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[Printable]
151
FXUS64 KFWD 300432 AAC
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
1132 PM CDT MON SEP 29 2014

.AVIATION...
VFR CONDITIONS WILL PREVAIL THROUGH 12Z WEDNESDAY. LIGHT EAST
WINDS OVERNIGHT WILL BECOME SOUTHEAST AT 10 KNOTS OR LESS BY 12Z
TUESDAY AS A SURFACE LOW CURRENTLY OVER EASTERN COLORADO MOVES
EASTWARD INTO THE CENTRAL PLAINS. THERE WILL BE AN INCREASE IN MID
AND HIGH LEVEL CLOUDS TUESDAY.

58

&&

.UPDATE...
OTHER THAN CIRRUS STREAMING ACROSS THE NORTHWESTERN COUNTIES OF
NORTH TEXAS...SKIES HAVE BECOME GENERALLY CLEAR ACROSS THE REGION.
ISOLATED SHOWERS ACROSS THE SOUTHEAST HAVE ALSO DISSIPATED. THE
CURRENT FORECAST IS IN GOOD SHAPE WITH ABOVE-NORMAL TEMPERATURES
THE NEXT FEW DAYS LEADING UP TO A COLD FRONT AND CHANCES FOR
SHOWERS AND THUNDERSTORMS THURSDAY.

30

&&

.PREV DISCUSSION... /ISSUED 409 PM CDT MON SEP 29 2014/

EARLY AFTERNOON WATER VAPOR SATELLITE IMAGERY SHOWED AN UPPER
LEVEL LOW PRESSURE SYSTEM EXTENDING OVER THE CONUS
ROCKIES...MOVING VERY SLOWLY TO THE EAST. SHORTWAVE RIDGING WAS
EVIDENT OVER THE SOUTHERN AND CENTRAL HIGH PLAINS...AND SHORTWAVE
TROUGHS WERE EVIDENT OVER NORTHERN WISCONSIN AND SOUTHWESTERN
BRITISH COLUMBIA. THIS LATTER SHORTWAVE WAS LOCATED ALONG THE FAR
SOUTHERN PERIPHERY OF A LARGER UPPER LEVEL LOW PRESSURE SYSTEM
OVER THE FAR NORTHEASTERN PACIFIC OCEAN...JUST WEST OF THE
CANADIAN COAST. THE ONLY OTHER SIGNIFICANT FEATURE OF INTEREST
ON WATER VAPOR SATELLITE IMAGERY THAT MAY HAVE SOME IMPACT ON LOCAL
AREA WEATHER IS THAT SOME OF THE MOISTURE ASSOCIATED WITH TROPICAL
STORM RACHEL...CURRENTLY LOCATED JUST WEST OF BAJA
CALIFORNIA...WAS STREAMING NORTHEAST OVER WEST TEXAS THIS
AFTERNOON.

THROUGH THIS EVENING...WENT AHEAD AND MENTIONED A 10 PERCENT
CHANCE OF RAIN SHOWERS FOR LOCATIONS ALONG AND SOUTHEAST OF A LINE
FROM ATHENS TO MARLIN. DESPITE SHORTWAVE RIDGING ALOFT AND
SUBSIDENCE IN PLACE OVER MOST OF THE REGION...ISOLATED RAIN
SHOWERS DEVELOPED NEAR TYLER AND PALESTINE EARLY THIS AFTERNOON.
THESE RAIN SHOWERS SEEM TO EXIST IN AN AREA OF HIGH THETA-E
ACCORDING TO 20Z/3PM OBJECTIVE SURFACE ANALYSIS. THERE WAS NO
OBVIOUS MECHANISM PROVIDING DYNAMIC LIFT IN THE ATMOSPHERE...SO
CURRENT THINKING IS THAT THESE SHOWERS ARE DRIVEN BY
BUOYANCY...AND AS A RESULT SHOULD DISSIPATE SHORTLY AFTER SUNSET.

MODELS INDICATE THAT THE SHORTWAVE TROUGH OVER SOUTHWEST BRITISH
COLUMBIA WILL SWING SOUTHEAST TOWARDS THE FOUR CORNERS REGION OVER
THE NEXT 24 HOURS...CAUSING THE UPPER LOW CURRENTLY IN PLACE OVER
THE CONUS ROCKIES TO WEAKEN...CONSOLIDATE AND MOVE NORTH OVER THE
CENTRAL PLAINS AND HEAD TOWARDS CANADA BY TOMORROW NIGHT. THIS
INTERACTION OF TROUGHS WILL HAVE VERY LITTLE DIRECT IMPACT ON THE
WEATHER ACROSS NORTH TEXAS...HOWEVER IT WILL SET THE STAGE FOR A
COLD FRONTAL PASSAGE ASSOCIATED WITH A SECOND SHORTWAVE TROUGH
EXPECTED TO MOVE OVER THE REGION ON THURSDAY. THE UPPER TROUGHS`
INTERACTION OVER THE NEXT 24 HOURS WILL BRING THE JET STREAM SOUTH
OVER THE SOUTHERN CONUS ROCKIES...ALLOWING LEE SIDE CYCLOGENESIS
TO OCCUR THROUGHOUT THE DAY TOMORROW...AND THEN LOCALLY PICK UP IN
INTENSITY NEAR THE OKLAHOMA AND TEXAS PANHANDLES ON WEDNESDAY AS
THE SECOND SHORTWAVE TROUGH APPROACHES THE REGION.

LEE SIDE CYCLOGENESIS RAMPING UP OVER THE NEXT 24 HOURS WILL CAUSE
LOW-LEVEL WINDS TO VEER AROUND FROM THE EAST TO THE SOUTHEAST BY
TOMORROW AFTERNOON. WE HAVE HAD LOW-LEVEL EASTERLY FLOW OVER THE
REGION FOR SEVERAL DAYS NOW WHICH GENERALLY KEEPS GULF MOISTURE
AWAY FROM THE CWA DUE TO THE ADVECTION OF CONTINENTAL AIR FROM THE
EAST/NORTHEAST OVER NORTH TEXAS. THIS IS NOWHERE NEAR AS DRY AS
WESTERLY LOW-LEVEL FLOW WOULD BE...HOWEVER EASTERLY WINDS STILL
GENERALLY PREVENT RICH GULF MOISTURE FROM MAKING ITS WAY OVER THE
AREA. 12Z RAOB ANALYSIS SHOWED VERY DEEP TROPICAL MOISTURE
CURRENTLY IN PLACE ALL ALONG THE GULF COAST...SO AS SOON AS WINDS
SHIFT AROUND TO A SOUTHERLY DIRECTION...POSITIVE MOISTURE
ADVECTION WILL OCCUR.

MODELS BRING A SURGE OF LOW-LEVEL MOISTURE NORTH TOMORROW
AFTERNOON...GENERALLY EAST OF THE INTERSTATE 35 CORRIDOR. SOME OF
THE HIGH RESOLUTION MODELS ARE SHOWING ISOLATED TO SCATTERED
AFTERNOON RAIN SHOWER ACTIVITY WITHIN THIS PLUME OF LOW-LEVEL
MOISTURE...SO IT IS POSSIBLE THAT WE WILL SEE A REPEAT OF TODAYS
AFTERNOON ISOLATED RAIN SHOWER ACTIVITY NEAR TYLER...PUSH A BIT
FURTHER WEST OVER THE EASTERN HALF OF NORTH AND CENTRAL TEXAS. FOR
NOW LEFT POPS OUT OF THE FORECAST BECAUSE 18Z AMDAR SOUNDINGS
INDICATED THAT OUR 600 TO 500 MB TEMPERATURES HAVE INCREASED BY
3-4 DEG C SINCE THE 12Z FWD RAOB. THIS IS INDICATIVE OF FAIRLY
STRONG SUBSIDENCE OVER THE AREA...WHICH MAY SIMPLY LEAVE TOO
STRONG OF A CAP IN PLACE TO SUPPORT ISOLATED RAIN SHOWERS OVER THE
AREA ASSUMING BUOYANCY IS ONCE AGAIN THE PRIMARY FORCING MECHANISM
FOR LIFT. MODELS INDICATE THAT THE UPPER-LEVEL TROPICAL REMNANTS
OF RACHEL WILL PUSH SOUTH OF THE CWA BY TOMORROW AFTERNOON.
DESPITE THE CHANNEL OF MOISTURE THAT LOOKS LIKE IS HEADED OUR WAY
FROM T.S. RACHEL...THIS MOISTURE LOOKS UNLIKELY TO BENEFIT NORTH
OR CENTRAL TEXAS AT THIS TIME.

THE SECOND SHORTWAVE TROUGH MENTIONED ABOVE IS EXPECTED TO MAKE
ITS WAY SOUTHEAST AND EVENTUALLY OVER THE SOUTHERN PLAINS DURING
THE DAY ON THURSDAY. FOR WEDNESDAY...WITH THIS SHORTWAVE TROUGH
HOLDING WELL OFF TO THE NORTHWEST OF THE CWA...MODELS ARE FINALLY
COMING TO A BETTER CONSENSUS THAT THE LEE SIDE CYCLONE...AND ITS
ASSOCIATED DRYLINE...WILL REMAIN TIED VERY CLOSE TO THE HIGH
PLAINS WEDNESDAY AFTERNOON. AS A RESULT...CURRENT THINKING IS THAT
ANY THUNDERSTORM ACTIVITY NEAR THE DRYLINE WEDNESDAY AFTERNOON
WILL REMAIN CLOSER TO THE TEXAS PANHANDLE THAN IT WILL TO WICHITA
FALLS...OR NORTHWEST/WEST CENTRAL TEXAS IN GENERAL. REMOVED POPS
FROM THE WEDNESDAY EVENING TIME FRAME ACROSS OUR NORTHWESTERN CWA
TO ACCOUNT FOR THIS.

FOR THURSDAY...12Z MODELS HAVE COME MORE IN LINE WITH YESTERDAY`S
12Z CANADIAN MODEL WHICH BRINGS THE UPPER LEVEL DYNAMIC SUPPORT
ASSOCIATED WITH THIS SECOND SHORTWAVE TROUGH SOUTH...OVER THE RED
RIVER DURING THE DAY ON THURSDAY. TODAY`S 12Z CANADIAN OFFERS UP A
SIMILAR/CONSISTENT SOLUTION...HOWEVER THE OPERATIONAL GFS AND
ECMWF MODELS HAVE COME ON BOARD AND ARE SIGNIFICANTLY FURTHER
SOUTH WITH THE SHORTWAVE TROUGH THAN THEY WERE YESTERDAY. THE
CANADIAN REMAINS SOUTH OF THE GFS AND ECMWF SOLUTIONS...HOWEVER
THIS SOLUTION SEEMS MUCH MORE PLAUSIBLE TODAY...AND AS A
RESULT...HAS BEEN INCORPORATED INTO THIS FORECAST PACKAGE.

ASSUMING THE UPPER DYNAMICS COME AT LEAST AS FAR SOUTH AS THE GFS
AND ECMWF ADVERTISE...FORCING FOR ASCENT ALONG THE COLD FRONT
THURSDAY WILL BE SIGNIFICANTLY STRONGER THAN PREVIOUSLY FORECAST.
WENT AHEAD AND BUMPED UP POPS ALONG THE FRONT INTO THE 40 TO 50
PERCENT RANGE TO ACCOUNT FOR THIS INCREASE IN CONFIDENCE IN
FORCING ALONG THE FRONT ON THURSDAY. WHILE THE CONSENSUS OF THE
12Z MODEL RUNS LOOKS PROMISING...THIS IS ONLY THE FIRST RUN OF
MODELS THAT CONSISTENTLY SUPPORTS A MORE SOUTHERN TRACK TO THE
SHORTWAVE TROUGH. IF FUTURE MODEL RUNS CONTINUE TO SUPPORT THIS
SOUTHERN TRACK...POPS AND RAINFALL AMOUNTS WILL NEED TO BE BUMPED
UP EVEN MORE IN LATER FORECASTS.

IF THE SOUTHERN TRACK OF THE UPPER TROUGH VERIFIES...WE WILL ALSO
BE MORE LIKELY TO SEE SOME SEVERE STORMS ALONG THE COLD FRONT
ACROSS NORTH CENTRAL TEXAS THURSDAY AFTERNOON. MODELS CONTINUE TO
SHOW 1500 TO 2000 J/KG OF CAPE ALONG THE FRONT WITH 35 TO 40 KTS
OF DEEP LAYER SHEAR PRESENT OVER THE AREA THANKS IN PART TO
ENHANCED WINDS ALOFT ASSOCIATED WITH THE MORE SOUTHERLY TRACK OF
THE SHORTWAVE TROUGH. THE COMBINATION OF CAPE AND SHEAR ALONE
WOULD FAVOR A SUPERCELL STORM MODE...HOWEVER STRONG FORCING FOR
ASCENT ALONG THE FRONT COMBINED WITH A PRIMARILY UNIDIRECTIONAL
SHEAR PROFILE WOULD PROBABLY FAVOR CELL MERGERS AND LINEAR STORM
STRUCTURES OVER DISCRETE SUPERCELLS...SO A LINEAR MCS/BOW ECHO
STORM MODE MAY BECOME DOMINANT...ASSUMING THIS SOLUTION PANS OUT
IN THE FIRST PLACE.

IF THE SHORTWAVE TROUGH REMAINS CLOSER TO THE OK/KS BORDER...
ESSENTIALLY WHAT THE MODELS HAD BEEN SHOWING CONSISTENTLY LEADING
UP TO TODAY...THEN OUR PRECIPITATION AND SEVERE WEATHER CHANCES
WILL BE QUITE A BIT LOWER IN GENERAL. THUNDERSTORM COVERAGE WOULD
LIKELY BE LIMITED TO 20 TO 30 PERCENT DUE TO LIFT STRUGGLING TO
OVERCOME THE EML CAP THAT IS EXPECTED TO ADVECT IN PLACE OVER THE
REGION BY WEDNESDAY AFTERNOON.

BEHIND THE FRONT...SIGNIFICANTLY DRIER CONDITIONS ARE EXPECTED TO
BUILD OVER THE REGION...RESULTING IN MUCH COOLER OVERNIGHT
TEMPERATURES FRIDAY AND SATURDAY MORNING WHEN COMPARED TO
WEDNESDAY AND THURSDAY MORNING. LOW TEMPERATURES ARE EXPECTED TO
DROP BY 15 DEGREES FOR MOST LOCATIONS THURSDAY TO FRIDAY MORNING.
WHILE COLD AIR ADVECTION BEHIND THE FRONT IS NOT EXPECTED TO BE
OVERLY STRONG...THE LOSS OF MOISTURE AND COOL START TO THE DAY ON
FRIDAY AND SATURDAY WILL KEEP HIGHS ABOUT 10 DEGREES COOLER ACROSS
THE CWA ON FRIDAY AND SATURDAY THAN WHAT IS FORECAST FOR THE AREA
ON WEDNESDAY AND THURSDAY. THESE COOLER AND DRIER CONDITIONS LOOK
LIKELY TO OCCUR REGARDLESS OF HOW MUCH RAIN WE GET ALONG THE
FRONT...SO EVEN IF WE END UP NOT BENEFITING FROM A LOT OF RAIN...A
VERY PLEASANT START TO THE WEEKEND TEMPERATURE WISE IS EXPECTED.

CAVANAUGH





&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  70  90  73  92  76 /   0   5   5   5  10
WACO, TX              67  91  71  92  74 /   0   5   5   5  10
PARIS, TX             65  85  68  87  72 /   0  10   5   5  10
DENTON, TX            65  89  71  91  73 /   0   0   5   5  10
MCKINNEY, TX          66  89  70  91  73 /   0  10   5   5  10
DALLAS, TX            70  90  73  92  76 /   0   5   5   5  10
TERRELL, TX           69  90  70  92  75 /   0  10   5   5  10
CORSICANA, TX         68  89  71  90  75 /   0  10   5   5  10
TEMPLE, TX            66  91  71  92  74 /   0   5   5   5  10
MINERAL WELLS, TX     64  90  69  92  71 /   0   0   5   5  20

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

58/30








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