MESOSCALE PRECIPITATION DISCUSSION 0558
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM EDT MON OCT 05 2015
 
AREAS AFFECTED...PORTIONS OF THE SOUTHWEST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 051948Z - 060118Z
 
SUMMARY...THUNDERSTORMS ARE EXPANDING IN COVERAGE NEAR THE AZ/NV
BORDER AND THE FOUR CORNERS REGION.  HOURLY RAIN RATES UP TO 1"
COULD CAUSE FLASH FLOODING AND ASSOCIATED DEBRIS FLOWS.

DISCUSSION...SATELLITE IMAGERY SHOWS AN UPPER LOW OVER SOUTHEAST
CA WITH TWO ASSOCIATED MOISTURE PLUMES -- ONE NEAR THE LOWER CO
RIVER AND THE SECOND EXTENDING FROM TUCSON AZ THROUGH THE FOUR
CORNERS.  PRECIPITABLE WATER VALUES OF 0.75-1.2" LIE ACROSS THIS
REGION PER GPS VALUES, WHICH IN SOUTHERN NV AND NEAR THE FOUR
CORNERS ARE OVER TWO SIGMAS ABOVE THE MEAN FOR EARLY OCTOBER;
ENOUGH FOR HEAVY RAIN ISSUES IN THE TERRAIN.  VAD WIND PROFILES
AND RAP FORECAST FIELDS INDICATE 700 HPA/CLOUD BASE INFLOW OF
20-40 KTS IN THIS REGION, WHICH HAS LED TO THE FORMATION OF CLOUD
STREETS.  WHEN COMBINED WITH DEEP SOUTHERLY FLOW,  NARROW
CONVECTIVE SEGMENTS HAVE OCCASIONALLY ATTEMPTED TO TRAIN.  MLCAPES
ARE IN THE 500-1000 J/KG RANGE PER SPC MESOANALYSES.

THE AVAILABLE MOISTURE ALLOWS FOR HOURLY RAIN RATES UP TO 1".  THE
CAM GUIDANCE ADVERTISED LOCAL AMOUNTS IN THE 1-2" RANGE, WHICH
ACROSS MUCH OF THIS REGION, WOULD EXCEED THE ONCE A DECADE RETURN
PERIOD FOR EACH INDIVIDUAL SPOT WITHIN A SIX HOUR PERIOD, IMPLYING
FLASH FLOOD ISSUES ARE POSSIBLE.  THE GUIDANCE SHOWS THUNDERSTORMS
ACROSS THE REGION BEGINNING TO FADE AROUND 01Z, WHILE THE BEST 700
HPA INFLOW MIGRATES/SHIFTS FROM WEST TO EAST ACROSS THE REGION. 
FLASH FLOODING, WITH ASSOCIATED DEBRIS FLOWS, IS POSSIBLE.

ROTH

ATTN...WFO...ABQ...FGZ...GJT...PSR...SLC...VEF...

ATTN...RFC...CBRFC...CNRFC...WGRFC...

LAT...LON   39791046 39610964 39190847 38450773 37740742 
            37370749 36810801 36340909 35750978 35380997 
            34591043 34661095 35091132 35751199 36411293 
            36081380 35171399 34241412 34901520 35831585 
            37111745 37481645 37801410 38031235 39001123