From the ABC 7 Weather team

Archive for August 2013

Ragweed pollen in Washington D.C.

August 3, 2014 - 11:15 AM

Ragweed is the highest cause of allergenic rhinitis in North America and will be making its annual visit to the D.C. area in the next couple of weeks. Thus far, pollen counts for Ragweed are relatively low.

Susan Kosisky, the Chief Microbiologist at the US Army Centralized Allergen Extract Lab stated in the pollen count last week, "I thought I was sneezing a bit more than usual this past weekend and concluded there just may be some ragweed in the air. Today we saw the first ragweed pollen of the season, which is not unusual for the last week in July. Ragweed is our most prolific area weed pollen producer. We document about 39% of the total annual ragweed pollen load in August, 57% in September, and 4% in October."

From a pollen report last season, she stated, "The first week of August is when we usually start to see the first glimpses of ragweed season. By the second week in August, daily average totals are around 4 grains/cubic meter of air."

She did note, however, that the latter part of August through early September is usually the point when ragweed really begins to increase in the D.C. area.

Ragweed plant

Ragweed, shown above, are annual or perennial herbs that range from small plants 3 feet tall up to 13 feet tall (Great Ragweed). 21 species of ragweed occur in North America, but most allergy problems are caused by just two species which account for more hay fever (bodies reaction to the pollen) than all other plants together. One single plant can release up to a billion pollen grains in a season. Pollen grains have been recorded around 400 miles out at sea and up to 2 miles up in the atmosphere, so the pollen can travel exceptionally far.

How can you beat the pollen? Here are a few tips.

Stay indoors as much as possible during high pollen days (We will let you know when those days are!)

Keeps windows in your house and car shut as much as possible

Change clothes after being outdoors for a prolonged period of time

Shower before bed to wash off pollen

Equip your home with HEPA air filters

Remember to take your allergy medications (Claritin is my friend during the late summer and early fall!)

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Yosemite National Park Rim Fire 2013 time lapse

August 30, 2013 - 04:19 PM

While perusing the web, I came across this amazing time lapse of the Rim Fire which has continued in Yosemite National Park. It was actually shared on the parks Facebook Page and has been shared over 5000 times. Here is what the post said,

"Time-lapse photography shows various perspectives of the 2013 Rim Fire, as viewed from Yosemite National Park. The first part of this video is from the Crane Flat Helibase. The fire is currently burning in wilderness and is not immediately threatening visitors or employees. The second half of the video is from Glacier Point, showing Yosemite Valley, and how little the smoke from the fire has impacted the Valley."

The fire has burned nearly 200,000 acres of land and it is now 32% contained, up from 7% contained on Monday.

Finally, if you're interested helping to restore trails, facilities and wildlife habitat destroyed by fire, you can make a gift today to Yosemite Conservancy for the Yosemite Fire Restoration Fund at

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Labor day weekend 2013 weather forecast for the D.C. area

August 28, 2013 - 08:24 AM

As Labor Day weekend approaches, everyone is sharpening up their plans to head to the beach, head to the pools and get outside for one last nice summer weekend before more area schools get back into session and vacation schedules quiet down. Looking back at the past two Labor Day weekends, heavy rain has paid a visit each time, with 1.64" on Saturday of last year and 1.36" on Labor Day Monday back in 2011. What about this year? Some questions still remain, but here is your first look.

Labor Day Weekend Forecast

Once today's area of low pressure pushed through the region (be sure to follow radar here!), a calmer weather pattern will take shape for the remainder of the work week. While this is nice for people that have Thursday and Friday off, it may not necessarily be good for the holiday weekend ahead.

The pattern features very weak upper-level energy swinging into the area Saturday. This will allow for a possibility of a couple thundershowers, but looking at the atmospheric profiles, Saturday will have the lowest instability and I think the best chance for storms will be closer to the Blue Ridge Mountains and points west. Keep an eye out if hiking or camping.

Weekend Consecutive Waves of Upper-Level Energy

Sunday will have better instability and another weak wave of energy, allowing for more showers and storms which I think will be in the afternoon and evening hours. There should be a higher likelihood that storms will be closer to the D.C. Metro Sunday afternoon and evening, but the majority of the day should feature partly cloudy skies.

Labor Day Monday looks to be the worst out of the group. A potent cold front is expected to pay a visit to the region, bringing widespread showers and storms to the area by the afternoon and evening. There may even be the potential for a few severe storms, though at the current time, forecast confidence is low as it is still 5 days out.

Related: Not that we trust it, but the Farmers Almanac is out with some pretty interesting statements about the winter!

Basically, shower and storms are in the forecast this weekend, but we are NOT expecting a washout of a weekend. Looking at the above graphic, you have to note that this also includes precipitation today, which is expected to be rather heavy in and around D.C. Saturday and Sunday will be the better part of the weekend. If you're heading to the Delmarva Beaches, I think this will also be the case, with Monday again having the best chance for storms. Highs at the beaches are expected to reach the low to mid 80s.


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D.C. Summer: Soggy and Green

August 21, 2013 - 09:36 PM

Had to mow the lawn frequently this summer? It sure has been a wet summer in the nation’s capital and the numbers prove it.

Ten days remain in meteorological summer, which is defined as the three hottest months of the year, and the rainfall totals across the board have been much higher than average. Take the official reporting station for Washington, D.C., Reagan National Airport, for instance. Precipitation has totaled 15.55 inches, which is 6 inches about the average of 9.55”. For the entire summer, the average is 10.44 inches.

How does this compare to the wettest summers ever recorded in Washington? There have only been 28 summers since 1871 with higher rainfall totals. The wettest summer on record was 1906 with 27.05 inches of rain.

Notice in the graph below that besides a few wet summers in the early 2000s, the DC region hasn’t experienced such a soggy pattern since the early 1970s.


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Blue Moon, Full Moon both appear on Aug. 20

August 20, 2013 - 10:00 AM

As I was checking our WeatherBug cameras for good views of the fog this morning, I spotted the nearly full moon in Ijamsville and was reminded that not only is the moon “full” Tuesday, it is also “Blue.” Here is a cool timelapse of that moon and fog between 5:30 and 8:30 a.m. You’ve heard the term before, you’ve heard the song, and you’ve probably even used those words yourself when describing something out of the ordinary. But, Tuesday’s “Blue Moon” means something you likely didn’t know before reading this article.

Most of us describe a Blue Moon in terms of astronomy, as the second full moon in a calendar month. This happens seven times out of a 19-year moon cycle.

But, wait! At 9:45 p.m., we saw the only full moon in August, so how can this be true? It all started by a simple mistake made in Sky and Telescope magazine decades ago.

And the definition we use now for a Blue Moon is relatively recent. Previously, moons would be assigned a name based on their appearance in order during each season.

For example, in the summer months the first moon would be called the early summer moon, the second moon called the mid-summer moon and the last moon of the summer season would be called the late summer moon.

But, on occasion, there would be a fourth moon during that period. So, in order to keep the name of the last moon in the season as the “late” moon, the third moon of the season in a four moon cycle would be called the “Blue” moon. That is what we experienced Tuesday. Confused? More in depth at Sky and Telescope's website.

If you took any great photos of the moon, we'll put them on Good Morning, Washington.  Please post them on our Stormwatch7 facebook page or send them to me on twitter @JacquiJeras

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Dense Fog: Why It Forms

August 20, 2013 - 05:15 AM

A beautiful clear night coupled with calm winds and just enough moisture in the atmosphere equals the perfect recipe for the development of fog.  So how exactly does fog form?  Well, here's a quick explainer.

Fog is a deck of low clouds that develops very close to the surface.  Radiation fog, one of the most common types of fog, especially in our area, develops during the overnight hours when there is enough moisture present in the low levels of the atmosphere.  As the temperature drops overnight, the temperature gets closer to the dewpoint.  This means the air is becoming more saturated.  With clear skies, there is more radiative cooling at the surface promoting the development of fog. 


Radation fog generally dissipates rather quickly after sunrise.  As the sun gets higher in the sky, it warms the surface which decreases the relative humidity and helps to evaporate the water droplets that make up the low clouds and fog. 

The best advice with dense fog is to drive with extra caution and use your low-beams.  Sometimes you would think you would want to turn on your high-beams to see more, but the light reflects off the fog, which makes it much harder to see anything. 

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Cool spell ends and daylight continues its decline

August 19, 2013 - 01:44 PM

The past 6 days have seen temperatures at or below 81°F. This coming in the month of August, with the average high of 87°F and now 86°F starting today. Yesterday only reached 74°F and today might not get out of the 70s either! To put it in perspective, this stretch of unseasonably cool weather hasn't occurred in the month of August since 2000, about 13 years ago. The stretch of 6 days from the 17th-23rd were also below 82 degrees. Pretty crazy to think!

So far this month has had 11 days with below average temperatures, and the average for the month is sitting at 2.4 degrees below normal (As of the 18th). Last year, August only had 4 days with below average temperatures. The whole summer last year featured only 18 days with below average temperatures, while this summer has had 30! This is the most days below average since 2009 when there were 39 during the summer months.

The heat returns this week, however, with temperatures forecast to be in the upper 80s and possibly back to the 90 degree mark. 90 degree days have been relatively absent this summer as well, with only 23 so far, compared to 48 which we had by this time last year.

Meteorological Summer is just about over though, and the one place that has really seen the difference hasn't been the temperatures, but the duration of daylight.

This Saturday marked the day in D.C. where the sun sets at 8:00pm. The latest sunsets are around the solstice in late June at 8:37pm. Looking ahead in the calendar, the sun sets at 7:00pm by September 25th, which is only a month and 6 days from now. The big difference will come with fall, as it does every year, with the sunset coming in the 6 o'clock hour. Fall back occurs on Sunday, November 3rd, when the sun sets at 5:05pm. The earliest is 4:46pm December 1st-12th.

Countdown to the winter solstice sits at 125 days. Enjoy the warm air and remainder of the summer!


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Could D.C's next chance of rain be tropical?

August 14, 2013 - 08:49 AM

It's been a quiet month so far in the tropics, thanks to dry, stable air and wind shear. But as we head into the busier climatological peak of the season, things are starting to look at least a little more interesting.

National Hurricane Center

As of this morning, the National Hurricane Center has alerted two areas of possible development. One near the Cape Verde Islands off the coast of Africa and the other in the Western Caribbean.

Possible Tropical Development Areas- National Hurricane Center

Believe it or not, one of those areas could turn into D.C.'s next best chance for rain early next week. While it's too soon to say with any certainty that we will have tropical downpours, it's looking increasingly likely that a tropical system will impact the Gulf of Mexico late in the week. This is a satellite picture of the cluster of thunderstorms in the Western Caribbean that is becoming more organized.

Tropical Floater Satellite NOAA

It has a 50% chance of developing a closed tropical circulation in the next 48 hours and it's even more likely that it will become at least a tropical depression when it enters the Gulf of Mexico late week. This is the latest computer model forecast (GFS) for the system by Friday night.

GFS Computer Model Forecast Friday Night

While this is just one possible solution, if the disturbance takes the track near the central Gulf, it will bring heavy rainfall to a part of the country that is already waterlogged. The Southeast coast will get soaked with a significant flood threat on this track regardless if it becomes a tropical storm or not. Other possible tracks look like this:


The second area we are watching is in the far eastern Atlantic and it has a high probability of becoming a tropical depression or storm in the next two days. However, after that time, it will encounter wind shear that will likely limit it's potential to strengthen. It will be a "race" so to speak as to which could get a name first. Erin and Fernand are next on the list.

2013 Hurricane Names List

We'll keep you posted on chances of them affecting the U.S and/or D.C. in the days ahead. You can also find the latest at The National Hurricane Center website at .

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Perseid Meteor Shower 2013: Best time to watch

August 9, 2013 - 09:32 AM

It’s that time of year again! Time to view one of the most popular meteor showers during the year: the Perseids. The meteor shower originates from the Swift-Tuttle comet and first appeared in A.D. 36, but it is named but named because they appear to originate from the Perseus constellation.

Images: Perseus Constellation











The active start date was July 1 7, but the peak time to view these bright and colorful meteors (that fall at a rate of 60 – 100 meteors per hour) is during the overnight hours between Aug. 11 and 12, Sunday night into Monday.

If that is not enough to grab your attention to head out for a view, this particular meteor shower is also known for its fireballs – meteors that shine at least as brightly as the planet Venus. The good thing about this year is that the moon will be in the waxing crescent stage and the forecast is looking decent with just a few clouds in the sky and temperatures in the upper 60s/lower 70s!

Image: Waxing Crest Moon


What exactly is a meteor shower, anyway? To sum it up – meteors are pretty much “shooting stars” or debris in space made of dust particles that to us, imitate streaks of lights that are moving at an incredibly fast rate. Originating from comets, the icy and dusty debris around a comet sheds as it orbits in space. Tracking them correctly is the key to finding the meteor showers at a given point during the year.
Image: Swift-Tuttle Comet

Every year during this time, the Earth crosses the orbital path of Swift-Tuttle. The comet's orbit is close enough for these particles or debris to be swept up by the Earth's gravitational field, and they then move into the Earth's upper atmosphere at about 130,000 miles per hour!

This is where the meteor showers begin. These meteors sometimes leave persistent trains which are ionized trails of gas that last for a few moments after the meteor has already faded away. During the peak time, as in this Sunday night, these persistent trains should become more frequent, making the spectacular viewing more pleasurable.

Since they began in July, the Perseids are happening now. So anytime before the peak on Aug. 11 is a great time to view them.

After Aug. 12, though, the number of meteors per minute declines. If you want to go out and take a gander for yourself, make sure you are in a location away from the light pollution of the city and feel free to look in any direction!

All meteors can be seen with the naked eye so no fancy gadgets are required. You may be able to catch a few from the early to mid-evening hours but the number of meteors will increase as the night goes on, mainly after midnight.

Before dawn is the best time to view the most numerous of them, but make sure you allow time for your eyes to adjust to the darkness (which could be as long as twenty minutes) and give yourself time to enjoy the view; my suggestion is up to an hour.

Bring a lawn chair and just set up shop! You will be in for a lovely and free  show brought to you by space!


And keep with it: Follow me on TWITTER and FACEBOOK for all updates!

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Hurricane season 2013; Still forecast to be above normal says NOAA

August 8, 2013 - 11:22 AM

Two days ago, the USA Today reported that so far this has been a "snoozer of a hurricane season". Despite the fact we are just now approaching the peak of the hurricane season, apparently some sources are already begin to write it off as a quiet year. NOAA doesn't agree with that sentiment apparently, as in their latest tropical update, they continue to predict an above-normal season.

Gerry Bell, the lead seasonal hurricane forecaster at NOAA's Climate Prediction Center had this to say, "“Our confidence for an above-normal season is still high because the predicted atmospheric and oceanic conditions that are favorable for storm development have materialized. Also, two of the four named storms to-date formed in the deep tropical Atlantic, which historically is an indicator of an active season.”

NOAA's Tropical Update

The updated outlook calls for a 70 percent chance of an above-normal season. Above-normal sea-surface temperatures and a stronger than normal rainy season across Africa are two reasons for the continued high outlook.

The new outlook is above, which is slightly less than the original outlook in May which called for 13-20 named storms, 7-11 hurricanes and 3-6 major hurricanes.


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Record highs and record lows on the same day, sort of...

August 6, 2013 - 05:38 PM

It was cloudy, cool and a bit on the dreary side through the day Tuesday in the D.C. Metro, but a couple of interesting things happened you would probably never think about. August 6 marks the day at Reagan National Airport (and Washington D.C. for the matter) with the highest record high for the year set in 1930. It is tied with July 20, 1918 at 106°F. Interestingly enough, there hasn't been a 100°F day so far this year, while July of 2012 had 7 alone.

That wasn't the only thing that stood out for a weather nerd, as the high temperature for the day only hit 74°F. Why is that a big deal? It actually tied as the record low maximum for the day. The last time it was this cool on the date was in 2004. On another note, that is actually the warmest record low maximum for the month, as the majority of them are actually in the 60s.

It's interesting to see just how big the difference is between records with record highs in the 100°F+ range and record lows in the 50°F range. February 11th is the date with the largest difference between record high and record low for the date in D.C., with a record high of 76°F and a record low of -15°, a difference of 91°F!

The remainder of the week will feature warmer temperatures, approaching the 80 degree mark Wednesday and mid to upper 80s Thursday and Friday. This will get temperatures back near normal after this stretch of 12 of the past 13 days below normal.

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NASA photographs of Earth

August 5, 2013 - 09:58 AM

Meteorologist Joe Witte used to work at ABC 7 as our Weekend Meteorologist but decided to go back to school to get his doctorate and work for NASA Goddard for Earth Science Outreach. He often forwards along great information, websites and anything of interest that NASA has produced. This week, he sent us a website highlighting the number of photographs taken from the International Space Station (ISS).

This website (found here) features an ever growing list of pictures and associated captions to explain where it was taken and what it shows. For instance, the picture above is of the Great Lakes, showing Lake Erie, Ontario, Huron as well as the Finger Lakes with sunglint. Here is the corresponding webpage discussing what you are looking at.

Credit: NASA

Above is a picture of the Appalachian Mountains which also shows the Chesapeake Bay, Potomac River and D.C. Many pictures like this can be found not only of the United States but also across the world. You have to remember, the astronauts aboard the ISS are circling the globe once every 92 minutes, so they experience 15-16 sunrises and sunsets daily. I guess that makes plenty of sense since they are traveling around the Earth at 17,200 mph.

Big thanks to Joe Witte for forwarding along this great site. We hope you enjoy it as much as we do!

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Mammatus clouds invade the D.C. area Thursday (Photos)

August 2, 2013 - 12:19 PM

A cluster of thunderstorms moved south of D.C. yesterday allowing for a spectacular cloud show right around sunset. The unusual clouds that many people were noticing were the clouds that seemed to bubble down from above, looking like balloons. These are called Mammatus Clouds.

Mammatus Clouds in Hartwood, VA sent in by Robert Rufio

These clouds often form on the under side of anvil clouds. For a little more detailed explanation, the University of Illinois at Urbana-Champaign's Department of Atmospheric Sciences has a great website that explains all kinds of atmospheric phenomenon.

Michelle Schrotz from Richmond, VA sent this picture in

As far as mammatus clouds are concerned, "As updrafts carry precipitation enriched air to the cloud top, upward momentum is lost and the air begins to spread out horizontally, becoming a part of the anvil cloud. Because of its high concentration of precipitation particles (ice crystals and water droplets), the saturated air is heavier than the surrounding air and sinks back towards the earth.

Thornburg, VA mammatus from Brittney Wagner

The temperature of the subsiding air increases as it descends. However, since heat energy is required to melt and evaporate the precipitation particles contained within the sinking air, the warming produced by the sinking motion is quickly used up in the evaporation of precipitation particles. If more energy is required for evaporation than is generated by the subsidence, the sinking air will be cooler than its surroundings and will continue to sink downward."

Mammatus in Fairfax from Meteorologist Alex Liggitt

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Government leases 165,000 acres of offshore land for wind farms

August 2, 2013 - 04:00 AM

The Department of the Interior discussed in a press release that Deepwater Wind New England, LLC won two leases for nearly 165,000 acres of land offshore of Rhode Island and Massachusetts. The company plans to build winds farms, that once completed may possibly generate enough energy to power more than one million homes.

The Wind Energy Area is located 9.2 nautical miles off the coast of Rhode Island and has the potential to generate 3,395 megawatts of power. Here is a good site to give you an idea how energy is measured. The lease went through for just about $3.8 million, lasted a day and went through 11 rounds to determine the provisional winner.

This company will still need to be approved by the FTC for antitrust reasons, then will continue to go through the process for submitting a Site Assessment Plan and Construction and Operations Plan in the coming years. Overall, this appears like it will be a very slow process, but will potentially be a very rewarding outcome years down the road.

This isn't the only auction in the works, as another one much closer to home will occur on September 4th of this year. Nearly 113,000 acres of land are up for auction off the coast of Virginia, which could lead to the potential of developing up to 2,000 megawatts of electricity from offshore wind generation. This area is good for a wind farm because of the "shallow continental shelf that extends nearly 30 miles off the coast, proximity to load centers, availability of local supply chain infrastructure, and world class port facilities," says Dominion Power.

Wind farms offshore have a higher energy production potential due to less frictional effects over the water than land which leads to typically stronger and more consistent wind speeds over the ocean. The downside is the fact that a company would need to build these in the ocean, which is a very costly venture and the maintenance will be much more difficult to perform.

These projects have come about as the President challenged the Dept. of the Interior to "re-double efforts on the renewable energy program by approving an additional 10,000 megawatts of renewable energy production on public lands and waters by 2020," says the DOI's press release.

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