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

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000
FXUS64 KFWD 050853
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
353 AM CDT TUE MAY 5 2015

.DISCUSSION...

REGIONAL RADAR IMAGERY SHOWED A LARGE CLUSTER OF THUNDERSTORMS
EXTENDING FROM THE EASTERN TEXAS PANHANDLE SOUTH ACROSS WEST
CENTRAL TEXAS. A FAIRLY WELL ORGANIZED MESOSCALE CONVECTIVE VORTEX
WAS EMBEDDED IN THIS CONVECTION...AND WAS FAIRLY EASY TO PICK OUT
BY SIMPLY LOOPING THE REGIONAL MOSAIC REFLECTIVITY. THE MCV WAS
LOCATED EAST-NORTHEAST OF LUBBOCK, AND APPEARED TO BE SLOWLY
MOVING EAST TOWARDS NORTH TEXAS AT 08Z/3AM CDT. WATER VAPOR
SATELLITE IMAGERY SHOWED THAT THIS CONVECTION WAS OCCURRING
IMMEDIATELY DOWNSTREAM OF A STRONG AREA OF DIFFLUENCE ALOFT
ASSOCIATED WITH A BROAD UPPER LEVEL TROUGH CENTERED OVER ARIZONA,
AND A WEAK UPPER LEVEL RIDGE OVER THE ARKLATEX REGION. THE 00Z FWD
RAOB OBSERVED A LAYER OF VERY DRY AIR IN PLACE FROM 700 TO 400 MB
YESTERDAY EVENING.

TODAY...THE WIDESPREAD EARLY MORNING CONVECTION WEST OF THE CWA
CERTAINLY COMPLICATES THE PRECIPITATION FORECAST FOR NORTH AND
CENTRAL TEXAS TODAY. PERSISTENT CONVECTION RELEASES A GREAT DEAL
OF HEAT INTO THE MIDDLE AND UPPER TROPOSPHERE. THIS HEAT RELEASE
RESULTS IN THE CREATION OF POTENTIAL VORTICITY (PV) IN THE MIDDLE
ATMOSPHERE, AND MORE OR LESS DESTROYS UPPER LEVEL PV BY BUBBLING
UP THE TROPOPAUSE. WITH AN UPPER LEVEL TROUGH TO THE WEST OF THE
ONGOING CONVECTION...THIS PROCESS CAN HELP PROVIDE STRONGER
FORCING FOR ASCENT OVER WEST TEXAS AGAIN THIS MORNING AS
DIFFERENTIAL VORTICITY ADVECTION AND ITS DEEP LAYER LIFT ARE
ENHANCED. ALSO... WHEREVER THE MID-LEVEL GENERATED LOW PRESSURE
SYSTEM (MCV) MOVES, IT WILL TEND TO ALTER THE MID-LEVEL FLOW
FIELD WHICH HAS AN IMPACT ON WHERE MID-LEVEL MOISTURE WILL MOVE
LATER THIS AFTERNOON.

WITH DRY AIR IN PLACE AT THE MID-LEVELS OVER NORTH TEXAS...THE
ADVECTION OF MID-LEVEL MOISTURE BACK OVER THE REGION IS SOMETHING
TO WATCH CAREFULLY THROUGHOUT THE DAY TODAY. IF WE GET A SURGE OF
MID-LEVEL MOISTURE, THE CHANCES OF PRECIPITATION DEVELOPING FROM
LATE THIS AFTERNOON THROUGH THE EVENING HOURS ARE QUITE HIGH AS
MOST MODEL GUIDANCE INDICATES A SHORTWAVE TROUGH EMBEDDED WITHIN
THE LARGER ARIZONA UPPER TROUGH WILL MOVE OVER OUR NORTHWESTERN
CWA TODAY AFTER 00Z. BASED ON THE CURRENT TRACK OF THE MCV EAST OF
LUBBOCK...IT SHOULD GENERALLY REMAIN ALONG OR JUST NORTH OF THE
RED RIVER...ASSUMING IT CONTINUES TO MOVE EAST THIS MORNING. AS
LONG AS IT TAKES THAT TRACK...OR SIMPLY STOPS MOVING TOWARDS NORTH
TEXAS...OUR GOOD RAIN CHANCES SHOULD REMAIN IN TACT FOR THE
NORTHWESTERN HALF OF THE CWA FROM LATE THIS AFTERNOON THROUGH THIS
EVENING.

EARLY MORNING SURFACE ANALYSIS ALSO SHOWED A PLUME OF LOW-LEVEL
MOISTURE IN PLACE OVER SOUTH TEXAS, JUST SOUTHEAST OF THE AUSTIN-
SAN ANTONIO AREA. THIS MOISTURE IS EXPECTED TO ADVECT NORTH
THROUGHOUT THE DAY TODAY AS WELL. THIS MOISTURE IS EXPECTED TO
INTERSECT WITH THE PLUME OF MID-LEVEL MOISTURE MOVING NORTHEAST
OVER THE REGION OVER OUR EASTERN CWA AFTER 18Z TODAY. AS A RESULT,
MOST MODELS CAUSE CONVECTION TO DEVELOP EAST OF I-35 BY EARLY THIS
AFTERNOON...ALLOWING IT TO TAPER OFF AFTER THE PEAK HEATING HOURS
OF THE DAY THIS AFTERNOON. WITH NO COHERENT LIFTING MECHANISM
IDENTIFIED TO CAUSE THIS ACTIVITY TO DEVELOP EARLY THIS
AFTERNOON...THINK THAT THIS CONVECTION IS LIKELY DRIVEN BY DAYTIME
HEATING AND THE RETURN OF DEEPEST MOISTURE TO THE CWA. THE ONLY
OBVIOUS LIFT IN PLACE IS DIFFLUENCE ALOFT...ABOVE THE 500 MB
LEVEL, SO KEPT POPS IN THE 40 TO 50 PERCENT RANGE FOR NOW EAST OF
I-35 AS A LACK OF DISCERNIBLE LIFT AT THE LOW-LEVELS CAN
OFTENTIMES RESULT IN LESS THAN EXPECTED CONVECTIVE DEVELOPMENT.

FOR WEDNESDAY THROUGH FRIDAY...THE ARIZONA UPPER TROUGH IS
EXPECTED TO MOVE NORTHEAST OF THE REGION BY WEDNESDAY MORNING
WHILE ANOTHER STRONG UPPER TROUGH MOVES SOUTH ALONG THE WESTERN
CONUS COAST AND SETTLES IN OVER THE NV/AZ BORDER BY FRIDAY
MORNING. IN THIS TRANSITION PERIOD...UPPER LEVEL DIFFLUENCE IS
EXPECTED TO PERSIST OVER MUCH OF NORTH AND CENTRAL TEXAS UNDER
PERSISTENT SOUTHWEST FLOW ALOFT. SOUTHWEST FLOW ALOFT TYPICALLY
SENDS AN ELEVATED MIXED LAYER OVER NORTH TEXAS WHICH EFFECTIVELY
SHUTS OFF PRECIPITATION FOR A FEW DAYS UNTIL STRONGER FORCING FOR
ASCENT ARRIVES TO HELP LIFT AND COOL THE EML. WHILE 700 MB WARM
AIR ADVECTION IS CERTAINLY INDICATED BY MODELS, THE LACK OF ANY
LOW-LEVEL FRONT PUSHING ACROSS THE CWA KEEPS A VERY DEEP AND MOIST
AIRMASS IN PLACE. AS A RESULT...WEAK PERSISTENT LIFT IN THE
PRESENCE OF DEEP MOISTURE AND ONLY WEAK CAPPING ALOFT HAS MODELS
ESSENTIALLY ADVERTISING SCATTERED THUNDERSTORMS FOR EACH PERIOD
FROM WEDNESDAY THROUGH FRIDAY.

THINK THAT MODELS MAY BE OVERDOING THIS A BIT...SO WENT AHEAD AND
BACKED OFF ON POPS A BIT DURING THIS PERIOD...KEEPING 20 OR 30
POPS IN PLACE FOR MOST DAYS. THUNDERSTORMS WILL PROBABLY DEVELOP
EACH DAY, BUT WITH ONLY WEAK SYNOPTIC FORCING FOR ASCENT IN PLACE,
MESOSCALE LIFT OR SUBSIDENCE WILL DOMINATE OUR PRECIPITATION
CHANCES EACH DAY. BECAUSE MESOSCALE PHENOMENA ARE NOT ONLY SMALL
ON A SPATIAL SCALE, BUT ALSO ON A TEMPORAL SCALE, THE DETAILS OF
THE MESOSCALE ENVIRONMENT ARE TYPICALLY NOT WELL RESOLVED OR
FORECAST BY MODEL GUIDANCE UNTIL THESE FEATURES ARE ABOUT 9 TO 12
HOURS OUT IN TIME. THUNDERSTORMS WILL LIKELY OCCUR IN SOME PARTS
OF THE CWA EACH PERIOD FROM WEDNESDAY THROUGH FRIDAY, BUT IT WILL
BE DIFFICULT TO NARROW DOWN THOSE AREAS MOST LIKELY TO RECEIVE
THUNDERSTORM ACTIVITY UNTIL WE GET A LITTLE CLOSER IN TIME.

SATURDAY THROUGH MONDAY...MODELS INDICATE SYNOPTIC SCALE LIFT AND
FEATURES WILL MOVE TOWARDS NORTH TEXAS WHICH WILL LIKELY RESULT IN
WIDESPREAD THUNDERSTORM ACTIVITY ACROSS THE AREA DURING THIS
PERIOD. THE LARGE UPPER TROUGH IS EXPECTED TO MOVE OVER THE
SOUTHERN HIGH PLAINS AND OVER THE CENTRAL PLAINS LATE ON SATURDAY
SENDING ONE ROUND OF CONVECTION SOUTHEAST ACROSS THE SOUTHERN
PLAINS. A DRYLINE AND COLD FRONT ARE EXPECTED TO SHARPEN UP ON
SUNDAY AS A RESULT OF THE MOVEMENT OF THE UPPER TROUGH AND WILL
LIKELY SET OFF ANOTHER WIDESPREAD ROUND OF STORMS ACROSS THE
REGION ON SUNDAY. FINALLY ON MONDAY, IF THE COLD FRONT HAS NOT
MOVED ACROSS NORTH TEXAS ALREADY DUE TO THE ENHANCEMENT OF COLD
AIR GENERATED BY SUNDAY`S STORMS...THEN WE WILL LIKELY SEE ANOTHER
ROUND OF STORMS AFFECT THE CWA ON MONDAY AS THE COLD FRONT MOVE
ACROSS THE AREA. THE PRESENCE OF STRONGER SYNOPTIC SCALE FEATURES
PROVIDING A FAVORABLE ENVIRONMENT FOR THUNDERSTORM DEVELOPMENT
ALSO MAKES SEVERE STORMS MORE LIKELY DURING THIS PERIOD. GENERALLY
WENT AHEAD WITH 50-60 POPS FROM SATURDAY THROUGH SUNDAY TO ACCOUNT
FOR THE HIGHER CONFIDENCE IN WIDESPREAD THUNDERSTORM COVERAGE THIS
WEEKEND.

CAVANAUGH


&&

.AVIATION...
/ISSUED 1122 PM CDT MON MAY 4 2015/
A 45 KNOT LOW LEVEL JET HAS DEVELOPED ACROSS THE REGION AS PER THE
KFWS WSR-88D VAD WIND PROFILE. WE ANTICIPATE THAT LOW CLOUDS
BETWEEN 1000 AND 2000 FT WILL BEGIN TO DEVELOP ACROSS SOUTH TEXAS
OVER THE NEXT FEW HOURS. THESE CLOUDS SHOULD REACH WACO BETWEEN 08
AND 09Z AND THE METROPLEX TAF SITES AROUND 10Z. THE LOW CLOUDS
WILL LINGER THROUGH THE MORNING HOURS TUESDAY AND SLOWLY LIFT
ABOVE 3000 FT DURING THE AFTERNOON. MVFR CEILINGS SHOULD RETURN TO
ALL TAF SITES LATE TUESDAY EVENING ONCE THE LOW LEVEL JET SETS UP
AGAIN.

PRECIPITATION CHANCES SHOULD INCREASE ACROSS NORTH TEXAS ON
TUESDAY AS AN UPPER LOW MOVES FROM THE DESERT SOUTHWEST TO THE
CENTRAL HIGH PLAINS. THE BEST FORCING WILL REMAIN WEST OF THE
REGION. HOWEVER...MID LEVEL LAPSE RATES WILL INCREASE THROUGH THE
DAY AND SCATTERED SHOWERS AND THUNDERSTORMS SHOULD DEVELOP. STORM
CHANCES WILL BE MOST LIKELY ACROSS NORTH TEXAS FROM LATE AFTERNOON
THROUGH THE EVENING.

A SOUTHEAST TO SOUTH WIND WILL PREVAIL THROUGH TUESDAY EVENING AT
SPEEDS BETWEEN 12 AND 18 KNOTS ALONG WITH SOME HIGHER
GUSTS...ESPECIALLY DURING THE DAY TUESDAY.

79


&&

.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  80  66  82  68  82 /  40  60  30  20  30
WACO, TX              79  66  83  69  82 /  40  50  30  20  30
PARIS, TX             78  64  79  65  80 /  50  60  30  20  30
DENTON, TX            80  65  81  67  81 /  40  70  30  30  30
MCKINNEY, TX          78  65  79  67  81 /  40  50  30  20  30
DALLAS, TX            80  66  81  68  82 /  40  50  30  20  30
TERRELL, TX           78  66  80  68  82 /  40  50  30  20  30
CORSICANA, TX         78  66  81  68  82 /  50  50  30  20  30
TEMPLE, TX            81  66  83  69  82 /  40  50  30  20  30
MINERAL WELLS, TX     77  65  82  67  81 /  50  70  30  30  30

&&

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

&&

$$



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