745
ACUS11 KWNS 172045
SWOMCD
SPC MCD 172045
SDZ000-NEZ000-MTZ000-WYZ000-172215-

Mesoscale Discussion 1306
NWS Storm Prediction Center Norman OK
0345 PM CDT Mon Jun 17 2024

Areas affected...portions of eastern Wyoming...southeastern Montana
and far western South Dakota

Concerning...Severe potential...Watch possible

Valid 172045Z - 172215Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms are expected to develop off the Bighorns and
higher terrain later this afternoon. A few supercells may evolve
with a risk for large hail and damaging winds. There remains some
uncertainty on the southern and eastern extent of the severe risk,
but a WW is being considered.

DISCUSSION...Across portions of central and northeastern WY,
afternoon visible imagery showed increasing vertical development of
cumulus near the Bighorn Mountains and higher terrain. Over the last
several hours, diurnal heating and upslope flow have increased ahead
of an approaching upper trough and a deepening surface low over
south-central WY. As forcing for ascent increases, remaining
inhibition will quickly be removed supporting thunderstorm
development this afternoon. Confidence in convective development
remains highest across north-central WY near the Bighorns where
low-level upslope flow is maximized beneath the coldest mid-level
temperatures. However, strong low-level mass response is occurring
ahead of the deepening surface low over southeastern WY which could
support an isolated storm or two farther south.

While low-level moisture is not overly deep or rich, low 50s F
surface dewpoints have surged westward into eastern WY and portions
of southern MT. With 500-1000 J/kg of MLCAPE in place, a few
stronger updrafts are likely to evolve as the initial convection
moves off of the higher terrain. There remains some uncertainty on
the eastward extent of destabilization given lingering cloud cover,
though clearing is ongoing. Strong flow aloft ahead of the upper
trough is supporting robust vertical shear profiles with relatively
long hodographs and 50+ kt of effective shear. More than sufficient
to support organized rotating updrafts, these storms will likely be
capable of large hail and damaging gusts. A brief tornado can also
not be ruled out given some low-level veering and potential for
terrain enhanced low-level shear. Given the potential for a few
supercells capable of hail and damaging winds, a new WW may be
needed in the next 1-2 hours.

..Lyons/Halbert/Gleason.. 06/17/2024

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

ATTN...WFO...UNR...CYS...BYZ...RIW...

LAT...LON   42870395 42480400 42290421 42250460 42740553 43680688
            44030721 45480711 45890652 46080591 46080526 45960471
            45570434 45160407 44710385 44360382 43780390 42870395