Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Tue Nov 05 2019
Valid 12Z Fri Nov 08 2019 - 12Z Tue Nov 12 2019
...New England coastal storm and heavy snow threat Friday...
...Multiple cold air surges to winterize the central and eastern
U.S...
...Pattern Overview and Guidance/Predictability Assessment...
Guidance still depicts an amplified West Coast/Alaska ridge and
e-central U.S. trough upper pattern over medium range time scales
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.
This favors a composite guidance blend that is now more reasonable
as the models and ensembles are finally converging upon a more
common solution with respect to potentially deep storm development
off the Northeast U.S. by Day3/Fri and the Canadian Maritimes into
the weekend. The GFS/UKMET are now more in line with recent runs
of the ECMWF/CMC. The stormy solution has been best supported by
GEFS and especially ECMWF ensembles along with WPC continuity over
the past number of days.
By early next week, recent GFS/ECMWF runs and their ensembles
means further open the possibility for greater amplification/depth
of the next shortwaves set to dig into the long-term mean trough
over the east-central U.S. This seems to support coastal low
developments off the Eastern Seaboard. WPC progs show modest low
developments given uncertainty that are albeit close enough
offshore to effect coastal areas and maritime interests given how
far west/inland the main upper trough axis is dug.
...Weather Highlights/Threats...
To the west of the Rockies expect mainly warm and dry conditions.
One exception may be with some modest Pacific
moisture/precipitation that may work into the West Coast mean
upper ridge position into Pacific Northwest terrain.
The downstream pattern under a mean upper trough position laden
with embedded shortwave impulses favors periodic reinforcement of
colder than normal temperatures from the Rockies and Central U.S.
to the East as post-frontal surface high pressure centers track
south/southeast from Canada. A lead cold airmass will cross the
central/eastern states into Fri-Sat with fairly broad coverage of
highs 10-20F below normal and perhaps localized colder pockets
that could produce a few record values. Then by Sun-Tue the next
cold surge with highs 10-25F below normal will again envelop the
central and eastern U.S. and produce some more local record values.
Strong high pressure and sufficiently cold air behind the lead
front may bring potential for some wintry precipitation into
portions of the northeastern U.S. where amounts will be focused by
coastal/offshore low development by Fri. WPC Winter Weather
Outlook graphics depict the upward trending 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 digs southward.
Schichtel/Rausch
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