California, Arizona, New Mexico, and the western half of the US will simmer in 25C-plus temperatures–well above average for the first week in December.
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Warm weather will hold out for much of the week before a cold front dampens the fire of the warm spell.
Jim Dale, US weather correspondent and meteorologist for British Weather Services, said: “A pulse of warmth from Mexico will sweep the western half of the US this week, and we could see temperatures, unusually, hit 24C or 25C.
“This is above average or the time of year, and there will be some humidity with the heat as its origin is tropical in origin.
“This is likely to hold out through the week before it turns a bit colder.”