Merry Christmas!
We expected mixed showers today and this is what we saw. Except that there was not much NOTHING in the western valleys. Now we know the drier models have been okay… so far. Only 0.03 in Portland so far!
Of course, if those dry patterns are okay and we don’t have that many showers tonight / tomorrow then no sledding for many of us. At the moment, temperatures are between 30 and 30 in the metropolitan area, the coolest in the higher areas of course.
That’s a few degrees more than I expected for 8pm when I last worked Thursday night. Regardless, the atmosphere above the head continues to cool as the cold showers continue to pivot toward the shore. I see it descended to -6 (in degrees Celsius ~ 4000 above) above Salem during the afternoon balloon sounding. It should reach -9 by dawn. With temperatures a few degrees above the freezing point, any heavy snow showers could linger tonight until the early hours of daylight on Sunday. In fact, just in the 10 minutes I typed, the floor of our Seaside camera, including the sand on the beach, turned white! We may not see too much weather at noon tomorrow, but still quite cold tomorrow night and night.
STRONG POINTS
- Anyone in the area north of Florence on the coast and inland can pick up snow accumulation from this point.
- Expect a wide range of build-up in the lower elevations. A Trace at 3 ″ should cover most of us. An outlier of 4-5 ″ could appear somewhere, and in the higher hills around Portland, Newberg, Amity, Salem, I could see 4-6 ″. It is possible that some of that will fall before 10am tomorrow, and then a little more tomorrow night / night. I know the NWS has a winter storm warning but this is a technical detail as a location needs 4 or more to qualify as a WSW in the lowlands. These showers come and go… not a single big storm that lasts 12 to 24 hours.
- Expect all roads to freeze over on Sunday night for the Monday morning commute
I still like this graphic, note that many main roads can be fine tomorrow noon
FOR WEATHER GEEKS
It is rare for the lower elevations to experience significant snowfall when the wind blows from the south. It was the case today and it will still be the case tomorrow, although not as strong. This wind keeps the air mixed and is definitely not coming from a colder region = more difficult to get sticky snowflakes at sea / ground level. That is why I am always cautious about using “snow map” templates in these situations. So marginal. Remember some models were showing sticky snow today… at 35-38 degrees. This does not happen and that is why we said “mixed showers on Christmas day” for several days before that.
Arctic air coming out of British Columbia created a surface low just west of Forks, WA. Cold arctic air is bottled north of the red line. Bellingham is 19 with northeasterly gusts of 40 mph! Of course, the cold air over the ocean picks up moisture, sending downpours inland over southern Washington and Oregon.
To get rid of the southerly breeze, it must either die or go south of us. We will still be in a similar setup tomorrow morning at 10am, with the remnants of the low somewhere between Olympia and Mt. Adams.
As of noon tomorrow, the cold / dry arctic air has NOT arrived, so after getting close to freezing tonight, we will be heading back to the mid-1930s tomorrow. That’s why I think many roads could be fairly reasonable at noon, UNLESS very heavy snow showers develop. Generally I would say little / no snow with this setup. But temperatures of 850 mb are -9 tomorrow, which should barely overcome the continuous (weak) flux on land. IF WE DON’T HAVE HEAVY SHOWERS from tonight until tomorrow night, we will have very little snow. He has to descend at a steady pace if we are to sled by Monday morning. By this time (4 a.m. Monday) the low has collapsed and is off the Oregon coast
Most of our models produce somewhere between a trace and 3 ″ of snow along the I-5 corridor from Longview to Albany, as we expected. The new GRAF model release tonight looks good; now until monday morning when it dries up
The last Euro was drier, producing more like a 2 ″ Trace
The cool WRF-GFS is really trying to improve the bands of snow that hit the shore… 0.5 ″ north up to (swallow!) 10 ″ around the Salem or Albany areas. It seems unlikely, but… we’ll see!
That’s all for this Christmas night, I’ll be on TV at 10 p.m. I’ll be at work tomorrow and hope to take a look further in the next week
Chief Meteorologist Mark Nelsen
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