ITHACA, N.Y. — For those looking for a break from the hot, humid and unstable weather conditions, it’s not yet coming. Until a cold front moves in very early Thursday morning, we have a few more torrid bouts before things cool down and calm down for later in the week.
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A few things are driving this sultry state of affairs. The first is a high pressure system located near Bermuda in the middle of the Western Atlantic Ocean. Since air flows clockwise around high pressure systems in the Northern Hemisphere, that means the system is churning up hot, moist air from its southwest – the Atlantic Ocean and the Gulf of Mexico – and advecting it northward, into the Mid-Atlantic and the Northeast. That creates warmer than normal conditions, and with the deep moisture from the Atlantic and the Gulf, it also means very humid air. Humid air is inherently more unstable than drier air. Like a summer night after a thunderstorm, it doesn’t cool off as quickly because water holds onto heat better than dry air alone. That makes a moist parcel more capable of rising faster and higher into the atmosphere, which is the primary ingredient in the development of pop-up (convective) showers and thunderstorms.
So that covers your typical pop-ups. But if you’re looking for a more intense and better organized set of thunderstorms, what you typically need is a forcing mechanism – a physical nudge to jostle the atmosphere and get those hot, moist near-surface air parcels to rise in concert with each other. In Sunday’s case, a mild shortwave pulse of instability was trucking along in the mid-levels of the atmosphere, which like pushing a ball downhill, triggered a lot of those air parcels to rise through the atmosphere. The result was an organized and rather potent squall line of thunderstorms that rumbled eastward through the Southern Tier and Hudson Valley with hail, damaging winds, and a reminder that the Albany-hole, or “A-Hole” as we called it in grad school, was mostly a figment of the imagination of disappointed meteorology majors.
Anyway, there’s your atmospheric dynamics 101 for the week. Onto the weather. With the heat of the day subsiding and the storms through the region, most of today’s storm are dying down, and any rain tonight will be sporadic and the result of decaying storms from the western part of the state that manage to hold together long enough to drop some light rain over Tompkins County. But overall, expect a muggy. partly cloudy night with lows in the upper 60s.
Monday is going to be a lot like today was, with the exception that there won’t be much of a forcing mechanism. As the day goes on and sunlight heats the surface, showers and storms will develop with that injection of heat energy and unstable, rising air, but nothing severe is expected. Aside from those showers and storms from late morning through the evening, it will be partly cloudy and very muggy. With highs near 90 °F, it will feel more like the upper 90s, so be mindful of heat illness, and take all the usual precautions to stay cool and hydrated. Monday night will see the storms diminish with the lose of diurnal heating, and it will be partly cloudy and rather humid with lows in the mid 60s.
Tuesday will see more stable conditions as a secondary bubble of high pressure moves over the Southern Tier, quashing most shower and storm development, though a few may manage to fire up during the late afternoon and early evening. It’s a modest if welcome reprieve for the Ithaca College students who will be moving into the dorms that day. Otherwise, plan for partly cloudy skies and a little less mugginess, with a high in the upper 80s. Tuesday night will be partly cloudy with lows in the upper 60s, with increasing clouds towards daybreak as the next system begins to move in.
Wednesday will be an active day as a trough of low pressure begins to approach from the northwest, and its counterclockwise flow dredges up hot, moist from the south ahead of the system. This will be a dangerously hot and humid day punctuated with strong thunderstorms all day long, but primarily in the 2-8 PM timeframe. Highs will be in the upper 80s with heat indices in the mid to upper 90s. This storminess will continue into Wednesday night until the front passes in the early AM hours of Thursday morning, so plan for scattered showers and thunderstorms with mostly cloudy conditions and a low in the mid 60s.
Once that front passes through, however, things should quiet down quickly. The last showers east of Ithaca will clear out by mid-morning and clouds will slowly break up and decrease in number during the day. Highs will be in the upper 70s as much cooler, less humid air filters in as part of a Canadian high pressure system to the northwest. Thursday night will be partly cloudy and dry with a low in the mid 50s.
The high pressure will move southward over Michigan Friday, and it will be another pleasant day, with a few passing clouds and high in the mid 70s, a fairly comfortable move-in day for all the freshmen making their way to East Hill for Cornell Orientation. Friday night will be mostly clear with a low in the mid 50s.
This weekend, apart from being mobbed with returning students and their parents, will be pleasant from a meteorological perspective. Saturday and Sunday will be dry as high preesure retains its grip, shifting eastward and allowing warmer air into the Southern Tier for Sunday. Highs will be in the upper 70s Saturday and mid 80s Sunday, with lows Saturday night in the upper 50s.
Looking ahead towards Labor Day weekend, a trough in the jet stream will bring cooler conditions to the Mississippi River Valley, but the coasts will be under the influence of ridges and warmer than normal temperatures. Slightly wetter than normal conditions are also expected during the period, so it seems fitting that a hot, humid summer like this one would have a hot and humid last hurrah. September is expected to see near normal temperature and humidity based on some of the interseasonal models, but we’ll see if anomalous conditions start to show up as we get closer to the end of the month.