How Thunder and Lightning Form

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

Warmest May on Record for Planet Earth

This past May was fairly warm across most of the United States, including here in New York City. The average temperature for the Earth as a whole, however, soared into the record books.

According to a report released on Monday by NOAA’s National Climatic Data Center, May 2014 was the warmest May ever recorded for the entire planet.  Earth’s combined average temperature for the month – over both land and sea surfaces – was 59.93°F.  That is 1.33°F above the 20th century average. May 2014 also marked the 351st consecutive month that our global temperature was above its long-term norm.

The report also noted that four of the five warmest Mays on record have occurred in the past five years: 2010 (second warmest), 2012 (third warmest), 2013 (fifth warmest), and 2014 (warmest); 1998 holds fourth place. Additionally, it highlighted the fact that this past meteorological spring (March, April, and May) was the planet’s second warmest on record. For the same period, only 2010 was warmer.

Year to date, 2014 is currently ranked as the Earth’s fifth warmest year on record. Global temperature records date back to 1880.


Image Credit: NOAA’s National Climatic Data Center

Summer Solstice 2014

Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially began at 10:51 UTC, which is 6:51 A.M. 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 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 and marks 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 start to decrease.


The position of the Earth during different seasons. 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 the Tropic of Cancer on the Summer Solstice. Image Credit: NASA

Twin Tornadoes Tear Through Nebraska

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

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

A Soggy Week in NYC

One word can sum up the weather in New York City this past week – soggy.  Over the last five days, we received 2.97 inches of rain, most of which fell as heavy downpours on two separate occasions.

On Monday, 1.6 inches was measured in Central Park. Then on Friday, after a few days of scattered showers, another 1.28 inches came down in a single twenty-four hour period. It is only mid-June and the city has already had 3.96 inches of rain. The Big Apple, on average, receives 4.41 inches for the entire month.

It is interesting to note that June is now the third month in a row that NYC experienced at least one significant heavy rain event.

The Great Lakes Finally Thaw

It is now June, the first month of meteorological summer, but it seems winter is only just coming to a close on the Great Lakes.

For the first time since November, according to NOAA, the Great Lakes are ice-free. This marks the latest total thaw on the lakes since record keeping began in the 1970s. Back in March, during one of the coldest winters the region has seen in decades, more than 92% of the Great Lakes were covered by ice. That was the second highest percentage on record.

While a recent string of warm days in the area helped to melt the lingering ice, the U.S. Coast Guard also played a key role. They have reported conducting over 2000 hours of ice-breaking operations throughout this past winter and spring.

Only recently thawed, water temperatures in the lakes are expected to remain rather chilly for most of the summer.


After a frigid winter, the Great Lakes are finally ice-free. Image Credit: NOAA

EPA Seeks to Cut Carbon Pollution 30% by 2030

The issue of climate change mitigation was front and center in Washington, DC yesterday as the EPA unveiled its new Clean Power Plan. The proposed regulation would reduce carbon dioxide (CO2) emissions from all the fossil fuel based power plants across the United States.

According to the EPA, “The combustion of fossil fuels to generate electricity is the largest single source of CO2 emissions in the nation, accounting for about 38% of total U.S. CO2 emissions in 2012.”  Since coal is known to release more CO2 than any other fossil fuel, this new regulation targets existing coal-fired power plants.  Specifically, it calls for a 30% cut in carbon pollution compared to 2005 levels by 2030.

To comply with this new national regulation, individual states will have flexibility in how they choose to cut emissions. Some options include increasing energy efficiency, maximizing renewable energy sources like solar and wind, and joining a regional cap-and-trade program like RGGI in the northeast.

In addition to fighting climate change, this new rule would also improve air quality and human health. Issued at the direction of President Obama under the authority of the Clean Air Act, the EPA says this regulation will “reduce pollutants that contribute to the soot and smog that make people sick by over 25 percent.” In fact, the agency projects the lower emissions will help avoid as many as 6,600 premature deaths and over 100,000 asthma attacks in children.

While this new rule is not without its critics, EPA Administrator Gina McCarthy emphasized the need for action. In a press conference, she said: “This is not just about disappearing polar bears and melting ice caps. This is about protecting our health and it is about protecting our homes.”  The new regulation – scheduled to be finalized next summer – will also help the U.S. meet its commitment to the U.N. to cut carbon pollution by 17% by 2020.

US Carbon Dioxide Emissions by Source.  Credit: EPA/Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2012

US Carbon Dioxide Emissions by Source.                          Credit: EPA/Inventory of US Greenhouse Gas            Emissions and Sinks: 1990-2012

NYC Monthly Summary: May 2014

May 2014 was fairly warm in New York City. High readings in the 80s on six separate days helped push the city’s average temperature for the month up to 64°F, which is 2°F above normal. Following what felt like an endless winter, May was the first time all year that NYC had an above average monthly temperature.

In terms of precipitation, the city received 4.37 inches of rain. Most of this fell during two significant rain events, 1.54 inches on May 16th and 0.91 inches on May 23rd. On average, the Big Apple normally gets 4.19 inches for the entire month.

Graph: The Weather Gamut

Graph: The Weather Gamut

Names for the 2014 Atlantic Hurricane Season

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