Thursday, August 20, 2009

Minneapolis tornado, New York City's violent winds, Anchorage's tremors

Twin Cities Doppler Radar display around 2 pm yesterday, showing a tight velocity "couplet" over south Minneapolis. The bright red area is wind moving away from the Doppler site in Chanhassen, the bright green smudge is high velocity air moving toward the radar - evidence of a small, tight, vigorous mesocyclone, a rotating thunderstorm capable of damaging winds, in all probability, an EF0 or EF1 tornado. We were in a "slight risk" of isolated severe storms, according to SPC. But no watches were in effect at the time the tornado touched down, the local NWS would issue a tornado warning for this cell approximately 15-20 minutes later, around 2:20 pm, after the circulation had passed directly over downtown Minneapolis (debris was spotted from a number of downtown high-rise office buildings!) Thankfully it was a "minor" tornado - had it been a major tornado there would be a lot more red faces today.

Nature reminded several American cities of its powerful presence in the last 24 hours.

Both Minneapolis and New York City are cleaning up, the former after a tornado struck south of downtown on Wednesday, the latter after a storm brought hurricane-force winds Tuesday night that toppled scores of trees in Central Park, including giant American elms more than 100 years old.

Meanwhile, Anchorage, Alaska was shaken on Wednesday by a magnitude 5.0 earthquake which apparently jangled some nerves but didn't break anything.

According to the Minneapolis Star-Tribune, the Minneapolis tornado destroyed trees and caused some damage to buildings but caused no injuries.

An excerpt:

"This dispels myths that tornadoes don't hit urban areas, they go where they want to," said Pete Boulay, assistant state climatologist. "It doesn't happen very often, but they do happen."
Northbound Interstate 35W at Hwy. 62, already a tangled mess at the southern edge of Minneapolis because of construction, is closed due to flooding.
Central Lutheran Church in downtown had an old copper steeple damaged, and two tents used for entertaining also were struck. One was blown into the street and the other was collapsed, said church spokesman Joe Bjordal. The tents were set up in connection with the national gathering of about 2,000 at the Evangelical Church in America at the Convention Center. "We're thankful that nobody was hurt," Bjordal said.
Representatives on the convention floor could hear rain on the roof, but only became aware of the turbulence outside when unofficial convention-goers were moved in from the outside corridors for their safety.

(There is still some question about whether the wind damage in Minneapolis was caused by a real tornado or straight-line winds, a "wet downburst", I've heard a number of competing theories. But after looking at the video [check it out on WeatherNation's main web site here], after hearing the reports from survivors - those in the path of the storm - AND - after seeing the Doppler SRV, storm relative velocity image from 2 pm yesterday, sorry, I don't think there's any question this was a tornado).

I know this makes a number of people uncomfortable - no severe watches or warnings were in effect at the time, no local media was on the air giving advance notice of this potentially dangerous/deadly situation. A lot of people would LOVE for this to go away, or be designated as straight-line wind, which doesn't have quite the stigma, or impact of a TORNADO. I'll be amazed if it was anything but a small EF0 or EF1 tornado. BTW, the rest of the article from NPR is right here.

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