Tag Archives: rain

From Snow to Freezing Rain, Winter Precipitation Can Take Several Forms

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The winter season can produce various types of precipitation – rain, freezing rain, sleet, or snow. The form we see at the surface 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

December 2018: Ninth Wettest on Record for NYC

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December 2018 felt like a weather roller coaster in New York City. Highs ranged from a relatively balmy 61°F to a chilly 36°F. But, with 17 out of 31 days posting above average readings, the warmth won out in the end. The city’s mean temperature for the month was 40.1°F, which is 2.6°F above average.

In terms of precipitation, December was a month for the record books. The city received 6.48 inches of rain in Central Park, tying December 1996 as the ninth wettest December on record. Three different days produced rainfall totals greater than one inch. The end of the month saw a soggy New Year’s Eve with 0.99 inches of rain. It was the first time in 24 years that it rained on the revelers at the Times Square ball drop festivities.

Snowfall, however, was scarce. Only a trace amount was reported for the month. New York City, on average, sees 4 inches of rain and 4.8 inches of snow in December.

2018: Not Yet Over, But Already Among the Top Ten Wettest in NYC

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The northeastern United States has been rather soggy this year. With more than two weeks still left in 2018, many locations have already posted their wettest years on record.

Here in New York City, we have received 59.68 inches of rain to date, which is 12.08 inches above average. That means 2018 now ranks among the top ten wettest years ever recorded in the Big Apple.

Much of this impressive, and still building, total came down during several heavy rain events over the course of the year. Each of these caused street and subway flooding around the five boroughs. For the northeast region as a whole, heavy precipitation events increased 55% between 1958 and 2016, according to the latest National Climate Assessment.

Scientists attribute the increase in both frequency and intensity of heavy rain events to climate change. 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 water vapor available in the air to condense and fall as precipitation.

Credit: Climate Matters

November 2018: Seventh Wettest and Fourth Snowiest on Record in NYC

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November was unusually cold in New York City this year. Highs ranged from a relatively balmy 72°F to a chilly 28°F. But, with 22 days posting below average readings, the cold won out in the end. The city’s mean temperature for the month was 44.5°F, which is 3.3°F below average.

In terms of precipitation, November was a month for the record books. The city received 7.62 inches of rain in Central Park, making it the seventh wettest November on record. Snowfall was also abundant, despite the fact that it all fell during a single storm. Central Park reported 6.4 inches of snow, setting set a new daily record for the date. It was also the earliest 6-inch one-day snowfall on record for the city and the largest one-day November snowfall since 1882. Moreover, that one snow event was enough to make this November the city’s fourth snowiest on record.

New York City, on average, sees 4.02 inches or rain and 0.3 inches of snow for the entire month of November.

 

Weather and Art: Rainworks

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Rainy days can sometimes make people feel sad or depressed. This is what inspired artist Peregrine Church to create Rainworks – artwork activated by rain. His goal, he says, is “to give people a reason to smile on a rainy day”.

Based in Seattle, a city known for precipitation, he uses a super-hydrophobic spray to create images and sayings on concrete surfaces that are only visible when wet. As concrete gets wet, it gets darker. However, the areas covered in the waterproof coating stay dry and therefore lighter in color. This contrast allows the images and sayings to be visible to passersby.

Essentially street art, his first piece in 2014 was written on a city sidewalk and said “Stay Dry Out There”. He was soon joined his friend by Xack Fischer in creating Rainworks across the Emerald City.

In 2016, they started selling their specially formulated spray online. They also offer tutorials on their website to help people create their own Rainworks around the world. The spray according to the artists, is eco-friendly and biodegrades over the course of 2 to 4 months.

To date, more than 200 Rainworks have been created across five continents. You can find their locations (and add your own) on the Rainworks map.

A Rainwork in Yokohama, Japan. Image Credit: Rainworks Gallery

First Nor’easter of the Season Slams NYC

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The first nor’easter of the season slammed the northeastern United States on Saturday. Heavy precipitation, strong winds, and coastal flooding were reported across the region.

Here in New York City, the storm dumped 1.34 inches of rain in Central Park. Its powerful winds knocked down trees and caused power outages around the city’s five boroughs. The storm also caused significant travel delays, including shutting down part of the FDR Drive because of flooding.

While nor’easters are not uncommon at this time of year, this one was interesting because it started off as a hurricane in the eastern Pacific. Hurricane Willa made landfall near Mazatlan, Mexico on Tuesday night and then moved inland toward Texas. From there, the storm’s remnants merged with a cold front and became re-energized. Traveling in the jet stream, it worked its way up the eastern seaboard and became a nor’easter.

First nor’easter of the season downed trees and branches in Queens. Credit: D. Herrick

September 2018: Unusually Warm And Wet in NYC

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September 2018 was another temperature roller coaster in New York City. Highs ranged from an unseasonably cool 62°F to a sizzling 93°F. However, with fifteen days posting above average temperatures, including three with readings in the 90s, the heat won out in the end. This warm finish was also aided by the unusually balmy overnight lows that were seen throughout most of the month. In fact, on September 5, the low only dropped to 77°F. That tied the record high minimum temperature for the date, which was set in 1985. In the end, the city’s mean temperature for the month was 70.7F°, which is 2.7°F above average.

In terms of precipitation, September was a soggy month in the Big Apple. In all, 6.19 inches of rain was measured in Central Park. Of this impressive total, 51% fell on just two days, each of which saw flash flooding around the five-boros. The city, on average, gets 4.28 inches of rain for the entire month.

Remnants of Hurricane Florence Soak NYC and Its Subways

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The remnants of Hurricane Florence swept through New York City on Tuesday. While significantly weaker when compared to its time over the Carolinas, the storm still made its presence known with strong thunderstorms and bands of torrential downpours.

According to the NWS, 1.19 inches of rain was measured in Central Park. As impressive as that total is, it did not break the daily rainfall record for the date. That honor belongs to September 18, 1936 when 3.92 inches of rain was reported. New York City, on average, gets 4.28 inches of rain for the entire month of September.

The heavy rain caused flash flooding on roadways and disrupted travel across the city. Impacts were also felt underground as torrents of water poured into several subway stations through leaks in the ceiling and down the entrance/exit steps. Even the city’s infamous rats were seen sheltering from the rushing water.

This type of heavy rain event, according to NOAA, is expected to become more common as global temperatures continue to rise.

Heavy rain created underground waterfalls at several NYC subway stations on Tuesday. Credit: R.Mondshein/Twitter

 

Hurricane Florence Swamps the Carolinas

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Hurricane Florence, the 6th named storm of the Atlantic Hurricane season, slammed North and South Carolina this weekend.

Steered across the Atlantic by a strong area of high pressure, Florence made landfall near Wrightsville Beach, NC on Friday morning as a category-1 storm.  It peaked at category-4 strength while still over the ocean, but weakened as it moved closer to the US coast.

Despite this downgrade, Florence still packed a powerful punch. Its strong winds, flooding rains, and storm surge forced people to evacuate their homes and caused significant property damage as well as widespread power outages across the region. In the hard hit city of New Bern, NC, at the mouth of the Neuse River, a storm surge of more than ten feet was reported. Local officials there say upward of 4000 homes and businesses were damaged or destroyed.

Moving as slowly as 2 mph at one point, Florence essentially stalled out over the region, allowing it to unleash massive amounts of precipitation. Preliminary reports show that the storm set new state records for rainfall from a single tropical cyclone in both North and South Carolina. In Elizabethtown, NC, 35.93 inches was reported, crushing the previous record of 24.06 inches set by Hurricane Floyd in 1999. In South Carolina, the town of Loris, about 25 miles north of Myrtle Beach, reported 23.63 inches of rain, eclipsing the old record of 17.45 inches set by Tropical Storm Beryl in 1994.

If these numbers are confirmed by the NWS, that would mean four state tropical cyclone rainfall records were broken in the last thirteen months. The other two being Texas with 60.58 inches of rain from Hurricane Harvey in August 2017 and Hawaii with 52.02 inches from Hurricane Lane just last month.

Measuring 400 miles wide, Florence’s successive bands of heavy rain also caused catastrophic inland flooding as several rivers in the region overflowed their banks and inundated communities. In Fayetteville, NC – nearly 100 miles from the coast – more than 15 inches of rain was reported as of Monday. The Cape Fear River, which runs through the city, is forecast to crest at 61.8 feet on Tuesday, which is more than 25 feet above flood stage.

The death toll from this storm currently stands at 20, with most fatalities being water related. Sadly, as the rivers across the area continue to rise, that number is expected to increase in the coming days.

Hurricane Florence off the coast of the Carolinas. Credit: NOAA

The Continental Divide Determines Where Rain Goes After it Hits the Ground

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Most people are familiar with the various types of precipitation that falls from the sky. However, have you ever wondered where all that water goes after it falls or melts? The answer is largely dependent on what side of the continental divide it landed.

A continental divide is a natural boundary that separates the river systems of a continent. They are usually tall mountain ranges that direct the flow of rivers and streams to different oceans. Essentially, any precipitation that falls or melts on one side will flow into one ocean basin and anything that falls or melts on the other side of the divide will flow into another basin.

Sign in Rocky Mountain National Park marks the location of the Continental Divide in CO. Credit: Melissa Fleming

Every continent has at least one and some have multiple. In the United States, the main divide is the Rocky Mountains. It is part of the Great Continental Divide of the Americas, which runs from western Alaska through the Andes Mountains in South America. It separates water that runs into the Atlantic Ocean from water that flows into the Arctic or Pacific Oceans.

In some cases, water finds its way into an endorheic basin with no outlet to an ocean.  Utah’s Great Salt Lake and Oregon’s Crater Lake are well known examples.  Here, the water re-enters the water cycle via evaporation. A small percentage of precipitating water also seeps into the ground where it replenishes soil moisture and underground aquifers. That said, the vast majority of water returns to the world’s oceans where it will eventually be evaporated and fall as precipitation again somewhere on the planet.

North America has several drainage divides, but the Great Divide (red) is the largest. Credit: ContinentalDivide.net