FXUS64 KSHV 281122
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
522 AM CST SAT NOV 28 2009
.DISCUSSION...
WELL DEFINED SHORTWAVE NOTED ON THE IR AND WATER VAPOR LOOPS THIS MORNING
WAS ANALYZED OVER WCNTRL TX...AND WILL CONTINUE TO LIFT NE ACROSS DEEP
E TX/NCNTRL LA TODAY. ENOUGH MID AND UPPER LEVEL FORCING HAS BEEN
GENERATED THIS MORNING FOR WIDELY SCT ELEVATED -RA OVER EXTREME SE
TX/SW LA...AND THIS MAY PERSIST FOR A WHILE LONGER THIS MORNING AS IT
ENTERS CNTRL LA...BEFORE ENCOUNTERING A DEEPER/DRIER AIR MASS. CAN/T
RULE OUT A FEW SPRINKLES OVER THESE AREAS...BUT NOT ENOUGH TO WARRANT
MENTION IN THE FORECAST ATTM. SRLY RETURN FLOW WILL INCREASE ACROSS TX
IN WAKE OF THE DEPARTING SHORTWAVE...WITH LOW LEVEL MOISTURE GRADUALLY
DEEPENING ACROSS ECNTRL TX BY LATE AFTERNOON/EARLY EVENING ALONG A
DEVELOPING 30-40KT SSWRLY LLJ. THE ISENTROPIC LIFT ALONG THIS LOW
LEVEL MOISTURE/THETA-E AXIS HAS BECOME WEAKER/MORE SHALLOW IN THIS
MORNING/S RUNS...WITH ANY RESULTANT -SHRA MAINLY CONFINED TO E TX/SE
OK/SW AR/NW LA AFTER MIDNIGHT. THUS...HAVE REMOVED POPS TONIGHT FOR
THE ERN SECTIONS OF NCNTRL LA.
DEEP LYR FORCING STILL REMAINS WEAK FOR THE FIRST HALF OF SUNDAY...AS
WE AWAIT THE NEXT DEVELOPING LONGWAVE TO DIG SE THROUGH THE MIDWEST
AND INTO THE MS VALLEY/MID ATLANTIC STATES SUNDAY NIGHT. THE
SUBTROPICAL JET WILL APPROACH THE REGION BY AFTERNOON...AHEAD OF THE
DEVELOPING CLOSED LOW NOW TRAVERSING ACROSS CNTRL CA...AS IT DRIFTS E
ACROSS NRN MX. THUS...SCT SHRA AND ISOLATED CONVECTION SHOULD INCREASE
SUNDAY AFTERNOON...ESPECIALLY AS THE ATTENDANT COLD FRONT AHEAD OF THE
SEWD MOVING TROUGH SHIFTS SE INTO ERN OK/N TX. STILL HAVE VERY LOW
CONFIDENCE IN ANY ISOLATED SVR THREAT...GIVEN LACK OF
INSTABILITY...RELATIVELY WEAK SHEAR...AND POOR LAPSE RATES...THUS AM
EXPECTING HEAVY RAINFALL EMBEDDED WITH THE STORMS TO BE THE MAIN
THREAT...AS THEY TRAIN FOR SEVERAL HRS IN THE SWRLY UNIDIRECTIONAL
FLOW AHEAD OF THE SE MOVING COLD FRONT. GIVEN THE PERSISTENT DRY
PATTERN WE HAVE SEEN IN THE LAST MONTH...NOT EXPECTING FLASH FLOODING
TO BE A CONCERN...AS FFG REMAINS HIGH AND THE SOILS ABLE TO TAKE IN
THIS ADDITIONAL RAINFALL. THE HEAVIER RAINFALL AXIS HAS NOW SHIFTED A
BIT SE FROM PREVIOUS MODEL RUNS...AND CONCENTRATED MAINLY SE OF A
TYR...TO ELD LINE. 1-2" QPF AMOUNTS STILL A GOOD BET SE OF THIS
LINE...WITH 0.5-1" AMOUNTS POSSIBLE FARTHER NW.
SHRA AND EMBEDDED CONVECTION SHOULD BEGIN TO DIMINISH FROM NW TO SE
MONDAY WITH THE PASSAGE OF THE FRONT...ALTHOUGH SOME POSTFRONTAL SHRA
MAY PERSIST THROUGH THE AFTERNOON OVER DEEP E TX/NCNTRL LA BEFORE THE
DRIER AIR IS ABLE FILTER S. FOCUS WILL THEN TURN BACK TO THE W AGAIN
AS THE CLOSED LOW CONTINUES TO DRIFT E ACROSS NRN MX MONDAY
NIGHT/TUESDAY...ENTERING WCNTRL TX TUESDAY AFTERNOON. PREFER THE
SLIGHTLY SLOWER ECMWF...AS IT REMAINS PERSISTENT WITH PREVIOUS RUNS IN
THE TIMING OF THE LOW...TRAVERSING OUR REGION TUESDAY NIGHT/WEDNESDAY
MORNING. 850MB TEMPS JUST ENOUGH ABOVE FREEZING AND FREEZING LEVELS
BETWEEN 3-3.5KFT STILL FAVOR LIQUID PRECIP ATTM...ALTHOUGH THIS WILL
BEAR WATCHING SHOULD THICKNESSES FALL FURTHER AS THE LOW SHIFTS E. BUT
IN ANY CASE...STRONG OVERRUNNING WILL DEVELOP AHEAD OF THE CLOSED
LOW...WITH -SHRA POSSIBLY DEVELOPING/SPREADING BACK N TUESDAY ACROSS
PORTIONS OF E TX/NCNTRL LA...A BIT SLOWER THEN THE 00/06Z GFS. GIVEN
THIS...WILL NOT SEE MUCH WARMING DURING THE DAY...WITH MAX TEMPS
POSSIBLY REMAINING IN THE 40S THROUGH MUCH OF THE DAY OVER AT LEAST
THE CNTRL/SRN HALF OF THE AREA. HAVE ENDED PRECIP. WEDNESDAY
AFTERNOON...WITH A WNW FLOW COMMENCING IN WAKE OF THE LOW AS LONGWAVE
TROUGHING PERSISTS E OF THE ROCKIES THROUGH THE END OF THE FORECAST
PERIOD. THUS...ADDITIONAL SHOTS OF COLDER AIR MAY SPILL SWD KEEPING
TEMPS BELOW NORMAL BY THE MID/LATTER PART OF NEXT WEEK.
PRELIMS TO FOLLOW BELOW...
15
&&
.AVIATION...
VFR CONDITIONS WILL CONTINUE THROUGH THE DAY TODAY WITH A SHORT WAVE
MOVING THROUGH ACCOMPANIED BY MIDDLE CLOUDS AROUND 11 KFT FOLLOWED
BY LOWERING CLOUDS TO 6 KFT BY EARLY AFTERNOON OVER THE SOUTHWEST
SECTIONS/NORTHEAST TEXAS INTO NORTHWEST LOUISIANA. BY 28/22Z CLOUDS
WILL CONTINUE TO LOWER ACROSS EAST TEXAS WITH MVFR CEILINGS
SPREADING NORTHEAST AFFECTING MOST OF THE TERMINAL SITES ACROSS
EAST TEXAS...NORTHWEST LOUISIANA...AND SOUTHWEST ARKANSAS BY
29/03Z AND SOUTH CENTRAL ARKANSAS AND NORTH CENTRAL LOUISIANA AFTER
29/05Z. IFR CEILINGS POSSIBLE TOWARD 29/10Z ACROSS EAST TEXAS.
LIGHT AND VARIABLE WINDS NEAR TERMINAL ISSUANCE WILL INCREASE
TO SOUTH 8 TO 14 KNOTS AFTER 28/15Z. THE WINDS WILL DROP OFF SOME
AFTER 29/00Z BUT STILL REMAIN ELEVATED AROUND 5 TO 10 KNOTS. THERE
WILL BE SOME LIGHT RAIN AROUND BUT CHANCES WILL BE SMALL FOR
OCCURRENCE AND WILL OMIT. RAIN CHANCES INCREASE ON SUNDAY WITH THE
APPROACH OF A COLD FRONT. /06/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 69 55 68 50 54 / 0 20 50 80 50
MLU 67 49 68 52 54 / 10 10 50 80 60
DEQ 68 48 63 43 56 / 0 20 60 70 10
TXK 68 54 65 46 55 / 0 20 60 80 20
ELD 68 50 67 48 55 / 0 20 60 80 40
TYR 69 59 67 46 55 / 10 20 60 80 40
GGG 69 57 68 48 55 / 10 20 60 80 40
LFK 70 58 72 52 54 / 10 20 40 80 70
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
$$
15/06
