Vanishing Act

An SPC Moderate Risk was posted for the southern two-thirds of the state of Missouri on this day, Saturday, May 27, 2017. A Slight Risk extended up into the extreme southern and southeastern part of Iowa. Above, a small cell (arrow) begins to form between New Sharon and What Cheer, Iowa around 3:00 pm. It would become a "Tail-end Charlie" of a comma-shaped line of lesser storms forming in Mahaska County and moved in a generally easterly direction. At 3:20 pm I decided to depart Cedar Rapids in an attempt to intercept this cell, and hoped it would continue to hold its strength. On my way south on Interstate 380/US Highway 218, the storm became severe-warned at 4:00 pm, and I found my spotting position--a favorite spot in Washington County on Yucca Avenue, about 1 mile east of US Highway 218 and about 2 miles east of Ainsworth, Iowa.

This image shows my vehicle's severe weather equipment as I waited at 4:48 pm on Yucca Avenue, facing west. The approaching storm cell had become tornado-warned just minutes before.

The radar capture above shows the tornado-warned storm at 5:04 pm. Its most intense core was located about 32 miles distant, between the towns of Sigourney and Harper. My spotting position is the blue target at far right.

5:18 pm (above) and the most intense area has now moved east over the Harper, Iowa area.

Two minutes later. A funnel had been reported by other spotters with this storm. Its impressive structure began to materialize along the horizon to my west. I felt I was in perfect position here--if the cell stayed on its current track its southern edge would pass to the east just north of me. Temperature at this time was 73 degrees F, dew point 63 degrees, 69% humidity and the winds were out of the SSE.

5:25 pm. The structure is looking better than ever, and I was filled with anticipation. I had no reason to believe the storm would not maintain its current strength. Nikon D7200 DSLR camera.

By 5:30 pm my weather radio announced the storm had weakened and the tornado warning had been lifted (radar capture above). From 5:30-5:50 pm the cell went from tornado-warned to an area of mere light rain! An astounding and frustrating vanishing act, probably brought on by its entry into very stable air. It was time to return home.