SPC MD 435


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Mesoscale Discussion 0435
NWS Storm Prediction Center Norman OK
1121 AM CDT Wed May 16 2018

Areas affected...Portions of eastern Oklahoma...western
Arkansas...and far northeastern Texas

Concerning...Severe potential...Watch unlikely 

Valid 161621Z - 161845Z

Probability of Watch Issuance...20 percent

SUMMARY...Two MCVs over central and eastern Oklahoma are expected to
contribute to scattered thunderstorm development over the next few
hours. Severe wind gusts and marginally severe hail are the primary
threats.  A Severe Thunderstorm Watch is not anticipated at this
time, but conditions will be monitored closely.

DISCUSSION...Overnight convection has once again produced MCVs over
the area, partially as an enhancement of a subtle mid-level
perturbation moving over the top of the building ridge.  The 12z OUN
raob sampled the enhancement in mid-level flow associated with these
MCVs with wind speeds > 40 kt in the 650-500 mb layer and a peak
wind of 55 kt at 565 mb.  Moderate sub-tropical flow in upper
levels, perhaps enhanced by a separate area of convection over the
Texas panhandle, also is impinging on the area and is producing
moderate diffluence aloft.  Southeast and east of the MCVs, strong
heating is occurring on either side of a dying stationary front
amidst surface dewpoints in the upper 60s to low 70s.  

The above factors suggest thunderstorms will increase no later than
early afternoon over the area, which is supported by recent HRRR
guidance.  While the background wind/vertical shear would suggest
weakly organized thunderstorm clusters, the enhancement in vertical
shear and mesoscale lift provided by the MCVs is expected to produce
some convective organization in the form of a small MCS with perhaps
some transient bowing clusters.  Despite some convective overturning
in previous days, moderate mid-level lapse rates remain over the
area, and boundary-layer moisture is sufficient to support moderate
instability --1500-2000 J/kg of MLCAPE by early afternoon.  The
primary threat will be severe wind gusts with any of the storms,
particularly those that develop more persistent rotation.  A
marginally severe hail threat will also accompany the cells that
show some rotation.  While the extent of the severe coverage is not
expected to warrant a Severe Thunderstorm Watch at this time, trends
in both storm coverage and intensity will be monitored closely.

..Coniglio/Weiss.. 05/16/2018

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


LAT...LON   36239526 36439439 36399322 36149238 36029225 35599205
            34579198 34049219 33589254 33159319 33049402 33169465
            33509525 34119568 34529586 34819591 35239589 35399584
            35949564 36239526 

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