|Mesoscale Discussion 1336|
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Mesoscale Discussion 1336
NWS Storm Prediction Center Norman OK
0401 AM CDT Tue Jul 18 2017
Areas affected...Southern North Dakota and northern South Dakota
Concerning...Severe potential...Watch unlikely
Valid 180901Z - 181030Z
Probability of Watch Issuance...5 percent
SUMMARY...Potential for marginal severe hail/surface gusts is
expected to diminish through the 5-6 AM time frame.
DISCUSSION...The ongoing organized mesoscale convective system
appears to have been supported by an area of enhanced low-level warm
advection to the immediate cool side of a stalled surface frontal
zone near the North/South Dakota border area. The Rapid Refresh has
been consistent suggesting that this forcing will weaken during the
next couple of hours, which seems likely to lead to diminishing
convective trends, despite the current strength and organization of
the convective system. As 20-30 kt westerly deep layer mean flow
contributes to a continuing eastward progression of the convective
system, the latest objective instability analysis suggests that
system-relative inflow should become increasingly stable as activity
advances toward areas near/north of Aberdeen.
Warm advection above the outflow/outflow reinforced front in the
wake of the convective system may support continuing or renewed
convective development near the state border area through daybreak.
However, any appreciable risk for marginally severe hail and surface
gusts seems limited to the lead cluster.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 46499906 46579764 46589724 45919644 45099809 45239957
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