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 2026-09-14.

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 5% 2 5% 4 4 4 4 5% 7% 57%	157725
	Night	4 5% 2 6% 4 4 4 4 5% 7% 55%	150858
Transparency	Day	26% 5% 10% 22% 22% 16%	152486
	Night	29% 4 11% 22% 20% 13%	147099
Seeing	Day	6% 7% 22% 33% 23% 9%	17038
	Night	6% 4 21% 41% 23% 4	26545

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	4 10% 5% 11% 6% 6% 5% 4 6% 7% 36%	4722
	11th to 20th	Day	3 5% 3 7% 5% 4 5% 4 5% 6% 54%	4833
	21st to end	Day	4 9% 4 11% 6% 6% 5% 4 5% 7% 40%	5844
February	1st to 10th	Day	5% 8% 4 10% 6% 8% 6% 6% 7% 7% 34%	1890
	11th to 20th	Day	6% 7% 3 8% 6% 6% 5% 4 5% 10% 40%	2013
	21st to end	Day	3 7% 4 9% 6% 4 5% 5% 6% 9% 42%	1730
March	1st to 10th	Day	5% 11% 3 8% 5% 4 4 3 5% 6% 45%	4721
	11th to 20th	Day	4 7% 2 5% 4 4 5% 4 6% 7% 52%	5110
	21st to end	Day	6% 9% 3 8% 5% 5% 6% 5% 7% 8% 40%	5607
April	1st to 10th	Day	5% 6% 3 5% 5% 5% 5% 4 6% 8% 48%	2425
	11th to 20th	Day	4 7% 2 5% 6% 5% 5% 4 6% 7% 50%	2634
	21st to end	Day	6% 7% 2 5% 4 5% 4 3 5% 9% 51%	2730
May	1st to 10th	Day	4 4 1 4 3 3 4 3 5% 7% 61%	7626
	11th to 20th	Day	6% 6% 2 5% 3 3 4 4 5% 7% 55%	7596
	21st to end	Day	3 4 1 5% 4 4 4 4 5% 7% 59%	8370
June	1st to 10th	Day	3 3 2 4 4 4 5% 4 6% 8% 56%	2861
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 7% 64%	2940
	21st to end	Day	2 2 1 3 2 3 3 3 5% 6% 71%	2940
July	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	8219
	11th to 20th	Day	2 2 1 3 3 3 4 4 7% 8% 63%	8206
	21st to end	Day	3 2 1 3 2 3 3 3 6% 7% 66%	8304
August	1st to 10th	Day	2 1 1 2 2 2 3 3 4 6% 74%	7549
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 7% 66%	7565
	21st to end	Day	3 3 1 4 3 4 4 4 6% 8% 59%	8169
September	1st to 10th	Day	3 2 1 3 2 2 3 3 4 6% 70%	2394
	11th to 20th	Day	2 2 2 3 3 3 3 3 5% 6% 67%	2234
	21st to end	Day	4 3 1 3 3 2 3 2 3 5% 71%	2200
October	1st to 10th	Day	4 3 1 2 2 3 4 3 4 5% 70%	3572
	11th to 20th	Day	2 3 1 4 2 3 3 3 6% 8% 64%	3250
	21st to end	Day	4 4 1 3 3 3 3 3 5% 7% 64%	3300
November	1st to 10th	Day	5% 6% 2 6% 5% 5% 4 3 6% 8% 50%	1854
	11th to 20th	Day	4 6% 2 5% 4 5% 5% 5% 6% 7% 51%	1890
	21st to end	Day	4 9% 2 7% 6% 4 4 3 6% 6% 49%	1890
December	1st to 10th	Day	3 6% 2 6% 4 3 4 2 3 6% 61%	3040
	11th to 20th	Day	5% 9% 4 10% 7% 6% 5% 5% 7% 8% 34%	3405
	21st to end	Day	5% 11% 4 10% 8% 5% 5% 4 5% 7% 36%	4092
January	1st to 10th	Night	5% 10% 4 8% 5% 5% 5% 4 5% 7% 42%	8172
	11th to 20th	Night	3 5% 2 5% 5% 5% 6% 4 5% 6% 54%	8128
	21st to end	Night	3 7% 3 10% 6% 4 3 3 5% 6% 49%	8370
February	1st to 10th	Night	5% 8% 3 9% 6% 5% 5% 4 6% 8% 40%	2730
	11th to 20th	Night	5% 8% 3 8% 6% 4 4 3 5% 6% 47%	2489
	21st to end	Night	2 6% 3 8% 5% 5% 5% 5% 6% 6% 49%	2076
March	1st to 10th	Night	7% 9% 3 6% 4 5% 5% 4 6% 7% 45%	5393
	11th to 20th	Night	3 8% 2 6% 4 4 4 4 6% 7% 52%	5110
	21st to end	Night	6% 7% 2 6% 4 5% 5% 4 6% 7% 47%	5610
April	1st to 10th	Night	5% 6% 2 6% 5% 4 4 4 5% 6% 53%	2191
	11th to 20th	Night	6% 6% 2 5% 4 3 4 5% 6% 7% 52%	1934
	21st to end	Night	7% 6% 2 5% 4 4 3 3 5% 6% 54%	1890
May	1st to 10th	Night	5% 4 1 4 3 3 4 3 5% 5% 63%	5321
	11th to 20th	Night	5% 4 2 5% 4 3 4 3 5% 6% 60%	5296
	21st to end	Night	6% 4 2 6% 4 5% 4 4 5% 6% 54%	5837
June	1st to 10th	Night	4 4 1 4 4 5% 4 4 5% 8% 56%	1753
	11th to 20th	Night	4 3 2 4 4 3 3 3 4 7% 64%	1680
	21st to end	Night	2 2 1 3 2 2 3 3 4 6% 71%	1680
July	1st to 10th	Night	4 2 1 5% 3 4 4 3 4 5% 65%	4740
	11th to 20th	Night	2 3 1 5% 4 4 5% 4 6% 7% 60%	4740
	21st to end	Night	3 3 2 5% 4 4 5% 4 6% 7% 57%	5805
August	1st to 10th	Night	2 2 1 3 3 3 3 3 4 6% 69%	5273
	11th to 20th	Night	4 4 2 6% 4 5% 5% 4 6% 6% 56%	5291
	21st to end	Night	4 3 1 6% 4 5% 5% 4 5% 7% 56%	6055
September	1st to 10th	Night	2 3 1 4 2 3 3 3 4 6% 70%	2226
	11th to 20th	Night	5% 3 1 3 2 2 3 3 4 6% 68%	2233
	21st to end	Night	6% 3 1 3 3 2 3 1 3 4 72%	2200
October	1st to 10th	Night	4 3 1 3 2 2 3 2 3 4 74%	3627
	11th to 20th	Night	4 5% 2 5% 3 4 4 3 4 5% 60%	3898
	21st to end	Night	3 5% 1 4 4 4 4 3 5% 7% 59%	4495
November	1st to 10th	Night	7% 5% 2 6% 4 3 4 3 6% 7% 54%	2665
	11th to 20th	Night	4 6% 2 6% 3 3 4 4 6% 7% 56%	2730
	21st to end	Night	4 6% 2 6% 4 4 4 4 6% 7% 53%	2730
December	1st to 10th	Night	3 6% 2 6% 3 3 3 2 4 7% 61%	4370
	11th to 20th	Night	5% 9% 3 7% 5% 5% 5% 4 6% 9% 43%	5014
	21st to end	Night	6% 10% 3 9% 6% 5% 5% 4 6% 7% 38%	7106

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% 6% 23% 15% 7% 1	4723
	11th to 20th	Day	31% 5% 18% 31% 13% 2	4833
	21st to end	Day	46% 5% 14% 22% 14%	5844
February	1st to 10th	Day	46% 8% 17% 18% 7% 2	1890
	11th to 20th	Day	40% 5% 21% 21% 11% 2	2023
	21st to end	Day	37% 6% 18% 26% 11% 2	1730
March	1st to 10th	Day	39% 7% 13% 28% 11% 3	4721
	11th to 20th	Day	29% 5% 12% 34% 18% 2	5110
	21st to end	Day	40% 5% 19% 25% 9% 1	5607
April	1st to 10th	Day	32% 5% 15% 28% 16% 4	2425
	11th to 20th	Day	32% 5% 9% 28% 22% 3	2637
	21st to end	Day	29% 4 12% 29% 24% 3	2730
May	1st to 10th	Day	21% 4 7% 25% 32% 10%	7626
	11th to 20th	Day	26% 6% 4 19% 33% 12%	7599
	21st to end	Day	22% 5% 5% 24% 37% 8%	8371
June	1st to 10th	Day	23% 5% 8% 24% 31% 10%	2861
	11th to 20th	Day	19% 5% 6% 17% 30% 24%	2940
	21st to end	Day	13% 4 3 13% 33% 34%	2940
July	1st to 10th	Day	15% 4 2 10% 15% 53%	8151
	11th to 20th	Day	15% 5% 2 12% 24% 42%	8131
	21st to end	Day	15% 4 3 11% 28% 38%	8120
August	1st to 10th	Day	13% 4 2 10% 25% 46%	5978
	11th to 20th	Day	19% 4 8% 20% 28% 23%	5964
	21st to end	Day	17% 3 6% 24% 25% 26%	6412
September	1st to 10th	Day	15% 3 4 16% 30% 31%	2394
	11th to 20th	Day	16% 5% 6% 22% 29% 22%	2234
	21st to end	Day	17% 3 6% 21% 37% 15%	2200
October	1st to 10th	Day	17% 3 6% 18% 34% 20%	3572
	11th to 20th	Day	18% 4 6% 30% 34% 8%	3250
	21st to end	Day	20% 4 11% 41% 21% 3	3300
November	1st to 10th	Day	32% 5% 19% 25% 17% 2	1854
	11th to 20th	Day	32% 5% 19% 32% 11% 1	1890
	21st to end	Day	35% 4 18% 29% 12% 1	1890
December	1st to 10th	Day	28% 4 18% 38% 12% 1	3040
	11th to 20th	Day	48% 4 25% 19% 3	3404
	21st to end	Day	49% 5% 15% 21% 10%	4092
January	1st to 10th	Night	42% 6% 20% 23% 8% 1	8172
	11th to 20th	Night	32% 5% 19% 31% 11% 3	8128
	21st to end	Night	39% 4 15% 25% 16%	8370
February	1st to 10th	Night	42% 6% 19% 23% 8% 2	2730
	11th to 20th	Night	39% 5% 16% 25% 14% 2	2490
	21st to end	Night	34% 6% 17% 29% 12% 2	2076
March	1st to 10th	Night	37% 5% 14% 27% 14% 3	5393
	11th to 20th	Night	30% 4 12% 31% 21% 1	5110
	21st to end	Night	34% 5% 16% 29% 14% 2	5610
April	1st to 10th	Night	30% 5% 12% 27% 20% 5%	2191
	11th to 20th	Night	29% 5% 10% 27% 24% 5%	1934
	21st to end	Night	30% 4 11% 24% 29% 3	1890
May	1st to 10th	Night	23% 3 6% 23% 33% 12%	5319
	11th to 20th	Night	25% 4 4 17% 35% 15%	5297
	21st to end	Night	29% 5% 5% 18% 36% 7%	5838
June	1st to 10th	Night	25% 4 10% 22% 27% 11%	1753
	11th to 20th	Night	21% 4 6% 19% 28% 22%	1680
	21st to end	Night	15% 3 2 14% 31% 35%	1680
July	1st to 10th	Night	21% 4 2 8% 17% 48%	4700
	11th to 20th	Night	21% 5% 2 9% 20% 43%	4692
	21st to end	Night	24% 4 4 9% 24% 35%	5677
August	1st to 10th	Night	16% 4 3 9% 22% 47%	4168
	11th to 20th	Night	27% 5% 6% 17% 24% 22%	4168
	21st to end	Night	24% 4 5% 15% 22% 31%	4739
September	1st to 10th	Night	16% 4 5% 13% 28% 34%	2226
	11th to 20th	Night	19% 3 6% 16% 29% 27%	2233
	21st to end	Night	18% 2 4 17% 35% 23%	2200
October	1st to 10th	Night	15% 2 4 17% 32% 29%	3627
	11th to 20th	Night	25% 4 4 22% 33% 11%	3898
	21st to end	Night	24% 4 7% 34% 27% 4	4495
November	1st to 10th	Night	29% 4 14% 28% 21% 3	2665
	11th to 20th	Night	27% 4 17% 35% 15% 1	2730
	21st to end	Night	29% 5% 16% 35% 13% 1	2730
December	1st to 10th	Night	26% 4 15% 42% 13% 1	4370
	11th to 20th	Night	40% 6% 26% 23% 5%	5014
	21st to end	Night	46% 5% 19% 19% 10% 1	7106

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% 32% 20% 8%	220
	11th to 20th	Day	10% 3 19% 33% 22% 13%	236
	21st to end	Day	10% 3 17% 41% 23% 6%	363
February	1st to 10th	Day	8% 8% 28% 35% 15% 6%	330
	11th to 20th	Day	9% 9% 26% 35% 17% 4	498
	21st to end	Day	3 9% 29% 38% 18% 3	446
March	1st to 10th	Day	10% 7% 23% 37% 20% 3	540
	11th to 20th	Day	5% 11% 23% 34% 21% 6%	540
	21st to end	Day	11% 10% 32% 31% 13% 2	594
April	1st to 10th	Day	9% 13% 29% 24% 19% 7%	540
	11th to 20th	Day	10% 16% 28% 29% 12% 5%	532
	21st to end	Day	9% 16% 26% 29% 15% 5%	540
May	1st to 10th	Day	5% 16% 23% 31% 18% 7%	543
	11th to 20th	Day	11% 12% 25% 29% 17% 7%	568
	21st to end	Day	8% 8% 26% 26% 21% 11%	617
June	1st to 10th	Day	4 9% 22% 29% 24% 12%	570
	11th to 20th	Day	5% 11% 26% 31% 21% 5%	570
	21st to end	Day	3 4 24% 40% 19% 9%	570
July	1st to 10th	Day	3 3 21% 38% 27% 9%	566
	11th to 20th	Day	3 2 18% 37% 31% 8%	564
	21st to end	Day	2 2 16% 34% 36% 10%	619
August	1st to 10th	Day	3 2 19% 37% 26% 11%	567
	11th to 20th	Day	2 3 18% 30% 32% 15%	557
	21st to end	Day	4 3 17% 30% 32% 15%	627
September	1st to 10th	Day	2 4 14% 32% 31% 17%	570
	11th to 20th	Day	3 4 19% 34% 29% 11%	543
	21st to end	Day	6% 5% 17% 29% 31% 12%	530
October	1st to 10th	Day	5% 7% 18% 31% 25% 13%	515
	11th to 20th	Day	4 8% 20% 25% 28% 15%	330
	21st to end	Day	7% 9% 19% 35% 24% 6%	363
November	1st to 10th	Day	7% 10% 24% 32% 20% 8%	330
	11th to 20th	Day	5% 6% 21% 40% 22% 6%	330
	21st to end	Day	10% 6% 18% 35% 26% 6%	330
December	1st to 10th	Day	6% 9% 20% 35% 19% 11%	330
	11th to 20th	Day	7% 5% 20% 39% 24% 5%	308
	21st to end	Day	5% 9% 22% 33% 23% 8%	242
January	1st to 10th	Night	8% 5% 20% 36% 24% 6%	840
	11th to 20th	Night	8% 4 23% 37% 22% 6%	840
	21st to end	Night	7% 3 21% 39% 26% 4	924
February	1st to 10th	Night	8% 4 28% 39% 18% 3	840
	11th to 20th	Night	8% 4 24% 43% 19% 2	824
	21st to end	Night	4 5% 28% 42% 18% 3	692
March	1st to 10th	Night	8% 5% 24% 45% 14% 3	840
	11th to 20th	Night	5% 5% 23% 45% 20% 2	840
	21st to end	Night	8% 6% 31% 40% 15% 1	924
April	1st to 10th	Night	7% 9% 26% 36% 20% 2	840
	11th to 20th	Night	6% 9% 31% 39% 13% 2	686
	21st to end	Night	9% 8% 27% 36% 19% 1	630
May	1st to 10th	Night	7% 9% 29% 36% 18% 2	630
	11th to 20th	Night	9% 5% 19% 40% 22% 4	621
	21st to end	Night	9% 6% 23% 32% 26% 3	683
June	1st to 10th	Night	6% 5% 18% 41% 28% 2	493
	11th to 20th	Night	4 4 27% 42% 22%	420
	21st to end	Night	3 2 20% 46% 26% 3	420
July	1st to 10th	Night	2 2 12% 48% 31% 4	410
	11th to 20th	Night	2 1 14% 53% 27% 2	408
	21st to end	Night	3 1 10% 50% 33% 2	690
August	1st to 10th	Night	4 3 13% 52% 27% 1	627
	11th to 20th	Night	3 2 15% 47% 31% 2	624
	21st to end	Night	4 3 12% 48% 29% 5%	763
September	1st to 10th	Night	3 2 14% 41% 33% 8%	840
	11th to 20th	Night	5% 2 12% 39% 33% 8%	812
	21st to end	Night	7% 2 13% 35% 32% 11%	800
October	1st to 10th	Night	7% 4 16% 37% 30% 6%	800
	11th to 20th	Night	6% 5% 17% 36% 31% 6%	800
	21st to end	Night	4 4 21% 40% 26% 6%	880
November	1st to 10th	Night	8% 4 17% 41% 24% 6%	820
	11th to 20th	Night	6% 5% 20% 44% 20% 4	840
	21st to end	Night	6% 4 22% 38% 24% 6%	840
December	1st to 10th	Night	8% 4 21% 41% 21% 4	840
	11th to 20th	Night	10% 3 22% 44% 19% 3	840
	21st to end	Night	10% 6% 25% 44% 14% 2	924

Page generated at 2026-09-11 02:11:57. Version ac07

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