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


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HOME> Outlook Maps>Seasonal Forecast Discussion
 
Prognostic Discussion for Long-Lead Seasonal Outlooks 
NWS Climate Prediction Center College Park MD
830 AM EDT Thu Sep 16 2021

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS

ENSO-neutral conditions are present, as represented in current oceanic and
atmospheric observations. A transition from ENSO-neutral to La-Niña is favored
in the next couple of months, with a 70 to 80 percent chance of La Nina during
the Northern Hemisphere Winter 2021-22. Conversely, the chances of El Niño are
exceedingly small, with probabilities less than 5 percent through the upcoming
winter.

The October-November-December (OND) 2021 temperature outlook favors above
normal temperatures for the southern two-thirds of the Contiguous United States
(CONUS), the eastern third of the CONUS, and western Alaska, with the largest
probabilities (greater than 50 percent) forecast across the Southwest and New
England. The OND 2021 precipitation outlook depicts enhanced probabilities of
below normal precipitation amounts across the Southern Tier and much of the
central CONUS. Above-normal precipitation is more likely for the northwestern
CONUS, the Eastern Great Lakes, parts of the interior Northeast, and parts of
southwestern 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
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

The coupled oceanic and atmospheric observations reflect ENSO-neutral
conditions. In the last month, ENSO-neutral continued with near-to-below
average sea surface temperatures (SSTs) persisting in the central and eastern
equatorial Pacific. In the last week, the Niño 3.4 index value stood at -0.4°C.
Negative subsurface temperature anomalies (averaged from 180-100°W) remained
steady in August reflecting below-average temperatures that extended from the
surface to ~250m depth in the eastern Pacific Ocean. Low-level wind anomalies
were easterly over the western Pacific Ocean, while upper-level wind anomalies
were westerly over the western and east-central Pacific. Tropical convection
was suppressed near and west of the Date Line and enhanced over Indonesia.
Given these conditions, the ocean-atmosphere system reflects ENSO-neutral, but
is edging toward La Niña.

The Real-time Multivariate Madden Julian Oscillation (RMM) index depicts a
strengthening signal over the eastern Indian Ocean, where enhanced convection
has persisted for the past several weeks. There is considerable spread among
dynamical models on the future evolution of the Madden Julian Oscillation
(MJO). Models generally depict an MJO event crossing the Maritime Continent but
differ in the strength and evolution of this feature. Thus, uncertainty is
relatively high on the future evolution of the MJO at this time.

PROGNOSTIC DISCUSSION OF SST FORECASTS

The IRI/CPC plume average of forecasts for the Niño-3.4 SST region from the
last month favored borderline or weak La Niña during the fall and winter
2021-22. The current forecast favors the latest predictions from the NCEP CFSv2
and the North American Multi-Model Ensemble (NMME), which suggest higher
chances for the emergence of La Niña. At this time, La Niña is anticipated to
be of weak strength (seasonal average Niño-3.4 index values between -0.5°C to
-0.9°C). In summary, a transition from ENSO-neutral to La Niña is favored in
the next couple of months, with a 70-80% chance of La Niña during the Northern
Hemisphere winter 2021-22.

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

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.

Additionally, the official ENSO forecast depicts probabilities of La Niña that
are significantly higher than climatological probabilities through the upcoming
winter. This anticipated La Niña signal played a role in the construction of
these outlooks. At later leads, decadal trends in temperature and precipitation
were increasingly relied upon in creating the seasonal outlooks.

PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2021 TO OND 2022

TEMPERATURE

Above normal temperatures are favored throughout a majority of the southern and
eastern CONUS and western Alaska during OND. Conversely, below normal
temperatures are more likely for southeastern Alaska. Equal chances (EC) of
below, near, or above normal temperatures are forecast for the northwestern and
north-central CONUS. This EC area is due to weak or conflicting signals among
temperature tools. Probabilities of above normal temperatures are increased
relative to last month across the East due to stronger support among the
temperature guidance. Above normal temperatures are especially likely (greater
than 50 percent) for eastern New England due to good agreement among both
dynamical and statistical guidance. Guidance has trended colder across much of
Alaska relative to last month. Thus, increased probabilities of below normal
temperatures were introduced to southeastern parts of the state, which is also
consistent with composites from the current ENSO state.

From NDJ through FMA, impacts from the potential La Niña become more apparent
as above normal temperatures continue to be favored across the Southern CONUS
and the Eastern Seaboard while enhanced below normal temperature probabilities
persist across southeastern Alaska and expand southward to the northwestern
CONUS. Thereafter, the forecast pattern increasingly begins to reflect trends
with above normal temperatures generally favored across most of the southern,
western, and eastern CONUS next spring, summer, and into the fall.
Probabilities of above normal temperatures peak across the West next summer and
across the Eastern Seaboard next fall, consistent with trends . Across Alaska,
above normal temperatures become increasingly likely with time, with the
strongest warm signal emerging next summer, when probabilities of above normal
temperatures exceed 50 percent for most of the state.

PRECIPITATION

Model guidance remains consistent from previous months depicting elevated
probabilities of below normal precipitation for much of the southern and
central CONUS, and increased chances of above normal precipitation for the
Pacific Northwest during OND. Models are consistent in depicting an expansion
of a dry signal eastward across the Southeast, with influences from potential
tropical disturbances decreasing and La Niña influences increasing as we
progress deeper into the fall and early winter. Conversely, precipitation
guidance has trended wetter across the northwestern CONUS, resulting in an
increase in above normal precipitation probabilities relative to last month.
Additionally, an area of slightly increased probabilities of above normal
precipitation was introduced to the Great Lakes region and interior Northeast,
consistent with the latest C3S guidance. A slight tilt toward above normal
precipitation is also indicated for parts of southwestern Alaska, based
primarily on dynamical model guidance.  EC is indicated for the rest of the
forecast domain as signals for the various dynamical and statistical tools are
too weak or conflicting to issue a forecast with a sufficient degree of
confidence.

As we progress further into late fall and through the winter, dynamical and
statistical guidance persist with a dry signal across the southern CONUS,
consistent with a La Niña signature. An eastward expansion of enhanced above
normal precipitation probabilities is noted across the northwestern CONUS, as
well as a northward expansion across the Alaska Panhandle, peaking in coverage
during the winter. A wet signal is also favored to expand southward from the
Great Lakes to the Ohio Valley during the winter with the strongest signal
evident during JFM, consistent with La Niña composites. During next spring
through next fall, trends become the dominant factor with increased chances of
above normal precipitation generally indicated across parts of the Eastern
CONUS and Gulf Coast Region through much of the period. Conversely, trends
favor a dry pattern for much of the West next spring and summer, with increased
chances of dryness for parts of the Northern Plains next summer as well.
Thereafter, an area of slightly enhanced probabilities of above normal
precipitation makes a brief appearance across the Pacific Northwest in ASO,
based primarily on statistical guidance from trends and ENSO. A tilt toward a
dry pattern persists farther to the south across parts of the remainder of the
West into next fall, based primarily on trends . There exists high uncertainty
across much of Alaska through the period with large areas of EC indicated.
However, dynamical guidance supports increased odds of above normal
precipitation across parts of the western and northern Mainland through the MAM
season. Conversely, statistical guidance from trends and ENSO support a slight
tilt toward below normal precipitation for parts of the South Coast early in
the spring shifting toward the southwestern Mainland later in the spring.
Thereafter, trends support slightly increased chances for above normal
precipitation for parts of the eastern Mainland next summer and slightly
increased chances of below normal precipitation for parts of the Panhandle next
fall.

FORECASTER: Scott Handel

The Climatic normals are based on conditions between 1991 and 2020, 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 Oct 21 2021


1991-2020 base period means were implemented effective with the May 20, 2021
forecast release.
$$

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Page last modified: January 17, 2006
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