939
FXUS02 KWNH 070700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Thu Nov 7 2024

Valid 12Z Sun Nov 10 2024 - 12Z Thu Nov 14 2024

...Watching Hurricane Rafael as it tracks into the Gulf of
Mexico...


...Overview...

The National Hurricane Center continues to issue advisories for
Hurricane Rafael as it tracks across the Gulf this weekend into
early next week while weakening as it interacts with a mean upper
ridge stretching from the Bahamas. Models and the NHC forecast
reflect recent trends toward keeping the system well south of the
central Gulf Coast while it weakens. However the combination of
Rafael`s moisture and a frontal system supported by an upper low
ejecting northeast from the Plains may produce some areas of
locally heavy rainfall from the Gulf Coast northward through Sunday
before the front continues eastward with lighter rain. Farther
west, a large scale system will bring an episode of rain and high
elevation snow to the Pacific Northwest through the Rockies late
weekend into early next week with this system continuing into the
eastern half of the country by mid-late week. Another system should
focus additional precipitation over the Northwest by midweek.
Expect above normal temperatures over most of the East for a
majority of the period while the upper trough crossing the West
early next week will bring a couple days of cool temperatures to
the region.


...Guidance/Predictability Assessment...

Continue to monitor latest NHC products for additional information
on Hurricane Rafael which should weaken as it tracks over the Gulf
of Mexico. There are still the stray holdouts like the 00Z CMC and
one or more earlier machine learning (ML) model runs that bring
Rafael to the Gulf Coast, but otherwise guidance including the GFS
is furthering the recent trend toward the system not reaching any
farther north than the central Gulf due to sufficiently strong
ridging to the north. The ECMWF/UKMET continue to show an eventual
track into the southwestern Gulf.

Farther north, guidance remains fairly agreeable for the closed
upper low forecast to depart from the Upper Midwest early Sunday
onward. There is still a fair amount of spread for trailing
shortwave energy reaching the West on Sunday and continuing
eastward thereafter. Other guidance suggests that the 00Z CMC is
particularly suspect with its deeper trough that ultimately closes
off an upper low off the East Coast by Tuesday (with a
corresponding surface low offshore New England.

A blend/compromise approach among recent GFS/ECMWF runs and their
means appears most reasonable for resolving timing/amplitude
details of the large scale upper trough nearing the West Coast by
early Monday and continuing into the East after midweek, as well as
for the resulting surface evolution. The UKMET strayed a bit fast
by the end of its run early Tuesday. The ML model average agrees
well with the model/ensemble mean compromise for Plains into Upper
Midwest/Great Lakes/southern Canada low pressure during Wednesday-
Thursday. It will be worth monitoring for trends/continuity if the
deeper GFS/ECMWF surface solutions hold up as those would produce a
period of stronger winds over the Great Lakes region. CMC runs
have been running on the fast side with this trough as well as with
the trailing one that should reach offshore the West Coast by next
Thursday.

Forecast preferences were best represented by a blend of the
12Z/18Z GFS and 12Z ECMWF/UKMET early, followed by a trend toward
those GFS/ECMWF runs and the 18Z GEFS/12Z ECens means mid-late
period.


...Weather/Hazards Highlights...

While confidence is gradually increasing that Hurricane Rafael
should remain well south of the Gulf Coast as it weakens from the
weekend into early next week, guidance continues to show an axis
of anomalous moisture extending northward from the Gulf and
interacting with a front progressing across the east-central U.S.
(slower and more wavy over the South) along with some limited
instability. Model/ensemble solutions still vary in the details but
consistency with the overall pattern favors holding very close to
continuity for the existing Marginal Risk area extending from the
central Gulf Coast into the Ohio Valley/central Appalachians in the
Day 4 (Sunday-Sunday night) Excessive Rainfall Outlook. Anticipate
much lighter rainfall by Monday all but the farthest south part of
the front reaches the East Coast. Parts of Florida may see some
increase in rainfall around Sunday-Monday with a weak wave
brushing the southern part of the state.

An upper trough with leading surface front approaching the Pacific
Northwest and then moving inland Sunday-Monday will bring an
episode of focused precipitation to the region. For the Day
4/Sunday ERO there is still some variance for rainfall amounts but
first- guess guidance and neutral to damp soil conditions favor
maintaining the Marginal Risk area over western Washington into
northwestern Oregon. By Day 5/Monday the moisture axis should sink
a little south before progressing inland, while the GFS in
particular offers potential for modest instability. Thus the Day 5
ERO introduces a Marginal Risk area over parts of western Oregon
and far northwestern California. High elevation snow is likely from
the Cascades into the Sierra Nevada, while eastward progress of
moisture and dynamics will also spread snow into the northern-
central Rockies during the first half of next week. With some
difference of opinion regarding whether there may be a break around
Tuesday, additional meaningful precipitation is likely over the
Pacific Northwest by Wednesday-Thursday as another system
approaches.

The system affecting the West early in the week will progress
eastward and bring some areas of precipitation to the eastern half
of the country during at least parts of the Tuesday-Thursday
period. Important lower-predictability details still have to be
resolved before confidence can increase regarding specifics of
where/when the greatest totals will occur.

While system progression will provide some day-to-day variability,
much of the eastern half of the country should see well above
normal temperatures from Sunday into early next Thursday. Expect
the warmest anomalies to be for morning lows, including some
readings at least 20F above normal over the South early Sunday.
Broadest coverage of plus 10F or greater highs should be during
Monday-Wednesday. The northern and southern thirds of the Plains
will also see a period of warmth Sunday-Tuesday (and still southern
Texas on Wednesday). Corresponding to these relative anomalies,
there will be better potential for some record warm lows versus
more isolated records for daytime highs. Parts of the Northeast may
be near normal at times though. The southern Rockies/High Plains
will remain chilly to the extent that snow cover lingers, while the
upper trough crossing the West early next week will bring a brief
period of moderately below normal 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.phpSchichtel/Hamrick

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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