SOUTHERN MARYLAND — Residents across Charles, Calvert and St. Mary’s counties can expect a cooler but unsettled Friday, with clouds, humidity and scattered showers and thunderstorms remaining possible throughout the region.
The Southern Maryland regional forecast for Friday, Aug. 21, calls for a high near 79 degrees and an overnight low around 69. A roughly 40% daytime chance of rain is expected across the three-county area, though the likelihood of showers and thunderstorms is expected to vary by location and increase in some areas later Friday and Friday night.
The National Weather Service Baltimore-Washington office describes an unsettled pattern returning during the second half of Friday and continuing into Saturday. Forecast guidance shows temperatures substantially lower than the heat experienced Thursday, but humidity will remain noticeable.
As of Thursday night, no National Weather Service watches, warnings or advisories were in effect for Southern Maryland specifically for Friday. The absence of an alert does not mean thunderstorms are not expected. Watches and warnings are issued when conditions meet specific criteria or when hazardous weather becomes sufficiently likely or imminent.
Some forecast guidance indicates that thunderstorms developing Friday could produce locally heavy rain and gusty winds. In Leonardtown, for example, current forecast guidance calls for considerable clouds and humid conditions with showers and a thunderstorm possible. The forecast also notes the potential for localized damaging wind gusts and heavy rainfall with stronger storms.
Rain chances will not necessarily be uniform across Southern Maryland. Charles County locations may see periods of dry weather between showers, while communities farther south and east could experience a greater chance of thunderstorms depending on how the weather system develops.
The regional 40% rain chance represents a combined Southern Maryland forecast rather than a guarantee that 40% of the day will be rainy. It also does not mean every community will receive rain. Scattered thunderstorms can produce significant rainfall in one location while leaving another community several miles away largely dry.
Friday’s cooler temperatures will provide a noticeable change from Thursday. The regional high of about 79 degrees is based on forecast highs near 81 degrees in Charles County and around 78 degrees in both Calvert and St. Mary’s counties.
Overnight temperatures are expected to remain mild, with lows near 69 degrees across much of the region.
Winds should generally remain light, around 5 to 10 mph outside of thunderstorms. Gusts could temporarily become stronger near any thunderstorms that develop.
Humidity is expected to remain relatively high, averaging around 75% during the day. That moisture will contribute to the continued chance of showers and thunderstorms despite the lower temperatures.
Residents with outdoor plans should keep an eye on changing conditions, particularly during the afternoon and evening. Thunderstorms can develop or intensify quickly even when no watch or warning is in effect earlier in the day.
Anyone who hears thunder should move indoors. Heavy downpours can also quickly reduce visibility on Southern Maryland roads and cause water to collect in low-lying or poorly drained areas.
The unsettled pattern is expected to continue into Saturday. National Weather Service extended guidance shows rain and thunderstorms remaining possible along the Eastern Seaboard as a trough develops over the eastern United States.
Friday’s sunrise in Southern Maryland is approximately 6:26 a.m., with sunset around 7:52 p.m.
Air quality is expected to remain in the good category, although residents should remember that air-quality ratings measure pollution and do not reflect hazards associated with thunderstorms, lightning, heavy rain or high humidity.
Forecast conditions can change as new data becomes available. Residents should continue checking the latest National Weather Service forecasts and any watches or warnings issued during the day.
