5/13/09 FCST: IA/IL/MO/OK

[Colin Davis]

I'm rather puzzled as to where the talk of unidirectional winds and quick-change-to-line language is coming from. I've been keeping an eye on Wednesday for some time, and if anything, I'd say it's gotten better. 0z NAM has dropped things further south (Litchfield-STL), yes, but I'd say every other parameter is much better. The GFS gets rid of that MCS (it's over C KY by 18Z) well before crunch time, and the atmosphere recovers (to the tune of 2500 j/kg) well ahead of show time. And this is under an area of incredible directional shear. If it's the GFS, give me SPI. My ears are hurting from how loud that model is screaming.

Either way, the area from CTK (my hometown) to SPI, down 55 to Litchfield looks primed. If either of these models verify (especially the GFS), I'm sold.

If the naysayers want to stay home, I'll take the tornadoes, lol. I haven't seen a setup like this in IL for some time, and I've been called overly-negative before when it comes to past setups.

 

[Brandon Sullivan]

It still looks like a severe weather outbreak will effect parts of Illinois and Missouri on Wednesday Afternoon And Evening.

Synopsis: A low pressure system currently located in Alberta and Saskatchewan will continue to move east and deepen. The ~992mb low is forecast to be over the provinces of Manitoba and Ontario by 15z Wed. At 18z Wednesday a cold front will be found across DMX to DDC.

As morning convection exits the area ( which both American models picked up on in the 00z suite) subsidence should allow clearing in the late morning and afternoon.. If indeed this clearing occurs in wake of the morning MCS an active weather event is on tap for the area in the afternoon.

Various Lift Progs indicate that substantial lift will be present well ahead of the front to initiate supercellular convection across western Illinois and eastern Missouri in the late afternoon into the evening hours. Sizeable and curved hododgraphs will be found across the moderate risk area, in response to backed winds at the surface, and strong winds at H8 through most of the column. As storms develop, shear profiles would indeed support intense rotation, leading to multiple severe weather threats, including damaging winds, hail and tornadoes.

H5 flow is found to be a touch stronger on 00z suite, but with PWAT's very high, HP storm modes will be a good bet, storm motions will be slow to the northeast, and with the good Illinois road network, should not have much of a problem catching them.

The SBLCL's are found very low, and with the sizeable looped hodographs, and the associated EHI's & STP's into significant levels, I still think tornados are a good bet, with large tornadoes certainly in the web of ideas..

I guess the moderate risk in my opinion is well justified and well placed at this time. Andrew P has pretty much nailed the ideal target to me right now..

 

[Derek Weston]

I'm rather puzzled as to where the talk of unidirectional winds and quick-change-to-line language is coming from. I've been keeping an eye on Wednesday for some time, and if anything, I'd say it's gotten better. 0z NAM has dropped things further south (Litchfield-STL), yes, but I'd say every other parameter is much better. The GFS gets rid of that MCS (it's over C KY by 18Z) well before crunch time, and the atmosphere recovers (to the tune of 2500 j/kg) well ahead of show time. And this is under an area of incredible directional shear. If it's the GFS, give me SPI. My ears are hurting from how loud that model is screaming.

Either way, the area from CTK (my hometown) to SPI, down 55 to Litchfield looks primed. If either of these models verify (especially the GFS), I'm sold.

If the naysayers want to stay home, I'll take the tornadoes, lol. I haven't seen a setup like this in IL for some time, and I've been called overly-negative before when it comes to past setups.

Had been some rather veered low level flow that coupled with mid/upper jet streak made for some rather unidirectional profiles. Agree, though, NAM in particular has really been trending towards better directional shear. (looking at sim soundings 0z... mediocre around St. Louis... picking up nicely as you go NE towards and past Spriingfield)

As another poster mentioned... bigger concern now might be lack of cap and strong forcing where storm mode is concerned. June 5 2008 high risk was a good example of this across Kansas. (then again, flow was more unidirectional than desired)

A couple of my big concerns right now would be 1) Instability..mcs/junk conv issue. (well documented) and 2) forcing mechanism, should we attain a desirable thermodynamical environment.

Specifically: cold front forcing and resulting storm mode. I honestly haven't studied too many cases where the cold front was the primary forcing mechanism and we, in result, saw nice isolated supercells w/ appreciable tornado threat. (however... east of the mississippi, especially in the southeast, I do believe this is more common) I guess if we can get things to pop downstream from it a bit, or at least move off it a bit if it's a slow enough mover...

Obviously any good outflow boundries could positively impact our storm mode in that localized area...

Having a hard time getting a good reading on exactly how much of a warm front we're going to have to play with. Obviously an active warm front would be desirable here.

FWIW... 0Z GFS seems to be projecting a strong, faster, cold front and better warm sector where as the NAM is less forward with it. (though, model interpretation's of the precip situation differs)

All this said.... this looks like a pretty good day for this neck of the woods... with some pretty good potential.

 

[Ilya Neyman]

Taking a look at forecast progs Wednesday may be a fairly widespread severe event across a large part of the area highlighted in SPC's outlook. The timing and areal configuration of the front will be a factor in how the south-end of the outlook plays out. Right now the cold front is forecast to be NE-SW in MO and KS and more ENE-WSW in OK by Wed evening per the NAM. The GFS is slightly further north and less impressive as far as the co-location of most impressive shear with the moisture/instability/frontal axis. Right now, the models are trying to duke it out.

 

[Ryan Wichman]

All of this talk about people staying home for this show is exciting, more space on the road for me! For once there is a local chase, and of course there are a few questions to be answered (it is Illinois afterall). But I have to admit the prospect of an hour drive down the road to catch up to a sup is exciting.

At this point I think a play especially to the south and back west of any well-mentioned MCS has moved through will be a smart bet. Let the area clear out of rain and hope for some breaks in the clouds.

If I was expecting to chase EF-4 and EF-5 tornadoes tomorrow, then I would be pissed that 3-4k j/kg of CAPE isn't showing up on each model. But the fact of the matter is, if any area in this well sheared environment can approach 1500 then well organized sups are possible. IF the 3000 j/kg of the GFS verifies and sups break out it would be a very violent and dangerous situation, especially with these sob's being rain wrapped in short order.

At this point finding said boundaries and finding the clearing will the key to a nice chase day.

 

[Shane Adams]

While everyone prepares for the outbreak up north, OK has quietly become perhaps the best choice for Wednesday. The best instability in the outlook region and doable shear paint an interesting picture along the I-44 corridor tomorrow evening. Also, being well-displaced from the main upper support, there will be a much better chance of isolated, chaseable storms in this area IMO.

 

[Andrew Pritchard]

Still favoring south central Illinois per the 12z NAM run. Almost identical to last night's run, only with slightly higher cape values in that tongue nosing into SW IL around 4 PM.

We're still seeing a lot of convective returns across a lot of Illinois during the morning, towards noon. However there should be substantial clearing south of, and behind this cluster to allow for rapid destabilization on the order of 2500-2750 j/kg along Interstate 55 near and just south of Springfield. This is where I'd look for new cellular developement towards mid-afternoon. Given the favorable environment characterized by strong southerly surface flow and a westerly H5 jet at 50-60 knots discrete supercells should be the mode ahead of the cold front along the warm frontal boundary amplified by morning convection. LL helicity values aoa 350-400 m2/s2, strong southerly LLJ, and low LCL heights will be supportive of tornadoes as the threat moves NE towards evening. Check the kinks in the isobars in this image. It's definitely forecasting the warm front right along that area, likely enhanced by all the early day convection (similar to 4/20/04). This is where I'd watch for biggest tornado potential, some strong pending substantial heating. If areas along Interstate 72 can clear out during the afternoon and allow for rapid destabilization, I could see an enhanced threat for a damaging tornado in that corridor. With a dynamic system like this, and the high May sun it really won't take much sunshine. The more the better, of course.

Still time for things to be played out, but I'd continue watching a box outlined by Interstates 55 and 57, and Interstates 70 and 72 (St. Louis to Springfield to Champaign to Effingham). I'd still like to be in Litchfield by 3 PM.

 

[Andrea Griffa]

Cancel.this is the wrong thread.

 

[Joel Wright]

Another good play may be north-central IL. Right where the higher cape noses up into the very high shear near LaSalle. NAM forecasts near 500m2s2 0-3km helicity(!) with 1,500-2,000j/kg cape building into this area from the south. This area is a lot more of a risk though, since morning/early afternoon convection could screw this area up pretty badly. I think an initial target near Peoria may be a safer choice. An adjustment north or south if needed would be quite easy.

 

[John Farley]

Well, I hope the NAM is right because, despite better instability on the GFS, it also breaks out the precip a lot farther north, and as I mentioned earlier, I'm limited to a local (and somewhat early) chase. As others have noted, the instability has improved on the NAM, and there is a bullseye of very high EHI along I-55 near or a little southwest of SPI at 21Z. I agree with Andrew that as things currently look on the NAM, Litchfield by 3 would be a good starting point. And that I can actually do. One possible fly in the ointment remains earlier convection - the NAM has lots of precip all over the area throughout the day. But it does still generate CAPE of over 2000 around Litchfield. Of course if the GFS turns out to be right, Litchfield would be way too far south.

 

[Colin Davis]

New Day 2 is out...and not too much of a change, really. Imy moved the MDT a little further NW as per the 12z NAM and GFS, both of which have moved the better parameters north no more than maybe 40 or 50 miles. Personally, I think Springfield to Litchfield is the obvious target. Everything has been screaming that area for the last couple days. I'll hedge closer to Springfield, I think, partially because I want to be able to hedge a little bit on where exactly the best storm of the day is (I think I'll have to shoot down 55 a few miles, but that's no problem), partially because I don't get out of class until 1:10, and partially because of the interstate options in every direction out of SPI.

As per usual, Pritchard has hit it on the head, I think.

 

[Scott Weberpal]

This mornings 4km WRF run makes a few interesting statements:

1) It breaks out no convection in IL up to 00z.
2) It shows a massive supercell-type blob in SW IN at 22z
3) It makes SE IA appear to be the prime area for potential tornadoes breaking out a broken line of storms in the 22-23z range.
4) Illinois is completely clear of overnight convection by 16z-17z.

Not that the 4km WRF is above and beyond any other model, but it does have a positive track record in regard to where initiation is likely to occur, along with timing.

These are time sensitive links:
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/refd_1000m_f34.gif
http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/12/refd_1000m_f36.gif

 

[Andrew Pritchard]

Those looks like they're following the GFS a little more closely, as it did not produce much pre-frontal activity.

I've never really used that model out to 36 hours though, not sure how accurate it is that far out. It doesn't seem entirely unreasonable, but with the current placement of things on the 12Z models it seems a little bit too far west to me. Davenport, IA to Quincy, IL to Columbia, MO seems more reasonable to me.

It does destabilize eastern Iowa and surrounding areas nicely by 21Z...

http://charlie.wxcaster.com/model/MIDWEST/wrf/MIDWEST_WRF_SFC_CAPE_33HR.gif

http://charlie.wxcaster.com/wrfcentralnojava.php?fcsthour=36&type=SFC_SLPTHETA-E-CONV&region=MIDWEST

I don't know. I'll still hope for that big red blob in WC/SW IL on the 0Z run.

 

[Ryan Wichman]

I would really like to get into the nose of the highest CAPE which has been pinpointed near the KUIN to KIJX region for the past few runs of both the GFS and NAM. Getting on these storms close to inititation will be important for two main reasons:

1)Storms are likely to become rain intensive as they progress through their life cycles

2) Any large supercell which develops will push out cold pools which could spawn crapvection in the area

Another interesting note: All of the models are picking up nicely on the urban heat island effect in STL, granted its not a major factor in this set up it could prove a possible point of inititation for anyone playing that far south.


IMPORTANT: Anyone thinking about chasing in West Central Illinois or NE MO be aware of the massive radar hole in this area. The lowest scans in these areas are looking 8-10k feet into the storms. Happy Chasing

 

[Danny Neal]

Helicities are maxed out over NC IL, same with the STP model. Good CAPE is nosing up into S. La Salle County even. Shear is there still. I am not sure, but I don't I will have to go further south than Lincoln. The 4 KM WRF looks iffy as Scott mentioned above, however I still think we can fire off some convection along and west the 55 corridor. I just think I may be a little further north based on the latest models.