* WHAT...Dangerously hot conditions with heat index values of 110 to 115.
* WHERE...Portions of DC, central, north central, northeast, northern, and southern Maryland, and central, northern, and northwest Virginia.
* WHEN...Until 9 PM EDT this evening.
* IMPACTS...Heat related illnesses increase significantly during extreme heat and high humidity events.
* ADDITIONAL DETAILS...Prolonged excessive heat may impact power, water, and transportation systems. Heat index values around 100 to 105 are possible again Sunday afternoon.