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 2025-07-06.

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 7% 5% 4 4 4 6% 7% 37%	119783
	Night	14% 9% 4 8% 5% 4 4 3 5% 6% 38%	119204
Transparency	Day	45% 4 12% 23% 14% 2	123362
	Night	46% 3 11% 22% 15% 2	123766
Seeing	Day	17% 10% 28% 25% 16% 6%	16660
	Night	18% 9% 30% 30% 12% 1	26532

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% 11% 7% 14% 7% 4 5% 4 6% 6% 24%	3617
	11th to 20th	Day	11% 11% 6% 14% 6% 7% 4 6% 5% 4 25%	3620
	21st to end	Day	18% 17% 5% 10% 5% 3 3 3 4 6% 27%	4184
February	1st to 10th	Day	18% 12% 5% 9% 6% 5% 5% 3 5% 6% 26%	1854
	11th to 20th	Day	15% 11% 4 8% 7% 5% 4 3 5% 6% 32%	1948
	21st to end	Day	15% 13% 5% 10% 5% 4 3 3 5% 7% 30%	1650
March	1st to 10th	Day	20% 13% 3 6% 3 3 3 2 4 4 40%	4480
	11th to 20th	Day	8% 8% 4 7% 4 4 5% 4 6% 8% 42%	4676
	21st to end	Day	20% 12% 5% 11% 5% 5% 5% 3 5% 6% 23%	5967
April	1st to 10th	Day	17% 12% 3 7% 5% 4 4 3 5% 7% 33%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 3 5% 6% 37%	2374
	21st to end	Day	20% 8% 3 7% 5% 4 4 4 5% 7% 34%	2485
May	1st to 10th	Day	19% 7% 3 7% 4 5% 5% 4 6% 8% 32%	5862
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 6% 7% 41%	6126
	21st to end	Day	14% 6% 3 6% 5% 4 5% 4 6% 9% 38%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 4 6% 8% 45%	2800
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 7% 8% 44%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 6% 5% 7% 10% 40%	2800
July	1st to 10th	Day	11% 6% 3 7% 5% 6% 6% 5% 7% 9% 35%	4511
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 10% 47%	4440
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 4 7% 9% 41%	4813
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 3 7% 10% 46%	4257
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 4 8% 11% 44%	3729
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 10% 48%	4180
September	1st to 10th	Day	10% 6% 2 5% 4 5% 4 3 5% 7% 49%	2280
	11th to 20th	Day	11% 5% 2 4 3 3 4 4 5% 7% 53%	2161
	21st to end	Day	10% 7% 2 6% 5% 3 3 4 6% 8% 45%	2090
October	1st to 10th	Day	11% 7% 3 6% 3 4 3 4 5% 7% 47%	2038
	11th to 20th	Day	18% 7% 2 6% 4 4 5% 3 4 6% 40%	1900
	21st to end	Day	19% 9% 3 7% 3 4 4 4 6% 6% 36%	1886
November	1st to 10th	Day	13% 7% 2 5% 4 3 3 3 5% 7% 47%	1762
	11th to 20th	Day	17% 10% 4 7% 5% 4 3 3 5% 6% 35%	1800
	21st to end	Day	18% 12% 4 9% 4 3 4 3 4 5% 35%	1758
December	1st to 10th	Day	9% 11% 3 8% 5% 4 4 3 3 5% 44%	2610
	11th to 20th	Day	13% 16% 5% 11% 6% 5% 5% 4 6% 6% 24%	3008
	21st to end	Day	26% 20% 8% 12% 6% 4 3 2 3 4 12%	3982
January	1st to 10th	Night	14% 13% 7% 12% 6% 4 4 3 4 4 29%	6348
	11th to 20th	Night	13% 16% 7% 13% 8% 6% 5% 3 4 4 21%	6360
	21st to end	Night	19% 14% 6% 9% 4 4 4 3 3 3 31%	6793
February	1st to 10th	Night	17% 14% 5% 8% 6% 4 3 3 4 6% 31%	2545
	11th to 20th	Night	14% 10% 4 8% 6% 4 5% 3 5% 6% 34%	2338
	21st to end	Night	19% 11% 3 8% 4 4 4 3 4 5% 35%	1980
March	1st to 10th	Night	16% 11% 4 6% 4 3 3 3 4 5% 40%	5373
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 5% 6% 47%	5312
	21st to end	Night	20% 11% 4 9% 6% 6% 4 4 4 5% 28%	4962
April	1st to 10th	Night	15% 9% 3 7% 5% 4 4 4 4 7% 39%	2000
	11th to 20th	Night	18% 8% 2 6% 5% 4 4 3 4 7% 40%	1975
	21st to end	Night	19% 7% 2 6% 4 3 5% 5% 5% 7% 35%	1915
May	1st to 10th	Night	19% 8% 2 8% 5% 4 4 3 5% 7% 34%	4033
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 6% 9% 42%	3777
	21st to end	Night	15% 8% 3 6% 5% 4 4 4 5% 7% 39%	3942
June	1st to 10th	Night	9% 6% 2 5% 4 3 5% 3 5% 7% 51%	1600
	11th to 20th	Night	10% 5% 2 6% 5% 3 4 4 6% 10% 46%	1600
	21st to end	Night	9% 6% 2 5% 4 5% 5% 4 6% 9% 44%	1600
July	1st to 10th	Night	11% 5% 3 6% 4 5% 5% 4 6% 9% 41%	2570
	11th to 20th	Night	6% 4 1 5% 4 4 4 4 6% 7% 56%	2530
	21st to end	Night	5% 4 2 8% 5% 5% 6% 4 7% 8% 47%	2750
August	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 7% 9% 50%	2657
	11th to 20th	Night	8% 4 2 5% 4 4 5% 4 6% 8% 52%	3100
	21st to end	Night	7% 4 2 5% 4 4 4 3 5% 9% 54%	3476
September	1st to 10th	Night	11% 5% 1 4 4 3 3 3 4 8% 54%	1900
	11th to 20th	Night	9% 4 1 5% 3 3 4 4 5% 7% 55%	2000
	21st to end	Night	10% 6% 1 6% 5% 5% 6% 4 6% 7% 44%	2090
October	1st to 10th	Night	10% 5% 2 5% 3 4 3 3 4 6% 54%	2137
	11th to 20th	Night	16% 6% 3 6% 3 3 3 3 4 6% 48%	2280
	21st to end	Night	20% 8% 3 6% 4 3 3 3 5% 6% 40%	2710
November	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 4 6% 48%	2536
	11th to 20th	Night	14% 10% 3 7% 5% 5% 5% 3 5% 6% 38%	2600
	21st to end	Night	18% 11% 3 7% 4 5% 3 3 4 6% 37%	2640
December	1st to 10th	Night	12% 9% 3 8% 5% 3 3 3 5% 6% 43%	4580
	11th to 20th	Night	17% 14% 4 9% 5% 4 4 3 4 5% 32%	5199
	21st to end	Night	25% 18% 6% 11% 6% 4 4 3 4 4 16%	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	61% 2 12% 17% 7%	3618
	11th to 20th	Day	60% 3 9% 10% 14% 3	3620
	21st to end	Day	61% 2 12% 18% 7%	4184
February	1st to 10th	Day	58% 4 12% 16% 8% 2	1854
	11th to 20th	Day	52% 4 11% 23% 9% 2	1958
	21st to end	Day	55% 4 10% 21% 8% 3	1650
March	1st to 10th	Day	49% 2 8% 24% 14% 2	4480
	11th to 20th	Day	39% 3 11% 34% 12% 1	4676
	21st to end	Day	62% 3 12% 15% 7% 1	5969
April	1st to 10th	Day	52% 3 11% 20% 13%	2400
	11th to 20th	Day	49% 4 10% 22% 11% 3	2374
	21st to end	Day	50% 4 13% 19% 11% 2	2485
May	1st to 10th	Day	48% 4 11% 22% 13% 1	5897
	11th to 20th	Day	42% 4 12% 27% 13% 2	6130
	21st to end	Day	42% 4 10% 25% 15% 3	6949
June	1st to 10th	Day	36% 5% 12% 27% 17% 3	2800
	11th to 20th	Day	35% 6% 11% 24% 21% 3	2800
	21st to end	Day	39% 7% 14% 23% 15% 3	2800
July	1st to 10th	Day	45% 4 12% 24% 13% 2	4442
	11th to 20th	Day	31% 5% 16% 30% 17% 1	4365
	21st to end	Day	38% 5% 18% 18% 18% 3	4662
August	1st to 10th	Day	33% 4 17% 31% 13% 1	4242
	11th to 20th	Day	33% 4 12% 33% 16% 1	3765
	21st to end	Day	33% 4 12% 31% 17% 3	4179
September	1st to 10th	Day	34% 5% 13% 25% 19% 5%	2280
	11th to 20th	Day	30% 4 12% 28% 22% 4	2161
	21st to end	Day	37% 4 9% 27% 21% 2	2090
October	1st to 10th	Day	26% 3 7% 28% 33% 2	3389
	11th to 20th	Day	32% 3 11% 24% 29% 1	3140
	21st to end	Day	41% 3 9% 28% 17% 3	3086
November	1st to 10th	Day	37% 4 14% 26% 16% 2	1762
	11th to 20th	Day	51% 3 12% 22% 12% 1	1800
	21st to end	Day	53% 3 11% 23% 10%	1758
December	1st to 10th	Day	45% 2 13% 31% 8%	2610
	11th to 20th	Day	61% 3 12% 17% 5% 1	3005
	21st to end	Day	79% 3 7% 7% 4	3982
January	1st to 10th	Night	59% 3 10% 18% 10%	6348
	11th to 20th	Night	67% 3 9% 9% 12% 1	6360
	21st to end	Night	59% 2 9% 18% 11% 1	6793
February	1st to 10th	Night	56% 4 10% 18% 10% 2	2545
	11th to 20th	Night	50% 4 10% 23% 12% 1	2339
	21st to end	Night	52% 4 10% 20% 11% 3	1980
March	1st to 10th	Night	48% 3 10% 25% 10% 4	5373
	11th to 20th	Night	39% 3 12% 28% 16% 3	5312
	21st to end	Night	58% 3 9% 21% 7% 1	4962
April	1st to 10th	Night	46% 5% 12% 23% 13% 2	2000
	11th to 20th	Night	45% 4 8% 22% 17% 4	1975
	21st to end	Night	46% 6% 11% 22% 12% 3	1915
May	1st to 10th	Night	50% 3 12% 17% 14% 4	4060
	11th to 20th	Night	39% 5% 14% 26% 13% 4	3778
	21st to end	Night	44% 5% 10% 22% 16% 3	3950
June	1st to 10th	Night	33% 4 12% 26% 20% 4	1600
	11th to 20th	Night	34% 3 13% 24% 22% 3	1600
	21st to end	Night	36% 6% 16% 23% 16% 4	1600
July	1st to 10th	Night	41% 4 13% 24% 13% 5%	2530
	11th to 20th	Night	28% 4 13% 29% 24% 2	2482
	21st to end	Night	34% 5% 17% 21% 19% 5%	2662
August	1st to 10th	Night	31% 4 19% 29% 16% 1	2648
	11th to 20th	Night	30% 4 15% 29% 20% 2	3130
	21st to end	Night	29% 4 13% 33% 19% 3	3476
September	1st to 10th	Night	30% 4 11% 26% 23% 5%	1900
	11th to 20th	Night	29% 3 9% 28% 26% 4	2000
	21st to end	Night	36% 6% 10% 26% 18% 3	2090
October	1st to 10th	Night	21% 3 7% 34% 32% 3	3566
	11th to 20th	Night	32% 3 7% 25% 31% 2	3779
	21st to end	Night	39% 2 8% 26% 21% 4	4460
November	1st to 10th	Night	38% 4 9% 28% 18% 4	2536
	11th to 20th	Night	47% 3 11% 22% 14% 2	2600
	21st to end	Night	50% 3 11% 24% 12% 1	2640
December	1st to 10th	Night	43% 2 14% 29% 11% 1	4580
	11th to 20th	Night	56% 2 12% 17% 11% 1	5201
	21st to end	Night	73% 3 8% 10% 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	22% 11% 35% 21% 10% 1	300
	11th to 20th	Day	24% 16% 39% 15% 5%	300
	21st to end	Day	23% 21% 26% 23% 6%	330
February	1st to 10th	Day	22% 18% 38% 16% 6%	300
	11th to 20th	Day	23% 16% 36% 20% 4	300
	21st to end	Day	24% 18% 41% 14% 3	249
March	1st to 10th	Day	22% 20% 37% 17% 3	300
	11th to 20th	Day	23% 19% 34% 18% 6%	320
	21st to end	Day	29% 14% 34% 15% 6% 1	550
April	1st to 10th	Day	23% 12% 35% 22% 6% 1	500
	11th to 20th	Day	21% 17% 30% 18% 11% 2	492
	21st to end	Day	22% 13% 34% 21% 8% 2	500
May	1st to 10th	Day	22% 12% 28% 24% 11% 3	503
	11th to 20th	Day	20% 8% 29% 24% 14% 5%	636
	21st to end	Day	16% 8% 30% 22% 17% 8%	789
June	1st to 10th	Day	11% 9% 27% 29% 18% 6%	730
	11th to 20th	Day	11% 5% 27% 32% 19% 5%	730
	21st to end	Day	11% 8% 30% 30% 17% 5%	730
July	1st to 10th	Day	10% 3 17% 28% 27% 15%	697
	11th to 20th	Day	10% 3 20% 32% 22% 13%	668
	21st to end	Day	9% 2 17% 36% 28% 8%	739
August	1st to 10th	Day	7% 3 16% 34% 28% 13%	611
	11th to 20th	Day	13% 3 16% 28% 25% 15%	479
	21st to end	Day	8% 2 14% 33% 30% 13%	539
September	1st to 10th	Day	13% 6% 18% 26% 28% 10%	490
	11th to 20th	Day	11% 3 13% 30% 32% 12%	490
	21st to end	Day	14% 6% 25% 26% 21% 8%	490
October	1st to 10th	Day	15% 6% 29% 26% 19% 6%	438
	11th to 20th	Day	18% 19% 28% 26% 8% 1	300
	21st to end	Day	30% 11% 33% 19% 6% 1	330
November	1st to 10th	Day	17% 9% 40% 19% 11% 4	300
	11th to 20th	Day	25% 13% 34% 18% 9% 1	300
	21st to end	Day	25% 13% 34% 21% 8%	300
December	1st to 10th	Day	17% 16% 40% 19% 8% 1	300
	11th to 20th	Day	18% 17% 35% 23% 6% 1	300
	21st to end	Day	29% 15% 37% 15% 3	330
January	1st to 10th	Night	20% 15% 38% 22% 5%	1000
	11th to 20th	Night	22% 15% 37% 21% 5% 1	1000
	21st to end	Night	23% 12% 34% 26% 3	1100
February	1st to 10th	Night	24% 13% 36% 23% 4	945
	11th to 20th	Night	20% 13% 36% 27% 3	783
	21st to end	Night	25% 11% 40% 20% 4	660
March	1st to 10th	Night	21% 15% 35% 24% 5%	800
	11th to 20th	Night	18% 11% 38% 27% 6% 1	770
	21st to end	Night	27% 9% 35% 24% 5%	660
April	1st to 10th	Night	20% 11% 38% 26% 6%	600
	11th to 20th	Night	23% 11% 32% 27% 6% 1	593
	21st to end	Night	23% 8% 34% 29% 7%	600
May	1st to 10th	Night	19% 6% 32% 35% 8%	600
	11th to 20th	Night	16% 6% 32% 33% 12% 1	591
	21st to end	Night	13% 4 30% 35% 17% 1	650
June	1st to 10th	Night	11% 4 27% 45% 13%	600
	11th to 20th	Night	12% 3 26% 44% 14% 1	600
	21st to end	Night	10% 3 25% 43% 18% 1	600
July	1st to 10th	Night	9% 1 14% 40% 31% 5%	570
	11th to 20th	Night	7% 2 18% 43% 27% 3	552
	21st to end	Night	4 1 16% 48% 28% 2	624
August	1st to 10th	Night	7% 2 12% 46% 30% 4	567
	11th to 20th	Night	7% 3 13% 43% 31% 4	564
	21st to end	Night	7% 2 15% 39% 33% 3	627
September	1st to 10th	Night	12% 4 16% 38% 27% 3	570
	11th to 20th	Night	9% 4 15% 37% 30% 4	670
	21st to end	Night	12% 5% 23% 34% 23% 3	760
October	1st to 10th	Night	13% 5% 25% 35% 20% 2	760
	11th to 20th	Night	19% 11% 32% 27% 11%	760
	21st to end	Night	24% 11% 32% 24% 8%	836
November	1st to 10th	Night	16% 10% 37% 27% 9% 1	780
	11th to 20th	Night	19% 14% 35% 26% 6%	800
	21st to end	Night	21% 13% 34% 25% 6%	840
December	1st to 10th	Night	23% 12% 36% 24% 5%	1000
	11th to 20th	Night	25% 11% 33% 25% 6%	1000
	21st to end	Night	28% 13% 33% 23% 3	1100

Page generated at 2025-07-03 00:30:15. Version ac07

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