Plainfield Tornado of August 28th 1990

[Greg Manarik]

A good writeup on the storm the spawned the Plainfield, Illinois tornado August 28th 1990 the strongest August tornado to ever hit the U.S.

http://www.nislwx.com/coverstory2.html

 

[Tim Vasquez]

18Z surface chart. Surprisingly evident is the lack of easterly flow... a good case for the use of hodographs.

 

[Greg Manarik]

Plainfield Tornado Event

With LI's past -12 and a strong NWLY jet overhead anything can happen.

 

[Robert Dewey]

Re: Plainfield Tornado Event

Originally posted by Greg Manarik
With LI's past -12 and a strong NWLY jet overhead anything can happen.

With the northwesterly jet aloft, winds at the SFC out of the SW would still produce 90 degrees of shear. Same thing goes for if you have a southwesterly flow aloft, and a southeasterly flow at the SFC.

 

[Gabe Garfield]

Originally posted by rdewey
With the northwesterly jet aloft, winds at the SFC out of the SW would still produce 90 degrees of shear. Same thing goes for if you have a southwesterly flow aloft, and a southeasterly flow at the SFC.

This is true...

As Tim V. mentioned, the most important thing is the hodograph created by such a wind profile in combination with the storm motion. Even with somewhat minimal turning, if the storm motion deviates significantly to the right, you can get quite a bit of storm relative helicity.

Gabe

 

[Dave Carroll]

Plainfield sounding

The one thing that sticks in my mind from Plainfield is the positively buoyant area on the soundings that fateful day...not only the LI, but the incredible scope & depth of the + area throughout the atmosphere. With a modest cap, and CAPE of 8000j/kg, no wonder things went ballistic that afternoon!

-DC

 

[GPhillips]

The sounding from 00Z from Peoria that day was extremely unstable, as stated nearly 8000 J/kg for surface parcel CAPE. However, the 100 mb mixed layer CAPE was probably more representative at 5500 J/kg. Still extremely unstable.

[Broken External Image]:http://members.cox.net/geophi/plainfield_PIA.png

 

[Nick Smith]

That severe thunderstorm watch text is strange...doesn't match the narrative style in use at the time. The one shown there looks like the style adopted in early 1997.

I'd love to see scope photos of that storm.

 

[Greg Manarik]

Watch

Nick youre right. I converted the watch data nws gave me on paper to the 1997 style because it is easier to read. Thats what I think.