Lightning: The Five Second Rule

As a thunderstorm moves into an area, lightning  illuminates the sky followed by rumbles of thunder. Using this sequence of events and applying some simple math, you can estimate how far away the storm is.

Since lightning travels at approximately the speed of light – 186,000 miles per second – you see it almost instantly.  Thunder, on the other hand, travels at the speed of sound – about one mile in five seconds. These different rates of travel allow you to estimate the distance between yourself and the lightning.

To do this, count the seconds between seeing the flash of lightning and hearing the clap of thunder. Divide that number by five and you will know how far away the  lightning is. For example, if you count fifteen seconds between seeing lightning and hearing thunder, the lightning is about three miles away.

But, remember, if you can hear thunder, lightning is close enough to strike. So, as NOAA recommends, “When thunder roars, go indoors.”

Cloud to ground lightning strike. Credit: NWS

Second Heat Wave of the Summer Bakes the Big Apple

New York City is sweltering through its second heat wave of the summer.

The threshold for what constitutes a heat wave varies by region, but here in the NYC area it is defined as three consecutive days with temperatures reaching 90°F or higher. Wednesday marked the city’s fourth day of scorching conditions.

With the dew point temperature in the 70s, it felt even hotter. The heat index – the so-called real feel temperature – reached into the triple digits.

The main driver of this dramatic heat and humidity is a dominant Bermuda High, a large area of high pressure situated off the east coast. Spinning clockwise, it has been steering hot, humid air from the Gulf of Mexico toward the northeast.

While these conditions are oppressive, they can also be dangerous. The NWS issued both heat advisories and air quality alerts for the city over the past few days.

The normal high for this time of year in the Big Apple is 84°F.

Credit: The Weather Gamut

Weather and Health: Air Quality

The air we breathe is not always good for us. It often contains pollution, which can cause or aggravate a number of health issues including respiratory and cardiovascular diseases.

Under the Clean Air Act, the EPA is responsible for monitoring air pollution across the United States. Calculated on the Air Quality Index (AQI), a standardized indicator, the agency’s daily reports focus on the health effects people may suffer as a result of breathing polluted air. The scale runs from 0-500 with increasing AQI values correlating to higher levels of pollution and an escalating risk to public health. Values above 100 are considered unhealthy.

Unlike some other environmental challenges, air pollution is nearly impossible to avoid, as we all need to breathe. Caused mainly by vehicle exhaust, power generation, and industrial emissions, its sources are ubiquitous. The five major air pollutants measured on the AQI are, ground level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Pollutants often build to unsafe concentrations on days with very high temperatures and/or a lack of wind.  Ground level ozone, for example, forms when nitrogen oxides react with heat and U.V. light near the surface. Air quality alerts, therefore, are often issued in conjunction with heat advisories.

July 2018: Wettest July in Fourteen Years for NYC

July is usually the wettest month on the calendar for New York City and this year it did not disappoint. In fact, it was an overachiever. In all, 7.45 inches of rain was measured in Central Park. That marks the city’s wettest July in fourteen years. Of this impressive total, 2.24 inches fell on a single day, which caused flash flooding around the five-boros. The city, on average, gets 4.60 inches of rain for the entire month.

In terms of temperature, July started with an extended heat wave and then produced some below average readings toward the end of the month. Highs ranged from a relatively cool 77°F to a steamy 96°F. However, with six days in the 90s, the warmth won out in the end. The city’s mean temperature for the month was 77.6°F, which is 1.1°F above average.

Weather Lingo: Humidity

“It’s not the heat, it’s the humidity.” This old adage heard throughout much of the summer in the eastern US, refers to how the amount of water vapor in the air affects human comfort. Since the body’s main source of cooling is evaporation of perspiration, the more moisture there is in the air, the less evaporation takes place and the warmer we feel. Two ways to indicate atmospheric moisture content are relative humidity and the dew point temperature.

Relative humidity (RH) measures the actual amount of moisture in the air compared to the total amount of moisture that the air can hold. It is expressed as a percentage and is commonly used in generic weather reports and apps. A high RH can produce fog and a low RH can cause rapid dehydration in both people and plants – important information for some sectors such farmers and crews fighting wildfires. But, since warm air can hold more moisture than cool air, the relative humidity changes as the air temperature changes.

The dew point temperature, on the other hand, is an absolute measurement and is often the preferred metric of meteorologists. It is the temperature to which air must be cooled in order to reach saturation. In other words, when the air temperature and the dew point temperature are same, the air is saturated and the relative humidity is 100%. If the air were to cool further, the water vapor would condense into liquid water, such as dew or precipitation.

The classic example of this phenomenon is a glass of cold liquid sitting on a table outside on a warm, muggy day. The beverage cools the air around it and beads of water form on the outside of the glass. The temperature at which the beads of water form is the dew point.

Simply put, the closer the dew point temperature is to the air temperature, the more humid it feels. In summer, when the air is warm and can hold a lot of moisture, a dew point temperature in the 50s is generally considered comfortable. Dew points in the 60s are thought of as muggy and once they reach the 70s or higher, the air can feel oppressive. On the opposite end of the spectrum, dew points in the 40s or lower are considered dry, and dry air has its own set of comfort issues

Wildfires Are Scorching the American West

Summer is wildfire season in the American West and it is off to a blazing start.

As of Monday, according to the National Interagency Fire Center, fifty-nine large wildfires – defined as greater than 100 acres – are currently burning in nearly a dozen states. These include Alaska, California, Colorado, Idaho, New Mexico, Nevada, Oregon, Texas, Utah, Washington, and Wyoming.

One of the newest conflagrations, the Ferguson Fire, is raging just outside of Yosemite National Park in California’s Sierra Nevada mountains. At the height of tourist season, the fire has closed down Highway 140, one of the main entrances to the Park. It has forced the evacuation of several communities along Yosemite’s western edge as well as some hotels inside the Park. Ignited on Friday, the fire has burned more than 9,000 acres and is only 2% contained. Sadly, it has also claimed the life of one firefighter who was battling the flames.

Another hard hit state is Colorado, where seven large fires are burning. The largest is the Spring Creek Fire, which stared at the end of June and has burned more than 108,000 acres in Costilla and Huerfano counties.

These huge fires are being fueled by extremely hot and dry conditions that have left the region’s vegetation susceptible to any type of spark. Just a few days ago, excessive heat advisories were in effect for a large swath of the west as temperatures soared well above average.

Year to date, 3.3 million acres in the US have been charred, which is above average for this point in the season. The country’s worst wildfire year on record was 2015 when more than ten million acres burned.

Ferguson Fire in the Sierra National Forest, outside of Yosemite National Park in California. Credit: InciWeb/BlakeScott

What is a Rip Current and Why is it Dangerous?

Summer vacation season is in full swing across the US. As millions of people head to beaches to have fun and beat the heat, 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 speeds 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 area also usually appears 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

Credit: NOAA

What is a Monsoon and How Do They Affect the US?

The summer phase of the North American Monsoon is in full swing. But what, you may wonder, is a monsoon and how do they affect the United States?

While most people associate a monsoon with rain, that is only half the story. It is actually a wind system. More specifically, according to NOAA, a monsoon is “a thermally driven wind arising from differential heating between a land mass and the adjacent ocean that reverses its direction seasonally.” In fact, the word monsoon is derived from the Arabic word “mausim”, meaning seasons or wind shift.

In general, a monsoon is like a large-scale sea breeze.  During the summer months, the sun heats both the land and sea, but the surface temperature of the land rises more quickly. As a result, an area of low pressure develops over the land and an area of relatively higher pressure sits over the ocean. This causes moisture-laden sea air to flow inland. As it rises and cools, it releases precipitation. In winter, this situation reverses and a dry season takes hold.

Monsoon wind systems exist in many different parts of the world. In the US, we have the North American Monsoon that impacts states across the southwest. Summer temperatures in the region – mostly desert – can be extremely hot. Readings in the triple digits are not uncommon. This intense heat generates a thermal low near the surface and draws in moist air from the nearby Gulf of California. In addition, an area of high pressure aloft, known as the subtropical ridge, typically moves northward over the southern U.S. in summer. Its clockwise circulation shifts the winds from a southwesterly to a southeasterly direction and ushers in moisture from the Gulf of Mexico. This combination of heat and moisture rich air produces thunderstorms and heavy rainfall across the region. In fact, summer monsoon rains are reported to supply nearly 50% of the area’s annual precipitation.

Replenishing reservoirs and nourishing agriculture, these seasonal rains are a vital source of water in the typically arid southwest. Conversely, they can also cause a number of hazards such as flash flooding, damaging winds and hail, as well as frequent lightning.

Monsoon season in the American southwest typically runs from mid-June to the end of September.

The North American Monsoon pulls moist air (green arrows) inland over the typically arid southwest region of the US. Credit: NOAA/NWS

Aphelion 2018: Earth Farthest from Sun Today

The Earth will reach its farthest point from the Sun today – an event known as the aphelion. It will officially take place at 16:46 UTC, which is 12:46 PM Eastern Daylight Time.

This annual event is a result of the elliptical shape of the Earth’s orbit and the slightly 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 the sun”.

Earth is farthest from the Sun during summer in the northern hemisphere. Credit: TimeandDate.com

Four Day Heat Wave Bakes the Big Apple

New York City is sweltering through its first official heat wave of the summer.

The threshold for what constitutes a heat wave varies by region, but here in the northeastern United States it is defined as three consecutive days with temperatures reaching 90°F or higher. Tuesday marked the city’s fourth day of sweltering conditions.

In Central Park, the temperature reached 93°F on Saturday, 96°F on Sunday, 95°F on Monday, and 92°F on Tuesday. The humidity made it feel even hotter. The heat index – the so-called real feel temperature – reached into the triple digits in some spots.

The main driver of this dramatic heat and humidity is a dominant Bermuda High, a large area of high pressure situated off the east coast. Spinning clockwise, it has been steering hot, humid air from the Gulf of Mexico toward the northeast.

While these conditions are oppressive, they can also be dangerous. The NWS issued both an excessive heat warning and air quality alert for the city.

The normal high for this time of year in the Big Apple is 83°F.

Four day heat wave bakes the Big Apple. Credit: The Weather Gamut