From the ABC 7 Weather team

The Threat of Rain Continues This Week

August 19, 2014 - 02:42 PM

If you like cloudy, muggy and gloomy weather then this week is your week. Fortunately, temperatures will be held at bay, only reaching into the lower to mid-80s for daytime highs Tuesday, Wednesday and Thursday but the humidity will continue to stream into viewing area as the region is wedged between an area of high pressure to the north and an area of high pressure to the southwest (take a peek at the graphic below).


Courtesy of The National Weather Service Baltimore-Washington

A frontal boundary will also continue to be draped across our region and will continue to meander in the vicinity of central Virginia and the D.C. metro area at least through Thursday. That frontal boundary will be the main forcing mechanism for any showers or small thunderstorms that pop up around the region Tuesday afternoon. This means that generally any rain that pops up will be around the stationary front getting caught up in our easterly flow and will preside mainly just south of the Washington D.C. metro area on Tuesday afternoon and evening. Unfortunately, since there is so much moisture and the fact that there is no element that is moving these cells along quickly, are few could contain isolated downpours. Good news is that I don’t anticipate any widespread severe weather for Tuesday evening and into Tuesday night.


The frontal boundary is just to the south of Washington D.C. on Tuesday afternoon, draped across Fredericksburg through Southern Maryland and back to the west around the Eastern West Virginia Panhandle.

If you are headed out to Nats Park tonight, just know it will be a little on the steamy side but I do believe that we will remain dry. Plenty of clouds will stick around through the duration of the game against the Arizona Diamondbacks as temperatures drop through the 70s. There could even be some areas of fog that form while you make your way home from the stadium.


Overnight temperatures on Tuesday will only fall to right around 70 degrees in most locations and warm back up into the mid-80s once again tomorrow. There could be a few peeks of sunshine once again Wednesday but an upper level low, diving out of the northwest, will be headed this way.

A piece of energy out in front of that low will move into the region Wednesday afternoon through Wednesday evening. This means we have a good chance to see some showers and thunderstorms around the region. Most of the activity will die off in the evening hours as we lose our heating from the day but there is a about a 20% chance that a few showers or storms could linger into the late evening hours leading into Thursday.

By Thursday morning, that upper level low (reference the first graphic from the National Weather Service for more information on the upper level low) will be nearing our area, crossing through during Thursday afternoon and Thursday evening bringing us yet another chance of some showers and thunderstorms. This time, there is about at 50% chance of scattered showers and thunderstorms around the region on Thursday.

The best chance for a good soaking rain comes on Thursday but all in all expect less than a 1.00” in total rain accumulation from Tuesday throughThursday night. This will be good because if you have found yourself sniffling a little through the weekend and into the first part of this week, around the D.C. region mold, grasses and weed pollen is all running a little on the elevated side. So it will be good to get some rain to alleviate some of those allergies.


ZZZZZQPF or Quantitative Precipitation Forecast shows 1.00” of less of rain accumulation around the WJLA viewing area from Tuesday through early Friday morning

Due to the rain that we received through the first half of August, we are well over our normal averages for rain during the summer (June – August 19th) at Reagan National Airport as well as Baltimore-Washington Airport (in fact, the rain that fell on Tuesday, August 12th put BWI +4.38” over their normal rainfall amount for the summer). Dulles International Airport could still use some rain however, as they are behind a little over 1.50” for rain accumulation for the summer months.

And while we are at it, to be completely honest, I am still not sold on keeping Friday through the weekend dry. I have continued to have it dry in my forecast for the last two days but I believe it is going to be a wait and see game to if this pattern sticks through Friday and into the weekend or to see if high pressure can edge out bringing some more pleasant conditions. Either way, we will keep an eye on it for you and let you know as the picture becomes clearer.


3rd Coolest August on Record at Dulles and Baltimore

August 16, 2014 - 09:15 PM

While we have experienced some seriously beautiful weather so far this August we have also had several very chilly mornings in the Mid-Atlantic.  When you average the high and low temperatures together, we rank in the top three coolest months of August up to this point at Dulles and Baltimore.  Here is a graphic from the National Weather Service that shows our average temperature so far from August 1st through the 15th compared to the averages and records for the month.




August Statistics- National Weather Service





 Not once did the thermometer at Dulles or BWI reach 90 degrees in August of 2014.  87 was the hottest day of the month at Dulles, VA on the 5th.  If we take a look at Reagan National, while it was also cooler than average, it definitely tells a different story.




August Statistics at Reagan National Airport




  The average temperature here is less than two degrees below the normal of 77.1.  It did hit 90 degrees, but only once on the 5th.  And it doesn't even make the top ten coolest Augusts on record.  It really goes to show you how different weather can be just a few miles apart in our region.  Now that the month is half over, what can we expect as we end it?  Will there be a big warm up? 


6 to 10 day Outlook

Well, at least a bit of one...   The medium range forecast has temperatures near the seasonal average with above average temps nearby .  We could hit 90 in there for a day or two if we're lucky (yeah, I wouldn't mind one more).  So far, D.C. has had 16 days at 90 degrees or above.  On average, we get between 25 and 30 of them in a year.  The summers with the fewest 90 degree days were in 1905 and 1886 when there were only 7 days. (Thanks to Alex Liggitt and a previous blog for those last two stats). 



Rain to return to the region next week

August 15, 2014 - 09:48 AM

At this point in time, I think a lot of us Washingtonians are wondering where the summer has gone. With temperatures in the 50s to low 60s this morning, and highs only near 80 this afternoon, we'll be 7-10 degrees below average across the area. Looking ahead to the 7-Day forecast, summer is expected to return by the end of the weekend. But with the increasing levels of heat and humidity will come a higher likelihood for showers and thunderstorms.

Morning lows Friday, August 15

The eastern part of the U.S. has been beautiful this morning due to high pressure filtering in behind yesterday's weak reinforcing cold front. Temperatures were thought to possibly break into the 50s at Reagan National this morning, which would have been the first time in 10 years that has occurred, but low and behold, it only dropped to 62 degrees. I'm guessing chalk that up to the warm water temperature at 77 degrees in the Potomac next to the sensor.

Temperatures will rise slightly into Saturday, back into the mid 80s. By Sunday, a cold front currently situated over Canada will move into the region, bringing a chance for showers and storms by the afternoon and evening. Highs Sunday should reach the upper 80s.

Water Vapor imagery from Friday morning

Beyond Sunday, the forecast can be summed up by the one word many of you don't like hearing...unsettled. Monday and Tuesday will feature a chance for storms from a disturbance currently located over the northern Rockies. By Wednesday and Thursday, we'll be under the influence of a trough which is currently over the Pacific Northwest. This set-up will feature dewpoints in the upper 60s all week, along with showers and the chance for afternoon storms.

Forecast precipitation through Friday morning from the WPC

Taking a look at the precipitation forecast from the Weather Prediction Center above, the D.C. area may see 2 inches of rain or more with locally higher amounts through Friday morning of next week. Not exactly something we really need after the terrible flooding last week. Be sure to dust off the umbrella heading into next week!


Coolest August morning in 10 years? It's possible Friday

August 14, 2014 - 01:02 PM

So far, the month of August has been slightly cooler than normal. There have only been two days this month with above-average temperatures. Now, let me set the record straight: It hasn't been abnormally cold so far this month, but it will definitely be much cooler than normal over the next two days.

(Forecast morning lows Friday)

Low temperatures Friday morning and Saturday morning may drop into the 50s at Reagan National Airport. This hasn't happened in 10 years, since August 7th, 2004, when the mercury dropped to 58 degrees. Since 2009, temperatures haven't dropped into the 50s at Reagan National until September 1st, the 11th twice, the 14th and the 15th, so we're nearly a month ahead of where we've been over the past few years.

The average low doesn't eclipse the 50s until September 24th. Looking back a little further into the climate data, temperatures in the 50s in the month of August have been largely absent in D.C. after 2004.

There were numerous times prior to that date though, as Reagan National reached the 50s in August in 2000, 1998, and 1997, four times in 1994, once in 1992 and two times in 1989. That gives 12 occasions in the past 25 years, though none in the past 10. I guess we'll see if we can break the warm streak starting tonight.

(Secondary cold front will move through this evening)

The forecast low tonight for D.C. is 60 degrees. As a secondary frontal boundary pushes through the region this afternoon and evening, drier air will settle overhead along with clearing skies overnight. By the early morning, clear skies and light winds should lead to plenty of radiational cooling, which may help D.C. reach its potential. The wild card: The Potomac's water temperature still stands at 77.5 degrees. A slight shift in the wind could keep the temperature from dropping below 60.


Washington D.C.'s record rainfall Tuesday

August 13, 2014 - 06:33 AM

Yesterday's deluge was a significant one, with record rainfall in parts of the area. BWI recorded its second rainiest day in record history with 6.3 inches of rain (BWI's still-standing record is the 7.62 inches of rain that fell on July 23, 1933 during the 1993 Chesapeake-Potomac hurricane).

BWI wasn't the only location to get dumped on by the wet weather. The National Weather Service released additional rainfall totals from weather spotters across the region. Check out some of these impressive totals:
(National Weather Service totals)

Another interesting tidbit about yesterday's rain, this one from ABC 7 meteorologist Ryan Miller:

Yesterday's rain was courtesy of a strong frontal system sliding through the area. Heavy rain continues for New England today, while we begin to dry out.

Breezy winds will usher in lower humidity through the afternoon.  Tonight will be comfortably cool and clear, which should make for great viewing of the Perseid meteor show, which peaked last night.  It may be a little harder to see the shooting starts with the still bright, waning gibbous moon in the night sky, but it will still be a good night sky show.


Read More:

Areas of heavy rain in the D.C. area Tuesday

August 11, 2014 - 02:06 PM

An area of low pressure continues to move into the Great Lakes region today and an associated frontal boundary will bring the possibility of heavy rain through Tuesday. Showers will begin Monday evening, rather light in nature, and will continue to overspread the D.C. area overnight.

Surface map for Monday Evening

The Tuesday morning commute may be a wet one, but the heaviest rainfall is expected to fall Tuesday afternoon and evening. A few embedded thunderstorms will be possible, and some locations may see the potential of 1 to 2 inches of rain with isolated higher amounts.

RPM Precipitation Forecast

Our in-house RPM model shows the potential for much of the D.C. area to be closer to the 0.5" to 1" range, with isolated spots mainly north and west of D.C. with the higher amounts. This is in line with other modeling as well as the excessive rainfall discussion, which is pegging the state of Pennsylvania with the potential for the heaviest rainfall.

While ponding on the roadways will be possible, flooding doesn't appear to be a big threat at the moment. However, if some of the heavier showers and storms begin training over the same locations, some localized flash flooding may be possible, especially by the afternoon and evening hours on Tuesday.

Rain should wrap up for the most part overnight Tuesday into Wednesday morning. Drier air will filter back into the area Wednesday afternoon and at this point, conditions look about perfect Thursday through Saturday with plenty of sunshine and comfortable temperatures in the lower 80s.


Supermoon and Perseid Meteor Shower

August 10, 2014 - 05:00 AM

A lot going on in the night sky over the next several days.  The August full moon, which occurs tonight, may look a little bigger and brighter than normal.  In fact, it will be 14% bigger and 30% brighter.  The reason is because the moon is at lunar perigee.  This means the moon is about 30,000 miles closer to the Earth than normal.


You'll have to wait for breaks in the clouds to see the bright moon Sunday night.  If you don't get a chance to see the moon tonight, you'll get another chance at catching a 'supermoon' when it happens again on September 9, 2014.   The August supermoon will be the closest of all supermoons this year.  The moon will not be this close again until the full moon on September 28th, 2015.


Another fantastic night sky event is the annual Perseid meteor shower.  One of the most vibrant meteor showers of the year with nearly 60 to 100 meteors in an hour from a dark place at peak. The only caveat is the perseids will be competing with the very bright supermoon.  The perseid meteor shower peaks on the mornings of August 11th, 12th, and 13th. 


As for local weather, conditions won't be ideal for supermoon and meteor shower viewing.  It looks like skies will be rather cloudy for the next few nights with clear skies returning by Wednesday night.  You should still be able to see a few shooting stars by midweek, with the still bright waning gibbous moon.

The Stormwatch weather team would love to see your supermoon pictures.  Upload them to our Stormwatch Facebook page and maybe you'll see them on air! 


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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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Tropical Storm Bertha is the 2nd Named Atlantic Storm

August 1, 2014 - 04:18 PM

It has been a relatively slow start to the 2014 Atlantic hurricane season.  We've only had one named storm, so far... Arthur.  Arthur developed as a tropical depression east of Florida on June 31st and strengthened to a Category 1 hurricane by July 3rd and made landfall near Cape Lookout, NC that night.  Check out the track below:

Just as we start the month of August a new tropical storm is upon us.  Tropical Storm Bertha developed late Thursday night and is approaching the Lesser Antilles.  Bertha, as of the 5pm update from the National Hurricane Center has winds of 55 mph and is moving WNW at 24mph.  Check out the storm spinning on satellite imagery. 

Bertha, as of right now, is not expected to strengthen significantly. In fact, the latest track from NHC keeps Bertha at tropical storm strength through the extended forecast time frame.  Here's the latest track:


If you have travel plans to the Caribbean, Bahamas, etc., you'll certainly want to keep a close eye on the track of the storm.  Bertha is forecast to continue on its WNW track before turning to the NE late Monday after heading farther out to sea.  It doesn't look like Bertha will have an impact on the lower 48.

Remember Hurricane Bertha from 1996?  Bertha reached Category 3 hurricane strength with max winds to 115 mph on July 9th.  Bertha then made landfall between Wrightsville and Topsail Beach, NC as a Category 2 hurricane on July 12th.  Click here for an extensive overview of the storm courtesy of the National Weather Service in Newport/Morehead City, NC.  Check out the track below and the satellite image from when Bertha made landfall:

It looks like this time around Bertha will not have a similar effect on the east coast of the U.S., as it did in 1996. The Stormwatch7 weather team will continue to keep you informed of all tropical updates through the rest of the hurricane season, which goes through November 30th.


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Rain back in the forecast for the beginning of August

July 31, 2014 - 04:33 PM

The past few days have been just about perfect as far as the end of July is concerned. Low humidity levels and below average temperatures have made for very comfortable conditions. One thing has been missing now for a while through the majority of the D.C. area... rain.

Taking a look at some of the area climate reports, you wouldn't think the region has been hurting for precipitation. Reagan National has recorded over 4.5 inches of rain for the month of July. Even the drought monitor shows our area is doing well for precipitation. But taking a closer look, the area has been dry for the second half of the month.

Since July 16, Reagan National has only recorded 0.11" of rain, Dulles 0.13" of rain, and BWI Marshall has seen the most at 0.23" of rain. With the pattern changing as we speak, this should change over the next few days.

WPC Precipitation Outlook through Sunday evening

A frontal boundary south of the D.C. area is expected to push north along the east coast, which will help become the focus for showers and a few storms to ride along. The heaviest rain is expected to remain south and east of D.C., with upwards of 4 inches of rain possible over eastern portions of North Carolina and over 2 inches possible towards the Delmarva Peninsula.


Don't expect the weekend to be a complete washout just yet. Not all modeling is in agreement, but as of now, the highest likelihood for steady rain appears to be Friday night into Saturday morning.

Breaks in the overcast will be likely Saturday afternoon and through the day on Sunday. Temperatures will remain slightly below the average of 88 this weekend with highs only expected to reach the low to mid 80s.


Record low this morning, but was it a chilly July?

July 30, 2014 - 08:22 AM

The debate around town this morning has been about the best way to describe this morning's temperatures. Would you call it cool? Chilly? Crisp? Pleasant? Perfect? Well, if you live around Dulles Airport, you could call it record-breaking cold. The temperature briefly dipped to 48 degrees.


(Dulles Temperatures and Dewpoint this Morning)


Here's a look at morning low temperatures across the area.


(Morning Lows)


The old record at Dulles for July 30 was 51 degrees, set in 1981. The unusually chilly temperatures also managed to break the July 29 record, dipping below the previous mark at 11:58 p.m. Tuesday night. National Airport bottomed out above its record low of 56. Martinsburg, W.Va., hit a record low and Baltimore broke its record low with 55 degrees. 


(Records at Dulles)

So why has this fall-like weather made a mid-summer appearance? A trough in the upper atmosphere has drawn in cooler air from the north into the Mid-Atlantic. It has made it's way unusually far south for this time of the year. Many records were broken in the East.


(Preliminary Record Lows via


Typically, high temperatures are in the upper 80s in late July in D.C. While we will gradually see temperatures warm up today and tomorrow, the overall pattern keeps us cool to near average through mid-August.

(6 to 10 day Temperature Outlook NOAA)

If you're thinking to yourself that this is a cool July, you're right. As of this morning, Dulles has averaged 74.7 degrees this month, about two degrees cooler than normal. At Reagan National, the average temperature is a bit warmer at 79.8 degrees, right about average. Still, this July is the coolest we've enjoyed since 2009. There were nine days of 90 degree or higher temperatures at National Airport this month, including a high of 99 on July 2nd.  At Dulles, there were just five 90 degree days this month.

If we look ahead to August, climatologically speaking, we will start the month with an average high of 88 degrees and end it with an average high of 84. August is the last meteorological month of summer, with slightly fewer minutes of daylight.


Haze in D.C. today most likely smoke from Canadian wildfires

July 29, 2014 - 11:45 AM

What a beautiful morning it has been, with lows in the 50s and 60s across the region, including a record-tying low of 59 degrees at BWI Marshall. With such low humidity levels across the region though, you would expect to see deep blue colored skies with now a few white puffy cumulus clouds. Instead, a haze has settled in over the region.

Visible satellite image after 11am

Take a look at the visible satellite image above. Just by looking at this image by itself without motion, it is very hard to see anything that may signify smoke over the D.C. area. But click here to see the satellite in motion. Did you happen to see the very light colored area over D.C. right after sunrise? This is showing the possibility of either some extremely thin clouds, or more than likely, a very thin layer of smoke in the atmosphere.

Courtesy: NASA MODIS

A number of fires have not only been burning in the Pacific Northwest, but also well north of the border in the Northwest Territories of Canada. Above is a look at the NASA MODIS satellite world view which I stumbled upon while perusing the web. I circled the regions of smoke that were showing up yesterday in Northern Canada and over the Hudson Bay. Given the flow of the atmosphere, much of the smoke more than likely was pushed south and eventually southeast into the Midwestern U.S., Northeast and Mid Atlantic States.

Water Vapor Imagery Tuesday Morning the 29th

The upper-level flow shows a large trough through the eastern part of the U.S. and a large ridge over the western U.S. The resulting steering flow has been from Northern Canada southeast through the Midwestern States and directly into the D.C. area. Check out the water vapor loop here. Keep in mind the orange, black and dark grey show very dry air while the purple, blue and white areas show increased levels of atmospheric moisture.

The effects from smoke in the D.C. area will be minimal and air quality is still expected to be good through the next few days, though the haze may hang around tomorrow and Thursday.

NASA MODIS image from July 23rd

The fires have burned over two million acres of land in the Northwest Territories and are thought to have been caused by lightning.

Photos of the fires near Yellowknife, Canada.


Cooler and comfortable end to July

July 26, 2014 - 06:00 AM

After a hot start to July with eight of the first fourteen days above 90 degrees, the pattern shifted. Since then, high temperatures topped out in the low to mid 80s seven times and reached 90 degrees only once.

Looking ahead to the end of July and the beginning of August, temperatures are still expected to be cooler than normal. Once we get through the weekend, which will feature more heat, humidity, and the chance for showers and the possibility of severe storms, cooler air is forecast to filter in next week.

500mb vorticity plot for next Tuesday

While a large ridge is expected to continue to build over the southwestern U.S., a potent shortwave will move through the Midwest and into the Northeast this weekend bringing the potential for severe storms.

This shortwave will spin around an area of low pressure centered over the eastern part of the Hudson Bay in Canada (above), which looks like it will be blocked from moving anywhere as high pressure sets up east over Canadian Maritimes and the northern Atlantic.

6 to 10 day temperature outlook from the CPC

In reality, what does this mean for the D.C. area? Temperatures may only approach the 80 degree mark Tuesday and low to mid 80s Wednesday through Friday of next week. In addition, humidity levels should be low, with dew points in the 50s expected Tuesday through Thursday before more moisture slides back into the region Friday.

Tuesday afternoon 2-meter temperature anomalies (Credit: WeatherBell Models)

With record heat dominating the headlines, including the hottest global June on record per NOAA, this will most certainly be enjoyed throughout the eastern half of the U.S. next week. Portions of the eastern U.S. will enjoy afternoon temperatures 10 to possibly 20 degrees below the seasonal average.


Severe Storms Possible Sunday and Monday

July 25, 2014 - 03:07 PM

Say goodbye to the beautiful weather of Friday and hello again to summer in Washington, D.C. for the weekend. That means a return of heat and humidity as well as a return of summertime thunderstorms. Saturday will feature very warm temperatures, right around 90 degrees for a daytime high with increasing clouds and increasing humidity late in the day. Another thing that will increase on Saturday will be the chances of showers and thunderstorms. Albeit, it is only a slight chance of showers and thunderstorms through the PM and overnight hours on Saturday, but still a chance.

An upper level piece of energy will approach the region on Saturday night. Mainly our western areas will be the breeding ground for any action, but by Sunday, we all have equal chances to see showers and thunderstorms across the area as that disturbance passes through the D.C. area.



Also what we are watching after Sunday’s disturbance is a very strong cold front will be dropping out of the upper Midwest and down into the region for Monday. Therefore, we have a chance of showers and thunderstorms Saturday night – Monday, some of which could be strong to severe.
Above graphic, at the top, shows the slight risk area for severe weather Saturday through Monday. The risk moves from the Ohio Valley Saturday to our area on Sunday and Monday. On the bottom of the graphic, the surface features show an area of high pressure overhead bringing us very pleasant on conditions on Friday. Then through 8 p.m. Saturday, the area of high pressure scoots off the coast giving us a southerly flow bringing humid air from the south and transporting it right here into the D.C. area as a warm front approaches the region. By Sunday and Monday morning, the strong cold front is still to the north and west of the area.

So now that we know what is going on, what can we except through the weekend? Well considering that warm front is just to the south on Saturday night, lift from warm advection around the warm front and the piece of energy approaching us from westerly flow aloft will give us that about a 20% chance of storms on Saturday afternoon and evening continuing through the overnight hours. There will be a good chance of severe weather across our area through the day on Sunday as that disturbance moves through the region. One thing that still remains a question is temperatures on Sunday. Right now I have temperatures fairly warm, nearing 90 degrees. But, if we get some thunderstorms in the morning hours, that could down our temperatures for the afternoon and lessen the instability in the atmosphere. Either way, it will still be very muggy outside through the day on Sunday with mainly clouds hanging around. Some of our models do suggest that we get some thunderstorms during the first part of the day on Sunday.




Caption: Showers and thunderstorms around the region weaken slightly as they travel to our area from the north and west. This is around 11a.m. on Sunday.

We do know that any of these storms could produce damaging winds, possible hail and heavy rain. There will certainly be substantial moisture around the region given the nice southerly flow, therefore localized flash flooding is definitely a concern. Take a look at our precipitable water values:




You may have heard this term or “PWATS” quite a bit this summer. Really what preciptable water values are are the amount of water within a vertical column above the surface if it were all precipitated out. These values are over 2.00” in some spots and when we see that, we know there is enough moisture available to create flooding conditions.

By Monday, the chance of showers and storms remains through the day as the cold front finally travels through the region. Again, some of there could be strong to severe but by Tuesday, we are in for another treat.


A nice refreshing airmass moves into the region bringing low humidity and refreshing temperatures. Daytime highs on Tuesday are in the upper 70s to lower 80s! We just got to make it through some summertime storms to get the reward by mid-next week!


Cherrystone tornado rated EF-1

July 25, 2014 - 11:46 AM

The National Weather Service office in Wakefield, VA surveyed the damage from yesterday morning's storm in Northhampton County in southeastern Virginia and determined the damage was due to a tornado, straight line wind, and a large swath of hail.

Path of the tornado, straight line wind and large hail

Above is a look at the path of the tornado, wind and large hail. The tornado originated in the Chesapeake Bay as the storm rapidly intensified. The EF-1 tornado had estimated maximum wind speeds of 80 to 100 mph and was on the ground for 8 miles over a span of 15 minutes. It's maximum width was 150 yards. The tornado wasn't the only feature that caused damage in this storm.

A downburst resulting in straight line winds was observed in the yellow wind damage swath. Wind speeds were estimated between 65 and 75 mph and downed numerous trees and even contributed to overturning several camping trailers in the Cherrystone Campground.

The hail core fell mainly within the blue lines (first image above) in the size of golfballs to a few reports of baseball size. This caused considerable tree and leaf debris, crop damage and siding damage on homes in the path.

The storm caused 36 injuries and 2 fatalities.

See the rest of the preliminary storm survey here.


Average hottest days in D.C. in the rearview, daylight diminishes

July 23, 2014 - 12:18 PM

With temperatures forecast to be in the low to mid 90s, one wouldn't think the average hottest days are behind us, but the average high drops to 88 today. Don't worry, cold air isn't exactly going to march right into the D.C. area, as the average high temperature remains in the mid to upper 80s through the month of August. August also averages nearly 10 90-degree days, something we haven't seen too much of this year.

90 degree days in D.C.

In fact, D.C. is actually below average for 90-degree days so far this summer, with only 15 this year. Compare that to last year, which recorded 21 by the same time. Typically there are around 36 90-degree days per year in the D.C. area, so it appears this summer may go down as below average in that category. Ninety-degree days or not, this summer has still been above average, with temperature departures of +2°F in June and +0.5°F so far in July. We'll see how August fares.

Looking ahead, the heat will briefly subside Thursday and Friday but will return for the weekend. Highs should top out in the 90s both Saturday and Sunday, prior to a big-time cool down next Tuesday through the end of the month. Highs may only reach the 80-degree mark next Tuesday!

Duration of daylight for D.C.

Daylight continues to diminish since the summer Solstice, with 28 minutes gone in just a month's time. An additional 14 minutes of daylight will be lost by the end of the month, and over an hour more will be lost by the end of August, so enjoy it while it's here.

While this may be a depressing blog post for some, after summer, there's always cooler and crisp days, fall colors, the Nats playing in October, the Skins taking the field, and plenty of other great things to look forward to. Here's to a fantastic last 39 days of meteorological summer to go!


45th Anniversary of Landing on the Moon

July 20, 2014 - 05:00 AM

"One small step for man, one giant leap for mankind".  These are the words Neil Armstrong said 45 years ago today after he stepped onto the surface of the moon.

Astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins were all aboard the infamous Apollo 11 flight to the moon.


The three launched into space aboard Apollo 11 on July 16, 1969 via the Saturn V rocket at the Kennedy Space Center in Florida.  Armstrong and Aldrin then climbed into the lunar module Eagle (below) that would descend onto the moon, while Collins orbited in command module Columbia.


At 4:18pm EDT, Armstrong connected with mission control in Houston saying "Houston, Tranquility base here.  The Eagle has landed". 

At 10:56 pm EST, Armstrong set foot onto the surface of the moon.  You can see in the image below the American flag the astronauts planted on the lunar surface.


Buzz Aldrin then joined Armstrong on the moon and the two spent time deploying instruments that would be used for experiments, gathering samples of lunar soil, and taking pictures. 

Here's a great "Moonwalk Montage" that takes us back to that day:


The three astronauts accomplished something the Russians had not.  NASA states they did not want to focus on the "victory" of the mission, but rather emphasized the "peaceful lunar landing by the United States. 

The patch designed for the mission was created by Michael Collins.  On the patch, the American Bald Eagle is depicted landing on the lunar surface, delivering an olive branch of peace.   The words "Apollo 11" were chosen for the top of the patch above a distance crescent shaped Earth.


The United State's determination in exploration through the Space program has taken us to the point where we now have a rover on Mars.  The mission 45 years ago today reemphasizes the spirit of our country and the desire to explore and discover outer space.


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Severe Storms Likely Monday and Tuesday

July 13, 2014 - 06:39 PM

We've reached the climatological hottest time of the year in D.C. with our average high now 89°.  Some big changes on the horizon, as a strong cold front approaches the area.  This cold front will bring a welcome drop in the heat and humidity by Wednesday, but it will come with the price of severe weather for Monday and Tuesday.

Ahead of the front, our airmass remains very hot and humid.  Forecast high temperatures Monday are in the low to mid 90s.  Factor in the humidity and it will feel closer to the 100 degree mark.

The cold front will slide farther east Monday increasing the atmospheric dynamics for severe weather.  Take a look at the surface features, as of Sunday night.

The viewing area will remain under the very warm and moisture laden air until the cold front passes late Tuesday night.  That will help fuel the fire for the strong and severe storms.  The Storm Prediction Center has the entire vewing area (shaded in yellow in the image below) under a 'Slight' risk for severe storms Monday.   This means damaging winds (60+mph), large hail, and isolated tornadoes will be possible with any storms that develop.

Storm Prediction Center

A big dip in the jet stream will allow temperatures and humidity to drop off significantly by Wednesday and the rest of the week.  The clash of airmasses; however, is what is causing this elevated risk for severe weather.  Check out an upper level map (500mb level) that clearly shows the large trough digging into the area.  The brighter colors indicate higher wind speeds, which leads to increased wind shear.  Wind shear can cause damaging wind gusts and tornadoes.

WeatherBell - European Model 500mb heights and wind speed/direction

As mentioned, behind the front much cooler and drier air.  Take a look at the difference in forecast dewpoint temperatures on Monday and Wednesday.  Dewpoints will go from the mid 70s Monday afternoon to the low 50s Wednesday.  You will certainly feel the difference by midweek.

WeatherBell ECMWF Dewpoint Temperature Monday
WeatherBell ECMWF Dewpoint Temperature Wednesday

Remember to stay updated with the StormWatch7 weather team for the latest weather updates.  We also encourage you to download the free StormWatch7 weather app.  You'll have access to Live Super Doppler within the app, so you can track storms on the go.


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Cooler Air, but Not Cold Air Infiltrating the D.C. Area Next Week

July 12, 2014 - 05:10 PM

Once we get through the possibility of severe storms on Monday and Tuesday, cooler air will move right into our region for the end of next week.

Classification. Yes, we are a society that likes to name things: Snowmaggedon, Commutergedon, SnowGuinness, etc. Where a squall line is a “derecho” and where a spill of cold air from the north is coined the “polar vortex.” I get it. I really do. Classification of tornadoes or hurricanes is absolutely necessary, however, to call every snowstorm a “blizzard” just makes me shake my head-but then move on with my life.

Before 2012, we had NEVER heard of the term “derecho” and now it seems every storm that comes through during the summer is classified as that. Before last winter, we NEVER EVER heard the term “polar vortex” used before and now, several months later, we gravitate right to it.

It is all in the eye of the beholder and left up to interpretation amongst professionals in the meteorology field. Although I didn’t want to touch this subject with a ten foot pole, I feel that we are forced to say something. The storm on Tuesday night left so many people wondering whether a “derecho” in fact hit the area that we had to reach out to the Storm Prediction Center to include their thoughts. So now onto the “polar vortex” or let’s just say the “unusual pattern setting up for Mid-July.”

All in all, we do know that next week unseasonably cold air will migrate out of the north and into the United States, spreading out into the Mid Atlantic. There is so much misuse of several weather terms throughout the year that I thought we should revisit the term “polar vortex”.

Our friends at the National Weather Service in New York made this graphic after the hysteria in social media yesterday about “the return of the polar vortex.” They reminded everybody on their Facebook page that “the most basic definition for “polar vortex” is that it is a piece of energy that comes from the polar region. It is generated by the large difference in temperature between the tropics and the poles. The temperature gradient is strongest during the winter; therefore it is more likely to affect mid-latitudes (our area) in the winter. However, it can affect us in the summer, but it is not nearly as strong as it is in the winter.”


There are differing opinions in the meteorology field on whether this is a “true polar vortex’ and that is why you will see so many different articles ALL OVER the internet on whether this is or it is not. This is what the Weather Prediction Center put out yesterday:\


Great. So in the grand scheme of things I ask myself “does it really matter to the general public what we coin this?” The answer I give myself is “no”.
So here is what we know. We have some unseasonably cold air coming down from the north and spilling into the region. The Midwest will get the brunt of the cold weather where temperatures could be as much as 20-25 degrees below normal! That is very impressive for summertime climate. Our normal temperature in the D.C. area for this time of year is a warm 89 degrees. The Climate Prediction Center has given us about a 40%-50 of seeing below normal temperatures next week.

Climate Prediction Center

Now, I got to tell you, if you are expecting temperatures in the 50s/60s then you have to travel to the north and west of here. Temperatures next week (starting Wednesday) are going to fall below normal but we are still talking 70s/80s. Here is a look at our 7-day forecast:

However, before we even get to that cooler air moving in, as you notice on the 7-day we are heating up! Temperatures on Sunday, Monday and Tuesday will have no problem reaching into the 90s. With the added July humidity, we are talking about heat indicies approaching 100 degrees all with the added threat of severe weather each day. The Storm Prediction Center has ALREADY outlined us in an area for a shot at severe weather on Monday into Tuesday:

Storm Prediction Center

So all in all, are we cooling down slightly for the end of next week? Yes. Are we going to have to deal with heat and humidity and severe storms at the beginning of next week? Yes. It is going to be a roller coaster week and we will certainly welcome the cooler air by the end of next week, not matter what we want to call it.


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Full "Supermoon" Tonight

July 11, 2014 - 09:42 AM

It's that time of the lunar calendar where we approach full moon status.  The moon will be full tomorrow morning at 7:25am.  But even tonight, expect a 14% bigger and 30% brighter full moon than full moons of 2013.  The reason?

The moon is in perigee.  The terms perigee and apogee refer to the distance of the moon from the earth.  During perigee the moon is closest to Earth.  The opposite is true when the moon is at apogee. 


Tonight's full moon will be the first of three supermoons this year.  The next will occur on August 10th and the final on September 9th.  The full moon tonight will be less than 224,851 miles away from Earth.  To put that in perspective, at apogee the moon is roughly 252,000 miles away from Earth.  Here's a photograph of the two full moons overlayed on one another. 


The July full moon is referred to as the "Buck" or "Thunder" moon.  The buck moon came from deer's antlers pushing out of their forehead.  The moon is also referred to as the thunder moon because July is the most common month for thunderstorms.


Weather conditions for supermoon-viewing will fairly good. Aside from a few scattered clouds, the sky should feature the bright moon rising at 6:46pm tonight and setting at 5:02am tomorrow morning. If you take some moon pictures, we'd love to see and share them! Happy moon viewing!


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