SMWLWX The National Weather Service in Sterling Virginia has issued a * Special Marine Warning for. Tidal Potomac from Key Bridge to Indian Head MD. * Until 630 PM EDT. * At 504 PM EDT, a severe thunderstorm was located near Key Bridge, moving east at 10 knots. HAZARD. Wind gusts 34 knots or greater and large hail. SOURCE. Radar indicated. IMPACT. Boaters in small craft could be thrown overboard by suddenly higher winds and waves capsizing their vessel. Hail may damage your vessel. * Locations impacted include. Tidal Basin, Key Bridge, Reagan National Airport, National Harbor, and Alexandria.

The Maryland Department of the Environment has issued a Code ORANGE Air Quality Alert Thursday for the Maryland suburban DC region. A Code Orange Air Quality Alert means that air pollution concentrations within the region may become unhealthy for sensitive groups. Sensitive groups include children, people suffering from asthma, heart disease or other lung diseases and the elderly. The effects of air pollution can be minimized by avoiding strenuous activity or exercise outdoors. For more information on ground-level ozone and fine particles visit the web site mde.maryland.gov/programs/air/AirQualityMonitoring/Pages/index.aspx.

The Maryland Department of the Environment has issued a Code ORANGE Air Quality Alert Thursday for the Baltimore City Metro and Annapolis region. A Code Orange Air Quality Alert means that air pollution concentrations within the region may become unhealthy for sensitive groups. Sensitive groups include children, people suffering from asthma, heart disease or other lung diseases and the elderly. The effects of air pollution can be minimized by avoiding strenuous activity or exercise outdoors. For more information on ground-level ozone and fine particles visit the web site mde.maryland.gov/programs/air/AirQualityMonitoring/Pages/index.aspx.

* 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 Thursday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values 100 to 104 expected. * WHERE. Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, Perry, and York Counties. * WHEN. From noon Thursday to 8 PM EDT Friday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses. Heat-related impacts are likely in some health systems, heat-sensitive industries and infrastructure.

SVRPHI The National Weather Service in Mount Holly NJ has issued a * Severe Thunderstorm Warning for. Northeastern Talbot County in eastern Maryland. Southwestern Queen Anne's County in northeastern Maryland. * Until 515 PM EDT. * At 429 PM EDT, a severe thunderstorm was located over Chester, or 10 miles east of Severn River, moving southeast at 20 mph. HAZARD. 60 mph wind gusts and penny size hail. SOURCE. Radar indicated. IMPACT. Damage to roofs, siding, trees, and power lines is possible. * Locations impacted include. Easton, Romancoke, Queen Anne, Grasonville, Stevensville, Skipton, Copperville, Chester, Matthews, Wye Mills, Cordova, Queenstown, Hillsboro, Stevensville South, and Dominion.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. The northeastern District of Columbia. Southeastern Montgomery County in central Maryland. Northwestern Prince Georges County in central Maryland. * Until 530 PM EDT. * At 429 PM EDT, a severe thunderstorm was located over Fort Totten, moving east at 10 mph. HAZARD. 60 mph wind gusts and quarter size hail. SOURCE. Radar indicated. IMPACT. Damaging winds will cause some trees and large branches to fall. This could injure those outdoors, as well as damage homes and vehicles. Roadways may become blocked by downed trees. Localized power outages are possible. Unsecured light objects may become projectiles. * Locations impacted include. College Park, Greenbelt, Langley Park, Beltsville, Bladensburg, Fort Totten, University of Maryland, Howard University, Landover, Hyattsville, Takoma Park, East Riverdale, Adelphi, New Carrollton, Mitchellville, Lake Arbor, Chevy Chase, Riverdale Park, Cheverly, and Woodmore.

At 444 PM EDT, a severe thunderstorm was located over Grasonville, or 10 miles southwest of Centerville, moving southeast at 15 mph. HAZARD. 60 mph wind gusts and penny size hail. SOURCE. Radar indicated. IMPACT. Damage to roofs, siding, trees, and power lines is possible. Locations impacted include. Easton, Queen Anne, Wye Mills, Grasonville, Skipton, Copperville, Cordova, and Queenstown.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. The District of Columbia. Southeastern Montgomery County in central Maryland. Northwestern Prince Georges County in central Maryland. North central Arlington County in northern Virginia. Northeastern Fairfax County in northern Virginia. * Until 545 PM EDT. * At 501 PM EDT, a severe thunderstorm was located over Chevy Chase, or over Bethesda, moving east at 10 mph. HAZARD. 60 mph wind gusts and quarter size hail. SOURCE. Radar indicated. IMPACT. Damaging winds will cause some trees and large branches to fall. This could injure those outdoors, as well as damage homes and vehicles. Roadways may become blocked by downed trees. Localized power outages are possible. Unsecured light objects may become projectiles. * Locations impacted include. Arlington, Bethesda, College Park, Langley Park, Beltsville, Bladensburg, Mclean, University of Maryland, Howard University, Gallaudet University, Fort Totten, Potomac, North Bethesda, Hyattsville, White Oak, Takoma Park, Adelphi, Kemp Mill, Chevy Chase, and North Kensington.

At 450 PM EDT, a severe thunderstorm was located over Hyattsville, or over Bladensburg, moving east at 10 mph. HAZARD. 60 mph wind gusts and quarter size hail. SOURCE. Radar indicated. IMPACT. Damaging winds will cause some trees and large branches to fall. This could injure those outdoors, as well as damage homes and vehicles. Roadways may become blocked by downed trees. Localized power outages are possible. Unsecured light objects may become projectiles. Locations impacted include. College Park, Greenbelt, Langley Park, Beltsville, Bladensburg, University of Maryland, Landover, Hyattsville, Takoma Park, East Riverdale, Adelphi, New Carrollton, Mitchellville, Lake Arbor, Riverdale Park, Cheverly, Hillandale, Woodmore, Lanham-Seabrook, and Greater Landover.