Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1059 AM EST Mon Nov 04 2019
Valid 12Z Thu Nov 07 2019 - 12Z Mon Nov 11 2019
...Pattern Overview and Guidance/Predictability Assessment...
Latest guidance continues to show an amplified West Coast/Alaska
ridge and east-central U.S. trough pattern that tends to have
above average predictability for the large scale flow. However
there are lower-confidence embedded details that will be important
for resolving sensible weather effects over some areas.
One significant difference involves potential surface development
off the Northeast U.S. around day 4 Fri. Specifics of this
feature are closely tied to the evolution/timing of a shortwave
crossing the Upper Midwest/Great Lakes/Northeast Thu-Fri.
Multiple ECMWF/CMC runs have depicted this system and the past 2-3
ECMWF mean runs capture it as well. Meanwhile the 00Z UKMET and
GFS/GEFS mean are much farther east but the 06Z GFS/GEFS mean have
adjusted westward closer to the ECMWF/CMC cluster. Overall
preference follows a compromise among the past two ECMWF runs/00Z
CMC with minority input from the 06Z GEFS/00Z ECMWF means. This
maintains WPC continuity in representing a seemingly more
plausible scenario given upstream ridge amplitude and
baroclinic/dynamic environment to support development. Also
teleconnections relative to the multi-day means' negative height
anomaly center approximately between the Great Lakes and James Bay
support increased precipitation potential over the Northeast.
Short wavelength spacing and a distant Arctic/Alaska source region
of the energy aloft--which tend to lower predictability--still
keep confidence in specifics lower than desired.
As for other issues, along the front that trails the above system
the 00Z GFS becomes one of the more extreme western solutions for
a wave off the southeastern coast by early day 5 Sat. This is due
to a sharper shortwave aloft versus most other guidance. The 06Z
GFS has trended eastward to agree better with remaining
models/ensemble majority. By the latter half of the period there
is a notable trend in the GFS/ECMWF and their means toward greater
amplification/depth of the next shortwave digging into the
long-term mean trough. This leads to faster progression of the
next cold surge forecast to push into the central U.S. Also of
note, the 00Z CMC and to some degree CMC mean erode the western
ridge more than other solutions. This favors tilting the forecast
toward the latest ECMWF/GFS runs and their means by days 6-7
Sun-Mon.
...Weather Highlights/Threats...
To the west of the Rockies expect warm and mainly dry conditions.
The one exception may be with a little Pacific moisture that could
reach the northern Pacific Northwest terrain. Most locations will
likely see highs 5-15F above normal through the period.
The downstream pattern will favor periodic reinforcement of colder
than normal temperatures from the Rockies and Central U.S. to the
East as post-frontal high pressure centers track south/southeast
from Canada. One cold airmass will cross the central/eastern
states Thu-Sat with fairly broad coverage of highs 10-20F below
normal and perhaps localized pockets colder than that, mainly on
Thu-Fri. Then by Sun-Mon the next cold surge with highs 10-25F
below normal should reach the central U.S. and begin to push
eastward.
One area of focused moisture will be along the front reaching into
the South/East on Thu. Strong high pressure and sufficiently cold
air behind the front may bring potential for some wintry
precipitation into portions of the northeastern U.S. where amounts
will be very sensitive to possible coastal/offshore low
development by Fri. WPC Winter Weather Outlook graphics depict
the probabilistic aspect of the forecast. Elsewhere, clipper
systems and trailing cold cyclonic flow will bring periods of
precipitation (mostly snow) to the Great Lakes/Northeast with
activity prolonged by lake effect. Locations along the eastern
slopes of the northern-central Rockies may see a period of snow as
a front settles nearby. Any snow between these two areas should
be fairly light and brief.
Rausch/Schichtel
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards 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