ITHACA, N.Y. — As Perry Como once crooned, “(i)t’s beginning to look a lot like Christmas”. A low pressure system passing south and east of the Southern Tier on Tuesday will bring snow, filed by a second system and a shot of Arctic air later in the week before temperatures moderate in time for the first volley of holiday travelers this weekend.

Graphic courtesy of NWS Binghamton.

Your Weekly Weather

After this weekend’s rain-turned snow following the passage of a storm system to our west and east, some relative quiet is expected for tonight and Monday as a high pressure system continues to pass eastward to our south. With the high to our southwest and having a clockwise flow because we live in the Northern Hemisphere, that means the WNW winds pass directly over Lake Ontario, and because the lake water is warmer than the cold air directly above it, surface heat is transferred into the atmosphere, destabilizing it and leading to the development of lake effect snow bands. In this weekend’s case, a pulse of instability (shortwave) is riding around the edge of the high, leading to broad if weak enhancement of the bands. The clockwise flow is impressive enough to create snow bands from Lake Huron, weakening over Canada, enhanced over Lake Ontario and finally breaking apart over upstate New York.

Generally, as the shortwave moves out of the region and the atmospheric instability decreases, the lake effect bands will dissipate across the Southern Tier. The winds should also weaken as the core of the high moves into the region Sunday evening into Monday morning. For tonight, expect a fairly quiet December evening, with snow showers winding down by midnight and mostly cloudy skies with a low in the mid 20s.

Monday will be dry and partly cloudy to start, as the high continues east and southerly winds pick up behind it. Highs will be in the upper 30s. By Monday night, we’ll start to see the effects of the next storm system as it approaches, with increasing clouds and snow showers ahead of the system with a low in the upper 20s.

This low coming in for Tuesday will move on a track from the Tennessee River Valley, over the Virginias and New Jersey before heading into the Atlantic Ocean. This places us to the north and west of the low, which having counterclockwise flow means we’ll be in its cold sector. Since this low will move fairly quickly and there won’t be a lot of moisture available regionally, don’t expect a lot of snow, but enough that you’ll probably need to do a quick shovel, 2-4″ total. The majority of this will fall from about 4 AM-12 PM Tuesday, with showers lingering through sunset. Highs Tuesday will be in the mid 30s. Tuesday nigh should see some clearing skies, with partly cloudy conditions and a low in the mid 20s.

Wednesday looks like it’ll host round two. This low pressure center will come in from a totally different direction, moving southeastward from Hudson Bay in Canada. This system will have very little moisture available to it, and that’s because it’s an Arctic low, and very cold air has very little carrying capacity for moisture. This will only be a coating of snow at best, but after the temperature reaches the upper 20s late morning, the winds will begin to gust heavily out of the northwest as the low sweeps by just north of the Southern Tier. This will halt further diurnal warming and temperatures will decline precipitously Wednesday evening into Thursday morning. While still cloudy, the strong winds with Arctic air coming in from the northwest will drop low temperatures to +5-10 °F in Ithaca proper and 0 to +5 °F in the rural areas, and the wind chill will make it feel like -5 to -15 °F. Wednesday night will be a bitterly cold night to be outside.

Thursday is not much of an improvement with that Arctic air in place. While dry, substantial cloud cover is likely due to Lake Ontario, and temperatures will be around 20 °F for highs. As the Arctic high moves directly overhead Thursday night, winds will be calm and skies will be partly cloudy with temperatures a little warmer and without significant wind chill. Lows will be in the low teens in Ithaca and upper single digits elsewhere.

Friday will be warmer if still cold on the backside of those Arctic highs. Milder air will be advected in from the south, but the cold air from the high will mitigate its effects. Expect partly cloudy skies and highs in the upper 20s. Friday night will be mostly cloudy with lows in the mid teens.

With a high staying in place over Quebec, the weekend will remain sunny and seasonable. It will be partly cloudy to mostly sunny, and highs will be in the low to mid 30s Saturday and mid to upper 30s Sunday, with lows in the low 20s. The traditional work week is kinda gross this week, but the weekend will be fine travel weather for the first wave of holiday adventurers.

Graphic courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking ahead into the medium-range for a potential Christmas expectation, the outlooks are, well, neutral to below-average for a snowy White Christmas. Temperatures will be about average, meaning upper 30s, enough to melt the modest amounts of snow still on the ground after next weekend. It’s also expected to be on the dry side; some of the model ensembles suggest precipitation Monday into Tuesday/Christmas Eve, but it would be light and mostly in the form of rain. To be frank, apart from Alaska and the mountain resorts (especially the West Coast ones, which are about to get shellacked with a “Pineapple Express” atmospheric river of moisture), no one in the country is looking really good for a White Christmas next week.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.