The Mummers may have struck a deal with the city on costs, but they don't have one with Mother Nature for the weather.

Precipitation is on the horizon for New Year's Eve and New Year's Day, according to the National Weather Service.

A storm system moving up the coast was expected to bring light snow last night, and the snow was to start mixing with rain this morning, with accumulation of about an inch.

Temperatures are forecast to reach the upper 30s with a chance of rain New Year's Eve and a chance of snow after midnight, putting a damper on revelers ringing in 2010 outdoors, the weather service said.

Conditions could be wet for the 6 p.m. and midnight fireworks shows on the Delaware River.

The storm also will conceal the "blue moon" - the second full moon of December - behind a thick blanket of clouds.

And it's not going to be a pleasant strut up Broad Street for the Mummers.

On the heels of this week's bitter cold, highs will reach the relatively balmy lower 40s. There is a chance of snow in the morning, with 10 to 15 m.p.h. winds.

"Over the course of the whole storm, we'll have maybe up to a half an inch of rain," meteorologist Valerie Meola said. "It could be heavy at times, but it may be more of a steady rain."

If the weather is bad, the parade will be postponed to Saturday and then, if necessary, to Sunday.

The forecast for the weekend is dry, but winds remain a possible problem.

If this weekend's weather is bad, too, the parade will be rescheduled for Jan. 9, city officials said yesterday.

Regardless of the weather, the Fancy Brigade competition is to go on tomorrow in the Convention Center, at 12th and Arch Streets. Shows are scheduled for noon and 5 p.m.

Contact staff writer Sam Wood

at 215-854-2796 or samwood@phillynews.com.