Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
143 AM EST Mon Nov 08 2021
Valid 12Z Thu Nov 11 2021 - 12Z Mon Nov 15 2021
...Robust Midwest/Great Lakes Low into later this week...
...Multiple rounds of precipitation into the Pacific Northwest
later this week...
...Pattern Overview...
It remains the case that upper ridging to the southwest of
California as well as over the Canadian archipelago favors
amplified troughing over the central to eastern CONUS later this
week into the weekend. This favors a deepening central states
cyclone that will lift northeastward through the Midwest/Great
Lakes into Canada Thu-Sat. Milder air over much of the Lower 48
will trend cooler with time as the attendant cold front sweeps
eastward, favoring a widespread swath of modest to locally heavy
rain across much of the East. On the northwest side of the low
pressure, wrap-around and then lake effect snow is likely over the
Dakotas/Upper Midwest/Great Lakes late week and then the
central/northern Appalachians.
Upstream, there is a growing guidance signal bringing a long fetch
plume of Pacific moisture into the Pacific Northwest, especially
later this week. Favorable flow should focus heavy rains and
elevation snows over the Olympics and Cascades.
...Guidance/Predictability Assessment...
Guidance continues to illustrate a reasonably similar larger scale
pattern evolution and forecast clustering has improved slightly
Thu into Fri. A composite blend of the GFS/ECMWF/Canadian/UKMET
seems reasonable, is in line with the NBM and GEFS/NAEFS/ECMWF
ensemble means and maintains good WPC continuity in this time
frame. However, continued uncertainty in timing, track, and
strength of the embedded systems including run-to-run continuity
issues remains evident starting later Fri and onward. Given
uncertainty in recent trends, the WPC product suite was derived
from a composite blend of still compatible guidance from
GEFS/NAEFS and ECMWF ensembles and the National Blend of Models.
...Weather/Hazards Highlights...
Amplifying upper pattern will support surface cyclogenesis over
the Upper Midwest into Thu as Gulf moisture streams northward
along and ahead of the cold front. Surface wave development out of
the lower Mississippi Valley could act to enhance rainfall from
the southern Appalachians northward into the Northeast. As the
system moves into Canada, backside cold air flow by next Friday
will likely support some snow over the Dakotas/Upper Midwest/Great
Lakes and subsequently with cold flow off the lakes and into the
northern/central Appalachians. This could be the first
accumulating snow of the season for some areas of northern
Minnesota into the eastern Dakotas. Temperatures will be near to
above normal early in the week, with possible record highs ahead
of the front on Friday in the Mid-Atlantic, but trending cooler by
week's end especially into the Southeast (relative to typical
mid-November values there). Please see WPC links below for all the
details in graphical format.
Upstream, there is a growing guidance signal bringing several
rounds of rain and mountain snow to the Pacific Northwest,
especially later this week. Favorable flow should focus heavy
rains and elevation snows over the Olympics and Washington
Cascades.
Schichtel
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, winter weather outlook probabilities
and heat indices are at:
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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml