andyhb

Tornado down, power flashes. This is bad.

St. Louis might be in trouble here. Rapidly organizing low level circulation moving right towards downtown.

Veered surface winds are the only thing that is having me question the exact ceiling re: tornado threat with this one. Otherwise, pretty much everything is primed.

Lansing getting hammered by the strongest part of that line right now.

Tornado just made a direct hit on Mayville WI, pop. >5000.

Tornado in progress near Juneau WI right now.

Those are some impressive obs across N/central IL right now. Lots of upper 80s temps/low 70s dewpoints with backed surface winds. Should moisture stay near that level, this could really change the game (in a bad way) for the Chicago area later.

00z HRRR gets way too warm down south, outflowy/hail-driven mess if that's the case. Still has a few supercells in Wisconsin. Edit: And shows what would likely be a major severe weather outbreak on Friday across the OV/Mid South.

The MPAS variants like this idea too. Given the environment, that cell would be a whopper and probably significantly tornadic.

Most of the high res guidance has this now.

Friday (5/16) should be added to this thread. Think it has more potential to become a widespread severe episode than Thursday, which may be a bit more localized pending moisture quality.

Friday could also be a problem for areas further south into the Ohio and Tennessee Valleys. Shortwaves with zonal flow down there can be quite prolific.

Synoptics here are pretty favorable for a significant event including almost all of the sub-forum. Big EML with steep lapse rates, plenty of moisture, a trough that looks to swing negative tilt at a pretty ideal time of the day, and the LLJ responding to that. Will need to watch out how much areas further south mix out especially since convection should probably hold off until later in the day. Could definitely see the Madison/MKE and Chicago areas get in on this, and perhaps N IN/S MI later on. The pre-frontal wind shift is very obvious on most guidance.

The 12z UK is a must check for shits and giggles for this region.

This is going to be a major event for the region.