Here’s your summer weather preview
Many forecasters are projecting a hot few months ahead.
Meteorological summer began Wednesday, June 1. After a spring that turned out warmer, drier, and actually snowier than average, it’s time to look at what we can expect this summer.
Of all the seasons to predict, I think summer is the most difficult. The reason: The jet stream is at its weakest, and overall, the period of June through August is warm. When the weather is warm nationwide, the contrast between north and south is smaller and, thus, the weather features are less robust. Smaller phenomena are not forecast as easily because the computer models don’t handle them as well. In winter, we have the potential for bigger fluctuations, and the larger scale features can be easier—though not easy—for the models to forecast.
A weak jet stream also doesn’t bring a lot of weather, usually just scattered showers and thunderstorms. The question for forecasters is: Will it be warmer than summer’s typical heat, or will we see more outbreaks of Canadian air, keeping the extreme heat at bay?
The summer temperature outlook.
Most forecasters and models agree that this summer will be hotter than average.
This would mean more days over 90 degrees, or at least well into the 80s and more humidity. The past two summers have seen periods of comparable coolness in the middle of the summer, most notably during the first two weeks of August 2014, which were remarkably cool. There were also many nights last summer when temperatures fell to the 50s and lower 60s, making for a long stretch of great sleeping weather.
El Nino continues to weaken, and by this fall, it is likely—though not a sure bet—that we will come under the influence of La Nina. These temperature fluctuations of the Pacific Ocean are a piece of the reason for the hot summer forecast.
El Nino southern oscillation model predictions.
Hot summers, like the summer of 2010, have more 90 degree days than average—not just one or two more, but many. During that summer six years ago, there were 25 days reaching or exceeding 90 degrees at Logan Airport. It’s safe to bet, unless you live on the water, that you experienced even more.
Even Boston can have nearly a month of 90 degree days in a hot summer.
The chart below shows the total number of 90 degree days and is sorted by those years with the most. On average, Boston will experience about 14 such days per year, more inland, fewer in Northern New England, on the immediate coast, and of course on Cape Cod and the Islands.
Past summers with the greatest number of 90 degree days in Boston.
The National Weather Service is predicting that the greatest odds are for a hot summer in the northeast. This is, of course, an odd forecast. Although there is a 70-80 percent chance that we are going to have a hot summer, that still leaves a 20-30 percent chance of a summer with average heat.
The temperature outlook for the summer of 2016.
The other very important aspect of a summer forecast to keep in mind is that this is a three-month forecast. July could end up below average and June and August above, making the summer forecast of warmth valid.
The Canadian model agrees on a hot summer.
One of the sets of computer models I have found to be quite reliable is the Canadian model. This model is predicting a somewhat warmer summer, the June forecast having the highest anomaly or greatest variance above average.
The Canadian model summer forecast.
Because June is going to start with seasonable or even below seasonable temperatures, this means that either the forecast is wrong or the second half of the month will turn out quite hot.
Will there or won’t there be a summer drought?
The models are forecasting summer to bring adequate rainfall or even more than we typically see. Now, before you cancel your week at the beach, this is likely a result of the thinking of more heat, because with more heat comes more humidity and a greater chance of afternoon showers and thunderstorms, something that was lacking much of the past two years.
The precipitation outlook for summer 2016.
I’ll be updating the summer forecast over the next several weeks on Twitter @growingwisdom.
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