Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Tue Dec 13 2022

Valid 12Z Tue Dec 13 2022 - 12Z Thu Dec 15 2022

...Major storm system continues to bring significant, widespread weather
hazards from flash flooding to blizzard conditions to the central U.S....

...Wintry precipitation will spread from the Upper Great Lakes Tuesday to
the Northeast Wednesday...

...Snow lingers in the Northern and Central Rockies as temperatures remain
cool across the West...

A deep, closed low over the West will progress slowly eastward over the
Plains through the period. A strong, embedded vort max ejecting over the
High Plains as upper-level heights continue to fall ahead of the
approaching closed low has led to a deepening surface cyclone in the lee
of the Rockies. This storm system will continue to produce numerous,
widespread, and impactful weather hazards from the Rockies to the East
Coast. Both flash flooding and severe weather will be a risk from the
Southern Plains east into the Lower Mississippi Valley and Southeast in
the warm sector of the system. Anomalously high moisture for December will
flow northward from the Gulf ahead of a cold front sweeping eastward.
Increasing shear and cooling air aloft will provide the necessary
ingredients for a line of intense convection to continue along the front
as thunderstorms, including supercells, develop ahead of the front. There
is a Slight Risk of Excessive Rainfall (level 2/4) centered on the Lower
Mississippi Valley Tuesday as a couple rounds of rainfall between the
initial supercells and convective line will produce rainfall totals
between 1-2 inches, with localized areas of 2-4+ inches leading to some
scattered instances of flash flooding. In addition, there is an Enhanced
Risk of severe weather (level 3/5) from the Storm Prediction Center for
east-central Texas through northern Louisiana into southwest Mississippi.
Sufficient CAPE combined with strong low-level and upper-level shear will
be present for any initial supercells ahead of the line as well as
embedded within the line to carry the risk for severe hail, winds, and
tornadoes, including the potential for a couple strong tornadoes. A
broader Slight Risk (level 2/5) is in place for eastern Texas, southern
Arkansas, Louisiana, and southwestern Mississippi. The threat will remain
similar while shifting eastward on Wednesday. There is a Slight Risk of
Excessive Rainfall from the Lower Mississippi Valley northeastward into
the Southeast, Tennessee Valley, and southern Appalachians. The tendency
for heavy downpours within an expanding area of convection to move
parallel to the northeast-southwest oriented front will prolong rainfall
duration and lead to widespread rainfall of 2+ inches, locally 4+, and the
potential for scattered instances of flash flooding. There is also an
Enhanced Risk of severe weather along the central Gulf Coast as storms
will continue to have the potential to produce severe hail, winds, and
tornadoes, including strong tornadoes.

Meanwhile, frigidly cold air will continue to surge southward on the
backside of the low as warm air aloft surges northward leading to
widespread wintry precipitation and heavy snow for portions of the
Northern and Central Plains and Upper Midwest. Snow accumulations through
Wednesday morning will generally range between 10-18 inches, centered on
the Northern High Plains. The highest snow totals are currently forecast
for western South Dakota, eastern Wyoming, and northwestern Nebraska,
where upwards of 24+ inches will possible. Gusty winds upwards of 40-50
mph will accompany a tightening pressure gradient tightens east of the
Rockies with the deepening surface cyclone, leading to widespread blizzard
conditions and significant travel impacts across the High Plains. Farther
east, accumulating sleet and ice are also expected for portions of the
eastern Dakotas into the Upper Midwest. The current risk for the greatest
ice accumulation is for northeastern South Dakota, southwestern Minnesota,
and northwestern Iowa where Ice Storm Warnings remain in effect through
Tuesday afternoon for totals between 3 to 4 tenths of an inch of ice and
the potential for isolated power outages. Additional accumulations over a
tenth of an inch remains possible for the eastern Dakotas, southern
Minnesota, and into central Wisconsin. Some locations in the Dakotas in
particular will likely see both accumulating ice and snow. Up to a quarter
inch of sleet may also fall in the aforementioned areas. Ice Storm
Warnings are in effect for parts of far northeastern South Dakota.
Temperatures will be in the teens and 20s for the Northern and Central
High Plains and drop from the 50s Tuesday into the 40s Wednesday for the
Central and Southern Plains .

The wintry precipitation will begin to spread eastward over the Upper
Great Lakes late Tuesday and Wednesday and into the Northeast late
Wednesday as the storm system continues eastward. Warm air flowing
northward ahead of the system will make the movement of the rain/snow line
hard to pin down over the Great Lakes, and subsequently how long snow will
fall and how high the totals may be. Currently, the most confidence for
higher snow totals is for northern Wisconsin and the Upper Peninsula of
Michigan where temperatures should remain colder closer to the track of
the surface cyclone and 4-8 inches, locally higher, will be possible. The
threat will expand into the Northeast and late Wednesday as snow begins
for portions of the Interior Northeast with freezing rain likely for the
central Appalachians. The witnry precipitation will continue into
Thursday, though initial acculuations upwards of a tenth of an inch look
possible late Wednesday night through early Thursday morning.

Temperatures immediately ahead of the system will trend 10-20 degrees
above average from the Plains to the Lower Great Lakes, Ohio and Tennessee
Valleys, and the Southeast as an upper-level ridge shifts eastward between
the closed low to the west and another to the northeast over the Canadian
Maritimes. Snow will continue in the west under the influence of the
upper-level trough, with some additional accumulations for the Northern
and Central Rockies. Temperatures will remain 10-20 degrees below average
for this time of year, with highs ranging from the 20s and 30s for the
Great Basin and Northern and Central Rockies, 40s for the Pacific
Northwest and Southern Rockies, and 50s for California and the Southwest.

Putnam

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php