LATE SEASON STORMS....
Late August is not known for its severe weather outbreaks. Compared to spring and early summer the dynamics are often weak despite days with ample instability. However, there are times when the ingredients come together and Friday has some potential to be one of those days.
The threat revolves around an evolving pattern that brings heat, humidity, and occasional thunderstorm complexes (MCS's) to the central Midwest. The first round of storms arrives Thursday night. This complex is not expected to bring severe weather but it could bring pockets of moderate to heavy rain, especially where the strongest updrafts are focused.
Simulated radar off the NAM late Thursday night:
Things get more interesting and far more complex Friday as the remnants of Thursday night's storms become a player in Friday afternoon's severe weather potential. One key element that will make or break the event is how fast lingering morning convection departs.
Most models depict clouds breaking (to some degree) soon enough for instability to re-build. Severe storms will be contingent on the amount of clearing and instability that's realized ahead of an advancing trough.
If CAPE (convective available potential energy) reaches even moderate levels deep layer shear will be more than sufficient for supercell development. That said, all modes of severe weather would be possible. The GFS has this for supercell parameters friday.
The GFS has this for CAPE Friday evening.
Then there's the issue of the cap. Even if there's sufficient instability, warm air aloft on some models is shown suppressing updrafts. It's like a can of pop. Shake it up and you know it's going to blow when you pop the top. Keep the lid on and nothing happens...the potential is never realized. Same thing with the atmosphere. You build the cap, you need something to break it or storms are a no show.
At this point there are enough parameters in play to create severe weather but the two elements of instability and capping will need to be overcome.
Beyond Friday, the upper level flow turns zonal as a heat dome nudges into southern Minnesota.
On the northern edge of the heat (a region known as the ring of fire) there will be a threat for nocturnal storm complexes across the central and upper Midwest. How far south these get is difficult to say as outflow boundaries from any convection that does develop comes into play. Between storms, warm humid conditions will dominate the pattern
Short term, another fine day is expected Thursday before the action picks up Thursday night. The calm before the storms. Roll weather...TS
