Monthly Archives: June 2015

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

Seasonal Temperature Lag

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The June Solstice marks the official beginning of the summer season in the northern hemisphere. It is famous as the longest day of the year – a day when we receive the greatest amount of incoming solar radiation. The reason it is not also the warmest day of the year relates to a phenomenon known as seasonal temperature lag.

Air temperature depends not only the amount of energy we receive from the sun, but also the amount of energy absorbed by the planet’s landmasses and oceans. The heat capacity of both, which is defined as the amount of heat required to raise the temperature of a substance 1°C, play a major role. Given the fact that water has a much higher heat capacity than land and that oceans cover 71% of the Earth’s surface, it takes awhile for the atmosphere to warm up. Here in the mid- latitudes, we usually see our warmest days of the year in mid-July which are often referred to as the Dog Days of Summer.

In winter, the process works in reverse. The oceans take time to lose their heat. So, the coldest days generally lag the winter solstice by a few weeks.

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

May 2015: Warmest May on Record for Planet Earth

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Our global temperature continued to rise last month. In fact, May 2015 was the warmest May ever recorded for the entire planet.

According to a report by NOAA’s National Climatic Data Center, Earth’s combined average temperature for the month – over both land and sea surfaces – was 60.17°F. That is 1.57°F above the 20th century average. The previous record was set last year. NOAA also said the May 2015 global temperature “ties with February 1998 as the fourth highest monthly departure from average for any month on record. The two highest monthly departures from average occurred earlier this year in February and March.”

While heat dominated most of the planet last month, some places were particularly warm. Here in the US, five states – Alaska, Connecticut, Massachusetts, New Hampshire, and Rhode Island – each had a record warm May.

Rising ocean temperatures, according to NOAA, helped fuel the month’s record warmth. The global sea surface temperature for May was 1.30°F above the 20th century average of 61.3°F.  That is the warmest on record for any May surpassing the previous record set just last year. It should be noted, however, that moderate El Niño conditions were present across the central and eastern Pacific Ocean last month.

Year to date, the first five months of 2015 were the warmest of any year on record. Global temperature records date back to 1880.

Credit: NOAA

Credit: NOAA

Tropical Storm Bill Slams Texas

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Tropical Storm Bill, the second named storm of the 2015 Atlantic Hurricane Season, made landfall on Tuesday at Matagorda Island, which is between Houston and Corpus Christi in Texas. It slammed the southeast section of the Lone Star state with winds measured up to 60 mph and relentless heavy rain.

Rainfall totals, according to the NWS, averaged around 3 inches for most places, but some areas southwest of Houston saw much heavier precipitation. The cities of Ganado and El Campo received 11.77 inches and 9.91 inches, respectively. With the soil already saturated from a record wet May, there was widespread flash flooding. Luckily, no serious injures have been reported.

Moving inland toward Oklahoma, another state that experienced a record wet May, the storm was downgraded to a tropical depression on Wednesday. The rain, nonetheless, is ongoing. Looking ahead, the storm is forecast to travel northeast, riding a large ridge of high pressure situated over the southeastern states. The rainy remnants of Bill will likely arrive here in the NYC area by Sunday.

Given that this is an El Niño year – a time when the number of Atlantic hurricanes is usually below average – it is interesting to note that two named storms have already made landfall in the US this season. First Ana in May and now Bill. This shows that land-falling storms can occur even in “quiet” years and that it is important to be prepared throughout the hurricane season. 

Tropical Storm Bill making landfall on Texas coast. Credit: NOAA

Tropical Storm Bill making landfall on Texas coast. Credit: NOAA

Remnants of Tropical Storm Bill are forecast to impact the east coast by the weekend. Credit: NOAA

Traveling from the Gulf of Mexico across the mid-west, remnants of Tropical Storm Bill are forecast to impact the east coast by the weekend. Credit: NOAA

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.

May 2015: Wettest Month Ever Recorded in US

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When it rains, it pours – this old adage was literally proven to be true last month. With national weather data dating back to 1895, May 2015 was the wettest month ever recorded in the contiguous United States.

According to NOAA, an average of 4.36 inches of rain fell across the lower 48 states, which is 1.45 inches above average. The vast majority of this impressive total came down in the southern plains. Colorado experienced its wettest May on record. Texas and Oklahoma each had their single wettest month ever, with rain totals that were more than twice their respective long-term averages.

For people living on the either the west or east coasts of the country, this news may come as a bit of a surprise. California continues to be plagued by a devastating drought and many states along the eastern seaboard saw drier than average conditions for the month with six states recording a top-ten driest May.

While the torrential rain in the south central US caused deadly and destructive flooding this spring, it also abruptly ended the region’s multi-year drought. Nationally, the latest report from the US drought monitor shows that only 24.6% of the country is in some form of drought. That is down from 37.4% at the end of April. It is also the smallest national drought footprint since February 2011.

There were many factors that contributed to May’s excessive rainfall, including El Nino – a natural oceanic-atmospheric phenomenon that tends to bring wet weather to the southern part of the country. However, the National Climate Assessment, a US government report that came out last year, says that climate change has caused heavy rain events to become heavier and more frequent across most of the US. Experts expect this trend to continue, but as we saw last month the distribution of rainfall is not likely to be equal.

Credit: NOAA

Credit: NOAA

When it Rains, it Pours

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Torrential rain events and the flooding they cause are nothing new.  Global warming, however, is helping to make them more likely.

According to the most recent National Climate Assessment, heavy rain events – defined as the heaviest 1% of all rain events – have become heavier and more frequent across most of the US. The greatest increases have been observed in the northeast, mid-west, and southeast.

Climate scientists attribute this increase in heavy precipitation to our warming atmosphere. Simply put, warm air holds more moisture than cold air. And, the more moisture that builds up in the air, the more rain can fall.

The relentless rain and deadly floods in Texas last month made national headlines, but there are many other examples of similar events in the recent past. In September 2013, Colorado experienced catastrophic flooding caused by overwhelming amounts of rain in a short period of time. Locally, here in the NYC area, the town of Islip on Long Island saw more than 13 inches of rainfall in a single day last August. That equates to 29% of their average annual rainfall. The damage caused by that single event was estimated at $35 million.

As our global temperature continues to rise, experts say we should expect to see more extreme rain events, even in areas where overall precipitation is projected to decrease. In other words, when it rains, it will likely pour.

The map shows percent increases in the amount of precipitation falling in very heavy events (defined as the heaviest 1% of all daily events) from 1958 to 2012 for each region of the continental United States. These trends are larger than natural variations for the Northeast, Midwest, Puerto Rico, Southeast, Great Plains, and Alaska. The trends are not larger than natural variations for the Southwest, Hawai‘i, and the Northwest. The changes shown in this figure are calculated from the beginning and end points of the trends for 1958 to 2012.

The map shows percent increases in the amount of precipitation falling in very heavy events  from 1958 to 2012 for each region of the continental United States. These trends are larger than natural variations for the Northeast, Midwest, Puerto Rico, Southeast, Great Plains, and Alaska. The trends are not larger than natural variations for the Southwest, Hawai‘i, and the Northwest. Credit: 2014 US National Climate Assessment

NYC Monthly Summary: May 2015

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May was unusually warm and dry in New York City this year.

With 26 out of 31 days posting above average highs, including 18 days with readings in the 80s, May felt more like summer than spring. Overnight lows were also well above average throughout most of the month. All together, the city’s mean temperature for the month was 68.5°F, which is 6.1°F above average.  That makes May 2015 the city’s 3rd warmest May on record.

In terms of precipitation, May was exceptionally dry. Coming on the heels of a parched April, the city, according to the latest report (5/28) from the US Drought Monitor, is currently in a state of moderate drought. All told, the city received a mere 1.86 inches of rain in Central Park. Of this meager total, 1.46 inches fell in a single day – the last day of the month – and caused localized flash floods. May, on average, typically brings NYC 4.19 inches of rain.

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut