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Official 90-day Outlooks are issued once each month near mid-month at 8:30am Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.

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    0.5mn AMJ 2021
    1.5mn MJJ 2021
    2.5mn JJA 2021
    3.5mn JAS 2021
    4.5mn ASO 2021
    5.5mn SON 2021
    6.5mn OND 2021
    7.5mn NDJ 2021
    8.5mn DJF 2021
    9.5mn JFM 2022
   10.5mn FMA 2022
   11.5mn MAM 2022
   12.5mn AMJ 2022
    0.5mn Apr 2021


Tools Used (see Discussion for explanation)
   CCA
   OCN
   CMP
   SMT
   POE
 
HOME> Outlook Maps>Seasonal Forecast Discussion
 
Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD
830 AM EDT Thu Mar 18 2021

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS

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.

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.

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
Note: For Graphical Displays of the Forecast Tools Discussed Below See:
http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing

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.

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 .

FORECASTER: Jon Gottschalck

The Climatic normals are based on conditions between 1981 and 2010, following
the World Meterological 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 Apr 15 2021


1981-2010 base period means were implemented effective with the May 19, 2011
forecast release.
$$

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