2015-04-09 EVENT: IA/IL/MO/AR/MI/WI

[Robert Forry]

The warm front continues its trek northward, setting up north of Lansing tonight. HRRR has plenty of pretty winds aloft. All this happened during the day I'd be highly enthusiastic - at night in April is still a reasonable chase hope.

Agreed, Rob. That WF is sure taking it's time making it's way this way.

I was thinking an early show near that low out in SE IA today, but that don't look like that's going to happen. Glad I chose to stay close to home for a play later.

 

[John Farley]

Looks to me like decent potential anywhere between about St. Louis and the Quad Cities. Perhaps a little better instability south, a little better shear north. Definitely looking from this morning's model runs like the best area will be somewhat south of what it looked like last night. For those of you singing the blues about SPC, note they are now 10% hatched for tornadoes, which I think pretty much matches what this morning's model runs are showing. If I still lived in the STL area I would be out on this one for sure, probably starting somewhere around the Springfield/Lincoln/Peoria corridor and adjusting from there.

 

[Jeff Duda]

Going to be a negative Nancy here.

I think, like yesterday, this event is going to underperform. I'm surprised to see the addition of the 10% hatched tornado threat to the 1630 UTC convective outlook.

The one thing that is going great for this setup is low-level shear - there is gobs of it in a widespread area, and it is pretty intense. Experience tells me that even in the absence of other favorable conditions, strong low-level shear can still result in numerous tornadoes.

Now for the negatives.

-Deep layer shear: surprisingly weak given the flow magnitude. This is the result of a largely unidirectional wind profile, however. I don't see much indication that this will improve much throughout the day either. It's going to be a little harder to get tornadoes if the storm mode ends up being linear (outflowy).
-Insolation: just like yesterday, there is an awful amount of cloudiness over much of the warm sector. Visible satellite is showing that the clear area between the dryline/cold front and some early elevated convection now east of the Mississippi River is rapidly filling in with what appears to be low stratus. Cloud height obs from MO suggest some of these are higher, but some areas are really socked in. There are a few bands of clearing, but they don't look to remain over any one area too long. This will limit the degree of destabilization and keep CAPE down. The good news about this is that convective temps on the ILX and SGF soundings from this morning were only in the upper 70s to around 80, and it looks like many locations are going to get either really close to that or exceed it with even a little bit of heating. However, I'm not sure convective temps will remain that low because...
-The thermal axis at 700 mb is colocated with the surface dryline/cold front and is still well west of the areas highlighted as being in the higher probabilities for severe weather. While the temperatures in that ridge are not overly warm, the 12Z TOP sounding, located right in it, had a convective temperature of 84. I'm not sure areas of MO/IL/SE IA are going to get quite that warm. So the mid-level CAA isn't going to help with any capping that occurs today. 850 mb temperatures are generally 13-15 C, but that doesn't sound too particularly bad.

I think if there's an area that gets lucky with enough clearing to warm to 80 or more, there could be something interesting there, but I think this is going to be a messy event and probably difficult to chase for many. With the unidirectional shear profile, storm speeds aren't going to be the most friendly either. I think the best chances, though, are indeed in SE IA/far NE MO and into WC IL where the deep layer shear is marginally better and current instability looks to be a little higher (also closer to the triple point). Unfortunately it's also one of the cloudiest areas right now, too.

Last thing: I don't think the threat will make it as far north as Cedar Rapids. Looking at the IEM Time Machine (http://mesonet.agron.iastate.edu/timemachine/#1.201504091700), it's interesting to watch the KCID ob over the last few hours. It goes from saturated in the upper 40s with an east wind around sunrise followed by a rapid warming/moistening and veering of the winds to SEly by 11 AM, but then the wind flips back around to due N and the T/Td drops from 61/60 to 55/55 at noon, suggesting the boundary had moved back south. Keep an eye on the Iowa City ob to see if it does something similar soon.

 

[Caleb Grunzke]

Going to be a negative Nancy here.

I think, like yesterday, this event is going to underperform. I'm surprised to see the addition of the 10% hatched tornado threat to the 1630 UTC convective outlook.

The one thing that is going great for this setup is low-level shear - there is gobs of it in a widespread area, and it is pretty intense. Experience tells me that even in the absence of other favorable conditions, strong low-level shear can still result in numerous tornadoes.

Now for the negatives.

-Deep layer shear: surprisingly weak given the flow magnitude. This is the result of a largely unidirectional wind profile, however. I don't see much indication that this will improve much throughout the day either. It's going to be a little harder to get tornadoes if the storm mode ends up being linear (outflowy).
-Insolation: just like yesterday, there is an awful amount of cloudiness over much of the warm sector. Visible satellite is showing that the clear area between the dryline/cold front and some early elevated convection now east of the Mississippi River is rapidly filling in with what appears to be low stratus. Cloud height obs from MO suggest some of these are higher, but some areas are really socked in. There are a few bands of clearing, but they don't look to remain over any one area too long. This will limit the degree of destabilization and keep CAPE down. The good news about this is that convective temps on the ILX and SGF soundings from this morning were only in the upper 70s to around 80, and it looks like many locations are going to get either really close to that or exceed it with even a little bit of heating. However, I'm not sure convective temps will remain that low because...
-The thermal axis at 700 mb is colocated with the surface dryline/cold front and is still well west of the areas highlighted as being in the higher probabilities for severe weather. While the temperatures in that ridge are not overly warm, the 12Z TOP sounding, located right in it, had a convective temperature of 84. I'm not sure areas of MO/IL/SE IA are going to get quite that warm. So the mid-level CAA isn't going to help with any capping that occurs today. 850 mb temperatures are generally 13-15 C, but that doesn't sound too particularly bad.

I think if there's an area that gets lucky with enough clearing to warm to 80 or more, there could be something interesting there, but I think this is going to be a messy event and probably difficult to chase for many. With the unidirectional shear profile, storm speeds aren't going to be the most friendly either. I think the best chances, though, are indeed in SE IA/far NE MO and into WC IL where the deep layer shear is marginally better and current instability looks to be a little higher (also closer to the triple point). Unfortunately it's also one of the cloudiest areas right now, too.

Last thing: I don't think the threat will make it as far north as Cedar Rapids. Looking at the IEM Time Machine (http://mesonet.agron.iastate.edu/timemachine/#1.201504091700), it's interesting to watch the KCID ob over the last few hours. It goes from saturated in the upper 40s with an east wind around sunrise followed by a rapid warming/moistening and veering of the winds to SEly by 11 AM, but then the wind flips back around to due N and the T/Td drops from 61/60 to 55/55 at noon, suggesting the boundary had moved back south. Keep an eye on the Iowa City ob to see if it does something similar soon.

Thinking the same things. Additionally, thanks for the insight about the 700 mb thermal axis. I can't believe SPC went to 10% hatched tor probs...

 

[John Wills]

So the mid-level CAA isn't going to help with any capping that occurs today

Capping definitely won't be the issue today. Did you mean that it will not aid in creating a cap?

 

[John Farley]

First tornado of the day reported near Rome, IL, a little north of Peoria. This is from the southwesternmost cell of a cluster of storms in the warm sector, well ahead of the main frontal forcing and south of the warm front, though there does appear to be a poorly-defined baroclinic zone (but not a wind shift) between that storm and the Chicago area.

 

[John Farley]

The TOR-warned storm just NW of Davenport has been showing 142 knots of low-level gate-to-gate shear. Hope somebody is on that one. Since it is right near I-80 and the Quad Cities, I am guessing somebody is.

 

[JamesCaruso]

Nice looking storm west of Rochelle



Sent from my iPad using Tapatalk HD

 

[Dave Gallaher]

Impressive couplet on Lee County IL storm, PDS warning up. Debris knob too.

 

[Jeff Snyder]

Current live feed from Matt Salo has large tornado on the ground right now -- http://www.severestudios.com/livechase

It looks like the tornado went through a part of a town, perhaps Kirkland --

 

[John Olexa]

I saw that. Looks like it did some pretty serious damage. Hope everybody is ok!! Fairdale maybe?

 

[Brian McKibben]

What's up with that tornado warned cell in southern MS / LA? Doesn't it know it is not allowed to form outside of the SPC Day 1 tornado outlook? Mesoanalysis shows that area in becoming increasingly favorable to supercells

 

[Brian McKibben]

The 18z 4km NAM simulated reflectivity did a pretty good job today. It got the pre-front supers in N Illinois, The pre-front storm in E Texas, and it even got the lone supercell in S Miss/Louis. It missed the isolated supers in N Indiana/ S Michigan.

The 12z run wasn't as successful. 12z 4km WRF was ok. I wasn't impressed with HRRR.

 

[John Farley]

Chicago Tribune blog with many pictures of the tornado in the Rochelle, IL area:

http://www.chicagotribune.com/news/...torms-strike-illinois-20150409-htmlstory.html

 

[chrisbray]

I need to know...what killed the all the storms south of I-80? Sever cells couldn't quite make it that popped up in Illinois, and then there was a series of discrete supercells crossing the Mississippi River south of the Quad Cities into a supposedly favorable cape and sheer environment across IL and they all died....