Tag Archives: snow

NYC Monthly Summary: March 2013

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March roared like a lion in New York City this year, with cold and blustery conditions dominating the month. With all but ten days posting cooler than normal readings, the city’s average monthly temperature only reached 40.1°F.  That is 1.9°F below normal. In fact, this was the first March in twelve years that we did not have a single day break the 60°F mark. This was a huge departure from last March, which was the second warmest March on record for the Big Apple.

In terms of precipitation, snowfall was abundant.  March usually brings the city 3.6 inches of snow, but this year we saw 7.3 inches accumulate in Central Park.  Rainfall, however, was scarce.  The city only collected 2.90 inches, which is 1.46 inches below normal.

March2013Graph Credit: The Weather Gamut

Spring Chill for Much of the U.S.

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We are one week into  the new spring season and winter-like conditions are lingering across much of the United States.

With the polar jet stream plunging down from Canada, cold air continues to blast a large portion of this country.  Unseasonably cool temperatures have even been reported as far south as Florida.  These widespread chilly conditions, in turn, are supporting an extensive national snow cover.  According to NOAA, 48.7% of the continental U.S. is currently under a blanket of snow.  That is the largest area of coverage – for this point in the season – in ten years.

Snow_Cover 3.25.13

National Snow Cover on 3-25-2013.

Image Credit: NOAA

Winter 2013 Drought Update

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A plethora of winter storms have rolled across the continental U.S. this season, often producing impressive snow events.  Long-term drought, nonetheless, continues to plague many parts of the country.

According to the latest report from the US Drought Monitor, 51% of this nation is in some form of drought. While this number represents improvement for some areas, such as the southeast and mid-west, it is still bad news overall.  The heart of the drought remains in the High Plains, this nation’s agricultural breadbasket.  Conditions of moderate drought or worse cover 91% of the region with 24% suffering under exceptional drought, the worst possible category.

Experts say the High Plains require significant precipitation – at least 12 inches of rain or its snow equivalent – to quench the worst drought the area has seen in more than fifty years.

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Image Credit: U.S. Drought Monitor

A Taste of Spring in NYC

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A winter storm lingered over much of the northeast late last week.  In New York City, it deposited 4 inches of dense, wet snow in Central Park.  In the storm’s wake, however, Spring-like conditions swept across the area.

The city reached a high temperature of 55°F on Saturday and saw all of the recent snowfall melt away.  Only two days earlier, we had a high of 38°F.  Our normal high for this time of year is 47°F.

As pleasant as this spring preview has been for many winter-weary New Yorkers, forecasters expect to see cool conditions return by the end of the week.

The Difference Between Wet and Dry Snow

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A significant winter storm is expected to slam the northeastern United States tomorrow.  The type of snow it produces will depend on the temperature profile of the atmosphere.

Air temperatures hovering near the freezing point produce large, partially melted snowflakes – wet snow. This type of snow is very dense and good for making snow-people.  However, it is very heavy and difficult to shovel. Dry snow, on the other hand, is more powdery and does not pack as well.  It falls as numerous small flakes when the air temperature is below 28°F.

In terms of snow to liquid equivalency, the general rule of thumb is ten inches of snow melts into one inch of liquid water.  This ratio, however, tends to vary widely with different types of snow. For example, it can take as much as fifteen inches of dry, fluffy snow to yield one inch of liquid water, while only five inches of wet snow can do the same.

NYC Monthly Summary: February 2013

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February is usually New York City’s snowiest month, and this year it lived up to expectations.  We accumulated 12.2 inches in Central Park, which is 3.4 inches above average.  Most of this snow fell during the massive northeastern blizzard at the beginning of the month.  Rainfall was also abundant.  The city collected 4.25 inches, which is 1.16 inches above normal.

In terms of temperature, New York was fairly cold this February.   With eighteen out of twenty-eight days posting cooler than normal readings, the city’s average monthly temperature was only 33.9°F, which is 1.1°F below normal.  This was a significant departure from last February, which was the warmest February on record.

Feb2013Graph Credit: The Weather Gamut

 

Winter Weather and Climate Change

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Large snowstorms, like the recent northeastern Blizzard, can lead some people to question the existence of global warming. According to scientists, however, these intense snowstorms are actually signs of our changing climate.

Significant snow events require both a deep supply of moisture and freezing temperatures.  The cold temperature part of this equation is a natural part of the winter season, which is itself, a result of the tilt of the Earth’s axis.  Here in the northern hemisphere, winter means our half of the planet is tilted away from the sun and therefore receives the least amount of solar energy all year.

While global warming will not change the tilt of the Earth’s axis, it is affecting the moisture content of our atmosphere. Rising levels of greenhouse gases are warming the air, which in turn, allows it to hold more moisture.  As a result, storms are producing more intense precipitation, including heavier than normal snowfall when given the proper conditions.

As global temperatures rise, scientists say we should expect to see more large storms, but less snow overall in the winter season. The window for typical winter weather is also expected to shrink, as spring-like conditions continue to arrive earlier than in the past.

Blizzard of 2013

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A massive winter storm clobbered the northeastern Unites States overnight.  Snow accumulated from New Jersey to Maine with some areas collecting more than three feet.

This storm was a classic winter nor’easter.  It formed when two weather systems – one with cold air coming in from the west and the other with warm air approaching from the south – merged and moved up the coast.  The deep moisture content of this particular event, however, helped make it an exceptional snow maker. In producing both heavy snowfall and powerful winds, this storm brought travel of all kinds to a standstill across the region and caused widespread power outages.  Some communities also experienced coastal flooding.

In New York City, we received 11.4 inches of snow in Central Park.  While this was a minor accumulation compared to nearby cities and towns, it was the most snow the Big Apple has seen in two years.

The northeastern Blizzard of 2013, as seen from Space

The northeastern Blizzard of 2013, as seen from Space

Image Credit: NASA Earth Observatory

How Road Salt Works

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A major snowstorm is expected here in the northeast tomorrow.  In preparation, salt trucks have been out in force across the region.

Rock Salt – large pieces of NaCl – removes snow and ice from roads and walkways by lowering the freezing point of water.  Essentially, it melts frozen precipitation into a briny liquid and makes it harder to re-freeze, even if the air temperature is below freezing. In extremely cold conditions, however, when temperatures fall below 15°F, rock salt becomes less effective at de-icing surfaces.

While salting roads can help reduce traffic accidents, it does have negative environmental impacts. So, as with diet, it is best to use salt sparingly.

Winter Precipitation

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Snow is probably the most well known type of winter precipitation.  There are, however, several other forms in which precipitation can fall during the cold winter months.  It all 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 of at or below freezing.  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 comes in contact with, including roads, tree branches, and power lines.

Sleet is different than freezing rain – it is a frozen precipitation.  It falls at ground level in 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 any objects.  It can, however, accumulate.

Snow is another type of frozen precipitation.  It takes the shape of multi-sided ice crystals, often called flakes.  Snow will fall at the surface when air temperatures are 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 all 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.

Precipitation type depends on the temperature profile of the atmosphere.

Image Credit: NOAA