In short, my concern level is rather high for an event that is still 2 days away. The forecast models have been advertising a storm for the area for quite some time and we are starting to get close enough to where we can add some detail.
A consensus of the 00z/March 1 models takes a deepening surface low near Chicago, with a potentially moderately unstable and strongly sheared warm sector. Forecast soundings off the NAM are especially eye popping across much of the state and are very favorable for severe weather on Friday afternoon into Friday evening. Here is the 21z SREF significant tornado parameter, which shows an enhanced threat from southern Indiana southward.
Does this mean we can write off a threat farther north? Not at all. The SREF can be a great tool but one should always look into *why* it is showing what it is showing. I believe the main reason that it is not hitting a threat farther north is due to some uncertainty over the amount of instability. If adequate instability develops farther north, then higher probabilities should follow suit.
Although this is an early March event and temperatures/dewpoints are not quite as impressive, the CAPE/shear combination on the NAM is almost as impressive as what was seen during the Palm Sunday tornado outbreak of April 11, 1965. The upper trough configuration is similar and there are a few other similarities and also some important differences. This says nothing of the mesoscale environment, which will ultimately make or break this event, but the potential for a significant or major tornado outbreak is very real. There is a lot of room between a run-of-the-mill outbreak and a Palm Sunday type outbreak. Right now I would lean somewhere in between but things are subject to change between now and Friday.
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