Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Tue Apr 22 2025

Valid 12Z Fri Apr 25 2025 - 12Z Tue Apr 29 2025


...Overview...

Widespread showers and thunderstorms with locally heavy downpours
will gradually spread from portions of the central U.S. eastward
into the Northeast later this week into the weekend as a low
pressure/frontal system moves through. Meanwhile, ample upper
troughing will move from the eastern Pacific into the West and
promote modest precipitation, with a main focus over the Northwest.
Snow is likely for the higher elevations across the north-central
Rockies, enhanced by lee cyclogenesis and frontogenesis. Deep moist
inflow ahead of the ejecting upper trough and developing storm
system will significantly increase the spatial coverage of rain and
thunderstorm chances across the central U.S. once again over the
weekend and into early next week.

...Guidance/Predictability Assessment...

Model guidance remains in good overall agreement with its
depiction of the large scale pattern through most of the medium
range period. Generally minor differences begin to crop up by days
6 and 7, particularly with respect to the evolution of the smaller
scale shortwaves within the parent trough ejecting from the
Intermountain West into the central U.S. Despite the differences,
there was enough of a consensus as to not drastically impact
predictability. As a result, the WPC forecast was largely derived
from deterministic solutions stemming from the 00Z ECMWF, 00Z CMC,
and the 06Z GFS. Ensemble means from the 00Z EPS and the 06Z GEFS
gradually became more heavily weighed by the end of the period, but
combined were still slightly less than 50/50 of the total blend by
day 7. This blend offered a desirable compromise of higher
resolution details and large scale stability.

...Weather/Hazards Highlights...

A number of slowly progressive upper features and surface based
systems will continue to work over mainly the eastern half of the
nation into late week and the weekend. Recent and ongoing rainfall
over some portions of this broad region will make some areas
susceptible to additional rains. By Friday, a low pressure system
and its trailing front is likely to move across the Mississippi
Valley toward the Great Lakes and interior Northeast, spreading
thunderstorm chances into those areas. The Day 4/Friday WPC
Excessive Rainfall Outlook Marginal Risk area was expanded
northward into the eastern Great Lakes and interior Northeast given
a growing signal for heavier and more widespread QPF. The risk
across portions of the Northeast continues into Day 5/Saturday,
with the Marginal Risk area expanded into more of northern New
England and Maine from the inherited risk area of the northeastern
Mid-Atlantic to southern New England given higher QPF.

Meanwhile, upper trough amplification from the eastern Pacific
into the West late this week into the weekend, along with surface
system genesis and slow but steady system translation, will still
offer increasingly widespread rain chances and mountain snows.
Renewed moisture streaming in ahead of the trough plus lingering
boundaries in the area will allow for additional rounds of possibly
heavy rain and thunderstorms across portions of the central U.S. by
the weekend. The inherited Marginal Risk ERO for Day 5/Saturday was
expanded northward from portions of Texas and Oklahoma to a large
portion of Kansas and eastern Nebraska given favorable upper
trough
difluence combined with front/dryline instabilities. Organized
activity should then increasingly transform into an emerging comma-
shaped rainfall area broadly sweeping over the central U.S. into
early next week given expected surface low and wavy frontal
structure development and evolution. Episodes of severe weather are
possible along with the marginal heavy rain threat.

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