EXPLAINER: Stuck jet stream, La Nina causing weird weather

America’s winter wonderland is starting out this season as anything but traditional.

The calendar says December but for much of the country temperatures beckon for sandals. Umbrellas, if not arks, are needed in the Pacific Northwest, while in the Rockies snow shovels are gathering cobwebs.

Meteorologists attribute the latest batch of record-shattering weather extremes to a stuck jet stream and the effects of a La Nina weather pattern from cooling waters in the equatorial Pacific.

It's still fall astronomically, but winter starts Dec. 1 for meteorologists. This year, no one told the weather that.

On Thursday, 65 weather stations across the nation set record high temperature marks for Dec. 2, including Springfield, Missouri, hitting 75 degrees Fahrenheit (24 Celsius) and Roanoke, Virginia 72 degrees Fahrenheit (22 Celsius). Cheyenne, Wyoming, and Billings, Montana, broke long-time heat records by 6 degrees.

Parts of Canada and Montana have seen their highest December records in recorded history. On Friday, parts of South Carolina and Georgia hit record highs.

In Washington state, Seattle, Bellingham and Quillayute all set 90-day fall records for rainfall. Bellingham was doused by nearly two feet (60 centimeters) of rain. The Olympic and Cascade mountains got hit harder, with more than 50 inches (127 centimeters) in three months, according to the National Weather Service. Forks, Washington, received more rain in 90 days than Las Vegas gets in 13 years.

On top of that, there is a blizzard warning on Hawaii’s Big Island summits with up to 12 inches (30.5 centimeters) of snow expected and wind gusts of more than 100 miles per hour (161 kilometers per hour).

Meantime, snow's gone missing in Colorado. Before this year, the latest first measurable snowfall on record in Denver...