New winter outlook: Drier, warmer than normal weather will worsen drought

Weather

The Climate Prediction Center has issued the new monthly outlooks for precipitation and temperatures across the U.S. for the next year. Central Texas is part of a large area of the southern U.S. forecast to remain drier and warmer than normal through winter, and well into spring. The rainfall shortage is expected to worsen already severe to extreme drought conditions across Central Texas.

Latest 90 Day Precipitation Outlook
Drier than normal weather is forecast for much of the southern U.S. and all of Texas this winter
Latest 90 Day Temperature Outlook
Warmer than normal weather is forecast across much of the U.S. and all of Texas during winter 2020-2021
Precipitation outlooks through winter 2022
Temperature outlooks through winter 2022

Prognostic Discussion for Long-Lead Seasonal Outlooks
NWS Climate Prediction Center College Park MD
Thu Dec 17 2020

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
Moderate La Nina conditions are present across the equatorial Pacific Ocean, as
indicated by current oceanic and atmospheric observations. La Nina is expected
to continue through the Northern Hemisphere winter, with a potential transition
to ENSO-neutral (~50% chance) during Spring 2021. The January-February-March
(JFM) temperature outlook favors below normal seasonal mean temperatures for
approximately the southeastern quarter of Mainland Alaska and the Alaska
Panhandle, and from the Pacific Northwest eastward across the Northern Rockies
to the Northern Plains. Maximum probabilities for below normal temperatures
exceed 50% over the extreme southeast portion of Mainland Alaska, the Alaska
Panhandle, and Washington state. Above normal temperatures are favored across
parts of northern and western Alaska, and for approximately the southern
one-half of the CONUS, extending northward across the Ohio Valley, Central and
Northern Appalachians, Mid-Atlantic, and Northeast. Maximum probabilities for
above normal temperatures exceed 60% across parts of the Southwest, Southern
Rockies and Southern Great Plains. The JFM precipitation outlook favors above
normal precipitation for most of the northern tier of the CONUS, extending
southward from the Great Lakes across eastern portions of the Middle
Mississippi Valley, the Ohio Valley, and the Central and Northern Appalachians.
Above normal precipitation is also favored for northern and western portions of
Alaska. Maximum probabilities for above normal precipitation exceed 50% over
the Lower Ohio Valley. There are elevated odds of below normal precipitation
for approximately the southern one-third to one-half of the CONUS, and along
the southern Alaska coast from the eastern Alaska Peninsula to the southern
Panhandle region. Maximum probabilities of below normal precipitation exceed
60% from southeastern Arizona to the Big Bend area of Texas, and over parts of
northern Florida and southern Georgia.
Equal Chances (EC) are forecast for areas where probabilities for each category
of seasonal mean temperatures or seasonal total precipitation amounts are
predicted 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
Tropical oceanic and atmospheric observations reflect ongoing La Nina
conditions. During the past 30-days, a Pacific equatorial cold tongue with
negative sea-surface temperature (SST) anomalies was located from about 160 deg
E across the Date Line to about 100 deg W. SST anomalies for the period ranged
between 0.5 deg C to 1.5 deg C over most of this region. Subsurface
temperatures were colder-than-average for the same region, down to a depth of
about 175 meters. The Oceanic Nino 3.4 Index (ONI) for the latest observed
season (SON 2020) is -1.2 deg C, which qualifies as a moderate La Nina at this
time. Atmospheric observations feature enhanced easterly trade winds at 850-hPa
from the western to the east-central equatorial Pacific, westerly wind
anomalies at 200-hPa over most of the Pacific, and suppressed tropical
convection over the western and central Pacific.

PROGNOSTIC DISCUSSION OF SST FORECASTS
The CPC Nino3.4 SST consolidation depicts negative SST anomalies increasing
slightly in amplitude to about -1.3 or -1.4 deg C by the anticipated NDJ 2020
peak of this La Nina event, before slowly recovering to -1.0 deg C by JFM 2021.
The consolidation forecast predicts the ONI value will cross the -0.5 deg C
threshold into ENSO-neutral territory during MAM 2021, and reach the zero
anomaly line by MJJ 2021. The NMME ensemble mean SST plume for the Nino 3.4
region reaches the -0.5 deg C threshold by April 2021, and the C3S (Copernicus)
SST plume reaches the ENSO-neutral threshold slightly later in the spring. The
CPC-IRI consensus predicts the likelihood of La Nina will drop to the same
likelihood of ENSO-neutral by about AMJ 2021. The official ENSO forecast calls
for approximately a 95% chance for La Nina to continue through Northern
Hemisphere winter, with a potential transition during the spring 2021 (~50%
chance of Neutral during AMJ 2021).

PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
Given a very high likelihood of the persistence of La Nina conditions, the
seasonal outlooks utilized canonical impacts during past observed La Nina
events as guidance for many areas of the forecast domain through at least MAM
This guidance included regressions of temperature and precipitation
relative to the CPC consolidation forecasts of the Nino3.4 region and via
“bridging” techniques utilizing statistical relationships between dynamical
model forecasts of the Nino 3.4 index and observed temperature and
precipitation. Dynamical model guidance from the North American Multi-Model
Ensemble (NMME) and the model suite from the Copernicus program are a
significant component of guidance for the temperature and precipitation
outlooks through MJJ 2021. Beyond MJJ 2021, the consolidation of various
statistical tools, including decadal trends , was the primary basis for the
outlooks, with little remaining influence from ENSO or other reliable
large-scale signals of climate variability for these forecast leads. Also,
based on current and potential drought conditions in many areas across the
southern tier of the CONUS, low soil moisture conditions influenced the
temperature outlooks for the spring and early summer 2021. At later leads,
decadal trends in temperature and precipitation were the primary tool used in
creating the seasonal outlooks.

PROGNOSTIC DISCUSSION OF OUTLOOKS – JFM 2021 TO JFM 2022
TEMPERATURE
The temperature outlook for JFM 2021 favors below normal seasonal mean
temperatures for approximately the southeastern quarter of Mainland Alaska and
the Alaska Panhandle, based largely on La Nina composites/regressions and
climate model forecasts. Over the Lower 48 states, below normal temperatures
are also favored for the Pacific Northwest, the Northern Rockies, and much of
the Northern Great Plains, which is also characteristic of a mature cold season
La Nina. Perhaps the area of greatest uncertainty regarding below normal
temperatures is over South Dakota and portions of the Upper Mississippi Valley,
where there are significant differences between the tools. For example, tools
such as the Final CON and CBaM support anomalous cold across this region,
whereas the uncalibrated NMME, C3S(Copernicus) and CFS favor anomalous warmth.
Parts of this region are in drought, and are expected to be in drought in the
early spring. Any lack of snow cover would also support relative warmth during
JFM (please refer to CPC’s Monthly Outlook discussion for more information). It
was decided that EC was the best bet for the temperature pattern across most of
South Dakota and much of the Upper Mississippi Valley during JFM. Regarding the
odds for below normal temperatures over Alaska and the CONUS, maximum
probabilities exceed 50% over the extreme southeast portion of Mainland Alaska,
the Alaska Panhandle, and western Washington state. Above normal temperatures
are favored across portions of northern and western Alaska, and for
approximately the southern one-half and eastern one-third of the CONUS. Maximum
probabilities for above normal temperatures exceed 60% across parts of the
Southwest, Southern Rockies and Southern Great Plains. The above normal
(upper-tercile) temperatures favored in northwestern Alaska is consistent with
many of the objective tools, and temperature trends during the last 15 years.
The upper-tercile temperatures predicted over the southern, and much of the
eastern, CONUS, are supported by La Nina composites, most of the NMME inputs,
and the ENSO-OCN tool which combines ENSO information with trends .
The subsequent temperature outlooks for FMA and MAM are similar to the JFM
temperature outlook, which is reasonable given the intensity and anticipated
duration of the La Nina. As the region of favored below normal temperatures
fades across the northern tier states (from the Pacific Northwest to the
Northern Plains), the probabilities and spatial coverage for above normal
temperatures slowly increases across the eastern CONUS. In Alaska, the chances
of above normal temperatures increases to over 50% in MAM, based in part on the
earlier climatological breakup of sea ice, and longer-term temperature trends .
By AMJ 2021, the odds of La Nina and ENSO-neutral are roughly equal near 50%,
with a potential transition from La Nina to ENSO-neutral. From MJJ through SON,
warmer-than-normal temperatures are favored across most of the CONUS and
Alaska, supported by dynamical models , the statistical consolidation
(Stat-CON), and trends . From OND onwards, uncertainty (and therefore, EC)
gradually expands across the northwestern and north-central CONUS, while
temperature trends favor above normal temperatures in Alaska.

PRECIPITATION
The JFM 2021 precipitation outlook favors above normal precipitation amounts
from much of the northwestern quarter of the CONUS eastward across the Great
Lakes and interior Northeast, extending southward over the eastern CONUS across
the Ohio, Tennessee, and much of the Mississippi Valleys, and portions of the
Appalachians.. Above normal precipitation is also favored for northern and
western portions of Alaska. These areas of favored wetter-than-normal
conditions are consistent with what is typically observed during mature, cold
season La Nina’s, and are well supported by a majority of climate models.
Maximum probabilities of above normal precipitation exceed 50% over the Lower
Ohio Valley. There are elevated odds of below normal precipitation for
approximately the southern one-third to one-half of the CONUS, and along the
southern Alaska coast from about Kodiak Island and Cook Inlet southeastward
across the Alaska Panhandle. These favored regions of below normal
precipitation are also consistent with classic La Nina wintertime setups.
Maximum probabilities of below normal precipitation exceed 60% over far
southern New Mexico and adjacent parts of southwestern Texas, and over parts of
northern Florida and southern Georgia. Unfortunately, much of the southern
CONUS is also experiencing drought, after a lackluster summer monsoon season
and relatively dry autumn.
La Nina is the primary physical driver behind the subsequent FMA and MAM
precipitation outlooks, so only minor adjustments were needed to the
corresponding outlooks made last month. In MAM, the amplitude of La Nina and
its associated precipitation impacts are expected to begin to decline. In AMJ
2021, below normal precipitation amounts are forecast to diminish in spatial
coverage across the southern CONUS, and be centered over most of the
southwestern quarter of the CONUS before the signal disappears completely in
MJJ. Over much of the eastern CONUS during AMJ and MJJ, above normal
precipitation is favored, based in large part on the consolidation tool,
precipitation trends , the CFS, and the Constructed Analog on Pacific SSTs. In
JJA and JAS 2021, trends favor the development of a dry signal in the Northwest
CONUS. Trends also favor the reduction in coverage of the wet signal in the
East, beginning in JJA and continuing through OND. The final three leads (NDJ
2021-JFM 2022) feature a favored area of above normal precipitation in the
vicinity of the Northern Great Plains, which expands eastward with time towards
the Ohio Valley. The Alaska precipitation outlooks from AMJ 2021 through JFM
2022 indicate EC, based on the predicted conclusion of La Nina during the
springtime and weak and/or inconsistent precipitation signals among the
tools/trends thereafter.

FORECASTER: Anthony Artusa
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.shtml
(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 Jan 21 2021.
1981-2010 base period means were implemented effective with the May 19, 2011
forecast release.

Copyright 2021 Nexstar Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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