Snow, Ice, Avalanche and Blizzards are the most common of Winter's many hazards.
Winter storms are a frequent occurence across the Pacific Northwest. Many of
these storms bring snow amounts that cause road closures, especially through the
mountain passes. Wind, in combination with the snow, can cause reduced visibility
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 black ice. In some valleys, cool air trapped near
the surface remains below freezing, while warmer air aloft drops rain through
the sub-freezing air, causing glaze ice or freezing rain.
All of these hazards are forecast ahead of time by your local National Weather
Service forecast office. Winter storm watches are generally issued 1 to 3 days
prior to the storm's arrival. Winter storm warnings and ice storm warnings
are issued within a day and sometimes two days's warning.
1) Winter Storm Warning...issued when any combination of freezing
rain, sleet, wind and/or heavy snow occurs over an area that is expected to cause
significant widespread damage. Snow amounts required for winter storm warnings
vary, given the terrain and location. For low lying areas, which normally receive
very little snow, only 2 to 4 inches of snow is required for a winter storm warning.
On the other hand in mountainous areas, where nearly every storm brings at least
6 inches of snow, 8 to 10 inches (or more) of snow is required for a warning.
A winter storm warning means that road crews will have difficulty keeping roads
open and snow free, making travel difficult at best, and impossible at worst.
2) Blizzard Warning... is normally associated with severe
winter weather in the northern plains where strong northwest winds bring snow and
frigid temperatures. While rather common for the plains states, blizzard or near
blizzard conditions can occur in the Pacific Northwest. The National Weather
Service defines a blizzard as a combination of wind that is 35 mph or stronger
accompanied by snow with visibilities frequently below one-quarter of a mile.
3) Ice Storm Warning... in the Pacific Northwest are infrequent,
but can be extremely dangerous. Across interior locations, 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 contact with objects. These conditions cause trees to snap, power
lines to fall, and make roads nearly impossible to navigate.
4) Avalanche Warnings...
Avalanche Warnings are issued by the Northwest Avalanche Forecast Center, located
in Seattle. These products are issued when there is a significant threat of
avalanches in the Cascades and Olympics backcountry, possibly affecting mountain
roadways and other high country interests. Also, see the
NW Avalanche Center's website.
Thousands of avalanches occur each year in the mountains of the Pacific Northwest. With the popularity of winter sports, avalanches pose a great risk to skiers, hikers and snowmobilers. The risk is very real, as people die each year when sudden avalanches bury them. Avalanches can happen anywhere the slope is steep enough and has a heavy load of snow. They 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 the valleys away from avalanches chutes, in stands of dense trees, or on gentle slopes, you can minimize your risk to avalanches.
…AVALANCHE SAFETY RULES…
1) 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 April or May.
2) 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 occurs.
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.
Additional Links of Interest...
Remember, in times of hazardous winter weather, you can get all these vital NOAA/National Weather Service messages via NOAA Weather Radio, your favorite
local media, or through NOAA's National Weather Service websites.
- 1996 Flood Summary of Northwest Oregon/SW Washington
- Top 10 Weather Events of the 1900s for Oregon
- Top 10 Weather Events of the 1900s for Washington
- Each local office may have other historical data and photographs online (see office links below)
For questions about local Winter Weather Preparedness, contact your local NOAA National Weather Service Office: