Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 AM EDT Fri Nov 05 2021
Valid 12Z Mon Nov 08 2021 - 12Z Fri Nov 12 2021
...Guidance/Predictability Assessment...
Models and ensembles show a reasonably similar larger scale
pattern evoution aloft and overall precipitation focus through
medium range time scales despite the transitory nature of the flow
from onset of progression to somewhat more slowed and ampified
flow. However, surface system forecast variance, uncertainty and
continuity increases more significantly days 4-7 (Tuesday-Next
Friday). While identifying synotic areas of activity,
predictability of the local focus for heavier precipitation is
limited outside of favored terrain of the West. Accordingly, the
WPC medium range forecast package was primarily derived from a
composite of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian only
for day 3/Monday before rapidly transitioning to the compatible 18
UTC GEFS mean, the 12 UTC ECMWF ensemble mean and the 01 UTC
National Blend of Models for days 4-7. The latest 00 UTC models
continues to show above normal run to run continuity issues with
embedded systems that given the lack of a strong signal for a
particular solution, seems to lend creadance to the ensemble based
forecast approach.
...Pattern Overview and Weather/Hazards Highlights...
An amplified southern stream upper trough and deepened low off the
East Coast will increasingly shift over the Atlantic
Monday/Tuesday as a martime threat as a stable/warm upper trough
extends upstream from the Southern Plains to the Northeast/East.
Meanwhile, an uncertain series of lead Pacific systems will work
inland across the West, with upper troughing set to work over the
Northwest into midweek. This will highlight periods of terrain
enhanced rainfall from the Pacific Northwest to central California
and a heavy snow threat from the Cascades to the Sierra and inland
across favored terrain for the north-central Great Basin/Rockies
with cooling frontal passage. There is a trend in guidance that
ejecting energies may dig into the central to east-central U.S.
Wednesday-next Friday to carve out an amplified upper trough
slated to be sandwiched between amplifying upper ridges over the
West Coast and East Coast as the pattern transitions. Cyclogenesis
and frontogenesis would act to favor an emerging lead
rainfall/convective pattern over the east-central U.S. as thetae
advection increases. Backside cold air flow also suggests
potential for late next week snows over the Dakotas/Upper Midwest
as moisture feeds back around a developing main low. Please see
WPC links below for all the details.
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