The Heat is On, But is It a Heat Wave?

(Editor’s Note – This post was originally written for the blog hosted by the University of Massachusetts-Lowell Meteorology Program. This is the reason for the references to Lowell so often. For more information about the UML Weather Center, please visit their homepage at

A Heat Wave. Triple H weather.Bad Hair Days. The Dog Days of Summer. Whatever you like to call it, it’s something we have to deal with every year, though not nearly as much in New England as other parts of the country.

According the American Meteorological Society’s Glossary of Meteorology, the official definition of a heat wave is :”A period of abnormally and uncomfortably hot and usually humid weather.

The glossary adds further:

To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. In 1900, A. T. Burrows more rigidly defined a “hot wave” as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90°F. More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region. In the eastern United States, heat waves generally build up with southerly winds on the western flank of an anticyclone centered over the southeastern states, the air being warmed by passage over a land surface heated by the sun.

How often do we have an actual heat wave here in New England? For Lowell, we average 2 heat waves per year. The most common time for one is between the middle of June and middle of August, but they have occurred as early as the middle of April and as late as late September. In the summer of 1955, we actually had 8 separate heat waves between the end of June and late August. The worst of the bunch was 9 day heat wave that started on June 30 and ended on August 7. On 3 of the 9 days (July 31, August 4, August 5), the high temperature was 100 degrees.

So far, we have not had a heat wave in Lowell in 2016. We had one in 2015, a 3 day stretch from September 7-9, but 2014 also did not feature a 3-day stretch of temperatures above 90.

While a 3-day stretch of 90-degree weather isn’t that uncommon around here, a string of 7 or more days in a row is. In fact, in the 125 years of climate data we have for Lowell, we’ve had a stretch of 7 consecutive days above 90 degrees just 20 times. The last time it happened was just 3 summers ago – July 14-20, 2013. Longer stretches are even rarer. We had a 10-day stretch of 90-degree temperatures from August 27 through September 5, 1953. This occurred just one year after a brutal 13-day stretch from July 11-23, 1952 that featured 4 days with highs above 100 degrees. The worst heat have in Lowell though was a 15-day stretch from August 1 through 15, 1988 which capped off one of the hottest summers in Lowell history.As if having 15-days of 90-degree weather isn’t tough enough, 11 of those days featured highs of 96 or higher, one (August 3) had a high of 100, and most of those days were accompanied by high humidity, with dewpoints well into the 60s and 70s.

While there have been many memorable heat waves in New England, there’s only one day that is known simply as “The Hot Day”. On August 2, 1975, a ridge of high pressure settled into the Northeast. August 1 was hot in its own right, reaching 102 for a high here in Lowell. Temperatures didn’t drop much that night, with the stifling airmass in place. The low temperature on August 2 here in Lowell was only 79, the warmest low temperature on record here. With temperatures already starting the day so warm, and plenty of sunshine, it didn’t take much to send temperatures to levels that had never been seen around here before. On Nantucket, the high hit 100 for the only time on record. Providence, Rhode Island reached 104, setting a new state record. In Massachusetts, a new state record of 107 was set in both Chester and New Bedford. Here in Lowell, our records show a high of 108 was recorded that day, but this seems suspect. High temperatures from other nearby spots that day included 105 in Reading, 103 in Pepperell, 103 in Haverhill, 101 in Lawrence, 100 in Nashua, and 99 in Dracut.

Daily Weather Map for August 2, 1975. Image provided by NOAA.

Luckily, 100-degree heat isn’t common around here. On average, we hit 100 here in Lowell about once every 4 years.The last time it occurred was on July 22, 2011, when we reached 102. In both 1911 and 1952, we reached 100 degrees 5 separate times. 90-degree days occur and average of 14 times per year.So far in 2016, we’ve had 4 days with highs of 90 or higher.1932 is the only year on record in Lowell where the high temperature failed to hit 90 degrees.On the other hand, 1955 saw an incredible 46 days with highs of 90 or higher, just ahead of the 45 such occurrences in 1983.

Whether we hit 90 or not today is still to be determined (the temperature in Lowell was 87 at the time of this being written), but it certainly seems like there are more 90-degree days in our immediate future. The GFS model is showing the possibility of high temperatures in the lower to perhaps middle 90s Sunday and Monday ahead of a cold front, then the possibility of more heat late in the week.

High temperature forecast for Monday July 18 based on the GFS model. Image provided by WeatherBell.


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