MESOSCALE PRECIPITATION DISCUSSION 0197
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
143 PM EDT FRI MAY 25 2018

AREAS AFFECTED...WESTERN NV...NORTHEAST CA...FAR SOUTH CENTRAL OR

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 251740Z - 252340Z

SUMMARY...CONVECTION DEVELOPING IN A PLUME OF DEEP MOISTURE AHEAD
OF A CLOSED MID LEVEL LOW MAY POSE A FLASH FLOOD THREAT OVER
WESTERN NV/NORTHEAST CA/SOUTH CENTRAL OR INTO THE AFTERNOON HOURS.
THE FLASH FLOOD THREAT COULD BE ENHANCED IN AREAS WITH BURNS SCARS.

DISCUSSION...CONVECTION HAS BEGUN DEVELOPING OVER NORTHWEST NV
INTO SOUTH CENTRAL OR...IN RESPONSE TO SYNOPTIC SCALE ASCENT
ASSOCIATED WITH A CLOSED MID LEVEL LOW ALONG THE CENTRAL CA COAST.
THE CONVECTION WAS DEVELOPING IN AN AREA OF 500-1000 J/KG OF
MUCAPE...ALONG A PRECIPITABLE WATER GRADIENT (WITH PRECIPITABLE
WATER VALUES NEAR AN INCH...WHICH IS BETWEEN TWO AND THREE
STANDARD DEVIATIONS ABOVE THE MEAN).

THE CYCLONIC FLOW AROUND THE CLOSED MID LEVEL LOW OVER THE CENTRAL
CA COAST HAS BECOME BETTER ALIGNED WITH THE PROPAGATION VECTORS AS
SHOWN ON THE LATEST RAP. THIS IS EXPECTED TO RESULT IN AN
ENVIRONMENT CONDUCIVE TO TRAINING CONVECTION OVER WESTERN NV...FAR
NORTHEAST CA INTO SOUTH CENTRAL INTO THE MID AFTERNOON HOURS. MOST
OF THE AVAILABLE HIGH RESOLUTION GUIDANCE (INCLUDING THE MOST
RECENT HRRR AND EXPERIMENTAL HRRR) INDICATE THE POTENTIAL FOR
LOCAL 1.00/1.50 INCHES OF RAINFALL WITH THE CONVECTION...WITH THE
HIGHEST AMOUNTS OVER NORTHEAST CA AND NEARBY SOUTH CENTRAL OR.

INSTABILITY COULD END UP BEING THE LIMITING FACTOR FOR A MORE
WIDESPREAD FLASH FLOOD THREAT...AS THE MOST RECENT RAP INDICATED
THAT INSTABILITY MAY NOT INCREASE MUCH FROM ITS CURRENT VALUES.
HOWEVER...ANY CONVECTION THAT DEVELOPS WILL TAP THE DEEP MOISTURE
IN PLACE...AND TRAINING CONVECTION IN THIS MOISTURE PLUME WILL
BECOME THE MAIN FLASH FLOOD THREAT. THE FLASH FLOOD THREAT WILL BE
ENHANCED IN AREAS WITH BURN SCARS...WHICH COULD LEAD TO DEBRIS
FLOWS.

SINCE THE COVERAGE OF CONVECTION IS STILL IN QUESTION DUE TO
INSTABILITY...FLASH FLOODING IS ONLY CONSIDERED POSSIBLE.

HAYES

ATTN...WFO...BOI...EKA...LKN...MFR...REV...STO...

ATTN...RFC...CNRFC...NWRFC...

LAT...LON   43232064 42991988 41711920 38991841 38031885
            38482085 40862236 41552278 42122272 42682213
            43172098