Why doesn't summer "fade to fall" in Toronto, usually? (climate, snow storm)

[ColdCanadian]

I would like to hear from weather experts reasons for this, or opinions from anyone about why this happens.

Normally,
in a period of about 10-20 our highs become our previous lows, and our new lows become startlingly low.

Say around Labour Day our highs might be 70-74 F, (21-23 C) lows 52-58 F. (11-14 C)
Anytime between September 18-28th,
it's normal for our highs to suddenly become 52-58 F most days with lows from 35-48 F (2-9 C)
yet the difference in daylength is 11.5-12 hrs long vs. 12.5-12.75 hrs long.

I think that where people have a romantic notions of Autumn,
it's usually where a climate "fades" into autumn allowing some acclimatization.

In my opinion, autumn hits like a ton of bricks 1-in-2 autumns.
(it's not just lower temps, but much less sun and often faster windspeeds )

Probably once in 8-10 years we actually get a gradual cool down in autumn that seems to match the pattern of shortening days.
Last year was like this, as we had a late ending summer and it cooled very slowly and gradually into the Autumn season,
losing only about 2-5 F per week, not the 7-20 F per week that I'm familiar with.

If summer usually/always "faded" to autumn then I might actually like it.
My prefered cooldown rate would be a maximum-rate-of-change of 3 F for any given week.

Any guesses?

[ColdCanadian]

I guess an easier way to ask is,
where does all this sudden chill come from;
certainly has nothing to do with our local environment.

[wavehunter007]

Originally Posted by ColdCanadian

I would like to hear from weather experts reasons for this, or opinions from anyone about why this happens.

Normally,
in a period of about 10-20 our highs become our previous lows, and our new lows become startlingly low.

Say around Labour Day our highs might be 70-74 F, (21-23 C) lows 52-58 F. (11-14 C)
Anytime between September 18-28th,
it's normal for our highs to suddenly become 52-58 F most days with lows from 35-48 F (2-9 C)
yet the difference in daylength is 11.5-12 hrs long vs. 12.5-12.75 hrs long.

I think that where people have a romantic notions of Autumn,
it's usually where a climate "fades" into autumn allowing some acclimatization.

In my opinion, autumn hits like a ton of bricks 1-in-2 autumns.
(it's not just lower temps, but much less sun and often faster windspeeds )

Probably once in 8-10 years we actually get a gradual cool down in autumn that seems to match the pattern of shortening days.
Last year was like this, as we had a late ending summer and it cooled very slowly and gradually into the Autumn season,
losing only about 2-5 F per week, not the 7-20 F per week that I'm familiar with.

If summer usually/always "faded" to autumn then I might actually like it.
My prefered cooldown rate would be a maximum-rate-of-change of 3 F for any given week.

Any guesses?

The way I understand it :

The first 15/20 days of September the synoptic pattern resemble summer across the far northern USA and southern Canada (45-50 N):

The mean axis of the Pacific High is still near 39 N – about the latitude of the northern coast of California. On the other side of the North American mainland, the huge Azores/Bermuda High continues to dominate the weather from around 40 N (NYC) southward, still pumping in mild temperatures and even bouts of high humidity to the eastern USA. The main jet stream still enters North America in the vicinity of Vancouver Island and pursues an almost due-east course across North America, crossing Lake Superior and exiting North America over Newfoundland. Lastly (and most important) is that the path of high pressure (anticyclones) across the USA/Canadian border comes from the mild Pacific Ocean. This leads to the fair weather, mild temperatures, and sunny skies across the far northern USA/southern Canada in early/mid September.

However, by late September/early October, as the solar angle continues to diminish… the thermal differences start to change the synoptic pattern rapidly:

Not only is the Pacific High rapidly retreating southward down the West Coast of North America (the Bermuda High does likewise just a little slower)…but the main point of origin of the high pressure areas that crosses the US/Canadian boarded starts to change: Now, high pressure coming from the mild Pacific is met (and often modified) by cold polar highs that originate over the high latitudes of cold Northwest Canada (the Northwest Territories). These areas of high pressure are much colder, since their source region is no longer the mild North Pacific – but the cold interior of NW Canada. By late September/early October, as the solar angle is falling fast across the higher middle latitudes (45-50 N) and mean temps are falling, each front brings a new injection of colder air.

Of course as October continues into November…the storm track also follows the southward retreat of the isotherms: By early November, the storm track across North America has taken on the paths characteristic of the cold season. The Aleutian Low moves into its winter home in the northwest corner of the Gulf of Alaska and deepens. This is what leads to increased storm frequency in the Pacific Northwest with heavy rains on the lowlands and deep snows in the Mountains . When these storm coming off the Pacific meet up with the cold air dropping down from northwest Canada…the first snows in the Intermoutian West/ Northern Rockies fly. By mid November, lows/storm tracks from the Alberta and Colorado lows converge and deepen over/near the Great Lakes, where an area of maximum storm frequency is created. By late November even the Bermuda High has retreated south toward Florida, and rain/snow storms will on occasion go up the East Coast from the Virginia Capes to the Canadian Maritimes. Then comes December 1st…and the ugliness of winter north of 35 latitude in North America really gets going.

Sounds promising, huh.

PS. Don’t’ rush the next two months…savor them my friend.

[ColdCanadian]

Originally Posted by wavehunter007

The way I understand it :

The first 15/20 days of September the synoptic pattern resemble summer across the far northern USA and southern Canada (45-50 N):

The mean axis of the Pacific High is still near 39 N – about the latitude of the northern coast of California. On the other side of the North American mainland, the huge Azores/Bermuda High continues to dominate the weather from around 40 N (NYC) southward, still pumping in mild temperatures and even bouts of high humidity to the eastern USA. The main jet stream still enters North America in the vicinity of Vancouver Island and pursues an almost due-east course across North America, crossing Lake Superior and exiting North America over Newfoundland. Lastly (and most important) is that the path of high pressure (anticyclones) across the USA/Canadian border comes from the mild Pacific Ocean. This leads to the fair weather, mild temperatures, and sunny skies across the far northern USA/southern Canada in early/mid September.

However, by late September/early October, as the solar angle continues to diminish… the thermal differences start to change the synoptic pattern rapidly:

Not only is the Pacific High rapidly retreating southward down the West Coast of North America (the Bermuda High does likewise just a little slower)…but the main point of origin of the high pressure areas that crosses the US/Canadian boarded starts to change: Now, high pressure coming from the mild Pacific is met (and often modified) by cold polar highs that originate over the high latitudes of cold Northwest Canada (the Northwest Territories). These areas of high pressure are much colder, since their source region is no longer the mild North Pacific – but the cold interior of NW Canada. By late September/early October, as the solar angle is falling fast across the higher middle latitudes (45-50 N) and mean temps are falling, each front brings a new injection of colder air.

Of course as October continues into November…the storm track also follows the southward retreat of the isotherms: By early November, the storm track across North America has taken on the paths characteristic of the cold season. The Aleutian Low moves into its winter home in the northwest corner of the Gulf of Alaska and deepens. This is what leads to increased storm frequency in the Pacific Northwest with heavy rains on the lowlands and deep snows in the Mountains . When these storm coming off the Pacific meet up with the cold air dropping down from northwest Canada…the first snows in the Intermoutian West/ Northern Rockies fly. By mid November, lows/storm tracks from the Alberta and Colorado lows converge and deepen over/near the Great Lakes, where an area of maximum storm frequency is created. By late November even the Bermuda High has retreated south toward Florida, and rain/snow storms will on occasion go up the East Coast from the Virginia Capes to the Canadian Maritimes. Then comes December 1st…and the ugliness of winter north of 35 latitude in North America really gets going.

Sounds promising, huh.

PS. Don’t’ rush the next two months…savor them my friend.

Great explanation.

I live at 43'30-somthing btw.
45 N feels and looks decidedly cooler/colder than here; mixed coniferous.
44 N seems to be the northern limit of mixed deciduous or "Carolinian Forest."
Windsor is around 41-42 N and we have several cities straddling 43 N or a bit further south.
Imho, southern Ontario ends somewhere between 45-46 N;
it would seem a bit silly to me lumping North Bay in with southern Canada with their "northern Ontario" identity.

So I live in an area of traditional maximum autumn storm frequency?

That sounds like it explains why last summer DID fade to autumn,
because we were WAY drier than normal,
but sounds like lack of rain didn't cause the warmth;
not getting rain-bearing fronts also kept the cold away?

Last autumn was the first autumn in over a decade that I didn't hate.

Savour the next two months? Nay.
But I know I can rely on liking the weather until Labour Day and at least 4-7 days afterwards.
Probably Sep 12th is the earliest the weather can go sour here.
Sounds better where you live.

Once autumn begins,
I generally start waiting for our first powerful spring warm fronts to return.

[wavehunter007]

Originally Posted by ColdCanadian

Great explanation.

I live at 43'30-somthing btw.
45 N feels and looks decidedly cooler/colder than here; mixed coniferous.
44 N seems to be the northern limit of mixed deciduous or "Carolinian Forest."
Windsor is around 41-42 N and we have several cities straddling 43 N or a bit further south.
Imho, southern Ontario ends somewhere between 45-46 N;
it would seem a bit silly to me lumping North Bay in with southern Canada with their "northern Ontario" identity.

So I live in an area of traditional maximum autumn storm frequency?

Savour the next two months? Nay.
But I know I can rely on liking the weather until Labour Day and at least 4-7 days afterwards.
Probably Sep 12th is the earliest the weather can go sour here.

Latitude wise - it’s a bit hard to be specific down to a few degrees north/south. So I would think (a guess) that metro Toronto is fairly matched to the rhythm of the temp/precip of the eastern Great Lakes of the USA. The change in the path of polar lows that might affect metro Toronto…has much the same effect on the upper UP of Michigan (Grand Rapids, Flint…etc) or Lake cities like Erie or Buffalo. These patterns are broad and not able to be pinned down to a few hundred miles north or south…at least most of the time – lol.

One other note, perhaps I confused you (or myself): From what I understand…a large percentage of winter lows/storm tracks that cross North America from the Pacific to the Atlantic in the westerly flow between 35 and 55 North….will tend to go over/or very near the Great Lakes region in winter. I was attempting to set the stage in late autumn as to why and where the lows get going – and the severity of the winter season in/near the Great Lakes. The pattern that shows it’s face in this region is more of a late autumn/winter thing (November or so on)...than an early autumn thing (Sept/Oct), the way I understand it. You live in this region, so obviously you know what is the typical rhythm of when the storminess of the cold season returns.

To tell you the truth, I’m a bit surprised to see your distaste for late September/early October weather in the Great Lakes region. I was in Niagara Falls one fine early October week many years ago (before you need a passport to get to the Canadian side): Sunshine, temps in the lower 60’s, light winds…etc it was quite nice.

Never underestimate what people in other parts of the world are going through where they live at the same time you are: In October, Moscow has daily lows that Toronto will not see for another month...and in the absolute depths of a Toronto winter in late January...vast areas of the Northern Hemisphere have daily highs that are 30 to 40 F colder than the daily lows in Toronto. It's all realtive.

[ColdCanadian]

Originally Posted by wavehunter007

Latitude wise - it’s a bit hard to be specific down to a few degrees north/south. So I would think (a guess) that metro Toronto is fairly matched to the rhythm of the temp/precip of the eastern Great Lakes of the USA. The change in the path of polar lows that might affect metro Toronto…has much the same effect on the upper UP of Michigan (Grand Rapids, Flint…etc) or Lake cities like Erie or Buffalo. These patterns are broad and not able to be pinned down to a few hundred miles north or south…at least most of the time – lol.

One other note, perhaps I confused you (or myself): From what I understand…a large percentage of winter lows/storm tracks that cross North America from the Pacific to the Atlantic in the westerly flow between 35 and 55 North….will tend to go over/or very near the Great Lakes region in winter. I was attempting to set the stage in late autumn as to why and where the lows get going – and the severity of the winter season in/near the Great Lakes. The pattern that shows it’s face in this region is more of a late autumn/winter thing (November or so on)...than an early autumn thing (Sept/Oct), the way I understand it. You live in this region, so obviously you know what is the typical rhythm of when the storminess of the cold season returns.

To tell you the truth, I’m a bit surprised to see your distaste for late September/early October weather in the Great Lakes region. I was in Niagara Falls one fine early October week many years ago (before you need a passport to get to the Canadian side): Sunshine, temps in the lower 60’s, light winds…etc it was quite nice.

Never underestimate what people in other parts of the world are going through where they live at the same time you are: In October, Moscow has daily lows that Toronto will not see for another month...and in the absolute depths of a Toronto winter in late January...vast areas of the Northern Hemisphere have daily highs that are 30 to 40 F colder than the daily lows in Toronto. It's all realtive.

Yes but somehow most/all of the southeastern US misses out on our early autumn waves of cold.
I can understand NC missing it because of mountains, but TN also seems to miss it
and topographically they are just as exposed as us to Arctic winds.

No, not confused.
Seems any time a low pressure system is in eastern North America in autumn and all or part of they low is north of the 35th,
Toronto is at least blanketed by thick overcast. Watch maps of cloud patterns and you'll see that Toronto is like a cloud magnet.

A day in the low 60's F means some of the daylight hours will be in the mid 50's F which means it's not acceptable weather for shorts and a sweater or jacket will be needed at sunset... if not midday. Once I start to forget what summer feels like, highs of 61-63 F will feel good. (but by that time, highs of 60+ F will be a rare treat ) Highs of 61 F are "acceptable" to me after Oct 10th, but that is also when they become scarce.

In late September I'm still mostly summer acclimated.
Last September we had a day or two with highs from 61-63 F, 15+mph winds and sunny and I hated each entire day with a passion.
But last autumn overall was nice.
We actually had light to calm winds a lot of days, and a mix of sun and cloud throughout autumn. (sunnier than avg)

Winds easily make-or-break a sunny autumn day imho when we have marginally-cool highs forecast.
Lower autumn sun angles means longer shadows covering larger areas,
and if it's before frost the trees still have full canopies which now cast far more shade than they ever did in summer.
I think I would be more comfortable at 63 F with 20 mph winds in early June than even early September because of sun angle.

I am content that I'm not in Moscow,
but I'd rather live where the temperature ranges from "no particular chill" to "freaken-hot"

[MrMarbles]

Originally Posted by wavehunter007

Never underestimate what people in other parts of the world are going through where they live at the same time you are: In October, Moscow has daily lows that Toronto will not see for another month...and in the absolute depths of a Toronto winter in late January...vast areas of the Northern Hemisphere have daily highs that are 30 to 40 F colder than the daily lows in Toronto. It's all realtive.

Toronto is one of the warmest cities in Canada. Ottawa and Montreal, both only a couple of degrees farther north, are much colder. And compared to most of Russia (even densely populated areas), it is down right tropical. So yes, everything is relative.