Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
228 PM EST Wed Jan 01 2020
Valid 12Z Sat Jan 04 2020 - 12Z Wed Jan 08 2020
...Overview/Guidance Assessment...
Uncertainty regarding the track and intensity of a couple of low
pressure systems across the eastern U.S. will continue to be the
main concern during the medium-range period. Models generally agree
that the synpotic pattern across the U.S. will be dominated by a
progressive west-to-east flow with a couple of shortwave troughs
that could amplify into significant cyclones for the eastern half
of the country. The first of such cyclone should track across the
eastern U.S. this weekend. Model guidance has continued to slow
down the northeastward progression of this cyclone as a deeper
upper-level trough/cut-off low is being forecast over the Midwest
on Saturday with each successive model run. The ECMWF, being the
slowest piece of guidance, continues to slow down the forward
speed of the cyclone as of the 00Z run. Meanwhile, the faster and
more progressive GFS has successively slowed down the system
toward the ECMWF solution. Therefore, the WPC grids for the
weekend were based heavily on the 00Z ECMWF solution (70% 00Z
ECMWF vs. 30% 06Z GFS) together with some of their ensemble means.
The next upper trough of concern is forecast to reach the West
Coast on Sunday. Models generally agree that this feature will
track across the Rockies and then emerge into the Plains by next
Tuesday. However, the ECMWF and the GFS disagree with the
amplitude of the wave while it is still in the Pacific. The
deeper ECMWF solution eventually leads to the formation of quite
an intense cyclone for the eastern U.S. toward the middle of next
week. However, an accelerating trend is noted on the ECMWF track
for this potential storm. On the other hand, the faster GFS
hardly shows any development of this wave over the eastern U.S. at
all. Meanwhile, the 00Z ECMWF ensemble mean shows a faster motion
of the cyclone than its deterministic run. The WPC medium-range
grids used 30% ECMWF, 30% EC mean, 20% 06Z GEFS mean, and 20% 06Z
GFS to handle this system. This yielded a low pressure system
tracking eastward across the Great Lakes to the Northeast from
early to middle of next week.
...Weather Highlights/Threats...
Surface low moving through the eastern U.S. on day 3 will bring
mainly rain across the region ending with some wintry
precipitation from the lower Great Lakes into the Appalachians and
New England Saturday night into Sunday. Nearly daily bouts of
precipitation are likely for the Northwest into the Northern
Rockies during the period, focusing more over coastal locations
and the Coastal Range/Cascades. Depending on the evolution of the
trough/surface low development across the Central U.S. day 5-7,
some snow may be possible north and west of the low across parts
of the Ohio Valley to the Northeast toward end of the period.
Confidence remains low at this time regarding the specifics.
With a fast west-to-east flow across the country, no severe
outbreak of arctic air is anticipated. This will lead to
temperatures averaging near to slightly above normal with
relatively short periods of colder than normal temperatures behind
departing storms.
Kong
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 precipitation across portions of the Pacific Northwest and
the Northern Great Basin,
Sat-Sun, Jan 4-Jan 5and Mon-Tue, Jan 6-Jan 7.
- Flooding occurring or imminent across portions of the Northern
Plains.
- Flooding likely across portions of the Great Lakes.
- High winds across portions of the Central Rockies, the Central
Plains, the Northern Plains, and
the Northern Rockies, Sat-Sun, Jan 4-Jan 5.
- High winds across portions of the Southern Appalachians, the
Mid-Atlantic, the Central
Appalachians, and the Ohio Valley, Sun, Jan 5.
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