This day started off like alot of severe weather days around here...we had convection fire in northern IA in the early morning hours around 12z and develop into a nice storm complex as it headed into southern WI and northern IL but began to weaken as the LLJ faded and mid-level temps warmed. Although the convection died off, we still had clouds leftover to deal with before we began to destablize later in the afternoon. And just an FYI, there aren't any sfc maps from this day...only go back to 1998 on Plymouth's site which is kind of a buzzkill.
14z satellite image
Around 15z or so we began to slowly clear the clouds and have the almost June sun doe its job in heating up the atmosphere and it didn't take long before we had some real progress going on.
18z satellite image
We continued to destablize and by 20z, we got our first hint of DMC in central/eastern IA with a very strong mid-level jet pushing eastward and into the area creating more than enough, and actually quite alot of shear for supercells later in the day.
Quite the jet for late May...a 65kt weserly H5 jet at 0z that evening
Here is the 700mb chart, decided to contour some of the H7 temps to show you the thermal ridge/EML and also put the main jet over the area. H7 temps of 8 degrees C in the area were good until to hold off convection till just the right time in the afternoon.
Storms very going up like crazy in central/eastern IA that eventally pushed into WI/IL by late afternoon and looked very healthy on radar with a tornado watch already issued for that area with a new one likely further east.
As these storms pushed further eastward into IL, more storms fired further to the east along the WI/IL border and with the strong mid-level jet overhead and strengthening 30-40kt LLJ near 0z, the environment became very favorable for supercells and tornadoes as low-level shear increased and created curved and looping hodographs. Also, DVN and ILX both had 35kts at 925mb on the 0z raob soundings, very impressive.
By around 23:30z we had our first legit supercell near Woodstock, IL with a strong meso but there wasn't a tornado reported with this storm, even though it was very impressive for awhile. At the same time, we had the second supercell and associated meso beginning to get going further east.
Here is the VAD wind profile from KLOT at around the time of that image to an hour or so before it. This is exhibiting a veering signature near the boundary layer with increasing slightly veering winds through 3km. We had 0-3km helicity values of 420 m2/s2.
About 30 mins later or so the 2nd supercell to the east become dominant and really took off as the LLJ continued to strengthen and the low-level rotation beginning to really increase as it approached to town of Lindenhurst. This is about at the time right after the tornado dropped just west of town
This tornado went on to produce F2 damage in Lindenhurst.
zoomed out radar image at about the time of the tornado and you can see the red box across the area.
I will continue to do other discussions/write-ups on other northern IL tornado events from the mid-late 90's up to around 2005.
Matt
