MESOSCALE PRECIPITATION DISCUSSION 0503
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 PM EDT MON SEP 21 2015
 
AREAS AFFECTED...SOUTHERN ARIZONA...SOUTHWEST NEW MEXICO 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 211833Z - 212333Z
 
SUMMARY...CONTINUED STEADY TO BRIEFLY HEAVY RAINFALL MAY RESULT IN
FLASH FLOODING THIS AFTERNOON.

DISCUSSION...RAINFALL ASSOCIATED WITH TROPICAL DEPRESSION 16E
CONTINUES TO MOVE NORTHEAST INTO SOUTHERN ARIZONA AND NEW MEXICO
THIS AFTERNOON. WARMING CLOUD TOPS THE PAST SEVERAL HOURS WERE
INDICATIVE OF A WEAKENING OF CONVECTION...AND OBSERVED RAINFALL
RATES HAVE GENERALLY BEEN STAYING IN THE 0.25"-0.5" RANGE.
ALTHOUGH GIVEN THE EXTENDED DURATION OF THE STEADY RAINFALL...HAVE
SEEN TOTAL AMOUNTS AS HIGH AS 1.7" AS OF 1830Z ACROSS PORTIONS OF
FAR SOUTHERN ARIZONA.

FOR SOUTHEAST ARIZONA/SOUTHWEST NEW MEXICO...RECENT SATELLITE
TRENDS AND AMSU ESTIMATED RAINFALL RATES SUGGEST THAT THE
INTENSITY OF RAIN IS UNLIKELY TO INCREASE MUCH MORE THAN WHAT IS
CURRENTLY OCCURRING....AT LEAST THROUGH THIS AFTERNOON. GIVEN A
LACK OF INCREASING INSTABILITY OR FORCING...STEADY STATE OF
RAINFALL RATES SEEM TO MAKE SENSE. THE 12Z HIGH RESOLUTION
ARW/NMMB AND RECENT HRRR OPERATIONAL RUNS HAVE ALSO BACKED OFF ON
QPF AMOUNTS FROM RUNS EARLIER THIS MORNING. THESE EARLIER
RUNS...ALONG WITH THE EXPERIMENTAL HRRR...SUGGESTED A CORE OF
HEAVY RAINFALL NEAR THE DEPRESSIONS CENTER WOULD MOVE INTO
SOUTHEAST ARIZONA RESULTING IN THE HIGHER RATES/AMOUNTS. BASED ON
TRENDS MENTIONED ABOVE...THIS DOES NOT APPEAR TO BE HAPPENING.
WITH THAT SAID...GIVEN THE NEAR CLIMATOLOGICAL MAX PRECIPITABLE
WATER RESULTING IN EFFICIENT RAINFALL AND THE EXTENDED DURATION OF
THE STEADY RAIN...SOME FLOODING ISSUES ACROSS THE REGION SEEM
PROBABLE...WITH TOTAL RAINFALL OF 1-3" EXPECTED...LOCALLY HIGHER. 

ACROSS SOUTHWEST ARIZONA...LATEST SPC MESOSCALE ANALYSIS SHOWS AN
AREA OF MARGINAL INSTABILITY. THIS IS LOCATED IN A REGION OF
ENHANCED FORCING AHEAD OF MID LEVEL SHORTWAVE ENERGY SEEN ON WATER
VAPOR IMAGERY NEAR THE ARIZONA/MEXICO BORDER. ACCORDING TO GPS
DATA...PRECIPITABLE WATER VALUES IN THIS AREA ARE APPROACHING 2".
THIS COMBINED WITH THE INSTABILITY...WILL RESULT IN AREAS OF
CONVECTION WITH LOCALLY HEAVY RAINFALL RATES POSSIBLY EXCEEDING
FLASH FLOOD GUIDANCE. LATEST IR IMAGERY DOES INDEED SHOW COOLING
CLOUD TOPS AND INCREASING CONVECTION IN THIS AREA. AS MOISTURE
CONTINUES TO ADVECT NORTH...CONVECTION MAY INCREASE IN COVERAGE
ACROSS THE HIGHER TERRAIN OF SOUTH CENTRAL ARIZONA AS WELL...WHERE
SUNSHINE SHOULD ALLOW FOR SOME DESTABILIZATION.

CHENARD

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

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

LAT...LON   34361431 34291213 34240987 33350793 32430714 
            31290723 30820919 31331377 31951509 33211472