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
Today is Groundhog Day, the midpoint of the winter season.
On this day, according to folklore, the weather conditions for the second half of winter can be predicted by the behavior of a prognosticating groundhog. If the groundhog sees its shadow after emerging from its burrow, there will be six more weeks of winter. If it does not see its shadow, then spring will arrive early.
The practice of using animal behavior to predict future weather conditions goes back to ancient times. The particular custom that we are familiar with in the United States grew out of the old world tradition of Candlemas that German settlers brought to Pennsylvania in the 1880s. Today, many communities across the U.S. and Canada continue this age-old ritual with their own special groundhogs.
The most famous of these furry forecasters is Punxsutawney Phil from Pennsylvania – he was portrayed in the 1993 film, “Groundhog Day”. Here in New York City, our local weather-groundhog is Charles G. Hogg. A resident of the Staten Island Zoo, he is more popularly known as “Staten Island Chuck”. This year, the two groundhogs had a difference of opinion. Phil predicts six more weeks of winter and Chuck is calling for an early spring.
But, shadow or no shadow, as the planet warms spring is trending earlier. Below is a look at the temperature trend during the six weeks following Groundhog Day since 1950 in New York City.
Spring is trending earlier as the planet warms. Credit: Climate Central
January was another month of wild temperature swings in New York City. It produced part of the city’s third longest sub-freezing cold streak on record and a significant January Thaw. Overall, highs ranged from a frigid 13°F to an unseasonably balmy 61°F. In the end, however, these extremes just about balanced each other out. The city’s mean temperature for the month was 31.7°F, which is only 0.9°F below normal.
In terms of precipitation, January was unusually dry. In all, the city received 2.18 inches of rain, which is 1.47 inches below average. Snowfall, on the other hand, was abundant with 11.2 inches measured in Central Park. Of this total, 9.8 inches fell during a single storm on January 4 and set a new daily snowfall record for the date. The city, on average, gets 7 inches of snow for the entire month of January. Nonetheless, NYC is listed as “abnormally dry” in the latest report (Feb 1) from the US Drought Monitor.
Credit: The Weather Gamut
Auroras occur throughout the year, but the long nights of winter at high latitudes provide an optimal environment in which to see this amazing natural phenomenon.
These colorful patterns of light that dance across the night sky are the result of charged particles from the sun interacting with the Earth’s atmosphere. Originating in a massive explosion on the sun known as a coronal mass ejection, the protons and electrons travel nearly 93 million miles before some of them reach the Earth. When they encounter the planet’s magnetic field, they are pulled toward the poles, where the magnetic force is strongest. There, they interact with atmospheric gases and produce the variety of colors we see. The main factor in which colors are displayed, however, is altitude. Different gases, such as nitrogen and oxygen, vary in concentration at different levels of the atmosphere.
Oxygen molecules can generate green auroras up to 150 miles above sea level and red auroras further up. Nitrogen molecules produce blue lights up to 60 miles above the ground and violet colored lights at higher levels. Auroras, in general, extend from 50 miles to as high as 400 miles above the Earth’s surface.
The word aurora is Latin for dawn. Therefore, the “aurora borealis”, the northern lights, means “dawn of the north”. At the South Pole, the lights are known as the “aurora australis”, which means “dawn of the south”.
Aurora Borealis over Alaska. Credit SmithsonianMag
The calendar says January, but it felt more like spring in New York City on Tuesday. The temperature soared to 60°F in Central Park, a staggering 22°F above average for this time of year and 2°F shy of the record high for the date.
This unseasonable warmth is part of the “January Thaw” currently taking place in a large part of the eastern United States. After an extended cold blast, this is a period when winter’s grip relaxes a bit and temperatures rise at least 10°F above normal for a few days. It does not necessarily occur every year, but when it does, it is usually in mid to late January, hence the name.
With temperatures in the 50s since Saturday, many New Yorkers have been out in the parks enjoying the break from the cold. It is, however, still January. So, keep your winter gear handy.
Melting ice on The Lake in Central Park, NYC. Credit: Melissa Fleming
January is usually the coldest month of the year – the so-called dead of winter. There are times during the month, however, when temperatures soar well above average. This is known as a “January Thaw”.
This type of weather phenomenon typically occurs after an extended cold blast and is marked by temperatures at least 10°F above normal for few days. It does not necessarily occur every year, but when it does, it is usually in mid to late January, hence the name.
Credit: Melissa Fleming
The extended cold wave that has been gripping New York City earned a place in the record books as it came to an end on Tuesday when the temperature climbed above freezing for the first time since Christmas.
Brutally cold temperatures dominated the end of 2017 and beginning of 2018 in NYC. Credit: Melissa Fleming
In all, the city experienced fourteen consecutive days with temperatures below 32°F. That, according to the NWS, is the third longest sub-freezing cold streak ever recorded in Central Park. The coldest day came on January 6, when the mercury only made it to 13°F. The wind chill made it feel even colder.
These unusually frigid conditions were the result of a deep dip in the jet stream and a lobe of the polar vortex reaching southward over much of the eastern US. While a brief warm-up is expected over the next few days, it is still January so keep those hats and gloves handy.
A massive winter storm – known by some as Grayson – slammed the eastern US on Thursday. Producing heavy snow and strong winds, its impact was felt from northern Florida to New England.
Here in NYC, the storm dumped 9.8 inches of snow in Central Park, setting a new daily snowfall record for the date. The previous record of 4 inches was in place since 1988. The city, on average, gets 7 inches of snow for the entire month of January.
Developing as a classic nor’easter, this storm became an over-achiever as it rapidly intensified over the warm waters of the Gulf Stream. It underwent a process called Bombogenesis, the threshold for which is a drop in pressure of 24mb in 24 hours. This storm dropped 59mb in 24 hours, producing very powerful winds. At JFK airport, wind gusts up to 55mph were reported.
The snow left behind by this storm will not be going anywhere anytime soon. A re-enforcing shot of cold arctic air moved in behind the storm and dangerously cold temperatures are expected to remain in place through the weekend. Bundle up!
The first big winter storm of 2018 brought NYC 9.8 inches of snow. Credit: Melissa Fleming
If you enjoy winter and a good snow day, here are some fun facts about snow to ponder when the flakes fall:
- All snowflakes, regardless of shape, have six sides.
- Snow crystals are translucent, not white. The white color we see is caused by sunlight that is reflected off the crystals.
- Most snowflakes fall at a speed of two to five feet per second. That is roughly the same speed as a person walking casually.
Enjoy the snow!
Snowflakes come in a variety of shapes, but all have six sides or points. Credit: Wilson “Snowflake” Bentley
The Earth reached its Perihelion today at 5:34 UTC, which is 12:34 AM Eastern Standard Time. This is the point in the planet’s orbit where it comes closest to the Sun.
This annual event is due to the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Perihelion differs from year to year, but it’s usually in early January – winter in the northern hemisphere. The Earth will be furthest from the Sun in July.
While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, the Earth is 147.1 million kilometers (91.4 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) closer than it will be in early July. This position allows the planet to speed up by about one-kilometer per second. As a result, winter in the northern hemisphere is about five days shorter than summer.
The word, perihelion, is Greek for “near sun”.
Earth is closest to the Sun during the northern hemisphere’s winter. Credit: TimeandDate.com