SPC MD 1447


MD 1447 Image

Mesoscale Discussion 1447
NWS Storm Prediction Center Norman OK
0813 PM CDT Fri Jul 12 2019

Areas affected...Parts of southern Montana

Concerning...Severe potential...Watch unlikely 

Valid 130113Z - 130315Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated severe storms are expected to persist across the
area into the early evening hours. Large hail and damaging wind
gusts are expected to be the primary threats with the more intense
storms. Given the isolated nature of the severe threat, a WW
issuance appears unlikely.

DISCUSSION...Multicellular, to occasionally transient supercellular
storms, have been intensifying over the past few hours across
portions of southern MT, where buoyancy has been gradually
increasing (with up to 1000 J/kg MLCAPE noted). A well-mixed
boundary layer is in place, with a dry sub-cloud layer extending to
nearly 3000 m above ground level, suggesting that storms will be
high based in nature. A roughly dry-adiabatic layer (with subsequent
steep lapse rates of 7.5 to over 8.5 C/km) extends from the surface
up to about 500 mb, suggesting that efficient precipitation
evaporation/cooling should take place with the heavier cell cores.
While overall MLCAPE is relatively marginal overall, much of the
aforementioned CAPE is confined above the freezing level, suggesting
that at least a few marginally severe hail stones are possible with
the stronger, more organized updrafts. 

The overall lack of higher instability across the area will temper
the severe threat to a degree, with severe hail/wind being
relatively isolated in nature, and a WW issuance is not expected.

..Squitieri/Hart.. 07/13/2019

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


LAT...LON   45000925 45511155 46121212 46601202 47161109 47120949
            47020789 46580674 45850591 44990768 45000925 

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