Paul’s Chase Blog/Evaluation of the April 9th Weather events

Tornado Ashton Illinois

I began my day at 4 AM, by evaluating the models and meteorological data for the upcoming day before I headed to my day job.  After the events in Kansas on the 8th, I knew that the main energy for this system hadn’t been released yet, so I was cautiously  optimistic about the parameters that models were giving us for Thursday afternoon.  I knew before I left for work that this would be a triple point(warm front and low pressure system with a slightly trailing cold front) setup for the afternoon, but the placement of the low pressure core would be key.

By around noon on Thursday, at my location in Muscatine, Iowa, the dew points and relative humidity had become noticeably higher, and temperatures had already started climbing to the 68° mark.  I knew at this point that I would be in a near perfect position when storms did finally start to break through the capping inversion(a warmer layer of air around 10,000ft-35,000ft up in the atmosphere). I ended up getting off of work around 2PM, and immediately headed home to take one last look at current conditions and arrange for my support team to meet up so we could get into position.

Courtesy of the IES website

Courtesy of the IES website

Storms started to fire around southern Iowa along the I-35 corridor at around 12PM, and quickly showed signs that they would be in favorable conditions for severe weather, as they produced 1.25″ hail reports almost as soon as they formed(See above Animation).  We positioned ourselves to meet this set of cells as they crossed highway 218.  Our first sighting of the tornadic cell that formed near Washington, IA happened to be near Conesville, Iowa as the cell was recycling.  We viewed a wall cloud forming over the Nichols, Iowa area from just East of the cell, which was quickly pulled into the core of the cell.  This cell would become tornado warned again as it crossed I-80 just north of Durant, which stayed on the ground to just SW of DeWitt.  We were on this cell for the entirety of this cycle, but were unable to view the tornado, as it was rain wrapped for most of it’s life cycle.  (See Video link here: https://youtu.be/H33uuS3Jj74 ) This same cell went on to produce another tornado just to the East of DeWitt,Iowa to near Fulton, Illinois, which Brennan Jontz and Daniel Auel were able to see.  My team had already decided to move off to the East of this cell, as the road network was better, and the current  cell was becoming a high precipitation supercell with little visibility.

 

This decision ended up being a very good one.  We went NE on Interstate 88 in Illinois toward a boundary that had been left by storms earlier in the day, where we could see that temperatures had rebounded to near 75°, and  dew points were quickly rising into the mid 60’s.  As we arrived just West of Dixon, Illinois, we saw a cumulonimbus tower going up just to our south.  There was some very strong counter-clockwise rotation in the mid-levels of the atmosphere near the rain-free base of the cell.

This still shows the cell that eventually formed the large wedge tornado,  as it was just starting to develop a wall cloud.  Within 2 minutes, a funnel had formed and was a tornado less than 3 minutes later near Franklin Groove, Illinois.

This still shows the cell that eventually formed the large wedge tornado, as it was just starting to develop a wall cloud. Within 2 minutes, a funnel had formed and was a tornado less than 3 minutes later near Franklin Grove, Illinois.

This rotation formed a wall cloud within 1 minute, and quickly started moving off to the NNE.  We exited the Interstate at the Dixon exit and headed east on HWY 38.  As we came over a hill just to the west of Franklin Grove, Illinois, we saw the funnel touch down and become a tornado. I took video of this, but it was out of focus because it was shot while moving toward the storm.  We observed a small damage path just to the eastern side of Franklin Grove, but it was very small and didn’t create much damage.  We stopped our vehicle between Franklin Grove and Ashton and took some video and stills as the tornado entered it’s stovepipe phase.

This photo shows the transition from drillbit to stovepipe phases of the tornado, along with the strong Rear-Flank Downdraft Cut that formed on the SW edge of the cell.

This photo shows the transition from drillbit to stovepipe phase transition of the tornado, along with the strong Rear-Flank Downdraft Cut that formed on the SW edge of the cell.

The tornado in it's stovepipe phase near Ashton, Illinois just before it transitioned into a wedge.

The tornado in it’s stovepipe phase near Ashton, Illinois just before it transitioned into a wedge.

Just 4 minutes after the tornado had formed, it quickly had grown in to a wedge form, with collar cloud.

This capture was taken just to the NW of looking toward the area of Flagg Center. Illinois.

This capture was taken just to the NW of looking toward the area of Flagg Center. Illinois.

This happened just to the NW of Ashton, and continued off to the NNE toward the SE side of Rockford.  We called off our chase due to downed power lines and trees near Flagg Center, Illinois

Some tree damage just before we came across a large damage swath just outside of Flagg Center, Illinois.

Some tree damage just before we came across a large damage swath just outside of Flagg Center, Illinois.

At this point, we transitioned to see if we could help any of the affected households or Emergency Services.  Since there were still strong storms in the area, we transitioned to a stationary location just north of Flagg Center to observe and report any weather that could affect search and rescue operations that were ongoing.

a look over the damage path area as another storm rolled in around dusk.  It is possible that the feature in the center of the photo just left of the telephone pole is a briefly lived funnel cloud.

a look over the damage path area as another storm rolled in around dusk. It is possible that the feature in the center of the photo just left of the telephone pole is a briefly lived funnel cloud.

 

The one thing about the Illinois cell that sticks in my mind as I review Thursday’s events is just how quickly the cell went from nothing, to a wedge tornado.  I have reviewed the time-stamps on all of my video and photos, and the elapsed time from the formation of the wall cloud to the time that it transitioned to a 1/2 mile wide tornado was less than 15 minutes.  The wall cloud formed at 6:28 PM and by 6:43 PM, it was a large, damaging tornado tearing off to the NNE at 45-60MPH.

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