Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
326 PM EST Fri Nov 22 2019
Valid 12Z Mon Nov 25 2019 - 12Z Fri Nov 29 2019
The medium range period will begin with a low pressure
system/nor'easter exiting New England. Meanwhile, models are in
excellent agreement on the steady deepening of a broad scale
upper-level trough across the western U.S. as a cold front pushes
through the region Monday and Tuesday. A shortwave within the
broad upper trough is forecast to exit the central Rockies into
the central Plains where a low pressure system is likely to form
on Tuesday. The biggest forecast concerns continue to be the
run-to-run variability shown on the model forecast track for this
system. There has been an eastward shift of the model consensus
track for the past few deterministic runs. On the other hand, the
ensemble mean solutions show a track that is west of the general
deterministic consensus track. A blend of the 06Z GFS/GEFS with
the 00Z ECMWF/EC mean yielded a track slightly to the west of the
previous WPC forecast package. This basically takes the storm
center quickly across the Midwest Tuesday evening and then across
the central Great Lakes early on Tuesday.
The next area of concern will be along the West Coast as models
are showing a large-scale upper-level trough getting firmly
established by the middle of next week and then linger in the
vicinity into late next week. Models are showing a definite trend
for lowering heights to dig deeper into the Desert South for the
past couple of days. In response to this huge upper trough, a
high amplitude ridge is now indicated through the Great Plains
toward the end of next week. This appears to signal a major
synoptic pattern change for much of the U.S. by late next week.
The WPC morning grid package used a blend of about 60% 00Z EC mean
with about 40% 06Z GEFS mean for Days 6 and 7, mixing in with a
small percentage of their deterministic solutions to handle the
system. This agrees fairly well with continuity but with a
slightly deeper surface low near the California coast.
Despite the run-to-run variability on the forecast track of the
developing surface low in the central U.S., it appears that a
swath of wintry precipitation will be on the back side of this
system from the central Plains to the Upper Midwest/Great Lakes,
with snow possible on the northern edge of the precipitation
shield. As the surface low lifts into the Northeast on Wednesday,
some wintry precipitation is possible across northern/interior New
England. Depending on surface low intensity, a period of high
winds may also accompany this system. Rainfall will also be likely
along the trailing cold front as it moves from the lower
Mississippi Valley to the the Southeast Tuesday-Wednesday.
Across the West, heavy snowfall is likely in the higher terrain of
the Washington/Oregon Cascades, the Sierra Nevada range, and
eastward across the Great Basin/Rockies both with the initial
shortwave crossing the region Monday, and even more so with the
amplified troughing developing over the region by late in the
week. Another round of potentially heavy rainfall is possible
across the Southwest by mid to late next week, with rainfall also
developing by Friday eastward into the Southern Plains/Mid-Lower
Mississippi Valley ahead of the upper trough. Colder temperatures
across the West will also accompany this system, with daytime
highs averaging 10 to 20 degrees below normal across the Great
Basin and Northern Rockies.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
- Heavy precipitation across portions of the Central Great Basin,
California, and the Southwest,
Wed-Fri, Nov 27-Nov 29.
- Heavy precipitation across portions of the Great Lakes and the
Upper Mississippi Valley, Tue-Wed,
Nov 26-Nov 27.
- Heavy rain across portions of California and the Southwest,
Wed-Fri, Nov 27-Nov 29.
- Heavy snow across portions of the Central Great Basin,
California, and the Southwest, Tue-Fri,
Nov 26-Nov 29.
- Heavy snow across portions of the Southern Rockies, the Central
Rockies, the Central Great Basin,
and the Southwest, Wed-Fri, Nov 27-Nov 29.
- Flooding occurring or imminent across portions of the Northern
- Much below normal temperatures across portions of the
Northern/Central Great Basin, the Northern
Rockies, California, and the Pacific Northwest, Thu-Fri, Nov
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: