Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Mon Mar 31 2025

Valid 12Z Thu Apr 03 2025 - 12Z Mon Apr 07 2025


...Multi-day and significant heavy rain/flooding and severe threat
likely for Lower/Middle Mississippi, Tennessee, and Ohio Valleys
through next Saturday...


...Overview...

The medium range upper pattern will be amplified, blocky, and
active through the period. A frontal boundary will remain parked
over the Ohio Valley to Southern Plains in between an amplified
western trough and strong Atlantic to Gulf upper ridge. This
pattern sets the stage for a multi-day heavy rain and severe
weather event which should be ongoing by the start of the period on
Thursday from the lower Mississippi into the Ohio Valley, with
significant flooding increasingly likely. A gradually amplifying
Canada into northern U.S. upper trough nearing the East by Sunday-
Monday may finally help to push out the frontal boundary. Most of
the West should stay relatively cool underneath persistent
troughing with some progression eastward early next week into the
Central U.S., while upper ridging brings a warming trend to the
Northwest during the weekend. The East will see above normal
temperatures late this week and then a cooler trend that moves in
from the north and west.


...Guidance/Predictability Assessment...

The latest model guidance continues to agree fairly well on most
aspects of the forecast during Thursday-Saturday. There are
differences with some embedded lower-predictability details that
could have sensible weather impacts, with more time needed to
resolve. A building and blocky ridge over the Atlantic to Gulf
should help amplify troughing over the West. Shortwaves within that
trough show more spread, and may play a role in exactly where the
heaviest rainfall occurs. Either way, models have been extremely
consistent in showing a potentially significant flooding event from
the lower Mississippi Valley into the Ohio Valley. By Friday-
Saturday some spread develops for another shortwave digging through
the western side of the trough and how much of this eventually
ejects eastward next weekend, with influences on the wavy surface
front. An operational model composite looks good for this part of
the forecast, with no prominent clustering where differences exist
and some additional detail spread in the machine learning (ML)
models.

From late Saturday through Monday there are greater uncertainties
regarding the character of Canada into northern U.S. troughing and
how this feature interacts with energy ejecting from the Southwest.
Differences aloft lead to significant spread for surface evolution
over eastern North America. Dynamical ensemble means agree rather
well for consolidating low pressure to reach just north/east of New
England by early next Monday, with the 06Z GFS and 00Z ECMWF/CMC
fitting into this theme. However at that time the ML models show a
lot more variety aloft and in where low pressure emphasis may be
located between eastern Canada and the northern Mid-Atlantic/Upper
Ohio Valley, with some hint at slower timing. Preference stayed
with the dynamical majority with partial ensemble mean
incorporation, providing only modest adjustments from continuity.
Perhaps not surprisingly, the new 12Z models display a fair amount
of spread for surface details.

Farther west, some troughing should linger over the Southwest into
southern Rockies Sunday-Monday while an upper ridge pushes in from
the eastern Pacific. Then an upstream trough/surface front should
reach near the West Coast by early next Monday. For this system the
ML models lean to the middle/faster side of the dynamical spread
which is fairly modest for a 7-day forecast.


...Weather/Hazards Highlights...

A surface low exiting the Great Lakes on Thursday will leave
behind a wavy frontal boundary that essentially becomes stuck
between a strong upper ridge to the east and amplified troughing
over the West. Moist and unstable inflow pooling along the front
will lead to widespread severe weather and flash flooding concerns
which should begin during the short range period and continue for
several days. SPC shows severe probabilities from the lower
Mississippi Valley into the Ohio Valley. The greatest concern for
flash flooding for Thursday will stretch across a similar area, as
the front anchors storms for significant training concerns. For
several days now, models have been indicating several inch rainfall
totals, especially across Arkansas into western Kentucky where
24-hour totals in excess of 5-8 inches could be realized in some
spots (and this is on top of several inches of rainfall in the
short range as well). As such, a moderate risk remains in place for
this region for the Day 4/Thursday ERO. The heavy rainfall axis
should remain over similar areas into Friday as well, with a slight
shift to the south and west. Another moderate risk is in effect on
the Day 5 ERO from northeast Texas to southeast Missouri. High
Risks are not out of the question in future EROs as the event draws
nearer and it becomes clearer how the details could evolve,
especially into the timeframe of the CAMs. Heavy rainfall is likely
to continue into Saturday as well for roughly the same areas,
leading to the potential for high impact and life-threatening
flooding and flash flooding over the course of several days. By
Sunday, the heavy rain threat should finally begin to shift
eastward with moderate to heavy rains possible across the Gulf
Coast states into the Southeast, and more widespread rain also
moving into the East.

As upper troughing sets up over the West with multiple shortwaves
moving through, rounds of precipitation are possible from the
Intermountain West into the Rockies while the West Coast trends
drier. Expect generally lower elevation rain and higher elevation
snow, initially with mostly light to modest amounts. Into late
week, a possible upper low in the Four Corners region could lead to
enhanced precipitation totals across the southern and central
Rockies and Plains. Snow is likely in higher elevations of the
Rockies in Colorado and northern New Mexico, with uncertainty at
this point in if/how much snow could spill into lower elevations of
the High Plains.

Elsewhere by next Monday, the cold upper trough reaching the Great
Lakes should lead to unsettled weather over the region with rain
or snow depending on location and time of day, while the upper
shortwave/front reaching the West Coast may bring some light
activity to far western Washington/Oregon and northwestern
California.

Above normal temperatures will linger across much of the East
through the weekend with daytime highs 10 to 20 degrees above
normal. Best potential for daily records will be across the
South/Southeast into southern Mid-Atlantic. Temperatures should
moderate early next week as the upper ridge shifts eastward and
troughing moves into the East. Meanwhile, the West should trend and
stay cooler underneath upper troughing through Friday. By next
weekend, temperatures may moderate somewhat along the West Coast
while eastern Pacific upper ridging moves in. Parts of the
Northwest could see highs reach up to 10 to 15 degrees above
normal. This shifts cooler temperatures eastward, and daytime highs
across parts of the southern Rockies and High Plains could be 10
to 25 degrees below normal next weekend. Below normal temperatures
also shift into the central U.S. and Midwest by next Monday,
including highs as low as 10 to 15 degrees below normal over the
Great Lakes/Ohio Valley.


Rausch/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