While things have quieted down a bit since two severe storm systems hammered the area Monday, more rain could be on the way this week.
The storms, with winds in excess of 90 mph, caused widespread damage to trees and power lines in Will and Grundy counties. Several businesses and residences also were damaged, though no injuries were reported.
An EFI tornado was sighted between Plainfield and Romeoville; seven more were reported elsewhere in the region. The storms dumped more than 2 inches of rain in some areas.
Afterwards, temperatures dropped into the 50s and 60s.
But stormy weather could be back this week, said Matt Friedlein, a meteorologist with the National Weather Service.
“... It does look like we’ll get back into an active pattern next week,” Friedlein said. “Perhaps not as active as Monday, but one with the jet stream over us where we might have multiple thunderstorms.”
The fury of Monday’s storms almost was inevitable.
Heat and humidity had been building in the area for some time, Friedlein said. Temperatures were two degrees above normal throughout the month.
And June precipitation has been way above normal, the second wettest since 1928, he said.
“We were in a locked pattern of moist unstable air, a tropical air mass, for about two weeks,” Friedlein said.
The storms were generated as a wave of cooler air moved through northern Illinois.
“We’re kind of right at the northern edge, right in the battleground of dry, cool air to the north and warm, moist air to the south,” Friedlein said.
Jeremy Hylka, director of the Joliet Weather Center, said the two storms from last week have been classified as “derechos,” bow-shaped squall lines capable of causing wind damage for hundreds of miles.
Monday’s storms originated in Iowa and maintained their intensity through Iowa, Illinois and Indiana, Hylka said.
“To have two derechos in a day, let alone four hours apart, is a rare experience,” Hylka said.
Having the second storm – the worse of the two – hit at night only made things worse, Hylka said.
“Whenever you have that magnitude of storm at night, you can’t see it come in,” Hylka said. “These mini-circulations and rotations can pop up anywhere on the line and they are almost impossible to predict.”
The storms spawned several EF1 tornadoes across northern Illinois. Yet it was the wind alone that caused most of the damage.
“People get this mindset that only tornadoes can cause damage and that’s a fallacy,” Hylka said. “The straight line winds that hit Morris were 80 and 90 mph, as powerful as a small tornado.”
It’s hard to say what the rest of summer will bring. While the National Weather Service only forecasts out to 10 days, its Climate Prediction Center offers a generalized three-month outlook.
“The remainder of July through September show no strong sign of wetter or drier than normal weather,” Friedlein said, “though signs are that it will be wetter than normal in the Rockies and on the northern and western plains.”
The country is in a mild El Niño pattern, which generally has a limited effect on summer temperatures here, but can produce a milder winter depending on when and if it strengthens, Friedlein said. That pattern is caused by band of warm ocean water temperatures that periodically develops off the Pacific coast of South America.
Another long-term prognostication service, The Old Farmers Almanac, is calling for a hotter than normal summer (correct so far), rainfall slightly below normal (incorrect so far), with a tropical rainstorm threat in mid-July. (We’ll see, though perhaps it landed early last week.)
The almanac is calling for hot periods in early to mid-July and late August.