ITHACA, N.Y. — It’s been a rough week, meteorologically speaking. But now is not the time to let your guard down, as Christmas Eve and Christmas Day could be a wild ride for Santa Claus on his sleigh. A broad storm system will sweep across the Eastern United States Thursday into Friday, with heavy rain on the holiday eve and a steep decline in temperatures as you’re Zoom-chatting with your relatives on Christmas morning.
The storm that walloped communities south and east of Ithaca last week was the result of a couple different factors – one was the overall track of the storm, which was more northerly than initially forecast, and the second was the formation of an unusually intense deformation-zone snow band within the greater storm system. In a nutshell, when the storm draws in colder air behind its counter-clockwise spinning core, it can create an enhanced lapse rate (change in temperature with height), which makes for a more unstable atmosphere and can supercharge any existing precipitation within that atmospheric column.
With a lot of Atlantic Ocean moisture available to this storm in its larger circulation, it made for the right mix of ingredients at the right time for an absolutely monstrous storm system – which as many of you have read from other regional and national papers, wreaked havoc on the Binghamton area. The highest certifiable snowfall amount appears to be about 42″ at a site a couple miles southwest of the NWS office at the Binghamton airport, making this the new all-time record for a two-day event in the Binghamton area. A 43.3″ total in northern Pennsylvania might have set the state’s all-time record for a two-day event, pending confirmation.
In Tompkins County, the winner appears to be a co-op station on the southern edge of the town of Newfield, with 16 inches. Most towns south and east of Ithaca were in the 12-16″ range, Ithaca itself received a little over 9″, and towns north and west of Ithaca were in the 8-10″ range. This was followed by enough cold air funneled in behind the storm to bring temperatures plunging by Friday night, though it looks like Dryden was the only Tompkins community confirmed with a subzero reading.
The weather this weekend has been calmer if not especially pleasant; Saturday was sunny but cold with highs in the mid 20s, and after lows in the single digits last night, somewhat milder (if still cold) air has been channeled into the Southern Tier ahead of a weak area of low pressure passing to the north. This has brought temperatures up to around 30°F with cloudy skies and some scattered light snow showers, for which accumulations will be light, from a dusting to less than an inch. The next few days will be a mixed bag, but the real serious worries won’t start until Thursday, which will get to in a moment.
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The low to the north will move fairly fairly quickly to the east, and so the light snow showers associated with its passage will quickly move eastward with it. Precipitation should largely be over by this evening, leaving Tompkins County with a light southerly wind, mostly cloudy skies and lows around 30°F.
High pressure briefly bubbles in from the southwest for Monday, behind this weekend’s low and the next system to the west-northwest. It will be partly to mostly cloudy, with highs in the upper 30s. There’s enough relatively mild air present that when the next rather weak low arrives in the late evening hours Monday, the precipitation will mostly be in the form of a light rain rather than snow, though a few snow showers could mix in before sunrise Tuesday. Plan for increasing clouds by sunset and occasional rain showers Monday night, maybe a few flakes after midnight, with overcast skies and lows in the mid 30s.
Tuesday’s low is a slower mover, so the cloudiness and rain/show showers will linger through the day with mostly cloudy to overcast skies, and winds turning to the west-northwest as the system passes. Highs will be in the upper 30s. The showers should dissipate by evening, and those northwesterly winds will allow for some cooling off, with dry conditions, mostly cloudy skies and lows in the mid 20s Tuesday night.
Wednesday will be another nicer as high pressure once again builds in from the southwest. It will be a partly cloudy day with highs around 40°F. Wednesday night will be mostly cloudy with lows in the low 30s.
While we have our calm Wednesday, a major storm will be gathering strengthening over the northern Great Plains as it heads eastward. Models show the frontal trough with this powerful storm extending from Hudson’s Bay Canada all the way down to the Gulf of Mexico. This will allow for a very power channel of warm air ahead of the system, as well as a tap of deep moisture to feed its precipitation bands.
The concern here really starts to arise around sunrise Thursday, Christmas eve morning. Rain will spread across the region, and it will be heavy at times. Across the Northeast, widespread rainfall amounts of 1-2″ are expected. Now, the issue isn’t the rain itself. The issue is that much of this area is still buried under a lot of snow, with only a modest amount of that melting off between now and Thursday morning. This results in two major concerns – one, when you dump an inch of more of rain across a rooftop, it makes it very heavy and prone to collapse; and two, with temperatures climbing into the low 50s Thursday along with that rain, we will have a setup that promotes very rapid meltoff of a lot of snow, raising the risk for flooding. There is some uncertainty in where the heaviest rain will be, and chances are good it’s actually a little to the east – but the potential for roof damage/collapse and flooding is high enough that NWS Binghamton is calling it a “fairly concerning” possibility.
The next risk is heading into Friday, Christmas morning – temperature in the mid to upper 40s around midnight, will fall below the freezing point by 9 AM and upper 20s by afternoon. With widespread ponding of surface water from melt and heavy rain and little chance of dissipation during the overnight, the rapid fall of temperatures could create an extensive flash freeze event, making travel hazardous as everything ices over. Be very, very careful if you’re going to be driving or otherwise outdoors on Christmas morning. The only sliver lining is that cold air will also be quite dry, so no major snow in expected on the heels of this large storm system Christmas Day. It will be mostly cloudy by afternoon, and stay mostly cloudy through the night with lows around 20°F.
The weekend will be seasonably cold and quieter. At this point, Saturday and Sunday may have some lake-enhanced snow showers to the north of Ithaca, but otherwise partly to mostly cloudy with highs in the upper 20s and lows in the mid to upper teens.
Looking into the end of 2020 and when we say goodbye to this horrendous nightmare of a year, the pattern is slightly favorable to more coastal storm systems and Nor’Easters, but it’s looking like the position of the jet stream ridge over the northern Great Plains should push the downstream trough far enough east that storms would likely be just a little too far east to pose a major concern for Tompkins County. Temperatures are expected to be slightly above normal for the period as tendrils of the ridge edge into the region during the end of December and start of January 2021.