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Posted at 10:00 AM ET, 07/27/2010

An inside view of Sunday's severe weather

By Andrew Freedman

* Gradually becoming more humid: Full Forecast | NatCast *
* Storm news - Outages and closures | Plot storm damage | Post Local *

The severe thunderstorms that tore through the Washington metro area on Sunday afternoon were fueled by a combination of historically hot and oppressively humid weather, and ignited by a cold front sliding east-southeastward. They were not the strongest thunderstorms ever to affect the region - after all, there were no confirmed tornadoes - but they happened to barrel right through the heart of some of the most populated areas of Loudoun and Montgomery counties, as well as the District itself.

Packing winds between 60-75 miles per hour, and in some spots closer to 90 mph, the storms' ferocity caught many off guard, resulting in three deaths.

Even President Obama was sent scrambling for cover as he tried to get in a sweltering afternoon game of golf at Andrews Air Force Base.

But what made the storms so fierce?

20100725_1243.jpg
Storm clouds gather above the Washington Monument Sunday afternoon. By CWG photographer Ian Livingston

Radar and satellite imagery, as well as on-the-ground photos provide evidence for what set these storms apart from most of the afternoon downpours that typically rumble across the area during spring and summer.

One clue that is likely to jump out at any weather geek comes from the way the storms were oriented as they traveled from northwest to southeast ahead of the heat-wave busting cold front. From this radar image below, which shows the line of intense precipitation and their associated winds about to charge into Montgomery County, it's apparent that the storms formed a bow-like structure.

WUNIDS_map1.gif
Doppler radar base reflectivity image on Sunday afternoon, showing the line of intense precipitation (reddish echoes) pushing into Montgomery County, and headed for the District. Image credit: Weather Underground

While not a classic, mature "bow echo", the storms' appearance on radar signaled the possibility that they would produce strong wind gusts. Bow echoes are often associated with very strong winds that blow in one direction, which are appropriately referred to as "straight line winds." According to the Baltimore/Washington office of the National Weather Service (NWS), the damage (at least in Montgomery County) was consistent with such straight-line winds, which storm surveyors estimated at 60 to 75 mph, with locally higher gusts (more on that in a sec).

A bow-like appearance results from strong mid-level winds that push some thunderstorm cells out ahead of a pack, stretching a line of storms into a telltale bow shape. Thunderstorm downdrafts in the storms that are "bowing out" can bring the strong winds from the mid-levels down to the surface, resulting in hurricane-force wind gusts.

This radar loop from the entire event shows what I mean, as the line of storms moves across the metro area.

WUNIDS_map_20100725.gif
Radar loop showing the line of storms progressing rapidly across the area late Sunday. Note the heaviest precipitation, with the brightest red colors on this map, went through Loudoun and Montgomery counties and D.C., where much of the heaviest damage was located. Image credit: Weather Underground

The greatest damage was focused roughly near the tip of the bow, from west central Montgomery County to the National Mall

umbrellas-mall.jpg
Umbrellas topple at a refreshment stand at the National Mall Sunday. By CWG photographer Ian Livingston.

PEERING INSIDE THE STORMS

Doppler radar can detect the winds contained in storms as well as precipitation intensity, and the radar velocity measurements reveal that one of the storms in particular contained very strong winds. The colors in this loop of radar velocity images correspond to winds that are blowing either towards or away from the radar.

20100725_velocity-close.gif
Doppler radar velocity image, showing the winds blowing above the surface as the the severe thunderstorms progressed across the region. Winds blowing towards the radar appear in bluish hues (dark blue means strong winds blowing towards the radar), while winds blowing away from the radar show up as yellow/orange (reddish colors are strong winds blowing away from the radar). Image credit: Weather Underground

From this loop, you can track the core of strongest winds (first appearing as a darker blue region) embedded in the line as it marches from Oakton, Va towards Dulles Airport. Once the storms move past the radar site near the airport, the blues turn to orange and red, and that wind core continues across Montgomery County and D.C., as a general area of strong thunderstorm outflow winds pushes rain-cooled air ahead of the storms. This outflow was responsible for the strange "shelf clouds" that marked the storms' arrival for many.

At one point, radar detected weak rotation in part of the line of storms in Montgomery County, prompting a tornado warning. However, no tornado has been confirmed, and all of the damage the Weather Service has surveyed resulted from straight-line winds.

Here are some highlights from what the Weather Service found in their damage surveys of west central Montgomery County, and the Rockville, Derwood, Aspen Hill, and Glenmont areas.

storm-damage-072510.gif
Wind damage reports logged by the National Weather Service. Image courtesy Storm Prediction Center
Widespread damage to large hardwood and softwood branches and limbs was noted throughout the surveyed area. More sporadic but concentrated damage to entire trees also was observed...Consisting largely of uprooted or snapped pine trees. The most intense damage was found in the Potomac Chase Estates and along Travilah road... Where hardwood and softwood trees were snapped 30 to 50 feet off the ground. Fallen trees and limbs were to blame for bringing down utility lines and poles through much of the area.
Of particular interest was damage to a large container crane located at the Montgomery county transfer station in Derwood. The crane was installed on a track that was oriented from northwest to southeast such that the horizontal member of the crane faced toward the northwest. Winds orthogonal to the horizontal member of the crane likely produced sufficient bearing load force to push the unsecured crane along its track before causing it to topple down a hill adjacent to the transfer station.
In summary...All damage surveyed in Montgomery county was consistent with very strong thunderstorm outflow straight line wind. Widespread winds of 60 to 75 mph were assessed...With sporadic narrow focused swaths of 80 to 90 mph winds.

Thanks to CWG's Ian Livingston for his assistance with this post.

By Andrew Freedman  | July 27, 2010; 10:00 AM ET
Categories:  Freedman, High Winds, Recaps, Thunderstorms  
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Next: PM Update: Mini heat blast arrives tomorrow

Comments

No question the winds came before the rain. For a while, I was wondering if we were going to get any rain at all.

I guess I was lucky because I was watching the radar reports as the squall line intensified in western Pa., while listening to a lengthy opera stream on Sunday. And Brian, I believe, reported on wind damage in Garrett County, Md. well in advance of the storm hitting here.

I guess the question some people are asking is if CWG was on top of this storm, why did it catch so many people off guard?

Posted by: JerryFloyd1 | July 27, 2010 10:01 AM | Report abuse

@JerryFloyd1

I had posted about the damage to the north and west when I put up the Severe Thunderstorm Watch info at 1:50 p.m. Sunday. We're going to visit the "off-guard" question tomorrow...

Posted by: Jason-CapitalWeatherGang | July 27, 2010 10:03 AM | Report abuse

How could this storm catch people "off-guard" unless they had been in a basement for two hours? At about 2:30 the breeze changed to a NW direction and the western sky became cloudy. About 2:45 the NW sky turned a dark blue, almost black, and the clouds began rolling. Anyone who was outside had at least a thirty minute warning that this storm was coming unless they are absolutely clueless.

Posted by: MKadyman | July 27, 2010 10:43 AM | Report abuse

Another question that could be raised was the NWS's delay in posting severe thunderstorm warnings. These warnings popped up on the short range image maps, only as the storm bore down on our region.

It was clear by late morning-very early afternoon that the Alleghenies weren't going to shred the squall line. Had the warnings gone up even an hour sooner, maybe some lives could have been saved.

Posted by: JerryFloyd1 | July 27, 2010 10:56 AM | Report abuse

Re: "off guard". The main factor I can think of was the speed of the storms. I nearly missed making it to the Mall in time even though I knew they were coming well in advance. Storms often move fast (40-50 mph) but these were clocking along even faster. So, there was pretty limited time between seeing the dark clouds and being in the storm. I actually disagree re: warning times, from what I could tell the NWS was warning fairly far in advance compared to normal. Again, speed may have been an issue.

Posted by: Ian-CapitalWeatherGang | July 27, 2010 10:59 AM | Report abuse

On the general public being "caught off guard".
These storms moved very fast.
And most people are not weather junkies like the crowd on this blog. Folks probably listened to a weather forecast Sunday morning for "storms likely this afternoon & this evening". They thought that they'd be able to see it coming, get out of the pool, pack up the picnic & get home with time to spare.

Posted by: FIREDRAGON47 | July 27, 2010 11:14 AM | Report abuse

Sorry, there is no way anyone should have been caught by surprise by this storm. Weather forecasters were saying for several days prior that the cold front coming in could bring severe weather and that it could be bad because of the extreme heat. By morning on Sunday, they said it would hit between 2pm and 3pm. They were absolutely on target with this one and what it shows is that people are clueless and need to start paying closer attention during periods of extreme weather. If you need help, there are multiple ways to get text messages sent to your phones for weather reports and emergency warnings.

Posted by: SierraSun | July 27, 2010 11:15 AM | Report abuse

I happened to be a referee at a rowing regatta in Delaware on Sunday. We had been watching the storm move through Harrisburg and a decision was made to stop racing at 4pm (about 75 minutes early). Around 3:15pm, however, the western skies quickly darkened and we went from flat calm waters to 50+ MPH wind gusts with 2-3 foot swells and a torrential downpour in minutes, trapping dozens of rowers far from shelter. It took a group effort to get everyone safely off the water, but that was one of the scariest 15 minutes that I have every experienced outside.

Posted by: TheOneWhoHurtsMost | July 27, 2010 11:18 AM | Report abuse

No offense weather geeks, but not being one myself, I wouldn't have paid much attention to a "severe thunderstorm warning" since they are a near daily occurrence in the summer. I usually expect there to be a brief, intense shower with some thunder around 5p on most hot days and am more surprised when there isn't one.

That said, that storm on Sunday was NOT a typical summer late-afternoon blast. Yet I don't see why I should have had a reason to think the dark skies of gloom that came quickly overhead were a harbinger of 6 hours of no power, downed trees blocking nearby roads, and every loose object outside being strewn about the lawn. Nor did I expect it to happen as fast as it did, nor to blow out as fast as it did. What would I have heard on the radio or seen in the sky that was going to alert me to all that?

Posted by: tcfenstermaker | July 27, 2010 11:44 AM | Report abuse

Our first thunderstorm watch (from DC Alert - alert.ema.dc.gov) at 2:23pm Sunday didn't sound more alarming than usual. It said "A line of storms, currently located in West Virginia, will be moving over the D.C. area between appx 4PM and 5:30PM. These storms have the potential to be severe." I didn't expect to change my plan to run errands because we've had a lot of t-storms recently and, well, life goes on.

The thunderstorm warning at 3:17pm caught my attention because it said "Please seek shelter if possible." It also said "D.C. could see severe thunderstorms within 15-30 minutes" which sounded to me like the storms were moving faster than expected. I stayed in, but it wouldn't have been much notice for people already out.

It was an unusual storm. Hard to predict that danger would come not from flash floods but large trees that had withstood years of severe storms.

BTW the DC Alerts are very helpful - we've set them up to come to our cells & computers.

Posted by: skylinr | July 27, 2010 11:52 AM | Report abuse

I've lived in the area my whole life and I can't ever remember a year with such "extreme" weather.

I sure hope this does not become common place.

I've also never seen the trees around my house bend like that. Driving around the last couple of days the ones that have fallen all looked "splintered" and not just snapped.

That wind was crazy Sunday.

- Ray

Posted by: rmcazz | July 27, 2010 11:52 AM | Report abuse

Did the NWS have any idea ahead of time that this was going to be an exceptionally bad storm and, if so, how far in advance? Perhaps they need to consider having degrees of severe thunderstorm warnings, since (as others have noted) such warnings are a regular occurrence during this time of year.

My feeling right now would be akin to someone who didn't pay much attention to a hurricane warning because the warning didn't mention that this hurricane was a Category 5 while all the recent ones were a Category 1.

If thunderstorms were likewise graded, this one would have been at least a Category 4. (I'd reserve 5 for ones that spawn tornadoes.)

Posted by: kevinwparker | July 27, 2010 12:26 PM | Report abuse

No surprise to me...severe weather often "breaks" our intense summer heat waves around here.

One surprise, given what's been happening so far this year, is that it did NOT occur on one of my scheduled dance nights.

There were a couple of deaths due to falling trees. What's interesting around here these past few years is that we seem to have had more fatalities due to falling trees/branches than to lightning. This was also true during the nasty windstorm on New Year's Eve, 2008. In both cases straight-line rather than tornadic winds were involved, and a young child was killed in each instance--possibly avoidable on 12/31/2008, as the child shouldn't have out playing in the backyard on a cold, windy day.. The sudden onset of the storms was a factor on Sunday. There were only five or ten minutes between bright sunny weather and the first gusts on Sunday afternoon.

Posted by: Bombo47jea | July 27, 2010 12:35 PM | Report abuse

I live on Victor St, NE, facing north. I heard what sounded like a freight train coming up the alley behind the house, from the EAST. The house shook, trees bent, debris hit the house, and I saw trash moving in a circular motion outside the window. Upon seeing the damage, there were trees that fell in all directions, even toward the east from which the strong wind came.

Posted by: linroy62 | July 27, 2010 12:47 PM | Report abuse

I got the alert for the Severe Thunderstorm Warning from the push alerts from the weather app on my phone. I opened it and looked at the radar, could see the bow wave-ish front forming, and knew it was time to secure some items on the balcony.

Then again, it take a lot more weather savvy than average to notice that, along with the experience growing up of watching bow-wave lines come out of the prairie into the Chicago area.

Posted by: NoVAHoyaDan | July 27, 2010 12:58 PM | Report abuse

6 hours without power--that's nothing. we're coming up on 48 hours shortly.

Posted by: Chaucer2 | July 27, 2010 1:02 PM | Report abuse

Even in Bowie, far from the center, the strom was powerful enough to topple a tree that must have been 20 to 30 feet or more and about 6 feet tall at the base, I can only imagine the damage that was at the center of the strom

Posted by: minerdude | July 27, 2010 1:16 PM | Report abuse

I live roughly 1 1/2 miles west of the town of Vienna near Hunter Mill Road. About two weeks ago, we had an afternoon thunderstorm that was far worse than what we experienced on Sunday. In the case of that storm, we experienced sudden winds that did not diminish for 15-20 minutes. While I don't have a wind gauge, I would estimate that wind gusts associated with that storm must have been around sixty miles and hour. We also had branch and leaf litter scattered all over the yard.

In contrast, Sunday's storm here exhibited strong winds for only 3-4 minutes, and quickly died. There was practically no debris resulting from it. So it's no surprise that I was shocked at the loss of life, tree devastation and magnitude of power outages associated with Sunday's storm system across the Metro area.

I routinely check the both present and "futurecast" doppler radar on Weather.com whenever a severe thunderstorm warning is issued. I monitored doppler radar two or three times during the early afternoon, and the "futurecast" appeared to show the rain cells hitting the Oakton/Vienna area around 4:30 or so. In actuality, it hit around 3:30, and was over well before 4:00.

There is no question in my mind that the system sped up as it neared the Washington area, and I believe that was a definite factor why many people were caught off guard.

Posted by: MillPond2 | July 27, 2010 1:28 PM | Report abuse

I was leading a group hike on Sugarloaf Mt when the storms hit. I heard some thunder in the area and was wondering if it was just a passing cell or something more. When I came to a spot where I could get a look to the west, I saw a wall of rain coming towards us. Suffice it to say that my group got soaked, but thankfully had no trouble with falling trees/limbs. (We heard one large limb fall as the gust front hit, but that was it for falling limbs. I also am sure that the summit got struck by lighting at least twice.) I am grateful that we were close to the end of the hike when the storm hit.

Afterwards, driving back, we were behind the storm. It was like a black wall ahead of us, with regular flashes of lighting being seen. You had a sense of a serious storm being up ahead.

I will say that I have seen the light fade as a bad thunderstorm hit, and it was NOT like that on Sugarloaf Mt. on Sunday. Yes, there was a strong wind and soaking rain, but it was not all that bad out there. If you look at the first radar loop in this article, you will actually see that. (BTW - Sugarloaf Mt. is on the Montgomery County - Loudon County line near the Potomac River.) So my group missed the really bad part, and I am grateful for that.

Posted by: ems57fcva | July 27, 2010 1:47 PM | Report abuse

Moderators/weather experts, 100+ degree days, 90mph winds, blizzards....what's with the severe weather over the past 8 months?

Will next winter and summer be tamer (no snowstorms, hurricanes, etc)?

Posted by: superseiyan | July 27, 2010 1:49 PM | Report abuse

I'm not a weather expert, but I do check the hourly predictions on various websites, and the storms were projected for later in the evening when I left the house that morning for the Scouting events on the Mall. The speed of the storm was remarkable. When my boys headed down into the Smithsonian Station after the parade, it was still mostly clear and calm out. (We were begging for a breeze on Sunday.) By the time the train came out of the tunnel at Ballston, the storm had already passed. (We literally rode the train under the storm.)

I think it's a reminder that we're not as much "in control" as we seem to think.

Posted by: mwcob | July 27, 2010 2:05 PM | Report abuse

Contrary to what one of the above posters said, at least where I live (Laurel) there was no 30-minute warning. This was about the fastest moving storm I've seen. In ten minutes it went from partly sunny to total raging thunderstorm.

Posted by: mosere | July 27, 2010 2:05 PM | Report abuse

I was watching Storm Cell, a cheesy made-for-tv movie on Fox 5, which got interrupted for real storm coverage a couple of times.

The heavy stuff missed me to the north... we just got

At home with the tv and internet, I wasn't caught off guard, but I can easily see how that could happen to people out and about.

Regarding radar, I like Channel 9.2 (CBS weather) because it almost always shows their Doppler 9000 radar unlike the other local weather channels (NBC 4.2 and CBS 7.2). I'm not sure if those channels are included with cable subscriptions, but you can pick them up free over-the-air if you have a good antenna. On the internet, I like Intellicast.com's regional loop. Of course, I also recommend CWG for lively discussion and real time reports.

Posted by: spgass1 | July 27, 2010 2:36 PM | Report abuse

Can these straight-line winds cause a tree to twist? One giant evergreen in our neighborhood (Greenbelt, in Prince Georges County) was twisted around like a stick of licorice that bent in half, but never broke. It look like it might have been caused by a tornado-like circular wind.

Posted by: RedRodgers | July 27, 2010 2:49 PM | Report abuse

Since meteorologists are so reliant on models, I hope this type of fast-moving storm is factored into the modelling and next time the warnings are earlier and more urgent. One death or injury from a falling tree is one too many.

Even Veronica Johnson was caught by surprise by this storm. She mentioned last night on the news that she was kayaking on the Potmac when the storm blew in and they too had to scramble to get everyone to a safe location.

There are lessons to be learned from extreme weather events. Over to CWG re: further discussion of this aspect. (I wish CWG was on camera, on a non-cable venue, and could hold a round-table discussion about this storm, other extreme weather events in 2010. We have Redskins Report, Meet the Press, etc. and numerous other D.C.-based pundit shows. Time for the weather experts to have face time on camera.)

Posted by: JerryFloyd1 | July 27, 2010 2:53 PM | Report abuse

I was in Springfield by that time and saw a huge dust storm cover my car. Driving to the other edge of Springfield and got caught in a huge rain.

Looks like 2012 the movie to me

Posted by: us-itunes-code-email-buyfrompowerseller | July 27, 2010 3:08 PM | Report abuse

Seems to me one summer there was a series of downbursts around the DC area that made the news and that caused similar damage to what I've seen in photos from this storm. I seem to remember trees being smashed into toothpicks and houses having the roofs ripped off. I'm no "weather geek" so I'm sort of wondering if this storm had some of those going on?

Posted by: RazorGirl | July 27, 2010 3:23 PM | Report abuse

RedRodgers, my guess is that straight line winds can cause twisting if for instance the left side of a tree is sheltered behind another tree or structure and the right side is exposed...

It would be interesting to read about what the NWS looks for to determine tornado activity... probably the angles of debris looking for blowdowns in all directions?

Posted by: spgass1 | July 27, 2010 3:37 PM | Report abuse

tcfenstermaker makes a very valid point. I have lived in this area for 30+ years now, and when I was a kid in the 80's and 90's, if a severe thunderstorm warning was issued it meant business! In western MoCo, we would get an air raid siren with the alert on the television. Now, I get upwards of 20-30 "alerts" on my email from the NWS for storms that are nowhere near severe, let alone fully developed.

It is sort of like a fire drill at school, you got so used to the over abundance of them growing up that many people don't leave buildings now when you hear an alarm. Of course, this is how people die, and the NWS should really look into their warning system.

Posted by: TheMot | July 27, 2010 4:01 PM | Report abuse

Please explain the following:
I live in Rockville and work in Baltimore. I lost power for 16+ hours. None of my coworkers who live in Baltimore had any power problems and in fact they said the storm was rather mild. The wind pattern on radar seems to extend through the Baltimore area...why such severe damage in Montgomery, somewhat less in PG and seemingly none in Howard or Baltimore Counties? Is it all the tree cover?

Posted by: hfmd | July 27, 2010 4:45 PM | Report abuse

Technically speaking, if "extreme" weather becomes common place, isn't it then no longer extreme?

Posted by: ronjaboy | July 27, 2010 4:49 PM | Report abuse

Thanks for the bow echo explanation! I asked about this a couple of days ago and the CWG kindly answered, but this one was much easier to understand for this non weather geek.

Posted by: paperball | July 27, 2010 4:56 PM | Report abuse

hfmd, in reality I think much of the line (while visually interesting and still powerful) was sub-severe (in the official sense of the word). This was really one very intense wind area event within a broader line. It just happened to cross through a highly populated part of the region.

Posted by: Ian-CapitalWeatherGang | July 27, 2010 5:00 PM | Report abuse

All I can say, as a weather-geek-wannabe, is that Sunday's storm, watched from the parking garage of the Montgomery County mall, was AWESOME. A little scary too, but definitely one of the most amazing forces of nature I've seen in-person since 1986 when a tornado tore through my hometown of Manheim, PA and we had to high-tail it into the cellar of a dairy barn to take cover. I guess my experience growing up among alfalfa & tobacco fields is that if you see black clouds coming, you take cover, NWS warning or not. My heart goes out to families who lost loved ones as a result of being caught off-guard--in those cases storm speed must have really played a part. By the way, if any of you folks have an "in" at Pepco, please ask them to restore power to the 5300 block of Connecticut Ave. Two nights without showers and AC, paired with loud traffic noise wafting in my 1st floor windows, and I'm a cranky girl!

Posted by: yandymung | July 27, 2010 5:07 PM | Report abuse

If you are hiking on Sugarloaf Mountain I can understand why you wouldn't see a severe thunderstorm approaching. But anywhere else? Why would it be a surprise? Maybe I am weird because I look at the sky every so often. I am guessing that there must be people who cannot recognize a huge black cloud mass building up in the northwest sky.
That means thunderstorm folks.

Posted by: MKadyman | July 27, 2010 5:32 PM | Report abuse

I was driving on Route 1 in College Park near Cherry Hill Rd. right before the storm hit on Sunday. There it was way over to the west looking dark and green and ugly, and literally within several minutes it struck with a fury. Drivers started hightailing it. Sure, you could say we shouldn't have been out and about, but who knew it would be as bad as it was until it got here? You had to be in a certain place to have seen that thing coming. I agree with others who say the warning given may not have been severe enough. But is there always a way to tell what a storm will do in advance, even for meteorologists? Can storms get a lot worse all of a sudden? Pardon my ignorance if it's showing.
Also, if it wasn't a tornado, it had to have had tornado-like winds. I live in Greenbelt like Red Rodgers and there's a pine tree nearby with a flat strap of bark about 5 inches wide wrapped around it like a belt. What else could have caused that?

Posted by: emmily | July 27, 2010 9:28 PM | Report abuse

you can't give 2 hours of notice for a severe thunderstorm, as you never know exactly how the ongoing thunderstorms will evolve during a time period that long. There wasn't much doubt that strong storms would roll through the DC area a couple of hours out, but to say at that time that the most severe winds would be in a roughly 25 mile corridor from DC up to Gaithersburg sweeping east-southeast is way, way beyond current levels of predictability.

this is the entire purpose of a severe thunderstorm watch. It's issued to cover a large area in advance of significant t-storm activity developing or moving into the area. It tells you that conditions favor thunderstorms that could threaten life and property within the area, and you need to monitor what's going on. Most of the time you won't get anything too violent in any one spot, and you might not even get a drop, but you have to take them all seriously if you don't want to get caught off guard.

Posted by: foul_throw | July 27, 2010 11:36 PM | Report abuse

I can tell you how it caught people by surprise. The winds went from a routine breeze to something that knocked over large pots and flipped over tables in something like a minute. One minute I'm outside, saying, oh, I think we'll get some rain, and the next, I'm inside saying, wow, this sucks. Between the time I closed my patio door and the time I sat down in the couch to look at the Weather Channel, the power was out.

That's how quick it came and that's why people got caught off guard. Usually, you hear a little thunder, and you pack things up and go home. But we didn't get that in Bethesda. We went from storm clouds that were worth paying keeping an eye on to winds whipping around at 50-60 mph to torrential downpours in less than five minutes. I don't think I heard any thunder until the rains had actually slowed a little.

Posted by: tonyw44 | July 28, 2010 12:30 AM | Report abuse

This was a very interesting event from a dynamics perspective. There were about 155 total wind reports from this event, but they all were very narrowly concentrated in one area. Isolated damage like we saw in Montgomery County usually is the result of a discrete supercell, and not a line segment. Damage from a bow echo/squall line usually results in the damage being more evenly distributed across the metro area (i.e. June 2008 bow echo). The line on Sunday stretched all the way down to about Bull Run, but there seemed to be a dividing line in terms of intensity from about Reston southward. It's got the guys at the NWS baffled.

It just goes to show that this area can experience a significant severe weather event if all the right ingredients come together. It just usually seems to be the case around here that one of those ingredients is lacking, and tends to offset the other ones. I believe it's only a matter of time until we experience a hurricane making landfall here locally. It would put Isabel and some of these wind events to shame.

Posted by: wxvthokie | July 28, 2010 5:06 AM | Report abuse

I've lived in the DC area 51 yrs. (1/2 mi. S of Pinehurst Cir.) Years ago I was told that storms coming out of the northwest were "the bad ones". This seems to hold true. I remember ones in Jun '73 Jun '89, '91, '08 and this one. I happened to be online Sun. and saw the NWS radar and I had that "uh-oh" feeling. The storm wasn't too bad here but 1/2 hr later a tree limb fell across the feeder lines to the nearby substation and we lost power for nearly 36 hrs. Any comment as to why a storm coming from the NW would be stronger than ordinary (barring tropical storms from the South, of course)?

Posted by: Phyllis1753 | July 28, 2010 11:19 AM | Report abuse

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