Though temperatures neared a record high Monday, a wintry blast looms for the busiest travel day of the year Wednesday, with a mess of rain turning to snow expected along Interstate 95 and more than 6 inches of snow possible farther inland.
Highways officials and meteorologists urged travelers to prepare a "Plan B" and watch weather forecasts, with the potential for heavy precipitation that could snarl traffic and delay or cancel flights, even if snow accumulations are light. Several inches of snow are predicted along I-95 from Washington to Boston, with more just to the west. Tranquil — but cold — weather is forecast to follow for Thanksgiving.
A widespread power outage at Baltimore-Washington International Thurgood Marshall Airport on Monday showed it doesn't take much to disrupt things, especially with Thanksgiving travelers coming and going in their largest numbers since 2007. An electrical problem blacked out the airport for an hour and a half in the morning, halting security screenings and forcing airlines to delay or cancel more than 100 flights.
"If it was a normal day in the winter, it probably would not be a big deal, but it's coming on the heaviest travel day of the year," Rich Foot, founder of meteorology website Foot's Forecast, said of Wednesday's forecast. "It's not just a matter of when the rain changes to snow, or how much snow falls, but how people react to that."
Ingredients for the system were starting to develop Monday even as unseasonably warm weather spanned the Atlantic coast. Temperatures reached 72 degrees at BWI on Monday afternoon, one degree shy of a record dating to 1979. But cold air lurks behind a front across the Midwest, with highs in the teens and 20s across parts of the Plains states.
Disturbances in the upper levels of the atmosphere are forecast to wring heavy precipitation out of moisture-laden air as a low-pressure system moves up the coast from the Carolinas to New England, said Dan Hofmann, a meteorologist with the National Weather Service's Baltimore/Washington forecast office.
But there is uncertainty over whether and when it will be cold enough for more than an inch or two of snow to fall along the I-95 corridor. As is often the case with early-season snowfall, the dividing line between snow and a wintry mix of precipitation is expected to land near the major thoroughfare. But a difference of 10 or 20 miles could have a significant impact on snow accumulations and travel impacts.
"It looks like it's going to be only marginally cold enough for snow in the major cities, and it'll be moving pretty quickly," Hofmann said.
The weather service predicts an inch or two of wet snow from Washington to Baltimore coming Wednesday afternoon and evening, with less rain and higher snow totals in Carroll County, western Howard County and northern Baltimore County.
What path the storm takes could also mean more or less snow for the region — if it tracks slightly off the coast, it could pull more cold air over Baltimore and bring snow farther east, said Tom Kines, a senior meteorologist with AccuWeather.com. If it stays farther west, cold air might not reach some areas, giving them mostly rain.
Even if rain continues to mix with snow into the Wednesday afternoon rush hour, it could prove treacherous for travelers, Foot said.
"It could be snowing buckets and none of it could be sticking, but all it takes is one person slowing down on I-95 because they're new to the area, and you've got gridlock," he said.
It's also possible that the snow could fall heavy enough to accumulate more than it might otherwise with temperatures teetering on the freezing mark. Forecasters recalled a winter storm that hit during an evening rush hour in January 2011 and left thousands stranded in their cars.
Because that storm started out as rain, roads couldn't be pre-treated with a salt brine solution because it would have washed away, and State Highway Administration crews had difficulty responding because so many vehicles were stuck on the roads.
The agency is readying its crews for Wednesday, and could begin pre-treating roads Tuesday if forecasts suggest it would be effective, spokeswoman Valerie Burnette Edgar said.
Highway administration officials and AAA Mid-Atlantic urged drivers to check forecasts and alter travel plans if possible. AAA estimates nearly 1 million Marylanders will travel 50 miles or more for the holiday — the most since 2007 — and more than 90 percent of them by road.
"Wednesday can turn into a chaotic and frightening scene of events on the roadways along the East Coast," said AAA Mid-Atlantic spokeswoman Christine Sarames Delise in a statement.
Monday travelers at BWI said airport operations were thrown into disarray when the power went out about 10:20 a.m., halting security screenings on three concourses and grounding planes until shortly before noon.
"It's now chaos," said Karen Stickler, a Southwest Airlines flier who arrived at BWI from a business trip in San Antonio on Monday morning, en route to her home in Hartford, Conn. "The calmness apparent this [morning] is over even though the power is on."
According to airport spokesman Jonathan Dean, a "brief power fluctuation" was first reported about 9:30 a.m. in the main terminal food court near Concourse C. It was followed by the more widespread outage about 10:20 a.m.
A preliminary investigation revealed an electrical cable beneath the airfield had failed, Dean said in an email. The cable is about 20 years old and has been tested annually, he said. There was no sign of foul play, Dean said.
Airport personnel were able to isolate the damaged cable and restore power to the airport shortly before noon, though repairs to the cable were continuing about 5 p.m. The airport had readied a 2 megawatt generator to serve as an emergency back-up until the repairs are completed.
Aaron Koos, a spokesman for Baltimore Gas and Electric Co., which serves the airport and the broader region, said the problem at the airport did not involve the power supply, which was uninterrupted.
The flight-tracking website FlightAware.com showed 95 delayed flights and 24 canceled flights into and out of BWI as of about 5:30 p.m. Monday. Dean said some arriving flights had been diverted because of the outage.
By Monday afternoon, Stickler had booked another flight to Hartford on Tuesday. She has a sister in Kensington and planned to stay Monday night there, she said — albeit without her luggage, which was already on its way to Hartford.
"Hopefully, the airport will be functioning well by tomorrow morning," she said.
The majority of the flights were on Southwest, which operates more than 70 percent of traffic at the Anne Arundel County airport.
Thais Conway, a Southwest spokeswoman, said schedule changes forced by the outage likely would last all day Monday, but customers should be "back on track" on Tuesday.
It is the second consecutive year a coastal storm has threatened Thanksgiving travel in the Baltimore area. In 2013, heavy rain preceded the holiday in Baltimore, but predictions that snow would mix in did not come to pass. Heavy snow fell to the north and west of Maryland, however.
Dry but cold weather is forecast for the long holiday weekend. Highs are forecast around 40 degrees on Thanksgiving Day, with wind chills in the lower to mid-30s, and lows could drop to the lower- to mid-20s. Temperatures could peak in the upper 30s Friday and the lower 40s Saturday.