944
FXUS02 KWBC 071900
PMDEPD

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

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

...Heavy rain and potential flooding concerns 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 continues to show mean troughing aloft over the West and
southwesterly flow downstream, with ejecting shortwaves supporting
a series of progressive frontal systems 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 continues to show similar ideas for the large scale
pattern, but there are still 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. Guidance
preferences led to favoring a general 00Z/06Z deterministic model
composite for Monday-Tuesday given a good overall handle of the
major synoptic scale features. For Wednesday through Friday, the
deterministic blend rapidly increased weighting towards the 00Z
EC/GEFS/CMC ensemble means. Similar to last night, neither the 00Z
or 06Z runs of the deterministic GFS were considered beyond Day 4.
These runs were still much too slow with the evolution of the
shortwave that is progged to eject out of the Southwest Day 5 and
into the Atlantic Maritimes by Day 7. The deterministic runs of the
GFS were also too weak and spriest with the resulting low pressure
system that will track into the Ohio Valley and Northeast by late
in the week (though the latest 12Z run is at least starting to
trend towards the other more amplified solution). ML models seemed
to agree with the faster and more amplified cluster of guidance so
thus decided to lean heavily on that blend with anchoring from the
more stable ensemble means.

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.


...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 above normal moisture
anomalies along with possibly some instability, in addition to a
pattern that could favor training given a stationary boundary
nearby. Only minor changes were made to the inherited Day 4 ERO,
with a Marginal Risk area from eastern Oklahoma/northeastern Texas
into western Kentucky and Tennessee. Meanwhile, the Day 5 ERO
maintains a broad Marginal Risk area from eastern Texas into the
southern Appalachians. However, for this update, decided to go
ahead and introduce a targeted Slight Risk area from northern
Mississippi to south central Tennessee and extreme northwest
Georgia given increased confidence for an axis of heavy rainfall
(potentially in excess of 2 inches) amongst the latest guidance.

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.
Last night`s 50 to 70 percent probabilities for a quarter inch of
liquid equivalent snow/sleet largely 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. For this update, confidence increased enough to introduce 70
to 90 percent probabilities from the high elevations of West
Virginia eastward to near Washington DC. 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).

Miller/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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