Tag Archives: winter

From Snow to Freezing Rain, Winter Precipitation Can Take Several Forms

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The winter season can produce various types of precipitation – rain, freezing rain, sleet, or snow. The form we see at the surface 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

There is No Such Thing as Bad Weather, Only Bad Clothing Choices

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There is an old Scandinavian saying: “There is no such thing as bad weather, only bad clothing choices.” While it can be applied to any season, it seems most relevant in winter.

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

Perihelion 2019: The Earth is Closest to the Sun Today

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The Earth reached its Perihelion today at 5:20 UTC, which is 12:20 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’s Perihelion and Aphelion. Credit: Time and Date.com

What is the Winter Solstice?

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Today is the December solstice, the first day of winter in the northern hemisphere. The new season officially begins at 22:23 UTC, which is 5:23 PM 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 southward 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.

Earth’s solstices and equinoxes. Image Credit: NASA

The Snowiest Places in the US

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Snow is a common occurrence during the winter months for many parts of the US. But, some places tend to get more than others. In fact, there are locations that see triple digit snow totals every year.

In the east, the Great Lakes region is well known for lake effect snow events. With moisture laden snow bands forming down-wind of the massive lakes, it is not uncommon for some communities to see more than 100 inches of snow each season.  For example, Syracuse, NY, on average, gets 123.8 inches of snow annually.

In the west, even more snow is par for the course in the Cascade Range of Washington state. The Paradise Ranger Station in Mount Rainier National Park holds the record for the greatest average annual snowfall in the US. At 5400 feet in elevation, they see 643 inches of snow (53.6 feet) each year.

Storm systems that move in from the Gulf of Alaska run into the Cascade Mountains and are forced upward. As they rise, the moisture in the air cools, condenses, and falls as precipitation. At lower elevations, it comes out as rain, but at higher elevations, where the air is colder, it falls as snow. Standing at 14,410 feet above sea level, Mount Rainier is the highest peak in the Cascades.

Mount Rainer National Park sees the highest average annual snowfall in the US. Credit: Hemmings

Weather Lingo: Lake Effect Snow

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Winter snowstorms have a variety of names, such as Nor’easters and Alberta Clippers. It all depends on where and how they develop. In the Great Lakes region of the US, the vast bodies of fresh water influence the weather and create something 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 nearby, others will only get a dusting. The shape of the lake and the prevailing wind direction help to determine 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 impressive depths of the Great Lakes allow them to remain unfrozen longer into the winter season than more shallow bodies of water. This combined with their massive surface area, 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

Earth Posts 11th Warmest Feb and 5th Warmest Dec-Feb Season on Record

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Our global temperature continued its upward trend last month. February 2018 marked not only the eleventh warmest February on record, but also closed out the planet’s fifth warmest December – February season.

According to the State of the Climate report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for February – over both land and sea surfaces – was 55.07°F, which is 1.17°F above the 20th-century average. This February also marked the 398th 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 December, January, and February – meteorological winter in the northern hemisphere – was also unusually warm. NOAA reports that Earth’s average temperature for the season was 1.31°F above the 20th century average of 53.8°F. That makes it the fifth warmest such period on record.

While heat dominated most of the planet this season, some places were particularly warm, including Alaska, northern Russia, and parts of the Middle East. Here in the contiguous US, this winter ranked among warmest third of the nation’s 124-year period of record.

These soaring temperatures are largely attributed to the long-term trend of human-caused climate change. In fact, La Niña conditions – the cool counterpart of El Niño – were present in the Pacific during all three months of the season.

Global temperature records date back to 1880.

The Dec 2017- Feb 2018 season was the planet’s 5th warmest on record. Credit: NOAA

Why Are We Seeing So Many Nor’easters?

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The east coast of the United States has been slammed with three nor’easters in just eleven days – March 2, March 7, and March 13. The reason for this barrage of storms involves something called the North Atlantic Oscillation (NAO).

Based in the North Atlantic Ocean, this weather pattern is driven by the pressure differences between the semi-permanent Icelandic Low and Azores/Bermuda High. When the pressure difference between these two systems is low, the NAO is said to be in a negative phase. This means the winds of the jet stream are relatively relaxed and cold air from the north can spill down into the eastern US. The positive phase of NAO is characterized by a strong pressure difference between the two areas and a robust jet stream that keeps cold air bottled up in the northern latitudes.

Three nor’easters in eleven days. Credit: NOAA

Fluctuating between positive and negative, the strength and duration of these phases vary. Since late February, however, a strong negative phase has been locked in place. With an area of high pressure over Greenland, the jet stream is blocked and therefore dipping southward over the eastern US. As the jet stream is essentially a storm track, this pattern has allowed areas of low pressure to be steered over the warm waters of the Gulf Stream off the eastern seaboard, where they have intensified into nor’easters.

In terms of climate change, the connection between the warming Arctic and the storm track across the mid-latitudes is an active area of research. Sea level rise, however, is clearly amplifying the coastal flooding associated with these powerful storms.

NAO Patterns. Credit: NOAA

Second Nor’easter in Less Than a Week for NYC

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For the second time in less than a week, a nor’easter slammed New York City.

The storm intensified quickly and brought heavy snow, strong winds, and even thundersnow to the area. It downed trees and caused a number of travel disruptions, including nearly 2000 flight cancelations and the temporary suspension of all NYC Ferry service.

While the snow fell quickly, the surface temperature hovered just above freezing and did not allow much to accumulate. Only 3.2 inches of snow was reported in Central Park, according to the NWS. Areas north and west of the city received much higher storm totals.

GOES-16 image of nor’easter on March 7, 2018. Credit: NOAA

February 2018: Warmest on Record in NYC

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February 2018 was New York City’s warmest February on record. Its mean temperature of 42°F was a staggering 6.7°F above the long-term norm. The previous record of 41.6°F was set just last year in February 2017.

Overall, we had nineteen out of twenty-eight days that were warmer than normal. Five of those produced readings in the 60s and one even hit 78°F, marking the warmest February day ever recorded in NYC. A record warm minimum temperature was also set on February 21 when the city only cooled down to 55°F. The average low for that date is 30°F.

While a few warm days in February are not that uncommon, this extended pattern of sustained warmth was very unusual. Driven largely by a persistent ridge in the jet stream, warm southern air was funneled northward almost continuously throughout the month.

February is usually the city’s snowiest month on the calendar, but Central Park only received 4.9 inches of snow this year. That is 4.3 inches below normal. Of that total, 4.4 inches fell during a single, quick-hitting storm when the air was briefly cold enough to support frozen precipitation.

Rainfall, on the other hand, was abundant with seventeen days posting measurable precipitation. In total, Central Park reported 5.83 inches of rain. That is 2.74 inches above average.

New York City weather records date back to 1869.

February 2018 was the warmest February on record in NYC. Credit: The Weather Gamut