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

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

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

Powerful Thunderstorm Batters NYC

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

April 2018: Unseasonably Cold and Wet in NYC

April felt like a wild ride of weather in New York City this year. It produced both a record-breaking snowfall and a balmy summer preview with temperatures in the 80s. However, with 19 out 30 days posting below average readings, the cold won out in the end. The city’s mean temperature for the month was 49.5°F, which is 3.6°F below normal.

While unseasonably chilly, the month was not a record breaker. That dubious honor, according the NWS, belongs to April 1874 when the monthly temperature was only 41.1°F. The city’s warmest April on record was April 2010 with a mean temperature of 57.9°F.

In terms of precipitation, this April was unusually wet with 14 out of 30 days producing rain or snow. In all, the city received 5.78 inches of rain, which is 1.28 inches above average. Of that total, 49% fell during a single heavy rain event on April 16. Snow was also abundant with 5.5 inches measured in Central Park. Coming down during a single storm on April 2, it set a new daily snowfall record for the date. On average, the city gets 0.6 inches of snow for the entire month.

April was a wild ride of weather in NYC. Credit: The Weather Gamut

Why Heavy Rain Events are Becoming More Common

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

Heavy rainfall trends in NYC. Credit: Climate Central

According to the most recent National Climate Assessment, heavy precipitation events have increased in both frequency and intensity across the United States. While there are seasonal variations with different regions, the greatest increases have been observed in the northeast.

Climate scientists attribute this increase in heavy precipitation to our warming world. 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.

Heavy rain events have a number of consequences, including an increased risk of both flash floods and river floods. This, in turn, is a threat to life and property. Over the long-term, it also affects insurance rates and property values. According to NOAA, individual billion-dollar flooding events (excluding tropical cyclones) in the U.S. have added up to $39 billion in losses since 2010.

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.

Downpours have been getting more frequent and intense across the US. Credit: Climate Central and NCA4

Heavy Rain Drenches NYC and Its Subways

An intense rainstorm swept through New York City on Monday. With bands of torrential downpours, it unleashed more than half a month’s worth of rain in just a few hours.

According to the NWS, 2.82 inches of rain was measured in Central Park. While that is an impressive total, it did not break the daily rainfall record for the date. That honor belongs to April 16, 1983 when 3.29 inches of rain was reported. New York City, on average, gets 4.50 inches of rain for the entire month of April.

The heavy rain caused flash flooding and disrupted travel across the city. Torrents of water poured into several subway stations through leaks in the ceiling and down the entrance/exit steps. During the morning commute, the MTA announced that several stops, including the 145th St station on the Number 1 line and the 42nd St-Bryant Park stop on the F and M lines, would be bypassed because of “excess water”.  Significant delays and cancellations were also reported at the area’s airports.

This type of heavy rain event, according to NOAA, is expected to become more common in the northeast as global temperatures rise and precipitation patterns change.

Heavy rain sends water cascading down the steps of the 145th St Station of the No. 1 train in NYC. Credit: Josh Guild/Twitter.

Do April Showers Really Bring May Flowers?

The phrase, “April showers bring May flowers “ has been around for centuries. It is derived from a poem written in the 1500s by Thomas Tusser – an English poet and farmer. This old adage, however, does not hold true in the northeastern United States.

Coming on the heels of the snowy months of winter, April typically produces more rain than snow. Many people, therefore, consider it a rainy month. Since water is necessary for the overall survival of plants, they also associate it with the bloom of flowers in May. Nevertheless, according to botanists, perennials – the plants that go dormant in winter and re-grow in the spring – are more dependent on the soil moisture derived from winter snowmelt and the long-term local precipitation pattern.

In the end, though, temperature is the most significant factor in determining when a flower will bloom. As soon as the weather becomes more spring-like, flowers will start to blossom, regardless of how much it rained in April or whatever the prior month was. That said, a “false spring” – a warm spell that triggers flowering but is followed by a hard frost – can kill the fragile blooms.

It is also worth noting that April is not typically the wettest month of the year for most places in the US. In New York City, July, on average, takes that honor because of the downpours associated with its strong summer thunderstorms.

Peonies in bloom. Credit: Melissa Fleming

How Rainbows Form

St. Patrick’s Day is a holiday often associated with images of rainbows promising a path to a leprechaun’s pot of gold. For most people, however, just spotting a rainbow is enough to brighten a day.

These amazing displays of nature form when raindrops, which act like prisms, scatter sunlight. To see one, an observer must be facing a moisture source like rain or mist with the sun at their back. The sun also needs to be at a low angle in the sky, less than 42° above the horizon. The lower the sun angle, the more of a rainbow’s arc will be visible.

Refraction and reflection inside a raindrop. Credit: Met Office

Passing from the air into a denser raindrop, the light slows and refracts. Since the different wavelengths of light bend by different amounts, the white light is dispersed into the colors of the visible spectrum: red, orange, yellow, green, blue, indigo, and violet. Red, which has a long wavelength, is refracted the least and is always on the top of a single rainbow. Violet, with a shorter wavelength, is refracted the most and is always on the bottom.

The light also needs to reflect off the back wall of the raindrop towards the viewer at the critical angle of 48° before it refracts again when it re-enters the air. A lesser angle will let the light pass through the raindrop and a larger angle will allow the light to reflect straight back out of the drop.

A double rainbow is seen when the light reflects twice inside the raindrop. Since each reflection weakens the intensity of the light, the second bow appears dimmer. The order of the colors is also reversed, with blue on top and red on the bottom.

Rainbow and faint second rainbow form after a rainstorm in Bermuda. Credit: Melissa Fleming

Powerful Nor’easter Slams NYC

A powerful nor’easter slammed the northeastern United States on Friday. Heavy precipitation, strong winds, and coastal flooding were reported across the region.

LGA airport. Credit: Chris Rudnick/Instagram

Here in New York City, 2.24 inches of rain fell in Central Park and wind gusts as high as 67mph were reported at JFK airport. These powerful winds canceled hundreds of flights, knocked down trees, and caused power outages in four of the city’s five boroughs. They also tore off a section of the roof of the American Airlines hangar at La Guardia airport and caused two tractor-trailers to flip over on the Verrazano Bridge.

Starting as an area of low pressure moving in from the west, this storm developed into a nor’easter over the Atlantic and then rapidly intensified. It underwent a process known as bombogenesis, the threshold for which is a drop in pressure of 24mb in 24 hours.This storm dropped 26mb in only 21 hours, producing its damaging winds.

Nor’easter of March 2, 2018. Credit: NOAA

From Snow to Ice, Winter Precipitation Can Take Several Forms

The winter season can produce various types of precipitation – rain, freezing rain, sleet, or snow. It depends on the temperature profile of the lower atmosphere.

All precipitation starts out as snow up in the clouds.  But, as it falls toward the Earth, it can pass through one or more layers of air with different temperatures.  When the snow passes through a thick layer of warm air – above 32°F – it melts into rain.  If the warm air layer extends all the way to the ground, rain will fall at the surface.  However, if there is a thin layer of cold air – below 32°F – near the ground, the rain becomes super-cooled and freezes upon impact with anything that has a temperature at or below 32°F.  This is known as freezing rain.  It is one of the most dangerous types of winter precipitation, as it forms a glaze of ice on almost everything it encounters, including roads, tree branches, and power lines.

Sleet is a frozen type precipitation that takes the form of ice-pellets. Passing through a thick layer of sub-freezing air near the surface, liquid raindrops are given enough time to re-freeze before reaching the ground. Sleet often bounces when it hits a surface, but does not stick to anything.  It can, however, accumulate.

Snow is another type of frozen precipitation.  It takes the shape of six-sided ice crystals, often called flakes.  Snow will fall at the surface when the air temperature is below freezing all the way from the cloud-level down to the ground.  In order for the snow to stick and accumulate, surface temperatures must also be at or below freezing.

When two or more of these precipitation types fall during a single storm, it is called a wintry mix.

Precipitation type depends on the temperature profile of the atmosphere. Credit: NOAA