739
FXUS02 KWNH 270701
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Thu Mar 27 2025

Valid 12Z Sun Mar 30 2025 - 12Z Thu Apr 03 2025

...Overview...

A progression of systems should bring active weather northern-
central parts of the West with rain and higher elevation snow, as
well as the eastern half of the country where some wintry weather
is possible over far northern latitudes with rain to the south. Low
pressure tracking northeast from the Plains Sunday-Monday will
bring one round of eastern U.S. precipitation. A couple systems
affecting the West early in the period should ultimately lead to
another surface low emerging into the Plains by midweek with a
northeastward track thereafter. Guidance continues to have
difficulty for flow specifics within the blocky pattern over the
Pacific, leading to significant eastern Pacific into Lower 48
guidance spread for upper pattern and Pacific systems by Tuesday-
Thursday. Very warm temperatures will prevail ahead of the first
Plains/eastern U.S. system while trailing cooler air will briefly
bring readings back down to near or below normal before a likely
rebound.

...Guidance/Predictability Assessment...

The specifics of low pressure initially tracking northeast from
the Plains are dependent on smaller-scale shortwave details that
have fairly low predictability. Thus solutions continue to show a
fair amount of spread for strength/track/timing by early Monday.
Some UKMET runs and new 00Z ECMWF are a bit on the slow side
compared to most machine learning (ML) guidance that tended to
cluster over or somewhat north or south of Lake Ontario. A guidance
average with some ensemble mean inclusion provides a reasonable
intermediate solution.

Lower predictability details also come into play for the system
near the West Coast Sunday-Monday, with latest models leaning
toward a more separate and modest southern wave that may become
incorporated as part of the larger scale system off the Pacific
Northwest coast.

After Monday, guidance continues to disagree for exactly what will
happen with energy dropping south of Alaska. Among dynamical
guidance there is a majority ECMWF cluster that pulls off northern
Pacific energy to the southwest, leading to an eastern Pacific
ridge and a trough pushing into the West--with leading energy
supporting a Plains into Great Lakes system Wednesday-Thursday
(with ensemble means and ML models supporting this system). The GFS
has been dropping this energy southward to produce an eastern
Pacific trough and higher heights/ridging over the Lower 48. ML
models have not exactly been enthused about the ECMWF cluster`s
specifics over the Pacific but still yield the Wednesday Plains
system, while the GEFS at least tempers the GFS`s traits. Even
among these two clusters, solutions are dramatically different for
whether a significant system may reach the West Coast around
midweek. Current blend preferences temper the strength of such a
system, so significant changes are possible in future forecasts.

Early in the period the updated forecast started with more 12Z
ECMWF input than GFS/CMC, with 30 percent ensemble mean input (18Z
GEFS and 12Z ECens/CMCens). Then the blend eventually transitioned
to a quarter 12Z ECMWF and the rest ensemble means by next
Thursday.

...Weather/Hazards Highlights...

Guidance continues to show convection developing over the east-
central U.S. on Day 4/Sunday ahead of the wavy front pushing
eastward from the Plains. Latest solutions have not added much
definition in terms of more pronounced focus over specific regions
within the broad Day 4 ERO Marginal Risk area in place from the
Ohio Valley southwest into parts of the lower Mississippi Valley,
so the only adjustment for this cycle was a modest westward
expansion based on latest guidance. Will continue to monitor for
improved guidance clustering especially from the Ohio Valley
southward where soils are on the damp side, which could eventually
lead to an embedded upgrade in risk level. What potential exists
for excessive rainfall by Day 5/Monday should be confined more to
parts of the Southeast as the front continues onward, again with a
Marginal Risk area indicated. Meanwhile, the Storm Prediction
Center continues to monitor the potential for severe weather from
the east-central U.S. to the Mid-Atlantic/Southeast during Sunday-
Monday. Check latest SPC outlooks for more details on the severe
threats.

Farther north, there will be potential for some snow from the
Upper Midwest/Upper Great Lakes into northern New England (the
latter having up to 50-70 percent probabilities for 0.25 inch
liquid in the form of snow Sunday-Sunday night). A transition zone
of wintry mix may separate the snow area from the rain to the
south.

Expect multiple systems to bring rain and higher elevation snow to
the West during the period, with rapidly increasing uncertainty in
the details after early next week. During Days 4-5/Sunday-Monday
period of the EROs, the best precipitation focus should be over
southwestern Oregon and northern California. Day 5 looks to have
somewhat higher maximum rainfall totals near the coast, along with
some instability, so that day`s ERO introduces a Marginal Risk area
in this region. Some guidance signals potential for another
significant system after Monday but with a lot of spread for
details, while a weaker wave is another possibility. The overall
guidance signals suggest a somewhat heavier trend for precipitation
over the central West Coast/California toward midweek. Leading
dynamics reaching the West should support a central-eastern U.S.
system by Wednesday-Thursday, generating another episode of
meaningful precipitation over the eastern half of the country. Some
snow will be possible from the northern Plains into New England.

The warm sector ahead of the front crossing the eastern half of
the country Sunday-Monday will feature well above normal
temperatures. Expect plus 10-20F anomalies for highs and up to plus
20-25F anomalies for morning lows, the latter extending from the
Midwest to Mid-Atlantic. Northern New England should remain a lot
colder though, as a sharp front stays just to the south. Near to
below normal readings will progress eastward behind the eastern
U.S. front, with precipitation keeping some northern Plains
locations 10-15F or so below normal for highs into Sunday. Expect
more modest cool anomalies to the east. Temperatures may rebound
back above normal over the southern half of the Plains on Tuesday
with the warming trend spreading eastward thereafter. Periods of
unsettled weather will keep the diurnal spread over the West Coast
states more narrow than usual, with cool highs and near or slightly
above normal lows.

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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