The relatively balmy weather we've been enjoying will end abruptly early Tuesday with the arrival of a new storm system that could bring thunderstorms to the Fresno area on Tuesday and drop the daily highs this week back into the 50s.

Tuesday's forecast calls for rain and possibly afternoon thunderstorms in the Valley and snow in the Sierra, with 6 to 10 inches forecast and potentially up to a foot in some locations, says Andy Bollenbacher, a meteorologist with the National Weather Service in Hanford.

Snow will start out at 7,500 feet and then drop down to 6,000 feet, he said.

A winter storm warning will be in effect for the central Sierra on Tuesday.

Depending on conditions, some graupel -- tiny snowballs that form when ice sticks to snowflakes -- could fall in the Fresno area during thunderstorms. However, there won't be enough to stick around for a white Christmas, Bollenbacher said.

Folks heading east from the Valley to the upper Mojave should be prepared for wind gusts as high as 45 mph on Tuesday on the lee slopes of the Sierra.

Once the rain ends in Fresno on Thursday, the Valley will face the possibility of dense fog again, and that could impact a weekend warmup, Bollenbacher said.

"This time of the year, the sun angle is really weak. That means it's pretty easy for fog to form. So you could theoretically see a temperature forecast of 65, and then reality is like 58 because you had fog all day and it was hard to burn off or mix out by the afternoon hours and the temperature forecasts have gone awry," he said. "So basically what I'm telling you is there's a potential for a warm-up over the weekend, but we're going to have to see what the fog actually allows the afternoon highs to become."

There's also a slight chance for rain to return on Thursday to the Valley, although not all the forecast models agree with that prediction, Bollenbacher said.

The forecast highs and lows for Fresno for this week: Monday 64, overnight low of 57; Tuesday, 53, low of 43; Wednesday, 52, low of 44; Thursday, 54, low of 48; Friday, 56, low of 48; Saturday, 60, low of 48; and Sunday, 62.