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Winter Weather Awareness Week October 18, 2010

Posted by mikeheard in Uncategorized.
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Staying Aware of the Weather

Hazardous Weather Outlook: Winter storm conditions are possible in the next 7 days. Stay tuned to the National Weather Service and local media for updates.

Watch: The potential exists for hazardous winter weather to occur within the next 12 to 48 hours but the exact location and timing is not known. Actions can be taken to stock up on needed supplies such as water and food and to make sure you have a plan to protect pets and livestock.

Warning: Hazardous winter weather either is occurring or will be shortly. Immediate action should be taken to protect yourself as well as your pets and livestock. Only travel outside of your home if you absolutely have to.

Advisory: Winter weather conditions are expected to cause significant inconveniences and may be hazardous. If you are cautious, these situations should not be life threatening.

Stay tuned to these products throughout the winter storm for specific details on impacts expected.

Terminology

Blizzard: Winds of 35 mph or more with snow and blowing snow reducing visibility to less than 1/4 mile for at least 3 hours.

Winter Storm: A variety of winter conditions may be possible including heavy snow, blizzard conditions, significant accumulations of freezing rain or sleet and dangerous wind chills.

Wind Chill: A measure of how cold the atmosphere feels, taking not just actual temperature into account, but also wind, which can make the air considerably colder.

Ice Storm: A type of winter storm characterized by significant amounts of freezing rain. Heavy accumulations of ice can bring down trees and topple utility poles.

 

The following table outlines specific guidance our meteorologists in Montana use for issuing various winter weather bulletins.

Winter Weather
Watches
Criteria / Definition
Winter Storm Watch Conditions are favorable for hazardous winter weather conditions including heavy snow, blizzard conditions, or significant accumulations of freezing rain or sleet in the next 12 to 48 hours. It may also include wind chills if they are expected with the above listed events.
Blizzard Watch Conditions are favorable for blizzard conditions in the next 12 to 48 hours.
Wind Chill Watch Conditions are favorable for dangerous wind chills in the next 12 to 48 hours.
Winter Weather
Warnings
Criteria / Definition
Winter Storm Warning Any one or a combination of the following (the elevations are generalized in this criteria, some areas may have more specific criteria):
Eastern Montana and Western Montana Valleys: 6 inches or more in 12 hours or 8 inches or more in 24 hours.
Mountain Areas: 8 inches or more in 12 hours, 12 inches or more in 24 hours. Sustained winds of less than 34 mph causing blowing snow (with or without snowfall occurring) reducing visibility to more than a ¼ mile for 3 hours or more.
-Ice accumulations under a ¼” that last for three hours or more and occurs on 50% of a significant public use area on roadways and sidewalks.
-Sleet accumulations of a ½” or more.
-Wind chills of ≤ -40 degrees (east of the divide) or ≤ -20 degrees (west of the divide) with winds of ≥ 10 mph occurring with any of the above criteria.
Blizzard Warning Sustained or frequent gusts of 35 mph or more, frequent visibilities of ≤ ¼ mile, falling and/or blowing snow for 3 hours or more.
Ice Storm Warning Issued when significant and damaging accumulations of ice are expected, generally a ¼” accumulation or more.
Wind Chill Warning East of the Divide: Wind chills of ≤ -40 degrees with winds ≥ 10 mph, no precipitation occurring.
West of the Divide: Wind chills of ≤ -20 degrees with winds ≥ 10 mph, no precipitation occurring.
Winter Weather
Advisories
Criteria / Definition
Winter Weather
Advisory
Any one or a combination of the following:
-2 to 5 inches of snow in 12 hours below 6000 feet. Some mountainous areas may have other criteria, generally 4-7 inches.
-Wind driven snow that occasionally reduces visibilities down to a ¼ mile.
-Wind chill advisory criteria along with 2-5 inches of snow and/or blowing snow reducing visibility down to a ¼ mile, or 4-7 inches of snow in mountainous areas.
-Sleet accumulations of less than a ½”.
-An event that transitions to or from freezing rain into any of the above criteria.
Wind Chill Advisory East of the Divide: Wind chills of -20 degrees to -39 degrees with winds of ≥ 10 mph, no precipitation occurring.
West of the Divide: Wind chills of -10 degrees to -19 degrees with winds of ≥ 10 mph, no precipitation occurring.
Freezing Rain
Advisory
Glazing of freezing drizzle or freezing rain for a few hours with accumulations of less than ¼ inch. It generally covers less than 50% of the area.

Winter Storm
Photo Courtesy of Carter County – Highway 7 – Carter County, January 24, 2010.

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