River Flood Warning 40, NWS Shreveport, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
1033 AM CDT THU JUL 12 2007

.DISCUSSION...

KSHV 12Z SOUNDING SHOWS A MOIST...UNSTABLE AIRMASS IN PLACE...AND
SUGGESTS ANOTHER BALMY AFTERNOON AHEAD.  CURRENT SURFACE OBS SHOW
88F AT KSHV...SO WE/LL UPDATE TO BUMP AFTERNOON TEMPS UP A SKOSH.

&&

.AVIATION...

EXPECT MOSTLY VFR THROUGH THE DAY AND OVERNIGHT. THUNDERSTORM
COMPLEX OVER CENTRAL OK MAY DIMINISH AS IT MOVES SOUTHEASTWARD
TODAY...BUT MAY ALSO PRODUCE BOUNDARY FOR ADDITIONAL CONVECTION THIS
AFTERNOON...BEST CHANCES OF THIS IS GENERAL VICINITY IN AND AROUND
I 30. WILL KEEP AFTERNOON VCTS IN FOR MOST TAF SITES. IN AND NEAR
THUNDERSTORMS WINDS WILL HAVE THE POTENTIAL TO BE STRONG AND GUSTY
WITH SPEEDS UP TO 25 KNOTS...BRIEF BUT HEAVY RAINFALL...AND MVFR
CEILINGS. OUTSIDE AND AWAY FROM THUNDERSTORMS WINDS WILL BE S TO SW
5 TO 10 KNOTS THEN DECEASING TO S TO SE 3 TO 6 KNOTS AROUND
13/00Z. /17/

&&

.PREV DISCUSSION... /ISSUED 443 AM CDT THU JUL 12 2007/

DISCUSSION...
NW FLOW ALOFT WILL MAKE FOR A TRICKY FORECAST FROM NOW THROUGH
SATURDAY...AS IT WILL NOT TAKE MUCH TO FIRE OFF CONVECTION DURING PEAK
HEATING...AS WAS THE CASE ACROSS NE TX/SW AR/N LA WEDNESDAY. UPPER AIR
ANALYSIS INDICATES THAT OUR WEAK SHEAR AXIS STILL LINGER NW-SE ACROSS
NE TX/N LA...SANDWICHED BETWEEN THE W GULF OF MX/CNTRL TX RIDGE...AND
LONGWAVE TROUGH OVER THE OHIO/TN VALLIES INTO THE MID-ATLANTIC STATES.
9Z SURFACE THETA-E ANALYSIS INDICATES A WEAK SURFACE TROUGH/BOUNDARY
EXTENDING W-E FROM CNTRL OK...E INTO CNTRL AR THIS MORNING. THIS DIRTY
NW FLOW...AND STATIONARY SURFACE BOUNDARY TO THE N...WILL FOCUS
SCATTERED CONVECTION DURING PEAK HEATING MAINLY THIS AFTERNOON...WITH
STORMS BECOMING MORE OUTFLOW DOMINANT AS THEY TRAVERSE SE INTO EXTREME
NE TX/N LA. HAVE INCREASED POPS A TAD UP N TO REFLECT THIS
THINKING...AND CAN NOT RULE OUT ISOLATED SVR CONVECTION WITH LOCALLY HEAVY
RAINFALL. BELIEVE STORMS WILL BEGIN TO DIMINISH ONCE AGAIN AFTER
SUNSET...BUT WILL HAVE TO WATCH CLOSELY UPSTREAM ACROSS SW KS/E TX
PANHANDLE/W OK...FOR NEXT EMBEDDED SHORTWAVE THAT WILL DROP SE ACROSS
CNTRL/S OK OVERNIGHT.

PREFER THE SLIGHTLY MORE PROGRESSIVE NAM/NGM/UKMET SOLUTION INITIALLY
WITH THIS NEXT PERTURBATION...WITH A 25-30 KT SW LLJ ENHANCING MCS
DEVELOPMENT...SLIPPING SE ALONG THE RED RIVER VALLEY TOWARDS EXTREME
NE TX/SE OK/ADJACENT SW AR EARLY FRIDAY. INCREASED POPS TO HIGH CHANCE
FOR THE FAR N ZONES LATE TONIGHT...THEN LIKELY FOR FRIDAY...AS MCS
BEGINS TO DECAY FRIDAY MORNING WITH THE LOSS OF THE LLJ.
HOWEVER...ASSOCIATED OUTFLOW BOUNDARIES FROM THIS MCS WILL LIKELY
BECOME DEPOSITED ACROSS THE REGION...WITH SUFFICIENT HEATING BENEATH
CONVECTIVE DEBRIS ENOUGH FOR ADDITIONAL SCATTERED CONVECTION TO FORM
DURING THE AFTERNOON ACROSS E TX/SE OK/SW AR/EXTREME N LA. AT THIS
TIME...CONSIDERABLE UNCERTAINTY REMAINS AS TO THE EXACT
LOCATION/TIMING/TRACK OF THIS POTENTIAL MCS...AND ITS ASSOCIATED
SURFACE BOUNDARIES. THUS...CAN NOT PINPOINT HEAVY RAINFALL POTENTIAL
WITH ENOUGH CONFIDENCE TO MENTION IN THE FORECAST ATTM. HOWEVER...WILL
HIGHLIGHT HEAVY RAINFALL AND EVEN ISOLATED SVR THREAT IN THE MORNING HWO.

BELIEVE THE NAM/UKMET IS A BIT TOO FAST IN ACCELERATING THIS NEXT
SHORTWAVE TOO FAR S ACROSS E TX/N LA FRIDAY NIGHT/SATURDAY...AS
LONGWAVE ENERGY SHIFTS E TOWARDS THE E COAST...LEAVING THIS
TROUGH/SHEAR AXIS CUT OFF FROM THE MAIN FLOW/TRAPPED BENEATH LARGE W
U.S. RIDGE. THUS...SHEAR AXIS/WEAK CLOSED LOW WILL LIKELY BECOME
QUASISTATIONARY ACROSS NCNTRL/NE TX PER THE ECMWF. THUS...POTENTIAL
FOR ADDITIONAL HEAVY RAINFALL/FLOODING WILL INCREASE THIS WEEKEND
ACROSS THE WATERLOGGED AREAS OF NE TX/SE OK. TO MAKE MATTERS WORSE...W
U.S. RIDGE WILL BEGIN TO BREAK DOWN BY LATE SUNDAY IN RESPONSE TO
TROUGHING ACROSS THE PAC NW/BRITISH COLUMBIA...SHIFTING THE RIDGE A
TAD SE INTO THE CNTRL PLAINS BY MONDAY...MAINTAINING SHEAR AXIS OVER
N/NE TX. WILL KEEP CHANCE POPS GOING THROUGH MUCH OF THE EXTENDED FOR
NOW...ALTHOUGH ECMWF/GFS INDICATE BERMUDA RIDGE RETROGRADING W INTO
THE SE U.S. LATE MONDAY/TUESDAY...THUS SHIFTING THE SHEAR AXIS W
ACROSS TX AS WELL AWAY FROM THE REGION. SHOULD THIS INDEED
OCCUR...CONVECTION WILL BECOME LIMITED...WHILE TEMPS HEAT UP TO THE
MID/UPPER 90S...MORE TYPICAL OF MID JULY. HAVE REFLECTED THIS THINKING
INTO THE LATTER PERIODS OF THE EXTENDED FORECAST.

PRELIMS ARE NEXT...

15

AVIATION...
WITH THE EXCEPTION OF VISIBILITY REDUCTIONS AND POSSIBLY SOME LOWER
CLOUDS PRODUCING MVFR CATEGORIES THIS MORNING...EXPECT TO CARRY
MOSTLY VFR THROUGH THE DAY AND OVERNIGHT. DURING THE AFTERNOON
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO INCREASE OVER
MAINLY SE OK...SW AR...AND PARTS OF NORTHERN NE TX...AND PARTS OF NW
AND N CENTRAL LA ALONG AND NEAR A KLBR...KDNT...KSHV...KGMS...AND
KHEZ LINE. RAIN CHANCES WILL BE AROUND 30 PERCENT THIS AREA AND WILL
MENTION VCTS IN TAF SITES NEAR AND TO THE NE OF THIS LINE.  IN AND
NEAR THUNDERSTORMS WINDS WILL HAVE THE POTENTIAL TO BE STRONG AND
GUSTY WITH SPEEDS UP TO 25 KNOTS...BRIEF BUT HEAVY RAINFALL...AND
MVFR CEILINGS. OUTSIDE AND AWAY FROM THUNDERSTORMS WINDS WILL BE
S TO SW 5 TO 10 KNOTS AFTER 12/16Z THEN DECEASING TO S TO SE 3 TO 6
KNOTS AROUND 13/00Z. /06/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  75  94  73  89 /  20  30  30  40
MLU  74  92  72  89 /  30  30  30  30
DEQ  71  88  70  88 /  50  60  30  40
TXK  73  90  72  88 /  40  50  30  40
ELD  73  91  71  88 /  40  50  30  30
TYR  75  91  74  88 /  20  40  40  40
GGG  74  93  73  88 /  20  40  40  40
LFK  74  94  74  89 /  10  20  30  30

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
&&

17/44/12

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