ITHACA, N.Y. — With the start of October this week, it would only seem fitting that a brisk, autumnal pattern would follow. If you haven’t pulled the jackets and sweaters out of the closet, you’ll want to in the next day or two, as a strong cold front ushers in much cooler temperatures for the second half of the week.

Your Weekly Weather

Things are feeling a bit chillier this Sunday after a cold front rolled through the area Saturday night, allowing cooler air from a Canadian high pressure system to penetrate the region. The front brought an unseasonably warm stretch of weather to an end, one that brought record highs to Binghamton and Scranton. However, that break will be temporary as the ridge of warm air builds back northward from the southeastern U.S., displaced in part by the deep jet stream trough over the Mountain West, which as allowed a major low pressure storm system to deliver as much as four feet of snow to parts of Montana. Think of it like snapping a jump rope up and down. A big downward wave will have a corresponding upward wave of the same amplitude.

In the short-term, the entrance of the ridge will come in the form of a weak warm front Monday night. There will also be a couple minor pulses of instability along the edge of the ridge (i.e. over us), which could create a few rain showers, but nothing substantial to start off the week.

For tonight, expect fairly calm and dry conditions, with partly cloudy skies and winds shifting from light out of the north to light out of the south as the Canadian high shifts eastward. Lows will be in the upper 40s in Ithaca, along the lakeshore and the inner suburbs, with mid 40s in the more rural and elevated areas.

Monday will be somewhat warmer with that light southerly wind, and with a pulse of instability passing aloft, skies will be mostly cloudy with perhaps a light shower or two passing through Tompkins County during the day. Even then, precipitation will be very light. Temperatures will top out in the low 70s. Monday night will start off dry, but some showers and a weak thunderstorm or two is possible as the warm front passes through in the early morning hours. With the clouds and push of warmer air, it will be milder, with a low in the low 60s.

By Tuesday, Tompkins County will be firmly under the ridge of warm air, enhanced by the high, now sinking southward through New England, and the storm system over the Eastern Rockies. This air mass will be very humid, by July standards let alone October. Temperatures will max out in the mid 80s, but it will be very muggy, with dewpoints around 70 °F, and it will feel more like 90 °F. Oh boy, it’s the fun part of the year where you alternate between fans and sweaters in the same week. It’ll be mostly cloudy, so between that and moist air’s ability to limit atmospheric heating (just as it slows down cooling at night, it slows down warming during the day), don’t expect any records, but it will feel very summer-like for the start of October.

Another pulse of instability comes in for Tuesday night, and with the more unstable moist air in place, showers and thunderstorms will be more frequent in this round, though they’ll be scattered enough that the rain that falls will be brief. Between cells, it’ll be mostly cloudy and on the muggy side with lows in the mid 60s.

Wednesday will be a warm but very unsettled day as a cold front pushes through during the afternoon and early evening hours. A low that will have passed over the crest of the warm air ridge will then slide down to its east, slinging a cold front through with it and shoving the ridge back to our south. It will be another humid day, with scattered showers and thunderstorms throughout the day. It will steadily cool off as winds shift to the northwest by sunset, and some gusty breezes are possible as cooler air returns. Temperatures will reach around 80 °F prior to the frontal passage, but by the AM hours of Thursday, temperatures will have receded to a low of around 50 °F, with scattered showers remaining as the front finally collides with enough of the ridge’s air mass that it stalls out just to our south.

That stalled out front will serve as a channel for shortwaves, pulse of instability that will trigger more showers as they pass through. As a result, Thursday is looking like a yucky day. It will be mostly cloudy to overcast with scattered rain showers and a high in the mid 60s Ithaca south, low 60s to the north. Thursday night will see some of the showers clear out as the shortwave passes, but it will remain mostly cloudy with a few scattered showers and lows in the mid 40s.

A reinforcing trough will push in for Friday, shoving the ridge further south and allowing even cooler to infiltrate the Southern Tier. This will bring with it another round of showers, and with mostly cloudy skies and a north breeze, temperatures are likely to stay in the upper 50s for highs, maybe 60 °F right by Cayuga Lake.

For some of our higher elevations, Friday night is likely to be the first frost of the year. Northerly winds will allow cold air in overnight, and decreasing clouds will allow for some radiational cooling. In Ithaca proper, lows in the upper 30s are likely, with mid 30s further out. This will likely trigger many of the local trees to start changing color, so those fall colors will be coming on strong by mid-October.

The weekend will give another chance for first frosts, as mostly sunny skies and upper 50s on Saturday lead to another chilly, dry night with lows in the upper 30s in Ithaca and lower in the outlying towns. Sunday will be a little warmer as high pressure shifts east and winds take on a more southerly component, and highs will be in the low to mid 60s Sunday, with mostly sunny skies.

Graphic courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking ahead, for places that don’t have a first frost this weekend, the next chance will be another week or more. The ridge will return, if not quite as strong as before, so temperatures are looking to get near normal to modestly above normal (upper 60s to low 70s) with lows well above freezing the following week. Precipitation will trend near to somewhat above normal as storms ridge the edge of the ridge and clip the Southern Tier along the way. Just for the record, unlike Montana that dreaded four-letter s-word doesn’t appear to be in our forecast for some time yet. The warm pattern is expected to hold for most of October, as the Western U.S. continues to stay unseasonably cool in the presence of that deep jet stream trough.

Brian Crandall

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