2013-05-20 FCST: IL/MO/OK

[chrisbray]

Ok, I am going to try do some analysis on what appears to be a strong system moving through the Missouri Valley on Monday, May 20. I'm going to keep this in the introductory forum and just mimic the target area format because I'm a noob at this...so any additional thoughts on this forecast are very welcome, as well as any tips or feedback on other things to analyze for this!

Ok so...

Latest GFS shows great instability across the majority of Illinois and eastern Missouri with ML Cape from 2000-3000 by late afternoon. I'm aware GFS tends to overdo moisture, but the indications are Tds over 70 for the most part. So conservatively, I'm assuming they will more likely be mid-upper 60s.

Capping doesn't appear to be to much of a concern with 700 mb temps under 10 degrees, but I wonder if this will lead to a lot of early convection that could limit destabalization across Illinois?

500mb winds approach 60 knots by evening, and, correct me if I am wrong, but it looks like a low level jet develops in the evening as well, as it shows 850mb winds ramp up to 30-40 knots.

Wind shear looks great with 25-30 kts from sfc-850mb and sfc-500 appraoching 50-60 as the evening progresses.

Forecast hodographs in the area seem a bit confusing to me with random turns so I will hold out judgement until the take shape in later forecasts.

Anything else I am missing here? Other things I should check? Additional thoughts or advice? I know its still a long ways out and the forecast is going to undergo changes, but I wanted to try my hand at getting the basics down with forecasting a potentail event 5 or so days out. Thanks!

 

[Skip Talbot]

I agree, Chris, all the parameters appear to be there and I"ll probably be out there chasing somewhere. West central IL looks mostly great, with the shear and instability parameters you cited. The low level jet is kicking through there and the surface winds are nicely backed. It's lacking upper level support though. I'm also not sure where our source of lift would come from that far east. The bulk of the upper level energy is way out in western MO at 0z, and I don't see any obvious boundaries in IL. Even to the west over Missouri, it looks like the diverging flow aloft might be the primary source of lift. The dryline/coldfront both look super diffuse. Given that there isn't a ton of forcing, I don't think the cap opening up early is going to be too much of a problem. However, that diverging flow and open cap might lead to early afternoon initiation over western MO. Surface winds are veered quite a bit there, coupled with the lack of stronger anvil level winds, I'm worried about storm mode. We might be dealing with some quick transitions to messy HP's or clusters of storms, that eventually track into IL through the evening. If there is some sort of boundary we can work off in IL though, we might have a better shot at a tornado where that LLJ, helicity, and advertised instability are higher (not to mention, the terrain is much better for chasing). Hopefully the NAM gives us a little more to work off of when it's in range.

 

[Brian McKibben]

18z GFS has slowed this system down even more. It makes central OK look like a good play for the day. There is a meso low that develops in SW OK. Of course this is still 5 days out. Nevertheless, this EHI graphic is impressive.

It may be necessary to add OK to the thread if this trend continues.

 

[chrisbray]

A Day later, and my confidence is lower. Hopefully the models are wrong in slowing this system to a crawl, because I see what Skip pointed out. Latest run shows no upper level support in the afternoon/evening on Monday. Everything else seems to be there....obviously we can't depict much in the way of surface features from this range though. I'm hoping this doesn't turn into the typical Illinois "day after the event" where overnight convection most in overnight/morning and ruins the setup for the day.

I really don't want to/can't leave the state. I hope something happens in west-central Illinois.

What looks good about the 0z forecast up to this point:
Great instability and low level shear, breakable cap

What is concerning:
Luck of upper support lately with GFS runs.
Also, will overnight/morning convection ruin destabilization on Monday? What will cause initation?

Just a noob's thoughts, feel free to help out. Hopefully NAM helps shed light when it is available

 

[Joshua T. Clark]

Looking for some answers on central Oklahoma target area for Monday. Just looked at some forecasted soundings for central Ok, it looks like the models are primed for something big.

 

[chrisbray]

Ok can someone help me out here? I'm trying to figure out why SPC has removed Illinois from latest out look for this day (day 4). Is it because they models are tending to slow down the shortwave arrival? Is it that the initiation of storms only seems certain across missouri and not into Iowa/Illinois?

 

[Derek Weston]

Ok can someone help me out here? I'm trying to figure out why SPC has removed Illinois from latest out look for this day (day 4). Is it because they models are tending to slow down the shortwave arrival? Is it that the initiation of storms only seems certain across missouri and not into Iowa/Illinois?

Per 0z 5/17 GFS the ILL/IA would be under the gun, but, as you point out, I'm thinking the models the SPC is trusting here aren't putting the energy that far north and east. Watch to see what the NAM does in a bit as the 12z 5/17 run comes in.

 

[chrisbray]

Per 0z 5/17 GFS the ILL/IA would be under the gun, but, as you point out, I'm thinking the models the SPC is trusting here aren't putting the energy that far north and east. Watch to see what the NAM does in a bit as the 12z 5/17 run comes in.

OK 12z NAM run is out...its showing 500mb speeds around 60 kts at both 18z Monday and 0z Tuesday. 250 winds around 70 kts. Dews approach 70, cape over 2000. It doesn't have as great of helicity or EHI values as the last GFS model but still not bad.

Though the wind speeds look good, is this going to be a directional shear issue? Southwest winds at surface, southeast at 850, and southwest at 500 and up? Is that the "veer back veer?

 

[Derek Weston]

OK 12z NAM run is out...its showing 500mb speeds around 60 kts at both 18z Monday and 0z Tuesday. 250 winds around 70 kts. Dews approach 70, cape over 2000. It doesn't have as great of helicity or EHI values as the last GFS model but still not bad.

Though the wind speeds look good, is this going to be a directional shear issue? Southwest winds at surface, southeast at 850, and southwest at 500 and up? Is that the "veer back veer?

Right, direction shear isn't awesome, but may be good enough. I'm seeing 90 degrees separation (think quarter of a pie visually) from surface to 500mb. In my experience... that's enough, especially if you've got moist air to your west and south. Not really seeing veer-back-veer.... not seeing the southeasterly surface.

Big concern with Mon is storm mode. NAM puts out a strong precip signal around 0z that looks pretty linear for convective mode... cold front forcing. Unfortunately for us in the midwest that's a pretty common pattern. Couple big days with the dryline in the plains and then the CF that flys at you as the system ejects into the midwest. That said... sometimes early on you can get some tornadoes out of CF forcing, especially if the front isn't too vigorous. (as in... isn't surging forward very quickly)

 

[chrisbray]

OK I am getting a bit discouraged now....When I look at forecast surface to 500 crossover, I see hardly any change in direction. Speed shear plus little directional shear = squall line?

edit: nam shows a little better crossover, but still closer to 70 degrees than 90

 

[Adam Atkins]

I'd say this is Central Oklahoma's best shot for the weekend. Big time capping Sat/Sun with possibly a few nice storms. The cold front will stall out and become stationary on Monday morning...it may dip further south than the 2013051712 GFS positions it now depending on whether or not an MCS forms Sunday night.

Any heating near the front/dryline intersection will mean storm development and motions parallel to the frontal orientation for significant low level shear/helicity.

 

[chrisbray]

18z NAM run now makes it seem as though early morning precip and cloud cover finally clears western Illinois in the late afternoon and evening, allowing for destabilization to ramp up, and the winds turn form southwest to a more southerly component. It shows some storms firing up there and moving northeast through Illinois through the night.

Should be interesting to see this picture become more clear in the next couple days...I think it looks pretty solid still, but I'm a noob

edit: Interesting to note that NAM has way lower EHI values than the GFS, is this mostly because GFS is overdoing moisture and resulting in higher capes?

 

[chrisbray]

Looks like we will need a combination of the GFS's instability / moisture and the NAM's windspeeds

 

[chrisbray]

Does anyone have thoughts on the Illinois/eastern MO/IA area for tomorrow? Or is it kind wait and see still

 

[E Hale]

I don't think any model can really overdue moisture. Unless the convection tonight and tomorrow stabilizes the atmosphere (which it won't). We've got 75 DPs in OK right now. Incredible.