SPC MD 1021


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Mesoscale Discussion 1021
NWS Storm Prediction Center Norman OK
0628 PM CDT Fri Jun 07 2019

Areas affected...southeast MT...northwest SD...southwest ND

Concerning...Severe Thunderstorm Watch 340...

Valid 072328Z - 080100Z

The severe weather threat for Severe Thunderstorm Watch 340

SUMMARY...The severe risk is beginning to ramp up for areas over
northwest SD and southwest ND.  Severe gusts (60-75mph) and large
hail (1-2 inches in diameter) are the threats with the stronger

DISCUSSION...Water-vapor imagery shows a potent mid-level shortwave
trough moving through the Northern Rockies and northern
InterMountain regions early this evening.  Farther east over the
western Dakotas and southeast MT, the initial plume of 700-500mb
ascent will overspread this area during the next 1-2 hours according
to objective analyses.  

Surface analysis via observations and radar fine-line data indicate
a cold front is slowly pushing east across central ND with the
boundary stalling near the Black Hills.  Surface dewpoints in the
middle 50s are located over southwest ND into northwest SD.  It
appears most of the ongoing thunderstorm activity moving into the
western Dakotas is preferentially favoring the cool-side of the
boundary where shallow frontal lift is more supportive for storm
development compared to a capped warm sector farther east.  

Some short-term convection-allowing model guidance is suggestive
that the ongoing storms over southeast MT and the area along the
SD/WY border is the initial evolution of a severe-wind producing
cluster of thunderstorms expected to move northeast across southwest
ND/northwest SD and eventually into central ND later this evening. 
A new severe thunderstorm watch will likely be needed farther
northeast of severe thunderstorm watch 340.  However, during the
next 1-2 hours, the expectation is for a gradual intensification of
storms over southeast MT moving into the western Dakotas with the
risk for severe gusts coincidentally increasing.

..Smith.. 06/07/2019

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


LAT...LON   46590405 46710295 46360212 45910176 44180322 44220373
            45420525 45820539 46590405 

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