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

Showers are on the horizon for both New Year's Eve and New Year's Day, according to the National Weather Service.

A storm system moving up the coast could bring light snow tonight that will start mixing with rain into tomorrow morning.

Temperatures will reach a high of about 40 as showers continue throughout New Year's Eve, putting a damper on revelers ringing in 2010 outdoors, said meteorologist Valerie Meola.

Expect conditions to be "showery" for both the 6 p.m. and midnight fireworks shows on the Delaware River waterfront.

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 march up Broad Street for the Mummers.

Coming on the heels of this week's bitter cold, highs will reach a relatively balmy 40 degrees. But light showers are likely to persist through New Year's Day with wind gusts reaching 20 to 30 m.p.h., she said.

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

In the event of bad weather, the parade would be postponed first to Saturday and then, if necessary, to Sunday.

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

If there is bad weather on both those days, the parade would be rescheduled for Saturday Jan. 9, city officials said yesterday.

Regardless of the weather, the Fancy Brigade competition is to go on as planned Friday 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.