FXUS64 KSHV 230930
AFDSHV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SHREVEPORT LA
330 AM CST WED DEC 23 2009
.DISCUSSION...
ACTIVE WEATHER IS IN STORE FOR THE FOUR STATE REGION FOR THE NEXT
COUPLE OF DAYS AS A STRONG UPPER LEVEL DISTURBANCE IS EXPECTED TO
MOVE THROUGH THE REGION TODAY INTO THURSDAY. WATER VAPOR IMAGERY
THIS MORNING SHOWS THE UPPER LOW NOW CENTERED OVER AZ/NM WITH AN
INITIAL SHORTWAVE APPROACHING THE FOUR STATE REGION. THIS SHORTWAVE
HAS ALLOWED THUNDER TO BEGIN OVER PORTIONS OF EAST TEXAS AS SEEN ON
RECENT RADAR IMAGERY. THE UPPER TROUGH IS EXPECTED TO DIG INTO WEST
TEXAS BY MIDNIGHT TONIGHT. AS A RESULT THERE WILL BE A SURFACE LOW
DEVELOP OVER NORTH CENTRAL TEXAS BY THIS AFTERNOON...WHICH WILL
NORTHEAST TO BRING A COLD FRONT THROUGH THE CWFA DURING THE
OVERNIGHT HOURS AND INTO THURSDAY MORNING.
THE CWFA NOW SITS UNDER THE WARM SECTOR WITH A WARM FRONT NOW
POSITIONS WELL TO THE NORTH OF THE CWFA INTO NORTHERN OK/AR. RADAR
IMAGERY SHOWS SHOWERS ACTIVITY INCREASING OVER THE FOUR STATE REGION
EARLY THIS MORNING...WITH THUNDERSTORMS DEVELOPING OVER EAST TEXAS
AS MENTIONED BEFORE. THIS ACTIVITY SHOULD BECOME MORE WIDESPREAD
OVER THE NEXT FEW HOURS...ESPECIALLY OVER THE WESTERN AND NORTHERN
PORTIONS OF THE CWFA. THIS ACTIVITY IS BEGINNING TO SHOW
STRENGTHENING TRENDS...AND ARE BECOMING MORE SURFACE BASED. THROUGH
THE EARLY MORNING HOURS...THERE WILL BE AN INCREASED RISK FOR THESE
STORMS TO POSSIBLY PRODUCE SOME HAIL. THIS ACTIVITY WILL ALSO GIVE
THE GROUNDS A STARTING POINT IN BECOMING SATURATED...POSSIBLY
CREATING A PROBLEM FOR HEAVY RAIN EXPECTED LATER THIS AFTERNOON INTO
EARLY THURSDAY MORNING.
THE POSSIBILITY FOR SEVERE WEATHER CONTINUES TO BE A POSSIBILITY
WITH THIS SYSTEM. FOR THIS AFTERNOON INTO THIS EVENING THERE WILL BE
THE POSSIBILITY OF SEEING THUNDERSTORMS DEVELOP AHEAD OF THE FRONT.
THIS WILL PRIMARILY BE OVER THE WESTERN HALF OF THE CWFA.
INSTABILITY WILL BE LIMITED...BUT THERE SHOULD STILL BE ENOUGH TO
PRODUCE STORMS WITH MLCAPES BETWEEN 500-1000 J/KG EXPECTED. THE AREA
WILL SEE AN UPPER JET BEGIN TO APPROACH THE REGION THIS AFTERNOON
AND ESPECIALLY THIS EVENING...BRINGING DECENT DIVERGENCE TO THE FOUR
STATE REGION TO SUPPORT THUNDERSTORMS. PWATS OF AROUND 1.5 INCHES
WILL PROVIDE PLENTY OF MOISTURE. THERE WILL BE DECENT SHEAR FOR
THIS AFTERNOON INTO THIS EVENING. THERE WILL BE A LOW LEVEL JET
PROVIDING AROUND 40 KTS OF 850 MB FLOW. 500 MB WINDS THIS AFTERNOON
AND EVENING WILL APPROACH 50-70 KTS. ALL OF THESE FEATURES WILL
SUPPORT THE DEVELOPMENT OF SEVERE STORMS BY LATE AFTERNOON AND
ESPECIALLY INTO THIS EVENING. THESE THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING LARGE HAIL AND DAMAGING WINDS...IN ADDITION TO POSSIBLY A
FEW TORNADOES.
BETWEEN 00Z-06Z...A SQUALL LINE IS EXPECTED TO DEVELOP AND MOVE INTO
WESTERN SECTIONS OF THE FORECAST AREA. DAMAGING WINDS AND HEAVY RAIN
WILL BE THE PRIMARY CONCERN WITH THIS SQUALL LINE. ALTHOUGH HAIL AND
AN ISOLATED TORNADO OR TWO CAN NOT BE RULED OUT WITH THIS SQUALL
LINE. THE SQUALL LINE IS NOT EXPECTED TO MOVE TOO FAST. IT SHOULD
REACH SHV...OR POSSIBLY A LITTLE FURTHER EAST BY SUNRISE THURSDAY
MORNING. IT SHOULD BE EAST OUT OF THE CWFA BEFORE LUNCHTIME
THURSDAY. THUS THE SEVERE WEATHER RISK SHOULD BE ENDING FROM WEST
DURING THE OVERNIGHT HOURS TO EAST BY LUNCHTIME THURSDAY.
IN ADDITION TO SEVERE WEATHER...HEAVY RAIN WILL BE A CONCERN. RAIN
THAT WILL BE RECEIVED THIS MORNING WILL ALLOW THE GROUNDS TO BECOME
NEARER TO SATURATION. THIS WILL BE ESPECIALLY TRUE OVER THE
NORTHERN PORTIONS OF THE CWFA WHERE THE BULK OF THE RAIN IS EXPECTED
TO OCCUR THIS MORNING. WITH PLENTY OF MOISTURE MOVING INTO THE FOUR
STATE REGION...THUNDERSTORMS WITH THIS SYSTEM SHOULD BE EFFICIENT
RAIN PRODUCERS. RAINFALL TOTALS OF AROUND THREE TO FOUR INCHES ARE
HIGHLIGHTED OVER THE NORTHERN HALF OF THE CWFA BY HPC...WITH AMOUNTS
OF AT LEAST 2 INCHES ELSEWHERE. WOULD NOT BE SURPRISED TO SEE SOME
LOCALIZED HIGHER AMOUNTS AS WELL...ESPECIALLY OVER THE NORTHWEST
WHERE STORMS MAY TRAIN THIS AFTERNOON AND EVENING AHEAD OF THE
SQUALL LINE. THEREFORE A FLASH FLOOD WATCH HAS BEEN ISSUED
BEGINNING LUNCHTIME TODAY THROUGH 12Z THURSDAY MORNING FOR LOCATIONS
ALONG AND NORTH OF THE INTERSTATE 20 CORRIDOR. THIS WATCH MAY NEED
TO BE EXPANDED FURTHER SOUTH IF THOSE LOCATIONS ARE ABLE TO RECEIVE
ENOUGH RAIN TO GIVE THEM A STARTING POINT THIS MORNING. WILL LET
LATER SHIFTS MONITOR THE SITUATION FOR THAT POSSIBILITY.
THE NEXT POINT OF CONCERN WILL COME DURING THE AFTERNOON THURSDAY.
THERE WILL BE MUCH COOLER TEMPERATURES MOVING INTO THE REGION BEHIND
THE COLD FRONT...WITH THE HIGH EXPECTED TO OCCUR FOR MOST LOCATIONS
IN THE MORNING. OVERALL EXPECT A DRY SLOT TO MOVE INTO THE REGION TO
CUT OFF ANY MOISTURE AND BRING AN END TO PRECIP. HOWEVER...THERE IS
A BIT OF UNCERTAINTY AS TO HOW QUICKLY THIS DRY SLOT WILL MAKE IT
INTO THE REGION. LOCATIONS ALONG AND NORTH OF THE INTERSTATE 30
CORRIDOR MIGHT POSSIBLY SEE ENOUGH MOISTURE REMAINING WHEN THE COLD
AIR MOVES IN TO SEE SOME SNOW. FOR NOW HAVE JUST PUT IN A RAIN AND
SNOW MIX GIVEN THE LEVEL OF UNCERTAINTY. BUT IF MOISTURE REMAINS
JUST LONG ENOUGH...SNOW WILL DEFINITELY BE A POSSIBILITY FOR THESE
NORTHERN LOCATIONS.
THURSDAY WILL ALSO SEE SOME WINDY CONDITIONS BEHIND THE FRONT.
WINDS WILL LIKELY REACH AROUND 15-20 KTS WITH HIGHER GUSTS DURING
THE DAY THURSDAY. IT IS LIKELY THAT SOME SORT OF WIND PRODUCTS WILL
BE NEEDED FOR THURSDAY. BUT WILL LET LATER SHIFTS ASSESS THIS
SITUATION GIVEN EVERYTHING ELSE WE HAVE GOING ON TODAY.
OTHERWISE EXPECT DRIER AND COLDER CONDITIONS FOR CHRISTMAS DAY AND
THROUGH THE WEEKEND. MODELS SUGGEST ANOTHER DISTURBANCE APPROACHING
THE REGION BY THE BEGINNING TO MIDDLE OF NEXT WEEK. THEY ARE
SUGGESTING A SURFACE LOW DEVELOPING OVER THE NORTHERN GULF OF
MEXICO...WHICH WOULD MOVE TO THE EAST NORTHEAST. AGREEMENT BETWEEN
MODELS ON THE TIMING OF THIS SYSTEM IS RATHER POOR. SO FOR NOW WILL
JUST REMAIN CLOSE TO GUIDANCE POPS. REGARDLESS...RAIN CHANCES
SHOULD BEGIN TO RETURN TO THE AREA BY THE BEGINNING TO MIDDLE OF
NEXT WEEK. /22/
&&
.AVIATION...
STRONG FORCING IS ALREADY UNDERWAY ACROSS NE TX AS THE FIRST OF
SEVERAL WEAK SHORTWAVES ROTATE OUT AHEAD OF THE MAIN UPPER LEVEL
TROUGH EXPECTED TO EFFECT THE TERMINAL SITES LATER TONIGHT INTO
THURSDAY. FOR THE TIME BEING...STARTING OUT WITH MOSTLY MVFR
CEILINGS WITH A FEW LOCATIONS WITH IFR CEILINGS. CONVECTION THUS FAR
HAS BEEN CONFINED TO THE TYR/GGG/TXK TERMINALS AND WILL CONTINUE
THIS TREND THROUGHOUT A GOOD PORTION OF THE DAY AS THIS IS WHERE
GREATEST LAPSE RATES SHOULD RESIDE THROUGH THE DAY. WHILE THERE WILL
BE BREAKS IN THE RAIN/TSTM ACTIVITY THROUGH THE DAY...WILL PROBABLY
END UP PREVAILING THIS WEATHER INTO TONIGHT. CEILINGS WILL LIKELY
REMAIN LOW END MVFR/IFR IN AND OUT OF PRECIPITATION INTO TONIGHT AS
WELL. SOUTHEAST WINDS SUSTAINED AT 10-13KTS AREAWIDE TODAY WITH
AGAIN A FEW GUSTS ACROSS NE TX TERMINALS AS THIS IS WHERE THE
GREATEST PRESSURE GRADIENT RESIDES. /13/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 69 51 52 30 51 / 100 100 60 10 10
MLU 64 54 56 32 52 / 100 100 80 10 10
DEQ 64 55 55 25 41 / 100 100 70 10 10
TXK 65 51 52 28 47 / 100 100 70 10 10
ELD 62 53 55 29 50 / 100 100 80 10 10
TYR 71 48 49 27 46 / 100 100 50 10 10
GGG 70 49 50 29 48 / 100 100 50 10 10
LFK 70 50 55 31 51 / 100 100 40 10 10
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...FLASH FLOOD WATCH FROM NOON CST TODAY THROUGH LATE TONIGHT FOR
THE FOLLOWING ZONES: ARZ050-051-059>061-070>073.
LA...FLASH FLOOD WATCH FROM NOON CST TODAY THROUGH LATE TONIGHT FOR
THE FOLLOWING ZONES: LAZ001>006-012>014.
OK...FLASH FLOOD WATCH FROM NOON CST TODAY THROUGH LATE TONIGHT FOR
THE FOLLOWING ZONES: OKZ077.
TX...FLASH FLOOD WATCH FROM NOON CST TODAY THROUGH LATE TONIGHT FOR
THE FOLLOWING ZONES: TXZ096-097-108>112-124>126-136>138.
&&
$$
22/13
