The first severe thunderstorm of the season barreled through the New York City metro area early Tuesday evening. Strong winds and heavy rain were reported across the region.
After an unseasonably hot and humid day, a fast moving cold front moved in from the west and triggered the violent storm. According to the NWS, 0.58 inches of rain was reported in Central Park and wind gusts at JFK airport reached 55 mph. It is also interesting to note that the temperature in the city dropped from 88°F to 68°F in less than one hour.
The powerful and fast moving storm knocked down trees and caused power outages throughout the area. Rolling through the city a little after 5PM, the storm also wreaked havoc on the evening commute. All MetroNorth Railroad lines out of Grand Central Terminal were suspended because of downed trees on the tracks. Additionally, the city’s three airports reported significant delays.
Outside of the city, the storm turned deadly claiming the lives of at least five people. That number includes an eleven year old girl who was crushed by a tree while sitting in a car in Newburgh, NY. No injuries or fatalities were reported in the five boroughs.
A powerful thunderstorm moves across NYC. Credit: southerlysweet/Instagram
Severe weather, the type that can cause property damage and loss of life, can take a variety of forms depending on season and location. But during spring and summer in the northeastern United States, it usually takes the shape of an intense thunderstorm. In addition to thunder and lightning, these storms produce strong winds, heavy rain, hail, and the possibility of a downburst or tornado. Therefore, it is important to understand the difference between the various alerts issued by the National Weather Service. They include advisories, watches, and warnings.
- Advisory: Issued when significant, but not necessarily hazardous, weather conditions are likely to occur. Residents should exercise caution.
- Watch: Issued when dangerous weather conditions are possible over the next several hours. They generally cover a large geographic area. Residents should be prepared to take action.
- Warning: Issued when dangerous weather is imminent or already occurring. They cover a smaller, more specific geographic area. Residents should take action immediately.
Thunderstorms pose a number of familiar hazards, such as lightning and hail. The lesser-known downburst, however, is also a serious threat to life and property.
A downburst is a strong downward current of air that causes damaging winds on or near the ground. They initiate high up in the atmosphere, where relatively dry air is entrained inside of an intense thunderstorm. The dry air evaporates some of the storm’s raindrops, which has a cooling effect. Since this cooler air is denser than the warm air that surrounds it, it sinks rapidly toward the surface. When it hits the ground, it spreads out radially – in straight lines in all directions. Reaching speeds in excess of 100mph, a downburst will knock down trees and other obstacles leaving a trail of debris all facing the same direction.
These straight-line wind events, according to the NWS, can vary in size and duration. When they cover an area less than 2.5 miles, they are referred to as microbursts. These typically last between 5 and 15 minutes. Larger events, known as macrobursts, affect an area greater than 2.5 miles and last from 5 to 30 minutes.
While short-lived, these powerful winds can pose a threat to property on the ground as well as airplanes in the process of taking off or landing.
Spring is considered severe weather season in the Central US and on Tuesday the power of Mother Nature was on full display across the region. More than 300 severe storm reports were counted and the vast majority included very large hail.
In Kansas and Nebraska, hailstones the size of a grapefruit were reported. Those are balls of ice measuring about four inches in diameter. According to the NWS, once a thunderstorm produces hail with a one inch diameter or more it is considered severe. So, how does hail get that big?
The answer to that question lies with the speed of a storm’s updraft. Basically, the stronger the updraft, the longer the ice remains suspended in the cloud where it can grow larger. Below is a chart that shows approximately how strong an updraft has to be to support different sizes of hail.
The largest hailstone ever recorded fell in Vivian, South Dakota on July 23, 2010 and measured eight inches in diameter – about the size of a volleyball. To support a hailstone that size, the updraft likely exceeded 150mph.