MESOSCALE PRECIPITATION DISCUSSION 0492
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 PM EDT FRI JUL 20 2018

AREAS AFFECTED...PORTIONS OF THE SIERRA-NEVADA

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

VALID 201940Z - 210130Z

SUMMARY...SCATTERED SLOW-MOVING SHOWERS AND THUNDERSTORMS WILL
POSE A FLASH FLOOD RISK THIS AFTERNOON.

DISCUSSION...THE LATEST VISIBLE SATELLITE IMAGERY IS SHOWING
CONVECTIVE INITIATION UNDERWAY ACROSS PORTIONS OF THE CENTRAL
SIERRA-NEVADA AS AN INCREASINGLY MOIST AIRMASS COMBINES WITH
DIURNAL HEATING AND OROGRAPHICS FOR THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS. THE ACTIVITY IS TENDING TO FOCUS WITHIN A BROADLY
DIFFLUENT FLOW PATTERN ALOFT AS WELL...AND THE CONVECTION SHOULD
TEND TO BE RATHER SLOW-MOVING GIVEN THE WEAK STEERING FLOW.

THE MID LEVEL WV SATELLITE IMAGERY SHOWS A CHANNEL OF MORE FOCUSED
MOISTURE LIFTING UP TO THE NORTH AND TOWARD THE CENTRAL
SIERRA-NEVADA AT THIS TIME...AND THE PWATS ACROSS THE REGION ARE
FORECAST TO RISE THROUGH THE AFTERNOON HOURS...WITH THE ANOMALIES
BY 00Z REACHING ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL AS PER
THE 12Z GFS.

THIS WILL ALLOW THE CONVECTION TO BECOME A LITTLE MORE EFFICIENT
IN REGARDS TO RAINFALL PROCESSES AND THIS WILL SUPPORT SOME
LOCALLY HEAVIER RAINFALL RATES. THE 12Z ARW/NMMB CAM SOLUTIONS
SUGGEST AS MUCH AS 1 TO 2 INCHES OF RAIN THROUGH 00Z...WHICH MAY
CAUSE SOME ENHANCED RUNOFF PROBLEMS AND/OR FLASH FLOODING. THE
BIGGEST CONCERN WILL OVER AND NEAR ANY BURN SCARS.

ORRISON

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

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

LAT...LON   39091896 38411827 37371798 36301759 35991791
            36121850 36441881 37001898 37481942 38411990
            39051974