Is this a nor'easter with a bomb cyclone? Here's what all those weather terms mean
A nor’easter. A blizzard. Flurries are expected. This storm is going to bomb out. This storm will go through bombogenesis. It’s winter, and with that comes the chance for snow. And with the chance of snow comes many different terms weather forecasters used to describe what is happening with each storm.
Meteorologists have their own language, technical words and phrases to describe a weather pattern or phenomenon. Winter storms seem to bring this to the forefront as artic clippers pull into the station with temperature inversion in tow.
But what exactly do all those weather terms mean? Let's break down some of the ones you are hearing this winter.
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What is a blizzard?
Blizzards are dangerous winter storms that are a combination of blowing snow and wind resulting in very low visibilities.
While heavy snowfalls and severe cold often accompany blizzards, they are not required. Sometimes strong winds pick up snow that has already fallen, creating a ground blizzard.
Officially, the National Weather Service defines a blizzard as a storm that contains large amounts of snow or blowing snow, with winds in excess of 35 mph and visibilities of less than 1/4 mile for an extended period of time (at least 3 hours).
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Causes of a blizzard
Blizzard conditions often develop on the northwest side of an intense storm system.
The difference between the lower pressure in the storm and the higher pressure to the west creates a tight pressure gradient, or difference in pressure between two locations, which in turn results in very strong winds. These strong winds pick up available snow from the ground, or blow any snow which is falling, creating very low visibilities and the potential for significant drifting of snow.
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Where did the term blizzard come from?
In the 1870s, an Iowa newspaper used the word "blizzard" to describe a snowstorm. Previously, the term blizzard referred to a canon shot or a volley of musket fire. By the 1880s, the use of the word blizzard was used by many across the United States and in England.
The upper Midwest and Great Plains of the United States tend to be the region that experiences blizzards most often.
With few trees or other obstructions to reduce wind and blowing snow, this part of the country is particularly vulnerable to blizzards. However, blizzards can occur in any location that has a climate that experiences snowfall.
Northern Arizona can experience blizzard conditions when a strong low pressure system moves across southern Arizona and high pressure builds strongly into the Great Basin. However, these conditions are rarely met due to the infrequency of strong low pressure systems moving through the state.
What makes a blizzard dangerous?
Blizzards can create life-threatening conditions. Traveling by automobile can become difficult or even impossible due to "whiteout" conditions and drifting snow. Whiteout conditions occur most often with major storms that produce a drier, more powdery snow.
In this situation, it doesn't even need to be snowing to produce whiteout conditions, as the snow which is already on the ground is blown around, reducing the visibility to near zero at times.
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The strong winds and cold temperatures accompanying blizzards can combine to create another danger. The wind chill factor is the amount of cooling one "feels" due to the combination of wind and temperature. During blizzards, with the combination of cold temperatures and strong winds, very low wind chill values can occur. It is not uncommon in the Midwest to have wind chills below -60F during blizzard conditions.
Blizzards also can cause a variety of other problems. Power outages can occur due to strong winds and heavy snow. Pipes can freeze and regular fuel sources may be cut off.
What does bombogenesis mean? What is a bomb cyclone?
Bombogenesis, a popular term used by meteorologists, occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars (a measurement for atmospheric pressure) over 24 hours.
This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone.
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What are flurries?
Snow flurries are intermittent light snowfall of short duration with no measurable accumulation.
What is a nor'easter?
A Nor’easter is a storm along the East Coast, so called because the winds over the coastal area are typically from the northeast. These storms may occur at any time of year but are most frequent and most violent between September and April.
Nor’easters usually develop between Georgia and New Jersey, within 100 miles east or west of the East Coast. These storms progress generally northeastward and typically reach maximum intensity near New England.
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A nor'easter can bring heavy rain or snow, as well as winds of gale force, rough seas, and, occasionally, coastal flooding to the affected regions.
During winter, the polar jet stream brings cold Arctic air across the plains of Canada and the United States, then eastward toward the East Coast.
There it meets warm air from the Gulf of Mexico. The warm waters of the Gulf Stream helps warm the cold winter air over the water. This difference in temperature between the warm air over the water and cold Arctic air over the land is the fuel that feeds nor’easters.
What causes thundersnow?
Simply put, thundersnow is a thunderstorm that produces snow instead of rain.
But why does it do that?
According to USA Today, thunder and lightning are much more common in warm-season storms because of convection, the upward motion of air that helps produce thunderstorms. It's fairly rare to have convection within a winter storm.
Thundersnow forms when temperature and moisture conditions are just right – a mass of cold on top of warm air, plus moist air closer to the ground.
During a winter storm, snowflakes and sleet pellets high in the clouds can collide. Those collisions create the same static charges as in a summer thunderstorm. With enough static charge, lightning is created, and thunder naturally follows.
What does the meteorologist mean by heavy snow?
In New England, heavy snow is defined by the National Weather Services as snow accumulating to at least 6 inches in 12 hours.
What does wind chill really mean?
Wind chill takes into account the combined effect of lowering temperatures and the rate of heat loss from a human body, caused by the wind. Think of it like blowing on a hot cup of tea to cool it down. The more cool air that passes over the hot liquid, the faster the tea cools.
Meteorologists use a mathematical formula involving the speed of the wind and the actual temperature to determine who cold it actually "feels."
How to accurately measure snow
You will need a flat surface that does not produce heat and a ruler.
Take your measurements at a location where drifting does not usually occur. If you have snow drifts, then simply take measurements in several spots away from large drifts. Calculate the average of these measurements. Spots sheltered from the weather, such as those close to buildings or under trees, should be avoided.
Placing a snow board at a designated spot is the easiest way to measure snow. A snow board can be any light color board (roughly 2 feet by 2 feet) that is flat and placed on the ground or on top of newly fallen snow. Mark the location of the board with a flag or stake.
Push the ruler straight into the snow, perpendicular to the ground, until the ruler reaches the flat surface.
Record the measurement to the nearest tenth of an inch; e.g. 3.5 inches. Keep track of all your measurements for the duration of the storm to determine the storm total amount.
After you record the measurement, clear off the snow board (then place it on top of the snow), or whatever surface you have used, so it is ready for more snow!
And don’t forget to get your snow blowers ready, get your shovels out and make sure to charge all your devices! After all, it is winter! Be aware and stay safe.
This article originally appeared on The Providence Journal: Nor'easter, bomb cyclone, blizzard: What winter weather terms mean
