The National Weather Service has upgraded the winter storm warning for St. Lawrence County and is now calling for seven to 12 inches of snow across the area by Wednesday night.

Meteorologists say heavy snow is expected and drivers should expect difficult travel conditions, including during Tuesday morning's commute.

The NWS anticipates seven to 10 inches, with localized amounts up to 12 inches, between 1 a.m. Tuesday and 7 p.m. Wednesday.

Monday night leading into the snowstorm is expected to be cloudy with lows around 17 degrees, giving way to the likelihood of snow after 1 a.m., NWS said. Wednesday is forecast to be in the high 20s with a 90 percent chance of three to seven inches of snow, with another one to three at night and temperatures dropping to around 12 degrees.

The Star Lake area, which is under a winter storm watch instead of warning, is looking at the possibility of three to seven inches total over the same time period, and temperatures several degrees cooler at night.

Wednesday brings a 70 percent chance of less than a half inch of snow, with temperatures around 15 degrees.

Wednesday night brings as high as 50 percent chances of snow showers, followed by temperatures dropping to around 1 degree.

The detailed forecast for the Potsdam area:

Monday night - Snow likely, mainly after midnight. Cloudy, with a low around 16. Calm wind becoming northeast 5 to 7 mph after midnight. Chance of precipitation is 60%. Total nighttime snow accumulation of less than one inch possible.

Tuesday - Snow. High near 29. East wind 3 to 8 mph. Chance of precipitation is 90%. New snow accumulation of 3 to 5 inches possible.

Tuesday night - Snow likely before 8pm, then snow showers likely after 8pm. Cloudy, with a low around 13. West wind 6 to 11 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible.

Wednesday - Snow showers likely. Cloudy, with a high near 16. Wind chill values as low as -3. West wind 13 to 16 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible.

Wednesday night - A 50 percent chance of snow showers before 11pm. Mostly cloudy, with a low around 2. West wind 11 to 16 mph, with gusts as high as 26 mph. New snow accumulation of less than a half inch possible.

Thursday - Mostly sunny, with a high near 13. West wind 6 to 9 mph.

Thursday night - Mostly cloudy, with a low around 3. Light west wind.

Friday - Partly sunny, with a high near 20. Calm wind.

Friday night - A 30 percent chance of snow showers after 8pm. Mostly cloudy, with a low around 11. Light southwest wind.

Saturday - A 30 percent chance of snow showers. Mostly cloudy, with a high near 29. Southwest wind around 6 mph.

Saturday night - A 40 percent chance of snow showers. Mostly cloudy, with a low around 20. South wind around 7 mph.

Sunday - A 40 percent chance of snow showers. Mostly cloudy, with a high near 34. Southwest wind around 8 mph.

Sunday night - A 40 percent chance of snow showers. Mostly cloudy, with a low around 22. Southwest wind around 9 mph.

Monday - A 50 percent chance of snow showers. Mostly cloudy, with a high near 34. West wind 7 to 9 mph.