Mesoscale Discussion 1496
NWS Storm Prediction Center Norman OK
0536 PM CDT Mon Aug 14 2017
Areas affected...The Black Hills and surrounding northern high
Plains
Concerning...Severe potential...Watch unlikely
Valid 142236Z - 150030Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated to widely scattered severe storms are possible
into the 6-8 PM MDT time frame, accompanied by a continuing risk for
large hail and locally strong surface gusts. It is not clear that a
watch is needed, but trends will continue to be monitored.
DISCUSSION...Latest objective analysis suggests that appreciable
boundary layer destabilization is limited to a relatively narrow
corridor of the northern high Plains, south/southeast through
north/northwest of the Black Hills. This is where somewhat
amplified upper flow is confining steeper low/mid tropospheric lapse
rates, but modest boundary layer moistening on east/southeasterly
near surface flow appears to be supporting moderate CAPE of
1500-2000 J/kg.
In response to this destabilization, isolated storm development is
already well underway across parts of the Black Hills. This is
occurring in the presence of generally weak (10-15 kt), but strongly
sheared (due to pronounced veering of winds with height) westerly
deep layer mean flow. Given the environment, storm motions are
expected to remain slow, with a tendency to propagate
south-southeastward.
At least some increase in number of storms, including isolated
supercells, appears possible through the 00-02Z time frame. But,
coverage of stronger storms may remain widely scattered, with large
hail and localized strong wind gusts the primary severe hazards.
..Kerr/Thompson.. 08/14/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...UNR...BYZ...
LAT...LON 45680444 45550324 44480159 43600093 42930219 43320323
44100406 44670505 45280482 45680444
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