ITHACA, NY — It looks like Tompkins County is in for at least one more bout of hot and humid weather, with a muggy air mass expected to move in mid-week. Temperatures will return to more normal levels and drier weather will be expected by the end of the school week, but another round of unsettled weather is likely as we head into next weekend.

The current dry spell is the longest without measurable precipitation (trace or more) since late July, when there was almost a week of no rain. If the showers/storms stay in the east on Monday, the next chance for rain according to our climate data is Wednesday. pic.twitter.com/l20CSi5ZPN

– NWS Binghamton (@NWSBinghamton) 25 August 2024

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The weekend ends fairly quietly as a high pressure system over the Atlantic coast keeps air relatively stable while a weak low pressure system moves aloft over NNY and inland New England. Some early morning showers have moved well to the east and fair weather cumulus clouds dominate the satellite imagery with a local oasis effect (the opposite of the lake effect where cold water stabilizes warmer air moving over it) and plenty of sunshine in Tompkins County south of Cayuga Lake.

Temperatures are around 80 degrees at the time of this writing and should remain there for the next few hours. Skies will be mostly sunny and the air fairly humid as the high over the Carolinas re-solidifies and is pushed southeast by the low over New England. The night will be calm, skies will be mostly clear and lows will be around 50 degrees.

Monday will be another dry but fairly muggy day for Ithaca and the surrounding area. Mostly sunny weather is expected again as high pressure from the south remains in control, with highs a little above normal, at 27 to 30 degrees. Monday night will be mostly clear, with lows around 15 degrees.

High pressure will remain in place Tuesday, but a storm system will form over the western Great Lakes. Increasing southerly flow between the back (western) flank of the clockwise high pressure and the front (eastern) flank of the counterclockwise low pressure will result in a hotter and more humid air mass. It should remain dry and mostly sunny throughout the day, but highs of over 86 degrees Fahrenheit will feel more like temperatures in the 90s and 100s Fahrenheit due to high humidity. A few showers and thunderstorms will move in from the north-northwest Tuesday night, with increasing cloudiness after midnight. Lows at night will be humid, in the high 18s.

The frontal boundary of the low will drop to the south-southeast on Wednesday, and northern New York State is expected to see an unsettled day. Models indicate a swelteringly humid day with showers and thunderstorms, especially in the afternoon. Highs will be in the high 30s, but dew points in the 75s and 80s make it feel more like 90s, so take precautions when outdoors on Wednesday, stay hydrated, and take frequent breaks. Winds will shift to the north on Wednesday night, but skies will remain mostly cloudy, and some lingering showers and thunderstorms will continue. Lows will be in the high 15s as cooler air moves into the region.

A high pressure system will move in over Quebec on Thursday. A few lingering showers are likely, especially south of Ithaca, with partly cloudy skies and highs around 27°C. Thursday night will be mostly cloudy and dry, with lows around 15°C.

There may be some showers later in the day on Friday as a shortwave (instability pulse) moves southeast across Upstate NY. This is the precursor to a fairly large and strong storm system that is building over the Midwest and will impact the area over the weekend. Expect partly cloudy skies on Friday, with some possible afternoon showers, with highs around 80°F. The chance of showers will increase Friday evening as the storm system moves east and approaches the eastern Great Lakes, with mostly cloudy skies and lows around 60°F.

Looking ahead to next weekend, the low’s cold front should move eastward across the Upstate while the parent low moves across Eastern Canada. It should move out sometime Sunday and be replaced by a high pressure system building from the west. Highs will likely be above 25 degrees on Saturday with rain, and above 25 degrees on Sunday with increasing sunshine. Lows will be between 13 and 16 degrees.

Expanded outlook

A large-scale pattern is expected for early September that will bring cooler than normal temperatures across much of the Great Lakes and Northeast. This is part of a persistent low pressure system in the jet stream over the Mississippi Valley that would push cool, dry Canadian air into the Midwest. This would also push moisture from the Gulf of Mexico northeastward across the Mid-Atlantic and the New England coast, with slightly above-average precipitation possible for Tompkins County. Further upstream, a deep ridge will likely bring significantly warmer than normal temperatures across the entire West Coast.