MESOSCALE PRECIPITATION DISCUSSION 0593
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
716 PM EDT WED OCT 21 2015
 
AREAS AFFECTED...PORTIONS OF SOUTHEAST NM & WEST TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 212315Z - 220515Z
 
SUMMARY...A BURGEONING AREA OF THUNDERSTORMS WITH HOURLY RAIN
RATES UP TO 1.75" OVER THE NEXT SEVERAL HOURS COULD LEAD TO FLASH
FLOODING OVER SATURATING SOILS.

DISCUSSION...A MESOSCALE FRONTAL WAVE EAST OF EL PASO TX IS ACTING
AS THE FOCUS FOR CONVECTION ACROSS WESTERNMOST TX AND SOUTHEAST
NM.  INFLOW AT 850 HPA/NEAR CLOUD BASES IS 25-30 KTS PER VAD WIND
PROFILES, NEAR THE MAGNITUDE BUT AT A RIGHT ANGLE TO THE MEAN
850-400 HPA WIND.  THE AMOUNT OF DIRECTIONAL WIND SHEAR SHOULD
ALLOW FOR/CONTINUE FORWARD PROPAGATION.  THE REGION IS DIVERGENT
ALOFT TO THE EAST OF A SLOW-MOVING UPPER LOW IN AZ.  PRECIPITABLE
WATER VALUES ARE INCREASING, BETWEEN 0.8-1.4", WHICH IS 2-3 SIGMAS
ABOVE THE NORM FOR LATE OCTOBER.  CIN HAS FINALLY ERODED ACROSS
MUCH OF WESTERN TX, WHICH HAS ALLOWED FOR RECENT SURFACE-BASED
CONVECTION NEAR MIDLAND.  MLCAPES OF 1000-2000 J/KG LIE ACROSS THE
REGION.

AS A SHORTWAVE PIVOTS EASTWARD FROM SONORA STATE IN MEXICO,
CONVECTION SHOULD CONTINUE TO EXPAND IN COVERAGE ACROSS WESTERN TX
AND SOUTHEAST NM INITIALLY NEAR THE MESOSCALE BOUNDARY.  AFTER
02Z, SOME CIN COULD REDEVELOP WHICH WOULD ELEVATE THUNDERSTORM
ACTIVITY NORTH/ NORTHWEST OF THE SURFACE BOUNDARY.  INDIVIDUAL
CELLS SHOULD CONTINUE MOVING NORTH-NORTHEAST AT 25-30 KTS, WHICH
ORGANIZED CLUSTERS MOVING MORE NORTHEAST TO EAST-NORTHEAST AT
25-30 KTS PER FORWARD PROPAGATING CONVECTIVE VECTORS AND THE
1000-500 HPA THICKNESS PATTERN.    THE INCOMING SHORTWAVE IS
EXPECTED TO RAMP UP 850 HPA INFLOW TO ~50 KTS INTO THE BOUNDARY,
WHICH SHOULD HELP INCREASE CONVECTIVE ORGANIZATION, ALLOW
PRECIPITABLE WATER VALUES TO BREACH 1.5", AND ALLOW FOR THE
POSSIBILITY OF BACK BUILDING THUNDERSTORMS.  INSTABILITY ACROSS
THE REGION SHOULD BE FADING AFTER 05Z, WHICH SHOULD LEAD TO A
DOWNTURN IN COVERAGE AND INTENSITY THEREAFTER.  

THE ABOVE IDEAS ARE WELL ADVERTISED ON THE CAM GUIDANCE, WITH THE
12-18Z SSEO NEIGHBORHOOD PROBABILITIES FOR EXCEEDING THE THREE
HOUR FLASH FLOOD GUIDANCE VALUES JUMPING ABOVE 50% BY 01Z, AND 90%
AFTER 03Z ACROSS SOUTHEAST NM.  THE CAM GUIDANCE ADVERTISES LOCAL
2-3" AMOUNTS, WHICH COULD FALL QUICKLY AS THE AVAILABLE MOISTURE
SUPPORTS HOURLY RAIN RATES UP TO 1.75".  A COMBINATION OF THE 20Z
RAP/21Z HRRR/21Z EXPERIMENTAL HRRR/12Z ARW LOOKS MOST REASONABLE
FOR PLACEMENT OF THE HEAVY RAINFALL.  SOILS HAVE BEEN SATURATING
SINCE YESTERDAY, WHICH INCREASES SENSITIVITY TO HEAVY RAINFALL. 
FLASH FLOODING IS CONSIDERED POSSIBLE.   

ROTH

ATTN...WFO...ABQ...EPZ...LUB...MAF...SJT...

ATTN...RFC...ABRFC...WGRFC...

LAT...LON   34750319 34120111 32990063 31920114 31310285 
            31060419 31060530 32290611 33350575 33940517