ITHACA, N.Y. — It’s the last week of astronomical summer, but you could be forgiven for thinking otherwise this week. Temperatures will rise as the week goes on, with temperatures rising through the 70s and into the 80s by the end of the week, with mostly dry conditions on tap for the week ahead.

Your Weekly Weather

This weekend has been rather unsettled as a weak shortwave, a pulse of lower pressure and increased atmospheric instability, has skirted eastward across the Great Lakes this weekend. This has brought considerable cloudiness and some light to moderate showers into the region. The bulk of the rain, associated with a surface trough (weak cold front) enhanced by the short wave, will quickly exit our region this evening, but the instability in our column of atmosphere could allow for additional rain showers through the overnight hours and into tomorrow morning before high pressure builds back in from the north.

For tonight, mostly cloudy to fully overcast skies will persist across the region, with scattered light to moderate light showers. Winds will be calm and lows will be in the upper 50s, with some valley fog possible in the usual locations. New rainfall amounts will be less than a tenth of an inch.

Monday will start off overcast with some lingering rain showers, but those should dissipate and skies will begin to break up by the afternoon hours as drier, more stable air is introduced into our region through the Canadian high pressure system to the north. It will be seasonably mild, with highs in the low 70s and a light wind out of the north. Any rain that falls will be less than a tenth of an inch, though most places, especially towns west and north of Ithaca, can expect to stay dry after dawn. Monday night will be mostly clear and seasonably cool, with lows in the upper 40s in the outlying towns, to around 50 °F in Ithaca and along Cayuga Lake.

For most of the week ahead, that high pressure will maintain a firm grip over the Northeast and Mid-Atlantic. It’s a fairly strong high and works as an atmospheric barrier to block Tropical Storm Humberto, likely to become a hurricane tonight, from moving northward and posing any threat to the coast – think of the way a leaf might get jammed against and clumsily flow around a rock in a stream. However, as the high blocks its northward motion, the storm will tap into prevailing mid-latitude westerlies and then move northeastward around the barrier of the high. It’s outside our purview, but that easterly/northeasterly motion could mean that a strengthening Humberto could pose a significant threat to Bermuda later in the week.

The one tangible change we’ll notice as the week goes on is a climb in temperatures – air flows clockwise around areas of high pressure, so when they’re to our north and they move eastward with respect to Tompkins County, the flow goes from northerly, to easterly, to southerly, meaning cooler, to warmer, to much warmer air, as well as some higher humidity (though not really muggy) later in the week.

For your Tuesday, it will be delightfully dry and mild. We’ll see a few passing clouds and highs around 70 °F. Tuesday night will be mostly clear and on the brisk side given the lack of wind, with lows in the mid 40s under mostly clear skies (it’s not likely to get any lower than about 45 °F, even in the towns, due to some moisture in the air with dewpoints in the mid 40s as well; moisture prevents temperatures from dropping as much because water holds onto heat much better than air).

Wednesday will be a little warmer as we switch over to easterlies, with highs in the low 70s with mostly sunny skies. Wednesday night will see a few passing clouds with lows in the low 50s.

Thursday will be warmer still as we switch to southerly flow on the backside of the high pressure system, which then stalls out near the Gulf of St. Lawrence. Plan for a few passing clouds and highs in the upper 70s. Thursday night will be dry with a few clouds and a low in the mid 50s in the towns, and upper 50s in Ithaca and around the lakeshore.

Friday will be a bit warmer still as the core of the high shifts southwestward a bit in response to Humberto – this will enhance the southerly flow. It will be mostly sunny with a high in the low 80s. Friday night will be dry with a few passing clouds and a low in the upper 50s.

At this point in time, the weekend is looking pretty good, as the high remains rather stuck in place with Humberto running up its eastern flank out over the Atlantic. It will feel more like late July than late September. Highs will be in the low 80s Saturday and mid 80s Sunday with mostly sunny skies, and overnight lows in the low 60s. Weather-wise, Porchfest is looking pretty good next weekend.

Graphic courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Look into the last week of the month, the heat wave is set to continue as a strong ridge maintains its grip over the Eastern United States. Models indicate this will continue into the end of September, with temperatures running well above normal, but some medium-range outputs are suggesting a cold snap may be on the way by early October. You know winter is coming folks, so enjoy the warm temperatures while they last.

Brian Crandall

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