Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
830 AM EST Thu Dec 21 2023


30-DAY OUTLOOK DISCUSSION FOR JANUARY 2024

The January 2024 temperature and precipitation outlooks are based on: the Weeks 
3-4 model guidance (valid for early to mid-January), the North American 
Multi-Model Ensemble (NMME), and International Multi-Model Ensemble (IMME) for 
January, consolidation (statistical and dynamical tools), El Niño composites, 
consideration of the forecasted state of the Madden Julian Oscillation (MJO), 
and decadal trends. Above-average sea surface temperatures continue across the 
central and eastern equatorial Pacific, while enhanced convection was observed 
at the Date Line with suppressed convection around Indonesia during the past 
month. The oceanic and atmospheric observations reflect El Niño conditions 
which are likely to persist through the winter. 

El Niño remains the major climate driver and is expected to be the primary 
influence on the mid-latitude circulation pattern and associated January 
temperature and precipitation. Since late November, the MJO has propagated 
eastward from the Indian Ocean to the Pacific. As of mid-December, the enhanced 
(suppressed) phase of the MJO is centered over the Western (Eastern) 
Hemisphere. Lagged composites, based on phase 8 of the Real-time Multivariate 
MJO index, were considered for the January temperature outlook. However, 
enhanced convection across the western Indian Ocean, associated with the 
positive Indian Ocean Dipole (+IOD), along with El Niño may continue to disrupt 
any typical MJO response. Once the +IOD diminishes, the MJO could provide more 
influence on the mid-latitude circulation pattern over North America. The 
potential for a sudden stratospheric warming (SSW) is being monitored as zonal 
winds at 10-hPa over the Arctic are weaker than normal and many ensemble 
members from the GEFSv12 have a continued weakening. If a SSW were to occur, 
that could lead to high-latitude blocking, a negative Arctic Oscillation, and 
an increased chance of a colder outcome for parts of the contiguous U.S. 
(CONUS). A SSW event is uncertain but it will be monitored for the updated 
January outlook released on December 31. 

Month-to-date (December 1 to 19) temperatures have averaged above-normal 
throughout the CONUS with the largest anomalies (more than +7 degrees F) 
observed across the northern Great Plains and Upper Mississippi Valley. 
Following a positive Arctic Oscillation (AO) during mid-December, many of the 
GEFS ensemble members depict a more neutral or negative AO by the beginning of 
January. This change in the AO could promote at least more near normal 
temperatures for parts of the lower 48 States during January. Given the ongoing 
El Niño with enhanced Pacific flow over North America, overall mild 
temperatures are likely to continue from December 2023 into January 2024. The 
calibrated GEFS and ECMWF models for weeks 3-4 (valid January 3-16) feature 
increased above-normal temperature probabilities across most of the western and 
northern CONUS with a cold signal limited to the Southeast.  Despite this cold 
signal during early to mid-January, equal chances (EC) of below, near, or 
above-normal temperatures are forecast for the Southeast since no other monthly 
tool supports increased below-normal temperature probabilities. The most likely 
areas to experience above-normal temperatures for the month include the Pacific 
Northwest, Great Basin, Northern Rockies, much of California, and the northern 
tier of the CONUS.  This coverage is consistent with dynamical model guidance 
and El Niño composites. Sparse snow cover is expected to persist across 
Minnesota, the Dakotas, and eastern Montana heading into January which leads to 
enhanced above-normal temperature probabilities. The NMME, consolidation tool, 
and El Niño composites favor above-normal temperatures throughout Alaska with 
slightly lower probabilities forecast for southwestern Alaska. 

The January precipitation outlook reflects El Niño composites and the 
likelihood of an active southern storm track with above-normal precipitation 
most likely for much of the West Coast along with much of the Gulf Coast and 
Southeast. EC is forecast for Washington since input models to the NMME vary on 
the precipitation signal. The highest forecast confidence in the precipitation 
outlook exists across south Georgia and Florida where probabilities exceed 50 
percent for above-normal precipitation. The week 3-4 GEFS and ECMWF models, 
NMME, IMME, and El Niño composites all strongly support above-normal 
precipitation across that area of the Southeast. El Niño composites, the 
consolidation tool, and the IMME support increased below-normal precipitation 
probabilities from the Great Lakes southward to the Ohio Valley. For the 
remainder of the CONUS, weak or conflicting signals among the tools result in a 
forecast of EC. Based on the consolidation tool and week 3-4 model guidance, 
above-normal precipitation is slightly favored for parts of southeastern 
Alaska.  

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 Jan will be issued on Sun December 31 2023

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