Nature’s about ready to “throw the atmospheric switch” sending summer level warmth and humidity into the Chicago area.

It will easily be the most sustained string of 80-deg-plus days in eight months.

What’s unfolding is extraordinary weather shift in Chicago — one which has been modeled and talked about here for well over a week. From the unseasonably chilly mid-March level temps of last week, readings are to take off like a rocket with an accompanying surge of July-level humid air, over the next 24 hours.

The coming week’s temps will post double digit surpluses across the central U.S. This is the 5-day average temp departure for Tuesday through Saturday of this week


This week’s average temp is likely to come in an extraordinary 28-deg warmer than last week.

As part of this warm-up, temps here in some coming days will flirt with–if not set–new high records as well as likely producing the Chicago area’s first 90-deg temp and our first humid 72-degree dew point.

An official 90-deg reading would come nearly three weeks ahead of the May 29 date for the city’s first 90. And a 90 would also come earlier than last spring’s first 90-deg reading which occurred on May 24.

Full forecast details and more at the WGN Weather Center blog

A different story near the lake

I mentioned last week–and the reasoning still holds–that there’s the potential for a wind shift off Lake Michigan mid-week which could lead to a temporary pullback in warmth in in lakeshore areas. The warmth’s going nowhere in areas away from the shoreline–it’s to become firmly entrenched. The larger scale pattern is to remain a warm one/. A more southeasterly wind flow midweek would come ashore off the chilly waters of Lake Michigan and mainly impact immediate shoreline locations of northern Illinois. This could dampen warming there but areas like the Fox Valley or our southern suburbs and northwest Indiana away from the lake are to remain unseasonably warm.

Closer view of the 5-DAY precip

But what about rain?

With warmth aloft, it gets more difficult to sustain or support big rains or storms here. Having said that, some scattered weakening showers–the remnants of t-storms which flare to Chicago’s west in coming days–may swipe parts of the area Tuesday and Wed nights. Just how viable they’ll remain with such warmth aloft, will be interesting to see. On the whole, and you can see this in the 5-day total rainfall forecast I’m posting with the graphics below, the most appreciable rain and t-storms is likely to occur in the northern Plains, closer to the jet stream in the coming week.

Interactive Radar: Track Showers & Storms here

Driving this warm-up is the development of a huge dome of warm/hot air. A powerful southwesterly jet stream flow is playing a role in developing this dome. A little backround on the changes which occur when such abnormal warmth occurs.