10:30 p.m. - Weather Service says tornado caused damage in Reston
The Weather Service says a tornado touched down in Reston just before 9 p.m. near the intersection of Quietree and Crosswind drive. One house was reportedly condemned as a tree fell on the roof. The area will be further surveyed during the daylight hours on Saturday to determine the tornado intensity.
The images shown below are from tree damage on Bayfield Court which is just to the northeast of the damage reported above.
Farther northeast, multiples trees were also reported down in Reston on Center Harbor and Baron Cameron roads at 8:56 p.m.
A tornado warning had been issued for western Fairfax and eastern Loudoun counties at 8:53 p.m, which expired at 9:15 p.m.
10:00 p.m. - Severe storm and heavy rain risk ends
Update posted at 9:40 p.m., updated at 10:00 p.m.
The evening band of rain and thunderstorms was intense in spots and triggered several severe thunderstorm and tornado warnings, but it also moved through the heart of the region rather quickly. It has moved away to the north. Rainfall totals have varied widely, with Dulles picking up more than an inch, and D.C. less than half an inch.
Additional showers are possible overnight, but coverage is much lower and there is no more threat of flooding or severe weather locally. Temperatures settle through the 60s for lows.
Saturday features plenty of clouds, but it should be fairly dry. A passing shower or two is possible as highs rise into the near 70 to mid-70s zone.
Scroll down to the bottom of this post for earlier updates.
Detailed storm briefing from the afternoon
An intensifying, dynamic storm system sweeping up the Appalachian Mountains is set to trigger multiple rounds of showers and storms in the Washington region Friday afternoon and evening.
An initial round of rain and storms is likely to develop during the mid and late afternoon hours, before a second — possibly a more intense -- wave in the evening. It will not rain continuously, and some areas will get hit harder than others.
Some storms could contain damaging wind gusts (up to 70 mph), and isolated tornadoes are not out of the question.
The National Weather Service Storm Prediction Center has issued a tornado watch for much of the Washington/Baltimore region through midnight. A tornado watch means conditions are conducive to tornadoes; stay alert and be ready to take action, but a tornado may or may not happen.
If a tornado warning is issued, it means radar is indicating a tornado or a twister has been observed on the ground. In that case, you should seek shelter in the lowest level of a strong building (preferably underground), away from windows.
A flash flood watch is also in effect due to the possibility of storms with very heavy rainfall tracking over the same areas repeatedly. Some creeks and streams could overflow, and water could inundate poor drainage areas.
Approximate arrival time for storms:
- Round one: 2 to 5 p.m., generally hitting south/southwest areas first
- Round two: 6 p.m. to midnight, generally hitting southwest areas first
All clear: Midnight to 2 a.m. Saturday
Storm duration: 45 minutes, but longer if storms track over the same areas repeatedly
Chance of measurable rainfall in any location: 80 percent
Storm motion: Southwest to northeast
Likely storm effects: Heavy rain, gusty winds,
Possible storm effects: Damaging wind gusts, flash flooding, lightning, a few tornadoes
Rainfall potential: 1 to 1.5 inches but highly variable. Some places could receive up to 3 inches, while others 0.5 inches or less.
Severe storm discussion
Storms this afternoon through early Saturday morning will erupt in the energetic warm sector of a cyclone (low-pressure system) tracking to our west, along the spine of the Appalachians. In this sector, a modestly unstable but highly humid air mass will be overspread by strong winds in the middle atmosphere.
The high-resolution forecast models are advertising multiple rounds of storminess over the next 12 to 18 hours. The first batch is expected to develop during the afternoon, pushing from south to north. The second round is timed from 6 p.m. to midnight, in the form of a line (or lines) of storms developing just ahead of the cold front.
Through the afternoon, clouds should be widespread and persistent enough to prevent a strongly unstable air mass from developing. The lack of solar heating in this case, however, will be partially offset by the high low level moisture content of air. Water vapor contains significant heat energy, which is released into the atmosphere when that moisture condenses inside storm clouds.
The exceptionally strong winds aloft are a concerning ingredient for thunderstorms. Winds just 5,000 feet above ground will be screaming at 60-70 mph, and may approach 90-100 mph around 15,000 feet. The strong increase in winds with altitude, called wind shear, allows storms to become more intense, better organized and longer-lived.
But the wind fields and shear are even stronger across the Carolinas and central Virginia/Tidewater, also where the air mass is expected to be more unstable. Accordingly, the National Weather Service Prediction Center has issued a moderate risk of severe storms, level 4 out 5 on its 1 to 5 scale.
But even in the Washington region, the slight risk of severe storms (level 2 out of 5) indicates a 15 percent chance of damaging winds within 25 miles of any location.
The slight risk for severe storms is pretty common in the Washington region. However, the moderate risk zone from central Virginia to the Carolinas is uncommon. In the Carolinas, this is the most significant severe thunderstorm risk since 2016. There, one or more intense bow echoes may generate widespread, severe wind damage and perhaps also supercell-generated, strong tornadoes.
The zone of heavy rainfall from this storm is vast, with flash flood watches from North Carolina through New England.
While the amount of available moisture is abnormally high, there is still considerable uncertainty as to exactly where a lot of the water will be deposited. Thunderstorm rainfall is often highly variable over small distances and models project a big range of possible totals.
For example, here are projected rainfall amounts for Washington from several models:
- GFS: 0.8 inches
- European: 0.5 inches
- NAM: 0.6 inches
- High resolution NAM: 0.6 inches
- Canadian: 0.9 inches
- High resolution Canadian: 0.7 inches
- HRRR: 1 inch
Models generally project somewhat higher totals west of Washington.
Throughout the entire event (through about 1-2 a.m. Saturday), training storm cells will likely lead to localized flash flooding in several spots, with the potential for a relatively quick 3 to 4 inches of rain. Such heavy rainers are due to the very high moisture content of this air mass, and the tendency for storm cells to align parallel to the corridor of fast-moving airflow from the south.
To summarize, during Round 1 of storms later this afternoon, any strong to severe storms will be isolated to scattered. They will be heavy rainers though, with the greatest severe threat being isolated damaging wind gusts. However, given the amount of wind shear in the atmosphere — which can cause storm updrafts to rotate — a weak tornado cannot be ruled out.
Round 2 may be the more intense of the two, and impact more people in the Washington-Baltimore region. Like last Sunday night, we can expect one or multiple, parallel bands of intense showers and thunderstorms … including short bowing segments. These segments can create small corridors of damaging, straight-line wind. Small areas of rotation may also develop along these wavy lines, triggering a weak tornado or two.
In this second round, lightning activity may not play out everywhere . . . so the normal visual and audible cues that warn of impending storms could be absent. Accordingly, everyone should have ready access to a device that can provide automated weather alerts and warnings, or be tuned in to radio or TV.
Expired updates (no longer relevant)
9:15 p.m. - Tornado warning for parts of Montgomery County
Another tornado warning has been issued, this time for parts of Montgomery County until 9:45 p.m. Take cover in the area highlighted below.
8:58 p.m. - Tornado warning for parts of the area
Parts of Loudoun and Fairfax counties are under a tornado warning until 9:15 p.m. If you are in the area highlighted in the warning below, centered on Herndon, seek shelter or take cover in an interior room.
8:43 p.m. - Damaging wind threat progressing through western parts of area
A severe thunderstorm warning has been issued for much of the western part of the area, west of the Beltway, until 9:15 p.m. Storms have taken on a bit of a bow shape as they move through the area. This may enhance the risk of damaging winds, especially near its apex.
Areas to the east of this warning, including the city, will continue to see rain and wind increase in the near term as well.
Other intense storms have focused on far southern Maryland and south or east of that, where severe storm and tornado warnings have been in effect recently.
8:28 p.m. - Damaging wind threat in southwest parts of the area
Rain has moved into the city and strong to severe storms are approaching from the southwest. A big chunk of the southwest part of our area is under a severe thunderstorm warning until 9 p.m., and storms are moving northeast at 30 mph.
The main threat from these storms is damaging winds. An area of strong winds is approaching a corridor from Manassas to Stafford shortly, and will continue to move northeast from there. If the storm holds together, places like Fairfax and Dumfries will be in line near and after 9 p.m.
8:15 p.m. - Main evening band moving into immediate area
The final band of heavy activity for the evening is moving through western parts of the area and about to impact the city. For the most part, severe weather has remained south and southeast of the area. There is still some potential for wind damage or a tornado. A tornado warning is up near Boonsboro, Md. through 8:30 p.m.
6:10 p.m. - Showers redeveloping locally, heavier activity advancing this way
Most of the area has picked up about a quarter to a half inch of rain so far, and an extended lull has been ongoing for a few hours now. Shower coverage has increased again lately, but it remains hit-or-miss at this time. Rain becomes more widespread again as we get through the evening.
Over the next hour or two, the heaviest and most widespread rain and storms may focus west of Interstate-95 overall. The storm motion is a bit east of north, whereas most lines of storms around here go from west to east. In other words, eastward movement may be slower than usual.
For now, the closest severe weather is west of Richmond. The northward expansion of more unstable air has been a little less than modeled thus far. With some luck that may lower the severe risk slightly locally, but it’s too early to say that yet. Damaging winds and tornadoes remain possible through the evening. Heavy rain is the primary threat.
4:10 p.m. - Awaiting the evening round of storms, likely to arrive between 6 and 8 p.m.
The first wave of rain and storms was pretty tame, with just some general rain and brief downpours. But the next round, moving in this evening, may be more intense and may involve multiple periods of storminess.
The activity to watch is currently in southwestern Virginia and western and north central North Carolina. It will sweep northeastward toward our area, and some new storms may develop out ahead of it. Some of this activity to our southwest has a history of triggering flash flood, severe thunderstorm and/or tornado warnings. Whether it remains this intense as it progresses northeastward remains to be determined.
The time frame of concern for these storms is roughly 6 p.m. to midnight, arriving and departing first in our west/southwest areas and last in our east/northeast areas.
We’ll post our next update around 6 p.m. or as storms start closing in, whichever is first.
3:25 p.m. - First round of rain exiting, washing away peak pollen
The first wave of rain and storms is lifting north of the Beltway, with the heaviest activity now north of Interstate 70 in Maryland. No severe weather was reported from this first round. Generally around 0.1 to 0.5 inches of rain fell (0.22 inches at Reagan National Airport).
The rain did help wash tree pollen out of the air, which on Thursday reached its highest level of the year of 2570.93 grains of pollen per cubic meter of air, classified as “very high.” And, it’s now possible tree pollen has peaked for 2019.
Even though this first round of rain and storms have passed, some widely scattered trailing showers and storms are possible before the next wave expected to starting moving in around 6 p.m.
2:15 p.m. - Moderate to heavy rain approaching Beltway, but no severe storms for now
Rain, moderate to heavy in some areas, is moving into the immediate Washington area from the south. At the moment, there are no severe thunderstorm warnings in effect. However, some gusty winds and thunder are possible as some of the heavier activity moves through the region over the next couple of hours. And, it’s not out of the question some storms intensify, so we will be monitoring closely. The most intense activity may focus close to Interstate 95.
We still expect this initial wave of rain and storms to exit between 4 and 5 p.m (south to north). before another wave starts to move in on the area from the southwest between 6 and 8 p.m. or so.
1:25 p.m. - Strong to severe storms moving into far southwest part of Washington region
A large area of rain with embedded thunderstorms is approaching the Washington region from the southwest. A severe thunderstorm warning is in effect for parts of Fauquier, Stafford, Spotsylvania and Culpeper counties until 1:45 p.m.
This whole area of rain and storms should overspread the Washington region, especially along and west of Interstate 95, over the next hour. We will have to watch to see if any of the embedded storms begin to rotate given spin in the atmosphere triggering tornado activity.