2020-04-07 EVENT: IA/WI/IL/IN/MI

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Aug 18, 2018
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46
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Novi, MI
An early-season tornado/wind event could emerge in the Lower Great Lakes Tuesday afternoon and evening. A shortwave trough with an associated small low pressure system will move out of southwestern Canada into the Dakotas and eventually the Midwest. Increasing southerly flow behind an area of high pressure will begin northward advection of warmer, moist air on Monday and strengthen into Tuesday ahead of the low.

Ingredients don’t look the best for a tornado outbreak, but low LCLs, decent SRH (especially near the surface low), steep mid-level lapse rates, and a favorable CAPE/shear combo could lead to some supercells in the late afternoon/evening hours. Besides some modest backing of the wind in the low-levels, shear vectors straighten quickly with height, so a southeastward moving MCS/QLCS would probably take over by sunset with a high wind threat moving into southern Michigan and Indiana. The Euro and GFS have been advertising this scenario for a while now, but this afternoon they have finally come in line with each other, as the Euro was much farther south the last several runs.

Dews are progged to reach at least the low 60s into southern and even central Wisconsin during the afternoon increasing to the mid/upper 60s down into SE Iowa and central Illinois. The best shear will be up in Wisconsin/Michigan, but the boost in moisture/instability south of there may make up for that. The best tornado potential will probably emerge in NE Iowa and southern/maybe central Wisconsin.

Anyways, I’d expect storms to go up by late afternoon/early evening with linear storm mode along the cold front and a few supercells ahead of it. There is some capping evident that could be troublesome, but assuming we do get decent clearing behind early morning convection, daytime heating should be able to break it.
 
Aug 18, 2018
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Novi, MI
I’m very surprised the SPC hasn’t even acknowledged this event in their day 4 outlook. They’re discussing severe weather potentially beginning on Wednesday in the Mid-Atlantic, but quite frankly, Tuesday looks more organized than Wednesday.
 
Aug 18, 2018
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Novi, MI
The European model has been extremely consistent in producing a potentially high-end wind threat associated with a line of severe thunderstorms beginning in southern WI/northern IL and sweeping across the north half of IN, the southern half of Lower MI, and into western/northern OH. There are still capping concerns, primarily across IL and WI, but the fact the Euro has been so consistent with its solution makes me think the cap should break. Depending if these trends continue, I think an expansion of severe probabilities north/northwest and a potential upgrade seem likely.
 
Aug 18, 2018
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Novi, MI
I’d noticed that. Also of note is that the GFS initiates storms generally around the same time as the Euro. As NWS Chicago wrote, it kind of has a “loaded-gun” appearance. Whether or not the cap breaks will be the big ?
 
Jul 2, 2004
1,781
100
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Hastings, Michigan
www.stormhorn.com
Comparing the latest (12Z) NAM and 3km NAM runs and looking at sample fcst soundings across lower MI/northern IN, I see a few things mitigating against tornadoes in particular, at least in my neck of the woods. The NAM, of course, wants to cap off surface instability. The 3KM doesn't pose that problem, but it saturates the lower layer up to 850 mb, suggesting clouds, rain, and just all-around nastiness. That picture is, to me, bolstered in both models by the closeness of surface temperatures and dewpoints. The 0-3km CAPE is minimal. And, as Rob Dale was getting at (I think), the 3km NAM isn't popping anything promising on its forecast radar, nor, for that matter, is the NAM.

Admittedly, I haven't examined other models as closely. What I see right now suggests to me a cloudy, rainy day with forcing along the cold front. That's three days out, and maybe it'll change--not that it matters where I'm concerned. My car started acting up yesterday, and even if that weren't the case, I'm thinking twice these days before going anywhere.
 
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Aug 18, 2018
56
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Novi, MI
I’d agree. Wind appears to be the main threat associated with a linear complex along the front. Maybe some spin-ups in the line. Best potential for tornadoes would probably be in southern Wisconsin, where best low-level helicty will exist. However, even there it looks like a transition to wind pretty quickly.
 
Aug 18, 2018
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Novi, MI
Many of you have more experience than I do, but are there any models that have regular capping biases? The Euro/GFS/CMC show capping but not as much as the NAM, which has a very stout inversion, basically busting the entire event. The European has been so consistent in the last 48-72 hours that put is currently my model of choice for this event.
 
Aug 18, 2018
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Novi, MI
Looking at Euro ensembles, around 45/50 of them have temps into the mid 70s or higher near Chicago on Tuesday afternoon. This is compared to the NAM’s upper 60s (at best).

Alongside this, the NAM has an 850 mb temp near 20C (per the sounding) with those ground temps into the upper 60s. That seems unreasonably warm for ground temps that low, even with decent cloud cover (but with some sunshine definitely mixed in).

On the contrary, the Euro has mid to upper 70s with an 850mb temp of 12C. While it does exhibit a bit more sunshine, this seems much more reasonable than the NAM.

The GFS/CMC has temps in the low 70s with the ICON in the mid 70s, and all 3 still with 850 mb temps in a 12-13 C range. This seems like pretty good evidence the NAM is significantly over done in it’s capping.
 
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Reactions: Joey Prom
Aug 18, 2018
56
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Novi, MI
12z HRRR was showing some scary things across Lower Michigan tomorrow evening. But it’s definitely overdoing instability, likely a byproduct from too high dews. Anyways, I think mid-level ascent should be able to break the little cap there will be across Michigan.

Wisconsin and Illinois remain up for grabs. NWS Chicago is basically going 50/50 at this point.
 

Joey Prom

EF1
Feb 11, 2020
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23
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St. Paul, Minnesota
RAP models are the only ones showing the 60's dews getting that far north into MI. Both NAM and GFS confine the northern extent to N IN or extreme S MI. Also, the low level shear is very meh across much of the region. It is still very early for the HRRR, so I guess we wait and see, but the models had better start showing some more consistency, otherwise I guess we just pick our favorite model and hope its right... I do not envy the SPC right now...
 
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Reactions: Nick Dewhirst
Aug 18, 2018
56
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Novi, MI
I don’t think the upcoming Day 2 outlook is going to look anything like this morning’s. The HRRR will come back to its senses tomorrow, but the NAM has too strong of a cap. Probably something like the HRRR just not as tornadic is my bet. There has been some talk on Twitter of people considering to come up into Michigan to chase tomorrow evening.
 

rdale

EF5
Mar 1, 2004
7,213
773
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Lansing, MI
skywatch.org
Only @Ben Holcomb would be coming to Michigan to chase this :) I can't see why my state would be on the list for any chasing, let alone tornadoes. MAYBE southwest MI near the warm front, but that would be more of a response chase - not a focused point.

This looks like a muddy gray day with limited heating and limited CAPE. Maybe in early March this would have been more favorable?
 
Aug 18, 2018
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Novi, MI
The 18z HRRR is essentially the same as this morning. And there is a bit of support from the NWS. Detroit believes the warm front will win out, bringing temps well into the 60s, nearing 70 generally south of I-96 and west of I-275.

Dews still seem too high, but instability should be sufficient anyways. Definitely a big hail/wind risk with any storm that pops up with an isolated tornado threat near the front.
 
Jul 2, 2004
1,781
100
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Hastings, Michigan
www.stormhorn.com
I'm much more interested than at first, and I agree with you on that assessment. The latest NAM weakens CIN considerably, and other ingredients seem to be in place. Now I'm thinking, What's not to like, and maybe even be concerned about since HRRR wants to bring it right over my area. Maybe I'm guilty of a slight regional bias. :D (Particularly since my car is out of commission till I get it into the shop Wednesday.) At this point, I'll be watching to see how things shape up throughout the day and, from maybe 21Z on, depending, wishing my car wasn't out of whack.
 
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Reactions: Nick Dewhirst
Aug 18, 2018
56
46
6
Novi, MI
I’m in the exact same boat. I’m considering a chase should a threat evolve locally. I’m just NW of Detroit so it might be dark when storms roll in for me, but something around dusk would be really nice. Reed Timmer has been focusing attention on southern MI all day. The marginal risk really seems too low. At least a slight risk seems warranted.
 
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Reactions: Bob Hartig
Aug 18, 2018
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Novi, MI
The NAM/HRRR are actually in great agreement now. Both have nearly the exact same parameters in place. Based on where I live, I’m liking this🥳
 
Mar 3, 2012
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Hillsdale, MI
I can understand the SPC not wanting to oversell back to back reports in the same region. But they have upgraded to putting me almost right in the middle of the little 5% tornado bubble. Unfortunately it will probably be nighttime, like every other big day is around here lol. I'll definitely stay up for it and keep a close eye on it throughout the day.

Here, about 25 miles northeast of the Michigan/Indiana/Ohio border, it is currently still below 50, rain has mostly passed, still pretty gray but the sun just started trying to come through and the cloud cover isn't as thick.
 

rdale

EF5
Mar 1, 2004
7,213
773
21
50
Lansing, MI
skywatch.org
I'm feeling far more optimistic for today than I expected to a few days ago! With all convective models touching something up, and the HRRR still being the HRRR, there isn't much reason to doubt the threat of tornadoes this evening in the southern half of Michigan.

Nearly impossible chasing with storm motion (unless one starts in Grand Rapids and goes down I-96 :) ) but a worthy event still likely.
 
Aug 18, 2018
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Novi, MI
Per the GOES-16 satellite, clearing is already underway across northern IL/far southern WI/NW Indiana. Albeit there are still some higher level clouds that will move east out of Wisconsin into Lower Michigan, I’d expect most areas along/south of I-96 to have a good period of destabilization today. This will also aid in northward progression of the warm front, which is currently draped NW to SE across northeast IN and central OH.

MLCAPE values of 2000 J/kg should be realized across the slight risk alongside bulk shear of 50-60 kts. That’s a very favorable combo (I don‘t know where to find BRNs forecasted, but they’re probably in the 20s, which is very nice). Very steep mid-level lapse rates of up to -8.5 C/km will produce some very large hailstones, and 0-1 km SRH locally exceeds 200 m2/s2 in some locales in the 5% tornado probs.

Overall I think this threat has substantially increased in the last 18 hours or so, and the SPC is still talking about an upgrade to enhanced (seems likely).
 
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Reactions: Jamie G Cox
Mar 3, 2012
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Hillsdale, MI
Right on cue with the SPC, for mostly hail and wind apparently @Nick Dewhirst. Don't get large hail too often around my neck of the woods. Really wish the timing of the event was earlier. It feels like every single high/moderate/enhanced risk in
south central Michigan over the last decade, arrives after dark and fizzles out or becomes a mess by the time it arrives.
 
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Reactions: Nick Dewhirst
Aug 18, 2018
56
46
6
Novi, MI
I think the main thing helping this event is that storms will likely be firing NW of Grand Rapids and getting their strength together as they track southeast. I bet storms will be at peak intensity across far southern Lower Michigan. It‘ll probably transition to mainly wind in Ohio, but the fact that lapse rates are so steep in that EML plume will really aid the hail here. It’s not too often we get an EML this nice in Michigan *with* thunderstorm initiation.

I wouldn’t be surprised to hear of some 3” hailstones in localized spots this evening, along with the straight-line winds and isolated tornadoes.
 
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Reactions: Jamie G Cox
Mar 3, 2012
39
16
11
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Hillsdale, MI
Things really cleared up and warmed up fast in Hillsdale County, Michigan. Beautifully sunny and already 66. Looks like the temps are going to be a little higher than forecasted today.