Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Sun Mar 30 2025

Valid 12Z Wed Apr 02 2025 - 12Z Sun Apr 06 2025


...Multi-day heavy rain and severe threat for Lower/Middle
Mississippi, Tennessee, and Ohio Valleys next week...


...Overview...

The medium range upper pattern should trend more amplified,
blocky, and active through the period. A surface low emerging into
the Plains by Wednesday will track towards the Great Lakes as a
building upper ridge over the western Atlantic into the Gulf should
keep the associated frontal boundary from making much progress,
especially later in the week. This sets the stage for a multi-day
heavy rain and severe weather event from the Lower Mississippi into
the Ohio Valley. Late- season snow is likely north of this system
from the northern Plains to Great Lakes and Interior Northeast. The
West should stay relatively cool underneath of persistent
troughing, while above normal temperatures progress from the
central U.S. and Midwest, eventually settling late week across the
Southeast and into the Mid-Atlantic.


...Guidance/Predictability Assessment...

Model guidance is relatively agreeable on the large scale pattern
next week into the weekend, but still uncertain with some of the
details, which could have sensible weather impacts. A building and
blocky ridge over the Atlantic to Gulf should help amplify
troughing over the West through the period. Shortwaves within that
trough show relatively more spread, but the first shortwave/compact
upper low and its associated surface low tracking from the Central
U.S. to Great Lakes into Thursday shows increasing agreement.
Energy will allow for the Western U.S. trough to reload late week
with a stationary surface boundary setting up between the Southeast
ridge and Western trough. There are subtle differences still in
the exact placement of this front though, and energy riding along
the front, which has significant implications on the locations of
heavy rainfall expected to accompany the front. Expect these to
vary a bit in future forecasts, though the general idea of heavy
rain in parts of the east-central U.S. is pretty locked in. By
Friday and into the weekend, there is increasing uncertainty in the
details of another shortwave digging through the western side of
the trough and the ECMWF runs continue to be slightly on the
western side of the better consensus and becomes more broad/strung
out with the shortwave next weekend. To the north, a shortwave
should progress across western Canada and eventually into the Great
Lakes, but guidance has some variability on the timing of this,
which may help to slowly nudge the stagnant east-central U.S.
boundary eastward a bit next weekend.

The WPC forecast was able to utilize a deterministic model blend
through Day 4. By Day 5, began incorporating some ensemble mean
guidance to help temper the detail differences, for a 40 percent
models/60 percent mean blend by Days 6 and 7. This approach
maintained relatively good agreement with the previous WPC
forecast.


...Weather/Hazards Highlights...

Overall pattern amplification and a leading compact closed low
will support a surface low pressure system forming in the central
U.S. on Wednesday with widespread thunderstorms and heavy rainfall
across the east- central U.S. in its warm sector. Moist and
unstable inflow into the associated surface fronts along with the
strong upper level support will lead to widespread severe weather
and flash flooding concerns. SPC shows severe probabilities from
the south-central U.S. into the Midwest, with embedded higher
probabilities from portions of the Lower/Middle Mississippi Valley
and Tennessee/Ohio Valleys. The greatest concern for flash flooding
on Wednesday and Thursday will stretch across similar areas, as
the front anchors storms for training concerns. A Slight Risk
remains in place for the Day 4/Wednesday ERO from the Lower
Mississippi Valley into the Ohio Valley. This is considered a
higher- end Slight Risk as models already show 3 to 7 inches of
rain during the 12Z Wednesday to 12Z Thursday period alone. An
upgrade to a moderate may eventually be needed, but could be
dependent on heavy rainfall potential during the short range
period. The stagnating pattern will cause the front to stall and
allow for heavy rain to likely fall in much the same place on
Thursday. Due to this, a moderate risk has been introduced on the
Day 5/Thursday ERO from western Tennessee into western/northwestern
Kentucky, per coordination with the affected WFOs. Given the
multi-day risk over the same area, an eventual high risk is not out
of the question at some point as the event draws nearer if the
forecast remains on track. Heavy rainfall and severe weather across
similar areas may continue through Friday or Saturday, with some
extension westward into the Central Plains (and notable snow in the
Rockies), but the front may finally begin to shift south and
eastward with time.

On the backside of the low track, some April snow is likely across
the northern Plains, Upper Midwest, and into the interior
Northeast on Wednesday. Snow amounts have typical uncertainty, and
an axis of freezing rain and/or sleet is possible as well.

As troughing sets up over the West with multiple shortwaves moving
through, rounds of precipitation are possible from the West Coast
into the Intermountain West and Rockies. Generally lower elevation
rain and higher elevation snow are expected. Additionally, high
winds are possible for the central Rockies on Wednesday.

Above normal temperatures will shift into the Midwest on
Wednesday, and settle across much of the Eastern U.S. Thursday and
beyond. Daytime highs 10 to 20 degrees above normal are possible.
Meanwhile, the West should trend and stay cooler underneath upper
troughing through Friday. By next weekend, temperatures may
moderate somewhat while cooler temperatures shift slightly east as
eastern Pacific upper ridging moves in towards the West Coast.
Daytime highs across parts of the southern Rockies could be 10 to
20 degrees below normal next weekend.


Santorelli


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