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Posted at 11:10 AM ET, 07/27/2009

Saturday Evening Thunderstorms in Washington

By Ian Livingston

* Humidity Hangs On: Full Forecast | CWG's Photo Archive *


Lightning strikes behind Arlington National Cemetery as a second batch of storminess pushes toward the city. By CWG photographer Ian Livingston.

I was planning on going out to take photos on Saturday for much of last week, primarily because it looked like it was going to be a quiet evening (oops!). By late afternoon it was apparent that storms to the west would likely make it into the area, but I was still eager to go out and get some new shots. Since I'm always on foot when photographing the area, I decided to stage around the Lincoln Memorial where I could take refuge from rain as needed. Given that it was a summer weekend I was certainly not alone.

Continue reading for more photos and storm commentary...

By late afternoon it was increasingly apparent that storms which formed off to the west would make it into the area, even though most previous forecasts (including those here) discounted the chance of storms on Saturday. The thinking had been that with the D.C. area so far away from a cold front -- which was approaching from the west but on Saturday had only made it as far east as the Ohio Valley -- that any storms would likely fall apart upon reaching the region.

As it turned out, the lift in the atmosphere provided by a pre-frontal trough (an elongated area of low pressure out ahead of a cold front), which itself was created by an outflow boundary (a boundary separating thunderstorm-cooled from surrounding air, along which more thunderstorms sometimes form), in combination with the instability caused by the day's sun and heat, were enough to keep the storms going all the way through the metro area.

When I arrived on the mall just before 7 p.m., thunderstorms were approaching from the west and northwest and the sky was rather murky with just a few spots of blue. My original plan was to cross Memorial Bridge and photograph D.C. from the Virginia riverbank at dusk, but the weather had another idea.


Looking across the National Mall prior to the storms' arrival. Flags blow south to north on a wind from the south. By CWG photographer Ian Livingston.

The first 15-20 minutes on the mall were rather calm as a noticeable gust front, the leading edge of gusty winds ahead of approaching thunderstorms, descended upon the city. Winds were steady from the south and it was still quite warm after temperatures rose into the 90s earlier in the day. People began to notice that there was a storm coming and several stopped to take pictures of the cloud mass spreading into the city.


A ragged gust front approaches Washington. By CWG photographer Ian Livingston.


Storms move into D.C. as other parts of the area get hit harder. Radar image courtesy Weather Underground.

Around 7:20 p.m. (see live tweet just prior), a ragged gust front was moving into D.C. along a line of thunderstorms that produced isolated strong winds. Though Saturday's storms were only sporadically disruptive, the front-end gusts were strong with several bursts (probably 30 mph and higher) even in the weaker section of the line that passed over the Mall. Several of these gusts were able to kick up sizeable amounts of dust along the Lincoln Memorial Reflecting Pool.


Dust is whipped up by winds with the gust front. Flags previously pointed north are pointed southeast with a wind from the northwest. By CWG photographer Ian Livingston.


Anvil of the storm and lower-level clouds move over the National Mall. By CWG photographer Ian Livingston.

A period of moderate to briefly heavy rain pushed through and sent everyone still outside looking for cover. The previously packed National Mall was left deserted.


Rain falls on a previously packed National Mall. By CWG photographer Ian Livingston.


Second batch of rain and thunder prepares to move into D.C. as stronger activity goes just south. Radar image courtesy Weather Underground.

Additional storms strengthened to the southwest and moved in behind the first line. As I stubbornly began my walk across Memorial Bridge trying to stay to my original plan, several cloud-to-ground lightning strikes in the distance made me turn back. With the strikes still a fair way off I decided to stop for a lightning photo -- a single cloud-to-ground strike is seen in the first photo of this post.

I spent the rest of the second storm sitting on the ledge of the Lincoln Memorial with at least a hundred others seeking cover or sky-watching. The most intense part of the second storm passed south of the Mall, so I stowed my camera rather than test the National Park Service security and enjoyed the show.

Rainfall for the evening totaled .07" at National Airport, pushing this July (now at .89" total) away from the driest-ever reading of .82" in 1871. This July now stands as the second driest ever for D.C. Next up on the list: 0.93" in 1966, 1.01" in 1999 and 1.05" in 1957. Though more rain chances are in the forecast through the month's final days.

By Ian Livingston  | July 27, 2009; 11:10 AM ET
Categories:  Photography, Recaps, Thunderstorms  
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Next: PM Update: Sultry; Isolated Shower or Storm?

Comments

The forecasters generally goofed on this one--the forecasts were for no storms on Saturday, and a very active day yesterday.

Evidently the bad weather clustered on the pre-frontal trough rather than on the frontal passage. It's a bit of a mystery why the models don't seem to pick up on this, as it happens frequently in this area, accounting for the so-called "Washington Split".

This period of active weather will probably increase the number of thunderstorm days for this area, too.

Posted by: Bombo47jea | July 27, 2009 11:37 AM | Report abuse

Yes, as we were driving to Wolf Trap under menacing clouds, checking the forecasts which didn't mention anything about violent thunderstorms, I suggested that we check Capital Weather Gang, since they always got everything right. Needless to say my companions were underwhelmed. We ended up picnicking in the car & splurging for covered seats.

Posted by: DCLiz | July 27, 2009 12:11 PM | Report abuse

@DCLiz...

Sounds like my experience last year at the Hootie concert @ wolftrap. More over-performing thunderstorms made that a wet night. I feel like wolf trap is a magnet for summer storms...

Posted by: JJones-CapitalWeatherGang | July 27, 2009 12:28 PM | Report abuse

@DCLiz

Yeah, not a great forecast for Saturday evening. We had a 20-25% chance of a thunderstorm listed in that day's forecasts (and mention of an isolated storm chance in some previous forecasts), which certainly did not do justice to what ended up happening. The key question is, could we have done better? Looking back at the models, I think there may have been evidence to support more like a "30% chance of showers and thunderstorms," but probably not much more than that. So yeah, we could've done a little better but not dramatically so.

On the flip side, we weren't that convinced that Sunday was going to be a stormy day around here. Thus only the 50/50 chance we gave for storms compared to more bullish odds from other forecast outlets. So I'd say we performed much better with the Sunday forecast. -Dan (CWG)

Posted by: CapitalWeatherGang | July 27, 2009 12:30 PM | Report abuse

My original forecast for Saturday afternoon called for a 30-40% chance for thunderstorms as it looked like the lee trough would be plenty to ignite the instability that wed have with a temp near 90. In reviewing we decided to trend lower due to previous forecasts not having much mention of storm chances. Still, if you see a 25% chance for afternoon thunderstorm, I don't see how many are claiming "I had no idea."

Posted by: Brian-CapitalWeatherGang | July 27, 2009 1:45 PM | Report abuse

I think this may be the first time I've ever encountered an article/blog post of this kind: technical descriptions of weather coming through coupled with radar captures and "touristic" photos "on the ground". Very cool - thank you for posting this.

Posted by: B2O2 | July 27, 2009 1:46 PM | Report abuse

We sat on the lawn for four rain-free concerts @ Wolf Trap last year - I guess we got lucky.

First one we had a chance to make it to this year was Saturday. Lawn seats, of course...

Posted by: map408 | July 27, 2009 1:50 PM | Report abuse

As Brian noted, the forecast here did mention the possibility -- whether or not we were too low on percentages. From Friday morning's forecast including no storms it shifted to isolated later in the day and then a bit higher than that by Saturday. Most if not all places underdid the forecast of storm chances for Saturday afternoon, but it was not as if there was no clue it could happen.

And B2O2, thanks for the comment.

Posted by: Ian-CapitalWeatherGang | July 27, 2009 1:59 PM | Report abuse

The comments to this entry are closed.

 
 
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