2013-06-12 FCST: IL/IN/OH

[chrisbray]

Looks like a possible derecho tomorrow across parts of the great lakes and midwest.

GFS place a 500mb speed max going rapidly from Iowa across Illinois, Indiana and Lake Michigan by early afternoon, with NAM showing it a bit slower. Regardless, bulk wind shear approaches or exceeds 50 knots and overlays 3000-4000 cape, steep lapse rates, and decently curving forecast hodos over much of Illinois and Indiana.

Low level winds look to be relatively weak, though.

I know I will be going out for this event, even if it is a straight line only day!

 

[Bob Hartig]

I definitely wouldn't rule out tornadic activity along the warm front, wherever it lays down, in discrete storms that fire in advance of the line. I haven't done a ton of analysis, but today's 12Z NAM forecast sounding for Jackson, MI, in the afternoon (20Z on) and last night's for Kalamazoo looked convincingly tornadic. Granted, low-level winds look weak, but 1km and 3km helicities still top the threshholds, no doubt due to the combination of dramatic low-level curvature and strong 500mb winds. Storm-relative is what counts, after all. For instance, my Jackson sounding shows 14 kts from the SW at 850 mbs ground-relative, but storm-relative comes out to 37 kts from the SE.

So I'll be chasing in my backyard tomorrow, but I'll be watching for lone cells. I'm not much interested (yet) in the straight-line stuff.

 

[Jason Harris]

Hi Bob and Chris,

I'm wondering how things will come--or not--together exactly. Mid-level lapse rates seem like they will be more favorable in SW Ohio but the supercell model seems to indicate NW Ohio, but then the helicity seems to lag a bit for later on. Definitely hoping to get to something rotating before the rumored derecho might materialize. Mainly looked here http://weather.cod.edu/forecast/# and here http://www.emc.ncep.noaa.gov/mmb/namsvrfcst/ Interested to see how things look tomorrow. Where do you imagine the warm front will be and when? What are your prospective targets? I like the idea of getting a bit further west and south of where I am in Bowling Green. Napoleon is relatively convenient and has the N/S/E/W roads. If I'm reading things correctly, there could be a variety of periods of activity 11-2PM (and ongoing), 5-8 or so (and I'm skipping anything after dark).
Perhaps (based on looking at wind change towards the south, between 18z-21z is when warm front is entering Ohio?), so close to 2 PM might indeed be an important window for supercells?
__
Update, now they've got the hatched area through IL and up to halfway in IN--anybody targeting that, perhaps out to South Bend? I'm now thinking (depending on time) Bryan, OH might be a place to head, though Coldwater, MI down to Fort Wayne, might be a corridor to watch.
--Update 2
Disappointing to see now the 10% tornado is just gone period from OH and IN and the hatched pushed back just to IL. Hmm.

 

[John Vandehei]

I agree with Bob, here in the central Great Lakes region, the warm front is always a good location for storms to go tornadic. I think anywhere along I-80 between LaPorte to Toledo would be good. That should keep you near the warm front, yet leave lots of options to move north or south should anything good develop that way. The one problem I see, though, is the heavy cloud cover from last night's convection currently spread across much of Wisconsin, northern Illinois and much of Lower Michigan. This cloud cover could greatly limit destabilization across all of lower Michigan and portions of northern Ohio if it doesn't clear up by early afternoon. Past experience has shown that if anything is going to bust a severe weather event in Michigan, its the cloud cover. So definitely something to watch at the day progresses. I agree, though, that farther south, conditions look good for a squall line or derecho type event.

 

[chrisbray]

i agree about the cloud cover John. The same definitely applies here in Illinois.

Regardless, I am going to be heading out around lunchtime. My intial target is somewhere around Dixon, Illinois. EHI, shear and cape appear to be maximized in northwestern Illinois in the afternoon.

Other people playing Illinois today, I'd love to hear your thoughts. Unfortunately I will be chasing this one solo so I am a bit nervous

 

[John Vandehei]

I hope this doesn't stray too much off topic, but if anyone is coming to chase the central Great Lakes area, especially those who are in places like Missouri or Kentucky, be warned that gas prices across Michigan, much of Indiana and a parts of Illinois (esp. near in and near Chicago) are north of $4.00 a gallon. For us local chasers, we're already painfully aware. Now getting back on topic, it appears that some of that dense cloud cover that spread across Michigan and was trying to get into northern Indiana might be thinning somewhat. If that trend continues, that would be good news for better instability.

 

[truechampion]

Based on data available at this time, conditions appear most favorable for tornadoes just southwest of Chicago.

 

[John A. Sellers]

It looks like the SPC may upgrage to a high risk. The potential for tornadoes and high winds is increasing.
Remember if you chase, stay safe!

 

[chrisbray]

Well, they are upgrading to high risk. I'm still heading to the northwestern side of the state, I can track east if I need to, back towards home (I'm leaving from a county bordering Indiana)

I'm suprised there aren't more people discussing this...first high risk of the year!

I'm curious, why do you think southwest of Chicago when most of the outlooks are poitning towards the Illinois/Iowa border?

 

[Skip Talbot]

MOD Note: Posts in forecast threads must include your own forecast discussions, not just a reference to SPC. Posts benefiting chasers, but not discussing the forecast may be better suited in a MISC thread (reports from other chasers, road conditions, other non weather related factors influencing a setup). Questions about forecasts are best asked in the Intro forum.

Based on data available at this time, conditions appear most favorable for tornadoes just southwest of Chicago.

What data? What conditions? Why? I'm not saying this is wrong, but forecast discussions here usually include specific references to data sources and then an accompanying explanation as to how that results in the given forecast.

Looking briefly at the 12z RAP, NAM, and HRRR, they all seem to be in good agreement on the placement of the surface low over eastern IA/MS River by mid afternoon, with a shortwave trough ejecting over this area and northern IL at about the same time. The cap is forecast to open up fairly early in the afternoon over eastern Iowa. I'd expect initiation near the Cedar Rapids or Waterloo area and maybe just east of there with those 500 mb impulses moving through the area. With the surface winds backing along the northeast corner of the low and along the warm front, directional shear appears pretty decent for supercells and tornadoes. 70's dews are coming in from central Illinois as we speak with temps going into the 80's and 90's, so we should have plenty of CAPE. I'm not super sold on the tornado potential, however. The best directional shear is right on the warm front, and the models have been showing the warm front getting pretty messy fairly quick as clusters of cells go up and propagate southeast from there. With the veered 850's and strong westerlies aloft, I'd expect more of a linear mode and fast storm motions as storms build south of the warm front, with storms bowing out and racing east soon after maturing. Those wind probs on the day 1 will probably verify. I'm not seeing a tornado outbreak, however. Perhaps closer to when supercells initiate, and near the warm front if cells can stay discrete, there could be a tornado or two. The location is just terrible for that though. Eastern Iowa, southwest Wisconsin, and northwest IL are terrible places to chase due to terrain and the river crossing. I'll probably hang out just east of there and and pace back and forth, biting my nails waiting for storms to moving into more favorable terrain near Rockford. I'm not sure if cells will stay discrete that long, and wouldn't expect them to much further east of there.

 

[MGalloway]

I'm not super sold on the tornado potential, however. The best directional shear is right on the warm front, and the models have been showing the warm front getting pretty messy fairly quick as clusters of cells go up and propagate southeast from there.

Ok. I'm really new to this, so feel free to shred this post (forgive me, I have lots to learn). On the surface observtion map (spc site, Central Plains mesoscale analysis), as of 1:30 CDST, the low just north of Des Moines has surface winds that change direction in a very small area. There is a similar area maybe 150 miles east of that. I was going to mention that the SR Helicity - Sfc to 3km chart also shows numbers over 500 in northeastern Illinois...but that appears to now be moving over southern Lake Michigan. Surface CAPE in central Illinois is at 4K (with cin to the northeast), though. I would think there would be at least a few dramatic tornadoes somewhere in all this...even if short lived...but maybe I'm missing something.