Freezing Temperatures Loom, Snow Unlikely

How low can we go?

Arctic air swooping down the Canadian coastline is set to invade the region beginning tomorrow night, kicking off a bone-chilling week that could feature Seattle’s coldest overnight temperatures in nearly three years.

Low 20s, anyone?

We haven’t dipped below 24 degrees since February 2011, when the thermometer at Sea-Tac Aiport bottomed out at 19 in the wake of a frigid, late-winter arctic blast. This time around, the cold air is coming much earlier in the season—the official start of winter is still three weeks away—and it won’t be leaving anytime soon.

In the short term, it’s another balmy day out there, with temperatures hanging out in the mid 50s—nearly 10 degrees warmer than the early December average of 47. Although the Olympic rain shadow has worked wonders for Seattle today, keeping things dry since the morning, it’s also been pretty windy at times—Sea-Tac hit 41 mph just before 8 a.m.

As we head into the evening hours, we’ll begin a gradual cooldown as the winds subside, with temperatures dropping back into the mid 40s by 7 p.m., and into the upper 30s after midnight. Showers will fill in behind the cold front as morning approaches, and this is where things could get marginally interesting for snow.

A Puget Sound Convergence Zone will likely develop between Shoreline and Everett early tomorrow, and with temperatures in the mid or upper 30s, a little wet snow is possible in spots there—especially east of I-5. However, with road temperatures still pretty warm after today’s readings, any snow that falls is unlikely to stick to anything but grass.

In Seattle proper, it will be a mainly dry, snow-free morning, with just a couple scattered rain showers and temperatures hovering around 40 degrees. Further north in Whatcom County, highs will only make it to the low 30s as arctic air begins funneling in through the Fraser Valley. Light snow is also possible there through the morning hours.

The chilly air slowly marches south during the afternoon, dropping temperatures in the Seattle area back to the upper 30s by the time tomorrow’s Seahawks-Saints game begins. Importantly, though, no snow is expected, as the cold, dry air shoos away any leftover moisture. With breezy conditions picking up out of the north, the mercury should continue to creep downward as night sets in, leveling off near freezing Tuesday morning.

With arctic air firmly in place, temperatures will only make it to the mid 30s later Tuesday afternoon—despite clear skies overhead. Overnight, readings will plummet into the mid 20s. Wednesday looks sunnier and even colder yet, with highs barely climbing above 32 degrees.

It’s overnight Wednesday into Thursday when temperatures really fall like a rock, with Thursday morning’s low projected to only be in the lower 20s—good for Seattle’s chilliest reading since the February ’11 cold snap. In addition, highs on Thursday will struggle to reach the freezing mark—potentially giving us our first sub-freezing high since the ice storm of Jan. 19, 2012. The one positive? It’ll be dry and sunny yet again.

The cold then digs in its heels for Friday and Saturday, with temperatures once more only rising to the low 30s under daytime sunshine—and slumping back to the 20s at night.

Better get those mittens ready for the long haul.