SPC MD 1565

MD 1565 CONCERNING SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY FOR PORTIONS OF SD...NORTHERN NE...AND VICINITY

Mesoscale Discussion 1565
NWS Storm Prediction Center Norman OK
0257 PM CDT Fri Aug 25 2017

Areas affected...Portions of SD...northern NE...and vicinity

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 251957Z - 252230Z

Probability of Watch Issuance...80 percent

SUMMARY...The severe-thunderstorm risk is increasing across portions
of SD and NE, and will continue into the evening. The issuance of a
Severe Thunderstorm Watch is likely.

DISCUSSION...Moderate to strong destabilization is ongoing along the
southern and eastern flanks of a persistent MCV crossing the
Dakotas, with MCV-related convection suggesting trends of slight
intensification across parts of north-central SD. Areas of at least
filtered insolation amidst middle 60s to near 70F surface dewpoints
is supporting upwards of 2000-3000 J/kg of MLCAPE (aided by steep
lapse rates aloft) on the warm side of a convectively reinforced
surface front. This front arcs from northeast SD to the NE/SD border
west-northwest of Valentine NE. The Valentine surface observation
indicates temperatures breaching 90F within a warm-thermal axis
preceding the aforementioned front, resulting in continued erosion
of antecedent EML-related capping.

Consistent with the deepening moist boundary layer, cumulus fields
are becoming increasingly agitated in the vicinity of Cherry County
NE extending into adjacent SD, and surface-based convective
development will be likely near the front in the 2030-2200Z time
frame. This also potentially includes a transition to surface-based
convection in northeast SD, as ongoing MCV-related convection
eventually ingests surface-based effective inflow. Given the
aforementioned magnitude of buoyancy, along with 20-30 kt of
effective shear (locally enhanced by augmentations to mass fields
aloft around the MCV), organized convective structures/clusters
capable of severe hail and wind should spread eastward/southeastward
into the evening hours. Inflow for this activity, along with some
southward component to its motion, will be facilitated by a moderate
southwesterly low-level jet, which will offer sufficient low-level
shear for a very low chance for a short-lived tornado. However,
severe hail and wind will be the primary hazards, continuing into
the evening hours.

..Cohen/Grams.. 08/25/2017

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

ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

LAT...LON   42520024 43690050 44899875 44979710 43919646 42589685
            42139799 42520024 

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