Goodbye summer 2017

Summer is disappearing quickly, with the first hint of colour appearing in the trees on L'Ile Perrot this week. (Valley Weather Photo)

September is upon us, the start of meteorological fall. As I have mentioned before, forecasters like things neat and tidy, so they divide the seasons into 4 equal portions. Fall does not officially start until September 22nd, but the days are getting longer and the nights noticeably cooler.

Time to take a brief look back at what seemed like a very short summer. Montreal came off a cloudy, cool and wet spring, and that trend seemed to last well into July. As far as heat goes, there was none, only one lonely day above 30C, June 18 at 32.1C (90F). This would be the warmest day of meteorological summer. Montreal usually averages 8 or 9 days above 30C. Overall temperatures averaged close to normal for the three months, 18.7C in June, 20.8C in July, and 20.3C in August. Nothing spectacular, just normal, the cooler days being offset by warmer nights. Our average daytime high for summer 2017 (June through August), was 24.7C (76F). The normal long-term average is 25.1C (77F).

Rainfall was a little different, somewhat exceptional at times, especially for the first half of the summer, when it seemed to rain every second day. June measured 135.2 mm of rain, well above the normal of 87mm. July was wet as well, with 125.4mm, the normal is 89.3mm. The atmosphere dried out a touch in August, with 76mm, the normal is 94.1mm. The dry August has been helped along by the first stretch of dry weather this summer, no rain from the 23rd to the 29th. As far as thunderstorm activity goes, they were few and far between, but when they did occur, they were big. Most notable was the storm on July 31st in St Laurent, that caused flooding and power outages and of course the powerful microburst in NDG on August 22nd. Damage from that storm was significant.

Fall Outlook
At this time, the fall looks warmer and dryer than normal. We are not expecting extremely hot weather, but rather temperatures a degree or two above the long-term average. Rainfall is expected to be near normal, however there is always the risk of a wayward tropical system brushing our region with heavy rain. This historically happens more often than you think. As we enter September, the loss of additional daylight will start the process of the trees changing colour and eventually dropping their leaves. This process will be accelerated by any sub-freezing nights we have. Keep in mind, the average first frost for metro Montreal is October 12, earlier in the outlying suburbs.