Sunday, October 1, 2017

September 2017 Summary

Some historical temperatures during a dry September 

Well that was quite an end to September with the longest heat wave of the “summer” and some historical temperatures.  The most significant streak was the 15 days above 25°C between the 12th and the 26th, that is something we have never seen before in September during the 100+ years of weather records in the region (the previous record was 13 such days back in 1947).

Some other notable events were the 5 days in a row above 30°C, which is something we have only seen a few times, the last was back in 1952.  Finally, the high temperature on the 24th of 32.2°C was the highest seen that late in the year since September 24, 1931 when it was 32.8°C.

Not surprisingly, the overall temperature was almost 3 degrees above average, what might be surprising is that this is colder than the last 2 years although they didn’t have the extreme highs we saw this year.  It is also useful to remember that this year the month started off cool during the first week.

But since I have you here can we talk a bit about recent Septembers?  Fun fact: no other month has seen more consistently above average temperatures.  In the past 20 years of data at the UW weather station, there has not been one in the below average range and only once was it even slightly below average (by 0.1 degrees in 2006).

The month was also very dry with only 38.0 mm of precipitation compared to the average of 87.8 mm, with half of the total coming during the first 4 days.  This dry month puts the total precipitation for the year at 813.4 mm, which is still well above, but a bit closer to the average of 683.5 mm than it was at the end of August.

Summary for September 2017:
Maximum Temperature 32.2°C
Minimum Temperature 3.8°C
Average Daily High Temperature 24.1°C (Long term average 20.4°C)
Average Daily Low Temperature 10.7°C (Long term average 8.6°C)
Total Precipitation 38.0 mm (Long term average 87.8 mm)

(Long term averages based on 1981-2010 data for the Waterloo Wellington Airport)


Cyclenall said...

With the 5 days in a row above 30°C stat ("which is something we have only seen a few times"), is that just for past Septembers or is that any time of the year? If its the latter than that would be in line with the unbridled streaks and insanity of some mid-west records that were set.

This extreme heatwave was one of the most impressive ones I've seen. Record highs in some northern communities were demolished by almost 5ºC and the more anomalous half was the lows.

I wasn't aware that the last 20 Septembers were above normal except 2006, now that is a statistic that I virtually never come across as multi-year equilibrium would at least throw down a below average one before 10 go by...unreal. The closest statistic that I can think of to that is no violent tornadoes in Michigan (EF4+) since 1977. From 1950-1977 there were around 12-14 violent tornadoes in that state.

Frank said...

We have only seen the 5 30C days in a row a few times in September, it happens relatively often in July and August. Sorry if that wasn't clear.

Cory Janzen said...

Hi Frank, love the website and the blog. Is it possible to post the graphs for temperature and precipitation in a year to date format as well as the monthly format? i.e. from January until the end of September?

Kuhny said...

I think September is becoming another summer month - with the records over the past two decades suggesting that is this case. As our climate keeps on changing, perhaps a summerlike September (and a summerlike May at the beginning of the season) may become the new norm here.