Written by Sig Silber
Updated at 3:30 pm EDT March 19 to incorporate the Week 3 – 4 Weather Forecast which has some good news for California.
Here is the March 18, 2021, NOAA four-season forecast for CONUS and Alaska including the Early Outlook for April 2021. It covers a period that begins one month later than the forecast last month and extends one month longer. Also included is the updated three-month drought forecast. JAMSTEC has not published yet but when they do we will compare the two forecasts.
Please share this article – Go to the very top of the page, right-hand side for social media buttons. Please feel free to share this report with anyone you feel will find it useful.
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 for shorter time frames. 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 2021. 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, Southern Alaska and the Panhandle and the tip of CONUS Northwest is cool with Northern Alaska being warm and most of CONUS being warm with an EC transition zone between the warm anomaly and the small extreme Northwest cool anomaly. With respect to precipitation, Northwest Alaska and the Alaskan Panhandle are wet while most of CONUS is dry or EC. The dry anomaly has two centers with higher probabilities and does not include Southern California, Southern Arizona, and the extreme southwest corner of New Mexico. We will see the significance of that when we look at the three-month forecast.
* 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 two maps cover mostly March with the second map extending to April 1, 2021, and the third map as of today covers through April 9. Thus only the third of the three maps is useful for this purpose. The Seasonal Outlook was issued neither early nor late this month since the third Thursday fell on March 18. the earliest possible issue of the forecast is on the 15th of the month. We are publishing on a Thursday so we do not have the updated Week 3-4 forecast. 9 days is not an adequate basis for doing this visual consistency testing but it is worth looking at. There are 30 days in April. We will update this article tomorrow and we will then have 16 days which is marginally adequate for our purposes. Many readers will find the updated Week 3 – 4 forecast in this section when they first read this article and other readers can click on the article a second time to see how that forecast changed remembering it covers a different two-week period since it will be issued a week later.
Note: The March 19 Week 3 – 4 forecast has been updated and the commentary now reflect this updated. We now have 16 days of partial forecasts which is not ideal but it is something to work with and the first half of the Early Outlook forecast from NOAA is considered to be the more reliable part of the forecast.
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? |
| We have now updated this commentary since the Week 3 – 4 forecast was issued this Friday, March 19, 2021 Certainly, the Week 3-4 forecast fits well with the monthly forecast but we are only seeing how the full month forecast fits with the first two weeks of forecasts. We will revisit the forecast 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? |
| We have now updated this commentary since the Week 3 – 4 forecast was issued this Friday, March 19, 2021 Certainly the Week 3-4 forecast does not well with the monthly forecast but we are only seeing how the full-month forecast fits with the first two weeks of forecasts. We will revisit the forecast at the end of March when the April forecast is updated. |
Sometimes it is useful to look at the Week 3-4 Discussion. We have just added this when it was issued Friday afternoon March 19, 2022.
Week 3-4 Forecast Discussion Valid Sat Apr 03 2021-Fri Apr 16 2021
La Nina conditions are present across the Pacific Ocean. Equatorial sea surface temperatures (SSTs) are below average from the west-central to approximately 110 W longitude in the eastern equatorial Pacific Ocean with enhanced upper level westerly wind anomalies across the central and eastern tropical Pacific. The RMM index indicates an increase in the amplitude of the intraseasonal signal over the Western Hemisphere during the last week. Dynamical models continue to favor the eastward propagation of MJO during week-1, but favor an overall decrease in amplitude by week-2. The Week 3-4 temperature and precipitation outlooks are based primarily on dynamical model forecasts from the NCEP CFS, ECMWF, and JMA, and the Subseasonal Experiment (SubX) multi-model ensemble (MME) of experimental and operational ensemble prediction systems with additional considerations for La Nina and long-term trends, as well as the predicted evolution of the pattern from Week-2 forecasts.
Good agreement exists among the dynamical models regarding the anomalous 500-hPa height pattern over the week 3-4 period. Dynamical model 500hPa height anomaly forecasts during week 3-4 show a fairly consistent evolution from the forecast state during Week-2. Most dynamical models feature anomalous ridging with above normal 500-hPa heights over most of the CONUS. Another broad anomalous 500-hPa ridge is forecast across the North Pacific Ocean.Below normal 500-hPa heights are predicted over most of Mainland Alaska. Near normal 500-hpa height anomalies are likely over Hawaii.
Above normal temperatures are expected across much of the CONUS, under predicted above normal 500-hPa heights, except for the West Coast where near normal temperatures are indicated. The highest confidence for above-normal temperatures lies across the parts of the Central Plains and the Middle Mississippi Valley (greater than 80%) tied to the forecast position of the anomalous 500-hPa ridge axis. Predicted anomalous northerly flow results in increased probabilities of below normal temperatures for southern Mainland Alaska, while decadal trends lead to predicted above normal temperatures for northern Mainland Alaska, consistent with the manual blend tool.
The dynamical model guidance is in reasonably good agreement on the spatial pattern of anomalous precipitation during the Week 3-4 period. Below normal precipitation is favored throughout most of the CONUS, except for California, parts of southwestern Texas and southeastern New Mexico, where above normal precipitation is indicated, consistent with dynamical and statistical guidance. Anomalous troughing and several shortwave disturbances lead to enhanced probabilities of above normal precipitation over Mainland Alaska, supported by most of the dynamical tools.
Above-normal temperatures are favored over Hawaii, shifting to equal chances from west-to-east, given decreasing sea surface temperature anomalies oriented similarly. The SubX MME anomaly forecast indicates likely above median precipitation for the week 3-4 period for Hawaii.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g /March/April/May is shown as MAM. You will see such abbreviations often in this report.
Prior Temperature Outlook for AMJ 2021
New Temperature Outlook for AMJ 2021
Now Precipitation.
Prior forecast for AMJ 2021
New Precipitation Outlook for AMJ 2021
I can make the comparison easier by showing the prior forecast and the current forecast side by side.
| Prior Forecast | New Forecast | |
| Temperature | | |
| Precipitation |  | |
Now let us focus on the long-term situation.
First Temperature
Prior 14 Month Temperature Outlook: AMJ 2021 – MAM 2022
New 14 Month Temperature Outlook: MJJ 2021 – AMJ 2022
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 2021 – MAM 2022
New 14 Month Precipitation Outlook: MJJ 2021 – AMJ 2022
Because of the large number of changes I am trying something different namely to show the two graphics side by side. It is tricky because the array for the current month starts one month later. So you have to follow the instructions I provided with the temperature array of maps.
| Last Month | This Month |
| |
If you want larger versions of each newly issued 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 months.
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 months.
*The concept is that the probabilities of a deviation from climatology in the First Month and the combined Month Two-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 18, 2021. 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 NOAA Summary for AMJ, and finally the remainder of the 15-Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
La Nina conditions remain present in the equatorial Pacific Ocean as shown with both oceanic and atmospheric indicators. Equatorial sea surface temperatures (SSTs), however, have continued to become less negative with some spotty areas of small positive SST departures from climatology. The most recent weekly value of the Nino3.4 SST index is -0.3 degrees C. It is important to note, however, that the trend in less negative SSTs is likely being modulated by a recent and ongoing MJO event which has resulted in variations in low-level winds, cloudiness, solar radiation and precipitation. Below the surface, a shallow layer (to a depth of 100 meters) of negative ocean temperature anomalies is in place from 165 E to 100 W. A substantial area of positive subsurface oceanic heat content is located in the west-central Pacific Ocean ranging over a depth from 100 – 300 meters.
Suppressed convection persists across the equatorial Pacific surrounding the Date Line, while enhanced convection continues across much of Indonesia and the Philippines. Even with a recent reduction in the Trade winds associated with the MJO, the recent monthly average of 850-hPa winds continue to show enhanced trade winds compared to climatology. Cyclonic circulations at 200-hPa symmetric about the equator to first order also are evident in the recent monthly mean. The assessment of these ocean and atmospheric indicators show the coupled ocean-atmospheric system remains consistent with La Nina conditions.
PROGNOSTIC DISCUSSION OF SST FORECASTS
Forecasts of the Nino3.4 SST index from the NMME show considerable spread of ensemble members across the modeling center forecasts and within each modeling center ensemble. Most guidance continues to favor a continued decrease of negative SST anomalies to ENSO-neutral territory during spring 2021. Some variation begins during the summer months with some guidance favoring once again a decrease in Nino3.4 SST hinting at a potential return to La Nina conditions by autumn 2021. Some statistical components of the CPC Nino3.4 SST consolidated forecast favor a different trajectory – toward ENSO-neutral or El Nino territory by late spring 2021 for the CA and CCA forecasts respectively.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
Although equatorial Pacific SSTs continue to become less negative and are forecast to continue doing so through spring 2021, potential typical La Nina impacts are considered in preparing the AMJ and MJJ 2021 seasonal outlooks. ENSO composites, regressions anchored to Nino3.4 SST and forecast tools “bridged” utilizing Nino3.4 SST are used to inform the outlook in these seasons.
Current anomalous soil moisture and snow cover are considered and contributed to the outlook in some locations during some seasons. Dynamical model forecasts from the NMME and Copernicus (C3S) multi-model ensemble systems and the CA based on soil moisture anomalies are utilized heavily as was the objective, historical skill weighted consolidation – guidance that objectively combines both dynamical and statistical forecast tools. Due to a number of back-to-back La Nina events in the historical record since the 1950s, a re-emergence of La Nina by the autumn is considered. At later leads, long term trends in temperature and precipitation are utilized heavily to inform the seasonal outlooks.
30-DAY OUTLOOK DISCUSSION FOR APRIL 2021
The April 2021 monthly temperature and precipitation outlooks are based primarily on dynamical model forecast guidance in the context of persistent La Nina conditions that are expected to transition to ENSO neutral conditions later in spring. However, La Nina conditions are expected to persist into April and play a role in climate conditions over the forecast domain. In addition, some areas of the forecast domain consider current land surface soil moisture and nearby ocean surface temperatures.
The MJO was considered but played a lesser role in the outlook, as there is substantial uncertainty whether the MJO signal currently over Africa will persist and propagate eastward during April and lead to significant subtropical impacts. This uncertainty is due in part to expected interaction of any eastward propagating MJO convective signal with suppressed convection over the west-central equatorial Pacific, related to La Nina. Also, statistically significant impacts on higher latitudes from the MJO are smaller in spring, compared to winter months.
Temperature
The April 2021 temperature outlook favors above-normal monthly mean temperatures for nearly all of the CONUS, with the exception of the Pacific Northwest, eastward into parts of the northern Intermountain West, and southward along much of the immediate coastline of California. This outlook is supported largely by dynamical model forecast guidance, from the models of the NMME and IMME, which are in very good agreement over much of the CONUS. Decadal temperature trends contribute to higher probabilities for above-normal temperatures across the southern tier of the CONUS and into the Northeast region. A soil moisture deficit across much of the western CONUS may contribute to increased probabilities of above-normal temperatures in some regions of the West, particularly the Southwest, where model guidance leads to probabilities exceeding 60 percent in some areas of southeastern New Mexico and western Texas. A much larger area of probabilities for above-normal temperatures exceeding 50 percent over the West is supported by the consensus forecast of the NMME. Typical temperatures observed during April under La Nina conditions were considered, and support increased chances of below-normal temperatures over parts of the Pacific Northwest. Dynamical model guidance, as well as persistent impacts of La Nina, favor increased probabilities for below-normal temperatures across southern Mainland Alaska into the Alaska Panhandle, while decadal temperature trends are the primary forcing leading to likely above-normal temperatures across northwestern coastal areas of Mainland Alaska and the North Slope.
Precipitation
For precipitation, consistent dynamical model forecast guidance from models of the NMME and typical La Nina impacts in spring favor below-normal precipitation stretching from California and southern Oregon eastward across the Central and Southern Rockies into the Central and Southern Plains, the Lower Mississippi Valley, and much of the Southeast region. Increased precipitation variability and decreased predictability in dynamical model forecasts leads to a lower probability for below-normal precipitation for some areas of the Southern Plains. Equal Chances (EC) of above, near and below-normal precipitation are indicated for remaining areas of the CONUS, including drier areas of the Southwest. Inconsistency between the typical above-normal precipitation signal due to La Nina and dynamical model forecasts of below-normal precipitation for parts of the eastern Central Plains leads to a forecast of EC for this area in the April outlook.
The consensus of dynamical model forecast guidance favors above-normal monthly total precipitation amounts for parts of the southern Alaska Panhandle, supported by typical impacts of La Nina conditions. La Nina conditions support above-normal precipitation for western Mainland Alaska, as does the consensus of dynamical model guidance. EC is forecast for remaining areas of Alaska, where climate signals are weak and dynamical model forecasts are inconsistent.
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS (Focus on April/Ma y/June
La Nina conditions remain in place across the equatorial Pacific Ocean as indicated by both oceanic and atmospheric conditions. A transition to ENSO-neutral is favored during the late spring until autumn when La Nina once again becomes slightly more favored than ENSO-neutral at that time. In addition to the forecast ENSO evolution described above, current anomalous soil moisture and snow cover along with numerical and statistical model output inform the seasonal temperature and precipitation outlooks.
Temperature
The April-May-June (AMJ) 2021 temperature outlook favors above-normal seasonal mean temperatures for nearly all the contiguous U.S. and for portions of western and northern Alaska. Below-normal temperatures are most likely for a region from southeast Alaska to the extreme Pacific Northwest. Moreover, above-normal temperatures are most likely for the entire forecast domain as we move into and through the summer months.
Precipitation
The AMJ 2021 precipitation outlook favors above-normal seasonal total precipitation amounts for portions of the Great Lakes, Ohio Valley, mid-Atlantic and Northeast as well as the west coast of Alaska. Below-normal precipitation is most likely for a region from the West coast across the Rockies to the southern Great Plains. The highlighted area of below-normal precipitation is forecast to slowly shift north and east during the summer months while above-normal precipitation is favored to expand southward along the eastern seaboard over the same period. Elevated odds for above-normal precipitation is introduced for parts of the Southwest during the monsoon season.
Equal chances (EC) are indicated for areas where seasonal mean temperatures and seasonal total precipitation amounts are expected to be similar to climatological probabilities.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
PROGNOSTIC DISCUSSION OF OUTLOOKS – AMJ 2021 TO AMJ 2022
TEMPERATURE
The AMJ 2021 temperature outlook favors above-normal seasonal mean temperatures for nearly all the contiguous U.S. and for portions of western and northern Alaska. The greatest odds for above-normal temperatures is located from the Four Corners region in the Southwest to southern Texas due to the confluence of factors including overwhelmingly consistent dynamical model guidance, low soil moisture conditions, long-term positive temperature trends and other statistical forecast tools. Modestly elevated odds for above-normal temperatures extend eastward across the Southeast as well – supported by model guidance and strong trends . More uncertainty and disagreement in forecast tools and lower historical forecast skill in forecast guidance decrease probabilities for above-normal temperatures in the north central CONUS. Consistent with lingering La Nina influence as indicated by ENSO composites, regressions and “bridging” tools there are elevated chances for below-normal temperatures from the extreme Pacific northwest to the south coast of Alaska. Negative trends in sea ice coverage and thickness and positive SST trends favor above-normal temperatures for parts of the west coast of Alaska and the north Slope.
Consistent signatures across the range of model guidance and statistical forecast tools including those derived from land surface conditions favor continued elevated odds for above-normal temperatures for most of the forecast domain through the SON 2021 season with the greatest chances depicted for the western U.S. and along the eastern seaboard with slightly lower odds for the north central CONUS.
Thereafter, beginning in OND 2021 and continuing through FMA 2022, there is a gradual increase in the EC designation as odds for La Nina re-development and so potential impacts increase for much of the northern tier of the CONUS from the Pacific Northwest to the western Great Lakes, and later southeast Alaska. The inclusion of areas of favored below-normal temperatures may need to be considered in these areas over the next couple of seasonal outlook release packages if odds of La Nina increase, but also, and perhaps just as important, if odds for El Nino remain very low during the late autumn and early winter 2021 as they are now.
PRECIPITATION
The AMJ 2021 precipitation outlook favors above-normal seasonal total precipitation amounts for portions of the Great Lakes, Ohio Valley, mid-Atlantic and Northeast primarily based on lingering La Nina influence, positive precipitation trends , other statistical forecast tools and to a lesser degree some model forecasts from the NMME and C3S ensemble systems. There is considerably stronger agreement, however, for a region of favored below-normal precipitation from the central West coast across the Rockies to the southern Plains. La Nina considerations, dynamical model guidance and the CAS forecast tool support this forecast.
The highlighted area of below-normal precipitation is forecast to slowly shift north and east during the summer months – consistent with dynamical model guidance. Above-normal precipitation is favored to expand southward along the eastern seaboard through the summer months into the early autumn consistent with positive precipitation trends and a slight tilt favoring La Nina during the second half of the Atlantic hurricane season.
Below-normal soil moisture and snowpack in the Southwest and southern Rockies may allow for more efficient heating of the land mass and so potentially an enhanced monsoon circulation earlier all factors being equal. Along these lines, elevated odds for above-normal precipitation is favored for parts of the southwest from JJA through ASO 2021. Some dynamical model guidance also support this forecast.
La Nina conditions (first 2 leads) and dynamical model guidance support above-normal precipitation for the west coast of Alaska from AMJ – ASO 2021. The outlooks from OND 2021 through AMJ 2022 are primarily supported and based on long term precipitation trends .
Climate Normals
The Climatic normals are based on conditions between 1981 and 2010, following the World Meteorological Organization convention of using the most recent 3 complete decades as the climatic reference period. The probability anomalies for temperature and precipitation based on these new normals better represent shorter term climatic anomalies than the forecasts based on older normals.
For a description of of the standard forecast tools – their skill- and the forecast format please see our web page at http://www.cpc.ncep.noaa.gov/products/predictions/long_range/tools.html (Use Lower Cas e Letters) Information on the formation of skill of the CAS forecasts may be found at: http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Outlook/outlook.shtm l (use lowercase letters) Notes – These climate outlooks are intended for use prior to the start of their valid period. Within any given valid period observations and short and medium range forecasts should be consulted.
This set of outlooks will be superseded by the issuance of the new set next month on Mar 18 2021
1981-2010 base period means were implemented effective with the May 19, 2011 forecast release.
We will discuss this more when we compare the JAMSTEC to the NOAA forecast. But it is useful to look at the JAMSTEC discussion especially as it applies to Spring and Summer since their raising the issue that this is somewhat of a La Nina Mokoki raises questions about the use of statistical analysis in these forecasts. We will address this in more detail when we publish our NOAA v JAMSTEC comparison. NOAA hardly recognizes an El Nino Modoki let alone a La Nina Modoki. Fortunately, the major impact of a La Nina Modoki is seen in the Western Pacific as it impacts the track of cyclones headed west. But what heads west frequently turns north and then returns east at higher latitudes and impacts North America in that way but perhaps in a more subtle way. Below is the JAMSTEC discussion.
(not yet available)
Drought Forecasts
These two forecasts (Monthly and Season) are issued by the same agency but to obtain them you need to access two different links here (for the single month forecast which comes out at the end of the month and here for the forecast issued with the Seasonal Outlook.
Here is the Three-Month Drought Forecast which was issued on February 18, 2021
Discussion for the Seasonal Drought Outlook
Tools used in the U.S. Seasonal Drought Outlook (SDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for April 2021 and April through June (AMJ) 2021, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the Week 3-4 outlooks and tools from CPC, dynamic models at the monthly and seasonal time scales, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for April and AMJ, and initial conditions for parameters such as soil moisture. Existing drought areas on the forecast are based on the March 16, 2021 U.S. Drought Monitor. Forecasts currently reflect the presence of a moderate La Nina with a 60% chance of a transition to ENSO-neutral during AMJ. Therefore, ENSO’s influence is considered in the SDO for AMJ.
Drought is expected to persist across much of the West, with removal favored for south-central Washington and north-central Oregon. Snow water equivalent (SWE) and reservoir levels are above-normal for the season leading up to the AMJ period for the Pacific Northwest and northern Great Basin, falling quickly to below-normal southward in the Western Region. As surplus snowpack melts during the AMJ season, moderate (D1) and severe (D2) drought in southern Washington and northern Oregon will likely result in drought removal. Conversely, widespread above-normal temperatures and below-normal precipitation are favored for much of the central and southern Western Region, indicating drought is likely to persist across much of the remainder of the region, with development likely in D0 areas along the California coast and southwestern Arizona.
Forecast confidence is high for the Western Region.
The High Plains Region is a tail of weather and climate extremes. North Dakota saw its driest September-February period on record, with other states seeing below to much below-normal September to February periods for precipitation. This past week, however, the Central Plains experienced a major winter storm system, which dropped 2-3 feet of snow in portions of the Colorado Rockies and southeastern Wyoming. A swath of 5-10 inches of snow extended eastward from the central High Plains and into the Midwest. On the warm side of the storm, areas of northern Kansas and southern Nebraska saw widespread 2-3 inches of rainfall, with a pocket of 5-6 inches in southeastern Nebraska. Areas that saw the heaviest snowfall remain depicted in D0 (abnormally dry), but could continue to see short-term improvements as the snow melts and absorbs into the soils. Additionally, the High Plains Region is entering into a climatologically wetter time of year, particularly during the latter two-thirds of the AMJ period with an increasing potential for severe weather during the season. Despite the wetter time of year on average, medium and long-range models depict an enhanced potential for above-normal temperatures and below-normal precipitation for the season. The above-normal precipitation signal diminishes to equal chances for above or below farther north in the High Plains Region. However, antecedent short and long-term dryness will be difficult to overcome, even if near-normal precipitation is observed during the AMJ season, due to the likelihood of above-normal temperatures increasing the potential for soil moisture loss. Therefore, drought persistence is likely for the High Plains Region with drought development for portions of the Central Plains, and for D0 areas along the Front Range, where odds of above-normal temperatures and below-normal precipitation are greatest.
Forecast confidence is moderate for the High Plains Region.
Short to long-term dryness continued across portions of the Corn Belt since the March-April-May SDO release, with eastward to northeastward expansion of D0 and D1 across northern Ohio and southeastern Michigan. Additional eastward D0 expansion occurred across the upper Midwest Region into Wisconsin and the Upper Peninsula and western Michigan. Despite the short-term dryness, precipitation chances are above normal across much of the Great Lakes, stretching to the Mid-Atlantic, with equal chances for above or below normal precipitation west of the Great Lakes. Above-normal temperatures are also favored across this region, so any periods of dryness could prove detrimental in areas with existing abnormal dryness (D0). As such, drought persistence is favored for western areas of the Midwest Region with removal likely in D1 areas in the Corn Belt and along the west coast of Lake Erie, where probabilities of above-normal precipitation are greatest.
Forecast confidence is moderate for the Midwest Region.
With enhanced probabilities of above-normal temperatures and elevated odds of below-normal precipitation across the Southern Region, drought persistence with additional expansion is likely for large portions of Oklahoma and Texas. Below-normal precipitation signals diminish eastward in the Southern Region during AMJ. Farther east in the region, short-term wetness is favored through the Week-2 period, with drought removal likely in northern Louisiana in the short-term. Despite short-term wet signals in southern Louisiana, long-term guidance, monthly outlooks, and seasonal outlooks suggest increased odds for above-normal temperatures and below-normal precipitation, indicating persistence is more likely there.
Forecast confidence is high for Oklahoma and Texas and low to moderate for the Lower Mississippi Valley.
In the Southeast, recent heavy precipitation across Alabama, in addition to increased odds of above-normal precipitation across much of the Southeast during the next two weeks, favors drought removal in central Alabama in the near-term, with no re-development likely beyond that time. Eastern portions of the Southeast Region, including Florida, will begin the transition into a wetter time of year toward June. However, with increased odds of above-normal temperatures during AMJ, antecedent dryness, and the late transition to the wet season for these areas, drought development is favored in and around D0 areas in the central and southern Florida Peninsula.
Forecast confidence is low for Florida and moderate to high elsewhere for the Southeast Region.
In the Northeast, long-term drought has slowly diminished in recent months. However, D0 to D2 standardized precipitation indices (SPIs) are still prominent, extending from western Pennsylvania to northern New England. From April to June, the region typically receives an increasing percentage of its annual precipitation. Despite above-normal temperatures favored across the region, above-normal precipitation is also favored for much of the region and in D1 areas in New England and Upstate New York. Therefore, drought removal is likely.
Forecast confidence is moderate to high for the Northeast Region.
D0 currently covers much of northern Alaska, extending across the North Slope and Brooks Range southeastward to the Yukon Flats. Basin SWE estimates are currently below-normal across central Alaska, just south of the abnormally dry areas in the north. However, above-normal precipitation is favored throughout the period across the western Mainland, with equal chances for above or below elsewhere, which will help to stave off drought development. In Hawaii, many areas that experienced heavy rains and flooding are not currently depicted in drought. Although Hawaii typically transitions into a drier time of year, long-range models depict increased probabilities of above-normal precipitation for much of the state early in the period, with equal chances for above and below-normal precipitation to above-normal precipitation favored for the remainder of the season. As such, drought removal is forecast for Hawaii. Moderate drought is currently depicted in northwestern Puerto Rico. Above-normal temperatures and near-normal precipitation are favored during AMJ. However, with La Nina to ENSO-neutral conditions expected to persist, it could influence the tropics toward the end of the period as we enter the Atlantic Hurricane season, but drought persistence is likely during AMJ.
Forecast confidence is moderate to high for Alaska and Hawaii, and moderate for Puerto Rico.
ENSO Considerations
We have covered some of this when we reported on the IRI/CPC analysis on March 12, 2021. We may discuss it again when we do the NOAA/JAMSTEC Comparison.
Now let us look at the NOAA recent ENSO Update
ENSO Update. This happens every month on the second Thursday
We are still in La Nina but it should ease up for the Summer but it may double-dip.
Based on the survey of meteorologists AMJ is more likely to be neutral than remain in La Nina. But look further out. Of course, the level of confidence farther out is less.
Here we compare the current survey of meteorologists with the computer model analysis that they describe as being Mid-February. It is pretty similar but leans a bit more towards a double-dip.
NOAA has its own proprietary model which they rarely use. It is not exactly clear why they shun their own model.
In most cases, I freeze the models as of the date of publication but for this one, I am going to just let the above model run so if you refer to the article in the future, the values in the above may not relate well to the discussion. But I am doing that so if you refer to this article in say two weeks, you will see if there has been any change in the forecast from this model.
And the Australian BOM
And here is one more graphic that I created from a different NOAA source. It is a cross-section of the Pacific Equator from the surface down to 450 meters. What is shown in this graphic is the temperature anomalies not the absolute temperature. ENSO is measured at the surface since only the surface interacts with the atmosphere. But the future of the surface often is impacted by the water below the surface. At some point, NOAA will update the normal values for this area as they do that every five years but they have not done so yet. See the note at the beginning of this article.
The current situation and four prior months are shown.
| Last Month | Currently |
 |  |
| Three Months Ago | Two Months Ago |
 |  |
| Four Months Ago | |
 |
The Southern Oscillation Index or SOI being above 7 confirms that the Atmosphere is in tune with the Sea Surface Temperatures in the Pacific along the Equator. At least temporarily the SOI Index is in neutral territory and is not confirming the La Nina. This is another graphic that we have not frozen.
B. Conclusion
We are now in a La Nina. There may be an issue as to how westerly oriented this La Nina will be and what if any will be the impacts of it having some characteristics of a Modoki as JAMSTEC suggests.
NOAA has introduced the concept of a possible double-dip La Nina. That is not unusual. It would be devastating for the West.
