First Snow of the Season in NYC Breaks Several Records

New York City saw its first snow of the season on Thursday and it was one for the record books.

According to the NWS, 6.4 inches of snow was measured in Central Park, setting a new daily record for the date. The previous record of 1 inch had been in place since 1906. It was also the earliest 6-inch one-day snowfall on record for the city and the largest one-day November snowfall since 1882.

These superlatives came as a bit of a surprise. The forecast originally called for a wintry mix with only a dusting of snow at the onset. However, the temperature was colder than expected and the snow hung on longer. This was largely the result of an area of high pressure to the north being stronger than forecast and therefore able to funnel air toward the city that was colder than anticipated. Closer to home, evaporative cooling also played a part.  The air near the surface was very dry as the storm moved into the area. This allowed some of the snow to evaporate as it fell, cooling the air even further. As result, the change over to rain was delayed by several hours.

While pretty to see, the snow caused a number of problems around the city. Widespread travel delays and falling trees were reported across the five boroughs. As it is only mid-November, many of the trees still had their leaves. The combination of the heavy, wet, snow piling up on the foliage, weighing down the branches, and high winds was too much to bear for many trees, even the healthily ones. Many fell across streets and sidewalks as well as on top of parked cars. The city’s Parks Department has reported receiving over 2000 service requests for downed trees and dangling limbs.

This storm clearly outperformed expectations and caught the city off-guard. On average, New York City sees 0.3 inches of snow for the entire month of November.

Record breaking November snowfall topples trees in NYC. Credit: Melissa Fleming

Fall Foliage and Climate Change

Autumn is a season well known for its colorful foliage. Driven by the combination of sunlight, temperature, and precipitation, local displays vary from year to year. However, as the climate changes, so too will this familiar natural phenomenon.

As daylight hours decrease in the fall, there is less sunlight available to power photosynthesis – the chemical process that provides nutrients to trees by converting carbon dioxide and water into glucose, which is consumed by the tree and oxygen, which is released. This, in combination with falling temperatures, tells a tree to start preparing for winter.

To do this, a tree turns off its food producers by slowly corking the connection between leaf-stems and its branches.  This blocks the movement of sugars from the leaves to the tree as well as the flow of water from the roots to the leaves.  As a result, the leaves stop producing chlorophyll, the agent of photosynthesis and the reason for the green color of summer foliage.  As the green fades, other chemicals that have been present in the leaves all along begin to show.  These include xanthophyll and carotene, which produce yellow and orange leaves, respectively. Red to purplish colors are the result of anthocyanin, a chemical produced as a result any remaining sugars trapped in a leaf.

The change of leaf color happens every year, but the timing and duration of the displays are largely dependent on temperature and rainfall. Dry, sunny days and cool nights are the ideal recipe for beautiful fall foliage. Warmer and wetter conditions, on the other hand tend to delay the color change. However, extreme conditions, such as high heat, frost, excessive rain, or drought, can be a source of stress for trees and cause the colors to change early and the leaves to fall off faster.

As our climate changes, so too will displays of fall foliage. With warmer and wetter conditions forecast for the northeast, autumn colors are expected to peak later and disappear sooner. While there will still be variability from year to year, the fall foliage season in general is expected to get shorter. Furthermore, with the increasing probability of extreme weather events, such as storms with heavy rain, leaves could be swept from trees, effectively ending the season in a single day.

These changes will have more than an aesthetic affect. They are sure to have an impact on the multi-billion-dollar a year leaf-peeping ecotourism industry in several states.

Credit: Climate Central

NYC Monthly Weather Summary: October 2018

October had a split personality in New York City this year. It started off unseasonably warm, but then temperatures plunged dramatically in the middle of the month and remained mostly below average until Halloween. Highs ranged from a balmy 80°F to a brisk 50°F. But in the end, these extremes balanced each other out. The city’s mean temperature for the month was 57.7°F, which is only 0.8°F above average.

In terms of precipitation, the city was fairly dry. Overall, 3.59 inches of rain was measured in Central Park. Of this total, 35% fell in single day during the first nor’easter of the season. On average, the Big Apple gets 4.40 inches of rain for month. This October also marked first month since June that the city received below average rainfall.

Credit: The Weather Gamut

Weather Lingo: Indian Summer

Autumn is a season known for colorful leaves and falling temperatures. Every once in a while, however, summer warmth makes a resurgence. When this happens, it is often dubbed “Indian Summer”.

This weather phenomenon, according to the NWS glossary, is defined as “an unseasonably warm period near the middle of autumn, usually following a substantial period of cool weather.”  In the northeastern US, it is generally associated with an area of high pressure to the south that ushers warm air northward.

In popular use since the 18th century, the exact origins of the term are a bit foggy. One of the more reasonable explanations behind this unique phrase suggests a connection to when Native Americans began their hunting season, but no one knows for sure.

In other parts of the world, this summer-like weather goes by a variety of different names. In Europe, a number of countries associate the unusual warmth with the nearest saint’s day. It is known as “St. Luke’s Little Summer” if it develops in October or a “St. Martin’s Summer” if it occurs in November. In temperate parts of South America, it is simply known as “Veranico” (little summer).

The timing and intensity of these autumn warm spells vary from year to year. Nevertheless, when they do occur, they usually only last a few days. So, as we inevitably move toward winter, enjoy them while you can.

Fall foliage. Credit: Melissa Fleming

First Nor’easter of the Season Slams NYC

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

Fall Finally Arrives in NYC

After an unusually warm September and a rather balmy start to October, it finally felt like autumn in New York City this weekend.

According to the NWS, the temperature in Central Park only made it to 55°F on Saturday and 58°F on Sunday. The overnight lows were also rather chilly in the mid-40s. This was the coldest weather the city has seen since last spring. Its rather sudden arrival was a bit a jolt for many New Yorkers who had to scramble to find their jackets and sweaters that had been tucked away for months.

The average high and low for NYC at this time of year is 65°F and 51°F, respectively.

Credit: The Weather Gamut

Summerlike Heat in October for NYC

The calendar says October, but it still feels like summer in New York City.

The temperature in Central Park soared to an unusually balmy 80°F on Wednesday. While this did not break any records, the overnight low did.  The mercury only dropped to 71°F, setting a new record warm minimum temperature for the date. The previous record of 69°F had been in place since 1949.

It is also interesting to note that Wednesday’s low was warmer than the date’s normal high. The city’s average high and low temperatures for this time of year are 66°F and 52°F, respectively.

New record warm low temperature set in NYC. Credit: The Weather Gamut

September 2018: Unusually Warm And Wet in NYC

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.

What Causes the Autumnal Equinox

Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially begins at 9:54 PM Eastern Daylight Time.

The astronomical seasons, as opposed to the meteorological seasons,  are a product of Earth’s axial tilt – a 23.5° angle – and the movement of the planet around the sun. During the autumn months, the Earth’s axis is tilted neither toward nor away from the sun. This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across the sky has been sinking and daylight hours have been decreasing. Today, the sun appears directly overhead at the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

Transitioning from summer to winter, autumn is also a season of falling temperatures. According to NOAA, the average high temperature in most US cities drops about 10°F between September and October.

Earth’s solstices and equinoxes. Image Credit: NASA

How the Santa Ana Winds Help Wildfires Spread

The Santa Ana winds are notorious for exacerbating wildfires in southern California.

These strong winds blow warm, dry air across the region at different times of the year, but mainly occur in the late autumn. They form when a large pressure difference builds up between the Great Basin – a desert that covers most of Nevada and parts of Utah – and the coastal region around LA. This pressure gradient funnels air downhill and through the passes of the San Gabriel and San Bernardino mountains toward the Pacific. According to the NWS, the Santa Ana winds can easily exceed 40 mph.

Originating in the high desert, the air starts off cool and dry. But as it travels downslope, the air compresses and warms. In fact, it warms about 5°F for every 1000 feet it descends. This dries out the region’s vegetation, leaving it susceptible to any type of spark. The fast-moving winds then fan the flames of any wildfires that ignite.

The Santa Ana winds are named for Santa Ana Canyon in Orange County, CA.

Credit: NWS