National Weather Service team determines Saturday storms spawned an 8th ‘weak’ tornado

Belleville News-Democrat
Updated ·3 min read

Survey teams from the National Weather Service have determined an eighth tornado occurred in the St. Louis region over the weekend, the agency stated Monday.

“National Weather Service Teams have now surveyed 8 weak tornadoes from Saturday’s storms,” the agency stated in a Twitter post. “Additional surveys are not planned, but we will continue to review footage and aerial imagery to help determine if more tornadoes occurred or adjust the surveyed tracks.”

The latest update says the eighth tornado started northwest of Festus, Missouri, and headed northeast for four miles to Herculaneum along the Mississippi River. Its rating was EF-1, with a maximum width of 360 yards.

In all, survey teams that examined storm-damaged areas determined there were four tornadoes in southwestern Illinois and four in Missouri on Saturday night. The Illinois tornadoes included an EF-1 in Belleville, an EF-0 in Swansea, an EF-1 that began Monroe County and ended near Hecker, just over the border of St. Clair County and an EF-0 in the Valmeyer area.

Five of the eight tornadoes were rated EF-1 on the Enhanced Fujita Scale. The others were EF-0. The National Weather Service uses the EF scale to rate tornadoes based on wind speeds and damage left behind. The scale ranges from EF-0, with wind gusts of 65-85 mph, to EF-5, with gusts over 200 mph.

Here’s how the National Weather Service website defines the duties of a survey team:

“A survey team’s mission is to gather data in order to reconstruct a tornado’s life cycle, including where it occurred, when and where it initially touched down and lifted (path length), its width, and its magnitude.

“It should also be mentioned that survey teams are occasionally tasked with determining whether damage may have been caused by straight line winds or a tornado and assessing the magnitude of straight line winds. ”

How do the teams determine weather storm damage was caused by a tornado? Here’s another excerpt from the National Weather Service site, quoted here directly:

  • “The pattern of damage determines if it was a tornado. NOT how much damage was caused.

  • Tornado damage often has a chaotic appearance, with larger uprooted trees often crossing each other.

  • We often look at larger uproots of trees to get a true idea of where the wind was blowing from. Smaller branches/snapped trees are not as helpful, as they may fail based on the tree itself and now where the wind was coming from.

  • Large uprooted trees in a convergent pattern, crossing each other.

  • Especially in our area, tornadoes AND microbursts can cause the same amount of damage.

  • We conduct surveys to find out exactly what happened. This helps us to improve our warnings for the future. This is also important for historical reference. “

One of the survey teams working Monday determined storm damage in the Sullivan, Missouri, area was caused by straight line winds and not a tornado, the National Weather Service reported.