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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 SON 2019
    1.5mn OND 2019
    2.5mn NDJ 2019
    3.5mn DJF 2019
    4.5mn JFM 2020
    5.5mn FMA 2020
    6.5mn MAM 2020
    7.5mn AMJ 2020
    8.5mn MJJ 2020
    9.5mn JJA 2020
   10.5mn JAS 2020
   11.5mn ASO 2020
   12.5mn SON 2020
    0.5mn Sep 2019


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 Aug 15 2019

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS

The September-October-November (SON) 2019 temperature outlook favors above
normal temperatures throughout the entire forecast domain, although
probabilities vary. The highest probabilities for above normal temperatures are
forecast across New England, parts of the Southwest, and northern Alaska.
Probabilities for above normal temperatures are lowest across the northern
Great Plains.

The SON 2019 precipitation outlook indicates that above normal seasonal total
precipitation is most likely across the Florida Peninsula, mid-Atlantic, and
extending from parts of the Southwest north to the northern Great Plains and
upper Mississippi Valley. Above normal precipitation is also favored for
Alaska.

Equal chances (EC; white areas) of below, near, and above are forecast in areas
where the likelihood of seasonal mean temperatures or seasonal total
precipitation amounts are expected to be similar to their 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

Oceanic and atmospheric observations across the equatorial Pacific reflect a
transition to ENSO-neutral conditions during July into early August. The
observed weekly sea surface temperatures (SSTs), centered on August 7, are near
average from 140 degrees W to the coast of South America with slightly positive
anomalies limited to the central and western equatorial Pacific. The latest
weekly Nino 3.4 SST anomaly is +0.4 degree C.  Since mid-June, negative
subsurface temperature anomalies have expanded in the eastern Pacific.
Outgoing longwave radiation (OLR) anomalies indicated near average convection
across the equatorial Pacific from July 12 to August 6. The Madden-Julian
Oscillation (MJ0) has remained weak and incoherent for more than a month with
other modes of subseasonal variability influencing convection across the global
tropics. Enhanced trade winds have become more prevalent across the equatorial
central Pacific during early August.

Sea surface temperature anomalies of +2.5 to +3.5 degree C, or higher, persist
throughout areas surrounding Alaska. These anomalies and likelihood for another
fall season with low sea ice coverage were major factors in the temperature
outlook for Alaska this fall.

PROGNOSTIC DISCUSSION OF SST FORECASTS

A large spread in the dynamical and statistical model forecasts of SSTs across
the equatorial central and eastern Pacific during the fall and winter
continues. The statistical model forecasts, including the Canonical Correlation
Analysis, Constructed Analog, and Markov indicate a SST anomaly in Nino 3.4 at
or slightly above +0.5 degree C through winter 2019-2020. However, the North
American Multi-Model Ensemble (NMME) indicates near average SSTs during the
late fall and winter. The CPC/IRI consensus forecast indicates that
ENSO-neutral conditions are most likely through the winter with La Nina the
least likely to develop.

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

The temperature and precipitation outlooks were based on calibrated NMME
forecasts, a statistical-dynamical hybrid model combining calibrated NMME
forecasts with statistically bridged impacts from NMME Nino 3.4 forecasts, and
an ENSO-OCN tool. Due to the expectation that ENSO is unlikely to provide a
major influence on the mid-latitude circulation pattern at least through
earlier lead times, decadal climate trends were weighed more heavily during the
fall and winter 2019-2020. Decadal climate trends became the major tool for
temperature and precipitation outlooks at the longer leads.

PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2019 TO SON 2020

TEMPERATURE

Above-normal temperatures are favored throughout the forecast domain during
SON, based on excellent agreement among the dynamical models and statistical
tools. Given the strongest signal in decadal trends , probabilities are largest
across New England, the Southwest, and Alaska. Also, large positive SST
anomalies and the high likelihood for a lack of sea ice this fall support more
than an 80 percent chance of above normal temperatures across northern Alaska.
Probabilities for above normal temperatures are tempered across the northern
Great Plains where more variability is likely to occur during the three month
period and the signal is weaker among dynamical models . Also, the potential for
recurving tropical cyclones in the northwest Pacific and its effect on the
longwave pattern downstream over North America limits confidence in the
temperature outlook across the north-central CONUS. Probabilities for above
normal temperatures were decreased slightly across the Pacific Northwest during
OND and NDJ, based on the most recent NMME output and expectation of
ENSO-neutral conditions. During the late fall and continuing through the winter
2019-2020, coverage and probabilities for increased chances of above normal
temperatures were decreased across the central and eastern CONUS, compared to
previous outlooks. This change is related to higher uncertainty on the
evolution of ENSO this cold season. If ENSO-neutral conditions persist through
the upcoming winter, subseasonal variability such as the Arctic Oscillation
could play a greater role in temperatures.

Temperature outlooks during the spring and summer 2020 were not changed from
the previous month, since multi-decadal trends remain the primary tool. During
these seasons, above normal temperatures are most likely across Alaska and a
majority of the CONUS except for the north-central CONUS. By fall 2020,
increased chances of above normal expand to include all of the forecast domain
which follows long-term trends .

PRECIPITATION

Compared to the previous outlook for SON, an area favoring above normal
precipitation was added to include the Florida Peninsula, coastal Southeast,
and mid-Atlantic. The addition to the Florida Peninsula is supported by the
latest NMME output, while long-term trends support increased chances for above
normal precipitation across the mid-Atlantic during the fall. Enhanced odds for
above normal precipitation during SON extends from the southwestern CONUS
northeast to the northern Great Plains and upper Mississippi Valley, based
largely on dynamical model guidance. A slight tilt in the odds for above normal
precipitation, covering the desert Southwest and southeast California, during
SON is also related to potential surges of moisture with east Pacific tropical
cyclones (TC). SST anomalies are currently running +1.0 to +1.5 degree C in the
primary TC genesis region of the east Pacific. The increased chance for above
normal precipitation continues along the East Coast through OND, based on
long-term trends . Later in the fall, the increased chance for below normal
precipitation forecast for parts of the West Coast is maintained due to
precipitation tools that combine statistical and dynamical output.  During DJF
2019-2020 and JFM 2020, modifications to the previous outlooks were necessary
due to a decreasing chance of El Nino this winter. Therefore, the area that
favored above normal precipitation across the southern tier of the CONUS was
changed to equal chances for below, near, or above normal precipitation.
Increased chances of above normal precipitation for the north-central CONUS
during the winter is consistent with the latest NMME output and long-term
trends. A slight tilt in the odds for below normal precipitation across parts
of California and the Southwest during JFM 2020 is supported by the calibrated
NMME forecast. Enhanced odds for above normal precipitation forecast for parts
of Alaska throughout each lead time is supported in part by multi-decadal
trends.

At the longer leads, AMJ 2020 through SON 2020, the tilt in the odds towards
above normal precipitation across parts of the eastern U.S. is consistent with
long-term trends . Also, the favored area for below-median precipitation,
beginning with JJA 2020, across parts of the western and north-central CONUS is
also related to trends .

FORECASTER: Brad Pugh

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 Sep 19 2019


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

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