There is an old saying: “no two snowflakes are alike.” While that may well be true, their basic shapes are driven by temperature and atmospheric moisture content. Here is a look at their general categories.
Snowflake morphology diagram. Image Credit: Kenneth Libbrecht/CalTech
Another arctic outbreak has sent a large part of the US into a deep freeze. Across the East, temperatures tumbled this weekend with some places experiencing the coldest conditions they have seen in decades.
Here in New York City, the mercury fell to just 3°F in Central Park early Monday morning. That is the coldest temperature the city has seen in 11 years, but not quite a record. According to the NWS, the record low for the date was set in 1888 when the temperature was only 1°F. Our normal low for this time of year is 29°F.
Produced by a deep dip in the jet stream, our current frigid conditions will be staying in place for a while. In fact, a reinforcing shot of bitterly cold arctic air is expected to arrive in the region later this week. These types of temperatures can be life threatening, so remember to bundle up!
Frozen Fountain in NYC’s Bryant Park. Credit: FOX
Icicles are a classic symbol of cold winter weather. In order to form, however, they need a mix of both warm and cold conditions.
These hanging pieces of tapered ice develop when the air temperature is below freezing, but there is enough heat from the sun – or in the case of a building, a poorly insulated roof – to thaw some snow. As the melt water runs off the edge of a surface, it re-freezes in the cold air. Starting with only a few water droplets, an icicle can begin to form. Over time, as melt water continues to drip and re-freeze, an icicle gains both layers of thickness and length.
Often seen forming along the edge of roofs, icicles can also be found on tree branches, power lines, and rocks where water seeps out of the ground. The size and shape of an icicle, according to experts at the National Snow and Ice Data Center, depends on a few different factors. These include the shape of the surface on which it forms and the number of different directions from which melt water approaches the growing icicle.
Icicles can range in size from a few inches to tens of feet.
Icicles in the sunshine. Credit: MLE
January is typically the coldest month on the calendar for New York City and this year was no exception. We had nine days where the high temperature did not get above freezing and two overnight lows in the single digits. While there were also a few unseasonably warm days, the multiple bouts of extreme cold brought the city’s average monthly temperature down to 29.9°F. That is 2.7°F below normal.
On the precipitation side of things, the city had 11 days with measurable rainfall. In all, we received a remarkable 5.23 inches of rain, which is 1.58 inches above normal. Of this impressive total, 2.1 inches fell in a single day, January 18th, setting a new daily rainfall record for the date. Snow was also plentiful with 16.9 inches measured in Central Park. Most of this fell during a single storm – a clipper system that transitioned to a nor’easter – at the end of the month. On average, January usually brings the city a total of 7 inches of snow.
Credit: The Weather Gamut
Credit: The Weather Gamut
The “Dead of Winter” is an old saying that refers to the coldest part of the winter season. This annual chilly period, statistically, begins today.
While actual daily weather varies, historical average temperatures in most of North America reach their lowest point of the year between January 10th and February 10th. This cold period does not begin on the winter solstice, the day we receive the least amount of solar energy, because of a phenomenon known as seasonal temperature lag.
Air temperature depends on both the amount of heat received from the sun and the amount of heat lost or absorbed by the oceans and continents. From the start of winter through mid-February, both the oceans and land are losing more heat than they gain.
These few cold weeks are the climatological opposite of the “Dog Days of Summer.”
A massive arctic outbreak has sent most of the U.S. into a deep freeze. From the Mid-West to the Eastern Seaboard and down to the Gulf Coast, many cities are dealing with the coldest temperatures they have seen this season.
Here in New York City, the mercury fell to 8°F in Central Park this morning. Factoring in the wind chill, it felt like -8°F. Our normal low temperature for this time of year is 27°F.
As cold as it was today, it was not the coldest day the Big Apple has ever experienced. That dubious honor, according to the NWS, belongs to February 9, 1934, when the low temperature was a brutal -15°F.
Produced by a deep dip in the jet stream, our current frigid conditions are expected to stick around through the weekend. Bundle up!
November 2014 was another rollercoaster of a month in New York City in terms of weather. We had highs ranging from a relatively balmy 69°F to a chilly 36°F. In the end though, with 17 out of 30 days posting below average readings, the cold won out. The extended cold snaps helped lower the city’s mean temperature to 45.3°F, which is 2.7°F below normal.
Precipitation this November was fairly abundant. NYC received 4.51 inches of rain, which is 0.49 inches above average. Most of this fell during two significant rain events that each produced more than an inch of rain in 24-hours. The city also saw its first measurable snowfall of the season with 0.2 inches accumulating in Central Park. Nonetheless, following a parched August and September, the city is still listed as “abnormally dry” on the latest report from the US Drought Monitor.
A relentless snowstorm buried the Buffalo area of western New York State with more than 5 feet of snow this week. Situated on the shore of Lake Erie, the impressive accumulation was the product of a meteorological phenomenon known as “Lake-Effect Snow.”
Lake-effect snowstorms, according to NOAA, develop when cold air blows across the warmer waters of a large unfrozen lake. The bottom layer of the air mass is warmed by the water and allows it to evaporate moisture, which forms clouds. When the air mass reaches the leeward side of the lake its temperature drops again, because the land is cooler than the water. This releases the water vapor as precipitation and enormous amounts of snow can accumulate. The effect is enhanced if the air is lifted upward by local topography.
With the clouds typically forming in bands, the snowfall is highly localized. Some places can see the snow come down at a rate of more than 5 inches per hour, while others will only get a dusting. The shape of the lake and the prevailing wind direction determines the size and orientation of these bands.
Fetch, the distance wind travels over a body of water, also plays a key role. A fetch of more than 60 miles is needed to produce lake effect snow. In general, the larger the fetch, the greater the amount of precipitation, as more moisture can be picked up by the moving air.
The massive surface area of the Great Lakes in the northern United States make them excellent producers of lake-effect snow. With northwesterly winds prevailing in the region, communities along the southeastern shores of the lakes are often referred to as being in the “Snowbelt.”
Credit: NOAA
An early season arctic blast has sent temperatures across most of this country plummeting well below average this week and brought last winter’s buzzword, the polar vortex, back into the spotlight. From advertisements for winter coats to social media hashtags for almost anything cold, this technical meteorological term is being widely misused.
A polar vortex, according to NOAA, is a massive and persistent high altitude low-pressure system present over both poles of this planet. Basically a whirlpool-like wind pattern, the northern hemisphere’s polar vortex is anchored above the Arctic. It, as a whole, does not move south over the US. That said, pieces of it can ocassionally meander southward and influence our weather via the position of the polar jet stream.
When the polar vortex is strong, the jet stream generally flows in a smooth circular pattern from west to east and bottles up the Arctic’s coldest air. When weak or displaced by an area of high pressure, the shape of the jet stream distorts into a wavy, more north to south pattern. This allows cold air influenced by the polar vortex to push southward. When this happens, it is called a polar outbreak.
This week’s unseasonably cold temperatures are the result of a large ridge in the jet stream to our west that was enhanced by former typhoon Nuri in the Pacific. It, in turn, has caused a sizable trough to develop east of the Rocky Mountains and allowed cold arctic air to flow deep into the US.
In the video below, Dr. Mark Serezze, Director of the National Snow and Ice Data Center, explains exactly what the polar vortex is, how it works, and how climate change may play a role in its future.
Video credit: EarthVisionTrust and YouTube
The official start of winter is more than a month away, but New York City is experiencing an early preview.
A deep dip in the jet stream has ushered in cold arctic air and sent local temperatures plummeting. After reaching an unseasonably warm high of 65°F on Wednesday, the high in Central Park today was only 42°F. That is a difference of 23°F in just 48 hours. The city’s normal high for this time of year is 54°F.
The cold air also helped produce the city’s first snowflakes of the season. While nothing accumulated on the ground, the National Weather Service reported a trace of snow in Central Park early Friday morning. A trace of snow is defined as less than 0.1 inches.
Unlike earlier cold snaps this season, these current chilly conditions are expected to linger for at least a week.