Tag Archives: summer

Earth’s Aphelion 2015

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The Earth will reach its Aphelion today at 19:41 UTC, which is 3:41 PM Eastern Daylight Time. This is the point in the planet’s orbit where it is farthest from the Sun.

This annual event is a result of the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Aphelion differs from year to year, but it’s usually in early July – summer in the northern hemisphere.

While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, Earth is about 152 million kilometers (94 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) further than during the perihelion in early January. That means the planet will move more slowly along its orbital path than at any other time of the year. As a result, summer is elongated by a few days in the northern hemisphere.

The word, aphelion, is Greek for “away from sun”.

Image Credit: mydarksky.org

Image Credit: mydarksky.org

NYC Monthly Summary: June 2015

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June 2015 felt a bit like a weather rollercoaster in New York City. We had highs that ranged from an unseasonably cool 55°F to our first 90-degree day of the year.  In the end, however, the cold and warmth averaged each other out. The city’s mean temperature for the month was 71.2°F, which is only 0.2°F below normal.

On the precipitation side of things, the city had 14 days with measurable rainfall.  In all, we received 4.79 inches of rain, which is 0.38 inches above normal. Of this total, 1.41 inches fell in a heavy rain event during the last weekend of the month. June marked the first time since March that the city had above average monthly rainfall.

June_2015

JuneRain

A Look at the Different Types of Lightning

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Summer is the season for thunderstorms and the lightning they produce can light up the sky in a variety of ways. Here is a quick look at the different types of lightning.

While there are variations within each, these are the four primary categories:

Intra-Cloud: This is the most common type of lightning. It happens completely inside a single cloud, jumping between regions with different charges. It is sometimes called “sheet” lightning.

Cloud to Cloud: This is lightning that occurs between two or more separate clouds.

Cloud to Air: This type of lightning occurs when positive charges at the top of a cloud reach out to the negatively charged air around it.

Cloud to Ground: This lightning occurs between the cloud and the ground. It can be either positively or negatively charged.

While thunderstorms can be fascinating things to watch, is important to remember that all lightning is dangerous and strike locations are unpredictable. So, as NOAA recommends, “When Thunder Roars, Go Indoors.”

Different types of lightning. Credit: mshuntergi.com

Different types of lightning. Credit: mshuntergi.com

Summer Solstice 2015

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Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially begins at 16:38 UTC, which is 12:38 PM Eastern Daylight Time.

The astronomical seasons are produced by the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the summer months, the northern half of the Earth is angled toward the sun. This position allows the northern hemisphere to receive the sun’s energy at a more direct angle and produces our warmest temperatures of the year.

Since the winter solstice in December, the arc of the sun’s apparent daily passage across the sky has been moving northward and daylight hours have been increasing. Today, it reached its northern most position at the Tropic of Cancer (23.5° north latitude) marking the “longest day” of the year. This observable stop is where today’s event takes its name. Solstice is a word derived from Latin meaning, “sun stands still”.

Now, the sun will start to move southward again in our sky and daylight hours will slowly decrease.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

The Sun is directly overhead on Summer Solstice at the latitude known as the Tropic of Cancer. Image Credit: NASA

The Sun is directly overhead at 23.5° North latitude (Tropic of Cancer) on the Summer Solstice. Image Credit: NASA

El Niño is Strengthening and Expected to Last Through Winter

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The current El Niño event, which began in March, is continuing to evolve and strengthen.

According to NOAA, this El Niño has a 90% chance of lasting through the autumn and an 85% chance of sticking around until next winter. While it is more difficult to predict the strength of an El Niño than its duration, the current forecast is calling for a “strong” event, which will likely impact temperature and precipitation patterns around the country.

El Niño is the warm phase of the larger El Niño-Southern Oscillation, known as ENSO. It is a naturally occurring oceanic-atmospheric phenomenon that influences weather around the globe. Its main indicators are warmer than average sea surface temperatures in the eastern and central Pacific Ocean near the equator as well as a weakening of the Trade Winds.

Impacts from a moderate to strong El Niño are usually most noticeable during the autumn and winter months. This is because winter weather is governed more by large scale processes – like nor’easters – than summer weather.  In the US, these impacts include wetter than average conditions from southern California to parts of the east coast and for many of the southern states in-between. Drier than average conditions tend to settle over parts of the Ohio Valley, Great Lakes, and northern Rockies. In terms of temperature, the southwest and southern plains tend to be cooler than average while the northern tier of the country is generally warmer than average.

Although these are considered the typical regional impacts of an El Niño event, they are not guaranteed to happen. Every El Niño is different. It is also important to remember that El Niño is not the only driver of atmospheric circulation. When present, it works in concert with other major players such as daily variability and the influence of climate change.

During the summer months, impacts from El Niño in the US tend to be fairly weak. That said, its presence typically dampens the development of storms during the Atlantic Hurricane Season. As the water in the Pacific warms, it generates convection and creates westerly winds in the upper atmosphere over the Gulf of Mexico, Caribbean Sea, and Western Atlantic. This wind shear tends to limit the strengthening of any tropical cyclones in the area.

Coming on the heels of a record warm 2014, this El Niño event could help push 2015’s average global temperature to even higher record-breaking levels.  Year to date, according to NOAA, the first four months of 2015 have already been the warmest ever recorded.

Typical Winter El Nino

Typical Winter El Niño Pattern for US.  Credit: NOAA

Rip Current Awareness for the Summer Beach Season

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Summer vacation season has arrived and millions of people will be heading to beaches to beat the heat over the next few months. As such, it is important to remember that the ocean is a dynamic environment that can pose a number of hazards for swimmers.  Chief among these are rip currents.

Rip currents are fast, localized channels of water moving away from the shoreline. According to NOAA, they are a result of “complex interactions between waves, currents, water levels and nearshore bathymetry.” They can form in several different ways on any beach with breaking waves. That said, they are typically found at breaks in sandbars and along permanent structures that extend out into the water such as jetties or piers.

Moving at up to 8 feet per second – which is faster than an Olympic swimmer – rip currents can easily drag unsuspecting swimmers hundreds of yards out to sea.  While they will not pull anyone underwater, they can cause fatigue and panic. According to the U.S. Lifesaving Association, rip currents are responsible for 80% of all surf zone rescues. Nationally, they cause more than one hundred deaths every year.

To spot a rip current, look for a gap in the breaking waves.  This is where the water is forcing its way back out to sea.  The water in this area is also usually murky and darker than the surrounding water.  On guarded beaches, red flags indicate hazardous conditions for swimmers.

If caught in a rip current, the Red Cross recommends not trying to swim against it.  Instead, they say to swim parallel to the shoreline until you are out of the current. Once free, you can start swimming back toward the beach.

For more information on beach safety, visit: http://www.redcross.org/prepare/disaster/water-safety/beach-safety

rip-current

Image Credit: NOAA.

How a Circumhorizontal Arc Forms

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The sky puts on an amazing light show everyday. But sometimes, it produces something special like a circumhorizontal arc.

Often mistaken for a rainbow, a circumhorizontal arc is an entirely different optical phenomenon. It is formed by the refraction, or bending, of sunlight through plate-like hexagonal ice crystals that are situated horizontally in cirrus or cirrostratus clouds. More specifically, light enters through the vertical side of the crystals and exits through their horizontal bottoms.This angled pathway produces the well-separated colors of the spectrum that we see in the sky.  They are brightest where the cirrus clouds are thickest. Oriented parallel to the horizon, a circumhorizontal arc always sits below the sun.

Rainbows, by contrast, are produced by the combination of refraction and reflection of sunlight in liquid water droplets. These arching bands of color always appear in the part of the sky that is opposite the sun.

Circumhorizontal arcs are somewhat rare. In addition to the appropriate cloud conditions, they require the sun to be very high in the sky – at least 58° above the horizon.  They are usually only seen during the summer in the mid-latitudes.

A circumhorzontal arc seen by the author last summer in Colorado. Image Credit: Melissa Fleming

A circumhorizontal arc seen by the author last summer in Colorado.  Credit: Melissa Fleming

An Early Taste of Summer for NYC

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The official start of summer is more than a month away, but temperatures have been soaring in New York City!

A large ridge in the jet stream has ushered unseasonably warm air into the region. In fact, eight of the last twelve days have seen temperatures reach well into the 80s. Today, the mercury soared to 86°F in Central Park, making it the warmest day of the year to date. Our normal high for this time of year is 70°F.

While the pre-season warmth can be easy to acclimate to, especially after a cold and snowy winter, these summer-like conditions are not expected to last much longer. A cold front is forecast to move through the region late tonight sending temperatures back to more seasonable levels.

Summer 2014: Warmest on Record for Planet Earth

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Looking back at the summer of 2014, temperatures across most of the eastern United States were relatively moderate. Globally, however, it was a record warm season.

According to a recent report from NOAA, the meteorological summer of 2014 (June, July and August) was the warmest summer ever recorded on this planet. Earth’s combined average temperature for the season – over both land and sea surfaces – was 62.78°F. That is 1.28°F above the 20th century average.  The previous record was set in 1998.

Rising ocean temperatures, according to NOAA, helped fuel the season’s record warmth. Between June and August, the global ocean surface temperature was the highest ever recorded for the three month period at 1.13°F above average.

While the Earth’s atmosphere and oceans are warming overall, this summer’s temperature anomalies (both above and below average) highlight the fact that climate change is a complex global phenomenon that involves much more than what is happening in our own backyards.

Year to date, according to the report, 2014 is currently the Earth’s third warmest year on record. Global temperature records date back to 1880.

Credit: NOAA/NCDC

Credit: NOAA/NCDC

An Increasing Number of 90° Days in NYC

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The summer of 2014, overall, was fairly mild in New York City. We only had 8 days reach 90°F or higher. On average, the city typically gets 15. That said, this was just one season. Looking at long-term trends, the number of 90°F days in the Big Apple has actually been increasing.

The graph below shows the number of 90-degree days recorded in Central Park by the National Weather Service every year from 1870 to 2013. While there has been variability over the years, the trend is clearly on the rise.

To date, the most 90°F days that NYC has ever had in one year was 39. That happened in both 1991 and 1993. On the opposite end of the spectrum, 1902 only had one day hit the 90° mark. Last summer, we made it to 90°F or higher 17 times.

Credit: The Weather Gamut

The number of 90-degree days recorded in Central Park by the NWS every year from 1870 to 2013.  Graph Credit: The Weather Gamut