Missouri S&T Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Missouri S&T Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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	12% 8% 3 6% 4 4 4 4 5% 7% 43%	126482
	Night	13% 8% 3 7% 4 3 4 3 5% 6% 44%	123488
Transparency	Day	39% 5% 11% 25% 17% 3	130080
	Night	40% 4 10% 24% 18% 3	127966
Seeing	Day	18% 11% 28% 25% 14% 4	16917
	Night	18% 12% 31% 27% 12% 1	26663

By Month

Percentage Cloud Cover SE (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	14% 12% 4 12% 5% 4 4 3 4 4 35%	3781
	11th to 20th	Day	9% 12% 4 8% 4 4 4 3 5% 6% 42%	4080
	21st to end	Day	18% 10% 4 7% 3 3 4 3 5% 5% 38%	4488
February	1st to 10th	Day	16% 13% 4 8% 5% 4 4 3 4 6% 34%	1800
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 3 5% 6% 38%	1860
	21st to end	Day	14% 11% 3 7% 4 4 4 3 6% 6% 39%	1650
March	1st to 10th	Day	15% 11% 3 6% 3 3 2 2 3 4 47%	4816
	11th to 20th	Day	10% 7% 2 5% 3 3 3 3 5% 7% 53%	4980
	21st to end	Day	13% 9% 3 8% 5% 5% 6% 4 6% 7% 34%	5594
April	1st to 10th	Day	12% 7% 2 6% 4 4 4 3 6% 7% 44%	2400
	11th to 20th	Day	17% 8% 2 5% 4 4 4 4 5% 6% 40%	2374
	21st to end	Day	20% 8% 3 6% 4 4 5% 3 6% 6% 34%	2400
May	1st to 10th	Day	15% 8% 3 7% 5% 5% 6% 4 7% 9% 31%	5536
	11th to 20th	Day	14% 7% 3 7% 5% 6% 5% 4 6% 7% 36%	6125
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 6% 40%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 5% 7% 9% 43%	2800
	11th to 20th	Day	8% 4 2 5% 4 4 4 5% 6% 10% 48%	2800
	21st to end	Day	6% 3 2 4 4 4 5% 5% 8% 10% 50%	2800
July	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 6% 9% 45%	6360
	11th to 20th	Day	5% 5% 2 7% 5% 5% 6% 5% 8% 11% 41%	6090
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	6422
August	1st to 10th	Day	5% 3 1 5% 4 3 4 4 7% 11% 52%	4234
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	3942
	21st to end	Day	7% 4 2 5% 4 4 4 3 6% 9% 50%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 4 8% 49%	2400
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 5% 7% 50%	2400
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 7% 52%	2119
October	1st to 10th	Day	10% 5% 1 5% 3 3 3 3 4 6% 57%	2000
	11th to 20th	Day	14% 7% 2 4 3 3 3 2 4 4 55%	1980
	21st to end	Day	17% 9% 2 4 3 3 3 2 4 5% 46%	2090
November	1st to 10th	Day	13% 6% 2 5% 2 3 4 3 4 5% 53%	1858
	11th to 20th	Day	14% 8% 2 6% 4 3 3 2 4 6% 48%	1800
	21st to end	Day	14% 11% 4 5% 3 3 3 4 4 5% 45%	1656
December	1st to 10th	Day	10% 9% 3 7% 4 3 3 3 4 5% 50%	2610
	11th to 20th	Day	12% 11% 5% 7% 4 4 3 3 4 6% 42%	3008
	21st to end	Day	20% 20% 5% 9% 4 4 3 2 3 4 26%	3982
January	1st to 10th	Night	14% 12% 6% 13% 5% 4 4 3 3 5% 32%	6168
	11th to 20th	Night	11% 9% 4 13% 5% 4 6% 3 3 4 38%	5900
	21st to end	Night	17% 11% 5% 7% 4 3 3 3 3 4 40%	6490
February	1st to 10th	Night	16% 11% 4 8% 4 3 3 4 5% 5% 36%	2600
	11th to 20th	Night	15% 9% 4 7% 4 3 3 3 4 6% 41%	2426
	21st to end	Night	14% 10% 3 8% 4 4 3 3 4 5% 42%	1980
March	1st to 10th	Night	16% 13% 2 6% 3 3 3 2 4 5% 43%	5080
	11th to 20th	Night	12% 8% 2 5% 3 3 3 3 5% 6% 49%	4980
	21st to end	Night	15% 10% 3 7% 5% 5% 5% 4 5% 6% 34%	5335
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 5% 7% 48%	2000
	11th to 20th	Night	15% 8% 2 5% 3 2 4 3 5% 6% 47%	1975
	21st to end	Night	19% 7% 3 6% 5% 3 4 4 5% 7% 38%	2000
May	1st to 10th	Night	17% 9% 3 7% 4 3 3 3 6% 8% 36%	4361
	11th to 20th	Night	12% 9% 2 7% 4 4 4 4 6% 7% 41%	3787
	21st to end	Night	17% 9% 3 7% 5% 5% 5% 3 5% 6% 37%	3942
June	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 5% 8% 51%	1600
	11th to 20th	Night	6% 4 2 4 3 2 5% 4 7% 11% 53%	1600
	21st to end	Night	4 2 1 3 3 4 4 5% 7% 9% 60%	1600
July	1st to 10th	Night	11% 5% 2 6% 4 4 5% 4 6% 9% 45%	3618
	11th to 20th	Night	4 4 2 5% 4 4 4 3 6% 9% 53%	3883
	21st to end	Night	5% 5% 2 6% 4 5% 5% 4 7% 10% 48%	4449
August	1st to 10th	Night	4 3 2 4 3 3 3 3 6% 9% 60%	2926
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 5% 9% 49%	3110
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 9% 60%	3586
September	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 7% 53%	2000
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 4 8% 51%	2000
	21st to end	Night	9% 5% 2 4 4 3 4 3 4 6% 56%	2256
October	1st to 10th	Night	7% 3 1 4 3 3 3 3 4 8% 61%	2400
	11th to 20th	Night	14% 6% 2 4 3 3 3 2 4 6% 53%	2377
	21st to end	Night	19% 7% 2 4 3 3 3 2 4 5% 48%	2508
November	1st to 10th	Night	11% 6% 2 5% 2 3 3 3 4 5% 56%	2436
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 7% 49%	2600
	21st to end	Night	16% 10% 3 5% 3 3 2 2 4 5% 46%	2740
December	1st to 10th	Night	12% 9% 3 7% 3 3 3 3 4 6% 47%	4580
	11th to 20th	Night	15% 9% 4 7% 4 3 3 3 4 5% 42%	5199
	21st to end	Night	23% 17% 5% 9% 4 4 4 3 3 4 24%	6996

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	52% 4 9% 20% 13% 2	3782
	11th to 20th	Day	43% 3 7% 25% 17% 4	4080
	21st to end	Day	48% 3 8% 16% 16% 9%	4488
February	1st to 10th	Day	53% 4 10% 21% 11% 1	1800
	11th to 20th	Day	48% 4 11% 19% 15% 4	1869
	21st to end	Day	46% 4 6% 23% 16% 5%	1650
March	1st to 10th	Day	43% 3 6% 21% 19% 9%	4816
	11th to 20th	Day	32% 4 8% 24% 23% 9%	4980
	21st to end	Day	47% 6% 12% 26% 8% 1	5596
April	1st to 10th	Day	39% 5% 12% 23% 19% 2	2400
	11th to 20th	Day	44% 4 11% 22% 15% 3	2374
	21st to end	Day	50% 6% 11% 20% 12% 1	2400
May	1st to 10th	Day	47% 7% 12% 21% 13%	5571
	11th to 20th	Day	45% 7% 10% 22% 13% 2	6129
	21st to end	Day	44% 5% 9% 25% 16% 1	6949
June	1st to 10th	Day	35% 7% 14% 26% 16% 1	2800
	11th to 20th	Day	29% 8% 12% 30% 18% 3	2800
	21st to end	Day	26% 7% 18% 27% 16% 5%	2800
July	1st to 10th	Day	37% 4 11% 28% 18% 2	6291
	11th to 20th	Day	36% 6% 15% 30% 11% 1	6016
	21st to end	Day	35% 5% 17% 33% 10% 1	6240
August	1st to 10th	Day	26% 6% 18% 34% 17%	4220
	11th to 20th	Day	38% 6% 12% 26% 16% 1	3980
	21st to end	Day	30% 4 14% 35% 12% 4	4311
September	1st to 10th	Day	34% 5% 12% 25% 19% 5%	2400
	11th to 20th	Day	35% 4 8% 26% 25% 2	2400
	21st to end	Day	32% 5% 8% 26% 25% 3	2119
October	1st to 10th	Day	19% 2 6% 20% 42% 12%	3260
	11th to 20th	Day	23% 2 5% 23% 35% 11%	3220
	21st to end	Day	31% 3 7% 30% 26% 3	3428
November	1st to 10th	Day	34% 5% 10% 22% 23% 5%	1858
	11th to 20th	Day	38% 3 8% 23% 21% 6%	1800
	21st to end	Day	43% 4 8% 28% 17% 1	1656
December	1st to 10th	Day	38% 3 8% 35% 15% 1	2610
	11th to 20th	Day	44% 3 9% 24% 19% 1	3005
	21st to end	Day	63% 4 10% 14% 9% 1	3982
January	1st to 10th	Night	57% 3 8% 19% 12% 1	6168
	11th to 20th	Night	51% 4 6% 22% 15% 2	5900
	21st to end	Night	50% 3 8% 20% 17% 4	6490
February	1st to 10th	Night	50% 4 10% 21% 13% 2	2600
	11th to 20th	Night	45% 3 11% 21% 17% 3	2427
	21st to end	Night	45% 4 8% 22% 16% 4	1980
March	1st to 10th	Night	46% 3 6% 22% 19% 5%	5080
	11th to 20th	Night	37% 3 8% 23% 21% 8%	4980
	21st to end	Night	49% 6% 11% 22% 10% 1	5335
April	1st to 10th	Night	34% 5% 12% 26% 19% 3	2000
	11th to 20th	Night	38% 5% 11% 24% 17% 5%	1975
	21st to end	Night	46% 5% 9% 24% 15% 1	2000
May	1st to 10th	Night	45% 7% 14% 20% 13% 2	4391
	11th to 20th	Night	42% 5% 11% 23% 15% 3	3788
	21st to end	Night	47% 6% 11% 22% 13% 2	3950
June	1st to 10th	Night	31% 6% 17% 27% 17% 3	1600
	11th to 20th	Night	24% 7% 13% 30% 23% 4	1600
	21st to end	Night	20% 6% 20% 29% 19% 7%	1600
July	1st to 10th	Night	36% 6% 11% 24% 21% 2	3580
	11th to 20th	Night	28% 5% 13% 38% 14% 1	3837
	21st to end	Night	31% 4 18% 32% 13% 1	4320
August	1st to 10th	Night	21% 6% 19% 32% 22% 1	2916
	11th to 20th	Night	33% 5% 17% 28% 15% 2	3138
	21st to end	Night	23% 4 16% 38% 17% 3	3586
September	1st to 10th	Night	31% 4 11% 26% 23% 5%	2000
	11th to 20th	Night	31% 4 10% 25% 26% 3	2000
	21st to end	Night	30% 5% 9% 24% 29% 4	2256
October	1st to 10th	Night	14% 3 6% 18% 48% 11%	3920
	11th to 20th	Night	24% 2 6% 22% 32% 15%	3876
	21st to end	Night	33% 3 6% 27% 27% 3	4120
November	1st to 10th	Night	31% 4 9% 28% 21% 6%	2436
	11th to 20th	Night	37% 3 7% 23% 24% 6%	2600
	21st to end	Night	42% 4 9% 25% 18% 2	2740
December	1st to 10th	Night	39% 3 9% 33% 15% 1	4580
	11th to 20th	Night	46% 2 9% 23% 18% 1	5201
	21st to end	Night	64% 4 10% 15% 6% 1	6996

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	26% 22% 38% 12% 2	300
	11th to 20th	Day	31% 23% 35% 11%	300
	21st to end	Day	23% 25% 37% 13% 2	330
February	1st to 10th	Day	28% 20% 37% 13% 2	300
	11th to 20th	Day	30% 29% 28% 11% 2	300
	21st to end	Day	29% 21% 39% 11%	249
March	1st to 10th	Day	25% 22% 42% 9% 2	300
	11th to 20th	Day	33% 20% 35% 10% 2 1	300
	21st to end	Day	35% 20% 33% 11% 1	385
April	1st to 10th	Day	25% 17% 35% 17% 6%	500
	11th to 20th	Day	28% 18% 32% 16% 6%	492
	21st to end	Day	25% 17% 33% 19% 5% 1	500
May	1st to 10th	Day	22% 15% 36% 21% 6% 1	556
	11th to 20th	Day	19% 15% 27% 25% 12% 2	725
	21st to end	Day	15% 11% 32% 24% 13% 4	789
June	1st to 10th	Day	12% 5% 25% 31% 22% 6%	730
	11th to 20th	Day	9% 4 24% 37% 23% 3	730
	21st to end	Day	7% 6% 29% 36% 17% 5%	730
July	1st to 10th	Day	12% 3 17% 28% 29% 11%	721
	11th to 20th	Day	6% 3 22% 37% 26% 6%	718
	21st to end	Day	10% 3 16% 35% 27% 8%	794
August	1st to 10th	Day	10% 2 17% 43% 23% 5%	726
	11th to 20th	Day	11% 4 17% 36% 23% 9%	576
	21st to end	Day	13% 2 16% 32% 30% 9%	583
September	1st to 10th	Day	12% 4 16% 36% 26% 6%	530
	11th to 20th	Day	10% 1 20% 32% 25% 12%	530
	21st to end	Day	12% 6% 26% 33% 18% 5%	409
October	1st to 10th	Day	15% 8% 30% 29% 13% 3	330
	11th to 20th	Day	21% 13% 35% 22% 9%	324
	21st to end	Day	32% 16% 32% 17% 3	330
November	1st to 10th	Day	19% 15% 39% 19% 6% 2	300
	11th to 20th	Day	23% 18% 37% 16% 5% 1	300
	21st to end	Day	30% 15% 34% 15% 6%	300
December	1st to 10th	Day	19% 27% 32% 14% 6% 2	300
	11th to 20th	Day	25% 20% 37% 14% 3 1	300
	21st to end	Day	28% 25% 33% 11% 2	330
January	1st to 10th	Night	21% 20% 36% 19% 4	1000
	11th to 20th	Night	22% 24% 34% 16% 3	1000
	21st to end	Night	21% 20% 38% 20% 1	1100
February	1st to 10th	Night	24% 18% 39% 17% 2	1000
	11th to 20th	Night	23% 18% 41% 16% 1	871
	21st to end	Night	24% 22% 36% 17% 2	660
March	1st to 10th	Night	24% 16% 39% 19% 2	675
	11th to 20th	Night	24% 14% 36% 23% 3	600
	21st to end	Night	27% 17% 35% 17% 4	660
April	1st to 10th	Night	17% 17% 40% 24% 3	600
	11th to 20th	Night	20% 15% 34% 26% 4 1	593
	21st to end	Night	24% 12% 35% 23% 7%	600
May	1st to 10th	Night	20% 7% 34% 31% 8%	600
	11th to 20th	Night	19% 6% 30% 29% 15% 1	591
	21st to end	Night	13% 6% 31% 30% 17% 2	650
June	1st to 10th	Night	11% 4 19% 37% 27% 2	600
	11th to 20th	Night	8% 2 25% 41% 22% 2	600
	21st to end	Night	4 2 25% 48% 19% 2	600
July	1st to 10th	Night	12% 1 13% 35% 34% 6%	585
	11th to 20th	Night	5% 2 18% 42% 30% 3	582
	21st to end	Night	6% 2 16% 42% 33% 2	657
August	1st to 10th	Night	6% 2 16% 45% 29% 2	597
	11th to 20th	Night	7% 2 15% 43% 31% 2	594
	21st to end	Night	6% 2 14% 37% 36% 5%	660
September	1st to 10th	Night	13% 3 15% 39% 27% 4	600
	11th to 20th	Night	11% 3 15% 40% 27% 5%	600
	21st to end	Night	12% 5% 26% 31% 23% 4	739
October	1st to 10th	Night	9% 5% 28% 32% 23% 3	800
	11th to 20th	Night	17% 11% 34% 27% 11% 1	793
	21st to end	Night	24% 12% 33% 24% 6%	836
November	1st to 10th	Night	14% 12% 38% 27% 8%	780
	11th to 20th	Night	20% 15% 34% 24% 7%	800
	21st to end	Night	23% 17% 34% 21% 5%	940
December	1st to 10th	Night	24% 15% 36% 21% 4	1000
	11th to 20th	Night	24% 15% 35% 22% 4	1000
	21st to end	Night	27% 18% 35% 18% 2	1100

Page generated at 2025-10-16 00:50:26. Version ac07

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