Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
202 AM EST Mon Feb 10 2025
Valid 12Z Thu Feb 13 2025 - 12Z Mon Feb 17 2025
...Continued active weather pattern with periods of heavy rain and
winter weather across parts of the West and the eastern half of the
lower 48...
...Overview...
The medium range period will feature a series of systems producing
areas of significant rainfall and winter weather. The first system
should track through the Northeast on Thursday with snow for
northern New England at the same time a wet/snowy system reaches
the West Coast, with heaviest precipitation focused over
California. Continued progression of the West Coast system's upper
trough will likely support low pressure reaching the East by Sunday
and the Canadian Maritimes by Monday. This low should spread wintry
weather from the Upper Midwest through the Northeast, with heavy
rain farther south over some areas that may be affected by prior
heavy rain. The next Pacific system will track farther north than
the first one, confining the rain and higher elevation snow more
to the Northwest from the weekend into early next week. Parts of
the Plains will see the most pronounced cold anomalies, especially
on Thursday and the weekend, while gradually increasing Pacific
influence should help the West to moderate from its cold
temperatures as of Thursday. The Southeast will tend to see above
normal temperatures from late week through the weekend.
...Guidance/Predictability Assessment...
The updated forecast based on 12Z/18Z guidance placed more emphasis
on the 12Z ECMWF/18Z GFS relative to the 12Z CMC/UKMET early to mid
period, followed by incorporation of 30-40 percent ensemble means
(18Z GEFS/12Z ECens) while adjusting GFS input a little more toward
the 12Z run and eliminating the 12Z CMC.
Guidance consensus is fairly good for the system reaching the
Northeast on Thursday, with some lingering differences for strength
and the dynamical model average leaning a bit deeper than the
average of machine learning (ML) models. There are some lingering
differences for exact details of the upper trough, affecting cold
frontal timing over the Southeast.
GFS/ECMWF/UKMET runs, ensemble means, and most ML models clustered
well in principle for the system reaching the West Coast late this
week, but the 12Z CMC structure differed from the majority and was
not favored. As this system reaches the East by the weekend,
dynamical and ML models have differed somewhat on upper trough
details and the resulting surface reflection. However there has
been a consistent majority close to recent ECMWF/ECens mean runs
for a surface low track over or a little east of the upper Ohio
Valley as of early Sunday. GFS runs have waffled slower/faster
(18Z/00Z runs faster), while the new 00Z ECMWF has nudged a little
faster as well. Recent CMC/CMCens runs had strayed slow with the
upper trough and weak/suppressed with the surface wave, but the new
00Z run has adjusted close to the 12Z ECMWF. ML models support
fairly strong development of this storm as it reaches the Canadian
Maritimes by next Monday (versus the weak 18Z GFS).
Finally, dynamical guidance shows better than average agreement
with the North Pacific system that should affect the Northwest by
the weekend and early next week, with the surface low likely
tracking toward or close to Vancouver Island. ML models show
potential for a little more variation in timing/details of the
upper trough, leaning a tad faster than the dynamical majority on
average.
...Weather/Hazards Highlights...
The system tracking through the Northeast on Thursday will bring
meaningful snow to northern New England, while the trailing cold
front will cross the Southeast. Recent guidance runs have been
narrowing the spread for this front and its associated axis of
moisture. Models show some instability with this front and
potential for some locally heavy rainfall, mainly over parts of
northern Florida into Georgia. However this region has dry
antecedent conditions with very high flash flood guidance values.
Thus the Day 4/Thursday Excessive Rainfall Outlook continues to
depict no risk area for this activity. Will continue to monitor for
any trends toward broader organized heavy rainfall on the higher
end of the envelope.
With fairly strong low pressure and associated frontal system
reaching the West Coast Thursday into early Friday, guidance has
maintained good continuity over the past day regarding favorable
moisture anomalies/enhanced IVT values focusing heaviest rainfall
and higher elevation snow over California. Therefore the new Day 4
ERO carrying over from yesterday's Day 5 outlook has made no
changes at this time, with a Slight Risk area over a majority of
coastal California and extending into favored terrain of the Sierra
Nevada. This area reflects the best overlap of heaviest forecast
rainfall and current sensitivities from either wet antecedent
conditions or burn scars. Especially as shorter term guidance
refines the best focus of heaviest rainfall, it is possible an
eventual upgrade to a moderate risk may be needed across southern
California and in particular the burn scar areas. The new Day 5 ERO
introduces a Marginal Risk area along the far southern coast, with
lingering moisture early in the day and the upper trough passing
overhead to provide some possible instability.
Continued progression of this system will spread areas of rain and
heavy mountain snow farther inland, eastward to the Rockies. The
upper trough will likely support surface low development over the
eastern half of the country during the weekend. South-central areas
that will already be sensitive due to prior heavy rainfall may see
another episode of heavy rain, while areas from the Midwest into
the Northeast will see the best potential for significant snow. A
transition zone of wintry mix may separate the rain/snow areas.
There may be a period of gusty winds over parts of the East behind
this system.
A farther northward track of the next Pacific system will favor the
Northwest for the next round of rain and higher elevation snow from
the weekend into early next week. Amounts should start out on the
light to moderate side on Saturday but may trend somewhat heavier
on Sunday. Expect moisture to spread farther eastward/southeastward
into the Rockies By Monday.
Parts of the central U.S. will see well below normal temperatures
for most of the period, with some central-southern Plains
locations 20-30F below normal for highs on Thursday followed by
another cold surge bringing similar anomalies into the far northern
Plains on Friday and extending farther southward during the
weekend. Progression of an upper trough into the East will spread a
modified form of this cold air eastward by next Monday with most
of the northeastern quadrant of the lower 48 seeing highs 10-20F
below normal. Cold air will also extend into the Northwest through
late week but the West as a whole will gradually trend warmer as
Pacific flow gains influence. The Four Corners states and vicinity
may achieve above normal highs by the start of next week. Systems
forecast to reach the East around Thursday and Sunday should pull
some above normal temperatures northward from the Gulf
Coast/Southeast. A few locations over the Florida Peninsula could
challenge record highs on one or more days.
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