Show-Me-Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Show-Me-Stars Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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% 6% 2 6% 4 4 4 4 5% 7% 45%	131979
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	131416
Transparency	Day	37% 5% 11% 25% 18% 4	135579
	Night	36% 5% 10% 25% 20% 5%	135895
Seeing	Day	18% 11% 26% 25% 16% 5%	17577
	Night	18% 10% 28% 28% 15% 2	27439

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	15% 9% 3 5% 3 3 3 3 4 5% 47%	5028
	11th to 20th	Day	8% 6% 2 6% 3 3 3 3 4 5% 56%	5310
	21st to end	Day	19% 6% 2 5% 3 3 3 3 3 4 48%	5812
February	1st to 10th	Day	18% 8% 2 7% 4 4 3 3 5% 5% 41%	1890
	11th to 20th	Day	17% 8% 3 6% 4 4 3 3 4 6% 42%	2012
	21st to end	Day	16% 9% 3 5% 5% 4 5% 4 4 5% 41%	1730
March	1st to 10th	Day	17% 11% 3 5% 3 3 3 3 4 5% 41%	4880
	11th to 20th	Day	10% 5% 2 5% 3 3 4 3 5% 7% 54%	5090
	21st to end	Day	15% 6% 2 6% 5% 5% 4 4 6% 8% 40%	5759
April	1st to 10th	Day	14% 7% 2 6% 4 3 4 3 6% 6% 45%	2520
	11th to 20th	Day	16% 7% 3 7% 4 4 4 4 6% 6% 40%	2494
	21st to end	Day	17% 7% 3 8% 5% 4 5% 4 5% 7% 36%	2520
May	1st to 10th	Day	14% 7% 3 8% 6% 6% 6% 5% 7% 8% 30%	5525
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	6099
	21st to end	Day	20% 6% 2 6% 4 4 4 4 6% 7% 37%	7089
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	2801
	11th to 20th	Day	5% 4 2 5% 5% 5% 5% 5% 7% 10% 47%	2800
	21st to end	Day	4 4 1 5% 4 5% 6% 5% 7% 10% 49%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 6% 9% 45%	6360
	11th to 20th	Day	4 4 2 5% 4 4 5% 5% 6% 11% 50%	5978
	21st to end	Day	6% 5% 2 7% 5% 6% 6% 4 7% 10% 42%	6422
August	1st to 10th	Day	4 3 1 3 3 4 5% 3 6% 9% 59%	4216
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 3 6% 8% 46%	3849
	21st to end	Day	6% 3 2 5% 4 4 4 4 6% 9% 54%	4312
September	1st to 10th	Day	9% 5% 2 6% 4 4 4 3 4 9% 49%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 7% 48%	2400
	21st to end	Day	11% 5% 1 6% 3 3 3 3 5% 7% 54%	2140
October	1st to 10th	Day	8% 4 1 4 4 3 4 3 6% 6% 56%	2000
	11th to 20th	Day	13% 5% 2 4 3 3 2 2 4 4 57%	2000
	21st to end	Day	19% 6% 2 5% 3 3 3 3 3 6% 47%	2200
November	1st to 10th	Day	12% 6% 1 5% 3 3 3 3 4 6% 55%	1968
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 52%	1890
	21st to end	Day	20% 7% 3 6% 3 2 3 3 3 4 47%	1837
December	1st to 10th	Day	11% 8% 2 5% 3 3 3 3 4 6% 53%	2690
	11th to 20th	Day	16% 8% 3 6% 4 3 3 3 3 6% 46%	3088
	21st to end	Day	21% 16% 3 7% 4 3 4 2 4 5% 31%	4070
January	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 44%	7890
	11th to 20th	Night	10% 6% 2 6% 4 3 3 3 4 4 55%	7680
	21st to end	Night	18% 8% 2 5% 4 4 4 3 4 5% 43%	8402
February	1st to 10th	Night	17% 9% 2 6% 4 3 3 2 5% 5% 43%	2730
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 5% 45%	2491
	21st to end	Night	16% 7% 2 5% 4 4 3 2 5% 6% 45%	2076
March	1st to 10th	Night	18% 8% 3 6% 4 4 4 2 4 4 41%	5222
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	5090
	21st to end	Night	12% 6% 3 7% 5% 4 4 4 5% 7% 43%	5411
April	1st to 10th	Night	11% 6% 2 5% 3 3 3 4 5% 7% 51%	2100
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 5% 7% 47%	2075
	21st to end	Night	18% 6% 2 5% 4 4 4 4 6% 6% 41%	2100
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 6% 8% 40%	4590
	11th to 20th	Night	15% 9% 3 6% 4 4 3 3 5% 8% 40%	4012
	21st to end	Night	19% 8% 2 7% 5% 4 4 3 4 7% 37%	4030
June	1st to 10th	Night	8% 6% 2 5% 4 4 4 3 6% 9% 51%	1600
	11th to 20th	Night	5% 4 1 4 3 3 4 3 6% 11% 57%	1600
	21st to end	Night	4 3 1 4 3 4 3 3 7% 9% 60%	1600
July	1st to 10th	Night	6% 4 2 6% 4 5% 5% 4 7% 10% 47%	3618
	11th to 20th	Night	3 3 2 5% 3 4 5% 5% 6% 9% 55%	3980
	21st to end	Night	5% 4 2 5% 5% 4 5% 4 6% 11% 47%	4449
August	1st to 10th	Night	3 3 2 3 3 3 4 3 5% 9% 63%	2940
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 6% 9% 51%	3200
	21st to end	Night	5% 3 1 4 3 3 4 3 5% 9% 60%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 8% 54%	2000
	11th to 20th	Night	9% 5% 2 6% 4 3 4 4 6% 8% 49%	2000
	21st to end	Night	9% 4 2 5% 3 3 3 3 5% 6% 56%	2235
October	1st to 10th	Night	7% 4 2 4 3 2 3 2 4 6% 63%	2400
	11th to 20th	Night	12% 5% 1 4 3 3 2 2 4 5% 59%	2400
	21st to end	Night	19% 5% 2 5% 3 3 3 2 3 5% 49%	2640
November	1st to 10th	Night	13% 5% 2 4 2 2 2 3 4 6% 58%	2549
	11th to 20th	Night	13% 5% 1 4 3 3 4 3 5% 6% 54%	2730
	21st to end	Night	17% 6% 2 5% 4 3 3 3 4 6% 48%	2781
December	1st to 10th	Night	13% 8% 2 5% 3 3 3 3 4 6% 52%	4720
	11th to 20th	Night	17% 8% 2 6% 4 3 3 3 4 5% 46%	5339
	21st to end	Night	24% 10% 3 7% 5% 4 4 3 4 5% 31%	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	41% 3 9% 30% 14% 3	5029
	11th to 20th	Day	31% 3 6% 31% 23% 6%	5310
	21st to end	Day	41% 3 9% 19% 19% 9%	5812
February	1st to 10th	Day	46% 4 11% 23% 14% 2	1890
	11th to 20th	Day	45% 4 10% 21% 17% 4	2022
	21st to end	Day	45% 4 8% 20% 16% 7%	1730
March	1st to 10th	Day	46% 4 6% 21% 13% 10%	4880
	11th to 20th	Day	31% 4 6% 25% 23% 11%	5090
	21st to end	Day	42% 5% 12% 26% 14% 1	5761
April	1st to 10th	Day	39% 4 11% 24% 20% 2	2520
	11th to 20th	Day	43% 6% 11% 20% 16% 5%	2494
	21st to end	Day	46% 6% 11% 21% 15% 1	2520
May	1st to 10th	Day	47% 8% 14% 18% 12% 1	5560
	11th to 20th	Day	46% 8% 12% 20% 12% 1	6103
	21st to end	Day	44% 7% 10% 23% 14% 2	7103
June	1st to 10th	Day	36% 8% 14% 24% 16% 1	2801
	11th to 20th	Day	30% 7% 13% 30% 17% 3	2800
	21st to end	Day	27% 8% 18% 25% 18% 4	2800
July	1st to 10th	Day	34% 7% 12% 25% 20% 2	6291
	11th to 20th	Day	27% 8% 17% 32% 15% 2	5907
	21st to end	Day	35% 8% 14% 31% 11% 1	6240
August	1st to 10th	Day	20% 6% 17% 32% 24% 1	4202
	11th to 20th	Day	36% 6% 13% 27% 16% 2	3885
	21st to end	Day	26% 6% 14% 36% 14% 3	4311
September	1st to 10th	Day	34% 6% 10% 26% 17% 6%	2400
	11th to 20th	Day	36% 5% 9% 23% 26% 1	2400
	21st to end	Day	31% 5% 8% 24% 29% 3	2140
October	1st to 10th	Day	17% 4 5% 16% 44% 14%	3260
	11th to 20th	Day	22% 3 5% 21% 41% 8%	3240
	21st to end	Day	31% 3 7% 30% 25% 4	3538
November	1st to 10th	Day	32% 4 9% 26% 23% 6%	1968
	11th to 20th	Day	34% 3 7% 24% 23% 8%	1890
	21st to end	Day	43% 3 8% 23% 21% 3	1837
December	1st to 10th	Day	34% 3 9% 35% 17% 2	2690
	11th to 20th	Day	42% 4 7% 26% 20% 2	3085
	21st to end	Day	56% 4 10% 17% 10% 3	4070
January	1st to 10th	Night	41% 3 10% 29% 14% 2	7891
	11th to 20th	Night	32% 3 7% 23% 29% 5%	7680
	21st to end	Night	45% 3 8% 22% 18% 5%	8402
February	1st to 10th	Night	43% 4 10% 25% 16% 2	2730
	11th to 20th	Night	42% 3 10% 22% 19% 4	2492
	21st to end	Night	40% 3 9% 22% 19% 7%	2076
March	1st to 10th	Night	46% 4 6% 18% 16% 9%	5222
	11th to 20th	Night	35% 4 7% 24% 18% 11%	5090
	21st to end	Night	39% 5% 10% 28% 16% 1	5411
April	1st to 10th	Night	33% 5% 13% 24% 21% 4	2100
	11th to 20th	Night	37% 5% 10% 23% 19% 6%	2075
	21st to end	Night	42% 7% 11% 22% 17% 2	2100
May	1st to 10th	Night	42% 6% 15% 24% 11% 1	4620
	11th to 20th	Night	42% 7% 12% 23% 12% 3	4013
	21st to end	Night	47% 6% 10% 21% 13% 3	4038
June	1st to 10th	Night	30% 7% 14% 26% 22% 2	1600
	11th to 20th	Night	21% 5% 13% 34% 21% 5%	1600
	21st to end	Night	21% 6% 17% 30% 20% 7%	1600
July	1st to 10th	Night	32% 7% 14% 22% 23% 2	3580
	11th to 20th	Night	24% 9% 18% 33% 15% 2	3932
	21st to end	Night	30% 7% 17% 31% 14%	4320
August	1st to 10th	Night	18% 6% 17% 36% 22% 1	2930
	11th to 20th	Night	29% 6% 19% 27% 16% 2	3230
	21st to end	Night	22% 5% 13% 35% 21% 3	3586
September	1st to 10th	Night	28% 6% 10% 29% 20% 6%	2000
	11th to 20th	Night	31% 7% 10% 25% 23% 4	2000
	21st to end	Night	28% 5% 10% 22% 30% 5%	2235
October	1st to 10th	Night	14% 2 6% 16% 43% 18%	3920
	11th to 20th	Night	21% 2 6% 19% 35% 17%	3899
	21st to end	Night	30% 3 6% 26% 29% 6%	4252
November	1st to 10th	Night	29% 3 9% 28% 25% 6%	2549
	11th to 20th	Night	32% 3 8% 25% 24% 8%	2730
	21st to end	Night	39% 3 7% 25% 23% 3	2781
December	1st to 10th	Night	36% 3 9% 33% 17% 2	4720
	11th to 20th	Night	42% 3 8% 23% 21% 3	5341
	21st to end	Night	54% 5% 11% 20% 9% 2	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	28% 19% 36% 14% 2	330
	11th to 20th	Day	29% 25% 32% 13% 1	330
	21st to end	Day	26% 24% 37% 10% 3	363
February	1st to 10th	Day	27% 23% 34% 12% 3	330
	11th to 20th	Day	34% 23% 31% 9% 3	330
	21st to end	Day	36% 19% 34% 10% 1	273
March	1st to 10th	Day	31% 21% 34% 12% 2	330
	11th to 20th	Day	34% 17% 36% 12% 1	330
	21st to end	Day	28% 22% 36% 10% 4	436
April	1st to 10th	Day	27% 16% 34% 18% 6% 1	540
	11th to 20th	Day	28% 20% 30% 16% 6%	532
	21st to end	Day	21% 20% 32% 21% 5% 2	540
May	1st to 10th	Day	20% 18% 33% 20% 7% 1	543
	11th to 20th	Day	20% 12% 30% 23% 12% 3	733
	21st to end	Day	16% 8% 30% 28% 14% 4	844
June	1st to 10th	Day	9% 6% 24% 30% 23% 8%	731
	11th to 20th	Day	7% 3 21% 40% 24% 5%	730
	21st to end	Day	7% 3 26% 38% 22% 5%	730
July	1st to 10th	Day	9% 3 18% 32% 27% 11%	721
	11th to 20th	Day	6% 3 16% 34% 30% 9%	718
	21st to end	Day	9% 2 13% 33% 34% 10%	794
August	1st to 10th	Day	7% 3 14% 40% 28% 8%	721
	11th to 20th	Day	14% 3 16% 28% 28% 10%	519
	21st to end	Day	10% 1 13% 31% 30% 14%	583
September	1st to 10th	Day	8% 4 15% 38% 27% 8%	530
	11th to 20th	Day	10% 3 15% 31% 30% 12%	530
	21st to end	Day	13% 10% 24% 26% 19% 8%	450
October	1st to 10th	Day	9% 8% 28% 33% 17% 4	330
	11th to 20th	Day	17% 15% 33% 23% 10% 1	330
	21st to end	Day	29% 18% 28% 20% 5% 1	363
November	1st to 10th	Day	18% 14% 37% 22% 8% 1	330
	11th to 20th	Day	21% 17% 37% 15% 10% 1	330
	21st to end	Day	33% 15% 29% 15% 7% 1	330
December	1st to 10th	Day	22% 25% 30% 16% 6% 1	330
	11th to 20th	Day	27% 21% 31% 16% 5% 1	330
	21st to end	Day	32% 20% 34% 11% 3	363
January	1st to 10th	Night	23% 18% 35% 21% 4	1050
	11th to 20th	Night	23% 20% 35% 17% 4	1050
	21st to end	Night	22% 16% 38% 21% 2	1155
February	1st to 10th	Night	24% 16% 36% 22% 2	1050
	11th to 20th	Night	25% 17% 38% 18% 2	856
	21st to end	Night	25% 18% 36% 18% 3	692
March	1st to 10th	Night	25% 16% 33% 24% 3	725
	11th to 20th	Night	24% 15% 31% 27% 3	630
	21st to end	Night	22% 13% 37% 22% 5%	693
April	1st to 10th	Night	16% 15% 40% 24% 5%	630
	11th to 20th	Night	18% 17% 32% 25% 7%	623
	21st to end	Night	22% 9% 37% 24% 7%	630
May	1st to 10th	Night	16% 8% 35% 31% 10% 1	630
	11th to 20th	Night	19% 8% 29% 27% 14% 2	621
	21st to end	Night	14% 6% 25% 36% 16% 4	683
June	1st to 10th	Night	10% 4 20% 33% 31% 2	600
	11th to 20th	Night	5% 2 21% 45% 25% 3	600
	21st to end	Night	5% 2 18% 41% 31% 4	600
July	1st to 10th	Night	8% 1 11% 33% 40% 8%	585
	11th to 20th	Night	4 2 9% 37% 42% 6%	582
	21st to end	Night	6% 2 12% 37% 37% 7%	657
August	1st to 10th	Night	5% 1 11% 40% 38% 4	597
	11th to 20th	Night	8% 1 13% 36% 37% 4	594
	21st to end	Night	8% 1 10% 35% 41% 6%	660
September	1st to 10th	Night	11% 2 13% 36% 34% 4	600
	11th to 20th	Night	11% 1 13% 31% 38% 6%	600
	21st to end	Night	11% 5% 22% 30% 28% 3	760
October	1st to 10th	Night	9% 5% 21% 36% 27% 3	800
	11th to 20th	Night	15% 10% 30% 29% 16% 1	800
	21st to end	Night	23% 10% 30% 28% 9%	880
November	1st to 10th	Night	15% 9% 32% 31% 12% 1	820
	11th to 20th	Night	18% 11% 34% 29% 9%	840
	21st to end	Night	24% 13% 28% 26% 9%	891
December	1st to 10th	Night	23% 12% 32% 27% 5%	1050
	11th to 20th	Night	25% 13% 29% 28% 4	1050
	21st to end	Night	28% 14% 31% 24% 3	1155

Page generated at 2026-05-29 00:53:25. Version ac07

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