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 2024-03-23.

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	13% 8% 3 6% 5% 3 5% 5% 5% 7% 40%	78779
	Night	13% 8% 4 6% 5% 3 4 4 5% 6% 43%	81158
Transparency	Day	43% 6% 12% 24% 14% 2	78491
	Night	42% 5% 11% 24% 15% 3	80966
Seeing	Day	15% 10% 28% 28% 16% 5%	14783
	Night	15% 8% 32% 31% 12% 1	24848

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 13% 6% 3 4 4 4 7% 31%	2537
	11th to 20th	Day	12% 11% 4 8% 6% 4 8% 4 5% 6% 31%	2850
	21st to end	Day	15% 19% 8% 10% 5% 3 3 3 3 5% 25%	3135
February	1st to 10th	Day	15% 10% 3 8% 5% 3 5% 5% 6% 9% 32%	1710
	11th to 20th	Day	13% 9% 5% 7% 5% 3 4 4 6% 6% 39%	1671
	21st to end	Day	14% 10% 3 6% 5% 3 4 4 5% 6% 41%	1570
March	1st to 10th	Day	14% 11% 4 6% 5% 3 4 4 4 6% 38%	2063
	11th to 20th	Day	14% 10% 4 8% 6% 3 5% 5% 4 6% 35%	2090
	21st to end	Day	20% 12% 5% 8% 5% 3 4 4 4 6% 28%	2222
April	1st to 10th	Day	16% 8% 3 5% 6% 3 4 4 4 6% 40%	2160
	11th to 20th	Day	16% 10% 3 6% 5% 3 4 4 5% 5% 40%	2134
	21st to end	Day	21% 7% 3 6% 5% 3 5% 4 4 6% 35%	2171
May	1st to 10th	Day	16% 8% 3 7% 6% 4 5% 5% 6% 7% 33%	2340
	11th to 20th	Day	18% 7% 3 7% 5% 3 5% 5% 5% 7% 36%	2436
	21st to end	Day	14% 7% 3 6% 6% 4 6% 5% 6% 8% 35%	2725
June	1st to 10th	Day	7% 5% 2 5% 6% 4 5% 5% 7% 10% 45%	2520
	11th to 20th	Day	6% 6% 3 5% 6% 4 5% 6% 5% 9% 47%	2520
	21st to end	Day	9% 5% 3 5% 5% 3 5% 6% 6% 9% 45%	2520
July	1st to 10th	Day	7% 4 2 5% 5% 3 5% 6% 7% 10% 47%	2520
	11th to 20th	Day	7% 3 2 5% 6% 3 6% 6% 6% 8% 49%	2484
	21st to end	Day	8% 4 2 4 5% 3 5% 5% 6% 10% 46%	2546
August	1st to 10th	Day	8% 4 2 5% 6% 4 6% 7% 7% 11% 40%	2328
	11th to 20th	Day	8% 5% 3 5% 5% 3 6% 6% 6% 8% 44%	2270
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 8% 52%	2376
September	1st to 10th	Day	12% 4 2 5% 3 3 5% 4 5% 7% 50%	2160
	11th to 20th	Day	10% 3 2 4 3 2 4 4 5% 10% 52%	2160
	21st to end	Day	10% 4 2 4 5% 3 4 4 4 7% 53%	1879
October	1st to 10th	Day	14% 6% 3 5% 4 2 3 4 4 6% 49%	1800
	11th to 20th	Day	15% 8% 3 4 4 3 3 3 4 6% 48%	1800
	21st to end	Day	17% 7% 2 5% 4 2 4 4 5% 6% 43%	1980
November	1st to 10th	Day	10% 7% 3 4 4 2 4 4 4 6% 51%	1746
	11th to 20th	Day	14% 7% 3 7% 5% 2 4 4 4 6% 44%	1615
	21st to end	Day	18% 9% 4 5% 4 2 3 4 5% 5% 41%	1520
December	1st to 10th	Day	12% 11% 3 6% 5% 3 5% 5% 4 6% 39%	1520
	11th to 20th	Day	12% 9% 4 7% 4 3 4 5% 5% 7% 39%	1918
	21st to end	Day	21% 12% 9% 10% 6% 3 5% 4 4 4 23%	2783
January	1st to 10th	Night	11% 10% 7% 12% 7% 4 4 4 4 5% 32%	4414
	11th to 20th	Night	12% 11% 6% 9% 6% 3 8% 5% 6% 5% 28%	4120
	21st to end	Night	17% 14% 8% 9% 6% 3 4 4 4 6% 26%	4532
February	1st to 10th	Night	14% 10% 6% 8% 5% 3 4 4 5% 7% 35%	2470
	11th to 20th	Night	13% 9% 4 6% 5% 3 4 4 6% 8% 40%	2394
	21st to end	Night	14% 8% 4 6% 5% 2 4 3 4 5% 45%	1884
March	1st to 10th	Night	12% 9% 4 6% 4 2 4 4 5% 5% 46%	2133
	11th to 20th	Night	17% 9% 3 6% 4 3 4 4 4 6% 39%	2090
	21st to end	Night	22% 11% 4 7% 7% 3 6% 4 4 7% 25%	2178
April	1st to 10th	Night	11% 7% 3 5% 4 2 5% 4 4 7% 47%	1800
	11th to 20th	Night	14% 9% 3 5% 5% 3 5% 4 5% 6% 42%	1775
	21st to end	Night	18% 8% 3 5% 4 3 4 5% 5% 5% 41%	1785
May	1st to 10th	Night	14% 6% 3 6% 5% 3 4 6% 6% 7% 40%	1620
	11th to 20th	Night	13% 7% 4 6% 4 3 4 5% 5% 6% 43%	1457
	21st to end	Night	11% 6% 2 5% 5% 4 5% 5% 5% 8% 43%	1551
June	1st to 10th	Night	6% 3 1 3 5% 2 5% 4 7% 9% 54%	1440
	11th to 20th	Night	7% 4 3 5% 4 2 5% 5% 5% 9% 51%	1440
	21st to end	Night	6% 4 2 4 5% 3 4 5% 6% 8% 54%	1440
July	1st to 10th	Night	7% 3 1 4 4 2 5% 5% 5% 10% 53%	1440
	11th to 20th	Night	5% 3 2 4 4 3 4 4 5% 8% 59%	1472
	21st to end	Night	7% 4 2 4 4 2 4 5% 6% 9% 54%	1772
August	1st to 10th	Night	5% 4 2 4 4 3 5% 5% 7% 10% 51%	1611
	11th to 20th	Night	9% 4 2 4 4 3 4 3 4 7% 57%	1628
	21st to end	Night	6% 3 2 4 4 2 3 4 5% 8% 60%	1980
September	1st to 10th	Night	11% 4 2 4 4 2 3 3 5% 6% 56%	1800
	11th to 20th	Night	11% 5% 2 4 3 2 4 4 5% 7% 54%	1800
	21st to end	Night	7% 5% 2 4 4 3 4 3 5% 6% 58%	2060
October	1st to 10th	Night	12% 6% 2 4 4 3 3 3 4 6% 54%	2160
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 4 5% 52%	2160
	21st to end	Night	18% 7% 2 5% 4 2 3 4 4 4 47%	2376
November	1st to 10th	Night	10% 5% 2 3 4 2 3 3 4 7% 58%	2329
	11th to 20th	Night	13% 6% 3 5% 4 3 4 3 5% 6% 49%	2564
	21st to end	Night	18% 8% 3 6% 3 2 3 4 4 6% 43%	2660
December	1st to 10th	Night	13% 9% 3 7% 5% 2 5% 5% 5% 6% 40%	2660
	11th to 20th	Night	13% 9% 4 7% 5% 3 4 4 5% 6% 41%	3279
	21st to end	Night	21% 16% 8% 9% 6% 3 4 3 4 4 23%	4884

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	53% 5% 11% 21% 8% 1	2538
	11th to 20th	Day	55% 5% 11% 20% 8%	2850
	21st to end	Day	64% 4 9% 15% 7% 1	3135
February	1st to 10th	Day	48% 6% 14% 20% 10% 2	1710
	11th to 20th	Day	45% 4 13% 23% 14% 2	1680
	21st to end	Day	45% 5% 10% 25% 13% 2	1570
March	1st to 10th	Day	47% 6% 11% 21% 13% 2	2063
	11th to 20th	Day	50% 5% 9% 23% 12% 1	2090
	21st to end	Day	58% 6% 11% 17% 7% 1	2222
April	1st to 10th	Day	46% 6% 10% 26% 12% 1	2160
	11th to 20th	Day	46% 5% 10% 24% 14% 1	2134
	21st to end	Day	50% 6% 11% 21% 12% 1	2171
May	1st to 10th	Day	49% 8% 11% 20% 11% 1	2340
	11th to 20th	Day	47% 8% 11% 23% 11%	2440
	21st to end	Day	47% 7% 11% 21% 12% 1	2725
June	1st to 10th	Day	33% 9% 16% 28% 13% 1	2520
	11th to 20th	Day	34% 7% 13% 25% 19% 3	2520
	21st to end	Day	34% 8% 15% 25% 15% 2	2520
July	1st to 10th	Day	30% 9% 15% 27% 15% 4	2451
	11th to 20th	Day	32% 7% 14% 27% 16% 3	2409
	21st to end	Day	32% 6% 13% 31% 16% 1	2405
August	1st to 10th	Day	35% 11% 16% 25% 12% 1	2314
	11th to 20th	Day	35% 7% 13% 27% 17% 1	2270
	21st to end	Day	30% 6% 13% 26% 20% 5%	2376
September	1st to 10th	Day	33% 6% 12% 24% 19% 6%	2160
	11th to 20th	Day	29% 6% 11% 30% 21% 4	2160
	21st to end	Day	32% 5% 10% 30% 20% 3	1879
October	1st to 10th	Day	37% 4 10% 25% 21% 2	1800
	11th to 20th	Day	39% 4 7% 26% 21% 3	1800
	21st to end	Day	42% 5% 10% 23% 16% 3	1980
November	1st to 10th	Day	35% 4 13% 25% 20% 3	1746
	11th to 20th	Day	42% 5% 9% 25% 18% 2	1615
	21st to end	Day	46% 3 13% 23% 14%	1520
December	1st to 10th	Day	46% 5% 13% 22% 12% 1	1520
	11th to 20th	Day	44% 5% 14% 27% 9% 1	1915
	21st to end	Day	65% 3 9% 15% 6% 1	2783
January	1st to 10th	Night	54% 4 9% 21% 10% 1	4414
	11th to 20th	Night	57% 4 11% 17% 10% 1	4120
	21st to end	Night	61% 5% 10% 16% 7% 1	4532
February	1st to 10th	Night	50% 4 11% 20% 12% 2	2470
	11th to 20th	Night	43% 4 11% 25% 14% 2	2395
	21st to end	Night	43% 4 9% 23% 18% 4	1884
March	1st to 10th	Night	40% 4 11% 26% 18% 1	2133
	11th to 20th	Night	46% 5% 10% 21% 14% 3	2090
	21st to end	Night	59% 6% 11% 15% 7% 1	2178
April	1st to 10th	Night	37% 5% 13% 26% 16% 3	1800
	11th to 20th	Night	42% 4 9% 24% 16% 4	1775
	21st to end	Night	45% 5% 11% 21% 16% 2	1785
May	1st to 10th	Night	42% 7% 15% 23% 13% 2	1620
	11th to 20th	Night	41% 7% 14% 22% 16% 1	1458
	21st to end	Night	39% 6% 13% 25% 14% 3	1552
June	1st to 10th	Night	26% 8% 17% 30% 17% 2	1440
	11th to 20th	Night	30% 7% 12% 25% 23% 4	1440
	21st to end	Night	27% 8% 16% 25% 20% 4	1440
July	1st to 10th	Night	27% 7% 15% 31% 15% 6%	1400
	11th to 20th	Night	24% 6% 14% 33% 21% 3	1424
	21st to end	Night	25% 6% 14% 32% 20% 3	1673
August	1st to 10th	Night	26% 8% 18% 30% 16% 3	1601
	11th to 20th	Night	28% 6% 12% 32% 20% 2	1628
	21st to end	Night	22% 5% 14% 26% 24% 8%	1980
September	1st to 10th	Night	29% 5% 10% 26% 23% 7%	1800
	11th to 20th	Night	29% 5% 12% 27% 21% 5%	1800
	21st to end	Night	28% 4 9% 31% 24% 3	2060
October	1st to 10th	Night	33% 4 10% 24% 24% 5%	2160
	11th to 20th	Night	35% 5% 7% 26% 21% 5%	2160
	21st to end	Night	41% 5% 8% 23% 21% 2	2376
November	1st to 10th	Night	28% 4 15% 26% 22% 5%	2329
	11th to 20th	Night	37% 4 9% 29% 18% 3	2564
	21st to end	Night	44% 4 9% 27% 15% 1	2660
December	1st to 10th	Night	44% 6% 12% 26% 12% 1	2660
	11th to 20th	Night	44% 4 12% 26% 13% 1	3281
	21st to end	Night	66% 4 8% 14% 7% 1	4884

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% 36% 21% 8%	270
	11th to 20th	Day	26% 14% 43% 16% 1	270
	21st to end	Day	22% 14% 43% 18% 2	297
February	1st to 10th	Day	22% 19% 40% 16% 4	270
	11th to 20th	Day	20% 18% 37% 20% 4 1	270
	21st to end	Day	18% 19% 45% 13% 4	225
March	1st to 10th	Day	17% 17% 46% 18% 2	270
	11th to 20th	Day	25% 14% 36% 22% 4	270
	21st to end	Day	36% 18% 29% 13% 3 1	292
April	1st to 10th	Day	20% 15% 36% 21% 7% 1	420
	11th to 20th	Day	19% 14% 32% 24% 9% 1	412
	21st to end	Day	22% 15% 32% 23% 7% 2	431
May	1st to 10th	Day	20% 12% 35% 22% 9% 2	603
	11th to 20th	Day	21% 10% 29% 26% 12% 2	625
	21st to end	Day	17% 7% 25% 28% 17% 6%	679
June	1st to 10th	Day	6% 4 18% 36% 26% 9%	630
	11th to 20th	Day	9% 4 23% 38% 21% 5%	630
	21st to end	Day	11% 7% 28% 31% 18% 4	630
July	1st to 10th	Day	9% 3 14% 34% 26% 15%	621
	11th to 20th	Day	7% 5% 19% 37% 24% 9%	618
	21st to end	Day	8% 3 17% 38% 28% 6%	684
August	1st to 10th	Day	6% 3 16% 40% 28% 8%	626
	11th to 20th	Day	9% 3 14% 37% 30% 7%	584
	21st to end	Day	9% 2 14% 34% 29% 12%	495
September	1st to 10th	Day	13% 4 18% 31% 26% 7%	450
	11th to 20th	Day	10% 3 20% 32% 24% 11%	450
	21st to end	Day	9% 8% 32% 22% 22% 7%	277
October	1st to 10th	Day	20% 7% 31% 23% 13% 6%	270
	11th to 20th	Day	17% 22% 32% 21% 8%	270
	21st to end	Day	24% 16% 31% 21% 7%	297
November	1st to 10th	Day	15% 8% 40% 25% 9% 3	270
	11th to 20th	Day	17% 18% 34% 22% 7% 3	270
	21st to end	Day	21% 16% 34% 24% 4	270
December	1st to 10th	Day	11% 16% 41% 23% 6% 3	270
	11th to 20th	Day	17% 16% 40% 21% 6%	270
	21st to end	Day	24% 19% 41% 14% 3	297
January	1st to 10th	Night	14% 14% 41% 24% 7%	950
	11th to 20th	Night	16% 14% 41% 21% 6% 1	950
	21st to end	Night	16% 12% 41% 28% 3	1045
February	1st to 10th	Night	19% 12% 40% 26% 3	950
	11th to 20th	Night	17% 13% 38% 28% 3	920
	21st to end	Night	20% 13% 42% 21% 4	628
March	1st to 10th	Night	17% 10% 43% 25% 5%	613
	11th to 20th	Night	23% 9% 32% 29% 6% 1	570
	21st to end	Night	27% 11% 35% 22% 5%	600
April	1st to 10th	Night	14% 12% 40% 29% 5%	540
	11th to 20th	Night	19% 11% 34% 29% 8% 1	533
	21st to end	Night	20% 8% 34% 30% 8%	540
May	1st to 10th	Night	17% 5% 34% 35% 8%	540
	11th to 20th	Night	15% 6% 31% 33% 14% 1	531
	21st to end	Night	14% 5% 23% 36% 21% 1	584
June	1st to 10th	Night	6% 3 18% 47% 24% 2	540
	11th to 20th	Night	8% 3 22% 44% 22% 1	540
	21st to end	Night	6% 4 27% 42% 20%	540
July	1st to 10th	Night	7% 2 11% 40% 35% 5%	525
	11th to 20th	Night	6% 1 16% 44% 29% 4	522
	21st to end	Night	8% 1 15% 43% 33% 1	591
August	1st to 10th	Night	6% 2 13% 48% 29% 3	537
	11th to 20th	Night	9% 2 13% 41% 32% 4	534
	21st to end	Night	7% 2 12% 42% 34% 3	594
September	1st to 10th	Night	13% 2 17% 38% 27% 4	540
	11th to 20th	Night	12% 1 17% 38% 26% 5%	540
	21st to end	Night	8% 5% 25% 37% 20% 4	630
October	1st to 10th	Night	14% 4 30% 33% 17% 2	720
	11th to 20th	Night	15% 10% 35% 30% 9% 1	720
	21st to end	Night	22% 10% 33% 27% 8%	792
November	1st to 10th	Night	11% 9% 38% 32% 10% 1	740
	11th to 20th	Night	15% 11% 40% 26% 7%	854
	21st to end	Night	22% 9% 35% 27% 7%	950
December	1st to 10th	Night	18% 10% 39% 27% 6% 1	950
	11th to 20th	Night	21% 9% 36% 28% 6%	950
	21st to end	Night	22% 14% 37% 26% 2	1045

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