ITHACA, N.Y. — The leaves are changing, there’s a chilly nip in the evening air, and some people are turning Halloween into a personality trait. Fall is in full swing, but temperatures are a little cooler than they usually are for early/mid October as a persistent trough in the jet stream channels in Canadian air to the region. We’ll see some milder temps this week, but a cold front Thursday will send temperatures back below normal.

Your Weekly Weather

Conditions are generally quiet across the region as high pressure builds in from the southwest. A departing upper-level frontal trough over the St. Lawrence Valley and northwest winds over Lake Ontario are providing a fair amount of cloudiness and a few showers well to the northwest of Ithaca. Locally, though, it’s a dry day, as temperatures perk up into the low 60s for highs.

That expansive area of high pressure will retain control over Tompkins County’s weather for the next few days, and quiet conditions are expected with seasonable temperatures, trending higher as the high moves eastward and we start to see some southerly flow advected northward in the high’s clockwise circulation.

Expect a tranquil Sunday night ahead, as clouds persist with that northwesterly flow over the Lake Ontario – not intense enough to stir up showers, but enough to maintain some low-level cloud cover. Lows will be a little milder tonight, bottoming out around 40 in most areas, and low 40s in Ithaca’s urban core and along the lakeshore.

Monday will see a few isolated showers across Upstate as a weak, fast-moving shortwave (pulse of instability) skirts around the edge of the high and across New York. A few communities may see a quick spritz of light rain during the morning or afternoon, but rainfall amounts will be negligible. Skies will be mostly cloudy, turning partly cloudy by sunset, with highs in the upper 50s. Monday night will host partly cloudy as the shortwave departs, with calm air and lows in the upper 30s to around 40.

Tuesday will prove to be a little milder as the core of the high moves over the Mid-Atlantic states, channeling warmer air northeastward into the Southern Tier and Finger Lakes. A few morning clouds will wither away, leaving sunny skies and highs in the upper 60s. Some cloudiness does return Tuesday night, with partly cloudy skies by sunrise Wednesday. It will remain dry, however, with lows in the mid 40s.

A developing storm system will enhance southerly flow Wednesday, as well as increase cloud cover as the day progresses, from partly cloudy in the morning to near-overcast by sunset, with highs around 70. The storm system’s frontal boundary will extend from Hudson’s Bay Canada all the way down to the Gulf of Mexico, so this is fairly large storm system coming in. Rain will begin sometime between sunset and midnight, sooner to the west of Ithaca and later to the east, and continue overnight.

With Gulf moisture and the large area of atmospheric dynamic instability, rainfall amounts are likely to be substantial and there is at least a slight risk for excessive rainfall and related flooding Wednesday night into Thursday. This will need to be monitored for the next few days, and we’ll keep you posted if risks rise. Lows Wednesday night will be in the lower 50s.

Thursday will be a rainy day as that expansive area of rain takes a while to move through. Expect a grey, wet day with rain become more sporadic late in the day, and highs in the mid 60s. Thursday night will see periods of rain early, winding down after midnight, as winds turn to the northwest. Lows will be in the lower 40s.

Friday will be a cooler day as cold air aloft digs in behind the frontal boundary, while a high over the Southern Appalachians stabilizes the atmosphere. Skies will be mostly sunny with below-normal highs in the upper 50s. Friday night will be partly cloudy with some patchy frost possible as temperatures settle in the mid to upper 30s for lows.

Looking into next weekend, Saturday and Sunday are expected to be dry and cool, with highs in the upper 50s to low 60s, and lows in the upper 30s to around 40. The bigger question mark right now is a deep, powerful low seen in recent model runs spinning into Southern Ontario and bringing very cold air into the Great Lakes early next week, with some snow potential on the hilltops. We’ll have to see how model runs evolve over the week ahead, but now’s a good time to stock up on rock salt and get the snow brushes out of the closet, just in case.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

With that powerful low and deep slot of cold air expected early next week, the unseasonable cold is expected to linger several days, moderating somewhat as the week goes on. For what it’s worth, the cold air will also be fairly dry, limiting chances for snow and precipitation in general. Upstream, the persistent jet stream ridge will allow for warmer than normal conditions over the Pacific Northwest and U.S. West Coast, and moisture from the Pacific will create wetter-than-usual conditions in the Desert Southwest.

Brian Crandall

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