Tag Archives: storms

Arthur: First Named Storm of the 2014 Atlantic Hurricane Season

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Arthur, the first named storm of the 2014 Atlantic Hurricane Season, has officially formed. With winds speeds measured at 40 mph earlier today, the system developed into a tropical storm off the Atlantic coast of Florida.

According to forecasters at the National Hurricane Center, Arthur is expected to strengthen and move north along the eastern seaboard over the next few days. In addition to producing rain and gusty winds, the storm will also create dangerous rip currents at beaches up and down the east coast. Sadly, many July 4th holiday plans in the coastal regions of the Mid-Atlantic States will likely be disrupted.

Credit: National Hurricane Center

Credit: National Hurricane Center

How Thunder and Lightning Form

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Flash! Bang! Thunderstorms are impressive displays of the power of nature. But how, you may wonder, do lightning and thunder form?

First comes the lightning, an intense electrical discharge. While not completely understood, it is believed to form as a result of the separation of charges within a cumulonimbus cloud.  One theory of how this happens involves the collision of particles within these towering clouds, including hailstones, super-cooled liquid water droplets, and ice crystals.  When they mix and collide, according to NOAA, “electrons are sheared off the ascending particles and collect on the descending particles.” This results in a cloud with a negatively charged base and a positively charged top.

As the atmosphere is a good insulator, generally inhibiting the flow of electricity, the strength of this electrical field has to build up substantially before lightning can occur. Most discharges, about 75%, occur across the electrical field within the storm cloud itself. This is known as intra-cloud lightning.

Another electrical field can also develop below the cloud. Since the cloud base is negatively charged, it induces a positive charge on the ground below, especially in tall objects such as buildings and trees. When the charge separation becomes large enough, a negatively charged stepped leader – an invisible channel of ionized air, moves down from the base of the cloud. When it meets a channel of positive charges reaching up from the ground, known as a streamer, a visible flash of lightning can be seen.  This is called cloud to ground lightning.

Lightning can be as hot as 54,000°F, a temperature that is five times hotter than the surface of the sun. When it occurs, it heats the air around it in a fraction of a second, creating an acoustic shock wave.  This is thunder.  A nearby lightning strike will produce thunder that sounds like a sharp crack. Thunder from a distant storm will sound more like a continuous rumble.

While thunderstorms can be spectacular events to watch, they are also very dangerous.  So, as the National Weather Service recommends, “When thunder roars, go indoors.”

Credit: NWS

Credit: NWS

Twin Tornadoes Tear Through Nebraska

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Barreling across northeastern Nebraska on Monday, a pair of twin tornadoes leveled the small farming town of Pilger, NE. The so-called “sisters” claimed the lives of two people and injured numerous others.

The two wedge tornadoes were reported to have been on the ground for nearly an hour and traveled along parallel pathways getting as close as one mile apart. With winds ranging between 166 and 200 mph, the National Weather Service has rated both twisters EF-4. That is the second highest ranking on the Enhanced Fujita Scale.

Massive twin tornadoes are rare events. Experts say, if one thunderstorm spawns two separate twisters simultaneously, one usually dissipates or is overtaken by the other. The size, strength, and longevity of Monday’s tornadoes were extremely unusual.

With warm, moist air lingering over the region, violent weather returned to Nebraska on Tuesday. A multi-vortex tornado was spotted in Coleridge, NE, but that storm has not yet been rated. More severe weather, including possible tornadoes, is expected in the area again on Wednesday.

Rare twin tornadoes tear across Nebraska. Image Credit: KEYC

Rare twin tornadoes tear across Nebraska. Image Credit: KEYC

Green Skies

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Thunderstorms are fairly common in the late spring and summer in the United States. Every once in a while, though, they can be severe. When they are, the sky often turns green. You may wonder, what causes this odd coloration?

According to scientists, the phenomenon of green skies is not completely understood. The leading theory, however, involves the dense moisture content of cumulonimbus clouds and the time of day. Most thunderstorms develop in the late afternoon, a time when the sun’s rays have to travel a long way through the atmosphere before reaching the ground. This causes the light we see around sunset to be reddish-yellow. Thunderstorm clouds contain large amounts of rain and hail. This water and ice scatters blue light. So, when these towering clouds form in the late afternoon, the two colors mix to give the sky a green or blue-green appearance.

While severe thunderstorms can produce tornadoes, a green sky does not necessarily mean a twister is coming. Nonetheless, the color is associated with dangerous weather. If you see a thunderstorm heading your direction and the sky appears green, you should seek shelter immediately.

Green Sky. Image Credit: Sky7WX

Green Sky.   Image Credit: Sky7WX

Names for the 2014 Atlantic Hurricane Season

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Today is the first day of the Atlantic Hurricane Season. While it is expected to be fairly mild this year, names have already been chosen for any storms that may develop.

Since 1950, each Atlantic tropical storm or hurricane has had a unique name.  They come from a set of six rotating lists produced by the World Meteorological Organization. A name is retired only when a storm was particularly noteworthy – causing a large number of fatalities or an extraordinary amount of damage.  Sandy, for example, was retired after it devastated a large section of the northeastern United States in 2012.

The names for this year’s storms are below.

Data Source: NOAA/NHC

Data Source: NOAA/NHC

2014 Atlantic Hurricane Season Outlook

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From year to year, the number and strength of storms developing during the Atlantic hurricane season varies. This year, NOAA’s Storm Prediction Center  is expecting an average to slightly below average season.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In this country, we are most affected by the Atlantic hurricane season, which impacts the North Atlantic Ocean, Caribbean Sea and Gulf of Mexico. It runs from June 1 through November 30.

The main driver behind this season’s mild forecast is the likely development of El Niño later this summer.  While centered in the tropical Pacific, El Niño impacts weather around the planet. According to NOAA, “El Niño causes stronger wind shear, which reduces the number and intensity of tropical storms and hurricanes. El Niño can also strengthen the trade winds and increase the atmospheric stability across the tropical Atlantic, making it more difficult for cloud systems coming off of Africa to intensify into tropical storms.”

In addition to the seasonal outlook, announced at a press conference in New York City, NOAA also unveiled its new storm surge visualization product. Building on the lessons from super-storm Sandy, this new mapping tool will show the storm surge threat to specific communities beginning when a tropical storm or hurricane watch is issued. Hopefully, this will give the public a better understanding of the dangers of storm surge flooding and allow them to make more informed decisions.

While the overall number of storms expected to develop this year is relatively low, it is important to remember that it only takes one to cause serious damage, if it makes landfall.

Data Source: NOAA

Data Source: NOAA

A Day of Drenching Rain in NYC

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April is famous for its showers, but yesterday’s precipitation was extreme. Torrential downpours brought New York City more than a month’s worth of rain in a single day.

According to the NWS, 4.97 inches of rain was measured in Central Park. Not only is that a new daily record for the date, it was the 10th rainiest day ever recorded in NYC. On average, we normally get 4.50 inches of rain for the entire month of April.

Up until yesterday, the city’s rainfall total was running below average for the month. So, while the rain was beneficial for the area, the rate at which it came down and its extended duration caused a number of localized flooding problems.

Scientists say the frequency of extreme rain events like this one will increase as global temperatures rise and our climate changes.

Multi-Day Tornado Outbreak

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After getting off to a slow start, the severe weather season has kicked into overdrive. A multi-day tornado outbreak has been wreaking havoc across the southern and central United States since Sunday. Widespread destruction, power outages, and a mounting death toll have been reported across several states. Some of the hardest hit areas include Arkansas, Mississippi, and Alabama.

According to local authorities, the twister that hit Vilonia and Mayflower, Arkansas on Sunday night was on the ground for 29.2 miles and claimed the lives of at least 16 people. With winds in excess of 136 mph, the NWS has assigned it a preliminary rating of EF-3. On Monday, the same deadly storm system moved into Mississippi and Alabama and generated even more tornadoes. Local officials there say hundreds of homes were destroyed and at least a dozen people were killed. The strongest storm in this outbreak so far was an EF-4 (preliminary rating) that touched down in Louisville, Mississippi. With winds ranging between 166 and 200 mph, it was also the strongest tornado to form in the U.S. to date this year.

Tornadoes are par for the course in this part of the country in spring, but the longevity of this outbreak is unusual. With warm, moist air moving up from the Gulf of Mexico and feeding into a very slow moving low-pressure system, the threat of severe weather continues to linger.

Tornado ravaged Vilonia, Arkansas. Image Credit: EpochTimes/AP

Tornado ravaged Vilonia, Arkansas.  Image Credit: EpochTimes/AP

Slow Start to Tornado Season

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Spring is usually the height of severe weather season in the United States. This year, however, it has been slow going – at least so far.

According to NOAA’s Storm Prediction Center, there have only been 20 tornadoes rated EF-1 or higher to date in 2014. On average, we usually see 157 storms by this point in the season. Of the twisters that did form, none were rated EF-3 or stronger. That is fairly weak by tornado standards, which are measured from EF-0 to EF-5 on the Enhanced Fujita (EF) scale.

With colder than average temperatures dominating most of the country recently, storm development – which needs warm moist air and explosive convection – has been limited. That said, a slow start does not necessarily mean a slow season. It only takes one strong storm to devastate an area. Last year, for example, was a below average season, but it still produced an EF-5 that leveled Moore, OK.

May is typically the most active month of the year for tornadoes in the US.

Data Source: NOAA

Data Source: NOAA

Another Snowstorm Slams NYC

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A massive winter storm walloped the East Coast of the United States yesterday.  The impacts of snow, sleet and freezing rain were felt from Georgia to Maine.

Here in New York City, the storm came in two parts.  The first round brought us 9.5 inches of snow.  Coming down at a rate of 2 to 3 inches per hour, it piled up quickly.  Following a lull in the afternoon, round two produced heavy rain, thunder and lightning, and another 3 inches of snow.  In the end, this classic nor’easter dumped 12.5 inches of heavy, wet snow in the Big Apple.

So far this February, the city has received 25.7 inches of snow.  On average, we usually get 25.1 inches for the entire winter. This season, to date, we have accumulated 54 inches of snow in Central Park, making it our 9th snowiest on record.

More snow is forecast for the weekend.