The three-day Columbus Day holiday weekend, a time for both travel and traditional observance, ended here yesterday on the coldest day in more than five months.

At 4:10 a.m. the mercury slid to 47 degrees at the official measuring station at National Airport.

That was the lowest reading here since the 45 degrees recorded on May 10.

Meanwhile at Dulles Airport, the temperature plunged at midnight last night to the freezing mark, for the first time since April 17.

Forecasts indicate that temperatures today might plunge even lower.

A total of 69,329 vehicles passed through the Baltimore Harbor tunnel yesterday, which was described as "not a lot" by a police officer there, but which is about 8,000 more than the daily average of 61,209 recorded so far this year. The Saturday figure was 58,417 and the Sunday reading was 53,886.

At the Bay Bridge about 30,000 vehicles crossed yesterday in both directions, which "surprised me a little bit," said bridge police officer Daniel McCreary. A normal Monday in October might see about 22,000 vehicles cross, he said.

At National Airport, however, an operations officer said it was his impression that passenger traffic may have been a little less than on a normal weekend.

Despite a stiff October wind that whipped across the area at up to 25 miles an hour, with gusts as high as 36 mph, the traditional ceremony was held at the Columbus monument outside Union Station to honor Christopher Columbus, the Italian navigator and explorer whose discovery of America 488 years ago is commemorated by the holiday.