Severe Thunderstorm Warning 134, NWS Fort Worth, TX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
1032 PM CDT THU MAY 7 2015

.UPDATE...
THUNDERSTORMS HAVE ORGANIZED INTO A LINE EXTENDING FROM GRAYSON
COUNTY SOUTHWEST TO THE METROPLEX...AND ON EVEN FARTHER SOUTHWEST
THROUGH COMANCHE AREA. A BOWING SEGMENT IN GRAYSON/COLLIN
COUNTIES IS WHERE THE BEST CHANCE FOR SEVERE WEATHER EXISTS IN THE
SHORT TERM...WITH A PERSISTENT SUPER CELL ON THE BROWN/COMANCHE
COUNTY LINE THE OTHER NEAR-TERM THREAT FOR SEVERE. AN OVERALL
WEAKENING TREND IS EXPECTED FROM MIDNIGHT ONWARD...WITH LOCALLY
HEAVY RAIN BECOMING THE PRIMARY THREAT WITH ANY STORMS CONTINUING
THROUGH THE OVERNIGHT HOURS. POPS HAVE BEEN ADJUSTED PER
TRENDS...AND LOW TEMPS HAVE BEEN ADJUSTED DOWN ACROSS THE NORTHERN
HALF OF THE REGION WHERE OUTFLOW IS EXPECTED TO COOL THINGS OFF A
TAD.

30

&&

.AVIATION UPDATE...
THE METROPLEX IS CURRENTLY ENDURING A SQUALL LINE...WHICH IS
BRINGING TEMPORARY HEAVY RAIN AND STRONG WEST WINDS. THE LINE WILL
MOVE EAST OF THE METROPLEX TAF SITES BY MIDNIGHT...WITH WINDS
GRADUALLY COMING BACK AROUND TO THE SOUTH 04-06Z. FOR WACO...WE
WILL INCLUDE VCTS 05-08Z FOR LINGERING THUNDERSTORMS LATE TONIGHT.
OTHERWISE...MVFR CIGS ARE STILL EXPECTED EARLY MORNING FRIDAY.
ADDITIONAL CONVECTION IS POSSIBLE FRIDAY EVENING...AND WE WILL
LIKELY INCLUDE VCTS IN THE REST OF THE TAFS /SIMILAR TO THE
EXTENDED DFW TAF FROM EARLIER/ AT THE 06Z ISSUANCE FOR 09/00Z.

&&

.UPDATE...
PER NEW SEVERE DEVELOPMENT MOVING INTO YOUNG AND STEPHENS COUNTIES
AND HIGH RES MODEL PROJECTIONS...WE ARE EXPANDING THE CURRENT
SEVERE THUNDERSTORM WATCH SOUTHWARD TO INCLUDE AREAS FROM
STEPHENVILLE...TO ALL THE DFW METRO...TO ROCKWALL AND GREENVILLE.
ALL MODES OF SEVERE WEATHER POSSIBLE...BUT MAIN THREATS WILL
CONTINUE TO BE DAMAGING WINDS...LARGE HAIL...AND VERY HEAVY
RAINFALL AND POSSIBLE FLOODING. FEW TORNADOES WILL REMAIN POSSIBLE
THROUGH MID EVENING...AT WHICH TIME THE LLJ SHOULD MORPH AND COLD
POOL THIS ACTIVITY INTO AN MCS THROUGH MIDNIGHT OR POSSIBLY LATER.

05/

&&

.PREV DISCUSSION... /ISSUED 349 PM CDT THU MAY 7 2015/
AS DISCUSSED IN THE MORNING UPDATE...ALL OF THE INGREDIENTS FOR
SEVERE WEATHER AND HEAVY RAINFALL ARE IN PLACE OVER THE REGION
WITH THE EXCEPTION OF ORGANIZED FORCING FOR LIFT. WHAT MAKES THE
FORECAST SO DIFFICULT...IS THAT THE THUNDERSTORMS CAN AND OFTEN DO
FORM WITHOUT THIS ORGANIZED OR DISCERNIBLE LIFT...AND MESOSCALE
PROCESSES SUCH AS THE INFLUENCES FROM A MESOSCALE CONVECTIVE
SYSTEM CAN EFFECTIVELY DRIVE THE FORECAST. AN MCS HAS FORMED
TODAY OVER THE TEXAS PANHANDLE REGION AND HAS MOVED EASTWARD INTO
NORTHWEST TEXAS. THE MCS NOT ONLY PROVIDES A COLD POOL AND OUTFLOW
BOUNDARY TO HELP LIFT SURFACE PARCELS...IT ALSO GENERATES ITS OWN
MID-UPPER LEVEL VORTICITY ANOMALY THAT HELPS LIFT THE AIR FOR
CONVECTION OUT AHEAD OF IT. WITHOUT THE MCS...WE WOULD EXPECT TO
SEE JUST ISOLATED RANDOMLY GENERATED CONVECTION STREAM ACROSS THE
AREA...LIKE WHAT HAS OCCURRED SO FAR TODAY.

THE MCS IS GOING TO CONTINUE TO TRACK EASTWARD...GENERALLY ACROSS
SOUTHERN OKLAHOMA...BUT THE COLD POOL THAT IS LEFT BEHIND IT IS
LAYING DOWN A WEST-EAST OUTFLOW BOUNDARY OR EFFECTIVE COLD FRONT.
THE SYNOPTIC WIND FIELDS ALREADY IN PLACE MEANS THAT THIS BOUNDARY
IS SLOW MOVING...AND PROVIDES A FOCUS FOR THE REGENERATION OF
CONVECTION WHICH RESULTS IN CELL TRAINING. THIS PROCESS HAS
OCCURRED ALL DAY BETWEEN LUBBOCK AND CHILDRESS. AS THE MCS
CONTINUES TO MOVE EAST...EXPECT THE OUTFLOW BOUNDARY TO ALSO
BECOME DRAPED ACROSS THE NORTHERN ZONES THIS EVENING. THIS
INCREASES THE POTENTIAL FOR PROLONGED HEAVY RAINFALL AND FLASH
FLOODING AS THE MOIST LOW LEVEL JET RIDES UP OVER THE TOP OF IT.
A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE NORTHERN ZONES FOR
THIS POTENTIAL. IT SHOULD BE NOTED THAT WHILE THERE IS HIGH
CONFIDENCE THAT THIS PATTERN OFTEN RESULTS IN VERY HIGH
RAINFALL...AND WE KNOW THAT THE POTENTIAL EXISTS SOMEWHERE IN THE
REGION...THERE IS MAJOR UNCERTAINTY IN THE EXACT LOCATION OF WHERE
IT SETS UP. THUS THIS FLASH FLOOD WATCH IS NOT MEANT TO IMPLY THAT
HEAVY RAIN IS LIKELY OVER THE WATCH REGION...BUT JUST THAT THE
POTENTIAL FOR A HEAVY RAIN AND FLASH FLOOD EVENT IS THERE. IF THE
OUTFLOW BOUNDARY STAYS TOO FAR NORTH DUE TO A WEAK COLD POOL OR
MOVES TOO QUICKLY TO THE SOUTH DUE TO A STRONGER COLD POOL IT WILL
AFFECT THE LOCATION OF HEAVY RAIN.

ASIDE FROM THE HEAVY RAIN THREAT...THE ATMOSPHERE IS UNSTABLE AND
CONTAINS SUFFICIENT SHEAR FOR SEVERE WEATHER OVER THE ENTIRE
AREA. STORM CHANCES ARE ALL FAIRLY LOW SOUTH OF I-20 SO SEVERE
WEATHER THREAT IS LESS PROBABLE THERE. NORTH OF I-20...SOME
SUPERCELLS ARE POSSIBLE...BUT THE STORM MODE WILL MOST LIKELY BE
MULTICELL CLUSTERS. THE SEVERE WEATHER THREAT WILL BE HIGHEST FOR
INDIVIDUAL CELLS AHEAD OF THE MCS...OTHERWISE THE ACTIVITY THAT
MELDS INTO THE MCS WILL BE PRIMARILY A MARGINAL WIND/HAIL THREAT.

THE WEATHER OVER THE NEXT SEVERAL DAYS WILL REMAIN UNSETTLED WITH
A LARGE UPPER LEVEL TROUGH OVER THE WESTERN PART OF THE COUNTRY.
SOME OF THE MODEL GUIDANCE DOES INDICATE A SHORTWAVE MOVING OUT
FROM SW TEXAS INTO NORTH TEXAS DURING THE MIDDAY HOURS TOMORROW.
WHILE THIS WOULD RESULT IN SCATTERED CONVECTION...THE TIME OF DAY
WOULD TEND TO KEEP THE SEVERE WEATHER THREAT ON THE LOW SIDE. ON
FRIDAY AFTERNOON WE EXPECT THE DRYLINE TO REMAIN TOO FAR WEST OF
THE REGION FOR THE CONVECTION THAT FIRES ALONG IT TO AFFECT MOST
OF THE CWA...HOWEVER THE FAR NORTHWEST ZONES MAY BE IMPACTED IN
THE EVENING HOURS. HAIL/WIND/ISOLATED TORNADOES ARE POSSIBLE WITH
THIS ACTIVITY BEFORE IT MOVES NORTHEAST INTO OKLAHOMA. MOST OF THE
REGION SHOULD BE QUIET FRIDAY NIGHT BUT HIGHER POPS ARE IN THE NW.

ON SATURDAY THERE IS GOOD AGREEMENT IN THE MODEL GUIDANCE THAT THE
UPPER TROUGH WILL BE CLOSE ENOUGH TO PROVIDE ORGANIZED LIFT OVER
THE REGION FOR THUNDERSTORMS. THE STRONGER 700MB FLOW FROM THE
SOUTHWEST WILL BRING THE DRY LINE TO THE WESTERN CWA DOORSTEP AND
ALSO A CAP INTO THE REGION. THIS CAP SHOULD BE WEAK ENOUGH TO
BREAK DURING THE AFTERNOON HOURS. NEEDLESS TO SAY...SATURDAY
AFTERNOON AND EVENING REPRESENTS THE BEST CHANCE FOR SIGNIFICANT
SEVERE WEATHER...ESPECIALLY ALONG AND WEST OF I-35 WHERE
SUPERCELLS WITH A TORNADO THREAT WILL BE POSSIBLE.

ON SUNDAY THE MAIN UPPER TROUGH AXIS WILL MOVE THROUGH THE REGION.
WIDESPREAD RAIN AND THUNDERSTORMS ARE EXPECTED WITH A STRONG LOW
LEVEL FEED OF UNSEASONABLY RICH MOISTURE. CELL TRAINING AND
SEVERAL CLUSTERS OF STRONG CONVECTION ARE EXPECTED THROUGH THE
DAY AND INTO THE EVENING HOURS. SUNDAY WILL REPRESENT OUR HIGHEST
CHANCES OF RAINFALL AREAWIDE...WITH AN ENHANCED RISK OF FLASH
FLOODING. A SEVERE WEATHER POTENTIAL WILL EXIST AS WELL...BUT DUE
TO WIDESPREAD CONVECTION...THIS THREAT DOES NOT LOOK AS ORGANIZED
AS SATURDAY/S SETUP...ESPECIALLY FOR THE WESTERN HALF OF THE
REGION. THE EASTERN PARTS OF THE AREA WILL HAVE A BETTER THREAT
FOR SEVERE WEATHER SUNDAY AFTERNOON WHERE MORE INSTABILITY WILL BE
AVAILABLE FOR FEWER STORMS...AT LEAST INITIALLY. CONVECTION WILL
FINALLY END FROM WEST TO EAST AS A COLD FRONT PUSHES THROUGH
SUNDAY NIGHT.

COOLER CONDITIONS ARE EXPECTED EARLY NEXT WEEK...BUT THE COLD
FRONT WILL LOSE ITS SOUTHWARD PUSH. THIS MEANS THAT MOISTURE WILL
NOT BE FLUSHED OUT INTO THE GULF...AND AS THE NEXT WEAK UPPER
TROUGH MOVES IN FROM THE WEST THE GOOD CHANCES OF RAIN WILL
ARRIVE INTO THE THE SOUTHEASTERN PARTS OF THE AREA
TUESDAY...SPREADING NORTHWARD BY MIDWEEK. THIS UPPER SYSTEM LOOKS
WEAK...WHICH MEANS THAT WIND SHEAR LOOKS TOO LOW FOR A SEVERE
WEATHER THREAT. IN ADDITION THE RATHER COOL AIRMASS WILL REMAIN
OVER THE REGION AS LOTS OF MID-HIGH CLOUDS STREAMING NORTHWARD
KEEP THE MAY SUN AT BAY. WILL HAVE HIGHS IN THE 70S AND LOWS IN
THE 60S DURING THIS TIME PERIOD. RAIN CHANCES WILL RANGE FROM 20
IN THE NORTHWEST TO 50 IN THE SOUTHEAST MID-LATE WEEK. EXPECT
PRIMARILY RAIN SHOWERS...BUT THERE MAY BE ENOUGH INSTABILITY FOR A
FEW STORMS.

TR.92

&&

.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  68  81  71  83  69 /  60  40  40  50  60
WACO, TX              71  83  73  84  70 /  40  40  20  50  50
PARIS, TX             67  82  69  81  70 /  60  30  50  40  60
DENTON, TX            67  80  69  82  67 /  70  40  50  60  60
MCKINNEY, TX          67  81  70  82  69 /  60  40  50  50  60
DALLAS, TX            68  83  72  84  70 /  60  40  40  50  60
TERRELL, TX           69  82  72  82  70 /  60  30  30  40  60
CORSICANA, TX         70  83  72  83  71 /  40  30  20  40  40
TEMPLE, TX            71  82  73  85  71 /  30  40  20  40  40
MINERAL WELLS, TX     68  79  68  83  65 /  70  50  40  60  60

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 4 AM CDT FRIDAY FOR TXZ091>095-100>104.

&&

30

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
721 PM CDT THU MAY 7 2015

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-090030-
MONTAGUE-COOKE-GRAYSON-FANNIN-LAMAR-YOUNG-JACK-WISE-DENTON-COLLIN-
HUNT-DELTA-HOPKINS-STEPHENS-PALO PINTO-PARKER-TARRANT-DALLAS-
ROCKWALL-KAUFMAN-VAN ZANDT-RAINS-EASTLAND-ERATH-HOOD-SOMERVELL-
JOHNSON-ELLIS-HENDERSON-COMANCHE-MILLS-HAMILTON-BOSQUE-HILL-NAVARRO-
FREESTONE-ANDERSON-LAMPASAS-CORYELL-BELL-MCLENNAN-FALLS-LIMESTONE-
LEON-MILAM-ROBERTSON-
721 PM CDT THU MAY 7 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL TEXAS.

.DAY ONE...TONIGHT.

SEVERE STORMS ARE POSSIBLE TONIGHT. THE MAIN THREATS WILL BE
LARGE HAIL...DAMAGING WINDS...AND HEAVY RAINFALL WHICH MAY LEAD TO
AREAS OF FLOODING. HOWEVER...A FEW TORNADOES WILL BE POSSIBLE AS
WELL WITH ANY ISOLATED STORMS AHEAD OF THE MAIN LINE.

A COMPLEX OF STORMS WILL LIKELY IMPACT AREAS NORTH OF A STEPHENVILLE...
TO ENNIS...TO SULPHUR SPRINGS LINE TONIGHT WITH A THREAT FOR HEAVY
RAINFALL WHICH MAY RESULT TO FLASH FLOODING. HAIL AND STRONG WINDS
WILL REMAIN POSSIBLE OVERNIGHT. A FLASH FLOOD WATCH IS IN EFFECT
ALONG AND NORTH OF A LINE FROM GRAHAM TO MCKINNEY THROUGH 4 AM.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

THERE IS A CHANCE FOR THUNDERSTORMS ACROSS ALL OF NORTH TEXAS
FRIDAY THROUGH WEDNESDAY. SEVERE STORMS WILL BE POSSIBLE...MAINLY
FRIDAY THROUGH SUNDAY. THE MOST LIKELY AREAS AND ASSOCIATED
HAZARDS ARE FURTHER EXPLAINED BELOW...

FRIDAY...THE HIGHEST THREAT FOR SEVERE STORMS WILL BE NORTH OF A
PARIS TO ENNIS TO KILLEEN LINE. LARGE HAIL...DAMAGING
WINDS...HEAVY RAINFALL AND ISOLATED TORNADOES ARE ALL POSSIBLE.
THE BEST TIMING WILL BE IN THE AFTERNOON AND EVENING HOURS.

SATURDAY...THE BEST CHANCES FOR SEVERE STORMS THIS WEEKEND IS ON
SATURDAY ACROSS ALL OF NORTH AND CENTRAL TEXAS. LARGE
HAIL...DAMAGING WINDS...FLOODING AND TORNADOES WILL ALL BE
POSSIBLE.

SUNDAY...THE MAIN THREAT ON SUNDAY WILL BE HEAVY RAINFALL
RESULTING IN FLASH FLOODING. IN ADDITION...THERE WILL STILL BE A
THREAT FOR SEVERE STORMS PRODUCING LARGE HAIL AND DAMAGING
WINDS. AN ISOLATED TORNADO WILL ALSO BE POSSIBLE.

THUNDERSTORMS REMAIN IN THE FORECAST MONDAY THROUGH WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS LIKELY THIS EVENING AND MAY EXTEND INTO THE
OVERNIGHT HOURS NORTHWEST OF A STEPHENVILLE TO ENNIS TO GREENVILLE
LINE.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE FORT WORTH TX
1110 PM CDT THU MAY 07 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1105 PM     FLASH FLOOD      DENISON                 33.75N  96.55W
05/07/2015                   GRAYSON            TX   AMATEUR RADIO

            HIGH WATER RESCUES REPORTED IN SOUTHWEST DENISON

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE FORT WORTH TX
1120 PM CDT THU MAY 7 2015

TXZ104>107-119>123-080500-
ROCKWALL TX-HUNT TX-DALLAS TX-HOPKINS TX-RAINS TX-KAUFMAN TX-
DELTA TX-COLLIN TX-VAN ZANDT TX-
1120 PM CDT THU MAY 7 2015

...SIGNIFICANT WEATHER ADVISORY FOR ROCKWALL...HOPKINS...SOUTHEASTERN
DALLAS...HUNT...DELTA...NORTHWESTERN VAN ZANDT...NORTHERN KAUFMAN...
SOUTHEASTERN COLLIN AND RAINS COUNTIES UNTIL MIDNIGHT CDT...

AT 1119 PM CDT...DOPPLER RADAR WAS TRACKING A LINE OF STRONG
THUNDERSTORMS ALONG A LINE EXTENDING FROM NEAR WOLFE CITY TO NEAR
ROYSE CITY TO NEAR HUTCHINS...AND MOVING EAST AT 45 MPH.

DIME SIZE HAIL AND WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH
THESE STORMS.

LOCATIONS IMPACTED INCLUDE...
DALLAS...MESQUITE...DESOTO...ROCKWALL...LANCASTER...GREENVILLE...
BALCH SPRINGS...TERRELL...SULPHUR SPRINGS...SEAGOVILLE...FORNEY...
COMMERCE...HUTCHINS...WILLS POINT...ROYSE CITY...HEATH...FATE...
SUNNYVALE...WILMER AND FARMERSVILLE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THESE STORMS...AND MAY
LEAD TO FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

&&

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL MIDNIGHT CDT FOR
NORTH CENTRAL TEXAS.

LAT...LON 3300 9550 3296 9556 3296 9566 3290 9566
      3260 9612 3261 9689 3297 9634 3335 9629
      3341 9587 3346 9586 3346 9583 3350 9577
      3349 9562 3347 9559 3348 9556 3345 9553
      3345 9548 3339 9535
TIME...MOT...LOC 0419Z 267DEG 40KT 3340 9610 3298 9626 3266 9674

CAVANAUGH

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