The peak of the severe weather season passed us by more than 6 weeks ago. In keeping with the rest of the season, the days have passed quietly. In fact, when it comes to tornadoes 2018 is on track to be one of the least active on record. Only 571 have been reported through July 17th. In 2008 nearly 1700 had been registered over the same period.
In Iowa only 15 tornadoes (all weak) have touched down this year. The all-time record is 120 set in 2004. Average is about 55.
Here's some Iowa tornado statistics from the NWS in Des Moines.
While mid-July is not usually prime time for severe weather there is the chance some parts of the central Midwest will see strong to severe thunderstorms Thursday afternoon or evening. The threat will come from an unusually strong July surface low that is expected to track southeast across Iowa. You can see it making the trek below.
As is often the case, even with strong dynamics, if instability is lacking severe weather will be limited. How far into the Midwest moisture and warmth can get will determine the northern extent of the stronger storms. Right now the supercell index for early evening shows the greatest chance for surface based storms from the triple point west of Waterloo on to southeast Iowa and NE Missouri
With significant directional shear there is the chance of a few tornadoes. Again, the extent of that threat won't be realized until Thursday morning. It Warrants a close watch especially from central into southeast Iowa. Here's the significant tornado parameters at 4:00pm
Significant tornado parameters at 7:00pm
Where thunderstorms do develop the stronger updrafts will be capable of producing heavy rainfall on the order of 1-2" an hour. Not everybody will see strong storms but where they do develop they could be formidable, especially for July 19th. Roll weather...TS