Seasonable Weather to Close Out 2018

After a crazy-active week last week, there thankfully appear to be no major storms on the horizon for at least the rest of 2018. I say “thankfully” because although I am a storm fan, I’m also a meteorologist for a living coming off a week-and-a-half holiday vacation where weather was the last thing on my mind, and I’d much prefer to ease back into storm season than get pummeled with systems upon my return.

Credit: University of Washington

A weak front is currently moving ashore and will bring steady rain to the Portland metro area through the mid-morning before giving way to showers in the afternoon. Snow will continue to pile up in the mountains with this system, with 3-6 inches likely today and another 2-3 inches likely tonight above 2,500 feet. After getting off to a relatively slow start, snowfall is now just slightly below normal for much of the Washington Cascades and around 70-80% of normal for much of Oregon.

Credit: USDA/NRCS

Showers will decrease throughout the day on Thursday as a ridge builds offshore. This ridge will move onshore Friday but will flatten in the process as a weak system slides into Southern BC, and as a result, Friday will be a dry and cloudy day for much of Western Oregon while Washington sees lowland rain and mountain snow. This system will also be much weaker than the ones last week, but models show precipitation streaming into Washington for much of the day on Friday, and given the low snow levels, I wouldn’t be surprised to see winter storm warnings issued for the Olympics and Washington Cascades.

Predicted 72-hour snowfall from 4 am Friday to 4 am Monday
Credit: University of Washington

Models begin to diverge a little more with the details after Friday, but it looks like another weak front will push through the region Saturday night and Sunday with snow levels remaining on either side of 3,000 feet for the weekend.

Models were hinting at a switch to colder weather next week as a large trough formed over the Western US, but subsequent runs have moved that trough further east and it now looks like any arctic outbreak should stay well to the east of our area.

GFS Ensembles showing temperatures at 850 mb (around 5,000 feet) and precipitation. Note the large spread beginning around 12/29… this reflects the large uncertainty beginning at this time. The “climatology” plot stops at 12/31 because of a bug in my code… I’ll try and fix this tomorrow if I have time.

A weak El Nino continues to persist in the tropical Pacific, and it is generally after the New Year that El Nino’s effects become more pronounced over North America. The Pacific Northwest generally stays warmer and slightly drier-than-normal during El Nino winters, but since this is a weak El Nino, the jury is still out as to whether calmer weather will prevail for the rest of the winter.

Credit: Climate Prediction Center

Thanks for reading, and have a great rest of your week!
Charlie

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