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000
FXUS64 KSHV 210955
AFDSHV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
455 AM CDT TUE MAY 21 2013

.DISCUSSION...
COMPLICATED FORECAST THIS MORNING...GIVEN THE FACT THAT A SFC OBS
OUTAGE HAS BEEN WIDESPREAD FOR MUCH OF THE MORNING SUCH THAT IT HAS
BEEN HARD TO MAKE A MESO-ANALYSIS. HOWEVER...SOME OBS HAVE BEEN
TRICKLING IN RECENTLY...WHICH REVEALS THAT A W-E OUTFLOW BNDRY REMAINS
DRAPED ACROSS EXTREME N AND NE TX JUST S OF THE RED RIVER TO JUST W
OF TXK AS OF 09Z. SFC CAPES S OF THIS BNDRY REMAIN QUITE
UNSTABLE...RANGING FROM 1500-2000 J/KG...YET THE AIR MASS HAS BEEN
WORKED OVER WELL N OF IT ACROSS CNTRL/ERN OK. HOWEVER...CLUSTERS OF
ELEVATED CONVECTION CONTINUE TO DEVELOP OVER THESE AREAS IN VC OF A
WEAK STATIONARY BNDRY EXTENDING FROM SW OK INTO THE NE PART OF THE
STATE INTO SW MO. WATER VAPOR IMAGERY REVEALS PERSISTENT DIFFLUENCE
ALOFT NEAR THIS SFC BNDRY...WITH THE WRN AR CONVECTION NOW GUSTING OUT
AS IT PROPAGATES E...WITH CONVECTION NEAR THESE 2 BNDRYS BEING FED BY
A 30-40KT SWRLY LLJ. THE AR CONVECTION AND ITS ASSOCIATED GUST FRONT
HAS RESULTED IN A RECENT 45KT WIND GUST AT MEZ...WITH SCT CONVECTION
BEGINNING TO FIRE OVER NRN MCCURTAIN COUNTY OK AND NRN HOWARD COUNTY
AR. CURRENT TRAJECTORIES WOULD FAVOR THIS W-E BNDRY EXTENDING FROM
THESE AREAS E INTO CNTRL AR...WITH THE BNDRY JUST S OF THE RED RIVER
POSSIBLY DRIFTING BACK N A TAD LATER THIS MORNING ONCE THIS AIR MASS
BEGINS TO DESTABILIZE. HAVE CARRIED MENTION OF SVR FOR THE EXTREME NW
ZONES THIS MORNING IN VC OF THESE BNDRIES...BUT BELIEVE THAT MAIN SHOW
WILL AWAIT UNTIL LATER THIS AFTERNOON AND TONIGHT ONCE THE AIR MASS TO
THE S BECOMES VERY UNSTABLE.

THE SHORT TERM PROGS ARE IN REASONABLE AGREEMENT IN DEVELOPING
2500-3000+ J/KG OF MLCAPES THIS AFTERNOON AS SFC TEMPS WARM WELL INTO
THE 80S WITHIN A VERY MOIST SECTOR CHARACTERIZED WITH DEWPOINTS IN THE
UPPER 60S/LOWER 70S. THE AFOREMENTIONED BNDRYS WILL COME INTO PLAY
LATER TODAY AS THE PRIMARY UPPER TROUGH AXIS OVER CNTRL
NM...ORIGINATING FROM THE NE SD/SE ND CLOSED LOW...PROGRESSES E INTO
THE SRN PLAINS TODAY. THE PROGS HAVE THIS TROUGH TAKING ON A MORE
NEGATIVE TILT THIS EVENING...WITH STRONG DIFFLUENCE SETTING UP FROM NE
TX INTO SE OK/WRN AR...THE SAME AREAS THAT WILL BECOME VERY UNSTABLE
UNDER STRONG INSULATION. STEEP MID LEVEL LAPSE RATES OF 7.5-7.8 C/KM
WILL ONLY ENHANCE UPWARD VERTICAL MOTION THIS AFTERNOON WHILE BULK
SHEAR REMAINS STRONG NEAR 40-50KTS...SUCH THAT CLUSTERS OF STRONG/SVR
CONVECTION SHOULD DEVELOP. DAMAGING WINDS AND LARGE HAIL STILL APPEAR
THE PRIMARY THREATS...ALTHOUGH THE SHORT TERM PROGS HAVE INCREASED THE
0-1KM SHEAR AND HELICITY VALUES FROM 24 HOURS AGO LATE THIS AFTERNOON
AND EARLY EVENING...SUCH THAT AN ISOLATED TORNADO THREAT WILL BE
POSSIBLE WITH THE ONSET OF THIS CONVECTION...AND SHOULD EVENTUALLY
ORGANIZE INTO A MCS AND PROGRESS ESE ACROSS MUCH OF THE REGION
TONIGHT.

BUT PRIOR TO THIS OCCURRING...CONVECTION THAT DEVELOPS NEAR THESE
MESOSCALE BNDRYS FROM NE TX INTO SE OK/SW AR WILL TRAIN GIVEN THE
LARGELY UNIDIRECTIONAL FLOW ALOFT...WHICH WILL FOCUS PERIODS OF HEAVY
RAINFALL WHERE QPF/S RANGE FROM 1-3 INCHES. HAVE FOCUSED HEAVY
RAINFALL WORDING OVER THESE AREAS THIS AFTERNOON...WITH THE HEAVY
RAINFALL THREAT SHIFTING ESE TONIGHT ONCE THE MCS BEGINS TO PROPAGATE
ACROSS THE REMAINDER OF THE FORECAST AREA. DAMAGING WINDS WILL BECOME
INCREASINGLY LIKELY AS A 35-40KT SWRLY LLJ CONTINUES TO FEED THIS
SYSTEM ONCE IT BEGINS TO GUST OUT...ALTHOUGH A GRADUAL WEAKENING TREND
SHOULD OCCUR LATE AS INSTABILITY BEGINS TO WANE SOMEWHAT DUE TO THE
BNDRY LYR COOLING.

THE RESIDUAL CONVECTION SHOULD BEGIN TO GRADUALLY DIMINISH FROM W TO E
WEDNESDAY MORNING...WITH THE CNTRL OK STATIONARY BNDRY ACTUALLY
BEGINNING TO NUDGE SE IN WAKE OF THIS CONVECTION. THIS BNDRY SHOULD
EVENTUALLY PULL UP STATIONARY SOMEWHERE OVER E TX AND NCNTRL LA...BUT
MAY RESULT IN ISOLATED CONVECTION IN THE AFTERNOON EVEN IN WAKE OF THE
PRIMARY TROUGH PASSAGE ALONG AND S OF THE FRONT. FARTHER W...UPPER
RIDGING WILL BEGIN TO AMPLIFY N ACROSS THE WRN PLAINS AHEAD OF THE PAC
NW CLOSED LOW...AND THE TROUGHING FROM THE LOWER GREAT LAKES AND OHIO
VALLEY. THE PROGS HAVE BACKED OFF ON THE EXTENT OF VORTICITY
PERTURBATIONS DRIFTING SE INTO AR FROM OK...THUS HAVE DROPPED POPS
THURSDAY GIVEN THE LIMITED MOISTURE IN PLACE. HOWEVER...A WEAK
BACKDOOR COLD FRONT WILL DRIFT SW INTO THE AREA FRIDAY MORNING...WHICH
MAY FOCUS ISOLATED CONVECTION DURING THE AFTERNOON AS WEAK VORTICITY
ADVECTION CONTINUES ALOFT. THIS BNDRY SHOULD DRIFT W OF THE AREA
SATURDAY /FROM CNTRL OK INTO TX/...THUS WARM BUT LESS HUMID CONDITIONS
ARE EXPECTED FOR THE HOLIDAY WEEKEND AS MID LEVEL RIDGING BUILDS OVER
THE REGION. SHOULD START TO SEE A RETURN IN HOTTER/MORE HUMID
CONDITIONS BY EARLY NEXT WEEK ONCE A SRLY LOW LEVEL FLOW IS RE-
ESTABLISHED. DRY CONDITIONS SHOULD PERSIST THROUGHOUT THE REMAINDER OF
THE EXTENDED AS THE RIDGING ALOFT LINGERS.

PRELIMS TO FOLLOW BELOW...

15

&&

.AVIATION...
PATCHY STRATUS LEADING TO BRIEF MVFR CEILINGS THIS MORNING. SHOULD
SEE MVFR IMPROVING TO VFR BEFORE NOON...WITH TS ACTIVITY EXPECTED TO
GET UNDERWAY BY LATE AFTERNOON. SHOULDNT AFFECT TERMINALS
INITIALLY...ONLY CARRIED TSRA AT KTXK AT 22/00Z WITH VCTS ELSEWHERE.
ACTIVITY SHOULD OVERTAKE THE AREA FROM THE NW AFTER 22/00Z AND WILL
LIKELY STILL BE OVER KMLU/KELD AT 22/12Z. SOUTH WINDS 10-15KTS TODAY
WITH GUSTS TO 25KTS AT TIMES. WINDS WILL GO LIGHT AND TURN TO THE NW
WITH FROPA AFTER 22/08Z FOR WESTERN TERMINALS...WITH KSHV/KLFK
FOLLOWING SUIT SHORTLY THEREAFTER. /20/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  88  69  86  67  88 /  50  70  30  10  10
MLU  89  69  86  67  88 /  30  70  60  10  10
DEQ  80  63  86  65  86 /  70  70  10   5  10
TXK  86  66  86  65  87 /  70  70  10   5  10
ELD  88  68  86  65  87 /  50  70  30   5  10
TYR  87  67  86  68  89 /  60  70  10  10  10
GGG  88  67  86  68  89 /  50  70  20  10  10
LFK  90  70  89  69  90 /  20  60  30  10  10

&&

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

$$

15/20