462
FXUS02 KWBC 221900
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Wed Jan 22 2025

Valid 12Z Sat Jan 25 2025 - 12Z Wed Jan 29 2025


...Overview...

It remains generally the case that by the start of the period
Saturday, upper troughing will be exiting the East coast with weak
upper ridging developing behind for the weekend, finally helping
to moderate the bitterly cold short range temperatures. Meanwhile,
a shortwave dropping into the northern Rockies late this week will
split, sending northern stream energy across the northern tier of
the nation while trailing energy dives south to form a closed low
over the Southwest that will linger and slowly drift east into the
Southwest by early-mid next week. The upper low will likely bring
beneficial precipitation parts of southern California that have
been dealing with devastating wildfires and also some organized
rains/terrain snows downstream into parts of the Southwest.

Meanwhile, moderate to locally heavy rainfall will develop
downstream across the Lower Mississippi Valley Sunday and Monday as
a slow moving frontal boundary moves through the region.
Additional frontal wave genesis over the Southern Plains into the
middle of next week given Southwest low slowl approach may again
increase lead return flow and emerging rainfall to monitor.

...Guidance/Predictability Assessment...

On the large scale, the guidance continues to show reasonable
agreement, but there remains plenty of uncertainty in the details
and timing of individual systems. Relatively good clustering early
period as the shortwave amplifies and a low cuts off over the West
Coast Saturday-Sunday. By Monday though, some guidance holds the
low farther west (recent CMC and UKMET runs), while other guidance
(recent GFS, ECMWF and ensemble mean runs) pulls it farther east
faster. Mean northern stream troughing over the Northern Plains-
Great Lakes-Northeast shows uncertainty in the amplitude of
individual shortwaves dropping through and recent GFS runs remain the
most bullish with one shortwave from the northern Plains to the
Midwest next Wednesday-Thursday. All these solutions are viable,
with these trends overall remaining with latest 12 UTC guidance.

Accordingly, WPC guidance used a general model and ensemble blend,
gradually transitioned majority weightly from the models to the
ensemble means amid slowly growing forecast spread. This provided
a good starting point for the Southwest upper low evolution and
northern stream troughing/shortwaves. WPC continuity was good.

...Weather/Hazards Highlights...

Colder than normal temperatures will linger through Saturday for
parts of the South and Southeast with daytime highs still 5-15F
below normal with overnight lows below freezing. Temperatures will
gradually moderate, returning to near normal Sunday through early
next week. Anomalously cold temperatures will also develop in the
High Plains, Rockies, and much of the West this weekend under the
influence of upper troughing. The coldest anomalies will be in the
High Plains and Rockies where high temperatures could be 10-20
degrees below normal. Late period ridging over the northern tier
could allow temperatures to rise above normal next week.

Precipitation wise, a couple of clipper systems and reinforcing
cold fronts will periodically enhance lake effect snows downwind
of the Great Lakes. Meanwhile, more widespread rain and mountain
focusing snows will be dropping through the Great Basin to
Southwest this weekend bringing beneficial rain to Southern
California over the weekend. A tightened gradient behind the cold
front dropping south may produce some gusty winds along parts of
the Rockies late this week and California and Nevada on Saturday
with offshore flow and modestly favorable fire weather conditions
possible again behind the upper low next week to keep an eye on.

Farther east, Gulf moisture will interact with a front approaching
the Lower Mississippi Valley to Tennessee and Ohio Valleys by this
coming weekend/early next week. Latest guidance continues to trend
heavier with rainfall totals over parts of the southern U.S., with
the potential for heavy rain and thunderstorms on Sunday across
the Lower Mississippi Valley. There was enough support for a
marginal risk in the Day 5/Sunday Excessive Rainfall Outlook from
eastern Texas into Mississippi where storms may train along a slow
moving frontal boundary. There was a seemingly reasonable
convective signal shift slightly to the southwest compared to
earlier guidance that was incorporated. Snow or a wintry mix is
possible on the northern side of this precipitation shield mainly
over the Ohio Valley, south-central Appalachians, and possibly the
Tennessee Valley and vicinity. Precipitation may spread towards
the East Coast early next week as the frontal system progresses
with some rainfall redevelopment of across the Southern Plains and
lower Mississippi Valley as well. This signal is increasing with
development of an organized frontal wave with Southwest upper
system approach.

Santorelli/Schichtel


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







$$