953
FXUS02 KWBC 220600
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EDT Tue Apr 22 2025

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


...Overview...

Widespread rains/thunderstorms with locally heavy downpours will
steadily spread into the east-central and east/northeastern U.S.
with a low pressure/frontal system translation into late week.
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 elevations into the north-
central Rockies, as also enhanced by Plains cyclogenesis and
frontogenesis, and associated deep moist inflow ahead of the upper
trough and developing storm will significantly increase rain and
thunderstorm chances and spacial coverage across the central U.S.
once again over the weekend and into early next week to monitor.

...Guidance/Predictability Assessment...

Model and ensemble forecast spread has decreased in the latest
runs overall in line with machine learning guidance, bolstering
forecast confidence. However, recent cycle-cycle run consistency
issues do temper expectations in a early warm season pattern with
much lingering uncertainties with local convection. That said,
there is now a more defined signal favoring flow amplitude with
more orgainzed system genesis over time to build predictability.

Accordingly, the WPC medium range product suite was primarily
derived from a broad composite blend of best clustered guidance
from the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/Canadian and
ECMWF/Canadian ensemble means along with a compatible 01 UTC
National Blend of Models. This plan maintains good continuity,
generally in line with latest available 00 UTC guidance trends.

...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 to focus local weather/convection. 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, spreading thunderstorm
chances into those areas. A Day 4/Friday WPC Excessive Rainfall
Outlook Marginal Risk area remains from Arkansas through portions
of the Tennessee and Ohio Valleys for localized flooding with heavy
rain, with minor adjustments from continuity. Some guidance
suggests heavy rainfall farther northeast into the Upper Ohio
Valley into the Lower Great Lakes region to monitor for emergence
Friday into the weekend farther downsteam over the East. A WPC Day
5/Saturday ERO Marginal Risk area was introduced from the
northeastern Mid-Atlantic through southern New England given
favorable ingredients.

Meanwhile, despite some model guidance uncertainties in the
details, upper trough amplification and digging in the eastern
Pacific late this week moving into the West this weekend, along
with surface system genesis and slow but steady system translation
still offers increased light to moderate widespread rain chances
and mountain snows. Renewed moisture streaming in east of the
trough plus lingering boundaries in the area will allow for
additional rounds of possibly heavy rain and thunderstorms in the
Plains and Mississippi Valley by the weekend. Initial thought is
to offer a southern High Plains WPC Marginal Risk ERO for Day 5
(12 UTC Saturday to 12 UTC Sunday) given upper difluence with upper
trough approach and bisecting 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. This will likely
include some enhanced main low winds and strong to severe weather.

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






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