Put away those summer clothes and get out the wool coats again: Washington's rollercoaster weather is taking another dive.

Temperatures, which rose to 70 degrees yesterday evening, are expected to sink into the 20s tonight. Although showers are forecast for the early part of the day, no snow is expected to accompany the sharp change in temperature. It will be partly cloudy through the rest of the week, according to the National Weather Service.

"Temperatures will go back to where they belong at this time of year," said Harold Hess, District forecaster for the National Weather Service. The weather was expected to remain "warm and breezy" through last night and reach nearly 60 degrees today before plunging to the mid-20s in the suburbs and around 30 in the District early tomorrow morning, Hess said. It will become even colder tomorrow night, he added.

By Sunday, temperatures will be on their way back up again, reaching around 50 degrees, he said.

The impending cold front "is associated with" the blinding storm that hit Denver on Christmas Eve and spread to the Midwest this week, but mainly all that Washington will get is cold air, Hess said.

The sharp drop is not a record, Hess said, because there have been times when temperatures have dropped from the 60s to the teens within 24 hours.

The last-minute cold may ruin Washington's chance for a near-record-warm December. Temperatures until now have been well above average for the month, Hess said. Yesterday's warm air produced morning fog in parts of Washington and led to some minor delays but no flight cancellations at National Airport, a spokeswoman there said.

The sharp drop in temperatures probably will not adversely affect people's health,, according to a spokeswoman for George Washington University Medical School. But flowers may be confused.

"The quinces are poking their heads through and trying to flower," said an employe at Johnson's Flower Center on Wisconsin Avenue. He said there is not much to be done to protect plants now other than applying mulch and watering heavily, if this has not been done earlier. graphics/photo: By Larry Morris--TWP Yesterday's unseasonably warm air produced a heavy fog in the morning that later was cleared away by gusty winds.