FXUS64 KFWD 141801
AFDFWD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1201 PM CST MON DEC 14 2009
.AVIATION...
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF FORECAST PERIOD. A
COLD FRONT THAT EXTENDED SOUTHEAST OF A KADH /ARDMORE/...KSPS
/WICHITA FALLS/ LINE...WILL MOVE SOUTHEAST THROUGH THE METROPLEX
TAF SITES BY 22Z. HOWEVER...WINDS HAVE ALREADY SWITCHED TO THE
WEST...AND WILL SHIFT TO THE NORTHWEST 19-20Z...AHEAD OF THE
ACTUAL FRONT.
58
&&
.UPDATE...
RAN A QUICK UPDATE TO MAKE SOME MINOR TWEAKS TO THE HIGH
TEMPERATURES FOR TODAY AND THE HOURLY GRIDS. BUMPED UP
TEMPERATURES IN THE NORTHWEST 5 OR 6 DEGREES AND LOWERED THEM A
BIT IN THE SOUTHWEST WHERE LOW CLOUDS WILL STICK AROUND FOR MOST
OF THE DAY.
THE COLD FRONT IS CURRENTLY LOCATED IN SOUTHERN OKLAHOMA AND
STRETCHES INTO WEST TEXAS. CURRENT TIMING BRINGS IT TO THE RED
RIVER JUST AFTER NOON AND INTO THE METROPLEX AROUND 3 OR 4 PM. THE
FRONT WILL SLOW DOWN WITH ITS FORWARD MOVEMENT AS THE WEAK
SHORTWAVE RESPONSIBLE FOR SENDING THIS FRONT THROUGH MOVES INTO
THE MIDWEST. EXPECT IT TO MAKE IT TO OUT OF THE CWA SOMETIME LATE
THIS EVENING. STILL NOT EXPECTING ANYTHING OUTSIDE OF A FEW
SPRINKLES OR LIGHT RAIN IN OUR SOUTHERN ZONES WITH THE FRONTAL
PASSAGE...AS THE ATMOSPHERE REMAINS TOO DRY AND CAPPED. UPDATED
PRODUCTS HAVE BEEN SENT.
85/NH
&&
.PREV DISCUSSION... /ISSUED 437 AM CST MON DEC 14 2009/
TODAY AND TONIGHT...PRIMARY FORECAST CONCERN IS THE TIMING OF THE
COLD FRONT MOVING SOUTH THROUGH THE SOUTHERN PLAINS AND ANY
ASSOCIATED PRECIPITATION DURING THE PERIOD. AT FORECAST TIME THE
LEADING EDGE OF THE COLD FRONT WAS PUSHING JUST SOUTH OF THE KS/OK
BORDER. TEMPERATURES HAVE BEEN FALLING RAPIDLY 50 MILES OR SO
BEHIND THE LEADING EDGE OF THE FRONT AS THE AIR BEHIND THIS
BOUNDARY ORIGINATES OVER THE STILL SNOW COVERED NORTHERN PLAINS.
TEMPERATURES IN SOUTHERN KS HAVE FALLEN FROM THE UPPER 40S INTO
THE MID TEENS EARLY THIS MORNING. EXPECT THAT THIS AIRMASS WILL
MODIFY AS IT CONTINUES SOUTH OVER NON SNOWPACKED AREAS...HOWEVER
THERE IS SOME CONCERN THAT GUIDANCE IS UNDERESTIMATING THE
STRENGTH OF THIS SHALLOW COLD AIRMASS. IT WILL BE DIFFICULT TO
DETERMINE UNTIL THE FRONT GETS FURTHER REMOVED FROM SNOW COVERED
AREAS DURING THE DAY TODAY JUST HOW MUCH THIS AIR WILL BE MODIFIED.
FOR NOW HEDGED JUST UNDER GUIDANCE FOR OVERNIGHT LOWS AS THE COLD
FRONT IS EXPECTED TO SLOW DOWN A BIT AS IT MOVES THRU THE SOUTHERN
PLAINS.
THE PRIMARY REASON THE FRONT LOOKS TO SLOW DOWN IS THE APPROACH OF
A SHORTWAVE TROUGH MOVING THRU SOUTHERN CA AT 09Z. MODELS INDICATE
THAT AS THIS FEATURE MOVES OUT OVER THE SOUTHERN CONUS ROCKIES
LATE THIS AFTERNOON OR THIS EVENING THE FRONT WILL SLOW DOWN AND
MAY BE LOCATED SOMEWHERE AROUND THE GULF COAST BY MIDNIGHT. THIS
IS IMPORTANT BECAUSE GFS/NAM BOTH INDICATE THAT THE COLDEST/DRIEST
AIR IS ASSOCIATED WITH THE H850 REFLECTION OF THE SLOPING COLD
FRONT...WHICH WILL LIKELY NOT CLEAR OUR SOUTHEASTERN COUNTIES
BEFORE SUNRISE ON TUESDAY. WITH MODELS CONTINUING TO INDICATE SOME
SOUTHWESTERLY FLOW AT THE H850 LVL THRU 12Z TUE...THINK THE
SHALLOW COLD AIRMASS WILL SERVE TO PROVIDE STEEPER LOW LVL
ISENTROPIC SFCS OVER OUR SOUTHEASTERN COUNTIES. WITH CONTINUED
FLOW OVER THE COOLER LOW LVL AIRMASS THINK THAT RAIN SHOWERS WILL
LIKELY DEVELOP DUE TO ENHANCED LOW LVL ISENTROPIC LIFT AND WEAK
FRONTOGENETIC FORCING. NAM FORECAST SOUNDINGS JUST NORTH OF
COLLEGE STATION INDICATE RELATIVELY STEEP LAPSE RATES ABOVE THE
FRONTAL INVERSION. IF ISENTROPIC LIFT/FRONTOGENETIC FORCING IS
SUFFICIENT TO ALLOW RAIN SHOWERS TO DEVELOP...THERE IS SOME
POTENTIAL INSTABILITY THAT MAY ALLOW FOR SOME EMBEDDED THUNDER AS
WELL. PRECIPITATION CHANCES SEEM TO BE LIMITED TO AREAS ALONG AND
SOUTHEAST OF THE H850 FRONT TONIGHT...SO ONLY INCLUDED AREAS ALONG
AND SOUTHEAST OF A KILEEN TO ATHENS LINE IN THE MENTION OF RAIN
SHOWERS. OTHERWISE AS THE LEADING EDGE OF THE COLD FRONT MOVES
THROUGH SOMEWHAT QUICKLY THIS AFTERNOON...DO NOT SEE MUCH IN THE
WAY OF LIFT FOR MUCH MORE THAN SPRINKLES THRU SUNSET.
TUESDAY NIGHT THROUGH FRIDAY NIGHT...GFS/ECMWF BOTH INDICATE THAT
THE SOUTHERN CA TROUGH WILL CONTINUE SOUTHEAST THRU TX ON
WEDNESDAY. THIS TROUGH LOOKS TO REMAIN FAR ENOUGH SOUTH TO KEEP ANY
PRECIPITATION CHANCES OUT OF THE CWA AS ASSOCIATED CYCLOGENESIS
LOOKS TO OCCUR WELL OFFSHORE KEEPING PRECIPITATION ALONG THE GULF
COAST. AS THIS FEATURE TRANSLATES EAST OVER THE GULF OF MEXICO THE
UPPER AIR PATTERN OVER THE CONUS LOOKS TO AMPLIFY AS THE
NORTHEASTERN CONUS UPPER LOW RETROGRADES AND RIDGING BUILDS OVER
THE WEST. THIS WILL BRING NORTHWEST FLOW OVER THE GREAT PLAINS
WHICH IS TYPICALLY A DRY/COOL PATTERN FOR TX THIS TIME OF YEAR.
NORTHWEST FLOW WILL OPEN THE DOOR FOR SEVERAL PIECES OF ENERGY TO
MOVE SOUTHEAST INTO THE NORTHERN AND CENTRAL PLAINS. THE FIRST
SIGNIFICANT PIECE OF ENERGY LOOKS TO MOVE SOUTHEAST DURING THE DAY
ON FRIDAY...SENDING A COLD FRONT THOUGH THE CWA FRIDAY NIGHT. WITH
LITTLE OPPORTUNITY FOR MOISTURE RETURN PRECIPITATION CHANCES LOOK
SMALL AT THIS TIME. REMAINED BELOW GUIDANCE ON TUESDAY WITH THE
COLD AIRMASS OVER NORTH TX...AND THEN WENT CLOSER TO GUIDANCE
WEDNESDAY THRU FRIDAY AS AIRMASS MODIFIES FOR THE REMAINDER OF THE
WEEK.
EXTENDED...MODELS BEGIN TO DIVERGE STARTING THIS WEEKEND...WITH
THE PASSAGE OF THE COLD FRONT LATE FRIDAY OR FRIDAY NIGHT
TEMPERATURES IN GENERAL LOOK TO REMAIN BELOW NORMAL. THE ECMWF IS
MUCH MORE AGGRESSIVE WITH THE COLD AIR THIS WEEKEND AND HEADED INTO
NEXT WEEK THAN THE GFS. THE MEX INDICATES HIGHS IN THE MID TO
LOWER 50S THIS WEEKEND AND HEADED INTO NEXT WEEK. THE ECMWF WOULD
KEEP HIGHS IN THE LOWER 50S SATURDAY...BEFORE DROPPING HIGHS INTO
THE MID 30S BY TUESDAY NEXT WEEK. FOR NOW SIMPLY UNDERCUT MEX
GUIDANCE BY A FEW DEGREES WITH THE COOLER THAN NORMAL SIGNAL
ASSOCIATED WITH NORTHWEST FLOW ALOFT.
CAVANAUGH
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 67 36 46 30 55 / 10 10 5 0 5
WACO, TX 69 39 50 30 56 / 10 20 10 5 5
PARIS, TX 61 35 46 27 54 / 10 10 10 5 5
DENTON, TX 67 33 45 26 54 / 10 10 5 0 5
MCKINNEY, TX 66 35 46 28 54 / 10 10 5 0 5
DALLAS, TX 67 37 47 32 55 / 10 10 5 0 5
TERRELL, TX 67 38 48 31 56 / 10 10 10 0 5
CORSICANA, TX 66 39 50 31 57 / 10 30 10 5 5
TEMPLE, TX 65 40 51 33 57 / 10 30 20 5 5
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
58/85
