FXUS64 KSHV 291119
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
519 AM CST SUN NOV 29 2009
.DISCUSSION...
ISOLATED SHOWERS HAVE DEVELOPED OVER EXTREME SRN AR/N LA/ERN
TX...AND HAVE INCREASED A BIT IN THE LAST FEW HRS...ALONG THE NOSE
OF A 35-40KT SWRLY LLJ THAT HAS ENHANCED THETA-E RIDGING/WEAK
ISENTROPIC LIFT. THIS MAY WANE SOME BY MID/LATE MORNING WITH THE
LOSS OF THE LLJ...BUT EXPECTING MORE SHRA TO REDEVELOP THIS
AFTERNOON AS SUBTLE IMPULSES RIDE THE SUBTROPICAL JET...WHICH IS
ACCELERATING E ACROSS NRN MX/TX THIS MORNING. AS DEEP LYR MOISTURE
ADVECTION CONTINUES...WILL QUICKLY SEE AN INCREASE IN SHRA AND
EMBEDDED CONVECTION LATE THIS AFTERNOON/OVERNIGHT...AS A
DEVELOPING LONGWAVE TROUGH NOW DIGGING SE THROUGH THE DAKOTAS
TRAVERSES SE ACROSS THE GREAT LAKES/MS VALLEY...WELL AHEAD OF THE
CLOSED LOW THAT WILL DRIFT E ACROSS NRN BAJA INTO NW OLD MX
TONIGHT. THIS AREA OF RAIN WITH EMBEDDED CONVECTION WILL QUICKLY
DEVELOP AHEAD OF AN ATTENDANT COLD FRONT...WHICH WILL NEAR THE
I-30 CORRIDOR OF EXTREME NE TX/SW AR AROUND 00Z MONDAY. DESPITE
DEEPENING LOW LEVEL MOISTURE TODAY /DEWPOINTS CLIMBING TO THE
LOWER 60S AHEAD OF THE FRONT/...INSTABILITY REMAINS QUITE
MEAGER...WITH POOR LAPSE RATES ALOFT ALONG/AHEAD OF WEAK FRONTAL
CONVERGENCE. THUS...BELIEVE BRIEF HEAVY RAINFALL WILL BE THE MAIN
THREAT FROM ANY OF THE HEAVIER SHRA/EMBEDDED STORMS...ESPECIALLY
ALONG THE LOCALIZED MOISTURE CONVERGENCE ZONE ALONG THE FRONT THIS
EVENING/OVERNIGHT...WHERE PW/S INCREASE TO IN EXCESS OF 1.5".
AREAS S OF A JSO...TO GGG...TO ELD LINE WILL SEE THE HIGHEST
QPF...WITH 1-2" POSSIBLE...WHILE LIGHTER AMOUNTS BELOW AN INCH CAN
BE EXPECTED FARTHER NW. GIVEN THE HIGH FFG VALUES AND RELATIVELY
DRY CONDITIONS SEEN SINCE THE RECORD WET OCTOBER...THIS RAINFALL
SHOULD NOT POSE A FLOODING PROBLEM. THE SHORT TERM PROGS HAVE
ACTUALLY SPED THE FRONTAL MOVEMENT UP A TAD...WITH THE FRONT
EXITING THE FORECAST AREA AROUND DAYBREAK MONDAY...ALTHOUGH
POSTFRONTAL SHRA MAY PERSIST A WHILE UNTIL DEEP LYR DRY AIR HAS A
CHANCE TO FILTER S BEHIND THE FRONT. THIS WILL ALSO KEEP VERY
SIGNIFICANT RAINS IN CHECK.
WILL STILL SEE CONSIDERABLE CIRRUS AHEAD OF THE APPROACHING CLOSED
LOW MONDAY/MONDAY NIGHT...WHICH WILL LIMIT THE DIURNAL VARIATIONS
IN TEMPERATURE. THIS LOW WILL CROSS THE TX BIG BEND REGION TUESDAY
NIGHT...BEFORE TRACKING E THROUGH ECNTRL TX AND THE LOWER MS
VALLEY WEDNESDAY. PREFER THE SLIGHTLY SLOWER ECMWF
SOLUTION...ALTHOUGH OVERRUNNING WILL COMMENCE N OF THE SFC/850MB
LOW ALONG THE TX COAST AS EARLY AS LATE MONDAY NIGHT...BEFORE
INCREASING SIGNIFICANTLY TUESDAY. HAVE BEEFED UP POPS ACROSS THE
REGION TO MATCH...WITH HIGH END LIKELIES AREAWIDE TUESDAY NIGHT.
850 MB TEMPS AND PARTIAL THICKNESSES SUGGEST THAT THE PRECIP. WILL
REMAIN ALL LIQUID TUESDAY NIGHT ACROSS OUR REGION IN VC OF THE
COLD CORE LOW...ALTHOUGH THAT WILL LIKELY NOT BE THE CASE FARTHER
W ACROSS WCNTRL TX...WHERE THE COLD AIR WILL BE A BIT DEEPER IN
THE HIGHER TERRAIN. THE SHRA SHOULD DIMINISH FROM W TO E WEDNESDAY
AS THE LOW BEGINS TO OPEN UP AND ACCELERATE E ACROSS THE LOWER MS
VALLEY/SE STATES.
A DRY WNW FLOW WILL COMMENCE WEDNESDAY NIGHT IN WAKE OF THE
LOW...WHICH WILL PERSIST THROUGH WEEK/S END. THIS WILL TAP COLDER
AIR SE INTO THE SRN PLAINS/LOWER MS VALLEY...WITH A MORE
WIDESPREAD FREEZE POSSIBLE BY THURSDAY/FRIDAY MORNINGS AS A
CANADIAN SFC RIDGE BUILDS S ACROSS THE REGION.
PRELIMS TO FOLLOW BELOW...
15
&&
.AVIATION...
SURFACE HIGH PRESSURE CENTERED OVER SOUTHERN GEORGIA AND NORTH
FLORIDA EARLY THIS MORNING CONTINUED TO SUPPLY LOW LEVEL RETURN
MOISTURE ACROSS THE FOUR STATE REGION. JUST ABOVE THE SURFACE A
SOUTHWEST FLOW UP INTO THE MIDDLE LEVELS WAS SPREADING GULF OF
MEXICO AND PACIFIC MOISTURE THAT WILL PROVIDE A WIDESPREAD LOWERING
OF THE CLOUDS TO MVFR TO IFR CATEGORIES THROUGH THE LATE MORNING TO
EARLY AFTERNOON HOURS. WITH THE ONSET OF MORE WIDESPREAD RAIN THE
CEILINGS WILL RETURN BACK TO MVFR TO IFR WITH LOW VISIBILITIES IN
RAIN AND FOG DURING THE EVENING AND OVERNIGHT HOURS. MOISTURE WILL
BE COMBINING WITH A COLD FRONT THAT IS EXPECTED TO SPREAD OVER THE
AREA DURING THE AFTERNOON AND EVENING PRODUCING WIDESPREAD RAIN AND
SHOWERS WITH ISOLATED THUNDERSTORMS THAT WILL CARRY INTO THE
OVERNIGHT HOURS AND END FROM WEST TO EAST ON MONDAY. WINDS WILL BE
SOUTH 7 TO 14 KNOTS TODAY WITH A WIND SHIFT TO THE SOUTHWEST
FOLLOWED BY NORTHWEST OVERNIGHT. WINDS ON MONDAY WILL BE 8 TO 16
KNOTS WITH HIGHER GUSTS. /06/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 71 51 57 42 53 / 60 90 20 10 50
MLU 71 51 55 41 53 / 50 90 30 10 50
DEQ 65 44 58 32 54 / 60 70 0 0 30
TXK 67 46 57 37 54 / 60 90 10 0 30
ELD 68 49 56 37 54 / 60 90 20 0 30
TYR 69 46 58 41 52 / 60 90 10 10 60
GGG 70 49 58 41 52 / 60 90 10 10 60
LFK 74 54 57 44 49 / 40 90 40 30 60
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
$$
15/06
