FXUS64 KSHV 112125
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
325 PM CST FRI DEC 11 2009
.DISCUSSION...
OVERRUNNING BEGINNING TO OCCUR ACROSS THE SOUTHERN TIER OF
COUNTIES AND PARISHES BASICALLY SOUTH OF I20. NOTHING REACHING
THE GROUND AS OF YET AND IS LIKELY EVAPORATING IN THE DRIER
BOUNDARY LAYER. EXPECT TO SEE LIGHT RAIN BEGIN FALLING AFTER
SUNSET AND EXPANDING IN COVERAGE DURING THE OVERNIGHT HOURS. HAVE
PUT IN THE MENTION FOR LIGHT FREEZING RAIN IN THE NORTHERN
COUNTIES AS DEWPOINTS ARE STILL IN THE LOW TEENS AND WITH THE
ONSET OF THE RAIN...WET BULBING WILL CAUSE THE AIR TEMP AND
DEWPOINT TO MEET AROUND THE FREEZING MARK. HAVE BUMPED POPS UP TO
DEFINITE AREA WIDE SATURDAY AS ALL GUIDANCE IS NOW AT THE HIGH END
OF THE SCALE. HAVE ALSO REDUCED SATURDAY MAX TEMPS A FEW DEGREES
AND AM THINKING THE RAIN WILL KEEP TEMPS FAIRLY STEADY IN THE LOW
40S ON SATURDAY.
RAIN SHOULD END OVERNIGHT SATURDAY NIGHT FROM WEST TO EAST AND
ALLOW A MUCH ANTICIPATED WARM UP ON SUNDAY AND MONDAY. GUIDANCE IS
NOW SUGGESTING MAX TEMPS WILL APPROACH 70 ON SUNDAY AND MONDAY.
AN INCREASE IN CLOUDS ONCE AGAIN ON MONDAY AHEAD OF THE NEXT
SHORTWAVE WITHIN THE SUBTROPICAL JET...WHICH ENDS UP PHASING WITH
THE LONGER WAVE TROF OVER THE CENTRAL US AND TAPS SOME ARCTIC AIR
OVER THE NORTHERN PLAINS. ONLY FLY IN THE OINTMENT WILL BE THE
TIMING OF THE RAIN ON MONDAY AND ITS NORTHWESTWARD EXTENT. GFS IS
MUCH FASTER WITH THE ONSET EARLY ON MONDAY WHICH WOULD INHIBIT MAX
TEMPS FROM GETTING OVER 70. EITHER WAY...MONDAY SHOULD BE
RELATIVELY WARM COMPARED TO WHAT WE HAVE ENDURED.
BOTH THE ECMWF AND GFS AGREE ON THE GENERAL TIMING
OF LATE MONDAY NIGHT FOR THE ARCTIC FRONTAL PASSAGE. HAVE GONE
WITH THE GFS TIMING OF THE FRONT AND DRASTICALLY LOWERED TEMPS...7
TO 10 DEGREES ON TUESDAY OVER GUIDANCE...IN COORDINATION WITH THE
NEIGHBORS WHO ALSO AGREE. CANT QUITE FIGURE OUT WHY MODELS ARE SO
WARM WITH AN ARCTIC ORIGIN 1038 - 1043 MB HIGH OVER THE CENTRAL
PLAINS ON TUESDAY AND STRONG NORTH WINDS AT THE SURFACE ADVECTING
IN THE COLDER AIR. ECMWF AND GFS DIFFER SLIGHTLY ON THE AXIS OF
THE EAST COAST TROF ON TUESDAY WHICH ULTIMATELY PLAYS A ROLE ON
THE LOCATION OF THE ARCTIC SURFACE RIDGE...WITH THE ECMWF FURTHER
WEST AND SOUTH OVER KANSAS VS THE GFS FURTHER NORTH AND EAST OVER
IOWA AND ILLINOIS. GIVEN THE SOUTHERN EXTENT OF THE SNOWPACK AND
THE BITTER COLD TEMPS IN CANADA FROM WHICH THIS HIGH
ORIGINATES...FEEL GUIDANCE IS TOO HIGH TUESDAY THROUGH THURSDAY
NEXT WEEK AND HAVE THUS LOWERED TEMPS ACCORDINGLY.
&&
.AVIATION...
VFR CONDITIONS WILL PREVAIL FOR THE NEXT FEW HOURS ACROSS MOST
TERMINAL SITES BUT MVFR CEILINGS ARE CLOSE WITH THE LFK TERMINAL
JUST HAVING COME IN WITH A CEILING AT 3KFT AS OF 20Z. STARTING TO
SEE SOME LIGHT ECHOES APPEARING ON RADAR SOUTH OF LFK BUT NORTH OF
HGX WITH THIS PRECIPITATION QUICKLY MOVING EAST NORTHEAST. EXPECT
ISENTROPIC LIFT TO QUICKLY KICK IN AFTER 00Z ALONG THE GULF COAST
WITH SOME LIGHT RAIN MOVING NORTHWARD FROM THE SE TX/S LA COAST...
MOVING INTO THE LFK TERMINAL SHORTLY AFTER 00Z. LIGHT RAIN WILL
BEGIN APPROACHING THE I-20 CORRIDOR...AFFECTING THE TYR/GGG/SHV
TERMINALS NEAR 06Z WITH RAINFALL EVENTUALLY MAKING IT INTO THE
TXK/ELD/MLU TERMINALS BETWEEN 09Z AND 12Z SAT. DURING THE ONSET OF
PRECIPITATION...EXPECT CEILINGS TO BECOME MVFR WITH IFR CONDITIONS
LIKELY ACROSS TX/NW LA AND SW AR TERMINALS NEAR OR SHORTLY AFTER
06Z. CEILINGS MAY BRIEFLY BECOME LIFR DURING THE MORNING HOURS AT A
FEW TERMINAL LOCATIONS. LOOK FOR VISIBILITIES TO REMAIN MOSTLY IN
THE MVFR CATEGORY DURING THE ONSET OF PRECIPITATION WITH IFR VSBY
CATEGORIES THROUGH MUCH OF THE MORNING SATURDAY. /13/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 39 43 43 70 54 / 90 100 30 10 10
MLU 38 42 42 68 53 / 70 100 60 10 10
DEQ 35 42 38 67 43 / 40 80 10 10 10
TXK 38 42 39 67 53 / 60 90 30 10 10
ELD 36 40 40 67 50 / 50 100 50 10 10
TYR 41 46 44 71 54 / 80 80 20 10 10
GGG 40 45 43 73 53 / 80 90 30 10 10
LFK 43 49 44 74 53 / 90 90 30 10 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
LA...NONE.
OK...NONE.
TX...NONE.
&&
$$
04/13
