5/15 severe wx

[largetornado]

Starting a thread on this as the parameter space is fairly impressive with cape values exceeding 3500. looks like there will be an EML present which should keep convection limited and the 500-850 crossovers are favorable for discrete. 

[CheeselandSkies]

Would really need to see the timing of the system slow down (by just about 3 hours) compared to recent GFS solutions to maximize the severe threat in Wisconsin/Illinois Thursday afternoon. Today's SPC outlook notes that is in fact a bias with the model, but it continues to hold consistent with that through the current (06Z) run.

[Stebo]

I am fine with the GFS speed, IL doesn't need to get everything lol.

[A-L-E-K]

this is michigan's moment 

[Stebo]

7 minutes ago, A-L-E-K said:

this is michigan's moment 

Timing on Euro is actually similar, the only thing I don't like is that it could extend into the night time. Don't need night time tornadoes.

[CheeselandSkies]

12Z NAM came in pretty spicy. Again, there are some pattern fundamentals that suggest this one has a better chance of verifying a threat than 4/28, namely a pronounced negative tilt and a potent LLJ with a more southerly component. Still some details yet to iron out which held SPC back from pulling the trigger on a 30% zone.

[sbnwx85]

Sounding just west of South Bend for Thursday evening... Is this worse than posting a 3 foot snow map four days out? 

[andyhb]

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.

[CheeselandSkies]

3 hours ago, andyhb said:

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.

Been hoping you would chime in here and/or TW.

[largetornado]

Pretty solid EML showing in the NAM. Holographs are a little wonky (especially eastern fringe of risk area) but if the cap breaks, I could see a moderate risk level ceiling but that is a stout EML for this area. Large destructive hail is definitely in the cards though for anything that develops. LCLS are a tad high as well

[andyhb]

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.

[CheeselandSkies]

Initial Day 3 outlook was surprisingly underwhelming. Gun-shy after the one they put out for April 28? But this setup looks a lot more concerning simply from a trough geometry standpoint.

[Chicago Storm]

Initial Day 3 outlook was surprisingly underwhelming. Gun-shy after the one they put out for April 28? But this setup looks a lot more concerning simply from a trough geometry standpoint.

or it could be just because it just doesn’t look all that great and they actually realize it this time.

[CheeselandSkies]

27 minutes ago, Chicago Storm said:

or it could be just because it just doesn’t look all that great and they actually realize it this time.

What doesn't look great about it to you? There are some potential failure modes to be sure but I think it checks a lot more boxes than that day did.

*Edit Annnnnd 12Z 3K NAM coming in hot (unlike any of the CAMs at this range for 4/28). Unusual for this model to resolve semi-discrete convection like this. These simulated cells are moving through a strongly unstable and sheared environment. The solution verbatim would also resolve a lot of the timing issues that have been shown on the coarser models (especially the GFS).
 

[Malacka11]

Ig it's something to be able to roll the die during the day for once instead of at 11:30 p.m. but LOT doesn't exactly sound thrilled yet either. Between that and our old pal Chitown Storm, my hopes will remain tempered. Such is the life of a weather fan that relies essentially excusively on the word of others 

[andyhb]

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.

[Chicago Storm]

4 hours ago, CheeselandSkies said:

What doesn't look great about it to you? There are some potential failure modes to be sure but I think it checks a lot more boxes than that day did.

*Edit Annnnnd 12Z 3K NAM coming in hot (unlike any of the CAMs at this range for 4/28). Unusual for this model to resolve semi-discrete convection like this. These simulated cells are moving through a strongly unstable and sheared environment. The solution verbatim would also resolve a lot of the timing issues that have been shown on the coarser models (especially the GFS).

But, it really doesn't check more boxes, in a way. Capping, lack of frontal convergence (roughly south of the IL/WI border latitude), and the fact that the best dynamics are lifting further north into the Midwest/Western Great Lakes, are all significant concerns. The SPC overlooked concerns with that previous event and went with a balls to the wall approach...and failed. There is zero reason to do that once again this time across areas that are clearly more conditional.

Highest coverage of activity will most definitely be across MN/NE IA/WI, though I think quality will be a bit more in question there. South of there, it's really too conditional overall. S Wisconsin may have the greatest shot of the most interesting activity, as there may be a more optimal overlap of everything there. South of there, sure, the environment is great across IL, but the three aforementioned issues will be problematic.

[Chicago Storm]

To add the the above, if the Euro, which is sort of alone in with the idea right now, has any clue... Things could be more interesting southward.

Check out the significant dry line/bulge it depicts pressing across N and C IL. If frontal convergence can tighten up a bit more, and if that scenario were to be more realistic and gain support, then...

[CheeselandSkies]

8 minutes ago, Chicago Storm said:

But, it really doesn't check more boxes, in a way. Capping, lack of frontal convergence (roughly south of the IL/WI border latitude), and the fact that the best dynamics are lifting further north into the Midwest/Western Great Lakes, are all significant concerns. The SPC overlooked concerns with that previous event and went with a balls to the wall approach...and failed. There is zero reason to do that once again this time across areas that are clearly more conditional.

Highest coverage of activity will most definitely be across MN/NE IA/WI, though I think quality will be a bit more in question there. South of there, it's really too conditional overall. S Wisconsin may have the greatest shot of the most interesting activity, as there may be a more optimal overlap of everything there. South of there, sure, the environment is great across IL, but the three aforementioned issues will be problematic.

Fair. I agree S. WI looks like the most favorable area and that happens to be my backyard. I prefer to stay local on a work day and although the terrain isn't great, there are workable spots and I'm familiar with where they are. As long as the best storm(s) don't track through the Driftless area (especially Sauk/Vernon/Crawford/Richland Counties, which are pretty much all solidly tree-covered steep hills/ridgelines, river valleys and winding roads that seldom lead directly from anywhere to anywhere).

...and I wasn't necessarily calling for a balls to the wall approach from SPC. However I think a 30%/Enh with an all-hazards hatched area would have been warranted.

Anyway, looks like they're doing that now with the new Day 3 update. Further north than I would have liked to see, but the hatching does extend throughout the rest of S. WI and into IL/IN.
 

[CheeselandSkies]

Notable slowdown of the system across 18Z hi-res guidance. One of my main concerns with previous runs of models such as the GFS was their wanting to sweep the cold front practically all the way to Lake Michigan by 21Z (4 PM) Thursday (if nothing else, for the simple fact of giving me enough time to get on a storm after getting off work at 1 PM). SPC noted in their Day 4 outlook yesterday that it was possibly exhibiting its fast bias, and so far things would indeed seem to be trending in that direction.

As noted there are concerns with dry EML and mixing for Thursday; however, the difference in CAM initiation at this range between that and April 28 is quite stark. 3K NAM, MPAS and RRFS all develop discrete convection with pronounced UH swaths.

Very bizarre seeing that be the main failure mode; around here 99 times out of 100 it'll be excessive early convection working over the atmosphere and preventing destabilization.

[largetornado]

0z HRRR struggles to initiate any convection. 

[HillsdaleMIWeather]

Large Enhanced now, but with the caveat of the event either being boom or bust 

[Harry Perry]

Yeah, kinda looks like good bust potential here.
 

If the 12z HRRR comes to fruition, and there is little/no storm action off to the southwest allowing decent venting/tapping warm moist air riding along the tail of trailing convection, there could be a monster sup somewhere in the area. 
 

Big IF. But the potential is there. 
 

[A-L-E-K]

looks like timing and initiation location could deliver a photogenic setup here even with a miss

[andyhb]

22 hours ago, Chicago Storm said:

To add the the above, if the Euro, which is sort of alone in with the idea right now, has any clue... Things could be more interesting southward.

Check out the significant dry line/bulge it depicts pressing across N and C IL. If frontal convergence can tighten up a bit more, and if that scenario were to be more realistic and gain support, then...

Most of the high res guidance has this now.

[sbnwx85]

Going to be a real bummer if we can’t tap into the volatile atmosphere tomorrow. 50/50 shot in S MI/N IN.

[A-L-E-K]

long track tail end sup for n indiana on the 18z hrrr

[andyhb]

14 minutes ago, A-L-E-K said:

long track tail end sup for n indiana on the 18z hrrr

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

[sbnwx85]

20 minutes ago, A-L-E-K said:

long track tail end sup for n indiana on the 18z hrrr

This is my moment. rdy 2 b slabbed.

[largetornado]

Makes sense. Some of the parameters look like a pseudo triple point. Last night I was really liking n Indiana. Cool to see models supporting that idea