215
FXUS02 KWBC 082003
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Fri Nov 8 2024

Valid 12Z Mon Nov 11 2024 - 12Z Fri Nov 15 2024

...Hurricane Rafael not likely a threat to the Gulf Coast...

...Overview...

A reasonably progressive pattern is forecast next week as a couple
of shortwaves traverse the central and eastern U.S. early week
while a larger scale and deeper trough moves through the West
Monday-Tuesday, into the central U.S. midweek, and through the East
late week. This trough will direct an atmospheric river into the
Northwest early week for some heavy rain and snow, with additional
rounds of heavy precipitation there as the week progresses.
Generally moderate precipitation (mostly rain) is expected to
develop in the central U.S. around Tuesday and gradually shift into
the East by Thursday. Temperatures are forecast to vary from day
to day but with a general tendency toward warmer than average
temperatures in the central and eastern U.S. and near to cooler
than average in the West. Meanwhile the National Hurricane Center
forecasts what is currently Hurricane Rafael to weaken and decay
over the Gulf, with minimal impacts to the lower 48 during the
medium range period aside from perhaps providing moisture to some
lingering showers across the Southeast Monday.


...Guidance/Predictability Assessment...

Continue to monitor latest NHC products for additional information
on Hurricane Rafael, which should weaken by the start of the
medium range period as it tracks over the Gulf of Mexico. There
remains some uncertainty into next week on the exact track as some
ensemble members, older CMC runs, and a contingent of the 00Z AI/ML
models take a weak low into or riding near the central Gulf Coast.
The 12Z CMC has finally gotten into alignment with the better
consensus farther south. The most recent NHC forecast track
continues to show a preference more like the ECMWF/UKMET with a
southwestern dive toward the Bay of Campeche and possibly into
Mexico as a weak remnant surface low. Despite the lingering spread,
at least it is pretty clear that the center of Rafael itself
should not impact the U.S., aside from some tropical moisture
spreading northward into the Southeast.

Over the CONUS, the placement and strength of shortwaves remain
somewhat in question even early in the period. The 00Z CMC seemed
like the main outlier as it shows a stronger shortwave a bit
farther west in the central Plains on Monday, which almost closes
off an upper low when it reaches the Lower Ohio Valley Tuesday
while the consensus of other models is weaker and more progressive.
The 12Z CMC has somewhat better alignment with this feature though
still a bit on the slow side. Upstream, models seem to have a good
handle regarding the existence of the synoptic scale upper trough
moving into the West Monday and eastward through the week. There
are some timing differences though, with GFS runs now on the faster
side compared with the ECMWF, with a middle ground position
seeming most likely. An upper low may form out of this trough over
the Eastern Seaboard or western Atlantic by next Friday, but
without much convergence on where exactly yet. Upper ridging should
come in behind the trough in the amplified pattern, while another
trough axis looks to be near the West Coast by next Friday. With
this trough, GFS runs are on the slower side and CMC runs on the
faster side, with the ECMWF seemingly showing the best compromise
at this time.

The WPC forecast was based on a blend of the 06Z GFS, 00Z ECMWF,
and a little of the 00Z UKMET early in the period, with no CMC
given the 00Z run`s aforementioned issues. As the period
progressed, blended in the EC and GEFS means with increasing
proportions to try to create a middle ground forecast with the
pattern.


...Weather/Hazards Highlights...

Some tropical moisture from Rafael may extend northward and focus
along a frontal boundary through the Southeast early in the week,
but outside of very localized heavy rainfall pockets, low
instability is expected to limit any flash flooding threat.

A leading surface front focusing an atmospheric river ahead of an
upper trough will be moving southward through the Pacific Northwest
into northern California into Monday, bringing an episode of
focused precipitation to the region. Additionally, the next AR may
start to impact western Washington by late Monday/Monday night.
Thus both areas are covered by a Marginal Risk on the Day 4/Monday
Excessive Rainfall Outlook. The second AR may be longer-lasting and
move more slowly southward through the Pacific Northwest,
warranting a Marginal Risk for Day 5/Tuesday especially considering
the wet antecedent conditions from the first round. Heavy
precipitation is forecast to last into Wednesday and may gradually
lighten somewhat by Thursday. Accumulated snow may become heavy in
the Cascades as the week progresses, with modest snow amounts into
the northern Rockies.

The upper trough 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. The minor model disagreements in the trough
position do cause some spread for the positioning of precipitation
on individual days, but on a broad scale, modest precipitation
should affect parts of the Plains and Mississippi Valley Tuesday,
spreading into the Midwest/Great Lakes and Ohio/Tennessee Valleys
to Appalachians Wednesday, and toward the Eastern Seaboard
Thursday. Most precipitation looks to fall as rain given the warmer
than normal temperatures, until some ice and snow are possible in
higher elevations of the Interior Northeast mid- to later week. The
surface low track associated with this trough near the Great Lakes
could spread moderate to high winds especially over the waters but
possibly for some land areas like Michigan`s Upper Peninsula.

While system progression will provide some day-to-day variability,
much of the eastern half of the country should see well above
normal temperatures into midweek. The greatest anomalies will be
15-25F for lows over much of the southeastern U.S. Monday and
Tuesday mornings, with highs around 10-15F (locally higher) above
normal from Texas northeastward. Temperatures are forecast to
moderate behind a cold front across the Great Lakes region Tuesday
and over much of the Eastern Seaboard Wednesday, and finally in the
east-central U.S. Thursday behind the secondary cold front.
Meanwhile lingering snow cover in the central/southern Rockies will
promote cooler than normal highs there. The West otherwise should
generally near to a bit below normal, though ridging building in
the central U.S. should lead to above normal temperatures there by
later next week.


Tate


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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