After a stretch of warm weather, with overnight highs in the 50s and drenching atmospheric rivers that brought Seattle the wettest meteorological fall on record, December is expected to take a decidedly cooler turn.
The region’s return to more typical winterlike temperatures, with highs in the 40s and lows in the 30s, will probably feel colder than usual after the recent stretch of unseasonably warm days and nights, according to National Weather Service meteorologist Dustin Guy.
“It’s really just closer to what we’d expect in early December,” he said Friday morning, “but it’ll be a shock to the system after all the mild temps we’ve had.”
Over the last few days of November, daytime highs were in the 50s, but more significantly, nighttime lows were also in the 50s.
Typically at this time of year, we see highs in the 40s with lows in the upper 30s, he said.
Overnight temperatures on Nov. 29 dropped only to 52 degrees in Seattle, setting a new record high minimum temperature for the date. The previous record high minimum for Nov. 29 was 50 degrees, recorded in 1995, according to the weather service.
The cooler temps will be brought in by air coming out of the Gulf of Alaska, Guy said, unlike the warm tropical systems that brought us all those atmospheric rivers in November.
Last month’s parade of atmospheric rivers of rain brought widespread flooding, evacuations, landslides, water rescues, airport and freeway closures and the declaration of a severe weather emergency in 14 counties.
Unsettled weather remains in the forecast, Guy said, with rain in the lowlands and snow in the mountains expected Saturday, followed by a break on Sunday and more rain and snow on Monday. More of the same is expected all of next week, he said.
Overall, December is expected to be colder and wetter than usual due to La Niña conditions, he said, which typically kick in right around now.
“We usually don’t get the long-term shift (to La Niña weather) until we get deeper into the winter season, and that’s starting to pan out now,” he said.
The return to cooler weather is a good thing for the region, said Guy, as precipitation in the mountains will contribute to the snowpack instead of melting and adding to concerns about flooding.
Record-breaking rain was recorded throughout western Washington between September and November, a period known as meteorological fall. According to the National Oceanic and Atmospheric Administration, the more familiar astronomical seasons are based on the position of Earth in relation to the sun, whereas the meteorological seasons are based on annual temperature cycles.
Of November’s 30 days, it rained for 25, tying 1973, 1963 and 1953 for most rainy days in the month, according to the weather service.
In total, 19.4 inches of rain were recorded during that time period at Seattle-Tacoma International Airport, including 10.26 inches in November alone. The old record for meteorological fall, set in 2006, was 18.6 inches, according to the National Weather Service.
In Quillayute, 56.77 inches were recorded this year, over the old record of 51.81 inches set in 1975; and in Bellingham, 23.55 inches were recorded between September and November, topping the previous 1990 record of 17.14 inches.
On the coast, Forks received more rain this early fall than Las Vegas typically gets in 13 years, the weather service tweeted.