Wednesday brought the warmest December weather on record in Washington state, Montana, Wyoming, North Dakota and Canada as a sprawling heat dome spread across western and central North America.

These state and national extremes were among scores of records established in the western half of the United States and southwest Canada. It was the first day of meteorological winter (Dec. 1) but felt like mid-fall or mid-spring.

In many areas, it will be even warmer Thursday afternoon. About one-third of the contiguous United States is expected to have highs of at least 70 degrees, which in some places is 30 to 35 degrees above average. At least somewhat above average temperatures are expected almost everywhere.

“Dozens of daily high temperature records could be tied or broken,” the National Weather Service wrote. Oklahoma City, Denver, Kansas City and Omaha are among locations expected to see Dec. 2 records, with highs surging into the 70s.

The warmth will retreat somewhat on Friday into the weekend, but generally above-normal temperatures are expected over the United States through mid-December.

Wednesday’s records

The most exceptional warmth Wednesday, up to 35 degrees above normal, stretched from the Pacific Northwest through the western Dakotas.

Maximiliano Herrera, a climatologist who tracks world weather records, tweeted that high temperatures tied or broke December state records at the following locations:

  • Omak Airport, about 140 miles northeast of Seattle, hit 74 degrees, tying Washington’s December record.
  • Jordan, about 130 miles north-northeast of Billings, reached 78 degrees, tying Montana’s December record.
  • Hettinger, about 85 miles southwest of Bismarck, hit 71 degrees, breaking North Dakota’s December record.
  • Buffalo, about 105 miles north of Casper, hit 78 degrees, tying Wyoming’s December record.

Herrera noted that these temperatures matched or topped levels reached during a winter heat wave in early December 1939, which also featured a large heat dome over the Western states.

In British Columbia, Penticton soared to 72.5 degrees Wednesday, matching the highest temperature ever recorded in Canada during December. The city, about 160 miles east of Vancouver, broke the previous British Columbia record for December by 5.4 degrees, according to Thierry Goose, who tracks Canada’s climate extremes.

The exceptional warmth in Washington state and British Columbia comes just five months after an unprecedented summer heat wave. In late June, Lytton, British Columbia, established a national temperature record on three straight days, culminating in the scorching high of 121 degrees on June 29. The next day, much of the village went up in flames when a wildfire spread through the region.

In addition to the state and national December records set Wednesday, numerous cities had their warmest December day, tying or breaking records. They include Yakima, Wash. (high of 72); Dallesport, Wash. (high of 70); Ellensburg, Wash. (high of 66); Challis, Idaho (high of 62); Mobridge, S.D. (high of 71); and Tucson (high of 85).

Moreover, scores of daily records for Dec. 1 were set. Denver soared to 73 degrees, tying its Dec. 1 record, while also marking its highest temperature during the month in 41 years.

Thursday’s warmth

While the core of the warmth focused in the interior Pacific Northwest and northern Rockies on Wednesday, Thursday’s highest temperatures are predicted to expand southeastward and envelop the central United States.

Highs in the 70s or above are predicted over all of Texas, Oklahoma and Kansas, while extending through all of the Gulf Coast states into the Carolinas.

Most locations from eastern Colorado through the Central Plains are predicted to see record highs.

Friday into the weekend, the warmth will wane and be shunted southward by a cold front dropping into the central states. But longer-range forecasts predict another major pulse of warmth could affect the central and eastern United States during the second week of December.

While the configuration of weather systems is the primary driver of such warm patterns, human-caused climate change is increasing their frequency and intensity. Year-to-date, more than 60,000 record highs have been set in the United States compared with fewer than 30,000 record lows.