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Old 10-07-2009, 03:41 PM
 
Location: Perth, Western Australia
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I was looking at average daily sunshine hours (per month; ie. April avg. 6 hrs of sun per day)
on the "BBC Country Guides" website and noticed something very strange;

Almost all of Canada has MUCH sunnier Springs than Autumns...
especially all three Western Canada (the Prairies) cities; Edmonton, Saskatoon and Winnipeg.
Peak rainfall comes in the summer months, so there aren't that many more days with precip in Autumn vs. Spring.

I've also looked at sunshine hour trends in the U.S. Plains and northern Midwest and noticed that all but the northernmost parts are "immune" from this "Autumn Gloom" pattern. (ex: Minneapolis doesn't see this, but Duluth does)

Toronto is different in that it's Spring roughly equally as cloudy as its Autumn is.
*Basically, there is nowhere significantly sunnier in Canada than Toronto in Autumn, but many places are in Spring.

This is very perplexing for me...
Any weather-gurus/meteorologists want to take a stab at it?
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Old 10-07-2009, 05:28 PM
bjh
 
Location: Memphis - home of the king
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Something to do with the tilt of the earth on its axis?
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Old 10-07-2009, 05:34 PM
 
Location: Vermont, grew up in Colorado and California
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..I dunno..lake effect moisture/clouds?
We get it here all the time.
Even though the radar often says it's clear.
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Old 10-07-2009, 05:40 PM
 
Location: Perth, Western Australia
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Quote:
Originally Posted by Summerz View Post
..I dunno..lake effect moisture/clouds?
We get it here all the time.
Even though the radar often says it's clear.
Lake Effect doesn't explain it;
"The Prairies" should all have very little "Lake Effect" compared to Toronto...
(especially Saskatoon; one of Canada's driest cities )
and Toronto sees the opposite; more balance between Spring and Autumn sunshine levels.

Perhaps someone with more knowledge of northern-latitude weather patterns might know?
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Old 10-07-2009, 06:43 PM
 
Location: E ND & NW MN
4,818 posts, read 10,169,390 times
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Hi

I thought about it and looked up some data from The Weather Network for Canadian places and it's a tough question you posed. But I do forecast for North Dakota and Northwest Minnesota and have done so for more than 10 years so after thinking it over I will offer this possibility.

Like water temps....soil temps peak often peak in the early fall after talking all summer to warm up. During the fall as we transition toward winter...colder airmass begin to drop south from the Arctic. The Arctic in the early fall is still mostly ice free as well as all the inland lakes are ice free. The airmasses that generate over northwest into Central Canada contain more moisture as a result of the effects of more water coverage. Thus the colder airmasses that drop south are more moist and thus cloudier. Also colder air going over a warm ground produces a steep low level lapse rate (warm at the bottom to cold at the top). These upper low pressure systems which contain cold air aloft will have very low convective temps and when combined with moisture in the ground will cause clouds to form with minimal surface heating. What we call self destruct sunshine....any sun in the morning will lead to clouds quickly by noontime. This more moist airmass remains in place until replaced by drier arctic airmasses that form in the winter months once the lakes and the ground freezes. Thus the arctic and winter time airmasses do not contain nearly as much moisture and are often more cloud free. This would explain the increase in sun from Dec to Jan.

In the Spring....the ground is cold and often still snowcovered well into April in many spots from North Dakota and nrn Minnesota into south central Canada. March into early April can still contain dry arctic like airmasses with a good deal of sun. Even as we head into later April and early May the low level moisture is not present yet due to a colder ground and still frozen water until we hit more like mid May.

Toronto is very close to the storm track in most seasons. You have the warmer lake waters likely to produce extensive cloud cover in the fall into parts of the winter. Springtime in Toronto may not see such an effect as western Canada due to it being much closer to the east coast storm track and thus more storminess on average than in the Prairies.

That is my two cents worth...


Dan -- meteorologist Grand Forks ND
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Old 10-07-2009, 10:05 PM
 
Location: Perth, Western Australia
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Thanks DaninEGF.

That makes a lot of sense, even if we still don't know the real reason.
At first I was going to be annoyed at my arch-nemesis (ice & snow),
but it appears that being frozen is the only thing making the Canadian Prairies quite-sunny.
Contrasted with all the cities in the U.S. northern plains and upper Midwest, western Canada is still cloudier most of the year,
which I suppose means Canada is inherently-cloudy; even our semi-arid parts...
and in Spring, being frozen/cold helps limit their cloudiness???

*Any ideas why it doesn't affect typically-snowy cities in the U.S. Plains states, say around 41-45 degrees latitude?

"Destructive-Sunshine?"
Does this sound like what Toronto usually gets?
Morning scattered sun, clouding over between 8:30-11:30 am into full-overcast...
breaking up just after sunset into "partly-cloudy" night skies.
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