6/4/2010 FCST: IA/IL/MI/MO

[Tim Balassie]

Glancing at SPC earlier today I noticed the swath of SLGT across IL on Friday, so took at look at the WRF model at COD.

I thought 250H looked decent, with WNW 90kt flow reaching IL by 0z, with some difluence noted across the central part of the state.

500H not so good, with WNW flow at only 40kts by 0z. But, areas of vorticity are apparent across the area and Ts to -12 are not bad.

700H not so good also, with W flow at only 25kts. Ts stay around 4, so not much cap.

850H looked a little better, with 35kt WSW flow at 0z. Ts stay warm(er) at 14, with Tds initially at 14 as well. Overall not a terrific severe wx set-up.

Then I looked at sfc data, and was drawn away from IL and into IA. The only thing missing to me is a strong cold front/pressure trof. I was impressed by the ThetaE and Td ridge axes spread across C and E IA. Winds appear to back with height, with velocities stronger than further E. Thus I like the resultant helicity values. The CAPE and LI axes in alignment imply to me that if a storm gets going (again, not a lot of CINH towards 0z) it may be something to take a look at. There is some surface convergence to kick things off, so who knows?

I like to I380 corridor mid-afternoon right now. Heck I may be able to chase this one.

Tim B.

 

[Adam Lucio]

This could be a NW flow event if upper winds become more NWerly. If surface winds are even southerly under that I wouldn't rule out a tornadic supercell before a large MCS forms in the largely unidirectional profile as indicated by forecast soundings

Bulk shear of 50kts, EHI of 2 will support organized storms, and if there are any boundaries hanging around to locally enhance the SRH we could be in business for an isolated sup or 2 before the whole thing goes linear. Im definitely keeping an eye on Friday for a potential semi local chase.

No point in worrying about cape or moisture...it looks like there will be plenty of that to go around...although potential cloud cover could limit instability.

 

[Skip Talbot]

The NAM is showing what looks like a convectively reinforced warm front sitting across southern WI. If we can get storms to fire off that 90 knot diverging jet, and interact with the favorable directional shear along the warm front, we could definitely see some tornado activity. The NAM is also showing the cap wearing off to nothing by early afternoon, and depending when that jet arrives, it might be an early show with storms firing just after noon across a target of eastern IA/northern IL. The NAM is also hinting at ongoing convection across the warm sector throughout the day. Hopefully that junk doesn't spoil the environment if its true.

 

[Brandon Sullivan]

Based of 00z NAM I am adding IL to the thread..

Eerily similar setup to some good setups in the past..

By 21z there is a nice low across Wisconsin with a warm front draped from NW to SE. Strong moisture advection yields good afternoon instability.

Decent SW surface flow under strong NW flow, with southeast moving storms could yield some nice supercells, with 40 kt shear vectors perpendicular to the boundary. Definitely something to watch!

 

[Tim Balassie]

Funny how things can change in a day. Yesterday I was somewhat optimistic, and today less so. It seems the timing between surface features and upper air support is off. If things could just be slowed down a little …

Haven't look ed SPC yet, but based on what I’ve seen today with the WRF I agree IA now looks out, for the most part. I’m wondering if there would not be a window of opportunity for NW/NC IL and SW WI spreading E towards MLK.

I like the backed flow across IL ahead of the advancing trof/wind shift line along the MISS Riv towards 18z. However, the SE flow pulls in cold air across SE WI and I wonder if there can be enough recovery. The CAPE and LI numbers for NW IL look quite nice, but the upper air support seems to lag the sfc trof axis.

Helicities follow the trof axis from IA into WI, but again timing looks off. Surface features are E of Lk MI before strong flow with cold/dry are gets in.

My chase opportunities are so limited I start grasping at straws whenever there’s a wiff of severe. So, I’ll pull back from the I380 corridor of yesterday and look at a DVN-Dubuque-Dodgeville area instead.

TMB
(KC9JIB)

 

[Mike Kovalchick]

Probably should add Michigan to this thread.

The 12Z NAM shows backed winds, curved hodographs, good bulk shear, low-LCL's and EHI's above 3 near Lansing Friday evening suggesting some low-topped tornadic supercells are possible if we can get some surface heating. (GFS shows nothing.)

Will be looking at SAT/radar images carefully tomorrow morning to see if a backyard chase is in the cards and if the MCS dosen't ruin the show as usually is the case. The SPC hasn't bought into this possible scenario yet it appears.

 

[Robert Dewey]

NAM skew-t and hodographs are looking extremely impressive over MI tomorrow evening. Lots of directional shear, with 510m2/s2 of 0-3km helicity [430m2/s2 0-2km], and the CAPE profile isn't looking as skinny as it was. In fact, DTX showing 2500j/kg at 5/0z... creating a 0-1km EHI of 4.8.

Convection should erupt in SW MI between 18z-21z as the shortwave energy rides above the sfc boundary... sliding eastward across the state through 03z. If the NAM is correct, the threat for supercells is pretty significant.

 

[rdale]

Gotta pray that the MCS out over Iowa dies quickly enough that no clouds from it bother Michigan tomorrow... If we can get in plenty of sunshine, I'm sure the NAM is on to something. Otherwise, it's another "good shear / no juice" event, with two showers that drop EF0 tornadoes with no lightning

 

[Colin Davis]

Personally, I'm still quasi-optimistic about extreme Eastern Iowa and Western Illinois tomorrow. It all really depends on which verifies. NAM says crapshoot, GFS is more interesting. GFS treats it more like a more "traditional" NWrly flow setup (if there is such a thing), holding off precip until ~22z or so and giving us much more instability there when it does so. Surface winds are veered (although locally back in areas, albeit weak...the major problem of many 2009 setups, unfortunately), but are strong at times and there is decent turning especially between 850 and SFC. These northwesterly flow regimes are more difficult to predict, but if GFS is correct at 0z, I'll take my chances with Keokuk or Fort Madison around 2230z.

It's too damn close for me NOT to chase.

 

[Andrew Pritchard]

I'm more or less with Colin on this one target wise. The NAM looks less than ideal, with the GFS slightly more kind. I'm not inclined to believe one over the other. I'm not expecting a big day, but a surprise localized tornado event is certainly possible in an area from Ottumwa, Iowa to Galesburg, Illinois. Current thinking is that the outflow boundary from the dying mcs currently located over western Iowa should lay across the Highway 34 corridor in southern Iowa. Seasonable moisture with td's approaching 70 or even slightly above in some areas along the boundary coupled with ample surface heating and the approaching shortwave arriving in eastern Iowa in the early evening should aid in the development of isolated severe thunderstorms by early evening in southeast Iowa. Surface convergence should also increase considerably in the region as the boundary sags southward. Low level shear won't be overly strong, but with the aid of the potential interaction along the outflow boundary I think storm rotation should be manageable. HP storm mode is a concern.

Current thinking is that a tornado or two is possible with a nice slow moving supercell in southeast Iowa tomorrow evening in an area around Ottumwa to Mount Pleasant, Iowa. This area could shift tomorrow with the movement of surface features, but se Iowa into far nw Illinois has seemed pretty consistent over the last day or so.

 

[Jesse Risley]

This will be another case whereby it will be extremely important to analyze surface features in the morning to ascertain the location of any remnant OFB(s), should potential CAPE forecasts materialize. The MCS will need to be watched to see where it tracks and how quickly it clears out. While the models might have been flopping around a bit, the potential is there for a decent pocket of clearing across the central third on IL, far eastern IA and even NE MO.

The 00z run of the 4km WRF wants to develop some convection with decent updraft helicity in extreme SE IA and far NE MO tomorrow evening, and it shows the MCS clearing the area by early afternoon.

I posted a more detailed forecast here.

 

[Bob Hartig]

I've been kicking the scenario for Michigan around with me droogs, and I thought I'd share a couple RAOBS for eastern Michigan here as well. These NAM model soundings are for 23Z at Flint and 00Z at Pontiac.

A few observations from a backyard chase perspective: Surface winds back better on the eastern side of the state, best helicities lie in that direction, and CAPE is also good. There's a bit of capping around Flint and Pontiac, but nothing horrible. Sigtors focus around Flint--except for F5 Data's proprietary index, which continues to scream about Grand Rapids/Kalamazoo. That may be because NAM has the 500 mb jet max nosing in right around there.
Given the pronounced westerly midlevel flow, it may not matter if surface winds are a bit southwesterly, as they are throughout southwest Michigan. Still, call me a traditionalist if you will, but I'm a sucker for at least a slight easterly surface component if I can get it, particularly if I'm not sacrificing instability. So my eyes as of the 00Z NAM are on Flint.

Okay, fellow Michiganders, let's all sing that line from "Zippity-Doo-Da": "...Plenty of sunshine heading my way." (No clouds, pleeeeeeze!)

 

[rdale]

Not a good looking setup this morning... Clouds coming in, rain right behind them. Back to the "embedded EF0 and no chase" mode for now.

 

[Randall Cooper]

Might want to add MO to this thread. Looking over things early this morning I am planning on making the drive to chase in Northeast Missouri later this afternoon. Have a feeling it is mostly going to be a hail and wind event, but I wouldnt be surprised to see an isolated tornado or two.

 

[John Vandehei]

Not a good looking setup this morning... Clouds coming in, rain right behind them. Back to the "embedded EF0 and no chase" mode for now.

I noticed the same thing driving into work this morning. Looking at the latest VIS satellite, they are somewhat thin, with the thick clouds still over in Wisconsin. Also, I'm seeing decent patches of blue sky out my window as I type this. If we can get some good clearing, I think there is still some hope that things can destablize. Severe weather has been few and far between around here lately, so I'm really hoping for something.