FXUS64 KFWD 261222 AAA
AFDFWD
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
620 AM CST SAT DEC 26 2009
.AVIATION...
620 AM
WEAK WIND SHIFT TO NORTHWEST EXPECTED BY MID MORNING. NO CIG/VSBY
RESTRICTIONS EXPECTED THOUGH MONDAY. 84
&&
.DISCUSSION...
439 AM
WEATHER IS EXPECTED TO REMAIN QUIET BUT COLD THROUGH MONDAY NIGHT.
ENORMOUS WINTER CYCLONE OVER THE CENTRAL US WILL WEAKEN AND HEAD
OFF TO THE EAST DURING THE NEXT COUPLE DAYS. AS THE SYSTEM EXITS
AN UPPER TROUGH AXIS WILL ROTATE THROUGH THE REGION THIS EVENING.
THIS WILL SEND A REINFORCING COLD FRONT THROUGH NORTH TEXAS
TONIGHT...SO WINDS WILL SWITCH TO NW AND HIGH TEMPS MONDAY WILL BE
A LITTLE COOLER THAN TODAY DESPITE SUNNY SKIES.
MAIN FORECAST CHALLENGE CONCERNS THE SYSTEM ON TUESDAY...WHEN A
PRONOUNCED SHORTWAVE IN THE SOUTHERN/SUBTROPICAL JET STREAM MOVES
ACROSS...AND WHETHER TEMPS WILL BE COLD ENOUGH FOR FROZEN PRECIP.
THE FORECAST 500 MB SYNOPTIC PATTERN IN YESTERDAYS MODELS LOOKED
A BIT MORE FAVORABLE FOR A SNOW EVENT HERE BECAUSE THEY KEPT THE
UPPER HIGH PLANTED ACROSS THE NORTHERN ROCKIES. THIS CLOSELY
MATCHED A CLIMATOLOGICALLY FAVORED SYNOPTIC PATTERN FOR SNOW OVER
THE NW/N CWA. TODAY THE MODELS BREAK DOWN AND MOVE THE RIDGE INTO
THE NORTHERN PLAINS...WHICH CAUSES INTENSE WARMING OF THE 500-850
MB TEMPS VIA SUBSIDENCE ACROSS THE PLAINS. THIS MID-TROPOSPHERIC
WARMING WILL HAVE LITTLE IMPACT ON SURFACE TEMPS DUE TO INSULATION
EFFECTS OF HIGH ALBEDO SNOW COVER. BUT SNOW REQUIRES A COMPLETELY
SUBFREEZING LAYER...AND LATEST MODELS ARE NOW RIGHT AT 0C FROM
700-850 MB WHICH LEAVES LITTLE ROOM FOR ERROR. ADDITIONALLY...THIS
SYSTEM IS MERELY AN OPEN WAVE MOVING ACROSS...AND PRECIPITATION
WILL BE GENERATED VIA A BROAD REGION OF ISENTROPIC LIFT...WHICH IS
SYNONYMOUS WITH WARM ADVECTION. MODEL SOUNDINGS DEPICT THE COOLING
EFFECTS OF EVAPORATION COUNTERING THE WARM ADVECTION...AT LEAST
INITIALLY ON TUESDAY. THEREFORE EXPECT RAIN TO MIX WITH SLEET/SNOW
TUESDAY MORNING WITH A TRANSITION TO ALL RAIN FROM SOUTHEAST TO
NORTHWEST AS THE DAY PROGRESSES. HIGHEST QPF AND POPS WILL BE IN
THE SOUTHEAST WHERE GFS/ECMWF ARE BOTH SUGGESTING ENHANCED
VERTICAL MOTIONS WITHIN A FRONTOGENETIC BAND. WILL CONTINUE TO
MONITOR THE TRENDS IN THE MODELS TO DETERMINE WHETHER ANY
ACCUMULATION/IMPACTS WILL BE POSSIBLE WITH THIS SYSTEM...BUT ANY
RISK OF SUCH FAVORS THE NW CWA AT THIS TIME.
COLD RAIN SHOULD END TUESDAY NIGHT FROM WEST TO EAST...BUT KEPT
SOME LOW POPS IN ON WEDNESDAY DUE TO TIMING UNCERTAINTIES. MODELS
HINTING AT A SECOND SHORTWAVE MOVING ACROSS ON THURSDAY WITH GFS
INDICATING A POTENTIAL FOR SNOW FLURRIES. MOISTURE IS REALLY
LACKING WITH THIS WEAK SYSTEM...AND WILL KEEP FORECAST DRY.
OTHERWISE...THE COLDER THAN NORMAL CONDITIONS WILL CONTINUE AS
HIGH PRESSURE IN THE PLAINS WILL ENSURE NORTH WINDS FRI-SAT.
MODELS ARE SHOWING A TREMENDOUS AMOUNT OF UNCERTAINTY BY NEXT
WEEKEND. THE GFS SUGGESTS A GRADUAL WARMING TREND TO NEAR OR
SLIGHTLY ABOVE NORMAL. THE CANADIAN HAS ANOTHER SNOW EVENT AND
ARCTIC INTRUSION NEXT WEEKEND. THE ECMWF HAS BACKED OFF ON ITS
VERY COLD FORECAST AROUND NEW YEARS DAY WITH LESS AMPLIFICATION OF
A SHORTWAVE TROUGH IN CANADA...BUT NOW IS SUGGESTING AN EXTREMELY
FAVORABLE SYNOPTIC SET UP FOR A SIBERIAN ORIGIN AIRMASS AND 1050
MB SURFACE HIGH TO DROP INTO THE PLAINS BY DAY 10-12. IT WILL BE
INTERESTING TO SEE WHICH...IF ANY...OF THESE PATTERNS THE MODELS
TREND TOWARD DURING THE NEXT FEW DAYS.
TR.92
&&
.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX 48 27 45 28 45 / 0 0 0 0 0
WACO, TX 53 28 52 28 51 / 0 0 0 0 0
PARIS, TX 46 26 42 24 43 / 0 0 0 0 0
DENTON, TX 46 26 43 23 44 / 0 0 0 0 0
MCKINNEY, TX 46 25 44 24 44 / 0 0 0 0 0
DALLAS, TX 48 31 45 29 46 / 0 0 0 0 0
TERRELL, TX 49 29 46 28 46 / 0 0 0 0 0
CORSICANA, TX 52 30 50 29 48 / 0 0 0 0 0
TEMPLE, TX 53 30 53 29 50 / 0 0 0 0 0
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
