Mesoscale Discussion 1727
NWS Storm Prediction Center Norman OK
0523 PM CDT Sat Sep 11 2021
Areas affected...Parts of far eastern Wyoming...northeastern
Colorado into parts of western and central Nebraska
Concerning...Severe potential...Watch unlikely=20
Valid 112223Z - 120030Z
Probability of Watch Issuance...5 percent
SUMMARY...Scattered strong storms may produce localized strong
downbursts through 7-9 PM CDT, but the evolution of an organized
severe wind threat currently appears low.
DISCUSSION...Widely scattered thunderstorm activity is initiating
along and east of the Colorado Front Range and Laramie Mountains
vicinity. This appears aided by mid/upper forcing for ascent
associated with one low amplitude impulse now crossing the higher
terrain, and forecast to progress into the adjacent high plains
through this evening.
The boundary layer has become hot and deeply mixed across the high
plains, with sufficient moisture in the presence of steep lapse
rates to support weak CAPE. Boundary-layer dew points and
mixed-layer CAPE gradually increase with eastward extent across the
high plains, and this could allow for slow further intensification
of high-based storms through early evening. Deep-layer shear is
strong, and westerly mean ambient flow within the convective layer
appears on the order of 30 kt, which may contribute to increasing
potential for locally severe down bursts in stronger storms, before
convection begins to wane after dark.
Due to weak low-level forcing for ascent, the potential for
substantive upscale growth currently appears low. This appears to
limit the risk for a broader, more organized severe wind threat.
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