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 2025-05-26.

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	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	114112
	Night	14% 9% 3 8% 5% 5% 4 4 5% 7% 35%	115141
Transparency	Day	47% 7% 12% 21% 12% 2	117752
	Night	45% 7% 12% 21% 12% 2	119641
Seeing	Day	24% 17% 26% 19% 11% 4	15465
	Night	20% 14% 26% 28% 11% 1	25099

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	12% 15% 5% 17% 6% 4 4 4 4 4 25%	3735
	11th to 20th	Day	11% 16% 8% 15% 9% 6% 5% 3 4 4 18%	4060
	21st to end	Day	15% 14% 8% 9% 5% 5% 5% 3 4 5% 26%	4466
February	1st to 10th	Day	15% 15% 4 10% 6% 5% 5% 3 5% 5% 28%	1800
	11th to 20th	Day	14% 11% 6% 13% 5% 5% 4 4 5% 6% 28%	1753
	21st to end	Day	16% 13% 3 10% 4 4 4 4 5% 5% 31%	1638
March	1st to 10th	Day	17% 13% 4 7% 5% 4 4 3 4 5% 35%	4935
	11th to 20th	Day	12% 9% 4 7% 4 5% 5% 3 5% 8% 38%	4980
	21st to end	Day	13% 9% 3 8% 6% 5% 5% 4 5% 5% 37%	5465
April	1st to 10th	Day	17% 12% 3 8% 5% 5% 5% 3 5% 7% 31%	2393
	11th to 20th	Day	14% 11% 3 7% 6% 4 4 3 5% 5% 36%	2374
	21st to end	Day	20% 8% 3 7% 4 4 4 4 4 6% 36%	2483
May	1st to 10th	Day	27% 8% 2 7% 4 4 4 4 5% 6% 28%	4212
	11th to 20th	Day	24% 9% 3 6% 4 4 4 4 5% 7% 29%	4372
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 6% 9% 38%	4893
June	1st to 10th	Day	13% 6% 2 6% 6% 5% 6% 5% 7% 8% 36%	2660
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 8% 9% 35%	2660
	21st to end	Day	11% 4 2 7% 6% 5% 5% 5% 7% 10% 38%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 6% 5% 7% 10% 40%	4440
	11th to 20th	Day	6% 6% 3 7% 5% 5% 6% 5% 8% 10% 39%	4263
	21st to end	Day	11% 8% 3 8% 6% 5% 5% 4 6% 7% 37%	4466
August	1st to 10th	Day	17% 6% 2 7% 5% 6% 6% 5% 7% 9% 31%	4104
	11th to 20th	Day	10% 7% 2 7% 6% 6% 6% 4 7% 9% 35%	4015
	21st to end	Day	13% 5% 2 5% 4 4 4 5% 6% 8% 43%	4180
September	1st to 10th	Day	17% 5% 2 5% 4 4 4 4 5% 7% 43%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 4 3 5% 7% 46%	2237
	21st to end	Day	20% 8% 3 6% 5% 4 4 4 5% 7% 35%	2006
October	1st to 10th	Day	18% 6% 2 6% 4 5% 5% 3 5% 6% 40%	1900
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 4 6% 39%	1900
	21st to end	Day	17% 8% 3 6% 4 3 4 2 5% 7% 39%	2090
November	1st to 10th	Day	11% 7% 2 7% 5% 4 4 3 6% 6% 46%	1887
	11th to 20th	Day	15% 10% 4 7% 4 4 5% 4 6% 7% 36%	1655
	21st to end	Day	15% 13% 3 8% 5% 4 4 4 5% 7% 31%	1600
December	1st to 10th	Day	13% 8% 4 15% 7% 5% 5% 4 5% 7% 27%	2600
	11th to 20th	Day	21% 14% 5% 8% 4 4 4 3 4 5% 29%	2990
	21st to end	Day	18% 13% 6% 12% 6% 6% 5% 4 5% 5% 19%	3960
January	1st to 10th	Night	11% 12% 5% 16% 7% 6% 5% 4 5% 6% 24%	6193
	11th to 20th	Night	12% 12% 5% 15% 8% 6% 4 3 4 5% 26%	5900
	21st to end	Night	16% 12% 5% 9% 6% 5% 5% 4 4 5% 30%	6490
February	1st to 10th	Night	14% 12% 3 8% 5% 5% 5% 4 6% 6% 31%	2600
	11th to 20th	Night	15% 10% 4 11% 4 6% 5% 4 6% 6% 29%	2533
	21st to end	Night	15% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	1988
March	1st to 10th	Night	16% 9% 4 9% 5% 4 4 3 5% 5% 35%	4918
	11th to 20th	Night	10% 7% 5% 7% 4 4 3 3 5% 6% 46%	4980
	21st to end	Night	11% 8% 3 8% 5% 5% 5% 3 5% 6% 40%	5467
April	1st to 10th	Night	17% 12% 5% 8% 5% 4 4 3 4 5% 32%	2006
	11th to 20th	Night	13% 8% 2 7% 5% 4 4 4 5% 9% 39%	1975
	21st to end	Night	18% 6% 2 5% 5% 4 4 4 6% 7% 40%	1934
May	1st to 10th	Night	26% 10% 3 7% 5% 3 4 3 4 7% 27%	2903
	11th to 20th	Night	26% 10% 2 5% 4 4 4 3 5% 6% 29%	2740
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 4 7% 9% 39%	2778
June	1st to 10th	Night	11% 7% 2 6% 4 4 5% 3 5% 8% 45%	1520
	11th to 20th	Night	11% 6% 2 6% 5% 5% 5% 4 8% 8% 40%	1520
	21st to end	Night	10% 4 2 5% 5% 4 4 4 8% 11% 44%	1520
July	1st to 10th	Night	7% 6% 2 6% 5% 5% 6% 5% 8% 9% 42%	2520
	11th to 20th	Night	6% 4 2 6% 5% 5% 6% 5% 7% 10% 45%	2679
	21st to end	Night	11% 8% 3 8% 5% 4 5% 4 5% 7% 40%	3087
August	1st to 10th	Night	16% 7% 2 7% 5% 4 4 4 6% 8% 37%	2825
	11th to 20th	Night	12% 7% 2 6% 4 5% 3 4 6% 8% 43%	2785
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 8% 46%	3471
September	1st to 10th	Night	15% 5% 2 6% 3 4 3 3 5% 7% 46%	1900
	11th to 20th	Night	11% 6% 2 5% 3 3 4 2 5% 7% 51%	1939
	21st to end	Night	19% 7% 2 5% 4 4 4 4 5% 7% 41%	2173
October	1st to 10th	Night	16% 7% 2 5% 4 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	15% 6% 2 5% 4 4 4 4 5% 8% 43%	2280
	21st to end	Night	18% 7% 2 5% 4 3 4 4 5% 7% 41%	2508
November	1st to 10th	Night	10% 8% 3 6% 4 4 4 3 4 6% 50%	2408
	11th to 20th	Night	15% 10% 3 7% 5% 4 5% 4 5% 7% 36%	2740
	21st to end	Night	15% 9% 4 7% 6% 6% 5% 4 5% 6% 34%	2800
December	1st to 10th	Night	11% 10% 4 13% 6% 5% 4 4 5% 7% 31%	4580
	11th to 20th	Night	19% 11% 5% 10% 5% 4 5% 3 4 5% 28%	5205
	21st to end	Night	17% 14% 6% 11% 6% 5% 5% 4 5% 6% 22%	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	60% 6% 10% 17% 6% 1	3736
	11th to 20th	Day	66% 6% 8% 10% 7% 2	4060
	21st to end	Day	59% 5% 11% 15% 9% 1	4466
February	1st to 10th	Day	57% 6% 12% 18% 7% 1	1800
	11th to 20th	Day	56% 6% 11% 18% 8% 1	1762
	21st to end	Day	53% 7% 13% 17% 8% 3	1638
March	1st to 10th	Day	49% 6% 11% 20% 10% 4	4935
	11th to 20th	Day	41% 7% 14% 25% 9% 3	4980
	21st to end	Day	47% 7% 10% 21% 14% 2	5465
April	1st to 10th	Day	51% 6% 12% 17% 12% 2	2393
	11th to 20th	Day	46% 7% 10% 18% 16% 2	2374
	21st to end	Day	48% 7% 10% 21% 13% 2	2483
May	1st to 10th	Day	54% 8% 8% 19% 10% 1	4250
	11th to 20th	Day	52% 8% 12% 19% 8% 2	4376
	21st to end	Day	36% 11% 15% 22% 14% 2	4907
June	1st to 10th	Day	43% 9% 13% 21% 14% 1	2660
	11th to 20th	Day	42% 10% 14% 19% 13% 1	2660
	21st to end	Day	38% 9% 14% 25% 13% 1	2660
July	1st to 10th	Day	38% 9% 14% 26% 10% 3	4370
	11th to 20th	Day	36% 9% 15% 24% 15% 1	4189
	21st to end	Day	43% 7% 10% 22% 16% 1	4324
August	1st to 10th	Day	48% 9% 15% 20% 8%	4091
	11th to 20th	Day	44% 7% 10% 27% 11% 1	4054
	21st to end	Day	37% 7% 13% 27% 15% 2	4180
September	1st to 10th	Day	40% 7% 10% 21% 18% 3	2280
	11th to 20th	Day	36% 5% 11% 26% 19% 2	2237
	21st to end	Day	48% 6% 13% 16% 16% 1	2006
October	1st to 10th	Day	37% 5% 9% 26% 20% 4	3160
	11th to 20th	Day	39% 5% 12% 23% 11% 9%	3140
	21st to end	Day	29% 5% 15% 29% 22% 1	3428
November	1st to 10th	Day	38% 6% 14% 21% 17% 4	1887
	11th to 20th	Day	46% 6% 12% 22% 12% 2	1655
	21st to end	Day	51% 7% 13% 21% 8% 1	1600
December	1st to 10th	Day	55% 7% 17% 17% 3 1	2600
	11th to 20th	Day	57% 5% 13% 19% 6%	2986
	21st to end	Day	64% 8% 11% 10% 6%	3960
January	1st to 10th	Night	58% 6% 10% 16% 9% 1	6193
	11th to 20th	Night	56% 7% 11% 14% 8% 4	5900
	21st to end	Night	54% 6% 11% 19% 8% 2	6490
February	1st to 10th	Night	51% 8% 12% 21% 8% 1	2600
	11th to 20th	Night	53% 6% 10% 18% 12% 1	2535
	21st to end	Night	51% 7% 11% 19% 10% 2	1988
March	1st to 10th	Night	49% 5% 11% 23% 10% 3	4918
	11th to 20th	Night	35% 8% 15% 28% 9% 4	4980
	21st to end	Night	42% 6% 12% 19% 18% 2	5467
April	1st to 10th	Night	52% 7% 10% 17% 13% 1	2006
	11th to 20th	Night	41% 8% 12% 21% 16% 3	1975
	21st to end	Night	41% 8% 11% 24% 13% 3	1934
May	1st to 10th	Night	56% 8% 7% 17% 10% 2	2930
	11th to 20th	Night	51% 10% 12% 17% 8% 1	2741
	21st to end	Night	35% 12% 16% 24% 10% 3	2785
June	1st to 10th	Night	36% 8% 12% 27% 14% 2	1520
	11th to 20th	Night	38% 9% 14% 25% 12% 2	1520
	21st to end	Night	32% 9% 17% 26% 15% 1	1520
July	1st to 10th	Night	35% 10% 16% 21% 13% 4	2480
	11th to 20th	Night	32% 10% 16% 25% 16% 1	2631
	21st to end	Night	40% 9% 13% 18% 19% 2	2988
August	1st to 10th	Night	43% 9% 16% 23% 8%	2814
	11th to 20th	Night	38% 7% 12% 28% 13% 1	2812
	21st to end	Night	36% 6% 13% 30% 13% 2	3471
September	1st to 10th	Night	38% 7% 12% 22% 18% 3	1900
	11th to 20th	Night	32% 7% 10% 30% 20% 2	1939
	21st to end	Night	42% 6% 11% 23% 16% 2	2173
October	1st to 10th	Night	36% 4 10% 26% 22% 1	3800
	11th to 20th	Night	31% 6% 11% 25% 18% 9%	3779
	21st to end	Night	30% 5% 12% 29% 22% 3	4120
November	1st to 10th	Night	36% 5% 12% 24% 19% 4	2408
	11th to 20th	Night	45% 7% 10% 21% 14% 3	2740
	21st to end	Night	48% 7% 13% 21% 10% 1	2800
December	1st to 10th	Night	51% 5% 17% 21% 5%	4580
	11th to 20th	Night	57% 5% 13% 18% 7%	5208
	21st to end	Night	60% 8% 12% 13% 7%	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	37% 26% 23% 11% 2	230
	11th to 20th	Day	37% 26% 28% 8% 1	300
	21st to end	Day	29% 32% 28% 8% 3	330
February	1st to 10th	Day	34% 28% 28% 9% 1	300
	11th to 20th	Day	43% 27% 26% 3	300
	21st to end	Day	36% 26% 25% 12% 2	385
March	1st to 10th	Day	32% 22% 26% 17% 3	500
	11th to 20th	Day	33% 24% 25% 14% 3 1	500
	21st to end	Day	31% 23% 27% 12% 5% 1	550
April	1st to 10th	Day	32% 24% 25% 14% 5% 1	500
	11th to 20th	Day	25% 24% 25% 15% 8% 3	492
	21st to end	Day	32% 19% 27% 13% 8% 1	500
May	1st to 10th	Day	28% 19% 29% 13% 8% 3	503
	11th to 20th	Day	27% 18% 27% 16% 9% 3	527
	21st to end	Day	20% 14% 26% 21% 13% 6%	549
June	1st to 10th	Day	19% 17% 27% 20% 15% 3	490
	11th to 20th	Day	18% 11% 31% 24% 13% 3	490
	21st to end	Day	12% 14% 31% 25% 15% 3	490
July	1st to 10th	Day	11% 7% 24% 29% 20% 8%	485
	11th to 20th	Day	7% 8% 29% 30% 18% 8%	484
	21st to end	Day	14% 8% 27% 30% 16% 5%	532
August	1st to 10th	Day	13% 8% 23% 28% 20% 8%	486
	11th to 20th	Day	15% 7% 25% 25% 19% 10%	479
	21st to end	Day	14% 7% 22% 29% 17% 11%	539
September	1st to 10th	Day	20% 9% 19% 25% 18% 9%	490
	11th to 20th	Day	17% 5% 20% 30% 20% 8%	490
	21st to end	Day	29% 13% 22% 18% 12% 5%	490
October	1st to 10th	Day	23% 10% 22% 25% 16% 3	490
	11th to 20th	Day	23% 17% 26% 21% 13% 1	490
	21st to end	Day	21% 18% 32% 19% 9% 1	539
November	1st to 10th	Day	18% 17% 33% 21% 10% 2	460
	11th to 20th	Day	26% 23% 30% 15% 5% 1	255
	21st to end	Day	30% 23% 33% 11% 3 1	200
December	1st to 10th	Day	32% 29% 26% 9% 4 1	200
	11th to 20th	Day	31% 25% 28% 15% 2	200
	21st to end	Day	28% 25% 27% 18% 3	220
January	1st to 10th	Night	23% 24% 33% 17% 3	800
	11th to 20th	Night	28% 19% 30% 20% 3	800
	21st to end	Night	22% 24% 33% 20% 2	880
February	1st to 10th	Night	24% 20% 30% 23% 3	800
	11th to 20th	Night	27% 27% 29% 16% 1	783
	21st to end	Night	26% 21% 32% 19% 2	660
March	1st to 10th	Night	24% 20% 32% 21% 3	800
	11th to 20th	Night	27% 21% 27% 21% 4 1	800
	21st to end	Night	22% 18% 35% 20% 5%	880
April	1st to 10th	Night	26% 21% 28% 21% 4	800
	11th to 20th	Night	19% 17% 30% 26% 8%	791
	21st to end	Night	21% 15% 27% 29% 7%	734
May	1st to 10th	Night	24% 10% 24% 29% 13%	600
	11th to 20th	Night	23% 9% 26% 32% 10%	494
	21st to end	Night	16% 7% 22% 35% 18% 2	423
June	1st to 10th	Night	14% 5% 26% 36% 19% 1	380
	11th to 20th	Night	14% 5% 22% 39% 19% 1	380
	21st to end	Night	9% 5% 25% 46% 16%	380
July	1st to 10th	Night	11% 5% 17% 41% 23% 3	370
	11th to 20th	Night	8% 3 18% 40% 30% 3	462
	21st to end	Night	10% 3 19% 41% 25% 2	624
August	1st to 10th	Night	10% 2 16% 44% 27% 2	567
	11th to 20th	Night	12% 3 14% 41% 25% 4	564
	21st to end	Night	14% 4 16% 35% 27% 3	831
September	1st to 10th	Night	17% 4 18% 35% 23% 4	760
	11th to 20th	Night	13% 6% 18% 31% 29% 4	760
	21st to end	Night	22% 7% 22% 26% 20% 3	760
October	1st to 10th	Night	19% 8% 20% 31% 20% 2	760
	11th to 20th	Night	19% 14% 28% 28% 11% 1	760
	21st to end	Night	22% 13% 27% 28% 8%	836
November	1st to 10th	Night	15% 12% 30% 33% 9% 1	780
	11th to 20th	Night	23% 19% 26% 24% 7% 1	800
	21st to end	Night	23% 21% 27% 24% 5%	800
December	1st to 10th	Night	27% 20% 27% 21% 5%	800
	11th to 20th	Night	24% 18% 30% 26% 3	800
	21st to end	Night	23% 20% 27% 28% 2	880

Page generated at 2025-05-23 09:21:00. Version ac07

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