ITHACA, N.Y. — A summery spell in early fall can be a pleasant sendoff before preparing for cooler days, longer nights and the inevitable turn towards more wintry conditions. However, there can be too much of a good thing. The lack of rain in the past month has result in some drought-like conditions, and the city has a Limited Water Use Advisory in effect.

On the bright side, some substantial rain is coming for the middle of the week, which should help to alleviate some of our water woes. But after Monday, it may be quite a while before you see 80°F again.

Your Weekly Weather

At the moment, the dominant feature of our local column of atmosphere is a large and strong area of high pressure out over the Atlantic Ocean. being in the western flank of its clockwise flow has allowed warm, moist air to be channeled into the Southern Tier on southerly winds, and as a result. temperatures have broken into the 80s in many parts of Tompkins County this afternoon, with generous amounts of sun if also a tad on the humid side. Areas to the south and east are under flow with ample oceanic moisture aw well as the influence a small, weak coastal low embedded within the edges of the high, and that has resulted in a more persistent cloud cover towards Scranton and Albany.

The rest of your Sunday will be pleasant and summer-like as that high pressure maintains control for at least one more day. Temperatures will slowly slip back through the 70s as we head into sunset, and overnight, cloud cover will build back into the region, which will provide an insulating effect and keep overnight lows from falling any lower than the low 60s Sunday night, making it rather nice for those who fancy a night-time stroll.

Monday is likely to be the last of the warm, dry days as the high pressure begins to shift further east and a potent storm system begins to set up to the east, which we’ll get to in a moment. Monday will be partly to mostly cloudy through sunset, with some isolated rain showers possible late in the day, on the edge of the next incoming system. With that high’s southerly flow enhanced by the counterclockwise flow of the low to the east, highs will be in the low 80s. More numerous rain showers will set in for Monday night, with mostly cloudy skies and a low in the low 60s.

From Tuesday on, our weather pattern will change rather dramatically. A very large and powerful storm system will extend from its core in Southern Canada, along its cold frontal boundary all the way to the Gulf Coast. This front is effectively a conveyor belt of moisture from the Gulf of Mexico and all the up through the United States and into Canada. This low will move slowly through the region, so the combination of deep moisture, high instability and slow movement result in elevated chances for long-period heavy rain especially Tuesday night into Wednesday morning. Most areas can expect an inch, but two inches of rain is certainly possible in areas in the way of embedded heavier bands within the system. Thankfully, because of our current rain deficit, the risk of flooding is low.

The cold front and the channel of maximum moisture will roll through very late Tuesday. During the daytime hours, which will host the showers and rain bands ahead of the front, it will be rainy, but it will take time for the heavier rains to work their way in. Tuesday will host cloudy skies and periods of rain with highs in the low 70s. Rain will be lighter in the morning and early afternoon, but by late afternoon and evening it will be more consistently heavy, with downpours possible, and potentially a few weak thunderstorms. Expect less than one-quarter of an inch of rain before noon Tuesday, and another one-half an inch from the early afternoon through the late evening. Tuesday night will see another half inch or so of rain, and cooler if cloudy skies as the cold front begins to work in, with lows in the low 50s.

Wednesday will be showery after sunrise, but not nearly so soaking as Tuesday, as the bulk of the rains move away with the frontal boundary to the north and east. It will be mostly cloudy with scattered rain showers decreasing as the day progresses. Highs will be cooler, in the mid 60s. New rainfall amounts will be one-tenth of an inch or less. Wednesday night will be showery, mostly cloudy and cool, with lows in the upper 40s.

Thursday is likely to be an unsettled day as well as a shortwave (pulse of instability) sweeps in behind the storm system. This will produce a few more light scattered rain showers under mostly cloudy conditions, with a high in the mid 60s. Thursday night will finally see some substantial clearing as the shortwave moves eastward, and the cooler air behind the low and partly cloudy skies will allow for a rather brisk night, with lows in the low to mid 40s.

Friday will be drier and certainly feel like October, as west-northwesterly winds keep high temperatures capped in the low 60s. A few lake-enhanced rain showers are possible north of Ithaca, closer to Lake Ontario, but otherwise it will be partly cloudy. Friday night will be partly cloudy and generally dry away from Lake Ontario, with lows around 40°F.

The weekend is looking cool but dry, not bad for those planning apple picking or other socially-distanced fall activities. Both Saturday and Sunday will be see mostly sunny skies with highs in the low 60s, and mostly clear skies overnight with lows around 40°F.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

The expansive storm system that will affect our weather for Tuesday and Wednesday will usher in a new regime with a deep trough in the jet sttream over the eastern half of the country, and a deep ridge in the west. This will result in cooler-than-normal conditions as we go through the first week of October. The maximum amplitude of the trough will be to our west, so the maximum cold anomalies will also be to the west, most prominent in the Deep South. Here, we may see temperatures dip into the 30s early next week, but any new frost threats seem unlikely at the moment. Even with this high-amplitude ridge-trough setup, the jet stream will be starved of moisture and conditions across the continental United states are expected to be drier-than-normal or near-normal with the exception of Alaska and a chunk of Florida, outside of the high-amplitude pattern.

Brian Crandall

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