Estimated arrival of storms around Beltway and the district: 8:30 pm to 9:30 pm
Wednesday forecast: More rain likely
8:00 pm update: Storms approaching DC & # 39; s far northern suburbs. Warning of & # 39; golf ball size & # 39; Hail
Storms with a history of making golf ball hail around Frederick (see below) are slowly drifting south. A severe thunderstorm warning includes southern Frederick, northern Loudoun and northern Montgomery counties until 8:45 pm  Strive storm warning including Germantown MD, Frederick MD, Montgomery Village MD until 8:45 pm EDT pic.twitter.com/ AIEFIa4LmP
– NWS Strong Storm (@NWSSevereTstorm) May 15, 2018
In addition to the potential for large hail, gusts of wind could reach 60 mph. The rainfall is extremely heavy, dropping over 2 inches per hour and can cause flooding.
19:45 update: Weather Service says up to 4 inches of rain could fall
As this powerful bluff line is pushing south from the north of Maryland and slowing down, it has the potential to deliver a notable amount of rain, especially from the district and the north and east. In a special statement, the National Weather Service said that precipitation could reach 2 to 2.5 inches per hour with localized sums up to 4 inches. This type of rain would lead to a serious flash flood potential.
Even some areas northeast of Frederick have received at least 2.5 inches of rain.
Meanwhile, we have just received a report from Golf Ball Great Hail in Frederick
– Bob Haas (@ WeatherHaas) May 15, 2018
07:25 pm update: Big hail, strong Rain beats Frederick
The storm on Frederick is intense and unleashes marble-sized to quarter-sized hail or greater .
– Mary Kate McKenna Battles (@DCPhotog) 15 May 2018
A Twitter follower, Kevin Quinlan reported [more than 1 cm] of rainfall in less than 30 minutes and "crazy lightnings".
Everywhere in North Maryland, the storms produce a ton of lightning, very heavy rain and probably some very strong gusts of wind
When do we expect these storms to reach the Beltway? The storms seem to slow down as they move south, and the latest models suggest they could be closer to 9 or 9:30. rather than 20 or 20 o'clock. We keep you informed about your progress.
19.00 update: Storms are rapidly expanding south to northern Maryland; Frederick to Baltimore Warning
The southern part of the strike line, which was restricted to Pennsylvania less than an hour ago, has rapidly spread south and southwest and is now driving Frederick, Maryland, and much of northern Maryland east to Baltimore.
The National Meteorological Service has issued an expansive heavy thunderstorm warning from Frederick east of Baltimore, including northern Howard County and northern Montgomery County until 8 pm
Heavy Thunderstorm Warning including Baltimore MD, MD Columbia, Ellicott City MD to 8 pic.twitter.com/pI90q7ZCHt
– NWS Strong Storm (@NWSSevereTstorm) May 15, 2018
Storms along this line that pushed south at 20 miles per hour could blow pockets of 60 mph and hail, in addition to torrential rain and lightning. Go inside.
18:13. Update: Severe storm timer issued
Due to the total atmospheric fuel available for storms (see the 16:10 update), the National Meteorological Service has issued a heavy storm watch for the DC and Baltimore regions until 11:00 pm  "Thunderstorms seep south over Pennsylvania and into northern Maryland, while other storms are heading west," the guard says. "The conditions are favorable for locally gusty / damaging gusts of wind and hail in the strongest cells."
In the heaviest storms to be isolated, gusts of wind could reach up to 70 miles per hour and hail over two inches can not be ruled out.
Remember that a violent thunderstorm means the conditions for heavy storms are favorable, but they may or may not be formed. On the other hand, when a violent thunderstorm Warning is issued, it means that thunderstorms are imminent or happening, and you should seek refuge in a strong building, away from windows.
We think, for the immediate subway area near the Beltway and the District, the window for the most intense storms would be between 8pm and 9pm or so; a bit earlier in the west and north and later in the southeast.
Storms are already moving to northern Frederick County, where is a violent thunderstorm warning at 18:45 . In the southwest, the area from Front Royal Area to West Fauquier County is also under a severe thunderstorm warning that expires at 19:00 .
According to our previous updates, as soon as storms set in, they can stand around for a while and be repeated over some of the same areas while unloading torrential rain – hence the flash flood watch.
Our next update will be around 6:45 or 7:00 pm
5:40 pm update: Will storms connect to our southwest and north?
In short, probably.
A broad view of the weather radar shows an intense gust line from south-central Pennsylvania through eastern New England and a second dashed line of storms to our southwest along Interstate 81 in central Virginia. The model indicates that they will try to connect between 6pm and 8pm. in the northern and western parts of our region. The Virginia Line will grow to the northeast as the Pennsylvania Line expands to the southwest.
At 8 or 9 pm, storms in the immediate area should be numerous
16:10. update: Atmosphere is juiced for storms
Temperatures have risen in Washington during the early '80s and it is very humid (dew points in the low 70s). This means a very humid atmosphere, from which storms, which later come into motion, will come. While our biggest concern is the possibility of heavy rains and floods, there is more than enough atmospheric instability to avoid damaging wind threats, especially for storms that arrive before sunset.
Original contribution of 2:15 pm
For the fifth time in six days, the Washington region is armed against thunderstorms late Tuesday, usually between about 6pm and midnight. Some storms can be strong to strong, but less strong winds and hail should be less prevalent compared to Monday.
Floods are the biggest concern. Washington and many other areas have received more than two inches of rain in recent days, and the ground is getting saturated.
On Tuesday night storm cells can repeatedly pass through some of the same locations. This could cause the levels of streams to rise quickly and water to be on the roads. If you encounter a flooded road while driving, it is not safe to drive because it is difficult to gauge the depth of the water. Turn around, do not drown.
While we can not determine where the hardest fall will be, tonight one to three inches of new rainfall is possible within a district radius of the district and to the north. The heavy rainfall has prompted the National Weather Service to exhibit a torrent from 3pm. Tuesday until 1 pm Wednesday for this area
More storms probably late today and until tonight. While there are occasional cases of harmful wind and hail, the greater threat will be caused by heavy rains and the potential for flash floods. A Flash Flood Watch will be in effect from 15:00 to 13:00 for much of the region. #TurnAroundDontDrown pic.twitter.com/NtYzJQsDeY
– NWS DC / Baltimore (@NWS_BaltWash) May 15, 2018
Rain and storms could allow the leap to the Washington Capitals game Annoyance (allow extra time) and lead to a postponement of the National Yankees Showdown.
While some pop-up storms might develop in the late afternoon, we expect most of the rain to occur between 6pm and midnight, first in our northern and northwestern areas.
- Approximate arrival time for storms
- 17-19: 00: Northern Maryland
- 18-20 : Montgomery Counties Loudoun and Howard
- 19: 00-21: 00: remainder of the metro area except for the far south suburbs
- 8:00 pm to 10:00 pm: far south suburbs including Southern Maryland
 Storm Duration: Up to several hours
- Chance of measurable precipitation at each location: 50 to 90 percent from south to north
- Storm movement: northwest to southeast
- Probable storm phenomena: rains, thunderstorms, flood plains  Possible Storm Effects: Strong Wind, Small to Medium Hail
- Very Low Chance: Wind, Big Hail
- Rain Potential:
- Average one inch along Interstate 66 and Route 50 North. Locally up to three inches or more.
- Decreasing quantities in the south, 0.1 to 0.75 inches.
The atmosphere in our region is recovering from thunderstorm activity on Monday and early Tuesday morning. A large pool of cool downwind air (called outflow) has been left behind, which has temporarily stabilized the atmosphere. Warm air, which arrives at largely cloudless skies with southwesterly winds and strong sunshine, however, will quickly destabilize the atmosphere this afternoon. Computer models indicate that we will come deep into the 90s in places of high humidity.
There is evidence that Monday's frontal border, which served as a center for storms, has retreated to central Pennsylvania. Predictive models indicate that the front will retreat south in the afternoon and cross the district on Wednesday morning. With this front, which returns to an unstable air mass and plows, we are again prepared for evening storms.
It is expected that the amount of buoyant energy available for widespread coverage of thunderstorms will later become significant and reach a level where some severe to severe storms are possible. The front is likely to organize these storms into a broken line, oriented WSW-ENE and sinking south over the Mason-Dixon line in the early evening. In addition, one or two clusters of storms may emerge over the larger DC region (south of the line) in the very unstable air mass, triggered by air that converges along the residual outflow boundaries of Monday.
The National Weather Service's Storm Prediction Center (SPC) suggests that the area's largest serious threat (Enhanced Risk, Level 3 of 5) is far in the northeast near a wave of lower Pressure. The area northeast of us also contains stronger wind shear (winds with increasing altitude). We are in a marginal risk zone for heavy storms.
The danger of heavy storms will increase from south to north, from northern Virginia and the district towards Pennsylvania. Regionally, the risk is probably greatest along the Mason-Dixon line.
At the time, with the possible line of storms working towards the district in the evening south, the atmosphere is likely to stabilize, reducing storm strength. Any isolated storms that break out in front of this line in the late afternoon and early evening can reach high to potentially severe levels. Here, the degree of instability and wind shear is ideal for organized, multicellular storms.
SPC suggests a 5 to 15 percent risk of wind damage from south to north in our region (much less than Monday's 45 percent chance) and 5 percent chance of big hail.
As mentioned, the greatest threat is heavy rainfall and flooding, as western winds blow across the area from west to east, parallel to the front, what is referred to as training – when Storm Cells repeat over the same areas.