Written by Sig Silber
Edited at 6:30 pm EDT to incorporate the newly issued Week 3 – 4 Forecast.
Here is the May 20, 2021, NOAA four-season forecast for CONUS and Alaska including the Early Outlook for June 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 and the Early Outlook for the single month of June. The main change seems to be the removal of a slightly better than average North American Monsoon to one that is forecast to be below average in New Mexico but average in Arizona and extreme Southeast California. There is uncertainty about next Fall and Winter in terms of a possible return of La Nina which seems to be unlikely. That may be signaling a change in the Phase of the PDO and AMO. More on that in the article that we will publish tomorrow night. In two or three days we will publish the comparison with the JAMSTEC forecast.
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This is the first NOAA Seasonal Outlook since the adjustment of the Climate Normals. We have written about the change in Climate Normals here and we will be discussing a related topic tomorrow in our Weather Economics article. The tricky part is comparing forecasts made last month using the prior Climate Normals with forecasts issued today. We have not made a detailed analysis of how that impacts things but at different points in the article tonight we will comment on it a bit. |
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 June 2021. It is called the Early Outlook because it will be updated at the end of May. Only the June 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 June 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. When we do the comparison with JAMSTEC, we now receive monthly forecasts for the first three months so we will be comparing the NOAA and JAMSTEC forecasts for June. It is probably best in this article to just try to understand what NOAA is trying to convey about June*. For Temperature, there is a high probability for warm temperatures in the Southwest centered on Arizona and Utah. Southwest Alaska including the Aleutians are warm. There is a large EC area shown from Texas through Kentucky and Tennessee. That area may have been shown as warm with 33% probability if the prior temperature norms were used. We do not know that for sure but it is quite possible. With respect to precipitation, western Alaska is wet and there are two large anomalies in CONUS: A wet anomaly that includes a lot of the eastern half of the U.S. but not the northern tier or the East Coast and a dry anomaly that is centered on Idaho and Wyoming but extends in all directions but only extends to the south as far as the eastern half of NM and part of the Texas Panhandle. In particular, California and Arizona are not included. This may well be related to the new climate normals. By that I mean the level of precipitation forecast may be consistent with the newly issued Precipitation Normals but may have been considered dry under the prior Normals. One would have to look at the two sets of Normals carefully to really sort that out but in many respects, it is not important since the new Normals are more representative of our current climate.
* 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 only May and the third map as of today covers through June 11. Thus only the third of the three maps is at all useful for this purpose. The Seasonal Outlook was issued late this month since the third Thursday fell on May 20. 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. 11 days is not an adequate basis for doing this visual consistency testing but it is worth looking at. There are 30 days in June. We have now updated this article and we will now have 18 days which is substantially 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.
First Temperature
And then Precipitation
Sometimes it is useful (when it is more current than the discussion released by NOAA with the Seasonal Outlook) to look at the Week 3-4 Discussion. We have now added that when it was issued Friday afternoon May 21, 2021.
Week 3-4 Forecast Discussion Valid Sat Jun 05 2021-Fri Jun 18 2021
Neutral El Nino Southern Oscillation (ENSO) conditions prevail in the tropical Pacific, leaving an active Madden Julian Oscillation (MJO) and an atmospheric Kelvin wave as the main features of tropical variability. Current RMM indices indicate active convection over the Maritime Continent (Phase 4) and the dynamical models consistently propagate the MJO convective signal farther into the West Pacific in the coming days before weakening. However, the associated teleconnections to the extratropics, and thus the attendant impacts on North American temperature and precipitation, tend to be weaker during the summer months. With this in mind, MJO influences factor less into this week’s forecast which relies more on dynamical model blends as well as considerations from decadal trends.
The forecast large-scale atmospheric circulation, as indicated by anomalous 500-hPa anomalous height fields, exhibits good agreement among the dynamical model guidance (CFS, ECMWF, JMA, GEFS and the SubX multi-model ensemble). These models consistently feature ridging across the Gulf of Alaska as well over Nova Scotia and Newfoundland. The majority of the models also suggest weak height anomalies over much of CONUS, though the GEFS favors a more amplified pattern relative to the other models with troughing over the Great Lakes.
Due to the strong model agreement regarding the ridging over the Pacific and the Northeast, the temperature forecast tilts toward above normal probabilities for much of the eastern and western portions of CONUS with highest probabilities centered over the Southwest. While some of the models also indicate a warm solution from the Northern Plains down to the Texas/Louisiana coast, the aforementioned weak troughing indicated by the GEFS as well as increased soil moisture along the Gulf Coast would suggest a cool solution. Therefore, equal chances are carved out for those regions. Equal chances are also forecast over eastern Alaska due to conflicting signals from model guidance, while above normal temperature probabilities are consistently indicated over the western part of the state.
Despite the strong model agreement regarding the large-scale circulation patterns, the precipitation forecast is more uncertain due to conflicting solutions among the guidance. Thus equal chances are favored over much of CONUS. While the aforementioned ridging over the Northeast could potentially bring moisture and increased precipitation probabilities into the Northern Plains, the models disagree on placement of the wet signal, resulting in equal chances forecast throughout the region. Equal chances are also favored across the Gulf Coast region due to higher uncertainty, with the models indicating drier conditions but soil moisture is above normal in this region and could be further enhanced by a potential tropical disturbance that the National Hurricane Center is currently monitoring. Beyond the Texas coast into Oklahoma panhandle and the Southern Rockies, the models consistently tilt toward below normal precipitation probabilities. Model uncertainty yields an equal chances precipitation forecast over much of Alaska but drier conditions are consistently indicated over the Alaska panhandle and southern coast.
Surrounding Hawaii, sea surface temperatures are near-normal to slightly above average, elevating the chances for above normal temperatures during the forecast period. Dynamical model guidance from the SubX suite indicates a tilt toward below normal precipitation in the northwestern part of the state with probabilities decreasing to equal chances in the southeast.
Now we consider the three-month Outlook.
Notice that the three-month periods are abbreviated e.g June/July/August is shown as JJA. You will see such abbreviations often in this report.
Prior Temperature Outlook for JJA 2021
New Temperature Outlook for JJA 2021
Now Precipitation.
Prior forecast for JJA 2021
New Precipitation Outlook for JJA 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: JJA 2021 – MJJ 2022
New 14 Month Temperature Outlook: JAS 2021 – JJA 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.
I am now showing them side by side in addition to one after another. It is easier to make the comparison this way but to do it I have to make the maps smaller and readers have to remember how to compare two sets of maps when one starts a month later than the other. Here goes:
Forecast Issued Last Month | Forecast Issued This Month |
Based on this procedure, I conclude that:
Now Precipitation
Prior 14 Month Precipitation Outlook: JJA 2021 – MJJ 2022
New 14 Month Precipitation Outlook: JAS 2021 – JJA 2022
I am also going 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. So you can compare the forecast maps by looking at the large ones which are shown with the prior month forecast followed by the forecast this month or you can look at them side by side.
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 May 20, 2021, 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 (June), the NOAA Summary for JJA, and finally the remainder of the 15-Month Forecast.
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
The coupled oceanic and atmospheric observations reflect ENSO-neutral conditions. During the past four weeks (Apr 18 – May 14), sea surface temperatures (SSTs) were near to slightly below average with SST anomalies less than -0.5 degree C across the central and eastern equatorial Pacific. Positive subsurface temperature anomalies continue to persist at a depth of 50 to 150 meters throughout much of the equatorial Pacific. Integrated upper-ocean heat anomalies have remained positive since late March. Suppressed convection diminished during April across the equatorial central Pacific, due in part to a robust Madden-Julian Oscillation (MJO). Since early March the MJO has completed two circumnavigations of the global tropics. The enhanced phase of the MJO is currently over the Indian Ocean and is forecast to continue propagating eastward to the western Pacific and then Western Hemisphere entering June.
PROGNOSTIC DISCUSSION OF SST FORECASTS
The North American Multi-Model Ensemble (NMME) and the CPC SST consolidation for the Nino3.4 region depicts ENSO-neutral conditions persisting through summer 2021. Beyond this time, forecast tools diverge with the CFSv2 featuring a return of La Nina while other dynamical models such as the ECMWF and statistical tools maintaining ENSO-neutral conditions. The official CPC/IRI ENSO outlook indicates that ENSO-neutral conditions are the most likely outcome through August-September-October 2021 with probabilities for a return of La Nina increasing to 55 percent by October-November-December 2021 and continuing through the winter 2021-2022.
30-DAY OUTLOOK DISCUSSION FOR JUNE 2021
The June 2021 monthly outlook was prepared based on current surface conditions such as soil moisture and coastal sea surface temperatures (SSTs), potential impacts from the currently active MJO, dynamical model and statistical forecast guidance and newly derived long term trends from the 1991-2020 base period.
Temperature
La Nina conditions present during the winter and spring months has ended as both SSTs in the equatorial Pacific Ocean have warmed and coupling to the atmosphere has weakened. The MJO, however, has been active since mid-March and has been strong and is starting its third “cycle” around the global Tropics. The enhanced phase of the MJO is currently centered in the Indian Ocean and is forecast to continue to propagate eastward to the western Pacific by the beginning of June. The teleconnection to the mid-latitudes from MJO forcing during late spring and summer, even during a moderate to strong event, is typically considerably weaker, has a lower likelihood to occur and impacts highly variable. For this event, the forecast phase of the MJO at the start of June would favor above-normal temperatures for the western CONUS based on composites and statistical forecast tools as well as, but to a considerably lesser degree below-normal temperatures in the vicinity of the Great Lakes, the Ohio Valley and parts of the mid-South. These impacts, however, would be mainly during the first 10 days of the month June and impacts based on MJO composites and other tools are not statistically significant in subsequent MJO phases thereafter.
Favored above-normal temperatures for the western CONUS from the MJO perspective is consistent and further supported by overwhelming dynamical model forecast guidance, statistical tools, low soil moisture considerations and positive long term temperature trends . Conflicting and/or weak signals related to the MJO, dynamical model and statistical guidance, areas of very wet surface conditions in addition to favored above-normal precipitation for the month of June as a whole results in low confidence for the eventual category of June monthly mean temperatures for the southern Plains, lower Mississippi Valley and parts of the Southeast. Equal-chances (EC) for either of the three categories is forecast in these areas. Above-normal SSTs in the lower Bering Sea favor above-normal temperatures for southwest Alaska which is somewhat supported by model forecast guidance. Climate signals were weak for most of the remainder of the state.
Precipitation
The June 2021 precipitation outlook favors below-normal precipitation for a region from the Pacific Northwest and northern Rockies to the central Rockies southward to include parts of the state of New Mexico and Texas primarily based on consistent dynamical model forecast guidance. Elevated probabilities for above-normal precipitation is forecast for the western portion of Alaska supported by model guidance as well as potentially greater moisture availability for precipitation due to more open and warmer waters in the Bering Sea, especially the first half of the month. The likely MJO phase over the course of the month of June would tend to favor at various times enhanced odds of above-normal precipitation for the Gulf Coast, Southeast and Ohio Valley. This along with support from dynamical model guidance and long term positive precipitation trends favor above-normal monthly total precipitation amounts for these areas.
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS (with focus on June- July-August)
La Nina has ended and ENSO-neutral conditions are present across the equatorial Pacific Ocean, as represented in current oceanic and atmospheric observations. The official CPC ENSO forecast indicates that ENSO-neutral conditions are likely to persist through the summer.
Temperature
The June-July-August (JJA) 2021 temperature outlook favors above normal temperatures for a majority of the CONUS, with the largest probabilities (greater than 60 percent) forecast across the Southwest. The JJA 2021 precipitation outlook depicts enhanced probabilities of below normal precipitation amounts across the Pacific Northwest, Rockies, and High Plains.
Precipitation
Above-normal precipitation is slightly more likely across the East, parts of the Gulf Coast, and much of Alaska.
Equal chances (EC) are forecast for areas where probabilities for each category of seasonal mean temperatures and seasonal accumulated precipitation amounts are expected to be similar to climatological probabilities.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
Dynamical model guidance such as the North American Multi-Model Ensemble (NMME) and the Calibration, Bridging, and Merging (CBaM) version of the NMME were used. The consolidation tool, which includes NMME input and various statistical tools, was used as well, especially at later leads. Also, anomalously wet (dry) soil moisture conditions were factors in the temperature outlook across eastern Oklahoma, eastern Texas, and the lower Mississippi Valley (northern Great Plains) during June-July-August 2021. At later leads, decadal trends in temperature and precipitation were the primary tool used in creating the seasonal outlooks. Slight adjustments to the seasonal outlooks, especially temperature, were needed due to the change in the 30-year base period from 1981-2010 to 1991-2020.
PROGNOSTIC DISCUSSION OF OUTLOOKS – JJA 2021 TO JJA 2022
TEMPERATURE
Above normal temperatures are favored throughout a majority of the forecast domain during JJA, except for parts of the Midwest where equal chances (EC) of below, near, or above normal temperatures are forecast. This EC area is due to a weaker signal among temperature tools coupled with poor skill historically from the NMME during the summer months. Positive decadal temperature trends and low soil moisture (below the 5th percentile) support the largest probabilities (above 60 percent) for above normal temperatures across the Southwest. Compared to the previous month, probabilities for above normal temperatures are decreased from eastern Texas to the lower Mississippi Valley where recent heavy to excessive rainfall resulted in soil moisture exceeding the 70th percentile. In addition, the June temperature outlook calls for EC for that region. Above normal temperatures are favored throughout Alaska during JJA, but the largest probabilities (above 50 percent) were shifted from northern Mainland Alaska to the Aleutians based on the latest model guidance and recent SST anomalies.
Beginning in JAS through SON 2021, above normal temperatures are favored through the entire CONUS with the largest probabilities (above 50 percent) consistent with NMME dynamical model guidance and decadal trends . Although probabilities for above normal temperatures were reduced slightly across the North Slope of Alaska during SON and OND 2021 due to the new base period of 1991-2020, probabilities are larger compared to the remainder of Alaska. Seasonal temperature outlooks during the winter 2021-2022 and continuing through the summer 2022 are based on the CPC consolidation tool and decadal trends.
PRECIPITATION
Model guidance remains consistent from previous months depicting elevated probabilities of below normal precipitation for the Pacific Northwest, northern Rockies, and northern to central high Plains during JJA. Based on good agreement among the latest dynamical models , this favored area of below normal precipitation was expanded to include the southern high Plains and New Mexico during JJA and JAS. Due to a notable drying trend among the inputs to the NMME and C3S along with the consolidation tool, below normal precipitation is slightly favored for the desert Southwest through SON 2021. This favored dryness coincides with the monsoon, a wet time of year for the Southwest. The predicted MJO evolution is likely to provide a favorable large-scale environment for the development of an early season tropical cyclone in the Gulf of Mexico during June. This expectation along with it being a non-El Nino summer and fall support slightly elevated probabilities for above normal precipitation along parts of the Gulf Coast and Southeast. The favored area of above normal precipitation across the remainder of the eastern U.S. from JJA through ASO 2021 is related more to decadal trends . Based on the latest dynamical models, the coverage of elevated probabilities for above normal precipitation are increased to include more of mainland Alaska during JJA and JAS 2021.
Although the NMME begins to favor below normal precipitation across the southern tier of the CONUS during OND 2021, the precipitation outlook maintains EC at this time range due to large uncertainty on the return of La Nina. This will be reassessed during subsequent seasonal outlooks as we draw closer to the fall and winter 2021-2022 when confidence in the state of ENSO is likely to improve. Seasonal precipitation outlooks during the winter 2021-2022 and continuing through the summer 2022 are based on the CPC consolidation tool and decadal trends .
We will discuss this more when we compare the JAMSTEC to the NOAA forecast. But it is useful to look at the JAMSTEC discussion.
ENSO forecast:
As predicted earlier, observation shows that the La Nina Modoki-like state decayed from boreal spring. The SINTEX-F predicts that a neutral state will persist in this year.
Indian Ocean forecast:
Observation shows that the western tropical Indian Ocean is warmer-than-normal. The SINTEX-F predicts that the present state will persist in boreal summer and autumn. However, there is a large uncertainty in the prediction.
Regional forecast:
On a seasonal scale, the SINTEX-F predicts that most part of the globe will experience a hotter-than-normal condition in boreal summer (austral winter) except for northern part of the South American Continent and some parts of Northern Europe. In boreal autumn (austral spring), the model still predicts most part of the globe will experience a warmer-than-normal condition, except for northern part of the South American Continent, some parts of northern Africa, and Ukraine.
As regards to the seasonally averaged rainfall in boreal summer (austral winter), a drier-than-normal condition is predicted for central/eastern U.S.A., southern part of the South American Continent, some parts of the Eurasian Continent, and Gabon.
In contrast, Mexico, northern part of the South American Continent, Philippines, some parts of Indonesia, some parts of West Africa, northern part of the Eurasian Continent, some parts of the Indochina Peninsula, eastern China, and the Korean Peninsula will experience a wetter-than-normal condition. In boreal autumn (austral spring), a wetter-than-normal condition is predicted for the South American Continent, central Africa, India, Philippines, and Indonesia. In contrast, most part of U.S.A., La Plata Basin, some parts of West Africa, and some parts of China will experience a drier-than-normal condition.
The model predicts most part of Japan will experience a hotter-than-normal condition in summer and autumn as a seasonal average. As regards to the seasonally averaged rainfall, most part of Japan will experience a slightly wetter-than-normal condition in summer and autumn as a seasonal average. Monthly prediction suggests an active rainy season (Baiu) in June.
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 that was issued on May 20, 2021
We can compare the new forecast to the prior forecast recognizing that the new forecast is for a three-month period that begins one month later.
Prior Forecast | New Forecast |
There are two versions of the discussion of the seasonal drought outlook: long and short and this month I am providing the long version.
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 June and June through August 2021 (JJA), various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) totals 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, dynamical models at the monthly and seasonal time scales, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for the JJA season, and initial conditions such as soil moisture. The USDM, valid on May 18, was used for initial drought conditions. ENSO-neutral conditions are likely during this outlook period.
Short-term and long-term drought remains entrenched throughout a majority of the West with D2 (severe) to exceptional (D4) drought designated for parts of Washington, Oregon, California, Nevada, Idaho, Montana and the Southwest. As of mid-May, snow water equivalent remains below normal for California, the Great Basin, and the Four Corners region. Farther to the north across Washington, short-term drought expanded due to a lack of precipitation during the past 30 to 60 days. June-July-August is a dry time of year for Washington, Oregon and California. The Southwest is typically dry during June until monsoon rainfall begins later in July. Based on below normal precipitation during the past 30 to 60 days, low soil moisture conditions, and elevated monthly and seasonal probabilities of near to below normal precipitation and above normal temperatures for June and JJA, drought is expected to persist over the south-central West and to expand northward across parts of the Pacific Northwest and northern Rockies
Forecast confidence for the Western Region is high for persistence and moderate for development.
Soil moisture continues to decline across the Dakotas where drought continues to intensify due to precipitation deficits during the past 30 days. Due to the lack of wet signal among precipitation tools during the seasonal time scale along with the likelihood of above normal temperatures, persistence is forecast for a majority of the long-term drought across the central to northern High Plains with potential development over those D0 areas in the central High Plains. However, this region is entering their wettest time of year when 40 to 50 percent of its annual precipitation occurs from June through August. This wet climatology reduces forecast confidence of persistence or development.
Forecast confidence is moderate to low for the High Plains Region.
Drought varies in intensity across Oklahoma and Texas with the lowest soil moisture (below the 5th percentile) affecting western and southern Texas. Heavy rainfall during the past 30 days brought major improvements across much of Texas and predicted heavy rainfall in the next two weeks favors further improvement in these areas. Monthly to seasonal tools support elevated probabilities of below normal precipitation and above normal temperatures only across west Texas and the Texas Panhandle. Persistence is favored in parts of western Texas. Since June and JJA are one of the wettest months and seasons of the year across the western Southern Plains, this wet climatology reduces prediction confidence. The Southern Plains will be closely monitored in the monthly drought outlooks through the summer. Recent heavy rainfall and saturated soils make drought development unlikely throughout the lower Mississippi Valley and Tennessee Valley.
Forecast confidence is low for the Southern Region.
The severe long-term drought across the Midwest remains centered across northwest Iowa, based on 6 to 12-month SPI values. Given the long-term duration of this drought area, persistence is most likely but forecast confidence is low since June-July-August is a relatively wet time of year. Drought persistence is more likely across the Corn Belt, Upper Mississippi Valley, and Great Lakes areas based on: lack of wet signals and near to above normal temperatures at both monthly and seasonal time scales, while a wet climatology reduces the forecast confidence. The Corn Belt will be closely monitored in the monthly drought outlooks through the summer.
Forecast confidence is low for the Midwest Region.
The short-term moderate drought (D1) expanded for parts of the Carolinas due to precipitation deficit during the past 30 days. Due to the lack of a strong wet signal and likelihood of above normal temperatures among forecast tools from extended range forecasts to seasonal outlooks, drought persistence is likely for the Carolinas. Also, worsening drought conditions are anticipated in the short-term. For the short-term moderate drought (D1) over a small area in southern Florida, the onset of the convective season during June-July-August and a wet pattern from the monthly to seasonal outlook tools strongly favor removal of short-term drought across south Florida.
Forecast confidence is moderate for the Carolinas and high for southern Florida.
Moderate drought (D1) is ongoing across small parts of the Northeast, where soil moisture and streamflows are below the 20th percentile. Since the monthly and seasonal outlooks calls for elevated probabilities of above normal temperatures and it is a favorable time of year for soil moisture discharge, drought persistence is forecast through the end of August.
Forecast confidence is moderate for the Northeast Region.
Due to a lack of snowfall this past winter, abnormal dryness (D0) is designated for parts of northern and eastern Mainland Alaska. Based on an increasingly wet climatology for June-July-August, development is unlikely. Alaska is predicted to remain drought-free through August.
Forecast confidence is high for Alaska.
Abnormal dryness (D0) and moderate drought (D1) expanded across the leeward slopes of the Hawaii Islands. Since the Islands already enter its dry season, the monthly and seasonal outlooks favor below normal precipitation, drought is forecast to persist or develop for leeward parts of the Hawaii Islands.
Forecast confidence is moderate for Hawaii.
Drought (D1) coverage expanded across Puerto Rico, due to below normal rainfall during the past month. The North American Multi-Model Ensemble forecasts favor below normal precipitation from monthly to seasonal precipitation outlooks. Drought persistence is favored. Since June-July-August is its wetter season of the year, this reduces forecast confidence.
Forecast confidence is low to moderate for Puerto Rico.
ENSO Considerations
We have covered some of this when we reported on the IRI/CPC analysis on May 13, 2021. We may discuss it again when we do the NOAA/JAMSTEC Comparison.
Now let us look at the NOAA recent ENSO Update. This happens every month on the second Thursday. I show this because it is the information that NOAA works from in producing the Four-Season Forecast.
I am not going to spend a lot of time on the new ENSO Advisory issued on May 13, 2021. It was a forgone conclusion that the Advisory would indicate that we were no longer in a La Nina but it is not clear if La Nina will return next winter.
Below is the probability analysis from mid-April and the probability analysis released on May 13, 2021
The probability distribution on the left is based on a survey of meteorologists and the probability on the right is based on model results. It is a pretty big change. We will discuss this more next week when NOAA issues their Four-Season Outlook.
With respect to forecasts, this is interesting
It comes from the article written by Emily Becker and some may find that article very interesting. That forecast suggests a return of La Nina for next winter. This time of the year is not the best time to make predictions but the so-called Spring Prediction Barrier SPB applies more to predicting El Nino than predicting La Nina.
May 2021 ENSO update: bye for now, La Nina! Click to read
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 but recently has been rising. This is another graphic that we have not frozen.
Below is the graphic above but also one issued five days later. (I believe these images are five-day averages centered on the date shown.)
Prior Version | Updated Version |
Here is the BOM Nino3.4 tracker.
Here is their current forecast.
And here is the NOAA proprietary model that it seems they have decided to ignore.
B. Conclusion
From the perspective of NOAA, we are no longer in a La Nina. There may be an issue as to how long we remain in that condition. The tools NOAA uses to forecast the state of ENSO has introduced the concept of a possible double-dip La Nina. That is not unusual. It would be devastating for the West. That change since last month re the prediction for the North American Monsoon is by itself pretty devastating news.