|Mesoscale Discussion 1356|
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Mesoscale Discussion 1356
NWS Storm Prediction Center Norman OK
0706 PM CDT Wed Jul 19 2017
Areas affected...Portions of southeastern SD...northern NE...and far
Concerning...Severe Thunderstorm Watch 422...
Valid 200006Z - 200130Z
The severe weather threat for Severe Thunderstorm Watch 422
SUMMARY...Ongoing isolated large hail and damaging wind threat
across WW 422 remains confined to mainly Holt County NE and vicinity
in the short term.
DISCUSSION...Recent radar and visible satellite imagery shows a
small thunderstorm cluster over Holt County NE which has produced
isolated large hail and damaging winds over the past hour or so. A
hot/moist low-level airmass persists along and south of a weak front
located across northern NE into southeastern SD this evening. Steep
mid-level lapse rates present on the 12Z sounding from North Platte
are located across WW 422, which is contributing to strong
instability (MLCAPE 2500+ J/kg). Although enhanced mid-level flow
remains mostly to the north of northern NE/southern SD, veering and
modest strengthening of the wind field with height is supporting
around 30-40 kt of 0-6 km shear per recent VWP from KLNX.
The primary thunderstorm cluster across Holt County NE has exhibited
occasional supercell characteristics, and should continue to pose an
isolated severe threat for the next few hours as it attempts to
propagate slowly east-southeastward as a southerly low-level jet
modestly strengthens this evening across central/eastern NE.
Additional convection is attempting to develop farther west along
the surface boundary in northern NE, and may also pose an isolated
severe threat this evening. The loss of diurnal heating, increasing
convective inhibition owing to a warm elevated mixed layer, and lack
of large-scale upper level support all suggest the isolated severe
risk should slowly diminish later this evening (generally after
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 42940204 42959947 43469947 43479591 42179589 42120197
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