IAP 12.310
January 2008
Significant U.S. Weather Events
Mid-west Tornadoes Jan (7-8, 2008)
(AP Photo -- New Munster, WI)
It hasn't happened in over 60 years, but there were
tornadoes in Northern Illinois Monday evening. This proves that it
doesn't matter what the calendar says, but if the ingredients are
there, tornadoes can appear.
The tornadoes were not limited to Illinois, but they
were also spotted in Wisconsin, Arkansas, Tennessee, Missouri,
Oklahoma and possibly others.
(A huge side note: radar images, in general are
directly incapable of spotting tornadoes. The resolution of
the Doppler radars are roughly a kilometer. Tornadoes
generally are not that big -- that would mean a tornado that
stretched farther than from the Green Building over onto the other
side of the Mass Ave. bridge. They are typically 100m wide,
well below the resolution size. However, tornadoes usually
occur in the presence of mesocyclones (upper air rotations that are
more than a kilometer wide). This can be detected by
radars by looking at the radial velocities.)
What were the background conditions that helped
spawn these tornadoes? In short, the record warmth.
While the northern half of the country was still in "winter" mode,
the eastern half had warm temperatures as shown below:
Now look at the radar image around this time:
