Dark Sky Walker Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dark Sky Walker Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	12% 6% 2 5% 4 4 4 3 5% 7% 46%	100971
	Night	14% 6% 2 5% 3 3 3 3 4 7% 51%	98088
Transparency	Day	37% 5% 10% 21% 18% 9%	100782
	Night	35% 5% 11% 20% 18% 11%	97948
Seeing	Day	14% 8% 24% 31% 19% 4	14786
	Night	16% 8% 26% 35% 14% 1	24687

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% 8% 2 4 3 3 2 3 4 5% 53%	2847
	11th to 20th	Day	16% 6% 2 4 2 2 2 2 4 5% 57%	2850
	21st to end	Day	16% 8% 2 5% 3 2 3 2 4 9% 45%	3437
February	1st to 10th	Day	18% 7% 2 6% 4 4 3 2 4 4 46%	1900
	11th to 20th	Day	17% 8% 3 5% 4 4 4 3 5% 5% 46%	1849
	21st to end	Day	18% 6% 2 4 4 2 2 3 4 5% 50%	1570
March	1st to 10th	Day	16% 8% 2 6% 4 3 4 3 4 5% 44%	3347
	11th to 20th	Day	21% 11% 3 8% 5% 5% 4 3 4 4 33%	3480
	21st to end	Day	16% 7% 2 6% 3 3 3 3 5% 7% 45%	3814
April	1st to 10th	Day	14% 7% 3 7% 4 4 3 3 5% 6% 45%	2090
	11th to 20th	Day	21% 6% 2 6% 3 4 3 3 4 5% 42%	2111
	21st to end	Day	15% 8% 2 6% 6% 4 4 3 4 6% 44%	2384
May	1st to 10th	Day	23% 9% 2 7% 5% 4 4 3 5% 6% 32%	4082
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 5% 7% 43%	4082
	21st to end	Day	11% 7% 2 6% 5% 5% 5% 5% 7% 9% 37%	4477
June	1st to 10th	Day	6% 6% 2 5% 5% 5% 6% 5% 6% 9% 47%	2470
	11th to 20th	Day	8% 6% 2 6% 5% 4 5% 5% 6% 8% 45%	2470
	21st to end	Day	8% 6% 2 7% 6% 6% 6% 5% 7% 9% 38%	2470
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	4120
	11th to 20th	Day	5% 4 2 5% 4 5% 6% 4 7% 11% 48%	4120
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 6% 11% 38%	4465
August	1st to 10th	Day	1 1 1 2 3 3 3 3 5% 8% 69%	3978
	11th to 20th	Day	3 3 1 3 3 4 3 3 6% 11% 58%	3726
	21st to end	Day	4 4 2 7% 4 5% 5% 4 7% 11% 46%	4054
September	1st to 10th	Day	11% 7% 3 7% 5% 4 5% 3 5% 6% 43%	2090
	11th to 20th	Day	12% 6% 2 7% 4 5% 6% 4 7% 9% 39%	2090
	21st to end	Day	8% 5% 3 6% 4 4 4 3 7% 7% 49%	2090
October	1st to 10th	Day	7% 4 2 5% 3 4 5% 3 5% 6% 55%	2090
	11th to 20th	Day	12% 6% 2 4 4 3 4 3 5% 6% 51%	2000
	21st to end	Day	12% 4 2 4 4 3 3 2 4 5% 57%	2090
November	1st to 10th	Day	14% 7% 3 6% 4 4 4 4 5% 6% 44%	1868
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 5% 48%	1744
	21st to end	Day	17% 8% 3 5% 4 3 3 2 5% 5% 45%	1710
December	1st to 10th	Day	14% 7% 2 6% 3 3 2 3 4 6% 48%	1710
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 4 4 45%	2161
	21st to end	Day	16% 6% 2 4 2 2 2 2 3 4 56%	3135
January	1st to 10th	Night	18% 6% 3 4 2 2 2 2 3 6% 52%	4108
	11th to 20th	Night	13% 4 1 3 2 2 2 2 2 4 65%	4120
	21st to end	Night	19% 7% 2 6% 4 3 3 3 4 6% 43%	4244
February	1st to 10th	Night	17% 8% 2 5% 3 3 3 2 4 5% 49%	2280
	11th to 20th	Night	18% 8% 2 5% 3 3 2 2 3 5% 50%	2218
	21st to end	Night	20% 6% 1 4 3 3 3 3 4 5% 47%	1884
March	1st to 10th	Night	17% 9% 2 6% 4 3 4 3 4 6% 42%	3497
	11th to 20th	Night	23% 12% 3 7% 4 4 3 2 4 5% 35%	3480
	21st to end	Night	18% 7% 2 5% 3 3 3 3 4 5% 45%	3817
April	1st to 10th	Night	13% 7% 2 5% 4 3 4 3 5% 7% 47%	2090
	11th to 20th	Night	19% 7% 3 5% 4 3 3 3 4 6% 45%	2014
	21st to end	Night	20% 7% 2 5% 4 3 3 2 4 4 47%	1796
May	1st to 10th	Night	27% 9% 2 5% 3 3 3 2 4 5% 37%	2823
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 6% 50%	2823
	21st to end	Night	15% 6% 2 5% 3 4 4 3 5% 8% 44%	3090
June	1st to 10th	Night	6% 4 2 4 2 3 3 3 5% 8% 59%	1710
	11th to 20th	Night	5% 4 1 4 4 4 4 3 5% 8% 58%	1710
	21st to end	Night	8% 5% 2 4 5% 3 5% 3 6% 10% 50%	1710
July	1st to 10th	Night	6% 5% 1 4 3 3 4 4 6% 9% 54%	2850
	11th to 20th	Night	4 3 2 4 4 4 5% 5% 7% 10% 53%	2850
	21st to end	Night	11% 8% 3 6% 4 4 4 4 6% 9% 41%	3098
August	1st to 10th	Night	1 1 1 2 2 2 3 2 4 8% 73%	2956
	11th to 20th	Night	3 3 1 3 3 4 4 3 6% 12% 60%	3113
	21st to end	Night	5% 5% 1 4 4 3 4 4 6% 10% 53%	3606
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 6% 7% 49%	2090
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 9% 45%	2090
	21st to end	Night	9% 5% 2 5% 4 3 4 4 6% 8% 52%	2090
October	1st to 10th	Night	6% 4 2 4 3 3 3 3 5% 7% 60%	2090
	11th to 20th	Night	13% 5% 1 5% 4 3 4 3 4 5% 54%	2160
	21st to end	Night	14% 4 1 4 2 2 2 2 3 4 61%	2508
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 2 3 5% 53%	2233
	11th to 20th	Night	11% 6% 1 5% 3 3 3 3 4 6% 54%	2432
	21st to end	Night	19% 7% 2 4 2 3 3 3 4 7% 46%	2470
December	1st to 10th	Night	15% 6% 2 4 3 3 3 3 4 6% 51%	2470
	11th to 20th	Night	17% 7% 3 6% 4 3 3 2 3 4 47%	3036
	21st to end	Night	18% 6% 2 3 2 2 2 2 3 5% 54%	4532

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	35% 2 4 16% 25% 17%	2848
	11th to 20th	Day	33% 2 6% 13% 29% 17%	2850
	21st to end	Day	39% 3 7% 12% 29% 11%	3437
February	1st to 10th	Day	43% 3 5% 12% 20% 16%	1900
	11th to 20th	Day	42% 3 6% 17% 18% 14%	1859
	21st to end	Day	38% 4 6% 17% 20% 16%	1570
March	1st to 10th	Day	43% 4 6% 14% 22% 12%	3347
	11th to 20th	Day	55% 4 6% 9% 15% 10%	3480
	21st to end	Day	38% 4 10% 15% 19% 13%	3814
April	1st to 10th	Day	42% 4 8% 17% 17% 12%	2090
	11th to 20th	Day	44% 5% 7% 16% 18% 11%	2111
	21st to end	Day	43% 5% 5% 19% 18% 10%	2384
May	1st to 10th	Day	52% 5% 9% 13% 14% 6%	4120
	11th to 20th	Day	41% 6% 9% 18% 20% 7%	4086
	21st to end	Day	39% 9% 11% 29% 11% 2	4489
June	1st to 10th	Day	32% 8% 11% 25% 20% 3	2470
	11th to 20th	Day	35% 7% 10% 25% 19% 4	2470
	21st to end	Day	40% 9% 10% 23% 14% 4	2470
July	1st to 10th	Day	34% 6% 16% 37% 6% 1	4056
	11th to 20th	Day	29% 6% 18% 30% 15% 2	4051
	21st to end	Day	37% 6% 18% 29% 9%	4325
August	1st to 10th	Day	15% 4 11% 44% 26%	3964
	11th to 20th	Day	21% 4 24% 38% 11% 2	3762
	21st to end	Day	31% 7% 18% 24% 18% 2	4053
September	1st to 10th	Day	41% 7% 10% 18% 16% 8%	2090
	11th to 20th	Day	39% 9% 11% 18% 18% 5%	2090
	21st to end	Day	32% 7% 9% 22% 17% 13%	2090
October	1st to 10th	Day	29% 5% 10% 19% 24% 12%	2090
	11th to 20th	Day	34% 5% 9% 15% 19% 17%	2000
	21st to end	Day	30% 5% 5% 15% 26% 19%	2090
November	1st to 10th	Day	41% 4 8% 19% 17% 11%	1868
	11th to 20th	Day	38% 4 7% 16% 21% 14%	1744
	21st to end	Day	42% 4 6% 14% 20% 14%	1710
December	1st to 10th	Day	39% 3 7% 20% 21% 9%	1710
	11th to 20th	Day	42% 4 7% 9% 20% 17%	2159
	21st to end	Day	34% 3 5% 14% 28% 16%	3135
January	1st to 10th	Night	36% 3 5% 13% 23% 21%	4108
	11th to 20th	Night	26% 2 4 17% 27% 23%	4120
	21st to end	Night	43% 3 5% 11% 25% 13%	4244
February	1st to 10th	Night	40% 3 6% 12% 21% 18%	2280
	11th to 20th	Night	40% 2 6% 16% 20% 17%	2218
	21st to end	Night	40% 4 6% 14% 19% 17%	1884
March	1st to 10th	Night	44% 3 8% 14% 19% 11%	3497
	11th to 20th	Night	53% 4 8% 10% 14% 11%	3480
	21st to end	Night	40% 3 11% 15% 18% 12%	3817
April	1st to 10th	Night	38% 4 10% 18% 15% 15%	2090
	11th to 20th	Night	42% 5% 8% 14% 17% 15%	2014
	21st to end	Night	42% 4 8% 19% 17% 10%	1796
May	1st to 10th	Night	50% 4 8% 16% 12% 9%	2850
	11th to 20th	Night	35% 7% 10% 21% 19% 8%	2824
	21st to end	Night	38% 6% 14% 27% 11% 4	3099
June	1st to 10th	Night	23% 6% 17% 31% 21% 3	1710
	11th to 20th	Night	25% 5% 14% 30% 21% 5%	1710
	21st to end	Night	30% 7% 17% 27% 16% 3	1710
July	1st to 10th	Night	25% 7% 25% 36% 5% 1	2805
	11th to 20th	Night	25% 7% 21% 30% 15% 1	2796
	21st to end	Night	38% 6% 22% 26% 7% 1	2999
August	1st to 10th	Night	12% 4 16% 46% 22%	2946
	11th to 20th	Night	19% 6% 31% 34% 9% 2	3143
	21st to end	Night	26% 11% 20% 25% 16% 2	3606
September	1st to 10th	Night	34% 7% 15% 20% 17% 8%	2090
	11th to 20th	Night	36% 8% 15% 21% 15% 5%	2090
	21st to end	Night	30% 7% 12% 21% 18% 12%	2090
October	1st to 10th	Night	25% 5% 13% 22% 21% 14%	2090
	11th to 20th	Night	32% 5% 9% 16% 21% 18%	2160
	21st to end	Night	30% 2 6% 16% 25% 21%	2508
November	1st to 10th	Night	35% 4 8% 19% 21% 13%	2233
	11th to 20th	Night	33% 4 9% 18% 20% 16%	2432
	21st to end	Night	39% 4 8% 16% 20% 14%	2470
December	1st to 10th	Night	35% 4 8% 19% 21% 13%	2470
	11th to 20th	Night	43% 3 5% 11% 19% 19%	3037
	21st to end	Night	36% 3 5% 13% 28% 15%	4532

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% 18% 35% 20% 4	270
	11th to 20th	Day	28% 14% 30% 21% 6% 1	270
	21st to end	Day	19% 18% 37% 21% 6%	297
February	1st to 10th	Day	29% 18% 28% 22% 3	270
	11th to 20th	Day	27% 21% 36% 12% 3	270
	21st to end	Day	25% 19% 44% 11% 1	225
March	1st to 10th	Day	23% 19% 40% 17% 1	270
	11th to 20th	Day	20% 20% 41% 14% 5%	270
	21st to end	Day	22% 18% 41% 15% 3 1	297
April	1st to 10th	Day	20% 19% 43% 16% 2	270
	11th to 20th	Day	24% 17% 35% 20% 4	309
	21st to end	Day	19% 16% 39% 22% 4	564
May	1st to 10th	Day	21% 13% 35% 25% 5%	653
	11th to 20th	Day	20% 8% 31% 33% 6% 2	675
	21st to end	Day	18% 7% 31% 32% 12% 1	734
June	1st to 10th	Day	8% 4 19% 43% 23% 3	680
	11th to 20th	Day	8% 2 22% 48% 18% 3	680
	21st to end	Day	9% 5% 14% 39% 29% 5%	680
July	1st to 10th	Day	10% 2 14% 35% 30% 8%	671
	11th to 20th	Day	7% 7% 40% 42% 5%	668
	21st to end	Day	5% 2 8% 37% 40% 7%	739
August	1st to 10th	Day	3 1 4 43% 39% 10%	602
	11th to 20th	Day	6% 2 5% 41% 38% 8%	477
	21st to end	Day	4 2 8% 32% 40% 14%	465
September	1st to 10th	Day	12% 3 9% 29% 37% 9%	300
	11th to 20th	Day	7% 1 6% 33% 42% 11%	300
	21st to end	Day	6% 3 10% 36% 35% 9%	300
October	1st to 10th	Day	6% 2 17% 40% 30% 6%	300
	11th to 20th	Day	9% 4 24% 42% 17% 3	300
	21st to end	Day	19% 13% 27% 23% 15% 3	330
November	1st to 10th	Day	18% 7% 31% 30% 12% 3	273
	11th to 20th	Day	23% 10% 29% 26% 10% 3	270
	21st to end	Day	27% 17% 31% 15% 7% 1	270
December	1st to 10th	Day	17% 9% 36% 27% 9% 2	270
	11th to 20th	Day	22% 17% 33% 22% 6%	270
	21st to end	Day	22% 12% 37% 22% 5% 1	297
January	1st to 10th	Night	20% 10% 30% 31% 8%	950
	11th to 20th	Night	21% 12% 31% 29% 6%	950
	21st to end	Night	22% 11% 30% 30% 6%	874
February	1st to 10th	Night	24% 14% 31% 25% 6%	760
	11th to 20th	Night	28% 13% 31% 25% 3	744
	21st to end	Night	26% 14% 39% 20% 1	628
March	1st to 10th	Night	23% 12% 37% 25% 3	626
	11th to 20th	Night	25% 9% 38% 25% 4	570
	21st to end	Night	19% 13% 42% 23% 3	627
April	1st to 10th	Night	16% 14% 39% 27% 4	570
	11th to 20th	Night	21% 14% 39% 23% 2	563
	21st to end	Night	22% 9% 42% 21% 6% 1	570
May	1st to 10th	Night	20% 11% 40% 26% 4	570
	11th to 20th	Night	16% 8% 37% 32% 7%	561
	21st to end	Night	15% 8% 34% 34% 9%	617
June	1st to 10th	Night	8% 2 26% 44% 18% 1	570
	11th to 20th	Night	6% 2 34% 47% 10% 1	570
	21st to end	Night	8% 2 20% 46% 22% 3	570
July	1st to 10th	Night	11% 2 14% 44% 26% 2	555
	11th to 20th	Night	4 1 12% 56% 26% 2	552
	21st to end	Night	7% 1 10% 53% 26% 3	624
August	1st to 10th	Night	1 1 10% 54% 31% 2	567
	11th to 20th	Night	5% 1 8% 54% 28% 3	564
	21st to end	Night	7% 2 6% 46% 33% 6%	627
September	1st to 10th	Night	11% 1 10% 43% 32% 5%	570
	11th to 20th	Night	13% 1 8% 43% 31% 4	570
	21st to end	Night	11% 1 11% 40% 33% 4	570
October	1st to 10th	Night	8% 2 12% 48% 25% 4	570
	11th to 20th	Night	14% 4 21% 39% 19% 2	640
	21st to end	Night	16% 9% 24% 29% 21% 2	836
November	1st to 10th	Night	15% 7% 21% 39% 17% 2	745
	11th to 20th	Night	15% 8% 26% 35% 14% 1	912
	21st to end	Night	22% 12% 26% 29% 11% 1	950
December	1st to 10th	Night	19% 9% 28% 34% 9% 1	950
	11th to 20th	Night	24% 11% 28% 30% 7%	950
	21st to end	Night	20% 10% 28% 34% 7%	1045

Page generated at 2024-10-30 00:22:54. Version ac07

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