Area Forecast Discussion
Issued by NWS Shreveport, LA

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000
FXUS64 KSHV 251215
AFDSHV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
715 AM CDT MON MAY 25 2015

.AVIATION...
FOR THE 25/12Z TAFS...A VERY BUSY TAF CYCLE IS EXPECTED AS IFR AND
MVFR CIGS WILL LINGER THROUGH THIS MORNING...SLOWLY LIFTING INTO
LOW VFR RANGE BY AFTERNOON. THIS WILL COINCIDE WITH ADVANCING
CONVECTION FROM CNTRL TX INTO OUR WRN TAF SITES IN E TX. EXPECT
WIDESPREAD SHWRS AND TSTMS TO GRADUALLY SPREAD EAST...SOME STRONG
TO SEVERE WITH INCREASINGLY UNSTABLE AIR MASS. DAMAGING WINDS AND
HAIL WILL BE THE PRIMARY CONCERNS...ALONG WITH SEVERE TURBULENCE
IN THESE AREAS OF DEEP CONVECTION. SOUTH WINDS WILL INCREASE THIS
AFTERNOON TO AROUND 12-18 KTS WITH HIGHER GUSTS POSSIBLE...ADDING
TO THE RICH MOISTURE POOL TO HELP FUEL AFTERNOON SHWRS AND STORMS.
CONVECTION SHOULD GRADUALLY WIND DOWN TOWARD THE END OF THE TAF
PERIOD WITH LINGERING SHWRS AND VCTS STILL POSSIBLE OVERNIGHT.
/19/

&&

.PREV DISCUSSION... /ISSUED 526 AM CDT MON MAY 25 2015/

DISCUSSION...
ANOTHER COMPLICATED FORECAST THIS MORNING...GIVEN THE FACT THAT
THE MODELS ARE NOT IN GOOD AGREEMENT WITH THE TIMING AND PLACEMENT
OF THE QPF OF THE CONVECTION THAT WILL DEVELOP LATER TODAY AHEAD
OF THE NEGATIVE TILT SHORTWAVE NOW NOSING INTO FAR W TX. ALREADY
BEGINNING TO SEE SOME ELEVATED CONVECTION DEVELOPING THIS MORNING
NEAR WINK...WITH ANOTHER SMALL AREA OF CONVECTION DEVELOPING
FARTHER SE OVER NRN OLD MX JUST W OF DRT ALONG THE PERIPHERY OF
THIS SHORTWAVE...WITH THE ATTENDENT TROUGH AXIS SLATED TO LIFT NE
INTO RED RIVER VALLEY AND ECNTRL TX LATER THIS AFTERNOON. THE LOW
STRATUS HAS RETURNED TO MUCH OF THE REGION THIS MORNING...WHICH
SHOULD LIFT/SCATTER OUT ENOUGH BY MID TO LATE MORNING ALLOWING FOR
HEATING AND BNDRY LYR DESTABLIZATION THIS AFTERNOON OVER MUCH OF
THE REGION. THIS SHOULD RESULT IN MODERATE MLCAPES DEVELOPING AS
DEEP LAYER SHEAR INCREASES WITH THE APPROACH OF THIS TROUGH. THE
SHORT TERM PROGS ARE ALL OVER THE PLACE WITH REGARDS TO THE TIMING
AND PLACEMENT OF THE HIGHER QPF...WITH THE ECMWF/CANADIAN SLOWEST
IN KEEPING MUCH OF THE HIGHER QPF JUST W OF THE REGION ACROSS NRN
AND CNTRL TX THROUGH 00Z TUESDAY. MEANWHILE...THE 06Z NAM IS IN
FAIRLY GOOD AGREEMENT WITH THE LATEST HRRR RUN WITH TWO SEPARATE
AREAS OF CONVECTION...THAT COINCIDES WITH THE CURRENT TRENDS OVER
SW TX/MIDDLE RIO GRANDE VALLEY...WHICH MAY CONSOLIDATE INTO A BKN
SQUALL LINE/MCS BY MID TO LATE AFTERNOON AS IT ACCELERATES E INTO
NE TX/SE OK.

THE 06Z GFS IS CONSISTENT WITH ITS 00Z PREDECESSOR WITH A
SVR MCS DEVELOPING OVER WCNTRL/CNTRL TX BY LATE MORNING...BUT IS
SLOWER TO REACH NE TX UNTIL 00Z TUESDAY. THE GFS DOES ALSO DEVELOP
A SFC WAVE LATER TODAY AND AN INTENSIFYING 40-50KT SRLY LLJ OVER
ECNTRL TX...THUS ENHANCING CONVERGENCE AND FOCUSING A LARGE AREA
OF HEAVY RAINFALL AS IT SPREADS E INTO THE REGION THIS
EVENING/OVERNIGHT. THE CANADIAN IS ALSO IN AGREEMENT WITH THE GFS
IN THE PLACEMENT OF THE HEAVIER QPF ACROSS NE TX/SE OK/SW AR
BEFORE THE HEAVIER RAIN SPREADS/GUSTS E OVERNIGHT. THIS SPREAD IN
THE SOLUTIONS RESULT IN 2 POSSIBLE SCENERIOS...ONE WHERE A SVR MCS
DEVELOPS AND ACCELERATES E OVER THE REGION WHEN
HEATING/INSTABILITY IS MAXIMIZED...THUS RAMPING THE SVR THREAT UP
WITH DAMAGING WINDS/ISOLATED TORNADOES POSSIBLE...BUT ALSO
MINIMIZING THE FLASH FLOOD THREAT. THE OTHER BEING A SVR
MCS...WHICH WILL BE SLOWER TO MOVE BUT WILL AGAIN RESULT IN
DAMAGING WINDS/ISOLATED TORNADOES...BUT ALSO RESULT IN A
HEIGHTENED FLASH FLOOD THREAT SHOULD A SFC TROUGH DEVELOP OVER THE
AREA. THIS FORECAST HAS FOLLOWED MORE OF A BLEND IN THE MODEL
SOLUTIONS...WITH HEIGHTENED AWARENESS FOR THE SVR THREAT GIVEN THE
STRONG FORCING AND MODERATE INSTABILITY/SHEAR EXPECTED TO
DEVELOP/SPREAD INTO THE REGION LATER THIS AFTERNOON. THUS...THE
CONVECTION MAY ACCELERATE E ALONG A COLD POOL...BUT THE SWD EXTENT
OF THE CONVECTION MAY BE SLOWER MOVING AND TRAIN NE ALONG THE SRN
TAIL OF THE TROUGH OVER E TX/NCNTRL LA ONCE THE SHORTWAVE LIFTS
NE INTO NRN AR.

HAVE TONED DOWN QPF/S TO 1-3 INCHES WITH LOCALLY HIGHER AMOUNTS THIS
AFTERNOON/TONIGHT ACROSS THE REGION...AND HAVE MAINTAINED THE END
TIME OF THE FLASH FLOOD WATCH AS 12Z TUESDAY...AS THE STRONGER
CONVECTION SHOULD BE DEPARTING THE CWA BY THIS TIME. AN EXTENSION
MAY BE NEEDED IN LATER FORECASTS THOUGH FOR THE ERN ZONES AS SCT
CONVECTION SHOULD PERSIST THROUGH THE AFTERNOON. DRY SLOTTING
BEHIND THIS SHORTWAVE SHOULD ALSO RESULT IN A REDUCTION IN
CONVECTION FARTHER W TUESDAY...THUS HAVE TAPERED POPS BACK TO
CHANCE AND SLIGHT CHANCE FOR E TX/SW AR/WRN LA. MEANWHILE...TEMPS
SHOULD RETURN BACK TO NEAR CLIMO TUESDAY AFTERNOON.

THE GFS/ECMWF MAINTAINS FLAT RIDGING ALOFT OVER THE REGION
WEDNESDAY...AMPLIFYING NE FROM THE LOWER MS VALLEY INTO THE TN
VALLEY THURSDAY AS THE NEXT UPPER TROUGH BEGINS TO DIGS SE INTO
THE ROCKIES BY THURSDAY. WEAKNESSES RIDING ATOP THE RIDGE MAY
RESULT IN WIDELY SCT CONVECTION WEDNESDAY AND THURSDAY...WITH THE
CONVECTION MOSTLY DIURNAL IN NATURE. LOW CHANCE POPS SHOULD
SUFFICE FOR THIS PERIOD AREAWIDE...ALTHOUGH HAVE CONTINUED THE
TREND WITH MID-CHANCE POPS RETURNING FRIDAY THROUGH NEXT WEEKEND
AS SHORTWAVE PERTUBATIONS EJECT NE AHEAD OF THE BROAD TROUGHING
ALOFT TO OUR W. WHILE TEMPS LOOKS TO HOLD NEAR CLIMO THROUGH LATE
WEEK...GREATER CLOUD COVER/CONVECTION SHOULD RESULT IN SLIGHTLY
COOLER READINGS AS WE MOVE INTO NEXT WEEKEND.

THANK YOU WFO/S LZK AND TSA FOR COLLABORATION THIS MORNING.
PRELIMS TO FOLLOW BELOW...

15

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  83  69  86  71 /  60  80  40  20
MLU  86  70  83  70 /  60  90  70  20
DEQ  79  66  83  68 /  70  80  20  30
TXK  81  68  85  70 /  70  80  30  20
ELD  84  69  83  70 /  50  90  60  20
TYR  81  68  86  72 /  80  60  20  20
GGG  82  69  86  71 /  70  70  20  20
LFK  84  71  87  73 /  70  60  30  20

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR ARZ050-051-059>061-
     070>073.

LA...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR LAZ001>006-010>014-
     017>022.

OK...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR OKZ077.

TX...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR TXZ096-097-108>112-
     124>126-136>138-149>153-165>167.

&&

$$

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