Thursday Evening Updates
An extremely difficult forecast is unfolding for the next 18 hours over the eastern Finger Lakes.
So far, most of the attention with this storm system has focused on Friday night’s lake enhanced snow event. However, I have mentioned a few times the narrow band of heavy precipitation expected tonight.
That is turning out to be the most difficult part of this forecast.
The area of concern is the eastern Finger Lakes, generally around and east of Cayuga Lake into Central New York.
Rain is already developing over these areas and a band of heavy precipitation should set up from north to south overnight. Precipitation will stream north along the band, staying in generally the same places.
The very localized, heavy nature of the precipitation and razor thin temperature margin between snow and rain make a wide range of outcomes possible.
Let’s start with the position of the band.
There will be a very sharp cut off on the western edge of this band. The spatial difference between no precipitation and heavy precipitation may be as small as 15 miles. That leaves extremely little wiggle room for error, especially with the edge so close to Ithaca.
Next is the change over from rain to snow. Temperatures at the surface and aloft will be right near the freezing mark much of the night. If temperatures stay at 33 degrees, precipitation falls as rain. If it drops to 31 degrees, it is all snow.
Temperatures should eventually become cold enough for snow, but whether that happens at 1 am or 5 am has a huge implication.
Here are the possibilities:
Worst case scenario: Snow takes over shortly after midnight and the band develops further west. Ithaca could see 4-8 inches of snow by 8 am Friday morning. Areas just to the east, especially in higher elevations from south of Ithaca to north of Cortland, could see a foot.
Most likely scenario: Band sets up further east, still changes to snow sooner rather than later. Accumulations in Ithaca around or less than an inch. Snow amounts of 6”+ set up in higher elevations along and east of I-81.
Least snow scenario: Band stays east and/or stays rain: Little to no snow accumulation in the Finger Lakes.
Areas west of Cayuga Lake should not see anything more than a few flurries Friday morning.
Any snow should move out of the Finger Lakes for a time during the mid-morning hours Friday. Additional precipitation will wrap around the parent low pressure system, over Lake Ontario, and into the Finger Lakes.
Snow will become widespread through the afternoon and into the evening. Afternoon temperatures will be near or above freezing, so at least main roads should remain in decent shape as long as they are treated.
The snow will become most intense during the evening and overnight hours for areas to the north and east, as is common in lake effect situations. Snow amounts over 6 inches will be likely for eastern Cayuga, Onondaga, and northern Cortland County.
Moderate snow accumulations should spread west into Wayne County and south along Owasco Lake and into eastern Tompkins County.
Snow amounts for the remainder of the Finger Lakes should remain under 2 or 3 inches.
This snow will quickly end Saturday morning as dry air wraps into the region.
The snow map at the top of this post is for the entire duration of the snow event, including both any snow tonight and Friday night. The areas previously mentioned are circled in red to highlight the uncertainty. Again, I think the most likely scenario is for the heavy snow tonight to stay east of I-81, but heavy snow could come further west.
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