Initial Details: Arctic Low and Storm Front To Bring Significant Snow and Thundersnow Risks To The Pacific Northwest Friday into The Weekend


An arctic storm front will again impact the Pacific Northwest, bringing significant snow in some spots and a risk of thundersnow.  This one could be worse than the one that recently hit the area, so for those details read on.

An arctic surface low will exit Canada into the Pacific Ocean west of Washington State on Friday night.  This will start the snowfall for areas north of Seattle and of course the Northern/Northeast part of Washington State.

By Saturday the snow level will reach the Seattle zones as the surface low positions to the west-southwest of the area.  Because of the position of the surface low, wind sucking into it from the east, or offshore, will lower the snow level as drier surface air moves under moist low/mid, and upper-level air.  By then the Oregon zones should also be affected.

One thing to really note on this vs the many before is if we can get the instability right, this upper-level low is also positioned in a way to bring strong upper divergence (lift) into the region, being on the northeast section of it.  If it follows this path, I may be looking at monitoring the area for thunderstorms with the snow in spots, and if that happens, it would be thundersnow.

By Sunday this surface low moves just offshore of Southwest Oregon.  This will start the process of weakening snowfall from north to south across both states.  By later Sunday the only area hanging onto the snow into Monday morning would be the Grants Pass forecast area in Southwest Oregon.

Should the surface low drop further east along the coast, snowfall numbers in the Willamette Valley and Seattle will be drastically lower than the forecast would call for.  However, by looking at the past trend, the agreement is there that this surface low will be offshore and not on the shore so confidence is rising in a significant snow event, including snow once again in the Willamette Valley.  Should the Puget Sound Convergence Zone through Seattle ignite, heavy snowfall in city limits will be likely on Saturday.

Winds do not look strong with this surface low.  Being only 996mb at the lowest, a 20-30 mph wind gust is likely for Seattle with Southwest Washington have 30-35 mph from Aberdeen to Raymond on your Saturday.

Snow forecasts will come out a day before impact, but for now, the focus is on monitoring of the surface low trajectory as it comes out of Canada into the Pacific.

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