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ACUS11 KWNS 151829
SWOMCD
SPC MCD 151828=20
IAZ000-MOZ000-MNZ000-KSZ000-NEZ000-SDZ000-152030-

Mesoscale Discussion 2027
NWS Storm Prediction Center Norman OK
1228 PM CST Wed Dec 15 2021

Areas affected...Portions of eastern NE...northeastern KS...northern MO...western/central IA...far southeastern SD...and southern MN

Concerning...Severe potential...Tornado Watch likely=20

Valid 151828Z - 152030Z

Probability of Watch Issuance...95 percent

SUMMARY...Storms are expected to develop and rapidly intensify as
they race northeastward this afternoon. Widespread severe winds of
60-75 mph are likely, with gusts to 80-100 mph possible. A few
tornadoes, including the potential for a strong tornado or two, may
also occur. Tornado Watch issuance is likely by 2 PM CDT.

DISCUSSION...A compact and intense shortwave trough evident on water
vapor satellite imagery over the central High Plains will eject
quickly northeastward across KS/NE this afternoon, reaching the
upper MS Valley by this evening. A strong low-level mass response is
occurring ahead of this feature, with surface pressure falls
generally ranging from 3 to 5.5 mb per 2 hours based on latest
observations across western/central KS/NE. Meanwhile, over eastern
KS/NE into much of MO/IA, low-level moisture continues to rapidly
advect northward in tandem with a pronounced, 50+ kt
south-southwesterly low-level jet. Surface dewpoints have generally
increased into the mid 50s to low 60s across this region. As the
pronounced large-scale ascent associated with the shortwave trough
overspreads the warm sector, the sharp low-level inversion noted on
the 18Z sounding from TOP will quickly erode.

Based on linear extrapolation of the band of clouds/showers
attendant to the lift with the approaching shortwave trough
currently over western KS, convective initiation across parts of central/eastern NE and adjacent northern KS to the east of a surface
dryline appears increasingly likely by 20-21Z (2-3 PM CST). These
storms are forecast to rapidly strengthen and race northeastward as
they encounter at least a weakly unstable airmass and greater
low-level moisture with eastward extent over KS/NE. MLCAPE generally
ranging from 500-1000 J/kg will be more than sufficient to support surface-based convection.

Very strong flow at both low and mid-levels is expected to
overspread the warm sector as the shortwave trough ejects
northeastward through this evening. The potential for widespread
severe wind of 60-75 mph appears likely, with stronger gusts up to
80-100 mph possible, as these anomalously strong winds aloft reach
the surface through mixing and convective downdraft processes. With
the deep-layer shear vectors oriented at least partially orthogonal
to the surface boundary, some potential for supercells may exist.
Given the strength of the low-level shear, a few tornadoes appear
likely, and a strong tornado or two may also occur. Otherwise, a
broken band of low-topped storms will likely develop as convection
shifts into western/central I, southern MN, and vicinity later this
afternoon and early evening, with a continued widespread
severe/damaging wind threat and potential for a few tornadoes. The
rapidly increasing severe risk across this region will warrant
Tornado Watch issuance by 20Z (2 PM CST).

..Gleason/Thompson.. 12/15/2021

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!u18LLHiyJVVbk5vHFEOiNhxngwIEIS3qJuoVWgLg6k8Sma8BX0k6YBVOFs3n5sG41_qvvB9G$=
for graphic product...

ATTN...WFO...MPX...DMX...EAX...FSD...OAX...TOP...GID...

LAT...LON 39599797 40069834 41089875 41759827 43519643 44139571
44269506 44289418 44179307 42909303 42249237 40769248
40339286 39609504 39569735 39599797=20



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