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May Looking Warm

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The last day that the temperature reached or exceeded 70 degrees in Boston was October 29th when the max was 74. There have been 186 consecutive days below 70 degrees in the city! That stretch will stop today when the temperature will easily surpass 70 on its way closer to 80. That 80 is attainable if the wind direction is at least 210 degrees or in other words, west of due south. The record for May 4 is 90 set in 2001. That was the third day in a row of 90 or higher so the first heat wave of that year was established. The two previous day's highs were 91 and 92.

2015 Outlook2There is a seasonal shift in temperature that began to unfold last month. It mimics last year when we emerged from a very cold March to a flat April to just under a degree above average for the mean temperature of May. This year we had a super cold winter which was the coldest January through March period on record in the Northeast with only a couple of minor exceptions! It was followed by a flat April and now it appears the global factors in play will supply us with a May that will probably end up warmer than average with a mean temperature of more than a degree and possibly up to 1.5 degrees in the plus.

sstAPR2015With the expectation of very warm weather much of this week featuring high temperatures of 10-20 degrees above the average, you might conclude that this is the year of extremes with a frigid, harsh winter followed by a super sizzling summer. It's not going to happen primarily because of the sea surface temperature regime which remains locked in. Note above the warm water in the eastern Pacific and the horseshoe of cooler than average water in the Atlantic. The combo of this positive or warm phase of the Pacific Decadal Oscillation linked with the negative or cold phase of the Atlantic Multidecadal Oscillation should act as the dominant global players in keeping a lid on the summer heat. This setup was the main driver in creating our record-smashing snowy and cold winter. A notable change going forward is the apparent strengthening of El Nino. Taking these facts into consideration, a summer yielding slightly above average mean temperatures of close to a degree or so seems to be in the works. This means that we will have some hot days this summer and the support is there for more than last year's 8 days at 90 or higher in Boston. The average number is 14 and I think that the city will receive 10-12 this year and not a whopping 25 days that happened in 2010. Boston had no heat waves last summer which is most unusual but a couple of them are expected this summer. Yet, I do not see any long extended stretches of extreme heat and humidity. We shall see.

In the more immediate future, we'll be watching the potential for cooling sea breezes to develop from time to time later this week. There is a risk of a more significant backdoor cold front introducing some chilly air from the maritimes at some point next perhaps next weekend. Consequently, the outlook for Mother's Day is a low confidence forecast presently.

Make it a great week!

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