* Wind advisory 6 p.m. tonight to 11 a.m. Thursday morning *
1:45 p.m. update: Regional radar (screenshot below) shows the line of showers and storms - that should hit the immediate metro region between around 5 and 7 p.m. – cutting through West Virginia along the cold front. So far, this line has not shown severe weather characteristics, but we will continue to monitor it.
Winds are already turning very gusty ahead of the front, especially in western areas. Dulles Airport gusted to 48 mph around 1 p.m.
From 12:40 p.m.: The powerful cold front to rush through the region this evening may bring a few severe storms, but of greater concern is the onslaught of wind to blast into the region behind the front overnight – which could cause isolated-scattered power outages.
The storm threat: 4-8 p.m. tonight
As for the severe thunderstorm threat, we have become less concerned about a widespread outbreak of damaging storms. While a squall line (narrow band of showers and storms) is likely to zip through the region between 4 and 8 p.m., all the ingredients may not come together for a major severe weather episode.
Capital Weather Gang’s severe weather expert Jeff Halverson says he expects “a strong and gusty line” but reasons severe storms will be more isolated. “As depicted in the models, it is a very narrow line, fast-moving, and not very organized,” he says.
Cloud cover today could limit the available fuel for these storms and their potential to become intense.
“The high resolution visible satellite image shows fairly extensive overcast [to our west],” says Halverson. “We might get a few peeks of sun, but I don’t see an extended period of solar heating/destabilization [that could energize storms].”
Prior to the main line of the storms between 4 and 8 p.m., scattered non-severe showers are possible through the early and mid-afternoon hours.
The National Weather Service Storm Prediction Center places the region under a slight risk of severe thunderstorm. It says there’s a 15 percent of damaging winds within 25 miles of a point in the region and 2 percent chance of a tornado.
Raging winds behind the front overnight, power outage risk: 6 p.m. through Thursday morning
After this evening’s showers and storms burst through the region and the cold front passes, very strong winds blow into the region – probably starting between 6 and 8 p.m. from west to east. These winds will be sustained at 20-30 mph, with gusts in the 40 to 50 mph range. This will be a somewhat long duration strong wind event, with winds gusting over 30 mph into Thursday afternoon.
We don’t expect widespread power outages but isolated to scattered outages are certainly possible, especially tonight.
“I feel that the greatest likelihood for scattered outages is along Maryland’s northern tier of counties along the Mason-Dixon i.e. Carroll County,” says Halverson. “Up there, consistently through the winter, they have had significant ice accumulation and heavy, wet snow – with a lot of weakened/damaged tree limbs ready to come down.”
The abrupt drop in temperatures , 7 p.m. to midnight
We discussed it yesterday, but the mercury is likely to plummet 30-some degrees in the course of a just a matter of hours. Before the squall line passes this evening, the temperature should be around 70. By midnight, many locations are dropping into the 30s.
“Lows tonight will ultimately be 40 to 50 degrees cooler than today’s highs,” writes the National Weather Service.
As Dan Stillman wrote in his forecast post this morning, we go from near 70 this afternoon to single digit wind chills tomorrow morning – that’s a pretty radical swing.
“Something for everyone” over next 36 hours
With the winter-spring transition and the attendant battle of warm and cold air, this is the time of year to expect an alphabet soup of weather extremes. But I don’t know if I’ve ever seen the National Weather Service discuss this many hazards in one of its discussions:
WE SOMETIMES SAY THE FORECAST HAS SOMETHING FOR EVERYONE. I THINK WE CAN TAKE THAT LITERALLY AT THE MOMENT…AS THIS FORECAST HAS ALMOST EVERY POSSIBLE WEATHER TYPE/HAZARD…IN THE FIRST 36 HOURS. STRONG TO SEVERE STORMS…SNOW…WIND CHILLS…STRONG WINDS… UNSEASONABLY WARM TEMPS…UNSEASONABLY COLD TEMPS…POTENTIAL FIRE WEATHER CONCERNS…MINOR COASTAL FLOOD POTENTIAL…THERE IS NOT MUCH LEFT.
I haven’t discussed snow much, as it will probably be confined to the mountains. Still, I would be surprised if areas of Loudoun and Frederick County see a brief period of snow showers before the precipitation cuts off as cold air surges in.
In terms of the other hazards possible with this storm, here’s some brief information:
- Coastal flooding – today: The south winds ahead of the front are piling up water along the western shores of the Chesapeake Bay. As such a coastal flood advisory – for water level 1.5 feet above normal – is in effect for the shores of Calvert, St. Mary’s and Anne Arundel counties.
- Fire weather – Thursday: “Abundantly dry air will accompany the arctic airmass invading the area on Thursday…with dew points below zero expected,” writes the National Weather Service. “This will result in relative humidity values bottoming out in the teens Thursday afternoon. The dry and windy conditions may result in an enhanced fire spread potential Thursday afternoon depending on how. Much rainfall the area receives today.”