|Mesoscale Discussion 1287|
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Mesoscale Discussion 1287
NWS Storm Prediction Center Norman OK
0348 PM CDT Tue Jul 11 2017
Areas affected...the eastern Dakotas and western portions of MN
Concerning...Severe potential...Watch likely
Valid 112048Z - 112215Z
Probability of Watch Issuance...80 percent
SUMMARY...Convective initiation is forecast over the next 1-2 hours.
Severe thunderstorms capable of large to very large hail, severe
gusts, and possibly a tornado are forecast this evening. A
convective watch is likely in the next 1-2 hours.
DISCUSSION...Visible satellite imagery shows several areas of
clumping/agitated cumulus. Weak low level confluence is implied by
streamline analysis across east-central SD near Huron where a
cumulus field is present as of 2040Z. Other areas where storm
initiation may occur may evolve from where the boundary layer is
probably more deeply mixed near the MO River near the SD/ND border
and farther north to the north of Jamestown, ND.
RAP forecast soundings show a very unstable airmass (3000-4000 J/kg
MLCAPE) from east-central SD into east-central ND within a moist
axis with upper 60s-lower 70s degrees F dewpoints. Southerly
low-level winds veering and increasing with height to 35-kt in the
mid levels is resulting in around 40-45 kt effective shear. Once
updrafts break the cap, rapid severe storm development is forecast.
Large hail will be the initial risk. Hail diameters in excess of 2
inches in diameter are possible with the most intense supercells. A
risk for a tornado may develop towards evening dependent on both
convective mode and storms moving into an environment near the ND/MN
border and over west-central MN where hodographs are slightly
larger. Severe gust potential will likely increase as storms
congeal this evening.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 44049864 45929831 48029932 48719886 48809744 48159598
47209526 46029511 44599530 43729609 43719781 44049864
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