Montgomery County Storm History: What It Means for Your Roof
Officially documented severe weather in Montgomery County, Maryland, with verified figures from the National Weather Service and county government, and what each kind of storm does to a roof.
Roofs in Bethesda, North Bethesda and Chevy Chase deal with three kinds of severe weather: straight-line wind from derechos and thunderstorms, tornadoes, and heavy snow followed by ice. In older neighborhoods with mature trees, the biggest roof risk in a windstorm is often not the wind itself but trees and limbs falling on the house.
Every figure below comes from the cited source. For a complete event-by-event record, search Montgomery County in NOAA's Storm Events Database.
The National Weather Service confirmed two EF-1 tornadoes in Montgomery County: one from Poolesville to Seneca Creek State Park, and one from Gaithersburg to Ashton.
Trees and limbs damaged homes in Gaithersburg; seven houses near City Hall were condemned.
An uprooted oak fell into a house on Dogwood Drive, injuring five people.
Roof takeaway: Most of the damage came from trees and large limbs falling onto homes. A healthy roof does little against that, which is why a post-storm inspection matters even when shingles look intact from the street.
The National Weather Service recorded 38.5 inches of snow near Potomac, the highest total reported in Maryland, and 35.2 inches near Gaithersburg.
38.5 inches near Potomac, the greatest total reported in Maryland (NWS Storm Data).
35.2 inches near Gaithersburg (NWS Storm Data).
Roof takeaway: Snow loads that deep stress older framing and low-slope roofs. Melt and refreeze cycles afterward build ice dams at the eaves, pushing water under shingles and into ceilings.
A fast-moving line of severe thunderstorms knocked out power to 77% of Pepco customers in Montgomery County (238,000 of 309,583) at its peak.
Pepco peak outage in Montgomery County: 238,000 of 309,583 customers (77%) (Montgomery County Government).
About 80 homes in the county had significant damage in the first count (Montgomery County Government).
County DOT had collected 42,000 cubic yards of debris by July 18 (Montgomery County Government).
Wind gusts along the derecho path peaked as high as 91 mph (CBS News Baltimore).
Roof takeaway: Straight-line winds tear off shingles and peel back flashing, and they bring down mature trees, which are common in established Bethesda and Chevy Chase neighborhoods.
More than 24 inches of snow fell on the Bethesda and Chevy Chase area, according to National Weather Service totals reported by Bethesda Magazine.
More than 24 inches of snow in the Bethesda, Chevy Chase and Montgomery County area (NWS, via Bethesda Magazine).
Roof takeaway: Deep, long-lasting snow cover is the classic setup for ice dams and gutter damage. Gutters loaded with ice can pull away from fascia boards.
