Seasonal Forecasts Issued March 19, 2020: Part I, NOAA Four-Season Forecast

Written by Sig Silber

Here is the March 19, 2020, NOAA 15-month forecast for CONUS and Alaska including the Early Outlook for April 2020 and forecasts out through June 2021. The forecast is very similar to what was issued last month. NOAA is not very confident in their Early Outlook for April so we might expect a lot of revisions when that is updated on March 31. But in the short-term, it looks like the West is going to be somewhat dry. Soon (probably Sunday Night) we will compare the NOAA forecast to the JAMSTEC forecast. Among other things, we will look at the Monsoon Forecast. NOAA is leaning towards an average Monsoon and for JAMSTEC it depends on which of their models you rely on.

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A. Focus on the NOAA Update

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 my comments For the shorter-term maps, NOAA uses “N” instead of “EC” as they believe they can be more definitive with respect to shorter timeframes. So the words “warm”, “cool”, “wet”, “dry” should be generally interpreted as being relative to climatology/normal for that location and time of year.

First, we will take a look at the NOAA Early Outlook for April, 2020. It is called the Early Outlook because it will be updated at the end of March. Only the April Outlook will be updated at that time.

Temperature

Precipitation

We have nothing to compare these maps with as NOAA does not provide in their Update a forecast for each of the subsequent two months separate from their three-month forecast. Thus I do not have forecast maps for April from the previous NOAA Report to compare against. And the current month is not over so we can not really compare the forecast for next month against the actual for this month. It is probably best to just try to understand what NOAA is trying to convey about April*. For Temperature, it is mostly warm in the extreme western and northern Alaska but cool in southeast Alaska and the Panhandle. There is a very large warm anomaly stretching from the Mississippi River to the Atlantic Ocean and also the Southern Tier states as far west as eastern Arizona. There is a small cool anomaly centered on eastern Montana. With respect to precipitation, northern Alaska is wet but southeast Alaska and the Panhandle is dry as are the western parts of Washington and Oregon and northern California.  The Southeast is wet except for southern Florida which is EC. There is also a wet swath centered on Iowa and extending to the west and southeast to the other wet anomaly. The net result is a lot of water possibly flowing into the central and lower Mississippi River. So flooding could be an issue. 

* compared to normal/climatology for the indicated time of the year.

Visual Consistency Testing.

It is useful to see how the month forecast fits with the set of shorter forecasts that we have. The first map covers only March (so only two of the three maps are really useful for this purpose) and the third map only extends the coverage through the first seventeen days of March. The Seasonal Outlook was issued fairly late this month since the third Thursday fell on March 19, 2020. I think the latest it can be is the 21st of a month. Seventeen days of shorter forecasts is still not a solid basis for doing this visual consistency testing but it is what we have to work with and it is more than usual. It may tell us how the last thirteen days of the month should differ from the first seventeen days for the full-month forecast to be accurate.

First Temperature

The new monthly forecast is to the right. Does it appear to be reflective of the parts of the month for which we have forecasts? →		↑ ← The full month forecast fits well with the 8 – 14 Day and Week 3 – 4 forecasts which only covers Seventeen days of April as of when we published this article. Will the West Coast average out to be EC for the full month remains an issue? We will revisit this question and others at the end of March when the April forecast is updated.

And then Precipitation

The new monthly forecast is to the right. Does it appear to be reflective of the parts of the month for which we have forecasts? →		↑ ← The full month forecast does seem to fit fairly well with the 8 – 14 Day and Week 3 – 4 forecasts which only covers seventeen days of April as of when we published this article. We have to assume that the last thirteen days of the month will have a dry Northeast or the monthly forecast will not pan out. We will revisit this question at the end of March when the April forecast is updated.

Now we consider the three-month Outlook.

Notice that the three-month periods are abbreviated e.g. April/May/June is shown as AMJ. You will see such abbreviations often in this report.

Prior Temperature Outlook for AMJ 2020

New Temperature Outlook for AMJ 2020

Prior Precipitation Outlook for AMJ 2020

New Precipitation Outlook for AMJ 2020

Now let us focus on the long-term situation.

First Temperature

Prior 14 Month Temperature Outlook: AMJ 2020 – MAM 2021

New 14 Month Temperature Outlook: MJJ 2020 – AMJ 2021

To compare maps from one release to another, one needs to remember that the new release drops one three-month period and adds a later one. So to make the comparisons one has to shift the new maps to the right one position and that makes the map on the right drop down to become the left-most map in the next level. I do not have a computer software tool for doing that for you so you have to do it mentally. When I do the comparison, I print the two sets of maps and put them side by side and number the same three-month maps 1, 2, 3,…..,11 in both sets of maps to make it easier for me to easily compare the same three-month period in the new with the previous forecast. One uses the same procedure to compare the precipitation maps. Based on this procedure, I conclude that:

Now Precipitation

Prior 14 Month Precipitation Outlook: AMJ 2020 – MAM 2021

New 14 Month Precipitation Outlook: MJJ 2020 – AMJ 2021

If you want larger versions of each map (temperature and precipitation) you can find them here. And then each of those maps can be clicked on to further enlarge them.

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.

*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.

Below is the NOAA Discussion (slightly reorganized) released by NOAA on March 19, 2020. Headings that are “Initial Cap” only rather than all caps were added by the Author of this Update Report for clarity. Also, we have organized the sequence of the sections of NOAA Discussion to first present the Atmospheric and Oceanic Conditions and then the Initial Month (April), the new NOAA Summary for AMJ, and finally the remainder of the 15-Month Forecast.

CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS

ENSO-neutral conditions are in place across the Pacific Ocean at the current time. Sea surface temperature (SST) anomalies vary across the equatorial Pacific Ocean and range from greater than +1.0 degrees C west to just east of the Date Line while only small SST anomalies (positive and negative) are evident in the east-central Pacific portion of the basin. The Nino3.4 regional SST anomaly has oscillated between +0.2 to +0.6 degrees C for the last several months. At depth, there is a substantial area of positive ocean temperature anomalies from 160E to 120W primarily over a layer of 50 – 150 meters depth. Negative ocean temperature anomalies are present in the western Pacific and also in the far eastern Pacific Ocean close to the surface to a depth of 100 meters.

Atmospheric conditions do show enhanced convection along the equator near the Date line associated with the positive SST anomalies located in this region. This convective anomaly has linked with the subtropical and mid-latitude circulation in the northeast Pacific in recent weeks. Monthly mean wind departures from normal currently indicate a small region of westerly wind anomalies along and just south of the equator west of the Date Line. Anomalously high soil moisture content is present from the northern Plains to the western Great Lakes southward to include most of the Great Plains, Mississippi Valley, Ohio Valley, Tennessee Valley and Southeast. Severe and extreme drought conditions are now present across south Texas and deteriorating drought conditions continue across much of California, Oregon and the Florida Peninsula.

An additional factor this spring is the substantially below-normal snow cover and/or snow depth in many areas across the country due to the anomalously warm winter for most of the country. This is especially true for the Northeast, mid-Atlantic, parts of the Great Lakes, Ohio Valley and much of the upper Mississippi Valley and north central Plains.

Coastal SST anomalies are small in magnitude this year for waters in proximity to the Alaska south and west coasts and sea ice coverage in the Bering Sea and Bering Strait are for the first time in a while generally near the long term average – although ice is primarily first year ice, is thin and likely to melt out relatively quickly.

PROGNOSTIC DISCUSSION OF SST FORECASTS

The CPC Nino3.4 SST anomaly statistical forecasts indicate a continuation of ENSO-neutral with the CCA and Markov models on the positive side of the zero Nino3.4 SST anomaly line while the CA forecast trends  to slightly negative anomalies during the summer and autumn seasons. There are greater differences between these statistical forecasts and dynamical model forecasts as part of the NMME. All NMME model contributions forecast a decrease in the Nino3.4 SST anomaly from current values to either ENSO-neutral or weak La Nina ocean conditions. One of the most aggressive models is the CFS which forecasts crossing into La Nina territory by August 2020 along with a couple others. One ECCC and the 2 GFDL models decrease more gradually and remain in the ENSO-neutral category through October.

30-DAY OUTLOOK DISCUSSION FOR APRIL 2020  

The April outlooks for temperature and precipitation reflect the latest model  guidance, likely impacts from trends , tropical intraseasonal oscillations, antecedent soil moisture, current and likely snowpack, as well as sea ice near Alaska.  Over the western CONUS, the forecast is highly uncertain with initial model output from earlier in the month depicting conflicting signals  with more recent runs, and statistical tools depicting weak signals . The increased uncertainty is reflected in the increased coverage of equal chances, compared to many other CPC monthly outlooks.

Temperature

With respect to forcing factors for the outlook, trends would favor above normal temperatures at most locations, while high soil moisture would weakly favor below normal temperatures over the Great Plains. The MJO is forecast to emerge over the Indian Ocean and progress to the Maritime Continent by the beginning of the month, but the connection from the tropics to the mid-latitude is muted in April, relative to a winter.  Forecasts models predict a strong circumpolar flow in the mean, which would also mollify tropically teleconnected impacts, so the MJO was considered, but not any significant component for the April outlooks.

Snowpack (as assessed by NOHRSC) is below normal for much of the Great Plains and Northeast, which would favor above normal temperatures. Across the west, snowpack is generally lower than normal over the Southern Rockies, with closer to normal values in the Central Rockies. Late season storminess is predicted in the 6-14 day time frame, which could add significant snowpack to the West, though the impacts to temperature from snowpack are small, the potential for rapid changes just before the valid period does increase the uncertainty.  

Model outlooks from the NMME suite reflected generally above normal  temperatures, though some models had indications of below normal temperatures in the Northern Rockies and Northern Great Plains. More recent model output has significantly cooler solutions from the West Coast to the Great Plains, with the east remaining warm, so the uncertainty lead to low coverage in the temperature outlook from the West Coast to the Northern and Central Rockies and across the Central Great Plains. Recent dry conditions are not likely to abate in southern Texas, favoring above normal temperatures. Across the eastern CONUS, model outlooks and trends  favor above normal temperatures, while anomalously low snowpack (with the exception of areas around the Upper Great Lakes) enhances odds over the Northeast.  

Across Alaska, trends  favor above normal temperatures for much of the state, though ice coverage was near median in early March, so it’s higher coverage than many of the past few years, so probabilities for above normal temperatures are muted along the west coast of Alaska. Snowpack has recovered from a multiyear drought over southeastern Alaska and the Alaskan Panhandle, so that agrees with model forecasts favoring below normal temperatures for those areas.

Precipitation

The precipitation outlook is more uncertain than the temperature outlook as trends are not monotonic and weak in the spring. Model guidance and trends favor above normal precipitation from the southeast to the Middle Mississippi Valley, while the same predictors favor below normal precipitation across portions of the Pacific Northwest. A strong circumpolar flow could keep an active storm track focused into Alaska, which would favor above normal precipitation for central and northern Alaska, with below normal precipitation for the Alaska Panhandle and Southeast Alaska. Model guidance largely supports that pattern, so the official outlook reflects those patterns.

BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS

PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS

The temperature and precipitation outlooks for AMJ 2020 were based on a few factors, primarily bias-corrected and calibrated dynamical model guidance, statistical forecast tools utilizing various methodologies (including “bridging techniques”) and recent trends . Objective, historically skill based combinations of the above information was weighted quite heavily in the current set of outlooks. ENSO-neutral conditions have been assumed in these outlooks given current conditions and the high uncertainty moving forward through the summer and autumn months. This point in the seasonal cycle is historically the lowest forecast skill period for ENSO prediction. Recent climate trends  are considered for all leads but were relied on more heavily for the middle and later forecast leads. Simultaneous and lagged relationships between soil moisture anomalies and subsequent temperature and precipitation anomalies, along with snow cover / depth information was considered for the AMJ and MJJ outlooks.

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS  (Focus on AMJ)

ENSO-neutral conditions remain in place across the Pacific Ocean and ENSO-neutral conditions are favored to continue through summer 2020. Thereafter, there is considerable uncertainty for the phase of ENSO entering  autumn into early winter 2020.

Temperature

The April-May-June (AMJ) temperature outlook favors seasonal mean temperatures to be above-normal for nearly all of the United States with the greatest odds forecast for northwest Alaska, California and the Southwest, along the Gulf Coast and for the eastern one-third of the country. Lower probabilities for above-normal temperatures are forecast for areas of the central lower 48 and the Alaska Panhandle. A similar pattern is forecast through the summer and autumn months moving forward.

Precipitation

For precipitation, there are elevated odds for above-normal seasonal total precipitation amounts for northwest Alaska and for most of the central and eastern U.S. with the highest chances located across the Ohio Valley. Below-normal precipitation is most likely for the South coast of Alaska southward and eastward to include the Pacific Northwest and northern California, the central Rockies, New Mexico and western and southern Texas. Progressing into and through summer 2020, the aforementioned regions of above- and below-normal precipitation are maintained, but at decreased coverage and confidence.

PROGNOSTIC DISCUSSION OF OUTLOOKS – AMJ 2020 TO AMJ 2021

TEMPERATURE

The AMJ 2020 temperature outlook favors seasonal mean temperatures to be above-normal for nearly all of the United States. A small region in the northern High Plains is designated as “Equal Chances” (EC) where forecast probabilities for either above-, near- or below-normal temperatures are no different than the 33.3% climatological odds for a 3-class system. The greatest  odds for above-normal temperatures is for northwest Alaska, California and the Southwest, along the Gulf Coast and for the eastern one-third of the country. Overwhelming agreement between numerous seasonal forecast dynamical models across a number of operational forecast centers and general consistency from previous months model forecasts strongly support this outlook. Also, nearly all statistical guidance is consistent with the dynamical model guidance. Strong long term positive trends  (especially in the eastern CONUS, parts of the West and Alaska) and the lack of snow cover / depth in many areas also contributed to the elevated odds of above-normal temperatures. Lower probabilities for above-normal temperatures are forecast for areas of the central lower 48 due to some consideration of high soil moisture content in some of this region. This is also where the model spread and forecast uncertainty is the highest, where the confidence was the lowest and so probabilities here are only modest tilts to the warm side. The greatest odds for above-normal temperatures are across south Texas where severe and extreme drought are currently in place and odds for above-normal temperatures are slightly increased further across California and Oregon as a result of current below-normal soil moisture content.

A similar outlook pattern as shown in the AMJ 2020 outlook continues through the ASO 2020 season and is based on an objective, historical forecast skill weighted consolidation of dynamical model guidance and statistical forecast tools which indicates a quite robust signal. Outlooks from SON 2020 through DJF 2020-2021 are based on similar, compelling forecast guidance and indicate a decrease in odds for above-normal temperatures appearing and increasing in coverage from the north central CONUS to the Southeast and then the eastern CONUS by the DJF 2020-2021 season. Greater uncertainty, more coverage of EC and a more zonally oriented outlook is depicted with favored above-normal temperatures forecast for the southern CONUS from JFM 2021 into the spring 2021. Statistical guidance, primarily from long term trends  supports a small region of favored below-normal temperatures for areas of the far northern High Plains during FMA – MAM 2021.

PRECIPITATION

The AMJ precipitation outlook depicts elevated odds for above-normal seasonal total precipitation amounts for northwest Alaska and for most of the central and eastern CONUS. The primary driver for the outlook across the central and eastern U.S. is consistent signals  from the majority of dynamical model guidance, but also significantly due to positive long term trends  in much of this region. The highest odds are located across the Ohio Valley where there was a convergence of a wet signal among the dynamical model and statistical forecast guidance.

Below-normal precipitation is most likely for the South coast of Alaska southward and eastward to include the Pacific Northwest and northern California, the central Rockies, New Mexico and western and southern Texas. Similar information as noted above is utilized as the basis for the outlook in these regions. Below-normal soil moisture content to a small degree increased the odds for below-normal precipitation for parts of California, Oregon and southern Texas due to potential less local recycling of boundary layer moisture.

Progressing into and through JAS 2020, the aforementioned regions of above- and below-normal precipitation are maintained, but at decreased coverage and confidence (i.e., smaller regions with lower probabilities).

 Given the absence of a confident forecast for the phase of ENSO, the remainder of the precipitation outlooks through AMJ 2021 are largely based on precipitation long term trends  which are primarily positive. The coverage based on these trends  is minimized during the ASO 2020 through DJF 2020-2021 seasons and maximized at the longer leads of JFM – AMJ 2021 seasons.

New Seasonal Drought Forecast

ENSO Considerations

Since the ENSO phase is not likely to change very much and since NOAA does not make it clear which forecasts for the NOAA Phase they rely on, we have decided to greatly abbreviate our coverage of that topic for the time being but it is discussed well in the NOAA Discussion so you can read their thoughts on the matter there.

Here is the NOAA Proprietary ENSO Model which they pretty much do not use.

The below is possibly the probabilistic forecast NOAA used.But it was issued on the same day as the NOAA Seasonal Outlook so it is unlikely that they had this information when they developed their forecast.

Let’s take a look at the subsurface along the Equator. First I show the graphics for early- and mid-January.

January 3, 2020	January 13, 2020

Here is the new version

Let’s look at the Australian BOM Nino 3.4 Forecast

And the JAMSTEC evaluation

* Things have gotten a lot more complicated with JAMSTEC. They have upgraded their SINTEX I Model to SINTEX II and beyond. This is the second month working with this and we have moved to their latest version.

Here is the short JAMSTEC discussion. We will discuss it a bit more on Sunday. For our purposes tonight I have only highlighted the comments that apply to Alaska and CONUS.

ENSO forecast:

As predicted earlier, the El Niño Modoki-like state has started to decay. The SINTEX-F predicts that the tropical Pacific will return to a neutral-state from summer.

Indian Ocean forecast:

Now, the eastern tropical Indian Ocean is warmer-than-normal. The model predicts the evolution of a moderately positive Indian Ocean Dipole from boreal summer. However, there is a large uncertainty in the prediction (some members actually predict a negative event) at present.

As predicted earlier, the strong negative Indian Ocean Subtropical Dipole still persists although it has been decaying from January.

Regional forecast:

On a seasonal scale, the SINTEX-F predicts that most part of the globe will experience a warmer-than-normal condition in boreal spring. In boreal summer, almost all part of the globe will still experience a hotter-than-normal condition, except for northeastern Russia.

As regards to the seasonally averaged rainfall in boreal spring, a drier-than-normal condition is predicted for western U.S.A., Brazil, most part of Southeast Asia, Indonesia, Philippines, eastern Australia, and southern Africa. In contrast, eastern U.S.A., northern Brazil, central Africa, India, Sri Lanka, western China, and U.K. will experience a wetter-than-normal condition. In boreal summer, a wetter-than-normal condition is predicted for Mexico, India, some parts of Southeast Asia, Philippines, and eastern China. In contrast, California, northwestern Brazil, southern Australia, northern China, and Indonesia will experience a drier-than-normal condition. Some of them will be partly due to the expected positive Indian Ocean Dipole.

The model predicts most part of Japan will experience warmer and slightly wetter-than-normal condition in the coming spring as a seasonal average. In summer, most part of Japan will be warmer and wetter-than-normal.

B. Conclusion

There were some fairly minor changes to the three-month forecast and we did not have a prior one-month forecast to compare to but April, May, and June are forecast to be fairly similar.

The rest of the forecast is pretty much canonical ENSO Neutral plus long-term trends which in some circles is called Global Warming.