A freeze warning has been issued for the Chicago area early Saturday as an unusual polar vortex sweeps down from Canada.
The warning is in effect from midnight Friday through 7 a.m. Saturday, when temperatures are expected to drop into the upper 20s or lower 30s, according to the National Weather Service.
The late spring cold is being pushed into the area by a jet stream that is diving south and creating a “tropospheric polar vortex” over the Midwest and Northeast, the weather service said.
In the Chicago area, temperates will drop from the 40s through the 30s Friday, possibly dropping into the upper 20s during early Saturday. The record for Saturday’s date is 27 set in 1987.