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 2026-09-14.

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% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	149838
	Night	14% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	141205
Transparency	Day	47% 5% 13% 22% 11% 1	153434
	Night	48% 5% 12% 21% 13% 1	145697
Seeing	Day	18% 12% 29% 25% 12% 5%	17036
	Night	18% 10% 30% 29% 11% 1	26141

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	15% 12% 5% 14% 7% 6% 5% 4 6% 5% 21%	4661
	11th to 20th	Day	10% 19% 7% 16% 9% 7% 5% 4 4 4 13%	5160
	21st to end	Day	13% 15% 5% 14% 7% 6% 6% 5% 5% 6% 18%	5780
February	1st to 10th	Day	13% 15% 4 12% 7% 6% 5% 4 5% 6% 23%	1890
	11th to 20th	Day	12% 14% 5% 12% 8% 5% 5% 4 5% 6% 24%	1843
	21st to end	Day	16% 14% 4 11% 6% 5% 4 4 5% 6% 26%	1624
March	1st to 10th	Day	18% 10% 5% 9% 6% 4 5% 3 5% 5% 31%	5042
	11th to 20th	Day	11% 13% 4 9% 6% 4 5% 4 6% 8% 31%	5090
	21st to end	Day	17% 11% 4 9% 5% 4 4 3 4 5% 34%	5586
April	1st to 10th	Day	16% 11% 4 10% 6% 4 4 3 5% 7% 30%	2468
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 3 4 6% 35%	2589
	21st to end	Day	19% 9% 2 7% 5% 5% 4 3 5% 6% 34%	2730
May	1st to 10th	Day	18% 8% 3 8% 4 4 4 4 6% 7% 33%	7642
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	8120
	21st to end	Day	16% 5% 2 6% 3 4 4 3 6% 7% 43%	9060
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	2940
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 8% 9% 39%	2940
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 6% 10% 39%	3133
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 38%	8459
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 11% 48%	8280
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 9% 44%	8346
August	1st to 10th	Day	17% 7% 3 7% 4 4 5% 4 6% 7% 37%	6014
	11th to 20th	Day	8% 6% 3 8% 5% 5% 6% 5% 8% 10% 36%	5951
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 4 7% 9% 37%	6363
September	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 5% 6% 8% 41%	2520
	11th to 20th	Day	9% 6% 2 6% 5% 3 4 3 6% 9% 47%	2301
	21st to end	Day	14% 6% 2 7% 6% 6% 5% 4 7% 8% 35%	2170
October	1st to 10th	Day	18% 8% 2 6% 4 4 4 4 4 6% 38%	2000
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 4 5% 8% 30%	2000
	21st to end	Day	23% 11% 3 8% 6% 6% 4 4 6% 6% 23%	2200
November	1st to 10th	Day	14% 11% 3 7% 5% 4 6% 3 6% 8% 32%	1782
	11th to 20th	Day	13% 12% 4 9% 6% 6% 6% 5% 7% 7% 26%	1680
	21st to end	Day	15% 16% 5% 9% 6% 6% 5% 3 6% 7% 21%	1680
December	1st to 10th	Day	18% 15% 5% 13% 6% 6% 6% 4 5% 6% 15%	2680
	11th to 20th	Day	20% 17% 5% 9% 5% 4 4 3 4 6% 21%	3066
	21st to end	Day	26% 17% 6% 13% 5% 4 4 3 4 4 14%	4048
January	1st to 10th	Night	14% 12% 5% 11% 6% 6% 6% 4 6% 7% 24%	8234
	11th to 20th	Night	10% 17% 5% 14% 10% 8% 6% 4 5% 6% 16%	7722
	21st to end	Night	12% 11% 5% 11% 8% 6% 6% 4 6% 7% 22%	8401
February	1st to 10th	Night	12% 13% 5% 10% 6% 6% 5% 4 6% 6% 27%	2730
	11th to 20th	Night	12% 13% 5% 10% 7% 7% 5% 4 5% 6% 26%	2663
	21st to end	Night	12% 12% 5% 10% 7% 6% 6% 4 4 7% 28%	2180
March	1st to 10th	Night	15% 8% 4 8% 6% 6% 5% 4 6% 6% 31%	5018
	11th to 20th	Night	9% 8% 3 8% 5% 5% 6% 4 6% 10% 36%	5089
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 5% 40%	5588
April	1st to 10th	Night	17% 10% 3 9% 5% 4 5% 4 5% 6% 32%	2151
	11th to 20th	Night	15% 9% 3 7% 5% 5% 4 3 6% 6% 38%	1998
	21st to end	Night	15% 8% 2 7% 4 4 5% 4 6% 7% 38%	1890
May	1st to 10th	Night	18% 7% 3 7% 4 5% 4 4 5% 6% 37%	5257
	11th to 20th	Night	14% 8% 3 7% 4 4 4 4 5% 7% 39%	4739
	21st to end	Night	17% 5% 2 5% 4 4 3 3 4 7% 47%	5114
June	1st to 10th	Night	12% 5% 2 5% 5% 4 4 4 6% 8% 44%	1680
	11th to 20th	Night	8% 5% 3 6% 4 5% 5% 5% 6% 10% 44%	1680
	21st to end	Night	10% 5% 2 6% 4 5% 4 3 7% 8% 46%	1472
July	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 6% 10% 49%	4486
	11th to 20th	Night	7% 3 2 5% 4 4 5% 4 6% 9% 52%	4680
	21st to end	Night	8% 4 2 5% 4 4 4 4 5% 8% 51%	5727
August	1st to 10th	Night	12% 7% 3 6% 5% 4 4 4 5% 6% 43%	4135
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 8% 50%	4095
	21st to end	Night	11% 5% 3 6% 4 4 4 4 6% 9% 44%	4715
September	1st to 10th	Night	8% 5% 2 5% 5% 5% 4 4 7% 7% 48%	2100
	11th to 20th	Night	10% 4 2 4 2 3 4 3 5% 6% 56%	2162
	21st to end	Night	15% 7% 3 7% 5% 4 4 3 5% 7% 41%	2230
October	1st to 10th	Night	16% 6% 2 7% 4 4 4 3 6% 6% 42%	2400
	11th to 20th	Night	16% 9% 3 7% 4 5% 5% 3 5% 6% 37%	2400
	21st to end	Night	18% 9% 2 9% 5% 4 5% 4 6% 7% 30%	2640
November	1st to 10th	Night	15% 8% 2 7% 5% 4 4 4 6% 7% 37%	2731
	11th to 20th	Night	14% 10% 3 9% 6% 5% 6% 4 6% 7% 30%	2940
	21st to end	Night	18% 12% 3 9% 6% 5% 4 4 6% 7% 25%	2940
December	1st to 10th	Night	17% 14% 5% 12% 7% 5% 5% 5% 6% 6% 18%	4720
	11th to 20th	Night	15% 18% 5% 10% 6% 5% 5% 4 5% 6% 21%	5348
	21st to end	Night	24% 15% 7% 12% 5% 5% 4 3 4 5% 15%	7150

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	60% 7% 11% 12% 9%	4662
	11th to 20th	Day	71% 5% 8% 10% 5%	5194
	21st to end	Day	63% 5% 10% 13% 9%	5780
February	1st to 10th	Day	61% 5% 12% 17% 5% 1	1890
	11th to 20th	Day	60% 5% 11% 15% 8% 1	1852
	21st to end	Day	58% 5% 11% 17% 7% 1	1624
March	1st to 10th	Day	53% 5% 14% 15% 12% 1	5045
	11th to 20th	Day	50% 5% 15% 19% 8% 3	5090
	21st to end	Day	52% 4 10% 20% 12% 1	5586
April	1st to 10th	Day	54% 5% 11% 18% 11% 1	2468
	11th to 20th	Day	49% 5% 10% 21% 14% 1	2589
	21st to end	Day	51% 5% 11% 19% 11% 2	2730
May	1st to 10th	Day	49% 5% 13% 18% 11% 4	7651
	11th to 20th	Day	46% 8% 12% 20% 14% 1	8124
	21st to end	Day	40% 5% 10% 29% 14% 2	9061
June	1st to 10th	Day	41% 7% 11% 23% 16% 1	2940
	11th to 20th	Day	39% 6% 14% 25% 15% 1	2940
	21st to end	Day	38% 7% 14% 25% 14% 1	3133
July	1st to 10th	Day	39% 4 16% 26% 13% 1	8390
	11th to 20th	Day	28% 4 14% 37% 16% 1	8205
	21st to end	Day	35% 5% 14% 28% 17% 1	8161
August	1st to 10th	Day	45% 4 14% 18% 15% 4	6001
	11th to 20th	Day	40% 5% 19% 28% 8%	5990
	21st to end	Day	41% 5% 15% 31% 8%	6363
September	1st to 10th	Day	37% 8% 15% 28% 11% 1	2520
	11th to 20th	Day	33% 5% 15% 32% 14% 1	2301
	21st to end	Day	44% 7% 14% 25% 9%	2170
October	1st to 10th	Day	38% 6% 14% 27% 14% 1	3260
	11th to 20th	Day	39% 6% 15% 25% 15%	3240
	21st to end	Day	54% 5% 14% 20% 7%	3538
November	1st to 10th	Day	47% 7% 15% 21% 9% 1	1782
	11th to 20th	Day	54% 7% 14% 16% 9% 1	1680
	21st to end	Day	60% 6% 14% 16% 3	1680
December	1st to 10th	Day	68% 5% 14% 10% 3	2680
	11th to 20th	Day	63% 6% 12% 10% 8%	3066
	21st to end	Day	73% 5% 8% 8% 6%	4048
January	1st to 10th	Night	56% 6% 12% 20% 7%	8234
	11th to 20th	Night	66% 6% 9% 12% 6% 1	7763
	21st to end	Night	57% 6% 11% 13% 12% 1	8401
February	1st to 10th	Night	56% 6% 11% 20% 6% 1	2730
	11th to 20th	Night	57% 5% 11% 17% 9%	2665
	21st to end	Night	55% 5% 13% 18% 9%	2180
March	1st to 10th	Night	51% 5% 13% 18% 12% 2	5028
	11th to 20th	Night	42% 6% 18% 22% 10% 2	5090
	21st to end	Night	47% 4 9% 20% 18% 3	5588
April	1st to 10th	Night	52% 5% 11% 18% 14% 2	2151
	11th to 20th	Night	47% 6% 9% 21% 15% 2	1998
	21st to end	Night	44% 6% 10% 20% 17% 2	1890
May	1st to 10th	Night	48% 6% 10% 16% 15% 5%	5264
	11th to 20th	Night	44% 8% 12% 20% 14% 2	4740
	21st to end	Night	39% 4 11% 26% 18% 2	5115
June	1st to 10th	Night	36% 6% 11% 25% 19% 2	1680
	11th to 20th	Night	36% 6% 12% 24% 21% 2	1680
	21st to end	Night	37% 6% 13% 26% 17% 1	1472
July	1st to 10th	Night	32% 4 17% 28% 17% 2	4446
	11th to 20th	Night	29% 4 12% 33% 22% 1	4632
	21st to end	Night	32% 5% 13% 28% 22% 1	5597
August	1st to 10th	Night	42% 4 12% 22% 15% 5%	4124
	11th to 20th	Night	33% 4 17% 34% 11% 1	4122
	21st to end	Night	37% 4 17% 29% 12% 1	4715
September	1st to 10th	Night	33% 6% 15% 31% 14% 1	2100
	11th to 20th	Night	28% 6% 12% 35% 19% 1	2162
	21st to end	Night	42% 6% 12% 27% 12%	2230
October	1st to 10th	Night	33% 5% 9% 29% 24% 1	3920
	11th to 20th	Night	42% 4 12% 27% 13%	3899
	21st to end	Night	42% 5% 16% 26% 11% 1	4252
November	1st to 10th	Night	45% 6% 13% 24% 12% 1	2731
	11th to 20th	Night	50% 7% 14% 18% 10% 1	2940
	21st to end	Night	56% 6% 17% 18% 4	2940
December	1st to 10th	Night	64% 5% 14% 13% 4	4720
	11th to 20th	Night	62% 6% 10% 13% 9%	5348
	21st to end	Night	70% 6% 10% 9% 5%	7150

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	21% 17% 34% 22% 6% 1	220
	11th to 20th	Day	22% 26% 32% 14% 6% 1	314
	21st to end	Day	23% 20% 33% 20% 4	363
February	1st to 10th	Day	23% 23% 36% 12% 6% 1	330
	11th to 20th	Day	22% 22% 37% 17% 2	330
	21st to end	Day	28% 24% 33% 13% 2	282
March	1st to 10th	Day	21% 17% 35% 22% 6%	540
	11th to 20th	Day	23% 19% 33% 18% 5% 1	540
	21st to end	Day	27% 15% 32% 20% 6% 1	594
April	1st to 10th	Day	21% 19% 33% 20% 7%	540
	11th to 20th	Day	25% 17% 28% 18% 9% 2	532
	21st to end	Day	23% 13% 34% 21% 8% 2	540
May	1st to 10th	Day	21% 10% 30% 24% 10% 4	543
	11th to 20th	Day	17% 7% 32% 26% 13% 5%	567
	21st to end	Day	16% 6% 29% 29% 15% 5%	617
June	1st to 10th	Day	12% 9% 31% 32% 13% 3	570
	11th to 20th	Day	14% 8% 30% 29% 17% 2	570
	21st to end	Day	14% 7% 29% 33% 13% 3	763
July	1st to 10th	Day	8% 5% 23% 36% 21% 7%	628
	11th to 20th	Day	12% 4 23% 34% 18% 9%	564
	21st to end	Day	7% 3 26% 37% 19% 7%	620
August	1st to 10th	Day	12% 5% 20% 28% 23% 11%	566
	11th to 20th	Day	8% 5% 22% 33% 20% 13%	559
	21st to end	Day	12% 7% 22% 28% 21% 10%	627
September	1st to 10th	Day	12% 7% 23% 28% 18% 12%	570
	11th to 20th	Day	8% 5% 20% 23% 27% 18%	542
	21st to end	Day	16% 9% 27% 24% 18% 7%	530
October	1st to 10th	Day	21% 10% 25% 23% 14% 6%	530
	11th to 20th	Day	19% 14% 36% 21% 8% 3	530
	21st to end	Day	28% 13% 28% 25% 7% 1	583
November	1st to 10th	Day	21% 21% 28% 21% 9% 1	310
	11th to 20th	Day	25% 19% 32% 19% 4 2	220
	21st to end	Day	24% 17% 39% 18% 3	220
December	1st to 10th	Day	25% 18% 36% 18% 4	220
	11th to 20th	Day	28% 22% 31% 15% 4	220
	21st to end	Day	29% 19% 35% 14% 3	242
January	1st to 10th	Night	22% 16% 37% 21% 4	840
	11th to 20th	Night	25% 17% 33% 21% 4	840
	21st to end	Night	18% 11% 40% 23% 6%	924
February	1st to 10th	Night	20% 17% 38% 23% 3	840
	11th to 20th	Night	22% 14% 38% 22% 4	823
	21st to end	Night	19% 16% 38% 23% 4	692
March	1st to 10th	Night	19% 13% 38% 25% 5%	840
	11th to 20th	Night	20% 15% 35% 25% 5%	840
	21st to end	Night	21% 11% 33% 27% 7%	924
April	1st to 10th	Night	22% 10% 36% 28% 4	840
	11th to 20th	Night	19% 11% 35% 25% 8% 1	754
	21st to end	Night	19% 8% 29% 34% 9%	630
May	1st to 10th	Night	18% 6% 29% 32% 14% 2	630
	11th to 20th	Night	16% 4 29% 38% 12% 1	451
	21st to end	Night	13% 4 27% 36% 20% 1	455
June	1st to 10th	Night	13% 4 26% 38% 17%	420
	11th to 20th	Night	9% 6% 29% 40% 16%	420
	21st to end	Night	12% 5% 22% 46% 15%	420
July	1st to 10th	Night	6% 3 20% 48% 23% 1	410
	11th to 20th	Night	10% 2 22% 41% 22% 1	408
	21st to end	Night	8% 3 19% 45% 23% 2	680
August	1st to 10th	Night	10% 3 15% 42% 29% 2	627
	11th to 20th	Night	8% 3 15% 45% 27% 3	624
	21st to end	Night	10% 3 22% 37% 25% 2	772
September	1st to 10th	Night	11% 6% 22% 35% 21% 5%	840
	11th to 20th	Night	11% 4 18% 32% 30% 5%	813
	21st to end	Night	18% 6% 20% 33% 21% 4	800
October	1st to 10th	Night	18% 6% 27% 28% 19% 3	800
	11th to 20th	Night	21% 11% 29% 29% 10% 1	800
	21st to end	Night	25% 10% 32% 29% 5%	880
November	1st to 10th	Night	20% 11% 30% 29% 10% 1	820
	11th to 20th	Night	19% 15% 35% 24% 7% 2	840
	21st to end	Night	25% 11% 34% 24% 5%	840
December	1st to 10th	Night	27% 13% 36% 18% 5%	840
	11th to 20th	Night	23% 14% 42% 19% 3	840
	21st to end	Night	29% 14% 33% 21% 3	924

Page generated at 2026-09-11 04:11:53. Version ac07

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