Enjoy Sunday's clear blue skies and sunshine, because an incoming cold front means a couple of days of rain to start the workweek, the National Weather Service said.

The service's Upton office said Sunday's high temperatures of nearly 70 degrees across Nassau and Suffolk counties will be short-lived; high pressure passes off the coast Sunday, and cloudy conditions move in, lasting probably through Tuesday night.

Expect light south winds from 8 to 13 mph with the sunny Sunday skies and clear conditions overnight. Nighttime lows are in the mid-50s.

See also7-day weather forecast for LI

News 12 Long Island meteorologist Matt Hammer said "from sun up to sun down, nothing but sunshine" for Sunday.

"There will be a few high, thin fair-weather clouds, but that's it."

Conditions also should be clear Monday morning, but the incoming cold front delivers a slight chance of rain and possible thunderstorms, mostly from 3 p.m. to 3 a.m. Tuesday.

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Toward Monday evening we're expecting some changes," Hammer said. "A strong cold front will approach, and we'll be monitoring the development of showers and potentially strong thunderstorms."

Chance of rain increases to 60 percent from late Monday through Tuesday night, the service said.

"Throughout the day Tuesday there will be the chance for a pop-up shower or storm," Hammer said.

Rainfall amounts over that span could be from one-tenth to one-quarter inch, according to the National Weather Service forecast.

By Tuesday night, gradual clearing is expected and summerlike conditions return starting Wednesday, when skies once again are sunny and daytime highs are in the mid- to upper 70s.

Wednesday will be the pick of the week, Hammer said, with mostly sunny skies and highs in the low 80s.