ACUS11 KWNS 211942
SWOMCD
SPC MCD 211942=20
IDZ000-ORZ000-212145-

Mesoscale Discussion 0833
NWS Storm Prediction Center Norman OK
0242 PM CDT Sun May 21 2023

Areas affected...portions of eastern Oregon and western Idaho

Concerning...Severe potential...Severe Thunderstorm Watch likely=20

Valid 211942Z - 212145Z

Probability of Watch Issuance...80 percent

SUMMARY...Isolated to widely scattered thunderstorms will gradually
evolve off of the higher terrain this afternoon. A few supercells
capable of severe hail and winds are possible. A Severe Thunderstorm
Watch is likely.

DISCUSSION...Early this afternoon, regional WV imagery showed a
mid-level trough and associated cold front shifting eastward over
portions of the northwestern CONUS. Ahead of the front, forcing for
ascent and afternoon heating were supporting the gradual
destabilization of the air mass across portions of eastern OR and
western ID. Low 50s to upper 40s F surface dewpoints and mid-level
lapse rates near 8 C/km were supporting ~500 J/kg of MLCAPE from SPC mesoanalysis. Further heating should aid destabilization with peak
MLCAPE values of 1000-1250 J/kg while inhibition is diminished. As
the front slowly advances eastward, forcing for ascent and local
terrain circulations should result in the development of scattered thunderstorms from eastern OR into ID this afternoon.

Enhanced southwesterly flow ahead of the approaching trough was
supporting a broad area of 35-40 kt of 0-6km shear over much of the
Northwest. As storms develop this afternoon, a few high-based
supercells or multi-cell clusters will likely become organized and
track northeastward. The favorable mid-level shear profiles and
lapse rates will favor large hail, especially with sustained
supercells. Dry sub-cloud layers may also support a risk for severe
wind gusts as cells merge or cluster together later this evening as
strong downdrafts are established. While the coverage of severe
storms may remain isolated to widely scattered, confidence in storm organization is relatively high across parts of northeastern OR and
western ID. The favorable CAPE/shear space and storm coverage
suggest that conditions may warrant a Severe Thunderstorm Watch this
afternoon.

..Lyons/Grams.. 05/21/2023

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!6sove-pk1rX12KqmZaDMbiE53riCktduf47PovwNjfj5N4JxEzbXsq7u4gnGn64GIijn-VUdl= Ycte6tcB8jxTpEi7bc$ for graphic product...

ATTN...WFO...MSO...BOI...OTX...PDT...MFR...

LAT...LON 42011973 43831641 45411542 46161519 46361569 46091666
45501785 44361946 43302079 42332078 42011973=20


=3D =3D =3D
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