A blizzard warning for normally balmy Hawaii and an absence of snow in mountainous Colorado were among a series of bizarre weather forecasts and events in the US as December began.
Meteorologists attributed the latest batch of record-shattering weather extremes to a stuck jet stream and the effects of a La Niña weather pattern from cooling Pacific waters.
For US meteorologists, winter starts on 1 December. But on Thursday 2 December, 65 weather stations across the US set record high temperatures, including Springfield, Missouri, hitting 75F (24C) and Roanoke, Virginia, 72F (22C). Cheyenne, Wyoming, and Billings, Montana, broke longstanding heat records by 6F.
Parts of Canada and Montana have seen December records too. On Friday, parts of South Carolina and Georgia hit record highs.
In Washington state, Seattle, Bellingham and Quillayute set 90-day fall records for rainfall. Bellingham was doused by nearly 2ft of rain. The Olympic and Cascade mountains have been hit harder, with more than 50in in three months, according to the National Weather Service (NWS). Forks, Washington, received more rain in 90 days than Las Vegas gets in 13 years.
There was a blizzard warning on Hawaii’s Big Island summits with up to 12in of snow expected and wind gusts of more than 100mph. But snow has gone missing in Colorado.
Before this year, the latest first measurable snowfall in Denver was 21 November, back in 1934. There is a slight possibility of snow on Monday night, according to the NWS. Yet with no snow since 22 April this is the city’s third-longest stretch without it.
The jet stream, the river of air that moves weather from west to east, has been stuck. That means low pressure on one part of the stream is bringing rain to the Pacific north-west while high pressure over about two-thirds of the US produces dry and warmer weather, said Brian Hurley, a senior meteorologist at the NWS Weather Prediction Center in College Park, Maryland.
If the jet stream moves more or bends differently, rain and other extreme weather won’t be as concentrated, Hurley said. This is a typical weather pattern with a natural La Niña weather oscillation, he added.
The flip side of El Niño, a La Niña is a cooling of parts of the central Pacific that changes weather patterns across the globe. La Niñas tend to bring more rain to the Pacific north-west and make the south drier and warmer.
These bouts of extreme weather happen more frequently as the world warms, said meteorologist Jeff Masters, founder of Weather Underground who now works at Yale Climate Connections. But scientists have not done the required study to attribute these events to human-caused climate change.
In Boulder, Colorado, meteorologist Bob Henson enjoyed a rare December bike ride on Thursday. Still, “there’s a lot of angst about the lack of snow”, he said. “It puts you in a psychic quandary. You enjoy the warm weather while keeping in mind it’s not good for Earth to be warming.”