03/30/05 NOW: MO, IA, IL, WI, IN

Since convection is active already this morning, and is likely surface based by now, decided to kick off a nowcast thread for discussion of this event as it unfolds. Feel free to discussion reports and short-term forecast trends below.

I'll begin by noting new tornado watch posted by SPC:


Plumb of deeper moisture evident in the Little Rock sounding this morning could reach the axis cold temps aloft by mid-afternoon, and set the stage for some tornadic potential.

11:30 central update:

Vis sat showing nicely the northward progression of richer moisture as cumulus field now just east of Saint Louis, where a few low 60 dewpoints are observed. Winds are starting to veer across all of Missouri - so convergnce is increasing along the MS River valley. RUC estimates of SBCAPE reaching 1000 J/KG along MS River valley now - so 1500 quite possible by early afternoon across portions of northwest IL.

I'm in Peoria right now, and while the watch box makes it tempting to adjust west, the southern extent of the arc of cu ahead of the pac front as well as the capped presentation of the field makes me hesitate. Not to mention that when the storms finally go, they're going to haul, so if you're too close you might see them early, but you'll never keep up. Then again our window for isolated storms could be open very briefly, and if you wait, you might only have a squall line to greet you. Heh. This is what 45 knot storm speed is all about! :)

I expect another watch east of the current one and a new one covering central and southern Illinois as the enhanced cu field approaches. Where will tail-end Charlie be? I don't know. Maybe in Tennessee.

I might make a small adjustment west.
Great! Other folks are here. Yeah - the southern extent of development is tough to ascertain right now. Looking at the water vapor loop, you can see a band of strong subsidence along a line from Springfield to Quincy, which appears to be limiting the southern extent of development right now. Weak lift ahead of this generated an elevated cell north of the Quad cities and a cloud band now over central IL. RUC model showing marked lift swinging across this axis by late afternoon - so this may overcome current subsidence associated with mid-level CAA to produce favorable deep instability. I may head out in the next few hours if things continue to improve.

Update - rapid development now just east of Quincy -which unlike earlier stuff is ahead of the trough axis instead of behind it in the veered winds. May head out very shortly.

Tornado Watch #105

New Tornado watch issued by SPC:


Visible satellite confirms rapidly developing cumulus field in west central and NW Illinois . Thunderstorms are also continuing to rapidly develop in west central Illinois moving NE at 55. Severe thunderstorms currently in progress for Fulton/Shuyler county in Illinois as well. profiles contiune to indicate favorable shear for tornadic thunderstorms.
Just wanted to post a couple of quick observations about the storms that initiated over NW Missouri this morning and promptly moved NE ... two of the most noteworthy cells to the east of St. Joseph around 9:00 a.m. were very well structured ... hard, crisp cumulus and anvils both. The southern cell maintained an overshooting top for a while and looked very impressive from the west. If it hadn't been for work obligations I probably would have gone after it (and considered going anyway), but it was moving at around 50 mph and it seemed like everytime I looked up it was further and further away - so would have been REALLY tough to chase given the terrain it was moving over. Believe these later weakened as they moved into IA. Hopefully things will slow a bit as the system makes progress into IL ...
ILX (Lincoln, IL) evidently did a special 18z sounding which found CAPE to be ~1500 J/kg and LI of -5. Winds were up to 50+ knot velocities all the way until 800 mb with some veering of the winds below 850 mb.

The ongoing storms in central IL have storm motions of ~220 degrees with the cell motion ~40 knots. The cell southwest of Peoria looks to be the healthiest with an impending cell merger from the southeast likely to occur in the next 10 to 15 minutes. A severe thunderstorm warning has already been issued for it, expect large hail and winds in excess of 70mph. Could possibly be the first tornado producer, we'll have to see.
Peoria storm looking mean on radar. Looks like its trying to get the flying eagle look to it. Moving into some good air and wouldn't be surprised to see a hook form out of this guy. DBZ over 65 in places indicates very large hail in the core of this storm which is poised to pass right over the city. This storm is hauling northeast at 45mph. My only concern would be the convection to the southwest of this storm, but right now, this looks like the main show in Central Ill.
Tornado Warning just issued at 2:41 CST for the Peoria supercell via Doppler indicated rotation. It has a beautiful V-notch and has been a fun one so far to armchair chase.

Also of note is the Tornado Warning northeast of Madison, WI and also a reported touchdown in northern Iowa. A busy early afternoon in three seperately distinct portions of this system.
What's great about this Peoria storm is not only its strength but the road networks east of the city are perfect for chasing this cell. Wish I where there.

I can almost bet there is some baseball size hail in that core.

I hope those road networks have high speed limits.. this storm is hauling! Starting to take on a more HP look to it on radar. Looks like it'll pass just to the south of Ottawa here shortly. I guess I can see where the hook is (limited on software to zoom), but I'm guessing that's become a big hailer as opposed to what the radar was saying earlier. Tornado Warnings continue for this cell.

The storms in Southeastern Minn looks like crap. Tornado warnings with those as well, but they're buried in crap, so hardly chasable, I would imagine.

The storms in southern Wisconsin don't look quite as bad, but they are losing their isolation and look as if they'll be joining in a mass here shortly.

Definately looks like the best stuff's in Illinois, but I'm wondering if the good window is starting to close.
The tornado warned storm heading out of Peoria may be a huge mess for Rush Hour in Chicago if it continues on its course northeastward... if it holds it strength and at least remains severe warned, it'll likely start impacting the Chicago area in the next 2 hours.
The Tornado Warning continues for the central IL supercell as of 3:33 CST. The inflow environment of the storm is becoming contaminated but it is heading into a ~1500 CAPE environment near Chicago per the 21z SPC Hourly Mesoscale Analysis page. However, the 0-1 km shear is not nearly as favorable ~15 knots and LCL's are much higher that you would like for tornadic development ~1600 m. If this gets any closer to the Chicago area that may be for the best!

LOT was 79 over 52 as of 21z so low-level moisture appears to be lacking still.
Trained spotters reporting a tornado with the storm moving towards the Ottawa area. Some 65DBz still showing up in the reflectivity indicating some rather large hail with this storm. I think the storms to the southeast are interfering with this storm a bit which may explain the phase change in this storm in the past 30 minutes. Storms up near Sterling look to be trying to form a line with the Ottawa storm down towards the Peoria area. Storm isolation may be scarce from here on out as things are starting to head into the evening hours. BTW, that hail core is parked right on top of I-39, so I imagine motorists in the storm are probably getting more than they'd care to deal with right now.
LOT is down to 75 over 42 and continued cell mergers are turning this into an even larger HP mess with large hail. As of 3:56 CST there is still a funnel cloud being reported near Streator. However, the low-level wind fields appear too uni-directional into the south side of Chicago so it is only a matter of time before this evolves into an all-out squall line.

One interesting cell just popped up west of Bloomington, IL that appears to have enough isolation and can interact with the outflow boundary of the previous supercell to possibly become tornadic.

The attention now should be focused southward to northeastern Arkansas and western TN where a tongue of near 60 degree dew points is located and the cap is likely to break near 23z.
More news on the supercell that originated southwest of Peoria around 2pm CST this afternoon:

As of 4:28 CST the public reported a tornado on the ground 8 miles west of Morris, IL moving northeast at 45 mph.

Despite being an HP mess and moving into more stable air the supercell continues to have a tornado on the ground. In another 45 minutes it will approach the southwest suburbs of Chicago so this could possibly have a large impact. Latest ob. from LOT is 73 over 48
I agree... T-td depressions are pretty large, leaving LCLs quite high. In addition, surface winds are so strong that it's reducing helicity / SRH quite a bit. The tornadoes in se MN and ne IA kind of surprised me, but they appeared to be nonsupercell tornadoes. I wish we had a high density surface ob network in IL, as it'd be interesting to see the area near Chicago, which two supercells are currently aiming for (though, they are losing their supercell characteristics pretty quickly as they near the city). Those two particular storms are actually in a pretty marginal supercell environment, with 1000 CAPE and 40-45kt 0-6km shear with little directional shear. The storms farther south near Bloomington look interesting, however.
I was picking up a nice couplet on this storm until it moved just SE of Morris. Since then it appears the cell may be weakening. If it is still spitting baseballs the damage could be extensive, as it is moving into very populated areas. We should be able to get great reports, as the storm is on target to pass over the NWS office.
The Chicago WFO has gone with a Severe Thunderstorm Warning in DuPage and Will Counties. Golf ball sized hail has been reported 5 miles SW of Plainfield as thankfully the hook echo has disappeared during the past two volume scans. Large hail appears to be the main threat now for the Chicago metro. The cells down south near Bloomington have been dropping nickel sized hail and don't appear that they are losing their tornadic potential.

The cells downstate tracking toward Decatur, IL should be monitored however as they are still in a 1000 J/kg environment with better VGP of ~0.2 with 0-1 SRH Helicity of ~200. They are also near a bullseye of EHI of 2. Hindrance is still LCL's of ~1700 m and Td's of only 54 degrees.