Severe Weather 101
Frequently Asked Questions About Winter Weather
- Can it ever be too cold to snow?
- It rarely snows when the temperature drops below zero degrees Fahrenheit because the atmosphere is too stable. One of the ingredients for snow is enough lifting of saturated air that snow can develop aloft and fall to reach the surface. When it is said, “it is too cold to snow,” in reality it means there is not enough lifting of air to cause snow to reach the surface. Even at very cold surface temperatures, significant snowfall can occur. Intense lifting can produce significant precipitation, even at very low temperatures. The temperature higher in the atmosphere can be much warmer than the air temperature at the surface, and that warm air aloft can hold more moist air than the colder air at the surface. And, moisture can be transferred into the area where lifting is occurring through advection (the horizontal movement of an air mass).
- What is thundersnow?
- Although thunderstorms are less common in the winter, sometimes lightning can occur within snowstorms and is called thundersnow. Thundersnow can be found where there is relatively strong instability and abundant moisture above the surface, such as above a warm front. Thundersnow is sometimes observed downstream of the Great Salt Lake and the Great Lakes during lake-effect snowstorms too.
- How many inches of snow equals one inch of rain?
- On average, thirteen inches of snow equals one inch of rain in the US, although this ratio can vary from two inches for sleet to nearly fifty inches for very dry, powdery snow under certain conditions.
- Is it true a person loses most of his body heat through his or her head?
- Yes, it's true. It is important to keep the head and neck covered and as warm as possible to delay or prevent hypothermia.
- What is a nor'easter?
- The official definition of a “Nor'easter” is a strong low pressure system that affects the Mid-Atlantic and New England states. It can form over the land of the eastern U.S. or over the Atlantic coastal waters. These winter events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor'easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas. What makes them so strong is the warm and moist air from the Atlantic that feeds the storm, causing it to grow explosively.
- What is white lightning?
- White lightning is a colloquial term for thunderstorms occurring with snow.
- Are microbursts or downbursts present in snow squalls?
- We have not heard of this happening. Evaporation of snow in such storms typically doesn't produce enough cooling to drive a downdraft circulation in the squall.
- What are the important winter weather notices?
- Blizzard Warning: Issued when winds of 35 mph or greater are combined with blowing and drifting snow with visibilities of ¼ mile or less. Seek indoor shelter immediately and stay indoors until the severe conditions end.
Winter Storm Warning: Issued when a combination of hazardous winter weather in the form of heavy snow, heavy freezing rain, or heavy sleet is imminent or occurring. Winter Storm Warnings are usually issued 12 to 24 hours before the event is expected to begin.
Winter Storm Watch: Issued 12-48 hours in advance of the onset of severe winter conditions. The watch may or may not be upgraded to a winter storm warning, depending on how the weather system moves or how it is developing.
Winter Storm Outlook: Issued prior to a Winter Storm Watch. The Outlook is given when forecasters believe winter storm conditions are possible and are usually issued 3 to 5 days in advance of a winter storm.
Winter Weather Advisories: Issued for accumulations of snow, freezing rain, freezing drizzle, and sleet which will cause significant inconveniences and, if caution is not exercised, could lead to life-threatening situations.
Lake Effect Snow Warning: Issued when heavy lake effect snow is imminent or occurring.
Lake Effect Snow Advisory: Issued when accumulation of lake effect snow will cause significant inconvenience.
Wind Chill Warning: Issued when wind chill temperatures are expected to be hazardous to life within several minutes of exposure.
Wind Chill Advisory: Issued for a wind chill situation that could cause significant inconveniences, but do not meet warning criteria. Criteria for issuing Windchill Warnings and Advisories are set locally.
Dense Fog Advisory: Issued when fog will reduce visibility to ¼ mile or less over a widespread area.
Snow Flurries: Light snow falling for short durations. No accumulation or light dusting is all that is expected.
Snow Showers: Snow falling at varying intensities for brief periods of time. Some accumulation is possible.
Blowing Snow: Wind-driven snow that reduces visibility and causes significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind.