Saturday, August 19, 2017

Three Recent Twisters That Didn't Get a Tornado Warning Until After Touchdown, if at All

Brian Donegan
Published: August 18,2017

Three tornadoes that touched down this summer had no tornado warnings issued before they formed. They each occurred during separate, unrelated events, with the strongest rated EF2.
However, it doesn't take a violent EF4 or EF5 tornado to cause damage and put people in harm's way – even EF1 and EF2 tornadoes can cause considerable damage.
Here's a rundown of the factors in play during the three tornadoes that were either warned too late or not at all.
(MORE: Why Some Tornadoes May Not Get Warned Even as Technology Improves)

Aug. 7 – Salisbury, Maryland

An EF1 tornado was confirmed in Salisbury, Maryland, on Aug. 7. A severe thunderstorm warning was issued at 1:37 p.m. EDT, and the tornado struck at 1:40 p.m. EDT. However, a tornado warning was never issued for Salisbury – only the severe thunderstorm warning.
"There was not high confidence in a tornado developing, though the organization of the showers and rotation supported some possible wind damage," said Jeff Orrock, meteorologist in charge at the National Weather Service (NWS) office in Wakefield, Virginia.
Due to the low confidence, the office issued only a severe thunderstorm warning but included a tornado tag – a new feature added last year to the NWS's impact-based warning system – within that warning.
"We use this enhanced severe thunderstorm warning in instances where a severe storm shows signs of rotation, but not tight enough (rotation) for a tornado warning," said Orrock.
The severe thunderstorm warning issued for Salisbury read:
Remain alert for a possible tornado! Tornadoes can develop quickly from severe thunderstorms. If you spot a tornado go at once into the basement or small central room in a sturdy structure. For your protection move to an interior room on the lowest floor of a building.
"As such, it is as important as ever to read what is contained in our warnings, as we are adding additional information to all our severe/tornado warnings," said Mike Dutter, science and operations officer at the NWS office in Wakefield.
Tornado tags are not frequently used, Orrock added.
"There was no history of severe weather with the Salisbury storm, and there was little, if any, lightning. Both of these factors weigh into the warning decision-making process," said Bill Sammler, warning coordination meteorologist at the NWS office in Wakefield.
Tornado circulations are often visible on Doppler radar into the mid-levels of a storm. One exception: tornadoes associated with tropical storms and hurricanes, where the circulations are generally only visible below 10,000 feet in elevation, according to Sammler.
"In the Salisbury tornado, rotation was basically limited to the lower 5,000 feet in the storm, which is quite unusual, especially considering we were not being impacted by a tropical system," Sammler added.
There were no injuries blamed on the Salisbury twister, but many photos and videos showing overturned cars circulated on social media.
(MORE: Tornado Flips Cars, Downs Trees in Salisbury)
"The key feature to this storm was that the greatest shear (change in wind speed and direction with height) was very low to the ground, and given the fact that these storms were fairly low-topped, it is quite possible that the lowest radar beam did not even see or detect the strongest rotation below the 0.5-degree beam," said Dutter.
Can a similar situation occur again? The answer is yes, especially if it involves a weak tornado.
"Weak tornadoes (EF0/EF1) are always the hardest to effectively warn for (because) their circulations are often fleeting, lasting only a couple minutes, as was the case ... in Salisbury," said Sammler.

Aug. 6 – Tulsa, Oklahoma

Four tornadoes struck the Tulsa metro area on Aug. 6, the strongest of which was rated EF2 in the city of Tulsa.
The Tulsa EF2 tornado touched down at 1:19 a.m. CDT, but a tornado warning was not issued until 1:25 a.m. CDT. However, a severe thunderstorm warning was issued at 1:08 a.m. CDT, 11 minutes before the tornado formed.
A man stands outside a Fridays restaurant after a storm moved through the area in Tulsa, Oklahoma, Sunday, Aug. 6, 2017. A tornado struck near midtown Tulsa causing power outages and roof damage to businesses.
(Tom Gilbert/Tulsa World via AP)
Sometimes, brief tornadoes spin up quickly along the leading edge of a squall line of severe thunderstorms with otherwise damaging straight-line winds, which is essentially what happened in Tulsa.
"This particular storm spun up at such a quick rate between scans of the radar, and by the time the NWS issued the warning, the storm was crossing into Broken Arrow," the city of Tulsa said in a statement to the Tulsa World.
(MORE: 4 Reasons You Should Take a Squall Line as Seriously as a Tornado Warning)
These spin-up tornadoes often dissipate as quickly as they form, and the tornado lifted by 1:25 a.m. CDT, but not before causing significant damage in the city.
"Tornadoes originating in squall lines, such as the Tulsa area tornadoes, can normally be accompanied by straight-line winds that are as strong, or stronger than the tornado itself, can last slightly longer than the tornado and often produce a wider swath of damage than the tornado," said Greg Schoor, acting severe weather program leader at the NWS.
Twenty-six people were injured in Tulsa by the tornado, which had maximum estimated winds of 120 to 130 mph. Numerous homes and businesses were damaged in the city.
(MORE: No Sirens Sounded as Tornadoes Leave Damage, Injuries in Tulsa)
"That is why severe thunderstorm warnings should always be taken just as seriously as tornado warnings, especially ones with the impact-based warning system's tornado tag," Schoor added.

July 20 – Hamburg, New York

Four tornadoes were confirmed in western New York on July 20, the strongest rated EF2 near Hamburg.
The Hamburg tornado touched down at 12:30 p.m. EDT, and a severe thunderstorm warning – not a tornado warning – was issued at 12:31 p.m. EDT.
A tornado warning did not come until 12:36 p.m. EDT; the tornado had already been on the ground for six minutes.
The storms originated in Ontario, Canada, where they formed into a cluster before crossing Lake Erie into western New York. The damage path began in Hamburg and then continued across Orchard Park.
"Hundreds of car windows were blown out at the Hamburg Fairgrounds where trees were downed and several buildings, including the Grandstand, sustained damage," the NWS office in Buffalo said in its event summary. The tornado then continued across Chestnut Ridge Park and the town of Orchard Park, causing more structural and tree damage.
No injuries were caused by any of the July 20 western New York twisters, though a home surveillance camera was able to capture the Hamburg EF2 tornado's strong winds lifting a car off the ground.
(MORE: Tornadoes Leave Damage in Western New York)
"Over the last three years, NWS warning lead time for the stronger, more violent tornadoes (EF3 or greater) is around 17 minutes, and we are able to detect around 95 percent of these tornadoes in this range of intensities. Add in EF2 tornadoes and the average lead time is still around 14 minutes with a rate of detection over 80 percent," said Schoor.
Brian Donegan is a meteorologist at Follow him on Facebook and Twitter.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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