508
FXUS02 KWNH 100700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Fri Jan 10 2025

Valid 12Z Mon Jan 13 2025 - 12Z Fri Jan 17 2025

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


...Overview...

The start of the period early Monday should feature a southern
Canada/Upper Midwest into western U.S. upper trough. Guidance shows
this trough quickly splitting, depositing an upper low offshore
southern California as a ridge builds into the Northwest and
Rockies while the rest of the trough, with some reinforcement from
upstream energy, drifts across the East. This pattern evolution
will lead to cold temperatures over the central U.S. on Monday and
settling into the East thereafter, along with multiple days of lake
effect snow plus a couple potential episodes of synoptic-scale snow
over/near the Great Lakes in association surface lows/frontal
systems. Toward the end of the week some Pacific shortwave energy
rounding the ridge should begin to amplify into the Northwest
and/or northern Plains while the offshore upper low opens up and
ejects inland.

...Guidance/Predictability Assessment...

During Monday-Wednesday there is fairly good agreement in most
guidance for specifics of the forecast. The primary exception is
the CMC, whose 12Z run was a slow extreme with the upper low
expected to track across the Upper Great Lakes and New England with
both 12Z and 00Z runs which are more reluctant to close off an
upper low offshore California. Remaining dynamical models do show a
moderate/typical amount of spread for upper low position by early
Wednesday, with the machine learning (ML) models showing a fair
amount of spread mostly in east-west fashion near 30N latitude.
Meanwhile to varying degrees the dynamical and ML models are now
hinting at a Midwest to southern Mid-Atlantic/Southeast surface
wave around Tuesday-Wednesday in response to shortwave energy whose
specifics may continue to adjust in future runs. Overall the 18Z
GFS/12Z ECMWF with minority input from the 12Z UKMET represented
the best ideas of guidance for this part of the forecast.

After midweek most guidance shows North Pacific shortwave energy
pushing into/around initial western U.S.-Canada ridge and
beginning to amplify into the Northwest and/or northern Plains as a
new ridge builds over the eastern Pacific. Meanwhile the upper low
offshore California should open up and eject inland while eastern
troughing should reach near the East Coast by early Friday. The
primary theme from at least some of the ML models is the potential
for northwestern height falls to be quicker/more pronounced than
most dynamical guidance, and leading to surface low pressure
reaching the Plains by next Friday. This at least favors leaning
more to recent ECMWF/ECens/CMCens means rather than the 12Z/18Z
GFS runs that were slow with the incoming Pacific shortwave and
actually still had high pressure over the central U.S. on Friday.
The new 00Z GFS has adjusted favorably toward the other guidance.
The 18Z GEFS mean was at least closer to the ECMWF cluster than the
operational run. Farther east, ML models generally favored a
compromise between the amplified ECMWF/flatter GFS with the upper
trough nearing the East Coast.

...Weather/Hazards Highlights...

The forecast pattern will support another surge of Arctic air that
should progress from the central U.S. early in the week to the
East/Southeast by Tuesday-Thursday. Of particular note, expect
areas of hazardous cold over the far northern Plains Monday-Tuesday
and then most of the southern half or so of the East by Tuesday-
Thursday. Within these areas temperatures should be 10-20F 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, while separate low
pressure/frontal systems on Monday and then after midweek may
produce broader coverage of at least light snow over the Great
Lakes and vicinity.

Elsewhere, a wavy front crossing the Gulf of Mexico on Monday may
produce rain of varying intensity over Florida, while some mostly
light rain may extend into southern Texas for a time. Upper ridging
that builds over the West through Thursday should keep most of the
region dry. Some light precipitation may reach the Northeast by
late week with the arrival of a front. An upper low closing off to
the west/southwest of southern California may produce scattered
light precipitation over the Southwest/Four Corners by late week as
it opens up and ejects inland, though latest trends have been
lighter and slower to develop this activity. Mostly below normal
temperatures over the West will gradually moderate to near/slightly
above normal into Thursday, followed by a cooler trend in the
Northwest on Friday. Warmest temperature anomalies next week should
be over the northern Plains/Upper Midwest during Wednesday-Friday
with some locations 10-20F or so above normal.

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












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