Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 PM EST Sun Nov 07 2021
Valid 12Z Wed Nov 10 2021 - 12Z Sun Nov 14 2021
...Robust Midwest/Great Lakes Low mid-later week...
...Multiple rounds of precipitation into the Pacific Northwest
later in the week...
...Pattern Overview...
Upper ridging to the southwest of California as well as over the
Canadian archipelago favors 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, some wrap-around snow is likely over parts of
the Dakotas/Upper Midwest/Great Lakes and central/northern
Appalachians next weekend.
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, but with continued uncertainty in timing,
track, and strength of the embedded systems including run-to-run
continuity issues. Given uncertainty in recent trends, a composite
blend was a prudent starting point that largely downplayed more
seemingly errant deterministic runs including the 06Z GFS and at
times the 00Z ECMWF. General overlap between many GEFS and ECMWF
ensembles favored using the National Blend of Models for most
grids with enhancements to its QPF overall, especially around the
Great Lakes next weekend but also in the East with the surface
low/front.
...Weather/Hazards Highlights...
Amplifying upper pattern will support surface cyclogenesis over
the Upper Midwest late Wed 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 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.
Fracasso/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