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 2025-05-26.

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	8% 6% 2 6% 4 4 4 3 5% 6% 51%	117777
	Night	11% 8% 3 7% 4 4 5% 4 5% 6% 43%	120290
Transparency	Day	32% 6% 11% 20% 18% 13%	117521
	Night	39% 7% 12% 19% 15% 9%	120135
Seeing	Day	10% 5% 16% 26% 27% 16%	15106
	Night	13% 3 18% 39% 24% 3	24468

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	16% 15% 5% 13% 7% 7% 5% 4 4 5% 19%	3639
	11th to 20th	Day	13% 12% 4 8% 5% 5% 7% 4 6% 7% 29%	3640
	21st to end	Day	18% 11% 5% 9% 4 4 4 3 5% 6% 31%	4004
February	1st to 10th	Day	14% 12% 4 9% 6% 6% 4 3 4 6% 31%	1736
	11th to 20th	Day	12% 10% 3 8% 7% 6% 5% 5% 5% 6% 33%	1950
	21st to end	Day	10% 9% 3 8% 6% 5% 6% 4 6% 8% 35%	1650
March	1st to 10th	Day	6% 11% 4 11% 6% 5% 5% 5% 6% 9% 33%	4518
	11th to 20th	Day	7% 8% 3 7% 4 4 5% 4 5% 6% 48%	4732
	21st to end	Day	8% 9% 3 8% 6% 6% 6% 5% 7% 8% 33%	5851
April	1st to 10th	Day	10% 8% 3 7% 5% 4 5% 4 6% 7% 42%	2400
	11th to 20th	Day	6% 6% 2 7% 5% 4 5% 4 6% 7% 48%	2387
	21st to end	Day	7% 6% 2 6% 4 4 5% 3 5% 8% 49%	2600
May	1st to 10th	Day	8% 6% 2 5% 4 4 4 3 5% 6% 53%	4240
	11th to 20th	Day	6% 3 1 3 2 3 3 2 4 6% 67%	4450
	21st to end	Day	5% 4 2 5% 4 4 4 3 6% 8% 54%	4886
June	1st to 10th	Day	8% 6% 2 6% 4 4 5% 5% 7% 8% 46%	2660
	11th to 20th	Day	7% 3 1 4 3 3 3 3 6% 7% 59%	2660
	21st to end	Day	2 4 1 3 3 3 2 3 4 5% 71%	2660
July	1st to 10th	Day	2 1 1 2 2 2 2 2 2 4 82%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 2 1 2 2 2 2 2 4 5% 77%	4790
August	1st to 10th	Day	4 4 2 4 3 3 3 2 4 7% 64%	4318
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 5% 79%	3978
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4180
September	1st to 10th	Day	2 2 1 2 2 3 3 2 4 5% 74%	2280
	11th to 20th	Day	4 4 1 4 2 3 4 4 4 7% 63%	2138
	21st to end	Day	5% 3 1 4 4 3 4 3 4 6% 65%	2090
October	1st to 10th	Day	4 4 1 4 3 3 2 2 4 5% 67%	3472
	11th to 20th	Day	7% 6% 2 5% 3 3 4 3 5% 7% 56%	3016
	21st to end	Day	9% 7% 2 7% 4 3 5% 4 6% 7% 45%	3101
November	1st to 10th	Day	14% 7% 3 6% 5% 4 6% 4 5% 7% 39%	1764
	11th to 20th	Day	14% 9% 3 8% 6% 5% 5% 4 6% 7% 34%	1800
	21st to end	Day	10% 10% 4 9% 8% 6% 7% 4 7% 6% 29%	1695
December	1st to 10th	Day	10% 8% 4 12% 7% 7% 7% 5% 6% 6% 29%	2620
	11th to 20th	Day	20% 15% 6% 15% 8% 5% 4 3 5% 5% 16%	3028
	21st to end	Day	17% 12% 5% 12% 7% 6% 6% 5% 6% 5% 19%	4004
January	1st to 10th	Night	19% 17% 5% 11% 6% 6% 6% 5% 5% 5% 15%	6306
	11th to 20th	Night	16% 12% 3 8% 6% 5% 7% 6% 7% 6% 24%	6320
	21st to end	Night	17% 12% 5% 8% 4 4 3 3 5% 7% 31%	6952
February	1st to 10th	Night	16% 12% 3 8% 7% 6% 6% 5% 6% 6% 26%	2659
	11th to 20th	Night	13% 10% 2 8% 6% 5% 6% 4 7% 7% 32%	2338
	21st to end	Night	11% 12% 3 8% 6% 6% 6% 5% 7% 7% 29%	1980
March	1st to 10th	Night	9% 11% 4 9% 6% 8% 7% 4 5% 7% 32%	5376
	11th to 20th	Night	12% 12% 3 6% 4 3 3 3 4 5% 44%	5267
	21st to end	Night	9% 8% 3 8% 7% 7% 6% 5% 7% 8% 32%	5121
April	1st to 10th	Night	11% 7% 3 6% 4 4 5% 4 6% 6% 45%	2000
	11th to 20th	Night	10% 6% 3 6% 4 4 5% 4 6% 5% 48%	1960
	21st to end	Night	8% 4 2 5% 4 4 5% 4 6% 8% 50%	1800
May	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 6% 7% 49%	2950
	11th to 20th	Night	4 3 1 5% 3 3 3 3 7% 6% 62%	2648
	21st to end	Night	8% 6% 2 6% 5% 4 4 3 5% 7% 50%	2805
June	1st to 10th	Night	9% 5% 2 7% 5% 4 5% 4 6% 7% 47%	1520
	11th to 20th	Night	7% 4 1 5% 3 4 3 3 4 6% 59%	1520
	21st to end	Night	3 3 2 3 3 2 4 3 5% 6% 66%	1520
July	1st to 10th	Night	1 1 2 1 2 2 2 3 4 82%	2540
	11th to 20th	Night	1 2 2 2 2 3 4 5% 79%	2540
	21st to end	Night	3 3 1 3 2 3 3 3 5% 5% 69%	2761
August	1st to 10th	Night	4 3 2 5% 4 4 4 3 5% 7% 59%	2614
	11th to 20th	Night	1 2 1 2 2 2 2 2 4 5% 76%	2860
	21st to end	Night	4 3 1 2 1 2 2 2 3 3 77%	3498
September	1st to 10th	Night	3 3 1 2 2 2 2 2 4 5% 75%	1900
	11th to 20th	Night	4 4 2 4 3 3 3 3 5% 6% 64%	2041
	21st to end	Night	7% 3 1 4 2 3 2 3 4 5% 67%	2090
October	1st to 10th	Night	5% 3 2 4 2 2 3 2 3 4 70%	3507
	11th to 20th	Night	5% 4 2 4 3 4 3 3 5% 6% 60%	3917
	21st to end	Night	9% 5% 2 6% 3 4 5% 4 6% 8% 47%	4457
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 6% 6% 43%	2535
	11th to 20th	Night	17% 8% 3 8% 4 5% 5% 4 5% 6% 35%	2600
	21st to end	Night	14% 8% 3 7% 5% 5% 6% 5% 5% 7% 35%	2700
December	1st to 10th	Night	11% 7% 3 9% 7% 7% 8% 6% 7% 7% 29%	4560
	11th to 20th	Night	20% 15% 6% 12% 7% 6% 6% 3 4 5% 16%	5176
	21st to end	Night	18% 13% 4 10% 7% 7% 7% 5% 6% 5% 19%	6952

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	63% 10% 14% 11% 2	3639
	11th to 20th	Day	53% 9% 17% 18% 3	3640
	21st to end	Day	51% 10% 12% 19% 5% 2	4004
February	1st to 10th	Day	54% 11% 17% 14% 4 1	1736
	11th to 20th	Day	48% 11% 16% 18% 6%	1960
	21st to end	Day	43% 10% 19% 18% 9% 1	1650
March	1st to 10th	Day	44% 9% 15% 21% 11% 1	4518
	11th to 20th	Day	34% 6% 13% 32% 14% 1	4732
	21st to end	Day	43% 10% 18% 19% 8% 2	5851
April	1st to 10th	Day	38% 7% 17% 23% 13% 3	2400
	11th to 20th	Day	32% 7% 13% 26% 18% 4	2390
	21st to end	Day	32% 6% 14% 28% 18% 3	2600
May	1st to 10th	Day	28% 6% 10% 24% 26% 5%	4240
	11th to 20th	Day	18% 4 9% 26% 30% 13%	4453
	21st to end	Day	23% 8% 14% 33% 18% 4	4887
June	1st to 10th	Day	32% 9% 12% 23% 21% 2	2660
	11th to 20th	Day	22% 6% 9% 25% 27% 11%	2660
	21st to end	Day	16% 4 7% 19% 32% 22%	2660
July	1st to 10th	Day	9% 2 3 9% 21% 57%	4351
	11th to 20th	Day	10% 2 2 7% 21% 58%	4345
	21st to end	Day	10% 2 2 8% 31% 46%	4639
August	1st to 10th	Day	21% 4 5% 10% 26% 35%	4302
	11th to 20th	Day	10% 2 3 17% 36% 32%	4017
	21st to end	Day	13% 2 4 21% 35% 24%	4179
September	1st to 10th	Day	13% 3 5% 19% 32% 28%	2280
	11th to 20th	Day	20% 5% 10% 23% 30% 13%	2138
	21st to end	Day	21% 4 9% 28% 30% 8%	2090
October	1st to 10th	Day	21% 4 7% 22% 39% 7%	3472
	11th to 20th	Day	29% 4 14% 31% 19% 4	3016
	21st to end	Day	36% 5% 14% 30% 14% 1	3101
November	1st to 10th	Day	42% 9% 17% 24% 8%	1764
	11th to 20th	Day	48% 9% 19% 18% 5% 1	1800
	21st to end	Day	50% 11% 18% 15% 5%	1695
December	1st to 10th	Day	54% 7% 19% 17% 2	2620
	11th to 20th	Day	69% 8% 14% 7% 2	3028
	21st to end	Day	62% 11% 15% 10% 2	4004
January	1st to 10th	Night	66% 11% 13% 8% 2	6306
	11th to 20th	Night	56% 9% 14% 15% 7%	6320
	21st to end	Night	49% 8% 13% 19% 8% 2	6952
February	1st to 10th	Night	52% 11% 17% 16% 4 1	2659
	11th to 20th	Night	45% 10% 18% 18% 8% 1	2339
	21st to end	Night	47% 10% 15% 20% 7% 1	1980
March	1st to 10th	Night	44% 10% 13% 23% 9% 1	5376
	11th to 20th	Night	41% 4 9% 30% 16%	5267
	21st to end	Night	43% 9% 17% 23% 7%	5121
April	1st to 10th	Night	37% 8% 12% 24% 17% 2	2000
	11th to 20th	Night	34% 8% 10% 25% 19% 4	1960
	21st to end	Night	29% 6% 13% 26% 23% 3	1800
May	1st to 10th	Night	28% 9% 11% 24% 24% 5%	2950
	11th to 20th	Night	19% 5% 9% 25% 33% 8%	2648
	21st to end	Night	30% 7% 10% 31% 19% 3	2805
June	1st to 10th	Night	34% 7% 14% 23% 20% 2	1520
	11th to 20th	Night	26% 6% 8% 22% 29% 10%	1520
	21st to end	Night	18% 4 6% 18% 33% 21%	1520
July	1st to 10th	Night	8% 2 3 10% 18% 60%	2500
	11th to 20th	Night	7% 3 3 8% 20% 59%	2492
	21st to end	Night	16% 3 2 8% 27% 44%	2674
August	1st to 10th	Night	24% 4 5% 10% 22% 35%	2606
	11th to 20th	Night	11% 3 4 12% 28% 42%	2887
	21st to end	Night	14% 2 3 15% 33% 33%	3498
September	1st to 10th	Night	13% 2 5% 14% 29% 36%	1900
	11th to 20th	Night	21% 4 7% 20% 25% 22%	2041
	21st to end	Night	20% 3 6% 22% 33% 16%	2090
October	1st to 10th	Night	20% 3 5% 18% 35% 19%	3507
	11th to 20th	Night	25% 3 12% 28% 27% 4	3917
	21st to end	Night	34% 6% 12% 31% 17% 1	4457
November	1st to 10th	Night	39% 7% 14% 25% 14% 1	2535
	11th to 20th	Night	46% 8% 15% 23% 8%	2600
	21st to end	Night	44% 8% 18% 21% 8% 1	2700
December	1st to 10th	Night	49% 8% 22% 18% 4	4560
	11th to 20th	Night	68% 8% 14% 8% 2	5176
	21st to end	Night	59% 12% 14% 11% 4	6952

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	22% 5% 11% 35% 22% 6%	200
	11th to 20th	Day	21% 4 15% 29% 21% 11%	200
	21st to end	Day	20% 3 12% 30% 25% 10%	220
February	1st to 10th	Day	18% 4 23% 28% 20% 6%	314
	11th to 20th	Day	18% 5% 18% 32% 21% 6%	495
	21st to end	Day	14% 6% 26% 28% 20% 7%	414
March	1st to 10th	Day	16% 9% 22% 32% 18% 3	500
	11th to 20th	Day	14% 8% 20% 29% 21% 8%	500
	21st to end	Day	14% 10% 20% 29% 20% 6%	550
April	1st to 10th	Day	13% 12% 19% 22% 20% 13%	500
	11th to 20th	Day	9% 12% 25% 25% 18% 11%	492
	21st to end	Day	8% 8% 26% 27% 23% 9%	500
May	1st to 10th	Day	7% 12% 23% 25% 21% 13%	503
	11th to 20th	Day	14% 9% 17% 26% 22% 13%	528
	21st to end	Day	8% 4 16% 22% 30% 19%	550
June	1st to 10th	Day	9% 4 16% 27% 25% 19%	490
	11th to 20th	Day	8% 6% 22% 27% 26% 12%	490
	21st to end	Day	3 2 16% 29% 31% 19%	490
July	1st to 10th	Day	3 1 11% 28% 36% 21%	486
	11th to 20th	Day	2 1 9% 30% 39% 18%	484
	21st to end	Day	3 1 6% 26% 42% 22%	531
August	1st to 10th	Day	6% 1 7% 26% 38% 22%	487
	11th to 20th	Day	2 1 7% 24% 35% 31%	477
	21st to end	Day	4 2 11% 22% 33% 28%	539
September	1st to 10th	Day	5% 1 9% 18% 35% 31%	490
	11th to 20th	Day	6% 2 11% 22% 31% 26%	490
	21st to end	Day	5% 3 14% 25% 29% 24%	490
October	1st to 10th	Day	8% 4 13% 21% 28% 25%	490
	11th to 20th	Day	9% 3 14% 26% 27% 20%	409
	21st to end	Day	12% 5% 18% 26% 28% 11%	330
November	1st to 10th	Day	17% 4 15% 27% 29% 8%	300
	11th to 20th	Day	16% 3 16% 29% 27% 8%	300
	21st to end	Day	17% 2 13% 24% 33% 10%	247
December	1st to 10th	Day	21% 3 12% 27% 22% 17%	200
	11th to 20th	Day	25% 5% 20% 29% 19% 4	200
	21st to end	Day	20% 4 16% 31% 21% 8%	220
January	1st to 10th	Night	22% 4 17% 35% 19% 4	800
	11th to 20th	Night	20% 4 17% 33% 22% 4	800
	21st to end	Night	19% 3 13% 38% 23% 4	880
February	1st to 10th	Night	23% 2 20% 37% 17% 2	800
	11th to 20th	Night	18% 2 18% 39% 21% 2	784
	21st to end	Night	15% 4 25% 37% 17% 2	660
March	1st to 10th	Night	15% 5% 23% 39% 16% 2	800
	11th to 20th	Night	15% 5% 20% 38% 19% 2	800
	21st to end	Night	15% 5% 21% 40% 17% 1	880
April	1st to 10th	Night	12% 5% 22% 38% 22% 2	800
	11th to 20th	Night	12% 6% 26% 34% 20% 2	772
	21st to end	Night	9% 5% 27% 41% 18% 2	600
May	1st to 10th	Night	8% 7% 23% 42% 19% 1	600
	11th to 20th	Night	8% 5% 21% 35% 26% 4	433
	21st to end	Night	9% 5% 18% 38% 25% 5%	422
June	1st to 10th	Night	9% 5% 23% 36% 24% 4	380
	11th to 20th	Night	9% 4 28% 34% 22% 2	380
	21st to end	Night	3 2 24% 44% 26% 1	380
July	1st to 10th	Night	2 3 18% 50% 26% 1	370
	11th to 20th	Night	1 1 20% 58% 20%	368
	21st to end	Night	3 1 15% 52% 28% 2	416
August	1st to 10th	Night	5% 14% 47% 31% 2	424
	11th to 20th	Night	2 1 13% 48% 34% 3	587
	21st to end	Night	4 2 13% 41% 35% 4	836
September	1st to 10th	Night	4 1 11% 42% 37% 5%	760
	11th to 20th	Night	5% 2 12% 35% 40% 6%	760
	21st to end	Night	8% 3 13% 37% 33% 7%	760
October	1st to 10th	Night	10% 1 16% 40% 29% 5%	760
	11th to 20th	Night	9% 3 15% 37% 30% 6%	760
	21st to end	Night	11% 3 17% 40% 26% 3	836
November	1st to 10th	Night	17% 3 15% 38% 24% 2	780
	11th to 20th	Night	21% 2 16% 39% 21% 2	800
	21st to end	Night	18% 3 16% 36% 24% 4	800
December	1st to 10th	Night	21% 2 16% 37% 21% 4	800
	11th to 20th	Night	25% 2 15% 39% 17% 2	800
	21st to end	Night	27% 4 19% 37% 12% 2	880

Page generated at 2025-05-23 06:20:56. Version ac07

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