Storm Highway by Dan Robinson
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Tornadic supercell and giant hail from Jefferson City to St. Louis: April 22, 2011

ABOVE LEFT: Four-inch hail in McKittrick, Missouri on April 22, 2011; RIGHT: the supercell near Holts Summit, MO.

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By DAN ROBINSON
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MCKITTRICK, MO - A tornadic supercell moved from near Booneville, Missouri along I-70 into the St. Louis metro, producing a violent EF4 tornado in north St. Louis and giant hail along its track.

The setup for the day was a warm front draped along the I-70 corridor across Missouri. As the day progressed, a surface low moved eastward into the area, pushing the warm front slowly north as a cold front moved east. Clearing skies allowed the warm sector ahead of the low to destabilize. Above, strong southwesterly 500mb winds overspread the threat area, providing deep-layer shear. Storms were expected to fire on the cold front and potentially go tornadic in the warm sector. Storms interacting with the warm front had the highest potential for tornadoes. The ideal area for a supercell to form was north and west of Columbia, where backed winds and warm frontal interaction would maximinze the tornado potential. Consequently, I targeted I-70 in the vicinity of Columbia, leaving New Baden, IL around 3PM. Just prior to departing for the expedition, a Fox 2 crew stopped by for a quick interview:

VIDEO: Fox 2 interview

As I drove west on I-70, I passed a major traffic backup in the eastbound lanes near Foristell due to multiple chain-reaction accidents (cause unknown, it was dry and sunny). This would have major implications for the expedition, as I had originally expected I-70 to be a good way to reposition eastward for a storm that might track along the highway. Finally, convection was getting organized south of Booneville, near Sedalia. This storm was too far south of the warm front for a high tornado threat, but as the minutes ticked by it became apparent that no storm to its north would be getting established.

I headed south toward Jefferson City on Highway 54 from the Fulton area to intercept the storm. I turned west on Highway Oo at Holts Summit and could already see dramatic supercell structure from the storm about 20 miles away.

The terrain here was hilly, and I had to drive a considerable distance to find a good view. I ended up on a dead-end gravel road past the end of Highway Oo before finding an acceptable viewing spot. Supercell structure was dramatic:

Despite the appearance, low-level cloud motion under the storm's base was weak, and it did not have any indication of producing tornadoes in the short term. I finally had to move back east to Highway 54 to keep from getting overtaken by the storm, now approaching the highway fast:

The storm's circulation beat me across the highway by about 2 miles near New Bloomfield. A difficult decision had to be made now. I could take a curvy, winding east road here to cut over to Highway 94 and stay with the storm (which I saw several other storm observers do), or I could go back up to I-70 and blast east ahead of the storm, then drop south to re-intercept. The problem with the Highway 94 option was that I now realized how fast the storm was moving east, and I doubted I could keep up with it safely on the wet, curvy, hilly roads. The danger with the I-70 east route was the aforementioned traffic jam, which there was no way to know whether it had been cleared or not. Fortunately, there were frontage roads along I-70 that I could use to bypass any jams.

I made it back to I-70 north of Fulton and began the trek eastward, very nervous about hitting the traffic jam. Getting caught in a shut-down interstate would end the expedition. I needed to get across a creek west of Williamsburg before I'd have unbroken eastbound frontage road options - if I hit traffic before then, it would be "expedition over". I breathed a sigh of relief when I reached Williamsburg, exiting and taking the frontage road east from there. I still didn't know if the traffic backup was still in progress, but didn't want to find out the hard way.

I now had another choice - keep blasting east on the frontage roads to near Jonesburg before turning south ahead of the storm, or making an earlier turn south at Mineola on Highway J then Highway 19 to McKittrick. I chose the earlier option, mainly due to the fact that I was already entrenched in the storm's northern flank precip and apparently not making good headway on the wet and lower-speed frontage road. I figured I needed to take my chances and intercept now, then try and keep up on Highway 94 east of McKittrick. I knew it would be a close call with the storm's core.

I encountered the first hailstones as I reached Highway 19 at Big Spring. As I traveled south, it was obvious I'd lost the race with the storm. As the hail increased in size to golfballs, I slowed it down to around 30mph. There were tennis ball hailstones in the grass on the sides of the road. The falling hail was slowly letting up, so I cautiously crept southward. Finally, the hail and rain subsided as the storm rocketed away to the east. As I traveled south on 19, the hail on the side of the road increased in size. Finally I could see softballs along the road. I found a small grassy area along the road and stopped to collect and photograph some of the hailstones. Most of the hail was 2.5" (tennis ball sized), with some baseball (3") and softball (+4") sized stones scattered around. The big stones had embedded themselves in the soft ground, creating craters.

Like a kid at an easter egg hunt, I searched the field, picking up the biggest hailstones I could find. I brought two armfuls back to the truck, getting my arms and shirt muddy and dirty in the process (but not caring at all about it).

After spending about 10 minutes with the hail, I tossed the 20 or so stones I'd collected into the back of my truck (I'd wished I'd had a cooler) and continued the expedition. I decided to try and get back to I-70 and atempt to catch up with the storm before it entered the St. Louis metro. It would be a long shot due to the storm's fast movement and my now being 20 miles behind. But when I turned east on Highway 94 at McKittrick, a 'bridge closed ahead' sign brought all hopes of re-intercepting the storm to an end. This caused me to miss the nighttime EF4 tornado as it moved through northern parts of St. Louis, striking Maryland Heights, St. Ann and Lambert Field.

My only option now was to drop south to I-44 for the next supercell in the line. Once again, it appeared it would be a close race to beat the meso/hail core to the interstate. Four slow vehicles in front of me traveling 5 to 10 mph below the 55mph speed limit, with limited passing zones, hampered my southeastward progress on Highway 100 toward Gray Summit. Consequently although I made it to I-44 ahead of the large hail, I was deep inside the heavy forward-flank precip. Traveling a steady 60mph east on I-44, I was not making any progress. Each time I flipped open the laptop to glance at the radar, the storm was actually gaining on my GPS marker with each new scan. I finally decided to stop the race and get ahead of the storm for some hail video, choosing Highway 141 south to Arnold where I stopped at a gas station to let the core pass over. Other than a few 1.5" stones, the hail was not very impressive.

At this stage, the expedition was over. I knew that with the storm speeds that I'd never be able to catch up again, so I called it a day and headed back home.

Other observer reports from this day:

Hey Dan, I'm the guy you met in the Cadillac when you shot the hail pics. Nice Job!
- Posted by Bill from Jefferson City
Hi Bill, thanks for the note!
- Posted by Dan R. from New Baden, IL
Thank goodness the Easter bunny didn't take out any glass :)
- Posted by Paul from Decatur, IL
Yeah - I kept thinking about how that would have really ruined the day! I didn't expect the hail to be that big.
- Posted by Dan R. from New Baden, IL
wow, you are getting some awesome weather there! glad you dodged those stones! getting nailed by those would be a buzzkill to say the least!
- Posted by Michael Thompson
Looks like you and I made the same play once the storm got into the St. Louis area. I tried to catch up to the storm on 94/364. After getting caught in blinding rain/wind in the trailing line I bailed on the storm in Maryland Heights and tried to catch the southern storm.
- Posted by Jeff Deason from Crystal City
These were definitely fast movers - WxWorx markers on the storm indicated 40mph, but I could not get ahead of the Gray Summit storm even while going 60-65mph on I-44. It was actually overtaking me - couldn't go faster than 65 due to the heavy rain.
- Posted by Dan R. from New Baden, IL
Wow is all I can say!
- Posted by Beau Dodson from Metropolis, IL
Wowza! I've never seen hail that big.
- Posted by Danielle from Wickliffe, KY
The birth of that storm was just to my west about 8 miles, about 17 miles south of Sedalia, MO. The storm tried to put down small finger funnels, but didn't go any further., just trucked to the ene really fast. Good back build on the storm when it was trying to put down. Small hook on radar at that time.
- Posted by Tom Eckhoff from Cole Camp, MO
Excellent writeup, Dan, and nice photos, too! Impressive hail - I'm glad that stayed north of my route on 94, though apparently not by much.
- Posted by John Farley from Edwardsville, IL
when I heard the news about the tornado hitting Lambert field in St Louis Missouri, my first thought that came to mind was your site and how you moved to Missouri and would probably be following it :)
- Posted by Jeremy
I'm surprised I didn't see you out there Dan. I was in the Big Spring hail storm as it was happening. I stopped going South after a few golf balls hit the car and went into town after it passed. Some of the stuff i measured was near 5 inches in diameter. I had a great view of the wall cloud as it passed over Hermann. I was at Cranes Store in Williamsburg as it passed by Fulton so I went after it from there. I stayed off I 70 like you did until I hit 19 and went South from there. It was a great chase on one mean storm. I went into Hermann for a bit and then headed back to Williamsburg. I didn't think I could keep up with it.
- Posted by Karl K. from Columbia MO area

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