Truman State University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Truman State University Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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 7% 4 4 4 4 5% 7% 41%	120190
	Night	12% 8% 3 7% 4 4 4 3 5% 6% 43%	118849
Transparency	Day	41% 5% 11% 24% 16% 2	123833
	Night	41% 5% 11% 24% 17% 3	123349
Seeing	Day	15% 10% 28% 27% 15% 4	16644
	Night	15% 9% 32% 31% 12% 1	26512

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	12% 12% 5% 14% 4 4 5% 4 5% 6% 29%	3641
	11th to 20th	Day	9% 9% 3 9% 5% 6% 7% 4 4 6% 38%	4080
	21st to end	Day	14% 17% 6% 10% 5% 4 3 3 3 5% 31%	4488
February	1st to 10th	Day	15% 11% 3 8% 4 5% 4 4 6% 9% 32%	1800
	11th to 20th	Day	12% 11% 4 8% 5% 4 3 3 6% 6% 37%	1762
	21st to end	Day	13% 10% 3 7% 4 4 4 3 5% 5% 43%	1650
March	1st to 10th	Day	16% 11% 3 5% 3 3 3 2 3 5% 47%	4884
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 4 5% 8% 48%	4980
	21st to end	Day	16% 12% 3 8% 5% 4 5% 4 5% 7% 30%	5525
April	1st to 10th	Day	16% 9% 3 7% 5% 4 4 3 4 6% 39%	2400
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 5% 5% 40%	2374
	21st to end	Day	21% 8% 2 7% 4 4 5% 4 5% 6% 34%	2413
May	1st to 10th	Day	13% 7% 2 7% 5% 5% 4 4 7% 8% 37%	5862
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 5% 7% 43%	6220
	21st to end	Day	16% 7% 3 6% 4 4 4 4 5% 6% 40%	6935
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	2800
	11th to 20th	Day	6% 6% 3 6% 5% 5% 5% 5% 6% 9% 46%	2800
	21st to end	Day	9% 6% 2 5% 5% 4 5% 4 6% 9% 45%	2800
July	1st to 10th	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 9% 36%	4511
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 6% 9% 48%	4362
	21st to end	Day	7% 4 2 5% 5% 5% 6% 4 8% 11% 43%	4465
August	1st to 10th	Day	5% 3 1 5% 4 5% 5% 5% 8% 12% 45%	4104
	11th to 20th	Day	14% 5% 2 5% 4 4 5% 4 6% 9% 42%	3982
	21st to end	Day	6% 4 2 6% 3 5% 4 4 6% 9% 51%	4180
September	1st to 10th	Day	12% 4 2 5% 3 4 4 3 5% 7% 52%	2280
	11th to 20th	Day	11% 4 2 5% 3 3 4 4 5% 9% 51%	2280
	21st to end	Day	11% 5% 1 5% 3 4 4 3 4 7% 53%	1983
October	1st to 10th	Day	13% 6% 2 5% 4 3 3 3 4 6% 51%	1900
	11th to 20th	Day	14% 7% 3 5% 3 3 3 3 4 5% 50%	1900
	21st to end	Day	16% 8% 2 6% 4 4 3 3 5% 6% 44%	2090
November	1st to 10th	Day	11% 8% 2 5% 4 3 4 2 5% 6% 50%	1840
	11th to 20th	Day	14% 8% 3 8% 4 3 3 3 4 6% 44%	1699
	21st to end	Day	17% 11% 3 6% 4 3 3 3 5% 5% 41%	1600
December	1st to 10th	Day	7% 8% 2 6% 4 3 4 3 4 6% 53%	2610
	11th to 20th	Day	12% 8% 4 9% 4 5% 5% 5% 6% 7% 36%	3008
	21st to end	Day	21% 17% 8% 10% 4 4 4 2 5% 4 19%	3982
January	1st to 10th	Night	13% 11% 6% 16% 5% 5% 4 3 4 5% 28%	6320
	11th to 20th	Night	10% 10% 5% 12% 7% 5% 6% 3 5% 4 33%	5900
	21st to end	Night	14% 12% 6% 10% 5% 4 4 3 4 5% 33%	6490
February	1st to 10th	Night	13% 11% 5% 9% 5% 4 3 3 5% 7% 35%	2600
	11th to 20th	Night	13% 10% 4 7% 4 4 4 3 5% 7% 38%	2523
	21st to end	Night	14% 9% 3 7% 4 3 3 2 4 5% 46%	1980
March	1st to 10th	Night	18% 11% 3 5% 3 3 3 3 3 5% 44%	5012
	11th to 20th	Night	12% 8% 2 5% 3 3 4 3 4 5% 53%	4980
	21st to end	Night	16% 10% 4 10% 6% 5% 5% 3 4 6% 30%	5404
April	1st to 10th	Night	12% 7% 3 5% 4 4 5% 3 4 8% 46%	2000
	11th to 20th	Night	13% 9% 2 6% 4 4 4 3 6% 6% 42%	1975
	21st to end	Night	17% 8% 3 6% 4 4 4 4 5% 5% 39%	1983
May	1st to 10th	Night	14% 8% 3 7% 4 4 5% 4 6% 7% 38%	4053
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 4 7% 8% 44%	3693
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 7% 43%	3942
June	1st to 10th	Night	6% 4 1 4 4 3 5% 4 7% 9% 53%	1600
	11th to 20th	Night	7% 4 2 5% 3 4 5% 3 6% 9% 52%	1600
	21st to end	Night	6% 4 2 4 4 5% 4 3 6% 7% 54%	1600
July	1st to 10th	Night	13% 4 2 5% 4 3 5% 4 5% 9% 46%	2570
	11th to 20th	Night	4 3 1 5% 3 4 3 3 6% 8% 60%	2590
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 7% 9% 50%	3098
August	1st to 10th	Night	4 3 1 4 3 3 4 3 6% 9% 60%	2836
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 6% 54%	2852
	21st to end	Night	4 3 2 4 3 3 4 3 6% 9% 58%	3476
September	1st to 10th	Night	10% 4 1 4 3 3 3 2 5% 6% 58%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 53%	1900
	21st to end	Night	8% 6% 2 5% 3 4 3 3 5% 6% 57%	2175
October	1st to 10th	Night	11% 6% 2 4 4 3 3 2 4 5% 55%	2280
	11th to 20th	Night	12% 5% 1 5% 3 3 4 3 4 5% 54%	2280
	21st to end	Night	17% 7% 2 6% 3 3 3 3 4 5% 47%	2508
November	1st to 10th	Night	11% 5% 2 4 3 2 3 2 4 6% 57%	2455
	11th to 20th	Night	12% 7% 3 5% 4 4 4 3 5% 6% 48%	2699
	21st to end	Night	17% 9% 3 7% 3 3 3 3 4 6% 42%	2800
December	1st to 10th	Night	9% 8% 2 7% 4 3 4 3 5% 5% 50%	4580
	11th to 20th	Night	12% 10% 3 8% 4 4 4 4 5% 7% 39%	5199
	21st to end	Night	22% 17% 6% 9% 5% 4 3 2 4 4 23%	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	55% 5% 10% 18% 10% 2	3642
	11th to 20th	Day	47% 4 10% 19% 14% 6%	4080
	21st to end	Day	57% 4 9% 19% 10% 1	4488
February	1st to 10th	Day	48% 6% 14% 20% 10% 2	1800
	11th to 20th	Day	47% 4 12% 22% 14% 2	1771
	21st to end	Day	43% 5% 10% 25% 15% 2	1650
March	1st to 10th	Day	42% 4 8% 24% 20% 3	4884
	11th to 20th	Day	35% 5% 9% 27% 21% 3	4980
	21st to end	Day	52% 6% 15% 21% 5% 1	5527
April	1st to 10th	Day	46% 5% 10% 26% 12% 1	2400
	11th to 20th	Day	46% 5% 10% 23% 15% 1	2374
	21st to end	Day	50% 6% 12% 20% 12% 1	2413
May	1st to 10th	Day	42% 7% 13% 18% 19% 1	5900
	11th to 20th	Day	40% 6% 10% 27% 14% 2	6224
	21st to end	Day	44% 5% 9% 24% 16% 1	6949
June	1st to 10th	Day	33% 9% 15% 28% 13% 2	2800
	11th to 20th	Day	34% 7% 13% 25% 18% 3	2800
	21st to end	Day	34% 8% 15% 26% 15% 2	2800
July	1st to 10th	Day	42% 7% 11% 25% 12% 2	4442
	11th to 20th	Day	30% 7% 13% 30% 18% 2	4287
	21st to end	Day	32% 9% 16% 28% 14% 1	4325
August	1st to 10th	Day	29% 8% 14% 34% 15% 1	4090
	11th to 20th	Day	38% 6% 12% 26% 17% 1	4021
	21st to end	Day	30% 6% 17% 29% 13% 5%	4179
September	1st to 10th	Day	32% 5% 11% 24% 21% 6%	2280
	11th to 20th	Day	30% 5% 11% 30% 21% 3	2280
	21st to end	Day	33% 5% 10% 30% 21% 3	1983
October	1st to 10th	Day	23% 3 6% 18% 47% 4	3160
	11th to 20th	Day	24% 3 6% 22% 36% 8%	3140
	21st to end	Day	39% 4 8% 25% 23% 2	3428
November	1st to 10th	Day	36% 4 13% 25% 20% 3	1840
	11th to 20th	Day	42% 4 8% 24% 18% 2	1699
	21st to end	Day	46% 3 13% 24% 13%	1600
December	1st to 10th	Day	33% 4 17% 30% 15% 1	2610
	11th to 20th	Day	47% 5% 13% 24% 10% 1	3005
	21st to end	Day	70% 3 11% 12% 5% 1	3982
January	1st to 10th	Night	59% 4 9% 20% 8% 1	6320
	11th to 20th	Night	54% 3 10% 17% 13% 3	5900
	21st to end	Night	54% 4 9% 18% 13% 2	6490
February	1st to 10th	Night	50% 4 12% 20% 12% 2	2600
	11th to 20th	Night	45% 4 11% 24% 14% 2	2524
	21st to end	Night	42% 3 9% 23% 19% 4	1980
March	1st to 10th	Night	44% 3 6% 23% 21% 2	5012
	11th to 20th	Night	35% 4 7% 29% 20% 5%	4980
	21st to end	Night	55% 6% 12% 18% 7% 2	5404
April	1st to 10th	Night	37% 5% 13% 26% 17% 3	2000
	11th to 20th	Night	42% 4 10% 24% 17% 4	1975
	21st to end	Night	46% 5% 11% 20% 16% 1	1983
May	1st to 10th	Night	43% 6% 12% 23% 13% 2	4080
	11th to 20th	Night	35% 8% 13% 26% 14% 3	3694
	21st to end	Night	40% 6% 10% 22% 21% 1	3950
June	1st to 10th	Night	26% 8% 17% 30% 16% 3	1600
	11th to 20th	Night	29% 7% 12% 27% 22% 3	1600
	21st to end	Night	27% 7% 15% 26% 21% 4	1600
July	1st to 10th	Night	35% 5% 12% 26% 17% 3	2530
	11th to 20th	Night	22% 6% 15% 32% 24% 2	2542
	21st to end	Night	28% 8% 20% 25% 18% 2	2999
August	1st to 10th	Night	21% 6% 17% 35% 19% 1	2826
	11th to 20th	Night	32% 5% 12% 28% 22% 1	2879
	21st to end	Night	23% 5% 19% 32% 16% 5%	3476
September	1st to 10th	Night	28% 4 10% 26% 25% 8%	1900
	11th to 20th	Night	30% 5% 12% 27% 21% 5%	1900
	21st to end	Night	29% 4 9% 30% 24% 3	2175
October	1st to 10th	Night	20% 2 7% 20% 47% 4	3800
	11th to 20th	Night	25% 3 7% 22% 32% 10%	3779
	21st to end	Night	40% 3 7% 24% 22% 3	4120
November	1st to 10th	Night	30% 4 14% 27% 21% 5%	2455
	11th to 20th	Night	38% 4 9% 28% 18% 3	2699
	21st to end	Night	45% 4 9% 27% 14% 2	2800
December	1st to 10th	Night	36% 4 11% 36% 12% 1	4580
	11th to 20th	Night	45% 5% 12% 24% 14%	5201
	21st to end	Night	66% 4 10% 14% 5% 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	19% 15% 37% 21% 7%	300
	11th to 20th	Day	24% 17% 43% 15% 1	300
	21st to end	Day	22% 16% 44% 17% 2	330
February	1st to 10th	Day	22% 19% 40% 16% 3	300
	11th to 20th	Day	21% 20% 36% 18% 4 1	300
	21st to end	Day	18% 18% 47% 12% 4	249
March	1st to 10th	Day	17% 18% 46% 17% 2	300
	11th to 20th	Day	25% 15% 36% 21% 3	300
	21st to end	Day	34% 19% 30% 14% 3 1	355
April	1st to 10th	Day	22% 16% 35% 20% 6% 1	500
	11th to 20th	Day	21% 18% 30% 22% 8% 1	492
	21st to end	Day	22% 15% 34% 22% 6% 1	513
May	1st to 10th	Day	18% 12% 36% 23% 9% 2	703
	11th to 20th	Day	20% 10% 28% 28% 13% 2	725
	21st to end	Day	17% 9% 26% 27% 16% 6%	789
June	1st to 10th	Day	7% 5% 20% 37% 23% 8%	730
	11th to 20th	Day	9% 5% 25% 36% 20% 5%	730
	21st to end	Day	10% 8% 31% 30% 17% 4	730
July	1st to 10th	Day	9% 4 15% 34% 25% 13%	697
	11th to 20th	Day	7% 4 20% 37% 23% 9%	668
	21st to end	Day	9% 3 17% 38% 28% 6%	739
August	1st to 10th	Day	6% 3 18% 39% 26% 7%	676
	11th to 20th	Day	10% 4 16% 36% 28% 6%	632
	21st to end	Day	8% 3 14% 35% 29% 12%	539
September	1st to 10th	Day	12% 4 18% 33% 26% 8%	490
	11th to 20th	Day	10% 3 20% 32% 24% 11%	490
	21st to end	Day	11% 7% 33% 21% 21% 7%	307
October	1st to 10th	Day	18% 6% 31% 24% 14% 6%	300
	11th to 20th	Day	16% 22% 32% 22% 8% 1	300
	21st to end	Day	24% 17% 32% 20% 6%	330
November	1st to 10th	Day	16% 9% 39% 25% 8% 3	300
	11th to 20th	Day	18% 18% 35% 21% 6% 2	300
	21st to end	Day	22% 16% 35% 23% 4	300
December	1st to 10th	Day	11% 18% 41% 22% 6% 3	300
	11th to 20th	Day	18% 17% 40% 19% 6%	300
	21st to end	Day	25% 18% 39% 14% 3	330
January	1st to 10th	Night	14% 14% 41% 24% 7%	1000
	11th to 20th	Night	16% 15% 41% 22% 6% 1	1000
	21st to end	Night	16% 11% 41% 28% 3	1100
February	1st to 10th	Night	20% 12% 40% 25% 3	1000
	11th to 20th	Night	18% 15% 38% 27% 3	969
	21st to end	Night	19% 13% 42% 22% 4	660
March	1st to 10th	Night	17% 12% 41% 25% 4	645
	11th to 20th	Night	23% 10% 33% 28% 6% 1	600
	21st to end	Night	26% 11% 38% 20% 5%	660
April	1st to 10th	Night	15% 12% 39% 29% 5%	600
	11th to 20th	Night	18% 12% 34% 28% 7% 1	593
	21st to end	Night	21% 9% 33% 30% 7%	600
May	1st to 10th	Night	18% 5% 34% 36% 7%	600
	11th to 20th	Night	15% 6% 31% 34% 14% 1	591
	21st to end	Night	14% 5% 25% 36% 19% 1	650
June	1st to 10th	Night	7% 3 19% 46% 24% 2	600
	11th to 20th	Night	8% 3 23% 44% 21% 2	600
	21st to end	Night	6% 4 29% 41% 19%	600
July	1st to 10th	Night	8% 2 12% 40% 34% 4	570
	11th to 20th	Night	6% 1 16% 45% 28% 4	552
	21st to end	Night	8% 15% 42% 33% 1	624
August	1st to 10th	Night	6% 2 14% 48% 28% 3	567
	11th to 20th	Night	10% 2 14% 40% 30% 4	564
	21st to end	Night	7% 2 12% 43% 34% 2	627
September	1st to 10th	Night	12% 2 17% 38% 28% 4	570
	11th to 20th	Night	12% 2 17% 39% 25% 5%	570
	21st to end	Night	9% 5% 25% 37% 20% 4	665
October	1st to 10th	Night	13% 4 29% 33% 18% 2	760
	11th to 20th	Night	15% 10% 35% 30% 10% 1	760
	21st to end	Night	21% 11% 33% 28% 7%	836
November	1st to 10th	Night	12% 9% 37% 32% 9% 1	780
	11th to 20th	Night	16% 12% 39% 26% 7%	899
	21st to end	Night	22% 10% 36% 26% 7%	1000
December	1st to 10th	Night	17% 10% 39% 27% 6% 1	1000
	11th to 20th	Night	21% 10% 36% 27% 5%	1000
	21st to end	Night	23% 13% 36% 26% 2	1100

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