* WHAT. Heat index values up to 104 expected. * WHERE. In Maryland, Washington County. In Virginia, Shenandoah, Frederick VA, Page, Warren and Clarke Counties. In West Virginia, Morgan, Berkeley and Jefferson Counties. * WHEN. From noon to 8 PM EDT Friday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values up to 107 expected. * WHERE. Portions of central, northeast, northern and southern Maryland, The District of Columbia and central and northern Virginia. * WHEN. From noon to 8 PM EDT Friday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values up to 106 expected. * WHERE. Portions of central, north central and northern Maryland and central, northern and northwest Virginia. * WHEN. From noon to 8 PM EDT Friday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. South winds around 10 kt with gusts up to 20 kt. * WHERE. Tidal Potomac River from Key Bridge to Cobb Island MD, Chesapeake Bay north of Sandy Point MD, Patapsco River including Baltimore Harbor, Chester River to Queenstown MD, and Patuxent River to Broomes Island MD. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Conditions will be hazardous to small craft.

* WHAT. South winds around 10 kt with gusts up to 20 kt. * WHERE. Tidal Potomac River from Key Bridge to Cobb Island MD, Chesapeake Bay north of Sandy Point MD, Patapsco River including Baltimore Harbor, Chester River to Queenstown MD, and Patuxent River to Broomes Island MD. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Conditions will be hazardous to small craft.

* WHAT. South winds around 10 kt with gusts up to 20 kt. * WHERE. Tidal Potomac River from Key Bridge to Cobb Island MD, Chesapeake Bay north of Sandy Point MD, Patapsco River including Baltimore Harbor, Chester River to Queenstown MD, and Patuxent River to Broomes Island MD. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Conditions will be hazardous to small craft.

* WHAT. Heat index values up to 108 expected. * WHERE. In Maryland, Central and Southeast Montgomery and Central and Southeast Howard Counties. In Virginia, Fairfax, Stafford, Spotsylvania, Southern Fauquier and Central and Southeast Prince William/Manassas/Manassas Park Counties. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Dangerously hot conditions with heat index values up to 110 expected. * WHERE. The District of Columbia, Anne Arundel, Calvert, Cecil, Charles, Prince Georges, Southeast Harford, Southern Baltimore, and St. Mary's Counties in Maryland, and Arlington/Falls Church/Alexandria and King George Counties in Virginia. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Extreme heat and humidity will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities.

* WHAT. Heat index values up to 104 expected. * WHERE. In Maryland, Washington County. In Virginia, Shenandoah, Frederick VA, Page, Warren and Clarke Counties. In West Virginia, Morgan, Berkeley and Jefferson Counties. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values up to 106 expected. * WHERE. Portions of central and northern Maryland, and central and northern Virginia. * WHEN. From noon today to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values 100 to 104. * WHERE. Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, Perry, and York Counties. * WHEN. Until 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses.