ITHACA, N.Y. — The week will start off with a humid and unsettled spell of weather as a weak cold front presses through Monday, followed by the soggy if weakened remnants of Hurricane Ida Wednesday night. But after that, it’s looking like a pleasant spell for the remainder of the week, with comfortable temperatures and low humidity through most of the weekend.

Quantified Precipitation Forecast (QPF) courtesy of the Weather Prediction Center.

Your Weekly Weather

It’s a typically hazy, hot and humid August day across the Finger Lakes and Southern Tier this Sunday, as high dewpoints and above-normal temperatures create an environment suitable for the development of convective (pop-up) showers and thunderstorms. For the moment, most of the regional activity is with an area of showers and embedded strong thunderstorms north of Ithaca, but some rain will be possible this evening across Tompkins County. The slow movement in tandem with the amount of precipitable water in the atmosphere (that is, the amount of water vapor in the atmosphere overhead) is favorable for extended heavy downpours and flash flooding, so pay close attention for any flash flood warnings if you live in a low-lying, creekside or urban area where the risk tends to be highest.

Otherwise, we’re looking at mostly cloudy skies for the remainder of the day outside pop-up storms, with temperatures in the mid 80s and a very uncomfortable dewpoint in the low 70s, which makes it feel more like the low 90s because your skin can’t breathe in this humidity and your body therefore perceives the ambient air as being hotter than it is. The showers and storms will wither after sunset with the loss of daytime heat energy, but a shortwave (pulse of instability) ahead of a cold front and its parent low over Canada will raise the chances for more showers and storms after midnight. It will be a humid night with mostly cloudy skies and a low around 70°F.

Monday will likely be one of the most humid days of the year as the dewpoint climbs into the mid 70s ahead of the cold front, the counterclockwise flow around the parent low amplifying the hot, moist southwesterly flow ahead of the system. The air temperature will top out in the low 80s, but it’ll feel more like 90°F. With this much moisture, the atmosphere will be quite unstable, so with mostly cloudy skies expect showers and thunderstorms throughout the morning and afternoon, with the primary line of storms being in the late morning as the front passes through. The pop-up storms will wind down by evening, though even as the air turns to the northwest, it will remain muggy as an extended trough drapes across the Ohio River Valley to the south and west. It will be dry if still rather humid overnight Monday, with partly cloudy skies and lows in the mid 60s.

Graphic courtesy of the National Hurricane Center in conjunction with the Weather Prediction Center.

Tuesday is a rather complicated setup, because there will be a low pressure area in the upper levels of the atmosphere over the Great Lakes (making the atmosphere less stable aloft), the frontal trough to the south, and the remnants of Ida moving up the lower Mississippi River Valley. If you imagine a bed sheet stretched tight, that trough is like a deep crease in the sheet, and Ida’s a heavy ball that’s going to roll along that crease. Thankfully, that setup should be far enough south and east to not severely impact the Southern Tier, but if you’ll be heading to Pittsburgh, Philadelphia, New York, Boston, 2-4 inches of rain is possible, with localized amounts of 6-10 inches of rain, which means widespread concerns of flash flooding, so be very careful if you’re heading south and east Tuesday evening through Thursday afternoon.

Locally though, the effects will be limited, just out of range from the system’s major impacts. Ahead of the remnants of Ida Tuesday, expect partly cloudy skies with a touch of humidity and highs in the low 80s. Tuesday night will see mostly cloudy skies with a few showers by morning, with lows in the low 60s.

Wednesday is when Ida and the trough should deliver the most rain to Tompkins County, generally of on-and-off bands of heavy rain pressing northeastward and clipping the Ithaca area on the north end. Expect near overcast conditions with occasional heavy rain, particularly in the afternoon and evening hours, and highs in the mid 70s. New rainfall amounts locally will be in the one-half an inch to one inch range, with lower amounts north and west of Ithaca, and higher amounts south and east. Wednesday night will see another one-quarter to one-half of an inch, primarily before midnight, with drier air and clearing skies towards sunrise as winds pick up from the northwest behind Ida’s remnant low. Lows Wednesday night will be in the upper 50s.

Thursday will be a more pleasant day as Ida and the trough move eastward and high pressure builds in from Hudson’s Bay Canada. It will be a dry day with comfortable humidity, partly cloudy skies and highs in the lower 70s. Thursday night will host a few passing clouds with some morning fog possible in the usual suspect areas, with a low in the low 50s.

Friday will be a similar day as the high shifts slightly eastward but otherwise synoptic-scale conditions will be largely the same as Thursday. Expect a few passing clouds with highs in the lower 70s, and as the high moves closer Friday night and the tap of northwesterly flow eases, lows will be slightly milder, with mostly clear skies and lows in the mid 50s.

Labor Day weekend is looking generally pleasant to start as the high passes overhead Saturday and shifts east of Tompkins County Sunday, though a frontal trough will begin to push in from the northwest late Sunday, introducing the risk of showers, and early indications do show a rainy, unsettled Labor Day. Highs over the weekend will be in the upper 70s both days, with overnight lows in the upper 50s.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking beyond Labor Day weekend, the large scale pattern favors a trough and cooler than normal conditions over the Ohio River Valley and Eastern Great Lakes, and between the trough’s instability and the possibility of some Gulf of Mexico moisture, wetter than normal conditions are also expected. Wildfire conditions out in the Western United States will likely be exacerbated as unseasonably warm and dry conditions continue.

Brian Crandall

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