MESOSCALE PRECIPITATION DISCUSSION 0399
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1113 AM EDT SAT SEP 27 2014
 
AREAS AFFECTED...CNTRL/NRN ARIZONA INTO UTAH 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 271510Z - 272100Z
 
SUMMARY...WRN ARIZONA INTO WRN UTAH SHOULD CONTINUE TO SEE FLASH
FLOODING WITH A SLOW MOVING LINE OF TRAINING CONVECTION OVER THE
NEXT FEW HOURS. MEANWHILE ADDITIONAL CELLULAR DEVELOPMENT IS
EXPECTED EAST OF THIS LINE WITH THE ONSET OF DAYTIME HEATING.

DISCUSSION...THE LATEST WV IMAGERY CONTINUED TO SHOW A SLOW MOVING
CUTOFF LOW...CENTERED OVER THE CNTRL CALIFORNIA/NEVADA
BORDER...WITH STRONG UPPER DIFFLUENCE OVER MUCH OF ARIZONA.
MAXIMUM 850-700 MB FLOW OF ROUGHLY 40 KTS HAS BEEN CONFINED WITHIN
A SMALL CORRIDOR OVER NWRN ARIZONA...COINCIDENT WITH THE HEAVIEST
RADAR ESTIMATED RAINFALL RATES OF 1-2 IN/HR...OVER PORTIONS OF
MOHAVE COUNTY. UNIDIRECTIONAL WIND PROFILES HAVE BEEN SUPPORTING
TRAINING CONVECTION WITH A SLOW EWD CRAWL SINCE 12Z.

LOW LEVEL INFLOW WITHIN THE 850-700 MB LAYER IS FORECAST BY THE
RAP TO WEAKEN TO ABOUT 30 KTS BY 18Z...BUT SHOULD CONTINUE TO
SUPPORT REPEAT CELL MOTIONS UNDER STRONGLY DIFFLUENT FLOW ALOFT.
IN ADDITION...DESPITE EXTENSIVE CLOUD COVER...INSTABILITY WILL
INCREASE THROUGHOUT THE AFTERNOON WITH SOME CONTRIBUTIONS FROM
DAYTIME HEATING AND INCREASED LOW LEVEL MOISTURE ADVECTION. THE
EXPECTATION IS FOR THE CURRENT LINE OF TRAINING CONVECTION TO
CONTINUE TO SLOWLY MOVE EASTWARD...PERHAPS LOSING SOME
ORGANIZATION WITH WEAKENING 850-700 MB FLOW...BUT WITH ADDITIONAL
CELLS TO DEVELOP AND TRAIN TOWARD THE EAST. FLASH FLOODING IS
CONSIDERED LIKELY GIVEN STRONG HI-RES MODEL SUPPORT FOR ADDITIONAL
HEAVY RAINFALL.

OTTO

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

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

LAT...LON   39911291 39661170 38501139 36701134 35161020 
            34021019 33411158 34161370 35941383 37411372 
            38951372