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 2025-02-06.

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	13% 6% 2 6% 4 4 4 3 5% 7% 46%	108436
	Night	13% 6% 2 5% 4 3 3 3 5% 7% 48%	109986
Transparency	Day	36% 5% 11% 25% 19% 4	112075
	Night	35% 5% 10% 25% 20% 4	114489
Seeing	Day	17% 11% 26% 25% 16% 5%	15780
	Night	17% 10% 28% 28% 15% 2	25727

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	16% 9% 3 5% 3 3 3 2 3 5% 47%	3870
	11th to 20th	Day	9% 6% 2 6% 3 3 4 3 4 5% 53%	4080
	21st to end	Day	22% 6% 2 4 3 3 3 3 4 5% 47%	4488
February	1st to 10th	Day	17% 8% 2 7% 5% 4 3 3 5% 5% 41%	1755
	11th to 20th	Day	17% 8% 3 7% 5% 4 3 3 4 6% 42%	1814
	21st to end	Day	17% 9% 3 6% 5% 4 5% 4 4 5% 39%	1570
March	1st to 10th	Day	21% 10% 3 6% 3 2 3 3 4 4 40%	3330
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 6% 52%	3480
	21st to end	Day	16% 7% 2 6% 5% 4 4 4 5% 7% 40%	3931
April	1st to 10th	Day	13% 7% 2 6% 4 3 4 3 5% 6% 46%	2280
	11th to 20th	Day	16% 7% 3 6% 4 4 4 4 5% 6% 40%	2254
	21st to end	Day	18% 7% 2 8% 5% 4 5% 3 5% 6% 37%	2280
May	1st to 10th	Day	13% 7% 3 7% 5% 6% 6% 4 7% 8% 34%	3765
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	4159
	21st to end	Day	13% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	4824
June	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 7% 9% 43%	2660
	11th to 20th	Day	5% 3 2 4 5% 5% 5% 5% 7% 10% 48%	2660
	21st to end	Day	4 4 1 5% 4 5% 6% 5% 7% 9% 49%	2660
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	4440
	11th to 20th	Day	5% 3 1 4 4 4 4 5% 6% 11% 53%	4170
	21st to end	Day	8% 5% 3 9% 6% 7% 7% 4 7% 10% 34%	4465
August	1st to 10th	Day	4 3 1 3 3 4 5% 3 6% 9% 58%	4086
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 3 6% 8% 46%	3729
	21st to end	Day	6% 3 2 5% 4 4 4 4 6% 9% 54%	4180
September	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 4 8% 49%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 7% 48%	2280
	21st to end	Day	10% 5% 1 6% 3 3 3 3 5% 8% 54%	2033
October	1st to 10th	Day	8% 5% 1 4 3 3 4 3 6% 6% 56%	1900
	11th to 20th	Day	14% 5% 2 4 3 3 2 2 4 4 57%	1900
	21st to end	Day	18% 6% 2 5% 3 3 3 3 4 6% 47%	2090
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 4 5% 55%	1873
	11th to 20th	Day	13% 6% 2 5% 3 4 3 3 5% 6% 52%	1800
	21st to end	Day	19% 6% 3 6% 3 2 3 3 3 4 47%	1750
December	1st to 10th	Day	12% 8% 2 5% 3 3 3 3 4 6% 53%	2610
	11th to 20th	Day	16% 8% 3 6% 4 3 3 3 3 5% 45%	3008
	21st to end	Day	21% 16% 3 7% 4 3 4 2 4 5% 31%	3982
January	1st to 10th	Night	16% 7% 3 6% 3 4 4 3 5% 6% 42%	6090
	11th to 20th	Night	12% 6% 2 7% 4 4 3 3 4 4 50%	5900
	21st to end	Night	19% 8% 2 5% 3 3 3 2 3 5% 45%	6490
February	1st to 10th	Night	17% 9% 2 7% 4 3 3 3 5% 5% 42%	2536
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 5% 47%	2249
	21st to end	Night	17% 8% 2 5% 4 4 3 2 5% 6% 44%	1884
March	1st to 10th	Night	22% 7% 2 5% 3 4 3 2 5% 5% 42%	3551
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	3480
	21st to end	Night	13% 7% 3 6% 4 4 4 4 5% 7% 42%	3700
April	1st to 10th	Night	11% 6% 2 5% 3 3 4 4 5% 6% 52%	1900
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 5% 6% 48%	1875
	21st to end	Night	17% 6% 2 6% 4 4 3 4 6% 6% 41%	1900
May	1st to 10th	Night	18% 6% 1 5% 3 3 4 2 5% 7% 45%	3130
	11th to 20th	Night	13% 7% 2 6% 4 3 3 3 6% 9% 44%	2724
	21st to end	Night	12% 7% 2 7% 5% 4 4 4 5% 8% 41%	2743
June	1st to 10th	Night	8% 5% 2 4 4 4 4 3 6% 9% 51%	1520
	11th to 20th	Night	4 3 1 3 3 3 3 3 6% 11% 59%	1520
	21st to end	Night	3 3 1 4 3 4 4 3 6% 9% 60%	1520
July	1st to 10th	Night	8% 4 1 5% 3 4 4 4 7% 11% 48%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 4 6% 8% 61%	2781
	21st to end	Night	7% 6% 3 7% 6% 6% 5% 5% 6% 9% 41%	3098
August	1st to 10th	Night	3 3 1 3 3 3 4 3 5% 8% 64%	2850
	11th to 20th	Night	7% 5% 2 5% 4 4 4 4 6% 9% 51%	3100
	21st to end	Night	5% 3 1 4 3 3 4 3 5% 9% 60%	3476
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 8% 54%	1900
	11th to 20th	Night	9% 5% 2 6% 4 3 4 4 6% 8% 49%	1900
	21st to end	Night	8% 4 2 5% 3 3 3 3 5% 7% 57%	2123
October	1st to 10th	Night	7% 4 2 4 3 2 3 2 4 6% 63%	2280
	11th to 20th	Night	12% 5% 1 4 3 3 2 2 4 5% 59%	2280
	21st to end	Night	18% 5% 2 5% 3 3 3 3 4 5% 50%	2508
November	1st to 10th	Night	13% 5% 2 4 2 2 2 3 4 6% 58%	2425
	11th to 20th	Night	14% 5% 1 4 3 3 3 3 5% 7% 53%	2600
	21st to end	Night	17% 6% 2 5% 4 3 3 3 4 6% 49%	2648
December	1st to 10th	Night	13% 8% 2 4 3 3 3 3 4 5% 52%	4580
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 4 5% 46%	5199
	21st to end	Night	24% 10% 3 7% 5% 4 4 3 4 5% 30%	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	42% 3 9% 27% 16% 3	3871
	11th to 20th	Day	33% 3 8% 28% 21% 7%	4080
	21st to end	Day	41% 3 9% 17% 21% 10%	4488
February	1st to 10th	Day	45% 4 10% 24% 14% 2	1755
	11th to 20th	Day	45% 4 10% 21% 17% 4	1824
	21st to end	Day	47% 4 9% 19% 14% 7%	1570
March	1st to 10th	Day	47% 5% 7% 20% 12% 9%	3330
	11th to 20th	Day	35% 4 8% 27% 21% 6%	3480
	21st to end	Day	42% 5% 15% 22% 15% 1	3931
April	1st to 10th	Day	39% 4 10% 25% 20% 2	2280
	11th to 20th	Day	43% 6% 10% 20% 16% 5%	2254
	21st to end	Day	47% 6% 10% 21% 16% 2	2280
May	1st to 10th	Day	44% 9% 14% 20% 12% 1	3800
	11th to 20th	Day	42% 9% 13% 23% 12% 1	4163
	21st to end	Day	41% 8% 12% 23% 15% 1	4837
June	1st to 10th	Day	36% 8% 14% 24% 16% 1	2660
	11th to 20th	Day	29% 7% 14% 30% 17% 4	2660
	21st to end	Day	27% 8% 18% 25% 18% 4	2660
July	1st to 10th	Day	35% 8% 14% 27% 13% 3	4371
	11th to 20th	Day	25% 6% 12% 34% 20% 3	4099
	21st to end	Day	43% 9% 14% 26% 8% 1	4325
August	1st to 10th	Day	21% 6% 17% 31% 24% 1	4072
	11th to 20th	Day	37% 6% 13% 26% 17% 2	3765
	21st to end	Day	26% 6% 14% 36% 14% 3	4179
September	1st to 10th	Day	34% 6% 11% 25% 17% 7%	2280
	11th to 20th	Day	36% 5% 9% 22% 26% 1	2280
	21st to end	Day	30% 5% 9% 25% 28% 3	2033
October	1st to 10th	Day	17% 4 5% 16% 44% 14%	3160
	11th to 20th	Day	22% 3 5% 20% 42% 8%	3140
	21st to end	Day	30% 3 7% 30% 25% 4	3428
November	1st to 10th	Day	33% 4 9% 24% 23% 7%	1873
	11th to 20th	Day	34% 3 7% 24% 24% 8%	1800
	21st to end	Day	42% 3 8% 23% 21% 3	1750
December	1st to 10th	Day	34% 3 8% 35% 17% 2	2610
	11th to 20th	Day	42% 4 7% 26% 20% 2	3005
	21st to end	Day	56% 4 10% 16% 10% 3	3982
January	1st to 10th	Night	42% 4 9% 26% 17% 2	6090
	11th to 20th	Night	36% 4 9% 25% 24% 3	5900
	21st to end	Night	43% 3 7% 23% 18% 6%	6490
February	1st to 10th	Night	44% 4 9% 24% 16% 2	2536
	11th to 20th	Night	41% 3 10% 22% 19% 4	2250
	21st to end	Night	42% 4 10% 21% 18% 6%	1884
March	1st to 10th	Night	45% 5% 7% 20% 15% 8%	3551
	11th to 20th	Night	35% 6% 10% 25% 19% 5%	3480
	21st to end	Night	40% 6% 11% 29% 13% 1	3700
April	1st to 10th	Night	33% 5% 12% 25% 22% 4	1900
	11th to 20th	Night	36% 5% 10% 23% 19% 6%	1875
	21st to end	Night	42% 7% 10% 22% 17% 2	1900
May	1st to 10th	Night	39% 6% 15% 24% 14% 2	3160
	11th to 20th	Night	36% 9% 16% 22% 16% 2	2725
	21st to end	Night	39% 8% 13% 24% 14% 1	2751
June	1st to 10th	Night	30% 7% 14% 26% 21% 2	1520
	11th to 20th	Night	19% 5% 13% 36% 21% 5%	1520
	21st to end	Night	21% 6% 17% 29% 20% 7%	1520
July	1st to 10th	Night	29% 7% 17% 26% 18% 2	2490
	11th to 20th	Night	21% 6% 11% 38% 21% 3	2730
	21st to end	Night	39% 8% 14% 27% 12% 1	2999
August	1st to 10th	Night	18% 6% 18% 36% 22% 1	2840
	11th to 20th	Night	30% 6% 19% 26% 17% 2	3130
	21st to end	Night	22% 5% 13% 36% 20% 3	3476
September	1st to 10th	Night	28% 7% 10% 29% 20% 6%	1900
	11th to 20th	Night	31% 7% 10% 24% 24% 4	1900
	21st to end	Night	27% 5% 10% 23% 29% 5%	2123
October	1st to 10th	Night	14% 3 6% 16% 43% 19%	3800
	11th to 20th	Night	21% 2 5% 18% 36% 17%	3779
	21st to end	Night	29% 3 7% 26% 29% 6%	4120
November	1st to 10th	Night	30% 3 9% 27% 24% 6%	2425
	11th to 20th	Night	32% 3 8% 23% 25% 8%	2600
	21st to end	Night	39% 3 7% 25% 23% 3	2648
December	1st to 10th	Night	35% 3 8% 33% 18% 2	4580
	11th to 20th	Night	42% 3 8% 23% 21% 3	5201
	21st to end	Night	55% 5% 11% 19% 9% 2	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	28% 20% 36% 13% 2	300
	11th to 20th	Day	30% 24% 31% 13% 1	300
	21st to end	Day	25% 24% 38% 11% 3	330
February	1st to 10th	Day	27% 21% 36% 12% 3	285
	11th to 20th	Day	33% 21% 31% 11% 4	270
	21st to end	Day	38% 20% 33% 8% 1	225
March	1st to 10th	Day	30% 20% 35% 12% 3	270
	11th to 20th	Day	36% 16% 33% 14% 1	270
	21st to end	Day	29% 23% 33% 10% 5%	363
April	1st to 10th	Day	25% 16% 34% 18% 6% 1	460
	11th to 20th	Day	28% 18% 30% 17% 7%	452
	21st to end	Day	21% 21% 30% 22% 5% 2	460
May	1st to 10th	Day	22% 16% 33% 20% 8% 2	463
	11th to 20th	Day	19% 10% 29% 25% 14% 4	637
	21st to end	Day	13% 7% 31% 28% 16% 5%	734
June	1st to 10th	Day	9% 5% 23% 30% 24% 9%	680
	11th to 20th	Day	6% 3 21% 41% 24% 5%	680
	21st to end	Day	7% 4 27% 36% 21% 5%	680
July	1st to 10th	Day	9% 3 18% 32% 28% 11%	671
	11th to 20th	Day	6% 4 16% 34% 31% 10%	668
	21st to end	Day	9% 2 13% 33% 33% 10%	739
August	1st to 10th	Day	8% 3 13% 39% 29% 8%	671
	11th to 20th	Day	15% 3 17% 28% 28% 8%	479
	21st to end	Day	10% 1 11% 31% 31% 15%	539
September	1st to 10th	Day	9% 4 15% 36% 28% 8%	490
	11th to 20th	Day	11% 3 16% 31% 28% 12%	490
	21st to end	Day	12% 10% 24% 26% 19% 8%	414
October	1st to 10th	Day	10% 8% 28% 32% 17% 4	300
	11th to 20th	Day	18% 16% 33% 23% 9% 1	300
	21st to end	Day	27% 18% 28% 21% 5% 1	330
November	1st to 10th	Day	19% 13% 37% 22% 8% 1	300
	11th to 20th	Day	21% 16% 36% 15% 11% 1	300
	21st to end	Day	32% 15% 30% 15% 7% 1	300
December	1st to 10th	Day	22% 24% 30% 16% 7% 1	300
	11th to 20th	Day	29% 20% 29% 16% 5% 1	300
	21st to end	Day	33% 21% 32% 11% 4	330
January	1st to 10th	Night	23% 18% 34% 21% 4	1000
	11th to 20th	Night	24% 19% 35% 18% 4	1000
	21st to end	Night	22% 16% 38% 22% 2	1100
February	1st to 10th	Night	24% 16% 35% 23% 2	976
	11th to 20th	Night	24% 17% 40% 18% 2	774
	21st to end	Night	26% 18% 36% 16% 3	628
March	1st to 10th	Night	24% 15% 32% 26% 3	656
	11th to 20th	Night	23% 15% 31% 28% 3	570
	21st to end	Night	23% 12% 36% 23% 6%	627
April	1st to 10th	Night	16% 15% 40% 24% 5%	570
	11th to 20th	Night	17% 17% 31% 26% 8%	563
	21st to end	Night	22% 9% 38% 25% 6%	570
May	1st to 10th	Night	15% 7% 35% 31% 11% 1	570
	11th to 20th	Night	19% 6% 30% 28% 16% 2	561
	21st to end	Night	12% 5% 24% 37% 17% 4	617
June	1st to 10th	Night	10% 4 19% 33% 31% 2	570
	11th to 20th	Night	4 1 22% 45% 26% 3	570
	21st to end	Night	5% 2 19% 41% 29% 4	570
July	1st to 10th	Night	7% 1 12% 33% 39% 8%	555
	11th to 20th	Night	3 2 10% 38% 41% 6%	552
	21st to end	Night	6% 2 12% 36% 37% 7%	624
August	1st to 10th	Night	5% 1 11% 39% 39% 4	567
	11th to 20th	Night	8% 1 14% 36% 36% 5%	564
	21st to end	Night	8% 1 10% 33% 41% 7%	627
September	1st to 10th	Night	11% 2 13% 35% 35% 4	570
	11th to 20th	Night	11% 1 14% 31% 37% 6%	570
	21st to end	Night	10% 6% 23% 30% 28% 3	722
October	1st to 10th	Night	9% 4 21% 35% 27% 3	760
	11th to 20th	Night	15% 10% 31% 29% 15% 1	760
	21st to end	Night	22% 10% 29% 29% 9%	836
November	1st to 10th	Night	16% 9% 32% 31% 12% 1	780
	11th to 20th	Night	18% 11% 33% 28% 10%	800
	21st to end	Night	23% 13% 28% 27% 9%	848
December	1st to 10th	Night	23% 12% 31% 27% 5%	1000
	11th to 20th	Night	26% 12% 29% 29% 5%	1000
	21st to end	Night	29% 14% 31% 24% 3	1100

Page generated at 2025-02-03 02:05:49. Version ac07

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