MESOSCALE PRECIPITATION DISCUSSION 0526
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
546 PM EDT MON JUL 23 2018

AREAS AFFECTED...PORTIONS OF THE SIERRA-NEVADA

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

VALID 232145Z - 240345Z

SUMMARY...SCATTERED SHOWERS AND THUNDERSTORMS WILL BECOME ANCHORED
UP OVER THE HIGH TERRAIN OF THE SIERRA-NEVADA. SOME FLASH FLOODING
WILL BE POSSIBLE THIS AFTERNOON AND EVENING.

DISCUSSION...THE LATEST VISIBLE SATELLITE IMAGERY SHOWS CONVECTION
INITIATING OVER PORTIONS OF THE CENTRAL SIERRA-NEVADA AND THERE
HAS BEEN AN UPTICK IN CG LIGHTNING ACTIVITY OVER THE LAST HOUR AS
STRONGER UPDRAFTS ENSUE AND THE CONVECTION GAINS GREATER VERTICAL
STATURE WITH COOLING CLOUD TOPS. THE ACTIVITY IS FOCUSING WITHIN
AN ANOMALOUSLY MOIST ENVIRONMENT WITH DIURNALLY ENHANCED
INSTABILITY AND TERRAIN-DRIVEN CIRCULATIONS IN PLACE.

THE LATEST RAP ANALYSIS SHOWS MLCAPE VALUES OF LOCALLY NEAR 1500
J/KG AND THE PWATS ACROSS THE THREAT AREA ARE ABOUT 0.7 TO 0.9
INCHES WHICH IS ABOUT 2 TO 2.5 STANDARD DEVIATIONS ABOVE NORMAL.
THIS WILL CONTRIBUTE TO RELATIVELY EFFICIENT RAINFALL PROCESSES
AND ENHANCED RAINFALL RATES THAT MAY LOCALLY EXCEED 1 INCH/HR.

EXPECT CONVECTION TO BE VERY SLOW MOVING WITH SOME CELLS LIKELY
BECOMING STATIONARY OR ANCHORED OVER THE SAME AREA GIVEN WEAK
700/300 MB LAYER MEAN FLOW...AND THE PERSISTENCE OF THE
AFOREMENTIONED TERRAIN CIRCULATIONS.

THE CONVECTION SHOULD EXPAND A BIT MORE IN COVERAGE AND GAIN A BIT
MORE INTENSITY GOING THROUGH 00Z...WITH CONVECTION LIKELY
PERSISTING THROUGH AT LEAST 03Z. EXPECT AS MUCH AS 2 TO 3 INCHES
OF RAIN WITH LOCALLY HEAVIER AMOUNTS. SOME FLASH FLOODING WILL BE
POSSIBLE GIVEN THESE EXPECTED TOTALS AND ALSO WITH SOME ADDED
SENSITIVITY CONCERNING SOME OF THE RECENT HEAVY RAINFALL FROM THE
LAST SEVERAL DAYS. BURN SCAR AREAS IN PARTICULAR WILL NEED TO BE
CLOSELY MONITORED FOR ENHANCED RUNOFF AND FLASH FLOODING CONCERNS.

ORRISON

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

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

LAT...LON   40192058 39962012 39271965 38701905 38321855
            37641820 36601781 36111798 36211860 36801888
            37221926 37791964 38312010 39202059 39842086