A "convective outlook" issued Wednesday by the National Weather Service shows in red an area that faces a moderate risk of severe storms. More than 18 million people live in that area.

Menacing Derecho Storms Possible in D.C. Area Wednesday Night and Into Thursday

High winds are possible if storm front remains strong as it passes over the Appalachian Mountains.

A "convective outlook" issued Wednesday by the National Weather Service shows in red an area that faces a moderate risk of severe storms. More than 18 million people live in that area.
By + More

A line of severe storms is expected to gust into the mid-Atlantic region Wednesday night through Thursday, possibly bringing destructive winds as part of a derecho storm front similar to the June 2012 weather system that snapped trees, left millions without power and contributed to the deaths of 22 people.

"Widespread damaging wind and large hail are expected to be the main threats... though a few tornadoes cannot be ruled out" in an area stretching from north of Philadelphia to Richmond, Va., according to a forecast issued around noon Wednesday by the National Weather Service's Storm Prediction Center in Norman, Okla.

Derechos, the Washington-area radio station WTOP noted last year, "are long-lived complexes of severe thunderstorms that track more than 250 miles and produce wind gusts of 60 mph or more."

The Storm Prediction Center's weather outlook notes that the possible menacing storms sweeping down from the Midwest might actually break up on the western side of the Appalachians.

[STUDY: West Experiencing New 'Dust Bowl']

"It might be difficult for any ongoing storms to survive crossing the mountains," the outlook said, before speculating the storms would form anew from the eastern side of the mountains along a convergence zone as a "cold front overtakes the destabilizing warm sector" currently offering the heavily populated area temperatures in the high 80s and low 90s.

The National Weather Service's Sterling, Va., branch warned just before noon Wednesday that computer models can't say with certainty what will happen.

"There is a threat for severe weather," the local NWS branch said, if the storm "holds up after crossing the Appalachians."

"[The] majority of hi-res models weaken this [Mesoscale Convective System] as it crosses the Appalachians," says the forecast, "but there may be sufficient instability downstream of the [system]. Accordingly... there is plenty of caution with these models and low confidence with the [forecast]."

[READ: Is More Global Warming Hiding in Oceans?]

Jason Samenow of the Washington Post's "Capital Weather Gang" reiterated in an early afternoon post Wednesday that there's no guarantee a line of derecho storms will actually hit the area.

"[W]e think the odds of a derecho in the D.C. area overnight are low, but a cluster of storms with heavy rains, dangerous lightning and strong winds are possible," Samenow wrote.

The destructive June 2012 derecho storm travelled 700 miles in twelve hours, according to an analysis posted on the NWS Storm Prediction Center's website.

"The [2012] derecho raced east across the mountains of West Virginia, western Virginia, far southwest Pennsylvania, and western Maryland during mid-evening, where widespread destruction continued... Although radar reflectivity data suggest that the storms slightly weakened during this period," the recap said. "The convective system regained strength as it continued east and southeast of the Appalachians" before pummeling Virginia and the Washington metro area with reported wind gusts topping 74 mph.

Watch: Footage of the 2012 derecho storm in D.C.:

More News: