...WINTER INFORMATION WEEK 2008: NOVEMBER 17TH THROUGH NOVEMBER 21ST...

The National Weather Service will feature a different educational topic each week day during winter information week.

TODAYS TOPIC: NATIONAL WEATHER SERVICE WINTER FORECAST TERMINOLOGY.

FREEZING RAIN: rain that freezes upon contact with a cold surface.

SLEET: Solid grains of ice that form from rain that freezes before reaching the ground. These pellets of ice tend to bounce upon contact and may accumulate enough to cover the ground...even to a depth of several inches.

SNOW SQUALL: An intense fall of accumulating snow...reducing visibility significantly and often accompanied by increased winds.

HEAVY SNOW: 8 inches or more of snow in 24 hours across Pennsylvania for widespread snow and 6 inches in 12 hours for lake effect snow.

Just as with summer weather...the national weather service issues a Watch to alert the public of the potential for severe winter weather.

A WINTER STORM WATCH means conditions exist for the possible occurrence of severe winter weather such as blizzard conditions...heavy snow... significant freezing rain or heavy sleet. A Watch is usually issued 24 to 48 hours in advance of the winter storm.

A WINTER STORM WARNING is issued when heavy snow...significant freezing rain...or heavy sleet is expected to occur. Usually issued 6 to 18 hours in advance of the storm. Normally a Warning is issued after a winter storm watch has been in effect. If a winter storm develops quickly then the Warning may not have been preceded by a Watch.

A BLIZZARD WARNING is issued when sustained or gusty winds of 35 mph or more are expected to reduce visibility at or below a quarter of a mile due to falling or blowing snow for at least three hours.

WIND CHILL WARNINGS are issued for wind chills below -25 degrees Fahrenheit.

A less severe winter weather event will prompt the issuance of an ADVISORY. An Advisory is named specific to the weather event expected and issued when the event is expected to be widespread.

Travel by foot or vehicle may be dangerous during an Advisory even if the winter weather is not expected to reach winter storm criteria. Some examples of advisories:

WINTER WEATHER ADVISORY for snow means snowfall within 12 hours an average of 3 inches or more of snow is expected in central Pennsylvania.

WINTER WEATHER ADVISORY FOR FREEZING RAIN means a glaze of ice expected from
Freezing rain that will hamper travel is expected to occur.

WIND CHILL ADVISORY means wind chill temperatures are expected to be around 15 below zero for an extended time.

DENSE FOG ADVISORY is issued when dense fog is forecast to form that reduces visibility to less than one quarter of a mile.

WINTER WEATHER ADVISORY is issued when two or more of the above advisory conditions are expected.

Knowing winter weather terms provides you with useful information for planning and safety purposes.