Black Bear Hollow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Bear Hollow Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	149264
	Night	14% 9% 3 9% 5% 5% 4 4 5% 7% 35%	142119
Transparency	Day	47% 7% 12% 21% 12% 2	152861
	Night	46% 7% 12% 21% 12% 2	146594
Seeing	Day	24% 17% 26% 19% 10% 3	17267
	Night	20% 14% 26% 27% 11% 1	26748

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	13% 14% 5% 16% 6% 5% 5% 4 5% 5% 23%	4841
	11th to 20th	Day	10% 15% 7% 17% 9% 6% 5% 3 4 4 19%	5280
	21st to end	Day	14% 11% 7% 10% 7% 6% 5% 3 4 5% 28%	5780
February	1st to 10th	Day	14% 15% 4 10% 6% 5% 5% 3 5% 5% 29%	1890
	11th to 20th	Day	14% 11% 6% 14% 5% 5% 3 4 5% 6% 28%	1843
	21st to end	Day	16% 13% 3 10% 4 4 4 4 5% 5% 31%	1718
March	1st to 10th	Day	17% 13% 4 7% 5% 3 4 3 4 5% 35%	5045
	11th to 20th	Day	13% 9% 4 8% 5% 5% 5% 4 5% 8% 37%	5090
	21st to end	Day	13% 9% 3 8% 6% 5% 5% 4 5% 5% 37%	5586
April	1st to 10th	Day	17% 12% 3 8% 5% 5% 5% 3 5% 6% 32%	2513
	11th to 20th	Day	14% 11% 3 7% 6% 4 4 3 6% 6% 37%	2494
	21st to end	Day	20% 8% 3 7% 4 4 4 4 4 6% 36%	2607
May	1st to 10th	Day	21% 8% 2 7% 5% 5% 6% 4 6% 7% 29%	7616
	11th to 20th	Day	20% 7% 2 6% 5% 5% 5% 4 6% 8% 32%	7922
	21st to end	Day	23% 7% 2 6% 5% 5% 5% 4 5% 6% 32%	9045
June	1st to 10th	Day	13% 6% 2 6% 6% 5% 6% 5% 7% 8% 37%	2940
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 8% 9% 34%	2940
	21st to end	Day	12% 4 2 7% 5% 5% 5% 5% 7% 11% 38%	2940
July	1st to 10th	Day	10% 6% 2 8% 6% 5% 6% 5% 6% 8% 40%	8280
	11th to 20th	Day	6% 6% 3 8% 6% 6% 7% 5% 8% 10% 35%	7963
	21st to end	Day	9% 7% 3 8% 5% 5% 5% 5% 7% 8% 38%	8340
August	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 5% 8% 9% 26%	6014
	11th to 20th	Day	13% 7% 2 8% 6% 6% 6% 4 7% 9% 32%	5908
	21st to end	Day	10% 4 2 5% 4 5% 5% 5% 8% 10% 41%	6080
September	1st to 10th	Day	15% 5% 2 5% 4 4 4 4 5% 7% 45%	2520
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 7% 46%	2473
	21st to end	Day	22% 8% 3 6% 5% 4 4 3 5% 7% 34%	2197
October	1st to 10th	Day	18% 6% 2 6% 4 4 4 3 5% 6% 42%	2000
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 4 6% 39%	2000
	21st to end	Day	16% 8% 3 7% 4 4 5% 2 5% 7% 39%	2200
November	1st to 10th	Day	10% 7% 2 7% 5% 5% 4 3 7% 6% 46%	1983
	11th to 20th	Day	14% 10% 4 8% 5% 4 5% 4 6% 6% 35%	1738
	21st to end	Day	15% 13% 4 8% 5% 4 4 4 5% 7% 31%	1680
December	1st to 10th	Day	13% 9% 4 15% 7% 5% 5% 4 5% 7% 26%	2680
	11th to 20th	Day	20% 14% 4 8% 4 4 4 3 4 5% 29%	3070
	21st to end	Day	18% 13% 6% 12% 6% 6% 5% 4 5% 5% 19%	4048
January	1st to 10th	Night	10% 12% 5% 16% 7% 7% 5% 4 5% 6% 23%	8035
	11th to 20th	Night	10% 11% 5% 14% 8% 6% 4 3 5% 5% 28%	7680
	21st to end	Night	13% 11% 4 8% 8% 6% 5% 3 4 5% 31%	8401
February	1st to 10th	Night	14% 11% 3 9% 6% 5% 5% 4 6% 6% 31%	2730
	11th to 20th	Night	16% 10% 4 12% 4 6% 5% 4 6% 6% 29%	2663
	21st to end	Night	15% 11% 4 9% 6% 4 5% 4 6% 6% 32%	2084
March	1st to 10th	Night	16% 10% 4 8% 5% 4 4 3 5% 5% 35%	5028
	11th to 20th	Night	10% 7% 5% 7% 4 4 3 3 5% 6% 46%	5090
	21st to end	Night	11% 8% 3 8% 6% 5% 5% 3 6% 6% 40%	5588
April	1st to 10th	Night	17% 12% 5% 8% 5% 4 4 3 4 6% 32%	2106
	11th to 20th	Night	13% 8% 2 7% 4 4 4 4 5% 9% 39%	2075
	21st to end	Night	17% 6% 2 5% 5% 4 4 4 6% 7% 40%	2031
May	1st to 10th	Night	21% 9% 3 8% 5% 4 4 4 5% 7% 29%	5237
	11th to 20th	Night	21% 8% 2 6% 5% 4 4 3 6% 9% 32%	4937
	21st to end	Night	24% 8% 3 7% 4 4 3 3 5% 6% 33%	5108
June	1st to 10th	Night	11% 7% 2 6% 4 4 5% 3 5% 7% 46%	1680
	11th to 20th	Night	11% 6% 3 6% 5% 5% 5% 4 8% 8% 40%	1680
	21st to end	Night	10% 4 2 5% 5% 4 4 4 7% 10% 44%	1680
July	1st to 10th	Night	11% 8% 2 6% 4 4 5% 4 7% 9% 41%	4678
	11th to 20th	Night	7% 7% 3 8% 6% 6% 6% 5% 7% 10% 38%	4976
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 4 5% 8% 41%	5736
August	1st to 10th	Night	14% 8% 3 9% 5% 5% 5% 5% 7% 8% 31%	4135
	11th to 20th	Night	12% 7% 3 7% 5% 5% 4 4 6% 8% 39%	4095
	21st to end	Night	12% 5% 2 6% 4 4 4 3 6% 9% 44%	5040
September	1st to 10th	Night	14% 5% 2 6% 3 4 3 3 5% 7% 46%	2100
	11th to 20th	Night	12% 6% 2 6% 3 3 4 3 5% 7% 50%	2143
	21st to end	Night	20% 7% 2 6% 4 4 4 4 5% 7% 39%	2379
October	1st to 10th	Night	16% 7% 2 5% 4 4 3 3 5% 6% 45%	2400
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 5% 8% 43%	2400
	21st to end	Night	18% 7% 2 5% 4 3 4 4 5% 7% 41%	2640
November	1st to 10th	Night	9% 8% 3 6% 4 4 4 3 4 6% 49%	2532
	11th to 20th	Night	15% 10% 3 7% 5% 4 5% 4 5% 7% 36%	2877
	21st to end	Night	14% 9% 4 8% 6% 6% 5% 4 5% 5% 34%	2940
December	1st to 10th	Night	11% 10% 4 13% 6% 5% 4 4 6% 7% 31%	4720
	11th to 20th	Night	19% 11% 5% 10% 5% 4 4 3 4 5% 28%	5345
	21st to end	Night	17% 14% 6% 11% 6% 5% 5% 4 5% 6% 22%	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	60% 5% 12% 17% 6% 1	4842
	11th to 20th	Day	66% 5% 7% 11% 7% 3	5280
	21st to end	Day	58% 5% 11% 18% 8% 1	5780
February	1st to 10th	Day	56% 6% 12% 18% 8% 1	1890
	11th to 20th	Day	57% 6% 11% 18% 8%	1852
	21st to end	Day	53% 6% 13% 18% 7% 3	1718
March	1st to 10th	Day	49% 6% 11% 20% 10% 4	5045
	11th to 20th	Day	42% 7% 14% 24% 9% 3	5090
	21st to end	Day	47% 7% 10% 21% 13% 2	5586
April	1st to 10th	Day	51% 6% 12% 17% 12% 2	2513
	11th to 20th	Day	46% 7% 11% 18% 16% 3	2494
	21st to end	Day	48% 6% 10% 22% 12% 2	2607
May	1st to 10th	Day	52% 7% 10% 19% 10% 1	7651
	11th to 20th	Day	48% 7% 11% 24% 9% 1	7926
	21st to end	Day	49% 7% 10% 17% 15% 1	9061
June	1st to 10th	Day	42% 8% 12% 21% 16% 1	2940
	11th to 20th	Day	43% 10% 14% 19% 13% 1	2940
	21st to end	Day	39% 9% 14% 25% 13% 1	2940
July	1st to 10th	Day	42% 8% 11% 24% 13% 2	8210
	11th to 20th	Day	39% 9% 14% 28% 10%	7889
	21st to end	Day	40% 7% 10% 24% 18% 1	8156
August	1st to 10th	Day	51% 9% 13% 16% 9%	6001
	11th to 20th	Day	46% 8% 13% 24% 9%	5947
	21st to end	Day	35% 8% 16% 26% 14% 1	6080
September	1st to 10th	Day	38% 8% 12% 22% 18% 3	2520
	11th to 20th	Day	37% 5% 11% 26% 19% 2	2473
	21st to end	Day	49% 6% 12% 15% 16% 2	2197
October	1st to 10th	Day	37% 5% 9% 27% 20% 4	3260
	11th to 20th	Day	39% 5% 12% 24% 11% 9%	3240
	21st to end	Day	30% 5% 15% 29% 22% 1	3538
November	1st to 10th	Day	37% 6% 13% 21% 18% 4	1983
	11th to 20th	Day	47% 6% 12% 21% 12% 3	1738
	21st to end	Day	51% 6% 13% 21% 8% 1	1680
December	1st to 10th	Day	55% 7% 16% 16% 3 1	2680
	11th to 20th	Day	57% 5% 13% 19% 6%	3066
	21st to end	Day	64% 8% 11% 10% 7%	4048
January	1st to 10th	Night	58% 6% 12% 16% 7% 1	8036
	11th to 20th	Night	55% 6% 9% 15% 11% 4	7680
	21st to end	Night	54% 5% 11% 22% 8% 1	8401
February	1st to 10th	Night	51% 7% 12% 20% 9% 1	2730
	11th to 20th	Night	54% 6% 10% 18% 11% 1	2665
	21st to end	Night	51% 7% 11% 19% 10% 2	2084
March	1st to 10th	Night	50% 5% 11% 23% 10% 3	5028
	11th to 20th	Night	36% 8% 15% 28% 10% 4	5090
	21st to end	Night	42% 6% 12% 19% 18% 2	5588
April	1st to 10th	Night	51% 7% 10% 17% 13% 1	2106
	11th to 20th	Night	41% 7% 12% 21% 16% 3	2075
	21st to end	Night	41% 8% 11% 24% 13% 3	2031
May	1st to 10th	Night	53% 7% 11% 16% 11% 2	5264
	11th to 20th	Night	46% 8% 13% 24% 8% 1	4938
	21st to end	Night	49% 8% 11% 21% 10% 2	5115
June	1st to 10th	Night	36% 8% 11% 27% 16% 2	1680
	11th to 20th	Night	39% 9% 14% 24% 13% 2	1680
	21st to end	Night	33% 9% 16% 26% 15% 1	1680
July	1st to 10th	Night	39% 9% 14% 22% 14% 2	4640
	11th to 20th	Night	40% 9% 14% 24% 12% 1	4931
	21st to end	Night	39% 8% 11% 21% 20% 1	5606
August	1st to 10th	Night	48% 10% 13% 20% 9% 1	4124
	11th to 20th	Night	42% 8% 14% 25% 11% 1	4122
	21st to end	Night	36% 6% 15% 29% 13% 1	5040
September	1st to 10th	Night	37% 6% 12% 23% 18% 3	2100
	11th to 20th	Night	33% 7% 10% 29% 19% 2	2143
	21st to end	Night	44% 6% 11% 21% 16% 2	2379
October	1st to 10th	Night	36% 4 10% 26% 23% 1	3920
	11th to 20th	Night	32% 6% 11% 25% 18% 8%	3899
	21st to end	Night	30% 5% 12% 29% 22% 3	4252
November	1st to 10th	Night	36% 5% 12% 24% 19% 4	2532
	11th to 20th	Night	46% 6% 10% 21% 13% 3	2877
	21st to end	Night	49% 6% 13% 21% 10% 1	2940
December	1st to 10th	Night	51% 5% 17% 21% 5%	4720
	11th to 20th	Night	57% 5% 12% 19% 7%	5348
	21st to end	Night	60% 8% 12% 13% 7%	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	38% 26% 23% 11% 2	253
	11th to 20th	Day	40% 26% 26% 7% 1	330
	21st to end	Day	32% 32% 26% 7% 2	363
February	1st to 10th	Day	34% 28% 27% 10% 1	330
	11th to 20th	Day	42% 27% 27% 3	330
	21st to end	Day	36% 26% 25% 11% 1	416
March	1st to 10th	Day	33% 22% 25% 16% 3	540
	11th to 20th	Day	34% 23% 25% 13% 3 1	540
	21st to end	Day	32% 24% 27% 11% 5% 1	594
April	1st to 10th	Day	33% 23% 25% 14% 4 1	540
	11th to 20th	Day	25% 24% 27% 14% 8% 3	532
	21st to end	Day	32% 19% 27% 12% 8% 1	540
May	1st to 10th	Day	28% 21% 28% 13% 7% 3	543
	11th to 20th	Day	26% 19% 27% 17% 9% 3	567
	21st to end	Day	24% 14% 25% 20% 12% 5%	617
June	1st to 10th	Day	19% 18% 26% 21% 14% 3	570
	11th to 20th	Day	19% 13% 31% 22% 11% 3	570
	21st to end	Day	14% 13% 30% 26% 14% 3	570
July	1st to 10th	Day	12% 7% 24% 30% 19% 8%	565
	11th to 20th	Day	7% 8% 30% 29% 18% 7%	564
	21st to end	Day	13% 8% 28% 30% 15% 5%	620
August	1st to 10th	Day	13% 8% 23% 29% 19% 8%	566
	11th to 20th	Day	16% 7% 25% 26% 18% 9%	559
	21st to end	Day	13% 8% 24% 30% 15% 10%	627
September	1st to 10th	Day	18% 9% 19% 27% 18% 9%	570
	11th to 20th	Day	16% 5% 21% 29% 20% 8%	570
	21st to end	Day	31% 12% 23% 18% 11% 5%	562
October	1st to 10th	Day	22% 10% 22% 26% 16% 4	530
	11th to 20th	Day	23% 17% 27% 20% 12% 1	530
	21st to end	Day	20% 20% 32% 19% 8% 1	583
November	1st to 10th	Day	19% 18% 32% 19% 10% 2	496
	11th to 20th	Day	28% 23% 28% 14% 5% 1	278
	21st to end	Day	30% 24% 33% 10% 3	220
December	1st to 10th	Day	33% 30% 25% 8% 3 1	220
	11th to 20th	Day	31% 27% 27% 14% 2	220
	21st to end	Day	31% 24% 26% 16% 2	242
January	1st to 10th	Night	23% 24% 33% 17% 3	840
	11th to 20th	Night	28% 21% 29% 19% 3	840
	21st to end	Night	23% 24% 32% 19% 2	924
February	1st to 10th	Night	24% 20% 30% 23% 3	840
	11th to 20th	Night	27% 26% 30% 16% 1	823
	21st to end	Night	27% 21% 32% 18% 2	692
March	1st to 10th	Night	24% 20% 33% 20% 3	840
	11th to 20th	Night	28% 20% 27% 20% 4	840
	21st to end	Night	23% 18% 35% 19% 4	924
April	1st to 10th	Night	27% 21% 28% 20% 4	840
	11th to 20th	Night	19% 17% 30% 25% 8%	831
	21st to end	Night	21% 15% 26% 30% 7%	771
May	1st to 10th	Night	23% 11% 25% 28% 12%	630
	11th to 20th	Night	22% 9% 27% 32% 10%	519
	21st to end	Night	18% 8% 22% 34% 16% 2	455
June	1st to 10th	Night	13% 5% 26% 36% 19%	420
	11th to 20th	Night	15% 6% 23% 38% 17% 1	420
	21st to end	Night	10% 5% 24% 44% 16% 1	420
July	1st to 10th	Night	11% 5% 17% 40% 23% 3	410
	11th to 20th	Night	8% 3 19% 39% 29% 3	512
	21st to end	Night	10% 3 19% 41% 26% 2	690
August	1st to 10th	Night	10% 2 15% 43% 28% 1	627
	11th to 20th	Night	12% 4 15% 41% 24% 4	624
	21st to end	Night	14% 4 17% 36% 26% 3	919
September	1st to 10th	Night	16% 4 18% 36% 23% 3	840
	11th to 20th	Night	13% 6% 17% 32% 28% 4	840
	21st to end	Night	23% 6% 23% 27% 19% 3	833
October	1st to 10th	Night	18% 8% 20% 31% 21% 2	800
	11th to 20th	Night	19% 14% 28% 28% 10% 1	800
	21st to end	Night	22% 13% 28% 28% 8%	880
November	1st to 10th	Night	16% 12% 30% 32% 9% 1	820
	11th to 20th	Night	24% 18% 26% 23% 7% 1	840
	21st to end	Night	24% 21% 27% 23% 5%	840
December	1st to 10th	Night	26% 20% 28% 21% 5%	840
	11th to 20th	Night	25% 18% 29% 25% 3	840
	21st to end	Night	24% 20% 27% 27% 2	924

Page generated at 2026-09-26 04:18:39. Version ac07

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