A front bringing some showers overnight Tuesday into Wednesday morning is ushering in some cold air -- cold enough to keep the region below 60 degrees for a week and possibly to bring fall's first frost for much of the immediate Baltimore suburbs.
Temperatures could top out in the upper 50s Wednesday and then the lower 50s Thursday through Saturday. Lows are meanwhile forecast in the 30s for that stretch, dropping as cold as the lower 30s by early Saturday morning.
Though temperatures may be cold enough for frost, whether one occurs will also depend on the dew point and winds, according to a National Weather Service forecast discussion for the Baltimore/Washington region.
If a frost occurs, it would be just about right on schedule. In one out of every three years, the first frost occurs at Baltimore-Washington International Thurgood Marshall Airport by Oct. 23; in 50 percent of years, it occurs by Oct. 28, according to the University of Maryland Home and Garden Information Center.
More outlying suburbs may have already seen patches of frost on chilly mornings, or else are highly likely to over the next several days. Bel Air sees its first frost by Oct. 16 and Westminster by Oct. 20 in one out of every two years.
If you aren't a farmer, the first frost means little more than having to cover your flower beds or bring house plants indoors, or perhaps leaving your car running to warm up for the first time. But the seasonal milestone is still a sign of what's to come.
The stretch of chilly daytime highs below 60 degrees would meanwhile be Baltimore's longest since March 29.