Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Wed Nov 03 2021
Valid 12Z Sat Nov 06 2021 - 12Z Wed Nov 10 2021
...Overview...
The medium range period will be characterized by an upper ridge
with its axis gradually shifting from the central U.S. over the
weekend toward the East by Tuesday-Wednesday, separating weekend
troughing in the East and rounds of troughing in the eastern
Pacific/West. A series of fronts and shortwaves coming into the
West Coast will keep precipitation chances high there, while a
front and developing low pressure system off the East Coast will
spread some rain across Florida and up the Southeast coast this
weekend.
...Guidance/Predictability Assessment...
Model guidance begins the medium range period with reasonably good
agreement this weekend, indicating a shortwave over the
Midwest/Great Lakes and southern stream troughing over the
Southeast beginning to combine in the Eastern Seaboard, shortwave
energy tracking through the Northwest, and upper ridging in the
central U.S. The main exception is the 12Z CMC in the eastern
Pacific/West, as it has less initial energy with the Pacific
Northwest shortwave but more energy dropping southward around
Sunday in the eastern Pacific, causing a mid-upper trough to dig
along the West Coast by Monday. This is not supported by other
guidance including almost all GEFS/EC/CMC ensemble members. The
new 00Z CMC appears to be more in line with consensus, another
indication that leaning away from the 12Z is a good move. Other
than that, a multi-model deterministic blend favoring the 12Z
ECMWF and UKMET and 18Z GFS was used for the beginning of the
period. At the surface, this maintains a low track from the
Florida Peninsula northeastward into the western Atlantic.
As the workweek begins, there are some differences with placement
of shortwaves among guidance, but nothing too out of the ordinary
for that time range. For the most part, deterministic and ensemble
guidance indicate deeper troughing and likely a closed low just
offshore of the Pacific Northwest Tuesday, with troughing/energy
making its way quickly eastward Wednesday. The 18Z GFS and 12Z
ECMWF were both quite strong with this upper closed low and the
associated surface low, and this updated forecast showed an
increase in its strength, though not to the level of 957 or 965 mb
respectively at the surface Tuesday at 12Z. Other than that, the
main change to the previous forecast issuance was pushing a cold
front more quickly through the central U.S., per the recent model
guidance indicating a faster movement of incoming troughing for
the western/central U.S. and upper ridging pushing eastward. The
latter part of the medium range forecast utilized a fairly even
blend of the 18Z GFS and GEFS mean and 12Z ECMWF and EC mean.
...Weather/Hazards Highlights...
As a surface low pressure and frontal system develops near/over
Florida Saturday and tracks northeastward into the western
Atlantic, it will spread rain across Florida and into the coastal
Carolinas and possibly the Mid-Atlantic region on the backside of
the low over the weekend. Current forecasts do not show rainfall
reaching very far inland, given a well offshore track of the low,
but small shifts of the low track could lead to significantly more
or less rainfall in coastal areas, especially for the Carolinas.
Abundant moisture ahead of frontal systems and upper-level
shortwaves edging in from the Pacific will result in periods of
enhanced precipitation this weekend into early next week near the
West Coast. Through the period, the Pacific Northwest and northern
California can expect the heaviest precipitation, with normal
terrain enhancements and higher elevation snow. Precipitation is
likely to spread into the Intermountain West and Rockies as well,
with amounts there increasing by next Monday into Wednesday.
Behind the low pressure system in the western Atlantic, a cold
surface high to the west will bring northerly winds and high
temperatures that are 10-20F below normal to the Southeast through
the weekend. Lows could be 5-10F below normal farther north in
this pattern as well, with temperatures in the mid to low 30s for
much of the Ohio Valley Saturday morning, which could result in
the first frost or freeze of the season for some places.
Meanwhile, a persistent upper-level ridge over the west-central
U.S. should lead to temperatures that are above average by 10-20
degrees over the Plains into the Midwest through early next week,
with highs 5-10F above normal stretching toward the East Coast by
Tuesday-Wednesday. Periods of unsettled weather will keep highs
somewhat below normal over the West Coast on most days, eventually
entering into the Great Basin and Rockies by midweek.
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, 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