Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 211845
SWOMCD
SPC MCD 211845
CAZ000-ORZ000-212115-

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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