FXUS64 KFWD 290246 AAB
AFDFWD
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
846 PM CST SAT NOV 28 2009
.UPDATE...
COLD FRONT IS CURRENTLY LOCATED IN KANSAS AND IS JUST BEGINNING TO
ENTER THE TX PANHANDLE. INCREASING MOISTURE WILL CONTINUE
OVERNIGHT...BUT DO NOT THINK WE SHOULD SEE FOG DEVELOPMENT UNTIL
AFTER 3 OR 4 AM. ALSO...THE BEST MOISTURE WILL BE IN THE EASTERN
TWO THIRDS OF THE CWA AND TOOK OUT THE MENTION FOR FOG IN THE
NORTHWESTERN ZONES AS WELL AS THE DRIZZLE AFTER DAYBREAK.
OTHERWISE...NO OTHER CHANGES WERE MADE TO THE FORECAST. TOMORROWS
RAINFALL EVENT ALONG THE FRONT WILL BE A CASE OF 50 TO 60 POPS
WITH AVERAGE RAINFALL TOTALS OF LESS THAN 1/10 OF AN INCH EXCEPT
IN THE SOUTHERN ZONES WHERE THE BEST DEEP LAYER MOISTURE WILL BE
LOCATED.
85/NH
&&
.AVIATION...
CEILINGS WILL LOWER OVERNIGHT...WITH MVFR CEILINGS EXPECTED BY
04Z AT THE METROPLEX TAF SITES. CEILINGS WILL LOWER FURTHER TO
IFR AFTER 07Z. AREAS OF FOG AND DRIZZLE ARE ALSO EXPECTED LATE
TONIGHT INTO SUNDAY MORNING. SOUTHERLY WINDS WILL PREVAIL THROUGH
18Z SUNDAY. AS A COLD FRONT APPROACHES....WINDS WILL SHIFT TO
SOUTHWEST AND WEST. WINDS WILL THEN SHIFT TO THE NORTH AT 15
KNOTS WITH GUSTS TO 25 KNOTS BETWEEN 20-22Z AS THE COLD FRONT
MOVES THROUGH THE METROPLEX. AN ISOLATED THUNDERSTORM IS POSSIBLE
SUNDAY AFTERNOON...BUT THE CHANCES ARE TOO LOW TO MENTION IN THE
TAFS. CEILINGS SHOULD IMPROVE TO MVFR AFTER THE FRONTAL
PASSAGE...AND WIND SPEEDS SHOULD DECREASE AFTER SUNSET.
58
&&
.PREV DISCUSSION... /ISSUED 309 PM CST SAT NOV 28 2009/
PRIMARY FORECAST CONCERNS ARE THE TWO ROUNDS OF PRECIPITATION IN
THIS FORECAST...THE FIRST ASSOCIATED WITH A COLD FRONT THAT WILL
MOVE THROUGH NORTH TX TOMORROW AFTERNOON AND THE SECOND ASSOCIATED
WITH THE POWERFUL UPPER LEVEL SYSTEM THAT LOOKS TO MOVE THROUGH
THE AREA ON TUESDAY.
TONIGHT THROUGH SUNDAY NIGHT...FORECAST CHALLENGE DURING THIS
PERIOD IS THE TIMING OF THE COLD FRONT AS IT MOVES THRU NORTH TX
TOMORROW AFTER SUNRISE. 20Z WATER VAPOR IMAGERY INDICATES A BROAD
POSITIVELY TILTED TROUGH OVER THE WESTERN CONUS. DIGGING INTO THIS
TROUGH IS A STRONG SHORTWAVE TROUGH PUSHING SOUTHEAST CROSSING THE
CANADIAN BORDER. MODELS INDICATE THAT THIS FEATURE WILL CAUSE THE
NORTHERN STREAM BRANCH OF THIS TROUGH TO DETACH FROM THE LONGER
TROUGH THAT CONTINUES INTO THE SOUTHWESTERN CONUS AND PUSH
SOUTHEAST THROUGH THE PLAINS TOMORROW. AS THIS OCCURS A COLD FRONT
IS EXPECTED TO PUSH SOUTHEAST THROUGH NORTH TX. HOW MUCH
PRECIPITATION DEVELOPS ALONG THE FRONT SEEMS DEPENDENT UPON THE
AMOUNT OF MOISTURE THAT IS ALLOWED TO RETURN FOR THE REMAINDER OF
THE DAY TODAY AND THEN THROUGH THE OVERNIGHT HRS. NAM AND GFS
FORECAST SOUNDINGS INDICATE RELATIVELY SHALLOW MOISTURE RETURN
DURING THE OVERNIGHT HRS WHICH IS EXPECTED TO RESULT IN LOW
CLOUDS...FOG AND DRIZZLE OR LIGHT RAIN TO START OFF THE DAY.
DURING THE DAY ON SUNDAY MOISTURE WILL CONTINUE TO RETURN TO THE
REGION...BUT AT THE SAME TIME THE COLD FRONT WILL BEGIN PUSHING
SOUTHEAST THROUGH THE FORECAST AREA.
THE BIGGEST CHALLENGE IS DECIDING WHEN AND WHERE THE COLD FRONT
WILL INTERCEPT DEEPER MOISTURE TO ENHANCE OVERALL PRECIPITATION
COVERAGE AND CHANCES. DEEPER MOISTURE LOOKS TO MOVE AHEAD OF THE
FRONT AFTER 18Z...AND AT THAT TIME THE LEADING EDGE OF THE COLD
FRONT IS EXPECTED TO BE NEAR A PARIS TO DFW TO COMANCHE LINE.
WITH THIS IN MIND...DURING THE MORNING HRS KEPT POPS RELATIVELY
LOW WITH ONLY SHALLOW MOISTURE TO WORK WITH...AND THEN
DURING THE AFTERNOON HRS...EXTENDED LIKELY POPS FOR AREAS ALONG
AND SOUTHEAST OF THE EXPECTED FRONTAL POSITION AT 18Z. DEEPER
MOISTURE IS ASSOCIATED WITH SOME NEGATIVE LIFTED INDEX VALUES AFT
18Z...SO EMBEDDED TSTMS LOOK POSSIBLE AS WELL AS ENHANCED CHANCE
FOR RAIN SHOWER ACTIVITY. AS THE NORTHERN STREAM TROUGH CONTINUES
EAST INTO THE TN VALLEY SUNDAY NIGHT...THE FRONT IS EXPECTED TO
LOSE SOME STEAM AND EVENTUALLY STALL OUT SOMEWHERE NEAR THE GULF
COAST. WITH THE FRONT SLOWING DOWN AND ENCOUNTERING BETTER
MOISTURE TO THE SOUTHEAST...KEPT THE 80 POPS FROM PREVIOUS
FORECAST IN FOR AREAS SOUTHEAST OF AN ATHENS TO TEMPLE LINE AFTER
SUNSET ON SUNDAY. KEPT QPF VALUES FAIRLY LOW AS NOTABLY MISSING
FROM THE EQUATION HERE IS LARGE SCALE FORCING FOR ASCENT. THE
FRONT ITSELF SEEMS TO BE THE PRIMARY LIFTING MECHANISM...AND
WITHOUT MUCH IN THE WAY OF LARGE SCALE SUPPORT THINK COVERAGE AND
INTENSITY OF RAINFALL ALONG THE FRONT WILL BE SOMEWHAT LIMITED.
MONDAY AND MONDAY NIGHT...NOW CUT OFF FROM THE NORTHERN
STREAM...THE STRONG UPPER LEVEL TROUGH OVER THE SOUTHWESTERN CONUS
WILL DRIFT SLOWLY EAST TOWARDS THE SOUTHERN PLAINS DURING THE
PERIOD. MODELS INDICATE THAT BEHIND SUNDAY'S COLD FRONT MUCH
DRIER AIR PUSHES SOUTH INTO NORTH TX...SO HAVE CUT POPS OUT OF
THE NORTHERN PORTIONS OF THE CWA FOR THIS PERIOD. KEPT MENTION IN
SOUTHERN ZONES HOWEVER AS THE SUBTROPICAL JET LOOKS TO BRING IN A
DECENT AMOUNT OF MID AND UPPER LVL MOISTURE OVER THE SOUTHERN
PLAINS DURING THE PERIOD. WHERE THIS MOISTURE OVERLAPS WITH
POSITIVE UPPER LVL PV ADVECTION/LARGE SCALE FORCING FOR ASCENT
THINK ISOLATED TO SCATTERED RAIN SHOWER DEVELOPMENT REMAINS
POSSIBLE.
TUESDAY AND TUESDAY NIGHT...THE 28/12Z GFS/ECMWF AND THE 28/00Z
NAEFS ALL BRING SIGNIFICANT LARGE SCALE FORCING FOR ASCENT OVER
NORTH TX FROM SOUTHWEST TO NORTHEAST DURING THIS PERIOD. ALTHOUGH
LOW LVL MOISTURE RETURN LOOKS TO REMAIN VERY LIMITED FORECAST
SOUNDINGS INDICATE SUFFICIENT MOISTURE ABOVE THE H800 LVL TO
SUPPORT PRECIPITATION DEVELOPMENT. IN THE PRESENCE OF VERY STRONG
FORCING FOR ASCENT INCREASED POPS INTO THE 50 TO 60 PERCENT RANGE
FOR THE ENTIRE FORECAST AREA DURING THE PERIOD. THE RELATIVELY DRY
LOW LVLS COMPLICATE THE FORECAST IN TWO WAYS...THE FIRST IS THAT
PRECIPITATION MUST SATURATE THE LOWER LVLS BEFORE MEASURABLE
PRECIPITATION IS LIKELY...LIMITING PRECIPITATION EFFICIENCY AND
COVERAGE TO SOME DEGREE. THE SECOND COMPLICATION IS THE FORECAST
SOUNDINGS INDICATE A WET BULB ZERO OF THE LOWEST 200 MB JUST ABOVE
FREEZING. IF THIS VERIFIES...IT WILL SIMPLY MEAN COLD RAIN ACROSS
THE AREA...HOWEVER THERMAL PROFILES AND MOISTURE CONTENT WILL HAVE
TO BE EVALUATED CAREFULLY AS THIS EVENT APPROACHES TO DIAGNOSE ANY
POTENTIAL FOR FROZEN PRECIPITATION DEVELOPING. FOR NOW AREAS MOST
LIKELY TO SEE ANY FROZEN PRECIPITATION MIXED IN WITH THE RAIN
SHOWERS ARE AREAS WEST OF INTERSTATE 35. FOR NOW THIS LOOKS TO BE
ONLY A BRIEF WINDOW FOR A RAIN/SNOW MIX TUESDAY NIGHT. SOMETHING
TO KEEP AN EYE ON...HOWEVER AT THIS TIME PRECIPITATION LOOKS TO
REMAIN IN LIQUID FORM THROUGHOUT THIS EVENT.
EXTENDED...NO CHANGES MADE TO THE PREVIOUSLY DRY FORECAST. NO
SIGNIFICANT UPPER LEVEL SYSTEMS LOOK TO AFFECT NORTH TX FROM
WEDNESDAY THROUGH NEXT WEEKEND AT THIS TIME.
CAVANAUGH
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 58 64 42 56 38 / 10 50 40 10 20
WACO, TX 60 69 45 54 41 / 10 60 80 40 50
PARIS, TX 57 64 44 58 35 / 10 60 50 10 10
DENTON, TX 57 64 39 56 36 / 10 50 30 10 10
MCKINNEY, TX 59 65 41 57 37 / 10 50 40 10 10
DALLAS, TX 59 65 42 56 42 / 10 50 40 10 20
TERRELL, TX 58 67 45 57 40 / 10 60 60 10 20
CORSICANA, TX 59 69 45 54 41 / 10 60 80 20 40
TEMPLE, TX 60 70 46 53 42 / 10 60 80 50 50
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
58/85
