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Looking at the day-by-day temperature averages for the last 100 years on this site: NW3 Weather - LTA temperature detail I notice the hottest days of the year on average are between 23rd-28th July each with an average low of 14C and high of 22.7C (57/73F). The average high is 22.7C right through from 19th July to 3rd August, but the peak for the average low only lasts those six days.
In winter the lowest average max is 7.0C (45F) right from December 31st to January 31st, but the lowest low of 2.3C (36F) only runs from January 19th-28th.
I'd have thought over a hundred years freak results would have evened themselves out and you'd get the peak high/low temperatures for day and night occuring around the same dates, but that's not the case. Can anybody explain why, and does the same thing happen elsewhere?
Looks as though the values have been artificially smoothed (easiest to see this from the graph at the bottom). I think you're right that the raw data would show more fluctuation.
That's an interesting observation. With your post in mind, I decided to take a peek at what the day-to-day averages show for Toronto's airport station (with data from 1938-2011) through Environment Canada's website.
-Summer
Looks like from the averages, the hottest day of the year statistically would have been July 23rd, peaking at a high/low of 27.2C/15.2C (81F/59F). It's only that day, according to the stats.
The highest average high of 27.2C is on July 23rd, with 27.1C the day before and after.
But the highest average low, 15.2C runs from July 22nd to July 29th.
- Winter
From the averages, the coldest days of the year run throughout from January 21st to January 29th at -2.4C/-10.9C (28F/12F).
The lowest average high, -2.4C, goes from January 20th to January 29th.
The lowest average low, -10.9C, goes from January 21st to January 30th.
So, the summer hottest average high lasts only one day, while the hottest average low lasts just over a week.
But the winter coldest average high and low both have the same duration of ten days, with the low just lagging behind the high by a day.
So it's not just you, with a bit more than 70 years of data, my climate shows a bit of difference in how the high/low reaches its extremes too, though more noticeable in summer. For winter, (perhaps we could even give the benefit of the doubt and say it's due to rounding error or something) days and nights almost reach their coldest at the same time.
It's also interesting that in your climate, the daytime highs stay at their coldest or hottest longer than the night time lows; not so in mine.
I see a lowest low of 1.8°C in February from 14th-16th on those tables, not in January. February tends to be sunnier and dryer than January and has a larger diurnal range which might explain this.
I see a lowest low of 1.8°C in February from 14th-16th on those tables, not in January. February tends to be sunnier and dryer than January and has a larger diurnal range which might explain this.
Ah yes, you're right, how did I not notice that? Strange how it gets milder and then colder again, though Feb being sunnier/dryer might explain it. So if those figures are to be believed then the coldest time of year here by mean temperatures is from February 12th-15th.
I don't know about other countries, but the National Weather Service in the US does "smooth" their averages so it shows (as it should) a gradual daily warming to a certain point in the year, then a gradual daily cooling to a point, etc. I think they noted that for the 1981-2010 normals just released they did it differently so that although there is "smoothing", if a particular time of year had more extremes, the smoothing might reflect that more (i.e. instead of late July being the "warmest" time of year as one would expect, it could be early July, etc.).
Wunderground doesn't seem to smooth the averages they put up. Day to day average values fluctuate up and down throughout the entire year, rather than up to a point, and then back down again.
Check that out (from a French website) : meteo-londres.eu: temperatures Londres - extrmes et moyennes (http://www.meteo-londres.eu/records-temperatures.html - broken link)
The blue column are daily cold records (coldest min, coldest average, coldest max)
The central column are daily averages (min, avg, max)
And the red one, daily warmth records
According to it, the warmest day in the year in London is July 29 (15.9°C to 24°6°C) and the coldest, Feb 14 (2.6°C - 7.7°C) - I don't know how reliable this data is though.
I once used tutiempo to work out the average highs for certain days of the year. The warmest time of year in London is between 23rd July and 8th August, with the high averaging 24.6C.
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Strange how it gets milder and then colder again, though Feb being sunnier/dryer might explain it. So if those figures are to be believed then the coldest time of year here by mean temperatures is from February 12th-15th.
