Summary for April 13, 2007.
Risk Area: High Risk for North/Central Texas, Moderate surrounding the High Risk.
What Went Wrong: My forecast certainly did not verify, although 4-6 tornadoes did occur. I expected more than what happened and especially something in central Texas. Looking at the surface data from the late afternoon, a cold front had caught up to the dryline. The result of this push was that a line of storms developed and were pushed by the cold front. Storms tried to go discrete/supercellular but could not move off the boundary. This greatly reduced the severe threat for central Texas. Eventually the outflow boundary outran the storms and they lost intensity.
Across north Texas a storm developed ahead of the initial line and this supercell produced at least two tornadoes in the DFW Metro. Farther west a storm moved into northwest Texas and along the retreating warm front. This storm was likely in a favorable region at the right time, while the surface low was strongest and the warm front favorably oriented west to east. This storm produced at least one tornado, which was rather large at one point. The storm moved north of the warm front and became elevated.
The big question in my mind is what caused the cold front to surge south. This is rather unexpected with the upper system farther west. I think two things occurred, which resulted in a more rapid southward movement of the cold front. 1) Strong cold air advection occurred with the system and intensified the base of the trof. This action appeared to cause a surface low to form in old Mexico by late afternoon. The NAM hinted at this situation and I ignored it. 2) The 850mb low was over south-central Oklahoma. The result was cold air advection on the backside of the 850mb and frontogenesis over west Texas.
The good thing is the threat didn't materalize but it also resulted in a blown forecast.
Damage Survey from Fort Worth:
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FORT WORTH TX
645 PM CDT SAT APR 14 2007
…PRELIMINARY FINDINGS FROM APRIL 13TH TORNADO DAMAGE SURVEYS…
A TEAM FROM THE NATIONAL WEATHER SERVICE IN FORT WORTH CONDUCTED
DAMAGE SURVEYS IN TARRANT…DALLAS…AND ROCKWALL COUNTIES DUE TO
WIND DAMAGE ON APRIL 13TH.
ONE PARENT SUPERCELL THUNDERSTORM MOVED ACROSS TARRANT…DALLAS…
AND ROCKWALL COUNTIES IN THE EVENING HOURS PRODUCING TORNADOES AND
HAIL UP TO 3 INCHES IN DIAMETER.
THE FIRST TORNADO TOUCHED DOWN AT APPROXIMATELY 555 PM IN
BENBROOK…OR SOUTHWEST FORT WORTH…IN TARRANT COUNTY. KNOWN DAMAGE
AT THIS TIME CONSISTS OF DOWNED FENCES…HOWEVER THE NATIONAL
WEATHER SERVICE CONTINUES TO GATHER ADDITIONAL INFORMATION OF
IMPACTS IN THIS AREA. STORM CHASER VIDEO CONFIRMS A BRIEF TORNADO
TOUCHDOWN. A PRELIMINARY EF-SCALE RATING HAS NOT BEEN ESTABLISHED.
THE SECOND TORNADO TOUCHED DOWN AT APPROXIMATELY 609 PM JUST EAST OF
DOWNTOWN FORT WORTH…NEAR THE VICINITY OF SYLVANIA PARK SOUTHWEST
OF THE INTERSECTION OF NORTH BEACH AND BELKNAP STREETS. THE TORNADO
THEN MOVED EAST ALONG WHEELER STREET AND ELLIOTT REEDER ROAD IN
HALTOM CITY. THE MOST SEVERE DAMAGE EXTENDED ALONG WHEELER STREET
FROM NORTH BEACH TO HALTOM ROAD…AND ALONG ELLIOTT REEDER ROAD FROM
HALTOM ROAD EAST APPROXIMATELY ONE HALF MILE. ONE STORM-RELATED
FATALITY WAS ALSO REPORTED IN THIS AREA. THERE WAS SUBSTANTIAL ROOF
DAMAGE TO A GROCERY STORE…SEVERAL HOMES…AND A CHURCH STEEPLE
ALONG WHEELER STREET. ADDITIONALLY…SEVERAL COMMERCIAL BUILDINGS
ALONG ELLIOTT REEDER ROAD WERE DAMAGED AND NUMEROUS RECREATIONAL
VEHICLES AND TRACTOR TRAILERS WERE DAMAGED OR DESTROYED.
FURTHERMORE…NUMEROUS TREES AND POWERLINES WERE DOWNED IN THIS
AREA. NEAR THE INTERSECTION OF RIVERBEND AND JACK NEWELL…A
COMMERCIAL BUILDING SUFFERED PARTIAL COLLAPSE OF AN EAST-FACING
WALL. BASED ON THIS INFORMATION…THIS TORNADO HAS BEEN ASSIGNED A
PRELIMINARY UPPER-END EF-1 RATING ON THE ENHANCED FUJITA
SCALE…WITH MAXIMUM WIND SPEEDS BETWEEN 100 AND 110 MPH. PATH
LENGTH IS ESTIMATED TO BE 2 MILES AND A PATH WIDTH OF APPROXIMATELY
A THIRD AREA OF CONCENTRATED WIND DAMAGE WAS NOTED IN EAST DALLAS
NEAR THE INTERSECTION OF JOHN WEST AND BUCKNER BLVD. SEVERAL
TREES…TREE LIMBS…AND FENCES WERE DOWNED. SOME DAMAGE TO AREA
APARTMENT ROOFS WAS ALSO OBSERVED. THE EXACT CAUSE OF THIS WIND
DAMAGE HAS NOT BEEN DETERMINED…ALTHOUGH THE STORM THAT PRODUCED
THE FORT WORTH/HALTOM CITY TORNADO WAS OVER EAST DALLAS AT THIS
TIME. ADDITIONAL GROUND-TRUTH INFORMATION FROM SPOTTERS AND
EMERGENCY MANAGERS WILL BE USED TO DETERMINE IF A TORNADO OR
STRAIGHT-LINE WINDS CAUSED THIS DAMAGE. THIS DAMAGE HAS BEEN
ASSIGNED THE PRELIMINARY RATING OF EF-0…WITH WINDS ESTIMATED TO BE
IN ROCKWALL COUNTY…AN AREA OF WIND DAMAGE WAS SURVEYED 5 MILES
SOUTH OF ROYSE CITY…JUST EAST OF THE INTERSECTION OF FM 548 AND
STATE HIGHWAY 276. TWO BARNS WERE COMPLETELY DESTROYED AND A FEW
FENCES WERE DOWNED. THIS DAMAGE HAS BEEN ASSIGNED THE PRELIMINARY
RATING OF EF-0…WITH ESTIMATED WIND SPEEDS OF 80 MPH.
THE AFOREMENTIONED DETAILS ARE SUBJECT TO REVISION BASED ON FUTURE
DISCUSSIONS WITH SPOTTER GROUPS AND EMERGENCY MANAGEMENT PERSONNEL.
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