Tired of scraping ice off your windshield every day? Cheer up — frost-free mornings are likely to return by Wednesday.
Forecasters expect a weak winter storm to blow through Southern Oregon today, ending the air inversion that shoved the Rogue Valley into the freezer for most of January. The cold spell fell far short of setting any records, either for duration or low temperatures, but "regardless of all that, it's been cold," said Mike Ottenweller, a meteorologist at the National Weather Service office in Medford.
As of Monday, below-freezing temperatures were recorded at the weather service office on all but four nights of the new year (Jan 6-9). The coldest nights were Jan. 14 (18 degrees) and Jan. 20 (19 degrees), but it has been 25 degrees or colder every night since Jan. 11.
Our chilly interlude doesn't begin to compare with previous episodes of local cold. In January 1963, for example, there were 20 consecutive nights with a temperature of 26 degrees or less. And as recently as 2007, there were 13 straight nights of 26 degrees or less in late January and early February.
Ottenweller said cold, dry weather in January is quite common for Southern Oregon, and may occur anytime something interrupts the regular flow of relatively warm marine air from the Pacific Ocean. When there's little wind, cold air settles and collects in low places, and it stays there until something (usually a winter storm) stirs the pot.
The resulting temperature inversion upsets the normal pattern of colder temperatures at higher altitudes. During the height of the inversion on Sunday, some workers at the Mt. Ashland Ski Area were tending chairlifts in their shirtsleeves. Ottenweller said some high-altitude weather stations recorded temperatures in the 60s.
Ottenweller said the current cold spell may have been influenced by a large storm in the western Pacific, which allowed high pressure air to collect over the eastern Pacific. The resulting "ridge" of high pressure diverted the flow of marine air north into Canada. That same Japanese storm prompted the weather service to issue warnings for big storm swells and sneaker waves on the Oregon Coast last week.
As high-altitude, jet-stream winds return to their more typical winter flow pattern over the Northwest, forecasters were expecting another storm to reach Southern Oregon as early as Saturday. Overnight low temperatures were expected to hover at least a few degrees above freezing, as clouds cover the region and act as a giant insulating blanket.
While we complain about our heating bills and slick streets, it's important to know it could have been so much colder. Medford's record low temperatures for January days range as much as 20 degrees colder than what we've been shivering through. The record low for Jan. 22, for example, is 0 degrees, set during a 1962 cold spell that saw temperatures fall below 10 degrees on four consecutive nights.
And you can always be glad you don't live on the east side of the Cascades. Klamath Falls set several new records last week for daily low temperatures, with readings near or below zero. Lakeview, about an hour further east, had the coldest night — 26 below zero — on Jan. 13.
Bill Kettler is a freelance writer living in Rogue River. Reach him at firstname.lastname@example.org.