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 2026-10-29.

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%	149856
	Night	12% 8% 3 7% 4 4 4 3 5% 6% 44%	142611
Transparency	Day	41% 5% 12% 25% 16% 2	153457
	Night	40% 5% 11% 24% 17% 3	147089
Seeing	Day	15% 10% 29% 27% 14% 4	18489
	Night	15% 9% 32% 31% 12% 1	28240

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	11% 12% 4 12% 5% 4 5% 3 5% 6% 33%	4729
	11th to 20th	Day	7% 8% 3 9% 6% 6% 7% 4 5% 6% 40%	5310
	21st to end	Day	11% 16% 6% 10% 5% 4 3 3 3 5% 34%	5812
February	1st to 10th	Day	14% 10% 3 8% 4 5% 4 4 6% 10% 32%	1890
	11th to 20th	Day	12% 11% 4 8% 5% 4 3 3 6% 6% 38%	1853
	21st to end	Day	13% 10% 3 8% 4 4 4 3 5% 5% 43%	1730
March	1st to 10th	Day	16% 11% 3 5% 3 3 3 2 3 5% 47%	4993
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 4 5% 8% 47%	5090
	21st to end	Day	16% 12% 3 8% 5% 5% 5% 4 5% 7% 31%	5647
April	1st to 10th	Day	17% 9% 3 7% 5% 4 4 3 4 6% 38%	2520
	11th to 20th	Day	15% 9% 3 7% 4 4 4 3 5% 5% 40%	2494
	21st to end	Day	20% 8% 2 7% 4 4 5% 4 5% 7% 34%	2534
May	1st to 10th	Day	14% 7% 2 7% 5% 5% 4 4 6% 8% 38%	7617
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 5% 7% 44%	8097
	21st to end	Day	17% 8% 3 8% 5% 5% 4 4 5% 6% 37%	9047
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	2940
	11th to 20th	Day	6% 6% 3 6% 6% 5% 5% 5% 6% 9% 46%	2940
	21st to end	Day	9% 6% 2 5% 5% 4 5% 4 6% 9% 44%	2940
July	1st to 10th	Day	8% 6% 2 6% 5% 4 5% 4 7% 9% 43%	8280
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	8146
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 7% 10% 40%	8337
August	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 5% 7% 11% 43%	6014
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 4 6% 8% 38%	5859
	21st to end	Day	5% 4 2 5% 3 5% 4 4 7% 11% 52%	6080
September	1st to 10th	Day	11% 4 2 5% 3 4 4 3 5% 7% 52%	2520
	11th to 20th	Day	10% 5% 2 6% 3 3 4 4 5% 9% 49%	2520
	21st to end	Day	12% 5% 2 5% 3 4 4 4 4 6% 51%	2191
October	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 5% 53%	2100
	11th to 20th	Day	13% 7% 3 4 3 4 4 3 4 5% 50%	2100
	21st to end	Day	15% 7% 3 6% 4 4 3 3 5% 6% 44%	2280
November	1st to 10th	Day	11% 8% 2 5% 3 3 4 2 4 6% 50%	1934
	11th to 20th	Day	13% 8% 3 8% 4 3 3 3 4 6% 44%	1784
	21st to end	Day	17% 11% 3 6% 4 3 3 3 5% 5% 41%	1680
December	1st to 10th	Day	7% 8% 3 6% 4 3 4 3 4 6% 53%	2690
	11th to 20th	Day	13% 8% 4 9% 4 5% 5% 4 6% 7% 36%	3088
	21st to end	Day	21% 17% 8% 11% 4 4 4 2 5% 4 19%	4070
January	1st to 10th	Night	12% 12% 5% 14% 5% 5% 4 3 4 5% 32%	8190
	11th to 20th	Night	8% 8% 4 10% 6% 5% 6% 4 5% 5% 38%	7680
	21st to end	Night	12% 12% 6% 10% 6% 4 4 3 4 5% 35%	8402
February	1st to 10th	Night	13% 10% 5% 9% 5% 4 4 3 5% 7% 35%	2730
	11th to 20th	Night	12% 10% 4 7% 4 4 4 3 5% 7% 38%	2652
	21st to end	Night	14% 8% 3 7% 4 4 3 3 4 5% 45%	2076
March	1st to 10th	Night	18% 11% 3 5% 3 3 3 3 3 5% 44%	5124
	11th to 20th	Night	12% 8% 2 5% 3 3 4 3 4 6% 52%	5090
	21st to end	Night	16% 10% 4 10% 6% 5% 5% 4 4 6% 30%	5524
April	1st to 10th	Night	13% 7% 3 5% 4 3 5% 3 4 7% 46%	2100
	11th to 20th	Night	13% 9% 2 6% 4 4 4 3 6% 7% 42%	2075
	21st to end	Night	17% 9% 3 6% 4 4 4 4 5% 5% 39%	2082
May	1st to 10th	Night	13% 8% 3 7% 4 4 5% 4 5% 7% 41%	5266
	11th to 20th	Night	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4793
	21st to end	Night	15% 7% 2 7% 4 4 4 4 5% 7% 40%	5139
June	1st to 10th	Night	7% 4 1 4 4 3 5% 4 7% 9% 52%	1680
	11th to 20th	Night	7% 4 2 5% 3 4 4 3 6% 9% 51%	1680
	21st to end	Night	6% 5% 2 5% 4 5% 4 3 6% 7% 53%	1680
July	1st to 10th	Night	9% 4 2 5% 3 3 4 3 5% 11% 50%	4708
	11th to 20th	Night	5% 4 2 6% 4 4 4 4 5% 8% 53%	4823
	21st to end	Night	9% 5% 2 5% 4 4 4 4 7% 10% 46%	5770
August	1st to 10th	Night	7% 4 1 5% 4 3 4 3 6% 8% 55%	4156
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 7% 49%	4200
	21st to end	Night	3 2 2 4 3 3 4 4 6% 9% 61%	5046
September	1st to 10th	Night	9% 4 1 5% 3 3 3 2 5% 6% 58%	2100
	11th to 20th	Night	11% 6% 2 6% 3 4 4 3 5% 7% 51%	2100
	21st to end	Night	9% 6% 2 5% 3 3 3 3 5% 5% 55%	2404
October	1st to 10th	Night	11% 6% 2 4 3 3 3 2 4 5% 57%	2520
	11th to 20th	Night	13% 6% 2 6% 3 3 4 3 4 5% 53%	2520
	21st to end	Night	17% 7% 2 6% 3 3 3 3 4 5% 47%	2737
November	1st to 10th	Night	10% 6% 2 5% 3 2 3 2 4 6% 57%	2581
	11th to 20th	Night	12% 7% 3 5% 4 4 4 3 5% 6% 48%	2834
	21st to end	Night	17% 9% 3 7% 3 3 3 3 4 6% 41%	2940
December	1st to 10th	Night	9% 8% 3 7% 4 3 4 3 5% 5% 49%	4720
	11th to 20th	Night	12% 10% 3 8% 4 4 4 4 5% 7% 39%	5339
	21st to end	Night	22% 17% 6% 9% 5% 4 3 2 4 4 23%	7150

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 11% 19% 12% 2	4730
	11th to 20th	Day	45% 4 9% 20% 17% 5%	5310
	21st to end	Day	55% 3 9% 22% 9% 1	5812
February	1st to 10th	Day	47% 6% 14% 21% 10% 2	1890
	11th to 20th	Day	47% 4 11% 23% 13% 2	1862
	21st to end	Day	43% 5% 10% 26% 15% 2	1730
March	1st to 10th	Day	42% 4 8% 24% 19% 3	4993
	11th to 20th	Day	35% 5% 9% 27% 21% 3	5090
	21st to end	Day	52% 6% 15% 21% 5% 1	5649
April	1st to 10th	Day	47% 5% 9% 25% 12% 1	2520
	11th to 20th	Day	46% 5% 10% 23% 15% 1	2494
	21st to end	Day	49% 6% 12% 20% 12% 1	2534
May	1st to 10th	Day	43% 6% 11% 21% 19% 1	7655
	11th to 20th	Day	39% 6% 11% 27% 15% 2	8101
	21st to end	Day	47% 5% 9% 22% 16% 1	9061
June	1st to 10th	Day	34% 9% 15% 27% 13% 2	2940
	11th to 20th	Day	34% 7% 12% 25% 19% 2	2940
	21st to end	Day	35% 8% 15% 26% 15% 2	2940
July	1st to 10th	Day	36% 6% 13% 28% 15% 1	8211
	11th to 20th	Day	32% 7% 15% 26% 17% 3	8071
	21st to end	Day	37% 7% 17% 29% 9%	8155
August	1st to 10th	Day	34% 7% 13% 29% 17% 1	6000
	11th to 20th	Day	43% 7% 13% 24% 12%	5898
	21st to end	Day	27% 5% 17% 31% 16% 4	6079
September	1st to 10th	Day	31% 5% 12% 25% 21% 5%	2520
	11th to 20th	Day	32% 6% 11% 29% 19% 3	2520
	21st to end	Day	35% 4 9% 28% 20% 3	2191
October	1st to 10th	Day	23% 3 6% 19% 47% 4	3360
	11th to 20th	Day	25% 3 6% 22% 36% 8%	3340
	21st to end	Day	39% 4 8% 25% 22% 2	3618
November	1st to 10th	Day	35% 4 13% 25% 20% 3	1934
	11th to 20th	Day	42% 4 8% 25% 18% 2	1784
	21st to end	Day	47% 3 13% 23% 14%	1680
December	1st to 10th	Day	34% 4 17% 30% 15% 1	2690
	11th to 20th	Day	47% 5% 12% 25% 10% 1	3085
	21st to end	Day	69% 3 11% 12% 5% 1	4070
January	1st to 10th	Night	55% 4 13% 19% 8% 1	8191
	11th to 20th	Night	47% 3 9% 21% 17% 3	7680
	21st to end	Night	53% 4 10% 19% 12% 2	8402
February	1st to 10th	Night	49% 4 11% 22% 12% 2	2730
	11th to 20th	Night	45% 4 11% 25% 13% 2	2653
	21st to end	Night	42% 3 10% 23% 18% 3	2076
March	1st to 10th	Night	44% 3 6% 23% 21% 2	5124
	11th to 20th	Night	35% 4 7% 29% 20% 6%	5090
	21st to end	Night	54% 6% 12% 18% 7% 2	5524
April	1st to 10th	Night	38% 5% 12% 26% 16% 2	2100
	11th to 20th	Night	42% 4 10% 24% 16% 4	2075
	21st to end	Night	46% 5% 11% 21% 16% 1	2082
May	1st to 10th	Night	42% 5% 10% 26% 14% 3	5293
	11th to 20th	Night	35% 7% 14% 24% 17% 4	4794
	21st to end	Night	43% 6% 10% 20% 20% 1	5149
June	1st to 10th	Night	27% 8% 16% 30% 16% 3	1680
	11th to 20th	Night	29% 7% 12% 27% 22% 4	1680
	21st to end	Night	28% 7% 15% 26% 20% 4	1680
July	1st to 10th	Night	29% 6% 15% 28% 20% 2	4670
	11th to 20th	Night	29% 8% 14% 25% 22% 2	4778
	21st to end	Night	32% 7% 20% 30% 10% 1	5641
August	1st to 10th	Night	26% 6% 15% 33% 19% 1	4146
	11th to 20th	Night	35% 6% 17% 26% 15% 1	4227
	21st to end	Night	21% 5% 17% 36% 17% 4	5046
September	1st to 10th	Night	28% 4 10% 27% 25% 7%	2100
	11th to 20th	Night	32% 5% 12% 27% 20% 5%	2100
	21st to end	Night	31% 4 9% 28% 24% 3	2404
October	1st to 10th	Night	20% 2 6% 21% 47% 4	4040
	11th to 20th	Night	26% 3 7% 22% 32% 10%	4019
	21st to end	Night	40% 3 7% 24% 22% 3	4349
November	1st to 10th	Night	30% 4 14% 27% 21% 4	2581
	11th to 20th	Night	38% 4 9% 29% 18% 3	2834
	21st to end	Night	46% 4 9% 26% 14% 1	2940
December	1st to 10th	Night	37% 4 11% 36% 12% 1	4720
	11th to 20th	Night	45% 5% 11% 24% 14%	5341
	21st to end	Night	66% 4 10% 14% 5% 1	7150

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	20% 16% 37% 21% 7%	330
	11th to 20th	Day	22% 19% 44% 14% 1	330
	21st to end	Day	21% 17% 45% 16% 1	363
February	1st to 10th	Day	22% 18% 40% 17% 3	330
	11th to 20th	Day	20% 22% 36% 17% 4 1	330
	21st to end	Day	18% 18% 48% 12% 4	273
March	1st to 10th	Day	20% 19% 44% 16% 2	330
	11th to 20th	Day	26% 15% 35% 21% 3	330
	21st to end	Day	33% 20% 32% 12% 2 1	389
April	1st to 10th	Day	24% 16% 35% 19% 6% 1	540
	11th to 20th	Day	21% 19% 31% 20% 7% 1	532
	21st to end	Day	21% 15% 34% 22% 6% 1	554
May	1st to 10th	Day	18% 13% 36% 22% 8% 2	753
	11th to 20th	Day	20% 10% 29% 27% 12% 2	775
	21st to end	Day	17% 8% 26% 27% 16% 6%	844
June	1st to 10th	Day	7% 5% 22% 36% 22% 7%	780
	11th to 20th	Day	9% 6% 25% 36% 19% 4	780
	21st to end	Day	12% 7% 32% 30% 16% 3	780
July	1st to 10th	Day	8% 4 15% 35% 24% 13%	771
	11th to 20th	Day	7% 4 19% 36% 24% 9%	768
	21st to end	Day	9% 3 18% 38% 27% 5%	849
August	1st to 10th	Day	6% 4 19% 39% 26% 7%	776
	11th to 20th	Day	10% 4 17% 37% 27% 6%	728
	21st to end	Day	8% 3 16% 36% 28% 11%	627
September	1st to 10th	Day	12% 4 18% 35% 25% 7%	570
	11th to 20th	Day	11% 4 20% 33% 22% 10%	570
	21st to end	Day	13% 7% 30% 22% 21% 8%	367
October	1st to 10th	Day	16% 6% 32% 26% 14% 6%	360
	11th to 20th	Day	17% 20% 30% 24% 9% 1	360
	21st to end	Day	22% 17% 32% 21% 7%	387
November	1st to 10th	Day	16% 10% 40% 24% 7% 3	330
	11th to 20th	Day	18% 18% 36% 21% 6% 2	330
	21st to end	Day	24% 16% 34% 22% 5%	330
December	1st to 10th	Day	12% 18% 41% 22% 5% 3	330
	11th to 20th	Day	18% 16% 41% 18% 6%	330
	21st to end	Day	25% 18% 40% 14% 3	363
January	1st to 10th	Night	14% 14% 41% 24% 7%	1050
	11th to 20th	Night	16% 16% 42% 21% 5% 1	1050
	21st to end	Night	16% 13% 41% 27% 3	1155
February	1st to 10th	Night	19% 13% 40% 25% 3	1050
	11th to 20th	Night	18% 15% 37% 27% 3	1018
	21st to end	Night	19% 14% 42% 21% 4	692
March	1st to 10th	Night	18% 12% 41% 25% 4	677
	11th to 20th	Night	23% 10% 33% 28% 6% 1	630
	21st to end	Night	25% 11% 38% 20% 5%	693
April	1st to 10th	Night	16% 12% 40% 28% 5%	630
	11th to 20th	Night	18% 13% 35% 27% 7% 1	623
	21st to end	Night	21% 9% 33% 30% 7%	630
May	1st to 10th	Night	17% 6% 35% 35% 7%	630
	11th to 20th	Night	15% 7% 31% 33% 13% 1	621
	21st to end	Night	14% 5% 25% 36% 19% 1	683
June	1st to 10th	Night	8% 3 19% 45% 24% 2	630
	11th to 20th	Night	8% 3 24% 43% 20% 1	630
	21st to end	Night	7% 4 29% 40% 19%	630
July	1st to 10th	Night	7% 2 12% 40% 34% 4	615
	11th to 20th	Night	6% 2 15% 43% 29% 5%	612
	21st to end	Night	8% 1 16% 43% 32% 1	690
August	1st to 10th	Night	6% 2 15% 46% 28% 3	627
	11th to 20th	Night	10% 2 15% 39% 31% 4	624
	21st to end	Night	6% 2 12% 44% 34% 2	693
September	1st to 10th	Night	11% 2 17% 40% 27% 3	630
	11th to 20th	Night	12% 2 17% 39% 25% 4	630
	21st to end	Night	10% 5% 24% 35% 21% 4	735
October	1st to 10th	Night	13% 4 29% 34% 19% 2	840
	11th to 20th	Night	15% 10% 34% 31% 9%	840
	21st to end	Night	20% 11% 33% 29% 7%	913
November	1st to 10th	Night	12% 10% 38% 32% 9%	820
	11th to 20th	Night	15% 12% 40% 26% 7%	944
	21st to end	Night	23% 10% 35% 26% 6%	1050
December	1st to 10th	Night	18% 11% 39% 26% 6% 1	1050
	11th to 20th	Night	21% 10% 36% 27% 5%	1050
	21st to end	Night	23% 13% 37% 26% 2	1155

Page generated at 2026-10-26 03:37:46. Version ac07

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