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Dave Epstein

Things will remain uncomfortably hot and muggy through the end of June

The jet stream is forecast to remain to the north of New England throughout the rest of June, keeping above normal temperatures in place.
The jet stream is forecast to remain to the north of New England throughout the rest of June, keeping above normal temperatures in place.Tropical Tidbits

Lots of people look forward to the heat and humidity of summer and it is now firmly entrenched across much of New England.

This weekend, after low clouds and fog dissipate each morning, temperatures are going to reach near or even a little above 90 degrees. This pattern actually could go on well beyond the weekend and continue for the next 10 days. This doesn’t mean that the high temperature won’t reach a homely 88 or 89 during that time, but we are not going to see any retreating temperatures for a while.

The GFS model keeps 90-degree weather over inland areas through July Fourth.  This is just a model forecast and can be too warm in the longer range.
The GFS model keeps 90-degree weather over inland areas through July Fourth. This is just a model forecast and can be too warm in the longer range.WeatherBell

If you’re living or vacationing on Cape Cod it will certainly not be as hot. Temperatures there will end up in the upper 70s to mid-80s each day this weekend.

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Now that you know the forecast for the next couple of days, let’s look at what lies ahead and the reason it’s going to be so hot. You’ve seen those big blue H’s on weather maps. That represents high pressure. High pressure builds up when high-level air sinks to the surface of the planet and forms a pool of air higher in pressure than the surrounding environment. The sinking process dries out the air and also warms it up. Think about hiking down a mountain and how the temperatures get warmer as you get lower in elevation.

It will be near 90 degrees over the Merrimack valley Sunday for the first full day of Summer, but in the 70s over Cape Cod.
It will be near 90 degrees over the Merrimack valley Sunday for the first full day of Summer, but in the 70s over Cape Cod.WeatherBell

The sun this time of the year is as strong as it gets, so any heat is accompanied by very intense ultraviolet light that makes the heat harder to deal with than if it were this warm in late August or early September.

Many areas will have at least three days in a row of 90-degree high temperatures, making for an official heat wave and for some that heat wave is going to be around for a while. Some forecasting models keep a 90-degree high temperature in the suburbs away from the coast all the way through the end of the month and maybe even into early July. Typically, we would get some sort of a break, especially this early in the summer season.

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The jet stream has gotten itself stuck in a position that is keeping cooler and drier Canadian air from getting to New England. It’s impossible to accurately look out a full two weeks but the amount of refreshing dry air and comfortably warm temperatures looks to be at a minimum into early July.

High pressure generally brings dry weather to an area it impacts. Notice the H over Alabama and Mississippi, which stretches into New England.
High pressure generally brings dry weather to an area it impacts. Notice the H over Alabama and Mississippi, which stretches into New England.NOAA

There is likely to be a break in the humidity at some point, as slightly drier air can work into these patterns even if the heat doesn’t break. The timing of any lower dew points can be difficult to predict and I wouldn’t expect a significant drop until sometime next week.

The winter of 2014-15 was an extreme outlier with some of the coldest and snowiest weather ever recorded, I’m starting to wonder if the summer of 2020 is going to be a mirror image of that year.