Schaefer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schaefer Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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% 5% 4 5% 4 6% 8% 43%	127514
	Night	14% 7% 2 5% 3 3 3 3 5% 7% 47%	124806
Transparency	Day	38% 6% 12% 20% 16% 9%	131244
	Night	36% 6% 12% 20% 17% 10%	129139
Seeing	Day	12% 7% 19% 27% 24% 10%	16388
	Night	15% 7% 24% 35% 18% 2	26395

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	18% 12% 3 6% 3 2 3 2 3 4 42%	4167
	11th to 20th	Day	15% 6% 2 5% 4 3 3 2 4 5% 50%	4170
	21st to end	Day	30% 7% 2 5% 3 2 2 2 5% 5% 36%	4699
February	1st to 10th	Day	21% 8% 3 4 3 4 3 3 4 5% 43%	2000
	11th to 20th	Day	20% 9% 3 6% 4 4 3 2 3 5% 40%	1949
	21st to end	Day	20% 8% 2 6% 4 3 3 3 4 5% 42%	1720
March	1st to 10th	Day	13% 6% 3 6% 4 4 4 4 5% 7% 45%	4936
	11th to 20th	Day	14% 6% 3 7% 4 4 3 3 4 5% 48%	4980
	21st to end	Day	18% 8% 2 6% 5% 3 4 3 5% 6% 40%	5462
April	1st to 10th	Day	14% 8% 3 7% 6% 4 4 4 5% 5% 40%	2200
	11th to 20th	Day	16% 7% 2 8% 5% 4 5% 4 4 5% 40%	2215
	21st to end	Day	13% 8% 2 6% 5% 4 4 3 6% 7% 42%	2421
May	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 5% 7% 8% 32%	5862
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	5862
	21st to end	Day	10% 6% 2 6% 6% 5% 6% 5% 7% 9% 37%	6434
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 4 7% 9% 47%	2600
	11th to 20th	Day	5% 4 1 6% 5% 5% 6% 5% 8% 11% 44%	2600
	21st to end	Day	6% 6% 3 7% 8% 7% 8% 6% 8% 10% 34%	2600
July	1st to 10th	Day	9% 6% 2 7% 6% 6% 6% 5% 7% 11% 35%	5900
	11th to 20th	Day	5% 6% 2 7% 5% 6% 6% 6% 9% 13% 36%	5900
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 12% 37%	6422
August	1st to 10th	Day	1 1 1 3 3 4 5% 3 6% 10% 63%	4234
	11th to 20th	Day	3 2 1 4 3 4 6% 6% 10% 13% 48%	4082
	21st to end	Day	4 4 2 7% 6% 6% 7% 6% 8% 10% 41%	3961
September	1st to 10th	Day	7% 5% 2 8% 5% 6% 5% 6% 7% 8% 41%	2200
	11th to 20th	Day	9% 6% 3 7% 6% 5% 5% 4 6% 9% 41%	2200
	21st to end	Day	6% 6% 1 5% 5% 5% 5% 4 6% 9% 48%	2200
October	1st to 10th	Day	5% 4 1 5% 4 5% 4 3 6% 7% 56%	2183
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 5% 6% 53%	2000
	21st to end	Day	11% 6% 2 5% 3 3 3 4 4 6% 54%	2200
November	1st to 10th	Day	11% 7% 2 6% 5% 4 5% 3 5% 7% 46%	2058
	11th to 20th	Day	10% 6% 2 6% 4 3 4 3 4 6% 52%	2100
	21st to end	Day	15% 8% 3 6% 4 3 4 3 5% 6% 41%	1899
December	1st to 10th	Day	26% 9% 3 7% 4 3 3 3 3 5% 35%	3030
	11th to 20th	Day	16% 8% 2 6% 5% 4 4 3 5% 5% 42%	3481
	21st to end	Day	14% 7% 2 5% 4 3 3 3 4 5% 50%	4587
January	1st to 10th	Night	21% 8% 2 4 3 2 3 2 3 4 46%	6018
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 56%	6030
	21st to end	Night	32% 6% 2 4 3 2 2 2 3 6% 37%	6564
February	1st to 10th	Night	20% 9% 3 5% 3 3 3 3 5% 5% 41%	2400
	11th to 20th	Night	22% 7% 2 6% 3 3 3 2 3 4 45%	2338
	21st to end	Night	23% 8% 2 6% 4 4 3 3 4 4 41%	1909
March	1st to 10th	Night	18% 10% 2 5% 4 4 4 3 5% 6% 40%	4919
	11th to 20th	Night	19% 7% 3 5% 3 3 3 3 3 5% 45%	4980
	21st to end	Night	20% 11% 2 5% 4 3 2 2 4 5% 42%	5467
April	1st to 10th	Night	14% 7% 2 5% 4 3 5% 4 5% 7% 43%	2200
	11th to 20th	Night	18% 7% 2 6% 4 3 3 3 5% 6% 44%	2131
	21st to end	Night	15% 8% 2 7% 4 4 3 3 5% 7% 43%	1973
May	1st to 10th	Night	25% 9% 3 6% 5% 4 3 4 5% 7% 29%	4053
	11th to 20th	Night	11% 7% 2 6% 3 4 4 3 6% 9% 45%	4053
	21st to end	Night	13% 8% 2 7% 5% 5% 5% 4 8% 9% 33%	4443
June	1st to 10th	Night	6% 4 2 5% 3 3 5% 3 7% 9% 56%	1800
	11th to 20th	Night	4 4 1 4 4 3 5% 4 6% 9% 55%	1800
	21st to end	Night	6% 4 2 5% 5% 5% 5% 5% 8% 10% 46%	1800
July	1st to 10th	Night	7% 6% 3 7% 5% 4 5% 4 7% 10% 43%	4078
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 7% 10% 50%	4077
	21st to end	Night	6% 7% 2 7% 5% 5% 5% 4 6% 11% 44%	4449
August	1st to 10th	Night	1 1 1 1 2 2 3 3 5% 8% 74%	2926
	11th to 20th	Night	1 2 1 3 2 3 4 5% 8% 12% 58%	2972
	21st to end	Night	3 3 1 4 4 5% 4 4 8% 13% 52%	3934
September	1st to 10th	Night	7% 4 2 6% 3 4 5% 4 6% 9% 49%	2200
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 6% 8% 48%	2200
	21st to end	Night	8% 4 2 5% 3 4 4 3 6% 7% 55%	2200
October	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 8% 63%	2200
	11th to 20th	Night	11% 5% 1 5% 3 3 2 2 3 6% 60%	2395
	21st to end	Night	11% 5% 2 4 2 3 3 2 4 5% 61%	2640
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 7% 52%	2460
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 4 6% 52%	2520
	21st to end	Night	15% 7% 2 6% 4 3 3 3 5% 7% 46%	2718
December	1st to 10th	Night	24% 10% 3 8% 4 3 3 2 4 4 33%	4380
	11th to 20th	Night	17% 9% 3 5% 3 3 3 2 4 5% 45%	4946
	21st to end	Night	15% 7% 2 4 3 3 3 2 3 5% 54%	6633

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	46% 5% 5% 18% 18% 7%	4168
	11th to 20th	Day	36% 4 5% 19% 21% 15%	4170
	21st to end	Day	50% 3 4 10% 19% 13%	4699
February	1st to 10th	Day	45% 4 6% 13% 18% 14%	2000
	11th to 20th	Day	48% 4 7% 15% 16% 11%	1959
	21st to end	Day	43% 6% 8% 15% 16% 11%	1720
March	1st to 10th	Day	38% 6% 8% 18% 14% 16%	4936
	11th to 20th	Day	39% 6% 6% 8% 17% 24%	4980
	21st to end	Day	44% 5% 8% 18% 18% 7%	5464
April	1st to 10th	Day	45% 5% 8% 16% 14% 12%	2200
	11th to 20th	Day	46% 6% 7% 13% 18% 10%	2215
	21st to end	Day	41% 5% 8% 21% 17% 8%	2421
May	1st to 10th	Day	47% 7% 11% 19% 12% 3	5900
	11th to 20th	Day	36% 6% 13% 20% 19% 6%	5866
	21st to end	Day	38% 8% 13% 28% 12% 1	6447
June	1st to 10th	Day	31% 8% 15% 26% 18% 2	2600
	11th to 20th	Day	31% 9% 15% 24% 18% 3	2600
	21st to end	Day	41% 12% 15% 21% 11% 1	2600
July	1st to 10th	Day	42% 6% 26% 22% 3	5836
	11th to 20th	Day	37% 7% 23% 25% 8%	5831
	21st to end	Day	39% 6% 19% 25% 9% 1	6240
August	1st to 10th	Day	17% 7% 13% 43% 20%	4220
	11th to 20th	Day	24% 8% 30% 30% 6% 1	4121
	21st to end	Day	36% 10% 18% 22% 12% 1	3960
September	1st to 10th	Day	39% 10% 12% 18% 15% 6%	2200
	11th to 20th	Day	38% 9% 15% 19% 16% 4	2200
	21st to end	Day	31% 8% 12% 20% 16% 13%	2200
October	1st to 10th	Day	18% 4 7% 13% 21% 38%	3560
	11th to 20th	Day	22% 4 8% 18% 30% 18%	3240
	21st to end	Day	29% 4 6% 19% 27% 15%	3538
November	1st to 10th	Day	35% 7% 10% 16% 20% 12%	2058
	11th to 20th	Day	34% 4 11% 15% 21% 14%	2100
	21st to end	Day	42% 6% 8% 15% 17% 12%	1899
December	1st to 10th	Day	53% 3 6% 14% 19% 5%	3030
	11th to 20th	Day	43% 4 9% 11% 22% 11%	3479
	21st to end	Day	37% 3 5% 19% 21% 14%	4587
January	1st to 10th	Night	42% 4 6% 17% 19% 12%	6018
	11th to 20th	Night	32% 4 5% 20% 25% 15%	6030
	21st to end	Night	51% 3 3 11% 18% 13%	6564
February	1st to 10th	Night	45% 4 7% 11% 18% 14%	2400
	11th to 20th	Night	44% 4 7% 16% 17% 12%	2338
	21st to end	Night	48% 4 7% 13% 16% 13%	1909
March	1st to 10th	Night	45% 6% 7% 15% 16% 11%	4919
	11th to 20th	Night	41% 6% 6% 12% 14% 21%	4980
	21st to end	Night	46% 5% 7% 15% 17% 10%	5467
April	1st to 10th	Night	40% 7% 11% 17% 15% 11%	2200
	11th to 20th	Night	40% 6% 10% 15% 14% 15%	2131
	21st to end	Night	42% 5% 11% 20% 15% 8%	1973
May	1st to 10th	Night	53% 7% 9% 17% 10% 4	4080
	11th to 20th	Night	35% 6% 13% 23% 17% 6%	4054
	21st to end	Night	43% 9% 16% 24% 7% 1	4452
June	1st to 10th	Night	22% 9% 19% 31% 18% 1	1800
	11th to 20th	Night	25% 7% 15% 32% 18% 4	1800
	21st to end	Night	30% 10% 19% 28% 12% 1	1800
July	1st to 10th	Night	36% 6% 31% 24% 3	4035
	11th to 20th	Night	29% 6% 26% 31% 8%	4026
	21st to end	Night	35% 7% 22% 25% 9% 2	4320
August	1st to 10th	Night	9% 5% 19% 49% 18%	2916
	11th to 20th	Night	17% 8% 34% 35% 6% 1	2999
	21st to end	Night	23% 12% 26% 26% 12% 1	3934
September	1st to 10th	Night	30% 10% 19% 21% 14% 6%	2200
	11th to 20th	Night	32% 9% 16% 24% 15% 5%	2200
	21st to end	Night	27% 7% 15% 23% 16% 12%	2200
October	1st to 10th	Night	14% 4 9% 17% 18% 38%	3590
	11th to 20th	Night	17% 3 9% 21% 31% 20%	3894
	21st to end	Night	21% 3 6% 25% 29% 17%	4252
November	1st to 10th	Night	31% 6% 11% 19% 20% 13%	2460
	11th to 20th	Night	33% 5% 11% 16% 20% 14%	2520
	21st to end	Night	39% 4 10% 16% 18% 12%	2718
December	1st to 10th	Night	54% 4 6% 14% 14% 8%	4380
	11th to 20th	Night	42% 3 10% 9% 20% 15%	4947
	21st to end	Night	35% 4 5% 15% 28% 12%	6633

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	23% 11% 35% 22% 7% 1	330
	11th to 20th	Day	23% 12% 31% 25% 8% 1	330
	21st to end	Day	23% 14% 29% 23% 10% 1	363
February	1st to 10th	Day	27% 13% 28% 23% 9%	300
	11th to 20th	Day	27% 19% 28% 19% 7% 1	300
	21st to end	Day	29% 10% 37% 20% 4	249
March	1st to 10th	Day	19% 18% 35% 21% 7%	300
	11th to 20th	Day	15% 19% 39% 20% 6% 1	300
	21st to end	Day	18% 15% 34% 26% 7%	330
April	1st to 10th	Day	19% 16% 34% 23% 6% 1	300
	11th to 20th	Day	20% 12% 32% 26% 11% 1	333
	21st to end	Day	18% 12% 30% 29% 11%	521
May	1st to 10th	Day	12% 12% 40% 26% 9%	703
	11th to 20th	Day	14% 7% 27% 32% 16% 3	725
	21st to end	Day	12% 5% 27% 36% 18% 3	789
June	1st to 10th	Day	7% 3 13% 36% 32% 9%	730
	11th to 20th	Day	7% 1 13% 39% 31% 8%	730
	21st to end	Day	7% 2 9% 32% 34% 16%	730
July	1st to 10th	Day	8% 3 6% 30% 35% 18%	721
	11th to 20th	Day	4 2 4 25% 46% 19%	718
	21st to end	Day	5% 1 6% 24% 43% 21%	794
August	1st to 10th	Day	2 1 4 21% 46% 26%	726
	11th to 20th	Day	4 1 3 24% 44% 24%	665
	21st to end	Day	6% 2 4 16% 31% 41%	375
September	1st to 10th	Day	8% 1 6% 23% 34% 28%	330
	11th to 20th	Day	5% 2 6% 22% 39% 27%	330
	21st to end	Day	10% 1 4 22% 42% 22%	330
October	1st to 10th	Day	6% 1 10% 30% 36% 17%	330
	11th to 20th	Day	10% 3 15% 32% 27% 13%	330
	21st to end	Day	16% 10% 20% 23% 24% 7%	363
November	1st to 10th	Day	17% 6% 17% 33% 19% 8%	330
	11th to 20th	Day	15% 7% 20% 32% 22% 4	330
	21st to end	Day	21% 15% 27% 21% 12% 4	330
December	1st to 10th	Day	21% 8% 29% 29% 8% 5%	330
	11th to 20th	Day	21% 13% 28% 24% 12% 3	330
	21st to end	Day	17% 8% 35% 27% 10% 2	363
January	1st to 10th	Night	23% 8% 31% 28% 9%	1050
	11th to 20th	Night	21% 11% 29% 30% 8%	1050
	21st to end	Night	25% 9% 29% 30% 6%	1125
February	1st to 10th	Night	27% 10% 30% 28% 5%	800
	11th to 20th	Night	26% 11% 33% 26% 4	784
	21st to end	Night	26% 14% 38% 19% 3	589
March	1st to 10th	Night	22% 13% 36% 27% 3	600
	11th to 20th	Night	20% 12% 34% 28% 6%	600
	21st to end	Night	18% 7% 43% 27% 5%	660
April	1st to 10th	Night	15% 11% 41% 30% 4	600
	11th to 20th	Night	18% 10% 36% 29% 6%	593
	21st to end	Night	20% 8% 37% 28% 7% 1	600
May	1st to 10th	Night	17% 9% 40% 29% 6%	600
	11th to 20th	Night	12% 6% 33% 37% 10% 1	591
	21st to end	Night	10% 3 29% 41% 15% 1	650
June	1st to 10th	Night	5% 2 18% 51% 24% 1	600
	11th to 20th	Night	5% 1 22% 53% 18% 1	600
	21st to end	Night	5% 3 12% 42% 34% 5%	600
July	1st to 10th	Night	6% 2 8% 44% 36% 5%	585
	11th to 20th	Night	3 2 6% 45% 41% 3	582
	21st to end	Night	5% 2 5% 45% 40% 4	657
August	1st to 10th	Night	1 4 49% 41% 4	597
	11th to 20th	Night	3 1 5% 45% 41% 6%	594
	21st to end	Night	5% 1 5% 30% 53% 7%	660
September	1st to 10th	Night	7% 1 7% 34% 45% 7%	600
	11th to 20th	Night	9% 2 6% 37% 43% 4	600
	21st to end	Night	9% 11% 32% 43% 5%	600
October	1st to 10th	Night	5% 1 10% 44% 36% 4	600
	11th to 20th	Night	11% 3 21% 42% 21% 3	795
	21st to end	Night	11% 8% 23% 37% 18% 2	880
November	1st to 10th	Night	12% 5% 21% 40% 20% 1	820
	11th to 20th	Night	13% 7% 24% 38% 16% 1	840
	21st to end	Night	18% 9% 28% 30% 14% 1	1038
December	1st to 10th	Night	22% 8% 27% 30% 12% 1	1050
	11th to 20th	Night	24% 10% 27% 30% 8% 1	1050
	21st to end	Night	21% 9% 28% 33% 8% 1	1155

Page generated at 2026-01-29 00:21:44. Version ac07

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