month forecasts.

Sometimes it is useful to compare the forecast for the current month with the prior three-month forecast to see if the updated forecast for October might impact the prior forecast for October/November /December issued ten days ago.

October 2018 Plus October  –  December 2018 Outlook

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.

*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.

For comparison purposes, here are the NOAA October/November and December forecast maps on the first set of rows and the September – October – November JAMSTEC forecast maps for North America in the second set of rows. * JAMSTEC  did not publish an OND forecast but a SON forecast.

NOAA October – December  2018 Temperature	NOAA October – December  2018 Precipitation
JAMSTEC September October November 2018 Temperature	JAMSTEC September October November Precipitation

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 the approach of the Tropical Cyclone and the other Pacific Low arriving and doing their FujiWhara dance.

Tonight, Monday October 1, 2018, as I am looking at the above graphic, of most interest is the Low off the West Coast. We know what Rosa is doing but the off shore Low is harder to forecast.

This graphic is about 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.

And Now the Day One and Two CONUS Forecasts

Additional useful forecasts from the Storm Prediction Center and be found here.  Storm events are covered by Met Watch which can be accessed here. Explanation of symbols can be found here.

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.

You can enlarge the below daily (days 3 – 7) weather maps for CONUS by clicking on Day 3 or Day 4 or Day 5 or Day 6 or Day 7. These maps auto-update so whenever you click on them they will be forecast maps for the number of days in the future shown.

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 forecasted 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. Actually all the small graphics below can be clicked on to enlarge them.

Big changes. When I look at this Day 7 forecast, we see the Hawaiian High with surface central pressure of 1026 hPa. The Aleutian Low is weak with surface central pressure of 1000 hPa and it is located over the western Aleutians but extends to the Northwest coast of CONUS. To the northeast, there is a huge Western Canadian High with surface central pressure of 1032 hPa. Further east, over Greenland there is a High with surface central pressure of 1008 hPa. North of Hudson Bay there is a Low with surface central pressure of 1004 hPa. There is a High over Northeast Canada with surface central pressure of 1028 hPa. To the southwest of where we would normally look for the Four Corners High there is a low and an inverted trough entering from Mexico with surface central pressure of 1008 hPa.

I provided this write up that provides a simple explanation on the importance of semipermanent Highs and Lows and another link that discussed possible changes in the patterns of these highs and lows which could be related to a Climate Shift (cycle) in the Pacific or Global Warming. Remember this is a forecast for Day 7. It is not the current situation.

The table below showing the Day 3, Day 4, Day 5, Day 6 and Day 7 of this graphic can be useful in thinking about how the pattern of Highs and Lows is expect to move during the week.

From left to right and then down, Days 3 and 4 top row, Days 5 and 6 second row and Day 7 to the right. These are small images but you can if you want click on them and get larger images but even with the small images you can trace the evolution of the pattern. The graphics update but my commentary below does not so it is just a guide for how to read these graphics.
Things to look for in general are the position and strength of the Aleutian Low, the Hawaiian High and any troughs especially if they extend far to the south and are over water.

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 that trough from the Pacific	The trough digs south.

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.

Here is the whole suite of similar maps for Days 3, 4, 5, 6 and repeated for Day 7.  It is quite complicated.

Day 3 Above, 6 Below	Day 4 Above,7 Below	Day 5 Above.

Here is the seven-day cumulative precipitation forecast. More information is available here.

 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 October 1, 2018 was 5 out of 5

8 – 14 Day Temperature Outlook issued today (Note the NOAA Level of Confidence in the Forecast Released on October 1, 2018 was 4 out of 5).

–

Looking further out.

Now – Precipitation

6 – 10 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on October 1, 2018 was 5 out of 5)

8 – 14 Day Precipitation Outlook Issued Today (Note the NOAA Level of Confidence in the Forecast Released on October 1, 2018 was 4 out of 5)

Looking further out.

Here is the 6 – 14 Day NOAA discussion released today October 1

6-10 DAY OUTLOOK FOR OCT 07 – 11 2018

THERE IS VERY GOOD MODEL AGREEMENT IN TERMS OF THE 500-HPA GEOPOTENTIAL HEIGHT  PATTERN FROM TODAY’S DYNAMICAL MODEL RUNS. BOTH THE GFS AND THE ECMWF ALONG  WITH THEIR ENSEMBLE MEANS FORECAST A HIGHLY AMPLIFIED PATTERN WITH A STRONG  RIDGE OVER ALASKA WITH TROUGHING DOWNSTREAM OVER THE CENTRAL AND WESTERN CONUS.  RIDGING IS FAVORED OVER THE EASTERN CONUS. THE AMPLITUDE OF THESE FEATURES IS  FAVORED TO BE STRONGEST EARLY IN THE PERIOD WITH SOME DECAY FORECAST TOWARD DAY 10. 

THE 500-HPA HEIGHT PATTERN DISCUSSED ABOVE WOULD FAVOR ABOVE NORMAL TEMPERATURES FOR ALASKA, BELOW NORMAL TEMPERATURES FOR THE WESTERN AND PARTS OF THE CENTRAL CONUS, AND ABOVE NORMAL TEMPERATURES FOR THE EASTERN CONUS.  THERE IS VERY HIGH CONFIDENCE IN THIS TEMPERATURE PATTERN WITH THE HIGHEST PROBABILITIES FOR BELOW NORMAL TEMPERATURES FAVORED FOR THE NORTHERN PLAINS INTO THE NORTHERN ROCKIES, WITH THE HIGHEST PROBABILITIES FOR ABOVE NORMAL  TEMPERATURES FAVORED IN THE MID-ATLANTIC.

THE TROUGH OVER THE CENTRAL AND WESTERN CONUS WILL FAVOR HIGHER PROBABILITIES  FOR ABOVE NORMAL PRECIPITATION FOR THE GREAT PLAINS NORTHEAST TO THE UPPER  MISSISSIPPI VALLEY. MULTIPLE SHORTWAVE DISTURBANCES AND ASSOCIATED SURFACE LOW  PRESSURE AREAS ARE FORECAST TO ROUND THE BASE OF THE TROUGH AND TRACK  NORTHEASTWARD FAVORING THE ABOVE NORMAL PRECIPITATION CHANCES FOR THE  AFOREMENTIONED REGIONS. BOTH TODAY’S 00Z ECMWF ENSEMBLE MEAN AND 00Z GEFS HAVE  A LARGE AREA OF TOTAL PRECIPITATION AMOUNTS OF 2-4 INCHES OVER THE ENTIRE 6-10 DAY PERIOD. HEIGHTENED POTENTIAL OF ABOVE NORMAL PRECIPITATION IS ALSO FAVORED  FOR THE CENTRAL AND NORTHERN ROCKIES, ESPECIALLY EARLY IN THE PERIOD. DUE TO  THE FAVORED BELOW NORMAL TEMPERATURES IN THIS REGION, WINTRY PRECIPITATION WILL  BE POSSIBLE. DYNAMICAL GUIDANCE FROM THE 00Z ECMWF ENSEMBLE MEAN AND 06Z GEFS  FAVOR ENHANCED PROBABILITIES FOR BELOW NORMAL PRECIPITATION ACROSS THE EASTERN CONUS AND INTO PARTS OF THE DEEP SOUTH.  TELECONNECTIONS WITH THE 500-HPA HEIGHT ANOMALY CENTERED IN THE NORTHEAST CONUS FAVOR THE HIGHEST PROBABILITIES  FOR BELOW NORMAL PRECIPITATION OVER SOUTHEAST NEW ENGLAND. ANALOG GUIDANCE ALSO  FAVORS ELEVATED PROBABILITIES FOR BELOW NORMAL PRECIPITATION FOR PARTS OF THE EASTERN CONUS. WHILE RIDGING OVER ALASKA WILL FAVOR BELOW NORMAL PRECIPITATION  OVER THE NORTHERN PART OF THE STATE, UPSTREAM TROUGHING AND CYCLONIC INFLUENCE  WILL KEEP PROBABILITIES FOR ABOVE NORMAL PRECIPITATION INCREASED FOR WESTERN  ALASKA THE ALEUTIANS.  

FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: WELL ABOVE AVERAGE, 5 OUT OF 5,  DUE TO GOOD AGREEMENT AMONG THE MODELS AND TEMPERATURE TOOLS AND A WELL-DEFINED  HIGHLY AMPLIFIED PATTERN

8-14 DAY OUTLOOK FOR OCT 09 – 15 2018 

THE 00Z ECMWF ENSEMBLE MEAN AND 06Z GEFS MAINTAIN GOOD AGREEMENT FOR THE WEEK-2 PERIOD WITH THE SAME OVERALL PATTERN AS THE 6-10 DAY PERIOD, EXCEPT NOT AS  AMPLIFIED. THE HEIGHT PATTERN OVER ALASKA IS FORECAST TO BE MORE TRANSIENT WITH THE LARGE RIDGE PRESENT IN THE 6-10 DAY PERIOD WEAKENING AND THE REGION BEING INFLUENCED BY TROUGHING SHIFTING EASTWARD FROM THE BERING SEA. 

THE TEMPERATURE FORECASTS FOR WEEK-2 ARE SIMILAR TO THE 6-10 DAY PERIOD WITH ABOVE NORMAL TEMPERATURES FAVORED IN THE EASTERN CONUS, AND BELOW NORMAL  TEMPERATURES FAVORED IN THE WESTERN CONUS. ABOVE NORMAL TEMPERATURES ARE STILL  FAVORED FOR ALASKA. WHILE THE RIDGE IS FORECAST TO WEAKEN, ABOVE NORMAL SSTS  SHOULD CONTINUE TO INFLUENCE TEMPERATURES.    FOR PRECIPITATION, THE HIGHEST CONFIDENCE FOR ABOVE NORMAL PROBABILITIES IS IN THE MISSISSIPPI VALLEY, DOWNSTREAM OF THE DECAYING TROUGH WHERE FRONTAL FORCING IS STILL FAVORED TO BE DOMINANT. DUE TO THE PATTERN NOT BEING AS AMPLIFIED AS IN THE DAY 6-10 PERIOD, THE STORM TRACK IS PROJECTED TO HAVE MORE OF AN EASTERLY COMPONENT RATHER THAN NORTHERLY, FAVORING HIGHER PROBABILITIES FOR THE  NORTHEAST CONUS RELATIVE TO THE 6-10 DAY PERIOD. THERE IS SOME UNCERTAINTY IN  THE DEEP SOUTH WHERE THE DYNAMICAL MODELS AND ANALOG GUIDANCE CONTINUE TO FAVOR  BELOW NORMAL PRECIPITATION PROBABILITIES FROM THE 6-10 DAY PERIOD, BUT THE  SIGNAL IS WEAKER. THERE ARE SOME INDICATIONS THAT THE REMNANTS OF TROPICAL  STORM SERGIO, CURRENTLY AN EASTERN PACIFIC TROPICAL CYCLONE, ARE DRAWN INTO THE  SOUTHWESTERN CONUS DURING THE WEEK-2 PERIOD, ENHANCING PRECIPITATION PROBABILITIES IN THAT REGION. ALSO, THERE IS AN INCREASED CHANCE OF TROPICAL CYCLONE DEVELOPMENT IN THE WESTERN CARIBBEAN DURING THE WEEK-2 PERIOD WITH THE TRACK OF THE POTENTIAL SYSTEM CURRENTLY FAVORED TO BE AWAY FROM THE CONUS.  ALASKA IS FORECAST TO SEE AN ACTIVE STORM TRACK IN ASSOCIATION WITH THE  AFOREMENTIONED TROUGHING FAVORING THE HIGHEST PRECIPITATION PROBABILITIES FOR  THE WESTERN HALF OF THE STATE.

FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO GOOD MODEL AGREEMENT.

THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON  OCTOBER 18.

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.

Below is a graphical explanation of the Arctic Oscillation

Left: Effects of the Positive Phase of the Arctic Oscillation. Right:Effects of the Negative Phase of the Arctic Oscillation. —Credit: J. Wallace, University of Washington.

NAO Positive	NAO Negative
Notice the strong Icelandic Low and strong Bermuda High but located east of where it is usually found	Notice the weak Icelandic Low and Bermuda High.
There are many variations on a theme when talking about the NAO.	Some use Lisbon or Gibraltar as the sub-arctic reference point. And there appears to be a low-frequency cycle related to the AMO to some extent. Thus the NAO is a lot more complicated than I am able to show here.  I like this explanation better than the graphics I have shown. It better captures the impact of the changing relative strength of the two control factors in the Atlantic namely the Northern and Southern semi-permanent Highs and Lows.

But it gets even more complicated. With a Negative NAO the position of the pattern more east than west or vice versa changes the impacts.

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.

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. 

First we look at two models that I find very helpful. On the first 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.

 First.

And then

This tool allows one to translate the location of the forecast MJO to the impacts on CONUS. To make it easier for the reader I am displaying the highest probability interpretation for the time period in question namely September/October/Novermber. This (70% match) of course might miss some other impacts which have less statistical confirmation but may none-the-less be valid.

Remember we are interested in Phase 8 as it impacts CONUS weather during August September and October. So that is what I have displayed.

Temperature

Precipitation

I can not display it in the article but this is another link to an application that allows you to figure out the “lagged” impacts on temperature of the MJO. There is a lot of statistical analysis available to predict the impacts of the MJO which is different from predicting the location of the MJO. I am not sure if the lagged impacts are better than what you get with the link I provided earlier.

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.

(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.

* Index reads positive for that month but that was a period of time that was generally PDO Negative.

The spread among the analogs from September 10 to October 10 is 30 days which is about the same as last week. 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 September 25. These analogs are centered on 3 days and 4 days ago (Sept 27 or September 28). So the analogs could be considered to be just a bit out of sync with respect to weather that we would normally be getting right now  i.e. a few days late {had said early by mistake].

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 El Nino Analogs, zero Neutral analogs and six La Nina Analogs. The pre-forecast analogs this week are most non-supportive of McCabe D which is the prmary Drough Condition so this supports the NOAA 6 – 14 Day forecast. Many of the analogs are associated with AMO Negative.

The seminal work on the impact of the PDO and AMO on U.S. climate can be found here. Water Planners might usefully pay attention to the low-frequency cycles such as the AMO and the PDO as the media tends to focus on the current and short-term forecasts to the exclusion of what we can reasonably anticipate over multi-decadal periods of time. One of the major reasons that I write this weather and climate column is to encourage a more long-term and World view of weather.

In color	Black and White same graphics

You may have to squint but the drought probabilities are shown on the map and also indicated by the color coding with shades of red indicating higher than 25% of the years are drought years (25% or less of average precipitation for that area) and shades of blue indicating less than 25% of the years are drought years. Thus drought is defined as the condition that occurs 25% of the time and this ties in nicely with each of the four pairs of two phases of the AMO and PDO.

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.

Recent CONUS Weather

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

And the 30 Days ending September 15, 2018	And the 30 Days ending September 22, 2018
We see the impact of Florence but it is less than one might have expected. The Temperature anomalies are more extreme especially in the East.	The Western Drought is more intense and the Warm anomaly is breaking down.
Remember, these maps are a 30 average so the most distant seven days are removed and the most recent seven days are added.

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 October and we should be returning from the set of positions shown below for July back slowly to the Winter Pattern. For CONUS, the seasonal repositioning of the Bermuda High and the Pacific High are very significant.

World Forecasts

A. Today (University of Maine)

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

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

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

And now precipitation

Additional Maps showing different weather variables can be found here.

B. 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

Please remember this graphic updates every six hours so the diurnal pattern can confuse the reader.

Now Precipitation

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

First Temperature

Then Precipitation

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

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 and
• The changes in the temperature anomalies since that may provide clues as to how the surface anomalies will change based on the current trend of changes. This is not that easy to do since the oceans are deep, there are many currents, winds have an impact etc

When we look in more detail at the current Sea Surface anomalies below, we see a lot of them not just along the Equator related to ENSO.

First the categorization of the current daily SST anomalies.
Mediterranean, Black Sea and Caspian Sea	Western Pacific	West of North America	North and East of North America	North Atlantic
The Mediterranean. Black Sea and Caspian Sea are slightly warm It is cool off Somalia	Warm around Kamchatka	Very warm Chukchi Sea, Bering Strait and Bering Sea Warm offshore of Alaska Panhandle Warm off Baja	Hudson Bay cool Cool west of the British Isles way south of Greenland. Warm offshore of Nova Scotia down to Cape Hatteras Slightly warm northern Gulf of Mexico	Warm northeast of Scandinavia
Equator	Still looks a bit warmer
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Warm offshore of the west coast of Africa along the  Equator. Cool south of Gulf of Guinea Warm between Mozambique and Madagascar and beyond.	Very Cool	Cool to the southwest	Fairly Neutral	Warm off 20S to 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.
Mediterranean, Black Sea and Caspian Sea	Western North Pacific	West of North America	East of North America	North Atlantic
Mediterranean is mostly Neutral. Black Sea is cooling. Southern Caspian Sea is warming. Warming in the Arabian Sea	Cooling north of Japan but warming east and south of Japan.	Warming in Bering Sea Warming around and south of Alaska. Very intense south of the western end of the Aleutians.	Cooling Davis Straits and Nova Scotia Some warming east of Southeast Coast Cooling east of South America along the Equator.	Significant cooling around British Isles and further to the northwest.
Equator	Eastern Pacific showing an El Nino Pattern
Africa	West of Australia	North, South and East of Australia	West of South America	East of South America
Cooling west of North Africa. Warming between Tanzania and Madagascar.	Neutral	Slight warming to the southeast	Warming offshore 20S to 30S	Cooling at and north of the Equator Warming 30S to 40S Cooling offshore at 40S to 50S

Switching gears, below is an analysis of projected tropical hazards and benefits over an approximately two-week period.

 * Moderate Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.** High Confidence that the indicated anomaly will be in the upper or lower third of the historical range as indicated in the Legend.

Tropical Activity

Atlantic

Tropical Weather Discussion NWS National Hurricane Center Miami FL 157 PM EDT Mon Oct 1 2018

Tropical Weather Discussion for North America, Central America Gulf of Mexico, Caribbean Sea, northern sections of South America, and Atlantic Ocean to the African coast from the Equator to 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through 1715 UTC.

…SPECIAL FEATURES…

Tropical Storm Leslie is centered near 33.2N 54.3W at 01/1500 UTC or 535 nm E of Bermuda moving WSW at 4 kt. Estimated minimum central pressure is 990 mb. Maximum sustained wind speed is 50 kt  with gusts to 60 kt. Scattered moderate convection is within 120 nm north and northeast of the center, with weaker convection elsewhere within 180 nm of the center. A slow southwestward or southward motion is forecast during the next few days. Gradual  strengthening is expected during the next 48 hours, and Leslie is forecast to become a hurricane on Tuesday. The Public Advisories  for Leslie are transmitted via the WMO header WTNT33 KNHC, and via the AWIPS header MIATCPAT3. The Forecast/Advisories for Leslie are transmitted via the WMO header WTNT23 KNHC, and via the AWIPS header MIATCMAT3.

…TROPICAL WAVES…

An Atlantic Ocean tropical wave is along 42W from 02N-14N, moving W around 20 kt. The southern portion of the wave has a 700 mb trough associated with it. Scattered showers and isolated thunderstorms are from 08N-10N between 41W-45W.

An Atlantic Ocean tropical wave is along 56W from 05N-17N, moving W at 10-15 kt. The wave has a well defined 700 mb trough associated with it. The GOES-16 TPW imagery also shows a moist area around the wave axis. Isolated showers are seen from 15N-16N between 53W-54W.

…MONSOON TROUGH/ITCZ…

The monsoon trough passes through the coastal sections of Senegal near 13N17W, to 10N25W to 08N35W. The ITCZ extends from 07N43W to the coast of French Guiana near 05N52W. Aside from the convection associated with the tropical waves, scattered showers and thunderstorms are within 90 nm north and 180 nm south of the monsoon trough between 21W-28W.

…DISCUSSION…

GULF OF MEXICO…

An upper level trough oriented NNE-SSW is over E Texas. Upper level diffluence E of this feature covers much of the central and northeast Gulf. Scattered moderate convection is noted off the coast of Texas from 26N-30N west of 93W. Isolated showers and thunderstorms are also occurring from 27N-29N between 85W-87W. At the surface, east winds of 10-15 kt cover most of the Gulf.

Expect ridging to prevail over the forecast area during the next few days. A surface trough will develop each evening in the Yucatan peninsula. The trough will move into the SW Gulf of Mexico overnight, where it will dissipate each morning. Moderate to fresh winds will accompany the trough.

CARIBBEAN SEA…

Upper level troughing extends over much of Cuba and the northwest Caribbean Sea. Scattered showers are over the Yucatan Channel and the Windward passage. Broad upper level ridging is over the central and eastern Caribbean with westerly upper level flow, leading to fair weather east of 70W.

A surface trough over the central Caribbean Sea has been nearly stationary along 76W. Scattered moderate to strong convection is seen from 12N-16N between 72W-82W. The trough will remain nearly stationary or perhaps move very slowly toward the western Caribbean over the next several days. A large cyclonic gyre is expected to develop over this area by Friday. A large NNE swell generated from Leslie will continue to move through the Atlantic passages into the Caribbean.

ATLANTIC OCEAN…

A remnant cloud line from a front that dissipated during the last 24 hours is producing scattered showers and thunderstorms off the east coast of north-central FL and north of the northwest  Bahamas. Broad surface cyclonic wind flow covers the central Atlantic within a large distance surrounding Tropical Storm Leslie. In between Leslie and a mid-level high near 17N33W, numerous moderate convection is being generated from 25N-30N between 41W-47W. Isolated showers and thunderstorms are occurring elsewhere from 22N-28N between 47W and the coast of north-central Florida, to the north and east of the Bahamas.

A tropical wave still over west Africa is producing an area of scattered moderate convection offshore from 03N-08N between 12W-17W. Scattered moderate to isolated strong convection is also occurring over Sierra Leone and Guinea.

For additional information please visit

http://www.hurricanes.gov/marine

Eastern Pacific

Tropical Weather Discussion NWS National Hurricane Center Miami FL 2143 UTC Mon Oct 1 2018

Tropical Weather Discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis.

Based on 1800 UTC surface analysis and satellite imagery through 2100 UTC.

…SPECIAL FEATURES…

Tropical Storm Rosa centered near 28.1N 116.2W at 01/2100 UTC or 60 nm WNW of Punta Eugenia Mexico moving NNE at 9 kt. Estimated minimum central pressure is 1002 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. Rosa is completely exposed,  with no significant showers or thunderstorms in its vicinity.  Rosa will move across the southern half of Baja California Norte this evening and tonight, then weaken to a depression over the northern Gulf of California late tonight into early Tue morning.  Rosa’s remnants are then expected to move across the Desert  Southwest on Tuesday. Currently, heavy rain associated with Rosa  continue to spread northward across the southwest United States.  Swells generated by Rosa are affecting portions of the coasts of  southwestern Mexico, most of the west coast of the Baja California peninsula, and southern California, and will persist through Tuesday. These swells are likely to cause life-threatening surf and rip current conditions. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP5/WTPZ25 KNHC for more details.

Farther south, Tropical Storm Sergio centered northwest of Clipperton Island near 11.3N 111.0W at 01/2100 UTC or 600 nm SW of Manzanillo Mexico moving W at 12 kt. Estimated minimum central pressure is 995 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Numerous moderate to strong convection is noted within 150 nm of the center of Sergio. In addition, scattered moderate to isolated strong convection is active within 60 nm either side of a band reaching from 06N113W to 09N108W. Strengthening is forecast during the next 48 hours, and Sergio is expected to become a hurricane tonight as it continues westward and a major hurricane by late Thu as it starts moving more to the northwest. See latest NHC forecast/advisory under AWIPS/WMO headers  MIATCPEP1/WTPZ31 KNHC for more details.

…INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH…

The monsoon trough extends from 09N76W to 11N100W. Another segment of the monsoon trough reaches from 15N120W to beyond 10N140W. Scattered moderate convection is noted within 30 nm of the monsoon trough between 85W and 100W. Scattered moderate convection is also noted within 60 nm of the monsoon trough between 120W and 125W.

…DISCUSSION…

OFFSHORE WATERS WITHIN 250 NM OF MEXICO…

See Special Features above for information on Hurricane Rosa and Tropical Storm Sergio.

Swell associated with Rosa will continue to propagate across the offshore forecast waters W of Baja California. Seas in the form of mixed swell in excess of 8 ft are observed from 20N to 30N east of 120W. Farther south, swell generated by Sergio in excess of 8 ft is observed in various altimeter passes reaching to just beyond 120 nm off the coast of Mexico between Acapulco and Cabo Corrientes. Some of this swell may be reaching the coastal areas and producing dangerous surf. 

In the Gulf of California, a recent scatterometer pass confirmed fresh to strong west winds across the far northern Gulf, ahead of Rosa. These winds will veer more SE to S tonight as Rosa approaches, with seas building to around 10 ft late today north of Tiburon Island. Tropical storm conditions from Rosa are possible across the northern Gulf of California tonight. Winds and seas will diminish rapidly thereafter over the northern Gulf of California through late Tue.

In the Gulf of Tehuantepec, pulsing winds of 20 to 30 kt are expected during the overnight and early morning hours through at least early Wed morning. Seas are forecast to build to 9 or 10 ft with the strongest winds.

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR…

The monsoon trough will meander between 09N and 12N through Fri, with gentle to moderate winds expected on either side of the  trough axis. Scattered showers and thunderstorms are possible  near the coast, mainly at night.

REMAINDER OF THE AREA…  

See Special Features above for information on Tropical Storm Rosa and Tropical Storm Sergio.

A cold front reaching from 30N130W to 24N140W will sweep eastward across the waters north of 20N through mid week, but become diffuse before reaching 120W. This weather pattern will keep the trade wind flow minimal farther south into the deep tropics. NW swell in the wake of the front will propagate across the NW waters through Tue, while seas associated with Rosa will subside to less than 8 ft W of the Baja California Peninsula. Later in the week, seas associated with Sergio will mix with additional pulses of long period NW swell. By Thu, seas of 8 ft or greater are expected to cover most of the waters N of 10N W of 105W, including the entrance of the Gulf of California.