An early heat wave took hold Saturday in parts of the Pacific Northwest, with temperatures nearing or breaking records in some areas and heat advisories in place through Monday.

Forecasters are warning of treacherous holiday travel and life-threatening cold for much of the nation as an arctic air mass blows into the already-frigid southern United States.

Models used to predict flooding are based on long-term, historical records that do not reflect changes to the climate over the past decade, scientists say..