Tornado watch

The entire area is under a tornado watch until 10pm. A severe thunderstorm watch was likely but conditions favorable for tornadoes escalated and SPC went that route. And right on cue a tornado-warned storm is near the Illinois-Wisconsin line at 2:30pm. Other non-severe storms are approaching from the west. Damaging winds, lightning and torrential downpours are possible anytime through tonight (although most hours will be dry). Slightly cooler tomorrow.

tornado watch until 11pm

All that sunshine during peak heating hours today has destabilized the atmosphere, and SPC has placed the entire area under a tornado watch until 11pm. The good news is that most of the Chicago metro area is on the fringe of the main threat area, but a tornado or another otherwise severe storm is still possible anywhere in the area. The prime time for storm development will be 5-6pm, and a couple of models are putting a supercell into the Chicago area around 7pm. We'll see -- the atmosphere is juiced but getting the development (let alone the exact timing and location) of severe storms right is difficult. 

Severe t'storm warning

The whole area is warned until 6:45 AM as a line of severe storms approaches from the NW. Winds above 60 mph are the main threat.

Storms, flash flood watch

The whole area is under a flash flood watch from pre-dawn tomorrow (Monday) through tomorrow night. An inch or two of rain could fall of storms develop as projected.

We are also under "Moderate" risk for severe storms. There is a building line of storms several hundred miles to our NW that could be in here around 4-8am tomorrow (Monday). A second round of storms is also possible in the afternoon. Neither scenario is assured but storms that do develop could easily become severe, with high winds the main threat.

More storms: "Enhanced" severe threat and Flash Flood Watch tonight

Bad news then good news, plus a recap of Monday night's storms.

Bad news:

• We are again under an "Enhanced" threat of severe storms tonight -- the whole area is outlooked, but south is more likely than north.
• The whole area is under a Flash Flood Watch starting tonight and running through Thursday morning.
• Several waves of heavy rain are likely to emerge from Iowa and traverse the area tonight. Some storms may pop this evening, but 12-6am is most likely for the heavy storms.
• Some spots might be missed but 1" looks like a good bet for most locations, with some getting 3-5" of rain if things come together. Lake County might get off easy, while Will County and points south are more favored for heavy rain.
• There is 2.0" of precipitable water in the lower atmosphere -- that is almost off the charts for this area. We're also sitting right on the edge of a huge dome of heat (triple-digit highs today on the Plains). Those two factors have often combined in the past with explosive results. 
• Some areas have already seen 7-8" of rain this month, and the whole area is running well ahead of normal for rain -- soils are saturated and the flood risk is higher than normal.
• After many locations saw ~4" of rain (expected roughly once per decade)  just 10 days ago on the 15th, a second such event would be truly unusual and potentially very problematic in flood prone areas.

Good news:

• Starting tomorrow, this exceptionally wet and stormy pattern looks like it will break down. From this distance, it looks like the Friday-Monday period should be sunny and dry with temps in the 70s and 80s.
• Tom Skilling is back from his umpteenth three-week vacation of the year.

Monday storms:

• The severe storms that came through far western and southern sections of the area on Monday night produced nine tornadoes. 
• One tornado near Coal City was rated a strong EF-3, with estimated winds near 160 mph -- the damage was impressive. There were seven injuries but none serious, and that seems miraculous given that this tornado occurred late at night and was obscured by a lot of rain.
  
• This is the strongest Chicago-area tornado since the Plainfield F5 of August 1990. (The monster EF-4 that hit Rochelle/Fairdale in April was not technically in the Chicago MSA). The Coal City tornado's path was 16.5 miles long and three-quarters of a mile wide at its peak. 
• Imagine this storm track about 30-40 miles (a rounding error) to the northeast...
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Severe storms

There is a confirmed tornado on the ground west of Channahon and Joliet. This supercell is moving ESE and will affect Will and southern Kane counties. It might weaken as it approaches but redevelopment is also possible. A new tornado watch until 2:00 am is in place for Will and Kane (but not including Cook, Dupage or Lake).

Other big storms are popping elsewhere. One storm is just north of Carol Stream and is tracking east toward O'Hare. The atmosphere is primed and these storms show that the "cap" has been breached so more development is possible.

severe t'storm watch

We've just been put under a severe thunderstorm watch until 3pm. (And another one is possible for the evening hours after a break this afternoon.)

SPC almost went with a "PDS" -- Particularly Dangerous Situation -- watch, which is rare territory. They ultimately went against that, but the chance of severe weather is pegged at 80%, which is very high. 

A line of severe storms is approaching from the northwest right now. It will arrive in the far western suburbs between 10-11am and downtown between 11am and noon.

This line has a history of 80+ mph gusts and significant wind damage along with frequent lightning and brief heavy rains. 

A severe t'storm warning is likely with this line of storms. I won't sent an update unless something significant changes -- expect strong to severe storms across the area from ~10:30 through ~12:30.