Depth Afield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Depth Afield Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	3 7% 3 7% 5% 4 5% 4 5% 7% 51%	135244
	Night	2 7% 3 7% 4 4 4 4 5% 7% 52%	132306
Transparency	Day	31% 8% 9% 19% 21% 12%	130002
	Night	29% 8% 10% 22% 21% 10%	128551
Seeing	Day	9% 18% 32% 26% 12% 3	16461
	Night	6% 7% 26% 38% 19% 2	26776

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	1 10% 6% 13% 6% 6% 5% 4 7% 8% 34%	4098
	11th to 20th	Day	1 12% 6% 18% 6% 4 4 3 4 4 37%	4100
	21st to end	Day	1 11% 6% 11% 4 3 3 2 4 5% 50%	4510
February	1st to 10th	Day	3 14% 6% 12% 6% 6% 5% 5% 5% 5% 33%	1800
	11th to 20th	Day	4 16% 6% 11% 7% 5% 6% 3 5% 6% 32%	1798
	21st to end	Day	2 13% 5% 13% 6% 7% 4 3 6% 6% 34%	1650
March	1st to 10th	Day	1 13% 6% 13% 7% 5% 5% 3 5% 6% 37%	4885
	11th to 20th	Day	1 9% 6% 10% 7% 6% 6% 5% 6% 7% 37%	5000
	21st to end	Day	2 16% 6% 13% 8% 7% 6% 4 6% 5% 28%	5486
April	1st to 10th	Day	3 13% 5% 7% 5% 5% 5% 4 6% 7% 40%	2241
	11th to 20th	Day	4 13% 4 9% 6% 5% 5% 5% 5% 6% 38%	2484
	21st to end	Day	5% 12% 3 7% 5% 4 5% 3 5% 6% 44%	2600
May	1st to 10th	Day	5% 11% 4 7% 4 4 5% 5% 7% 8% 40%	5880
	11th to 20th	Day	5% 8% 2 6% 5% 5% 6% 5% 7% 9% 43%	5841
	21st to end	Day	4 6% 2 6% 4 4 5% 4 6% 9% 50%	6423
June	1st to 10th	Day	3 3 2 5% 4 4 5% 4 6% 8% 55%	2760
	11th to 20th	Day	4 4 1 4 4 3 4 3 5% 7% 62%	2800
	21st to end	Day	2 2 1 4 3 3 4 3 5% 6% 67%	2697
July	1st to 10th	Day	2 2 1 3 2 3 4 3 4 5% 72%	5879
	11th to 20th	Day	2 3 1 4 4 4 5% 4 7% 9% 56%	5880
	21st to end	Day	2 2 1 3 3 3 4 3 5% 6% 68%	6401
August	1st to 10th	Day	2 2 1 4 3 3 4 4 6% 7% 66%	5779
	11th to 20th	Day	1 2 1 3 3 4 4 3 4 6% 69%	5798
	21st to end	Day	4 3 1 5% 5% 5% 5% 4 6% 7% 55%	6348
September	1st to 10th	Day	3 3 1 3 3 4 4 3 5% 7% 63%	2295
	11th to 20th	Day	4 4 1 4 3 4 4 4 5% 7% 61%	2200
	21st to end	Day	4 5% 1 5% 2 3 3 2 4 5% 66%	2200
October	1st to 10th	Day	3 4 2 5% 3 3 3 3 3 5% 67%	3402
	11th to 20th	Day	6% 8% 2 4 3 4 4 3 4 6% 55%	3250
	21st to end	Day	3 7% 2 4 4 4 4 3 4 5% 59%	3548
November	1st to 10th	Day	5% 7% 3 7% 5% 5% 4 4 5% 6% 49%	1812
	11th to 20th	Day	4 11% 2 6% 4 4 5% 3 5% 7% 50%	1800
	21st to end	Day	1 8% 5% 11% 6% 5% 3 4 6% 6% 45%	1609
December	1st to 10th	Day	2 7% 2 6% 4 3 3 3 6% 8% 57%	2620
	11th to 20th	Day	1 10% 4 10% 7% 6% 6% 4 7% 9% 37%	3026
	21st to end	Day	2 12% 5% 13% 7% 6% 5% 4 5% 6% 34%	4344
January	1st to 10th	Night	1 9% 7% 16% 7% 5% 5% 3 5% 6% 36%	5867
	11th to 20th	Night	1 9% 6% 14% 9% 6% 5% 3 5% 6% 37%	5880
	21st to end	Night	1 10% 6% 9% 4 3 4 3 4 5% 50%	6468
February	1st to 10th	Night	2 11% 5% 12% 5% 6% 5% 4 7% 6% 37%	2600
	11th to 20th	Night	2 12% 4 9% 6% 5% 5% 4 6% 7% 41%	2487
	21st to end	Night	2 10% 4 10% 7% 6% 4 4 7% 6% 40%	1980
March	1st to 10th	Night	1 12% 5% 13% 6% 5% 5% 4 6% 6% 39%	4996
	11th to 20th	Night	1 9% 4 9% 5% 5% 5% 5% 7% 9% 40%	5000
	21st to end	Night	2 11% 5% 9% 6% 5% 5% 4 6% 6% 42%	5489
April	1st to 10th	Night	4 13% 2 7% 4 4 4 3 4 6% 49%	2157
	11th to 20th	Night	3 9% 3 5% 3 4 5% 5% 7% 7% 47%	1860
	21st to end	Night	5% 10% 3 6% 5% 4 4 4 7% 8% 46%	1800
May	1st to 10th	Night	4 9% 3 6% 5% 4 5% 3 5% 7% 50%	4100
	11th to 20th	Night	2 5% 2 5% 3 4 4 4 6% 8% 57%	4074
	21st to end	Night	3 4 2 5% 4 4 4 4 6% 8% 59%	4474
June	1st to 10th	Night	3 4 1 4 4 4 3 4 6% 8% 59%	1635
	11th to 20th	Night	3 2 1 4 3 4 3 3 4 6% 67%	1600
	21st to end	Night	1 1 1 3 3 3 4 3 5% 6% 69%	1693
July	1st to 10th	Night	2 2 1 3 3 3 4 3 4 5% 70%	4100
	11th to 20th	Night	2 3 1 4 4 5% 5% 5% 7% 8% 55%	4100
	21st to end	Night	1 2 1 4 3 4 5% 4 5% 7% 65%	4472
August	1st to 10th	Night	2 2 1 3 3 3 4 3 5% 7% 67%	4033
	11th to 20th	Night	2 2 1 4 3 4 5% 3 5% 7% 63%	4051
	21st to end	Night	2 3 2 5% 4 4 5% 4 6% 6% 58%	4627
September	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 6% 67%	2101
	11th to 20th	Night	3 2 1 3 3 3 4 3 5% 7% 64%	2200
	21st to end	Night	4 4 1 3 2 3 2 2 5% 6% 68%	2200
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 73%	3792
	11th to 20th	Night	5% 6% 2 5% 3 3 4 3 4 6% 59%	3898
	21st to end	Night	3 6% 2 5% 3 3 4 3 6% 7% 58%	4252
November	1st to 10th	Night	3 7% 3 6% 4 4 3 4 7% 7% 52%	2527
	11th to 20th	Night	3 9% 2 5% 3 4 5% 3 6% 8% 52%	2600
	21st to end	Night	2 8% 4 8% 5% 4 5% 4 5% 7% 48%	2767
December	1st to 10th	Night	1 6% 2 6% 4 3 3 3 5% 8% 59%	4570
	11th to 20th	Night	2 8% 3 8% 5% 4 5% 4 6% 8% 45%	5181
	21st to end	Night	3 11% 5% 13% 6% 6% 5% 4 6% 7% 34%	6675

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	39% 14% 15% 16% 14% 1	4099
	11th to 20th	Day	47% 8% 9% 18% 14% 4	4100
	21st to end	Day	35% 7% 13% 19% 21% 5%	4510
February	1st to 10th	Day	52% 9% 11% 15% 11% 3	1800
	11th to 20th	Day	50% 8% 12% 18% 11% 2	1807
	21st to end	Day	47% 9% 12% 18% 11% 2	1650
March	1st to 10th	Day	43% 9% 8% 19% 13% 7%	4885
	11th to 20th	Day	38% 11% 14% 24% 11% 1	5000
	21st to end	Day	50% 13% 13% 17% 6% 1	5486
April	1st to 10th	Day	41% 10% 11% 20% 14% 4	2241
	11th to 20th	Day	43% 8% 12% 21% 14% 2	2487
	21st to end	Day	38% 8% 11% 25% 17% 1	2600
May	1st to 10th	Day	33% 13% 11% 21% 20% 3	5880
	11th to 20th	Day	31% 9% 9% 27% 22% 2	5844
	21st to end	Day	26% 10% 9% 25% 28% 2	6424
June	1st to 10th	Day	23% 7% 10% 24% 29% 7%	2760
	11th to 20th	Day	22% 4 7% 19% 29% 20%	2800
	21st to end	Day	17% 4 5% 14% 30% 31%	2697
July	1st to 10th	Day	15% 3 4 7% 18% 53%	5816
	11th to 20th	Day	20% 6% 6% 13% 29% 27%	5811
	21st to end	Day	16% 4 5% 10% 27% 37%	6217
August	1st to 10th	Day	20% 6% 7% 23% 23% 21%	4208
	11th to 20th	Day	20% 5% 7% 17% 29% 22%	4197
	21st to end	Day	19% 5% 7% 15% 29% 25%	4579
September	1st to 10th	Day	21% 5% 7% 17% 27% 23%	2295
	11th to 20th	Day	23% 6% 8% 19% 26% 18%	2200
	21st to end	Day	20% 5% 7% 20% 35% 13%	2200
October	1st to 10th	Day	22% 4 5% 15% 38% 16%	3402
	11th to 20th	Day	30% 4 6% 29% 26% 5%	3250
	21st to end	Day	26% 5% 10% 27% 27% 4	3548
November	1st to 10th	Day	33% 8% 11% 23% 20% 4	1812
	11th to 20th	Day	33% 7% 13% 26% 19% 2	1800
	21st to end	Day	38% 7% 11% 24% 15% 5%	1609
December	1st to 10th	Day	25% 7% 11% 38% 16% 3	2620
	11th to 20th	Day	40% 8% 15% 21% 14% 1	3024
	21st to end	Day	48% 7% 9% 14% 18% 3	4344
January	1st to 10th	Night	41% 13% 12% 16% 16% 2	5867
	11th to 20th	Night	46% 9% 9% 19% 15% 2	5880
	21st to end	Night	35% 7% 12% 20% 21% 4	6468
February	1st to 10th	Night	43% 10% 15% 19% 10% 3	2600
	11th to 20th	Night	40% 8% 12% 20% 17% 2	2488
	21st to end	Night	40% 9% 13% 21% 12% 5%	1980
March	1st to 10th	Night	39% 11% 8% 21% 15% 5%	4996
	11th to 20th	Night	34% 11% 14% 27% 12% 2	5000
	21st to end	Night	36% 11% 16% 22% 13% 1	5489
April	1st to 10th	Night	34% 8% 13% 22% 18% 5%	2157
	11th to 20th	Night	31% 9% 13% 25% 19% 3	1860
	21st to end	Night	32% 8% 14% 26% 18% 1	1800
May	1st to 10th	Night	29% 10% 12% 22% 24% 3	4097
	11th to 20th	Night	20% 9% 11% 31% 25% 4	4075
	21st to end	Night	20% 8% 8% 30% 32% 2	4474
June	1st to 10th	Night	23% 7% 10% 23% 29% 8%	1635
	11th to 20th	Night	18% 6% 7% 18% 31% 20%	1600
	21st to end	Night	14% 4 5% 14% 28% 34%	1693
July	1st to 10th	Night	17% 3 5% 7% 15% 54%	4055
	11th to 20th	Night	23% 5% 5% 11% 25% 30%	4046
	21st to end	Night	18% 5% 6% 10% 26% 34%	4344
August	1st to 10th	Night	20% 6% 9% 20% 23% 22%	2928
	11th to 20th	Night	23% 7% 7% 15% 27% 21%	2928
	21st to end	Night	16% 5% 9% 14% 28% 29%	3327
September	1st to 10th	Night	17% 5% 7% 18% 27% 26%	2101
	11th to 20th	Night	19% 6% 8% 20% 27% 20%	2200
	21st to end	Night	19% 4 6% 19% 36% 17%	2200
October	1st to 10th	Night	16% 4 6% 17% 36% 21%	3792
	11th to 20th	Night	26% 5% 6% 31% 26% 7%	3898
	21st to end	Night	23% 6% 8% 32% 28% 4	4252
November	1st to 10th	Night	28% 8% 12% 24% 22% 5%	2527
	11th to 20th	Night	29% 6% 14% 29% 19% 2	2600
	21st to end	Night	35% 7% 11% 23% 20% 5%	2767
December	1st to 10th	Night	23% 5% 11% 37% 19% 3	4570
	11th to 20th	Night	34% 9% 18% 26% 12% 1	5182
	21st to end	Night	43% 10% 14% 18% 13% 3	6675

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	12% 16% 34% 22% 14% 3	300
	11th to 20th	Day	8% 17% 34% 28% 11% 2	300
	21st to end	Day	7% 19% 32% 30% 10% 2	330
February	1st to 10th	Day	18% 22% 37% 17% 4 1	300
	11th to 20th	Day	12% 24% 38% 20% 6% 1	343
	21st to end	Day	10% 28% 35% 22% 4 1	414
March	1st to 10th	Day	14% 23% 38% 18% 7% 1	500
	11th to 20th	Day	11% 27% 33% 22% 6% 1	500
	21st to end	Day	17% 30% 32% 17% 4	550
April	1st to 10th	Day	14% 26% 29% 20% 8% 4	500
	11th to 20th	Day	17% 30% 30% 17% 5% 1	492
	21st to end	Day	17% 24% 30% 21% 8% 1	500
May	1st to 10th	Day	14% 22% 34% 20% 8% 1	503
	11th to 20th	Day	12% 22% 32% 22% 9% 4	528
	21st to end	Day	10% 20% 30% 24% 12% 4	573
June	1st to 10th	Day	6% 13% 30% 29% 18% 3	690
	11th to 20th	Day	8% 17% 32% 28% 14% 1	730
	21st to end	Day	3 15% 35% 31% 13% 3	627
July	1st to 10th	Day	3 10% 36% 37% 13% 2	526
	11th to 20th	Day	4 8% 38% 32% 13% 5%	524
	21st to end	Day	3 7% 33% 36% 15% 6%	575
August	1st to 10th	Day	4 13% 35% 30% 15% 3	527
	11th to 20th	Day	3 9% 35% 32% 14% 6%	517
	21st to end	Day	4 10% 32% 32% 16% 5%	583
September	1st to 10th	Day	4 12% 28% 31% 15% 9%	530
	11th to 20th	Day	7% 18% 30% 27% 13% 5%	530
	21st to end	Day	7% 14% 25% 32% 17% 5%	530
October	1st to 10th	Day	8% 16% 26% 25% 17% 8%	410
	11th to 20th	Day	12% 14% 29% 22% 17% 6%	330
	21st to end	Day	12% 15% 32% 26% 15% 1	363
November	1st to 10th	Day	15% 16% 27% 23% 15% 4	306
	11th to 20th	Day	9% 19% 27% 29% 12% 4	300
	21st to end	Day	8% 12% 28% 32% 16% 5%	300
December	1st to 10th	Day	6% 15% 29% 31% 14% 5%	300
	11th to 20th	Day	6% 14% 38% 32% 10%	300
	21st to end	Day	13% 19% 33% 24% 9% 2	330
January	1st to 10th	Night	7% 9% 33% 32% 17% 2	800
	11th to 20th	Night	8% 8% 30% 38% 14% 2	800
	21st to end	Night	6% 8% 33% 37% 13% 3	880
February	1st to 10th	Night	8% 9% 38% 34% 9% 2	800
	11th to 20th	Night	7% 8% 37% 34% 13% 1	784
	21st to end	Night	7% 9% 36% 38% 10% 1	660
March	1st to 10th	Night	7% 12% 32% 36% 11% 2	800
	11th to 20th	Night	5% 8% 30% 39% 16% 2	800
	21st to end	Night	8% 13% 33% 34% 11% 1	880
April	1st to 10th	Night	11% 13% 27% 36% 13% 1	757
	11th to 20th	Night	9% 11% 32% 38% 10%	593
	21st to end	Night	11% 11% 26% 34% 17% 2	600
May	1st to 10th	Night	7% 9% 31% 37% 16% 1	600
	11th to 20th	Night	6% 7% 22% 39% 23% 3	591
	21st to end	Night	6% 6% 26% 36% 22% 3	650
June	1st to 10th	Night	4 8% 22% 41% 24% 2	600
	11th to 20th	Night	5% 9% 26% 40% 19% 1	600
	21st to end	Night	2 3 23% 41% 30% 2	600
July	1st to 10th	Night	3 2 15% 41% 36% 3	585
	11th to 20th	Night	3 3 12% 49% 30% 3	582
	21st to end	Night	2 1 11% 40% 44% 2	657
August	1st to 10th	Night	4 1 17% 45% 31% 1	597
	11th to 20th	Night	4 1 13% 45% 33% 4	594
	21st to end	Night	2 3 14% 44% 35% 2	660
September	1st to 10th	Night	4 3 15% 42% 32% 5%	701
	11th to 20th	Night	5% 4 19% 38% 29% 6%	800
	21st to end	Night	6% 5% 17% 35% 32% 6%	800
October	1st to 10th	Night	8% 7% 23% 38% 22% 3	800
	11th to 20th	Night	7% 6% 24% 39% 22% 4	800
	21st to end	Night	7% 7% 25% 38% 21% 3	880
November	1st to 10th	Night	7% 8% 26% 37% 20% 3	788
	11th to 20th	Night	9% 6% 30% 39% 12% 4	800
	21st to end	Night	7% 9% 31% 35% 16% 3	967
December	1st to 10th	Night	6% 8% 32% 40% 13% 1	1000
	11th to 20th	Night	9% 9% 32% 39% 11% 1	1000
	21st to end	Night	11% 12% 34% 33% 9% 1	970

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