6/05/05 FCST: Great Lakes

Warren Eckels

(I'll confess, part of the reason I'm posting this is so that we no longer have 666 topics...but if I didn't have a gig Sunday afternoon I might now be planning some kicks on 66 (I-57) between Joliet and Champaign)

The 12 UTC NAM and MRF are setting up interesting weather for much of northern and central Illinois, Wisconsin SE of I-43 and Indiana west of a South Bend-Terre Haute line.

The low in Kentucky this morning will weaken and move east, so Gulf moisture will have fewer problems entering the region this weekend.

On the side of severe weather, 0-6 km shear will be about 35 knots, a moderate jet streak (50-80 kt) will be crossing the Mississippi, moderate levels of humidity at 700 mb favor severe thunderstorms and surface dewpoints near or above 70 F are expected. Temperatures of 17-18 C at 850 mb indicate that areas with much sun will see 85 F by 1 pm. Finally, SW winds at the surface around 10 kt will keep Lake Michigan from slapping down convection near Chicago.

On the side against severe weather, we will be in the right-front quadrant of the jet streak, which favors sinking air. Whatever we do get Sunday will probably not be a tornado, since wind shear would be horizontal (at least until frontal passage overnight).

What happens on the eastern Plains Saturday will affect Sunday afternoon's weather and can work either way. An active Saturday in western Iowa means MCSs and lots of cloud cover Sunday, which in turn lowers temperatures. Move Saturday's activity east to the Mississippi, and the MCSs clear Illinois by dawn after dumping some rain and developing a pool of low-level moist air that would give convection an extra kick.

Sunday night, a cold front should pass through, probably attended with the usual line of heavy thunderstorms.
Little change to forecast

There's more excitement than expected on the Plains today, and some of it is headed to northern and central Illinois and Indiana west of a South Bend-Terre Haute line. I anticipate severe thunderstorms, and would not be surprised by a derecho screaming north-northeastward into Wisconsin with rain-wrapped tornadoes on its right flank.

Last night's ETA run looks for 36 hours of WAA through 7 pm Sunday, moderate (ideal) mid-level humidity, sticky surface dewpoints near 70F and 850 mb temperatures supporting afternoon highs ranging from 90 in Chicago to 94 in metro St. Louis. Other models and the Eta surface forecast are less excited, indicating 85-90, with warmest temps again near St. Louis. Unidirectional wind shear on the order of 30-40 kts is anticipated, on top of 15 kt surface winds. Moderate humidity is confirmed by looking at 700 mb T-Td spreads upstream.

The SPC believes that boundaries set up by the Great Lakes may create directional windshear, but the SW winds will probably push lake boundaries offshore. Great Lakes chasers (and their loved ones) should be aware that the SPC may be upgrading the Great Lakes region to a higher category of risk.

Going out on a limb, I would place the maximum (but slight) risk of tornadoes east of I-57 and north of Rantoul, and only if a squall line develops to the north and west. I'll also be grateful that the location of my gig (a memorial service in NW Indiana) will be in a very small church with few windows and a convenient windowless storage room.
Yeah, there's only a couple of us true Great Lakes chasers left :wink:

Height falls are pretty strong with this setup... Wind fields are pretty strong through the layer, and with good moisture pooling, instability gets up over 2500J/KG pretty easily. My bet is that convection today will be dying off tomorrow morning, and laying down some outflow boundaries across southern WI/IL. Things will begin to heat up in the afternoon, with the development of supercells quite likely.

That's when things get tricky... Where will the intitial supecells develop, and then what happens to the convection afterwards? For the first question, the NAM shows a decent CAP covering most of IL through about 21Z, at which point it errodes. But, the NAM still doesn't develop any convective precipitation over that area. Further north into WI, spreading into MI, the NAM shows some moisture in the mid levels with some associated convective precipitation. It's hard to pin down a real source of convergence (cold front, pseudo-dryline, etc.), so that leads me to believe that convection may actually be more cellular in nature, wherever it should develop. As for squall line / derecho prospects - it's tough to say. We have moisture pooling and high theta-e, intense height falls, strong wind fields, etc., so we shall see...

Whatever happens today will have a strong influence on what will happen tomorrow...
Originally posted by rdewey

Whatever happens today will have a strong influence on what will happen tomorrow...

That is what i'm worried about the most tomorrow. If there is a large MCS moving NE out of iowa/missouri, Will that kill the heating for our, michigan, illinois, etc. storms tomorrow? Also, the lack of a source of good convergence is somewhat worrying. This, however, could be where a dying MCS is helpful, leaving outflow boundries that might be the source of convergence.

With the complete lack of storms over michigan this year, i really hope this event pans out. I don't care if its supercells, large severe squall line, etc. I will take anything at this point.

Plan on being out tomorrow, staying pretty close to home.
I won't even begin looking seriously at tomorrow until I see what happens tonight. I'm sure the atmosphere will be very worked over in portions of the outlook area. It's all a matter if and how fast the atmosphere can fully recover.
We will have to see what kind of air mass recovery takes place from any mcs's & whatnot... If the sun comes out even for a couple of hours, even as far south as S. Illinois could get hammered to some degree. We will be ready. im initally targeting Mt. Vernon IL - St. Claire CO. Im puter chasing in Kansas, Looks to be nasty in Hiawatha about right now. All you chasers be careful & get the reports out.
I like tomorrow's prospects across much of Illinois..primarily central and northern IL...into Indiana. It's got everything needed for some more supercells, except for the surface winds. We're fine until mid-morning when winds over the entire state swing out of the SW pretty much ruining any LL turning we might have early on.

Instability is there...temps will be back in the low 90s, with dew's in the 70s. Winds aloft are really bookin out of the SW. I guess we're going to see if we can get some outflow boundary wandering around out there to get some locally enhanced turning for a storm to root into...or even a mesolow to get some backed winds.

All in all, severe weather looks like a good bet over a good portion of the area...but something will have to be done about the surface winds if we want to see any tornadoes in this area.

Be interesting if the SPC holds with their previous discussion, and does issue a moderate risk. If this does occur, it'd be for high winds I'm sure, because the tornado potential just isnt there to warrant a moderate risk right now.
I don't have a forecast to share, but being this is a Jun 5 thread, I'd like to let everyone know that the North Webster, Indiana radar (located between South Bend and Ft. Wayne) will be out until further notice. It has been down since Friday. So anyone chasing NRN IN tomorrow or moving into that region may find themselves 75 to 110 NM from a WSR-88D. Just thought I'd provide a heads up. Mods, feel free to remove this post if you think it doesn't belong here.

It is in my belief that today will become a very active severe weather event over much of SE Michigan. With proper destabilization, moisture convergence later on this afternoon, and good upper-level motion, we could see one of the first 'big Michigan days' in over a year.

CAPES will be rather high, between 2500 and 3000, with localized areas approaching 3500. Helicity is going to be moderate, between 130 and 170 (but still high enough to generate tornadoes in this environment, in my opinion). The main factor is the jet stream, which is moving into close proximity to Michigan. It is therefore my opinion that tornadic supercells may begin firing across southern Michigan around 2pm this afternoon, with the heaviest, and possibly the best tornado-producing activity, approaching the Flint-Detroit Corridor of Michigan around 5pm.

DTX Spotter Activation is likely, so I'm getting my gear together and getting ready to give chase.
Danville, IL

For what it's worth, the SPC redboxed parts of northern and central Illinois early this morning in response to an MCS moving through. Today's most severe weather is expected in Michigan, northern and central Wisconsin and northeast Indiana...

The MCS in northeastern Missouri will shortly cross the Mississippi and march through the state between now and noon. My guess is that it will weaken until it crosses US 51/I-39, then strengthen as it hits the 75/67 conditions east of Springfield. I would not be surprised by a line of heavy-to-severe thunderstorms from Chicago, IL to Kentland or Fowler, IN around 10:30 am.

South of St. Louis-Fowler, heating will continue uninterrupted and into the low 90s. Vertical shear will be moderately favorable, though horizontal shear will be clockwise.

If I were chasing, I'd probably position myself on the northern outskirts of Danville, IL. That way I'd have a shot at any tail-end Charlie moving through (probably to the north) yet find myself close to the most unstable air as the front itself approached (particularly if the morning MCS fizzled).
I'm really liking the prospects of severe weather for MI. In fact, it looks somewhat similar to the setup that occured on June 8th, 1953 - The date which several violent tornadoes tracked across MI (F5, F4's, and several F3's). The position of the lows is the most similar, the strength is a bit weaker with today's system as well. The biggest difference is at 500mb, where June 8th 1953 featured a closed low. The mid level jet during the June 8th 1953 event also had a more westerly component.

For todays setup...Winds in small area of central lower MI appear to back, at least on the RUC, giving way to nearly 300m2/s2 in 0-3km helicity, while nearly 3000J/KG of CAPE is available. Looking at the 00Z NAM and attempting to verify it's 12HR forecast with the 12Z SFC data, it's about 10-20 degrees too west with the SFC winds across much of the midwest (particularly over IL). If this trend verifies, then the RUC's helicities may not be too far from the truth. The main source for convective initiation will likely be the outflow boundaries that are thrown around, in addition to some convergence along the nose of the 850/700MB jets.

There is currently nothing in the way of debris clouds over the main threat area, so I could see temps easily soaring into the upper 80's, possibly even lower 90's. I don't think dewpoints will make it much past 70F, but that still yields quite a bit of instability...

June 8th, 1953 - 850MB

June 8th, 1953 - 700MB

June 8th, 1953 - 850MB