10:00 AM FRI - Well, short range models might be signaling something for Saturday. Consistency could definitely be better run to run, model to model. In general; weak short wave will provide some upper level support. 12Z Hres-NAM was probably too fast/aggressive showing a late morning/noon strong cell in central WI + afternoon redevelopment south. Possible. There is a range of timing from NAM to GFS (slowest), if you take the mean it's centered on the afternoon. So in conclusion; I expect the short wave/surface low to move through during peak heating. Supported by most/all short range models.
Next question is t-storm severity?
The instability pool appears restricted with pockets of weak instability likely contaminated by morning rain and residual cloud cover. Wind shear overall on the weak side however GOOD in the lower 0-3km. The 12zNAM had an interesting 850mb jet streak pushing in during the PM hours (timing different with 06GFS) and if that could be paired with peak heating we may have something here. Trigger in the form of weak short wave + no capping.
Here's a sounding from the HresNAM.
12Z hres NAM shows GOOD veering with height, especially in the lowest 0-3km.
This signals a weak brief tornado threat. I expect numerous cells....but only a few capable of low-end severe weather. Isolated strong to severe cells within the STRONG zone.
Will be watching closely. The details such as timing & location may change - purposely not covering that - but the big picture is interesting.
10:00AM THU - Models this morning are weaker with the short wave energy. GFS "pulling back" energy, refocusing west in the days ahead. SATURDAY SPECIFICALLY... nothing that concerns me right now however there's still a chance this event will over perform it's 2-3 day forecast in terms of storm strength/intensity across southern WI/northern IL. Keeping an eye on it. Could be two rain/storm rounds across the zoned region.. morning. then afternoon redevelopment. The aft redevelopment would have the greatest potential for strong/svr storms. Parameters look weak but veered sounding + adequate instability could materialize (specifically within target area).
2:30PM WED - Timing and location of short wave will make a large difference. GFS and EC today were showing mostly an SAT PM passage. It wouldn't take much for things to come together so will be keeping an eye on this period. This opportunity for storms could blend into SAT AM or SUN AM periods too. I'm mainly watching the SAT PM hours right now.
9:55AM WED - Looks to be mostly centered on SAT now. Big differences on morning runs with EC look more aggressive. Will wait for rest of the 12z run today.
11:45 AM TUES - All hinges on timing and location of short wave. Just keeping an eye on it. 12GFS was interesting but probably too aggressive. 00EC was faster and less pronounced with the short wave. Typically when upper level support is there the rest of the event comes together as we get closer.
500mb jet streak per 12GFS. EC is different.
JP