MESO: Mesoscale Discussion 0793

ACUS11 KWNS 120641
SWOMCD
SPC MCD 120640
LAZ000-TXZ000-120745-

MESOSCALE DISCUSSION 0793
NWS STORM PREDICTION CENTER NORMAN OK
0140 AM CDT SAT MAY 12 2012

AREAS AFFECTED...SE TX INCLUDING THE HOUSTON METRO AREA

CONCERNING...TORNADO WATCH 274...

VALID 120640Z - 120745Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 274 CONTINUES.

SUMMARY...THE OVERALL SEVERE WEATHER THREAT IS EXPECTED TO CONTINUE
DIMINISHING ACROSS WW 274...GIVEN WEAK LAPSE RATES AND DECREASING
BULK SHEAR. MEANWHILE...HEAVY RAINFALL RATES /1-1.5 INCH PER HOUR/
ARE EXPECTED TO BE THE GREATER CONCERN THROUGH THE OVERNIGHT PERIOD
WITHIN A 25 MILE WIDE CORRIDOR FROM FORT BEND COUNTY EWD THROUGH SRN
HARRIS AND CHAMBERS COUNTIES.

DISCUSSION...AT 0545Z...WATER VAPOR IMAGERY SHOWED A SLOW ENEWD
MOVING SHORTWAVE TROUGH ACROSS ERN OK/NERN TX...WITH THE SRN EXTENT
OF APPARENT STRONGER FORCING FOR ASCENT AIDING IN MAINTAINING THE
ONGOING TSTMS OVER THE NRN PART OF WW 274 AND W-E THROUGH THE
HOUSTON METRO AREA. REGIONAL RADAR IMAGERY INDICATED A COMPOSITE
OUTFLOW BOUNDARY ASSOCIATED WITH THE LATTER TSTM ACTIVITY EXTENDING
FROM CENTRAL GALVESTON COUNTY WWD THROUGH NRN BRAZORIA TO SRN FORT
BEND COUNTIES. A SWLY 20-30 KT LLJ FROM THE MIDDLE-UPPER TX COASTAL
AREA WILL PROVIDE A FEED OF MODERATE-STRONG MUCAPE /2000-3000 J PER
KG/ RESIDING OVER THE MIDDLE-SRN TX COAST INTO THE ONGOING EWD
TRAINING TSTMS FROM FORT BEND TO CHAMBERS COUNTIES. PW VALUES RANGE
FROM 1.5-1.75 INCH ACROSS SE TX/UPPER TX COAST AND PROPAGATION
VECTORS ARE EXPECTED TO WEAKEN TO AROUND 10 KT BY 12Z. THESE
FACTORS SUGGEST TSTMS SHOULD CONTINUE TO DEVELOP OVER FORT
BEND/HARRIS COUNTIES AND TRAIN EWD...WITH LOCAL RAINFALL RATES UP TO
2 INCH PER HOUR POSSIBLE.

FARTHER N OVER THE NRN PART OF WW 274...STRONGER FORCING FOR ASCENT
WITH THE SHORTWAVE TROUGH SHOULD SUPPORT ADDITIONAL TSTM DEVELOPMENT
OVERNIGHT...BUT WEAKER AVAILABLE INSTABILITY AND WEAK LAPSE RATES
SUGGEST THE OVERALL SEVERE WEATHER THREAT WILL BE LOW.

..PETERS.. 05/12/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...LCH...SHV...HGX...

LAT...LON 29519331 28779472 28689513 28789557 29349597 29779605
30279589 30889577 31379500 31119463 31189351 30379368
29789384 29759330 29519331

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