11:15 am UPDATE: State of Emergency declared in eastern South Dakota
Update (5/13/22 at 11:15 a.m): “After discussion with the NWS SPC [National Weather Service Storm Prediction Center], the storms that moved through the Northern Plains will be classified as a “Derecho”,” says the Sioux Falls NWS office. The fastest wind speed observed was 107 mph in Tripp, SD.
PIERRE, S.D.- Governor Kristi Noem has declared a State of Emergency and “ordered state personnel and resources to communities impacted by the damaging storms that occurred Thursday in eastern South Dakota.”
A line of severe thunderstorms sparked warnings across the eastern portions of South Dakota late Thursday, including both thunderstorm and tornado warnings.
Videos showed bright spring skies turning dark, as massive swaths of dust blocked out the sun. Golf-ball sized hail was reported along with some heavy bursts of rains, which reduced visibility quickly.
Reports of tornado damage also came in from Castlewood, with photos of funnel clouds being taken from both Sisseton and Watertown.
One fatality has been been confirmed as a result of this storm.
Straight-line winds of 80 to 90 miles per hour were also reported on the eastern border of the state. These winds can sometimes be even more destructive than small tornadoes, so it can be hard to distinguish straight-line wind damage from tornado damage.
According to social media posts from the National Weather Service station at Aberdeen, they’ll be “performing multiple damage surveys today to assess the damage from the tornadoes and straight-line winds that occurred on Thursday, May 12th. “We will be providing the results of the surveys as soon as possible after the surveys are completed,” NWS officials say.
So, what exactly was this storm? A squall line? Dust storm? Derecho?
It might be a combination of a few different things. However, meteorologists from NWS offices as well as the Storm Prediction Center will assess photos, videos, and damage to determine if criteria were met for tornados and derechos.
A dust storm can be determined from photos and remnants of dust in structures or vehicles, but derechos and tornadoes must fit certain wind speed and damage criteria. For an event to be upgraded from a squall line to a derecho, the National Weather Service says the wind damage must extend more than 400 miles and include winds of at least 58 mph for most of that length.
The Enhanced Fujita Scale is used to assess tornadic activity based on the amount of damage left behind. So heavily damaged and collapsed structures will be reviewed for this possibility as well.