46 degrees might not seem that cold -- especially with all the talk of the upcoming arctic air (more on that in a moment). But as Tuesday's high temperature at Sea-Tac, it snapped an impressive streak of 59 consecutive days with high temperatures at or above normal, starting on Dec. 17. (That's two days before the rain streak started).
But you know the saying -- what goes up, must come down. And now, we'll start a little streak of temperatures below normal as arctic air is still making its way southwest from Alberta toward the Pacific Northwest.
Aside from yesterday's 46, other early signs are already here, as temperatures overnight Tuesday dropped into the low 20s in some spots (Shelton got down to 20, Olympia dropped to 22, and even Bellevue got down to 27.)
Tonight is sort of our last night with semi-reasonable temperatures before we slip into the icebox for a couple of days. Overnight lows will be similar to last night -- perhaps a degree or two colder. That means around 27-30ish for Seattle and 18-24ish for the outlying area. The weather will be mostly clear.
The arctic air will start to push into the area Thursday via an arctic front. The first to feel it will be up in the Bellingham/Ferndale/Lynden/Blaine Whatcom County areas, where cold air will begin funneling through the Fraser River Valley as the front passes -- probably around late morning.
The front will be a slow-mover, probably taking until Thursday afternoon to pass the greater Seattle/Puget Sound area, and then into Thursday evening before reaching the Southwestern Washington and the coast.
Generally speaking, it'll bring clouds, strong northerly winds, and likely the coldest temperatures we've seen in quite a few years -- although recent winters have been pretty mild, so that's not as impressive as it might sound.
I'll break it down by each feature:
Aside from the cold, this will be the most noticeable feature with this event. As the front passes Thursday, strong northeasterly winds will push arctic air through the Fraser River Valley and into northwestern Whatcom County.
Cold air is very dense, so arctic air masses are typically linked with very strong areas of high pressure. The bulk of the high pressure will be in eastern B.C. and Alberta (the arctic air's "home base"). But with lower pressure off our coast, that will create a big difference in pressure between inland B.C. and us.
That air will come shooting through the gaps in the mountains to try and equal that pressure -- and the biggest gap is the Fraser River Valley, which acts like a funnel to channel the arctic air from inland B.C. to western Washington. And, of course, northwestern Whatcom County sits right at the end of the funnel!
This is along the same physics as what makes Cascade foothill windstorms -- high pressure in Eastern Washington, lower pressure in the Pacific, and air rushes through the Cascade gaps and hits the foothill towns situated near the end of the gaps. And sure enough, some of that arctic will also come westward through the gaps, making for windy conditions along the foothills too.
Anyway, A High Wind Watch is in effect for the Northwest Interior, where northeast winds will pick up to 30-40 mph along northwestern Whatcom County, with potential gusts as high as 50-60 mph starting midday Thursday. Those winds will spread out as they pour into the rest of Western Washington through the rest of the afternoon and evening as the front slides south.
As for other area's wind speeds, It'll end up be a sliding scale downward of how strong the winds will be at your place versus how far away you live from Bellingham. For instance, the San Juans, North Sound and north/northeastern Olympic Peninsula areas might see gusts to 40-50 mph, while down in Seattle, it'd be more gusts of 20-35 -- although perhaps a little stronger right along Puget Sound.
The exception is the aforementioned Cascade foothill communities that usually get the east winds. You could see east winds of 20-35 mph, gusting to 40-55 mph through the period as well, and a High Wind Watch is in effect there too through Friday morning.
For everyone else, those winds are expected to continue overnight Thursday and through the day Friday and even into Friday night as well before finally relaxing into Saturday.
I did this second, because while these numbers are pretty low -- it'll feel considerably colder with the gusty winds around.
Anyway, Thursday will begin with temperatures probably making it up to around 40 or so, but then they will quickly fall as that front passes from north to south during the afternoon and evening. So by the time sunset rolls around, you might be a lot colder than you were at lunch.
The arctic air will continue to push in overnight Thursday, and by daybreak Friday, temperatures will likely only be in the teens in the outlying areas and Seattle might be the "warm" spot at about 21-22 or so. On the other hand, the usual cold and wind-sheltered places like Olympia and places near the arctic outflow like Bellingham might actually drop to single digits.
Friday's "highs" will then struggle to get out of the 20s for most areas-- although Seattle and the Central Puget Sound area might crawl to the freezing mark.
Clear and very cold again Friday night, with similar lows in the teens (single digits?) to low 20s in the city. (Seattle is typically always a little warmer at night due to the "urban heating" effect, where the city gives of its own heat generated from concrete and asphalt absorbing heat from the day and releasing it at night.)
Now, factor in the wind, and it'll feel a lot colder through the period. For example, temperatures in the mid 20s with a 25-30 mph wind feels like 9 degrees. (You can see a wind chill chart at this link. )
[A quick aside -- for those of you who are thinking, "Hey, 9 degrees is nothing, I remember when wind chills here used to drop to -10 in the winter" -- a few years ago, the National Weather Service revised their formula to calculate wind chill, so the numbers aren't as low as they used to be. Under the old formula, a 25 degree temp with a 25 mph wind would have been a wind chill of 7 below zero. Now, it's 9 degrees above.]
That brings up another point -- the mountains. If you think it'll be cold down here, it will be bitter cold up there. So while the sun might entice you to hit the slopes, just be sure to dress for very cold temperatures -- probably single digits and teens, plus the wind to boot. Also take extra special cold-weather precautions if will be hiking up there.
The winds will relax on Saturday, but we'll stay cold, with highs still in the upper 20s to mid 30s. By Sunday, we'll be climbing back to the low 40s.
WILL THIS COLD BE RECORD COLD?
It's marginal. On the one hand, there have been only two times in the past 10 years when the temperature at Sea-Tac has dropped below 20 degrees -- once in January of 1996 and another in December 1998.
However, Seattle's official record low for Thursday appears safe -- a matter of bad timing, really. While most record lows around this time of year are in the low 20s, Thursday's record low is 13, set in 1956, and I don't think we'll be that cold.
Friday night's record low is 23, set in 1993, and that has a shot of being tied or broken. Guess we'll see.
WHAT ABOUT SNOW?
While the temperatures are easily in the realm for snow, unfortunately for snow fans, we really don't have much moisture to work with.
Our best hope is with that arctic front coming through Thursday, but the forecasting models are not impressed, barely showing any moisture as the front moves through.
But sometimes arctic fronts can create their own weather, perhaps dropping a quick inch or two of snow as it blows through late Thursday and into early Friday. But sometimes they're dry too, so it's hard to gauge what if any snow will come from that.
We think it will cloud up a bit, and there might be some flurries or maybe a light snow shower here and there, but chances of a widespread snow event are quite remote. By Friday, we'll be back to the sun and stay that way through the weekend.
So It's Not Minnesota, But Who Is?
OK, so it's going to get cold by Northwest standards, but I know a lot of us here are getting some flak from our friends back and the Midwest and East Coast who chide us for getting all excited over temperatures in the teens and 20s.
But get this: Minneapolis' all-time record for consecutive rainy days in a row? It's 10. Can you imagine the local news' panic if their weather forecasters came out and said it was going to rain for 12 days straight there?
We've already had not one, but *two* streaks of rain greater than 12 days here. So, it's all relative as to what you're used to.
The long range forecast does moderate us at least to the low-mid 40s for next week, but we do look to stay cooler than normal through the next week. And that would make sense. Did you know that before our streak of 59 days above normal, we had a streak of 36 days at or below normal?
Could we be heading for another streak of that length? Hard to say, but in this "winter of the streak", it wouldn't surprise me. Although I admit, Minnesota natives, that a 36-day streak of below normal temperatures there would probably be a good story to lead the newscasts :)