Dozens of Baltimore County schools that do not have air conditioning are closed Friday because of the heat.

The temporary closures of 37 schools are because of a measure approved by the county's board of education earlier this month that says non-air-conditioned public schools must close when the heat index for the next day is forecast to reach 90 degrees by 11 a.m.

The rest of the county's 173 schools have air conditioning and are staying open.

The National Weather Service is forecasting temperatures in the lower 90s and high humidity by early Friday afternoon, which translates to a heat index of 98 or 99 degrees.

Superintendent Dallas Dance says if more heat-related closures occur he will seek a waiver from the state requirement that students be in school for 180 days.