Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
440 PM EST Wed Feb 10 2021
Valid 12Z Sat Feb 13 2021 - 12Z Wed Feb 17 2021
...Arctic air forecast to set multiple cold temperature records
this weekend across the Plains and MS Valley but should gradually
moderate by early to middle of next week...
...Stormy pattern with multiple winter precipitation events...
Models and ensembles are in general agreement that a large dome of
arctic air will surge south across central U.S. into the weekend
as the center of a polar vortex slides eastward across the Great
Lakes. Models have continued to make further adjustments to
important shortwave energies that rotate around the vortex. Both
the 06z GFS and 12z Tue/00z Wed ECMWF models have come into better
agreement with each other as shortwave energy emerges from the
southern Rockies onto the southern Plains on Sunday, resulting in
an area of likely snow in northwest Texas across central to
western OK and KS. As this system ejects to the northeast on Mon
15 Feb., the area of heavy snow northwest of low extends across
mid MS Valley to the Great Lakes. Further southeast, significant
mixed sleet and freezing rain area expected from the lower MS
Valley to the TN Valley, central Appalachians, and Piedmont of
NC/VA/Mid Atlantic. On Tue 16 Feb, the parent low moves across the
Great Lakes into Canada, with cold advection producing lake effect
snow in MI and northwest PA/western NY. The low weakens, but not
before producing a round of snow in northern NY/northern New
England with potential for a change over to sleet/freezing
rain/rain in southern New England/southeast New York before the
system departs.
Widespread moderate rain is expected further south in the
southeast to the coastal mid Atlantic states.
Confluent flow in the west results in a series of progressive 700
mb waves that produce rounds of snow in the terrain, starting on
Day 4 Sat/early Sun from the WA/OR Cascades into the ranges of
northern CA and northern Great Basin. On Day 5, the first wave
crosses NM/southern CO, bringing snow to the mountains there
before the wave exits on the Plains. The next Pacific northwest
disturbances brings snow back to the WA/OR Cascades. On Monday
the water vapor transport onshore and inland combines with a wave
to produce snow starting with the WA/OR Cascades and continuing to
the ranges of ID to western WY and northern UT. On Tuesday 16 Feb,
the mid-upper level northwest flow brings moisture and
light-moderate snows from the northern to central Rockies and
Great Basin.
With the arctic high pressure system in the Plains, many cold
temperature records will be likely down the Plains and into the
lower to mid MS Valley this weekend to early next week. Record
lows/low maxima should be most numerous on Sunday before the
airmass gradually moderates next week.
The WPC medium-range forecast package was derived from a blend of
the 12Z-00z ECMWF/00z EC Ensemble mean, and the 06Z GFS/GEFS Mean.
The large scale pattern looks similar across most models/ensembles
with a reamplifying 500 mb ridge off the west coast and persistent
central US upper trough, and ridge off the southeast coast.
The 00z Canadian deamplified the ridge off the west coast and
became a progressive outlier with systems across the country, so
was not included in the blend.
Petersen/Kong
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy precipitation across portions of the Lower Mississippi
Valley, the Central/Southern
Appalachians, the Tennessee Valley, the Mid-Atlantic, the
Southeast, the Southern Plains, and the
Ohio Valley, Mon-Tue, Feb 15-Feb 16.
- Heavy precipitation across portions of the Mid-Atlantic and the
Northeast, Tue-Wed, Feb 16-Feb 17.
- Heavy rain across portions of California and the Pacific
Northwest, Sat, Feb 13 and Mon, Feb 15.
- Heavy rain across portions of the Southeast and the
Mid-Atlantic, Sat, Feb 13.
- Heavy snow across portions of California, the Pacific Northwest,
and the Northern Great Basin,
Sat-Tue, Feb 13-Feb 16.
- Heavy snow across portions of the Central/Southern Plains, the
Central/Southern Rockies, the
Central Great Basin, the Pacific Northwest, and the Southwest,
Sun, Feb 14.
- Heavy snow across portions of the Central Plains, the Rockies,
the Central Great Basin,
California, the Northern Great Basin, and the Southwest, Sat, Feb
13.
- Heavy snow across portions of the Central/Southern Plains, the
Middle/Lower Mississippi Valley,
the Tennessee Valley, the Great Lakes, and the Ohio Valley, Mon,
Feb 15.
- Heavy snow across portions of the Great Lakes, the Mid-Atlantic,
the Northeast, the Central
Appalachians, and the Ohio Valley, Tue-Wed, Feb 16-Feb 17.
- Much below normal temperatures across portions of the Pacific
Northwest, the Northern Rockies,
and the Northern Great Basin, Sat-Sun, Feb 13-Feb 14.
- Much below normal temperatures across portions of the Plains,
the Mississippi Valley, the
Central/Southern Appalachians, the Tennessee Valley, the Great
Lakes, the Northern/Central
Rockies, the Southeast, and the Ohio Valley, Sat-Tue, Feb 13-Feb
16.
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