...Damage survey update for the may 24th storms...

National Weather Service crews spent the day conducting additional
damage surveys from the thunderstorms which occurred on Tuesday
may 24th. The survey team started in northwestern Tarrant and
northeastern Parker counties...where damage was found in an area
bounded by Haslet...Azle...and Springtown. This damage was found
to be consistent with straight line damaging winds...approximately
75 to 85 mph.

The crew then assessed damage in Denton County and determined
there was one tornado...which occurred in the city limits of Denton.
This will decrease the preliminary number of tornadoes to 8 for
the afternoon and evening of may 24th.

The storm survey team assessed damage in the far southwestern
portion of the city of Denton. In this area...close to the Denton
and Argyle city limits boundary...substantial tornado damage was
found in numerous homes in a subdivision. Additional damage...consistent
with straight line winds were observed across the western portions
of the city of Corinth. 

The team spent additional time considering the photographs...video
...And eyewitness evidence of the Denton County damage. It has
been determined that the numerous reports of funnel clouds...tornadoes...and
damage in Corinth area were actually from the tornado which
occurred along the Denton/Argyle border...now commonly referred to
as the Argyle tornado.

The Denton tornado has been given a preliminary damage rating of
EF-2 on the Enhanced Fujita scale. Damage was found that was
consistent with wind speeds between 115 and 125 mph. The path
length of this tornado was approximately 1.2 miles...and had a
maximum path width of 220 yards.

While there will be undoubtedly other evidence and other damage
areas to consider...the total number of tornadoes now stands at 8
for the evening of may 24th. The listing of tornadoes and their
damage ratings are as follows:

A brief tornado was observed by spotters 2 miles southeast of St.
Jo. This tornado has been given a preliminary damage rating of
EF-0.

A brief tornado was observed by spotters 4 miles northeast of
Nocona...near Lake Nocona. This tornado has been given a
preliminary damage rating of EF-0.

A tornado was observed and photographed 2 miles southwest of
Gainesville. This tornado has been given a preliminary damage
rating of EF-0.

A brief tornado was observed by spotters 3 miles north of Rhome
in Wise County. This tornado has been given a preliminary rating
of EF-0.

A tornado occurred in Irving. This tornado has been given a
preliminary rating of EF-1. 

A tornado occurred in the far southwestern sections of
Denton...along the Denton and Argyle city limits. This tornado has
been given a preliminary rating of EF-2.

A tornado was observed by spotters near the intersection of I-20
and I-45 in southeast Dallas County...along the Trinity River
bottom. This tornado has been given a preliminary rating of EF-0.

A tornado was observed by spotters near Cedarville in Kaufman
County. This tornado has been given a preliminary rating of EF-0.

For the calendar year 2011 so far...there have now been 37
confirmed tornadoes in the 46 counties in the WFO Fort Worth area
of responsibility.

So far there have been two tornadoes known to occur within the Metroplex. One in Irving, rated an EF-1 which damaged houses and an apartment building. The second at Dallas Love field, but no damage occurred.

This is a radar snapshot from 01:25 Z / 8:25 pm CDT 5/24/11. Top left corner is standard reflectivity, top right is velocity, bottom left is maximum estimated hail size, bottom right is the altitude of the storm tops. Hail size estimates show 3.32 inch according to radar, with hail everywhere from 2 to 4.25 inches actually falling. The EF-1 tornado in Irving hit during the time of this radar snapshot, the small red square in the middle indicates the location of the tornado damage.

Below is the statement from the National Weather Service.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FORT WORTH TX
317 PM CDT WED MAY 25 2011

...PRELIMINARY WIND DAMAGE ASSESSMENT FROM MAY 24TH...

A NATIONAL WEATHER SERVICE DAMAGE SURVEY TEAM CONTINUES TO ASSESS
WIND DAMAGE FROM THUNDERSTORMS DURING THE AFTERNOON AND EVENING
OF MAY 24TH 2011. PRELIMINARY INFORMATION FROM DALLAS COUNTY
INDICATES THAT TREE DAMAGE AT AN APARTMENT COMPLEX IN THE OAK LAWN
AREA OF DALLAS WAS DUE TO STRAIGHT-LINE THUNDERSTORM WINDS. ONE
FATALITY WAS REPORTED AT THIS LOCATION DUE TO ELECTROCUTION WHERE
POWER LINES WERE DOWNED BY FALLING TREES.

A BRIEF TORNADO REPORTED AT DALLAS LOVE FIELD AIRPORT WAS VERY
LOCALIZED AND NO APPRECIABLE WIND DAMAGE HAS BEEN FOUND.

THE TEAM FOUND EVIDENCE OF AN EF-1 TORNADO IN IRVING BETWEEN 820
PM AND 840 PM CDT. THE TORNADO TOUCHED DOWN NEAR THE INTERSECTION
OF BELTLINE AND CONFLANS AND TRAVELED ONE-HALF MILE TO NEAR THE
INTERSECTION OF STORY ROAD AND ROCK ISLAND. THE PATH WIDTH
AVERAGED 150 YARDS. MAXIMUM WINDS WERE BETWEEN 95 AND 105 MPH.
FOUR HOMES SUFFERED ROOF DAMAGE AND A NEARBY APARTMENT COMPLEX
LOST A PORTION OF ITS ROOF.

ADDITIONAL INFORMATION CONTINUES TO BE GATHERED FROM THE
WIDESPREAD THUNDERSTORMS THAT OCCURRED TUESDAY. UPDATED
INFORMATION STATEMENTS WILL BE ISSUED AS NEEDED.

Other high wind and storm damage reports came in from Argyle and Corinth, just north of DFW. Houses were damaged in Saginaw and trees down near Wilmer.

I will try to update this post with more storm damage reports as they come in.

Additionally, I was able to capture a few pictures from the severe storms that rolled through here in Plano, TX. Unfortunately these pictures aren’t terribly remarkable in any way. Gallery available for viewing here.

24-May-2011 19:32PENTAX Corporation PENTAX K10D , 5.0, 18.0mm, 0.033 sec, ISO 400

Preliminary tornado reports from around the Metroplex:

A similar feature is observed with the northeast Ellis/southeast Dallas counties tornado. A noteworthy hook echo and velocity couplet are observed by radar.

…PRELIMINARY DAMAGE REPORT…

A TOTAL OF SIX TORNADOES OCCURRED ON WEDNESDAY SEPTEMBER 8TH. FOUR
TORNADOES WERE RATED EF0 ON THE ENHANCED FUJITA SCALE. ONE TORNADO
WAS RATED EF1…AND ONE TORNADO WAS PRELIMINARILY RATED EF2. ONLY
TWO MINOR INJURIES HAVE BEEN REPORTED FROM ALL OF THESE STORMS.

THE EF2 TORNADO DAMAGE WAS LOCATED IN THE CITY OF DALLAS NEAR THE
INTERSECTION OF MOCKINGBIRD LANE AND IRVING BOULEVARD. THIS
TORNADO CAUSED MINOR ROOF DAMAGE TO SEVERAL BUILDINGS AND CAUSED
MORE EXTENSIVE DAMAGE TO A WAREHOUSE. AN EXTERIOR NON LOAD BEARING
WALL COLLAPSED…LEADING TO A PARTIAL COLLAPSE OF THE ROOF. THIS
DAMAGE WAS RATED EF2 ON THE ENHANCED FUJITA SCALE WITH WIND SPEEDS
OF APPROXIMATELY 115 MPH. THE LAST TIME THE CITY OF DALLAS HAD A
TORNADO RATED AT F2/EF2 OR HIGHER WAS F2 TORNADO DAMAGE ON APRIL
11 1974. THE LANCASTER TORNADO OF APRIL 25 1994 PRODUCED F4 DAMAGE
IN THE CITY OF LANCASTER BEFORE DISSIPATING WITHIN THE CITY LIMITS
OF DALLAS.

THE EF1 TORNADO DAMAGE WAS LOCATED IN THE CITY OF SEAGOVILLE JUST
EAST OF HIGHWAY 175. AT LEAST THREE APARTMENT BUILDINGS SUFFERED
SIGNIFICANT ROOF DAMAGE. WIND SPEEDS IN THIS TORNADO ARE ESTIMATED
TO BE NEAR 90 MPH.

THE REMAINING TORNADO DAMAGE WAS GIVEN A PRELIMINARY RATING OF
EF0. THESE TORNADOES OCCURRED NEAR LINDSAY IN COOKE COUNTY…NEAR
FERRIS IN ELLIS COUNTY…IN HEATH IN ROCKWALL COUNTY…AND NEAR
BLOSSOM IN LAMAR COUNTY.

THE ENHANCED FUJITA SCALE RATES TORNADO DAMAGE.

ENHANCED FUJITA SCALE APPROXIMATE WIND SPEED RANGE

EF0 65-85 MPH
EF1 86-110 MPH
EF2 111-135 MPH
EF3 136-165 MPH
EF4 166-200 MPH
EF5 200 MPH OR GREATER

As if the flooding rainfalls weren’t enough, Hermine brought the risk of tornadoes to the region with several damage reports in Dallas, Highland Park, Seagoville, Ferris and Trumbull. Tornadoes embedded within the outer rain bands of tropical systems aren’t uncommon to coastal regions in the Gulf, but it is fairly unusual to get those type of tornadic storms this far away from the Gulf. Tornadoes in this type of environment tend to develop without warning and are difficult to detect with current radar technology, but are very brief and usually weak. The Dallas Morning News reported ripped up roofs in Cockrell Hill, Oak Cliff, West Dallas, and the Love Field areas. (source: Dallas Morning News) A Tornado Warning was also issued for a storm 4 miles south of Hebron at 5:37pm. The warned area included Frisco, Plano, and The Colony. The storm showed rotation on radar, and storm spotters observed a rotating wall cloud within the storm. Thankfully no tornado damage has been reported with this storm. Its center of circulation traveled north along the Denton/Collin county line, passing over Highway 121 and Plano Parkway, then dissipating. I got the pleasure of evacuating to our work’s ‘shelter’ area which amasses to little more than an open hallway, without access to my computer with accurate radar data.

A Tornado Watch still remains in effect for the entire DFW Metroplex, southeastern Oklahoma and western Arkansas until 1am. Another rain band is approaching from the west, with an approximate ETA of around 11pm to midnight tonight to Frisco/Plano/The Colony. Rain chances will continue Thursday, however nowhere near the levels observed the past two days. Hot and humid conditions should be expected the remainder of the week and weekend as the sun comes out and starts evaporating the abundance of water on the ground.

Lastly ill end with a quote from the local weather forecast office regarding the heavy rains the last two days…

DFW AND WACO HAVE BOTH SET CALENDAR-DAY PRECIPITATION RECORDS TODAY (SEPT 8). FOR BOTH SITES…THE 24-HR TOTALS (SEPT 7-8) WILL RANK AMONG THE TOP 10 ALL-TIME. PRECISE NUMBERS WILL BE AVAILABLE THURSDAY MORNING.

AT THE PRESENT TIME…THIS MONTH WILL RANK AS THE 4TH WETTEST SEPTEMBER ON RECORD FOR BOTH DALLAS/FORT WORTH AND WACO.

Below is radar estimated rainfall since 6pm Monday, you can easily see the areas where rainfall is most concentrated… the Green FFL icons indicate reports of Flash Flooding, the green polygons show current Flash Flood Warnings.

30% change of rain exists for the remainder of the day today… then 30% rain chances return again for Thursday. The weekend will likely be dry and bring a return to warm temperatures with highs in the mid to upper 80s.

The very unfortunate thing I would like to point out here is that this single storm was not severe storm warned or tornado warned at any point in its life cycle which unfortunately may cast a negative light on the hard working folks at the NWS office in Ruskin. I grabbed some archived level 2 radar data from the NCDC and I would like to show you radar snapshots of what forecasters at the NWS would have seen as this storm was unfolding. You can click any of these for full size.

A little background on the day’s forecast first. The area was under a severe thunderstorm watch which had just expired at 9pm. The severe thunderstorm watch notated an elevated risk for an isolated waterspout or tornado to develop along boundary collisions. The day had already brought severe storms widespread across the state, with CAPE values at or around 4000 J/KG. Excerpt from the watch’s discussion quoted below:

SEASONABLY STRONG NLY FLOW ALOFT WILL CONTINUE ACROSS
FL THIS AFTERNOON/EVENING AS DEEP MID LEVEL TROUGH DIGS OFF THE NERN
FL COAST.  AIR MASS REMAINS VERY UNSTABLE…DESPITE EARLIER LINEAR
MCS…WITH SUFFICIENT SHEAR FOR ORGANIZATION INTO LINES/CLUSTERS AND
PERHAPS A BRIEF SUPERCELL OR TWO.  DAMAGING WINDS AND ISOLATED LARGE
HAIL WILL REMAIN PRIMARY THREATS…ALTHOUGH A BRIEF
WATERSPOUT/TORNADO COULD ACCOMPANY STORMS ALONG RESIDUAL SURFACE
BOUNDARIES.

Now with this information in mind, I would be particularly mindful of any rapidly developing low level rotations. Florida tends to not get strong tornadoes, but those we do get form very rapidly and can be hard to detect, generally along strong boundary collisions from multiple thunderstorms. The below summary is an excellent example of this situation. The summary begins below:

06/23/09 9:58pm EDT – This is how the storms began. Note the large cluster of thunderstorms east and southeast of Tampa Bay. These generated an outflow boundary which shows up on the radar very well (thin line of reflectivity from about Parrish through upper Tampa Bay into Tarpon Springs). This boundary was moving very slowly to the west over Tampa Bay. Overall storm motion for the day is to the south-southeast. Another outflow boundary not visible to radar is moving south near New Port Richy. This boundary collision is kicking off new storms near New Port Richy and just offshore in the gulf.

06/23/09 10:29pm EDT – Storms continue to grow larger along the two intersecting outflow boundaries. Gusty winds around 27 knots show up on doppler radar near New Port Richy. Overall storm motion is to the south-southeast.

06/23/09 10:59pm EDT – At this time the storms are very strong, borderline severe. Radar indicates 0.77 inch hail near Anclote Key and into Dunedin with wind gusts to 37 knots in this same area. The leading edge of this storm’s reflectivity now begins to indicate the location of the southerly moving outflow boundary. Note the storm and the westerly moving outflow boundary are now colliding over Pinellas Park. Additionally there apears to be a very small area of possible rotation over Clearwater, however this is the only volume scan this feature appeared in.

06/23/09 11:15pm EDT – This is the aproximate start time of the microburst damage in Pinellas Park. What we see here is the southward moving outflow with strong storm development to its north, colliding with the now stalled out westerly outflow boundary. Radar indicates 0.93 inch hail near Feather Sound and the Gandy area. Additionally radar velocity now shows 50 knot winds in Highpoint, just west of St. Pete Clearwater Intl Airport. 50 knots is the baseline for a storm to be considered severe. At this time it would have been appropriate to issue the severe storm warning considering the hail size and wind speeds indicated by radar met severe criteria. Additionally the environment was still forecast to be favorable for producing severe weather, so this storm was likely to only intensify.

06/23/09 11:19pm EDT – This is the time the microburst likely hit Pinellas Park. You can see the leading edge of the storm had just passed to its south. Additionally I remember looking at this storm live as it was moving through and noticing this scan appeared to have an inflow region right over I-275 and 62nd Ave N, the area impacted by the microburst. The velocity scan shows outbound velocity in this area, paired with very strong inbound just to its west, this is the area where the two outflow boundaries were colliding. Note the radar indicates 0.89 inch hail over old northeast St. Pete, and the southerly moving outflow is now visible on the velocity scan.

06/23/09 11:25pm EDT – The next radar volume scan, note the storm has a very well defined Weak Echo Region (WER) just north of St Petersburg. This indicates an area of strong inflow to the storm, with very gusty winds. The velocity scan confirms the outbound winds flowing into this area. Strong inbound winds are indicated by the green color in downtown St Petersburg. Radar indicates 0.65 inch hail in this area.

06/23/09 11:30pm EDT – This is a zoomed out version of a radar snap I took and posted on a previous blog entry. This shows very well pronounced low level rotation over downtown St Petersburg. The reflectivity plot on the left shows a classic hook echo, and the velocity plot on the right shows a inbound/outbound couplet which existed in radar volume scans all the way up through 8000 feet! While no confirmed tornado formed from this, I would have strongly considered issuing a tornado warning at this point. Considering the day’s forecast and all available information at the time, this storm appeared ready to produce a tornado at any time. I will re-post the zoomed in version of this radar snap below:

In this zoomed in version, you can clearly see the Weak Echo Region (WER) on the left, with the precipitation wrap around forming the hook echo shape. On the right, you can see a velocity couplet very well defined. Again if I were watching this storm unfolding live, I would consider this storm to be producing a tornado or at least very strong winds. This is actually something which validated as a reader of my site who lives in Coquina Key confirmed damage in her neighborhood from this event! Quote listed below:

We live on Coquina Key and experienced quite a bit of damagage. It was very localized and could have been some sort of tornado. The noise I heard just before the storm broke was the scaries thing I’ve heard.

06/23/09 11:35pm EDT – The strongest winds with the storm have moved off into the middle of Tampa Bay at this time, though low level rotation still appears to be present. Approximately 10,000 power outages are reported around this time from the strong winds including around Treasure Island.

06/23/09 11:45pm EDT – The storm now moves into Manatee County, over Port Manatee first. Emergency Management reports a funnel cloud visible around11:49pm, only 4 minutes after this radar scan. Considering the current radar and velocity plots, it is likely to of occurred closer to 11:45pm and been 4 minutes delayed in reporting, though that’s just an assumption. No well defined rotation shows on this velocity plot, but at the very least you can see areas of strong winds moving ashore near Port Manatee.

6/24/09 12:15am EDT – This is just 6 minutes before the storm moved across Fruitville Road and produced the eF-1 tornado. You can see the intense winds and possible rotation right along the Sarasota and Manatee county lines. Outbound winds are reaching 64 knots and inbound winds show 4 knots. 68 knots of shear in this area, this would be capable of producing a weak tornado.

06/24/09 12:21pm EDT – This is taken as the storm passes over Fruitville Road to the east of Sarasota. This is likely the time that the tornado began to develop, though radar velocities do not show a very compact circulation in this area. You can see an area on the reflectivity that vaguely resembles a hook, though it is not a very well pronounced one. There is also another area to its east that does have some gate to gate shearing. This is likely the area that the tornado began to develop.

06/24/09 12:25pm EDT – This is just a minute before the tornado passed over Fruitville Road and into the Plant Farm. You can see a very small area of shearing winds occuring just southwest of Verna. The highest winds in this area are 66 knots outbound, which equals 75mph. The Plant Farm impacted by this is immediately south of this area of red/green color. Fruitville Road is the pink road traveling west to east across the middle of this image.

The storm gusted out after this point and lost its severity. Again, this storm should have been severe warned back at 11:15pm, and possibly even tornado warned at 11:30pm. Thankfully nobody was hurt during these events (as far as I know). Unfortunately this storm had the potential to be tornado warned up to 55 minutes in advance when the first signs of strong rotation were detected, before the tornado near Sarasota touched town. At the very least this storm should probably have been severe warned as there were numerous volume scans indicating wind speeds exceeding severe criteria.

Below are a few damage pictures taken by the NWS. These are pictures around the Plant Farm east of Sarasota.

Link to the NWS’s full damage survey is located below:

http://www.srh.noaa.gov/images/tbw/TopNews/TornadoHitsPlantFarm.htm

Location of the tornado damage noted on the google map below:

An area of strong thunderstorms moved south across central Pinellas county Tuesday June 23, 2009
between 11 PM and midnight.  The thunderstorms generally produced winds of 40 to 50 MPH, however
a micorburst occurred in Pinellas Park which produced winds of  approximately 60 MPH which caused
damage to numerous homes in the Southernaire Mobile Home Park on 62nd Ave N, just west of
Interstate 275.  One tree and numerous limbs were downed just northwest of the mobile home park
along 27th St North from 59th Ave N to 62nd Ave N.  Linear damage occurred from northwest to southeast
in this area which indicates this was the result of straight line winds and not a tornado.  Most damage in
the mobile home park was the result of wind getting under carports and lifting them up and over
homes, in some cases taking part of the roof off the home where the carport was attached.