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.

• 11:20 – KPIE (Pinellas County) – St. Pete/Clearwater Intl Airport recorded a 53mph wind gust.
• 11:25 – Seminole (Pinellas County) – Tree fell on cars
• 11:31 – KSPG (Pinellas County) – Albert Whitted Airport recorded a 43mph gust.
• 11:48 – Tampa Bay – 56mph wind gust measured at C-CUT station in lower Tampa Bay.
• 11:49 – Piney Point (Manatee County) – Emergency Manager reported a funnel cloud near Port Manatee.
• 11:54 – Piney Point (Manatee County) – 51mph wind gust measured at Port Manatee.

Other damage reports not relayed to the NWS include trees down, powerlines down, stop lights offline and roof damage in St Pete including Downtown. According to Bay News 9 10,000 homes and businesses were without power including some in the beach communities.

For those of you asking why this storm was not severe storm warned, technically the wind gusts recorded are just bairly under severe storm criteria. Severe criteria equals wind gusts of 58mph or higher, hail the size of dimes.

At one point this storm did have a rather well defined low level rotation directly over downtown St Pete but the storm was not tornado warned. I figure one of a few reasons, the rotation was only in the low levels of the storm and not present through the mid levels and the storm was moving offshore into Tampa Bay.

During the afternoon of June 18, 2009, a line of strong thunderstorms moved south colliding with other thunderstorms developing along the west coast sea breeze (see radar loop below). When this collision occurred the storms became severe over Riverview producing a downburst. Downbursts are generated when rain-cooled, dense air sinks inside a thunderstorm. Also, some of the strong winds aloft are carried down with the downburst by a process called “momentum transfer”. As precipitation begins to fall, it drags some of the air with it. This “precipitation drag” initiates a downburst. The downburst is intensified by evaporative cooling as drier air from the edges of the storm mix with the moist air within the storm. Downbursts are divided into two categories, macrobursts and microbursts. A macroburst is more than 2.5 miles (4 km) in diameter while microbursts are smaller. Based on the NWS survey this event would be defined as a microburst.

…SUMMARY OF STORM IMPACTS FROM JUNE 10 THROUGH JUNE 14…

AN UNUSUALLY ACTIVE SERIES OF SEVERE WEATHER EVENTS…EVEN BY NORTH
TEXAS STANDARDS…IMPACTED THE AREA FROM THE LATE AFTERNOON OF JUNE
10 THROUGH THE EARLY MORNING HOURS OF JUNE 14. BASED ON RADAR
DATA…STORM SPOTTER REPORTS…AND COORDINATION WITH LOCAL
OFFICIALS…HERE IS A BRIEF PRELIMINARY SUMMARY OF THE STORM IMPACTS.

JUNE 10…
A CLUSTER OF SEVERE STORMS DEVELOPED OVER WEST CENTRAL TEXAS AND
MOVED EAST. THE STORMS ORGANIZED INTO A BOW ECHO JUST WEST OF THE
DALLAS-FORT WORTH METROPLEX AND PRODUCED EXTREMELY STRONG WINDS.
NUMEROUS 70-80 MPH WIND GUSTS OCCURRED ACROSS NORTHERN PARKER…
SOUTHERN WISE…NORTHERN TARRANT…SOUTHERN DENTON…NORTHERN
DALLAS…AND SOUTHERN COLLIN COUNTIES. WIND GUSTS IN EXCESS OF 60
MPH OCCURRED ACROSS MUCH OF THE REMAINDER OF THE METROPLEX.

WITHIN THE BROAD AREA OF DAMAGING WINDS…AT LEAST THREE BRIEF
TORNADOES OCCURRED. SPOTTERS OBSERVED THE TORNADOES FROM ROANOKE TO
TROPHY CLUB AT APPROXIMATELY 640 PM…IN FLOWER MOUND AT ROUGHLY 650
PM…AND IN THE COLONY-HEBRON AT ROUGHLY 705 PM. THE ROANOKE AND
COLONY TORNADOES WILL LIKELY BE RATED EF-0…WHILE THE FLOWER MOUND
TORNADO WILL LIKELY WARRANT AN EF-1 RATING. FURTHER INVESTIGATION
MAY REVEAL ADDITIONAL BRIEF TORNADOES WITHIN THE DAMAGE SWATH.

JUNE 11…
THE STORMS FROM THE EVENING OF JUNE 10 LEFT BEHIND AN AREA OF
RAIN-COOLED AIR. THE BOUNDARY BETWEEN THE RAIN-COOLED AIR AND THE
WARM HUMID AIR SAGGED TO THE SOUTH OF THE I-20 CORRIDOR. WARM MOIST
AIR WAS FORCED UP AND OVER THE BOUNDARY…RESULTING IN A NEARLY
CONTINUOUS STREAM OF THUNDERSTORMS DURING THE MORNING AND EARLY
AFTERNOON OF JUNE 11. MORE THAN THREE INCHES OF RAIN FELL FROM JACK
COUNTY SOUTHEAST TO HENDERSON COUNTY. THE HEAVIEST RAIN FELL FROM
NORTHERN TARRANT TO KAUFMAN COUNTY…WITH MORE THAN EIGHT INCHES
ACROSS MUCH OF DALLAS COUNTY. THE RESULTING HEAVY RAIN CAUSED
WIDESPREAD FLOODING IN THE AREA.

A SEPARATE CLUSTER OF SEVERE THUNDERSTORMS DEVELOPED WEST OF THE
HEAVY RAIN AREA…FROM EASTLAND COUNTY SOUTHWARD. LARGE HAIL FELL
FROM NEAR CISCO TO NORTH OF LAMPASAS…WITH THE HAIL REACHING
BASEBALL SIZE IN LAMPASAS COUNTY.

JUNE 12…
A SUPERCELL THUNDERSTORM DEVELOPED OVER NORTHERN JACK COUNTY AND
MOVED SOUTH-SOUTHEAST. THE STORM PRODUCED AT LEAST TWO CONFIRMED
TORNADOES…WINDS IN EXCESS OF 70 MPH…AND HAIL LARGER THAN
BASEBALLS. THE TORNADOES WERE APPROXIMATELY 5 MILES SOUTH OF
JACKSBORO JUST BEFORE 530 PM…AND JUST WEST OF PERRIN AT AROUND 550
PM. DAMAGE TO OUTBUILDINGS AND ROOFS RESULTED…AND THESE WILL
LIKELY BE RATED AS EF-1.

AS THE STORM MOVED THROUGH WESTERN PARKER COUNTY…POSSIBLE
TORNADOES IMPACTED AREAS NEAR THE COMMUNITY OF COOL…AND TO THE
SOUTHWEST OF WEATHERFORD. THE STORM UPROOTED TREES AND DESTROYED
STORAGE BUILDINGS IN THESE LOCATIONS. THE STORM CONTINUED PRODUCING
LARGE HAIL AND SEVERE WINDS INTO JOHNSON…HOOD…AND BOSQUE
COUNTIES.

TO THE SOUTHWEST…A CLUSTER OF SEVERE STORMS MOVED INTO COMANCHE
AND MILLS COUNTIES. HAIL UP TO NICKEL SIZE WAS REPORTED WITH THESE
STORMS.

JUNE 13-14…
A COMPLEX OF THUNDERSTORMS MOVED THROUGH WEST CENTRAL TEXAS ON THE
EVENING OF JUNE 13. THE STORMS MOVED INTO YOUNG AND MONTAGUE
COUNTIES BEFORE WEAKENING. DAMAGING WINDS IN EXCESS OF 70 MPH MOVED
THROUGH THE NOCONA AREA SHORTLY AFTER MIDNIGHT JUNE 14. A LARGE
TREE WAS BLOWN DOWN WEST OF NOCONA…AND ROOF DAMAGE OCCURRED IN
NOCONA.

YOUR NATIONAL WEATHER SERVICE WILL CONTINUE INVESTIGATING THE
IMPACTS FROM THIS SERIES OF SIGNIFICANT THUNDERSTORM EVENTS.
ADDITIONAL DETAILS AND INFORMATION WILL BE PROVIDED IN UPDATED
STATEMENTS AND POSTED TO OUR WEBSITE. FOR THE LATEST INFORMATION…
VISIT /LOWER CASE/ WWW.WEATHER.GOV/FORTWORTH

This is the scene all around the Frisco Bridges area where I live and work, numerous trees down in the area. The tree limb pictured here appears to be about 8 inches in diameter, snapped at the base.

• 4:30pm I notice a cluster of supercells merging into a large storm complex near Abilene TX about 130 miles west of Frisco.
• 5:00pm this storm appears to have evolved into a severe line of storms looking like a bow echo. This storm is in a favorable environment and at current speed will reach Frisco by 7:30pm
• 6:04pm Tornado Warning is issued for Denton county, does not include Frisco yet but the storm’s track is still set to move very close to Frisco.
• 6:40pm Tornado is spotted on the ground in Roanoke, 22 miles WSW of Frisco. Spotted by Amateur Radio operators.
• 6:43pm Tornado Warning is issued for Denton, Collin, Tarrant, Dallas and Rockwall counties. This includes Frisco and The Colony.
• 6:50pm Tornado spotted by retired NWS employee, brief touchdown in Flower Mound, 15 miles WSW of Frisco.
• 6:53pm Tornado ripped roof off and collapsed wall to apartment building in Flower Mound, 15 miles WSW of Frisco.
• 6:56pm Tornado sirens finally start to sound for Frisco, note the 13 minute discrepency. This is EXACTLY why I tell everyone not to trust the sirens.
• 7:00pm I get out of work, the storm is now less than 8 miles away from Frisco,
• 7:05pm I drive one mile west along Warren Pkwy. At the intersection of Warren & Legacy I observe power flashes on the horizon about 3 miles to my WSW. At this time I turn around and head back home, 1.5 miles away.
• 7:12pm I arrive at home just as the very high winds and rains hit. Sirens are still going off.
• 7:14pm The strongest rotation made a last minute right turn and passes 4 miles south of Frisco, into Plano. The sirens stop at this time.
• 7:14pm 72 MPH wind gust observed at Frisco Fire Station on Main Street and Preston Road.
• 7:19pm 78 MPH wind gust observed at a school in Plano, near Independance and Spring Creek.

Allow me to reiterate how close this storm was. The storm’s center of circulation passed only 4 miles south of the T-Mobile site in Frisco (where I was at the time). At the time the tornado warning was issued for Frisco, the storms current track took it within 1/2 mile of the T-Mobile site in Frisco. Below is a Google map I just made demonstrating this.

The red circles indicate tornado sightings and tornado damage reports. The red line indicates the path of the storm’s center of circulation. The blue line indicates the storms projected path when the tornado warning was issued for Frisco. The purple circle shows where the T-Mobile building is, and where I was at the time. As you can see… this was a close call. If the storm had maintained its current track and not turned right in Lewisville, Frisco could have been hit head on.

Above is a radar snap from 7:09pm CDT, when the storm’s center of circulation was at its closest to Frisco. Left side is standard precipitation and the right is base velocity. You can see a weak reflectivity couplet that is unfortnately a tad obscured by the large yellow warning box. The yellow and red icons indicate areas of wind damage, and tornado reports respectively.

At this time, some damage reports in Frisco have come in according to Fox News KDFW. Some homeowners had their fences blown down, satelite dishes blown off their houses and windows broken. Another reports states at least three seperate 18-wheeler trucks blown off the road and tipped over due to high winds, mostly around Fort Worth. The Denton County Sherrifs Office reported a minor explosion at a gas station due to the weather. Across the metroplex, a whopping 260,000 homes are reported without power.

Now we will wait and see what the NWS in Fort Worth states after they conduct their damage surveys, before we officially declare this as a tornado. Considering the numerous spotter reports, storm damage reports, and the radar velocity couplet, there is a good chance this will be classified as a tornado event. I will publish updates to this once the storm damage survey is released.