A prolonged period of on and off lake effect snow is expected, starting Thursday and lasting through the weekend.
Cold air is streaming into the Finger Lakes behind a cold front Thursday morning. Limited lake effect is already developing downwind of both Lake Erie and Lake Ontario. For the vast majority of the upcoming snowy period, winds will be out of the west. This will keep the Finger Lakes focused on Lake Erie, with the Lake Ontario snows well north of the area.
Lake effect will gradually organize through the day Thursday and into Thursday evening. Overnight and into Friday, a healthy band of snow will extend far inland off of Lake Erie. Especially with bands traveling this far inland, even a slight adjustment to the wind can cause the band to shift substantially.
There is a chance that the band may wobble back and forth quite a bit on Friday into Saturday. However, if it stays steady, a few inches could fall in the eastern Finger Lakes, where the higher elevations give some extra lift to the air and the snow falls a bit heavier.
Early Saturday, winds will briefly become more northwesterly. The lake effect should dive south into northern Pennsylvania and dissipate. By the afternoon and evening, west winds will take over and lake effect will redevelop into the Finger Lakes.
A second, more substantial wind shift will take place after midnight on Saturday. Lake effect off of Lake Erie will move well south of the region as northwest and then north winds take over. Lake Ontario should spread some snow into the eastern Finger Lakes which will persist into Monday.
Some areas of the Finger Lakes will escape this event without seeing more than a couple of flakes. Most of the region will probably see an inch or two. If the Lake Erie band stays steady on Friday, and depending on how long the Lake Ontario activity lingers on Monday, some of the eastern Finger Lakes could see a few inches to a half-foot of new snow.
Temperatures will change little throughout this evening, with daily highs mostly in the low and mid 30s and lows in the upper 20s. There is an uncertain potential for a blitz of arctic air next week. More details on that in the coming days as forecast confidence increases.