- After a first round of storms hit our west and northwest areas between 6 and 9 p.m., we await the next round, expected between midnight and 4 a.m. from west to east. We expect this second round to be more widespread and intense.
- Some storms could be severe with heavy rain, damaging wind gusts, hail, and even some brief tornadoes.
- A tornado watch is in effect through 4 a.m., which means conditions are conducive for tornadoes but may or may not happen. Stay alert. But, if a tornado warning is issued for your area, it means radar has detected a tornado or one has been observed on the ground. Seek shelter in an interior room in the lowest level of a strong building.
- Have a way to get warnings (activate your weather radio or download FEMA app) overnight as hazardous weather could occur while you’re sleeping.
11:15 p.m.: Storms lined up to the west and will enter region by 1 a.m. or so
A vigorous line of storms stretch from central Pennsylvania (near State College) all the way south through Cumberland, Md. and into east central West Virginia, just west of Harrisonburg, Va. Severe thunderstorm warnings are in effect along the entirety of the line for the potential for damaging gusts.
Storms (from this line or possibly from a new line that develops east of the mountains) are still expected to reach Washington’s western areas around 1 a.m. and the immediate metro between 2 and 3 a.m. It’s fairly likely we’ll have severe thunderstorm warnings as these come through and a short-lived tornado could be embedded in a couple of the storms.
Most storms should exit by 4 a.m. or so.
You can track warnings in effect over night at the following links
If the weather is particularly severe (multiple tornado warnings, for example), we may update overnight but will pass if it is not. In any event, we suggest just having a way to receive warnings and seeking shelter in a safe place if a tornado warning is issued (in a strong building at the lowest level in an interior room). Stay safe and get some rest.
9:15 p.m.: Awaiting the second round of storms
Showers and storms, along a skinny line, continue cycling through western Loudoun and Frederick counties, but these are not severe and may not hold together much longer. Otherwise, radar is pretty quiet and the first round of storms is over for the most part.
We’re now turning our attention to the storms expected to sweep through the region after midnight. Some of them could contain strong or even damaging winds and heavy rain. A brief tornado or two can’t be ruled out. In the immediate metro area, the most likely timing for these storms is between 1 and 3 a.m.
Here’s a simulation of how they may approximately look on radar as they come through (actual details will differ):
We’ll check in with another update around 11 p.m.
8 p.m.: Tornado warning discontinued in Carroll County as first round of storms is weakening
For the first time in 90 minutes, there are no active severe thunderstorm or tornado warnings in the region. In addition, most of the rain associated with this evening’s first batch of the storms is now north of Washington and moving northeast at a swift pace. While our northern areas will see some moderate to heavy rain for the next hour or two, a break is coming (and is already happening in our southern areas).
We should reemphasize that it’s never been this first batch of storms that is our greatest concern. It’s the next round coming through between midnight and 4 a.m. that has the potential to be pretty intense with different severe weather hazards over a large area, including perhaps a few tornadoes. A tornado watch remains in effect for the region until 3 a.m.
7:35 p.m.: Heaviest storms in first round pushing toward Mason Dixon line. Tornado WARNING for Westminster area until 8:15 p.m.
Radar continues to show some intense storm activity east of Frederick and around Westminster. In fact, a tornado warning is in effect until 8:15 p.m. in northeast Carroll County, including Westminster and Manchester.
To the south, we’re mostly just seeing moderate to heavy rain. The storms — which had been severe earlier — are weakening a bit.
For the next couple of hours, this first round of storms should primarily be a rain generator affecting areas mostly west and north of the Beltway. But there is still a small chance of damaging winds or a brief tornado in isolated pockets. We can’t totally let our guard down as there is enough spin in the atmosphere to continue monitoring these storms closely.
6:55 p.m.: Strong to severe storms from northern Loudoun County through Frederick County
The tornado warning which had been in effect for southern and eastern Frederick and western Carroll counties has been discontinued but heavy storms with very strong winds continue tracking through this area, which is under a severe thunderstorm warning until 7:45 p.m.
The warning includes Leesburg, Frederick, and Westminster.
Radar indicates winds may be gusting to at least 60 to 70 in the Westminster area which is catching the brunt of this storm. This storm is racing to the northeast at 40 mph.
6:40 p.m.: Severe thunderstorm WARNING for northern Loudoun and southern Frederick counties until 7 p.m.
6:25 p.m.: Tornado WARNING for southern and eastern Frederick county until 6:45 p.m.
6:15 p.m.: Tornado watch issued until 3 a.m. for entire region
The National Weather Service Storm Prediction Center has issued a tornado watch for the entire Washington region through 3 a.m. “Damaging winds and a tornado risk will exist with a potential multiple round of storms,” the Weather Service writes.
A tornado watch means conditions are conducive for tornadoes to form, but not a certainty. Stay alert.
If a tornado warning, on the other hand, is issued, it means a tornado has been detected by radar or observed on the ground and you should take cover immediately.
6:10 p.m.: Tornado watch likely coming for southern part of Washington region
The National Weather Service is probably about to issue a tornado watch for areas just south of Washington in northern Virginia.
“The latest radar analysis shows a small cluster of strong to severe thunderstorms in western Virginia,” the Weather Service writes. “This cluster will continue to move northeastward into central Virginia where strong deep-layer shear and instability will be sufficient for a severe threat. Wind damage, hail and an isolated tornado threat will exist with this activity.”
Several tornado warnings are in effect southwest of Charlottesville and all of this activity is heading northeast and could affect the Washington region between 7 and 10 p.m.
5:50 p.m.: First round of storms developing in Loudoun County
A strong line of storms is developing in western Loudoun County between Middleburg and Lovettsville which could turn severe as it pushes northeast toward the west side of Leesburg and southern Frederick County over the next hour. Heavy rain and wind gusts of at least 40 to 50 mph are likely with this area of storms.
These storms may mostly affect our far western and northwest areas over the next couple of hours.
But there are some storms down near Charlottesville, some of which have triggered tornado warnings, which could affect the immediate metro region between 7 and 9 p.m. They may weaken some but that is not a given and we’ll be closely monitoring.
The main concern continues to be the overnight period, between about 1 and 4 a.m., as noted below. “With this threat of severe weather occurring at night, it is extremely important to ensure you and your family have multiple ways to receive warnings and respond if they are issued for your area,” the National Weather Service cautioned.
Original post from 3 p.m.
A potent storm system that delivered widespread severe weather across the South Saturday is moving toward the Mid-Atlantic. Showers and storms, some which could be intense, are likely in at least two rounds.
We expect an initial round of showers and a few thunderstorms this evening, as warm and humid air surges northward ahead of a cold front. A few of these storms have the potential to be on the strong or severe side.
The second round, which will arrive after midnight, poses more of a widespread severe risk. This band will be right along the cold front itself, and will tap into exceptionally strong winds aloft. Damaging winds are the main threat, but the extreme wind shear (change in wind speed and direction with altitude) may generate sufficient spin for one or more tornadoes.
This article will be updated as storms approach and/or if any watches or warnings are issued.
Approximate arrival time for storms:
- Round 1: 5 to 10 p.m. west to east (6 to 8 p.m. most likely immediate area)
- Round 2: Midnight to 4 a.m. (Monday) west to east (1 to 3 a.m. most likely immediate area)
Storm duration: 30-45 minutes or so for each round
Chance of measurable rainfall in any location: 80 percent
Storm motion: Southwest to northeast
Likely storm effects: Heavy rain, lightning, gusty winds
Possible storm effects: Damaging wind gusts, flash flooding, brief/isolated tornado, hail
Very small chance of: Multiple tornadoes, possibly strong, large hail
Rainfall potential: Average 0.5 inches, but highly variable. Localized amounts of 2 to 3 inches possible.
The National Weather Service Storm Prediction Center has been closely monitoring this large, springtime cyclone that has proved to be quite vigorous across the Gulf Coast and Southeast. Accordingly, a very large region east of the Mississippi is under at least a slight risk of severe thunderstorms.
Early this afternoon, the risk for the Washington, D.C., region has been upped another notch to the enhanced level. This level three on the center’s 1 to 5 scale for thunderstorm risk.
This afternoon, a warm front is lifting north through the region. Our region remains socked under thick layers of low and mid level clouds, but this may thin somewhat for a few hours later in the afternoon, under a surge of southerly winds. By mid- to late afternoon, we will enter the more potent “warm sector” of the cyclone. Humidity values will climb to very high levels for this time of year.
The upper atmosphere is quite volatile, with a pronounced dip in the jet stream taking on a configuration we call a “negative tilt”, which means the uplift of air will intensify as this region moves over us later tonight. Additionally, winds in the middle atmosphere will be on the uptick, and this means a further strengthening of wind shear. This will feature winds that veer (turn clockwise) with height, as well as speed up, and this creates some concern for rotating storm potential.
Our one limiting factor for severe weather — and this is a good thing — is the lack of a very unstable air mass. Clouds this afternoon are holding the destabilization at bay. But this is a type of weather setup which has other ways of generating some instability — namely, the expected surge of warm, humid air in low levels from the south, which will really kick in around sunset.
For the first round of storms this evening, the expectation is that we will have a less unstable atmosphere to work with. Additionally, the trigger for the first round is somewhat diffuse, as the cold front still remains far to the west. However, judging from satellite loops, some thinning of cloud or even breaks are possible in the late afternoon to evening, before sunset. Pockets of air could destabilize such that a few spots may experience a strong to severe thunderstorm, including an isolated supercell (rotating thunderstorm) or two, especially in our western areas.
By 1 or 2 a.m., the cold front begins to move from west to east across our region. That’s when all of the high resolution forecast models develop a squall line of showers and thunderstorms, and push this rapidly through the area.
With strong uplift along the front, dynamic uplift triggered aloft by the jet stream, potent wind shear and perhaps just enough unstable air (from those southerly winds) . . . the setup favors some embedded severe storms. It’s not the classic time of day one would expect an intense storm line, for sure. If this same setup played out hours earlier, with hours of heating by the afternoon sun, we’d be dealing with a significant severe weather outbreak in the Mid Atlantic.
The storm line will probably be wavy in appearance, with bowing segments, a type we refer to as a quasi linear convective system (QLCS). In the crooks between the arcs and bows, small vortices (mesocyclones) may tap into rotational energy contained in the rich wind shear. One or more of these mesocyclones could generate a couple transient tornadoes. These are not expected to be the strong types of tornadoes that were unleashed Saturday in Texas and Mississippi.
But the most likely severe threat, after midnight, will be scattered pockets of damaging, straight-line wind. Also, because of high levels of humidity, some cells could be very heavy rain producers, locally. Some spotty flash flooding is possible, but the rapid movement of these storms should limit more widespread flooding concerns.
Stay tuned for updates on this situation, which we publish at the top of this article. A severe thunderstorm watch is possible for our region, and we cannot completely rule out an overnight tornado watch. A watch would mean conditions are favorable for severe thunderstorms and/or tornadoes.
Have a way to receive any storm warnings issued this evening and tonight (activate your weather radio, follow @dcweatheralerts and @capitalweather on Twitter, or download an app with severe weather push notifications such as the FEMA App), which would signal severe weather is imminent or already happening in or close to your location.
Forecast for Monday
Rain and thunderstorms should be well east of the area by sunrise Monday, but we can’t rule out a lingering shower at some point during the day. Skies are generally partly sunny with cooler temperatures and gusty winds. Highs will top out in the upper 50s to low 60s with a strong west/northwest wind at 15-20 mph and gusts up to 35+ mph. Clear, cool and windy tomorrow night with lows in the upper 30s and low 40s and winds out of the northwest at 10-20 mph.