Feb 3, 2020

Winter Weather Words

The National Weather Service defines a blizzard as having strong winds greater than 35 mph, combined with heavy or blowing snow to produce "very poor visibility." Visibility needs to be under a quarter-mile to qualify as a blizzard.
The swirling storms that typically bring heavy snow, rain, and coastal flooding to areas in the Northeast are known as "Nor'easters." The storms moving up the East Coast of the U.S. received their name, because their winds typically blow from the northeast, even though the storm is moving from southeast to northeast. That is because the winds are moving in a counter-clockwise around the area of low pressure.

Winter storms that strengthen rapidly, including nor'easters, are dubbed "bomb cyclones." The term “bombogenesis” comes from mid-latitude storms that intensify rapidly, dropping 24 millibars (atmospheric pressure) over a 24-hour span, according to the National Oceanic and Atmospheric Administration (NOAA). A typical range in millibar change is around 10 to 15 in 24 hours. A bombogenesis storm can be tropical or non-tropical. “The term bombogenesis comes from the merging of two words: bomb and cyclogenesis. All storms are cyclones, and genesis means the creation or beginning.

Sleet is known as a combination of a snowflake and water that is frozen, according to forecasters. One of the types of precipitation people commonly describe as "hail" is actually sleet. Sleet is ice pellets or granulates of frozen rain, and occurs when rain falls through air with temperatures below freezing, according to the NWS. While the raindrop is falling, if it goes through above-freezing air, it turns back into liquid-- until it refreezes before hitting the ground.

Freezing rain is defined as rain that falls and lands on a surface with a temperature that is below freezing, causing it to freeze on contact. The rain that falls and freezes eventually forms a coating of ice or glaze that can make walking or driving extremely difficult. A freeze may or may not be accompanied by a frost, which is the formation of ice crystals that develop when dew gathers in temperatures of at least 32 degrees.
A flash freeze occurs when temperatures drop quickly below 32 degrees and cause a rapid freeze.
When there is a flash freeze, water on untreated surfaces can form "black ice." If the water present is very thin and on a surface such as black asphalt, it can be difficult to see. It can be extremely dangerous and very slippery.

The NWS counts snow showers as snow falling with varying intensity over brief periods, possibly accumulating. Snow squalls, however, are more intense snow showers and the most common. Brief, intense weather is typically accompanied by strong, gusty winds and may produce significant accumulations.

In addition to temperatures on a thermometer, "wind chill" tells us how it feels outside. The NWS defines a wind chill index as the apparent temperature, plus the effect of falling temperatures and the rate of heat loss from a human body, caused by the wind.

"As the wind increases, heat is carried away from a person's body at a more accelerated rate, driving down the body temperature," according to the NWS. The only effect wind chill has on inanimate objects, such as car radiators and water pipes, is to more quickly cool the object to the current air temperature. The object will not cool below the actual air temperature.

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