Mesoscale Discussion 1721

Issued

Oct 21, 2017, 1:23 PM CDT (18:23 UTC)

Expired

Oct 21, 2017, 4:00 PM CDT

In force

3 hr

Issued by

the Storm Prediction Center

Chance of a watch

95%

The Topeka radar (KTWX), 13 km from the middle of the area, began a volume at 18:22 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.

• Severe Thunderstorm Watch 502Oct 21, 2:25 PM CDT

663 
ACUS11 KWNS 211823
SWOMCD
SPC MCD 211823 
MOZ000-IAZ000-KSZ000-NEZ000-212100-

Mesoscale Discussion 1721
NWS Storm Prediction Center Norman OK
0123 PM CDT Sat Oct 21 2017

Areas affected...eastern Kansas...far southeast Nebraska...far
southwest Iowa and northwest Missouri

Concerning...Severe potential...Watch likely 

Valid 211823Z - 212100Z

Probability of Watch Issuance...95 percent

SUMMARY...Thunderstorms are expected to develop along the
east-southeastward progressing cold front across eastern Kansas
later this afternoon. Once initiation occurs, storms will quickly
intensify with damaging wind gusts, hail and a tornado or two
possible into the evening hours. A watch will likely be needed by
20-21z.

DISCUSSION...Breaks in low level clouds have allowed temperatures to
warm into the mid to upper 70s across much of eastern KS early this
afternoon. With dewpoints in the low and mid 60s, MLCAPE values have
increased to 1500-2000 J/kg. The VAD wind profile from the DDC radar
also has shown a slight increase in midlevel winds over the last 30
minutes or so, suggesting the shortwave impulse over northeast NM is
beginning to eject east/northeast into the Plains. Furthermore,
cumulus along the front from far northwest OK into central/eastern
KS and southeast NE is becoming increasingly congested with some
vertical growth evident. In conjunction with hi-res HRRR guidance,
this suggests convective initiation should occur within the next
couple of hours.

Steep midlevel lapse rates and effective shear in excess of 35 kt
will aid in storms quickly becoming severe with at least a brief
window of opportunity for semi-discrete cells. However, the quickly
progressing cold front and front-parallel deep-shear vectors will
result in rather fast upscale growth. Any cells that can stay
semi-discrete will pose a threat for large hail and damaging wind.
Once upscale growth occurs, a transition to mainly a damaging wind
threat is expected. While forecast low-level hodographs are
unimpressive, they are adequate for low-end tornado potential and a
tornado or two can not be ruled out either in an isolated cell or
within embedded mesovorticies along the leading edge of the squall
line. A watch will likely be needed between 20-21z.

..Leitman/Thompson.. 10/21/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...SGF...DMX...EAX...OAX...TOP...ICT...

LAT...LON   37799510 37369554 37069617 37049691 37009757 37059809
            37249826 37629815 37879805 38379762 39069719 39599690
            40569669 41019645 41289596 41299538 41179467 40929423
            40579408 40009408 38909433 38309470 37799510

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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.