Spring has finally sprung here in Northern Illinois. There is a threat for thunderstorms, some possibly severe for the next several days. Currently tomorrow [Wednesday] and Thursday look to hold the best chance for severe weather. I will probably head out for a chase at some point, but am currently torn. Despite the chance for severe weather, the pattern is summer-like and tornadoes don’t appear to be a big threat. They certainly can’t be ruled out though.
What we have is a quasi-stationary frontal boundary draped across the region, and much of the country in fact. This boundary wiggles and wobbles back and forth for days over the same areas. Waves of energy move along this boundary and fire off multiple rounds of thunderstorms. These thunderstorms play havoc with the atmosphere, making it difficult to determine where the best threat areas setup. Storms can move through one area too late in the morning, and choke off instability, or they can quickly depart and lay down a boundary that fires off new storms.
Taking a look at the Northern Illinois area for Wednesday the 2nd, I am at first not too impressed. A large area of unstable air will be in place, with dewpoints in the 60s and CAPE approaching 2000. This is good.
The bad though, as is typically the case with such patterns, is lacking shear, both speed and directional. There is no real forcing mechanism to spark storms, and even if a storm bubbles up on instability alone, the overall shear parameters aren’t all that great for tornadoes. A wind gust and some hail would be the main threats.
Now there is a potential saving grace, and its not an easy one either. Currently there is a line of storms taking shape out west where a severe thunderstorm watch just went up.
What can and sometimes does happen is these storms will thrive all night and move through the Northern Illinois area in the morning. These storms could potentially lay down an outflow boundary that can spark storms later in the day. In addition to that, shear can be enhanced along the boundary as well, adding to tornado potential. These kinds of scenarios are almost impossible to figure out even 12 hours before, and is something that has to be monitored the day of. If the storms move through too late, their associated cloud cover and subsidence [sinking air] behind them can ruin the chance for the entire day. This is why severe thunderstorm outlooks drastically change during setups like this.
So overall, the potential for severe weather isn’t that great in Northern Illinois without this boundary, but will need to be monitored.
A better chase target exists out west near the NE/IA/SD/MN border regions. Here better fronts, forcing and shear will serve as a better focal point for severe storm development, as well as tornadoes. The question is, which target to chose? Drive 9 hours west for the better play on paper, or hope the local magic can materialize and be heavily rewarded.
These decisions are never easy. Stay Tuned.