ITHACA, N.Y. — It’s no fun to rake wet leaves. Hopefully you had a chance to enjoy the sun this weekend, because the week ahead will be a rainy one, though at least it should remain on the warm side of normal.

Your Weekly Weather

Clouds are beginning to push into the region from the west-southwest, part of an area of low pressure currently centered over the Central United States. The large-scale atmospheric setup is a pronounced jet stream trough along the West coast, enhanced by a “bomb cyclone” (a rapidly strengthening low pressure storm system), with a ridge in the jet stream over the inner Mountain West, and a less pronounced trough over the Central United States, and a ridge straddling the East Coast.

Quick scientific aside, but when it comes to the mid-latitude jet stream, it helps to think of it like a rope being snapped up and down – it propagates downstream, eastward in the Northern Hemisphere, and while they may vary in strength and size, ridges have corresponding troughs. Something like that big Pacific Coast storm is in practice the initial force, the “snap” of the rope. When there are no “snaps”, you have zonal west-east flow in the jet stream and seasonally near-normal conditions.

With that in mind, that trough to the west, upon which that Central U.S. low is riding, will be moving downstream, which means into the Great Lakes and Northeast. In other words, an unsettled, often rainy week ahead.

The remaining daylight hours should stay dry, but shortly after sunset, an area of rain associated with the warm front extending from that Central U.S. low will begin to push into the region. It will be a rainy night tonight as that passes through, though the rain and thick cloud cover will keep lows in the upper 40s overnight, about ten degrees above normal. New rainfall amounts tonight will be between one-half of an inch and three-quarters of an inch with locally higher amounts possible.

The rain will become more intermittent by sunrise Monday, with scattered showers during the morning and a few scattered showers during the afternoon. Now firmly within the warm sector of the low, temperatures will climb on that southerly wind to about 70°F for a high. The regional weather pattern becomes more dynamic Monday night, as the initial low, passing to the south, transfers its energy to a developing coastal storm system during the overnight hours, a setup not unlike some Nor’Easters. This will place us behind the coastal low longitudinally, so in its strengthening counterclockwise flow, cooler air will be drawn in from Canada Tuesday, and between the two lows there will be ample moisture for more rain. Monday night will be rainy, particularly after midnight, with overcast skies and lows in the low 50s. New rainfall amounts will be between one-quarter and one-half of an inch.

Looking into Tuesday, the rain will continue as the coastal low, now southeast of Cape Cod, pulls oceanic moisture around itself and into the Northeast. Tuesday will be overcast with occasional rain, and considerably cooler, with highs in the upper 50s. New rainfall amounts will be between one-quarter and one-half of an inch. Tuesday night will see the rain taper off to light scattered showers, with overcast skies and lows in the mid 40s.

Wednesday sees the coastal storm pull away slowly to the east, and while it will still be an unsettled day, most of the day will be dry, with a few scattered showers and mostly cloudy skies, with a few more breaks of sun during the afternoon and evening. A weaker northerly flow as the low pulls away will allow high temperatures to be a little warmer, around 60°F. Wednesday night will be dry and partly cloudy, and the drier conditions and more open skies will allow temperatures to cool off to the low 40s overnight.

Thursday will be a fairly nice day for late October, with partly cloudy skies and highs in the low 60s. The next system begins to move in late Thursday night into Friday morning, a high-amplitude frontal boundary (meaning, it extends from the Gulf of Mexico to Canada) with a Gulf Coast low that will ride northward along the boundary. This shouldn’t really arrive until Friday, so only a few showers are likely during the overnight hours, with increasing clouds and lows in the upper 40s.

Friday is interesting, because the moisture shield begins to pinwheel around the low, becoming a very broad and strong low pressure storm system over the Ohio River Valley. On the edge of that development, Ithaca and Tompkins County will see an unsettled day, but not washout, with scattered showers, mostly cloudy skies, and highs in the low 60s. As the system continues to spin over the Ohio River Valley Friday night, only moving slightly eastward (a stubborn ridge over Atlantic Canada will make its path eastward slow and difficult), plan for mostly cloudy skies and scattered showers with lows in the upper 40s.

The weekend is looking dicey as the low slowly but steadily makes its way east and then northeast by Sunday. It’s looking like it’ll be far enough away that Halloween night will be suitable for trick-or-treaters, with a few scattered showers, mostly east of Ithaca, and temperatures that evening in the low 50s. Daytime highs Saturday will be around 60 °F with on-and-off rain showers, and in the mid 50s Sunday with showers early. If you haven’t had a hard freeze already, there’s no indication of one happening anytime in the next seven days.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Here’s something we haven’t seen too often lately – a broad area of cooler-than-normal temperatures across the Eastern United States. The large-scale pattern in early November favors a large ridge over the West Coast with a downstream trough funneling cooler air into the Eastern U.S. and into the Southeast, though Tompkins County will be on the edge of that and closer to normal temperature-wise. This dry, continental air is expected to result in broadly below-normal amounts of precipitation, and less moisture will allow for some cooler overnight lows that will likely shut down what’s left of the growing season in many areas. Once again, on the fringe of that dry, cool air mass, precipitation will be near-normal in the Southern Tier during that period.

Brian Crandall

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