ITHACA, N.Y. — It’s been a dry August so far, but we have the chance to make up some of that deficit as a humid, hot and stormy pattern prevails over the next couple of days. Wednesday offers up a pleasant if brief reprieve, and potentially we could see the remnants of yet another tropical system impact our local weather towards the end of the week.
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It’s an unsettled Sunday afternoon as pop-up showers and thunderstorms spread across upstate New York, some of which have produced small hail and strong winds along with some needed rain, though the effect is muted because much of a downpour runs off before the ground can absorb it. Much of Tompkins County is currently experiencing moderate drought conditions as a result of the a warmer and drier than normal August we’ve had so far, with total rain to-date a little over an inch below normal.
The cause of this is a high parked over the Atlantic near Bermuda. Its clockwise flow is channeling air from the Southeastern U.S. and Gulf of Mexico into the Mid-Atlantic and Northeast – warm, moist air, arguably even moister than usual thanks to Hurricane Marco in the Gulf,. Marco is moistening the air around its circulation, and the adjacent flow within the atmosphere is picking up that water-laden air and advecting it our way. Moist air is inherently more unstable (it’s more buoyant than dry air, meaning if lifts more easily), and being on the fringe of the high means you don’t really get the stabilizing effect of high pressure. So with the heat of the day destablizing the lower atmosphere, the moist air is rising, it’s condensing as it enters the cooler upper atmosphere, and eventually when enough has been lofted and condensed, it sinks back down, and you get the convective pop-up showers and thunderstorms summer is known for. The more unstable the atmosphere is and the energetic those updrafts are, the more intense the pop-up storms.
Anyway, the first storm cells have already traveled across Tompkins County, and more are likely through the rest of the afternoon and evening, so long as the sun keeps pumping energy into the ground and atmosphere, and sustaining the heat energy that makes the surface air rise. Otherwise, it’ll be hot and humid, with mostly cloudy skies and a high around 90°F. Tonight will see the storms mostly dissipate, thought a few isolated cells could persist into the early AM hours. It will be partly cloudy with lows in the mid 60s.
Monday will be more of the same, basically. The high remains over the Atlantic, channeling that moist air up from the Gulf as Marco makes landfall on Louisiana during the day Monday. Expect a hot and muggy Monday, with partly cloudy skies, scattered showers and thunderstorms in the PM hours, and highs around 90°F. Monday night will see the pop-up storms dissipates, leaving behind partly cloudy skies and humid conditions, with a low in the upper 60s.
Tuesday will attempt to break the hot and humid pattern as a cold front associated with a Canadian low moves through the Southern Tier during the late morning hours. Expect mostly cloudy skies and scattered showers and thunderstorms with a high in the mid 80s. The cooler, drier air will start to work its way in after sunset, and Tuesday night will be much more comfortable, with partly cloudy skies and a low in the upper 50s.
Wednesday will be quite pleasant, with light winds out of the north-northwest, between the Canadian low and a high to its west. Expect mostly sunny skies, comfortable humidity, and highs in the upper 70s. Wednesday night will be a little unsettled as a shortwave (pulse of instability) jaunts through the Great Lakes region, and so a few showers are possible, but nothing substantial. Lows Wednesday night will be in the upper 50s.
Thursday is where we start to potentially get a little complicated. After that shortwave, the Atlantic high moves to fill in the atmospheric void, returning us to a southerly flow with heat and humidity, as dewpoint reach the mid to upper 60s and temperatures top out in the mid 80s, and Thursday night will be partly cloudy and a touch humid with lows in the low 60s. The question mark is Tropical Storm Laura, which will make landfall on Louisiana Wednesday night or early Thursday morning as a potent hurricane, stronger than Marco. Models suggest Laura’s remnant circulation could be wrapped in and around the high pressure area, which would send it in our direction, and merge it with another shortwave to create a potential mess for Friday onward.
At this point, it’s hard to make firm calls with where Laura’s remnants will go and when. For now, let’s defer to NWS Binghamton’s “continue to monitor”, and presume it’s primarily a shortwave enhanced with gulf moisture. Expect mostly cloudy skies Friday with thunderstorms in the afternoon and evening, and highs in the low to mid 80s. Friday night will be mostly cloudy and humid with lows in the mid 60s.
The weekend, once again predicated on the non-tropical outcome, calls for partly cloudy skies and highs in the upper 70s Saturday as cooler air comes in behind that Friday system, and then even cooler air makes an entrance for the end of the month, with mostly sunny conditions and highs in the low 70s next Sunday.
Looking into the Labor Day weekend, the pattern calls for wetter than normal and near-normal temperatures. Much of this latest NOAA CPC run is influenced by the presence of Tropical Storm Laura’s remnants – as they trek up the Mississippi River Valley and then through the Great Lakes, its counterclockwise rotation will pull down air from Canada on its western flank, as well as drag tropical moisture well into the Midwest. After that, abnormally warm and dry conditions are expected for the second part of the first week of September as a high pressure system settles in over the Northeast.