MESOSCALE PRECIPITATION DISCUSSION 0631...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
600 PM EDT SAT AUG 05 2017

CORRECTED FOR GRAPHICAL ADJUSTMENT

AREAS AFFECTED...SIERRA-NEVADA AND ADJACENT FOOTHILLS

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

VALID 052200Z - 060300Z

SUMMARY...SLOW-MOVING SHOWERS AND THUNDERSTORMS WITH HEAVY
RAINFALL WILL BE EXPANDING IN COVERAGE UP OVER THE SIERRA-NEVADA
MOUNTAINS AND WESTERN FOOTHILLS OVER THE NEXT FEW HOURS.

DISCUSSION...THE MID-AFTERNOON NON-OPERATIONAL GOES-16 0.64
MICRON/VIS IMAGERY SHOWS A CU/TCU FIELD BECOMING INCREASINGLY
AGITATED OVER MUCH OF THE SIERRA-NEVADA MOUNTAIN CHAIN ALONG WITH
THE ADJACENT FOOTHILLS TO THE EAST AND WEST OF THE CREST. ALREADY
A CLUSTER OF SLOW-MOVING THUNDERSTORMS HAVE DEVELOPED WEST OF
MAMMOTH LAKES AND BISHOP...AND SOME SUGGESTION OF ACTIVITY
INITIATING IN BETWEEN BLUE CANYON AND TRUCKEE.

A NARROW CHANNEL OF MID LEVEL VORTICITY AND LOCALLY ENHANCED
MOISTURE CONCENTRATION IS SEEN UP ALONG THE SIERRA-NEVADA CREST
AND THIS COUPLED WITH OROGRAPHIC FORCING AND DIURNAL HEATING
SHOULD ALLOW CONVECTION TO DEVELOP AND BECOME LOCALLY CONCENTRATED
THROUGH THE AFTERNOON AND EARLY EVENING HOURS ACROSS THE REGION.
THE PWATS ACROSS THE REGION ARE RATHER ANOMALOUS...UPWARDS OF 2 TO
3 SIGMAS ABOVE NORMAL...AND WITH NOTABLE CONTRIBUTION FROM THE
GREATER MID/HIGH LEVEL MOISTURE CONCENTRATIONS AS SEEN IN CIRA-LPW
DATA.

EXPECT THE CONVECTION TO BE CAPABLE OF PRODUCING AS MUCH AS 1 TO
1.5 INCHES OF RAIN IN AN HOUR....WITH LOCALIZED STORM TOTALS
EXCEEDING 2 TO 3 INCHES THROUGH 03Z GIVEN THE EXPECTED SLOW CELL
MOTION AND POTENTIAL FOR SOME REPEATING CELL ACTIVITY OVER THE
HIGH TERRAIN. THE LATEST HRRR AND HRRRX GUIDANCE ALONG WITH THE
12Z NMMB/NSSL-WRF RUNS SUPPORT THIS SCENARIO.

RUNOFF MAY BE LOCALLY ENHANCED GIVEN THE STEEP TERRAIN...AND FLASH
FLOODING WILL BE POSSIBLE AS A RESULT. AREA BURN SCARS WILL BE
PARTICULARLY SUSCEPTIBLE TO THESE THREATS GOING INTO THE EVENING
HOURS. WILL CONTINUE TO MONITOR.

ORRISON

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

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

LAT...LON   41692011 40951977 39881961 38901919 37931819
            37391791 36681779 36271780 35981823 36301857
            37101907 37571959 38212026 38872080 40222123
            41062124 41662088