Graphic for MPD #0511

MESOSCALE PRECIPITATION DISCUSSION 0511
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EDT WED JUL 19 2017

AREAS AFFECTED...NORTHWEST AZ & SOUTHWEST UT

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

VALID 191808Z - 200008Z

SUMMARY...CUMULI ARE BEGINNING TO DEVELOP ACROSS NORTHERN AZ AND
UT.  HOURLY RAIN RATES IN THE RESULTANT THUNDERSTORMS OF UP TO 2"
WITH LOCAL AMOUNTS TO 3" ARE EXPECTED LATE THIS MORNING INTO THIS
AFTERNOON.

DISCUSSION...MORNING THUNDERSTORM ACTIVITY ACROSS NORTHWEST AZ AND
SOUTHERN CA HAS SENT OUT AN OUTFLOW BOUNDARY WHICH ALONG WITH
EARLIER CLOUD COVER IS AN EFFECTIVE FRONT ACROSS THE REGION. 
ALOFT, MCVs ARE LOCATED ACROSS EXTREME NORTHWEST AZ AND SOUTHWEST
UT.  ML CAPES ARE ESTIMATED TO BE 500-1000 J/KG AT THIS TIME. 
EFFECTIVE BULK SHEAR SHOULD BE NEAR 20 KTS.  PRECIPITABLE WATER
VALUES ARE 1-1.5" WITHIN THE TERRAIN IN THIS REGION.

THE GUIDANCE INDICATES THAT CONVECTION SHOULD INITIATE DURING THE
NEXT COUPLE HOURS, WHICH SHOULD BECOME MORE RESTRICTED TO THE
TERRAIN WITH TIME AS 700 HPA TEMPERATURES WARM ACROSS THE REGION,
ACTING AS A CAPPING INVERSION ACROSS NEARLY VALLEYS.  WITH THE
AVAILABLE MOISTURE AND BUILDING INSTABILITY, WHICH SHOULD BUILD
ANOTHER 1000+ J/KG INTO THIS AFTERNOON, HOURLY RAIN RATES UP TO 2"
ARE POSSIBLE.  THE MEAN 850-400 HPA WINDS ARE WEAK, WHICH SHOULD
CONTRIBUTE TO SLOW CELL MOTIONS.  THE MESOSCALE GUIDANCE INDICATES
THAT LOCAL AMOUNTS TO 3" ARE POSSIBLE, WHICH COULD BE PROBLEMATIC
IN UT WHERE SUCH RAINFALL IS INFREQUENT/UNUSUAL.  FIRES DURING THE
PAST MONTH ACROSS NORTHERN AZ AND SOUTHWEST UT (PER AN SAB/NESDIS
BRIEFING) INDICATE THAT RECENT BURN SCARS COULD MAGNIFY HEAVY RAIN
ISSUES.

ROTH

ATTN...WFO...FGZ...SLC...VEF...

ATTN...RFC...CBRFC...

LAT...LON   39811105 39001098 38061073 37281136 36321139
            35541093 34601080 34111114 34201247 35051345
            36331401 37691392 38811292 39711207


Last Updated: 209 PM EDT WED JUL 19 2017