The SI Weather
30Nov/12Fri

11:30 AM | West Coast onslaught continues

Discussion

The onslaught of Pacific Ocean moisture continues to pummel much of the west coast and this pattern will last right through early next week. A deep upper level trough of low pressure has stalled out over the northeastern Pacific Ocean sending wave after wave inland with an onshore flow of air that has its origins back over the tropical central Pacific. The next five days will likely see rainfall amounts range from 6 inches or more along the Pacific Northwest coast to 12 inches or more in northern California - and this is on top of any rainfall earlier this week. Topography plays a key role out west and given this particular pattern and wind flow, those mountains facing the south and west will get the highest rainfall (and snowfall) amounts over the next few days.

Speaking of snow, for now the snow levels are quite high given the mild nature of this Pacific Ocean air, but those critical levels may gradually lower later this weekend as colder air aloft increases with each passing disturbance. Despite the warm nature of the current air mass, some of the snowfall amounts will be quite incredible in the higher elevations of the northern Sierra and Cascades of Washington and Oregon. In the northern Sierra, the snow might be best measured by the yard stick by early next week with 3 or 4 yards expected along with wind gusts of up to 100 mph. Several feet of snow are likely to fall in the same time period over the Cascades of Washington and Oregon as well as the Bitterroots of Idaho and Montana. This onslaught will likely avoid producing snow initially in the Colorado Rockies, but that could change by late Sunday or Monday.

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