The first Winter Weather Advisories of the season go into effect tonight and into early Tuesday morning.
High pressure moving across eastern Canada will deliver cold air to the region on Monday. Temperatures will rise little during the day from the 20s to the low 30s. Temperatures will retreat back to near or just below 30 degrees tonight, even as a storm system approaches from the west.
Warm air associated with this storm system will ride up and over the cold air in place near the surface. This will lead to a break out of precipitation from southwest to northeast. Initially, this precipitation will start out as a brief period of snow.
As warm air takes hold aloft, the snow will change to sleet, and then freezing rain overnight. An inch or two of snow and sleet followed by a coating to a couple tenths of an inch of ice is likely, especially over higher elevations and areas further east. Combined with gusty winds, this could be enough to cause some sporadic power outages, in addition to hazardous travel.
Temperatures will rise above freezing at the surface from west to east during the early morning hours on Tuesday. Precipitation will transition to rain and become lighter and more spotty as this occurs. For the western Finger Lakes, this change over could occur as soon as 3-5am. For the eastern Finger Lakes, the change over will be closer to 6-8am.
By the mid-morning hours, conditions will be rapidly improving across the area. Temperatures will continue to rise and should end up in the mid 40s by Tuesday afternoon. Only a few rain showers will be expected.
Some more rain showers will be possible on Wednesday and early Thursday before the coldest air of the season starts to filter in. Lake effect snow will become a nuisance by later in the week, with some areas of the Finger Lakes receiving several inches. By the weekend, high temperatures will only be in the 20s. There are some indications that this flip to winter will be a more permanent change for the coming weeks and months.