Afternoon temperatures in the 90s and very muggy air led to the development of thunderstorms across North Central Maryland which produced heavy downpours, frequent lightening, and damaging winds in excess of 55 MPH. The storms moved through Washington, Frederick, Carroll, and Howard Counties between 3:30 PM and 5:30 PM EDT.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LWX wrote it up.
Afternoon temperatures in the 90s and very muggy air led to the development of thunderstorms across North Central Maryland which produced heavy downpours, frequent lightening, and damaging winds in excess of 55 MPH. The storms moved through Washington, Frederick, Carroll, and Howard Counties between 3:30 PM and 5:30 PM EDT. An observer near Westminster reported 1.5 inches of rainfall in 45 minutes. In Washington County, large tree limbs were downed by severe winds onto Interstate 68 near Boonsboro and on Shepherdstown Pike near Sharpsburg. In Frederick County, trees and power lines were downed onto Route 180 at the intersection of Mt. Zion Road, Main Street in New Market, Route 75 between Route 80 and Ed McClain Road, and Route 144. A concentrated area of tree damage also occurred between Monrovia and Bartholows Road. The city of Monrovia was hit especially hard. One home lost part of its roof when several trees fell onto the structure. A car in the driveway was also damaged by a fallen tree. A nearby 150 year old log home valued at $130,000 was hit by lightning and burned to the ground. The fire department reported delays reaching te structure because of roads blocked by downed trees. In the city of Frederick, one house was damaged and 22 intersections were blocked by fallen trees. 150,000 customers in and around Frederick County lost power as a direct result of the storm. Winds gusted to 69 MPH at 4:30 PM EDT at Mt. Airy in Carroll County. Several trees were downed near Mt. Airy and Sykesville, including one that fell across busy Interstate 70 near mile marker 72. The storm was still powerful enough to topple a handful of trees in the western part of Howard County. By the time the storms reached Baltimore County, lightning was the biggest threat. 21,000 customers in the county lost power due to electrical surges directly related to the storm.
The Sterling radar (KLWX), 50 km away, was scanning. The volume nearest the first event began at 19:58 UTC.
7 thunderstorm wind, 1 lightning. Local standard time, as filed.
22 intersections closed by fallen trees and power lines, one home damaged by downed tree
60 trees downed with a concentration between New Market and Green Valley
150 year old log home hit by lightning and burned to the ground
Large tree limbs downed on Interstate 68
Large tree limbs downed on Shepherdstown Pike
Trees downed
69 MPH gust, trees downed including one across Interstate 70
Trees downed
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 1999Every state in 1999This day in weather historyWarnings in Maryland, July 1999
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-10-01. Each event’s entry at NCEI: 5709957, 5709958, 5709959, 5709960, 5709961, 5709962, 5709963, 5709964.