ITHACA, N.Y. — Sorry, but you all knew that climatologically, it was coming sooner or later. A potent slug of cold air will slosh through Tompkins County during the middle of the week, and a few snow showers may be possible during the early morning hours as temperatures stay below normal. If it makes you feel any better, a substantial recovery to above normal temperatures is in the cards for next weekend.

Your Weekly Weather

It’s been a fairly quiet as high pressure has allowed dry air and a stable atmosphere to preside over most of Upstate New York. However, a low pressure storm system is gathering strength over the Great Lakes, and its associated cold front will press into the area Monday.

For the remainder of your Sunday, it will be a fairly pleasant October evening. Under mostly clear skies, temperatures will recede from highs in the low 60s and into the mid 40s overnight. Cloud cover will build in after midnight as the storm system approaches, and a few rain light rain showers will enter into the Ithaca/Tompkins area by sunrise, with mostly cloudy to near-overcast conditions for your Monday morning commute.

These Monday showers will primarily be a morning event, a quick spritz of light rain and largely clearing out by afternoon and some more breaks of sun develop in the cloud sheet. It will be cooler, with highs in the mid to upper 50s. Cooler air coming in on the backside of the low will produce a chilly night Monday night, with clearing skies and lows in the low to mid 30s, with frost likely in outlying areas and higher elevations.

The incoming storm system will be rather unusual in that there’s really two lows, a surface low near the surface and a low further aloft in the atmosphere. Either one on its own would likely scoot in and out quickly. On the other hand, when they’re stacked on top of each other in the same column of air, forward motion tends to stall out and you often end up with an initially strong, multi-day storm system.

Here, however, they’re not quite stacked up. The upper-level low hangs over the Great Lakes while the surface low swings northeastward towards Quebec. The proximity of these two lows will actually cause them to spin around each other in a counterclockwise motion, spiraling in towards each other. This process is known in meteorology as a binary cyclonic interaction, the “Fujiwhara Effect“.

What that means from a practical standpoint is that the system doesn’t quite stall out, but you have an expansive low-pressure circulation consisting of two lows in a counterclockwise dance over the Great Lakes and Southern Canada. This is going to keep things unsettled for a few days and draw down a lot of polar air into the Midwest and Northeast. Not being quite fully aligned, however, the lows will still be pushed out and northeastward by broader jet stream flow, eventually weakening and falling apart later in the week over Northern Ontario and Quebec.

So, there’s your weather lesson for the week. As this storm system is so large, rain will be well to the east, and Ithaca/Tompkins will be in the “dry slot” of the low. There will be ample sunshine Tuesday, even with broad cold air advection from the southwest. No, that’s not a typo. The wind will be from the southwest because it’s wrapping around the counterclockwise circulation of the large storm system – so in this case, it’s gusty cold air from the southwest. Temperatures will struggle to make into the low 50s with partly cloudy skies. Tuesday night will see partly cloudy skies with lows in the mid 30s. Those breezy winds might create a stronger wind chill, but they also agitate the air and keep temperatures from dropping further.

Around sunrise Wednesday, some showers are likely to move through as wraparound moisture penetrates into the region. With temperatures in the low 30s, it’s here that you might some snowflakes in the air as you’re heading off to work. Accumulations are not expected. Temperatures will warm up through the morning and showers will change over to rain, as skies remain partly cloudy with brisk highs around 50. Wednesday night will be partly cloudy and dry as the system lifts northward, with lows in the lower 30s.

Thursday will be the last of the really chilly days as the broad cyclonic flow of the storm system continues north. Skies will be mostly sunny with highs in the low 50s. Thursday night will be mostly cloudy and chilly, with lows in the low to mid 30s.

High pressure near Bermuda begins to work northwestward and into the Southern Tier and Finger Lakes later in the week. This will allow for a warm-up, and more stable conditions. Friday will me markedly warmer, with mostly sunny skies and highs in the upper 50s. Friday night will host partly cloudy skies with lows around 40.

Looking into next weekend, the substantial warming trend will continue as the high funnels in air from the southwest – by some definitions, “Indian Summer“. Both Saturday and Sunday will be pleasant and dry, with partly to mostly sunny skies and highs in the mid 60s for Saturday and low 70s for Sunday. Lows will be in the 40s Saturday and around 50 Sunday.

Images courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Initial indications show an unseasonably warm pattern for the last week of October. Forecast models suggest temperatures in the low to mid 70s for several days as the ridge of high pressure ushers in ample mild air into Upstate New York and the Northeast, with near-normal precipitation. Further upstream, troughiness in the jet stream will create cooler and wetter than normal conditions over the Mountain West.

Brian Crandall

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