317
FXUS02 KWBC 190608
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
108 AM EST Sun Jan 19 2025

Valid 12Z Wed Jan 22 2025 - 12Z Sun Jan 26 2025

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


...Overview...

Troughing over the Eastern Seaboard to start the period should
shift east helping to gradually moderate bitterly cold temperatures
to start the period. Reloading of the trough is expected though as
another amplified pattern develops upstream across the Central to
Eastern U.S. Thursday-Friday. Ridging over the West should shift
inland late week as an amplified shortwave into the Northwest drops
down the coast with increasing agreement that a closed low could
develop over southern California/the Southwest late next weekend.
Much of the early period precipitation should be confined to the
northern tier/Great Lakes and light in nature, with light to
moderate precipitation moving into the West mid to late week and
next weekend.


...Guidance/Predictability Assessment...

Model guidance shows generally good agreement on the large scale
pattern through the entire extended range period, but plenty of
uncertainty on the details. Timing of the reloaded deep trough
through the east-central to East on Friday is in question, with the
UKMET and CMC guidance generally on the slower side of the spread.
New 00z guidance seems to be coming into better alignment.
Otherwise, the biggest model uncertainty for the period lies with
the next shortwave into the Northwest on Friday. Model guidance
shows agreement on the timing of this, but a lot of uncertainty on
the evolution. The 18z/Jan 18 GFS was an outlier in showing a
flatter and more progressive shortwave whereas the ECMWF and CMC
(with support from ensembles) showed a deepening system and a deep
closed low over southern California next Sunday. The new 00z run of
the GFS came in more amplified with that system. Despite the
general agreement now, given the late period timing, it is likely
the forecast will continue to waffle before settling on a
consensus.

The WPC blend for tonight leaned more heavily on the GFS and ECMWF
guidance early period, blending in the ensemble means with the
ECMWF and CMC late period.


...Weather/Hazards Highlights...

Bitterly cold temperatures moving into the central U.S. and the
Midwest this weekend should moderate by the start of the period,
but much colder than normal temperatures will continue through at
least Thursday or Friday for parts of the East and the South.
Daytime highs could be 20+ degrees below normal, especially
Wednesday. Daily record low max and min temperatures are possible.
Temperatures should finally trend back closer to normal by next
weekend.

Precipitation across the CONUS during the medium range period
should be relatively quiet. Some modest rains are possible across
Florida associated with lingering frontal boundaries Wednesday and
Thursday, with rain or light snow up the Southeast/Mid-Atlantic
coast with weak surface lows lifting northward. Some light
precipitation is expected across the Northern tier with a couple of
weak cold fronts through the region on Wednesday. More widespread
rain and mountain snows will move into the West by Friday and shift
south with time.


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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