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 2024-11-08.

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 8% 3 7% 5% 4 4 4 5% 7% 49%	104977
	Night	3 7% 3 8% 5% 4 4 4 6% 7% 50%	102875
Transparency	Day	32% 8% 10% 19% 20% 12%	104742
	Night	31% 8% 11% 21% 19% 10%	102699
Seeing	Day	9% 17% 32% 26% 12% 3	15129
	Night	7% 7% 26% 38% 20% 2	25455

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	2 10% 7% 16% 8% 7% 4 3 6% 6% 30%	2858
	11th to 20th	Day	2 16% 7% 19% 7% 4 4 3 4 4 30%	2860
	21st to end	Day	2 15% 8% 12% 4 3 4 2 4 5% 40%	3146
February	1st to 10th	Day	3 14% 6% 11% 6% 6% 5% 5% 5% 5% 33%	1710
	11th to 20th	Day	4 15% 6% 10% 6% 5% 6% 3 5% 6% 33%	1705
	21st to end	Day	3 14% 5% 14% 6% 7% 4 3 6% 6% 33%	1570
March	1st to 10th	Day	1 10% 6% 14% 8% 6% 5% 4 6% 8% 32%	3401
	11th to 20th	Day	2 10% 4 9% 5% 5% 5% 4 6% 8% 41%	3490
	21st to end	Day	3 21% 7% 14% 7% 6% 5% 4 6% 6% 22%	3825
April	1st to 10th	Day	3 13% 5% 7% 5% 5% 5% 4 6% 7% 40%	2129
	11th to 20th	Day	4 14% 4 9% 6% 5% 5% 5% 5% 6% 38%	2358
	21st to end	Day	5% 12% 3 7% 5% 4 4 3 5% 6% 44%	2470
May	1st to 10th	Day	5% 15% 5% 9% 5% 5% 5% 5% 6% 7% 34%	4110
	11th to 20th	Day	4 5% 2 5% 4 4 6% 4 7% 9% 49%	4071
	21st to end	Day	5% 7% 2 6% 5% 5% 5% 5% 7% 9% 45%	4477
June	1st to 10th	Day	3 3 2 5% 4 5% 5% 4 6% 8% 55%	2622
	11th to 20th	Day	4 4 1 4 4 3 4 3 5% 7% 61%	2660
	21st to end	Day	2 2 1 4 3 3 4 3 5% 6% 67%	2562
July	1st to 10th	Day	2 1 1 2 2 3 3 2 4 6% 75%	4110
	11th to 20th	Day	2 3 1 5% 4 5% 5% 5% 8% 10% 53%	4110
	21st to end	Day	3 3 1 4 4 4 4 4 5% 6% 62%	4454
August	1st to 10th	Day	2 2 1 4 3 4 5% 4 6% 8% 59%	4092
	11th to 20th	Day	2 2 1 4 4 4 5% 4 5% 6% 63%	4028
	21st to end	Day	2 2 1 4 4 4 4 4 5% 6% 65%	4440
September	1st to 10th	Day	3 3 1 3 3 3 4 3 5% 7% 64%	2180
	11th to 20th	Day	4 4 1 4 3 3 4 3 5% 7% 62%	2090
	21st to end	Day	4 5% 1 5% 2 2 3 2 4 5% 67%	2090
October	1st to 10th	Day	3 4 2 5% 3 2 3 3 3 5% 67%	3298
	11th to 20th	Day	6% 8% 2 5% 3 4 4 3 4 6% 55%	3150
	21st to end	Day	3 7% 2 4 4 4 4 3 4 5% 59%	3438
November	1st to 10th	Day	5% 7% 3 7% 5% 5% 4 5% 5% 6% 48%	1766
	11th to 20th	Day	5% 11% 2 6% 4 4 5% 3 5% 7% 49%	1710
	21st to end	Day	1 8% 5% 11% 6% 5% 3 4 6% 6% 45%	1529
December	1st to 10th	Day	3 11% 3 8% 5% 4 5% 4 7% 8% 41%	1520
	11th to 20th	Day	2 11% 4 12% 8% 6% 6% 4 6% 7% 34%	1926
	21st to end	Day	2 11% 5% 11% 6% 5% 5% 4 5% 7% 39%	3022
January	1st to 10th	Night	1 10% 8% 18% 7% 5% 4 3 5% 5% 34%	4097
	11th to 20th	Night	2 13% 8% 15% 9% 6% 4 3 4 5% 31%	4110
	21st to end	Night	2 15% 7% 11% 5% 4 4 4 6% 6% 37%	4521
February	1st to 10th	Night	2 11% 5% 12% 5% 6% 5% 5% 7% 6% 37%	2470
	11th to 20th	Night	2 12% 4 9% 6% 5% 5% 4 6% 7% 41%	2360
	21st to end	Night	2 10% 5% 11% 7% 5% 4 4 8% 6% 39%	1884
March	1st to 10th	Night	1 8% 4 15% 7% 5% 6% 4 6% 7% 36%	3473
	11th to 20th	Night	1 7% 3 6% 4 5% 5% 4 7% 10% 48%	3490
	21st to end	Night	2 14% 7% 11% 7% 5% 5% 4 5% 6% 35%	3828
April	1st to 10th	Night	4 13% 2 7% 4 4 4 3 4 7% 48%	2049
	11th to 20th	Night	3 9% 3 5% 3 4 5% 5% 7% 7% 47%	1766
	21st to end	Night	6% 10% 3 6% 5% 3 3 4 6% 8% 47%	1710
May	1st to 10th	Night	4 11% 4 7% 5% 5% 6% 4 6% 7% 40%	2860
	11th to 20th	Night	2 4 1 4 3 3 3 4 6% 8% 62%	2834
	21st to end	Night	3 5% 2 5% 4 4 4 4 6% 8% 54%	3110
June	1st to 10th	Night	3 4 1 4 4 4 3 4 6% 8% 58%	1553
	11th to 20th	Night	3 2 1 4 3 4 3 3 4 6% 66%	1520
	21st to end	Night	1 1 1 3 3 3 3 3 6% 7% 69%	1608
July	1st to 10th	Night	3 2 1 2 2 3 3 2 4 5% 72%	2860
	11th to 20th	Night	2 3 1 4 5% 5% 6% 5% 8% 9% 51%	2860
	21st to end	Night	2 3 2 5% 4 5% 6% 4 6% 7% 58%	3109
August	1st to 10th	Night	2 2 1 4 4 4 5% 4 5% 8% 61%	2847
	11th to 20th	Night	2 3 2 6% 4 4 5% 3 5% 7% 59%	2811
	21st to end	Night	1 2 1 3 3 3 3 3 5% 6% 70%	3225
September	1st to 10th	Night	3 2 1 3 3 3 3 3 5% 6% 68%	1996
	11th to 20th	Night	3 2 1 3 3 3 4 3 5% 8% 64%	2090
	21st to end	Night	4 4 2 3 2 3 2 2 4 6% 69%	2090
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 73%	3676
	11th to 20th	Night	5% 5% 2 5% 3 3 4 3 5% 6% 59%	3778
	21st to end	Night	3 6% 2 5% 3 3 4 3 6% 7% 58%	4120
November	1st to 10th	Night	3 7% 3 6% 4 4 3 4 7% 7% 51%	2469
	11th to 20th	Night	4 9% 2 5% 3 4 5% 3 6% 8% 51%	2470
	21st to end	Night	2 8% 4 8% 5% 5% 5% 4 5% 7% 47%	2628
December	1st to 10th	Night	2 10% 3 8% 6% 4 5% 3 5% 8% 45%	2660
	11th to 20th	Night	4 10% 4 10% 5% 5% 6% 4 7% 9% 36%	3271
	21st to end	Night	2 10% 4 15% 7% 5% 5% 4 6% 7% 34%	4672

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	45% 15% 11% 16% 11% 1	2859
	11th to 20th	Day	56% 8% 12% 14% 8% 2	2860
	21st to end	Day	43% 9% 18% 18% 10% 2	3146
February	1st to 10th	Day	51% 9% 11% 16% 10% 2	1710
	11th to 20th	Day	49% 8% 12% 19% 11% 2	1714
	21st to end	Day	49% 9% 12% 18% 11% 1	1570
March	1st to 10th	Day	43% 12% 12% 20% 10% 4	3401
	11th to 20th	Day	33% 13% 17% 27% 9% 2	3490
	21st to end	Day	56% 14% 11% 14% 5% 1	3825
April	1st to 10th	Day	41% 10% 12% 19% 13% 4	2129
	11th to 20th	Day	44% 8% 12% 21% 14% 1	2361
	21st to end	Day	38% 8% 11% 26% 16% 1	2470
May	1st to 10th	Day	39% 13% 11% 19% 15% 3	4110
	11th to 20th	Day	24% 9% 11% 31% 23% 2	4074
	21st to end	Day	29% 11% 11% 23% 23% 2	4477
June	1st to 10th	Day	24% 7% 10% 24% 28% 7%	2622
	11th to 20th	Day	23% 4 7% 19% 29% 18%	2660
	21st to end	Day	17% 4 5% 14% 28% 32%	2562
July	1st to 10th	Day	12% 3 5% 9% 15% 56%	4046
	11th to 20th	Day	22% 6% 7% 14% 26% 25%	4041
	21st to end	Day	20% 5% 7% 11% 23% 34%	4314
August	1st to 10th	Day	21% 6% 7% 23% 23% 20%	4078
	11th to 20th	Day	20% 5% 7% 17% 29% 22%	4067
	21st to end	Day	18% 5% 7% 15% 29% 26%	4439
September	1st to 10th	Day	20% 5% 7% 16% 27% 24%	2180
	11th to 20th	Day	22% 6% 8% 19% 26% 19%	2090
	21st to end	Day	20% 5% 7% 20% 36% 13%	2090
October	1st to 10th	Day	22% 4 5% 14% 39% 16%	3298
	11th to 20th	Day	30% 4 6% 28% 26% 5%	3150
	21st to end	Day	27% 5% 10% 28% 26% 5%	3438
November	1st to 10th	Day	33% 9% 11% 23% 20% 4	1766
	11th to 20th	Day	33% 7% 14% 25% 19% 2	1710
	21st to end	Day	39% 7% 12% 23% 14% 5%	1529
December	1st to 10th	Day	39% 10% 18% 18% 9% 5%	1520
	11th to 20th	Day	46% 8% 12% 20% 12% 1	1924
	21st to end	Day	42% 7% 12% 14% 20% 4	3022
January	1st to 10th	Night	44% 14% 10% 17% 13% 1	4097
	11th to 20th	Night	55% 9% 11% 15% 7% 3	4110
	21st to end	Night	44% 9% 18% 19% 8% 3	4521
February	1st to 10th	Night	43% 10% 16% 19% 10% 2	2470
	11th to 20th	Night	40% 8% 13% 21% 17% 2	2361
	21st to end	Night	41% 10% 13% 22% 12% 3	1884
March	1st to 10th	Night	37% 15% 11% 21% 14% 2	3473
	11th to 20th	Night	26% 12% 16% 32% 11% 3	3490
	21st to end	Night	44% 13% 10% 19% 12% 2	3828
April	1st to 10th	Night	35% 8% 14% 21% 16% 6%	2049
	11th to 20th	Night	32% 9% 14% 25% 18% 2	1766
	21st to end	Night	33% 8% 14% 26% 19% 1	1710
May	1st to 10th	Night	35% 12% 11% 19% 20% 3	2860
	11th to 20th	Night	18% 9% 13% 31% 24% 6%	2835
	21st to end	Night	23% 11% 10% 29% 25% 2	3110
June	1st to 10th	Night	23% 7% 10% 24% 28% 7%	1553
	11th to 20th	Night	18% 6% 7% 19% 31% 19%	1520
	21st to end	Night	14% 4 6% 15% 27% 35%	1608
July	1st to 10th	Night	16% 4 6% 8% 13% 54%	2815
	11th to 20th	Night	25% 6% 7% 13% 24% 25%	2806
	21st to end	Night	23% 6% 8% 13% 21% 28%	3011
August	1st to 10th	Night	21% 6% 9% 21% 23% 21%	2838
	11th to 20th	Night	24% 7% 7% 15% 27% 21%	2838
	21st to end	Night	15% 4 8% 14% 28% 30%	3225
September	1st to 10th	Night	17% 5% 7% 17% 27% 27%	1996
	11th to 20th	Night	18% 6% 9% 20% 26% 20%	2090
	21st to end	Night	19% 3 6% 19% 37% 17%	2090
October	1st to 10th	Night	16% 4 6% 17% 36% 21%	3676
	11th to 20th	Night	25% 5% 6% 30% 27% 7%	3778
	21st to end	Night	23% 6% 8% 32% 28% 4	4120
November	1st to 10th	Night	29% 8% 13% 25% 21% 5%	2469
	11th to 20th	Night	30% 6% 15% 28% 19% 3	2470
	21st to end	Night	35% 7% 11% 22% 19% 5%	2628
December	1st to 10th	Night	37% 8% 17% 22% 12% 4	2660
	11th to 20th	Night	42% 11% 13% 20% 13% 1	3272
	21st to end	Night	42% 11% 14% 15% 13% 4	4672

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	13% 17% 32% 21% 14% 3	270
	11th to 20th	Day	9% 16% 34% 28% 11% 2	270
	21st to end	Day	7% 20% 30% 30% 11% 1	297
February	1st to 10th	Day	17% 21% 39% 18% 4 1	270
	11th to 20th	Day	13% 22% 37% 20% 6% 2	310
	21st to end	Day	11% 29% 35% 21% 2 1	382
March	1st to 10th	Day	13% 23% 38% 18% 6% 1	460
	11th to 20th	Day	10% 26% 33% 23% 6% 1	460
	21st to end	Day	17% 30% 32% 17% 3	506
April	1st to 10th	Day	15% 26% 29% 20% 7% 3	460
	11th to 20th	Day	17% 30% 30% 16% 6% 2	452
	21st to end	Day	17% 23% 30% 21% 8% 1	460
May	1st to 10th	Day	15% 23% 35% 19% 7% 1	463
	11th to 20th	Day	11% 21% 32% 23% 9% 4	488
	21st to end	Day	11% 20% 31% 23% 11% 4	529
June	1st to 10th	Day	6% 14% 30% 29% 18% 3	642
	11th to 20th	Day	8% 17% 31% 27% 15% 1	680
	21st to end	Day	3 14% 36% 31% 13% 3	582
July	1st to 10th	Day	3 9% 35% 38% 13% 2	486
	11th to 20th	Day	4 9% 38% 31% 13% 5%	484
	21st to end	Day	3 6% 32% 37% 15% 6%	531
August	1st to 10th	Day	4 11% 35% 31% 16% 3	487
	11th to 20th	Day	4 9% 34% 33% 14% 5%	477
	21st to end	Day	4 10% 33% 32% 17% 5%	539
September	1st to 10th	Day	4 12% 29% 31% 15% 9%	490
	11th to 20th	Day	7% 18% 30% 27% 13% 4	490
	21st to end	Day	8% 15% 24% 31% 17% 5%	490
October	1st to 10th	Day	8% 16% 26% 25% 18% 8%	376
	11th to 20th	Day	11% 13% 29% 22% 18% 7%	300
	21st to end	Day	12% 15% 33% 25% 13% 1	330
November	1st to 10th	Day	16% 16% 28% 21% 14% 4	291
	11th to 20th	Day	8% 19% 27% 29% 13% 4	270
	21st to end	Day	8% 12% 26% 33% 17% 6%	270
December	1st to 10th	Day	7% 17% 30% 31% 10% 5%	270
	11th to 20th	Day	6% 14% 37% 33% 10%	270
	21st to end	Day	13% 18% 33% 25% 10% 2	297
January	1st to 10th	Night	8% 8% 31% 33% 17% 3	760
	11th to 20th	Night	9% 8% 29% 38% 13% 3	760
	21st to end	Night	6% 8% 31% 38% 14% 3	836
February	1st to 10th	Night	7% 8% 38% 35% 10% 2	760
	11th to 20th	Night	7% 8% 36% 34% 13% 1	744
	21st to end	Night	7% 9% 36% 38% 10% 1	628
March	1st to 10th	Night	7% 12% 32% 36% 10% 2	760
	11th to 20th	Night	5% 8% 29% 39% 17% 2	760
	21st to end	Night	9% 12% 32% 34% 12% 1	836
April	1st to 10th	Night	12% 13% 26% 35% 13% 1	719
	11th to 20th	Night	9% 11% 32% 37% 10%	563
	21st to end	Night	11% 11% 26% 34% 17% 2	570
May	1st to 10th	Night	7% 9% 31% 36% 15% 1	570
	11th to 20th	Night	6% 6% 21% 40% 24% 3	561
	21st to end	Night	7% 6% 26% 36% 22% 3	617
June	1st to 10th	Night	5% 8% 22% 40% 24% 2	570
	11th to 20th	Night	5% 9% 26% 40% 19% 1	570
	21st to end	Night	1 3 23% 42% 30% 2	570
July	1st to 10th	Night	3 2 14% 41% 37% 3	555
	11th to 20th	Night	4 3 11% 49% 31% 3	552
	21st to end	Night	2 1 10% 39% 46% 2	624
August	1st to 10th	Night	5% 1 15% 46% 32% 1	567
	11th to 20th	Night	4 1 13% 44% 35% 4	564
	21st to end	Night	2 3 15% 43% 35% 2	627
September	1st to 10th	Night	4 3 14% 42% 32% 5%	666
	11th to 20th	Night	5% 4 17% 38% 30% 6%	760
	21st to end	Night	6% 5% 16% 34% 32% 6%	760
October	1st to 10th	Night	8% 7% 22% 38% 23% 3	760
	11th to 20th	Night	6% 5% 23% 39% 23% 4	760
	21st to end	Night	7% 7% 24% 37% 21% 3	836
November	1st to 10th	Night	7% 8% 25% 37% 20% 3	770
	11th to 20th	Night	9% 5% 29% 40% 13% 4	760
	21st to end	Night	6% 8% 30% 36% 16% 3	918
December	1st to 10th	Night	7% 8% 32% 39% 13% 1	950
	11th to 20th	Night	9% 9% 31% 39% 11% 1	950
	21st to end	Night	11% 12% 34% 33% 9% 1	922

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