Tag Archives: storms

How Hail Forms

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The thunderstorms of spring and summer are notorious for their powerful winds and heavy rain. However, when strong enough, they can also produce hail.

Hailstones start off as water vapor that is lifted high into the atmosphere by the updraft of a thunderstorm. Rising into cooler air, it condenses and forms water droplets. Once these liquid droplets reach a level where the temperature is below freezing, they turn into tiny ice crystals. Overtime, they get larger as other water droplets freeze to them on contact, forming layers like an onion.  Once a hailstone gets too heavy for the updraft, it falls to the ground.

The stronger the updraft of a storm, the longer a hailstone remains suspended, and the larger it can grow. For a ball of ice to be considered a hailstone, according to the AMS, it has to measure at least 5mm in diameter.

The largest hailstone ever recorded in the US was found in Vivian, South Dakota on June 23, 2010. It measured 7.9 inches in diameter and weighed 1.94 pounds. The updraft supporting it would have had to exceed 150 mph.

Needless to say, hail can cause serious damage to people and property.

Names for the 2018 Atlantic Hurricane Season

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Today is the first day of the Atlantic Hurricane Season. Although one named storm, Alberto, already formed this year, the season officially runs from June 1 to November 30.

Since 1950, each tropical storm or hurricane to form in the Atlantic has been given 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. Some notable retired Atlantic Basin storm names include: Andrew, Harvey, Irma, Irene, Katrina, Maria, and Sandy. The names for this year’s storms are listed below.

Credit: NOAA

Subtropical Storm Alberto Makes Landfall in Florida and Travels North to Canada

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Subtropical storm Alberto, the first named storm of the 2018 Atlantic hurricane season, made landfall near Laguna Beach in the Florida Panhandle on Monday. It was the second time this decade that a named storm hit the southeast coast on Memorial Day.

Classified as a subtropical storm, Alberto was a hybrid between a tropical storm and a regular low-pressure system usually found at higher latitudes. A tropical system is fueled by the latent heat released by the evaporation of ocean water while a regular storm is powered by the temperature contrast between air masses. Hybrids are able to access both energy sources.

Despite this somewhat confusing hybrid status, Alberto still packed a punch. Strong winds, downed trees, and heavy rain were seen across a large swath of the southeastern United States. A wind gust of 59-mph was reported at Fort Tyndall Air Force Base near Panama City, FL. Storm surge flooding was another concern. Water levels rose between 1 and 3 feet from Tampa Bay, FL to the Mississippi River delta in Louisiana.

Moving northward, heavy rain from the remnants of Alberto unleashed flash flooding in the several states and caused landslides in North Carolina’s Blue Ridge Mountains. Nearly 10 inches of rain was reported in Black Mountain, NC.

Forming in the waters off the Yucatán Peninsula in Mexico on May 25, Alberto traveled all the way to Lake Huron near the Canadian border before dissipating on May 31. It was the first named storm to reach that far north this early in the season, according to researchers at the University of Miami.

The Atlantic hurricane season officially begins on June 1.

Track of Subtropical Storm Alberto. Credit: Supportstorm

Catastrophic Flooding Hits Ellicott City Twice in Two Years

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For the second time in less than two years, heavy rain unleashed catastrophic flooding in Ellicott City, Maryland this Sunday.

According to the NWS, the area received between 8 and 12 inches of rain in less than four hours. On average, the area gets 4 inches of rain for the entire month of May. This massive amount of precipitation in such a short period overwhelmed streams throughout the region and turned Ellicott City’s historic Main Street into a raging river. The floodwater, which reached as high as the second floor of most buildings, damaged or destroyed numerous businesses and swept away dozens of cars and trees. Local officials say that one man, a sergeant with the National Guard, was killed while trying to rescue people from the fast flowing water.

This type of rainfall is considered a one in one thousand year event. However, that does not mean it can only happen once every thousand years. It is the recurrence interval, a statistical calculation that means an event has a one in one thousand chance (0.1%) of happening in any given year in a given location. Ellicott City experienced an eerily similar event in July 2016.

There were several drivers behind this deadly deluge. First, “training” thunderstorms developed along a stationary front. This is a situation where strong thunderstorms continuously form over the same area – like train cars traveling along a track – dumping excessive amounts of rain.

Although climate change did not cause these storms, it has altered the environment in which they form and is making them more common. As greenhouse gases warm the atmosphere, the air is able to hold more water vapor. More specifically, according to the Clausius–Clapeyron relation, for every increase of 1°F, the saturation level of the atmosphere increases by about 4%. That means there is more evaporation from oceans, rivers, and lakes, and therefore more water vapor available to condense and fall as precipitation.

Another major player in Sunday’s flood was the area’s topography. Founded as a gristmill town in 1772, Ellicott City sits in a valley surrounded by several streams that feed into the Patapsco River. Just ten miles outside of Baltimore, it is a highly urbanized area with extensive amounts concrete and asphalt. These impervious surfaces leave the rainwater with no place to go but racing downhill and through the town.

All of these factors will have to be considered as Ellicott City decides how to rebuild for the second time in two years.

Torrential rain turned Main Street in Ellicott City, MD into a raging river. Credit: S. Baranoski

2018 Atlantic Hurricane Season Outlook: Average to Above Average

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The number of hurricanes that develop in the Atlantic basin varies from year to year. For 2018, NOAA’s Climate Prediction Center is forecasting an average to above average season.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In this country, we are most impacted by the Atlantic hurricane season, which affects the North Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. It runs from June 1 through November 30.

Overall, NOAA predicts a 70% likelihood of ten to sixteen named storms forming this season, of which five to nine could become hurricanes, including one to four major hurricanes. An average season produces twelve named storms, including six hurricanes and three that become major hurricanes. A major hurricane is one that is rated category 3 or higher on the Saffir-Simpson scale.

This outlook, according to NOAA, is based on the possibility of the development of a weak El Niño and near-average sea surface temperatures in the tropical Atlantic. El Niño conditions in the Pacific tend to cause increased wind shear in the Atlantic, which suppresses tropical development in that basin.

Last year, 2017, was the most active Atlantic Hurricane season in more than a decade.  It produced seventeen named storms, including Harvey, Irma, and Maria. But regardless of the number of storms that actually form this year, it is important to remember that it only takes one land-falling system in your community to make it an impactful season.

Source: NOAA

 

The Eastern Pacific Hurricane Season Begins Today

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Hurricane season in the eastern Pacific begins today.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In the northeastern Pacific, they tend to form between May 15 and November 30. This early start, compared to the Atlantic, is due to the basin’s warm sea surface temperatures and relatively low wind shear.

While powerful, these Pacific storms are generally not as familiar to Americans as those that form in the Atlantic Ocean or Gulf of Mexico. This is because they rarely make landfall in this country. In fact, it has only happened twice. A hurricane slammed San Diego, CA in 1858 and a tropical storm battered Long Beach, CA in 1939. This low rate of occurrence is attributed to the cold water of the California Current that flows south along the west coast. Nonetheless, Pacific hurricanes can still impact the US.

Developing in the tropics, Pacific storms deteriorate as they travel north to cooler waters and in some cases over the mountains of Mexico. However, their remnants are still laden with moisture when they reach the southwestern US, where they often unleash flooding rains.

East Pacific storms can also cross into the Central Pacific and affect Hawaii. (The dividing line between the two basins is 140°W longitude). One such storm was 1992’s Hurricane Iniki, the worst hurricane in the state’s history. With wind speeds measured up to 145mph, it was rated category-4 on the Saffir-Simpson scale.

On average, the eastern Pacific produces 15 to 16 named storms in any given year. Of those, eight to nine develop into hurricanes with 4 to 5 becoming major hurricanes.

Source: NWS

Hurricane Names Harvey, Irma, Maria and Nate Retired

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There will never be another hurricane by the name of Harvey, Irma, Maria, or Nate. The World Meteorological Organization (WMO) has announced that it is officially retiring these names from its list of Atlantic cyclones.

The WMO is responsible for naming tropical storms and hurricanes around the world.  It maintains a set of six rotating lists for each hurricane-prone region. After a six-year cycle, names are re-used.  Names are only retired when a storm was particularly noteworthy – causing a large number of fatalities or an extraordinary amount of damage.

The 2017 Atlantic hurricane season was brutal, but four storms were particularly destructive. Hurricane Harvey, a category-4 storm, made landfall in Texas and dumped a record-breaking amount of rain in the Houston area, unleashing catastrophic flooding. Irma clobbered the Florida Keys as category-4 hurricane, but its impacts were felt throughout the entire Sunshine state. Hurricane Maria made landfall in Puerto Rico as a high end category-4 storm and knocked out power to more than 90% of the island for months. Nate hit the US Gulf Coast as a category-1 storm, but most of its deadly impacts were felt in Central America when it was still a tropical storm.

According to the National Hurricane Center, 86 storm names have been retired since the current naming system began in 1953. This year marks the fifth time that four or more names have been retired from a single season. Three of those -1955, 1995, and 2004 – each had four names retired. In 2005, five names were retired – the most ever from one hurricane season.

Starting in 2023, when last year’s list is recycled, the names Harvey, Irma, Maria, and Nate will be replaced by Harold, Idalia, Margot, and Nigel. Some other notable retired Atlantic Basin storm names include: Andrew, Katrina, Irene, and Sandy.

The 2018 Atlantic hurricane season officially begins on June 1.

Four names from the 2017 Atlantic hurricane season are retired. Credit: WMO

March 2018 was More of a Lion Than a Lamb in NYC

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There is an old saying that March comes in like a lion and goes out like a lamb. It refers to the transition from winter to spring that takes place during the month and the change in weather that usually follows. In New York City this year, however, that tradition went out the window as March turned out to be colder than February.

This type of temperature flip-flop, according to the NWS, has only occurred three other times in New York City history – 1890, 1891, and 2017.

This March, twenty-six out of thirty-one days posted below average temperatures. Four of those days had highs that did not get out of the 30s. In the end, the city’s mean temperature for the month was 40.2°F, which is 2.3°F below normal.

The month was also unusually wet. The four nor’easters that blasted the region in as many weeks brought the city copious amounts of precipitation. In all, we received 5.17 inches of rain, which is 0.81 inches above average. Snowfall was also abundant, with 11.6 inches measured in Central Park. Of that total, 8.4 inches fell during the fourth and final nor’easter of the month. March, on average, usually only brings the city 3.9 inches of snow.

New York City weather records date back to 1869.

March was colder than February in NYC. Credit: The Weather Gamut

Fourth Nor’easter of the Month Slams NYC

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The calendar says spring, but it felt more like winter in New York City on Wednesday as the fourth nor’easter of the month slammed the region.

According to the NWS, the storm dumped 8.4 inches of heavy, wet snow in Central Park, setting a new daily snowfall record for the date. The previous record of 7.1 inches had been in place since 1958. The city, on average, gets 3.9 inches of snow for the entire month of March.

This storm was the fourth nor’easter to affect the city and region in less than three weeks. The others were on March 2, March 7, and March 13. This one, however, was by far the snowiest. It was also the first time since 1992 that the city saw at least 6 inches of snow from a spring storm.

The reason for the plethora of nor’easters this month involves something called the North Atlantic Oscillation (NAO). Stuck in its negative phase for weeks, it has caused the jet stream to dip south over the eastern US and steer storms toward the northeastern seaboard.

View of the fourth nor’easter to hit the east coast this March. Credit:  RAMMB/CIRA/CSU

Why Are We Seeing So Many Nor’easters?

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The east coast of the United States has been slammed with three nor’easters in just eleven days – March 2, March 7, and March 13. The reason for this barrage of storms involves something called the North Atlantic Oscillation (NAO).

Based in the North Atlantic Ocean, this weather pattern is driven by the pressure differences between the semi-permanent Icelandic Low and Azores/Bermuda High. When the pressure difference between these two systems is low, the NAO is said to be in a negative phase. This means the winds of the jet stream are relatively relaxed and cold air from the north can spill down into the eastern US. The positive phase of NAO is characterized by a strong pressure difference between the two areas and a robust jet stream that keeps cold air bottled up in the northern latitudes.

Three nor’easters in eleven days. Credit: NOAA

Fluctuating between positive and negative, the strength and duration of these phases vary. Since late February, however, a strong negative phase has been locked in place. With an area of high pressure over Greenland, the jet stream is blocked and therefore dipping southward over the eastern US. As the jet stream is essentially a storm track, this pattern has allowed areas of low pressure to be steered over the warm waters of the Gulf Stream off the eastern seaboard, where they have intensified into nor’easters.

In terms of climate change, the connection between the warming Arctic and the storm track across the mid-latitudes is an active area of research. Sea level rise, however, is clearly amplifying the coastal flooding associated with these powerful storms.

NAO Patterns. Credit: NOAA