835
FXUS02 KWBC 261836
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
236 PM EDT Sat Apr 26 2025

Valid 12Z Tue Apr 29 2025 - 12Z Sat May 03 2025


...Heavy rainfall threat over the southern half of the Plains
Tuesday-Wednesday...

...Overview...

A cold front pushing across the northeastern quadrant of the lower
48 will hang back over the Plains while awaiting ejection of a
Southwest U.S. shortwave. This feature and dynamics coming in
behind it should ultimately generate a surface low that brings a
front through more of the East by the end of the week as upper
troughing amplifies. The Tuesday-Wednesday pattern will favor
episodes of heavy rainfall over and near the southern half of the
Plains before system progression spreads less pronounced rainfall
totals across the East. A trailing upper ridge should move into the
Northwest after early Wednesday, reaching the Plains by the start
of the weekend, while a Pacific upper trough should reach the West
Coast around Saturday with some precipitation over the Northwest.


...Guidance/Predictability Assessment...

The latest model and ensemble guidance continues to offer good
agreement on the overall pattern evolution, but plenty of
uncertainty in the details. There are still some timing differences
as low pressure crossing southeastern Canada Tuesday- Wednesday
pushes a trailing cold front through the Great Lakes/Northeast,
with an average providing a reasonable starting point. Then as
Southwest U.S. shortwave energy ejects northeastward, solutions
still vary for details of developing low pressure that tracks
northeastward. Northern stream energy merging with the southern
stream shortwave late week shows some disagreement in the details,
and there are some timing questions with the next trough into the
West next weekend. A trend towards half ensemble means in the blend
worked as a reasonable starting point, maintaining good
consistency with the previous WPC forecast as well.


...Weather/Hazards Highlights...

During Tuesday-Wednesday, low pressure lifting away from Lake
Superior will push a cold front across the northeastern quadrant of
the lower 48 while the trailing part over the Plains stalls and
develops a wave as a Southwest U.S. shortwave ejects northeastward.
This pattern combined with anomalous moisture and sufficient
instability will favor a heavy rainfall threat over and near the
southern half of the Plains in this time frame. The Day 4/Tuesday
Excessive Rainfall Outlook introduced a slight risk from far north
Texas into southwestern Missouri, consistent with increasing model
QPF signals and high soil moisture. A broader marginal risk extends
from the southern Plains into the lower Ohio Valley.
Models/ensembles and first- guess fields generally strengthen the
heavy rainfall signal on Day 5/Wednesday with maybe a slight shift
eastward. Thus the Day 5 ERO continues the Slight Risk area
introduced overnight encompassing parts of Texas/Oklahoma and
western Arkansas/southern Missouri. The surrounding Marginal Risk
covers a similar area as the Day 4 ERO. The Storm Prediction Center
is also monitoring for severe threats on Tuesday from the eastern
Great Lakes and vicinity southwest into northern Texas, with a
smaller Wednesday risk area for parts of northern Texas. Check the
SPC outlooks for the latest info on severe threats.

After early Wednesday, continued progress of low pressure and its
trailing cold front should push rainfall across much of the East
but with lesser totals than forecast over the central U.S. Farther
west, shortwave energy and a frontal system should spread rain and
some high elevation snow from the Northwest through the northern
and central Rockies Tuesday-Thursday. By the end of the week some
rain may develop over the southern High Plains with the help of
easterly low level flow. An upper trough/cold front reaching the
West Coast by Friday-Saturday should bring rain and high elevation
snow into the Northwest.

Expect unseasonably warm temperatures over the eastern U.S. on
Tuesday ahead of an advancing cold front. Plus 10-20F anomalies
will equate to highs reaching into the 80s over the Ohio Valley.
Morning lows will be even a little more anomalous. Northern parts
of the East will trend cooler by midweek but locations farther
south should remain somewhat above normal through Friday. A more
amplified upper trough will likely push the next cold front farther
south, bringing temperatures over the East to within a few degrees
on either side of normal by Saturday. Meanwhile an upper ridge
drifting from the Northwest into the Plains after Wednesday will
support corresponding eastward progress of an area of highs 10-20F
above normal.

Santorelli/Rausch


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







$$