Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1224 AM EDT Thu Apr 24 2025

Valid 12Z Sun Apr 27 2025 - 12Z Thu May 01 2025


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


...Overview...

Wrap-back rains lingering over northern New England will depart
Sunday as the supporting deepened low and frontal system exits
offshore. Meanwhile, an 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 much of the central and into
east central U.S. early-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 and ensemble forecast clustering has improved through medium
range time scales, bolstering forecast confidence. Smaller scale
guidance differences remain, but seem somewhat less of an issue
given a pattern evolution trend toward amplification and with
better system organization that tends to increase predictability.

Accordingly, the WPC medium range product suite was mainly derived
from a composite blend of guidance from the 18 UTC GFS/GEFS mean
and the 12 UTC ECMWF/UKMET/Canadian/ECMWF ensemble mean along with
compatible 01 UTC National Blend of Models and WPC continuity.

...Weather/Hazards Highlights...

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 early next week.

Downstream, rich moisture streaming in ahead of a strengthening
storm system over the Plains will fuel rounds of heavy rain and
thunderstorms across portions of the central U.S. from the weekend
into next week. A WPC Marginal Risk Excessive Rainfall Outlook was
reduced, but remains in place for Day 4/Sunday and Day 5/Monday
from portions of Montana and the Dakotas into the Upper Midwest
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 with
potential for emerging convection down over the south-central
Plains and Mississippi Valley. Thunderstorms will likley become
more
organized and robust with training runoff threats into
Tuesday/Wednesday with strong frontal proximity, instability and
focus under favorable upper trough/jet support. SPC has already
issued a medium range threat for severe weather to further monitor.
Focus may also eventually work into some moisture laden soils of
the east-central U.S. into next midweek given further surface low
and wavy frontal structure, evolution and downstream punch.

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.

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