Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Wed Nov 27 2019
Valid 12Z Sat Nov 30 2019 - 12Z Wed Dec 04 2019
...Major Winter Storm will track from the Northern Plains to the
Northeast Saturday through Monday...
...Pattern overview and Guidance/Predictability Assessment...
The medium range period (later Saturday through Wednesday) begins
with a developed low over the north-central low pressure system as
the low over The West shifts east, merging into the shortwave
through that had been wrapping around and tracking through the
Desert SW. This newly developed phase of this major winter storm
then shifts east across the southern Great lakes through Sunday.
Additional southern stream shortwave energy rounding the base of
this cold core upper low allows for a new surface low to form off
the northern Mid-Atlantic coast Sunday night which then tracks up
the New England Coast through Monday. A notable difference in the
latest guidance with the low track on Day 3/Saturday. The GFS
continues to bring the system farther northwest, well into South
Dakota while the consensus low is closer to the South
Dakota/Nebraska border at 12Z Saturday. The cause of this track
difference in the GFS appears to be a combination of a stronger
shortwave coming in from the Southwest that is a bit ahead of the
consensus and allows a track farther to the northwest. This low
position has notable implications for where the warm sector
develops and thus precipitation type. As a note on this low track,
the swath of snow across the central Plains to Lake Superior may
affect the low level temperature gradient and thus the exact track
of the low, though probably more Saturday night as the low moves
over IA. WPC pressures/fronts/temperatures/precipitation did
incorporate the 06Z GFS in a blend with the 00Z ECMWF/UKMET/CMC
through Day 5. There are further uncertainties with the exit of
the low off New England on Day 6 with the GFS now closer to the
New England coast on Tuesday. Therefore ensemble means were
heavily weighed on Days 6/7, leaning toward the 00Z ECENS.
The next low approaches The West Coast Saturday and wobbles nearer
and farther from the coast as it drifts south to a point off
southern California by the middle of next week. The ECMWF
continues to have decent run-to-run continuity with this system
while the 06Z GFS resembles the 00Z ECMWF enough to warrant those
models being the focus of a model blend for that region.
...Weather Highlights/Threats...
A major winter storm with widespread hazardous weather is expected
for parts of the Central and Eastern U.S. over the Thanksgiving
holiday weekend through Monday. To the north and west of the
surface low, heavy and significant accumulating snow is likely
from the Dakotas to the Upper Great Lakes Saturday into Sunday.
Precipitation then focuses to the developing coastal low Sunday
night through Monday with the risk for accumulating currently
farther inland over New England. High winds will also accompany
this storm, making for difficult and hazardous travel across much
of the region. To the south, locally heavy rainfall is possible
along the attendant cold front as it shifts eastward across the
Deep South/Ohio Valley/Mid-Atlantic states this weekend. Severe
thunderstorms are also possible across the Lower Mississippi
Valley on Saturday as indicated by the latest Day 4 SPC severe
outlook.
Another round of heavy precipitation affects California mainly
Saturday night through Monday as the offshore low brings onshore
flow. Expect mountain snows in northern and central California,
with rain in the lower elevations. As of now a wobble back toward
the southern California coast Tuesday night into Wednesday would
bring rain and high elevation snow to southern California.
Temperatures remain cold across The West through Sunday with
daytime highs 10 to 25 degrees below normal over much of the Great
Basin, Rockies into the High Plains. This shifts to the eastern
states Monday with high temperatures generally 10 to 15 degrees
below normal which replaces weekend above normal temperatures
(generally 10 to 20 degrees above normal over the central CONUS on
Saturday). Anomalies moderate through the midweek as ridging
develops over the west-central CONUS.
Jackson
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 rain across portions of California, Sat-Mon, Nov 30-Dec 2.
- Heavy snow across portions of the Central Great Basin,
California, and the Southwest, Sat-Mon,
Nov 30-Dec 2.
- Heavy snow for parts of the Central Plains, the Great Lakes, the
Upper Mississippi Valley, and
the Northern Plains, Sat, Nov 30.
- Heavy snow across portions of the Great Lakes, the Mid-Atlantic,
the Northeast, the Central
Appalachians, and the Upper Mississippi Valley, Sun-Mon, Dec 1-Dec
2.
- Severe weather for parts of the Southeast, the Lower Mississippi
Valley, the Southern Plains, and
Tennessee Valley, Sat, Nov 30.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Flooding likely across portions of the Northern Plains.
- High winds across portions of the Plains, the Central and
Southern Rockies, the Central Great
Basin, the Great Lakes, the Mississippi Valley, the Ohio Valley,
and the Southwest, Sat-Sun, Nov
30-Dec 1.
- Much below normal temperatures across portions of the Central
Great Basin, the Northern Rockies,
California, the Northern Great Basin, the Pacific Northwest, and
the Southwest, Sat-Sun, Nov 30-Dec
1.
- High significant wave heights for coastal portions of the Great
Lakes and the Upper Mississippi
Valley, Sat-Sun, Nov 30-Dec 1.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Tue, Dec
1-Dec 3.
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