MESOSCALE PRECIPITATION DISCUSSION 0676...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
751 PM EDT SAT SEP 17 2016
 
CORRECTED FOR TYPOS IN LAST PARAGRAPH

AREAS AFFECTED...SOUTHERN PERMIAN BASIN IN TX/NM 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 172342Z - 180542Z
 
SUMMARY...ORGANIZED THUNDERSTORMS ARE GROWING IN COVERAGE NEAR THE
NM/TX BORDER IN AND NEAR THE MAF/MIDLAND TX CWA.  HOURLY RAIN
RATES UP TO 2" ARE POSSIBLE WHERE CELLS MERGE AND/OR TRAIN, WITH
LOCAL AMOUNTS UP TO 4" POSSIBLE.

DISCUSSION...SUPERCELL THUNDERSTORMS ARE GROWING MORE NUMEROUS
NEAR THE BORDER OF WEST-CENTRAL TX AND SOUTHEAST NM AS CELLS SPLIT
VAGUELY NEAR THE PECOS RIVER WITHIN THE SOUTHERN PERMIAN BASIN. 
PRECIPITABLE WATER VALUES OF 0.9-1.3" LIE ACROSS THE REGION PER
GPS VALUES, 1-2 SIGMAS ABOVE THE MEAN FOR MID-SEPTEMBER.  A
FRONTAL ZONE LYING ACROSS THE AREA, ALONG WITH THE DAVIS AND
GUADELUPE MOUNTAINS, APPEAR TO BE ACTING AS FOCI FOR STORM
INITIATION.  ACTIVITY IS MOVING EAST AT ROUGHLY 15 KTS, WHICH
ELEVATES THE STORM RELATIVE INFLOW TO 25-30 KTS (AFTER ACCOUNTING
FOR THE 10-15 KTS OF INFLOW AT 850 HPA SEEN ON VAD WIND PROFILES).
 MLCAPES OF 1000-4000 (AND MUCAPES OF 2000-5000) J/KG EXIST ACROSS
THE AREA PER SPC MESOANALYSES.  THE 12Z SSEO MEAN IS SLIGHTLY
DISPLACED TO THE NORTH, BUT ADVERTISED A BROAD AREA OF 1"+ AMOUNTS
IN THIS AREA.

FORWARD PROPAGATION SHOULD BE THE NAME OF THE GAME AS THE STORMS
GROW UPSCALE.  LOW-LEVEL INFLOW IS EXPECTED TO INCREASE AND VEER
TO THE SOUTH-SOUTHEAST WITH TIME WHILE PRECIPITABLE WATER VALUES
INCREASE AN ADDITIONAL QUARTER-INCH.  SINCE THE STORM MOTION IS
VARIABLE, RANGING FROM EAST-SOUTHEAST TO EAST-NORTHEAST,
COLLISIONS/ MERGERS APPEAR TO BE THE INITIAL CAUSE FOR HEAVY
RAINFALL OTHER THAN THE SUPERCELL NATURE OF THE CONVECTION, THOUGH
CELL TRAINING SHOULD BE POSSIBLE AS CONVECTIVE COVERAGE CONTINUES
TO INCREASE AND THE LOW-LEVEL INFLOW BECOMES MORE NORMAL TO THE
THERMAL BOUNDARY.  HOURLY RATES UP TO 2", WITH LOCAL AMOUNTS OF UP
TO 4", ARE EXPECTED OVER THE NEXT SEVERAL HOURS.  USED A SIX HOUR
WINDOW AS THE GFS-BASED GALVEZ-DAVISON INDEX (VALUES OF 30-40)
INDICATES THAT AREAS NEAR THE PERMIAN BASIN SHOULD EXHIBIT
SCATTERED TO NUMEROUS THUNDERSTORM COVERAGE THROUGH 06Z.  A COLD
POOL IS DEVELOPING ACROSS SOUTHEAST NM NEAR A PARTICULARLY
LONG-LIVED CELL.  THIS COLD POOL SHOULD BEGIN TO SHORTEN THE
BREADTH OF THE CONVECTIVE COVERAGE WITH TIME.  USED THE EASTERN
EXTENT OF THE 1000 J/KG MLCAPE AND 20-25 KT 850 HPA INFLOW AS A
GUIDE FOR HOW FAR EAST TO GO.  

ROTH

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

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

LAT...LON   33220338 32890073 30640002 30310422 31260563 
            32370501