Wednesday, June 24, 2015

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...

  • Tornado damage in Coal City, Ill. <span class=meta></span>

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