Light the yule log and mull some cider if you live in the Northeast United States because chances of a white Christmas improve if snow still is on the ground by tomorrow, Dec. 18.

After examining historical records and extrapolating possibilities, a researcher at Cornell University's Northeast Regional Climate Center has found that if there is an inch or more of snow on the ground on Dec. 18, regardless of when it fell, the chances for a white Christmas in certain areas greatly improve.

For example, the chances of a white Christmas for Concord, N.H., are 76 percent. But these averages indicate that when there is an inch or more of snow on the ground in Concord a week before Dec. 25, the probability of a white Christmas jumps to 85 percent, says Keith Eggleston, senior climatologist at the center.

Eggleston calculated the probabilities using Dec. 18 as a benchmark only if the Northeastern city had a history of 10 or more years with snow on that date.

In the same way, the chances of spending a white holiday in Portland, Maine, are 71 percent normally; but the probabilities take a giant leap to 96 percent if an inch or more of snow is measured on Dec. 18. When there is an inch of snow on the ground in Albany, N.Y., a week before yuletide, the city's chances for a white Dec. 25 soar to 74 percent from a 51 percent probability.

But Caribou, Maine, the snowiest populated town in the region, has a 94 percent chance of a white Christmas, regardless of whether there is snow on Dec. 18.

December 2002 has been a snowy month for the Northeast, although snow totals in the region are not being affected by El Niño weather patterns in the Pacific Ocean, says Eggleston. Between Dec. 1 and 15, Syracuse has had 25.4 inches of snow, which is 10.9 inches more than normal for the period. However, Syracuse would need a major snowfall in the second half of the month to break the record 70.3 inches that fell in December 2000.

Probability of a white Christmas

Note: this table will line up in a fixed-width font such as Courier

Data compiled by the Northeast Regional Climate Center at Cornell University.

"White Christmas" is defined as 1 inch or more of snow on the ground Christmas morning.

Probabilities based on the period 1951-2000.

Second probability is only calculated when there were 10 or more years with snow on Dec 18.