The first significant heat wave of the summer has kicked off with an “extreme” heat advisory forecast for much of Pennsylvania.

The dangerous temperatures are expected to last all week.

The National Weather Service reports the record-breaking heat is expected to hit widespread daily high temperatures and possibly set some new June records from the Ohio Valley to the Northeast, with local indices approaching 105 degrees.

According to messages from the NWS, “The longevity of dangerous heat forecasted for some locations has not been experienced in decades.”

Heat advisories are in effect from June 17 through June 21 with excessive heat watches forecasted from June 17 through June 22 across the Great Lakes, Northeast and Mid-Atlantic.

NWS forecast warns of prolonged dangerously hot conditions, including high humidity that may cause heat illness.

This article originally appeared on Pocono Record: Week-long heatwave to bring extreme heat across Pennsylvania