2018-05-20 EVENT: IA/IL/IN/KY/OH

[chrisbray]

Thought I'd bite on this since no one else has....despite the SPC only having a day 3 marginal.

Weak surface low pressure and a short wave trough will work across Eastern Iowa/Northern Illinois on Sunday, with a warm from progged to be draped across Illinois/IN around I-80 south of Chicago. This has the looks of a very nice local chase, and imagine most chasecationers will be following this system from Saturday's event in NE/KS/MO/IA as well.

Pros:
-Large cape augmented by a good looking EML transplanted from the plains, as well as good moisture (progged around 70 but I doubt it gets quite that high).
- An Illinois Warm front!
- Sufficient bulk shear I imagine will hover around 40 knots.
- Favorable storm motions/speeds around 20 knots to the East.
- Capping not much of a concern

Cons:
- Some question of upper support- we don't know exactly how strong/weak the upper level flow will be
- Surface pattern is weak - leading to veered surface winds, backing more to the east along the front. EURO has the surface low at 1008, NAM at 1012
- Open warm sector - too much storm coverage? Insta MCS?
- Weak 0-1km shear/helicity, although 0-3km situation is much better

Posting a few images from the latest NAM. We will see how this trends leading forward

 

[Jeff House]

I agree Sunday is worth watching, and it is 1/3 the distance from me compared to the Plains. Pros and Cons look good to me. I will only add a couple more pieces of data.

Surface to 850 mb is moist upstream, here in the South. Sunday IL/IN should be able to keep dewpoints around 68, in contrast to the Plains struggling to 65 and mixing out to 60. BNA sounding is quite moist this morning. Forecast ILX/IND soundings look good Sunday.

GFS backed off so much midday rain. Looks more like the less rainy ECMWF. 700 mb temps look close to just right, esp thru 18Z, which favors the Euro a bit. 12Z NAM high-res radar is a super-fest, but probably too good to be true at 60 hours.

I would like to see the LLJ either stronger and/or less veered, but it is OK for Hoosier Alley. Outflow could provide the needed local helicity. Also need that north of I-70, preferably I-74, to avoid jungle.

 

[chrisbray]

I agree Sunday is worth watching, and it is 1/3 the distance from me compared to the Plains. Pros and Cons look good to me. I will only add a couple more pieces of data.

Surface to 850 mb is moist upstream, here in the South. Sunday IL/IN should be able to keep dewpoints around 68, in contrast to the Plains struggling to 65 and mixing out to 60. BNA sounding is quite moist this morning. Forecast ILX/IND soundings look good Sunday.

GFS backed off so much midday rain. Looks more like the less rainy ECMWF. 700 mb temps look close to just right, esp thru 18Z, which favors the Euro a bit. 12Z NAM high-res radar is a super-fest, but probably too good to be true at 60 hours.

I would like to see the LLJ either stronger and/or less veered, but it is OK for Hoosier Alley. Outflow could provide the needed local helicity. Also need that north of I-70, preferably I-74, to avoid jungle.

Only thing I would add to that is south of i-74 is not a jungle in Illinois, but in Indiana if you get too far south it is hilly and jungley. In Illinois you are good down through I-70 corridor.

 

[Ethan Schisler]

I've been watching Sunday for a couple days. Good instability (given that morning rain/clouds clear), along with great storm relative helicity along the warm front....just need storm mode to be supercellular as storms go up and track eastward. That is the one part of the forecast I'm uncertain of, in addition to the location of the boundary. I think storm mode could quickly go QLCS and travel eastward along the warm front promoting damaging winds and rainwrapped brief tornadoes. I also could see a scenario where the warm front is suppressed further south by morning storms....this is a scenario being shown by the 3km NAM model I think there the storm initiation is taking place in Indiana and pretty far south at that. All variable that will need to be considered over the next 36 hours.

 

[chrisbray]

Welp don't look now, but every model has pretty much pooped on tomorrow. Front has turned to crashing lake breeze/cold variety and takes warm sector all the way down by I-70. Surface pattern is terrible looking. Will be a look and see type situation in the morning, but I've kinda lost faith for this one.