ITHACA, N.Y. — At last check, hardly halfway through the month, the Ithaca-Tompkins Airport had recorded 5.73″ of rain so far this July. If no further rain were received for the remainder of the month, it would be the 13th wettest July in the 128 years of valid precipitation observations in and around Ithaca. Yes, we’re all tired of the rain.
This week will offer something of a reprieve, though not completely. The chance for showers and thunderstorms will hang in there for much of the week, though the chances of a heavy rainfall and flash flood will be limited. Temperatures will be seasonable as we attempt to dry out a little this week.
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The low pressure system responsible for yesterday’s frequent heavy rains is currently centered over Downstate New York and Connecticut and slowly heading eastward, with a few lingering light to moderate showers across Upstate, but nothing that has significant potential to cause flooding. With the thick cloud cover of the storm system and cold air advection on northwest winds, it’s a cool day for July, with high temperatures in the upper 60s to just above 70°F for most of Tompkins County.
With the slow movement of the storm system, cloud cover will only slowly break up as we head through Sunday evening and into the overnight hours, with a decreasing number of showers as the system continues to move away and our local column of atmosphere settles down. As the cloud cover should generally persist onward into Monday morning, and given how saturated the ground is (moistening the air and slowing and limiting the air’s ability to cool off), temperatures won’t fall much tonight, into the low 60s under those largely cloudy if dry skies, with fog likely in the valley areas, so use caution if out on the roads late tonight.
There will be steady clearing throughout the day Monday, from mostly cloudy skies at sunrise, the partly cloudy by noon, to just a few lingering clouds by sunset. However, with saturated ground releasing moisture into surface air, it will be fairly muggy, and that surface moisture rising into the atmosphere with a weak shortwave (pulse of instability) passing aloft will destabilize the atmosphere and allow a few scattered rain showers to pop up, as well as an isolated thunderstorm or two. Highs will be around 80°F. Monday night will see a few passing clouds and dry conditions, though humid once again due to the saturated ground slowly dries out into the air above it. Lows will be in the lower 60s.
Tuesday will be warmer as the light northwest wind dies down and turns more westerly with a high pressure system encroaching from the Midwest. Another weak shortwave working its way around the high will sag southward into Upstate New York later Tuesday, once again providing conditions for a few late-day showers and thunderstorms to fire off as highs make it into the mid 80s along the lake and upper 80s elsewhere. The short wave will hang around overnight Tuesday, allowing more showers and thunderstorms to develop with mostly cloudy skies. New rainfall will generally be less than one-quarter of an inch through Wednesday morning. Lows will be in the mid 60s.
Wednesday will be unsettled as the shortwave closes off into a closed low (storm system) over Southern New England while high pressure slowly works in from the west. Plan for a mostly cloudy day early with a few light scattered showers, especially to the east of Ithaca, turning partly cloudy and drier as the day progresses. Highs will be in the upper 70s. As the high pressure system continues to work into the Finger Lakes Wednesday night, skies will continue to clear out, with a few passing clouds overnight and lows in the upper 50s.
Thursday will be a largely dry day as high pressure holds on for most of the day before a weak shortwave trough begins to dive in from the northwest towards the end of the day. Expect partly cloudy skies turning mostly cloudy by sunset with a few isolated showers late in the day, with highs around 80°F. Thursday night will be mostly cloudy with a few scattered showers, primarily after midnight, with lows in the low 60s.
The weak trough will slowly move southward Friday, allowing the chance for rain showers to persist most of the day, but generally, most areas will remain dry with partly cloudy skies, clearing somewhat by sunset. Highs will be in the low 80s. Friday night will be partly cloudy and dry, with lows in the low 60s.
Conditions will remain unsettled into the weekend, though no major rainfall is expected. Saturday will be mostly sunny with highs in the low 80s, and a weak short wave moving in Saturday night into Sunday will usher in a few showers and mostly cloudy skies overnight with lows in the low 60s, but generally it will remain dry with partly to mostly cloudy skies and highs once again in the low 80s Sunday.
The large-scale weather pattern being identified in most medium-range forecast models identified a pronounced ridge in the jet stream over the upper Great Plains, with anomalously hot conditions expected over Minnesota and the Dakotas. This fairly broad ridge is less pronounced over the Pacific Northwest, and will allow for Pacific flow to bring cooler-than-usual air and potentially some much-needed rainfall to the desert Southwest and parts of California.
However, for us in the Northeast, downstream of the ridge, we will get the trough portion of the jet stream – think of the mid-latitude jet stream like as a rope being snapped up and down, where there’s a wave upward, there is always a corresponding wave in the rope downward. As a result, cooler than usual conditions are expected to close out July. The continental air working in will also be on the dry side even as storm systems slide in along the jet, so those meteorological circumstances largely cancel each other out. Overall, expect normal to slightly drier-than-normal conditions, which like our friends across the country will be a welcome reprieve.