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In the wake of the strong Pacific weather system that swept through Western Washington Wednesday and Wednesday night, a much cooler and unsettled air mass will move onshore through the weekend with a mix of rain and snow showers, a threat of thunderstorms, and sun breaks.

Snow levels popped up near 4,000 feet on Wednesday.

Snow levels are set to plunge well below the passes Thursday and by Friday morning, around 500 feet. Lowland areas can once again expect spotty snow showers with accumulations primarily on grassy areas and rooftops.

February ends and March begins feeling more like the first half of January. Temperatures will remain several degrees below normal with low snow levels.

— NWS Seattle (@NWSSeattle)

The mountains are expected to pile up more snow with airflow from the west moving east into the terrain, rising and producing copious amounts of snow. One to three feet of new snow is anticipated by late Friday creating difficult driving conditions. Some higher elevations may get as much as four feet of new snow.

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All the new snow is great for skiers and snowboarders, as well as water managers. This year’s mountain snowpack has been well below average and this week’s snow surge is helping play some catch-up.

All the fresh new snow will pile up on the existing preserved snowpack, raising avalanche danger. In a coincidence, Friday, March 1 is when the deadliest avalanche in American history occurred near Stevens Pass back in 1910.

In the days leading up to that fateful and tragic day, a lot of snow fell in the region. On one day alone in late February, 11 feet of snow fell. Then the weather turned warmer with rain, adding more weight to all that fresh snow on the slopes.

Along the Great Northern Rail Line, snowplows could not keep up with all that heavy snowfall. Two trains both bound for Seattle from Spokane were trapped just beyond the west portal of the Stevens Pass rail tunnel at the depot town of Wellington.

Early in the morning of March 1, a thunderstorm unleashed a massive avalanche from the side of Windy Mountain, sending a wall of snow, half a mile long and a quarter mile wide, down the slopes. The avalanche plowed through the depot and swept the two trains 150 feet down the hill into the Tye River valley. Ninety-six people were killed and 23 survived.

More on Washington snow: Mountain snowpack sending major warnings about water supplies

Avalanches carry tremendous power. If you’re planning to venture into the mountains for fun in the snow, be fully aware of avalanche conditions before you go. Visit the for all the latest mountain and avalanche forecast conditions. Heed any avalanche warning information. In addition, be sure to use the buddy system and have all the appropriate avalanche gear when heading out into the backcountry.

Looking ahead to this weekend, the weather system responsible for the cool showery weather is expected to head east into the Rockies. As a result, the showery weather will tend to taper off with some sun breaks mixed in. Temperatures will remain cool with highs only in the 40s, and lows generally in the 30s.

Ted Buehner is the ³ÉÈËXÕ¾ Newsradio meteorologist. You can read more of Ted’s stories here and follow him on .