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Mesoscale Discussion 1483
NWS Storm Prediction Center Norman OK
0642 PM CDT Mon Jul 15 2019

Areas affected...Eastern Wyoming into southwestern South Dakota and
western into central Nebraska

Concerning...Severe Thunderstorm Watch 510...

Valid 152342Z - 160115Z

The severe weather threat for Severe Thunderstorm Watch 510

SUMMARY...The severe threat continues across Severe Thunderstorm
Watch 0510. Large hail and severe wind gusts remain the primary
threat. Upscale growth of convection remains possible across
northwestern portions of the watch, where severe winds may become
the predominant threat. Outflow from earlier storms have stabilized
the airmass across southeast parts of the watch, where the short
term severe threat has been tempered.

DISCUSSION...Semi-discrete to discrete storms, including transient
supercell structures, have developed and matured across the
lower-terrain areas in eastern Wyoming over the past few hours.
Ample buoyancy (1500-2500 J/kg MLCAPE) and adequate deep-layer shear
(35-45 knots of bulk effective shear) are in place to foster the
maintenance of this convection. Poor speed and directional shear in
the lowest 3 km, however, suggests that some outflow dominant
tendencies should exist with some of the more intense cells with
more robust, water/hail loaded downdrafts. As such, cold-pool
merging is expected to commence over the next few hours, promoting
upscale growth for potential MCS development, as suggested by both
the 12Z HREF and the last few runs of the HRRR. Should this occur,
severe wind gusts should become the main threat, particularly in far
east WY into southwest SD. The intensity of the potential MCS is
somewhat uncertain, as a meager to negligible low-level jet is
expected to develop during the evening. As such, robustness of the
MCS will depend entirely on cold pool propagation processes, and the
amount of buoyancy available ahead of the convective leading line.

Meanwhile, multicellular convection in northern Nebraska, supported
by 3000+ J/kg MLCAPE, have exhibited copious outflow given the very
weak low-level and deep-layer shear environment in place. A
substantial cold pool has been left behind across southeast parts of
Severe Thunderstorm Watch 0510, suggesting that the severe threat
has been dampened to a degree via boundary layer stratification and
mid-level convective overturning/diminishing of lapse rates. Still,
at least a few hours of diurnal heating remain, and the chances for
additional severe weather will hinge on the trajectory and intensity
of the potential aforementioned MCS.

..Squitieri/Grams.. 07/15/2019

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


LAT...LON   41280519 44830716 44820124 41289960 41280519 

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