|Mesoscale Discussion 1003|
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Mesoscale Discussion 1003
NWS Storm Prediction Center Norman OK
0700 PM CDT Mon Jun 12 2017
Areas affected...Portions of southern MT and northern/central WY
Concerning...Severe Thunderstorm Watch 318...
Valid 130000Z - 130130Z
The severe weather threat for Severe Thunderstorm Watch 318
SUMMARY...An isolated threat for large hail and damaging winds
continues across WW 318. A tornado or two also remains possible
mainly across southern/eastern portions of the Watch.
DISCUSSION...Convection has increased in coverage and intensity
across northern/central WY over the past several hours as an upper
low moves northeastward across the northern Great Basin. Strong mid
to upper-level winds are contributing to generally 40-50 kt of
effective bulk shear in/near the Severe Thunderstorm Watch. Although
low-level moisture is more limited across this region (mid/upper 40s
to mid 50s dewpoints) compared to southeastern WY, steep mid-level
lapse rates overlying this sufficient moisture and diurnal heating
have resulted in MLCAPE of 500-1500 J/kg. Multiple supercell
structures have been observed per KRIW and KBLX radars, and isolated
large hail and damaging winds will continue to be a threat through
the evening hours as storms move northward into southern MT. A
tornado or two will also remain possible, particularly across the
Bighorn Basin and vicinity. Across this area, slightly greater
low-level moisture (dewpoints in the low to mid 50s) is allowing for
lower LCL heights, and a supercell over Johnson County WY has
recently produced a tornado (as of 2342Z), along with 2+ inch hail.
Diurnal cooling later this evening will act to reduce available
instability to maintain storm intensity, and the overall severe
threat should slowly lessen over the next few hours.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 44711100 46691065 46720783 45820637 44960607 43230617
42810648 43010749 43390927 44041014 44711100
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