Winter storms normally bring ordinary rain, freezing rain and sleet as well as snow. All extratropical storms are a mixture of warm and cold air. In parts of the storm, especially the areas ahead of a warm front, warm air is flowing over cold air near the ground. The result is a layer of air that's above 32 degrees Fahrenheit between a layer of colder air near the ground and a layer of colder air higher up.
Precipitation that begins as snow in the higher level of colder air melts into rain in the layer of air that's above the melting point of ice - 32 degrees F. In places where the warmer air extends to the ground, the precipitation will fall as rain. If the layer of cold air near the ground is relatively thin and if things on the ground are below 32 degrees, the falling rain cools below 32 degrees but doesn't turn into ice until it hits something - this is freezing rain.
When the layer of cold air is thick enough, the falling rain freezes into ice pellets, which are generally called "sleet." In places where there is no layer of warm air, the snow falls all of the way to the ground as snow. Often, rain, freezing, rain and snow fall on the same places as a storm moves by.
Here are some of the weather statements that NWS may issue leading up to a winter event.
Winter Storm Watch -- a significant winter weather (ie. heavy snow, heavy sleet, significant freezing rain, or a combination of events) is expected, but not imminent, for the watch area; provides 12 to 36 hours notice of the possibility of severe winter weather.
Winter Storm Warning -- a significant winter storm or hazardous winter weather is occurring, imminent, or likely, and is a threat to life and property.
Blizzard Warning -- winds that are at least 35 mph or greater, blowing snow that will frequently reduce visibility to 1/4 mile or less for a duration of at least 3 hours, and dangerous wind chills are expected in the warning area.
Winter Weather Advisory -- when a significant winter storm or hazardous winter weather is occurring, imminent, and is an inconvenience.
Rapid snow melt and rain can cause ice on frozen streams and rivers to break into chunks and form ice jams. Ice jams often cause flooding as rivers are forced out of their banks.
On average, Southern New Hampshire receives between 60 to 100 inches of snow every year. The Northern part of the state receives over 100 inches of snow on average.
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