MESOSCALE PRECIPITATION DISCUSSION 0198
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
455 PM EDT FRI MAY 25 2018

AREAS AFFECTED...NORTHERN NV...EASTERN OR...SOUTHWEST ID

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

VALID 252100Z - 260200Z

SUMMARY...CONVECTION TRAINING IN A HIGH MOISTURE ENVIRONMENT COULD
POSE A FLASH FLOOD THREAT LATE THIS AFTERNOON/EARLY THIS EVENING.

DISCUSSION...CLEAR SKIES OVER NORTHERN NV/EASTERN OR INTO WESTERN
ID EARLY THIS AFTERNOON HAS ALLOWED FOR THE AIRMASS OVER THESE
AREAS TO DESTABILIZE. THE GOES-16 VISIBLE IMAGES HAVE SHOWN FAIRLY
RAPIDLY DEVELOPING CUMULUS AS A RESULT...AND THE GOES-16 CLEAN IR
LOOP SHOWED CLOUD TOP TEMPERATURES NEAR -60 CELSIUS.

REGIONAL RADARS SHOWED AN INCREASE IN SCATTERED CONVECTION
STRETCHING FROM NORTHERN NV INTO SOUTHEAST OR...IN AN AXIS OF
500-1000 J/KG OF MLCAPE. WHILE THE BEST MOISTURE PLUME LIES WEST
ACROSS NORTHERN CA...THE MOST RECENT RAP ANALYSIS AND BLENDED TPW
SHOWED PRECIPITABLE WATER VALUES NEAR 0.75 INCHES (WHICH
APPROACHES TWO STANDARD DEVIATIONS ABOVE THE MEAN). CELLS
DEVELOPING IN THIS AIRMASS HAVE PRODUCED HOURLY RAINFALL RATES
BETWEEN 1.00 AND 1.25 INCHES. DRY AIR IN THE MID LEVELS (AS SEEN
ON RAP SOUNDINGS) SUGGEST THE PRESENCE OF HAIL...SO THESE RAINFALL
RATES COULD BE CONTAMINATED.

IN ANY EVENT...SPOKES OF SHORT WAVE ENERGY ROTATING AROUND A
CLOSED MID LEVEL LOW OVER THE CENTRAL CA ARE PROVIDING SYNOPTIC
SCALE ASCENT OVER THIS REGION....AND THE ENHANCED LIFT IS EXPECTED
TO ALLOW THE COVERAGE TO EXPAND THROUGH 26/00Z. THE MID LEVEL FLOW
BECOMES BETTER ALIGNED WITH THE PROPAGATION VECTORS THROUGH ABOUT
26/01Z...WHICH WOULD PROMOTE TRAINING...ESPECIALLY OVER EASTERN OR
INTO SOUTHWEST ID.

MOST OF THE AVAILABLE HIGH RESOLUTION GUIDANCE (INCLUDING THE MOST
RECENT HRRR AND EXPERIMENTAL HRRR) SHOWED THE POTENTIAL FOR LOCAL
1.00 TO 2.00 INCH RAINFALL AMOUNTS...WITH THE HIGHEST AMOUNTS OVER
EASTERN OR. THIS MUCH RAINFALL COULD RESULT IN LOCAL FLASH FLOOD
ISSUES...WHICH WOULD BE ENHANCED IN AREAS WITH BURN SCARS...
POSSIBLY PRODUCING DEBRIS FLOWS. SINCE THE OVERALL CONVECTIVE
COVERAGE COULD REMAIN SCATTERED...FLASH FLOODING IS ONLY
CONSIDERED POSSIBLE.

HAYES

ATTN...WFO...BOI...LKN...MFR...MSO...PDT...REV...

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

LAT...LON   45671900 45621669 44801570 41961556 40631627
            40181668 39621733 39611736 39611917 41481997
            44131990