NATIONAL WEATHER SERVICE FORT WORTH TX

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AREA FORECAST DISCUSSION...UPDATED FOR AVIATION
NATIONAL WEATHER SERVICE FORT WORTH TX
505 AM CST WED FEB 11 2004


VERY BUSY FORECAST SHIFT THIS MORNING WITH A VERY COMPLEX FORECAST
TO PRODUCE. MODELS NOT HELPING MUCH EITHER...AS NONE OF THEM SEEMED
TO HAVE A CLUE ABOUT THE PRECIP CURRENTLY ONGOING OVER OUR NW CWA.
TWO MAIN FORECAST PROBLEMS OF THE DAY WILL BE HEAVY RAIN THREAT
TODAY AND ANY WINTRY PRECIP ACROSS NORTH TEXAS TONIGHT.

DESPITE NOT PICKING UP ON THE PRECIP ACROSS OUR NWRN CWA...ETA AND
NGM ARE PRETTY CLOSE WITH PRODUCING SOME SIGNIFICANT QPF ACROSS OUR
SERN ZONES TODAY. THIS AREA WAS WORKED OVER RECENTLY AND FFG VALUES
ARE PRETTY LOW THIS MORNING. ETA SHOWS PRETTY STRONG ISENTROPIC LIFT
OVER N TEXAS...ESPECIALLY THE EASTERN SECTIONS...TODAY AS H5 LOW
MOVES CLOSER AND DRAWS WARM AND MOIST AIR OVER THE SOMEWHAT COOL
SURFACE AIRMASS. HAVE OPTED TO ISSUE FFA FOR SE ZONES THROUGH THIS
AFTERNOON WHERE 1 TO 2 INCHES...WITH ISOLATED 3 INCH AMOUNTS...SEEM
POSSIBLE. BRUNT OF THIS RAIN SHOULD TAPER OFF THIS EVENING AS
SURFACE LOW TRACKS NE ACROSS LA TONIGHT.

NOW FOR THE WINTRY PRECIP CHANCES. DESPITE GOOD CAA WITH STRONG COLD
FRONT TONIGHT...THIS IS NOT A FAVORABLE PATTERN FOR A SIGNIFICANT
WINTER PRECIPITATION EVENT ACROSS NORTH TEXAS AS THE COLD AIR WILL
BE ARRIVING AS THE LIFTING PROCESSES EXIT. ETA DIV-Q AND OMEGA
FIELDS SHOW DOWNWARD MOTIONS THROUGH THE ATMOSPHERE BY 12Z THURSDAY
AND ISENTROPIC DOWNGLIDE IS INDICATED OVER THE LOWER DEPTHS OF THE
ATMOSPHERE AS WELL. WITH SHALLOW DRIER AIR ADVECTING INTO THE
REGION...BL MOISTURE WILL BE LACKING BY THE TIME THE CRITICAL
PARTIAL THICKNESS VALUES ARE REALIZED. NOW THAT BEING SAID...AND
GIVEN THE LOW CONFIDENCE OF THE SHORT RANGE MODELS OF LATE...WE HAVE
OPTED TO INCLUDE SOME CHANGE OVER TO VERY LIGHT SNOW OR A LIGHT SNOW
AND RAIN MIX FOR AREAS NORTH OF I-20. WE SIMPLY DO NOT HAVE ENOUGH
CONFIDENCE THAT THE PRECIP WILL INDEED BE OVER BEFORE THE AIR GETS
COLD ENOUGH FOR WINTRY PRECIP. WE DO HOWEVER FEEL PRETTY CONFIDENT
THAT PRECIP AMOUNTS SHOULD BE LIGHT AND WE DO NOT EXPECT ANY SNOW
ACCUMULATION...AS IS TYPICAL WHEN WE DO NOT HAVE THE COLD AIR
ALREADY IN PLACE. THE NEXT SHIFT WILL OBVIOUSLY BE LOOKING CLOSELY
AT THIS AS WELL.

PRECIP WILL END OVER MOST OF N TEXAS THURSDAY MORNING WITH CAA
CONTINUING THROUGH EARLY FRIDAY MORNING. SLOW WARM UP FOR THE
WEEKEND WITH NEXT CHANCE OF PRECIP ON MONDAY AND TUESDAY.

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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
120 PM CST WED FEB 11 2004

***WINTER PRECIPITATION POSSIBLE OVER NORTH TEXAS FRIDAY INTO
SATURDAY***

...FORCING/PRECIPITATION...
ALL GLOBAL MODELS ARE CONVERGING ON A SOLUTION THAT BRINGS UPPER LOW
OUT OVER NORTH TEXAS FRIDAY NIGHT INTO SATURDAY. ETA BEGINS
ISENTROPIC LIFT OVER ALL OF NORTH TEXAS BY 18Z FRIDAY. WITH
DEEP-LAYER SATURATION BY 00Z. WE EXPECT THAT SOME LIGHT PCPN WILL
DEVELOP FROM W TO E DURING THE AFTERNOON FRIDAY FROM ISENTROPIC
LIFT. FRIDAY NIGHT...PCPN SHOULD INTENSIFY AS STRONG FORCING MOVES
IN AHEAD OF APPROACHING UPPER LOW. THE DYNAMICS OF THIS SYSTEM
SUGGEST THAT A SIGNIFICANT SWATH OF HEAVY PCPN MAY DEVELOP NW OF
UPPER LOW IN STRONG DEFORMATION ZONE DURING THE DAY SAT. THIS WILL
HAVE TO BE WATCHED CLOSELY. ALL MODELS TRACK UPPER LOW ACROSS THE
CWA DURING THE DAY SAT WITH PCPN ENDING W TO E DURING THE
AFTERNOON. IT IS FAR TO EARLY TO QUANTIFY QPF AT THIS TIME...BUT
GUIDANCE ALREADY SUGGESTING A QUARTER TO HALF INCH BY 18Z SATURDAY
FROM I-20 SOUTH. THE TRACK OF THE UPPER LOW IS CLIMATOLOGICALLY
FAVORABLE FOR A WINTER EVENT IN NORTH TEXAS.

...PCPN TYPE ANALYSIS...
ALL PARTIAL THICKNESS AND SOUNDING ANALYZES (USING NEW TOP-DOWN
APPROACH FOR MICROPHYSICAL CONSIDERATIONS) INDICATE WINTER
PRECIPITATION OVER THE NW TWO-THIRDS OF THE CWA FRIDAY INTO FRIDAY
NIGHT...THEN OVER THE ENTIRE AREA SATURDAY. OUR INITIAL THOUGHTS
ARE THAT WARM ADVECTION WILL LIKELY BE CONVERTED INTO VERTICAL
MOTIONS RATHER EFFICIENTLY SUCH THAT THERE MAY BE RELATIVELY LITTLE
SENSIBLE HEATING IN THE MID-LEVELS. THE EXCEPTION TO THIS MAY BE IN
THE SOUTHEAST ROW OR TWO OF COUNTIES WHERE MID-LEVELS WILL ALREADY
BE MARGINAL FOR FREEZING/FROZEN PCPN. JUST A LITTLE WARMING FROM
WAA WOULD CREATE AN ALL RAIN THERMODYNAMIC PROFILE (SOME ICE PELLETS
MAY MIX IN AT THE ONSET THROUGH EVAPORATIVE COOLING). FURTHER NORTH
(NORTH OF A KILLEEN TO ATHENS LINE BUT SOUTH OF AN EASTLAND TO PARIS
LINE)...PRECIPITATION MAY BEGIN AS A SLEET/SNOW MIXTURE FRIDAY
AFTERNOON... THEN CHANGE TO SLEET AND FREEZING RAIN OVERNIGHT. THE
AREAS NORTH OF EASTLAND TO PARIS MAY STAY ALL SNOW DURING THE ENTIRE
EVENT.

...FORECAST...BEST ESTIMATES...
WE WILL INTRODUCE CHANCE OF SLEET AND LIGHT SNOW NW OF KILLEEN TO
ATHENS FOR FRIDAY AFTERNOON. SOUTH OF THIS LINE...LIGHT RAIN
DEVELOPING POSSIBLY MIXED WITH SLEET.

TO THE NORTH OF KILLEEN TO ATHENS BUT SOUTH OF EASTLAND TO
PARIS...LIGHT SLEET AND SNOW DEVELOPING W TO E FRIDAY
AFTERNOON...THEN CHANGING TO SLEET AND FREEZING RAIN FRIDAY NIGHT.

NORTH OF EASTLAND TO PARIS...ALL SNOW FRIDAY THROUGH SATURDAY.
THESE ARE OUR BEST GUESSES AT THIS TIME. WE WILL BE ISSUING A
SPECIAL WEATHER STATEMENT/ WINTER STORM OUTLOOK WITH THE AFTERNOON
PACKAGE.