Hail in Louisiana, February 12, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
429 AM CST TUE FEB 12 2013

.DISCUSSION...
SCT -SHRA WITH ISOLATED -TSRA HAVE QUICKLY BEGUN TO DEVELOP THIS MORNING
ACROSS E TX/N LA...AS LARGE SCALE FORCING HAS INCREASED AHEAD OF AN
UPPER TROUGH EXTENDING FROM THE SRN ROCKIES INTO CNTRL NM. THIS TROUGH
REMAINS PROGGED TO SHIFT E ACROSS THE TX PANHANDLE TODAY...AND INTO
CNTRL/NE OK THIS EVENING BEFORE CROSSING THE MS RIVER WEDNESDAY. A
25-35KT SWRLY LLJ SHOULD INCREASE LATER THIS MORNING FROM SE TX INTO
LA/SRN MS...THUS ENHANCING OVERRUNNING RAINS. THE 09Z SFC ANALYSIS
INDICATES AN INVERTED SFC TROUGH EXTENDING JUST OFF MUCH OF THE TX
COAST INTO THE NRN GULF JUST S OF THE LA COAST...WHICH SHOULD MIX N
TODAY AS WEAK SFC CYCLOGENESIS COMMENCES ALONG THE BNDRY...AND THE
SWRLY LLJ INCREASES. THIS BNDRY SHOULD REMAIN JUST S OF THE REGION
THIS AFTERNOON...WITH MUCH OF THE FORECAST AREA REMAINING IN THE COOL
SECTOR. MARGINAL LAPSE RATES ALOFT AND THE INCREASING LLJ AND THETA-E
ADVECTION WILL RESULT IN ISOLATED EMBEDDED TSRA...WITH THE HEAVIER QPF
CONCENTRATED JUST N OF THE SFC BNDRY OVER CNTRL LA/MS. HAVE RAISED
POPS TO HIGH END CATEGORICAL TODAY...TAPERING POPS OFF TO
LIKELY/CHANCE THIS AFTERNOON ONCE MID/UPPER LEVEL DRY SLOTTING
INCREASES BENEATH THE UPPER TROUGH AS IT TRAVERSES OK. SHOULD NOT SEE
MUCH OF A RISE IN TEMPS THIS AFTERNOON AS WELL EVEN AS THE CONVECTION
DIMINISHES FROM SW TO NE...AND HAVE NUDGED THEM DOWN A TAD BELOW
GUIDANCE.

THE SHORT TERM PROGS MAINTAIN THE COLD CORE CENTER OF THE TROUGH
PROGRESSING E ACROSS NE OK/SE KS/MO/NW AR TONIGHT...AS COLDER AIR
BEGINS TO SPILL SE IN WAKE OF THE DEPARTING SFC LOW/FRONTAL BNDRY.
MODEL PARTIAL THICKNESSES SUPPORT THE POTENTIAL FOR A -RA/IP/SN MIX
ACROSS MCCURTAIN CO OK AS WELL AS THE FAR NRN COUNTIES OF SW
AR...WITH FORECAST SOUNDINGS ACROSS THIS AREA MAINTAIN THE FREEZING
LEVEL GENERALLY 1.5-2.3KFT. HOWEVER...SFC TEMPS SHOULD REMAIN ABOVE
FREEZING OVER THESE AREAS SHOULD THIS LIGHT WINTRY MIX INDEED
FALL...THUS NO ACCUMULATION IS EXPECTED. THIS POSSIBLE WINTRY MIX
SHOULD QUICKLY DIMINISH BY DAYBREAK WEDNESDAY...WITH POSTFRONTAL
STRATOCU GRADUALLY MIXING OUT BY AFTERNOON. SFC HIGH PRESSURE SHOULD
BUILD SE THROUGH TX WEDNESDAY AND BE IN PLACE OVER THE REGION
THURSDAY...WITH MODEST TEMP RISES EXPECTED THURSDAY AS WRLY WINDS
COMMENCE ATOP THE SFC RIDGE OVER THE LOWER MS VALLEY.

THE MODELS INDICATE THE NEXT DEVELOPING LONGWAVE TROUGH DIVING S INTO
THE PLAINS AND MS VALLEY FRIDAY...WHICH WILL DRIVE ANOTHER STRONGER
COLD FRONT S INTO THE AREA. THE BNDRY MAY BE INITIALLY SHALLOW AT
FIRST...BEFORE IT GRADUALLY DEEPENS DURING THE DAY IN RESPONSE TO
SFC HEIGHT RISES AHEAD OF STRONG CANADIAN HIGH PRESSURE BUILDING SSE
FROM THE PLAINS. THE GFS REMAINS THE WET OUTLIER IN DEVELOPING
POSTFRONTAL -SHRA ALONG THE 850MB TROUGH...JUST IN TIME AS MUCH COLDER
AIR BEGINS TO SPILL S FRIDAY NIGHT. THE ECMWF IS CONSIDERABLY
DRIER...BUT WILL MAINTAIN SLIGHT CHANCE POPS AREAWIDE BUT EXPAND THE
POTENTIAL FOR A LIGHT WINTRY MIX FARTHER S ACROSS E TX/N LA.
ATTM...MOISTURE AVAILABILITY APPEARS TO BE A PROBLEM EVEN IN THE
PRESENCE OF STRONG LARGE SCALE FORCING...AND TEMPS SHOULD BE NEAR OR
ABOVE FREEZING FOR THE MOST PART. THUS NOT EXPECTING MUCH IN THE WAY
OF WINTRY ACCUMULATIONS ATTM.

BELOW NORMAL TEMPS ARE EXPECTED SATURDAY BEFORE TEMPS BEGIN TO
MODERATE SUNDAY INTO EARLY NEXT WEEK ONCE A SRLY LOW LEVEL FLOW IS RE-
ESTABLISHED. CONVECTION SHOULD BEGIN TO INCREASE AHEAD OF THE NEXT
PROGRESSIVE SHORTWAVE ENTERING THE SRN PLAINS LATE MONDAY THROUGH
TUESDAY.

PRELIMS TO FOLLOW BELOW...

15

&&

.AVIATION...
CEILINGS AND VISIBILITIES PRIOR TO TERMINAL ISSUE TIME OF 12/12 UTC
WILL BE VFR...HOWEVER WITH SCATTERED SHOWERS AND THUNDERSTORMS
SPREADING RAPIDLY NORTHEAST THROUGH THE FOUR STATE REGION...EXPECTING
A GRADUAL LOWERING OF CEILINGS AND VISIBILITIES. BY 12/14 UTC TO
12/17 UTC MOST OF THE FORECAST SITES WILL BE MVFR WITH SOME LOWER
IFR FLIGHT CATEGORIES. MVFR/IFR FLIGHT CATEGORIES WILL PREVAIL
THROUGH THE REMAINDER OF THE FORECAST PERIOD ENDING 13/12 UTC
WEDNESDAY...AND BEYOND FOR SOME LOCATIONS. SOME FOG WILL DEVELOP
DUE TO RAIN AND MOISTURE PROVIDING A MORE SATURATED AIRMASS.
RAINFALL WILL END FROM WEST TO EAST BETWEEN 13/00 TO 13/06 UTC AS A
DRY SLOT OCCURS. SURFACE WINDS FORECAST TO BE EASTERLY 7 TO 11 KNOTS
THROUGH THE AFTERNOON AND THEN BECOMING NORTHEAST TO NORTHWEST AS A
SURFACE LOW PRESSURE SYSTEM MOVES ACROSS THE UPPER TEXAS COAST LATE
TODAY...AND THROUGH SOUTHERN LOUISIANA INTO THE EVENING. WINDS WILL
MOST LIKELY INCREASE FROM THE WEST TO NORTHWEST 10 TO 15 KNOTS
OVERNIGHT AS THE PRESSURE GRADIENT TIGHTENS IN WAKE OF THE SURFACE
LOW AND COLD FRONT AS HIGH PRESSURE FILLS INTO THE FOUR STATE
REGION. /06/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  54  42  56  36  65 / 100  10  10   0   0
MLU  55  45  55  36  63 / 100  20  10   0   0
DEQ  47  36  55  29  63 / 100  40  10   0   0
TXK  49  38  55  36  63 / 100  30  10   0   0
ELD  50  40  54  35  63 / 100  30  10   0   0
TYR  54  39  56  36  65 / 100  10   0   0   0
GGG  53  40  56  35  65 / 100  10   0   0   0
LFK  60  42  58  35  67 / 100  10   0   0   0

&&

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

15/06

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