Mesoscale Discussion 1570

Issued

Aug 20, 2021, 7:06 PM CDT (00:06 UTC)

Expired

Aug 20, 2021, 8:30 PM CDT

In force

84 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 453

The Topeka radar (KTWX), 77 km from the middle of the area, began a volume at 00:07 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 454Aug 20, 7:40 PM CDT

742 
ACUS11 KWNS 210006
SWOMCD
SPC MCD 210006 
MOZ000-KSZ000-IAZ000-NEZ000-210130-

Mesoscale Discussion 1570
NWS Storm Prediction Center Norman OK
0706 PM CDT Fri Aug 20 2021

Areas affected...Central/Eastern Kansas...Eastern
Nebraska...Northwest Missouri...and Southwestern Iowa

Concerning...Severe Thunderstorm Watch 453...

Valid 210006Z - 210130Z

The severe weather threat for Severe Thunderstorm Watch 453
continues.

SUMMARY...The severe threat continues across WW 453. Damaging winds
may emerge as the primary threat as a transition to a linear
convective mode and upscale growth continues to occur.

DISCUSSION...Regional radar depicts a north-south oriented line of
severe thunderstorms that has developed along a southeastward moving
cold front, with the strongest cells located over portions of
southeast Nebraska and north-central Kansas. Damaging wind gusts of
50-60 mph and severe hail have occurred with this activity. This
trend is expected to continue in the short term, with damaging winds
likely being the primary threat. Warm/moist surface conditions ahead
of the front should help to maintain relatively steep low-level
lapse rates (7-8 C/km) and large instability (MLCAPE 3000-4000 J/kg)
for the next couple of hours, particularly across the southern
portion of the watch area.

Somewhat marginal deep-layer shear, which is mainly colocated or
lagging behind the front, and mid-level lapse rates near 6 C/km may
limit the potential for large hail, though severe hail will remain
possible where multicell modes can be sustained. However, the
transition to a more linear mode is already occurring and is
expected to continue as low-level jet onset helps promote upscale
growth and a transition to primarily a damaging wind threat.

Additional convective development may continue to occur across
central/south-central Kansas along the northern periphery of a more
deeply mixed boundary layer where surface dew point temperatures in
the low to mid 70s F exist. This trend will continue to be monitored
for the next few hours should an additional/downstream watch
issuance need to be considered.

..Karstens.. 08/21/2021

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

ATTN...WFO...EAX...OAX...TOP...ICT...GID...

LAT...LON   41009706 41399599 41129513 39909496 37939512 37559646
            37829771 38649816 40189756 41009706

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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.