Prognostic Discussion for Monthly Outlook
NWS Climate Prediction Center College Park MD
300 PM EST Sun Jan 31 2021


30-DAY OUTLOOK DISCUSSION FOR FEBRUARY 2021

The updated temperature and precipitation outlooks for February 2021 are based 
on the WPC temperature and precipitation forecasts during the first week of 
February, the CPC 8-14 day and Week 3-4 outlooks, and the latest monthly 
forecasts from the CFS model. Below average sea surface temperatures (SSTs) 
across the equatorial central Pacific along with a strong coupling with the 
atmosphere represent La Niña conditions. The amplitude of the Madden-Julian 
Oscillation (MJO) increased during late January, as it shifted eastward to the 
West Pacific. A continued eastward propagation of the MJO would favor 
anomalously cold temperatures across parts of the central and eastern U.S. 
during February. In addition, residual effects related to the recent Sudden 
Stratospheric Warming (SSW) may help to reinforce this MJO cold signal. 

Major revisions were needed to the updated February temperature outlook, due to 
higher forecast confidence in a colder pattern for the CONUS. The large 
coverage with enhanced probabilities of below normal temperatures is due to a 
high amplitude longwave pattern favorable for anomalous cold during early to 
mid-February. The week-2 ensemble means remain consistent and in excellent 
agreement, depicting a high amplitude 500-hPa ridge extending from the North 
Pacific poleward over Alaska with a full-latitude trough centered over the 
Rockies. This amplified longwave pattern favors intrusions of Arctic Air 
shifting south from Canada into the western and north-central CONUS. The 
largest probabilities (more than 60 percent) of below normal temperatures are 
forecast from the Northern Great Plains to the Upper Mississippi Valley where 
anomalous cold is most likely to persist for multiple weeks. MJO composites 
would favor an expansion of the anomalous cold to the east, but equal chances 
(EC) of below, near, or above normal temperatures are forecast for much of the 
East Coast since temperatures are likely to average near to slightly above 
normal during the first ten days of the month. Due to large positive 
temperature anomalies early in the month, above normal temperatures are 
slightly favored for northern New England. Increased probabilities of above 
normal temperatures are forecast for parts of the Southeast based on model 
guidance from weeks 2 through 4. Despite anomalous cold early in the month, EC 
is forecast for much of the Southwest due to signs of a moderation in 
temperatures later in the month, typical influences from La Niña, and decadal 
trends. The updated February temperature outlook for the CONUS is generally 
consistent with a combined La Niña and negative Arctic Oscillation composite. 

Above normal precipitation remains favored for a majority of the central and 
eastern CONUS which is likely to be downstream of an amplified 500-hPa trough 
axis through at least mid-February. Probabilities of above normal precipitation 
are increased from the Ohio and Tennessee Valleys east to the mid-Atlantic due 
to the expectation of a thermal gradient and persistent storm track. A 
relatively dry (less than 0.25 inch) first week of February and mean 500-hPa 
ridging through much of the month elevate probabilities of below normal 
precipitation for Florida along with parts of the Gulf Coast. This wet/dry 
dipole from the Ohio Valley to Florida is consistent with La Niña, but high 
latitude blocking may shift the storm track at times closer to the Gulf Coast. 
A consistent wet signal among daily CFS model runs supports an increased chance 
of above normal precipitation from the Great Lakes and Upper Mississippi Valley 
west to the Northern and Central Rockies. Expected periods of upslope flow 
elevate probabilities of above normal precipitation for the Northern High 
Plains.  The updated precipitation outlook is drier for the Pacific Northwest 
due to the highly amplified ridge upstream and the absence of predicted 
atmospheric river activity after the beginning of the month. Below normal 
precipitation remains favored for California along with parts of the Southwest 
and Rio Grande Valley based on a consistent dry signal among model guidance at 
multiple time scales during February. 

Only minor changes were needed for the updated Alaska temperature and 
precipitation outlooks. Due to the amplified 500-hPa ridging early in the month 
and likelihood of Arctic Air shifting more southward over the CONUS, a 
relatively warmer February outlook is anticipated. However, the location of the 
500-hPa ridge axis early in the month and model consensus continue to support 
increased chances of below normal temperatures for southeast Mainland Alaska 
and the Alaska Panhandle. Elevated probabilities of below normal precipitation 
forecast for these areas of Alaska are consistent with below normal 
temperatures being favored. Daily CFS model runs are consistent with increased 
chances of above normal precipitation across western Mainland Alaska. 


----------- Previous message (from January 21) is shown below ------------

The February 2021 temperature and precipitation outlooks are based on Weeks 3 
to 4 forecasts from the CFS and ECMWF models, the North American Multi-Model 
Ensemble (NMME), typical influences from the ongoing La Niña, and decadal 
trends. Below average sea surface temperatures (SSTs) across the equatorial 
Pacific along with a strong coupling with the atmosphere represent La Niña 
conditions. Although dynamical models depict a strengthening Madden-Julian 
Oscillation (MJ0) during late January into early February, La Niña is likely to 
be 
the major tropical forcing due to the well-established anomalous enhanced 
(suppressed) convection over the Maritime Continent (equatorial Central 
Pacific).  
 
Despite high latitude blocking with a persistent negative Arctic Oscillation 
(AO), 30-day temperatures since mid-December have averaged above normal for 
nearly all of the CONUS. This mild temperature pattern was due in part to 
enhanced Pacific flow overspreading the higher latitudes of North America and 
cross polar flow generally limited to the Eastern Hemisphere. Week-2 model 
guidance (Jan 28-Feb 3) remains consistent that an amplified and full-latitude 
500-hPa ridge becomes centered over the Aleutians and extends poleward. The 
Week 3-4 ECMWF model indicates this anomalous ridging persisting through at 
least early February, which is likely to promote cross polar flow and result in 
below normal temperatures across parts of Alaska. Based on good model 
continuity with this feature and support from a number of inputs to the NMME, 
below normal temperatures are favored for southeastern Mainland Alaska and the 
Alaska Panhandle. Although the source region is expected to become more 
favorable for Arctic air to shift south across the western and north-central 
CONUS during the next month, the NMME supports equal chances (EC) of below, 
near, or above normal temperatures for much of the West and Northern Great 
Plains. Sparse snow cover across the Canadian Prairies and Northern Great 
Plains may be a limiting factor to anomalously cold temperatures heading into 
February. Below normal temperatures are slightly favored for parts of the 
Pacific Northwest and Northern Rockies, due to the predicted close proximity of 
anomalous cold during the first half of February and this is also consistent 
with La Niña composites.
 
The largest probabilities (above 50 percent) of above normal temperatures are 
forecast from the Rio Grande Valley eastward to the Gulf Coast, based on the 
week 3-4 model guidance, calibrated NMME, and La Niña composites. Although a 
high latitude block over the Davis Strait and negative phase of the NAO are 
forecast to promote periods of below normal temperatures along the East Coast 
during the remainder of January, the GFS ensemble members depict a transition 
to a neutral or even positive phase of the NAO by the beginning of February. As 
the negative NAO diminishes during the next two weeks, La Niña is expected to 
become a more dominant factor which increases probabilities of above normal 
temperatures across the Southeast. Above normal temperatures are only slightly 
favored for the Northeast, Great Lakes, and Upper Mississippi Valley due to 
lower forecast confidence and the potential for a variable temperature pattern 
during February. It remains unclear when or even if the recent stratospheric 
warming event would influence temperatures across the CONUS and this will be 
reassessed for the updated outlook released on January 31.
 
The precipitation outlook for February is consistent with La Niña composites 
and supported by the NMME. Below normal precipitation is most likely across the 
southern tier of the CONUS, while above normal precipitation is favored from 
the Pacific Northwest eastward to the Upper and Middle Mississippi Valley and 
Great Lakes. Elevated probabilities of below normal precipitation, forecast for 
southeastern Mainland Alaska and the Alaska Panhandle, are consistent with 
below normal temperatures favored for these areas. A majority of inputs to the 
NMME support increased probabilities of above normal precipitation across the 
Aleutians. Probabilities throughout the forecast domain are tempered due to 
large uncertainties during this monthly outlook time range.

FORECASTER: Brad Pugh

The climatic normals are based on conditions between 1981 and 2010, 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 Mar ... will be issued on Thu Feb 18 2021

These outlooks are based on departures from the 1981-2010 base period.
$$