SPC MD 1424


MD 1424 Image

Mesoscale Discussion 1424
NWS Storm Prediction Center Norman OK
0135 PM CDT Sat Aug 08 2020

Areas affected...northwest Kansas and central Nebraska

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 081835Z - 082030Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms are expected to develop and increase in
coverage and intensity this afternoon into the evening. Large hail
and damaging thunderstorm winds will be the primary threats. A
severe thunderstorm watch will likely be needed this afternoon.

DISCUSSION...Satellite imagery continues to show bubbling mid-level
cumulus/ACCAS across northwest Kansas and western Nebraska, with
episodic updrafts strengthening enough for lightning across
west-central Nebraska. Here, steep mid-level lapse rates
approaching, and locally exceeding, 9 C/km currently exist atop
surface dewpoints ranging from low 50s F across northwest Kansas to
near 70 F across central Nebraska. Surface temperatures currently
range from the mid 80s F to low 90s F. At the base of the steep
mid-level lapse rates, and above the boundary layer, a warm nose on
the order of 25 C exists, resulting in a strongly unstable
environment, with most-unstable CAPE ranging from near 3000 J/kg to
5000 J/kg, albeit a capped environment, with convective inhibition
on the order of 200-250 J/kg.  

Continued diurnal heating this afternoon will result in an
increasingly well-mixed boundary layer, allowing for temperatures to
warm into the 90s F to near 100 F across the area which will act to
weaken surface-based inhibition. An increase in mid-level cloudiness
across eastern Colorado depicted in recent satellite imagery
suggests western Kansas and Nebraska are immediately downstream of a
mid-level tough and associated ascent. As the mid-level ascent
overspreads the highlighted area, the combination of warming
low-level temperatures and the ascent/cooling of the warm nose
should weaken convective inhibition sufficiently to allow for
sustained thunderstorm updrafts. The most likely time for more
robust thunderstorm initiation will be in the 20-22Z time period.

Given the degree of instability and steep mid-level lapse rates,
coupled with increasing effective shear in excess of 30 knots,
thunderstorms will pose a large hail and damaging wind threat
initially. With time, increasing cold pool mergers and increasing
mid-level will support an increase in damaging wind potential as
thunderstorms increase in forward speed to the north and east.

A severe thunderstorm watch will likely be needed for portions of
the highlighted area early this afternoon.

..Marsh/Grams.. 08/08/2020

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


LAT...LON   42040167 42760058 42489883 40689921 39030159 42040167 

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