ITHACA, N.Y. — This is like a “Family Feud” game show episode where the category is “four-letter ‘s’ words you don’t want to hear out of your kids mouth.” But alas, we’re in late October, and while we can have warm spells and cold snaps, climatology says we eventually get cold enough for snow. With an active weather pattern on tap this week, it’s going to be rather gray with the potential for snow Thursday night before we transition into a drier weekend.
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It’s been a cool and mostly cloudy day across the Southern Tier following the passage of a cold front through the region earlier Saturday. An area of low pressure has been moving northeastward into the Atlantic, and extending from its core is an inverted trough, which is the scientific way of saying that instead of extending equatorward (south, in the Northern Hemisphere) as a trough typically does from a low, it extends poleward. They are more likely to occur when the core of a low pressure system is south of ridges in the mid-latitude jet stream, as it is in this case. (Inverted troughs also form in the tropics from westward-moving waves of low pressure that roll off the African coast, and many of the strongest hurricanes we see in the Atlantic develop from African Easterly Waves. Fun fact of the day folks.)
Anyway, what this all means is that late tonight and Monday are going to be unsettled. As we head through the overnight tonight, clouds will continue to thicken, and rain will begin in most areas in the 2-4 AM time frame, with a few precursor showers south and west of Ithaca. The cloudy skies and rain will keep temperatures on the mild side for late October, with lows in the low 40s. New rainfall amounts will total less than one-tenth of an inch.
For Monday, expect a rather dreary day with cloudy skies and periods of rain throughout the day as the trough slowly moves east-northeastward. Temperatures will top out in the mid 50s with a light south wind, and new rainfall amounts will be between one-tenth and one-quarter of an inch. The periods of rain will continue through most of the night Monday, only begin to wind down closer to sunrise. Winds will turn to the north-northwest as the trough moves through, and this will bring some cooler air in, though the wet and cloudy conditions will keep lows from falling farther than the upper 30s.
Tuesday will be cooler, and conditions will remain unsettled as a major storm system rails against the lower Great Plains and Texas. The frontal boundary of this system, which will extend from the lower Great Plains along the jet stream into the Northeast, will channel unstable air and several disturbances towards the Southern Tier through the middle of the week. For what it’s worth, the trough’s lack of movement keeps the worst of the cold at bay in the Upper Midwest. It just also makes for continued showery conditions as the first disturbance, a short wave (pulse of instability), passes through Tuesday. Plan for mostly cloudy skies and a few scattered showers with highs around 50 °F. Tuesday night will see drier conditions as the first short waves move out, with mostly cloudy skies, a few isolated showers early, and lows in the upper 30s.
Wednesday will be somewhat nicer as high pressure over the Midwest briefly shoves the channel of instability southward. Some cloud cover is likely to bubble up due to the amount of remnant moisture present, but it will be dry and milder, with highs in the upper 50s. Wednesday night will host mostly cloudy skies with lows in the low 40s.
Thursday’s is going to be meteorologically interesting. The lower Great Plains storm system will begin to lift northeastward along the jet stream. Meanwhile, Zeta will be making landfall at or close to the Louisiana-Mississippi Gulf Coast, likely as a minimal hurricane. The remnants of Zeta will join with the other storm system and realign the channel of instability towards us, and so the whole messy conglomeration, a large storm system with lots of Gulf of Mexico moisture, will be heading our way. This large low pressure area will draw down lots of cooler air as they pass east of our latitude, and that’s where the risk of snow comes into play Thursday night, and if it taps into the ample moisture it hand it could be accumulating.
Models do not have a great grasp of how this will affect Ithaca and Tompkins County. They’ve ranged from drier outcomes to an all-rain event to a widespread accumulating snowfall. It’s going to depend on the exact track of the Plains system and how that storm interacts with Zeta after Zeta’s landfall. Right now, the most likely outcome is a rainy Thursday with some snow mixing in overnight. In this case, expect a cloudy, rainy day Thursday with about a quarter-inch of precipitation and highs in the low 50s. Thursday night will be cloudy with rain showers early, and snow showers mixing in during the early AM hours as temperatures drop into the mid 30s. Should this forecast change to show a more substantial snow as being the outcome, we will get an update out.
Friday will be chilly if mostly dry, with a few snow showers around sunrise giving way to partly cloudy skies. With that cold air wrapping in behind the low pressure storm system and a Canadian high building in, highs will only be in the upper 40s. Friday night will be partly cloudy and likely one of the coldest night yet in the season for many areas, with lows in the upper 20s in Ithaca’s urban core and mid 20s in the outlying towns. If anyone escaped the killing frost up to now, Friday night will likely finish the job.
For those planning some socially distanced Halloween celebration Saturday, as the high’s core shifts eastward and tamps down the northwesterly flow. Expect partly cloudy skies and highs in the low 50s. Saturday night will be mostly clear with temperatures in the mid 30s. Sunday will be a little warmer as the high shifts further east and southerly air is channeled in its rear clockwise flow. Highs will be in the mid to upper 50s with partly cloudy skies.
Looking into the start of November, the prevailing pattern calls for a warm western continental United States and a cool east as a jet stream ridge remains over the west coast and a downstream trough over the eastern United States, with cooler than normal conditions in the Northeast. On the bright side, perhaps literally, very little moisture will be available and there will be few storm systems as they mostly divert north and south of the lower 48, with the exception of slices of Florida and the Pacific Northwest. This bodes well for a dry Election Day across much of the country, though perhaps it’s the last thing the Mountain West wants to see given their wildfire situation.