Mesoscale Discussion 1703
NWS Storm Prediction Center Norman OK
0656 PM CDT Thu Sep 17 2020
Areas affected...Willamette Valley and Vicinity
Concerning...Severe potential...Watch possible
Valid 172356Z - 180200Z
Probability of Watch Issuance...40 percent
SUMMARY...A few organized/rotating storms are expected to develop
later this afternoon and early evening along and west of the Cascade
crest. Storms will be capable of strong wind gusts as well as large
hail. Buoyancy is limited across the region which increases the
uncertainty in the coverage of severe-caliber storms. A severe
thunderstorm watch may be considered if convective trends warrant.
DISCUSSION...A lobe of mid-level ascent is evident on satellite
water vapor imagery off the southwest coast of Oregon. This ascent
has already contributed to increasing low to mid-level cumulus
development from the coastal ranges to the southern Cascades. In
spite of persistent smoke cover, temperatures have managed to climb
into the mid 70s F near Portland to the upper 70s F near Medford.
Continued mid-level cooling into the evening is expected to support
500-1000 J/kg MLCAPE. With limited buoyancy, the coverage of severe
storms is a bit uncertain. However, with strong effective shear
(45-55 kts) present, a few organized/rotating storms will likely
evolve out of the deepening cumulus activity along and west of the
Cascade crest. The primary threats from this activity will be
strong/damaging wind gusts as well as large hail. Storms may
additionally impact ongoing wildfires in the region. A severe
thunderstorm watch may be considered if convective trends warrant.
..Wendt/Thompson.. 09/17/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PDT...MFR...PQR...
LAT...LON 42632394 42842423 43632413 45042333 45372301 45332226
44732170 43102205 42472249 42352339 42632394
Read morefrom SPC Forecast Products http://www.spc.noaa.gov/products/md/md1703.html
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