ITHACA, N.Y. — High pressure will provide for fairly quiet conditions over the first half of the week, but a developing winter storm threatens to make travel very difficult heading into Christmas weekend. Current projections have Ithaca initially in the warm sector, but you’ll want to keep a very close eye on Friday and Saturday if you’ll be traveling or receiving travelers for the holiday.

Your Weekly Weather

At present, a weak clipper low to the north is weakening as it transfers its energy to a stronger low pressure storm system over Atlantic Canada. Meanwhile, high pressure is steadily building in from the Ohio River Valley to the southwest.

In the near-term, the biggest risk is from lake effect snow bands, but the generally westerly flow means that the bands are largely confined to communities directly west of Lakes Ontario and Erie. Several inches can be expected south of Buffalo, and two feet north of Syracuse, but for Tompkins County, there will only be a few instability snow showers with the low’s passage, resulting in total accumulations that are less than one inch through Monday night.

For the remainder of your Sunday, expect high temperatures to top out in the mid 30s with near-overcast skies and a few scattered snow showers – as the low to the north is weakening, there isn’t enough local forcing in the atmosphere to produce more than that, and the weakening circulation means the associated “cold front” isn’t much of a cold front. Tonight will be cloudy with a westerly breeze and lows in the mid 20s, with upper 20s along Cayuga Lake and in urban Ithaca.

Monday will see a brisk northwest breeze, more the results of counterclockwise flow around the Atlantic Canada low than the remnants of Sunday’s system. Winds will be W-NW 10-15 MPH with some 20-25 MPH gusts likely. It’ll be mostly cloudy to overcast thanks to heat energy/destabilization provided by Lake Ontario, with highs in the mid 30s. More northwesterly winds Monday will direct a few lake enhanced snow showers into Tompkins County, with a new coating of snow possible. Winds will slacken but skies will remain mostly cloudy to overcast, with lows in the lower to mid 20s.

As the Atlantic Canada low shifts east and high pressure builds into the Finger Lakes, there will be a few more breaks in the clouds, but northerly flow on the northeast flank of the high’s clockwise circulation will keep highs in the lower 30s. Tuesday night will see the high move directly overhead, with calm winds that will allow the temperatures to drop a little further. Skies will be mostly cloudy, but lows will be in the upper teens Tuesday night.

Wednesday will be a quiet day as the high pressure system shifts modestly eastward during the day. This will allow for a light south wind, resulting in partly to mostly cloudy skies and highs in the mid 30s. Wednesday night will host mostly cloudy skies with a light south wind and lows in the lower 20s.

The first impacts of the forecasted storm system will begin to affect Tompkins County Thursday night. This complex storm has two components – a developing storm system on the edge of a very deep, frigid trough over the Great Plains (for instance, the models show snow in Dallas), while a downstream coastal low develops over the Carolinas. The Great Plains system becomes the primary core as it rapidly strengthens over the Ohio River Valley, north-northeastward into the Toronto area and through the St. Lawrence Valley, and the coastal system will help it strengthen as well as provide enhanced moisture for significant precipitation.

I want to point out this is expected to be a very strong system with a very deep core; models currently show 958-962 mb, which one normally sees over the open ocean with mid-latitude systems. This low pressure will drive very strong winds over a wide part of the Northeast, Ithaca included. Right now, the storm track keeps Ithaca in the warm sector until the storm passes our local longitude. Once it does, however, precipitation will rapidly change from rain to snow as arctic air moves in.

The caveat to this is that we are still several days out, and a shift of 100-150 miles will have very significant impacts on the amount and type of precipitation Tompkins County sees. The more the storm shifts east in model runs, the more likely a heavy, prolonged snow occurs. Further west, and it stays rain until longitudinal passage. Regardless, travel Friday and Saturday will be very difficult across the Northeast and Mid-Atlantic, so if you can leave Thursday or earlier, you’ll stand a better chance of getting to your destination on-time.

As it stands, Thursday will see a few morning showers turn to rain showers as warm air moves in ahead of the low. Skies will be cloudy with highs in the upper 30s. Thursday night will actually see temperatures warm further, with a heavy, prolonged rain and highs in the lower 40s (as noted before, do not pin your hopes on this, because it could end up being heavy snow instead if the storm shifts east).

Friday is going to start off rainy, but as cold air builds in on the rear flank of the low, this will cool from the lower 40s in the morning to lower 30s by sunset, and the rain will transition to snow as gusty winds begin to build with the strengthening storm system. Arctic air begins to enter Friday night as steady snows taper to snow showers; winds will gust at over 30 MPH from the west, with lows in the mid teens, but a windchill likely in the subzero (-0 to -5 F) range.

With ample west-northwest arctic flow on the backside of the low, the holiday weekend’s looking pretty darned cold. While generally dry conditions are expected with partly to mostly cloudy skies, temperatures will struggle to break 20 F for highs, and lows will be in the single digits. The wind will still be whipping on Saturday, so near-zero and subzero windchills are likely Christmas Eve into Christmas morning, though the wind chill Christmas Day should lighten up as the winds slacken with the storm system moving northward into the Arctic.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking into the end of the year and New Year’s Day, travel back to your destinations of choice should be somewhat less chaotic on the weather front. Medium-range models show the cold air becoming fairly depleted by the end of December, with near normal temperatures in the Eastern U.S. and an upstream jet stream ridge providing warmer-than-normal conditions for your friends along the West Coast. The pattern is favorable towards continental clipper-type low that drop quick batches of precipitation, so precipitation will likely be a little above normal for the period.

Brian Crandall

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