Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1243 PM EST Sat Jan 11 2025

Valid 12Z Tue Jan 14 2025 - 12Z Sat Jan 18 2025

...Arctic airmass to reinforce east of the Rockies next week...


...Overview...

Into midweek the guidance shows a ridge building into the
Northwest while elongated energy to the south most likely forms a
closed low somewhat southwest of southern California, while deeper
mean troughing extends over the northeastern U.S. into the Plains.
Then shortwave energy reaching British Columbia by early Thursday
will amplify south/east with time while eastern Pacific/Alaska
ridging builds, by Saturday yielding a northern Canada through
southwestern U.S./Rockies trough that could also include the
sheared remains of the upper low previously off California. Eastern
U.S. mean troughing should pass into the Atlantic by the end of
the week. This pattern evolution will lead to cold temperatures
over the East Tuesday-Thursday followed by another push of cold air
dropping down the High Plains and vicinity by next Saturday. The
Great Lakes will see a combination of lake effect and synoptic-
system snow during the first half of the period. Then by next
Saturday organized precipitation should develop over the east-
central U.S. along a cold front, while an area of snow pushes down
the northern half of the Rockies.

...Guidance/Predictability Assessment...

Latest guidance shows fairly good agreement on the overall
synoptic set up across the CONUS for the medium range, but plenty
of uncertainty in the details. A cut off low continues to show
variability on its proximity to the Southern California coast early
period. Latest GFS, ECMWF, and UKMET runs have displaced this low
much farther west/farther away than previous runs, but the CMC
(with support from the ensemble means) continues to hold it closer
to the coast. This has little impact on sensible weather initially,
but may impact how much energy gets sheared from this low with the
larger mean trough as it progresses eastward with time. A sharper
shortwave by late week across the south-central U.S. may allow more
moisture to get pulled northward and heavier precip across this
region and east. The UKMET was much faster with the mean trough
progression and with less sheared energy across the Southwest, so
it was excluded completely from today's blend. GFS and ECMWF are
slightly faster and sharper with the shortwave from western Canada
into the north-central U.S.. The WPC blend for today utilized a
GFS, ECMWF, and CMC blend for the first half of the period,
transitioning to 60 percent GFS/ECMWF with 40 percent total of
their respective means. This maintained good continuity with the
previous WPC forecast as well.

...Weather/Hazards Highlights...

The forecast pattern will support another surge of Arctic air that
should reach the eastern half of the country by Tuesday-Thursday.
Of particular note, expect areas of hazardous cold to extend from
the Upper Midwest into the southern half to two-thirds of the East
for one or more days during that time frame. Temperatures should be
10-25F below normal with even colder wind chills. A few locations
around the upper Ohio Valley/central Appalachians could challenge
daily records for cold highs on Tuesday. Cold cyclonic flow will
promote periods of lake effect snow, some of it heavy, through
Thursday while a frontal system may produce some light synoptic-
scale snow on Thursday as well. Eastern U.S. temperatures will
moderate by Friday-Saturday as a front pushes into the central U.S.
and eventually Great Lakes. This front may also begin to generate
precipitation over the east-central U.S. by Saturday with some
heavier totals possible somewhere between the Ohio River and Gulf
Coast.

Elsewhere, a wavy front may bring lingering rainfall to the
Florida Peninsula into Tuesday while some mostly light rain may
extend into southern Texas for a time. Upper ridging that builds
over Northwest through Thursday should keep most of the western
U.S. dry. However, strong Interior West and Rockies high pressure
through Tuesday-Wednesday will lead to a threat of high winds over
parts of southern California, enhancing the fire weather
conditions. Some light and scattered precipitation may reach the
Northwest by late week with the arrival of a front. Then some
upslope-enhanced snow may move down the eastern slopes of the
Rockies Friday- Saturday behind the front. Slightly below normal
temperatures over the West will moderate to near/slightly above
normal into Thursday, followed by a cooler trend in the Northwest
on Friday and much colder readings dropping through the northern-
central Rockies on Saturday (highs 10-20F or so below normal).
Warmest temperature anomalies next week should be over the northern
Plains/Upper Midwest during Wednesday- Friday with some locations
10-20F above normal for highs with anomalies perhaps a few degrees
higher for morning lows. The southern Plains into the South may see
some above normal temperatures Friday- Saturday.

Santorelli/Rausch


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw