Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EST Sun Dec 31 2023


30-DAY OUTLOOK DISCUSSION FOR JANUARY 2024

The updated monthly temperature and precipitation outlooks for January 2024 are 
based on the latest dynamical models, WPC temperature and precipitation 
forecasts during the first week of the month, the CPC 6-10/8-14 day temperature 
and precipitation outlooks, and the week 3-4 outlook (valid January 13-26). El 
Niño remains a major climate driver and is expected to be one of the influences 
on the mid-latitude circulation pattern and associated January temperature and 
precipitation. Since late November, the Madden-Julian Oscillation (MJO) has 
completed a circumnavigation of the global tropics with its enhanced phase 
recently propagating east to Africa. The evolving longwave pattern with a high 
amplitude trough developing over the western contiguous U.S. (CONUS) during 
early January is consistent with MJO forcing. Lagged composites, based on phase 
2 of the Real-time Multivariate MJO index, were considered and would favor 
below (above)-normal temperatures across the southwestern (eastern) CONUS for 
much of the month. A negative Arctic Oscillation (AO) is predicted through at 
least mid-January and the high-latitude blocking is likely to result in a week 
or more of below-normal temperatures across much of the western and central 
CONUS. The longevity of a full-latitude 500-hPa ridge over Alaska would dictate 
the duration of this anomalous cold, especially for the Great Plains. 

The GEFS, ECMWF, and Canadian ensemble means remain consistent and in good 
agreement that a highly amplified 500-hPa trough shifts east to the Rockies and 
Great Plains during early January. This leads to a wetter revised precipitation 
outlook throughout the CONUS with enhanced above-normal precipitation 
probabilities expanded to include the Southwest, Great Basin, Central to 
Southern Rockies, and parts of the Great Plains. The January outlook continues 
to lean wet along the West Coast, but probabilities are modest given 
uncertainty on the primary storm track. Above-normal precipitation is slightly 
favored for parts of the drier climatological areas of the Midwest where there 
are increased chances of one or more low pressure systems to track northeast 
through this region by mid-January. Although the first week of January is 
expected to be mostly dry across the Great Lakes and Ohio Valley, the favored 
dryness in the initial January outlook (released December 21) was changed to 
equal chances (EC) for below, near, and above-normal precipitation due to the 
amplified 500-hpa trough and the 8-14 day outlook leaning wet. El Niño 
continues to strongly favor above-normal precipitation across the Southeast and 
much of the Gulf Coast. Enhanced above-normal precipitation probabilities are 
forecast throughout the eastern and much of the south-central CONUS due to a 
wet signal in the 8-14 day and week 3-4 tools. Above-normal precipitation 
probabilities are raised to 50-60 percent across the Lower Mississippi Valley 
based on 1 to 3 inches of precipitation forecast during the first week of 
January and a continued wet signal into the latter half of the month.  El Niño 
composites along with week-2 and week 3-4 outlooks support increased 
above-normal precipitation probabilities for southeastern Alaska. 

The highest forecast confidence in the revised monthly outlook exists for New 
England where above-normal temperatures are likely given the consistent signal 
for above-normal temperatures each week throughout the month and sparse snow 
cover heading into January. Month-to-date (December 1 to 30) temperatures have 
averaged above-normal throughout the CONUS with the largest anomalies (more 
than +9 degrees F) observed across the northern Great Plains and Upper 
Mississippi Valley. With a negative AO likely to persist through at least 
mid-January and a high-amplitude trough predicted to become established over 
the West and Great Plains, there are signs for a much colder outcome for the 
January mean temperature for parts of the lower 48 states. Increased 
below-normal temperature probabilities extend from southern California and the 
Southwest east to the Great Plains where below-normal temperatures are likely 
to accompany the amplified 500-hPa trough and model solutions are depicting 
Arctic high pressure shifting south from Canada during the second week of 
January. A CPC tool that uses a period-weighted method of temperature forecasts 
throughout the month flipped today towards below-normal temperatures across the 
Great Plains and supports the revised monthly outlook. Despite the model trend 
towards anomalous cold across the northern Great Plains by mid-month, 
probabilities are tempered due to above-normal temperatures to start the month 
and the week 3-4 tools indicating that temperatures could moderate during late 
January. Above-normal temperatures are slightly favored for parts of northern 
California and the coastal Pacific Northwest based on forecasts at the 
beginning of the month and week 3-4. El Niño composites favor above-normal 
temperatures throughout Alaska but EC is forecast for northern parts of the 
state due to the proximity of Arctic high pressure nearby during early to 
mid-January. 


***************** Previous discussion, released on December 21, is below  
*********************


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.

The next monthly outlook...for Feb ... will be issued on Thu Jan 18 2024

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