* WHAT. Heat index values up to 104 expected. * WHERE. Portions of north central and western Maryland, northwest and western Virginia and eastern West Virginia. * WHEN. From 11 AM this morning to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur. * ADDITIONAL DETAILS. Oppressive heat and humidity will overspread the area today and last into Sunday. Little relief from the heat is expected tonight with low temperatures in the lower to mid 70s, which will compound heat stress on those without air conditioning.

* WHAT. For the first Heat Advisory, heat index values up to 105. For the second Heat Advisory, heat index values up to 102 expected. * WHERE. Washington County. * WHEN. For the first Heat Advisory, until 8 PM EDT this evening. For the second Heat Advisory, from 11 AM to 7 PM EDT Sunday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur. * ADDITIONAL DETAILS. Oppressive heat and humidity will overspread the area through Sunday before a cold front tracks through early Monday. Little relief from the heat is expected tonight with low temperatures in the low to mid 70s, which will compound heat stress on those without air conditioning.

* WHAT. Heat index values up to 104 expected. * WHERE. Portions of western Maryland, northwest and western Virginia and eastern and panhandle West Virginia. * WHEN. Until 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur. * ADDITIONAL DETAILS. Oppressive heat and humidity will overspread the area through Sunday before a cold front tracks through early Monday. Little relief from the heat is expected tonight with low temperatures in the low to mid 70s, which will compound heat stress on those without air conditioning.

* WHAT. Maximum heat index values around 100. * WHERE. A portion of central Pennsylvania. * WHEN. Until 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause an increase in heat-related illnesses. * ADDITIONAL DETAILS. The risk of heat-related impacts is expected to reach its highest level this afternoon. The early season heat persisting over multiple days combined with light winds, limited cloud cover, and very warm nights will exacerbate heat stress.