Monthly Archives: December 2017

The Chances for a White Christmas

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The Holidays are here and many people are dreaming of a White Christmas. The likelihood of seeing those dreams come true, however, is largely dependent on where you live.

According to NOAA, a White Christmas is defined as having at least one inch of snow on the ground on December 25th. In the US, the climatological probability of having snow for Christmas is greatest across the northern tier of the country. Moving south, average temperatures increase and the odds for snow steadily decrease.

Here in New York City, the historical chance of having a White Christmas is about 12%. This low probability is largely due to the city’s proximity to the Atlantic Ocean, which has a moderating influence on the temperature. This year, with an area of low-pressure developing off the coast and cold arctic air moving in from the northwest, snow is a possibility for the Big Apple. It all depends on the track of the low.  If it stays close to the coast, NYC will see rain or a wintry mix while inland areas will get snow. If the low moves further off-shore, the cold air will be able to push eastward and NYC will get snow for Christmas.

Snow or no snow, The Weather Gamut wishes you a very Happy Holiday!

The historical chances for a White Christmas across the continental US. Image Credit: NOAA

What the Winter Solstice Means

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Today is the December solstice, the first day of winter in the northern hemisphere. The new season officially begins at 16:28 UTC, which is 11:28 AM EST.

The astronomical seasons, which are different than meteorological seasons, are produced by the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the winter months, the northern half of the Earth is tilted away from the sun. This position means the northern hemisphere receives the sun’s energy at a less direct angle and brings us our coolest temperatures of the year.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across the sky has been dropping toward the southern horizon and daylight hours have been decreasing. Today, it will reach its southernmost position at the Tropic of Capricorn (23.5° south latitude), marking the shortest day of the year. This observable stop is where today’s event takes its name. Solstice is derived from the Latin words “sol” for sun and “sisto” for stop.

Soon, the sun will appear to move northward again and daylight hours will slowly start to increase. Marking this transition from darkness to light, the winter solstice has long been a cause for celebration across many cultures throughout human history.

Solstices and Equinoxes. Credit: NASA 

Planet Posts Fifth Warmest November and Fourth Warmest Autumn on Record

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Our global temperature continued its upward trend last month. November 2017 tied November 2016 as the fifth warmest November on record and closed out the planet’s fourth warmest September to November period, which is known as meteorological autumn in the northern hemisphere.

According to the State of the Climate report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for November – over both land and sea surfaces – was 56.55°F, which is 1.35°F above the 20th-century average. November also marked the 395th 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.

The three-month period of September, October, and November was also unusually warm. NOAA reports that Earth’s average temperature for the season was 1.35°F above the 20th century average of 57.1°F. That makes it the fourth warmest such period on record.

While heat dominated most of the planet this season, some places were particularly warm, including parts of southern North America and southern Asia. For the contiguous US as a whole, it was our tenth warmest autumn on record.

These soaring temperatures are largely attributed to the long-term trend of human-caused climate change. In fact, a weak La Niña – the cool counterpart of El Niño – developed in the tropical Pacific during October and prevailed in November.

Year to date, the first eleven months of 2017 were the third warmest such period of any year on record. With only one month left, 2017 is expected to end up among the top three warmest years ever recorded on this planet and become the warmest year without an El Niño. Global temperature records date back to 1880.

Credit: NOAA/NCEI

Weather Lingo: Alberta Clipper

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The winter season can produce a number of different types of storms. One of these is an Alberta Clipper.

These systems originate in western Canada, on the lee side of the Rocky Mountains. As  Pacific air spills downslope, an area of low pressure develops. From there, it gets caught up in the jet stream and moves to the southeast across the US. Traveling over land, these systems lack a significant source of moisture and generally do not produce much snow- usually around 1 to 3 inches. However, they are known for their strong winds and bitterly cold temperatures.

This type of quick-hitting storm takes its name not only from its place of origin near Alberta, Canada but also from the clipper ships of the 19th century – the fastest ships of the time.

Credit: NOAA

Dressing for Cold Weather

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When winter rolls around, I am often reminded of the old Scandinavian saying: “There is no such thing as bad weather, only bad clothing choices.”

Since the weather is going to do whatever it is going to do, it is important to be prepared for anything that Mother Nature throws your way. In winter, that means cold temperatures.

Extreme cold causes the body to lose heat faster than it can be generated. Prolonged exposure, according to the CDC, can cause serious health problems such as hypothermia and frostbite.

To stay safe this winter, remember to bundle up in layers and wear hats and gloves to minimize the loss of body heat.

Credit: NOAA

Report Finds Hurricane Harvey’s Record Rainfall Linked to Climate Change

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Hurricane Harvey – one of the big names of the 2017 Atlantic hurricane season – unleashed catastrophic flooding in southeast Texas at the end of August. Now, after months of reviewing the data, scientists say the storm was exacerbated by climate change.

According to a peer-reviewed report by World Weather Attribution (WWA), an international coalition of scientists, human-caused climate change made Harvey’s devastating rainfall three times more likely to occur and fifteen percent more intense. Using historical rainfall data and high-resolution climate models to compare conditions in a pre-warming world to those at the time of the storm, the WWA team was able to separate the climate signal from natural variability. They found that the deluge caused by Harvey would have been a 1-in-2400-year event in the absence of global warming, but is now a 1-in-800-year event and becoming more likely.

Heavy rainfall events, in general, are becoming more frequent in many different places, because as the atmosphere warms it can hold more moisture. In fact, it can hold four percent more moisture for every 1°F of warming. This means there is more water vapor available in the air that can fall as precipitation.

After rapidly intensifying in the Gulf of Mexico, Hurricane Harvey made landfall as a category-4 storm in the Texas Coastal Bend region on August 25. It then stalled over the area for several days, unleashing massive amounts of rainfall. Cedar Bayou, outside of Houston, reported a staggering 51.88 inches of rain, setting a new record for the continental US. The storm claimed the lives of 80 people and more than 120,000 residents across the area had to be rescued from their homes. The economic impacts of the deluge are still being tallied, but it is expected to be one of the most expensive in US history.

The WWA study only analyzed the impact of climate change on Harvey’s rainfall, not its role in the storm’s formation or strength.  Those connections remain an active area of research.

Climate change made Hurricane Harvey’s rainfall worse. Credit: Climate Central. (World Weather Attribution is led by Climate Central, a non-profit research group.)

First Snowfall of the Season in NYC

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New York City saw its first measurable snowfall of the 2017-2018 season on Saturday. According to the NWS, 4.6 inches of snow was measured in Central Park.

While not a blockbuster event, it was enough to leave the city looking like a winter wonderland. With all the holiday lights and decorations on display, the softly falling flakes added to the festive atmosphere.

The timing of this first snowfall was about normal for the Big Apple. On average, the first flakes of the season are seen by December 14. Our earliest first snow event on record was on October 21, 1952, and our latest was January 29,1973. New York City typically gets 25.3 inches of snow for the entire winter season.

First flakes of the season fly in NYC. Credit: Melissa Fleming

How the Santa Ana Winds Help Wildfires Spread

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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

The Supermoon and Other Moon Names

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The first and only supermoon of 2017 will rise on Sunday.

Supermoons are the result of the moon’s elliptical orbit around the Earth. They occur when the moon reaches perigee – its closest point to our planet (less than 223,694 miles). As it is so close, a supermoon looks 7% larger and 16% brighter than an average full moon. When seen near the horizon – where buildings or mountains provide a foreground – an illusion is created that makes the super moon look even bigger. They happen about every thirteen months or so.

When the moon is furthest from Earth – at apogee – it is called a micro-moon.

Full moons occur every 29.5 days when the moon is on the side of the Earth directly opposite the Sun. It reflects the sun’s rays and appears as a beautiful silver disk in the sky.

Ancient civilizations used full moons as a guide to schedule important activities, such as hunting and farming. They gave them each a name based on the dominant weather pattern or typical animal and plant activity during a particular month. In North America, according to National Geographic, native tribes used the moon names listed below. Many are still in use today.

  • January: Wolf Moon or Ice Moon
  • February: Snow Moon
  • March: Worm Moon or Sap Moon
  • April: Sprouting Grass Moon
  • May: Flower Moon
  • June: Strawberry Moon
  • July: Buck Moon
  • August: Sturgeon Moon or Grain Moon
  • September: Harvest Moon
  • October: Hunter’s Moon
  • November: Beaver Moon
  • December: Cold Moon or Long Night Moon

A blue moon is when a second full moon occurs in a single month. Given the uneven nature of our calendar system, these happen roughly every 2.5 years.

The apparent size of the moon as seen from Earth. Credit: KQED

Autumn 2017: Fourth Warmest in NYC

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The winter solstice is still a few weeks away, but meteorological Fall (September, October, and November) has officially ended and it was the fourth warmest on record in New York City.

The season, a transitional period between summer and winter, can often feel like a temperature roller coaster. This year, highs ranged from 91°F to 38°F. In the end, though, the warmth came out on top. The city’s average temperature for the three months was 60.4°F, which is 2.9°F above normal.

In all, fifty-nine days posted above-average readings and two of the season’s three months were warmer than their long-term norms. In fact, October 2017 was the city’s warmest October on record.  

This autumn was dominated by a pattern of warm spells separated by a few short-lived blasts of cold air. It was largely driven by the jet stream staying well to the north for most of the season with just a few dips southward.

The city’s warmest autumn on record, according to the NWS, occurred in 2015, which tied 1931 with an average temperature 61.8°F.  The coldest was 1871 when the three-month average was only  51.7°F.  Central Park weather records date back to 1869.

Credit: The Weather Gamut