From the ABC 7 Weather team

Archive for July 2013

Atlantic Tropics Update

July 31, 2013 - 05:34 PM

Andrea, Barry, Chantal, Dorian -- these are the four named storms, so far, in this 2013 Atlantic hurricane season.  As of the last day of July, there are no storms that the National Hurricane Center is watching for possible tropical development. 

So does this mean we're in for a quiet rest of the hurricane season?  Not so fast.  The Atlantic hurricane season starts June 1st and lasts all the way through November 30th.  The peak of the Atlantic hurricane season doesn't occur until the beginning of September.  By then, ocean temperatures are usually warm enough to support tropical development.  Remember, tropical storms and hurricanes feed off of warm waters (around 80° F), saturated air, and low vertical wind shear.  Large bodies of water take much longer to heat compared to land, which is why Atlantic tropical storms and hurricanes are much more common in the early fall. 


The National Hurricane Center prediction for the Atlantic hurricane season estimates (prediction from May 2013) a 70% probability of 13-20 named storms, 7-11 hurricanes, and 3-6 major hurricanes.


As for any immediate tropical development, it looks rather unlikely.  One of the main reasons is because of the Saharan Air Layer (SAL).   The SAL is a mass of very dry, dusty air that forms over the Sahara Desert during the late spring, summer, and early fall and usually moves out over the tropical North Atlantic Ocean every 3-5 days.  This dry air can have a negative imact on tropical cyclone development because of the very dry air in the mid levels of the atmosphere, as well as the strong winds associated with this layer which makes for a very hostile enviornment for tropical wave development.  Check out the latest satellite imagery depicting the very dry air (bright yellow and orange colors) off the west coast of Africa.

A neat simulation via NOAA visualization that uses a recently enhanced version of the NOAA NGAC aerosol model to show how the plume is expected to travel across the Atlantic Basin over the next four days.

Here's another image of the SAL moving off the west coast of Africa via a NASA MODIS image. 

MODIS - TERRA satellite

More research is being done on the effect of the Saharan Air Layer on tropical cyclone formation and intensification.  With this very dry air mass moving off the west coast of Africa, and looking at the latest computer model guidance, there does not seem to be any tropical development within the next 7 days.  As always, the StormWatch7 weather team will keep you updated with tropical updates right here on our our weather homepage.

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August brings shorter days and slightly cooler temperatures on average

July 31, 2013 - 03:30 AM

It’s been feeling far from the Dog Days of Summer and we finish up July on a “cool” note. The past 6 consecutive days have had cooler than average temperatures. As we launch into August, the forecast calls for more seasonable temperatures in the upper 80s. But, what can we typically expect? July is on average the hottest month of the summer. If you love the summer daylight and heat, I am sorry to tell you that the days are getting shorter and we have fewer minutes of sunshine heating the earth each day. In fact, as of this writing, we have lost 41 minutes of daylight since the solstice on June 21st. Sunrise now is at 6:08 a.m. and sunset is at 8:21p.m. Naturally our average temperatures drop just a bit.

August Averages- National Weather Service

The average high on August 1st is 88 degrees. By the 31st, it drops to 84. Still, warm. Average lows range from 71 on the 1st to 68 at month’s end. The hottest temperature ever recorded in August was 106 degrees in 1918, while the coolest temperature recorded was 49 degrees in 1890. Those are long standing records! As for rainfall, we typically see a slight dip from the wettest month of May to an average of 2.93” (of course, we are in hurricane season and one tropical storm can top that total in a day). We could stand to have less rain around here for now. Since June first, we have a surplus of more than seven inches. Hope you enjoy the last month of summer.


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NASA celebrates 55th birthday

July 29, 2013 - 06:46 PM

It's amazing the scientific and technological advancements on organization can accomplish in the span of 55 years.  NASA, the leader in space exploration, celebrates its 55th birthday today, July 29th.

Dwight D. Eisenhower signed the National Aeronautics and Space Act on July 29th, 1958, which led to the birth of NASA on October 1st, 1958.  Over a span of more than five decades, NASA has created a network of satellites, sent robots to Mars, and even put a man on the moon, among a number of other accomplishments. 

NASA satellites
NASA - Mars Curiosity Rover

One woman who deserves special recongnition is Eilene Galloway.  Eilene was a pioneer in NASA's development.  She began working for the Congressional Research Service Library of Congress in 1941.  According to NASA, "In 1958, then-U.S. Senator Lyndon B. Johnson asked her to help with Congressional hearings that led to the creation of NASA and America's entry into the Space Race. "The only thing I knew about outer space at that time," she said, "was that the cow had jumped over the Moon."  NASA went on to say, "Galloway helped write the legislation, emphasizing international cooperation and peaceful exploration. She also proposed that NASA be an Administration rather than an Agency, enabling the new National Aeronautics and Space Administration to plan and coordinate across federal agencies the variety of activities involved in the development and uses of outer space."  Watch her full NASA TV interview shortly before her 100th birthday.

A very happy birthday to NASA and continued success in future missions that delve into this wonderful world we live in. 

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Are you more prone to mosquito bites?

July 23, 2013 - 05:20 PM

I always thought the reason I got so many mosquito bites during the summer was because I was so sweet -- hey, that's what my mom told me!  Apparently, it's a bit more scientific than that. 

A new study suggests 20% of people are more "delicious" to mosquitoes.  Mosquitoes are lured by sight and smell, says Jonathan Day, a professor of medical entomology at the University of Florida in Vero Beach.  So what are the sights and smells these pesky bugs thrive off of? Well, believe it or not, one of the triggers is blood type.  85% of people secrete a chemical signal that indicates what blood type they have.  In a controlled setting, mosquitoes tended to land on people with Type O blood nearly twice as often as those with Type A blood.   The reason mosquitoes bite us is because they harvest protein from our blood.

Another factor has to do with the amount of carbon dioxide we emitt from our breath.  People that exhale more gas have been shown to attract more mosquitoes.  That is one reason why adults get bit more than children. 

There are many other elements that play into your "mosquito attractiveness factor" such as excercise, metabolism, and genetics.   Bugs tend to gravitate towards people who relase certain substances expelled from sweat; as well as those with a higher body temperature. 

And whether you like it or not, beer can also "up" a mosquito's tendency to bite you.  The ethanol your body releases in your sweat can attract the biting bugs. 

Read the full list of mosquito bite factors from Smithsonian magazine. 

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Full "Buck" Moon Tonight

July 22, 2013 - 06:34 PM

Another full moon cycle and yet another supermoon this year.  The July full moon is commonly referred to as the "Buck moon" or "Hay moon". 

U.S. Naval Observatory

Remember the supermoon in May and June?  You may be wondering, why all the supermoons lately?  Well, they aren't any more common in recent years, but the term 'supermoon' has become more widely used across media platforms and the term is becoming more recognizable.  Astrologer Richard Nolle has defined a supermoon as " … a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit.".   According to Nolle, there is an average of 4 and 6 supermoons per year. 


The July full moon is referred to as the 'Buck moon'.  The Farmers' Almanac's definition of the July full moon: "July is normally the month when the new antlers of buck deer push out of their foreheads in coatings of velvety fur. It was also often called the Full Thunder Moon, for the reason that thunderstorms are most frequent during this time. Another name for this month’s Moon was the Full Hay Moon." 

There will be some clouds overnight, but you should be able to catch a glimpse of the full 'buck' moon tonight across the WJLA/NewsChannel8 viewing area.  Tomorrow morning will feature some great sky sights, too! 

Earth Sky

Happy gazing!

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7 days in a row above 90° - when will we catch a break?

July 22, 2013 - 08:17 AM

Last Wednesday (7/17) was the hottest day so far this year at DCA with a high of 97°, and the coolest high in 7 days was 93°.  It's July in D.C., so it's supposed to be hot as the average high at DCA stands at 89°, and that's close to where we'll be today and Tuesday.  However, it looks like cooler temperatures and a break from the humidity is on the way.

This time of year in Washington, any big break from the heat and humidity is usually brief, and this next break should follow that convention.  Also, I want to point out that I chat about this comfortable shift in our weather with a degree of skepticism because experience shows that July cold fronts often stall overhead or before they  even make it to D.C. proving model guidance wrong.

Though as it stands now, a cold front should travel here from the Upper Midwest and pass through Washington on Wednesday, so the effects will mostly be felt by Thursday and Friday.  Highs in the mid 80s are expected for Thursday and Friday, but even lower 80s are a possibility on Thursday.  Dewpoints should also drop from the muggy lower 70s into the comfortable 50s/near 60°. 

Cooler & less humid air on the way


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Excessive Heat Warning for D.C., Heat Advisory for Metro Area

July 19, 2013 - 10:30 AM

Just when you thought this summer wasn't going to be that hot, this week showed up. Temperatures over the past 4 days have seen highs in the mid 90s and the temperature hasn't feel below the 80 degree mark during the same time period.

Excessive Heat Warning and Heat Advisory until 8pm

Today, an Excessive Heat Warning is in effect from Noon to 8pm for D.C., Arlington, Alexandria, Falls Church and the City of Baltimore. Other counties along and east of the Blue Ridge to the Chesapeake Bay are under a heat advisory for the same time period. Heat index values will soar to 105°F to 110°F this afternoon.

How "extreme" is this heat wave though? The heat has been getting extreme media attention, and though it is dangerous and potentially deadly heat, it is not uncommon in July. Remember, our average high is 89 degrees this time of year, so we're only averaging 6 to 7 degrees above the normal high temperature. In addition, this year hasn't even begun to touch the extreme heat from the last couple of years.

July 2012 Heat

In 2012, July started off with a period of 8 straight days at or above 95 degrees. This included 4 days in a row at or above 100°F! That was just the beginning though, as the month accounted for 7 days at 100+, 16 days at 95+ and 22 90-degree days.

2011 wasn't much better, with only 3 100 degree days, 14 days at 95+ but a whopping 25 90-degree days. The coolest July in the past 5 years was 2009, when there were only 7 90-degree days for the month and only 1 day at 95 or better. I'm sure by now we are all beginning to miss cooler weather.

Overnight Low Temperatures at or above 80°F for 4 days straight

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How hot does it gets inside a car on a hot summer day?

July 17, 2013 - 04:15 PM

You can tell just how hot it gets in your car when you come outside from work, shopping or just about anywhere and get into your car. Some days, it gets so bad you need to turn your car on and open the windows to get the hot air out before driving. Our partners at WeatherBug decided they would do an experiment to see how hot a car would get during this current heatwave.

See the WeatherBug story here

This video features Jacob Wycoff, who is a meteorologist at WeatherBug who decided to be the test subject of this potentially dangerous experiment. On a side note, ABC 7 thought about doing this for our Surviving Severe Weather Special, but we could not get a doctor who would be willing to put one of us in harms way. Needless to say, this is very dangerous, do not try it!

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D.C. Heatwave 2013

July 16, 2013 - 11:38 AM

Current Temps  |  Heat Index  |  Local Radar  |  7 Day Forecast


6:00pm:  DCA reached 96° again today.  Not a record, but still hot! 

5:06pm: 94°F now with a heat index of 98°, so it appears the heat is falling just a bit in the late afternoon hours. That's good news to everyone! Tonight, expect low temperatures around 80 degrees in the city and 70s in the outlying suburbs.

The rest of the week will continue to have temperatures in the mid to upper 90s through Saturday. A disturbance will move into the region Saturday bringing a chance for showers and thunderstorms. A few storms may be strong to severe Saturday. Temperatures should drop back into the 80s by Sunday.

4:23pm: I have heard of multiple cases of heat exhaustion today even without the Heat Advisory. Here is a good link to the University of Maryland Medical Center that shows the signs and symptoms of heat exhaustion.

4:06pm: Now it's 94°F and feels like 99°F at Reagan National. This is the 16th 90°F or higher day this year at Reagan National, which is well off the pace compared to the last few years. By this date last year, DCA recorded 25 days at or above 90°F.

3:55pm: Code Orange Air Quality is expected tomorrow through Friday in the D.C. area, which means not only will the dangerous heat continue, but the air will also be unhealthy for sensitive groups including children, the elderly and anyone with heart or breathing difficulties.

3:19pm: I've really slowed down on this live blog since the Heat Advisory has been dropped. Interestingly enough, Heat Index values are above 105°F south of D.C., which would mean it reaches the criteria. Right now at Reagan National, it is 95°F with a dew point of 68°F making for a heat index of 100°F.

2:12pm: The Heat Advisory has been canceled for the D.C. area but heat index values will remain close to 100 degrees across the region. The reason for the cancellation is the fact that dew points are a bit lower around D.C. which means the heat index won't reach the necessary 105°F needed for a Heat Advisory. Any cool news is good news to us!

2:01pm: Now it's 94°F with a dew point of 68°F, making for a heat index of 99°F. I actually wish it was 70°F with a dew point in the 40s... guess I'll have to wait a few months!

1:23pm: It's 93°F with a dew point of 70°F making the heat index 99°F once again at Reagan National as of 1pm.

1:08pm: Before we complain about it being hot this week... think back to last July. By the 16th, there had already been 12 days at or above 90°F, 10 days at or above 95°F and 4 days at or above 100°F just for the minth!

July 2012 at Reagan National Airport


12:51pm: Did you know for the month of July, every day has a record high of 100°F or higher besides three days?  Also, the record high minimum for today is 84°F, which is the highest for the month. Our low this morning was 80°F, which in 18 other days of the month would have broken or tied the record high minimum for the day. Confused yet?

12:39pm: Here's a good story about heat exhaustion in children forward along by Tommy McFly. It's a real danger during the summer months, not only today, so please know the signs!

12:31pm: This picture was taken by Jacob Wycoff yesterday when he entered his car in the afternoon. A good reminder to make sure no one is left inside your car as this heat can kill. It's happened 20 times too many so far this year.

12:23pm: Be sure to stay on top of this story about the Prince Georges County water outage as it is coming at the worst possible time.

12:14pm: I'm not opposed to sharing other meteorologists posts, such as this one from our friends at the Capital Weather Gang. Good write-up on the record-tying 500mb heights this weekend!

This height did fall a bit this morning to 5970m so I agree with Jason that the record heights will continue to fall as the ridge breaks down through the rest of the work week.

500mb height, temperature and humidity chart from 12z this morning

12:08pm: As of Noon, it is now a ripe 92°F outside with a heat index of 99°F. The dew point went down to 70°F which is why the heat index has stayed the same. We'll take it during the lunch hour!

The Heat Advisory continues through 7pm for D.C., Alexandria, Arlington, Flass Church and Baltimore.

12:06pm: A funny post from our friend TerpWeather on Facebook.

11:57am: Something interactive is always fun! How about a heat index calculator? You can find it here from the Weather Prediction Center.

11:48am: It's currently 91 degrees with a dew point of 71, making for a heat index at 99 degrees. This is already shaping up to be a pretty miserable afternoon! Take a look at the HRRR 3km model high temperature forecast for today. Upwards of 99 degrees in spots around the D.C. area! Once again, just a model forecast, but we think upper 90s will be reached in areas today. Thanks to Ryan Maue (@RyanMaue) of for the share.

HRRR 3km Model High Temperature Forecast

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Summer halfway point; July heat comparison

July 15, 2013 - 04:50 PM

Just one year ago, temperatures were extremely similar with highs in the mid 90s before hitting 100 degrees for two days in a row. The forecast for the same time period (15th through the 19th) this week has temperatures in the mid to upper 90s each day through the end of the work week. So far, the 96 degrees Reagan National hit today is the hottest so far this year. Sorry the graphic states 95 for today (Monday), it was 95 when I made the graphic, that's what I get for not waiting!

Last July 15-19 vs. this year's forecast through the 19th

This just happens to be the midpoint of the summer, as July 15th lies in the midst of Meteorological Summer which is from June 1st through August 31st. There is often a confusion between Meteorological Summer and Astronomical Summer, as the Summer Solstice occurs on the 21st of June, but this doesn't coincide with the hottest part of the year.

Halfway point of summer!

The hottest part of the year extends from July 7th through July 22nd, with an average high of 89 degrees and an average low of 71 degrees. This is in start contrast to the January coldest part of the year with an average high of 43 degrees and average low of 28 degrees.

July has been brutal over the past 3 years, averaging 20 or more days at or above 90 degrees each year. Last year was exceptionally rough, as it included 7 days at or above 100 degrees and 16 days at or above 95 degrees. The last time the month of July was below normal was in 2009, when there were only 7 90 degree days recorded. That year recorded 15 days with high temperatures at or below 85 degrees. Must've been nice!

Tips to beat the heat this week include staying inside as much as possible, wear lightweight and light colored clothing, including a hat and sunglasses. If you must exercise, do it indoors or as early as possible during the day. Try to drink as much water as possible and limit consumption of sugary or alcoholic beverages. If you know any relatives that are prone to heat illness such as the elderly, be sure to check on them. Don't forget about your pets either! Please bring them indoors and give them plenty of water!

The picture below is from our WeatherBug representative Jacob Wycoff who happened to be getting into his car when he recorded this temperature this afternoon. This is a serious reminder never to leave children or pets in your car in this heat. It can be dangerous and deadly, as 20 children have already lost their lives in the U.S. this year from heat stroke after being left inside vehicles.

Jacob Wycoff's car thermometer Monday afternoon

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Flooding Rains: What happened

July 12, 2013 - 08:32 AM

The D.C. area woke up to heavy rain and flooded roads this Friday morning.  As of 8:30 this morning, the rainfall totals ranged from 1-6"  Check out the official recordiing stations.  

24 hour Rainfall Totals

And here's a look at some of the highest totals we could find on our weather bug network. 

Weather Bug Rainfall Totals Since Thursday

While we did expect some wet weather, we didn't think it would exceed flash flood criteria.  So, why did we get so much rain?  The cold front that crossed our area yesterday was expected to keep pushing to the south and east of our area.  However, drier air to our west has been pushing up to the warm and moist air from the Atlantic and the two have been converging on top of us.  This is a water vapor image that I have added weather features on top of to help you understand what is happening in the atmosphere.  

Water Vapor Satellite

The brownish colors show dry air and the green colors are moisture.  They meet up right along the I-95 corridor.  The cooler, more dense dry air pushes underneath the warm and humid air creating lift on top of us.  This is what is causing all of the rain.  To further complicate matters, there is an area of low pressure in the upper atmosphere that is trying to dig in west of us.  The computer models are retrograding this low to the southwest.  If it continues to do that, it will allow some leftover moisture from Tropical Storm Chantal to try and sneak up here late weekend.  Here is where the remnants of Chantal's moisture is now near the Bahamas.  

NOAA Satellite

Even if that doesn't make it here, there should be enough instability and moisture Saturday to at least give us a 30% chance of showers to start the weekend.  We will have to continue to monitor closely.  In the meantime a flash flood watch is in effect through this evening. 


Flash Flood Watch through this Evening

After today, the Bermuda high off the Atlantic coast will hopefully push back and shift that convergence zone to our west and bring warmer and drier conditions in with 90+ temps next week.  Our forecast confidence for the weekend is a bit lower than average due to these tricky circumstances.


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WJLA Severe Weather Special: WIND TUNNEL (VIDEO)

July 11, 2013 - 03:00 AM

In a previous blog, I showed you a unique facility in rural South Carolina (IBHS) that does various natural disaster testing including dramatic hail and wind tests.  For this story, I became the test subject in a wind tunnel and didn't even have to travel outside the beltway to do so.

The wind tunnel at the University of Maryland is typically used to test the aerodynamics of aircraft, automobiles, sails, and even speed skating uniforms. Though recently I had the opportunity to test my strength against 115 mph (category 3 hurricane) winds.  See the video of my flapping cheeks and spectacular hair do afterward, here:


You can also follow me on Twitter and Facebook.

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Washington Monument lights up (VIDEO)

July 9, 2013 - 07:22 AM

The 555-foot Washington Monument will be illuminated each night at dusk by 488 lights.

The iconic obelisk will remain aglow while construction work continues to repair earthquake damage sustained by the 2011 5.8 magnitude earthquake.

Big thanks to Eileen Whelan for recording the splendor!

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Tropical Storm Chantal: A Threat to the U.S.?

July 8, 2013 - 06:31 PM

The Atlantic hurricane season officially began June 1st.  As of Sunday, there were only two named storms this season -- Andrea and Barry.  Now we're on to our third named storm, Chantal.  Tropical Storm Chantal developed late Sunday night over the central tropical Atlantic and was racing west-northwest toward the Lesser Antilles.  Here's the latest infrared satellite image of Chantal approaching the Windward Islands.


As of late Monday, Chantal is still a tropical storm and is on track to bring rain and wind to the Leeward and Windward Islands by Tuesday with tropical storm conditions expected near Puerto Rico by late Wednesday.  Here's the latest track from the National Hurricane Center.


As Chantal tracks northwest, the storm could be near hurricane strength before it reaches Hispaniola.  After Chantal moves past Hispaniola, the storm should be affected by environmental conditions that will weaken the cyclone.  As of now, there does not seem to be any threat to the U.S.  The rest of the tropics remain fairly quiet this early July. 

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What was the weather like on July 4, 1776 in Philadelphia?

July 3, 2013 - 11:55 AM

Have you ever thought what the weather was like in 1776 when the Declaration of Independence was being signed? Fortunately, one of our founding fathers was a weather enthusiast, so that information is available from one of his journals. This just happened to be Thomas Jefferson, who drafted the Declaration between June 11 and June 28, 1776.

Journal of Thomas Jefferson from July 1776

Above is a look at Thomas Jefferson's weather observations for the first 14 days in July in 1776. This gives an idea of the weather on the 4th, when the Declaration was signed. It reads:

6am:  68°         9am:  72.25°         1pm:  76°        9pm:  73.5°

It's pretty crazy to think that we have reliable weather data which dates all the way back to 1776. And it only hit 76 degrees, though the temperature could have been higher through the afternoon hours. He typically took temperatures when he woke up and once in the afternoon closer to 3pm or 4pm. Here's a link where you can read more about Jefferson's weather observing, which he did daily with most observations in Virginia at Monticello and in Williamsburg.

Fun Facts about the 4th of July from

More about the Declaration of Independence

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Washington is Warm while the West Coast is Demolishing Heat Records

July 2, 2013 - 02:49 PM

Death Valley. Sounds like a charming little area doesn’t it? How about the fact that it is measured as consistently one of the hottest places on Earth?


Temperatures normally reach or exceed 100 degrees F from mid-May to early October. On July 1st, 2013, a freelance meteorologist and his thermometer measured the temperature in Death Valley at a whopping 135 degrees F. However, due to this measurement being an unofficial thermometer and not associated with the Las Vegas National Weather Service, the record would not be recognized. Therefore, the temperature that was recorded does not break the old temperature of 134 degrees that was set on July 10th, 1913 in Greenland Ranch an area of Death Valley. In fact, that temperature was the highest reliable recorded air temperature with a properly sighted and maintained thermometer on Earth! There is even a celebration this year to commemorate the 100th anniversary of the world record high temperature.




This global high temperature record from 1913 has always been controversial. In El Azizia, Libya (on what was at that time an Italian army base off the Libyan coast) September 13th, 1922, a temperature of 136 degrees F was recorded! The World Meteorological Organization eventually certified this as the hottest global air temperature ever recorded. But of course, there was evidence after an investigation that suggested the reading was invalid. Most likely because of misinterpretation of the reading on the thermometer (where is Adam Caskey when you need him?).

(This is a drawing of the Six-Bellini thermometer, the antiquated type used to make the observation of the disputed world's hottest temperature in El Azizia, Libya)




Also, there were several inconsistencies measurements taken at the same site and nearby weather stations at this time. The reading in Libya was also taken over asphalt which would of course be hotter than its desert surroundings. On September 12, 2012 (100 years after the initial controversy) the World Meteorological Organization officially re-certified the 134 degree reading on July 10th, 1913 at Death Valley as the all-time higher air temperatures recorded globally.






The west coast is in the middle of a heat wave, a very dangerous heat wave where temperatures continue to top out in the triple digits with overnight lows barely bottoming out in the 80s.




A ridge of strong high pressure in the upper levels of the atmosphere set up shop on June 27th over northern New Mexico and since then has meandered back and forth from Utah, to Nevada and California continuing to pump life-threating heat into portions of western United States. This high pressure looks to hang tough over the west before it finally begins to break down towards the end of this week. However, until then – areas in the western US will continue to be under excessive heat warnings. So if you want to find the extreme heat – you know where to go!

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