219
FXUS02 KWNH 210658
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Fri Mar 21 2025

Valid 12Z Mon Mar 24 2025 - 12Z Fri Mar 28 2025


...Overview...

The early to middle part of next week will feature a large-scale
western U.S. upper ridge and eastern trough. The pattern should
flatten/progress some later in the week, as energy from an eastern
Pacific trough reaches into the West while the ridge moves into the
Plains/Mississippi Valley and the eastern troughing begins to lift
out. Expect very warm temperatures under the upper ridge with some
daily records possible over the West. The Great Lakes and East
Coast/Gulf Coast will see one episode of precipitation with a
Monday system with a possible Midwest wave on Tuesday potentially
spreading some moisture into the East by midweek. The upper
dynamics and leading front reaching the West will bring rain and
high elevation snow to the Northwest mid-late week. Meanwhile a
southern tier shortwave will bring a threat of locally heavy
rainfall to parts of the southern half of Texas late in the week.

...Guidance/Predictability Assessment...

Dynamical and machine learning (ML) guidance agrees quite well for
the system affecting the East on Monday into Tuesday. However
there is more spread for a potential wave reaching the Midwest on
Tuesday and with less confidence tracking near the Northeast coast
by Wednesday. This surface feature has fairly low predictability
due to being very sensitive to small scale detail differences in
supporting shortwave energy. ML guidance is rather ill-defined with
the surface reflection, but at least loosely suggests that the GFS
(which strays fast with the shortwave energy) may be underdone
with its surface reflection. Latest CMC runs are a slow extreme.
The 12Z ECMWF and latest UKMET runs as well as the ECens/CMCens
means offer the most coherent cluster for the depiction of this
system as well as decent continuity.

By the middle and latter half of the period, the ML guidance shows
some detail spread over the West but overall has decent troughing
pushing into the region. This supports leaning more in the
direction of the ECMWF and the ensemble means as opposed to recent
GFS runs that are noticeably flatter with energy reaching the West.
The new 00Z CMC may be overdone with its trough while it is
nearing the West Coast, while the 00Z ECMWF is deeper than previous
runs as energy moves through the West. Elsewhere, currently there
is not much support for the compact system the 00Z GFS brings
across the Northeast late in the week while a guidance consensus
looks reasonable for the southern stream trough that may reach
Texas by next Friday.

Dynamical and ML guidance comparisons led to an early-period
12Z/18Z operational model composite followed by swapping out the
GFS for the 12Z ECens/CMCens means and 18Z GEFS mean by Wednesday,
and 60-75 percent ensemble mean input thereafter with the 12Z ECMWF
being the only operational guidance remaining.

...Weather/Hazards Highlights...

Low pressure tracking from the Great Lakes eastward early in the
week will produce some snow over far northern areas, with best
potential for meaningful accumulation on Monday over central and
northern New England. Expect rain farther southward along the
trailing cold front. The Day 4/Monday Excessive Rainfall Outlook
holds onto a Marginal Risk area over parts of the South in light of
lingering training potential that is most prominently suggested in
the GFS. However other guidance is less enthusiastic QPF-wise and
it is a fairly progressive front, so would consider this a lower-
end threat at this time. Behind this system a weak wave may track
through the Midwest around Tuesday and then near the Northeast
coast by Wednesday. Any associated precipitation should be fairly
light and confidence in the system`s evolution is below average at
this time.

Far northern parts of the West may see lingering precipitation on
Monday with most of the region dry by Tuesday. Upper trough energy
and a leading cold front will bring rain and high elevation snow
into the Northwest and northern Rockies mid-late week. There is
some uncertainty over amounts and southward extent, with the best
consensus suggesting a compromise between the northern GFS and
heavier/southward CMC.

Around Tuesday-Tuesday night some guidance hints at the potential
for very localized potential of enhanced rainfall over the parts of
the southern Plains, near the front trailing from the weak Midwest
wave. This potential activity is not sufficiently agreeable or
organized in the guidance to merit an ERO risk area at this time.
Ground conditions are also fairly dry over this region. Then the
combination of an approaching southern stream trough along with
moist easterly low level flow from the Gulf may increase the
chances for more organized and heavier rainfall over parts of
southern Texas late in the week.

The strong upper ridge over the West early-mid week will bring
well above normal temperatures to the region, with a broad area of
highs 10-20F above normal with locally higher anomalies. There will
also be potential for numerous daily records for highs/warm lows,
especially on Tuesday and Wednesday. Some places over the Desert
Southwest could get close to 100 degrees. As the upper pattern
shifts eastward somewhat later in the week, the West will cool down
while already above normal anomalies over the central U.S. will
increase. Areas over and near the central Plains should see highs
reach 20-25F above normal by Thursday-Friday. Mean troughing aloft
will keep most of the East near to slightly below normal for
temperatures.

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







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