FXUS64 KSHV 070941
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
341 AM CST MON DEC 7 2009
.SHORT TERM /TODAY THROUGH WEDNESDAY NIGHT/...
AREA RADARS CONTINUE TO SHOW LIGHT RAIN FALLING THIS MORNING. JUST
ABOUT ALL OF THE PRECIPITATION WAS LOCATED ALONG AND AHEAD OF A WEAK
SURFACE TROUGH STRETCHING FROM JACKSONVILLE TEXAS TO EL DORADO
ARKANSAS AT 2 AM. THE MORNING SURFACE ANALYSIS ALSO SHOWS A COLD
FRONT FROM THE KANSAS CITY METRO TO GRAHAM TEXAS. WITH ONLY MEAGER
UPPER-LEVEL SUPPORT...THE FRONT IS FORECAST TO GRADUALLY FIZZLE AS
IT HEADS TOWARD SOUTHEAST OKLAHOMA AND NORTHEAST TEXAS.
THE SURFACE TROUGH IS FORECAST TO STALL JUST SOUTH AND EAST OF OUR
AREA THIS AFTERNOON. WITH MUCH OF THE SYNOPTIC SCALE FORCING
EXPECTED TO REMAIN ALONG AND EAST OF THE TROUGH...PARTS OF THE
FORECAST AREA MAY ACTUALLY SEE A BREAK IN THE RAIN BY THIS
AFTERNOON. FINAL FIRST PERIOD PRECIPITATION PROBABILITIES WILL BE
LARGELY BASED ON ONGOING RADAR TRENDS...BUT WILL GENERALLY BE LOWER
IN THE NORTH/WEST AND HIGHER IN THE SOUTH/EAST.
ANY SORT OF BREAK WILL BE RATHER SHORT-LIVED THOUGH. ANOTHER ROUND
OF RAIN WILL LIKELY DEVELOP AS ADDITIONAL PERTURBATIONS IN THE
SOUTHWESTERLY FLOW ALOFT COMBINE WITH ISENTROPIC FORCING. THIS WILL
PROBABLY OCCUR TONIGHT AS A STRENGTHENING LOW-LEVEL JET CONTINUES TO
DEEPEN MOISTURE OVER OUR REGION.
EVEN THOUGH SOME QUESTIONS STILL REMAIN...IT STILL LOOKS LIKE PARTS
OF THE FORECAST AREA COULD SEE AN ACTIVE WEATHER DAY TUESDAY. THE
SHORT-RANGE MODELS REMAIN CONSISTENT IN BRINGING THE SURFACE TROUGH
/AND DEEPER LOW-LEVEL MOISTURE/ NORTHWARD OVER THE REGION AS A WARM
FRONT SOMETIME TUESDAY MORNING. THIS WILL LIKELY OCCUR IN RESPONSE
TO A DIGGING SHORTWAVE TROUGH/COLD FRONT HEADING TOWARD OUR AREA.
BY TUESDAY AFTERNOON...A 50 TO 60 KNOT LOW-LEVEL JET COULD RESULT IN
DEWPOINTS APPROACHING 60 DEGREES OVER MY SOUTHERN TIER OF COUNTIES
AND PARISHES.
NEEDLESS TO SAY...SUSTAINED...ORGANIZED CONVECTION COULD BE THE
RESULT IF THIS COMES TO FRUITION. INSTABILITY WILL LIKELY BE THE
LIMITING FACTOR IN CONVECTIVE COVERAGE OVER OUR REGION. HOWEVER...
THE AMOUNT OF LOW-LEVEL WIND SHEAR IS STILL IMPRESSIVE. SURFACE TO
1KM HELICITY VALUES COULD EXCEED 300 M2/S2 IN VICINITY OF THE
BOUNDARY. GIVEN THIS...ISOLATED STRONG/SEVERE THUNDERSTORMS COULD
BE SEEN OVER PARTS OF OUR AREA ASSUMING CONVECTION IS ABLE TO
DEVELOP.
THE RISK AREA OF ANY HAZARDOUS WEATHER WILL BE LARGELY DEPENDENT
UPON THE ULTIMATE LOCATION OF THE SURFACE BOUNDARY. FOR NOW...I
PLAN ON KEEPING ANY RISK SOUTH OF A JACKSONVILLE TEXAS TO COLUMBIA
LOUISIANA LINE AS RAIN MAY PROHIBIT THE BOUNDARY FROM EVEN REACHING
IH-20.
SHOWERS AND STORMS WILL LIKELY CONTINUE OVER THE FORECAST AREA INTO
TUESDAY NIGHT...BEFORE A COLD FRONT ENDS PRECIPITATION FROM THE WEST
OVERNIGHT. IT STILL LOOKS LIKE WEDNESDAY WILL BE A DRY DAY OVER
MUCH OF THE AREA IN WAKE OF THE COLD FRONT WITH BREEZY WINDS AND
COOLER TEMPERATURES.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
A RATHER ACTIVE LATE FALL WEATHER PATTERN IS EXPECTED TO CONTINUE IN
THE DAY 4 THROUGH 7 TIME PERIOD.
SURFACE HIGH PRESSURE...CENTERED OVER THE MISSISSIPPI VALLEY...
SHOULD KEEP WEATHER CONDITIONS DRY HEADING INTO THURSDAY. TYPICAL
OF A NEARLY ZONAL FLOW ALOFT...THE HIGH IS EXPECTED TO QUICKLY SHIFT
EAST AND ALLOW GULF MOISTURE TO QUICKLY RETURN BY LATE THURSDAY
EVENING. THERE MIGHT ALSO BE A SLIGHT AMPLIFICATION OF THE UPPER
FLOW ABOUT THIS TIME...AS A SUBTLE SHORTWAVE TROUGH HEADS INTO WEST
TEXAS. THIS SHOULD ALLOW WEAK PERTURBATIONS TO MOVE ACROSS THE
FORECAST AREA IN A SLIGHTLY SOUTHWEST FLOW ALOFT.
IN ADDITION...MEDIUM-RANGE MODELS CONTINUE TO INDICATE STRENGTHENING
ISENTROPIC UPGLIDE ALONG THE 300K THETA SURFACE WITH CONDENSATION
PRESSURE DEFICITS FALLING BELOW 3MB. ALL OF THIS IMPLIES LIGHT RAIN
WILL LIKELY DEVELOP OVERNIGHT THURSDAY /MORE LIKELY BETWEEN MIDNIGHT
AND 6 AM FRIDAY/. PRECIPITATION SHOULD CONTINUE OVER MUCH OF THE
REGION THROUGH THE DAY FRIDAY...WITH THE ENDING TIME UP FOR
DEBATE.
TIMING DISCREPANCIES EXIST BETWEEN THE MAJOR MEDIUM-RANGE MODELS FOR
SATURDAY AND SUNDAY...WITH THE GFS RUNNING ALMOST 12 HOURS FASTER IN
THE MOVEMENT OF WEATHER SYSTEMS. CONSIDERING THE ALMOST ZONAL FLOW
ALOFT...I WILL CONTINUE TO LEAN TOWARD THE GFS WITH THIS PACKAGE.
THIS MEANS THAT MOST OF THE PRECIPITATION SHOULD GRADUALLY TAPER
FROM THE WEST FRIDAY NIGHT AS THE SHORTWAVE TROUGH PUSHES A WEAK
COLD FRONT ACROSS OUR AREA.
ASSUMING THIS SOLUTION HAPPENS...WEAK HIGH PRESSURE IS THEN SLATED
TO MOVE INTO THE REGION FOR SATURDAY AND SHOULD AFFORD A BRIEF BREAK
IN THE RAIN. HOWEVER...CONSIDERING THE UPPER-LEVEL PATTERN AND
RAPID PROGRESSION OF PERTURBATIONS...I WILL CONTINUE SMALL RAIN
PROBABILITIES THROUGH NEXT WEEKEND DUE TO THE RATHER LOW CONFIDENCE
NATURE OF THIS TIME PERIOD. STAY TUNED. /21/
&&
.AVIATION...
A WEAK SURFACE TROUGH COMBINED WITH SUFFICIENT LOW LEVEL MOISTURE
WILL ALLOW FOR PERIODS OF -RA ACROSS MLU/ELD TAF SITES THROUGH MID-
MORNING. CEILINGS AREAWIDE WILL RANGE FROM LIFR TO MVFR THROUGH 12Z
TUESDAY AS ANOTHER WET WEATHER SYSTEM SETS UP ACROSS THE REGION.
OTHERWISE...NORTHEAST WINDS 5-10KTS WILL PREVAIL THROUGHOUT THE
TERMINAL FORECAST PERIOD. /05/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 54 46 60 46 53 / 20 90 80 50 10
MLU 53 47 62 49 56 / 60 90 90 70 10
DEQ 53 39 52 37 49 / 0 70 60 30 10
TXK 52 41 57 41 50 / 10 80 80 40 10
ELD 53 43 56 42 52 / 20 90 90 60 10
TYR 54 45 61 42 52 / 20 80 60 30 10
GGG 56 45 61 44 54 / 20 80 70 40 10
LFK 57 51 65 48 58 / 20 90 60 30 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
&&
$$
PUBLIC FORECASTER... D. BUTTS
AVIATION/FIRE WEATHER FORECASTER... MAYEAUX
