MESOSCALE PRECIPITATION DISCUSSION 0585
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1017 AM EDT SUN OCT 18 2015
 
AREAS AFFECTED......CENTRAL AND SOUTHEAST CALIFORNIA...NEVADA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 181417Z - 181917Z
 
SUMMARY...INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS ARE
ANTICIPATED OVER THE NEXT FEW HOURS...WITH LOCALLY INTENSE
RAINFALL RATES. LOCALIZED FLASH FLOODING IS POSSIBLE.

DISCUSSION...SATELLITE WV AND GOES-RGB AIRMASS IMAGERY ARE
INDICATING A WELL-DEFINED SHORTWAVE TROUGH EJECTING EAST INTO
WEST-CENTRAL CA EARLY THIS MORNING. STRENGTHENING UPPER LEVEL
DIFFLUENCE (AND DIVERGENCE ALOFT) EAST OF THE SHORTWAVE IS
SPREADING INTO CENTRAL AND SOUTHEAST CALIFORNIA AND NEVADA...WHICH
COMBINED WITH THE ANOMALOUS MOIST ENVIRONMENT AND MODEST
INSTABILITY...IS ALLOWING FOR THE DEVELOPMENT OF  DISCRETE N-S
LINES OF CONVECTION THIS MORNING. PW VALUES OVER THE AREA CONTINUE
TO AVERAGE BETWEEN 4-4.5 STANDARD DEVIATIONS ABOVE NORMAL...WITH
THE OBSERVED PW OF 0.94 INCHES PER THE 12Z KVEF RAOB NEAR THE
RECORD VALUE FOR MID OCTOBER. 

THROUGH 19Z...STEEPENING 700-500 MB LAPSE RATES AHEAD OF THE
SHORTWAVE WILL PROVIDE SUFFICIENT DEEP LAYER INSTABILITY FOR
LOCALLY EXCESSIVE RAINFALL RATES...HOWEVER THE BEST INSTABILITY
WILL REMAIN FOCUSED OVER THE SOUTHERN PORTION OF THE OUTLOOK
AREA...WHERE MUCAPES WILL AVERAGE BETWEEN 500-1000 J/KG. GIVEN THE
ROBUST SYNOPTIC SCALE FORCING FOR DEEP-LAYER ASCENT ALONG WITH THE
ANOMALOUS MOIST PROFILE...VERY LITTLE INSTABILITY (LESS THAN 500
J/KG) WILL BE REQUIRED TO PRODUCE LOCALLY EXCESSIVE RAINFALL RATES
OF 0.75-1.00 INCH PER HOUR GIVEN THE LATEST RADAR QPE TRENDS. AT
THE SAME TIME...RAINFALL RATES OF 1 TO 1.5 INCHES/HR WILL BE
POSSIBLE OVER THE SOUTHERN PORTION OF THE OUTLOOK AREA WHERE THE
BETTER DESTABILIZATION IS EXPECTED TO PERSIST INTO THE AFTERNOON. 

WHILE THERE REMAINS SUFFICIENT SHEAR TO SUPPORT FORWARD (DOWNWIND)
PROPAGATION (CELL MOTIONS N-NE)...THE SLOW EASTWARD PROGRESSION OF
THE HIGHLY-AMPLIFIED TROUGH WILL ALLOW FOR SOME TRAINING OF
CONVECTION WITHIN THE N-S ORIENTED LINES. THUS...PER SOME OF THE
LATEST HIGH-RES CAM GUIDANCE INCLUDING THE HRRR... EXPERIMENTAL
HRRR...WRF-ARW...WRF-NNMB...AND NAM CONEST... ISOLATED 2 TO 3+
INCH AMOUNTS WILL BE POSSIBLE THROUGH 19Z. THESE RAINS WILL RESULT
IN LOCALLY SIGNIFICANT RUNOFF PROBLEMS IN THE VICINITY OF HIGHER
TERRAIN...AND WILL ALSO FOCUS CONCERNS FOR FLASH FLOODING IN AND
AROUND DRY WASHES/ARROYOS. 

HURLEY

ATTN...WFO...HNX...LKN...REV...STO...VEF...

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

LAT...LON   41491644 41071519 39831435 37651420 36341451 
            35501507 34981606 34831758 35321904 36961971 
            38861977 40221931 41221793