Mound City Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mound City Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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 6% 3 6% 4 4 5% 4 6% 7% 51%	105226
	Night	2 6% 3 7% 5% 4 5% 4 6% 8% 51%	103298
Transparency	Day	30% 5% 11% 19% 21% 13%	104991
	Night	30% 6% 13% 22% 19% 10%	103122
Seeing	Day	8% 16% 31% 29% 13% 3	15180
	Night	7% 7% 24% 39% 21% 3	25581

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	1 9% 5% 14% 9% 6% 6% 5% 7% 6% 31%	2858
	11th to 20th	Day	2 11% 7% 19% 7% 5% 4 3 4 5% 32%	2860
	21st to end	Day	2 13% 7% 11% 5% 4 5% 3 5% 6% 40%	3146
February	1st to 10th	Day	2 13% 4 10% 6% 5% 5% 6% 7% 6% 35%	1710
	11th to 20th	Day	3 13% 4 10% 7% 5% 5% 5% 6% 6% 35%	1712
	21st to end	Day	3 12% 4 11% 6% 6% 6% 4 6% 8% 34%	1570
March	1st to 10th	Day	1 8% 6% 13% 6% 6% 6% 4 7% 8% 35%	3382
	11th to 20th	Day	2 8% 3 8% 6% 5% 5% 5% 7% 9% 42%	3490
	21st to end	Day	3 15% 5% 13% 8% 7% 6% 5% 6% 8% 24%	3825
April	1st to 10th	Day	3 10% 4 7% 6% 6% 5% 4 6% 8% 41%	2123
	11th to 20th	Day	4 10% 4 8% 5% 5% 6% 4 7% 7% 40%	2370
	21st to end	Day	4 8% 3 6% 6% 5% 5% 4 6% 7% 45%	2470
May	1st to 10th	Day	5% 12% 4 8% 6% 6% 6% 5% 6% 7% 35%	4110
	11th to 20th	Day	3 4 2 4 4 5% 5% 4 7% 10% 53%	4071
	21st to end	Day	4 5% 2 6% 4 4 5% 5% 7% 9% 48%	4477
June	1st to 10th	Day	3 3 1 4 4 4 5% 4 6% 8% 56%	2593
	11th to 20th	Day	4 4 1 4 3 3 4 3 4 6% 64%	2660
	21st to end	Day	2 2 1 2 2 3 3 4 5% 5% 70%	2536
July	1st to 10th	Day	1 1 1 2 2 2 3 3 4 6% 76%	4110
	11th to 20th	Day	2 2 1 4 3 4 5% 5% 9% 10% 55%	4110
	21st to end	Day	3 2 1 3 3 4 4 4 6% 7% 63%	4454
August	1st to 10th	Day	2 2 1 3 2 3 3 4 6% 8% 65%	4092
	11th to 20th	Day	2 1 1 3 2 4 4 4 5% 7% 68%	4028
	21st to end	Day	2 2 1 3 3 3 4 4 5% 7% 68%	4459
September	1st to 10th	Day	3 2 1 3 3 3 3 3 5% 7% 67%	2170
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 7% 63%	2090
	21st to end	Day	4 3 1 3 3 3 3 3 4 6% 68%	2090
October	1st to 10th	Day	3 4 1 4 3 3 3 3 4 5% 68%	3304
	11th to 20th	Day	5% 5% 1 4 4 3 4 3 6% 7% 57%	3150
	21st to end	Day	3 7% 2 4 3 3 4 4 6% 6% 59%	3438
November	1st to 10th	Day	5% 7% 3 6% 4 5% 4 4 6% 7% 49%	1783
	11th to 20th	Day	5% 9% 3 4 4 4 4 3 6% 7% 50%	1800
	21st to end	Day	2 8% 4 8% 6% 5% 5% 4 6% 7% 46%	1625
December	1st to 10th	Day	4 8% 3 8% 5% 6% 4 4 6% 8% 45%	1584
	11th to 20th	Day	2 10% 4 11% 5% 6% 7% 5% 8% 7% 35%	1926
	21st to end	Day	2 9% 6% 11% 8% 5% 5% 4 6% 7% 39%	3050
January	1st to 10th	Night	2 8% 5% 14% 8% 6% 6% 5% 7% 7% 33%	4097
	11th to 20th	Night	2 11% 6% 18% 8% 6% 6% 4 5% 6% 29%	4110
	21st to end	Night	2 12% 6% 13% 6% 5% 5% 4 6% 7% 34%	4521
February	1st to 10th	Night	2 10% 4 9% 5% 5% 6% 4 7% 10% 36%	2470
	11th to 20th	Night	2 10% 3 8% 6% 5% 5% 4 7% 8% 42%	2350
	21st to end	Night	2 9% 4 9% 6% 6% 5% 5% 7% 8% 39%	1884
March	1st to 10th	Night	1 8% 4 10% 6% 6% 6% 5% 8% 9% 36%	3490
	11th to 20th	Night	1 6% 2 6% 4 4 6% 5% 7% 9% 48%	3490
	21st to end	Night	2 11% 5% 10% 7% 6% 5% 5% 6% 6% 36%	3828
April	1st to 10th	Night	4 10% 3 6% 5% 4 4 3 5% 7% 48%	2057
	11th to 20th	Night	3 7% 1 5% 5% 4 6% 6% 7% 7% 49%	1755
	21st to end	Night	5% 8% 2 6% 4 4 4 4 6% 7% 49%	1710
May	1st to 10th	Night	3 10% 3 9% 6% 5% 5% 4 6% 8% 40%	2860
	11th to 20th	Night	2 3 1 4 3 3 4 4 7% 8% 60%	2834
	21st to end	Night	4 5% 2 5% 4 3 4 4 5% 8% 55%	3110
June	1st to 10th	Night	3 4 1 4 4 4 4 4 6% 8% 58%	1577
	11th to 20th	Night	3 3 1 4 2 2 4 4 4 6% 68%	1520
	21st to end	Night	1 1 1 3 3 3 3 4 4 8% 70%	1635
July	1st to 10th	Night	2 1 1 3 3 3 3 3 4 5% 73%	2860
	11th to 20th	Night	2 2 1 4 3 4 5% 5% 8% 10% 56%	2860
	21st to end	Night	1 2 1 4 3 4 5% 5% 6% 8% 60%	3109
August	1st to 10th	Night	2 2 1 3 3 4 4 3 6% 9% 63%	2847
	11th to 20th	Night	2 2 1 5% 4 4 5% 4 5% 6% 62%	2811
	21st to end	Night	1 2 1 3 2 3 3 3 5% 6% 71%	3207
September	1st to 10th	Night	2 3 1 3 3 2 3 3 5% 6% 69%	2006
	11th to 20th	Night	4 2 1 2 3 3 4 4 4 8% 65%	2090
	21st to end	Night	5% 3 1 3 3 2 3 2 3 5% 71%	2090
October	1st to 10th	Night	3 3 1 2 2 2 2 3 3 4 74%	3668
	11th to 20th	Night	4 5% 1 4 3 3 4 4 7% 7% 58%	3778
	21st to end	Night	2 4 2 5% 3 2 3 3 6% 8% 61%	4120
November	1st to 10th	Night	3 6% 2 5% 5% 3 4 4 5% 8% 53%	2512
	11th to 20th	Night	4 8% 2 4 4 3 4 4 6% 11% 52%	2600
	21st to end	Night	3 7% 3 7% 5% 5% 5% 3 6% 9% 48%	2750
December	1st to 10th	Night	2 8% 3 8% 5% 4 4 4 5% 9% 47%	2779
	11th to 20th	Night	4 10% 3 8% 5% 5% 6% 5% 7% 11% 36%	3271
	21st to end	Night	2 8% 4 12% 7% 6% 6% 5% 8% 10% 31%	4642

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% 8% 15% 17% 11% 1	2859
	11th to 20th	Day	55% 6% 14% 15% 8% 2	2860
	21st to end	Day	45% 5% 20% 19% 9% 2	3146
February	1st to 10th	Day	47% 7% 15% 17% 11% 2	1710
	11th to 20th	Day	46% 5% 14% 21% 12% 2	1721
	21st to end	Day	47% 6% 15% 21% 11% 1	1570
March	1st to 10th	Day	42% 7% 15% 21% 11% 4	3382
	11th to 20th	Day	33% 8% 18% 29% 10% 2	3490
	21st to end	Day	55% 5% 17% 16% 5% 1	3825
April	1st to 10th	Day	41% 6% 16% 19% 14% 4	2123
	11th to 20th	Day	42% 5% 14% 22% 16% 1	2373
	21st to end	Day	37% 5% 11% 26% 18% 2	2470
May	1st to 10th	Day	42% 5% 12% 19% 17% 4	4110
	11th to 20th	Day	23% 5% 12% 30% 26% 3	4074
	21st to end	Day	29% 5% 15% 23% 25% 4	4477
June	1st to 10th	Day	23% 6% 10% 23% 29% 9%	2593
	11th to 20th	Day	22% 4 7% 18% 30% 20%	2660
	21st to end	Day	15% 2 5% 12% 31% 35%	2536
July	1st to 10th	Day	10% 3 4 8% 16% 59%	4046
	11th to 20th	Day	18% 5% 9% 14% 26% 28%	4041
	21st to end	Day	17% 6% 6% 12% 23% 36%	4314
August	1st to 10th	Day	16% 5% 8% 21% 27% 24%	4078
	11th to 20th	Day	16% 5% 8% 16% 32% 24%	4067
	21st to end	Day	15% 4 7% 14% 29% 31%	4458
September	1st to 10th	Day	18% 3 6% 16% 28% 28%	2170
	11th to 20th	Day	20% 4 8% 19% 27% 22%	2090
	21st to end	Day	19% 3 7% 21% 37% 14%	2090
October	1st to 10th	Day	20% 4 5% 15% 37% 20%	3304
	11th to 20th	Day	25% 5% 8% 28% 27% 7%	3150
	21st to end	Day	23% 5% 13% 27% 26% 5%	3438
November	1st to 10th	Day	33% 5% 14% 23% 20% 5%	1783
	11th to 20th	Day	32% 5% 14% 28% 19% 2	1800
	21st to end	Day	36% 5% 14% 25% 15% 4	1625
December	1st to 10th	Day	36% 7% 19% 24% 10% 4	1584
	11th to 20th	Day	44% 7% 14% 21% 13% 1	1924
	21st to end	Day	42% 5% 15% 15% 21% 3	3050
January	1st to 10th	Night	47% 7% 14% 21% 10% 1	4097
	11th to 20th	Night	54% 8% 14% 15% 7% 2	4110
	21st to end	Night	44% 10% 18% 18% 8% 2	4521
February	1st to 10th	Night	42% 7% 19% 20% 10% 2	2470
	11th to 20th	Night	39% 6% 15% 23% 17% 1	2351
	21st to end	Night	39% 5% 16% 26% 12% 2	1884
March	1st to 10th	Night	37% 8% 18% 23% 13%	3490
	11th to 20th	Night	27% 7% 22% 31% 12% 1	3490
	21st to end	Night	45% 6% 14% 22% 11% 2	3828
April	1st to 10th	Night	34% 5% 17% 21% 17% 5%	2057
	11th to 20th	Night	30% 5% 17% 26% 20% 2	1755
	21st to end	Night	32% 6% 15% 26% 20% 1	1710
May	1st to 10th	Night	37% 5% 14% 20% 21% 2	2860
	11th to 20th	Night	18% 7% 13% 33% 23% 6%	2835
	21st to end	Night	24% 4 13% 32% 25% 2	3110
June	1st to 10th	Night	23% 4 11% 25% 28% 8%	1577
	11th to 20th	Night	17% 4 7% 20% 31% 21%	1520
	21st to end	Night	13% 2 6% 13% 29% 36%	1635
July	1st to 10th	Night	14% 2 6% 9% 13% 56%	2815
	11th to 20th	Night	19% 6% 9% 14% 26% 27%	2806
	21st to end	Night	20% 5% 9% 15% 22% 29%	3011
August	1st to 10th	Night	17% 5% 10% 21% 24% 24%	2838
	11th to 20th	Night	22% 5% 8% 16% 26% 22%	2838
	21st to end	Night	13% 4 9% 14% 30% 30%	3207
September	1st to 10th	Night	16% 4 6% 17% 26% 30%	2006
	11th to 20th	Night	17% 4 11% 21% 26% 21%	2090
	21st to end	Night	18% 3 6% 20% 38% 16%	2090
October	1st to 10th	Night	15% 2 6% 20% 34% 22%	3668
	11th to 20th	Night	23% 4 9% 30% 27% 7%	3778
	21st to end	Night	19% 5% 12% 32% 28% 3	4120
November	1st to 10th	Night	28% 5% 14% 27% 21% 5%	2512
	11th to 20th	Night	27% 6% 15% 32% 18% 3	2600
	21st to end	Night	34% 5% 14% 26% 19% 4	2750
December	1st to 10th	Night	33% 6% 18% 27% 12% 3	2779
	11th to 20th	Night	41% 7% 18% 22% 12% 1	3272
	21st to end	Night	44% 7% 17% 17% 13% 1	4642

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	11% 16% 31% 24% 13% 4	270
	11th to 20th	Day	7% 16% 32% 30% 13% 2	270
	21st to end	Day	6% 14% 29% 34% 15% 3	297
February	1st to 10th	Day	12% 20% 38% 21% 7% 1	270
	11th to 20th	Day	9% 21% 37% 25% 6% 2	317
	21st to end	Day	10% 26% 35% 23% 6% 1	382
March	1st to 10th	Day	10% 23% 38% 22% 7% 1	460
	11th to 20th	Day	9% 23% 33% 27% 7% 1	460
	21st to end	Day	15% 28% 32% 21% 4	506
April	1st to 10th	Day	11% 25% 32% 22% 9% 2	460
	11th to 20th	Day	14% 27% 34% 17% 7% 1	452
	21st to end	Day	11% 26% 29% 24% 9% 1	460
May	1st to 10th	Day	12% 23% 35% 20% 9% 1	463
	11th to 20th	Day	9% 19% 33% 24% 11% 3	488
	21st to end	Day	10% 17% 33% 24% 13% 4	529
June	1st to 10th	Day	6% 14% 29% 30% 17% 4	613
	11th to 20th	Day	8% 15% 31% 28% 17% 1	680
	21st to end	Day	3 15% 31% 36% 13% 3	556
July	1st to 10th	Day	2 8% 35% 40% 12% 3	486
	11th to 20th	Day	4 5% 36% 36% 14% 5%	484
	21st to end	Day	3 5% 30% 38% 18% 5%	531
August	1st to 10th	Day	4 9% 34% 33% 17% 3	487
	11th to 20th	Day	3 10% 29% 37% 16% 5%	477
	21st to end	Day	4 9% 32% 33% 18% 5%	539
September	1st to 10th	Day	4 10% 28% 33% 17% 8%	490
	11th to 20th	Day	6% 16% 29% 28% 16% 4	490
	21st to end	Day	6% 14% 24% 32% 19% 5%	490
October	1st to 10th	Day	7% 15% 27% 27% 16% 8%	382
	11th to 20th	Day	8% 15% 23% 26% 21% 6%	300
	21st to end	Day	9% 15% 33% 29% 12% 2	330
November	1st to 10th	Day	13% 17% 28% 22% 16% 4	300
	11th to 20th	Day	6% 19% 28% 30% 12% 4	300
	21st to end	Day	8% 11% 28% 28% 20% 5%	300
December	1st to 10th	Day	5% 14% 30% 31% 16% 5%	294
	11th to 20th	Day	6% 12% 35% 36% 9% 2	270
	21st to end	Day	12% 16% 30% 31% 10% 1	297
January	1st to 10th	Night	8% 7% 28% 34% 20% 3	760
	11th to 20th	Night	8% 7% 27% 40% 16% 3	760
	21st to end	Night	7% 6% 27% 40% 17% 3	836
February	1st to 10th	Night	8% 6% 32% 41% 11% 2	760
	11th to 20th	Night	7% 7% 32% 38% 14% 2	744
	21st to end	Night	6% 10% 29% 42% 12% 1	628
March	1st to 10th	Night	8% 9% 32% 38% 11% 2	760
	11th to 20th	Night	5% 7% 29% 39% 17% 2	760
	21st to end	Night	8% 12% 30% 35% 13% 1	836
April	1st to 10th	Night	12% 12% 23% 39% 13% 1	727
	11th to 20th	Night	7% 11% 32% 37% 12%	563
	21st to end	Night	10% 9% 26% 34% 19% 2	570
May	1st to 10th	Night	8% 7% 27% 41% 15% 1	570
	11th to 20th	Night	6% 5% 22% 38% 26% 2	561
	21st to end	Night	9% 6% 23% 37% 22% 4	617
June	1st to 10th	Night	5% 9% 18% 41% 25% 2	570
	11th to 20th	Night	5% 11% 23% 42% 19%	570
	21st to end	Night	1 3 22% 41% 30% 2	570
July	1st to 10th	Night	3 3 16% 36% 39% 3	555
	11th to 20th	Night	4 3 11% 47% 33% 3	552
	21st to end	Night	2 1 10% 37% 48% 2	624
August	1st to 10th	Night	5% 2 13% 45% 34% 1	567
	11th to 20th	Night	3 1 15% 44% 34% 3	564
	21st to end	Night	4 2 14% 44% 34% 2	627
September	1st to 10th	Night	4 3 14% 40% 34% 5%	676
	11th to 20th	Night	5% 5% 16% 38% 30% 6%	760
	21st to end	Night	6% 4 16% 33% 34% 7%	760
October	1st to 10th	Night	9% 5% 20% 38% 25% 3	760
	11th to 20th	Night	6% 4 18% 43% 24% 4	760
	21st to end	Night	7% 6% 24% 37% 22% 4	836
November	1st to 10th	Night	7% 8% 23% 37% 22% 3	780
	11th to 20th	Night	9% 5% 27% 40% 16% 4	800
	21st to end	Night	7% 8% 30% 34% 18% 3	950
December	1st to 10th	Night	7% 6% 31% 39% 15% 2	993
	11th to 20th	Night	10% 7% 29% 41% 11% 1	950
	21st to end	Night	10% 11% 29% 37% 10% 1	905

Page generated at 2024-12-06 01:54:48. Version ac07

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