Timing:
The snow should begin moving into the southern portions of northern New York just before sunset and quickly spread across the rest of the eastern Lake Ontario region within the couple hours after sunset. The snow will continue all night, becoming heavy at times. The snow will continue Tuesday though it should be lighter for the most part. However, there could still be a few heavier snow showers around at times. The snow should come to an end Tuesday evening. However, some areas to the east of Lake Ontario will immediately begin to pick up lake effect snow after this system pushes away, leaving no true break in the snowfall.
Precipitation Amounts:
The snow will be somewhat heavy at times across the region but there appears to be some large differences in where the snow will stay steadiest the longest. The heaviest snow will likely fall in the few hours around the midnight hour. The 18Z run of the NAM model (right) depicts liquid equivalent precipitation totals ranging from a quarter inch to around one inch. In this scenario the heaviest snow would fall in the Tug Hill region and the lower totals would be across central St. Lawrence County. Meanwhile, the 12Z run of the ECMWF model tends to show the same areas of high and low precipitation totals but the higher amounts across the Tug Hill are only around 3/4 of an inch. The 12Z Canadian GEM model appears to have a similar solution to the 12Z ECMWF but may also bring through a heavier area of precipitation early Tuesday morning. The 12Z run of the GFS model (right) is potentially the worst (best) case scenario, blanketing the north country in at least half an inch of precipitation with areas of near or just over an inch across a large area. This would result in snowfalls of 6 inches or more across the entire area if this were to come true.Snow Ratios and Amounts:
The snow growth region for this event will begin around 12,000 to 14,000 feet, which means there is a lot of time for riming to occur (condensing of the snowflakes). However, the region below the snow growth region should remain at or below freezing all night. Taking this into consideration, it appears that snow will begin with a snow ratio around 15:1 tonight. Tomorrow, as the snow growth region falls and the only concern becomes the temperature of the surface, snow ratios will increase to 20:1 for much of the day and likely to around 30:1 by nightfall (this is when the lake effect would be beginning and the general show showers would be wrapping up). Some areas may see a changeover to rain during portions of the afternoon tomorrow closer to the lake shore.So knowing the ratios and the precipitation totals, it is possible to come up with some snow amounts for the area. I think on the low end, 2 to 3 inches should be expected for the whole area. However, higher amounts will likely occur for many areas, especially the Tug Hill area. Across the Tug Hill, amounts up to a foot may fall before the lake effect starts up tomorrow night. My map to the right is my best general prediction at this point of how much snow may fall by tomorrow evening. The gray area will see the lowest amounts, generally 2 to 4 inches in this region. The blue region can expect 3 to 7 inches with perhaps a few isolated areas up to 10 inches. The heaviest amounts will be in the pink region where amounts of 6 inches or more will be likely. A few areas in this region could get a foot or more of snow, as I mentioned previously.
Lake Effect:
I will not comment that much on this in this post, but figured that I should mention it. There will be a period of lake effect snow following this system for Tuesday night into Wednesday. The most likely area to receive this will be east of Lake Ontario and amounts will likely prompt a Lake Effect Snow Warning for this region.
Impacts:
Travel will become difficult after nightfall this evening as snow moves into the area and will likely stick to roads fairly quickly with the sun being down already. Additionally, winds will become stronger tonight and thus have promoted a wind advisory for the area. This will cause blowing and drifting snow and lead to whiteout conditions. Winds will become sustained around 20 mph with gusts to 50 mph in some areas, especially those favored for high winds under a southeast flow, such as areas to the northwest of the Tug Hill Plateau. Take it easy, especially tonight, if you need to travel. Winter is not over yet!
