SPC MD 301

MD 0301 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR FAR SOUTHWESTERN OREGON....FAR NORTHWESTERN CALIFORNIA

Mesoscale Discussion 0301
NWS Storm Prediction Center Norman OK
0145 PM CDT Tue Mar 21 2017

Areas affected...Far southwestern Oregon....far northwestern
California

Concerning...Severe potential...Watch unlikely 

Valid 211845Z - 212115Z

Probability of Watch Issuance...5 percent

SUMMARY...A localized threat for a brief tornado and marginally
severe hail will emerge this afternoon in far northwestern
California and southwestern Oregon as convection moves onshore in a
low-level wind profile conducive for rotation. However the threat
will be isolated enough to preclude a watch.

DISCUSSION...A compact vorticity maximum evident in visible and
water vapor imagery is moving steadily east-northeastward toward the
coast of far northwestern California. A localized band of ascent
leading this vorticity maximum is supporting a north-south broken
line of convection offshore that has increased in intensity the past
hour.  The convection is supported by a narrow corridor of MUCAPE
values now above 500 j/kg extending a few counties inland in the
latest mesoanalysis. Steadily increasing mid-level lapse rates and
some surface heating through the abundant breaks in the stratus
should allow for further deepening/intensification of the convection
through the afternoon as it approaches/moves onshore.

At the same time, the low-level wind shear will increase with time
and obtain enough hodograph curvature to support 0-1 km SRH of
150-225 m2/s2 after about 2000 UTC.  The combination of these
factors will support scattered thunderstorms...possibly mini
supercells...over the region from early afternoon through the
evening, with a low threat for a brief tornado and marginally severe
hail in the more persistent updrafts.  However, the threat should
remain isolated enough to preclude a watch.

..Coniglio/Hart.. 03/21/2017

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

ATTN...WFO...MFR...EKA...

LAT...LON   42962455 43032406 42322326 41362313 40922326 40282348
            39762375 39712401 39722424 39812435 40242449 40562450
            42182469 42962455 

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