South Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Park Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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 5% 2 6% 4 4 5% 4 6% 8% 51%	147077
	Night	2 5% 2 5% 3 3 4 3 5% 7% 60%	143489
Transparency	Day	26% 8% 13% 23% 22% 9%	142025
	Night	21% 6% 14% 27% 25% 8%	139550
Seeing	Day	7% 17% 26% 28% 16% 5%	17909
	Night	4 9% 32% 39% 14% 2	27907

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 2 8% 4 3 4 3 5% 8% 61%	4720
	11th to 20th	Day	1 1 4 4 4 4 4 6% 7% 66%	5135
	21st to end	Day	2 2 6% 3 4 4 3 6% 8% 61%	5844
February	1st to 10th	Day	3 3 5% 3 4 3 4 7% 8% 61%	1890
	11th to 20th	Day	3 1 4 4 3 4 4 6% 9% 62%	1990
	21st to end	Day	3 2 6% 4 5% 4 4 6% 8% 60%	1730
March	1st to 10th	Day	4 3 7% 4 3 4 3 5% 7% 59%	4683
	11th to 20th	Day	1 6% 3 9% 5% 5% 5% 4 7% 10% 45%	5110
	21st to end	Day	1 5% 2 6% 5% 4 5% 4 7% 11% 51%	5866
April	1st to 10th	Day	1 5% 2 5% 3 4 4 4 8% 9% 55%	2520
	11th to 20th	Day	3 8% 3 6% 6% 4 5% 3 6% 8% 48%	2491
	21st to end	Day	3 7% 3 6% 5% 5% 5% 5% 7% 9% 46%	2520
May	1st to 10th	Day	4 11% 3 9% 5% 5% 6% 5% 7% 8% 38%	7311
	11th to 20th	Day	5% 6% 2 7% 5% 5% 5% 5% 7% 8% 44%	8191
	21st to end	Day	3 6% 2 6% 5% 5% 6% 5% 8% 9% 45%	9026
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 5% 8% 9% 47%	2940
	11th to 20th	Day	5% 4 1 4 4 4 5% 4 6% 8% 55%	2940
	21st to end	Day	4 4 2 4 5% 5% 6% 5% 7% 8% 51%	2940
July	1st to 10th	Day	4 4 2 5% 4 5% 6% 5% 7% 7% 52%	6479
	11th to 20th	Day	5% 5% 2 6% 6% 6% 7% 6% 8% 10% 38%	6480
	21st to end	Day	7% 6% 2 8% 6% 6% 6% 5% 6% 8% 39%	6683
August	1st to 10th	Day	7% 6% 2 8% 6% 7% 7% 6% 8% 11% 33%	5779
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 8% 9% 44%	5417
	21st to end	Day	6% 7% 3 8% 6% 6% 6% 5% 7% 9% 37%	5984
September	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 4 5% 6% 52%	2400
	11th to 20th	Day	6% 4 1 6% 4 4 5% 3 5% 7% 56%	2400
	21st to end	Day	6% 4 1 4 3 4 3 3 5% 6% 62%	2170
October	1st to 10th	Day	3 3 1 3 3 3 3 3 3 5% 69%	3270
	11th to 20th	Day	3 5% 1 4 4 4 5% 4 6% 9% 54%	3250
	21st to end	Day	2 3 1 3 2 2 3 3 4 7% 70%	3524
November	1st to 10th	Day	1 3 1 3 2 2 3 2 4 6% 73%	1853
	11th to 20th	Day	3 1 2 2 2 2 2 4 8% 73%	1890
	21st to end	Day	3 2 4 2 3 3 3 5% 8% 66%	1753
December	1st to 10th	Day	2 2 5% 2 2 3 2 3 6% 73%	2700
	11th to 20th	Day	2 1 3 2 3 3 3 5% 9% 69%	3106
	21st to end	Day	2 2 5% 3 3 4 3 6% 11% 59%	4092
January	1st to 10th	Night	2 3 8% 4 3 4 3 4 7% 61%	8201
	11th to 20th	Night	1 3 4 3 3 3 5% 6% 72%	7913
	21st to end	Night	4 2 6% 3 3 3 3 4 6% 67%	8370
February	1st to 10th	Night	2 2 5% 3 3 4 3 4 8% 67%	2730
	11th to 20th	Night	1 3 2 6% 3 3 3 3 5% 7% 64%	2515
	21st to end	Night	4 2 5% 3 2 3 2 5% 7% 66%	2076
March	1st to 10th	Night	6% 3 6% 3 4 3 3 4 7% 60%	5409
	11th to 20th	Night	1 7% 4 7% 3 3 3 3 5% 7% 57%	5110
	21st to end	Night	1 5% 2 5% 4 3 4 4 6% 8% 59%	5337
April	1st to 10th	Night	1 5% 2 4 2 3 4 3 4 8% 64%	2100
	11th to 20th	Night	3 8% 3 5% 3 3 3 4 5% 7% 56%	2077
	21st to end	Night	4 9% 2 6% 4 4 3 2 5% 7% 56%	2100
May	1st to 10th	Night	4 12% 4 6% 4 4 5% 4 5% 7% 45%	5628
	11th to 20th	Night	6% 8% 3 6% 3 3 4 4 5% 7% 52%	4701
	21st to end	Night	7% 9% 3 6% 4 3 4 2 5% 7% 51%	5181
June	1st to 10th	Night	4 5% 1 4 3 3 3 3 5% 9% 61%	1680
	11th to 20th	Night	5% 2 1 3 2 3 3 3 5% 7% 66%	1680
	21st to end	Night	4 4 1 3 3 3 4 4 6% 10% 59%	1680
July	1st to 10th	Night	3 5% 2 4 4 3 4 4 6% 7% 57%	3720
	11th to 20th	Night	2 4 1 4 4 5% 6% 5% 9% 11% 49%	3720
	21st to end	Night	4 5% 2 5% 4 5% 5% 6% 8% 10% 46%	4407
August	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 7% 11% 48%	4033
	11th to 20th	Night	3 4 2 4 4 4 6% 6% 8% 10% 49%	4430
	21st to end	Night	7% 7% 3 8% 6% 6% 6% 5% 7% 8% 37%	4993
September	1st to 10th	Night	5% 4 1 4 3 4 4 4 6% 8% 55%	2000
	11th to 20th	Night	6% 4 1 4 3 3 5% 3 5% 7% 59%	2000
	21st to end	Night	6% 5% 2 4 3 3 3 2 4 6% 63%	2223
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 4 73%	3920
	11th to 20th	Night	3 5% 2 4 3 3 3 3 4 6% 64%	3898
	21st to end	Night	2 3 1 3 2 2 2 2 4 6% 73%	4252
November	1st to 10th	Night	1 3 1 2 2 2 3 3 3 6% 73%	2655
	11th to 20th	Night	2 1 2 2 2 3 2 4 7% 74%	2730
	21st to end	Night	1 5% 1 4 2 2 3 3 5% 7% 66%	2861
December	1st to 10th	Night	2 1 3 2 2 2 2 3 6% 78%	4710
	11th to 20th	Night	2 1 3 2 2 3 2 5% 7% 72%	5321
	21st to end	Night	4 2 5% 4 4 4 3 6% 9% 59%	7128

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	22% 4 13% 31% 23% 7%	4723
	11th to 20th	Day	14% 4 19% 25% 28% 10%	5135
	21st to end	Day	19% 5% 10% 28% 26% 13%	5844
February	1st to 10th	Day	22% 4 18% 27% 20% 9%	1890
	11th to 20th	Day	18% 6% 13% 28% 29% 7%	2000
	21st to end	Day	21% 5% 13% 21% 28% 12%	1730
March	1st to 10th	Day	20% 5% 10% 18% 31% 15%	4683
	11th to 20th	Day	29% 10% 10% 27% 20% 4	5110
	21st to end	Day	22% 9% 15% 36% 15% 2	5866
April	1st to 10th	Day	25% 7% 14% 23% 22% 8%	2520
	11th to 20th	Day	33% 7% 13% 21% 21% 5%	2494
	21st to end	Day	33% 9% 12% 27% 18% 3	2520
May	1st to 10th	Day	35% 10% 15% 20% 17% 3	7311
	11th to 20th	Day	31% 10% 13% 21% 21% 5%	8195
	21st to end	Day	28% 9% 14% 20% 23% 5%	9027
June	1st to 10th	Day	30% 10% 14% 19% 21% 7%	2940
	11th to 20th	Day	26% 7% 9% 19% 23% 16%	2940
	21st to end	Day	28% 8% 9% 20% 21% 13%	2940
July	1st to 10th	Day	23% 9% 10% 14% 18% 25%	6411
	11th to 20th	Day	32% 12% 15% 20% 14% 7%	6405
	21st to end	Day	38% 10% 14% 13% 13% 11%	6495
August	1st to 10th	Day	41% 12% 17% 13% 12% 4	4208
	11th to 20th	Day	34% 11% 14% 14% 19% 8%	3921
	21st to end	Day	33% 9% 14% 16% 20% 8%	4311
September	1st to 10th	Day	31% 6% 11% 17% 22% 13%	2400
	11th to 20th	Day	27% 6% 12% 19% 27% 10%	2400
	21st to end	Day	24% 5% 7% 23% 32% 8%	2170
October	1st to 10th	Day	18% 5% 7% 19% 34% 18%	3270
	11th to 20th	Day	23% 7% 10% 28% 25% 6%	3250
	21st to end	Day	15% 4 7% 31% 37% 6%	3524
November	1st to 10th	Day	14% 4 12% 24% 36% 10%	1853
	11th to 20th	Day	12% 4 10% 36% 28% 9%	1890
	21st to end	Day	17% 4 12% 30% 26% 11%	1753
December	1st to 10th	Day	14% 5% 10% 36% 26% 9%	2700
	11th to 20th	Day	14% 4 15% 36% 27% 5%	3104
	21st to end	Day	18% 5% 12% 28% 29% 9%	4092
January	1st to 10th	Night	22% 4 10% 33% 25% 5%	8202
	11th to 20th	Night	12% 5% 15% 29% 25% 15%	7913
	21st to end	Night	18% 4 11% 22% 31% 13%	8370
February	1st to 10th	Night	17% 4 15% 33% 23% 7%	2730
	11th to 20th	Night	19% 5% 13% 30% 27% 6%	2515
	21st to end	Night	19% 3 10% 28% 30% 11%	2076
March	1st to 10th	Night	22% 4 9% 19% 36% 10%	5409
	11th to 20th	Night	25% 6% 10% 23% 29% 7%	5110
	21st to end	Night	21% 6% 20% 37% 13% 2	5337
April	1st to 10th	Night	19% 5% 15% 31% 24% 5%	2100
	11th to 20th	Night	28% 5% 12% 30% 21% 4	2077
	21st to end	Night	29% 6% 13% 30% 19% 2	2100
May	1st to 10th	Night	31% 10% 16% 27% 13% 4	5626
	11th to 20th	Night	28% 8% 17% 24% 22% 2	4702
	21st to end	Night	31% 7% 15% 20% 24% 3	5182
June	1st to 10th	Night	21% 6% 19% 28% 16% 9%	1680
	11th to 20th	Night	17% 6% 13% 22% 25% 16%	1680
	21st to end	Night	21% 7% 13% 24% 22% 13%	1680
July	1st to 10th	Night	23% 8% 11% 19% 23% 17%	3680
	11th to 20th	Night	22% 10% 24% 26% 13% 5%	3672
	21st to end	Night	27% 11% 24% 20% 8% 10%	4283
August	1st to 10th	Night	33% 12% 22% 18% 11% 4	2928
	11th to 20th	Night	25% 11% 22% 17% 19% 6%	3202
	21st to end	Night	32% 11% 17% 19% 18% 3	3597
September	1st to 10th	Night	25% 8% 13% 24% 22% 9%	2000
	11th to 20th	Night	24% 6% 15% 22% 21% 12%	2000
	21st to end	Night	23% 5% 9% 28% 28% 7%	2223
October	1st to 10th	Night	16% 5% 9% 25% 34% 12%	3920
	11th to 20th	Night	18% 7% 14% 31% 24% 7%	3898
	21st to end	Night	13% 3 8% 30% 38% 8%	4252
November	1st to 10th	Night	14% 4 11% 27% 34% 10%	2655
	11th to 20th	Night	11% 4 11% 35% 30% 8%	2730
	21st to end	Night	17% 4 12% 30% 27% 9%	2861
December	1st to 10th	Night	11% 3 11% 37% 32% 6%	4710
	11th to 20th	Night	12% 4 12% 34% 34% 4	5322
	21st to end	Night	21% 5% 14% 25% 28% 7%	7128

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	4 22% 29% 33% 9% 4	330
	11th to 20th	Day	9% 23% 33% 27% 7% 2	330
	21st to end	Day	2 21% 37% 29% 9% 2	363
February	1st to 10th	Day	2 38% 33% 23% 2 2	330
	11th to 20th	Day	3 34% 32% 25% 5% 1	330
	21st to end	Day	8% 30% 33% 24% 4	273
March	1st to 10th	Day	3 26% 32% 26% 12% 1	361
	11th to 20th	Day	8% 24% 33% 24% 10%	540
	21st to end	Day	6% 31% 35% 21% 7% 1	594
April	1st to 10th	Day	6% 27% 34% 24% 7% 1	540
	11th to 20th	Day	11% 36% 29% 17% 7% 2	532
	21st to end	Day	10% 26% 33% 23% 7% 1	540
May	1st to 10th	Day	10% 23% 31% 24% 10% 3	596
	11th to 20th	Day	9% 16% 25% 32% 14% 4	775
	21st to end	Day	9% 16% 21% 31% 19% 3	844
June	1st to 10th	Day	6% 13% 23% 28% 22% 7%	780
	11th to 20th	Day	7% 13% 24% 34% 17% 4	780
	21st to end	Day	5% 11% 26% 31% 20% 7%	780
July	1st to 10th	Day	7% 5% 14% 34% 29% 10%	771
	11th to 20th	Day	7% 3 11% 32% 36% 11%	768
	21st to end	Day	9% 4 16% 26% 33% 10%	689
August	1st to 10th	Day	12% 5% 21% 31% 22% 9%	527
	11th to 20th	Day	9% 6% 20% 33% 21% 11%	517
	21st to end	Day	11% 7% 21% 25% 26% 10%	583
September	1st to 10th	Day	10% 7% 22% 29% 25% 8%	530
	11th to 20th	Day	6% 9% 27% 31% 21% 5%	530
	21st to end	Day	6% 11% 18% 31% 22% 11%	340
October	1st to 10th	Day	6% 15% 22% 23% 24% 10%	330
	11th to 20th	Day	9% 19% 23% 30% 15% 4	330
	21st to end	Day	8% 18% 27% 33% 13% 2	363
November	1st to 10th	Day	6% 20% 32% 26% 11% 4	330
	11th to 20th	Day	6% 18% 29% 34% 11% 3	330
	21st to end	Day	4 17% 37% 32% 8% 2	330
December	1st to 10th	Day	7% 21% 31% 30% 8% 4	330
	11th to 20th	Day	7% 20% 37% 28% 6% 2	330
	21st to end	Day	8% 23% 34% 25% 8% 2	363
January	1st to 10th	Night	1 14% 41% 33% 10% 2	1050
	11th to 20th	Night	2 18% 40% 32% 7% 1	934
	21st to end	Night	2 10% 43% 37% 7% 1	924
February	1st to 10th	Night	12% 51% 30% 5%	840
	11th to 20th	Night	2 14% 46% 31% 6%	824
	21st to end	Night	2 10% 48% 38% 2	692
March	1st to 10th	Night	2 11% 40% 40% 6% 1	840
	11th to 20th	Night	3 8% 40% 40% 8% 1	840
	21st to end	Night	4 9% 45% 37% 4	806
April	1st to 10th	Night	4 13% 43% 37% 4	630
	11th to 20th	Night	6% 11% 41% 34% 8% 1	623
	21st to end	Night	8% 9% 35% 39% 8%	630
May	1st to 10th	Night	9% 8% 32% 38% 11% 1	630
	11th to 20th	Night	10% 6% 21% 47% 14% 2	621
	21st to end	Night	9% 6% 24% 41% 17% 2	683
June	1st to 10th	Night	5% 4 20% 46% 23% 2	630
	11th to 20th	Night	5% 4 27% 50% 13% 2	630
	21st to end	Night	5% 2 22% 44% 25% 3	630
July	1st to 10th	Night	6% 2 10% 42% 35% 4	615
	11th to 20th	Night	4 1 5% 45% 42% 4	612
	21st to end	Night	6% 1 6% 38% 44% 4	687
August	1st to 10th	Night	9% 2 8% 41% 36% 4	597
	11th to 20th	Night	6% 2 8% 46% 33% 5%	594
	21st to end	Night	8% 2 9% 42% 34% 4	660
September	1st to 10th	Night	5% 2 11% 50% 26% 5%	600
	11th to 20th	Night	7% 1 18% 48% 24% 3	600
	21st to end	Night	7% 4 24% 43% 18% 4	635
October	1st to 10th	Night	6% 4 29% 42% 17% 3	800
	11th to 20th	Night	3 7% 34% 42% 13% 2	800
	21st to end	Night	5% 7% 33% 44% 10% 2	880
November	1st to 10th	Night	2 10% 38% 39% 10% 1	1015
	11th to 20th	Night	2 12% 40% 39% 6% 1	1050
	21st to end	Night	3 11% 38% 39% 8%	1050
December	1st to 10th	Night	2 13% 41% 36% 7% 1	1050
	11th to 20th	Night	2 13% 43% 35% 7% 1	1050
	21st to end	Night	2 17% 43% 31% 6% 1	1155

Page generated at 2026-07-28 01:25:23. Version ac07

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