Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EST Tue Dec 31 2024


30-DAY OUTLOOK DISCUSSION FOR JANUARY 2025

The January 2025 Monthly Temperature and Precipitation Outlooks are updated 
with input from the Climate Prediction Center (CPC) Extended Range and 
Subseasonal Outlooks, dynamical model guidance for week 2 and weeks 3-4, 
background climate states such as the Madden Julian Oscillation (MJO) and El 
Niño Southern Oscillation (ENSO), recent Climate Forecast System version 2 
(CFSv2) monthly forecasts of temperature and precipitation, and experimental 
monthly forecasts of temperature and precipitation from extended runs of the 
Global Ensemble Forecast System version 12 (GEFSv12) and the European Centre 
for Medium-Range Weather Forecasts (ECMWF) models. ENSO-neutral conditions are 
currently present, however, equatorial sea surface temperatures (SSTs) are 
near-to-below average in the central and eastern Pacific Ocean, with the latest 
weekly Niño3.4 SST departure reaching -1.1 degrees Celsius. While ENSO-neutral 
conditions are present, these colder SSTs may lead to some La Niña-like impacts 
in the atmosphere and over the U.S., though the impacts are more likely to be 
weak and transient compared to those during a stronger La Niña. Perhaps more of 
a player and in contrast to the previous mid-month discussion, the MJO has 
become more coherent, and has propagated from the Maritime Continent into the 
Western Pacific. Dynamical model forecasts of the Realtime Multivariate MJO 
(RMM) index are in agreement favoring continued eastward progression of the MJO 
signal over the next two weeks, which typically leads to increased troughing 
over the central and eastern Contiguous United States (CONUS), consistent with 
a negative Arctic Oscillation and North Atlantic Oscillation. Overall, the more 
certain MJO forecasts and subsequent eastern CONUS troughing will allow for the 
potential for cooler air from the North entering the eastern CONUS during 
January. 

Models and teleconnections, particularly the MJO and its potential progression, 
were more uncertain during the mid-month release of the Monthly Temperature 
Outlook. As such, the forecast was based mainly on dynamical models such as the 
North American Multi-Model Ensemble (NMME), the potential for La Niña-like 
impacts leading to above normal temperatures over much of the southern tier, 
and the potential for a warm start to January, though we expected a transient 
pattern throughout the month. Given the uncertainty in models and expected 
transient pattern a large area of Equal Chances (EC) of above, near, and below 
normal temperatures was favored for much of the CONUS. Short- (6-10 and 8-14 
Day) and long-term (Weeks 3-4) forecasts have come into agreement on a fairly 
persistent pattern of 500-hPa ridging over the West and troughing over the 
East. This pattern is expected to begin in early January and persist through 
near the end of the month, though ECMWF forecasts show some moderation of the 
pattern by Week 4 (ending January 28th). This persistent pattern is a typical 
response to the active and forecast MJO, and the troughing will allow for cold 
air from the North to overspread the eastern CONUS, and as such a swath of 
below normal temperatures are indicated from the Northern and Central Plains to 
the Southeast. Probabilities are higher where there is strong model agreement, 
and aligning with regions where extended range and Weeks 3-4 forecasts favor 
persistence of the below normal temperatures. Above normal temperatures are 
favored over the CONUS from the West Coast to the Rockies and extending 
eastward across much of the Southern Plains and for southern Alaska beneath 
forecast ridging throughout much of the month of January and where there was 
strong model agreement. Over Alaska, the above normal temperatures transition 
to EC over the North where some models favored a weak tilt toward below normal, 
however, this is highly dependent on the northern extent of the ridge. 
Interestingly, though we are seeing cooler SSTs in the Niño3.4 region which 
would typically support below normal temperatures over Alaska, models have and 
currently favor above normal temperatures. It is possible that Alaska may see 
these cooler temperatures particularly over the South as the winter season 
progresses, but have a warm start to the winter. Above normal temperatures are 
also favored over northern parts of the Northeast ahead of the expected 
troughing over the East. Finally, EC is indicated over the Great Lakes, much of 
New York State, and southern New England, given weak or inconsistent model 
signals. 

Despite the forecasted change in pattern for January and changes to the Monthly 
Temperature Outlook, the Monthly Precipitation Outlook is similar to the prior 
released version. Recent precipitation forecasts still resemble a La Niña-like 
response in the models over some of the key teleconnection regions. Above 
normal precipitation is favored over the Northwest and Northern Plains, which 
is a hallmark of the winter La Niña teleconnection. Below normal precipitation 
is favored over the southwestern CONUS to eastern Texas and reaching into parts 
of the Lower Mississippi Valley, also coincident with a La Niña-like response. 
On the other hand, precipitation is more uncertain over much of the eastern 
CONUS than previously indicated in the Monthly Precipitation Outlook. Another 
La Niña-like teleconnection would be expected to lead to above normal 
precipitation over the Great Lakes stretching into the Ohio Valley, with below 
normal precipitation over the Southeast, however, the differences in the 
atmospheric pattern, MJO, and inconsistencies in model forecasts from 
run-to-run now support EC over the Great Lakes, much of the East Coast, and 
Southeast. Above normal precipitation is favored over parts of New England 
downstream of the forecasted trough. Finally, over Alaska, above normal 
precipitation is favored over the South transitioning to below normal 
precipitation over the North, given model agreement.

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*****           Previous mid-month discussion below                      ***** 
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Following a few months of weakly below normal sea surface temperatures (SSTs), 
SST departures reached -0.6 degrees Celsius in the Niño3.4 region over the past 
week. The current El Niño Southern Oscillation (ENSO) Alert System Status is a 
La Niña watch. The extended period of weakly below normal SSTs and recent drop 
to -0.6 degrees Celsius may lead to some La Niña-like impacts over the 
contiguous United States (CONUS) during January and the upcoming season, 
however, we expect that any impacts may be weak and variability to be high, 
leading to uncertainty in some of the typical impacts. Though the Madden-Julian 
Oscillation (MJO) has been a significant player in the tropics in recent weeks 
and dynamical models depict continued eastward propagation of the MJO envelope 
with a slowed phase speed, the emerging La Niña has the potential to interfere 
with propagation and amplitude of the MJO. Should the MJO continue into 
January, this may lead to cooler than average temperatures for the northern 
parts of the CONUS and Northeast, but the potential interference from La Niña 
and slow phase speed add to the uncertainty. In addition to the large-scale 
drivers of La Niña and the MJO, coastal or local SSTs, sea ice, and snow cover 
are taken into account for this forecast where appropriate. Monthly forecasts 
of temperature and precipitation by dynamical models from the North American 
Multi-Model Ensemble (NMME), Copernicus Climate Suite (C3S), and CFSv2 were 
utilized in preparing this Outlook. Week 3-4 predictions for the first part of 
January from GEFSv12, ECMWF, and CFSv2 and the expected transition in the 
atmospheric pattern from the Week 2 period were also considered. 

Enhanced ridging is forecast over most of the CONUS toward the end of December, 
leading to the potential for above normal temperatures to end the year. 
However, this strong ridging is expected to moderate by the beginning of 
January, giving way to ridging over the West and neutral to above normal 
heights over the remainder of CONUS. Week 3-4 models forecasting the beginning 
of January favor weak ridging over the West and troughing over the East, though 
the position, exact timing, and strength of the pattern is uncertain. Given the 
atmospheric pattern leading into January and the forecasts for early January, 
we expect a warm start to the month followed by a transient pattern. 
Uncertainty is high due to the potential for this transient pattern, 
particularly for temperatures. 

The January 2025 Temperature Outlook features above normal temperatures over 
the southern half of the western CONUS, Southern Plains, and the East Coast. 
This pattern is fairly typical of La Niña, and reflects dynamical model 
predictions that favor a La Niña like response for the month. However, given 
the expected transient height pattern during the month, probabilities are 
overall low for temperatures. Probabilities are enhanced over the Southern 
Plains where there was the best agreement among available tools. Some models 
such as the C3S suite and CFSv2 favored higher probabilities of above normal 
temperatures over the Southwest, however, NMME and statistical tools that 
include decadal trends which are below normal in parts of the Southwest more 
strongly favor near-normal temperatures. Given this discrepancy, a weak tilt 
toward above normal temperatures is favored despite some of the model results 
showing stronger probabilities in the region, which also aligns with forecast 
below normal precipitation in the region. Similarly, some models indicate 
stronger probabilities for above normal temperatures over the East Coast 
relative to the Outlook, but given Week 3-4 models that tilt toward below 
normal temperatures over the East, probabilities are again weakened. Equal 
chances (EC) of above, near, and below normal temperatures are favored over the 
northern tier of the CONUS and Central Plains where tools had weak or uncertain 
signals, and, moreover, both MJO and La Niña may lead to cold air intrusions 
into the region, though both influences are currently somewhat uncertain. In 
addition, given the forecasted warm start to the month of January, it is 
uncertain if periods of colder temperatures will be strong or long enough to 
tilt the probability to below normal over the northern tier. Over Alaska most 
models favored above normal temperatures, particularly CFSv2, and as such a 
tilt toward above normal temperatures is indicated in the Outlook. 

Despite the transient pattern, precipitation signals were more consistent in 
tools than temperatures. While SSTs in the Niño3.4 region just recently dropped 
below -0.6 Celsius, it is possible that tools are picking up the extended 
period of weakly below normal SSTs and forecasts of a weak La Niña as many of 
the tools are showing a La Niña like precipitation pattern over the CONUS.  For 
example, both NMME and C3S probabilistic multi-model ensemble probabilistic 
forecasts show a general pattern of below normal precipitation over the 
southern tier of CONUS, and above normal precipitation over the Northwest and 
Great Lakes and interior Southeast, which are hallmarks of a La Niña pattern. 
The January 2025 Precipitation Outlook thus resembles a La Niña like pattern, 
featuring enhanced probabilities of above normal precipitation over the 
Intermountain West and parts of the Northern and Central Plains, the Great 
Lakes and interior Southeast, and a tilt toward below normal precipitation from 
the Southwest along the southern CONUS and parts of the coastal Southeast. Over 
Alaska, above normal precipitation is favored for western and northern parts of 
the state, with a small area of below normal precipitation over its southern 
coast. Some uncertainty exists along the West Coast where EC is indicated. NMME 
and C3S favor below normal precipitation over the southern West Coast and above 
normal precipitation over the northern West Coast, while CFSv2 tilts toward 
below normal over the northern West Coast. Given the potential for periods of 
above normal precipitation over the West Coast during winter months, EC is 
favored despite some of the tools leaning toward below normal. Models and tools 
also had mixed signals along the coastal northeast and New England, and there 
is potential for variability during the month due to uncertainty in storm 
tracks, leading to the favored region of EC. Finally, over Alaska, below normal 
precipitation is favored over its southern coast given La Niña teleconnections, 
and above normal is favored over the western and northern parts of the state 
given La Niña teleconnections, dynamical model agreement, and above normal 
decadal trends over the northern coast. 


FORECASTER: Johnna Infanti

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 16 2025

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