Bonny Doon Airfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bonny Doon Airfield clear sky chart from 2005-11-06 to 2025-09-04.

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	7% 4 1 4 3 3 3 3 5% 7% 59%	134479
	Night	9% 5% 2 5% 3 3 3 3 6% 7% 54%	131706
Transparency	Day	25% 4 9% 20% 25% 17%	129415
	Night	30% 5% 10% 18% 21% 15%	127759
Seeing	Day	9% 8% 23% 33% 22% 6%	16572
	Night	10% 5% 16% 31% 30% 8%	25922

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	13% 5% 2 5% 3 3 2 3 5% 7% 51%	3977
	11th to 20th	Day	13% 5% 2 6% 4 3 3 3 4 5% 53%	4100
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 41%	4510
February	1st to 10th	Day	23% 5% 2 4 4 3 3 2 6% 5% 44%	1800
	11th to 20th	Day	15% 7% 2 5% 4 4 3 4 6% 7% 43%	1860
	21st to end	Day	15% 7% 3 6% 4 3 4 3 4 5% 46%	1650
March	1st to 10th	Day	14% 8% 3 9% 6% 5% 6% 5% 6% 7% 32%	4883
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 5% 8% 48%	5000
	21st to end	Day	16% 8% 2 6% 4 5% 5% 4 7% 9% 34%	5565
April	1st to 10th	Day	14% 6% 2 5% 3 4 4 3 5% 6% 48%	2400
	11th to 20th	Day	9% 5% 2 5% 3 3 4 4 5% 8% 52%	2369
	21st to end	Day	6% 5% 2 6% 4 3 3 4 6% 8% 54%	2400
May	1st to 10th	Day	5% 3 1 2 2 2 2 3 4 6% 71%	5558
	11th to 20th	Day	3 2 2 3 2 2 3 3 4 8% 67%	5883
	21st to end	Day	2 4 1 3 2 2 2 2 4 6% 70%	6902
June	1st to 10th	Day	4 5% 2 5% 3 3 3 4 5% 8% 59%	2800
	11th to 20th	Day	3 2 1 3 2 2 3 2 5% 7% 69%	2800
	21st to end	Day	2 2 1 3 2 2 2 3 3 7% 72%	2800
July	1st to 10th	Day	1 1 1 2 2 1 2 2 5% 7% 76%	6239
	11th to 20th	Day	1 2 1 3 2 2 3 4 6% 8% 68%	5880
	21st to end	Day	2 1 3 2 2 3 3 6% 11% 67%	6402
August	1st to 10th	Day	1 2 1 2 2 2 3 3 6% 9% 69%	5777
	11th to 20th	Day	1 2 2 2 2 2 5% 7% 77%	5474
	21st to end	Day	2 1 3 2 2 2 3 6% 7% 72%	5981
September	1st to 10th	Day	2 2 1 2 2 1 2 2 3 7% 76%	2317
	11th to 20th	Day	3 3 2 4 3 3 3 3 5% 9% 61%	2280
	21st to end	Day	3 2 1 2 2 2 2 2 4 6% 74%	2016
October	1st to 10th	Day	2 3 1 3 2 2 3 2 5% 7% 71%	3180
	11th to 20th	Day	4 2 1 3 3 2 3 4 4 8% 66%	3161
	21st to end	Day	5% 4 1 4 2 3 3 3 5% 9% 61%	3448
November	1st to 10th	Day	9% 4 2 4 3 3 4 4 4 8% 55%	1945
	11th to 20th	Day	11% 5% 2 4 3 3 3 4 6% 6% 52%	1800
	21st to end	Day	14% 4 1 3 3 3 2 3 4 7% 54%	1670
December	1st to 10th	Day	9% 5% 2 4 3 3 4 3 6% 9% 52%	2620
	11th to 20th	Day	25% 6% 2 6% 4 4 3 4 5% 6% 36%	3028
	21st to end	Day	28% 8% 2 5% 3 3 3 3 5% 7% 32%	4004
January	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 8% 53%	5981
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 5% 5% 51%	5880
	21st to end	Night	15% 6% 2 7% 5% 4 3 3 5% 6% 44%	6468
February	1st to 10th	Night	20% 5% 2 4 3 3 3 3 5% 6% 47%	2600
	11th to 20th	Night	14% 6% 2 5% 3 3 4 4 6% 8% 45%	2425
	21st to end	Night	12% 8% 2 5% 3 3 3 3 6% 7% 50%	1980
March	1st to 10th	Night	17% 9% 3 7% 5% 4 5% 5% 6% 6% 34%	4994
	11th to 20th	Night	15% 6% 2 5% 3 2 3 3 5% 6% 50%	5000
	21st to end	Night	18% 9% 2 7% 4 3 3 3 4 6% 40%	5408
April	1st to 10th	Night	12% 6% 2 4 4 3 3 5% 5% 8% 49%	2000
	11th to 20th	Night	10% 5% 2 5% 4 3 3 4 6% 7% 52%	1979
	21st to end	Night	5% 5% 2 4 3 3 3 3 7% 9% 55%	2000
May	1st to 10th	Night	3 4 2 6% 2 2 2 2 5% 5% 66%	4432
	11th to 20th	Night	2 3 6% 6% 4 4 4 4 7% 7% 54%	4010
	21st to end	Night	2 3 1 3 2 2 3 4 7% 6% 68%	3972
June	1st to 10th	Night	3 3 1 4 4 3 4 4 7% 9% 57%	1600
	11th to 20th	Night	1 3 2 4 3 4 3 3 7% 7% 65%	1600
	21st to end	Night	2 3 1 2 3 4 3 3 6% 7% 68%	1600
July	1st to 10th	Night	1 1 5% 3 2 2 3 9% 7% 66%	3719
	11th to 20th	Night	1 3 2 7% 5% 4 3 5% 11% 7% 51%	4100
	21st to end	Night	2 2 5% 4 3 5% 6% 9% 9% 54%	4472
August	1st to 10th	Night	1 2 1 5% 4 4 4 4 10% 9% 56%	4035
	11th to 20th	Night	1 1 2 2 2 2 3 12% 8% 67%	4388
	21st to end	Night	1 2 1 5% 3 3 3 3 8% 7% 65%	5015
September	1st to 10th	Night	2 1 3 3 3 3 3 5% 6% 72%	1930
	11th to 20th	Night	4 3 2 5% 3 3 3 4 5% 9% 60%	1900
	21st to end	Night	2 4 1 3 2 2 2 2 4 6% 72%	2157
October	1st to 10th	Night	2 2 1 3 3 2 3 2 5% 6% 70%	3800
	11th to 20th	Night	3 4 1 3 2 2 3 4 6% 7% 64%	3777
	21st to end	Night	5% 3 1 4 2 3 3 3 4 6% 65%	4121
November	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 7% 59%	2350
	11th to 20th	Night	10% 5% 1 4 3 3 3 4 6% 9% 53%	2600
	21st to end	Night	10% 5% 2 5% 2 3 3 3 5% 7% 56%	2725
December	1st to 10th	Night	10% 3 1 4 3 3 4 3 5% 6% 58%	4560
	11th to 20th	Night	22% 7% 2 6% 3 3 4 4 7% 9% 33%	5176
	21st to end	Night	28% 8% 2 6% 4 4 4 3 4 5% 32%	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	30% 4 19% 25% 17% 5%	3977
	11th to 20th	Day	34% 4 9% 15% 18% 20%	4100
	21st to end	Day	42% 4 7% 14% 18% 14%	4510
February	1st to 10th	Day	41% 3 7% 20% 18% 11%	1800
	11th to 20th	Day	38% 5% 11% 20% 19% 8%	1869
	21st to end	Day	38% 5% 8% 23% 18% 8%	1650
March	1st to 10th	Day	44% 7% 8% 19% 19% 2	4883
	11th to 20th	Day	33% 4 16% 29% 10% 8%	5000
	21st to end	Day	42% 8% 16% 20% 11% 2	5565
April	1st to 10th	Day	34% 5% 15% 21% 21% 4	2400
	11th to 20th	Day	29% 6% 14% 25% 20% 6%	2372
	21st to end	Day	28% 5% 13% 28% 21% 4	2400
May	1st to 10th	Day	15% 4 8% 29% 29% 14%	5558
	11th to 20th	Day	20% 4 10% 33% 27% 6%	5886
	21st to end	Day	18% 4 9% 31% 36% 3	6904
June	1st to 10th	Day	25% 6% 12% 26% 25% 6%	2800
	11th to 20th	Day	18% 4 10% 23% 32% 14%	2800
	21st to end	Day	18% 3 4 17% 32% 25%	2800
July	1st to 10th	Day	11% 3 6% 8% 23% 50%	6172
	11th to 20th	Day	15% 3 9% 6% 19% 48%	5811
	21st to end	Day	15% 4 5% 20% 31% 26%	6217
August	1st to 10th	Day	18% 3 6% 14% 29% 29%	4206
	11th to 20th	Day	11% 3 3 12% 46% 25%	3955
	21st to end	Day	16% 3 4 13% 35% 28%	4311
September	1st to 10th	Day	15% 2 3 14% 29% 37%	2317
	11th to 20th	Day	23% 3 8% 22% 30% 14%	2280
	21st to end	Day	15% 2 6% 21% 37% 19%	2016
October	1st to 10th	Day	15% 2 6% 13% 29% 35%	3180
	11th to 20th	Day	17% 4 8% 25% 30% 16%	3161
	21st to end	Day	21% 2 7% 24% 29% 16%	3448
November	1st to 10th	Day	28% 4 8% 26% 24% 11%	1945
	11th to 20th	Day	30% 4 11% 24% 23% 9%	1800
	21st to end	Day	30% 2 10% 18% 28% 11%	1670
December	1st to 10th	Day	29% 3 7% 22% 32% 8%	2620
	11th to 20th	Day	46% 4 11% 17% 14% 7%	3028
	21st to end	Day	51% 4 11% 21% 11% 3	4004
January	1st to 10th	Night	28% 4 20% 26% 17% 5%	5981
	11th to 20th	Night	33% 5% 11% 15% 22% 14%	5880
	21st to end	Night	40% 4 9% 12% 17% 18%	6468
February	1st to 10th	Night	39% 3 8% 17% 19% 14%	2600
	11th to 20th	Night	36% 5% 11% 20% 21% 7%	2427
	21st to end	Night	31% 4 12% 28% 17% 7%	1980
March	1st to 10th	Night	46% 5% 11% 18% 17% 3	4994
	11th to 20th	Night	34% 6% 11% 24% 16% 8%	5000
	21st to end	Night	42% 7% 13% 23% 13% 2	5408
April	1st to 10th	Night	33% 5% 15% 24% 18% 6%	2000
	11th to 20th	Night	32% 7% 11% 27% 17% 7%	1979
	21st to end	Night	25% 8% 12% 29% 20% 6%	2000
May	1st to 10th	Night	20% 4 11% 22% 28% 14%	4429
	11th to 20th	Night	32% 9% 8% 23% 21% 7%	4011
	21st to end	Night	17% 11% 10% 19% 40% 3	3972
June	1st to 10th	Night	25% 10% 10% 24% 23% 8%	1600
	11th to 20th	Night	22% 5% 8% 15% 30% 20%	1600
	21st to end	Night	24% 6% 4 13% 27% 27%	1600
July	1st to 10th	Night	16% 4 11% 6% 17% 45%	3678
	11th to 20th	Night	23% 5% 14% 6% 14% 38%	4046
	21st to end	Night	26% 8% 8% 15% 22% 21%	4345
August	1st to 10th	Night	26% 6% 10% 12% 24% 23%	2929
	11th to 20th	Night	16% 5% 8% 8% 35% 29%	3176
	21st to end	Night	20% 6% 8% 10% 35% 23%	3608
September	1st to 10th	Night	17% 5% 4 10% 28% 36%	1930
	11th to 20th	Night	25% 5% 5% 21% 29% 16%	1900
	21st to end	Night	18% 3 4 18% 35% 22%	2157
October	1st to 10th	Night	16% 3 6% 10% 21% 43%	3800
	11th to 20th	Night	20% 7% 7% 24% 23% 20%	3777
	21st to end	Night	22% 2 5% 22% 26% 22%	4121
November	1st to 10th	Night	26% 3 8% 25% 23% 14%	2350
	11th to 20th	Night	28% 4 11% 23% 24% 10%	2600
	21st to end	Night	29% 4 9% 20% 23% 16%	2725
December	1st to 10th	Night	27% 3 7% 23% 26% 15%	4560
	11th to 20th	Night	45% 5% 11% 15% 17% 7%	5176
	21st to end	Night	53% 4 11% 18% 10% 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	28% 11% 23% 21% 15% 2	343
	11th to 20th	Day	17% 9% 23% 32% 16% 4	400
	21st to end	Day	17% 7% 25% 28% 20% 3	440
February	1st to 10th	Day	24% 11% 21% 22% 18% 5%	400
	11th to 20th	Day	19% 15% 27% 26% 13% 1	449
	21st to end	Day	12% 13% 29% 32% 13% 2	414
March	1st to 10th	Day	23% 16% 26% 26% 9% 1	500
	11th to 20th	Day	24% 12% 24% 23% 14% 4	500
	21st to end	Day	17% 13% 32% 26% 11% 2	550
April	1st to 10th	Day	17% 11% 31% 26% 12% 2	500
	11th to 20th	Day	11% 14% 29% 28% 14% 3	492
	21st to end	Day	6% 14% 32% 29% 14% 5%	500
May	1st to 10th	Day	9% 14% 28% 31% 15% 3	503
	11th to 20th	Day	10% 8% 30% 31% 16% 4	528
	21st to end	Day	7% 10% 28% 31% 19% 6%	573
June	1st to 10th	Day	5% 8% 25% 38% 20% 5%	530
	11th to 20th	Day	3 9% 27% 39% 19% 3	530
	21st to end	Day	2 3 20% 46% 24% 5%	530
July	1st to 10th	Day	2 2 17% 43% 30% 6%	526
	11th to 20th	Day	1 14% 47% 30% 8%	524
	21st to end	Day	1 13% 41% 36% 8%	575
August	1st to 10th	Day	3 2 20% 42% 27% 7%	527
	11th to 20th	Day	1 2 16% 42% 31% 9%	517
	21st to end	Day	2 3 13% 40% 33% 9%	583
September	1st to 10th	Day	2 2 15% 40% 33% 9%	503
	11th to 20th	Day	3 6% 25% 36% 24% 6%	490
	21st to end	Day	3 6% 16% 33% 32% 9%	490
October	1st to 10th	Day	3 4 23% 30% 29% 10%	490
	11th to 20th	Day	6% 6% 18% 31% 29% 10%	490
	21st to end	Day	8% 6% 22% 29% 26% 8%	539
November	1st to 10th	Day	7% 12% 20% 27% 26% 9%	481
	11th to 20th	Day	12% 7% 21% 27% 23% 10%	300
	21st to end	Day	12% 8% 20% 29% 23% 7%	235
December	1st to 10th	Day	15% 8% 20% 28% 23% 7%	200
	11th to 20th	Day	16% 16% 21% 19% 21% 9%	200
	21st to end	Day	22% 18% 22% 20% 14% 5%	220
January	1st to 10th	Night	18% 7% 18% 27% 24% 6%	800
	11th to 20th	Night	18% 5% 14% 32% 23% 9%	800
	21st to end	Night	18% 5% 15% 30% 27% 5%	880
February	1st to 10th	Night	21% 9% 14% 27% 23% 6%	800
	11th to 20th	Night	16% 9% 19% 31% 20% 5%	784
	21st to end	Night	14% 8% 22% 32% 19% 3	660
March	1st to 10th	Night	21% 9% 20% 26% 21% 3	800
	11th to 20th	Night	18% 7% 16% 29% 25% 5%	800
	21st to end	Night	15% 8% 25% 31% 18% 3	880
April	1st to 10th	Night	14% 8% 22% 32% 21% 3	800
	11th to 20th	Night	11% 12% 20% 30% 21% 6%	791
	21st to end	Night	7% 7% 29% 28% 22% 8%	800
May	1st to 10th	Night	6% 5% 24% 33% 26% 6%	750
	11th to 20th	Night	5% 5% 19% 33% 31% 7%	567
	21st to end	Night	5% 8% 20% 37% 24% 6%	433
June	1st to 10th	Night	4 4 16% 40% 32% 6%	400
	11th to 20th	Night	2 4 17% 44% 31% 4	400
	21st to end	Night	3 2 11% 36% 42% 7%	400
July	1st to 10th	Night	2 9% 35% 45% 9%	416
	11th to 20th	Night	2 1 3 32% 43% 19%	582
	21st to end	Night	2 5% 32% 47% 14%	657
August	1st to 10th	Night	3 2 10% 32% 43% 9%	597
	11th to 20th	Night	1 2 11% 34% 42% 10%	737
	21st to end	Night	2 1 9% 29% 47% 12%	880
September	1st to 10th	Night	1 1 8% 32% 44% 13%	772
	11th to 20th	Night	4 2 13% 33% 39% 9%	760
	21st to end	Night	3 3 10% 28% 42% 15%	760
October	1st to 10th	Night	4 3 13% 32% 36% 12%	760
	11th to 20th	Night	7% 4 11% 25% 40% 12%	760
	21st to end	Night	8% 4 12% 30% 30% 16%	836
November	1st to 10th	Night	9% 5% 15% 27% 33% 11%	780
	11th to 20th	Night	11% 4 14% 33% 31% 8%	800
	21st to end	Night	12% 4 17% 34% 27% 7%	800
December	1st to 10th	Night	17% 5% 18% 30% 25% 7%	800
	11th to 20th	Night	22% 6% 16% 33% 21% 4	800
	21st to end	Night	19% 12% 20% 29% 18% 3	880

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