ITHACA, N.Y. — If you’re going to be out tonight or tomorrow morning, bring the umbrella and be on the lookout for flooded streets – the cold front that will end our latest summer broiler will tap into the deep layer of moisture and create a potential flash flooding threat.
— NWS Binghamton (@NWSBinghamton) July 15, 2018
While temperatures last week may have been a bit below average, few would argue that it wasn’t a nice week to be out and about. The relatively dry air and moderate temperature came to an end, however, with this latest tap of hot, moist air from our southwest. This weekend was hot, humid, and occasionally stormy, with strong thunderstorms bubbling up throughout the region.
If Saturday’s high is any indication, the 90 °F count for this year is now up to six, the number of 90 °F days Ithaca typically sees in an entire year. Sunday came close at 89 °F, but close only counts in horseshoes and weather forecasts. Monday will most likely add another notch to the 90 °F tally, though with any luck the rest of the week should be cooler.
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Most places are starting off the morning with sunny skies and a muggy feeling in the air – temperatures are already near 80 °F in many parts of Tompkins County. With dewpoints in the low 70s and temperatures topping out in the low 90s, the heat index will be near 100 °F – exercise precaution if outdoors, drink plenty of fluids, take frequent breaks, and be on the lookout for signs of heat-related illness.
As the day goes on, clouds will start to build up and some showers and thunderstorms will build up by sunset. A cold front will be approaching from the west, which will trigger the development of numerous showers and thunderstorms ahead of it, and models suggest these may aggregate into one large mass of rain with embedded thunderstorms. With the air as moisture-heavy as it is, there is potential for torrential downpours and flash flooding, particularly in poorly drained areas or low-lying places. For Monday night, expect cloudy skies, showers and thunderstorms especially towards daybreak, and temperatures only falling back to the low 70s.
On Tuesday, the cold front should pass through by mid morning, with a high pressure area over the Great Lakes ushering in cooler, drier air behind it. Expect cloudy, stormy conditions to start the day with downpours possible, but to steadily clear out as Tuesday progresses, with mostly cloudy skies and a few lingering showers by early afternoon, and dry, partly cloudy skies by sunset. Highs will be in the low to mid 80s. For Tuesday night, things should be quiet, with a few passing clouds, much lower dewpoints, and temperatures bottoming out in the upper 50s.
Wednesday should be quite pleasant, if slightly cooler than average. Sunny skies will prevail, with a light north breeze, and temperatures in the mid to upper 70s. Wednesday night will be a “sleep with the window open” kind of night, with clear skies and lows in the low 50s.
The northerly breeze will die down for Thursday as the high pressure area sits directly overhead, and that should allow temperatures to percolate a few degrees warmer. With comfortable humidity, you can bask in those sunny skies and enjoy temperatures reaching the low 80s. Thursday night will host a few passing clouds and lows in the upper 50s.
Friday will be mostly sunny and warmer still, as the high pressure shifts east and its clockwise circulation churns a light south wind. Temperature will get into the mid and upper 80s, but it should still be fairly comfortable with dewpoints around 60 °F. Friday night will be mild but comfortable, with lows in the low 60s.
The weekend is looking a bit dicey. Saturday should be nice with partly cloudy skies and highs in the low to mid 80s, but models are suggesting a low pressure area could stall in the Ohio River Valley while the high pressure area is parked off the East Coast, resulting in a large tap of moist air and potentially multiple rounds of heavy rain for Saturday night and Sunday. The models are not in great agreement just yet, but if you have outdoor plans Sunday, you’ll want to keep an eye on it.
Cutoff lows like the one that’s expected this weekend tend to be long-lived affairs because they’re separated from the flow of the jet stream (think of it like an eddy in a creek). As a result, there’s potential for a multi-day rain event that would make a good dent in our precipitation deficit, if it pans out. Temperatures during the period should be near to a little above normal, so expect persistently warm if muggy conditions.
Meanwhile, for those who like their forecasts to look in the really long term, NOAA has issued an El Nino advisory, with 70% chances for an El Nino event to be in effect by this winter.
What does that mean for our weather? Typically, not a whole lot. El Nino, or more scientifically the warm phase of the El Nino Southern Oscillation (ENSO), is a smaller driver in the large scale atmospheric oscillations than can affect our weather patterns in the Northeast – typically, the Arctic Oscillation and its close relative, the North Atlantic Oscillation play a much bigger role for us, and neither of those is especially predictable because they’re driven by atmospheric pressure patterns, and lack atmospheric teleconnections to oceanic pools of heat. A typical El Nino will adjust the polar jet northward, so we tend to be drier and a few degrees warmer during El Nino winters, but very strong El Ninos such as 1997-98 and 2015-16 can produce extreme warm conditions.