San Antonio, Austin, Houston, Victoria, College Station all in the bullseye for severe weather on Tuesday. Tue-Thursday will be nasty, with flooding likely.
DISCUSSION... /ISSUED 402 PM CST MON MAR 7 2016/
AN ACTIVE WEATHER PATTERN IS SETTING UP FOR SOUTHEAST TEXAS AS AN
ANOMALOUSLY STRONG/DEEP UPPER LOW FOR THIS TIME OF YEAR APPROACHES
THE REGION. AFTERNOON WATER VAPOR IMAGERY SHOWS THIS FEATURE
BEGINNING TO TAKE SHAPE OVER SOUTHERN/BAJA CALIFORNIA AND WILL
TRANSLATE DIG SOUTHEAST INTO NORTHERN MEXICO OVER THE NEXT 24 TO
36 HOURS. AS THIS HAPPENS... FAVORABLE UPPER LEVEL SUPPORT
COMBINED WITH EXCEPTIONALLY MOIST LOW LEVEL INFLOW WILL RESULT IN
PERIODS OF SHOWERS AND THUNDERSTORMS CAPABLE OF SEVERE WEATHER AND
HEAVY RAINFALL ACROSS SOUTHEAST TEXAS TUESDAY AFTERNOON THROUGH
WEDNESDAY AFTERNOON.
GENERALLY DRY CONDITIONS ARE EXPECTED TO PERSIST THIS AFTERNOON
AND EVENING... WITH ISOLATED TO SCATTERED SHOWERS DEVELOPING
OVERNIGHT TONIGHT ACROSS THE REGION AS A 45 TO 50 KNOT LOW LEVEL
JET INTENSIFIES ACROSS THE REGION. AS THE UPPER LOW DIGS FARTHER
INTO MEXICO DURING THE DAY ON TUESDAY... INCREASINGLY DIFFLUENT
FLOW ALOFT WILL ALLOW FOR THE FIRST ROUND OF CONVECTION TO GET
GOING TUESDAY AFTERNOON WITH WIDESPREAD SHOWERS AND THUNDERSTORMS
DEVELOPING ACROSS THE REGION.
WITH
MLCAPE VALUES APPROACHING 1000-2000 J/KG... 0-6 BULK SHEAR
VALUES AROUND 40-50 KNOTS... AND 0-1 KM SHEAR VALUES EXCEEDING 25
KNOTS TUESDAY AFTERNOON AND EVENING... STRONG TO SEVERE
THUNDERSTORM DEVELOPMENT WILL BE POSSIBLE ACROSS MOST OF THE
REGION. ISOLATED TORNADOES AND DAMAGING WIND WILL BE THE PRIMARY
THREATS WITH THIS ACTIVITY... WITH
THE AMOUNT OF WIND ENERGY
ASSOCIATED WITH THIS STORM SYSTEM ALLOWING THE TORNADO AND
DAMAGING WIND THREAT TO PERSIST WITH ANY THUNDERSTORM THAT
DEVELOPS WELL INTO THE EVENING AND OVERNIGHT HOURS AS THE LOW
LEVEL JET REINTENSIFIES. HOWEVER... AN UPPER LEVEL SPEED MINIMA
MOVING ACROSS THE REGION AROUND MIDNIGHT WEDNESDAY MIGHT BE ENOUGH
TO PROVIDE A BRIEF BREAK IN RAIN CHANCES LATE TUESDAY. THIS WILL
QUICKLY CHANGE AS
THE UPPER LOW DRAWS CLOSER EARLY WEDNESDAY
MORNING... WITH AN ASSOCIATED THUNDERSTORM COMPLEX BLOSSOMING
ACROSS SOUTH CENTRAL TEXAS AND MOVING EASTWARD THROUGH THE
REMAINDER OF THE DAY WEDNESDAY.
ADDITIONALLY... A THREAT FOR HEAVY RAIN WILL EXIST ACROSS THE
REGION DURING THIS TIME AND PEAK LATE TUESDAY INTO WEDNESDAY
MORNING COINCIDENT WITH THE HIGHEST ATMOSPHERIC MOISTURE LEVELS. WHILE
ANTECEDENT CONDITIONS ARE NOT THE MOST SUPPORTIVE FOR RUNOFF
LEADING TO FLASH FLOODING GIVEN THE RECENT DRY SPELL THE REGION
HAS BEEN UNDER /HOUSTON INTERCONTINENTAL IS OVER 3 INCHES BELOW
NORMAL FOR RAINFALL FOR THE YEAR SO FAR/... FORECAST SOUNDINGS
SHOW PRECIPITABLE WATER VALUES CLIMBING TO 1.7 TO ALMOST 1.9
INCHES WEDNESDAY MORNING. THESE VALUES ARE NEAR RECORD LEVELS
WHEN COMPARED WITH SOUNDING CLIMATOLOGY FOR CORPUS CHRISTI AND
LAKE CHARLES. ADDITIONALLY... STORM MOTION OF INDIVIDUAL CELLS IS
EXPECTED TO BE VERY QUICK /CELLS MOVING SOUTH TO NORTH AROUND 35
TO 40 KNOTS/ BUT GENERALLY UNIDIRECTIONAL SHEAR PROFILES DURING
THIS TIME WILL ENCOURAGE STORMS TO TRAIN ACROSS THE SAME AREA.
AS A RESULT... HAVE ISSUED A FLASH FLOOD WATCH FOR ALL OF
SOUTHEAST TEXAS BEGINNING NOON TUESDAY AND LASTING THROUGH
WEDNESDAY AFTERNOON. SREF PLUME MEANS SHOW RAIN TOTALS GENERALLY
AROUND 5 INCHES ACROSS MUCH OF THE REGION... BUT LOCAL FLASH FLOOD
GUIDANCE OFFERS SOME SUPPORT FOR ISOLATED HIGHER AMOUNTS THAT
OUTLIERS ARE ADVERTISING /AROUND 10 INCHES/ GIVEN THE ANTICIPATED
TRAINING... INSTABILITY... AND HIGH AVAILABLE ATMOSPHERIC
MOISTURE. ACCORDINGLY...
WIDESPREAD RAIN TOTALS OF 3 TO 7 INCHES
WILL BE POSSIBLE WITH LOCALLY HIGHER AMOUNTS OF 10 TO 12 INCHES.
GIVEN THE ANTICIPATED TIMING OF THIS COMPLEX... TRAVEL IMPACTS
WILL BE POSSIBLE ACROSS MUCH OF THE REGION WEDNESDAY MORNING.
SUBTLE DISTURBANCES TRANSLATING ACROSS THE REGION IN THE
SOUTHERLY FLOW ALOFT AHEAD OF THE UPPER LOW WILL RESULT IN PERIODS
OF SHOWERS AND THUNDERSTORMS CONTINUING ACROSS THE REGION
WEDNESDAY EVENING INTO THURSDAY MORNING... BUT THE BEST
INFLOW/MOISTURE SHIFTS EAST OF THE REGION AND WILL HELP LIMIT THE
HEAVY RAIN THREAT DURING THIS TIME. MEDIUM RANGE GUIDANCE
CONTINUES TO STRUGGLE WITH CONSISTENCY GIVEN THE PLACEMENT/TRACK
OF THE UPPER LOW... BUT WITH THIS FEATURE IN THE VICINITY OF THE
REGION THROUGH THE END OF THE WEEK HAVE MAINTAINED SHOWER AND
THUNDERSTORM CHANCES IN THE FORECAST THROUGH SATURDAY.