863
FXUS02 KWBC 031845
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 PM 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 during the short range period should finally move
east on Sunday as an amplifying upper trough drops into the north-
Central U.S. and interacts with southern stream energy ejecting
northeastward. There will be potential for moderate to locally
heavy rainfall in the Southeast as the front moves through Sunday
into Monday. On the other side of the CONUS, a shortwave moving
into the West will likely support precipitation chances across the
Northwest through early next week. By Tuesday, the forecast should
trend 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...

Model guidance continues to show very good agreement today on the
overall weather pattern through the medium range period. Model
spread tends to increase in the second half of the period, which is
typical at this time frame, which will have some impact on the
finer scale details at the surface. The main question will be with
the strength and timing of troughing/shortwave energy moving toward
the West Coast next week and how that will affect a downstream
system over the Central U.S. on days 6 and 7 (Wednesday and
Thursday). The GFS favors a faster evolution while the ECMWF and
CMC are slower. Overall, the WPC forecast favored a slower
evolution closer to the CMC and ECMWF, which also maintains WPC
forecast continuity.

Given good agreement, the WPC forecast model blend consisted of
even parts of the deterministic GFS/ECMWF/CMC/UKMET for the first
half of the period, and ensemble means from the GEFS and ECENS were
added for the second half of the period to help smooth out model
differences.


...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 from the Central Gulf Coast into portions of the
Southeast. The Slight Risk area may need to be extended north
across central Alabama and northern Georgia, where model guidance
has been trending wetter. The front may slow for a period across
parts of the Southeast on 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 and/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 have increased since the last forecast
but still remain below 30 percent during the Tuesday-Tuesday night
period.

Meanwhile upstream, the upper shortwave/front expected to reach
the West Coast early next week will be accompanied by a brief
increase in moisture, but the system will be fairly progressive.
Thus, expect mostly light precipitation 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 with daytime highs 10 to 20 degrees.
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.

Dolan/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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