Rain Moves In Statewide Tonight, Heavy Downpours Possible South of the Beltway

Good evening, Maryland. The dry, mostly sunny afternoon we just had is about to give way to a wet, unsettled stretch that runs through tomorrow. Per NWS Baltimore/Washington (issued 3:07 PM), rain develops statewide tonight as low pressure organizes to our south, with the heaviest totals — potentially 1 to 2 inches or more — targeting St. Mary’s County, where a flood watch scenario for the St. Marys River at Great Mills is being watched closely. NWS Mount Holly (2:43 PM) and NWS Wakefield (2:29 PM) echo the same theme for the Eastern Shore and southern counties: periods of showers and a few thunderstorms tonight into Saturday, with locally heavy rain capable of flash flooding, especially near the Bay and shore. No watches or warnings are active yet, but keep an eye on the sky — and your basement.

⏱ Timing Tonight Into Saturday

• Evening (now–10 PM): Skies increase in cloud cover statewide; far western Maryland (Garrett/Allegany) sees isolated showers first as the front stalls nearby.
• Late evening–Midnight: Rain fills in from west to east across Central Maryland, Frederick/Carroll, and the DC suburbs. A few rumbles of thunder possible.
• Midnight–Dawn Saturday: Widespread rain, locally heavy, especially south of the Beltway (Southern Maryland) and toward the Bay. This is the best window for downpour-driven ponding and localized flooding, particularly St. Mary’s County.
• Saturday Morning: Steady rain continues, gradually tapering to showers by late morning across the I-95 corridor; a low overcast lingers even after the rain lightens.
• Saturday Afternoon–Evening: A lull, then a second round of showers/storms redevelops toward the mountains and pushes east overnight Saturday into early Sunday.
• Sunday: A cold front crosses; drying trend takes hold with a stray shower possible early, then clearing.

🗺️ Region by Region

Western Maryland — Garrett & Allegany

Garrett County (Deep Creek/Oakland) drops to around 57° tonight under scattered showers and thunderstorms (46% chance), winds light out of the southeast. Cumberland/Allegany cools to near 59°, with mostly cloudy skies turning to scattered storms overnight (51% chance) — the leading edge of the wetter pattern that builds through Saturday, when Garrett sees a 70% shower/storm chance and Cumberland 60%. If you’re camping at Deep Creek tonight, have the rainfly ready.

Northern & Central — Washington, Frederick, Carroll

Hagerstown falls to around 62° overnight with a 70% chance of rain developing after a partly cloudy start. Frederick and Carroll counties are similar, near 63°, with rain chances climbing to 72% overnight and areas of fog expected to develop as the rain lingers into Saturday morning (80% coverage). Umbrella by the door for the Saturday commute — such as it is on a weekend.

Baltimore Metro — City, County, Harford, Howard, Anne Arundel

Baltimore City and County, plus Harford, Howard, and Anne Arundel, share a gridpoint tonight near 68° — and the rain here is about as sure a bet as forecasting gets, with a 97% chance of widespread showers developing after dark and continuing into Saturday (also 97%, with embedded thunder). This is the core of the wet overnight; expect steady, sometimes heavy rain from roughly midnight through Saturday midday before a lull sets in.

DC Suburbs — Montgomery & Prince George’s

Silver Spring’s gridpoint (representative of both counties) bottoms out near 66° tonight with a 100% chance of widespread showers and storms — essentially a lock. Saturday continues wet with areas of fog layered on top of lingering showers. This is as saturated a forecast as you’ll see all summer; plan indoor weekend errands accordingly.

Southern Maryland — Charles, Calvert, St. Mary’s

This is ground zero. Prince Frederick’s gridpoint — standing in for Charles, Calvert, and St. Mary’s — holds near 67° overnight with a 100% chance of widespread showers and storms, continuing at 100% through Saturday. NWS is flagging St. Mary’s County specifically for potential 1-2

MD Weather Alerts · issued 6:01 PM, Friday, August 21