Braidwood Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Braidwood Dark Sky Site clear sky chart from 2005-11-06 to 2026-10-29.

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	13% 8% 3 8% 5% 4 5% 4 6% 8% 37%	149515
	Night	14% 9% 3 8% 5% 4 4 3 5% 6% 38%	142862
Transparency	Day	45% 3 12% 24% 14% 2	153049
	Night	46% 3 11% 23% 15% 2	147405
Seeing	Day	17% 10% 28% 25% 15% 6%	18512
	Night	18% 9% 30% 30% 12% 1	28272

By Month

Percentage Cloud Cover SE (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	13% 12% 6% 13% 6% 5% 5% 4 6% 7% 23%	4691
	11th to 20th	Day	9% 11% 6% 14% 7% 7% 6% 5% 5% 4 27%	4710
	21st to end	Day	14% 15% 4 11% 6% 4 4 3 5% 6% 27%	5414
February	1st to 10th	Day	17% 12% 5% 10% 5% 5% 5% 4 5% 6% 26%	1947
	11th to 20th	Day	15% 11% 5% 8% 7% 4 4 3 5% 6% 33%	2048
	21st to end	Day	15% 13% 5% 10% 5% 4 3 3 5% 7% 30%	1730
March	1st to 10th	Day	19% 13% 3 6% 3 3 3 2 4 4 40%	4580
	11th to 20th	Day	9% 8% 4 7% 4 4 5% 4 6% 8% 42%	4779
	21st to end	Day	19% 12% 5% 11% 5% 5% 5% 3 5% 6% 23%	6099
April	1st to 10th	Day	17% 12% 3 7% 6% 4 4 3 5% 7% 32%	2520
	11th to 20th	Day	15% 10% 3 7% 5% 5% 4 3 5% 6% 36%	2494
	21st to end	Day	20% 8% 3 6% 5% 4 4 4 5% 7% 35%	2609
May	1st to 10th	Day	18% 7% 3 7% 4 5% 4 4 6% 8% 34%	7616
	11th to 20th	Day	14% 6% 2 7% 4 5% 4 4 6% 7% 40%	7975
	21st to end	Day	14% 6% 3 7% 5% 4 5% 4 6% 9% 37%	9047
June	1st to 10th	Day	11% 5% 2 6% 5% 4 4 4 6% 8% 44%	2940
	11th to 20th	Day	9% 4 2 6% 4 5% 5% 4 7% 8% 45%	2940
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2940
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 41%	8280
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 7% 10% 45%	8280
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	8990
August	1st to 10th	Day	11% 5% 2 7% 5% 4 4 4 6% 10% 42%	6256
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 7% 10% 37%	5486
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 10% 50%	6080
September	1st to 10th	Day	10% 6% 2 5% 4 4 4 3 5% 7% 51%	2520
	11th to 20th	Day	12% 5% 2 4 3 3 4 4 5% 7% 52%	2389
	21st to end	Day	10% 7% 2 6% 5% 4 3 4 5% 8% 45%	2310
October	1st to 10th	Day	11% 6% 3 6% 3 5% 3 4 5% 6% 48%	2252
	11th to 20th	Day	18% 7% 2 6% 4 4 4 3 4 6% 41%	2100
	21st to end	Day	18% 9% 2 7% 3 4 4 4 6% 6% 37%	2057
November	1st to 10th	Day	13% 8% 2 5% 4 3 3 3 5% 7% 47%	1852
	11th to 20th	Day	17% 10% 4 7% 5% 4 3 3 5% 6% 35%	1890
	21st to end	Day	18% 12% 4 9% 4 3 4 3 4 4 35%	1846
December	1st to 10th	Day	9% 11% 3 9% 5% 4 4 3 3 5% 44%	2690
	11th to 20th	Day	13% 16% 5% 11% 6% 5% 5% 4 6% 6% 24%	3088
	21st to end	Day	26% 20% 7% 12% 6% 4 3 2 3 4 12%	4070
January	1st to 10th	Night	13% 13% 7% 11% 6% 4 4 3 4 5% 30%	8232
	11th to 20th	Night	10% 14% 6% 14% 8% 6% 5% 4 5% 4 23%	8280
	21st to end	Night	16% 13% 5% 8% 4 5% 4 3 4 5% 32%	8786
February	1st to 10th	Night	16% 14% 5% 8% 5% 4 3 2 4 6% 31%	2672
	11th to 20th	Night	14% 10% 3 8% 6% 4 5% 3 5% 6% 35%	2458
	21st to end	Night	18% 11% 3 8% 4 4 4 3 4 5% 35%	2076
March	1st to 10th	Night	16% 11% 4 6% 4 3 3 3 4 5% 40%	5493
	11th to 20th	Night	11% 6% 3 6% 5% 4 4 4 5% 6% 46%	5430
	21st to end	Night	19% 11% 4 9% 6% 6% 4 4 5% 5% 28%	5072
April	1st to 10th	Night	16% 9% 3 7% 5% 4 4 4 4 7% 37%	2100
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 5% 7% 40%	2075
	21st to end	Night	19% 7% 2 6% 4 3 5% 5% 6% 7% 36%	2011
May	1st to 10th	Night	18% 8% 2 8% 5% 5% 4 3 5% 7% 36%	5237
	11th to 20th	Night	11% 5% 2 5% 4 4 5% 4 7% 10% 43%	4901
	21st to end	Night	14% 7% 3 7% 5% 5% 4 4 6% 8% 38%	5139
June	1st to 10th	Night	10% 5% 2 5% 4 3 5% 3 5% 6% 51%	1680
	11th to 20th	Night	10% 5% 2 6% 5% 3 4 4 6% 10% 46%	1680
	21st to end	Night	10% 6% 2 5% 5% 5% 5% 4 6% 8% 44%	1680
July	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 6% 10% 44%	4708
	11th to 20th	Night	7% 5% 2 6% 4 4 4 3 6% 8% 51%	4707
	21st to end	Night	7% 4 2 7% 5% 4 6% 4 6% 7% 46%	5117
August	1st to 10th	Night	14% 5% 2 5% 4 4 4 4 6% 8% 45%	3885
	11th to 20th	Night	12% 5% 2 6% 4 5% 5% 4 7% 8% 42%	4560
	21st to end	Night	7% 3 2 5% 4 4 4 3 5% 9% 55%	5046
September	1st to 10th	Night	10% 4 1 4 4 3 2 3 4 8% 54%	2100
	11th to 20th	Night	10% 4 1 5% 3 4 4 3 5% 7% 55%	2210
	21st to end	Night	10% 6% 1 6% 5% 5% 6% 4 6% 7% 44%	2310
October	1st to 10th	Night	10% 5% 2 6% 3 4 3 3 4 5% 56%	2362
	11th to 20th	Night	16% 6% 3 6% 3 3 3 3 4 6% 47%	2520
	21st to end	Night	20% 7% 3 6% 4 3 3 3 5% 6% 41%	2958
November	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 4 6% 48%	2666
	11th to 20th	Night	14% 10% 3 7% 4 5% 4 3 5% 6% 38%	2730
	21st to end	Night	18% 11% 4 7% 4 4 3 3 4 6% 36%	2772
December	1st to 10th	Night	12% 9% 3 8% 5% 3 4 3 5% 6% 43%	4720
	11th to 20th	Night	17% 14% 5% 9% 5% 4 4 3 4 5% 31%	5339
	21st to end	Night	25% 18% 6% 11% 6% 4 4 3 4 4 16%	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	61% 2 15% 15% 6%	4692
	11th to 20th	Day	60% 3 7% 15% 13% 2	4710
	21st to end	Day	59% 2 13% 19% 7%	5414
February	1st to 10th	Day	58% 3 13% 17% 7% 2	1947
	11th to 20th	Day	52% 4 11% 23% 8% 2	2058
	21st to end	Day	55% 4 10% 21% 7% 2	1730
March	1st to 10th	Day	49% 2 8% 24% 14% 2	4580
	11th to 20th	Day	40% 3 11% 34% 12% 1	4779
	21st to end	Day	61% 3 12% 16% 7% 1	6101
April	1st to 10th	Day	53% 3 11% 20% 13%	2520
	11th to 20th	Day	49% 4 10% 22% 11% 3	2494
	21st to end	Day	49% 4 13% 20% 11% 2	2609
May	1st to 10th	Day	47% 4 10% 23% 15% 1	7651
	11th to 20th	Day	44% 4 12% 24% 15% 2	7979
	21st to end	Day	43% 4 10% 22% 17% 4	9061
June	1st to 10th	Day	36% 5% 12% 26% 17% 3	2940
	11th to 20th	Day	35% 6% 10% 24% 21% 3	2940
	21st to end	Day	40% 6% 14% 23% 15% 3	2940
July	1st to 10th	Day	39% 3 14% 27% 16% 1	8211
	11th to 20th	Day	35% 3 14% 32% 15% 1	8205
	21st to end	Day	40% 3 16% 25% 14% 2	8794
August	1st to 10th	Day	38% 4 14% 29% 14% 1	6241
	11th to 20th	Day	43% 4 13% 28% 12% 1	5522
	21st to end	Day	31% 3 12% 35% 16% 2	6079
September	1st to 10th	Day	33% 4 12% 27% 19% 4	2520
	11th to 20th	Day	32% 4 11% 27% 23% 4	2389
	21st to end	Day	37% 4 9% 27% 21% 2	2310
October	1st to 10th	Day	27% 3 7% 29% 33% 2	3603
	11th to 20th	Day	32% 3 11% 24% 29% 2	3340
	21st to end	Day	41% 2 9% 28% 17% 3	3257
November	1st to 10th	Day	37% 4 14% 27% 16% 2	1852
	11th to 20th	Day	51% 3 12% 22% 12% 1	1890
	21st to end	Day	53% 3 10% 23% 10%	1846
December	1st to 10th	Day	46% 2 13% 31% 8% 1	2690
	11th to 20th	Day	61% 3 12% 18% 5% 1	3085
	21st to end	Day	79% 3 7% 7% 4	4070
January	1st to 10th	Night	58% 2 12% 19% 8%	8233
	11th to 20th	Night	65% 2 9% 12% 11% 1	8280
	21st to end	Night	56% 2 11% 21% 10% 1	8786
February	1st to 10th	Night	56% 3 11% 19% 10% 2	2672
	11th to 20th	Night	49% 4 10% 24% 12% 1	2459
	21st to end	Night	52% 4 10% 20% 11% 3	2076
March	1st to 10th	Night	48% 3 10% 25% 10% 4	5493
	11th to 20th	Night	40% 3 12% 27% 16% 3	5430
	21st to end	Night	58% 3 9% 21% 8% 1	5072
April	1st to 10th	Night	47% 4 11% 22% 13% 2	2100
	11th to 20th	Night	45% 4 8% 22% 17% 4	2075
	21st to end	Night	46% 6% 12% 23% 12% 3	2011
May	1st to 10th	Night	48% 3 10% 21% 15% 3	5264
	11th to 20th	Night	37% 4 15% 25% 17% 3	4902
	21st to end	Night	44% 4 9% 20% 18% 4	5149
June	1st to 10th	Night	34% 4 12% 26% 21% 3	1680
	11th to 20th	Night	34% 3 13% 24% 23% 3	1680
	21st to end	Night	37% 6% 16% 23% 16% 3	1680
July	1st to 10th	Night	38% 3 12% 28% 16% 3	4670
	11th to 20th	Night	33% 3 12% 28% 22% 2	4662
	21st to end	Night	37% 3 14% 24% 18% 3	5002
August	1st to 10th	Night	38% 3 15% 26% 17% 1	3876
	11th to 20th	Night	40% 4 17% 23% 14% 1	4590
	21st to end	Night	29% 3 12% 36% 18% 2	5046
September	1st to 10th	Night	29% 4 11% 28% 23% 5%	2100
	11th to 20th	Night	30% 3 9% 28% 26% 4	2210
	21st to end	Night	37% 6% 10% 25% 19% 3	2310
October	1st to 10th	Night	21% 3 7% 33% 33% 3	3791
	11th to 20th	Night	32% 3 7% 24% 31% 2	4019
	21st to end	Night	39% 2 8% 26% 21% 4	4708
November	1st to 10th	Night	38% 4 9% 27% 18% 4	2666
	11th to 20th	Night	47% 3 11% 23% 14% 2	2730
	21st to end	Night	51% 3 11% 23% 12% 1	2772
December	1st to 10th	Night	44% 2 13% 28% 11% 1	4720
	11th to 20th	Night	57% 2 12% 17% 11% 1	5341
	21st to end	Night	73% 3 8% 10% 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	22% 12% 35% 22% 9% 1	330
	11th to 20th	Day	24% 18% 39% 14% 5%	330
	21st to end	Day	22% 22% 28% 23% 6%	363
February	1st to 10th	Day	21% 17% 38% 18% 5% 1	330
	11th to 20th	Day	23% 17% 36% 21% 4	330
	21st to end	Day	23% 19% 41% 14% 3	273
March	1st to 10th	Day	23% 19% 38% 17% 3	330
	11th to 20th	Day	24% 18% 34% 17% 5%	351
	21st to end	Day	28% 15% 35% 14% 6% 1	594
April	1st to 10th	Day	24% 13% 36% 21% 6% 1	540
	11th to 20th	Day	22% 18% 31% 17% 10% 2	532
	21st to end	Day	21% 13% 34% 21% 8% 2	540
May	1st to 10th	Day	22% 13% 29% 23% 10% 3	543
	11th to 20th	Day	20% 10% 30% 23% 13% 5%	682
	21st to end	Day	15% 8% 30% 22% 18% 7%	844
June	1st to 10th	Day	11% 9% 28% 29% 18% 6%	780
	11th to 20th	Day	11% 7% 29% 31% 18% 5%	780
	21st to end	Day	12% 7% 30% 29% 16% 5%	780
July	1st to 10th	Day	10% 3 16% 30% 26% 15%	771
	11th to 20th	Day	11% 3 19% 32% 22% 13%	768
	21st to end	Day	10% 2 18% 36% 26% 8%	849
August	1st to 10th	Day	7% 4 15% 35% 26% 13%	704
	11th to 20th	Day	13% 3 17% 28% 25% 13%	559
	21st to end	Day	7% 3 15% 33% 30% 12%	627
September	1st to 10th	Day	12% 6% 19% 26% 27% 10%	570
	11th to 20th	Day	11% 3 13% 29% 31% 12%	570
	21st to end	Day	15% 6% 25% 25% 21% 10%	570
October	1st to 10th	Day	14% 6% 29% 27% 19% 5%	512
	11th to 20th	Day	18% 17% 29% 25% 9% 3	360
	21st to end	Day	28% 11% 32% 21% 7% 2	387
November	1st to 10th	Day	17% 12% 38% 19% 10% 4	330
	11th to 20th	Day	26% 15% 32% 18% 9% 1	330
	21st to end	Day	26% 13% 34% 20% 7%	330
December	1st to 10th	Day	17% 14% 40% 20% 8% 1	330
	11th to 20th	Day	19% 18% 35% 22% 5% 1	330
	21st to end	Day	31% 14% 37% 15% 2	363
January	1st to 10th	Night	20% 15% 38% 22% 5%	1050
	11th to 20th	Night	22% 15% 38% 20% 4	1050
	21st to end	Night	23% 13% 35% 25% 3	1155
February	1st to 10th	Night	24% 13% 36% 23% 4	992
	11th to 20th	Night	20% 13% 36% 28% 3	823
	21st to end	Night	24% 12% 40% 20% 4	692
March	1st to 10th	Night	21% 16% 35% 24% 5%	840
	11th to 20th	Night	19% 12% 37% 26% 6%	809
	21st to end	Night	26% 10% 36% 23% 5%	693
April	1st to 10th	Night	21% 11% 37% 25% 5%	630
	11th to 20th	Night	23% 11% 32% 27% 7%	623
	21st to end	Night	22% 7% 34% 29% 7%	630
May	1st to 10th	Night	20% 6% 33% 34% 8%	630
	11th to 20th	Night	16% 7% 33% 33% 12% 1	621
	21st to end	Night	13% 4 30% 35% 17% 1	683
June	1st to 10th	Night	11% 4 27% 45% 13%	630
	11th to 20th	Night	12% 3 27% 43% 13% 1	630
	21st to end	Night	11% 4 26% 42% 17% 1	630
July	1st to 10th	Night	10% 1 14% 41% 30% 5%	615
	11th to 20th	Night	7% 2 17% 43% 28% 3	612
	21st to end	Night	5% 2 16% 48% 28% 2	690
August	1st to 10th	Night	8% 2 12% 45% 30% 3	627
	11th to 20th	Night	7% 3 13% 43% 31% 4	624
	21st to end	Night	7% 2 14% 41% 33% 3	693
September	1st to 10th	Night	12% 3 16% 39% 27% 3	630
	11th to 20th	Night	10% 4 16% 37% 30% 4	740
	21st to end	Night	13% 5% 23% 34% 23% 3	840
October	1st to 10th	Night	13% 5% 25% 36% 19% 2	840
	11th to 20th	Night	19% 10% 32% 27% 11%	840
	21st to end	Night	23% 11% 32% 26% 8%	913
November	1st to 10th	Night	16% 10% 38% 27% 9% 1	820
	11th to 20th	Night	19% 14% 35% 26% 5%	840
	21st to end	Night	23% 14% 33% 24% 6%	882
December	1st to 10th	Night	23% 12% 36% 24% 5%	1050
	11th to 20th	Night	25% 12% 33% 25% 6%	1050
	21st to end	Night	29% 13% 33% 23% 2	1155

Page generated at 2026-10-26 03:37:49. Version ac07

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