A tornado moving away from the observer, over rural land outside Grandview in Louisa County, Iowa around 1:51pm, Tuesday, September 25, 2018 — The report from the photographer is that this cloud was rotating. In addition, the time and location the photo was captured lends to the cloud being a tornado. -can’t really see what’s going on below the tree line or in the wider view of the prevailing cloud structure- It’s a stunning photo. Generally, when the rotating funnel condensation appears to reach more than halfway to the ground, it is in fact a tornado on the ground. / Photo credit: Kathy Ruschmeyer/Tiffany Fraise
Connie Timmerman-Massey’s incredible video of the wall cloud and small tornado passing by outside Grandview, Iowa at around 1:51pm, Tuesday, September 25, 2018
Posted by Connie Timmerman-Massey on Tuesday, September 25, 2018
A sharp cold front set off a few severe thunderstorms in the northern portion of our listening area on Tuesday afternoon. Three storms of noteworthy value in order of occurrence include a supercell that came through the Wyman/Winfield, Iowa area, a severe segment that affected Wapello, Iowa, and a supercell near Little York, Illinois. These storms each had sufficient rotation and development prospects to warrant tornado warnings.
The clouds of both supercells only reached to around 25 to 30 thousand feet into the atmosphere — low-top storms. This late-September variety differs drastically form our May and June storms that often reach 50 to 60 thousand feet. This is important since, with increasing distance from the Quad Cities radar site, the lower-top variety can be very challenging to spot storm structures and radar-indicated rotation areas sufficient for tornado production. I’ve seen these low-top storms occasionally produce tornadoes on up to EF-1 and even EF-2 strength, so they’re no slouches. With the first supercell mentioned above, the storm produced a confirmed, brief tornado just outside the Columbus Junction/Grandview, Iowa area. No damage or injuries have been reported.
The Wapello, Iowa storm had a little inflow notch — looks like a dog’s hind leg on the radar image below. That inflow area brings in warm, moist air from the southeast while rain-cooled air within the thunderstorm surges forward. That creates a localized area of counterclockwise spin/rotation. A tornado will sometimes sit in that notch. Tornadoes in these cases tend to be brief and intermittent — making monitoring the storm a true minute-by-minute proposition. Very luckily, the storm had cycled into a weaker state as it hit Wapello — and thankfully there has been no report that a tornado came through Wapello. That was a set-up that could have gotten ugly.
The red box shown in the radar image below is the area that was tornado-warned by the National Weather Service out of the Quad Cities. I’ve drawn the yellow arrows to show the wind flow around the notch. The second image shows the winds — with green areas moving generally toward the Quad Cities radar site and red areas moving generally away. The neighboring red and green areas signal opposing winds — rotation. As shown in the third image below, the Wapello storm reached higher than the low-top supercells, reaching 40 thousand feet, or about 7.5 miles, into the atmosphere.