For about a
7-8 days prior to April 9th, the models
suggested the
potential for severe weather in the northern Illinois area. From a forecaster's perspective, the potential for supercells and tornadoes was very muddy up through the late morning -- even early afternoon! -- of the event as the models were all over the place with their handling of precipitation and severe weather fields. Simply, confidence was low that we would experience tornadic storms by evening. By early afternoon,
visible satellite imagery did reveal a narrow window of clearing/surface heating would occur across the region as morning convection shifted east and, furthermore, that the warm front would remain anchored between I-88 and the IL/WI state line. This suggested that there would be a narrow window where instability would juxtapose with increasing shear due to the approaching trough, slow moving warm-front, and backing winds affiliated with the intensifying low. NWS LOT summarizes the severe weather setup nicely in this
graphic, with a more technical forecast provided in the
1630 SPC outlook. The big question by afternoon was whether you could get an isolated storm ahead of the cold front, which itself was causing a
HP-mess of severe convection in eastern Iowa. By mid-afternoon, I became confident enough to roll the dice west on I-88 from DeKalb ... heading to Dixon to hang out and work on some papers. As I sat in Dixon Aldi parking lot, I kept an eye on the radar; the first series of storms formed south of Dixon but never organized as they moved northeast. Then, another cell formed east of the Quad Cities, shifting north of Dixon and then south of Rockford. I actually followed this storm north of Dixon for a bit, but it was laminar and appeared to be sucking on cool outflow. I couldn't follow it northeast as I was cutoff by the Rock River and wanted to remain back west just in case there was new development, or if the Iowa stuff became the only game to play. Moreover, I had noticed that this previous storm, which eventually became tornado warned south of Rockford, had laid down a nice boundary along I-88. Hmmm ... I thought. Based on my observation, this was a critical feature (boundaries provide localized areas of enhanced low-level shear that can be critical for assisting with tornadogenesis) and was the reason why we ended up with a high-end event that evening. Soon, a new cell formed south of Dixon and appeared to split, producing a healthy right mover that got "that" shape just east of Dixon. The radar evolution is provided
here. I watched a nice updraft base south of Dixon, waiting patiently for the hail core to pass to my east before I jumped on I-88. Once I was on I-88 and scurrying around the south side of the storm, things ramped up
quickly ... the base produced a narrow but distinct lowering that eventually coalesced into a funnel and then tornado between Franklin Grove and Ashton. After calling 911 to report, I stopped a couple times along I-88 to snap a few pics (see Ashton area images below). I had to then push it east on
I-88 to I-39, then north, never losing visibility of what had grown into a large wedge northwest of Rochelle. As I moved north on I-39, I got closer to the beast, eventually jumping off at sr-64. At that point, I watched it cross the interstate. Then I played catch-up for the next 20-30 minutes as the relatively fast-moving storm traversed rural areas. Unfortunately, as we all know, it did hit the very small community of Fairdale, IL -- I was
several miles south as the town was hit. After witnessing a couple of satellites in the decaying light, I finally called it a chase north of Kirkland and drove home.
I participated in the storm survey the next day with the
National Weather Service, assessing damage northwest of Rochelle and in the town of Fairdale. As always in these post mortem surveys, it is humbling to see the damage up close, but such perspective helps us assess the intensity of the tornado, as well as provide evidence of what works and doesn't work in mitigation. I won't post my damage pictures in this blog -- instead, visit Stephen Strader's (NIU Ph.D. student and my advisee) wonderful account
here.
Below are my pics, as well as shaky video.
Just after formation, the tornado intensifies and strikes
Crest Foods in Ashton, IL.
Tornado with Ashton in the Foreground.
New perspective as I head north on I-39.
Exit 104 on I-39, looking north.
Backlit wedge with satellite (between wedge and tree) north of Kirkland
My video of the event -- note, I'm not a big videographer and it shows. Taking pictures and video at the same time usually means both are of degraded quality, I've learned.
