Turning up the heat.

Record-breaking heat sounds like summer news. But records were smashed last winter when the contiguous 48 states in the U.S. experienced the warmest January ever measured.

Surprisingly, there's no initial evidence that global warming caused the wacky weather. Winter temperatures in the 48 states normally plunge when the jet stream, a current of high-altitude winds, carries cold Arctic air southward. Last January, the jet stream stayed far to the north. Without the cool air from the Arctic, the average temperature in the contiguous states was 8.5 degrees Fahrenheit warmer than average for the month.

The jet stream sometimes makes detours. "But it's rare for this type of pattern to persist for an entire winter month," says Jay Lawrimore, a climatologist at the National Climatic Data Center.

JANUARY 2006 TEMPERATURES IN 48 CONTIGUOUS STATES

The map and its key show the number of states that fall into each of
three temperature categories for January 2006. Use the data to
calculate the percentage of states in each category and replace each
"?" in the graph with a percentage.

Above Normal:         7
Much Above Normal:   26
Record Warmest:      15