Devil's Playground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Devil's Playground clear sky chart from 2005-11-06 to 2025-05-11.

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	4 6% 2 6% 4 4 4 3 5% 7% 55%	118039
	Night	4 6% 2 6% 4 4 4 3 5% 7% 54%	119753
Transparency	Day	28% 5% 10% 22% 21% 14%	117794
	Night	30% 5% 12% 23% 19% 11%	119587
Seeing	Day	6% 8% 22% 33% 23% 9%	15231
	Night	6% 4 21% 41% 24% 4	24923

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	3 10% 5% 11% 6% 6% 6% 4 7% 8% 34%	3639
	11th to 20th	Day	4 6% 3 9% 7% 5% 6% 4 5% 7% 44%	3705
	21st to end	Day	4 11% 5% 13% 7% 6% 5% 3 5% 5% 37%	4510
February	1st to 10th	Day	5% 9% 4 10% 6% 8% 6% 6% 7% 7% 32%	1800
	11th to 20th	Day	6% 7% 2 8% 6% 6% 5% 4 5% 10% 40%	1915
	21st to end	Day	3 8% 4 9% 6% 4 5% 5% 6% 9% 41%	1650
March	1st to 10th	Day	5% 11% 3 8% 5% 4 4 3 5% 6% 45%	4619
	11th to 20th	Day	4 7% 2 5% 4 4 5% 4 6% 7% 52%	5000
	21st to end	Day	6% 9% 3 8% 5% 5% 6% 5% 7% 8% 40%	5486
April	1st to 10th	Day	5% 6% 3 5% 5% 5% 5% 4 6% 8% 48%	2310
	11th to 20th	Day	4 7% 2 5% 5% 5% 5% 3 6% 7% 50%	2507
	21st to end	Day	6% 7% 2 5% 4 4 4 3 5% 9% 51%	2600
May	1st to 10th	Day	6% 6% 2 5% 4 4 5% 4 6% 7% 52%	4240
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 8% 62%	4073
	21st to end	Day	4 5% 2 5% 4 4 5% 3 5% 7% 56%	4477
June	1st to 10th	Day	3 4 2 4 5% 5% 5% 4 6% 8% 55%	2589
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 7% 63%	2660
	21st to end	Day	2 2 1 3 2 3 3 3 4 5% 72%	2660
July	1st to 10th	Day	1 2 2 2 2 2 2 4 5% 77%	4420
	11th to 20th	Day	2 2 1 3 3 3 4 4 7% 9% 62%	4406
	21st to end	Day	3 2 1 3 3 3 4 4 6% 7% 64%	4454
August	1st to 10th	Day	3 2 1 3 2 3 3 3 5% 8% 67%	4092
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 6% 71%	4028
	21st to end	Day	2 3 1 3 2 2 2 2 3 5% 74%	4407
September	1st to 10th	Day	3 1 1 3 2 2 3 3 4 6% 72%	2166
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 6% 67%	2090
	21st to end	Day	4 3 1 3 3 2 3 2 3 5% 71%	2090
October	1st to 10th	Day	3 3 1 2 2 3 4 3 4 5% 70%	3463
	11th to 20th	Day	2 3 1 4 2 3 3 3 5% 8% 65%	3150
	21st to end	Day	4 4 1 3 2 3 3 3 5% 7% 64%	3198
November	1st to 10th	Day	6% 6% 2 6% 5% 5% 4 3 6% 8% 49%	1764
	11th to 20th	Day	4 6% 2 5% 4 4 5% 5% 6% 7% 52%	1800
	21st to end	Day	4 9% 2 7% 6% 4 4 3 5% 6% 49%	1800
December	1st to 10th	Day	3 6% 2 6% 4 3 4 2 3 6% 60%	2950
	11th to 20th	Day	5% 9% 4 10% 7% 6% 5% 5% 7% 8% 34%	3317
	21st to end	Day	5% 11% 4 10% 8% 5% 5% 4 5% 7% 36%	4004
January	1st to 10th	Night	4 9% 4 8% 5% 5% 5% 4 6% 8% 44%	6306
	11th to 20th	Night	4 6% 3 7% 6% 7% 8% 4 6% 8% 42%	6254
	21st to end	Night	4 8% 4 12% 7% 5% 4 3 4 5% 44%	6468
February	1st to 10th	Night	6% 8% 3 9% 6% 5% 5% 4 6% 8% 40%	2600
	11th to 20th	Night	5% 8% 3 8% 5% 4 4 3 5% 6% 48%	2368
	21st to end	Night	2 6% 3 8% 5% 5% 5% 4 6% 6% 49%	1980
March	1st to 10th	Night	7% 9% 3 6% 4 5% 5% 4 6% 7% 45%	5275
	11th to 20th	Night	3 8% 2 6% 4 4 4 4 6% 7% 51%	5000
	21st to end	Night	6% 7% 2 7% 4 5% 5% 4 6% 7% 47%	5489
April	1st to 10th	Night	5% 7% 2 6% 5% 4 4 4 5% 6% 53%	2087
	11th to 20th	Night	6% 6% 2 5% 4 3 4 5% 6% 7% 52%	1841
	21st to end	Night	7% 6% 2 5% 4 4 3 3 5% 6% 55%	1800
May	1st to 10th	Night	8% 7% 2 5% 3 4 4 3 5% 6% 55%	2950
	11th to 20th	Night	5% 5% 2 4 3 3 4 3 5% 5% 62%	2838
	21st to end	Night	6% 5% 1 5% 4 5% 5% 4 5% 6% 54%	3110
June	1st to 10th	Night	4 4 1 4 4 5% 4 4 5% 8% 55%	1587
	11th to 20th	Night	4 3 2 4 4 3 3 3 4 7% 62%	1520
	21st to end	Night	2 2 1 3 2 2 3 3 4 6% 71%	1520
July	1st to 10th	Night	3 2 1 2 2 3 3 2 3 4 74%	2540
	11th to 20th	Night	2 3 1 5% 4 4 5% 3 6% 8% 59%	2540
	21st to end	Night	3 3 2 5% 4 3 4 4 5% 6% 62%	3109
August	1st to 10th	Night	3 2 1 4 4 3 4 4 5% 7% 62%	2847
	11th to 20th	Night	2 2 1 4 3 3 4 3 4 5% 69%	2811
	21st to end	Night	3 2 1 3 2 2 3 2 3 5% 75%	3261
September	1st to 10th	Night	2 2 1 4 2 3 3 3 4 6% 71%	2014
	11th to 20th	Night	5% 3 1 2 2 2 3 3 4 6% 68%	2090
	21st to end	Night	6% 3 1 3 3 2 3 1 2 4 73%	2090
October	1st to 10th	Night	3 3 1 2 2 2 3 2 3 4 75%	3516
	11th to 20th	Night	4 5% 2 5% 3 4 4 3 4 5% 60%	3778
	21st to end	Night	3 5% 1 4 4 4 4 3 5% 7% 59%	4355
November	1st to 10th	Night	7% 5% 2 6% 4 3 4 3 6% 7% 53%	2535
	11th to 20th	Night	3 6% 2 6% 3 3 4 4 6% 7% 57%	2600
	21st to end	Night	4 6% 2 6% 5% 4 4 4 6% 7% 53%	2600
December	1st to 10th	Night	3 5% 2 6% 3 3 3 2 4 7% 62%	4240
	11th to 20th	Night	5% 9% 3 7% 5% 5% 5% 4 6% 8% 43%	4882
	21st to end	Night	6% 10% 3 9% 6% 5% 5% 5% 6% 7% 37%	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	48% 7% 20% 17% 8% 1	3639
	11th to 20th	Day	40% 6% 18% 22% 11% 2	3705
	21st to end	Day	51% 5% 11% 20% 13%	4510
February	1st to 10th	Day	48% 8% 17% 17% 7% 3	1800
	11th to 20th	Day	40% 5% 21% 21% 10% 2	1925
	21st to end	Day	38% 6% 18% 25% 11% 2	1650
March	1st to 10th	Day	39% 7% 13% 28% 11% 3	4619
	11th to 20th	Day	29% 5% 12% 34% 18% 2	5000
	21st to end	Day	40% 5% 20% 26% 9% 1	5486
April	1st to 10th	Day	33% 5% 16% 26% 16% 4	2310
	11th to 20th	Day	31% 5% 10% 29% 21% 3	2510
	21st to end	Day	29% 4 12% 29% 23% 3	2600
May	1st to 10th	Day	28% 5% 8% 26% 25% 9%	4240
	11th to 20th	Day	20% 5% 6% 23% 36% 11%	4076
	21st to end	Day	26% 5% 8% 24% 33% 5%	4477
June	1st to 10th	Day	24% 5% 8% 25% 29% 8%	2589
	11th to 20th	Day	21% 5% 7% 18% 30% 21%	2660
	21st to end	Day	13% 4 3 13% 32% 36%	2660
July	1st to 10th	Day	10% 3 2 9% 14% 62%	4351
	11th to 20th	Day	15% 5% 2 8% 22% 48%	4331
	21st to end	Day	16% 5% 4 10% 30% 37%	4314
August	1st to 10th	Day	15% 4 3 13% 28% 37%	4078
	11th to 20th	Day	14% 3 3 14% 33% 32%	4067
	21st to end	Day	14% 3 2 13% 31% 37%	4406
September	1st to 10th	Day	15% 3 4 16% 30% 32%	2166
	11th to 20th	Day	16% 5% 7% 23% 28% 22%	2090
	21st to end	Day	17% 3 6% 21% 37% 16%	2090
October	1st to 10th	Day	17% 3 6% 18% 34% 21%	3463
	11th to 20th	Day	18% 4 7% 29% 35% 8%	3150
	21st to end	Day	20% 4 11% 40% 22% 3	3198
November	1st to 10th	Day	33% 5% 19% 24% 17% 2	1764
	11th to 20th	Day	31% 6% 19% 33% 11% 1	1800
	21st to end	Day	36% 5% 18% 29% 12% 1	1800
December	1st to 10th	Day	28% 4 17% 38% 12% 1	2950
	11th to 20th	Day	48% 4 26% 19% 3	3316
	21st to end	Day	49% 5% 15% 21% 10%	4004
January	1st to 10th	Night	39% 7% 19% 25% 10% 1	6306
	11th to 20th	Night	41% 7% 21% 21% 8% 3	6254
	21st to end	Night	46% 5% 14% 21% 14%	6468
February	1st to 10th	Night	43% 7% 19% 22% 8% 2	2600
	11th to 20th	Night	38% 5% 17% 25% 14% 2	2369
	21st to end	Night	34% 6% 17% 28% 12% 2	1980
March	1st to 10th	Night	37% 5% 14% 26% 14% 3	5275
	11th to 20th	Night	31% 4 12% 31% 21% 1	5000
	21st to end	Night	34% 6% 16% 29% 13% 1	5489
April	1st to 10th	Night	30% 6% 13% 27% 19% 6%	2087
	11th to 20th	Night	29% 5% 10% 27% 24% 5%	1841
	21st to end	Night	30% 4 11% 25% 28% 3	1800
May	1st to 10th	Night	29% 4 6% 25% 29% 6%	2950
	11th to 20th	Night	23% 4 6% 19% 36% 12%	2839
	21st to end	Night	29% 5% 8% 22% 34% 3	3110
June	1st to 10th	Night	25% 4 11% 24% 26% 9%	1587
	11th to 20th	Night	23% 4 7% 20% 29% 18%	1520
	21st to end	Night	15% 3 2 14% 28% 37%	1520
July	1st to 10th	Night	14% 3 3 8% 14% 58%	2500
	11th to 20th	Night	21% 5% 3 6% 21% 45%	2492
	21st to end	Night	22% 4 3 8% 26% 37%	3011
August	1st to 10th	Night	19% 4 3 10% 27% 36%	2838
	11th to 20th	Night	18% 4 3 15% 28% 32%	2838
	21st to end	Night	13% 3 3 12% 25% 44%	3261
September	1st to 10th	Night	16% 4 5% 13% 28% 35%	2014
	11th to 20th	Night	18% 3 7% 16% 28% 27%	2090
	21st to end	Night	18% 2 4 17% 36% 23%	2090
October	1st to 10th	Night	15% 2 4 17% 32% 30%	3516
	11th to 20th	Night	25% 3 4 22% 34% 12%	3778
	21st to end	Night	24% 4 7% 34% 27% 4	4355
November	1st to 10th	Night	29% 4 14% 28% 21% 3	2535
	11th to 20th	Night	26% 4 17% 36% 16% 1	2600
	21st to end	Night	30% 5% 16% 35% 14% 1	2600
December	1st to 10th	Night	25% 4 14% 43% 13% 1	4240
	11th to 20th	Night	41% 6% 26% 23% 4	4882
	21st to end	Night	46% 5% 19% 19% 10% 1	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	9% 8% 24% 31% 21% 8%	200
	11th to 20th	Day	11% 4 21% 32% 21% 12%	214
	21st to end	Day	10% 3 18% 39% 22% 7%	330
February	1st to 10th	Day	9% 8% 30% 35% 14% 5%	300
	11th to 20th	Day	10% 8% 25% 35% 18% 4	460
	21st to end	Day	3 8% 29% 37% 20% 3	414
March	1st to 10th	Day	10% 6% 22% 37% 21% 3	500
	11th to 20th	Day	5% 10% 22% 34% 22% 6%	500
	21st to end	Day	12% 11% 31% 32% 13% 1	550
April	1st to 10th	Day	9% 14% 30% 23% 18% 6%	500
	11th to 20th	Day	10% 16% 28% 29% 12% 5%	492
	21st to end	Day	9% 15% 27% 30% 15% 5%	500
May	1st to 10th	Day	6% 17% 23% 30% 17% 7%	503
	11th to 20th	Day	11% 10% 24% 30% 18% 7%	489
	21st to end	Day	9% 8% 26% 25% 21% 11%	529
June	1st to 10th	Day	5% 9% 21% 29% 25% 11%	490
	11th to 20th	Day	6% 12% 27% 29% 21% 5%	490
	21st to end	Day	3 4 23% 40% 20% 10%	490
July	1st to 10th	Day	2 3 21% 38% 26% 9%	486
	11th to 20th	Day	4 1 20% 38% 31% 6%	484
	21st to end	Day	2 2 15% 34% 35% 11%	531
August	1st to 10th	Day	4 3 18% 37% 27% 10%	487
	11th to 20th	Day	2 3 18% 31% 31% 15%	477
	21st to end	Day	3 3 17% 30% 30% 16%	539
September	1st to 10th	Day	3 4 12% 32% 32% 18%	490
	11th to 20th	Day	3 4 18% 35% 29% 11%	490
	21st to end	Day	6% 4 18% 28% 32% 12%	490
October	1st to 10th	Day	5% 8% 18% 31% 25% 13%	476
	11th to 20th	Day	4 8% 20% 23% 28% 17%	300
	21st to end	Day	7% 9% 19% 37% 22% 5%	330
November	1st to 10th	Day	7% 11% 25% 30% 20% 7%	300
	11th to 20th	Day	5% 6% 22% 41% 20% 6%	300
	21st to end	Day	11% 6% 18% 33% 26% 7%	300
December	1st to 10th	Day	7% 8% 18% 35% 20% 12%	300
	11th to 20th	Day	8% 3 21% 40% 24% 5%	280
	21st to end	Day	5% 9% 21% 35% 24% 7%	220
January	1st to 10th	Night	8% 5% 20% 36% 25% 7%	800
	11th to 20th	Night	8% 4 24% 37% 21% 6%	800
	21st to end	Night	7% 3 21% 37% 26% 5%	880
February	1st to 10th	Night	8% 4 29% 39% 17% 3	800
	11th to 20th	Night	8% 4 24% 43% 19% 2	784
	21st to end	Night	4 5% 28% 41% 19% 3	660
March	1st to 10th	Night	8% 5% 23% 45% 15% 4	800
	11th to 20th	Night	5% 5% 22% 45% 21% 2	800
	21st to end	Night	8% 6% 30% 39% 16% 1	880
April	1st to 10th	Night	7% 10% 26% 36% 19% 2	800
	11th to 20th	Night	6% 9% 30% 39% 13% 3	653
	21st to end	Night	9% 8% 27% 36% 20% 2	600
May	1st to 10th	Night	7% 9% 29% 35% 18% 2	600
	11th to 20th	Night	8% 5% 19% 40% 23% 5%	563
	21st to end	Night	9% 6% 22% 32% 27% 3	617
June	1st to 10th	Night	6% 5% 17% 40% 29% 3	447
	11th to 20th	Night	4 4 26% 42% 23%	380
	21st to end	Night	2 2 19% 46% 27% 3	380
July	1st to 10th	Night	2 2 13% 46% 33% 4	370
	11th to 20th	Night	2 15% 53% 27% 2	368
	21st to end	Night	2 1 10% 48% 36% 3	624
August	1st to 10th	Night	4 2 12% 51% 29% 2	567
	11th to 20th	Night	3 2 15% 46% 32% 2	564
	21st to end	Night	4 3 12% 46% 30% 5%	690
September	1st to 10th	Night	3 2 13% 39% 34% 8%	760
	11th to 20th	Night	5% 2 11% 40% 34% 9%	760
	21st to end	Night	7% 2 13% 35% 32% 11%	760
October	1st to 10th	Night	7% 4 16% 37% 30% 6%	760
	11th to 20th	Night	6% 4 16% 36% 32% 6%	760
	21st to end	Night	4 4 21% 40% 26% 6%	836
November	1st to 10th	Night	8% 4 18% 40% 25% 6%	780
	11th to 20th	Night	6% 5% 21% 44% 20% 5%	800
	21st to end	Night	6% 4 22% 37% 24% 7%	800
December	1st to 10th	Night	8% 4 21% 41% 22% 5%	800
	11th to 20th	Night	10% 3 21% 44% 19% 3	800
	21st to end	Night	10% 5% 24% 45% 14% 2	880

Page generated at 2025-05-08 07:33:55. Version ac07

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