The relatively mild weather we’ve been enjoying comes to an abrupt end early Tuesday with the arrival of a new storm system that could bring thunderstorms to the Fresno area on Tuesday and drop daytime highs back into the 50s this week.

The weather forecast for Tuesday calls for rain and possible afternoon thunderstorms in the Valley and snow in the Sierra, with 6 to 10 inches forecast and possibly up to 12 inches in some locations, said Andy Bollenbacher, meteorologist with the National Weather Service in Hanford.

It will initially snow at an altitude of 7,500 feet and then drop to 6,000 feet, he said.

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

Depending on conditions, some sleet — tiny snowballs that form when ice sticks to snowflakes — could fall in the Fresno area during thunderstorms. But it won’t be enough for a white Christmas, said Bollenbacher.

Those heading east from the valley into the upper Mojave Mountains should prepare for wind gusts of up to 45 miles per hour on the leeward slopes of the Sierra on Tuesday.

The fog returns on Christmas Day

Once the rain stops in Fresno on Thursday, the valley will face dense fog again, and that could impact the weekend warmup, Bollenbacher said.

“At this time of year the angle of sunlight is really weak. This means that fog can form quite easily. “So you could theoretically see a temperature forecast of 65°C and then the reality looks like 58°C because you had fog all day and it was difficult to burn it off or mix in the afternoon hours and the temperature forecasts went wrong.” he said. “So basically what I’m telling you is there’s potential for a warmup over the weekend, but we’ll have to see what the fog actually allows for to get to the afternoon highs.”

There is also a small chance that rain will return in the valley on Thursday, although not all forecast models agree with that forecast, Bollenbacher said.

The forecast high and low for Fresno 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.