Posted by Rufus La Lone on

Friday December 17
Colder weather is still on the way, although getting enough moisture to arrive at the same time may hold off a White Christmas this year.  That said, we still have the chance for some surface snow after Christmas.  Let’s explain.
This weekend.  A wet system will swing across the PNW, north-to-south, starting later tonight and Saturday into Sunday.  Breezy.  Vancouver Is & the Puget Sound will be first to get rain, then OR; freezing levels will rise ahead of the system.  Colder, dry air will be drawn into NW WA out of the Fraser Gap as an outflow begins to develop.  Not super cold.  A Low pressure trough west of the OR coast will spin some moisture over OR and SW WA Monday & Tue.  Snow showers will remain in the mountains.  That Low will remain off the coast next week, before slowing moving south to impact CA with plenty of rain & mountain snow.  Probably mostly dry and chilly Wed & Thu next week.
Christmas Eve, Day and weekend:  A relatively weak “Juneau Low" will move south from Juneau Alaska, setting up the chance for SNOW showers in the far north corner of WA late Christmas Day or night, as the Low will position just right to crank up quite a Fraser Gap outflow.  For the rest of us, it will be on the chilly side, but moisture will be limited, with temps generally remaining above freezing.  That Christmas Juneau Low will continue south, impacting CA by Sunday/Mon Dec 26,27.  (Please note: as discussed previously, this system has charted, at times, as strong and wet, with the potential for a snowy period across much of the PNW during the holiday weekend.  That was probably a model error, but model projections do shift, back and forth, so we’ll keep an eye on this next week.)
Post Christmas Uncertainty.  We have seen another Juneau Low on the extended-range wx charts for the week after Christmas, combined with a strong Fraser River outflow, it may set up a snowy pattern before the end of the year.  Several models are agreeing on a colder period after Christmas, but not firm enough to stick a forecast.  Anyway, that week may be rather cold, with frosty mornings if the sky clears in your location, or wet at times with snow in the foothills.  Stormy in CA.  Models also toy with a possible modified Arctic outbreak, too.  We are not confident about that at this time; maybe there will be less uncertainty for our next writing.  Keep your Mug handy.
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