A fire weather watch is in effect for the D.C. area: What that means

The fire danger will be elevated starting Tuesday afternoon when winds could begin gusting to near 30 mph. Winds are forecast to peak Wednesday afternoon into the evening, when gusts could reach 45 mph. At the same time, relative humidity values may dip to about 20 percent in some locations. Winds will start to ease on Thursday but could still be a bit gusty.

These winds out of a westerly direction will intensify while passing over the Appalachians and then rushing down the eastern slopes — or “downsloping.” As the air descends from higher elevations, it warms, dries out and accelerates. Many firestorms have been fanned by downsloping winds such as the disaster in Maui during August, but winds from this event won’t be nearly that strong.

“These strong winds could result in isolated downed trees and power lines,” the Weather Service wrote in a discussion. Sometimes fires ignite because of downed lines.

The strong winds are a result of a difference in pressure between a storm in eastern Canada and a zone of high pressure sinking southward in the central United States.

March and April are two of the more common months for elevated fire risks in the Mid-Atlantic. The fall can also present these risks, too, especially after dry summers.

Fire weather watches are not that unusual in our region and happen most years. Last year, they were issued in mid-April.

Fire weather watches can be upgraded to what’s known as a “red flag warning” should forecasters become confident in the elevated fire threat. The last red flag warning issued for the Washington region was on April 18 last year.

Fire threats are common in March because it is the windiest month of the year, followed closely by April. As a transition season, the spring sees the frequent passage of fronts, which are accompanied by changes in air temperature and pressure — these stir up the wind.

March also precedes a large-scale green up, when moisture is limited because the lack of leaves reduces evapotranspiration in which planets release water vapor into the atmosphere and dry fuels (grasses, dried-out plants and leaves, etc.) are exposed.

A mitigating factor for fires right now is that the ground isn’t unusually dry. Until the past 4 to 6 weeks, it had been a wet winter and even among the wettest on record in December and part of January. But not a lot of precipitation has fallen since and the Mid-Atlantic, Appalachians and South dealt with drought during lengthy periods in 2023.

As long as it remains windy and unless significant precipitation returns, we could see additional fire threats into April.

The Weather Service says fire risks can be reduced if people avoid throwing cigarettes or matches out of a moving vehicle and extinguish all outdoor fires properly, among other safety tips.

Jason Samenow contributed to this report.