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 458 PM EDT, a strong thunderstorm was located 16 nm west of Key Bridge, moving southeast at 20 knots. HAZARD. Wind gusts 34 knots or greater. SOURCE. Radar indicated. IMPACT. Boaters in small craft could be thrown overboard by suddenly higher winds and waves capsizing their vessel. * Locations impacted include. Fort Washington, Tidal Basin, Reagan National Airport, Woodrow Wilson Bridge, Key Bridge, Fort Hunt, National Harbor, and Alexandria.

* WHAT. During the Excessive Heat Warnings, dangerously hot conditions with heat index values around 105 to 108 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. For the first Excessive Heat Warning, until 8 PM EDT this evening. For the second Excessive Heat Warning, from 11 AM to 8 PM EDT Tuesday. * IMPACTS. Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities. * ADDITIONAL DETAILS. Very warm and humid conditions will persist into the overnight hours, adding heat stress to those without air conditioning. Ensure to stay hydrated and find ways to stay cool.

* WHAT. During the Excessive Heat Warnings, dangerously hot conditions with heat index values around 110 expected. * WHERE. Portions of central, northeast, northern and southern Maryland, The District of Columbia and central and northern Virginia. * WHEN. For the first Excessive Heat Warning, until 8 PM EDT this evening. For the second Excessive Heat Warning, from 11 AM to 8 PM EDT Tuesday. * IMPACTS. Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities. * ADDITIONAL DETAILS. Very warm and humid conditions will persist into the overnight hours, adding heat stress to those without air conditioning. Ensure to stay hydrated and find ways to stay cool.

* WHAT. During the Heat Advisories, hot conditions with heat index values around 105 expected. * WHERE. Portions of central and north central Maryland and central, northern and northwest Virginia. * WHEN. For the first Heat Advisory, until 8 PM EDT this evening. For the second Heat Advisory, from 11 AM to 8 PM EDT Tuesday. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur. * ADDITIONAL DETAILS. Very warm and humid conditions will persist into the overnight hours, adding heat stress to those without air conditioning. Ensure to stay hydrated and find ways to stay cool.

* WHAT. For the Excessive Heat Warning, dangerously hot conditions with heat index values up to 107. For the Heat Advisory, heat index values up to 103 expected. * WHERE. Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, Perry, and York Counties. * WHEN. For the Excessive Heat Warning, until 8 PM EDT Tuesday. For the Heat Advisory, from 8 PM Tuesday to 8 PM EDT Wednesday. * IMPACTS. Heat related illnesses increase significantly during extreme heat and high humidity events.

The Maryland Department of the Environment has issued a Code ORANGE Air Quality Alert Monday 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 Monday 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.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. West central Montgomery County in central Maryland. Central Loudoun County in northern Virginia. * Until 530 PM EDT. * At 440 PM EDT, a severe thunderstorm was located near Leesburg, moving east at 15 mph. HAZARD. 60 mph wind gusts. 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. Germantown, Leesburg, Lansdowne, Lowes Island, Poolesville, Boyds, Clarksburg, Darnestown, Belmont, Barnesville, Paeonian Springs, Waterford, Lucketts, Dickerson, Beallsville, and Dawsonville.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. Southwestern Montgomery County in central Maryland. Southeastern Loudoun County in northern Virginia. Northwestern Fairfax County in northern Virginia. * Until 530 PM EDT. * At 456 PM EDT, a severe thunderstorm was located over Ashburn, or over Broadlands, moving southeast at 25 mph. HAZARD. 60 mph wind gusts. 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. Reston, Herndon, Broadlands, Lansdowne, Lowes Island, Brambleton, Dulles International Airport, Ashburn, Sterling, Great Falls, Countryside, Arcola, Darnestown, Belmont, Gleedsville, and Sterling Park.

At 452 PM EDT, a severe thunderstorm was located near Leesburg, moving east at 15 mph. HAZARD. 60 mph wind gusts. 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. Germantown, Leesburg, Lansdowne, Lowes Island, Poolesville, Boyds, Clarksburg, Darnestown, Belmont, Barnesville, Paeonian Springs, Waterford, Lucketts, Dickerson, Beallsville, and Dawsonville.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. Northeastern Carroll County in north central Maryland. * Until 545 PM EDT. * At 506 PM EDT, a severe thunderstorm was located near Westminster, moving northeast at 25 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. Westminster, Eldersburg, Hampstead, Manchester, New Windsor, Carrollton, Linwood, Patapsco, Reese, Wagners Mill, Millers, Greenmount, and Marston.

At 516 PM EDT, a severe thunderstorm was located over Westminster, moving northeast at 25 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. Westminster, Hampstead, Manchester, Carrollton, Patapsco, Reese, Wagners Mill, Millers, and Greenmount.

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. Eastern Loudoun County in northern Virginia. Arlington County in northern Virginia. The City of Falls Church in northern Virginia. Northeastern Fairfax County in northern Virginia. The City of Alexandria in northern Virginia. * Until 600 PM EDT. * At 513 PM EDT, a severe thunderstorm was located over Great Falls, moving east at 25 mph. HAZARD. 60 mph wind gusts. SOURCE. Trained weather spotters reported numerous downed trees and power lines in Loudoun County with this storm. 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, Alexandria, Germantown, Rockville, Bethesda, Gaithersburg, Reston, Annandale, College Park, Herndon, Greenbelt, Langley Park, Beltsville, Vienna, Falls Church, Lowes Island, Bladensburg, Mantua, Pimmit Hills, and National Harbor.

At 508 PM EDT, a severe thunderstorm was located over Lowes Island, moving east at 20 mph. HAZARD. 60 mph wind gusts. 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. Germantown, Leesburg, Lansdowne, Lowes Island, Poolesville, Countryside, Boyds, Clarksburg, Darnestown, Belmont, Barnesville, Beallsville, Dawsonville, and Dickerson.

SVRLWX The National Weather Service in Sterling Virginia has issued a * Severe Thunderstorm Warning for. Southeastern Fauquier County in northern Virginia. Culpeper County in northern Virginia. Northern Spotsylvania County in central Virginia. * Until 545 PM EDT. * At 503 PM EDT, a severe thunderstorm was located over Culpeper, moving east at 15 mph. HAZARD. 60 mph wind gusts. 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. Culpeper, Bealeton, Opal, Remington, Midland, Catalpa, Elkwood, Stevensburg, Brandy Station, Lois, Winston, Lignum, Cardova, Mitchells, Rixeyville, Richardsville, Morrisville, Alanthus, Somerville, and Goldvein.