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. 

Severe threat Monday

We have two chances at severe storms on Monday. The first is a line that may develop late morning into early afternoon. The second looks less certain but is potentially more significant -- it would develop toward sunset. The set up has a lot of moisture and a lot of wind shear so things could get ugly. SPC has us under "enhanced" risk of severe storms and that is a fairly big deal. Definitely worth paying attention tomorrow.

tornado warning cancelled; flood threat increasing

The tornado warning has lapsed. (Note that reports of sirens outside the warned area were due to local officials jumping the gun.) In any case the threat has already passed, although isolated severe weather (wind, hail) remains possible. The ongoing threat of significant flooding is also increasing by the minute as wave after wave of drenching thunderstorms is orienting along an axis from west to east, right through the heart of the area. Everything in a corridor 30 miles to the north and south of downtown is under the gun right now, and significant downpours will continue for several more hours. Hardest-hit areas will see very high rainfall totals. Roadways, creeks/streams/rivers and low-lying areas are all at risk of flooding. Do not take any chances in crossing any water in a vehicle or on foot.

Traffic times are already very high, and both airports are being severely impacted. Train delays are likely as well. 

Tornado warning and flooding threat

Central Cook is under a tornado warning -- radar indicated a tornado near Maywood and Westchester moving east near/along the Eisenhower. This is unlikely to be a strong tornado but that will not prevent damage or injury. Take notice in the area and pay attention in areas to the east.

Most of the area is under a flash flood warning. After many places saw heavy rain earlier today, a new round of moderate to heavy rain is moving through. The earlier projections look light, if anything. Many places could see 2-4" of rain today, which comes on saturated soils.

The good news is that the rain should clear toward midnight and tomorrow looks dry and beautiful. But there will likely be significant water problems tonight for some spots.

flash flood watch

The entire area is under a flash flood watch until tomorrow morning. With all the recent rain the ground is already saturated, and today and tonight look likely to produce more heavy rain. 1-2" is a good bet across most of the area, with isolated 3-5" totals possible in spots that get stuck under a series of storms. Isolated severe weather is also possible. 

Severe t'storm watch, heavy rain

Severe t'storm watch for the area until 11pm. Several non-severe storms approaching from the west now. Big storms south near Joliet. All moving NE and most places will see storms tonight. Model estimated totals for the next 36 hrs are 1-3" across the area with local 4-5" totals possible.

Heavy rain

Starting tonight through tomorrow morning we're under the threat of heavy rain. An inch or more is a decent bet for almost the entire area (less north, more south) and certain spots could see a lot more than that. Areas along and south of I-80 are most favored, and given the deluge they've received recently the flooding threat is elevated there. Areas SW of Chicago are also under a tornado watch and isolated severe weather is possible throughout the area as well.

Weekend looks mixed. Saturday will be mostly dry (if cloudy) with just some light, passing showers. Sunday looks wet but won't be an all-day washout.

severe t-storm warning

A line of severe-warned thunderstorms is approaching from the west. Suburbs in Dupage are feeling the effects now, and if they hold together the storms will arrive along the lakefront before 5:00 pm. These are not terribly impressive storms, but CTG lightning, 60mph gusts, and small hail may occur along with brief heavy downpours.