000
ACUS01 KWNS 191254
SWODY1
SPC AC 191252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Tue Sep 19 2017

Valid 191300Z - 201200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EASTERN DAKOTAS
AND WESTERN MN...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE UPPER
MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE
UPPER MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS WEST TX TO
SOUTHWEST OK...

...SUMMARY...
Some tornadoes and numerous severe hail and wind events, a few of
which should be significant, are expected across parts of the
eastern Dakotas into western Minnesota from about 4 pm to 4 am CDT.

...Synopsis...
A vigorous shortwave impulse embedded within the broader longwave
trough over the Northwest will eject east and reach the Dakotas by
early Wednesday. An associated jet will intensify with 500-mb
southwesterlies approaching 100 kt overnight. Primary surface
cyclone over the northern High Plains will move north into the
southern Prairie Provinces, while an attendant cold front sweeps
east of the central Dakotas by late afternoon and into
western/central Minnesota overnight. A warm front to the
east-southeast of the cyclone should stall from north-central ND to
northwest MN.

...Upper Midwest...
Increasing low-level moisture is underway beneath an EML from the
Coteau des Prairies south across the Lower Missouri Valley. A plume
of middle 60s surface dew points should become established from the
Red River Valley south by this evening. Amid very steep 700-500 mb
lapse rates around 8 C/km as sampled by 12Z Bismarck and Rapid City
soundings, MLCAPE of 1500-2500 J/kg will become common from eastern
SD south with lesser buoyancy to the north and east.

Initial surface-based storm development is expected by late
afternoon near the more narrow portion of the warm sector in
central/eastern ND and north-central/northeast SD. Additional storm
development should occur during the evening farther south as
large-scale ascent overcomes MLCIN. Strengthening wind profiles
yielding increasingly elongated and enlarging hodographs will
strongly favor supercells. While broken bands of storms may evolve
with all hazards possible, at least a few tornadoes are likely with
a couple long-track supercells possible across parts of
northeast/east-central SD on the southern periphery of storm
development which should have the longest available window for
inflow of richer boundary-layer moisture.

Forcing along the cold front is progged to strengthen late evening
and this should foster an increasingly linear mode as activity moves
east toward and into MN. While instability will be weaker to the
north and east, intensifying kinematic profiles may compensate and
yield a continued severe risk into early morning, likely dominated
by strong to severe wind gusts, before storms wane late in the
period.

...West TX to southwest OK...
The dryline will be the focus for isolated to scattered storm
development late afternoon to early evening. Steep 700-500 mb lapse
rates of 7-8 C/km will support moderate buoyancy with MLCAPE
reaching 1500-2500 J/kg. While mid-level winds will be modest,
veering of the wind profile with height should yield 25-30 kt
effective shear, supporting a few transient supercell and multicell
clusters. Isolated occurrences of large hail and damaging winds are
possible before storms wane after sunset.

..Grams/Kerr.. 09/19/2017

$$