ITHACA, N.Y. — This is a good week to be stocked up on ice cream and frozen popsicles. As a jet stream ridge continues to sit overhead, hot, moisture-laden air will continue to dominate the local weather pattern through Wednesday, with oppressive heat and humidity likely during the day, and only modest respite at night. Thunderstorms will be present just about every day, further adding to that sticky, muggy feeling. Cooler if still unsettled conditions will return for the end of the week.

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At present, a fairly broad ridge of high pressure is centered over the Western Atlantic Ocean near Bermuda. As high pressure systems have clockwise circulation in the Northern Hemisphere, and this one is quite large, it’s tapping into hot, moist air over the Gulf of Mexico and Deep South. This is being advected northward and northeastward in its circulation and into the Southern Tier, resulting in hot and humid conditions. A Heat Advisory is in effect from 11 AM to 8 PM today, and more advisories are likely to be issued during the week.

This is a high-amplitude ridge (i.e. strong and tough to dislodge) reinforced by a trough over the central U.S. and an even more pronounced ridge over the Western U.S., which tapped into hot desert Southwest air and carried it all the way into Oregon and Washington, where all-time high temperature records are being smashed as places like Seattle, which normally sees June highs in the mid-70, is pushing past 100°F, extremely dangerous for a city where only half of homes have some form of air conditioning. This air is also extremely dry, which worsens an already dire wildfire outbreak situation.

For Ithaca and Tompkins County, the situation is less extreme but still potentially dangerous, as the combination of high temperatures and high humidity will result in the heat indexes pushing into the upper 90s and low 100s during the afternoon and evening hours for today through Wednesday. As reported yesterday, take precautions if outdoors, try to stay cool and hydrated, and know the signs of heat stroke and heat exhaustion medical emergency.

For the rest of Sunday, expect the heat and humidity to continue under partly cloudy skies; there’s plenty of energy in the atmosphere, but there’s just enough of a dry atmospheric layer aloft to prevent shower and thunderstorm development. Highs will be in the mid 90s with the heat index near 100°F, though a modest southwesterly breeze may provide some comfort. Tonight will be mostly clear but humid, with lows around 70°F.

Monday is likely the hottest and muggiest day of the week. The models suggest actual temperatures in the mid to upper 90s (warmer in valleys, cooler by the lake and at higher elevations), and with the dewpoint in the low 70s, that would feel like the mid 100s. This additional humidity and a weak short wave (pulse of instability) passing to the north will be enough to moisten and destabilize the atmospheric column and trigger the development of afternoon and evening thunderstorms, particularly between 1 PM and 7 PM. These will be numerous but the atmospheric dynamics aren’t favorable for severe thunderstorm development. Partly cloudy skies in the morning will give way to mostly cloudy skies during the PM hours with those thunderstorms brewing. These convective storms will whittle away with the loss of daytime heating, leaving a few passing clouds overnight and humid conditions, with lows in the low 70s.

Tuesday will be slightly cooler but still oppressively muggy with highs in the low 90s and dewpoints in the low to mid 70s. Partly cloudy skies in the morning will once again give way to mostly cloudy skies with scattered pop-up showers and thunderstorms by noon and continuing through the rest of the day. Once again, severe storms are unlikely, but heavy downpours are expected given the moist atmosphere. A frontal boundary will begin to press at the edges of the ridge by Tuesday night, so this activity will continue overnight into Wednesday morning, though reduced with the loss of diurnal heating. Between the overnight storms it will be mostly cloudy with lows will be in the low 70s.

The high pressure ridge shifts eastward Wednesday, and the incoming frontal boundary will create very unsettled conditions. The greater cloud cover will likely cap high temperatures in the upper 80s, but expect frequent periods of showers and thunderstorms throughout the day with mostly cloudy to overcast skies, and very muggy conditions reinforced by those frequent spells of rain. Wednesday night will see the thunderstorms decrease, but scattered rain showers will continue, with periods of rain overnight, mostly cloudy skies, and lows in the upper 60s.

Thursday is an improvement in that it’s not as hot; highs will be in the low 80s. Otherwise, it will still be an unpleasant day, with high humidity, frequent shower and thunderstorms as the front slowly moves eastward, and mostly cloudy to overcast skies. In fact, many of the model runs show the Canadian parent low pressure area for the cold front detaching from the flow of the jet stream as it pushes south-southeast, and getting stuck over the Great Lakes and and Ohio River Valley as a cutoff low, which would strand it for days and create days of scattered rain showers and thunderstorms. Thursday night will continue to be unsettled, with scattered showers and thunderstorms, mostly cloudy skies, and lows in the mid 60s.

Friday will be marginally more comfortable with highs in the upper 70s and dewpoints in the mid 60s, but with scattered and thunderstorms mixed into partly cloudy skies, you’d want your umbrella on hand if you’ll be out and about. Friday night will see more showers and storms with mostly cloudy skies and lows in the low 60s.

For your Independence Day weekend, it’s not looking great, but it’s not awful. The presence of scattered showers and thunderstorms will continue, most prevalent in the afternoon and evening, but nothing that looks like a washout. Between the showers, expect partly cloudy skies both days with highs in the upper 70s and lows around 60°F. If the cutoff low is not as substantial as a few models suggest, Sunday, the Fourth of July itself, may actually be dry and pleasant for any fireworks viewing you might have planned.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking ahead towards the middle of July, a large-amplitude ridge is expected to shunt ample amounts of warm air poleward, with the core of the heat over the Mountain West, but abnormally warm conditions across the northern half of the continental U.S. from coast to coast. This large-scale displacement will result in cooler-than-normal conditions over the Southern United States, and a cut-off low will create wetter than normal conditions over the Desert Southwest and Texas, extending through the Ohio River Valley and slightly into the Northeast, mostly the result of moisture transport high pressure over the Atlantic Ocean.

Brian Crandall

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