10/30/09: FCST WI/MI/IL/IN/OH/KY/TN/MS/LA/TX/AR/MO

[David Draun]

Models are showing a very strong dynamic trough that negatively tilts across the Central Plains and Midwest. Height fall anomalies are currently forecasted as high as 6 standard deviations from normal. 65 degree dewpoints come up all the way into southern WI, even though these may be a bit overdone. By 7pm Friday, a 120kt 500mb jet streak rounds the base of the trough creating strong divergence aloft. In response to this, rapid cyclogenesis should be ongoing. One problem is the shear is largely unidirectional. SSE at the surface, S at 850 and 500mb, and SSW up at 200mb. But if a strong updraft can alter its local environment there could be a risk of a tornado. Instability may also be limited leading to just a strongly forced transcontinental line of showers and a few thunderstorms with very little lightning, with an attendant threat of damaging wind gusts. Nevertheless, this is something to watch. It also seems like it could become a Great Lakes bomb too.

 

[Scott Weberpal]

This system has all the makings of a typical fall tornado outbreak in the Ohio Valley through the deep south. Unfortunately, the GFS has been all over the place as of late. Just a few days ago, it looked like Wednesday would be the day, then it was Thursday, now its Friday. However exciting Friday looks, I'd like to see some consistency before I'm completely on board.

Unfortunately these extremely dynamic systems are almost always dictated by grungy storms with extremely low bases and very limited visibility. Couple that with storms moving at 55 mph and it doesn't make it very fun chasing. Of course, I'll be out no matter how many time I say I'm going to write off chasing these late/early season super-dynamic systems.

 

[Adam Lucio]

A 984mb low over MN by 0z is what an IL chaser likes to see. What surprises me is the Euro is even stronger with the system bringing it down to 976.

CAPE is a concern but it wont take much to get things going with a system like this. I could certainly see some low topped speed demons capable of damaging winds and tornadoes. If we can pull out even 750 j/kg I think we'll be in business. With the system going negative I would think a nice dry slot could from to allow for clearing especially if our jets line up.

Best hodos appear to be in IN and even into southern MI for low level turning but even with the profiles going linear above 850...with good low level turning and low topped storms I think a tornado threat is very real. Keeping a watchful eye on this one.

 

[Andrew Pritchard]

Thursday's 0Z forecast for 0Z October 31st:

http://twisterdata.com/data/models/...S_3_2009102300_F192_TMPF_2_M_ABOVE_GROUND.png

Friday's 0Z forecast for 0Z October 31st:

http://twisterdata.com/data/models/...S_3_2009102400_F168_TMPF_2_M_ABOVE_GROUND.png

Saturday's 0Z forecast for 0Z October 31st:

http://twisterdata.com/data/models/...S_3_2009102500_F144_TMPF_2_M_ABOVE_GROUND.png

Tonight's (Sunday) 0Z forecast for 0Z October 31st:

http://twisterdata.com/data/models/...S_3_2009102600_F120_TMPF_2_M_ABOVE_GROUND.png

I'll wait before I start getting at all excited about this one. While it's pretty clear a large storm system will affect the middle part of the country at the end of the week, just look at the disparities between those images, which are only 24 hours apart! I'll hold off before I start picking dates or locations on this one.

EDIT: Hell, look at the 12Z run from TODAY...

http://twisterdata.com/data/models/...S_3_2009102512_F132_TMPF_2_M_ABOVE_GROUND.png

 

[mikegeukes]

Here is some maps from the latest ECMWF that be of interest to some.

Latest ECMWF: 00Z 26 OCT 09 Run for the following forecast hour 120hrs: 00Z 31 OCT 09
-Winds: -200mb -500mb -700mb -850mb
-Heights: 500mb
-Surface -Pressure 2mb -Pressure 4mb
-Humidity -700mb -850mb
-Vorticity -500mb
-Dewpoint -850mb
-Theta-E: -850mb
-4 Panel

More ECMWF maps can be found here: http://models-ecmwf.blogspot.com

 

[Bob Hartig]

I've been eyeballing this system for a couple days. As Scott mentioned, it's been all over the place as far as timing, but if either of the latest ECMWF/GFS models do in fact pan out, then I could get happy for once about being in Michigan. The winds, though--ewww. Not much stairstepping. Sampling some 6Z GFS hodos, the best one I've come across is for around Toledo at 18Z, where there stands to be a decent overlay of Theta-e and helicity. But it's a narrow window, as these storms will be rocketing, and the sun sets early these days. Still, if this thing holds hope for even a rumble of thunder by the time it finally materializes, I'll be out.

 

[Robert Dewey]

Man does this storm continue to look impressive; deepening to 960-965mb just north of Lake Superior. Wind fields are beyond incredible - 80-100knts jet max at 850mb over MI & 125-150mph max at 500mb over northern IL, with a ribbon of low to mid 60's Tds reaching all the way into central lower MI ahead of the front by 0z FRI.

This does remind me of the extreme derecho October 24, 2001 with numerous embedded TORs.

If this comes to fruition, I think mode will be linear and extremely fast moving. Not much chasing; probably more of an intercept.

 

[jshields]

the 12Z models today show a 1004 mb low at 18Z on thursday and a 968mb low at 06Z saturday, thats only 36 hours! with such strong forcing and little turning with height, i think this is a damaging wind event if enough instability can develop.

Models are showing a very strong dynamic trough that negatively tilts across the Central Plains and Midwest. Height fall anomalies are currently forecasted as high as 6 standard deviations from normal. 65 degree dewpoints come up all the way into southern WI, even though these may be a bit overdone. By 7pm Friday, a 120kt 500mb jet streak rounds the base of the trough creating strong divergence aloft. In response to this, rapid cyclogenesis should be ongoing. One problem is the shear is largely unidirectional. SSE at the surface, S at 850 and 500mb, and SSW up at 200mb. But if a strong updraft can alter its local environment there could be a risk of a tornado. Instability may also be limited leading to just a strongly forced transcontinental line of showers and a few thunderstorms with very little lightning, with an attendant threat of damaging wind gusts. Nevertheless, this is something to watch. It also seems like it could become a Great Lakes bomb too.

 

[Greg Blumberg]

This is absolutely fascinating. It's a perfect example of bombogenesis per both the GFS and ECMWF. I'm not thinking chasing because like the others here, I'm seeing the cold front screaming across the Midwest on the GFS. I'm also in Oklahoma too, so that puts a damper on it. Either way, I think this should be an incredible event if the GFS verifies for Friday. I'll be leading a student based forecast shift on Friday, and this will definitely be mentioned.

I'm having a difficult time finding a decent website that will show me ECMWF data per temperatures. CoD has the initialization at 0z Monday, I'd like to see the 12z Monday.

I can't wait to see how Friday turns out!

 

[nickgrillo]

Yes, the overall kinematic profiles are unidirectional in nature -- BUT, this won't matter much since the convection will be shallow. Hence, the boundary layer directional shear that we do have (and there's plenty of it) WILL be sufficient to maintain fast-moving supercells. As for surface-based instability, total CAPE isn't a real helpful parameter with systems around this time of year. Using low-level 0-3km CAPE is a better way to determine available surface-based instability given the shallow nature of convection. I haven't looked at anything in-depth yet, but when I do, I will post a more detailed analysis.

the 12Z models today show a 1004 mb low at 18Z on thursday and a 968mb low at 06Z saturday, thats only 36 hours! with such strong forcing and little turning with height, i think this is a damaging wind event if enough instability can develop.

 

[Robert Dewey]

Well, the 0z and 6z GFS aren't looking good. The systems phase much further north, and the baroclinicity isn't as tight. The GEM still holds on to a 975mb low near Lake Superior (but is still further north and weaker than previous runs). The 12z NAM is only out to 72hr right now, but it's also further north.

It's not set in stone, of course... but my confidence is lowered significantly given the last few model runs, and the trend among most model guidance.

 

[Skip Talbot]

My preliminary target is the MO bootheel at 18z. The target and timing though will definitely shift as the models get a better grasp on this fast moving system.

Looking at the 12z WRF, the 3km Cape is mostly restricted south of I-70. With the very dynamic system, extreme low level shear, and lack of surface based Cape, this is the plot to watch. Thus I think areas to the north might be out of play. There is a bubble of 180 3km Cape over the MO bootheel at 18z. I'd rule out adjacent areas before and after simply because of the terrain. No doubt the shear is very impressive with 40 knots 1km shear and 200-300 1km SRH forecasted over this target at 18z. Low topped supercells and tornadoes are certainly supported with these parameters. I'm most worried about the precip plots the GFS and WRF have been showing. The entire warm sector looks like its going to be swamped with ongoing precip throughout the day. We don't need much instability with the dynamics involved, but this could completely kill any instability we do get. If we get a break, I think there might be a window of opportunity to follow northeast moving cells up the MS river valley, maybe along I-55 before they move off into the jungles of southern IL/IN. This is going to be a tough chase, but with the extreme shear and moisture advection forecasted, the severe/tornado potential is definitely there.

 

[Dan Robinson]

There is so much model uncertainty regarding timing/phasing with this event that all I'm planning at this point is to be up early Friday morning looking at what is actually happening at sunrise. For instance the 12z NAM has the squall line just arriving at STL at 00z, and there hasn't been much consistency on how long the surface winds will stay backed as the main low bombs to the northwest.

Any clearing in the warm sector will change the ballgame and thus will be the first item to check in the morning. Mount Vernon, IL to Paducah, KY is where I like right now - but as much as I want to speculate on a target, I know that it's going to be a "set the alarm for daybreak and get online"-type chase day.

 

[Robert Dewey]

I'm liking the 12z GFS better than the 0z and 6z. The 12z GEM is also pretty similar to the GFS. I'd like to see the monster 965mb low, but 975mb isn't something to turn your back on. Tds still in the low to mid 60's all the way into central MI by 18z FRI, and wind fields are still awesome (60-80knts vs. 80-100knts @ 850mb).

Lots of time for changes...

 

[Bob Hartig]

If you go by the GFS, then the play will be all in eastern MI by 18Z. The NAM slows things down a bit, bringing 60s Tds up into 1km helicities of 300+ in mid-Michigan by 21Z. (See attached map.) I like that better. NAM is more generous in its distribution of sfc-500 wind crossovers.

But there's absolutely no CAPE to speak of. Zilch. Just a ton of shear, making me think that this system will be hard to chase not just because of its speed, but also because any tornadoes will likely be hard-to-predict spinups. Kind of a park-somewhere-watch-your-radar-let-it-hit-you-and-hope-for-the-best scenario. (Let's see...that's 13 hyphens. Good thing I've been saving up.)