000
FXUS64 KSHV 261121
AFDSHV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
521 AM CST THU NOV 26 2009

.DISCUSSION...
SECONDARY SURGE OF COLDER/DRIER AIR CONTINUES TO BE REINFORCED SWD
ACROSS THE REGION THIS MORNING...AS THE PARENT LONGWAVE TROUGH ROTATES
SE ACROSS THE MS VALLEY ATTM. SFC WINDS ALONG THE LEADING EDGE OF THIS
SECONDARY COLD AIR SURGE HAS KEPT THE AIR QUITE MIXED THIS
MORNING...BUT HAVE DECOUPLED ACROSS THE NRN SECTIONS OF THE
REGION...SUCH THAT TEMPS ARE NEARING/BELOW THE FREEZING MARK ACROSS
THE CURRENT FREEZE WARNING AREA OF SE OK/ADJACENT SW AR. COLD
ADVECTION WILL PERSIST THIS MORNING BEFORE DIMINISHING...BUT WILL
ALLOW MAX TEMPS TO RUN SOME 3-4 DEGREES COOLER TODAY THAN WEDNESDAY.
CANADIAN SFC RIDGE IN PLACE OVER NW TX THIS MORNING WILL SLIDE SE
ACROSS THE STATE TODAY...BEFORE RESIDING ACROSS THE REGION TONIGHT.
THIS WILL SET UP IDEAL RADIATIONAL COOLING AREAWIDE TONIGHT...WITH THE
THIN CIRRUS SHIELD OVER THE RIO GRANDE VALLEY THIS MORNING AHEAD OF
THE PARENT SHORTWAVE JUST W OF THE SRN BAJA COAST EXPECTED TO REMAIN
JUST S OF THE REGION ACROSS SE TX/SRN LA. MOS HAS BEEN RUNNING A BIT
WARM THE LAST CPL. MORNINGS WITH MIN TEMPS...AND APPEARS TO BE DOING
THE SAME GIVEN THE GOOD RADIATIONAL COOLING EXPECTED OVERNIGHT...THUS
HAVE UNDERCUT GUIDANCE AGAIN...WITH FREEZING TEMPS EXPECTED TO SPILL S
ACROSS MUCH OF SW AR/PORTIONS OF NCNTRL LA BY FRIDAY MORNING.
THUS...WILL BE HOISTING A FREEZE WARNING FOR AREAS MAINLY EAST OF A
HOPE AND LEWISVILLE AR...TO MINDEN...CASTOR...AND JONESBORO
LINE...INCLUDING MLU AND W MLU. CAN/T RULE OUT ISOLATED POCKETS OF
FREEZING TEMPS ACROSS NW LA/E TX IN THE MORE PROTECTED AREAS...BUT
BELIEVE THIS WILL BE BRIEF AND NOT AS PROLONGED AS AREAS TO THE E. THE
WARNING AREA MAY NEED TO BE ADJUSTED FARTHER W AND S ACROSS N LA
SHOULD COLD ADVECTION BE STRONGER THAN FORECAST...THUS WILL ALLOW THE
DAY SHIFT TO MAKE THAT CALL.

CNTRL ROCKIES UPPER RIDGE WILL TRAVERSE E ACROSS THE PLAINS THROUGH
LATE FRIDAY...BEFORE QUICKLY BEING UNDERCUT BY THE BAJA SHORTWAVE AS
IT SHIFTS NE INTO WCNTRL TX FRIDAY NIGHT. THIS WILL ENHANCE A SWRLY
RETURN FLOW BY SATURDAY...ALTHOUGH LOW LEVEL MOISTURE RETURN WILL BE
DELAYED GIVEN THE CURRENT CP INTRUSION THIS MORNING. THUS...ONLY
EXPECTING MAINLY AC/CIRRUS CANOPY ASSOCIATED WITH THE PARENT
SHORTWAVE SATURDAY...BEFORE ISENTROPIC PROCESSES COMMENCE SATURDAY
NIGHT ALONG AN 850MB THETA-E RIDGE UNDER THE DEEPENING SW MEAN FLOW.
CAN/T RULE OUT ISOLATED SHRA DEVELOPING SATURDAY NIGHT...BEFORE DEEP
LYR MOISTURE INCREASES SUNDAY AHEAD OF THE CLOSED LOW EXPECTED TO DROP
SE ACROSS CA/NV.

QUITE A FEW CHANGES IN THE MEDIUM RANGE PROGS THIS MORNING REGARDING
THE TIMING/EVOLUTION OF THIS CLOSED LOW...AS NOW BOTH THE GFS/ECMWF
ARE IN AGREEMENT WITH THE NEXT LONGWAVE TROUGH DIGGING SE ACROSS THE
PLAINS WELL AHEAD OF THE CA LOW...WHILE TAPPING INTO THE SUBTROPICAL
JET AHEAD OF THE CLOSED LOW AS IT NEARS NRN BAJA SUNDAY. THE GFS
CONTINUES TO ADVERTISE MODIFIED GULF MOISTURE QUICKLY ADVECTING NE
ALONG THE SUBTROPICAL JET AXIS...WITH LOWER 60 DEWPOINTS AHEAD OF THE
ATTENDANT COLD FRONT EXPECTED TO SHIFT SE ACROSS ERN OK/N TX SUNDAY
NIGHT...AND INTO THE REGION MONDAY. INSTABILITY CONTINUES TO LOOK
RATHER MEAGER AHEAD OF THE LONGWAVE...WITH HEAVY RAINFALL THE
PREDOMINANT THREAT GIVEN SW UNIDIRECTIONAL FLOW AHEAD OF THE FRONT.
STILL LOOKING FOR WIDESPREAD 1-2" /WITH ISOLATED HIGHER AMOUNTS/ QPF
TOTALS WITH THIS SYSTEM...BEFORE ENDING FROM W TO E MONDAY. HAVE
BEEFED POPS UP AREAWIDE TO HIGH END LIKELIES SUNDAY NIGHT...AND
INCREASED POPS TO LIKELIES OVER THE SE 2/3RDS OF THE AREA
MONDAY...BEFORE REDUCING POPS SIGNIFICANTLY MONDAY NIGHT.
THICKNESSES/850MB TEMPS HAVE WARMED CONSIDERABLY BEHIND THE INITIAL
FROPA...SUCH THAT FROZEN PCP. SHOULD NOT BE A CONCERN BEFORE THE COLD
SFC TEMPS ARRIVE.

THE ECMWF IS A BIT SLOWER THAN THE GFS WITH THE TRACK OF THE CLOSED
LOW ACROSS TX/LOWER MS VALLEY TUESDAY NIGHT/WEDNESDAY...WITH A SLOWER
MOVEMENT DURING THE DAYTIME WEDNESDAY KEEPING ANY LIGHT PCP. LIQUID
GIVEN MODERATING SFC TEMPS. HOWEVER...MUCH OF THE COUNTRY APPEARS
HEADED FOR THE DEEP FREEZE AFTER MIDWEEK AS A LARGE LONGWAVE TROUGH
PULLS ARCTIC AIR SWD. SHOULD ANY CONSISTENCY PERSIST AMONGST THE
MEDIUM RANGE MODELS THROUGH THE WEEKEND...THIS CERTAINLY COULD BE THE
COLDEST AIR OF THE SEASON TO SURGE SWD LATE NEXT WEEK.

PRELIMS TO FOLLOW BELOW...

15

&&

.AVIATION...
A WEAK COLD FRONT WILL CONTINUE MOVING EAST ACROSS THE REGION THIS
MORNING. NORTHWEST WINDS WILL CONTINUE TODAY ACROSS THE TERMINALS
WITH WINDS SUSTAINED AROUND 10KTS DURING THE DAY BEFORE DECOUPLING
THIS EVENING. A CLOUDLESS SKY WILL RESULT IN VFR CONDITIONS THROUGH
THE NEXT 24 HOURS. /13/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  60  33  65  43  68 /   0   0   0   0  10
MLU  60  32  63  39  67 /   0   0   0   0   0
DEQ  58  28  64  37  67 /   0   0   0   0   0
TXK  59  35  65  45  67 /   0   0   0   0   0
ELD  59  30  63  39  67 /   0   0   0   0   0
TYR  62  37  67  48  68 /   0   0   0   0  10
GGG  61  34  66  45  68 /   0   0   0   0  10
LFK  63  34  68  45  70 /   0   0   0   0  10

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...FREEZE WARNING FROM 10 PM THIS EVENING TO 9 AM CST FRIDAY FOR
     THE FOLLOWING ZONES: ARZ060-061-071>073.

     FREEZE WARNING UNTIL 9 AM CST THIS MORNING FOR THE FOLLOWING
     ZONES: ARZ050-051-059.

LA...FREEZE WARNING FROM 10 PM THIS EVENING TO 9 AM CST FRIDAY FOR
     THE FOLLOWING ZONES: LAZ003>006-012>014.

OK...FREEZE WARNING UNTIL 9 AM CST THIS MORNING FOR THE FOLLOWING
     ZONES: OKZ077.

TX...NONE.

$$

15/13