National Weather Service / Idaho Bureau of Homeland Security
NEWS RELEASE
SEVERE WEATHER AWARENESS WEEK
Introduction to Severe Weather Awareness Week
Media contacts:
National Weather Service, Mr. Paul Flatt, (208) 334-9861
Idaho Bureau of Homeland Security, Lt. Col. Tim Marsano, (208) 422-5268
Topic for Wednesday, Oct. 6, 2004
Snow, Ice, Avalanche, Blizzards: The most common of winter’s many hazards
Winter storms are a frequent occurrence across the Pacific Northwest. Many of these storms bring snow amounts that cause road closures especially through mountain passes. Wind, in combination with the snow, can cause reduced visibilities and deep snow drifts. Along with the heavy snow comes an avalanche threat in areas of steep terrain. In valley locations, temperatures may be near freezing during the day but after the storm passes temperatures plummet causing wet roadways to become ribbons of ice. In some valleys, cool air trapped near the surface remains below freezing while warm air aloft drops rain through the sub freezing air causing freezing rain.
All of these hazards are forecast ahead of time by your local national weather service office. Winter storm watches are issued 1 to 2 days ahead of a storms arrival. Winter storm warnings, ice storm warnings, and heavy snow warnings are issued with a day and sometimes two days’ warning.
Winter Storm Warning:
Winter Storm Warnings are issued when any combination of freezing rain, sleet, wind, and snow occur over an area. When any one of the above elements strikes an area, a specific warning such as a Heavy Snow Warning or Freezing Rain Warning will be issued.
Heavy Snow Warning:
The amount of snow required for a warning to be issued varies by region and elevation. Low lying areas which normally receive little snow only require 2 to 4 inches for a warning. On the other hand, in mountainous areas where nearly every storm brings at least 6 inches of snow, a warning requires 8 to 10 inches or more. In general, a Heavy Snow Warning means that road crews will have some difficulty keeping roads open and snow free making travel difficult at best, and impossible at worst.
Blizzard Warnings:
The term Blizzard is normally associated with severe winter weather in the northern plains where northwest winds bring snow and frigid temperatures. While relatively common in the plains, blizzards or near blizzard conditions also happen in the Pacific Northwest. The National Weather Service defines a Blizzard as a combination of wind 35 mph or greater and snow with visibilities frequently below 1/4 mile.
Ice Storms:
Ice storms in the Pacific Northwest are an infrequent occurrence, but can be extremely damaging. Across interior locations of the Pacific Northwest, valley locations will have temperatures below freezing when a warm winter storm blows overhead. Rain falling out of the storm passes through the sub freezing air near the surface and freezes on everything. These conditions cause trees to snap, power lines to fall, and make roads nearly impossible to navigate.
Avalanche:
Thousands of avalanches occur each winter in the mountains of the Pacific Northwest. With the enormous popularity of winter sports, this poses a risk to skiers, hikers and snowmobilers. This risk is very real, each year people lose their lives when avalanches bury them. While thousands of avalanches occur in the back country, avalanches can happen anywhere the slope is steep enough with a heavy snow load. Avalanches typically occur during or just after snowstorms and most occur on a slope of 30 to 45 degrees. By waiting 36 hours after a big snowstorm you may allow the snow to settle. If you stay in valleys away from avalanche chutes, in stands of dense trees or on gentle slopes you can minimize your risk to avalanches.
Avalanche safety rules:
Never travel alone. Always have one or more companions. If you are alone and get trapped by an avalanche, you may not be found until spring.
If crossing a slope that may be prone to avalanches, do it one person at a time. You want to minimize the impact on your party if an avalanche is accidentally released.
When winter storms threaten, avoid travel if at all possible. Road crews work hard to keep roads open, stuck cars only make their job harder.
This week is Winter Weather Awareness Week. Now is the time to get prepared for winter weather. Public information statements will be issued throughout the week to give safety information, and help you know how to respond when winter weather threatens.
You may learn more from our internet preparedness web pages at
http://www.nws.noaa.gov/om/winter/index.shtml
http://www.nws.noaa.gov/om/severeweather/index.shtml
This message is brought to you by your local National Weather Service staff and the Idaho Bureau of Homeland Security.
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State of Idaho Military Division /
Idaho National Guard
Public Affairs Officer
208.422.5268
DSN 422.5268