With the coldest air of fall so far, chances are good that parts of the area will experience their first freeze of the season during at least one of the next two nights. Areas that do not quite reach freezing will nevertheless probably see frost.
“Temperatures around 33 to 36 degrees will result in frost formation,” the National Weather Service in Sterling, Va., wrote. “Frost could kill sensitive outdoor vegetation if left uncovered.”
Freeze warnings have been hoisted for areas north, west and south of the frost advisories, including Frederick County in Maryland and western Loudoun, Prince William and Fauquier counties in Virginia. These warnings are issued when temperatures are expected to fall to or below 32 degrees and the end of the growing season is anticipated.
“Frost and freeze conditions will kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing,” the Weather Service wrote in its warning statement.
Low temperatures Wednesday morning are forecast to dip to the low and mid-30s in most spots, but closer to 40 in downtown Washington.
The cold, coming in from the Arctic, is also supporting the first accumulating snow in the mountains of West Virginia, Western Maryland and southwest Pennsylvania.
Expect more frost and freeze alerts Thursday morning when temperatures could be a little lower. Predicted lows range from the upper 20s to mid-30s, except for upper 30s downtown and near the Chesapeake Bay.
These are not the first cold nights of autumn. Temperatures have already dipped into the 30s in much of the area this month, which has been colder than normal.
Temperatures have been as low as 36 in Baltimore and 34 at Dulles International Airport. In Washington, the temperature has been as low as 41, on the basis of measurements at Reagan National Airport.
Historical dates of first fall freeze and how this year compares
The potential for freezing lows north and west of Washington is coming pretty close to average or a little early, judging by observations over the past 30 years.
Dulles, on average, experiences its first freeze on Oct. 19. Baltimore, on the basis of measurements at BWI Marshall Airport, posts its first 32-degree low on Oct. 29.
In Washington, the average first freeze doesn’t come along until Nov. 11. But National Airport, where the District’s weather observations are made, is one of the last places in the region to experience freezing. This is mostly because it’s next to the Potomac River, which often helps keep temperatures milder than other spots.
Washington’s first freeze has come as early as Oct. 10 (that was in 1895, when temperatures were measured at 24th and M streets NW) and as late as Dec. 22 (in 2001 at Reagan National). The earliest first freeze at National occurred Oct. 20, 1972.
Baltimore’s earliest first freeze came Oct. 4, 1974, and the latest was Dec. 11, 1939, when that city’s temperatures were measured downtown rather than at BWI Airport. At Dulles, freezes have come as early as Sept. 24, in 1974 and 1983, and as late as Nov. 11, in 2005.
Last year, Washington’s first freeze occurred Nov. 17, and it happened in Dulles and Baltimore on Nov. 3 and Nov. 4, respectively.
Despite the somewhat early blast of chill this year, average first freezes have been arriving later over time because of human-caused climate change and urbanization.
Five decades ago, the city’s average first freeze came about 10 days earlier. A similar trend has been seen for the date of the last spring freeze. The District’s average final freeze has slipped from March 29 to March 24.