MESOSCALE PRECIPITATION DISCUSSION 0590
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT TUE OCT 20 2015
 
AREAS AFFECTED...PORTIONS OF AZ & NM 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 201853Z - 210053Z
 
SUMMARY...THUNDERSTORMS HAVE SHOWN A SHARP INCREASE IN DEVELOPMENT
OVER THE PAST COUPLE HOURS.  CELL MERGERS/TRAINING ACROSS THE AREA
COULD LEAD TO FLASH FLOODING/DEBRIS FLOWS.

DISCUSSION...AN UPPER LOW NEAR THE LOWER CO RIVER VALLEY IS BEING
CIRCUMNAVIGATED BY SEVERAL SHORTWAVES ON ITS WESTERN AND SOUTHERN
PERIPHERY PER WATER VAPOR IMAGERY.  THUNDERSTORMS APPEAR
CONCENTRATED NEAR ITS CENTER AND WITHIN ITS WARM CONVEYOR BELT
CIRCULATION NEAR THE NM/AZ BORDER.  GPS VALUES INDICATE
PRECIPITABLE WATER VALUES AROUND 1", WHICH IS SUFFICIENT FOR HEAVY
RAIN ISSUES IN TOPOGRAPHY.  CLOUD BASE INFLOW (NEAR 700 HPA) IS
20-25 KTS PER VAD WIND PROFILES, NEAR THE MAGNITUDE OF THE 850-400
HPA MEAN WIND, WHICH SUPPORTS THE CLOUD STREETS SEEN ON RECENT
VISIBLE SATELLITE IMAGERY.  THIS MAGNITUDE OF INFLOW SHOULD
FURTHER ORGANIZE CONVECTION.  MLCAPE VALUES NEAR AND SOUTH OF THIS
REGION ARE IN THE 1000-2000 J/KG RANGE.  DIRECTIONAL WIND SHEAR
WITH HEIGHT SHOULD ASSURE FORWARD PROPAGATION, TO THE NORTHEAST AT
25-30 KTS.

THE EXPECTATION IS FOR THUNDERSTORMS TO CONTINUE TO GROW IN
COVERAGE AND INTENSITY OVER THE NEXT 3-4 HOURS, FEEDING OFF THE
AVAILABLE INSTABILITY AND LOW-LEVEL INFLOW.  THIS WOULD OCCUR BOTH
NEAR THE CENTER OF THE UPPER LEVEL LOW, WITHIN THE SYSTEM'S WARM
CONVEYOR BELT, AND WHERE OUTFLOW BOUNDARIES INTERACT ACROSS
SOUTH-CENTRAL AZ.  THE 06Z/12Z SSEO NEIGHBORHOOD PROBABILITIES FOR
EXCEEDING THE 10 YEAR RECURRENCE INTERVAL FOR HEAVY RAINFALL
INDICATE THE PEAK OF THIS HEAVY RAIN EVENT SHOULD BE IN THE
21Z-00Z TIME FRAME.  MOST OF THE CAM GUIDANCE HAS BEEN TOO FAR
WEST/NORTHWEST WITH ONGOING THUNDERSTORM ACTIVITY.  THE CAM
GUIDANCE INDICATES LOCAL AMOUNTS OF 2-3" ARE POSSIBLE, WHICH COULD
FALL QUICKLY AND REACH 10-25 YEAR RECURRENCE INTERVALS WITHIN THIS
ARID REGION.  HOURLY RAIN RATES OF 1" ARE SUPPORTED BY THE
AVAILABLE MOISTURE, THOUGH IN AREAS WHERE CELL MERGERS ARE
POSSIBLE ACROSS CENTRAL AZ, COULD TEMPORARILY REACH 1.5".  FLASH
FLOODING, WITH ASSOCIATED DEBRIS FLOWS, ARE POSSIBLE THROUGH THE
AFTERNOON HOURS.

ROTH

ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC...VEF...

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

LAT...LON   36431077 35860926 36330757 35830668 35290613 
            33780621 32130612 31480611 31570663 31650750 
            31660810 31260815 31251080 31551180 32281334 
            32701402 34171364 34401341 35411176 36161172