The coolest air since May began making its way into the Chicago area Thursday afternoon. Strong northerly winds have prompted a small craft advisory on Lake Michigan until 10 p.m. Friday. The northerly winds traveling down the length of Lake Michigan provide a setup for lake effect rain showers Friday for Illinois lakeshore counties and northwest Indiana.

High temperatures on Friday will be about 20 degrees colder than the mid to upper 70s recorded on Thursday. Frost and freezing temperatures are expected Friday night into Saturday morning for locations away from Lake Michigan and the city of Chicago.

A cool start to the Chicago Marathon is expected Sunday morning. Temperatures should be in the low to mid 40s for the race start time with southwest winds 9 to 16 mph.

After a cool Saturday and Sunday, afternoon temperatures moderate to the mid 60s for Sunday and Monday with 70s forecast for Tuesday and Wednesday.

Mainly dry conditions persist with the best chance for rain over the next seven days expected Wednesday.

Freeze warnings are in effect early Friday for much of North and South Dakota.