ITHACA, N.Y. — Change your calendar pages, folks; September has arrived, that start of meteorological fall. Seemingly right on cue, cooler conditions are in store for the second half of the week, chilly enough that you’ll want to start digging the jackets and sweaters out of the closet. (Come on, no one really packs them away, right? Warm weather lasts only three months around here.)

Your Weekly Weather

Let me start this off by addressing the national weather briefly, and Hurricane Dorian. Dorian has the unusual distinction of being the only major hurricane to rapidly intensify in the open Atlantic and is now the strongest hurricane to move through the Bahamas in modern history. and as many folks are aware, it’s uncomfortably close to Florida’s East Coast. 

What impact will Dorian have on our weather? Not much. The storm will likely run close to the East Coast this week, but stay far away from our region. However, the cold front that will usher in cooler temperatures later this week, is the same jet stream trough that will steer Dorian away from the Southeastern coast. If that front is slower or weaker than expected, Dorian will be able to grind its way further west, risking a major hurricane landfall near Cape Canaveral as it curves to the north and northeast. The size of the wind field of the storm, as well as the exact motions of both the storm itself and surrounding weather features will make the difference between a rainy, blustery day on the Space Coast, and a multi-billion dollar disaster. So dig out your long sleeves and hope for a fast-moving and strong frontal boundary Tuesday night into Wednesday.

Anyway, it’s a wet Sunday night as a warm front associated with an area of low pressure system over the Ohio River Valley pushes into the region, bringing widespread light to moderate rain with a few embedded weak thunderstorms in the mix. The bulk of the rain, a SW-NE band enhanced by a low-level jet streak helping to drive atmospheric instability, will fall between midnight tonight and 6 AM tomorrow, though rain will persist in lighter quantities and more scattered cells throughout the day tomorrow. Lows tonight will be in the low 60s, and expect a 0.25″-0.5″ of rain by morning.

Monday will be a damp and cloudy Labor Day holiday as the system continues to push eastward through the Southern Tier, with a weak cold front coming in with the low pressure center. Expect cloudy skies and scattered light to moderate rain showers throughout the day with some drying out and modest clearing late in the day. Highs will be in the mid 70s. Expect another quarter to half an inch of rain during the day Monday – if you have outdoor plans, you might want to move them indoors. Monday night will be dry and partly cloudy as Canadian high pressure builds in, with lows in the upper 50s. Some valley fog will be possible in the usual locations, so use caution if you’ll be out on the roads late Monday night.

Tuesday will be a resurgence of warmer air ahead of a fast-moving but rather potent trough of low pressure over the upper Great Lakes (this is the one that will shunt Dorian away from the Eastern seaboard). With light southerly winds and with the low still well to the west, it should be a nice day, with partly cloudy skies and a high around 80 °F. Clouds will increase overnight Tuesday with scattered showers developing in and around Tompkins County as the low approaches near daybreak Wednesday morning. Plan for mostly cloudy skies and a low in the mid 60s.

As the low pushes northeastward into Canada, the trough will swing through our region in the form of a strong cold front during the day Wednesday. It doesn’t look like there will be much moisture, so rain will be present, perhaps 0.1-0.25″ or rain and partly cloudy skies otherwise. Highs will make it into the upper 70s before the front passes and winds shift to the northwest during the mid-late afternoon hours. Wednesday night will see a real cool down with those northerly breezes and incoming high pressure breaking up the cloud cover and allowing for some radiational cooling. Expect lows around 50 °F in Ithaca and the immediate urban areas, and mid to upper 40s in the more rural towns and higher elevations.

High pressure over the Great Lakes will dominate our weather for Thursday, with only a few passing clouds and that northerly breeze continuing. Highs will be in the upper 60s. Thursday night will see the high move eastward and closer to the Southern Tier, and skies will be mostly clear with a low in the upper 40s.

Friday will be another nice day with only a few clouds and a high in the low 70s as the northerly breeze weakens with the passage of the core of the high pressure system system to the north; Hurricane Dorian will likely be passing off the mid-Atlantic coast by this point, but model runs suggest it will remain offshore at this time (so those of you traveling to New York or Boston for the weekend need not worry). With the high shifting eastward by Friday night, winds will shift to the south and overnight lows will be a few degrees warmer with somewhat more moisture in the air advected (drawn in) from our south, which will help enhance cloud cover. Expect partly cloudy skies and a low in the low 50s.

Saturday and Sunday are looking good for now, though the American (GFS) and European (ECMWF) models suggest a reinforcing cold front Saturday night with some cloudiness and a few scattered showers. The daytime hours should be fine, with mid 70s and partly cloudy Saturday turning mostly cloudy late, the front passing overnight with mostly cloudy skies, a few showers and a low in the lower 50s, and partly cloudy skies and highs in the mid to upper 60s for Sunday, making for an unseasonably cool early September day even by Ithaca’s standards.

Graphic courtesy of the NOAA Climate Prediction Cent.er.

Extended Outlook

Looking into next week and the middle of the month, the week will start off on the cool side, but should moderate as the week goes on and the trough in the jet stream shifts eastward, allowing for a large ridge over the Central part of the United States to shift eastward as well and gain some influence over our local weather. This period looks like it will be quite dry to start, with near-normal precipitation as that warmer, moister and somewhat more unstable air makes it way into the region towards the middle of the month. Initial outputs suggest a drier and warmer-than-normal second half of September, but we’ll see how if that holds up  over the next several days and we approach the astronomical end of summer.

Brian Crandall

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