ITHACA, N.Y. — It’ll be a rainy start to the week, but don’t put the sun hats and hiking boots away. The second half of the week looks to be quite pleasant, with seasonable warmth and sunny skies. Fall may be coming, but let’s enjoy the last throes of summer while they’re in town.

Your Weekly Weather

The first half of the week will largely be under the influence of a large, slow-moving low-pressure storm system currently organizing itself over the Western Great Lakes. With weak steering flow aloft and high pressure over the Western Atlantic Ocean, the system will basically wobble in place for the next day or so before finally finding an exit via the Eastern Great Lakes and St. Lawrence River Valley.

What this means in terms of sensible weather is that it’s going to be rather stormy and unsettled over the next couple of days, though temperatures should remain seasonably mild, as Tompkins County will reside in the warm sector of the counterclockwise-spinning low.

Today is just the start, as the warm front of the low swings into the Southern Tier and Finger Lakes. Expect periods of light to moderate rain, generally in the 0.10-0.25″ range, with highs in the low 70s. The lack of atmospheric energy this morning will keep thunderstorm activity to a minimum. As the rain shield moves northeastward and Ithaca is firmly ensconced in the warm sector, there will be a break in the rain tonight, though it will remain cloudy. Lows overnight will be in the low 60s.

Monday will see those warmer temperatures build up, as highs approach 80 across most of the county, with near-overcast skies. As the low and its cold front begin to move east, there will be enough instability and heat energy to trigger a few isolated showers in the morning, followed by much more persistent rounds of showers and a few weak thunderstorms during the PM hours. New rainfall amounts Monday will be 0.10-0.25″. Periods of rain will continue through the overnight hours Monday into Tuesday as the cold front moves through around sunrise. Quantified precipitation forecast (QPF) models show another 0.10″-0.25″ likely overnight, with lows around 60.

Tuesday will be a little cooler with highs in the mid 70s, but with the front past and the low lifting slowly to the northeast into Canada, the rain will taper off as the day progresses and the cloud cover will begin to break up. Another 0.10-0.25″ is likely, though that’s primarily in the morning hours; by early evening, it will be drying out and partly cloudy. Tuesday night will continue the drying and clearing as high pressure builds in from the northwest. Skies will be mostly clear, and it’ll be a “windows-open” kind of night for sleeping with lows in the mid 50s.

With high pressure continuing to build in on Wednesday, it will be a pleasant September day, though there will be a rather stiff northwest breeze. Skies will be mostly sunny with highs in the mid to upper 70s. Wednesday night will see the winds calm with the loss of daytime heating and the approaching core of the high. This with largely clear skies will result in an optimal radiational cooling setup, and if you’re out late Wednesday night, you’ll want a jacket, as lows will be around 50 by the lake and in urban Ithaca, and upper 40s on the hilltops and in the outlying towns.

Thursday will see winds from straight north, bringing down cooler Canadian air. This will result in a pleasant if cooler day than we’ve seen in a while, with mostly sunny skies and highs in the upper 60s. Thursday night will be another optimal cooling environment, so with mostly clear skies and calm air, temperatures will sink into the mid 40s across the county for lows. Folks, we are approaching autumn, get used to it.

As the core of the high skirts eastward Friday, the southerly flow on the rear flank of its clockwise-flowing circulation will perk temperatures up a few degrees, into the low 70s for highs with sunny skies. Friday night will host partly cloudy skies with lows around 50.

The medium-range models do show a west-east frontal trough over Northern New York Saturday, and this will likely pass close to or through Tompkins County later Saturday or early next Sunday. At this time, the daylight hours Saturday look pleasant, with partly cloudy skies and highs in the upper 70s. Sunday looks a little dicier with some showers depending on the trough’s timing, though temperatures will once again be in the mid to upper 70s for highs. Lows will be in the mid 50s to around 60.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking into the second half of September, the large scale pattern favors a pronounced jet stream ridge and above-normal temperatures over the Central and Eastern United States, shifting further east closer to October, with a jet stream trough further upstream over the Western Continental U.S. Over the Northeast, precipitation is expected to be near-normal for the period. I’ll note the only real concern with a setup like this is that it tends to be favorable for landfalling hurricanes. However, down in the tropics, things are fairly quiet at present so any hurricane activity appears to be off the table for the next several days.

Brian Crandall

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