From the ABC 7 Weather team

Archive for category Seasonal July 2014

Cooler and comfortable end to July

July 26, 2014 - 06:00 AM
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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.

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45th Anniversary of Landing on the Moon

July 20, 2014 - 05:00 AM
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"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.

NASA

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.

NASA

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.

NASA

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.

NASA

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
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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
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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.”

NWS

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:\


“A DEEP UPPER LOW... NOT THE POLAR VORTEX AS ITS ORIGINS ARE FROM THE NE PACIFIC... WILL SWING THROUGH THE GREAT LAKES EARLY NEXT WEEK WITH AN IMPRESSIVE COLD SHOT OF AIR INTO THE CENTRAL AND THEN SOUTHERN PLAINS AND THE MIDWEST.”


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
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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. 

NASA

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. 

NASA

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.

NASA

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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July Weather in D.C.: Hot, Humid & Stormy

July 6, 2014 - 06:09 PM
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The mercury will soar into the 90s while heat indices climb close to 100 degrees early next week. In the meantime, a cold front will likely ram into this heat and humidity, triggering midweek thunderstorms once again.

Downpours and gusty winds are likely with the first round that breaks the heat spell either late Tuesday evening or Wednesday afternoon. This pattern is all too common across the Washington metro area.

Analyzing past weather trends since 1980, July tops the list for the most combined hail, wind and tornado events in the region (see table below).

July Climatology

The biggest threat from any single thunderstorm in July is wind gusts. In order to qualify as a severe thunderstorm, gusts must at least reach 58 mph. July also ranks #1 for the most tornadoes area-wide. On average, there are 6 tornadoes in the region (the western Maryland panhandle into the Shenandoah Valley, northern Virginia, the District and all the way to the Chesapeake Bay) during the month of July.

Notice the breakdown of severe weather reports per hour on any given day. Hail, gusty winds and tornadoes are most common at 6 p.m. (22 UTC = 6 p.m. between daylight saving time (in early March) and standard time (in early November). This makes sense given the atmosphere is generally most unstable late on a summer's day after the sun has been warming the ground all day.

Hourly Severe Climatology

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Arthur Update and Fireworks Forecast

July 4, 2014 - 09:05 AM
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Hurricane Arthur has put a damper on numerous firework's displays with many locations having to postpone or cancel.  Fortunately for us, the fireworks should be able to get off without a hitch in the Nation's Capital.  Here's a list of cities where fireworks have been rescheduled.

Hurricane Arthur made landfall near Beaufort, N.C. around 11:15 p.m. Thursday night.  Arthur was downgraded to a category 1 hurricane with winds at 90 mph as of the 9 a.m. update from the National Hurricane Center.  The storm has moved off the coast of the Outer Banks, NC and is quickly moving northeast.
(National Hurricane Center)
As a cold front slides through our area and Arthur moves farther out to sea, skies will clear from west to east, as drier air filters in.  It'll also be quite breezy, with winds gusting to around 30 mph through the day.
Winds will subside by the time the fireworks are set to go off downtown at 9:10pm.  And we couldn't ask for a more pleasant fireworks forecast.  It will be very comfortable, with low humidity and still just a bit breezy.  Click here for a full list of Fourth of July parades, events, and fireworks' displays.
The rest of the holiday weekend looks fantastic!  The humidity will remain low with plenty of sunshine and seasonable temperatures.

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Hurricane Arthur: First Hurricane of the Atlantic Season

July 3, 2014 - 06:14 AM
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As of the 8am update from the National Hurricane Center,  Arthur is now a Category 1 hurricane with max winds of 80 mph and moving north/northeast at 8 mph.  Check out the storm via satellite and radar.   

NOAA
Intellicast Radar

The storm is currently bringing rain to eastern South Carolina and is expected to pass over eastern NC later tonight.   Mandatory evacuations are already in place for Hatteras Island, NC.   Hurricane warnings are in effect for these areas, as heavy rain, gusty winds, coastal flooding, and dangerous surf are expected. 

NWS Morehead City, NC

Arthur is projected to brush the Carolina coast tonight and be off the mid-Atlantic coast by midday tomorrow.  Check out the latest track map from the National Hurricane Center.

National Hurricane Center.

Our local impact from Arthur will occur today.  As a cold front approaches from the west, and tropical moisture from Arthur feeds into our area, severe storms and flash flooding will be possible this afternoon and evening.  The Storm Prediction Center has our area in an elevated risk for severe storms with damaging winds.  The National Weather Service has also issued a flash flood watch for later today, as well.

Storm Prediction Center
NWS Sterling, VA

The cold front will slide east tomorrow morning and help push Arthur farther out to sea.  Drier air will slide in from west to east through the day tomorrow.  It should be rather delightful for the fireworks displays tomorrow evening with low humidity, comfortable temperatures, and a nice breeze.

The rest of the holiday weekend forecast looks great.   Have fun and be safe!

 

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