227
FXUS02 KWBC 200602
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
102 AM EST Mon Jan 20 2025

Valid 12Z Thu Jan 23 2025 - 12Z Mon Jan 27 2025

...Bitterly cold temperatures to continue through Thursday for
parts of the East and the South...


...Overview...

Mean troughing over the Central U.S. on Thursday will shift east
with time, exiting the East Coast by the weekend. Behind this, some
upper ridging should move in, finally helping to moderate bitterly
cold late week temperatures across the East and South. A shortwave
through western Canada on Thursday will split - sending northern
stream energy through the northern U.S. tier/Great Lakes/Northeast
as southern stream energy dives south and rapidly intensifies.
Guidance has come into better agreement that a closed upper low may
develop over California into the Southwest this weekend. This may
bring some much needed precipitation to parts of southern
California which has been stricken with devastating wildfires
lately.


...Guidance/Predictability Assessment...

Model guidance continues to show generally good agreement on the
large scale pattern through the entire extended range period, but
still some uncertainty in the details. As the initial trough swings
through the Southeast on Friday, there were some lingering timing
differences (UKMET and CMC faster, GFS and ECMWF slower) but a
general model blend seemed to provide a good starting point for
that feature. Out west, the guidance continues to show better
agreement for eventual closed low development over California which
shifts slowly south into the Southwest. The GFS was faster to
develop it, while the ECMWF holds it back a little longer than
consensus. Some uncertainty with amplitude of the downstream
shortwave across the Great Lakes/Midwest. Last couple of runs of
the GFS have been more zonal/suppressed. For the late period blend,
the WPC progs leaned on an equal model/ensemble consensus.


...Weather/Hazards Highlights...

Much colder than normal temperatures by 20-30 degrees will
continue for parts of the East and South and could set daily record
low max and min temperatures. Though still chilly Thursday and
Friday, temperatures will gradually moderate in the South and East,
reaching near normal this weekend. Meanwhile, California to the
Great Basin can expect warmer than normal temperatures through the
rest of the workweek before the West cools underneath the upper
trough next weekend.

Precipitation across the lower 48 during the medium range period
should be relatively quiet. Some rain is possible across Florida on
Thursday associated with a lingering frontal boundary, with rain
or light snow up the Southeast to Mid- Atlantic coast with a weak
surface low lifting northward. A couple rounds of light
precipitation are forecast from the Northern Plains to
Midwest/Great Lakes and Ohio Valley as cold frontal clipper systems
move through. More widespread rain and mountain snows will move
into the West by Thursday-Friday and shift south with time, likely
providing some much needed rain to Southern California next
weekend. Farther east, moisture return into the Lower Mississippi
Valley to Tennessee/Ohio Valleys is expected into next weekend for
some modest rain amounts, with snow possible farther north across
the Great Lakes.


Santorelli


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



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