Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 PM EDT Wed Apr 23 2025

Valid 12Z Sat Apr 26 2025 - 12Z Wed Apr 30 2025


...West/Rockies to Central U.S. Spring Storm...


...Overview...

Organized showers and thunderstorms with locally heavy downpours
will focus across the Northeast into the weekend as a deeply wavy
frontal system moves over and offshore. Meanwhile, unsettling and
cooling upper troughing will move from across the West and produce
widespread moderate precipitation. Expect enhanced snow for the
higher elevations from the Cascades down to the Sierra and inland
to the north-central Intermountain West/Rockies this weekend, with
Rockies activity enhanced by lee cyclogenesis and frontogenesis
into early next week. Deep moist inflow ahead of the upper trough
and developing storm system will significantly increase the
coverage of rains and strong to severe thunderstorms across the
central to east central U.S. into early to mid next week.
Temperatures will mostly remain above normal east of the
Continental Divide while trending near to below normal in the West.

...Guidance/Predictability Assessment...

Model guidance continues to be in good overall agreement through
the upcoming weekend into early next week. Aside from minor
differences with respect to smaller scale features, the depiction
of the large scale pattern was generally good enough to be
represented by a blend that featured mostly deterministic guidance
early on, followed by roughly 50% deterministic solutions and 50%
ensemble means later. Within the deterministic space, the 00Z CMC,
00Z UKMET and 06Z GFS were favored, with less weight placed on the
00Z ECMWF. This weighting was due to the 00Z ECMWF being a little
too slow, weak, and less negatively tilted with the
shortwave/trough lifting across the Great Lakes into the Northeast
early next week compared to the other guidance. Fortunately, the
12Z ECMWF came into better alignment with the other pieces of
guidance, including nearly all of the machine learning guidance,
lending to a higher confidence forecast in the later forecast
periods. The ensemble means featuring the 00Z EPS and 06Z GEFS were
used to offer more stability for days 5, 6, and 7.

...Weather/Hazards Highlights...

Modestly progressive upper shortwaves with wavy surface systems
remain slated to bring some concentrated enhanced rains over the
Northeast into Saturday, with trailing frontal convective activity
to the south sweeping through and exiting the Eastern Seaboard by
Sunday. As a result, a WPC Day 4/Saturday Excessive Rainfall
Outlook (ERO) Marginal Risk area remains in place over the
northeast Mid-Atlantic and New England.

Meanwhile, an amplified upper trough and surface system digging
across the West this weekend offers widespread rains and enhanced
snows for the higher elevations from the Cascades down to the
Sierra and inland over the north-central Intermountain West.
Mountain snows then expand into the central and northern Rockies
into early next week.

Downstream, rich moisture streaming in ahead of a deeply
strengthening storm system ejecting into the Plains will fuel
rounds of heavy rain and thunderstorms across portions of the
central U.S. from the weekend into next week. A Marginal Risk ERO
area remains in place for Day 4/Saturday, which includes portions
of Kansas, New Mexico, Texas, Oklahoma, Missouri and Arkansas given
favorable upper trough diffluence combined with front/dryline
instabilities. For Day 5, introduced a broad marginal risk from
portions of Montana/North Dakota/northern South Dakota to
Minnesota/northwest Wisconsin given an increasing signal for
anomalous moisture and an expanding convective QPF footprint.
Activity will be in the process of transforming into an emerging
comma-shaped rainfall area broadly progressing over the central
U.S. before tracking across some moisture laden soils of the east-
central U.S. early to mid next week given further surface low and
wavy frontal structure development and evolution. Episodes of
severe weather will also be monitored by SPC as predictability
grows closer to the event.

Temperatures along and east of the Continental Divide will largely
remain at or above normal through much of the medium range period
as upper level ridging builds. Meanwhile, temperatures across the
West will be near to below normal given unsettled conditions
underneath an upper level trough.

Miller/Schichtel


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