441
FXUS02 KWBC 180700
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Fri Apr 18 2025

Valid 12Z Mon Apr 21 2025 - 12Z Fri Apr 25 2025


...Guidance/Predictability Assessment...

The WPC medium range 500mb and surface progs were mainly derived
from a composite of reasonably well clustered guidance of the 18
UTC GFS and 12 UTC ECMWF/UKMET/Canadian models as valid for Monday
into Wednesday in a period with seemingly above average forecast
predictability. Growing forecast spread with features at the
surface and aloft portended a gradual transition to best
compatible 18 UTC GEFS and 12 UTC ECMWF ensemble means at longer
time frames later next week. This solution plan maintained good
WPC product suite continuity in line with a similar composite of
newer 00 UTC guidance as well as the National Blend of Models.
However, the early warm season pattern will likely offer difficult
to predict local thunderstorm foci to monitor closer to the event.

...Weather/Hazards Highlights...

A protracted series of generally progressive upper features and
associated surface based systems are set to work over the lower 48
next week in multiple stream flows to locally focus April weather.

An organized lead system next week will bring a deepened main low
and moderate wrapping rains from the Great Lakes/Midwest through
the Northeast early next week. A trailing cold front will
meanwhile act to focus deeper convective potential across the
South and the Appalachians mainly Monday that could lead to some
locally heavy downpours and runoff issues to monitor. Upstream
upper energies and surface response will also act to produce light
to moderate precipitation back over the Northern Rockies/Plains and
vicinity with approach and passage.

Accordingly, introduced a WPC Excessive Rainfall Marginal Risk
area for portions of the Southern Plains for Day 5/Tuesday given
the potential for some repeat/training of cells during the day and
with overnight activity with emerging moist and unstable return
flow into/over several frontal boundaries. Some portions of this
area is also forecast to have enhanced rainfall this weekend that
would lead to wet soil conditions. Heavy rain and runoff threats
along with strong convective potential in this region and into the
Mississippi Valley will also be monitored for mid-later next week
given lingering support and multi-day potential, albeit with less
certain upper level and surface focus details at these time ranges.

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






$$