453
FXUS02 KWNH 030635
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
234 AM EDT Thu Apr 3 2025

Valid 12Z Sun Apr 06 2025 - 12Z Thu Apr 10 2025


...Overview...

The frontal boundary responsible for significant and potentially
historic flooding and flash flooding during the short range period
should finally push east by Sunday. This happens from a gradually
amplifying Great Lakes to Northeast trough and eventual ejection of
southern stream energy. Some moderate to heavy rainfall potential
along the central Gulf Coast and parts of the Southeast with this
front. A shortwave reaching the West on Sunday-Monday could bring
mostly light precipitation to parts of the Northwest. After Monday,
the medium range period should trend much drier across the country
as the overall pattern briefly becomes flatter and more
progressive on the way toward a western ridge/eastern trough
configuration.

...Guidance/Predictability Assessment...

Overall, the latest guidance shows good agreement on the larger
scale pattern, but plenty of uncertainty still in the details of
smaller scale systems/energies. There are still some initial
questions on how fast southern stream energy ejects eastward on
Sunday-Monday, with the GFS still on the slightly faster side of
consensus. Elsewhere, latest GFS runs remain most aggressive with
the degree to which the digging Great Lakes trough closes off an
upper low by Tuesday, leading to a stronger/more wrapped surface
system. The CMC also shows this to some extent as well, but the
better consensus of models would favor more of an open trough, with
some potential for a neutral or negative tilt at times. Mean
troughing over the northeast Pacific should send a couple of
shortwaves into the West, which could eventually reach the Plains
by midweek. Both the GFS and ECMWF show a modest reflection of a
stronger system with a defined surface low, but the CMC is much
weaker. Ensemble means are also weak/flat which indicates there is
still a lot of uncertainty with this.

The WPC forecast for tonight favored a deterministic model blend
for the first half of the period, increasing the ensemble means to
half the blend by Day 7 to mitigate differences in the guidance.
This maintains good continuity with the previous WPC forecast, at
least through Day 6.


...Weather/Hazards Highlights...

By the start of the period on Sunday, the front responsible for
significant rainfall over the Lower Mississippi Valley to Ohio
Valley region should finally begin to shift eastward. Moderate to
heavy rain and strong storms are possible along the front from the
Gulf Coast states into the Tennessee Valley/Southeast, and farther
north into the Mid-Atlantic and Northeast near the front. The
Sunday ERO shows a Marginal Risk for this region with an embedded
Slight Risk farther south across parts of southern Alabama and
Mississippi where recent heavy rainfall has primed soils and the
greatest instability should be located. Guidance shows potential
for a band of somewhat heavy QPF to extend farther northeast across
northern Georgia into or near the far southern Appalachians, but
latest first-guess fields plus neutral ground moisture (and likely
drier by then given no rain forecast in the shorter term) favor
keeping this region in Marginal Risk for the time being. The front
may slow for a period across parts of the Southeast into Monday,
and anomalous moisture and instability favor just a marginal risk
for the Day 5 ERO at this point since current QPF signals are
modest at best.

Elsewhere by Monday, a cold upper trough reaching the Great Lakes
should lead to unsettled weather over the region with rain or snow.
This precipitation should extend into the Northeast as well.
Latest guidance shows significant differences for surface/upper
evolution over the Northeast early- mid week, with the more extreme
side of the spread producing some significant snowfall over parts
of New England in contrast to much lighter and scattered snow in
the greater proportion of solutions. Probabilities of 0.25 inch
liquid in the form of snow reach no higher than 10-15 percent or so
during the Tuesday-Tuesday night period, reflecting the guidance
majority.

Meanwhile upstream, the upper shortwave/front expected to reach
the West Coast into early next week will be accompanied by a brief
increase in moisture but the system will be fairly progressive.
Thus expect mostly light precipitation but with some terrain-
enhanced moderate activity over western Washington/Oregon and
northwestern California, with decreasing amounts inland over the
Northwest.

Above normal temperatures will linger along the East Coast into
Sunday with daytime highs 10 to 20 degrees above normal.Meanwhile,
well below normal temperatures will be in place across parts of the
southern Rockies and Plains where daytime highs 10 to 20 degrees
below normal may linger into Sunday. Moderated below normal
temperatures will also shift into the central U.S. and Midwest
Monday and the East by Tuesday-Wednesday. Highs over and near the
Ohio Valley could be up to 15 to 20 degrees below normal on
Tuesday. Warmer than average temperatures initially over the
Northwest this weekend should expand into the remainder of the West
and the northern/central Plains by next week. A strengthening
upper ridge will likely expand coverage of plus 10 to 20 degree
anomalies over the West on Wednesday and Thursday.

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

















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