Three days of beautiful weather and above-average temperatures could come crashing to an end tonight in harsh way, as the entire Chicago area and northwest Indiana are under a severe thunderstorm watch.

The National Weather Service has put watch in effect until 10 p.m. It includes virtually all of Illinois north of a line from Kankakee west to the Iowa border, as well as Lake and Porter counties in Indiana.

There is also a severe thunderstorm warning in the Elgin area, including northwest Cook County, until 6:15 p.m.

Scattered thunderstorms are expected throughout the evening, with strongest storms bringing half-dollar-size hail, locally damaging winds gusting over 60 mph, heavy downpours and frequent cloud-to-ground lightning, according to the Weather Service.

As of 5 p.m., a line of storms was forming from Kenosha southwest through Mundelein, Elgin, Wheaton and Crystal Lake. Those storms are expected to fill in and strengthen, then track east and south, with the most-powerful storms between 7-10 p.m.

Ther next chance of thunderstorms will come late Wednesday into Thursday, and again late Saurday into Sunday, the Weather Service

The storm is on the leading edge of a cold front that will take area temperatures, which have been in the 70s and 80s the last three days, back down into the 50s and 60s.