June 22, 2010 chase account

I was back and forth on chasing this day as I watched things develop through the morning and early afternoon hours. Finally at like 2:00 I decided to go for it, seeing increasing CAPE and shear, and a subtle boundary in SE NE heading north with time. I convinced Ben McNeill to join me, so after picking him up in Adel, we headed west towards Council Bluffs. When we got there, we saw a very strong reflectivity signature on KOAX showing the boundary, which had already lifted north of town. Thus we went up I-29 sort of chasing it. Numerous cumulus clouds had developed by this late afternoon juncture, and things were looking good. However, what I hoped wouldn't happen started to: the cap got stronger, as warmer 700 mb temperatures were moving in.

• 20Z
• 22Z
• 23Z

Some of the cumulus clouds developed into cumulus congestus towers, and it looked like a few might go. However, we noticed that they would choke off and die within a few minutes after really popping. It seemed like one parcel might've been able to get through the cap, but following parcels couldn't make it. I was able to get a picture of one such tower/incidence near Logan as we headed northeast after the only two storms we saw show any significant returns on radar.

The base of one of the better towers to go up...and eventually fail.


Tower near Logan that looked good, then fell apart as we were about to drive under it.

Every single updraft/tower that went up and started to produce > 40 dBZ reflectivity signatures died within 30 minutes of birth. By the time we got to Harlan, we were convinced we had cap busted. Thus we called off the chase and I was going to drop Ben off in Adel before going home to Ames.

Mother nature was not done for the day, however. Strangely enough, immediately after the initial storms died, a new batch of them developed in the same area! And these ones persisted. There were about four discrete storms, but they took a long time to develop and get organized. In fact, they took so long that they didn't develop into anything special looking by the time I got Ben back to Adel. Thus I shut my stuff off and was on the way home when Ben called me 20 minutes after I dropped him off to tell me one of the storms had gone tornado warned.

Picture of tornado warned storm from way to its southeast. At the time I took this picture I didn't knowk the storm was tornado warned. Really I was taking this picture to illustrate how some high level clouds can only be seen when the sun is at the correct angle to shine some light on them. Observe the cirrus clouds above the storm that seem to suddenly cut off in a line that can be traced back to behind the storm where the last bits of light from the setting sun show. Those cirrus clouds continue to the right in that shadow in a similar fashion as they do where they can be seen, but due to the angle of the light, they appear invisible.

I was pretty shocked to hear the news. After I got home I fired up GR2 and turned on the local media stations. Sure enough they were wall to wall. Although some reports of tornadoes would come in on these storms through late night, the Des Moines NWS FO never mentioned any tornadoes from these storms in their post event analysis. They only had one tornado near Tripoli (well east) around 2:45 AM. Other chasers in the area also mentioned the storms did not have great structure and it was difficult to see what was going on due to darkness (that's the other reason I didn't turn back northwest to chase these storms - I'm not a night chaser). I think these storms formed due to the arrival of synoptic scale lift from an advancing shortwave trough. The storms were probably initially elevated, but gradually worked their way down to the near-surface. I think it's funny how SPC issued a tornado watch AFTER the first few tornado warnings had already been issued and the first few reports had already come in. Talk about a reactive watch.

Activity loop from the late afternoon through late night hours

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