MESO: Mesoscale Discussion 1756

ACUS11 KWNS 221854
SWOMCD
SPC MCD 221854
NVZ000-ORZ000-CAZ000-222100-

MESOSCALE DISCUSSION 1756
NWS STORM PREDICTION CENTER NORMAN OK
0154 PM CDT THU AUG 22 2013

AREAS AFFECTED...NRN CA...NWRN NV...SRN OREGON

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 221854Z - 222100Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...STORMS ARE EXPECTED TO UNDERGO A GRADUAL INCREASE FROM NRN
CA...NW NV INTO SRN OREGON THIS AFTERNOON. THE STRONGER STORMS MAY
BECOME CAPABLE OF PRODUCING LARGE HAIL AND STRONG WIND GUSTS.

DISCUSSION...PRONOUNCED VORT MAX CENTERED OVER NWRN CA WILL CONTINUE
SLOWLY NWD TODAY. AHEAD OF THIS FEATURE...SCATTERED STORMS ARE
DEVELOPING WITHIN A COUPLE OF CONVERGENCE BANDS...ONE LOCATED FROM
SRN OREGON INTO NWRN NV AND ANOTHER OVER NRN CA. VISIBLE IMAGERY
SHOWS A LARGE AREA OF CLEARING OVER NRN CA IN THE IMMEDIATE WAKE OF
THE LEAD CONVECTIVE BAND. WITH STRONG INSOLATION...BOUNDARY LAYER
DEWPOINTS MAY MIX DOWN INTO THE 40S. HOWEVER...COLD AIR ALOFT
ATTENDING THE VORT MAX AND STEEPENING LOW-MID LEVEL LAPSE RATES
SHOULD SUPPORT 500-1000 J/KG MLCAPE. OROGRAPHIC FORCING AUGMENTED BY
HEATING OVER THE HIGHER TERRAIN WITHIN A ZONE OF PRONOUNCED DPVA
ATTENDING THE VORT MAX SHOULD CONTINUE TO SUPPORT THUNDERSTORM
DEVELOPMENT DURING THE AFTERNOON...AND ACTIVITY SHOULD UNDERGO A
GRADUAL INCREASE AS THE ATMOSPHERE DESTABILIZES. A BELT OF 30-40 KT
SLY MID-UPPER WINDS ALONG ERN PERIPHERY OF THE VORT MAX IS
CONTRIBUTING TO 30-40 KT EFFECTIVE SHEAR...WHICH MAY PROMOTE SOME
UPDRAFT ROTATION AND AUGMENT THE THREAT FOR HAIL WITHIN THE STRONGER
CORES.

..DIAL/CORFIDI.. 08/22/2013

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...REV...MFR...STO...EKA...

LAT...LON 39932092 40842230 41182371 42212319 43012106 42591949
41291942 39932092

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