686
FXUS02 KWBC 251900
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Fri Apr 25 2025

Valid 12Z Mon Apr 28 2025 - 12Z Fri May 02 2025


...Potent Rockies to Central U.S. Spring Storm expected early next
week...

...Overview...

The primary focus early next week will be on ejecting Rockies
upper trough energy and associated northern Plains through Upper
Great Lakes surface system, bringing some heavy rain potential to
the northern tier and likely severe weather to the central/east-
central U.S. The northern part of this system will continue onward
but the trailing part of the front should stall and develop some
waviness ahead of weaker southwestern shortwave energy, providing a
focus for enhanced central U.S. rainfall around midweek. Upstream
energy should push the evolving system and rainfall eastward
thereafter, with an upper trough axis reaching the east-central
states by Friday. A trailing upper ridge should move into the West
after early Wednesday, likely followed by a trough/cold front
nearing the West Coast by Friday.


...Guidance/Predictability Assessment...

Model guidance shows reasonable agreement among the larger scale
pattern described above. There is decent clustering with only
typical detail variations for northern Plains low pressure that
should track across the Upper Great Lakes and then eastern Canada,
with the trailing front ultimately stalling over the Plains as weak
shortwave energy lingers over the Southwest. By the latter half of
the week there is still better than average agreement among
model/ensemble guidance that northern stream energy should drop
into the Northwest around midweek and eject the southwestern
shortwave. This brings surface low pressure northeastward from the
southern High Plains Wednesday across the south-central U.S. and
toward the Lower Great Lakes by early Friday. This shortwave and
the surface low show some differences, including the newer 12Z
ECMWF that is deeper with the low. It may take additional time for
deterministic and AI/ML models to come to better agreement with the
details. Meanwhile there is also model spread with position and
depth of energy digging in the southwestern U.S. into Thursday or
so south of northern stream upper ridging, without any good
consensus. Additionally, there have been model differences in the
timing and depth of upper troughing nearing the West Coast by next
Friday. Older GFS runs had been faster and less amplified, but the
newer 12Z GFS run as well as the 12Z GEFS mean now agree better
with the non-NCEP consensus.

The WPC forecast used a blend of the deterministic models favoring
the ECMWF early in the forecast, and increased the proportion of
ensemble means to about half in the Day 6-7 period as spread
increased.


...Weather/Hazards Highlights...

The early week Rockies into central U.S. storm will bring high
elevation snow to the north-central Rockies. Farther east across
the northern Plains and Midwest, anomalous moisture reaching the
95th percentile and favorable dynamics aloft along the cusp of the
instability gradient is forecast to produce heavy rain. These areas
remain under a Marginal Risk of flash flooding in the Day 4/Monday
ERO with only minor adjustments from the previous forecast.
Portions of the Midwest into the south-central Plains can expect
severe weather potential on Monday as well, with the best focus
centered in Iowa. By Tuesday into early Wednesday the south-central
Plains part of the system`s trailing front should stall and
provide a focus for training/repeat convection. The Day 5/Tuesday
ERO reflects the runoff threats with an elongated Marginal Risk
area from central Texas into the Lower Ohio Valley. Severe weather
is a threat for these areas into the Lower Ohio Valley on Tuesday
as well. The central U.S. heavy rain potential will likely continue
through the rest of Wednesday before upper dynamics and surface
waviness/fronts progress into the East with somewhat lesser rain
totals. Farther west, shortwave energy pushing through the West
should spread rain and some high elevation snow from the Northwest
through the northern and central Rockies over the course of the
week.

Very warm temperatures over the Plains/Mississippi Valley on
Monday will progress into the East ahead of an advancing cold
front, with highs up to 10-20F above normal, leading to highs well
into the 80s into the Midwest and Ohio Valley. Morning lows will be
even a little more anomalous. The wavy front may not reach parts
of the Southeast/Mid-Atlantic, where temperatures could remain
somewhat above normal through Friday. Cool readings from the
Southwest to northern High Plains on Monday should moderate as the
air mass continues eastward. Then expect a trend to above normal
temperatures over the West mid-late week as an upper ridge builds
in. Highs may reach 10-15F above normal from the Pacific Northwest
into northern Rockies.


Tate/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



$$