084
FXUS02 KWNH 070701
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Fri Feb 7 2025

Valid 12Z Mon Feb 10 2025 - 12Z Fri Feb 14 2025

...Heavy rain developing in the southeastern quadrant of the lower
48 Monday-Wednesday...

...Rounds of snow and ice are possible stretching from the
central Plains to Mid-Atlantic/Northeast next week...


...Overview...

Guidance shows mean troughing aloft over the West and
southwesterly flow downstream, with ejecting shortwaves supporting
a series of frontal waves whose track and timing remain somewhat
uncertain. This pattern will produce an axis of potentially heavy
rainfall and flooding concerns from the southeastern Plains into
the Mid-Atlantic. Snow will be possible on the northern side of
the moisture shield, most likely from the central Plains into the
Northeast, and sleet or freezing rain will be possible between the
rain/snow areas. Meanwhile the character of western upper
troughing will change after Wednesday as western Canada flow
elongates westward, allowing an eastern Pacific system to track
into the West by Friday. This system should bring a broad area of
precipitation to the region late in the week but with uncertainty
regarding coverage/location of highest totals. Corresponding to the
mean pattern, expect below normal temperatures over much of the
western/central U.S. and above normal readings over the far
Southeast. Arrival of Pacific flow by next Friday should begin a
moderating trend over some areas.


...Guidance/Predictability Assessment...

Most guidance shows similar ideas for the large scale pattern, but
there are important differences yet to be resolved for individual
shortwaves ejecting from the western U.S. mean trough, and in turn
associated surface waves that will determine precipitation
coverage/type/amounts. There is also quite a bit of spread for
eastern Pacific low pressure tracking toward the West Coast, while
some solutions also diverge for the flow pattern over the
northeastern Pacific/western Canada by late next week.

Regarding the sequence of two primary shortwaves ejecting from the
western upper trough and supporting surface waves over the East,
there is decent clustering for a leading weak feature that should
ultimately generate a progressive wave over the western Atlantic by
early Wednesday (with a more suppressed trend in the new 00Z GFS)
but much greater spread for the trailing one. The latter shortwave
drops into the Northwest in east-west fashion by Monday night-
Tuesday, with spread increasing from there. Most 12Z/18Z machine
learning (ML) models favor shortwave timing closest to recent ECMWF
runs, in contrast to the slow GFS runs or fast 00Z UKMET. However
the new 00Z ECMWF leans to the northern side of the spread for
surface low pressure near the East Coast by next Thursday. The 00Z
GEFS has shifted more toward the operational runs but earlier GEFS
runs were more tempered and could be used as part of the favored
guidance blend.

Like the dynamical guidance, the ML models showed a fair amount of
spread for the character of the Pacific system eventually tracking
into the West. There does not seem to be too much support yet for
the fast arrival of a leading wave as per recent UKMET runs and 00Z
CMC. The past couple ECMWF runs leaned a little on the south side
of guidance but within the ML model envelope. However the new 00Z
ECMWF has adjusted northward.

There has been a lot of spread and variability for the northeastern
Pacific/western Canada pattern toward the end of the week. ML
models support a pattern closest to the ensemble means, in contrast
to earlier ECMWF runs that were more aggressive with
westward/southwestward elongation of western Canada troughing or
GFS runs that may lean too much toward weak ridging along the
British Columbia coast.

Guidance preferences led to favoring a 12Z/18Z model composite for
Monday-Tuesday, followed by replacing the 18Z GFS with the GEFS
mean plus eliminating the already minor UKMET input for Wednesday.
Then the blend rapidly increased ensemble mean weight (including
12Z ECens and CMCens runs) toward the end of the week.


...Weather/Hazards Highlights...

During the Monday through Tuesday night period covered by the
Excessive Rainfall Outlooks, expect rain to develop over the
south-central Plains and then trend heavier as it expands into the
Southeast. Guidance agrees on the presence of decent moisture
anomalies along with possibly some instability, along with a
pattern that could favor training. The new Day 4 ERO maintains a
Marginal Risk area from eastern Oklahoma/northeastern Texas into
parts of the Mississippi Valley, while the Day 5 ERO introduces a
broad Marginal Risk area from eastern Texas into the southern
Appalachians. Guidance is signaling potential for an embedded
Slight Risk area, but would like to see guidance refine the bounds
of such an area a little better before depicting it in the outlook.

The northern side of the precipitation shield may contain rounds
of potentially disruptive wintry precipitation next week. The
favored band for winter weather should extend from the central
Plains through the Middle Mississippi Valley, Ohio Valley, central
Appalachians, and Mid-Atlantic/Northeast where moisture
overrunning southern tier fronts will interact with cold air.
Currently the highest probabilities (50-70 percent) for a quarter
inch of liquid equivalent snow/sleet remain in place from the
central Appalachians into parts of the Mid-Atlantic for Tuesday to
Wednesday morning, including some of the larger I-95 metropolitan
areas. Meanwhile sleet and freezing rain are possible between the
chances for heavy rain to the south and snow to the north. Stay
tuned for refinements to the forecast as the placement, amount, and
type of precipitation remains uncertain at any individual
location. There may be another episode of enhanced precipitation
with a Thursday wave, but specifics in timing and the rain/snow
line are more uncertain.

Precipitation will likely taper off over the West early next week,
with just some light amounts in the Pacific Northwest and parts of
the northern-central Rockies. Models vary with the character of a
Pacific system/associated atmospheric river forecast to reach the
West later in the week, but generally suggest some areas may see
significant rainfall and higher elevation snow. Continue to monitor
forecasts for refinement of important details.

Northwestern and north-central parts of the lower 48 will see
colder than average temperatures next week. The cold will be
especially pronounced across Montana and North Dakota into
Minnesota as the workweek begins, with lows forecast to be
in the -10s and -20s, along with some below zero highs. Colder
than average temperatures will spread south behind a cold front
next week, displacing unseasonable warmth across the southern tier
during the weekend. Warmer than average temperatures should be
limited to Florida and the adjacent Southeast by midweek.
Introduction of Pacific flow should promote a moderating trend over
the western-central U.S. by next Friday (but remaining quite cold
over the northern Plains).

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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