The nation is gearing up for its first potential widespread severe weather event to take shape on Tuesday the 29th. As such, I am preparing for an early season chase. A quick look at SPC shows a very large risk for severe thunderstorms, especially across the lower MS river valley where a moderate risk is in place.
What we have going on is very strong, unseasonable moisture advection taking place. Already surface obs show dewpoints well above even the average temperatures.
This is forecast to only strengthen overnight, with all models in agreement of dewpoints in the upper 50s reaching as far north as Chicago, with 60s dewpoints further south across IL and into the lower MS valley. A deep trough with seasonably strong shear is forecast to plow through beginning early Tuesday, setting the stage for explosive thunderstorm development. These storms are expected to form in a SW to NE oriented line from roughly Quincy, IL down through Joplin, MO and even further.
These storms will have plenty of bulk shear (top left) to work with, which usually isn’t a problem this time of year, at least when it comes to speed shear. Directional shear and instability are often what lacks these early season setups and indeed they are forecast to be less than stellar. Cape values generally under 1000 (top right) which typically wouldn’t favor widespread severe weather. Still though, in early January speed shear can more than compensate for that as long as the moisture is in place, which it is. In spite of some limiting factors, storms will have plenty of helicity (the airs ability to rotate) to work with as shown in the chart below (bottom.) Values of 200 in this case would be more than enough to promote updraft rotation.
Directional shear is only modest in the lower levels, A quick glance at the crossovers show at least some veering with height between the low levels (red line) and the mid levels (blue line.) With such a low cape, high shear environment storms will probably be fairly low topped, so turning in the lowest levels is what counts here. Overall forcing and orientation of the fronts promote linear development along the front, but it is not out of the question a few isolated storms could get going ahead of that.
Overall the ingredients for an early season severe weather outbreak appear lined up. Storms will begin early Tuesday across parts of Kansas, Oklahoma and Missouri and begin marching eastward, reaching western Illinois and Arkansas by early afternoon or evening. As the jet strengthens even further Tuesday night as storms reach Eastern Arkansas and Mississippi, the greatest tornado potential should be realized. This looks to be especially concerning given the fact it will be dark. The Moderate risk seems warranted here and folks in this area need to pay particular attention.
For chasing, that is not an ideal setup. I plan to gamble on a potential rare event further north into Illinois. As such I am zeroing in on an area from around Quincy to Springfield. While climatology is working against me, I have spent many hours studying those rare events we do get in the month of January, and every single parameter that existed on those days, exists tomorrow.
Stay tuned for more updates!