High wind warning from 12 a.m. Friday to 6 a.m. Saturday *

(This article, originally published at noon, was last updated at 2:35 p.m. based on new information from the National Weather Service.)

As a powerful nor’easter rapidly intensifies off the Northeast coast Friday, a fierce high-wind event will unfold over the D.C. and Baltimore regions.

The combination of the intensity and duration of high winds may make this the worst wind storm in the region since Sandy in October 2012.

The National Weather Service is calling this is a “dangerous wind storm” and “one of the most powerful in recent years.”

Sustained winds on Friday are likely to reach 25 to 40 mph with frequent gusts to 50 to 60 mph. These winds will have the potential to bring down trees and cause scattered power outages. Loose objects will become projectiles and should be secured or brought inside on Thursday before the wind storm begins.

Wind timing and intensity

When most of us go to bed tonight, winds will still be mostly calm. But they will come roaring in suddenly between about 10 p.m. and 1 a.m. from west to east, with gusts topping 30 mph.

In the hours before sunrise, winds may well already be gusting over 50 mph. Potentially damaging gusts in the 45-to-60-mph range are likely to persist throughout the day Friday into the evening commute. During the day, isolated gusts of 60 to 70 mph are possible, especially at higher elevations and near/along the Chesapeake Bay.

NAM model peak wind gust forecast from Thursday night at 10 p.m. to Saturday night at 10 p.m.

On Friday night, peak gusts should ease into the 40-to-50-mph range — but that is still strong enough to snap tree limbs and cause some disruption.

The period of greatest concern is, therefore, between about 12 a.m. and 7  p.m. Friday, when the high wind warning is in effect.

During the day Saturday, it will remain quite windy, with gusts of 30 to 45 mph likely, highest in the first half of the day.

On Sunday, it will be on the breezy side, but gusts should drop below hazardous levels in the 20-to30-mph range.

Preparation and impacts

In addition to securing or moving inside loose outdoor objects, you should be ready for power outages. Have batteries and flashlights ready and any other necessary supplies.

If you’re flying on Friday, expect delays and cancellations. Monitor your flight status and check before leaving for the airport.

Motorists should use caution driving Friday and keep a firm grip on the steering wheel. Winds of 50 to 60 mph could coincide with Friday morning’s commute, causing delays. Drivers should look out for flying projectiles (signs, trash cans, pieces of metal, tree limbs, cones, and so on) that could damage their vehicles.

If you can avoid it, don’t park your vehicle near a tree or anything else that could topple on it.

High-profile vehicles such as trucks should delay travel. If you plan to cross the Bay Bridge, monitor its status as it may close for a time if winds are frequently gusting over 50 mph.

Finally, pedestrians should keep an eye out for flying projectiles and limit time outside when winds are blowing hardest. Schools may want to hold recess inside. Monitor your school status on Friday morning in case outages require some to close.

Comparable recent high-wind events

This event will share similarities to some other recent high-wind events:

The above list does not include summer thunderstorm outbreaks, including the June 2012 derecho, which is in a league of its own for wind damage. It unleashed widespread 60-to-80 mph gusts and resulted in more than a million outages.

Sandy is probably the most analogous wind storm to the one upcoming, based on the forecast winds and duration of the event (many of the other events listed above were quick-hitters). Power outages in this event should not be as high as during Sandy because 1) the ground will not be as wet as it was during Sandy, which unloaded several inches of rain, 2) we do not have foliage on trees this time, and 3) area power companies have conducted substantial tree mitigation since that storm.

What’s driving the wind?

The rapid intensification of the storm off the coast will really get the winds howling as its counterclockwise circulation drives wind from the Northeast along much of the Eastern Seaboard.

But the winds will be particularly strong in this storm because of the massive change in air pressure over a relatively small region; this change is known as the pressure gradient and is what really drives wind speed. The greater the pressure gradient, the stronger the winds.

The nor’easter and its center of low pressure (colored in blue and purple in the graphic below) will be surrounded by abnormally high pressure both to its northwest over the Great Lakes and to its north over Greenland (colored in red). Recall the “Greenland Block” we wrote about?

European model simulation of nor’easter low-pressure center Friday night and surrounding areas of high pressure to the northwest and north. (TropicalTidBits.com)

The difference in pressure between this beast of a storm and the enormous high-pressure zones surrounding it will set the stage for a memorable wind event not just in the D.C. area but also over the entire Mid-Atlantic and Northeast zones. Because of the configuration of weather systems, this zone is essentially going to turn into a raging wind tunnel.

Rain and snow

While Washington is missing the brunt of the precipitation from this storm, which will focus farther north, some rain and snow showers may cycle through the region on its backside – most likely Friday morning.

“Wrap around rain and snow showers are possible across most of Maryland as well as the Washington and Baltimore Metropolitan areas Friday morning,” the National Weather Service said. “Snow may coat the ground in a few spots but mainly on grassy surfaces given the marginal temperatures and recently warm conditions.”

GFS model hints that same rain and wet snow showers may cycle southward on the storm’s backside Friday morning.

We can’t totally rule out some additional spotty showers into the afternoon and evening Friday, especially toward northeast Maryland.

Coastal flooding and winds at the Maryland/Delaware/Virginia beaches

At the Maryland and Delaware beaches,  a coastal flood watch is in effect from 5 a.m. Friday to 2 a.m. Sunday.

“Locally minor flooding is possible with the high tide on Friday evening, moderate to locally major flooding is expected with the high tide on Saturday morning, and moderate flooding is forecast with the high tide on Saturday evening,” the National Weather Service says.

Water may rise up to one to three above normally dry land. Waves up to 9 to 12 feet are expected. “Numerous roadways are expected to flood and minor to moderate property damage is possible,” the Weather Service adds. “The tides and wave action will likely result in moderate beach erosion.”

Similar impacts can be expected down to Virginia Beach, where a coastal flood watch is in effect from 7 a.m. Friday to 5 p.m. Sunday.

A high wind warning is in effect for all of these coastal locations, for sustained winds up of 25 to 40 mph and gusts to 50 to 65 mph. Winds should generally be strongest the farther north you go.

(Coastal flooding is not a concern for the Tidal Potomac and Chesapeake Bay as winds from the north will tend to push water away from land rather towards it.)