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Severe Threat May 15-16, 2025

Certainly is concerning to see HRRR, NAM3k and RRFS all favoring clusters of discrete and semi-discrete cells developing through the MS and OH river valleys tomorrow afternoon/evening.

The synoptic pattern becomes pretty impressive between 21-00z with a slightly negatively tilted shortwave emerging out of the area of westerly flow that brings today's severe weather. While the broader trough is moving pretty slowly, the speed max which ejects out of Oklahoma 12z tomorrow and ends up in C IL as pictured below by 00z is moving roughly 50kts, above the 40kt threshold from OMEGA. So that's interesting.

1747304791961.png

Your aren't really going to get much more zonal than that with the trough not being overly amplified though is close enough to the warm sector to provide broad synoptic scale lift. In theory this would support (semi) discrete supercells for at least a time, and there are a couple events which produced significant outbreaks with a similar trough geometry to this.

That being said models display somewhat of a boundary representing the deep moisture. Not quite a warm front imo given there is no thermal change or wind shift, but some sort of boundary nonetheless. Where we get to get storm development along this boundary - parallel to the mid level flow, it's not hard to see a derecho/or MCS become the primary storm mode. Though even if this does occur I'm sure a mixed mode would be possible, at least early on.

1747305201372.png

Now if any sustained discrete supercell can mature in the warm sector, that will undoubtedly cause trouble.

1747305374119.png

Forecast profiles from almost all models suggest a very favorable environment for strong/intense tornadoes - even as early as 19/20z, which is less common this time of year when you typically rely on the nocturnally increasing LLJ.

I don't want to run in guns blazing like I did for the last setup (and we know how that turned out haha) but certainly the ingredients are there for a significant, higher end tornado event tomorrow. The question is to what extent do they come together?
 
All right, I hate to do the "what about this specific location bit", but what time can south central Michigan expect storms today and what seems to be the most likely storm mode(s) and outcome?

Incidentally, sure would be nice if it stopped raining in Pennsylvania. I can't figure out any way to dry my boot leather short of starting a fire.
 
View attachment 41576
Yeah seems very well forecasted so far. Nothing that sticks out too much in disagreement honestly. Could maybe see a small moderate around southern Illinois pushing into a small portion of western Kentucky.
IMG_9407.jpeg

I think the area where I drew the white circle is where I would think the moderate would be issued.
 
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Certainly is concerning to see HRRR, NAM3k and RRFS all favoring clusters of discrete and semi-discrete cells developing through the MS and OH river valleys tomorrow afternoon/evening.

The synoptic pattern becomes pretty impressive between 21-00z with a slightly negatively tilted shortwave emerging out of the area of westerly flow that brings today's severe weather. While the broader trough is moving pretty slowly, the speed max which ejects out of Oklahoma 12z tomorrow and ends up in C IL as pictured below by 00z is moving roughly 50kts, above the 40kt threshold from OMEGA. So that's interesting.

View attachment 41572

Your aren't really going to get much more zonal than that with the trough not being overly amplified though is close enough to the warm sector to provide broad synoptic scale lift. In theory this would support (semi) discrete supercells for at least a time, and there are a couple events which produced significant outbreaks with a similar trough geometry to this.

That being said models display somewhat of a boundary representing the deep moisture. Not quite a warm front imo given there is no thermal change or wind shift, but some sort of boundary nonetheless. Where we get to get storm development along this boundary - parallel to the mid level flow, it's not hard to see a derecho/or MCS become the primary storm mode. Though even if this does occur I'm sure a mixed mode would be possible, at least early on.

View attachment 41573

Now if any sustained discrete supercell can mature in the warm sector, that will undoubtedly cause trouble.

View attachment 41574

Forecast profiles from almost all models suggest a very favorable environment for strong/intense tornadoes - even as early as 19/20z, which is less common this time of year when you typically rely on the nocturnally increasing LLJ.

I don't want to run in guns blazing like I did for the last setup (and we know how that turned out haha) but certainly the ingredients are there for a significant, higher end tornado event tomorrow. The question is to what extent do they come together?
There is the discussion I’ve been waiting for! @UK_EF4 . Appreciate
 
All right, I hate to do the "what about this specific location bit", but what time can south central Michigan expect storms today and what seems to be the most likely storm mode(s) and outcome?

Incidentally, sure would be nice if it stopped raining in Pennsylvania. I can't figure out any way to dry my boot leather short of starting a fire.
If you're talking just south of Grand Rapids, sometime between 9 PM - 11 PM. At this point, expecting a line of storms to cross Lake Michigan in linear form. Threats would be damaging winds, (isolated 75+ MPH), large hail (isolated 2 inch+), and embedded tornadoes. Although of the three, I wouldn't be too nervous about the tornado part since this will be a linear structure.
 
Getting quite nervous here in downtown Chicago. NAM has been very persistent with at least 1-2 tornadic supercells raking part of the metro.

If I get something, I'll have a nice video for you all. I live in a 40 story high rise with unobstructed north, south and southwest/northwest views.

On the plus side, we're progged to get close to 4000 surface CAPE. Not sure I've ever experienced a value that high.
 
I don’t think a high will be issued, but I do believe a big moderate will be issued. But we will see.
Yea, I don't think they'll go with a HIGH. Everything was in place for both the March 15 and April 2 high risks; that doesn't seem to be the case here. I haven't been on since last night, are they still uncertain anything will happen in the ENH?
 
Yea, I don't think they'll go with a HIGH. Everything was in place for both the March 15 and April 2 high risks; that doesn't seem to be the case here. I haven't been on since last night, are they still uncertain anything will happen with either ENH?
April 2nd was a very surprising high risk upgrade to a lot of us, including me - I most certainly did not agree with it, but I stood corrected watching that day unfold. The reason they did it was because the SPC has access to a lot of things we do not and the tools they had pointed to a higher end solution than the regular CAM models like the HRRR and NAM were pointing to that day.

Whatever the SPC does is based on a lot more than what we have access to, for the most part.
 
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