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ACUS11 KWNS 222013
SPC MCD 222013

Mesoscale Discussion 1397
NWS Storm Prediction Center Norman OK
0313 PM CDT Sat Jul 22 2017

Areas affected...Portions of northern Kansas into northwest Missouri

Concerning...Severe potential...Watch unlikely

Valid 222013Z - 222245Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated severe thunderstorm development may occur around
the 21Z-22Z time frame in parts of northern Kansas, with activity
developing eastward -- toward and across the lower Missouri Valley
vicinity -- into the evening. Present indications are that Watch
issuance is unlikely.

DISCUSSION...Baroclinic circulations along a west-east frontal
zone -- stretching from southwest of the Hill City KS area to north
of Topeka KS to south of Kirksville MO -- are being amplified in the
vicinity of north-central KS. This is in response to the strongest
surface heating and resultant diurnally enhanced boundary-layer
circulations, while a precipitation-reinforced boundary is enhancing
mesoscale convergence between Hill City and Colby KS. A band of
boundary-layer cumulus congestus is already become agitated within
an arc from this focused zone of stronger convergence into
north-central KS. Continued erosion of antecedent capping owing to
surface temperatures nearing/breaching 100F may permit thunderstorm
formation within a couple of hours, with subsequent convective
development occurring eastward toward the Kansas River Valley
vicinity into the late afternoon, with activity spreading/developing
into the lower Missouri Valley vicinity into the evening hours.

Steep tropospheric lapse rates supporting a strongly buoyant air
mass on either side of the front should support vigorous updrafts.
Isolated severe hail could occur -- especially during incipient
updraft phases. However, effective shear around 20-25 kt suggests
limited potential for sustained, rotating updrafts -- limiting
severe-hail coverage and magnitude. Sizable surface dewpoint
depressions -- on the order of 20-25F -- suggest that evaporative
cooling will enhance strong convective downdrafts aided by DCAPE of
1700-2000 J/kg. Strong convective outflow could produce isolated
severe wind gusts, especially if smaller-scale convective
clustering/upscale growth were to develop eastward toward the lower
Missouri Valley region into the evening hours. However, the lack of
stronger vertical shear and forcing for ascent cast considerable
doubt on prospects for a larger/more organized convective system to

..Cohen/Grams.. 07/22/2017

...Please see for graphic product...


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