Mesoscale Discussion 2027

Issued

Dec 15, 2021, 12:28 PM CST (18:28 UTC)

Expired

Dec 15, 2021, 2:30 PM CST

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...tornado watch likely

Chance of a watch

95%

The Omaha radar (KOAX), 82 km from the middle of the area, began a volume at 18:32 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Tornado Watch 563Dec 15, 1:20 PM CST
• Severe Thunderstorm Watch 564Dec 15, 3:20 PM CST

054 
ACUS11 KWNS 151829
SWOMCD
SPC MCD 151828 
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 

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 www.spc.noaa.gov 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

Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Nebraska, 2021Mesoscale Discussions in Minnesota, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.