Brampton BrightSkies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brampton BrightSkies Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	14% 10% 3 9% 6% 5% 5% 4 6% 7% 32%	114288
	Night	14% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	114627
Transparency	Day	48% 6% 13% 20% 11% 1	117927
	Night	48% 6% 12% 21% 12% 1	119151
Seeing	Day	18% 12% 29% 24% 12% 4	15233
	Night	18% 10% 31% 29% 11% 1	24558

By Month

Percentage Cloud Cover NE (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	11% 12% 5% 15% 7% 6% 5% 5% 6% 6% 23%	3597
	11th to 20th	Day	10% 17% 6% 17% 10% 7% 5% 4 4 5% 15%	3954
	21st to end	Day	16% 16% 6% 14% 6% 5% 5% 4 4 5% 18%	4466
February	1st to 10th	Day	14% 15% 4 12% 8% 6% 5% 4 5% 6% 22%	1800
	11th to 20th	Day	12% 14% 5% 12% 8% 5% 5% 4 5% 6% 24%	1753
	21st to end	Day	16% 14% 4 11% 6% 5% 5% 3 5% 6% 26%	1549
March	1st to 10th	Day	18% 10% 5% 9% 6% 4 5% 3 5% 5% 31%	4932
	11th to 20th	Day	10% 13% 4 9% 6% 4 5% 4 6% 8% 31%	4980
	21st to end	Day	17% 11% 4 9% 5% 4 4 3 4 5% 34%	5465
April	1st to 10th	Day	16% 11% 4 10% 6% 4 4 3 5% 7% 30%	2350
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 3 4 6% 36%	2464
	21st to end	Day	19% 10% 2 7% 5% 5% 4 3 5% 6% 34%	2600
May	1st to 10th	Day	18% 8% 3 7% 5% 4 4 3 6% 8% 34%	4238
	11th to 20th	Day	16% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	4351
	21st to end	Day	11% 5% 2 6% 4 4 4 3 6% 8% 46%	4837
June	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 5% 6% 8% 38%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 5% 4 5% 8% 9% 40%	2660
	21st to end	Day	12% 6% 2 6% 4 5% 5% 5% 6% 9% 39%	2835
July	1st to 10th	Day	9% 4 2 6% 5% 5% 6% 5% 8% 10% 40%	4536
	11th to 20th	Day	9% 4 2 5% 4 4 5% 5% 8% 9% 45%	4440
	21st to end	Day	7% 5% 2 7% 6% 5% 6% 5% 7% 9% 41%	4472
August	1st to 10th	Day	16% 7% 3 6% 4 4 5% 4 7% 8% 37%	4104
	11th to 20th	Day	9% 7% 3 8% 6% 5% 6% 5% 7% 9% 35%	4044
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	4376
September	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 5% 6% 8% 41%	2280
	11th to 20th	Day	10% 6% 2 6% 5% 3 4 3 5% 9% 46%	2152
	21st to end	Day	14% 6% 3 8% 6% 6% 5% 4 6% 8% 35%	2062
October	1st to 10th	Day	18% 8% 2 7% 5% 4 4 4 4 6% 36%	1900
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 3 5% 8% 30%	1900
	21st to end	Day	23% 12% 3 8% 6% 5% 4 4 6% 6% 23%	2090
November	1st to 10th	Day	14% 11% 3 7% 5% 4 6% 3 6% 8% 32%	1695
	11th to 20th	Day	13% 12% 4 9% 6% 5% 7% 5% 7% 7% 25%	1600
	21st to end	Day	16% 16% 5% 9% 6% 5% 5% 3 7% 6% 22%	1600
December	1st to 10th	Day	18% 15% 5% 13% 6% 6% 6% 4 5% 6% 15%	2600
	11th to 20th	Day	21% 17% 5% 9% 5% 4 4 3 4 5% 21%	2986
	21st to end	Day	26% 17% 7% 13% 5% 4 4 3 4 4 14%	3960
January	1st to 10th	Night	14% 11% 4 10% 6% 6% 6% 4 6% 7% 25%	6349
	11th to 20th	Night	11% 13% 5% 15% 10% 7% 6% 4 5% 6% 17%	5928
	21st to end	Night	15% 12% 5% 11% 6% 6% 6% 4 6% 7% 21%	6490
February	1st to 10th	Night	12% 14% 5% 10% 6% 6% 6% 4 6% 6% 25%	2600
	11th to 20th	Night	12% 13% 5% 10% 7% 7% 5% 4 5% 6% 26%	2533
	21st to end	Night	12% 11% 5% 10% 7% 6% 6% 4 4 7% 28%	2079
March	1st to 10th	Night	15% 8% 4 8% 6% 6% 5% 4 6% 6% 31%	4908
	11th to 20th	Night	9% 8% 3 8% 5% 5% 6% 4 6% 10% 37%	4979
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 5% 40%	5467
April	1st to 10th	Night	17% 10% 3 9% 5% 4 5% 4 5% 6% 32%	2049
	11th to 20th	Night	16% 8% 2 6% 5% 5% 4 3 6% 6% 38%	1902
	21st to end	Night	15% 8% 2 7% 5% 4 5% 4 6% 7% 37%	1800
May	1st to 10th	Night	17% 7% 3 6% 4 5% 4 4 5% 6% 40%	2923
	11th to 20th	Night	15% 8% 3 7% 4 4 5% 4 5% 8% 38%	2547
	21st to end	Night	9% 4 2 5% 4 4 4 3 5% 9% 51%	2738
June	1st to 10th	Night	12% 5% 2 6% 5% 5% 4 4 6% 9% 42%	1520
	11th to 20th	Night	8% 6% 3 6% 4 5% 5% 5% 7% 10% 44%	1520
	21st to end	Night	11% 5% 2 6% 4 4 4 3 7% 7% 46%	1332
July	1st to 10th	Night	5% 5% 2 5% 4 4 4 4 6% 9% 52%	2417
	11th to 20th	Night	11% 3 2 4 3 4 4 4 6% 8% 52%	2520
	21st to end	Night	7% 4 2 5% 3 4 5% 5% 6% 8% 51%	3077
August	1st to 10th	Night	10% 5% 2 6% 5% 4 4 4 6% 7% 47%	2825
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 5% 8% 50%	2785
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 47%	3247
September	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 7% 7% 48%	1900
	11th to 20th	Night	10% 5% 2 4 2 3 4 3 5% 6% 55%	2024
	21st to end	Night	15% 7% 3 7% 5% 4 4 3 5% 7% 41%	2118
October	1st to 10th	Night	17% 7% 2 7% 5% 4 4 3 6% 6% 40%	2280
	11th to 20th	Night	16% 9% 3 7% 4 5% 5% 3 5% 6% 36%	2280
	21st to end	Night	19% 10% 2 9% 5% 3 6% 4 6% 7% 29%	2508
November	1st to 10th	Night	15% 8% 2 7% 5% 4 4 4 6% 7% 37%	2598
	11th to 20th	Night	15% 10% 3 9% 6% 5% 5% 4 6% 7% 30%	2800
	21st to end	Night	18% 11% 3 9% 6% 5% 4 4 6% 8% 26%	2800
December	1st to 10th	Night	17% 13% 5% 12% 7% 5% 5% 5% 6% 6% 17%	4580
	11th to 20th	Night	15% 18% 5% 10% 6% 5% 5% 4 5% 6% 21%	5208
	21st to end	Night	24% 16% 7% 12% 5% 5% 4 3 4 5% 15%	6996

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	57% 9% 11% 13% 10%	3598
	11th to 20th	Day	70% 5% 10% 10% 4	3988
	21st to end	Day	67% 6% 9% 10% 8%	4466
February	1st to 10th	Day	62% 6% 12% 16% 4 1	1800
	11th to 20th	Day	60% 6% 11% 14% 8% 1	1762
	21st to end	Day	58% 6% 11% 16% 7% 1	1549
March	1st to 10th	Day	53% 5% 14% 15% 12% 1	4935
	11th to 20th	Day	49% 5% 16% 19% 8% 3	4980
	21st to end	Day	52% 4 10% 20% 12% 1	5465
April	1st to 10th	Day	54% 5% 11% 18% 11% 1	2350
	11th to 20th	Day	48% 5% 10% 21% 14% 1	2464
	21st to end	Day	51% 5% 11% 19% 12% 3	2600
May	1st to 10th	Day	45% 7% 14% 19% 13% 2	4250
	11th to 20th	Day	47% 11% 13% 20% 8% 1	4355
	21st to end	Day	34% 7% 13% 24% 17% 3	4837
June	1st to 10th	Day	42% 8% 11% 23% 15% 2	2660
	11th to 20th	Day	38% 7% 14% 24% 16% 1	2660
	21st to end	Day	38% 7% 14% 25% 14% 1	2835
July	1st to 10th	Day	36% 5% 16% 26% 15% 2	4466
	11th to 20th	Day	31% 6% 14% 36% 12% 1	4365
	21st to end	Day	36% 7% 15% 22% 19% 1	4329
August	1st to 10th	Day	42% 6% 15% 22% 14% 1	4091
	11th to 20th	Day	42% 6% 18% 24% 10%	4083
	21st to end	Day	35% 6% 13% 35% 10% 1	4376
September	1st to 10th	Day	38% 9% 14% 27% 11% 1	2280
	11th to 20th	Day	34% 6% 14% 31% 15% 1	2152
	21st to end	Day	44% 7% 15% 25% 9%	2062
October	1st to 10th	Day	39% 6% 15% 26% 14% 1	3160
	11th to 20th	Day	39% 6% 15% 25% 15%	3140
	21st to end	Day	54% 5% 14% 21% 6%	3428
November	1st to 10th	Day	47% 7% 16% 21% 9% 1	1695
	11th to 20th	Day	54% 7% 15% 16% 9%	1600
	21st to end	Day	60% 6% 15% 16% 3	1600
December	1st to 10th	Day	68% 5% 15% 9% 3	2600
	11th to 20th	Day	63% 6% 12% 10% 8%	2986
	21st to end	Day	73% 5% 7% 8% 6%	3960
January	1st to 10th	Night	54% 7% 10% 21% 7%	6349
	11th to 20th	Night	66% 7% 10% 12% 4	5969
	21st to end	Night	59% 7% 11% 12% 11% 1	6490
February	1st to 10th	Night	57% 6% 12% 19% 6% 1	2600
	11th to 20th	Night	58% 5% 11% 17% 9%	2535
	21st to end	Night	54% 5% 13% 18% 9%	2079
March	1st to 10th	Night	51% 5% 13% 17% 12% 2	4918
	11th to 20th	Night	41% 6% 19% 22% 10% 2	4980
	21st to end	Night	46% 4 8% 20% 18% 3	5467
April	1st to 10th	Night	52% 5% 10% 18% 14% 2	2049
	11th to 20th	Night	46% 6% 9% 20% 16% 2	1902
	21st to end	Night	45% 7% 10% 19% 17% 2	1800
May	1st to 10th	Night	44% 8% 11% 18% 16% 3	2930
	11th to 20th	Night	43% 12% 13% 19% 10% 2	2548
	21st to end	Night	29% 8% 13% 24% 23% 3	2739
June	1st to 10th	Night	38% 7% 11% 25% 18% 2	1520
	11th to 20th	Night	35% 6% 12% 24% 21% 2	1520
	21st to end	Night	36% 6% 13% 26% 17% 1	1332
July	1st to 10th	Night	29% 5% 15% 26% 22% 4	2377
	11th to 20th	Night	31% 4 13% 34% 17% 1	2472
	21st to end	Night	30% 7% 16% 29% 17% 2	2979
August	1st to 10th	Night	37% 5% 12% 28% 15% 3	2814
	11th to 20th	Night	33% 5% 15% 33% 12% 1	2812
	21st to end	Night	35% 6% 13% 30% 15% 1	3247
September	1st to 10th	Night	33% 7% 15% 29% 15% 1	1900
	11th to 20th	Night	29% 6% 11% 34% 19%	2024
	21st to end	Night	42% 7% 13% 27% 11% 1	2118
October	1st to 10th	Night	33% 5% 9% 28% 24% 1	3800
	11th to 20th	Night	42% 4 13% 27% 13%	3779
	21st to end	Night	42% 5% 16% 26% 10% 1	4120
November	1st to 10th	Night	45% 6% 13% 24% 12% 1	2598
	11th to 20th	Night	50% 7% 14% 18% 9% 1	2800
	21st to end	Night	55% 6% 17% 18% 4	2800
December	1st to 10th	Night	64% 5% 15% 13% 3	4580
	11th to 20th	Night	62% 6% 10% 13% 9%	5208
	21st to end	Night	70% 6% 10% 9% 5%	6996

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	20% 18% 32% 24% 6% 1	200
	11th to 20th	Day	21% 26% 31% 14% 7% 1	285
	21st to end	Day	25% 20% 32% 20% 3	330
February	1st to 10th	Day	23% 24% 38% 10% 5%	300
	11th to 20th	Day	22% 23% 38% 15% 2	300
	21st to end	Day	28% 25% 33% 13% 1	258
March	1st to 10th	Day	21% 18% 34% 21% 6%	500
	11th to 20th	Day	22% 18% 35% 19% 6% 1	500
	21st to end	Day	27% 16% 31% 20% 6% 1	550
April	1st to 10th	Day	20% 18% 34% 21% 7%	500
	11th to 20th	Day	25% 17% 29% 18% 9% 2	492
	21st to end	Day	22% 14% 34% 20% 8% 2	500
May	1st to 10th	Day	21% 10% 30% 24% 11% 4	503
	11th to 20th	Day	17% 7% 30% 26% 13% 6%	487
	21st to end	Day	14% 6% 28% 29% 17% 5%	529
June	1st to 10th	Day	13% 10% 30% 32% 12% 3	490
	11th to 20th	Day	14% 8% 26% 31% 19% 2	490
	21st to end	Day	14% 8% 30% 32% 13% 3	665
July	1st to 10th	Day	8% 5% 24% 36% 20% 7%	542
	11th to 20th	Day	13% 5% 22% 33% 18% 9%	484
	21st to end	Day	7% 4 26% 38% 18% 7%	532
August	1st to 10th	Day	12% 6% 21% 27% 23% 11%	486
	11th to 20th	Day	7% 6% 22% 32% 20% 13%	479
	21st to end	Day	12% 7% 22% 29% 20% 10%	539
September	1st to 10th	Day	12% 7% 24% 29% 17% 11%	490
	11th to 20th	Day	9% 5% 21% 24% 25% 16%	490
	21st to end	Day	16% 9% 28% 23% 17% 7%	490
October	1st to 10th	Day	22% 11% 26% 22% 13% 6%	490
	11th to 20th	Day	19% 14% 35% 21% 9% 3	490
	21st to end	Day	29% 13% 27% 24% 7% 1	539
November	1st to 10th	Day	20% 20% 28% 21% 10% 1	283
	11th to 20th	Day	25% 19% 32% 19% 4 2	200
	21st to end	Day	25% 16% 40% 17% 3	200
December	1st to 10th	Day	27% 18% 37% 16% 4	200
	11th to 20th	Day	29% 22% 31% 15% 4	200
	21st to end	Day	27% 19% 36% 14% 4	220
January	1st to 10th	Night	22% 17% 36% 20% 5%	800
	11th to 20th	Night	25% 17% 33% 22% 4	800
	21st to end	Night	19% 11% 40% 24% 6%	880
February	1st to 10th	Night	20% 18% 38% 21% 3	800
	11th to 20th	Night	22% 15% 39% 21% 4	783
	21st to end	Night	18% 17% 38% 23% 4	660
March	1st to 10th	Night	19% 14% 38% 25% 5%	800
	11th to 20th	Night	19% 15% 35% 25% 5%	800
	21st to end	Night	21% 11% 33% 27% 8%	880
April	1st to 10th	Night	23% 10% 36% 28% 4	800
	11th to 20th	Night	19% 12% 36% 24% 8% 2	718
	21st to end	Night	20% 9% 30% 32% 10%	600
May	1st to 10th	Night	18% 6% 29% 31% 14% 2	600
	11th to 20th	Night	16% 4 28% 38% 12% 1	409
	21st to end	Night	11% 3 27% 36% 22% 1	411
June	1st to 10th	Night	14% 5% 27% 37% 17% 1	380
	11th to 20th	Night	8% 7% 28% 40% 17%	380
	21st to end	Night	12% 5% 23% 44% 16%	380
July	1st to 10th	Night	6% 3 21% 47% 21% 2	370
	11th to 20th	Night	11% 3 22% 41% 22% 2	368
	21st to end	Night	8% 3 19% 45% 24% 2	614
August	1st to 10th	Night	9% 2 16% 42% 28% 2	567
	11th to 20th	Night	8% 3 15% 43% 27% 4	564
	21st to end	Night	11% 3 23% 35% 26% 3	698
September	1st to 10th	Night	11% 7% 22% 34% 21% 5%	760
	11th to 20th	Night	12% 4 19% 31% 29% 5%	760
	21st to end	Night	17% 7% 20% 32% 20% 4	760
October	1st to 10th	Night	18% 6% 28% 27% 18% 3	760
	11th to 20th	Night	21% 11% 29% 28% 10% 1	760
	21st to end	Night	25% 10% 32% 28% 5%	836
November	1st to 10th	Night	19% 11% 30% 29% 10% 1	780
	11th to 20th	Night	19% 14% 35% 24% 7% 2	800
	21st to end	Night	25% 12% 34% 24% 5%	800
December	1st to 10th	Night	28% 13% 37% 18% 5%	800
	11th to 20th	Night	24% 14% 41% 19% 3	800
	21st to end	Night	29% 13% 33% 21% 3	880

Page generated at 2025-05-08 09:33:58. Version ac07

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