SPC MD 1705

MD 1705 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTHWEST OREGON...FAR SOUTHWEST WASHINGTON

Mesoscale Discussion 1705
NWS Storm Prediction Center Norman OK
0410 AM CDT Fri Sep 18 2020

Areas affected...Northwest Oregon...Far Southwest Washington

Concerning...Severe potential...Watch unlikely 

Valid 180910Z - 181115Z

Probability of Watch Issuance...5 percent

SUMMARY...An isolated severe threat is expected to continue across
parts of northwest Oregon and may affect far southwest Washington as
well. Hail and strong wind gusts will be possible but the threat is
expected to be too marginal for weather watch issuance.

DISCUSSION...The latest surface analysis shows a narrow corridor of
maximized low-level moisture from south-to-north in the Willamette
Valley of northwestern Oregon. Surface dewpoints along this corridor
are in the lower 60s F, which is contributing to MLCAPE estimated by
the RAP in the 500 to 750 J/kg range. A small cluster of
thunderstorms is ongoing along the instability axis. These storms
have formed in response to a band of large-scale ascent that is
spreading northward across western Oregon according to the
water-vapor imagery and RAP 500 mb analysis. The storms are located
in moderate deep-layer shear. The latest WSR-88D VWP at Portland has
0-6 km shear near 35 kt with some speed shear in the mid-levels.
This combined with the instability should be enough for an isolated
severe threat over the next few hours. Hail and marginally severe
wind gusts may occur with the stronger rotating storms.

..Broyles/Edwards.. 09/18/2020

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

ATTN...WFO...SEW...PQR...

LAT...LON   45182201 45772216 46252249 46372272 46392277 46422318
            46162360 45672375 45252368 44582342 44252300 44532227
            45182201 

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from SPC Forecast Products http://www.spc.noaa.gov/products/md/md1705.html