Tuesday temperatures produce a surplus for the first time in 15 days

Several clusters of gusty thunderstorms blossom in warm, humid air
The remnants of powerful thunderstorms, which bombarded the Dakotas and Minnesota with hail the side of golfballs Tuesday and Tuesday evening, then sent gusts ranging from 45 to 75 mph roaring across sections of Wisconsin overnight, are to move across sections of the Chicago area as Wednesday dawns. 

Heavier storms here threaten hail, powerful winds gusts and passing downpours before easing during the morning. Indications are these storms may impact 30-40% of the metro area.

The storms are to exit the area, a development...

ASK TOM WHY: Why does so much precipitation seem to stay south of I-80?

Dear Tom,
Why does so much precipitation seem to stay south of I-80?
-Ken Ross, Chicago

Dear Ken,

Averaged over sufficient time — years or even decades — just as much precipitation falls to the north of I-80 as to the south.

That said, the weather sometimes falls into a “rut” for a period of weeks or longer, and repeatedly produces the same kinds of weather in the same places (for example, more rain to the south of I-80 and less to the north).

Relatively small surface features like highways do not affect weather systems, but they do produce weather variations that, in...