Mega Snowstorm Headed For Pac NW?

Updated Tuesday Afternoon

Like many of you, I woke up this morning to the national, regional and local headlines reading something like this — Seattle and Portland bracing for mega snowstorm with up to 18″ in Seattle and up to 12″ in Portland. I even noticed that “Storm Tracker” Jim Cantore (The Weather Channel) will be reporting “live” from Seattle on what could be the biggest snowstorm in decades up there. Then I sat down and reviewed the exact same computer model guidance that every other forecaster looks at and thought to myself, “uhhhh, is this for real?”

After poring over all of the latest model guidance available through this afternoon (18z Tuesday) there are some obvious modeling trends taking shape in the past 24-48 hours. Maybe it is just me, but doesn’t it seem interesting that every time there is a big snowstorm possible for Portland or Seattle it becomes extremely hard for some folks to let go of the “hype” once it has started, even when the data suggests otherwise? Weather is always changing and snow is rarely forecast accurately within 12-18 hours in either Portland or Seattle. We should all know this by now. So, what I am about to say may let many of you down, while others will still have something to cheer about. Is this going to be the mega storm that it has been made out to be by some? Nope! Will there be plenty of disappointed kids tomorrow? Yep. Although I am sure some will be out of school regardless as school districts will likely play it safe since many have not used a single snow day yet this year. Will plenty of us see enough snow to be happy? Sure! I guess that depends on what your “snow standards” are. Snow amounts will all depend on where you are located geographically more so than anything else. Ok, I think it is time to take the Pepsi Challenge and put my thoughts on the line. If I can talk the talk, I better be able to walk the walk, as the old saying goes. Pending any MAJOR model shifts between now and this evening, or any incorrect model run initiations, I think the forecast is actually pretty direct. Here is what I see over the next 24-ish hours, with a focus on western Oregon and SW Washington —

2pm-6pm today — Mixed rain and snow showers will continue up and down the I-5 corridor today. Accumulating snow will stay above the valley floor (at about 1,000ft) just as it did yesterday. It may actually fall as all rain on the valley floor. Heavier showers will briefly bring snow all the way down to the valley floor. Areas above 1,000ft will see continuing snow all day with an additional 1-2″ possible. All valley locations will stay above freezing today, including locations below 1,500ft. No evening commute issues below 1,000ft west of the cascades. The coastal strip will see all rain.

6pm-11pm tonight — Models show that the air mass just above the surface will cool slightly this evening. Winds will switch from southerly this afternoon to very light northwesterly, if not completely calm early this evening. This is important to note, as I will explain below. The wind will then switch to offshore (easterly) ahead of the approaching storm after 11pm. All models now take the center of tonight’s storm to just west of Astoria by about 11pm. At the same time, colder air from the northwest will be filtering in across western Washington and northwest Oregon at just above the surface. Temperature profiles (soundings) all support additional cooling from the surface to about 2,500ft during this time. This will be cold enough for snow from Salem, Oregon north to Kelso, Washington. With a slightly drier and cooler easterly flow across these areas, steady light rain/snow mix will develop first in western Oregon, then move north into SW Washington by about 10pm, give or take an hour or so.

11pm-1am — All models continue to show moisture arriving from the Pacific tonight over the top of additional cold air that will already be in place. This is normally a good set up for snow in Portland. The 12z NAM and WRF model cross sections and soundings both show the winds will go nearly calm over NW Oregon and SW Washington during this time. With either calm or light easterly winds, sticking snow is likely in Portland during this time. There will likely be just enough cooling of the atmosphere above to allow the snow to come right down to the valley floor after 12 midnight. Moderate precipitation rates at the same time will also help to lower the snow down to the surface. This is the best time to see sticking snow in the lowest elevations and along the valley floor.

1am-5am — This is prime snow time for the valley floor in and near Portland. Precip will be heaviest, winds will be light from the east and temperatures will be the coldest of the night. I expect everyone in and around Portland will see snow accumulating all the way down to the valley floor during this time. Most of us will go to bed with nothing more than wet streets and likely wake up to white, to one degree or another.

5am-8am — Wednesday morning’s commute is going to be a messy one in and around Portland, especially at higher elevations. Snow from overnight will likely make for a slushy mess. However by 8am temperatures above the surface will slowly begin to moderate as southerly winds take over once again. As the storm passes by to the north, winds will pick up from the south. In fact, all of the models show a rapid warm up about 8-9am. One model has the surface temperature in Portland rising to near 45 degrees by tomorrow afternoon. That will surely melt any snowman left around from the morning.

9am-3pm — The big melt gets underway with the evening commute being more wet than white around Portland.

Here are my winners and losers in this storm, if you are someone who likes to see snow

Winner — The greater Portland / Vancouver metro area. Most all of us will see 1-4″ by morning. Higher elevations around the city will likely see the upper end of this scale. The city of Portland itself will likely ride somewhere in the 1-2″ category.

Winner — Anyone above 1,000ft metro wide, north Clark County, SW Washington, Western Washington County and the Columbia River Gorge. The cold air will hold on the longest in these areas. The gorge could get between 6-9″ of snow before this is all said and done.

Winner — Most kids who live in elevated areas around Portland and points north. They will likely have a snow day.

Loser — Parents who work all day and have kids who may not be in school tomorrow due to the weather.

Loser — Anyone living South of Portland. I just don’t see much of any snow in Salem or points south. I really think the Winter Storm Watch should be dropped for the valley, south of Salem.

Loser — Anyone who is looking for a hard freeze. No model shows temperatures getting below freezing tonight anywhere in the Portland metro area.

Loser — The coast. There won’t be any repeat of this past weekend’s snow down there. It will be all rain.

Loser — Any Weather Channel viewer who is waiting to see the great Seattle mega snowstorm. Cantore better park that live truck a little further south, say Olympia or Centralia!

In the end, we simply did not have any arctic air in place to draw from. If the eastern end of the Columbia River Gorge was 10-15 degrees colder, or we had a true arctic blast from the north a few days ago, it would have made a big difference in tonight’s set up. Be patient my friends, there is still time left this winter. Those are my latest thoughts! If anything changes between now and tonight, I will update the blog, so be sure and check back again.

Stay tuned!
Steve Pierce

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