Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
339 PM 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 across the central and eastern U.S...
...Pattern Overview and Guidance/Predictability Assessment...
The synoptic pattern at the beginning of the medium range period
(12Z Friday) is expected to be amplified featuring western
U.S./Alaska ridge and downstream troughing over the
central/eastern CONUS. Overall, forecast confidence in the large
scale pattern is above average; however, confidence in details,
particularly across the Northeast U.S. with respect to a coastal
storm and its sensible weather impacts are lower. The GFS
continues to be the more progressive/faster solution, with its
surface low more offshore while the ECMWF offers a trough axis
that is centered more over the eastern Great Lakes, allowing the
low to track further to the coast. For this cycle, the WPC
preference was mostly a blend of the deterministic GFS and ECMWF
with inclusion of the GEFS/ECENS means for Day 3-4.
Beyond that time frame, there is increasing signal for further
amplification of the large scale pattern over the CONUS with a
fairly anomalous trough developing over the east-central U.S. by
early next week (and ridging remaining in place over the western
U.S.). For these periods, a GEFS/ECENS blend was favored; however,
teleconnections suggest ridging is likely to be more pronounced
than what the ECENS mean suggests, so there was a higher weight of
the GEFS mean incorporated by Day 6-7. The most recent surface
progs show potential low development offshore the East Coast,
although there is considerable uncertainty in its proximity to the
coast and potential impacts.
...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/Taylor
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
Hazards:
- Heavy snow across interior northern New England, Fri, Nov 8.
- Heavy precipitation across coastal northern New England, Fri,
Nov 8 and Tue, Nov 12.
- Heavy snow across portions of the central Great Lakes, Tue, Nov
12.
- Heavy rain across portions of the southern Plains, Tue, Nov 12.
- Much below normal temperatures across much of the eastern
two-thirds of the U.S., Fri-Tue, Nov
8-Nov 12.
- Much below normal temperatures across portions of the Southeast,
the lower Mississippi Valley,
and the southern Plains, Fri-Sat, Nov 8-Nov 9.
- Much below normal temperatures across portions of the northern
and central Plains, and into the
northern Rockies, Sun-Tue, Nov 10-Nov 12.
- Much below normal temperatures across portions of the Northeast,
Mon-Tue, Nov 11-Nov 12.
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