646
FXUS02 KWBC 221855
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
155 PM EST Sat Feb 22 2025

Valid 12Z Tue Feb 25 2025 - 12Z Sat Mar 01 2025


...Overview...

The upper flow pattern should remain rather progressive through
much of the medium range period. By Tuesday, a northern stream
shortwave will be shifting through the Northeast, with a southern
stream wave through Florida and the western Atlantic. Out West, a
shortwave over the Pacific Northwest on Tuesday will progress
downstream, with eventual deepening over the East by Thursday with
reinforcing energy Friday. This allows for an amplifying ridge
upstream across the West late week, with a southern stream trough
or cutoff low moving inland across Southern California Friday-Saturday.


...Guidance/Predictability Assessment...

Model guidance shows reasonable agreement in the overall pattern
evolution described above, though with typical detail differences
that could have sensible weather impacts at times. For the initial
part of the period, models were clustered well enough for a multi-
model blend between the 06Z GFS, 00Z ECMWF, and 00Z CMC as a
starting point for the WPC 500s/fronts forecasts.

Models show a bit more spread with the digging trough over the
Midwest-East Wednesday and beyond, including with the possibility
of some southern stream energy hanging back across the southern
High Plains into Thursday. But most models are reasonably agreeable
with the eastward movement of the trough axis into Friday, with
the exception of the new 12Z CMC that seems to be a slow outlier.
Another shortwave coming through the Dakotas or so Friday and into
the Great Lakes next Saturday should support a surface low/clipper
system. With these features becoming better aligned, this forecast
trended the surface low deeper compared to the previous forecast
based on the newer guidance.

Farther west, there remains considerable timing uncertainty with a
cutoff low into California Friday or Saturday, though there is
general agreement on the presence of this feature. Interestingly
the 00Z/06Z GFS and 00Z ECMWF were rather agreeable on slower
timing of the upper low, with the CMC about the same longitude but
north of the GFS/EC consensus...but all the ensemble means were
quite a bit faster, so certainly lots of faster ensemble members.
AI models were split with some slower and some faster, likely
indicating that both faster and slower solutions have happened in
the past and would be reasonable. Preferred an in between solution
for now, with the EC mean an okay proxy. The WPC blend gradually
increased the proportion of ensemble means (favoring the EC
ensemble mean) to 60 percent Days 6-7 given the increasing spread.
The newer 12Z deterministic runs are a tad faster than their
00Z/06Z counterparts.


...Weather/Hazards Highlights...

Some lingering moisture will be present across the Pacific
Northwest to northern Rockies on Tuesday as the atmospheric river
event winds down, so rain and snow will taper off into Tuesday
night. Gusty winds are possible as the shortwave moves across the
northwestern to north-central U.S. on Tuesday. The highest winds
are expected along the northern/central Rockies ridges, with some
windy conditions spilling into the north-central Plains. Then the
West should dry out for the most part due to the upper ridge. The
model variability with the southern stream upper low approaching
California and moving inland late next week/weekend leads to
uncertainty in the precipitation forecast for California to the
Southwest and the south-central U.S. for the late period.

Downstream, a round of northern stream energy will spread light
precipitation from the Lower Great Lakes region through New England
Tuesday. Then a surface low will move across the northern U.S.
with a trailing cold front Wednesday and Thursday, spreading rain
and northern tier snow from the north-central to east-central U.S.
midweek and across the East by Thursday. A clipper system is then
forecast to bring another round of precipitation to the Great Lakes
region Friday.

By next week, much of the lower 48 will be much above normal in
terms of temperatures, with decent coverage of plus 10-25 degree
anomalies. The northern/central Plains can expect the highest
anomalies of +20 to locally +30 degrees above normal, with 60s for
highs as far north as Nebraska or perhaps even South Dakota at
times. The Southwest and Great Basin can also expect warmer than
average conditions underneath the building upper ridge. Parts of
the Desert Southwest could reach into the 90s especially Tuesday-
Thursday, and some sites could set daily record high max/min
temperatures in the vicinity. Areas east of the Mississippi should
also see warm conditions into midweek, but should cool back to near
normal (or slightly below in spots) by late week underneath upper
troughing.


Tate/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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