SPC MD 2013

SPC MD 2013


Mesoscale Discussion 2013
NWS Storm Prediction Center Norman OK
0202 PM CDT Fri Aug 18 2023

Areas affected…Northeast Idaho into central Montana

Concerning…Severe potential…Watch unlikely

Valid 181902Z – 182100Z

Probability of Watch Issuance…5 percent

SUMMARY…Isolated, high-based thunderstorms will migrate into
Montana through the mid/late afternoon hours, and may pose a risk of
sporadic severe winds. Watch issuance is not expected.

DISCUSSION…Evidence of destabilization is noted in GOES visible
imagery across central ID into southwest MT with building cumulus
noted within low-level horizontal convective rolls. Additionally,
lightning trends and cooling cloud top temperatures indicate that
residual weak convection associated with a decaying MCV over ID is
steadily intensifying. Recent RAP mesoanalyses depict MUCAPE
increasing downstream into central MT to around 250-500 J/kg. While
buoyancy will generally be limited across the region due to modest
low to mid-level moisture, elongated hodographs featuring effective
bulk wind differences on the order of 25-30 knots may compensate for
the meager instability and promote robust updrafts by mid/late
afternoon. Diurnal heating is driving deep boundary layer mixing
with LCLs approaching 2.5 to 3 km based on RAP forecast soundings
modified from observed surface temperatures and dewpoints. This
thermodynamic environment is conducive for downdraft acceleration
via evaporative cooling, which will support the potential for strong
to severe downburst winds. This threat will spread northeast into
central MT through the afternoon, but watch issuance is not expected
given the sporadic/isolated nature of the threat.

..Moore/Grams.. 08/18/2023

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


LAT…LON 46081447 47271064 47380995 47270946 46540834 46260816
45920826 45590859 45360916 45171026 44351192 44231222
44251278 44321315 45071443 45381464 45711460 46081447

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