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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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More Outlooks
    0.5mn MJJ 2021
    1.5mn JJA 2021
    2.5mn JAS 2021
    3.5mn ASO 2021
    4.5mn SON 2021
    5.5mn OND 2021
    6.5mn NDJ 2021
    7.5mn DJF 2021
    8.5mn JFM 2022
    9.5mn FMA 2022
   10.5mn MAM 2022
   11.5mn AMJ 2022
   12.5mn MJJ 2022
    0.5mn May 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 Apr 15 2021

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS

La Nina conditions continue across the equatorial Pacific Ocean as indicated by
oceanic and atmospheric conditions, while indications of a potential transition
to ENSO-neutral during the May through July period are apparent. The chance of
a return to La Nina increases over the summer, such that La Nina becomes
slightly more favored than ENSO-neutral in autumn. In addition to the forecast
ENSO evolution described above, current anomalous soil moisture along with
numerical and statistical model guidance inform the seasonal temperature and
precipitation outlooks.

The May-June-July (MJJ) 2021 temperature outlook favors above-normal seasonal
mean temperatures for nearly all the contiguous U.S. and for Mainland Alaska
and the Aleutian Islands. Equal chances (EC) of above-normal and below-normal
temperatures are predicted for a region from far southeastern Mainland Alaska
to parts of the Pacific Northwest, including northwestern Oregon and western
Washington. Above-normal temperatures are most likely for the entire forecast
domain from the summer into the beginning of autumn.

The MJJ 2021 precipitation outlook favors above-normal seasonal total
precipitation amounts for central and eastern areas surrounding the Great
Lakes, the Midwest, the Mid-Atlantic, and most of the Northeast, except for
northern Maine, as well as southward along the Eastern Seaboard and the eastern
Gulf Coast. Above-normal precipitation is also favored for northwestern areas
of Alaska, including the north-central coast. Below-normal precipitation is
most likely for a region from the West coast across the Rockies to the central
and southern Great Plains, excluding areas of the Southwest that are
climatologically drier at this time of year. The area of likely below-normal
precipitation is forecast to slowly shift northward and eastward during the
summer seasons while above-normal precipitation continues to be favored along
the Eastern Seaboard and expands westward along the Gulf Coast over the same
period. An area of elevated probabilities 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 continued but weakened during the last month in the
equatorial Pacific Ocean as shown by both oceanic and atmospheric indicators.
Equatorial sea surface temperature (SST) anomalies became less negative over
the central equatorial Pacific during the last month. The most recent weekly
value of the Nino3.4 SST index is -0.5 degrees C. SSTs and atmospheric
conditions are likely to be modulated by an ongoing MJO event over the next few
weeks. Below the surface, the depth and magnitude of negative ocean temperature
anomalies decreased and currently extend in a shallow layer to a depth of 50
meters from 175 E to 110 W. Positive subsurface oceanic heat content anomalies
are present below 50 meters to depths of 200 meters or more and have expanded
eastward in the western and east-central Pacific Ocean.

Suppressed convection persists across the equatorial Pacific surrounding the
Date Line, while enhanced convection weakened over the western Pacific but
remains over parts of Indonesia and the Philippines. Recent monthly average
850-hPa winds continue to show enhanced easterly trade winds across the western
and east-central equatorial Pacific. Westerly wind anomalies continued at
200-hPa over much of the equatorial Pacific Ocean. These ocean and atmosphere
indicators show the coupled ocean-atmosphere system is consistent with
weakening La Nina conditions.

PROGNOSTIC DISCUSSION OF SST FORECASTS

Forecasts of the Nino3.4 SST index from the NMME show considerable spread in
ensemble members both across the modeling center forecasts and within each
modeling center ensemble by the start of summer. Most guidance favors a
continued decrease in the magnitude of negative SST anomalies over the next
three months, and the official consensus calls for ENSO-neutral with a
probability of 80 percent. Forecasts begin to diverge during the summer months
with some guidance favoring a decrease in Nino3.4 sea surface temperatures,
suggesting a return to La Nina conditions by autumn 2021. The CA and Markov
statistical models in the CPC Nino3.4 SST consolidated forecast indicate a
trajectory towards ENSO-neutral in the autumn, while the CCA predicts a steady
rise in Nino3.4 SST towards El Nino conditions over the summer and autumn
months.

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

Although equatorial Pacific SSTs continue to rise towards climatological normal
values and are forecast to indicate ENSO-neutral oceanic conditions for MJJ
2021, typical impacts of La Nina are considered in preparing the MJJ 2021
seasonal outlook, as some impacts are likely to result at the start of the
season. Tools used to inform the outlooks include regressions of temperature
and precipitation on the Nino3.4 SST consolidation forecast and the CBaM
forecast tool, that statistically “bridges” dynamical model Nino3.4 SST anomaly
forecasts from the NMME with observed temperature and precipitation using a
Bayesian methodology.

Current anomalous soil moisture and snow cover are considered and contributed
to the outlook in some locations for the MJJ 2021 season. Dynamical model
forecasts from the NMME and Copernicus (C3S) multi-model ensemble systems are
used extensively for the first six leads when they are available, as was the
objective, historical skill weighted consolidation, that combines both
dynamical and statistical forecast tools. Due to the frequency of back-to-back
La Nina events in the historical record and the consensus ENSO outlook slightly
favoring La Nina over ENSO neutral, potential impacts of redevelopment of La
Nina is considered in the autumn and winter seasons. Decadal timescale trends
in temperature and precipitation are utilized extensively to inform the
seasonal outlooks at all leads.

PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2021 TO MJJ 2022

TEMPERATURE

The MJJ 2021 temperature outlook favors above-normal seasonal mean temperatures
for nearly all the contiguous U.S. (CONUS) and for the Alaska Mainland and the
Aleutian Islands. The greatest probabilities for above-normal temperatures are
located over the Southwest in the Four Corners region, exceeding 70 percent,
due to multiple factors including very consistent dynamical model guidance, low
soil moisture conditions, positive decadal temperature trends , and the support
of statistical forecast tools. Modestly elevated probabilities for above-normal
temperatures extend eastward across the Southeast and northward along the
Eastern Seaboard to New England, supported by model guidance and positive
decadal trends . Greater uncertainty, related to the early impacts of La Nina
and an MJO event, lower historical forecast skill in model guidance, and weaker
decadal temperature trends decrease probabilities for above-normal temperatures
in the north-central CONUS. Consistent with possible lingering La Nina impacts
as indicated by ENSO regressions and hybrid statistical-dynamical "bridging"
tools, equal chances of above-normal and below-normal temperatures are forecast
for southeastern areas of Alaska and parts of the Pacific Northwest, and the
probabilities of above-normal temperatures have been decreased for the southern
Alaska Mainland. Negative trends in sea ice coverage and thickness and positive
decadal temperature trends favor above-normal temperatures for northern areas
of Alaska.

Dynamical model guidance and statistical forecast tools, including those
derived from forecasts of the enhanced probabilities of ENSO-neutral or La Nina
conditions and decadal timescale trends , favor continued elevated probabilities
for above-normal temperatures for most of the forecast domain through the SON
2021 season with the greatest chances indicated for the western U.S. and along
the eastern seaboard with slightly lower probabilities for the north-central
CONUS.

Beginning in OND 2021 and continuing through FMA 2022, there is a gradual
increase in the area designated as EC, with an increased chance for La Nina
redevelopment with potential impacts over much of the northern tier of the
CONUS from the Pacific Northwest to the western Great Lakes, and later
southeast Alaska. Other areas of the forecast domain continue to favor likely
above normal temperatures, primarily due to positive decadal temperature trends .

PRECIPITATION

The MJJ 2021 precipitation outlook favors above-normal seasonal total
precipitation amounts for central and eastern areas of the Great Lakes region,
the Ohio Valley, the Mid-Atlantic, and most of the Eastern Seaboard, excluding
northern Maine, based on the continued influence of La Nina early in the
season, positive precipitation decadal trends , other statistical forecast tools
including the constructed analog from soil moisture conditions, and some
dynamical model forecasts from the NMME and C3S ensemble systems. There is
considerably greater agreement among dynamical models , however, for a region of
likely below-normal precipitation from the central and northern Pacific coast
across the Rockies into the Central and Southern Plains. Higher probabilities
for below-normal over the Northern Rockies, exceeding 50 percent in some areas,
are supported by typical La Nina impacts and dynamical model forecasts.

The area of likely below-normal precipitation is forecast to shift slowly
northward and eastward during the summer and southward into the west-central
CONUS during the autumn, consistent with dynamical model guidance. Above-normal
precipitation is predicted to persist along much of the Eastern Seaboard
through the summer months, and an area of likely above-normal precipitation
continues for parts of the southeast Atlantic coast and the eastern Gulf Coast
into the early autumn, consistent with the impacts of the likely La Nina or
ENSO-neutral climate conditions, with very low probability of El Nino
conditions over the tropics.

Below-normal soil moisture in the Southwest and southern Rockies may allow for
more efficient heating of the land mass and potentially an enhanced monsoon
circulation. Elevated probabilities for above-normal precipitation are
predicted for parts of the southwest from JJA through ASO 2021, supported in
part by dynamical model forecasts.

Dynamical model guidance supports above-normal precipitation for parts of the
northwestern coast of Alaska from MJJ through ASO 2021, while decadal
precipitation trends related to positive trends in SSTs support above-normal
precipitation for the northern coast through OND 2021. The outlooks from OND
2021 through MJJ 2022 are primarily based on decadal precipitation trends .

FORECASTER: Dan Collins

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 May 20 2021


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

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Page last modified: January 17, 2006
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