Arctic Blast Brings Record Cold Temperatures to NYC

The calendar says November, but it felt more like January in New York City on Wednesday as a blast of frigid arctic air plunged into the region.

In Central Park, the temperature dropped to 25°F late Tuesday night and hit 23°F early Wednesday morning, setting new record lows for both dates. According to the NWS, the previous records of 26°F for November 12 and 24°F for November 13 were set in 1926 and 1986, respectively.

The high temperature on Wednesday only reached 34°F, which is 8°F colder than the normal low for this time of year. The average high for the city in mid-November is 55°F.

Produced by a deep dip in the jet stream, these unusually cold conditions are expected to hang around for a while. Temperatures are forecast to moderate slightly but still remain below average as we move into next week. Keep those hats and gloves handy!

Credit: The Weather Gamut

Weather Lingo: Blue Norther

Autumn is a transitional season when the heat of summer fades away and the chill of winter gradually returns. But, sometimes winter can be aggressive and show up overnight.

When this type of rapid temperature change happens, it is often called a Blue Norther. This is a fast-moving cold front marked by a quick and dramatic drop in temperature. A fall of 20 to 30 degrees in just a few minutes is not uncommon. They also usher in a dark blue sky and strong northerly winds. Hence, the name.

Blue Northers are most common in the central US, where there are few natural barriers to slow or block arctic air masses from moving south. They can occur throughout the year, but are most common between November and March.

One of the most famous examples of this weather phenomenon was the “Great Blue Norther” of November 11, 1911. As the front passed through the southern plains, temperatures dropped from highs in the 70s and 80s to the teens in just ten hours. In Oklahoma City, for example, the temperature reached a record high of 83°F in the afternoon and then plummeted to a record low of 17°F by midnight. Both records, according to the NWS, are still in place.

Twenty-four temperature changes from The Great Blue Norther of 1911. Credit: FOX

First Freeze of the 2019 Fall Season in NYC

After a warm start to autumn, Mother Nature brought New York City a winter preview on Friday.

According to the NWS, the temperature in Central Park dropped to 29°F late Friday night. That was the coldest air the city has seen since March and marks the first freeze of the season.

Compared to the above-average temperatures the city has been experiencing this season, this first nip of frosty air was a bit jarring for some people. But, mid-November is when the city usually sees its first freeze. The earliest 32°F reading on record came on October 19 twice, first in 1940 and then again in 1974. Our latest first freeze was on December 22, 1998.

Produced by a deep dip in the jet stream, these chilly conditions are expected to last for a day or two. Then, after a brief warm-up, another shot of arctic air is forecast to hit the city next week. Keep those coats and gloves handy!

Average Dates for First Frost. Credit: Cornell

How Climate Change is Impacting Fall Foliage

Colorful foliage is the hallmark of autumn, especially in the northeastern United States. As the season heats up, however, this familiar natural phenomenon is reflecting the impacts of our changing climate.

While decreasing sunlight hours is a key factor that signals the annual color change, the timing and duration of the displays are largely dependent on temperature and precipitation. Dry, sunny days and cool nights are the ideal conditions for beautiful fall foliage. But, as our climate changes, warmer and wetter conditions are becoming more common across the region.

In general, this means autumn colors are expected to peak later and disappear sooner. While there will still be variability from year to year, the fall foliage season, overall, is expected to get shorter. Furthermore, with the increasing probability of extreme weather events, such as heavy rainstorms, leaves could be swept from trees effectively ending the leaf-peeping season in a single day.

More than just an aesthetic detail, these changes are sure to have an impact on the multi-billion-dollar a year ecotourism industry in several states.

Credit: Climate Central

Why Leaves Change Color in the Autumn

Autumn is a season well known for its colorful foliage. The often-celebrated aesthetic displays, however, are actually part of a process that trees use to survive the winter.

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. This, in combination with falling temperatures, signals the tree to stop producing food and prepare for a period of dormancy, which is similar to hibernation.

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 of any remaining sugars trapped in a leaf.

While leaves change color every year, 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 dull and delay the color change. Extreme circumstances, such as frost or drought, can be a source of stress for trees and cause the leaves to fall off faster.

It should also be noted that different species of trees react to atmospheric conditions differently. Therefore, the more diverse a forest, the wider the range of colors in autumn.

Tree in Autumn. Credit: Melissa Fleming

October 2019: Unusually Warm and Wet in NYC

October was unusually warm in New York City this year. We had 19 out of 31 days post above-average readings with one day reaching a record-breaking 93°F. This unseasonable heat helped drive the city’s mean temperature for the month up to 59.9°F, which is 3°F above normal.

On the precipitation side of things, October was rather soggy. Overall, 15 days produced measurable rainfall that added up to 6.15 inches in Central Park. Of this total, more than half fell during just two storms. On average, the Big Apple gets 4.4 inches of rain for the month. It is also interesting to note that October marked the first month since July that the city received above-average rainfall.

Credit: The Weather Gamut

How Wildfires Get Named

Wildfires, like major storms, are named for ease of communication and historical reference. But unlike hurricane names which are chosen from a pre-determined list each season, wildfires are labeled on a rolling basis.

According to CalFire, a wildfire is named as soon as it is reported. The moniker is usually selected by the dispatcher who takes the call or the initial first responders on the scene. Driven largely by geography, the names reflect a landmark such as a canyon, creek, or road, near where the fire started. For the sake of simplicity, they often tend to be one word titles. Although efficient, this can lead to some ominous or misleading names such as the “Witch Fire” of 2007 in San Diego or the “Easy Fire” that is currently burning in Simi Valley, CA.

If a fire occurs repeatedly in the same place, it will get a name and number such as “Bear Fire 2” or “Canyon Fire 3”.

While this may seem like a free-wheeling way to do things, the National Interagency Fire Center offers guidelines for the best practices in naming a fire. They advise against using the names of people, companies, or private property. They also discourage the use of “deadman” in any fire name.

Regardless of how arbitrarily selected or innocuous a name may sound, fires will ultimately be remembered for the destruction they cause.

Kincade Fire 2019. Credit: KTVU

How the Santa Ana and Diablo Winds Help Wildfires Spread

The Diablo and Santa Ana winds are notorious for exacerbating wildfires in northern and southern California, respectively.

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 large desert that covers most of Nevada  – and the California coast. This pressure gradient funnels air downhill and through mountain canyons and passes toward the Pacific. Squeezing through these narrow spaces, the wind is forced to speed up. According to the NWS, they 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.

These infamous zephyrs are named for the places from which they tend to blow. The Santa Ana Winds are named for Santa Ana Canyon in Orange County. The Diablo Winds take their moniker from Mount Diablo, which sits northeast of San Francisco.

Credit: Insider Inc

Weather Report: Exploring the Atmosphere Through Art

The weather is a hot topic in the arts these days, moving from the background of landscape imagery to the main subject. This transition is the focus of the exhibition, Weather Report at The Aldrich Contemporary Art Museum in Ridgefield, CT.

Curated by Richard Klein, the exhibit features a wide array of artists influenced by the workings of our atmosphere. Some examples that stood out to me include Kim Keever’s “Clouds” that were created with various pigments in a tank of water and Sarah Bouchard’s “Weather Box”, which makes music from weather data. The sculptures of weather map graphics by Bigert and Bergström, a Swedish art duo, also caught my eye as they explore the way weather has influenced historical events. Overall, the exhibition aims to highlight the sky as a place where the aesthetic, the political, and the scientific co-exist and inform each other.

The show is on view through March 29, 2020. For more information, visit: http://aldrichart.org

Bigert and Bergström’s “The Russian Campaign, 1812.” Photo: Melissa Fleming

September 2019: Earth’s Warmest September on Record

Our global temperature continued its upward trend last month. September 2019 tied September 2015 as the warmest September ever recorded on this planet.

According to NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for the month – over both land and sea surfaces – was 60.71°F. That is 1.71°F above the 20th-century average. September also marked the 417th consecutive month with a global temperature above its long-term norm. That means the last time any month posted a below-average reading was December 1984.

Furthermore, the ten warmest Septembers have all occurred since 2005, with the last five years being the five warmest on record.

While heat dominated most of the planet this September, some places were particularly warm, including Alaska, the southeastern United States, and large parts of Asia and Canada. For the contiguous US as a whole, the month tied September 2015 as the second warmest September on record.

With ENSO neutral conditions prevailing in the Pacific, these soaring temperatures are largely attributed to the long-term trend of human-caused climate change. As greenhouse gases continue to spew into the atmosphere, global temperatures are expected to continue to rise.

Year to date, the first nine months of 2019 were the second warmest such period of any year on record. At this point, it is very likely that 2019 will finish among the top five warmest years on record. Global temperature records date back to 1880.

September 2019 was Earth’s warmest September on record. Credit: NOAA