Crunching some recent temperature data...

[Paul Ont]

It's been a while since I updated my weather stats, and the appropriate USDA designation for where I garden. I started this a few years ago with a USDA style map for Nova Scotia, followed by one for Southern Ontario. I went this route because there was great confusion about the Canadian vs. USDA growing zone, with much inflation (and subsequent disappointment in certain plants) of how cold a place actually is. There is little doubt that my areas have seen a large bump in extreme minimum low over the past 30 years, and this trend has continued. I can't say for sure what ALL of the causes of this 'bump' are, but certainly for the Toronto data the urban heat island is a significant contributor. Kingston is a little different since the airport is located in a field, on the water, to the west of the city proper... I won't get in to the merits or downsides of the USDA system, but will only say that it is the best indicator we have, and that different areas will have their complicating factors (e.g. these location below have LONG, COLD, winters and relatively hot summers).

Previous ratings were based on a minimum of 30 years data (the USDA uses 15). I've only used the years 1990 to the present for 3 of the closest stations to me. Data are per YEAR, not per winter. Here is the graph showing absolute minimum winter temperature:
<img src="http://inlinethumb13.webshots.com/26444 ... 600Q85.jpg" alt="Weatehrchart1990-2010">

The trend lines indicate the trend in absolute winter minimum. I'll give a breakdown below:

20-year average:
Kingston: -25.34C (-13.9f). USDA zone 5b designation. The exclusion of the 1980's bumped this station 1/2 USDA zone.
Toronto (Pearson): -21.61C (-6.9f). USDA zone 6a. The exclusion of the 1980's bumped this station 1/2 USDA zone.
Toronto (Downtown): -19.35C (-2.8f). USDA zone 6b. The exclusion of the 1980's took the average low from -4f to -2f.

10 year average, 1990-2000:
Kingston: -26.36C (-15.28f) USDA 5a.
Toronto (Pearson): -22.57C (-8.62f). USDA 6a.
Toronto (DT): -19.96C (-3.92f). 6b.

10 Year average, 2001-2010:
Kingston: -24.63C (-12.3f). 5b.
Toronto (P): -20.56 (-5.008f). 6a. So close to 6b...
Toronto (DT): -18.69C (-1.64f). 6b.

Warmest year in the period:
Kingston: -20.0C (-4f). 2001*.
Toronto (P): -14.5C (5.9f). 2006.
Toronto (I):-13C (8.6f). 2006.
*-Kingston saw -23.5 in 2006, which seems out of place given that it's 10C colder than the other locations.


Coldest year in the period:
Kingston: -32.2C (-25.97f; zone 4a). 1994.
Toronto (P): -31C (-23.8f; zone 4b). 1994.
Toronto (I): -26.9C (-16.42f; zone 5a). 1994.

All-time record low:
Kingston: -34.5C (-30.1f; zone 3b). 1981.
Toronto (P): -31.3C (-24.34f; zone 4b). 1981.
Toronto (I): -27.8C (-18.04f; zone 5a). 1981.

I hope someone found this interesting!

[igor.glukhovtsev]

Paul, thank you so much for the such detailed analysis of the min winter temperature trend in my lovely Toronto (and Kingston of course). Now it would be easier comparing a similar data for Almaty (in the coldest place, i.e airport) and for my place (if I would able finding my mom weather diary for 20 years).

[TerdalFarm]

Paul,
I found it interesting. I'll do something similar for my area. --Erik

[Paul Ont]

The one big draw back to this is that the time period is too short to really see any trend... The lines indicate that it is getting warmer, but, we'll wait to see if the winters below -20C (-5f) do become rarer.