Claustonberry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Claustonberry Observatory clear sky chart from 2005-11-06 to 2026-09-14.

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% 9% 3 8% 5% 4 5% 4 6% 7% 37%	149291
	Night	12% 10% 4 8% 5% 4 4 3 5% 6% 38%	142140
Transparency	Day	44% 5% 11% 24% 14% 2	152799
	Night	45% 5% 11% 23% 15% 2	146709
Seeing	Day	16% 11% 30% 25% 13% 5%	18438
	Night	17% 9% 32% 29% 11% 1	28182

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% 13% 7% 14% 6% 6% 5% 4 5% 6% 23%	4691
	11th to 20th	Day	7% 12% 6% 13% 5% 4 5% 6% 6% 6% 30%	4710
	21st to end	Day	11% 13% 6% 10% 5% 5% 4 3 5% 7% 32%	5373
February	1st to 10th	Day	12% 14% 5% 10% 7% 6% 6% 4 5% 6% 25%	1890
	11th to 20th	Day	13% 11% 4 8% 6% 5% 4 3 4 5% 36%	2047
	21st to end	Day	12% 13% 5% 10% 6% 4 4 3 5% 6% 31%	1730
March	1st to 10th	Day	16% 10% 3 6% 4 3 3 3 4 5% 43%	4580
	11th to 20th	Day	11% 6% 2 7% 4 4 5% 4 6% 9% 42%	4812
	21st to end	Day	19% 13% 6% 12% 6% 5% 4 3 5% 5% 22%	6099
April	1st to 10th	Day	17% 12% 4 8% 6% 4 4 3 4 5% 31%	2520
	11th to 20th	Day	15% 10% 3 6% 6% 6% 5% 3 6% 6% 33%	2494
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	2612
May	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 9% 37%	7616
	11th to 20th	Day	12% 6% 2 7% 4 5% 6% 4 6% 7% 40%	8212
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 7% 8% 37%	9047
June	1st to 10th	Day	9% 6% 2 7% 5% 4 5% 4 6% 8% 45%	2940
	11th to 20th	Day	9% 6% 2 5% 4 4 5% 4 7% 10% 44%	2940
	21st to end	Day	10% 7% 2 6% 5% 4 5% 5% 6% 9% 40%	2940
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 6% 4 7% 8% 39%	8280
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 48%	8280
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 9% 42%	8990
August	1st to 10th	Day	12% 7% 2 7% 4 4 4 4 6% 9% 40%	6421
	11th to 20th	Day	15% 7% 2 6% 4 5% 4 4 6% 9% 37%	5486
	21st to end	Day	7% 6% 2 6% 4 4 4 4 6% 9% 49%	6080
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 47%	2520
	11th to 20th	Day	12% 4 1 4 4 3 3 3 6% 7% 53%	2333
	21st to end	Day	11% 7% 2 7% 4 5% 4 3 6% 7% 45%	2200
October	1st to 10th	Day	12% 7% 2 6% 4 3 4 3 5% 7% 47%	2105
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 5% 7% 35%	2000
	21st to end	Day	19% 9% 3 7% 4 4 4 2 5% 5% 38%	1989
November	1st to 10th	Day	12% 10% 2 6% 3 4 4 4 6% 7% 43%	1852
	11th to 20th	Day	14% 14% 4 9% 5% 4 4 4 5% 7% 31%	1890
	21st to end	Day	16% 13% 3 10% 5% 3 3 2 4 6% 34%	1764
December	1st to 10th	Day	8% 9% 4 9% 5% 4 4 3 5% 6% 41%	2690
	11th to 20th	Day	11% 15% 5% 12% 7% 5% 6% 4 6% 7% 22%	3088
	21st to end	Day	21% 22% 9% 12% 6% 4 4 2 3 5% 12%	4070
January	1st to 10th	Night	10% 14% 6% 14% 7% 5% 3 3 4 4 30%	8232
	11th to 20th	Night	10% 13% 6% 15% 6% 6% 6% 5% 6% 4 21%	8280
	21st to end	Night	12% 14% 6% 9% 5% 4 4 3 5% 6% 32%	8838
February	1st to 10th	Night	13% 14% 5% 9% 6% 5% 3 3 4 5% 32%	2730
	11th to 20th	Night	13% 10% 3 8% 5% 5% 4 3 5% 5% 38%	2458
	21st to end	Night	15% 13% 4 8% 4 3 4 3 4 6% 36%	2076
March	1st to 10th	Night	16% 10% 4 6% 4 4 3 3 4 5% 42%	5493
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 5% 7% 47%	5409
	21st to end	Night	19% 13% 5% 10% 5% 4 4 3 4 5% 28%	5072
April	1st to 10th	Night	17% 10% 3 6% 4 4 5% 4 4 6% 37%	2100
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 5% 6% 38%	2075
	21st to end	Night	17% 8% 3 7% 4 4 4 3 6% 7% 38%	2006
May	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 8% 40%	5237
	11th to 20th	Night	9% 5% 3 6% 4 4 5% 4 7% 9% 44%	4675
	21st to end	Night	13% 7% 2 7% 5% 5% 4 4 6% 7% 39%	5139
June	1st to 10th	Night	9% 6% 2 5% 4 5% 5% 4 7% 8% 47%	1680
	11th to 20th	Night	9% 6% 2 5% 4 5% 5% 4 6% 9% 46%	1680
	21st to end	Night	9% 6% 2 7% 5% 4 5% 3 6% 8% 43%	1680
July	1st to 10th	Night	10% 6% 2 6% 5% 4 4 4 6% 8% 43%	4708
	11th to 20th	Night	6% 4 2 6% 4 4 4 3 6% 9% 52%	4707
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 7% 8% 46%	5117
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 8% 45%	3732
	11th to 20th	Night	12% 8% 3 7% 4 4 4 3 6% 8% 40%	4560
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 9% 52%	5046
September	1st to 10th	Night	8% 5% 1 6% 4 3 4 4 4 7% 54%	2100
	11th to 20th	Night	10% 4 1 5% 4 4 4 3 5% 6% 55%	2112
	21st to end	Night	10% 6% 2 5% 4 4 4 3 6% 7% 48%	2200
October	1st to 10th	Night	10% 6% 3 5% 4 3 3 3 4 6% 52%	2290
	11th to 20th	Night	16% 8% 2 6% 4 3 4 3 4 6% 45%	2400
	21st to end	Night	18% 9% 3 6% 4 4 3 3 5% 6% 38%	2850
November	1st to 10th	Night	12% 8% 3 7% 3 3 3 3 4 5% 47%	2666
	11th to 20th	Night	14% 11% 3 9% 4 3 4 3 5% 6% 36%	2730
	21st to end	Night	15% 12% 4 9% 4 4 4 3 5% 5% 35%	2853
December	1st to 10th	Night	10% 9% 3 8% 5% 4 4 4 5% 6% 41%	4720
	11th to 20th	Night	15% 16% 5% 9% 5% 5% 4 3 4 5% 29%	5339
	21st to end	Night	22% 19% 7% 11% 5% 4 4 3 4 4 17%	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	63% 3 13% 15% 6%	4692
	11th to 20th	Day	53% 3 10% 16% 14% 3	4710
	21st to end	Day	53% 4 12% 22% 9%	5373
February	1st to 10th	Day	58% 5% 12% 14% 9% 1	1890
	11th to 20th	Day	50% 4 10% 24% 9% 2	2057
	21st to end	Day	53% 6% 9% 20% 10% 1	1730
March	1st to 10th	Day	45% 5% 10% 26% 11% 4	4580
	11th to 20th	Day	40% 5% 12% 32% 11% 1	4812
	21st to end	Day	64% 6% 9% 13% 7% 1	6101
April	1st to 10th	Day	55% 5% 9% 20% 9%	2520
	11th to 20th	Day	50% 5% 10% 21% 11% 2	2494
	21st to end	Day	51% 6% 13% 18% 12% 1	2612
May	1st to 10th	Day	43% 6% 9% 25% 17% 1	7651
	11th to 20th	Day	41% 7% 10% 25% 17% 1	8216
	21st to end	Day	42% 6% 10% 22% 15% 5%	9061
June	1st to 10th	Day	36% 7% 12% 27% 17% 2	2940
	11th to 20th	Day	34% 7% 13% 24% 20% 2	2940
	21st to end	Day	39% 9% 12% 24% 14% 2	2940
July	1st to 10th	Day	40% 7% 12% 25% 15% 1	8211
	11th to 20th	Day	31% 6% 13% 31% 18% 1	8205
	21st to end	Day	38% 7% 13% 23% 17% 2	8794
August	1st to 10th	Day	40% 7% 13% 28% 12% 1	6406
	11th to 20th	Day	42% 6% 13% 27% 11%	5522
	21st to end	Day	33% 5% 11% 33% 16% 1	6079
September	1st to 10th	Day	34% 7% 12% 27% 17% 3	2520
	11th to 20th	Day	30% 5% 11% 31% 21% 2	2333
	21st to end	Day	38% 5% 10% 27% 19% 1	2200
October	1st to 10th	Day	25% 4 7% 35% 28% 1	3430
	11th to 20th	Day	33% 4 11% 26% 24% 1	3240
	21st to end	Day	44% 3 8% 28% 13% 4	3189
November	1st to 10th	Day	40% 6% 14% 24% 15% 2	1852
	11th to 20th	Day	53% 4 11% 21% 9% 1	1890
	21st to end	Day	54% 5% 11% 23% 8%	1764
December	1st to 10th	Day	44% 4 18% 26% 7% 1	2690
	11th to 20th	Day	60% 5% 11% 17% 7% 1	3085
	21st to end	Day	77% 3 6% 9% 5%	4070
January	1st to 10th	Night	57% 3 11% 19% 9%	8233
	11th to 20th	Night	63% 4 9% 11% 12% 1	8280
	21st to end	Night	54% 4 11% 21% 11%	8838
February	1st to 10th	Night	55% 3 10% 18% 12% 1	2730
	11th to 20th	Night	48% 4 11% 23% 14% 1	2459
	21st to end	Night	50% 4 11% 21% 10% 4	2076
March	1st to 10th	Night	45% 4 12% 23% 11% 5%	5493
	11th to 20th	Night	36% 4 11% 31% 14% 3	5409
	21st to end	Night	59% 5% 8% 18% 10% 1	5072
April	1st to 10th	Night	48% 5% 10% 22% 14% 2	2100
	11th to 20th	Night	47% 5% 7% 21% 16% 4	2075
	21st to end	Night	44% 6% 11% 24% 12% 2	2006
May	1st to 10th	Night	41% 6% 10% 22% 18% 2	5264
	11th to 20th	Night	35% 8% 14% 24% 16% 3	4676
	21st to end	Night	42% 6% 9% 21% 18% 5%	5149
June	1st to 10th	Night	33% 7% 13% 25% 20% 3	1680
	11th to 20th	Night	34% 7% 10% 24% 23% 3	1680
	21st to end	Night	38% 7% 14% 22% 18% 2	1680
July	1st to 10th	Night	38% 6% 14% 24% 15% 2	4670
	11th to 20th	Night	28% 5% 12% 31% 23% 1	4662
	21st to end	Night	34% 8% 12% 26% 19% 2	5002
August	1st to 10th	Night	37% 6% 11% 26% 18% 1	3723
	11th to 20th	Night	40% 8% 13% 26% 13%	4590
	21st to end	Night	28% 6% 13% 34% 16% 2	5046
September	1st to 10th	Night	31% 6% 10% 29% 23% 3	2100
	11th to 20th	Night	30% 6% 7% 33% 23% 2	2112
	21st to end	Night	35% 5% 11% 29% 19% 2	2200
October	1st to 10th	Night	24% 4 7% 36% 28% 2	3745
	11th to 20th	Night	36% 3 7% 25% 26% 3	3899
	21st to end	Night	42% 4 8% 25% 18% 3	4600
November	1st to 10th	Night	39% 5% 9% 26% 18% 3	2666
	11th to 20th	Night	48% 5% 11% 22% 12% 1	2730
	21st to end	Night	52% 4 11% 22% 11% 1	2853
December	1st to 10th	Night	43% 5% 14% 27% 10% 2	4720
	11th to 20th	Night	58% 4 11% 16% 10% 1	5341
	21st to end	Night	70% 4 8% 11% 6%	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% 14% 35% 26% 5% 1	330
	11th to 20th	Day	21% 17% 42% 17% 2 1	330
	21st to end	Day	20% 16% 39% 20% 4 1	363
February	1st to 10th	Day	17% 18% 41% 20% 5%	330
	11th to 20th	Day	22% 20% 38% 16% 4	330
	21st to end	Day	23% 21% 38% 16% 3	273
March	1st to 10th	Day	21% 20% 40% 18% 2	330
	11th to 20th	Day	27% 18% 36% 12% 5% 1	331
	21st to end	Day	27% 15% 32% 19% 6% 2	594
April	1st to 10th	Day	26% 14% 34% 21% 4	540
	11th to 20th	Day	24% 20% 27% 19% 8% 2	532
	21st to end	Day	23% 13% 31% 23% 9% 2	540
May	1st to 10th	Day	19% 15% 31% 23% 9% 3	543
	11th to 20th	Day	21% 12% 30% 23% 12% 3	765
	21st to end	Day	16% 9% 31% 23% 15% 6%	844
June	1st to 10th	Day	10% 8% 33% 29% 15% 5%	780
	11th to 20th	Day	12% 9% 34% 28% 14% 4	780
	21st to end	Day	11% 9% 30% 32% 14% 4	780
July	1st to 10th	Day	8% 3 20% 32% 23% 13%	771
	11th to 20th	Day	8% 4 26% 32% 21% 9%	768
	21st to end	Day	8% 3 24% 38% 19% 7%	849
August	1st to 10th	Day	9% 3 21% 32% 23% 11%	766
	11th to 20th	Day	12% 5% 18% 28% 22% 15%	559
	21st to end	Day	9% 5% 18% 31% 26% 11%	627
September	1st to 10th	Day	14% 6% 22% 28% 23% 8%	570
	11th to 20th	Day	8% 3 21% 31% 24% 13%	542
	21st to end	Day	14% 10% 26% 24% 19% 7%	530
October	1st to 10th	Day	13% 9% 29% 26% 18% 5%	435
	11th to 20th	Day	21% 18% 31% 23% 7% 1	330
	21st to end	Day	29% 12% 31% 22% 5% 1	363
November	1st to 10th	Day	17% 17% 37% 18% 9% 2	330
	11th to 20th	Day	24% 20% 34% 14% 7% 1	330
	21st to end	Day	25% 11% 40% 18% 5%	330
December	1st to 10th	Day	17% 18% 42% 16% 6% 1	330
	11th to 20th	Day	17% 16% 38% 21% 7%	330
	21st to end	Day	27% 18% 39% 13% 3	363
January	1st to 10th	Night	19% 15% 37% 23% 5%	1050
	11th to 20th	Night	20% 15% 39% 21% 5% 1	1050
	21st to end	Night	19% 13% 37% 26% 5%	1155
February	1st to 10th	Night	22% 11% 39% 23% 5%	1050
	11th to 20th	Night	19% 14% 37% 26% 5%	823
	21st to end	Night	22% 14% 40% 21% 3	692
March	1st to 10th	Night	21% 11% 38% 24% 6%	840
	11th to 20th	Night	17% 10% 37% 28% 7%	782
	21st to end	Night	22% 12% 34% 25% 6% 1	693
April	1st to 10th	Night	21% 14% 36% 24% 5%	630
	11th to 20th	Night	23% 14% 31% 26% 6%	623
	21st to end	Night	22% 8% 34% 29% 8%	630
May	1st to 10th	Night	17% 9% 35% 31% 8%	630
	11th to 20th	Night	17% 8% 33% 32% 11%	621
	21st to end	Night	15% 5% 27% 35% 17%	683
June	1st to 10th	Night	10% 5% 26% 43% 15%	630
	11th to 20th	Night	10% 5% 33% 40% 11%	630
	21st to end	Night	8% 5% 30% 37% 19% 1	630
July	1st to 10th	Night	8% 2 18% 39% 29% 4	615
	11th to 20th	Night	9% 2 23% 39% 25% 2	612
	21st to end	Night	8% 1 22% 43% 25% 1	690
August	1st to 10th	Night	6% 16% 47% 27% 4	627
	11th to 20th	Night	10% 3 13% 42% 29% 4	624
	21st to end	Night	8% 2 16% 43% 29% 3	693
September	1st to 10th	Night	10% 3 20% 38% 24% 4	630
	11th to 20th	Night	11% 3 18% 36% 27% 3	691
	21st to end	Night	12% 8% 24% 32% 22% 3	800
October	1st to 10th	Night	13% 7% 27% 35% 17% 1	800
	11th to 20th	Night	21% 11% 32% 25% 10%	800
	21st to end	Night	24% 12% 32% 25% 8%	880
November	1st to 10th	Night	18% 10% 38% 23% 10% 1	820
	11th to 20th	Night	20% 15% 36% 23% 6%	840
	21st to end	Night	22% 13% 37% 23% 5%	963
December	1st to 10th	Night	22% 12% 38% 23% 5%	1050
	11th to 20th	Night	24% 12% 36% 24% 4 1	1050
	21st to end	Night	29% 13% 35% 20% 3	1155

Page generated at 2026-09-11 03:11:51. Version ac07

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