Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EST Thu Nov 17 2022


30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2022

The December 2022 temperature and precipitation outlooks are based on the Weeks 
3-4 model solutions (valid for early to mid-December), dynamical model output 
for December, La Niña composites, consideration on the forecasted state of the 
Madden Julian Oscillation (MJO), and decadal trends. Below-average sea surface 
temperatures continue across the central and eastern equatorial Pacific, while 
suppressed convection was observed near and west of the Date Line this past 
month. The oceanic and atmospheric observations reflect La Niña conditions 
which are likely to persist through the winter. 

The MJO is forecast to strengthen and propagate eastward to the West Pacific 
during late November. Although the GEFS and ECMWF models are in good agreement 
on this MJO evolution, large ensemble spread exists on the strength of the MJO 
with many GFS ensemble members depicting a higher amplitude MJO event compared 
to the majority of ECMWF ensemble members. Lagged composites, based on phase 5 
of the MJO RMM index, would favor below-normal temperatures overspreading the 
central and eastern contiguous U.S. (CONUS) during early to mid-December. Given 
the expected mild start to the month for most areas east of the Rockies, this 
would translate to a highly variable temperature pattern during December which 
lowers forecast confidence in the monthly temperature outlook for the central 
and eastern CONUS. Therefore, a large coverage of equal chances (EC) of below, 
near, or above-normal temperatures is necessary. Below-normal temperatures are 
favored for the northern Great Plains where the week 3-4 ECMWF model along with 
La Niña composites feature a cold signal. Above-normal temperatures are only 
slightly favored along the East Coast, consistent with the week 3-4 model 
solutions and the North American Multi-Model Ensemble (NMME). The dynamical 
model output along with La Niña composites support increased probabilities for 
above-normal temperatures throughout the southern tier of the CONUS. Although 
there is support for larger probabilities of above-normal temperatures across 
the Southeast, the GFS ensemble mean depicts a negative NAO heading into 
December which limits forecast confidence for this region. The highest forecast 
confidence in the temperature outlook exists across the Southwest where week 
3-4 solutions along with dynamical and statistical tools are in good agreement. 
 

La Niña composites for November-December-January (NDJ) are the major guidance 
relied upon for the December precipitation outlook along with the NMME. 
Above-normal precipitation is most likely across the Pacific Northwest, 
northern to central Rockies, and northern high Plains. Conversely, below-normal 
precipitation is favored for parts of the Southwest, central to southern Great 
Plains, Gulf Coast, and Southeast. Although statistical tools support a drier 
outcome for California, EC is forecast for the state due to a lack of support 
from monthly dynamical models and a robust wet signal evident in the week 3-4 
ECMWF model solution. Also, the ensemble means are in good agreement on an 
amplified 500-hPa trough centered near the West Coast during the final week of 
November. EC is also forecast for the Great Lakes and Ohio Valley where the wet 
signal, associated with La Niña, typically occurs later in the winter season. 

The dynamical and statistical tools are in good agreement and depict elevated 
probabilities for below (above)-normal temperatures for the Alaska Panhandle 
(western Mainland Alaska). Despite the NMME favoring above-normal temperatures 
across the Aleutians, EC was forecast for this region due to negative sea 
surface temperature anomalies nearby and a strong cold signal in the week 3-4 
ECMWF model. The NMME and decadal trends support increased probabilities for 
above-normal precipitation for northwestern Alaska. Although La Niña typically 
favors dryness for the Alaska Panhandle during the winter, EC was forecast due 
to a weak signal among the dynamical model output. 

FORECASTER: Brad Pugh

The climatic normals are based on conditions between 1991 and 2020, following
the World Meteorological Organization convention of using the most recent 3 
complete decades as the climate 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.

An updated monthly outlook... for Dec will be issued on Wed November 30 2022

These outlooks are based on departures from the 1991-2020 base period.
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