9:30 p.m. update: Showers and storms are still on track to make their way through the area tonight. While some locally heavy downpours are possible along with strong wind gusts to near 50 mph, widespread severe weather is not expected. But isolated damaging wind gusts can’t be ruled out with the heaviest activity, mainly from around 11 p.m. to 5 a.m. Everything should move off east of the metro area by around 6 a.m.
4:15 p.m. update: Some of the latest short-term model forecasts are hinting overnight showers and storms will not be particularly intense. Rain amounts may end up being fairly light and winds not as strong as feared. That said, we cannot totally let our guard down on this because winds are blowing so hard not far off the ground. It won’t take much for showers, even if weak, to draw down some significant gusts of at least 40 mph.
“Despite the lack of instability, the magnitude of the low-levels winds is so strong (45 mph just 1,500 feet off the ground) that the line [of showers and storms] should be able to produce 40-50 mph gusts as it moves through,” the National Weather Service said in its afternoon discussion.
Original post from midday
An energetic cold front sweeping through the region Monday night into early Tuesday is set to deliver some much-needed rain to the region. There is a chance, however, the front comes through with a bang, setting off a few thunderstorms with strong — even damaging — wind gusts.
Hit-or-miss showers could move in as early as between 7 and 9 p.m. Monday evening, arriving first in our western areas. But we don’t expect more widespread rain to overspread the region until between about 10 p.m. and 1 a.m.
The heaviest showers and storms, assuming they materialize, are most likely between 1 and 6 a.m. Tuesday.
The latest model forecasts suggest most of the rain should exit the region by around 6 a.m. or so, meaning it should not seriously affect the Tuesday morning commute.
Severe storm potential
The National Weather Service Storm Prediction Center has placed the region in its marginal risk zone for severe thunderstorms. Because any storms are expected to come through in the middle of the night, they’ll lack the heating and instability usually needed for a more significant and widespread outbreak of severe storms.
However, howling winds about 5,000 feet above the surface may be drawn down by any storms that form, causing pockets of strong-to-perhaps-damaging wind gusts in the neighborhood of 50 to 60 mph. Also, we can’t totally rule out a brief, isolated tornado developing — especially south and southeast of Washington — as the air will be spinning a bit.
“I could see a fairly intense squall line developing — with some lightning — and the threat of isolated damaging wind gusts between midnight and 6 a.m. Tuesday,” said Jeff Halverson, Capital Weather Gang’s severe weather expert.
Forecast rainfall amounts
Models generally forecast an average of about 0.5 inches as showers and storms move through overnight. But this is the kind of event in which there will be winners and losers — some which get about an inch of rain and some closer to 0.25 inches. It all depends where the heaviest showers and storms track.
GFS model rain forecast
High-resolution NAM model forecast
Generally, the heaviest totals are predicted to occur west of Washington into the mountains and from Baltimore to the northeast.
The region needs whatever rain can be squeezed out, as most areas have seen 1 to 1.5 inches less precipitation than normal this month. Large parts of Virginia, west and southwest of Washington, are abnormally dry because of the lack of rain this fall, and they’re nearing drought.
Capital Weather Gang’s Ian Livingston contributed to this post.
Source: Local Weather