River Flood Warning 37, NWS Fort Worth, TX

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

.DISCUSSION...
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

&&

.AVIATION...
/ISSUED 1243 PM CDT THU MAY 7 2015/
/18Z TAFS/

CONCERNS...CONVECTIVE TRENDS THROUGH THE PERIOD. MVFR AND IFR
CIGS.

AN ACTIVE WEATHER PATTERN WILL CONTINUE THROUGH THE VALID TAF
PERIOD AND THROUGH THE WEEKEND. SCATTERED SHOWERS CONTINUE MOVING
NORTH ACROSS THE REGION THIS AFTERNOON AND MAY IMPACT ANY OF THE
TAF SITES THROUGH SUNSET. AN ISOLATED THUNDERSTORM MAY ALSO IMPACT
THE AIRPORTS BUT THE CHANCE WAS NOT WORTH MENTIONING VCTS FOR THE
REMAINDER OF THE AFTERNOON HOURS. WILL PREVAIL A VCSH INSTEAD BUT
MAY NEED TO AMEND IF POP-UP THUNDERSTORMS BECOME MORE PREVALENT.

FOR THE REMAINDER OF THE AFTERNOON HOURS...POP-UP SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO OCCUR ACROSS NORTH AND CENTRAL TEXAS
BUT AREAS NORTH OF INTERSTATE 20 COULD BE IMPACTED BY A COMPLEX
OF STORMS THIS EVENING. CONFIDENCE IN THIS SOLUTION IS STILL LOW
TO MODERATE BUT WILL CARRY VCTS IN THE DFW METROPLEX TAFS FROM
08/01-05Z. WILL LEAVE ALL MENTION OF THUNDER OUT OF THE KACT TAF
FOR NOW AS CHANCES LOOK MUCH LOWER. THUNDERSTORMS ARE LIKELY TO
DEVELOP AGAIN ON FRIDAY AFTERNOON AND EVENING BUT CONFIDENCE IS
TOO LOW TO HIGHLIGHT A PERIOD IN THE TAF WITH VCTS AT THIS TIME.
SEVERE STORMS AND HEAVY RAINFALL MAY OCCUR WITH ANY STORMS IN THE
AREA TODAY AND TOMORROW...AND THROUGH THE WEEKEND.

MVFR AND VFR CIGS ARE OCCURRING ACROSS THE REGION AT THE START OF
THE TAF PERIOD BUT ARE EXPECTED TO LIFT INTO VFR BY 20-21Z. MVFR
CIGS WILL RETURN THIS EVENING AND PREVAIL THROUGH MUCH OF FRIDAY
MORNING. A FEW SITES MAY EXPERIENCE IFR CIGS AT TIMES BUT THINK
THE WIND SPEEDS WILL KEEP CIGS ABOVE 1 KFT FOR THE MOST PART.

JLDUNN

&&

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

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR TXZ091>095-100>104.

&&

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

TXZ091>095-100>107-115>123-129>135-141>148-156>162-174-175-081215-
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-
346 PM CDT THU MAY 7 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL TEXAS.

.DAY ONE...TONIGHT.

ISOLATED SEVERE STORMS ARE POSSIBLE THIS AFTERNOON. THE MAIN
THREATS WILL BE LARGE HAIL...DAMAGING WINDS...AND HEAVY RAINFALL
WHICH MAY LEAD TO AREAS OF FLOODING.

A COMPLEX OF STORMS WILL LIKELY IMPACT AREAS NORTH OF INTERSTATE
20 THIS EVENING AND OVERNIGHT WITH A THREAT FOR HEAVY RAINFALL
WHICH MAY RESULT TO FLASH FLOODING. HAIL AND STRONG WINDS WILL
ALSO BE POSSIBLE. 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...

LIMITED SPOTTER ACTIVATION MAY BE REQUESTED LATE THIS AFTERNOON
AND EVENING...MAINLY WEST OF INTERSTATE 35 AND NORTH OF INTERSTATE
20.

JLDUNN