Ontario(OR)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ontario(OR) clear sky chart from 2005-11-06 to 2026-09-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	7% 6% 2 6% 4 4 4 3 5% 6% 54%	157969
	Night	9% 7% 3 6% 4 4 5% 4 5% 6% 46%	150807
Transparency	Day	30% 5% 10% 20% 21% 15%	152743
	Night	37% 6% 11% 19% 17% 11%	147046
Seeing	Day	10% 5% 16% 26% 27% 16%	16883
	Night	13% 3 18% 39% 24% 3	26061

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 15% 5% 12% 7% 7% 5% 4 5% 5% 19%	4722
	11th to 20th	Day	10% 9% 3 10% 6% 7% 7% 5% 6% 7% 30%	4740
	21st to end	Day	15% 9% 5% 10% 5% 5% 5% 4 6% 7% 30%	5187
February	1st to 10th	Day	14% 12% 4 9% 6% 6% 5% 4 4 6% 31%	1824
	11th to 20th	Day	12% 10% 3 8% 7% 6% 5% 5% 5% 6% 32%	2050
	21st to end	Day	10% 9% 3 8% 6% 5% 5% 4 5% 8% 36%	1730
March	1st to 10th	Day	6% 11% 4 11% 6% 5% 5% 5% 6% 9% 33%	4618
	11th to 20th	Day	7% 8% 3 7% 4 4 5% 4 5% 6% 48%	4836
	21st to end	Day	8% 9% 3 8% 6% 6% 6% 5% 7% 8% 33%	5980
April	1st to 10th	Day	9% 7% 3 7% 4 4 5% 4 6% 8% 42%	2520
	11th to 20th	Day	7% 6% 2 7% 4 4 5% 4 7% 7% 47%	2508
	21st to end	Day	7% 6% 2 6% 4 4 5% 3 5% 8% 50%	2730
May	1st to 10th	Day	5% 4 1 3 3 4 4 3 4 6% 63%	7626
	11th to 20th	Day	5% 3 1 3 2 3 3 3 5% 7% 65%	8045
	21st to end	Day	3 3 1 4 3 4 4 3 6% 8% 61%	8992
June	1st to 10th	Day	7% 6% 2 6% 4 4 5% 5% 6% 8% 48%	2940
	11th to 20th	Day	7% 3 1 4 3 3 4 3 6% 7% 60%	2940
	21st to end	Day	2 4 1 3 3 3 2 3 4 5% 70%	2940
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 80%	8219
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 75%	8220
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 74%	8922
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 7% 71%	7966
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 6% 76%	7476
	21st to end	Day	4 4 1 4 3 3 3 3 4 6% 64%	7750
September	1st to 10th	Day	3 2 1 2 2 3 3 2 5% 5% 72%	2520
	11th to 20th	Day	4 4 1 4 2 3 4 4 4 7% 64%	2363
	21st to end	Day	5% 3 1 4 4 3 4 3 4 6% 65%	2289
October	1st to 10th	Day	4 4 1 4 3 3 2 2 4 5% 67%	3581
	11th to 20th	Day	7% 6% 2 5% 3 3 4 3 5% 7% 56%	3111
	21st to end	Day	9% 7% 2 7% 4 3 5% 4 6% 8% 46%	3200
November	1st to 10th	Day	14% 7% 3 6% 5% 4 6% 4 5% 7% 39%	1854
	11th to 20th	Day	13% 9% 3 8% 7% 5% 5% 4 6% 7% 34%	1890
	21st to end	Day	10% 10% 4 9% 8% 6% 7% 4 7% 6% 29%	1780
December	1st to 10th	Day	10% 8% 4 12% 7% 7% 7% 5% 5% 6% 29%	2700
	11th to 20th	Day	20% 15% 6% 14% 8% 5% 4 3 5% 6% 17%	3108
	21st to end	Day	17% 12% 5% 12% 7% 6% 6% 5% 6% 5% 19%	4092
January	1st to 10th	Night	19% 17% 5% 11% 6% 6% 6% 5% 5% 5% 15%	8172
	11th to 20th	Night	12% 9% 3 7% 5% 6% 9% 7% 8% 6% 26%	8220
	21st to end	Night	14% 10% 5% 9% 5% 5% 4 4 6% 8% 30%	8994
February	1st to 10th	Night	15% 12% 3 8% 6% 6% 6% 5% 6% 6% 27%	2791
	11th to 20th	Night	13% 10% 2 9% 6% 5% 6% 4 7% 7% 31%	2458
	21st to end	Night	11% 12% 3 7% 6% 6% 6% 5% 7% 7% 29%	2076
March	1st to 10th	Night	9% 11% 4 9% 6% 8% 7% 4 5% 7% 32%	5496
	11th to 20th	Night	12% 11% 3 6% 4 3 3 3 4 5% 44%	5383
	21st to end	Night	9% 8% 3 8% 7% 7% 6% 5% 7% 8% 32%	5234
April	1st to 10th	Night	10% 7% 3 6% 4 4 5% 4 6% 7% 45%	2100
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 6% 46%	2059
	21st to end	Night	8% 4 2 5% 4 3 5% 4 6% 7% 51%	1890
May	1st to 10th	Night	7% 4 1 3 2 3 3 3 4 7% 63%	5321
	11th to 20th	Night	4 4 1 5% 3 4 4 3 6% 7% 59%	4804
	21st to end	Night	6% 5% 2 5% 4 3 4 3 4 7% 58%	5181
June	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 5% 7% 49%	1680
	11th to 20th	Night	7% 4 1 5% 3 4 3 3 4 6% 60%	1680
	21st to end	Night	3 3 2 4 3 2 4 3 5% 6% 65%	1680
July	1st to 10th	Night	2 2 1 2 2 3 3 2 4 5% 76%	4740
	11th to 20th	Night	1 2 1 2 2 2 2 3 4 6% 77%	4740
	21st to end	Night	2 2 1 3 3 3 4 3 5% 7% 67%	5153
August	1st to 10th	Night	2 2 1 4 3 3 3 3 4 6% 69%	4834
	11th to 20th	Night	1 2 1 3 2 2 2 3 5% 6% 72%	5368
	21st to end	Night	5% 4 1 4 3 3 4 3 6% 6% 61%	6499
September	1st to 10th	Night	3 3 1 2 2 3 2 2 4 6% 72%	2100
	11th to 20th	Night	4 4 2 4 3 3 3 3 5% 6% 63%	2256
	21st to end	Night	7% 3 1 4 2 3 3 3 4 5% 66%	2288
October	1st to 10th	Night	5% 3 2 4 2 2 3 2 3 4 70%	3617
	11th to 20th	Night	5% 4 2 5% 3 4 3 3 5% 6% 59%	4041
	21st to end	Night	9% 5% 2 6% 3 4 5% 4 6% 8% 47%	4600
November	1st to 10th	Night	13% 8% 3 6% 4 3 4 4 6% 7% 42%	2665
	11th to 20th	Night	17% 8% 3 8% 4 5% 5% 5% 5% 6% 34%	2730
	21st to end	Night	14% 8% 3 8% 5% 5% 6% 5% 5% 7% 35%	2835
December	1st to 10th	Night	11% 7% 3 9% 7% 7% 8% 6% 7% 7% 29%	4700
	11th to 20th	Night	20% 14% 6% 12% 7% 6% 6% 4 4 5% 16%	5316
	21st to end	Night	18% 13% 4 10% 7% 7% 6% 5% 6% 5% 19%	7106

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	65% 9% 14% 10% 2	4723
	11th to 20th	Day	52% 7% 19% 18% 3	4740
	21st to end	Day	52% 9% 13% 19% 5% 1	5187
February	1st to 10th	Day	53% 10% 18% 14% 4 1	1824
	11th to 20th	Day	49% 10% 16% 19% 6%	2060
	21st to end	Day	43% 9% 19% 18% 10% 1	1730
March	1st to 10th	Day	44% 9% 15% 21% 10% 1	4618
	11th to 20th	Day	35% 6% 13% 31% 14% 1	4836
	21st to end	Day	43% 10% 18% 19% 8% 2	5980
April	1st to 10th	Day	37% 7% 17% 24% 13% 3	2520
	11th to 20th	Day	33% 7% 13% 26% 18% 4	2511
	21st to end	Day	31% 6% 13% 28% 19% 3	2730
May	1st to 10th	Day	21% 4 7% 25% 35% 9%	7626
	11th to 20th	Day	19% 4 7% 29% 30% 11%	8048
	21st to end	Day	20% 5% 10% 29% 28% 8%	8994
June	1st to 10th	Day	31% 8% 11% 23% 23% 4	2940
	11th to 20th	Day	22% 6% 9% 24% 28% 12%	2940
	21st to end	Day	17% 4 6% 20% 31% 22%	2940
July	1st to 10th	Day	10% 2 2 10% 28% 47%	8151
	11th to 20th	Day	14% 2 2 7% 23% 53%	8145
	21st to end	Day	12% 2 2 13% 32% 38%	8723
August	1st to 10th	Day	15% 3 3 8% 22% 50%	6313
	11th to 20th	Day	13% 2 5% 20% 34% 26%	5899
	21st to end	Day	19% 2 3 21% 35% 19%	6077
September	1st to 10th	Day	15% 3 5% 20% 31% 26%	2520
	11th to 20th	Day	20% 4 9% 24% 30% 12%	2363
	21st to end	Day	22% 4 9% 27% 30% 8%	2289
October	1st to 10th	Day	21% 3 7% 23% 39% 7%	3581
	11th to 20th	Day	29% 4 14% 31% 19% 3	3111
	21st to end	Day	35% 5% 14% 30% 14% 1	3200
November	1st to 10th	Day	41% 9% 17% 24% 8%	1854
	11th to 20th	Day	48% 9% 19% 19% 5% 1	1890
	21st to end	Day	51% 11% 18% 15% 5%	1780
December	1st to 10th	Day	55% 7% 19% 17% 2	2700
	11th to 20th	Day	68% 8% 13% 8% 2	3108
	21st to end	Day	61% 11% 15% 11% 2	4092
January	1st to 10th	Night	67% 10% 14% 8% 1	8172
	11th to 20th	Night	52% 7% 17% 17% 6%	8220
	21st to end	Night	48% 7% 15% 19% 8% 2	8994
February	1st to 10th	Night	52% 11% 17% 16% 4 1	2791
	11th to 20th	Night	46% 10% 17% 19% 8%	2459
	21st to end	Night	47% 10% 15% 20% 7% 2	2076
March	1st to 10th	Night	44% 10% 13% 23% 9% 1	5496
	11th to 20th	Night	41% 4 9% 29% 16%	5383
	21st to end	Night	43% 9% 17% 23% 7% 1	5234
April	1st to 10th	Night	36% 7% 12% 26% 17% 2	2100
	11th to 20th	Night	35% 8% 10% 25% 19% 4	2059
	21st to end	Night	29% 6% 12% 26% 24% 3	1890
May	1st to 10th	Night	19% 5% 6% 22% 37% 10%	5319
	11th to 20th	Night	23% 4 6% 29% 32% 6%	4804
	21st to end	Night	26% 5% 8% 29% 27% 6%	5182
June	1st to 10th	Night	32% 6% 13% 22% 23% 4	1680
	11th to 20th	Night	25% 6% 7% 20% 30% 11%	1680
	21st to end	Night	19% 4 6% 18% 33% 21%	1680
July	1st to 10th	Night	13% 2 2 11% 22% 49%	4700
	11th to 20th	Night	10% 2 2 7% 22% 57%	4692
	21st to end	Night	17% 3 2 13% 27% 38%	5040
August	1st to 10th	Night	17% 3 4 8% 18% 51%	3817
	11th to 20th	Night	15% 3 5% 15% 27% 36%	4232
	21st to end	Night	20% 3 3 17% 32% 26%	5092
September	1st to 10th	Night	15% 3 4 15% 29% 33%	2100
	11th to 20th	Night	21% 4 7% 21% 25% 21%	2256
	21st to end	Night	20% 3 6% 22% 33% 16%	2288
October	1st to 10th	Night	20% 3 5% 19% 35% 18%	3617
	11th to 20th	Night	25% 4 12% 28% 27% 4	4041
	21st to end	Night	33% 5% 12% 31% 17% 1	4600
November	1st to 10th	Night	40% 6% 15% 25% 13% 1	2665
	11th to 20th	Night	47% 8% 15% 23% 7%	2730
	21st to end	Night	46% 8% 18% 20% 7% 1	2835
December	1st to 10th	Night	50% 8% 22% 18% 3	4700
	11th to 20th	Night	68% 8% 14% 8% 2	5316
	21st to end	Night	59% 12% 15% 11% 4	7106

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	23% 5% 10% 35% 21% 6%	220
	11th to 20th	Day	19% 4 13% 28% 25% 11%	220
	21st to end	Day	18% 3 11% 29% 29% 10%	242
February	1st to 10th	Day	18% 4 22% 28% 20% 8%	342
	11th to 20th	Day	18% 5% 18% 31% 21% 6%	535
	21st to end	Day	15% 6% 26% 29% 18% 6%	446
March	1st to 10th	Day	16% 10% 21% 32% 18% 3	540
	11th to 20th	Day	15% 7% 19% 30% 21% 7%	540
	21st to end	Day	14% 10% 20% 30% 20% 6%	594
April	1st to 10th	Day	12% 11% 20% 21% 21% 15%	540
	11th to 20th	Day	10% 12% 23% 26% 18% 11%	532
	21st to end	Day	8% 8% 25% 26% 24% 9%	540
May	1st to 10th	Day	6% 11% 22% 26% 22% 13%	543
	11th to 20th	Day	13% 9% 17% 26% 22% 13%	568
	21st to end	Day	7% 4 17% 23% 30% 19%	617
June	1st to 10th	Day	8% 4 17% 27% 25% 19%	570
	11th to 20th	Day	8% 6% 21% 27% 26% 12%	570
	21st to end	Day	5% 2 16% 28% 31% 19%	570
July	1st to 10th	Day	3 1 11% 27% 37% 21%	566
	11th to 20th	Day	3 1 10% 30% 38% 19%	564
	21st to end	Day	3 1 6% 27% 40% 23%	619
August	1st to 10th	Day	5% 2 8% 26% 35% 23%	567
	11th to 20th	Day	2 1 7% 22% 37% 31%	557
	21st to end	Day	5% 2 10% 21% 33% 29%	627
September	1st to 10th	Day	6% 1 9% 20% 34% 30%	570
	11th to 20th	Day	6% 2 12% 21% 32% 27%	570
	21st to end	Day	5% 3 13% 25% 29% 26%	563
October	1st to 10th	Day	8% 3 15% 21% 28% 25%	530
	11th to 20th	Day	9% 3 15% 26% 27% 19%	444
	21st to end	Day	11% 5% 17% 26% 28% 13%	363
November	1st to 10th	Day	17% 4 15% 28% 27% 9%	330
	11th to 20th	Day	16% 2 15% 30% 27% 9%	330
	21st to end	Day	17% 2 14% 25% 32% 10%	272
December	1st to 10th	Day	20% 2 11% 30% 22% 15%	220
	11th to 20th	Day	25% 5% 18% 28% 20% 5%	220
	21st to end	Day	20% 4 17% 32% 19% 9%	242
January	1st to 10th	Night	22% 4 17% 35% 18% 4	840
	11th to 20th	Night	19% 4 16% 34% 23% 5%	840
	21st to end	Night	18% 2 12% 39% 24% 4	924
February	1st to 10th	Night	22% 2 19% 37% 18% 2	840
	11th to 20th	Night	17% 2 19% 39% 21% 2	824
	21st to end	Night	16% 4 25% 37% 17% 2	692
March	1st to 10th	Night	15% 5% 24% 39% 15% 2	840
	11th to 20th	Night	15% 5% 20% 39% 19% 2	840
	21st to end	Night	16% 5% 21% 40% 17% 1	924
April	1st to 10th	Night	12% 5% 21% 38% 23% 2	840
	11th to 20th	Night	13% 6% 25% 35% 19% 2	811
	21st to end	Night	9% 5% 26% 41% 18% 1	630
May	1st to 10th	Night	7% 7% 23% 42% 20% 1	630
	11th to 20th	Night	8% 5% 22% 36% 25% 4	455
	21st to end	Night	8% 5% 19% 38% 24% 5%	455
June	1st to 10th	Night	8% 5% 23% 36% 24% 3	420
	11th to 20th	Night	9% 5% 29% 35% 21% 2	420
	21st to end	Night	3 2 25% 43% 26% 1	420
July	1st to 10th	Night	2 2 18% 50% 26% 1	410
	11th to 20th	Night	1 1 19% 59% 20%	408
	21st to end	Night	3 1 15% 53% 28% 2	460
August	1st to 10th	Night	5% 2 14% 47% 31% 2	469
	11th to 20th	Night	2 1 14% 50% 32% 3	649
	21st to end	Night	5% 2 13% 40% 35% 4	924
September	1st to 10th	Night	5% 1 11% 42% 36% 5%	840
	11th to 20th	Night	5% 2 13% 36% 39% 6%	840
	21st to end	Night	8% 2 13% 37% 33% 7%	832
October	1st to 10th	Night	10% 1 16% 40% 28% 5%	800
	11th to 20th	Night	10% 3 16% 37% 29% 6%	800
	21st to end	Night	11% 2 17% 40% 26% 3	880
November	1st to 10th	Night	17% 3 16% 38% 25% 2	820
	11th to 20th	Night	21% 2 15% 39% 21% 2	840
	21st to end	Night	18% 3 15% 36% 24% 4	840
December	1st to 10th	Night	21% 2 16% 38% 20% 3	840
	11th to 20th	Night	25% 2 14% 39% 17% 2	840
	21st to end	Night	28% 3 18% 36% 13% 2	924

Page generated at 2026-09-26 01:18:44. Version ac07

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