Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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000
FXUS64 KFWD 211212
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
612 AM CST FRI NOV 21 2014

.AVIATION...
PRIMARY AVIATION WEATHER CONCERNS (1) IFR TO LIFR CONDITIONS THIS
MORNING WITH MVFR TO IFR CONDITIONS THIS AFTERNOON AND TONIGHT.
(2)INCREASING PRECIPITATION CHANCES MAINLY TONIGHT THROUGH
SATURDAY MORNING.

A STRONG LOW LEVEL WARM AIR ADVECTION PATTERN WILL REMAIN IN PLACE
ACROSS NORTH TEXAS TODAY AND KEEP A CONTINUOUS FEED OF LOW LEVEL
MOISTURE. IFR TO LIFR CEILINGS WILL CONTINUE AT ALL TAF SITES
THROUGH MID TO LATE MORNING WITH CEILINGS/VISIBILITIES GRADUALLY BECOMING
MVFR AT ALL NORTH TEXAS TERMINALS. ONCE THE SUN SETS...CEILINGS
WILL ONCE AGAIN LOWER BUT SHOULD STAY ABOVE 1000 FT SINCE THE LOW
LEVEL JET WILL INCREASE TO AROUND 35 KNOTS. MVFR CONDITIONS WILL
PREVAIL THIS EVENING THROUGH SATURDAY MORNING.

SOME LIGHT WARM AIR ADVECTION SHOWERS ARE POSSIBLE THROUGH THE
MORNING...ESPECIALLY AT WACO. THE MID LEVELS OF THE ATMOSPHERE WILL
DESTABILIZE THROUGH THE AFTERNOON AS THE UPPER LOW APPROACHES FROM
THE SOUTHWEST. HOWEVER...A STRONG CAP SHOULD REMAIN IN PLACE AND
KEEP THUNDERSTORMS MAINLY SOUTHWEST OF ALL TAF SITES. THUNDERSTORM
CHANCES WILL INCREASE OVERNIGHT THROUGH SATURDAY MORNING WITH
INCREASING LIFT AND SHEAR. FOR NOW WE WILL CARRY VCTS AT ALL TAF
SITES BEGINNING AT 10Z AND NOT INTRODUCE PREVAILING THUNDER UNTIL
AROUND 16Z SATURDAY IN THE EXTEND PORTION OF THE DFW TAF.

A SOUTH TO SOUTHEAST WIND WILL PREVAIL THROUGH SATURDAY MORNING AT
SPEEDS BETWEEN 10 AND 15 KNOTS.

79

&&


.PREV DISCUSSION... /ISSUED 359 AM CST FRI NOV 21 2014/
MORNING SATELLITE IMAGERY SHOWS EXTENSIVE LOW CLOUD COVER HAS NOW
SPREAD ACROSS ALL OF NORTH TEXAS WELL IN ADVANCE OF A VIGOROUS
SHORTWAVE TROUGH THAT WILL BRING RAIN AND THUNDERSTORMS TO THE
REGION THROUGH SATURDAY. 9Z SURFACE ANALYSIS INDICATES A WEAK
SURFACE LOW PRESSURE CENTER SOUTHWEST OF WICHITA FALLS WITH A
STATIONARY FRONTAL BOUNDARY EXTENDING NORTHEAST ACROSS SOUTH
CENTRAL OKLAHOMA. MID 50S DEWPOINTS HAVE SPREAD AS FAR NORTH AS
THE RED RIVER THIS MORNING. A SECONDARY BOUNDARY OF HIGHER
MOISTURE EXISTS ACROSS SOUTH CENTRAL TEXAS WHERE DEWPOINTS HAVE
RISEN INTO THE LOW AND MID 60S. WATER VAPOR IMAGERY SHOWS A LEAD
SHORTWAVE TROUGH NOW MOVING THROUGH THE TEXAS PANHANDLE. THIS
FEATURE WILL QUICKLY MOVE EAST OF THE REGION BY MIDDAY. THE SECOND
MORE POWERFUL SYSTEM IS CURRENTLY DIGGING INTO SOUTHERN CALIFORNIA
AND WILL ARRIVE IN TEXAS DURING THE DAY TOMORROW.

PERSISTENT LOW LEVEL WARM MOIST ADVECTION CONTINUES THIS MORNING
ACROSS MUCH OF TEXAS. THE AXIS OF STRONGEST LIFT IS EXPECTED TO BE
ACROSS THE SOUTHEAST PART OF THE CWA THROUGH MIDDAY. THIS LINES UP
WELL WITH ONGOING SHOWERS WHICH CURRENTLY EXTEND FROM NEAR
VICTORIA THROUGH BRYAN/COLLEGE STATION AND INTO THE PALESTINE
AREA. SCATTERED SHOWERS AND POSSIBLY SOME THUNDERSTORMS ARE
EXPECTED TO CONTINUE FOR THE NEXT SEVERAL HOURS ACROSS THESE
AREAS. LATER TODAY...LOW LEVEL WINDS WILL BEGIN TO BACK IN
RESPONSE TO THE STRONG UPSTREAM SHORTWAVE. THIS WILL ALLOW THE
WARM MOIST ADVECTION TO SHIFT WESTWARD THROUGH THIS AFTERNOON.
WHILE THIS WOULD TYPICALLY INDICATE A WESTWARD SHIFT IN ANY
ONGOING PRECIPITATION...THE DEPARTING LEAD SHORTWAVE CURRENTLY
OVER THE PANHANDLE WILL LEAVE WEAK SUBSIDENCE IN ITS WAKE. ALL OF
THE MODEL GUIDANCE INDICATES WEAK HEIGHT RISES CONTINUING INTO
THIS EVENING ACROSS MOST OF NORTH TEXAS. THIS SETS UP A BATTLE
BETWEEN THE WEAK SUBSIDENCE ALOFT AND LOW LEVEL FORCING FOR ASCENT
SPREADING WESTWARD THROUGH THIS EVENING. FORECAST SOUNDINGS
INDICATE MODERATE INSTABILITY DEVELOPING BY THIS AFTERNOON MAINLY
SOUTH OF I-20 AND WEST OF I-35 AS STEEPER LAPSE RATES FROM WEST
TEXAS ADVECT EASTWARD INTO THE AREA. WHILE THIS COULD POTENTIALLY
SUPPORT SOME STRONG TO SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING...THE LACK OF SIGNIFICANT FORCING ALOFT APPEARS TO BE THE
MAIN INHIBITING FACTOR...ESPECIALLY SINCE SIGNIFICANT CLOUD COVER
IS EXPECTED TO LIMIT HEATING THROUGH THE AFTERNOON HOURS.

BY TONIGHT AS THE SHORTWAVE GETS CLOSER...SUBSTANTIAL HEIGHT
FALLS WILL BEGIN TO OVERSPREAD NORTH TEXAS. THERE SHOULD BE A
SHIFT WESTWARD IN PRECIPITATION ALONG A SURFACE TROUGH AXIS WHICH
WILL LIKELY BE ACROSS THE NORTHWEST COUNTIES. SHOWERS AND
THUNDERSTORMS WILL INCREASE IN COVERAGE THROUGH THE MORNING HOURS
SATURDAY AS A SURFACE LOW BECOMES ESTABLISHED AND STARTS TO MOVE
EAST AHEAD OF THE UPPER TROUGH. PRECIPITATION COVERAGE ACROSS
NORTH TEXAS WILL LIKELY BE 100 PERCENT DURING THE DAY SATURDAY AS
THE SURFACE LOW AND BEST FORCING FOR ASCENT TRACKS RIGHT ACROSS
THE REGION. GIVEN THE PROXIMITY TO THE UPPER LOW...WIND FIELDS
WILL BE RATHER STRONG WITH THIS SYSTEM...YIELDING MODERATE TO
STRONG DEEP LAYER SHEAR VALUES. THE MAIN CONCERN REGARDING SEVERE
WEATHER POTENTIAL REVOLVES AROUND THE AMOUNT OF INSTABILITY THAT
ACTUALLY DEVELOPS DURING THE DAY SATURDAY. MOST OF THE GUIDANCE
CONTINUES TO SUGGEST THAT THE BEST INSTABILITY WILL REMAIN ACROSS
CENTRAL AND SOUTH TEXAS DURING THE DAY...WITH OUR SOUTHERN
COUNTIES HAVING THE BEST CHANCE FOR SEVERE WEATHER. FORECAST
SOUNDINGS FOR SATURDAY AFTERNOON INDICATE NEARLY MOIST ADIABATIC
PROFILES WITH VERY LITTLE CAPE SUGGESTING A LOW THREAT FOR SEVERE
STORMS. WIDESPREAD CONVECTION ACROSS NORTH TEXAS WILL LIKELY BE
WELL AHEAD OF THE COLD TEMPERATURES ALOFT ASSOCIATED WITH UPPER
TROUGH. THE MAIN CONCERN WITH THIS IS THAT IT WOULD ONLY TAKE A
LITTLE BIT OF WARMING OR A LITTLE MORE MOISTURE THAN ADVERTISED BY
THE MODELS TO SUBSTANTIALLY INCREASE SURFACE INSTABILITY IN A
STRONGLY SHEARED ENVIRONMENT. SO...CONFIDENCE REMAINS LOW
CONCERNING THE SEVERE POTENTIAL ACROSS OUR CWA. THE HIGHEST THREAT
FOR SEVERE STORMS WILL BE SOUTH OF INTERSTATE 20 THROUGH SATURDAY
EVENING. IF MORE ROBUST INSTABILITY DOES DEVELOP SATURDAY
AFTERNOON...THERE WOULD BE A THREAT FOR PRIMARILY DAMAGING WINDS
AND EVEN TORNADOES GIVEN THE STRONG SHEAR.

CONCERNING HEAVY RAINFALL POTENTIAL...PRECIPITABLE WATER VALUES
CLIMB IN EXCESS OF 1.25 INCHES WITH THIS SYSTEM LATER TONIGHT AND
APPROACH 1.5 BY SATURDAY WHICH IS QUITE HIGH FOR THIS TIME OF
YEAR. WIDESPREAD RAINFALL AMOUNTS OF 1 TO 3 INCHES APPEARS LIKELY
ACROSS A GOOD PORTION OF NORTH TEXAS. THE SPEED AT WHICH THIS
SYSTEM MOVES THROUGH AND EXTENSIVE DROUGHT CONDITIONS ACROSS NORTH
TEXAS SUGGEST THAT WE WILL BE ABLE TO HANDLE THAT AMOUNT OF RAINFALL
WITHOUT ANY SIGNIFICANT FLOODING CONCERNS. URBAN FLASH FLOODING
WILL REMAIN A THREAT THROUGH SATURDAY.

ALL OF THIS ACTIVITY WILL MOVE EAST OF THE AREA LATE SATURDAY
NIGHT WITH DRIER AIR MOVING IN FROM THE WEST. SUNDAY WILL BE NICE
WITH TEMPERATURES WARMING INTO THE 70S WITH MAINLY WESTERLY FLOW
IN PLACE. THE COOLER AIR WILL ARRIVE ON MONDAY WITH TEMPERATURES
FALLING BACK TO UPPER 50S AND LOWER 60S. THE REMAINDER OF NEXT
WEEK SHOULD BE MOSTLY DRY AND SEASONAL.

DUNN

&&



.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  70  60  67  54  72 /  30  70 100  70   5
WACO, TX              72  61  69  52  74 /  50  60 100  60   0
PARIS, TX             65  54  65  55  69 /  50  70  90 100  10
DENTON, TX            70  59  66  51  70 /  30  80 100  70  10
MCKINNEY, TX          69  58  66  51  70 /  40  70 100  90  10
DALLAS, TX            70  59  67  56  72 /  40  70 100  70   5
TERRELL, TX           69  58  68  54  72 /  50  60 100  90  10
CORSICANA, TX         71  58  69  55  74 /  60  40 100  80   5
TEMPLE, TX            73  61  69  52  75 /  50  50 100  50   0
MINERAL WELLS, TX     70  59  67  49  71 /  20  80 100  30   5

&&

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

&&

$$

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