Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 PM EST Mon Nov 25 2019
Valid 12Z Thu Nov 28 2019 - 12Z Mon Dec 02 2019
...Increasing confidence in a major winter storm for the
Thanksgiving Holiday Period...
...Pattern overview and Guidance/Predictability Assessment...
A robust upper-level low over the California/Great basin region
will spin up a potent winter storm that will spread rain and snow
from southern California across the Southwest, Southern/Central
Rockies, Plains and into the Great Lakes, Ohio Valley and
Mid-Atlantic region by through the course of the extended
forecast. Numerous shortwaves will round the base of the western
trough into the Central Plains Friday and Saturday as the surface
low pressure system tracks northeast over the Rockies. A strong
upper-level jet will increase the divergence aloft while enhancing
the orographic lift, which will aid in the development of higher
rain and snow amounts across this region. Additionally, tight
pressure gradients with this system along with the initial intense
pressure/height falls will result in very strong winds over much
of the Southwest U.S.
The ECWMF, GFS and their mean have been persistent in the
evolution of this feature, at least through the weekend (day 6)-
beyond that there are noticeable timing and location differences
for QPF across the Great Lakes and East Coast. As such, a blend
comprising of these solutions made up a majority of the forecast.
The CMC and UKMET continued to be slower with the progression of
the low lifting out of the Great Basin/Four Corners region and it
had the QPF shifted west of the rest of the guidance.
...Weather Highlights/Threats...
Heavy mountain snows are likely across parts of the Central Great
Basin, Desert Southwest and Rockies through Friday, with snow
levels expected to drop significantly. Additionally, another round
of heavy rainfall with a threat for runoff problems is likely
across Southern California and the Southwest (including burn
scars) Friday. As the surface low moves out into the Plains, a
swath of heavy to potentially significant accumulating snowfall is
possible to the north and west of the low from the Northern Plains
to the Upper Mississippi Valley and Upper Great Lakes Friday and
Saturday. Depending on surface low intensity, a period of strong
winds could accompany this system cause blowing and drifting snow.
These conditions would make for hazardous travel across this
region, especially with increased Holiday traffic. Across the
South, shortwave energies tapping into mid-upper level moisture
from the tropical East-Pacific will result in heavy to possibly
excessive rains shifting from the Southern Plains to the Ohio
Valley along and ahead of the main cold front.
Much of the Western states will have much below normal
temperatures, with some locations as low as 20 to 25 degrees below
seasonal average. For the Gulf region, temperatures will be warm
and above average, spreading northward into the Ohio Valley Friday
and Saturday. Once the front passes through the central U.S. the
temperatures will moderate and trend cooler.
Campbell
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 Central Great Basin
and California, Sun-Mon, Dec 1-Dec
2.
- Heavy rain across portions of the Central Plains, the Lower
Mississippi Valley, the Central Great
Basin, the Tennessee Valley, the Middle Mississippi Valley,
California, the Southern Plains, the
Ohio Valley, and the Southwest, Thu-Fri, Nov 28-Nov 29.
- Heavy rain across portions of the Lower Mississippi Valley, the
Central Appalachians, the
Tennessee Valley, the Middle Mississippi Valley, the Southern
Appalachians, the Great Lakes, and
the Ohio Valley, Sat-Sun, Nov 30-Dec 1.
- Heavy snow across portions of the Central Plains, the Central
Rockies, the Central Great Basin,
the Northern Plains, the Northern Rockies, the Southern Rockies,
the Northern Great Basin, the
Southern Plains, and the Southwest, Thu-Sat, Nov 28-Nov 30.
- Heavy snow across portions of the Central Plains, the Great
Lakes, the Upper Mississippi Valley,
and the Northern Plains, Fri-Sun, Nov 29-Dec 1.
- Heavy snow across portions of the Northeast and the Great Lakes,
Sun-Mon, Dec 1-Dec 2.
- Severe weather across portions of the Central Plains
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