FXUS64 KSHV 222117
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
317 PM CST TUE DEC 22 2009
.DISCUSSION...
DYNAMIC WEATHER PATTERN SETTING UP ACROSS THE REGION AS LOW-LEVEL
SOUTHERLY FLOW INTENSIFIES ABOVE THE BOUNDARY LAYER. KSHV VWP
INDICATES A 40 KNOT JET AT 4KFT...WHICH IS SLIGHTLY STRONGER THAN
12Z SOUNDING PREVIOUSLY INDICATED. MOISTURE HAS INCREASED ACROSS
THE REGION WITH SHOWER ACTIVITY BECOMING MORE WIDESPREAD EAST OF A
LINE FROM HOPE ARKANSAS TO LUFKIN TEXAS. SHOWERS FORECAST TO
CONTINUE INCREASING IN COVERAGE OVERNIGHT AS AN ISENTROPIC
SITUATION SETS UP ACROSS THE ARKLATEX.
ON WEDNESDAY...AN AMPLIFIED SHORTWAVE UPPER TROUGH WILL SLIDE EAST
ACROSS TEXAS. ASSOCIATED SURFACE FRONT CORRELATED WITH UPPER
TROUGH WILL PUSH INTO EAST TEXAS AROUND SUNSET. SHEAR ASSOCIATED
WITH SIGNIFICANT LOW LEVEL JET AND SURFACE DEWPOINTS IN THE 60S
WILL AID IN SUPPORTING A LINEAR BAND OF THUNDERSTORMS CAPABLE OF
PRODUCING LOCALLY DAMAGING WINDS AND ISOLATED TORNADOES. HOWEVER...SOME
UNCERTAINTY STILL EXISTS CONCERNING THE CONFIDENCE IN SEVERE
WEATHER DUE TO THE POTENTIAL FOR HEAVY RAINFALL AHEAD OF THIS
SQUALL LINE. THROUGH THURSDAY MORNING...QPF VALUES ARE FORECAST
TO AVERAGE AROUND 2 TO 3 INCHES AREAWIDE. UP TO HALF OF THIS
RAINFALL MAY BE OCCUR TONIGHT THROUGH WEDNESDAY AFTERNOON...WHICH
COULD LIMIT THE INSTABILITY NECESSARY IN SUPPORTING SEVERE
THUNDERSTORMS WEDNESDAY NIGHT. A COUPLE OF ADDITIONAL MAKE OR
BREAK FACTORS INCLUDE SURFACE TEMPERATURES AND CLOUD COVER ON
WEDNESDAY AFTERNOON RELATING TO INSTABILITY...AND IF OVERNIGHT
DECOUPLING PROVIDES A SURFACE SAFETY CUSHION ON WEDNESDAY NIGHT.
THESE ARE VARIABLES IN WHICH MINOR VARIATIONS MAY SIGNIFICANTLY CHANGE
THE OUTCOME.
A SECONDARY THREAT THAT CONTINUES TO BEAR WATCHING IS RAINFALL AMOUNTS.
ALTHOUGH 2 TO 3 INCHES OF RAINFALL IS EXPECTED...MOST OF THIS WILL
BE SPREAD ACROSS A 36 HOUR PERIOD. LOCALIZED URBAN AND SMALL
STREAM FLOODING AS WELL AS PONDING ON ROADWAYS COULD BE AN ISSUE
WITH SQUALL LINE PASSAGE. HOWEVER...LATEST ASSESSMENT IS THAT THE
REGION COULD HANDLE MOST OF THIS WATER. WILL HOLD OFF ON ISSUING
A FLASH FLOOD WATCH ON THIS PACKAGE WHILE CONTINUING TO EVALUATE
UPCOMING RAINFALL.
SQUALL LINE SHOULD EXIT THE REGION BY LATE MORNING THURSDAY WITH
COLD AND DRY AIR SETTING IN FOR CHRISTMAS MORNING THROUGH THE
SUNDAY. OVERNIGHT LOWS ARE FORECAST TO DROP INTO THE MID 20S
AREAWIDE WITH A REINFORCEMENT OF COLD AIR KEEPING LOWS AROUND
FREEZING THROUGH WEDNESDAY MORNING. /05/
&&
.AVIATION...
STILL EXPECTING MOSTLY VFR FLIGHT CONDITIONS THROUGH THE REMAINDER
OF THE AFTERNOON INTO THE EARLY EVENING...WITH CIGS 3 TO 5 KFT BKN.
CEILINGS GRADUALLY LOWERING TO MVFR AND AREAS OF IFR TONIGHT AS LOW
LEVEL MOISTURE INCREASES ACROSS THE REGION. PRESSURE GRADIENT WILL
CONTINUE TO INCREASE...KEEPING WINDS IN THE 10 TO 15 KT RANGE
OVERNIGHT. SOUTH TO SOUTHWEST LOW LEVEL WINDS WILL INCREASE AREAWIDE
WEDNESDAY WITH SURFACE GUSTS APPROACHING 25KTS. WIDELY SCATTERED
LIGHT SHOWERS TO CONTINUE INTO TONIGHT AND BECOMING MORE NUMEROUS
WITH ISOLATED THUNDERSTORMS POSSIBLE AFTER MIDNIGHT. /14/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 58 68 52 57 32 / 80 90 100 70 20
MLU 55 65 58 58 34 / 80 90 100 80 20
DEQ 56 64 48 50 27 / 80 90 100 70 20
TXK 57 66 51 56 31 / 80 90 100 70 20
ELD 56 64 54 59 32 / 80 90 100 80 20
TYR 60 68 46 53 30 / 80 90 100 50 10
GGG 59 68 49 56 30 / 80 90 100 50 10
LFK 60 69 51 58 32 / 80 90 100 50 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
&&
$$
05/14
