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 2025-03-27.

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% 53%	113015
	Night	2 4 2 5% 3 3 4 3 5% 7% 61%	115179
Transparency	Day	26% 7% 13% 23% 23% 9%	112764
	Night	21% 6% 14% 27% 25% 8%	115020
Seeing	Day	8% 17% 26% 28% 16% 5%	15960
	Night	4 9% 32% 39% 14% 2	26183

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 2 6% 4 3 4 3 5% 9% 62%	3638
	11th to 20th	Day	2 1 5% 5% 5% 5% 5% 7% 8% 58%	3937
	21st to end	Day	3 2 6% 4 4 4 3 6% 9% 59%	4510
February	1st to 10th	Day	3 3 5% 3 4 3 4 7% 7% 61%	1800
	11th to 20th	Day	4 1 4 4 3 4 4 5% 9% 63%	1893
	21st to end	Day	3 2 6% 4 5% 4 4 6% 7% 59%	1650
March	1st to 10th	Day	5% 3 7% 4 3 5% 3 6% 8% 56%	3286
	11th to 20th	Day	1 8% 3 8% 5% 5% 4 4 7% 11% 45%	3600
	21st to end	Day	1 5% 2 7% 5% 5% 5% 5% 7% 10% 48%	4068
April	1st to 10th	Day	1 5% 2 5% 3 4 4 4 8% 9% 55%	2280
	11th to 20th	Day	3 9% 3 6% 6% 5% 5% 3 6% 8% 47%	2251
	21st to end	Day	3 8% 2 6% 4 5% 6% 4 6% 9% 47%	2280
May	1st to 10th	Day	4 9% 3 9% 6% 6% 6% 5% 7% 7% 39%	3934
	11th to 20th	Day	5% 7% 2 7% 5% 5% 6% 6% 8% 9% 41%	4388
	21st to end	Day	3 5% 1 4 4 4 6% 5% 7% 9% 51%	4825
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 5% 8% 9% 48%	2660
	11th to 20th	Day	6% 4 1 4 4 4 5% 4 5% 7% 54%	2660
	21st to end	Day	4 4 2 4 5% 5% 6% 6% 8% 8% 49%	2660
July	1st to 10th	Day	5% 4 2 5% 4 4 5% 4 6% 6% 54%	4430
	11th to 20th	Day	6% 5% 2 6% 6% 6% 6% 5% 8% 11% 40%	4430
	21st to end	Day	7% 6% 2 6% 6% 6% 6% 5% 6% 8% 43%	4559
August	1st to 10th	Day	9% 7% 2 9% 7% 7% 6% 5% 8% 9% 31%	4092
	11th to 20th	Day	5% 5% 2 6% 5% 6% 7% 6% 8% 8% 41%	3764
	21st to end	Day	5% 5% 2 7% 6% 6% 6% 5% 7% 9% 42%	4180
September	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 4 5% 6% 52%	2280
	11th to 20th	Day	6% 4 1 6% 4 4 5% 3 5% 6% 57%	2280
	21st to end	Day	6% 4 1 4 3 4 3 3 4 6% 63%	2062
October	1st to 10th	Day	3 3 1 4 3 3 3 3 3 4 69%	3170
	11th to 20th	Day	3 5% 1 4 4 4 5% 4 6% 9% 54%	3150
	21st to end	Day	2 3 1 3 2 2 3 3 4 7% 70%	3415
November	1st to 10th	Day	1 3 1 3 2 2 3 2 4 6% 72%	1763
	11th to 20th	Day	3 1 3 2 2 2 3 4 8% 73%	1800
	21st to end	Day	3 2 4 2 3 3 3 5% 8% 66%	1670
December	1st to 10th	Day	2 1 5% 2 2 3 2 3 6% 73%	2620
	11th to 20th	Day	2 1 3 2 3 3 3 5% 9% 69%	3026
	21st to end	Day	3 2 5% 4 3 4 3 6% 11% 59%	4004
January	1st to 10th	Night	2 2 9% 5% 4 4 3 4 7% 60%	6327
	11th to 20th	Night	1 1 3 5% 4 4 3 5% 6% 68%	6087
	21st to end	Night	4 2 6% 3 3 3 3 4 6% 65%	6468
February	1st to 10th	Night	2 2 5% 3 3 4 3 4 8% 66%	2600
	11th to 20th	Night	3 2 6% 3 3 3 3 5% 7% 64%	2392
	21st to end	Night	5% 3 5% 3 2 3 2 5% 6% 66%	1980
March	1st to 10th	Night	6% 3 6% 3 4 3 3 4 7% 61%	3795
	11th to 20th	Night	1 10% 5% 7% 3 3 3 3 5% 7% 53%	3600
	21st to end	Night	1 5% 2 6% 4 4 4 4 6% 9% 55%	3715
April	1st to 10th	Night	1 5% 2 4 2 2 4 4 4 8% 65%	1900
	11th to 20th	Night	3 9% 3 5% 3 3 3 4 5% 7% 55%	1877
	21st to end	Night	4 8% 2 5% 4 4 3 2 5% 7% 56%	1900
May	1st to 10th	Night	4 10% 3 5% 4 4 4 3 5% 7% 52%	3028
	11th to 20th	Night	7% 10% 3 6% 4 3 4 4 5% 7% 47%	2517
	21st to end	Night	5% 7% 2 4 3 3 3 2 5% 7% 59%	2762
June	1st to 10th	Night	3 4 1 3 3 3 3 3 5% 9% 62%	1520
	11th to 20th	Night	5% 2 1 3 2 3 3 4 5% 8% 65%	1520
	21st to end	Night	4 3 1 3 3 3 4 4 6% 10% 59%	1520
July	1st to 10th	Night	4 5% 2 5% 4 3 3 4 6% 7% 58%	2540
	11th to 20th	Night	2 3 1 4 4 4 6% 5% 8% 9% 54%	2540
	21st to end	Night	4 4 1 4 3 5% 5% 5% 7% 10% 51%	3000
August	1st to 10th	Night	7% 6% 2 6% 4 5% 5% 5% 8% 11% 40%	2847
	11th to 20th	Night	4 4 1 4 4 4 6% 6% 9% 11% 47%	3073
	21st to end	Night	4 4 2 7% 6% 6% 6% 5% 8% 9% 44%	3487
September	1st to 10th	Night	5% 4 1 4 3 4 4 5% 6% 8% 55%	1900
	11th to 20th	Night	6% 4 1 4 3 3 4 3 5% 7% 60%	1900
	21st to end	Night	6% 5% 1 4 2 3 3 2 4 6% 64%	2111
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 4 74%	3800
	11th to 20th	Night	3 5% 2 5% 3 3 3 3 4 7% 64%	3778
	21st to end	Night	2 3 1 3 2 2 2 2 4 5% 73%	4120
November	1st to 10th	Night	1 3 1 3 2 2 3 3 4 7% 72%	2525
	11th to 20th	Night	2 1 2 2 2 2 2 4 7% 75%	2600
	21st to end	Night	1 5% 1 4 2 2 3 3 5% 7% 66%	2725
December	1st to 10th	Night	2 1 3 2 2 2 2 3 6% 79%	4570
	11th to 20th	Night	2 1 3 2 2 3 3 5% 7% 72%	5181
	21st to end	Night	4 2 6% 4 4 4 4 6% 9% 59%	6974

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	20% 4 15% 29% 24% 8%	3639
	11th to 20th	Day	18% 5% 21% 20% 29% 8%	3937
	21st to end	Day	20% 5% 11% 28% 24% 12%	4510
February	1st to 10th	Day	22% 4 19% 26% 20% 9%	1800
	11th to 20th	Day	18% 6% 13% 28% 29% 6%	1903
	21st to end	Day	22% 5% 13% 21% 26% 13%	1650
March	1st to 10th	Day	24% 6% 12% 21% 29% 8%	3286
	11th to 20th	Day	30% 11% 11% 31% 14% 3	3600
	21st to end	Day	25% 11% 16% 29% 18% 2	4068
April	1st to 10th	Day	25% 7% 15% 24% 22% 8%	2280
	11th to 20th	Day	35% 6% 13% 21% 20% 4	2254
	21st to end	Day	33% 9% 12% 27% 18% 2	2280
May	1st to 10th	Day	36% 7% 17% 15% 19% 5%	3934
	11th to 20th	Day	36% 11% 15% 20% 16% 2	4392
	21st to end	Day	25% 7% 15% 18% 29% 6%	4825
June	1st to 10th	Day	30% 10% 14% 19% 20% 7%	2660
	11th to 20th	Day	28% 7% 9% 18% 22% 15%	2660
	21st to end	Day	29% 8% 10% 20% 21% 12%	2660
July	1st to 10th	Day	26% 9% 9% 13% 18% 25%	4361
	11th to 20th	Day	31% 11% 13% 21% 16% 8%	4355
	21st to end	Day	34% 11% 14% 15% 12% 14%	4415
August	1st to 10th	Day	42% 12% 18% 13% 12% 4	4078
	11th to 20th	Day	35% 11% 13% 14% 19% 8%	3800
	21st to end	Day	33% 9% 14% 16% 20% 8%	4179
September	1st to 10th	Day	32% 6% 10% 16% 22% 14%	2280
	11th to 20th	Day	27% 6% 12% 18% 27% 10%	2280
	21st to end	Day	24% 5% 7% 24% 33% 8%	2062
October	1st to 10th	Day	18% 5% 6% 19% 34% 18%	3170
	11th to 20th	Day	23% 7% 10% 29% 25% 6%	3150
	21st to end	Day	15% 3 7% 32% 37% 6%	3415
November	1st to 10th	Day	15% 4 12% 23% 35% 10%	1763
	11th to 20th	Day	12% 4 11% 35% 29% 10%	1800
	21st to end	Day	17% 4 11% 29% 27% 12%	1670
December	1st to 10th	Day	14% 5% 10% 37% 26% 9%	2620
	11th to 20th	Day	14% 4 15% 36% 27% 4	3024
	21st to end	Day	18% 5% 12% 28% 28% 9%	4004
January	1st to 10th	Night	22% 4 12% 30% 25% 6%	6327
	11th to 20th	Night	14% 5% 15% 26% 25% 15%	6087
	21st to end	Night	20% 5% 12% 24% 28% 11%	6468
February	1st to 10th	Night	18% 4 16% 32% 23% 7%	2600
	11th to 20th	Night	19% 5% 13% 30% 27% 6%	2392
	21st to end	Night	20% 3 10% 28% 29% 11%	1980
March	1st to 10th	Night	22% 4 11% 24% 33% 6%	3795
	11th to 20th	Night	31% 7% 12% 28% 19% 3	3600
	21st to end	Night	23% 6% 20% 32% 16% 2	3715
April	1st to 10th	Night	19% 5% 15% 30% 25% 5%	1900
	11th to 20th	Night	29% 5% 12% 30% 20% 4	1877
	21st to end	Night	29% 5% 13% 31% 19% 1	1900
May	1st to 10th	Night	28% 6% 16% 23% 21% 6%	3028
	11th to 20th	Night	35% 8% 17% 25% 15% 1	2518
	21st to end	Night	25% 6% 14% 23% 28% 4	2762
June	1st to 10th	Night	21% 6% 20% 28% 17% 9%	1520
	11th to 20th	Night	18% 6% 14% 22% 25% 16%	1520
	21st to end	Night	20% 7% 14% 24% 23% 12%	1520
July	1st to 10th	Night	24% 8% 11% 20% 17% 19%	2500
	11th to 20th	Night	20% 9% 20% 31% 13% 7%	2492
	21st to end	Night	22% 11% 23% 23% 7% 14%	2906
August	1st to 10th	Night	34% 12% 22% 18% 10% 4	2838
	11th to 20th	Night	25% 12% 22% 16% 19% 7%	3103
	21st to end	Night	31% 11% 17% 19% 19% 3	3487
September	1st to 10th	Night	25% 8% 13% 23% 22% 9%	1900
	11th to 20th	Night	23% 6% 14% 22% 22% 13%	1900
	21st to end	Night	23% 5% 9% 28% 28% 6%	2111
October	1st to 10th	Night	16% 4 9% 25% 34% 12%	3800
	11th to 20th	Night	18% 7% 14% 32% 24% 7%	3778
	21st to end	Night	13% 3 8% 30% 38% 8%	4120
November	1st to 10th	Night	14% 4 12% 27% 33% 11%	2525
	11th to 20th	Night	11% 4 11% 34% 31% 9%	2600
	21st to end	Night	17% 5% 11% 29% 28% 10%	2725
December	1st to 10th	Night	11% 3 11% 37% 32% 6%	4570
	11th to 20th	Night	12% 4 12% 34% 35% 3	5182
	21st to end	Night	21% 5% 14% 25% 28% 7%	6974

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 21% 29% 32% 10% 4	300
	11th to 20th	Day	7% 23% 33% 28% 7% 2	300
	21st to end	Day	2 20% 37% 30% 10% 2	330
February	1st to 10th	Day	2 39% 33% 22% 2 1	300
	11th to 20th	Day	3 34% 33% 24% 5% 1	300
	21st to end	Day	6% 30% 35% 24% 4	249
March	1st to 10th	Day	3 26% 32% 25% 12% 1	330
	11th to 20th	Day	7% 22% 34% 26% 11%	500
	21st to end	Day	6% 32% 35% 20% 6% 1	531
April	1st to 10th	Day	7% 29% 33% 24% 6% 1	460
	11th to 20th	Day	12% 36% 28% 16% 6% 2	452
	21st to end	Day	10% 25% 33% 23% 6% 2	460
May	1st to 10th	Day	11% 25% 31% 22% 9% 2	510
	11th to 20th	Day	10% 15% 25% 32% 15% 4	675
	21st to end	Day	9% 16% 21% 30% 19% 4	734
June	1st to 10th	Day	6% 13% 22% 29% 22% 8%	680
	11th to 20th	Day	8% 12% 24% 35% 17% 5%	680
	21st to end	Day	5% 9% 25% 32% 22% 7%	680
July	1st to 10th	Day	8% 4 13% 35% 30% 10%	671
	11th to 20th	Day	7% 3 11% 33% 34% 11%	668
	21st to end	Day	10% 4 16% 27% 33% 10%	597
August	1st to 10th	Day	13% 5% 20% 30% 23% 9%	487
	11th to 20th	Day	10% 6% 20% 34% 20% 10%	477
	21st to end	Day	11% 6% 22% 26% 25% 10%	539
September	1st to 10th	Day	10% 7% 22% 28% 23% 9%	490
	11th to 20th	Day	7% 9% 27% 30% 21% 6%	490
	21st to end	Day	6% 12% 20% 29% 22% 11%	310
October	1st to 10th	Day	7% 16% 22% 21% 24% 10%	300
	11th to 20th	Day	8% 19% 22% 31% 16% 4	300
	21st to end	Day	8% 18% 28% 30% 15% 2	330
November	1st to 10th	Day	6% 19% 33% 26% 12% 4	300
	11th to 20th	Day	6% 19% 30% 33% 9% 3	300
	21st to end	Day	4 17% 38% 31% 8% 2	300
December	1st to 10th	Day	7% 20% 29% 31% 8% 4	300
	11th to 20th	Day	5% 20% 39% 29% 6% 2	300
	21st to end	Day	8% 23% 35% 24% 9% 2	330
January	1st to 10th	Night	1 15% 39% 33% 10% 2	1000
	11th to 20th	Night	2 18% 39% 33% 7% 1	890
	21st to end	Night	2 11% 42% 38% 8% 1	880
February	1st to 10th	Night	12% 51% 30% 5% 1	800
	11th to 20th	Night	2 14% 45% 32% 7%	784
	21st to end	Night	2 10% 47% 39% 2	660
March	1st to 10th	Night	2 11% 39% 40% 7% 1	800
	11th to 20th	Night	3 8% 38% 42% 9% 1	800
	21st to end	Night	4 10% 45% 36% 5%	755
April	1st to 10th	Night	4 13% 43% 36% 4	570
	11th to 20th	Night	6% 12% 38% 35% 8% 1	563
	21st to end	Night	9% 9% 34% 39% 8% 1	570
May	1st to 10th	Night	9% 8% 33% 38% 11% 1	570
	11th to 20th	Night	11% 6% 19% 47% 15% 2	561
	21st to end	Night	10% 6% 24% 40% 18% 2	617
June	1st to 10th	Night	4 4 21% 45% 24% 2	570
	11th to 20th	Night	5% 4 25% 50% 14% 2	570
	21st to end	Night	5% 2 18% 45% 28% 3	570
July	1st to 10th	Night	6% 2 9% 39% 38% 5%	555
	11th to 20th	Night	4 1 4 43% 44% 4	552
	21st to end	Night	6% 1 6% 37% 46% 5%	624
August	1st to 10th	Night	10% 2 7% 39% 38% 4	567
	11th to 20th	Night	7% 2 9% 45% 33% 5%	564
	21st to end	Night	8% 1 9% 41% 35% 5%	627
September	1st to 10th	Night	5% 2 11% 49% 27% 6%	570
	11th to 20th	Night	7% 1 17% 48% 24% 3	570
	21st to end	Night	7% 4 24% 43% 18% 4	603
October	1st to 10th	Night	6% 4 28% 42% 17% 3	760
	11th to 20th	Night	3 6% 33% 43% 13% 2	760
	21st to end	Night	5% 7% 32% 44% 11% 2	836
November	1st to 10th	Night	2 10% 37% 40% 10% 1	965
	11th to 20th	Night	2 13% 40% 38% 6% 1	1000
	21st to end	Night	3 11% 37% 40% 8% 1	1000
December	1st to 10th	Night	2 13% 40% 37% 7% 1	1000
	11th to 20th	Night	2 13% 42% 35% 7% 1	1000
	21st to end	Night	2 17% 41% 32% 6% 1	1100

Page generated at 2025-03-24 07:04:26. Version ac07

Copyright © 2025 Attilla Danko.