Black Bear Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Bear Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	17% 11% 4 9% 5% 5% 4 4 5% 6% 29%	131201
	Night	16% 12% 5% 10% 6% 4 4 3 4 6% 29%	129965
Transparency	Day	53% 6% 10% 19% 10% 1	134691
	Night	54% 6% 11% 18% 10% 1	134562
Seeing	Day	29% 16% 26% 17% 9% 3	16411
	Night	27% 16% 23% 23% 9% 1	25705

By Month

Percentage Cloud Cover NE (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% 15% 10% 23% 10% 3 3 2 3 4 16%	4661
	11th to 20th	Day	13% 14% 8% 20% 8% 6% 4 3 4 4 17%	4650
	21st to end	Day	15% 13% 8% 10% 7% 5% 5% 4 5% 6% 24%	5617
February	1st to 10th	Day	14% 14% 6% 13% 9% 5% 4 3 5% 4 22%	1890
	11th to 20th	Day	13% 13% 6% 14% 7% 5% 4 3 5% 7% 24%	1966
	21st to end	Day	17% 16% 4 10% 7% 4 3 3 4 5% 26%	1730
March	1st to 10th	Day	19% 16% 6% 10% 5% 4 3 2 4 4 27%	4496
	11th to 20th	Day	13% 13% 5% 9% 4 4 4 3 4 5% 35%	4922
	21st to end	Day	18% 12% 3 10% 5% 4 4 3 4 5% 30%	5828
April	1st to 10th	Day	18% 15% 3 10% 5% 4 4 3 4 5% 29%	2400
	11th to 20th	Day	16% 13% 3 7% 5% 4 5% 4 5% 6% 32%	2374
	21st to end	Day	19% 12% 4 7% 5% 4 4 3 5% 5% 32%	2401
May	1st to 10th	Day	29% 12% 3 7% 4 4 4 3 5% 6% 24%	6134
	11th to 20th	Day	19% 11% 3 8% 6% 5% 5% 4 5% 6% 28%	6318
	21st to end	Day	22% 9% 3 6% 5% 5% 5% 4 6% 7% 27%	6949
June	1st to 10th	Day	18% 7% 3 7% 6% 5% 5% 5% 6% 8% 30%	2800
	11th to 20th	Day	19% 8% 3 5% 6% 4 5% 5% 7% 8% 28%	2800
	21st to end	Day	18% 9% 3 6% 6% 4 5% 4 7% 9% 31%	2800
July	1st to 10th	Day	11% 7% 3 9% 6% 6% 5% 5% 7% 8% 34%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 6% 6% 5% 8% 10% 31%	6360
	21st to end	Day	14% 7% 3 7% 5% 4 5% 4 7% 8% 37%	6926
August	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 7% 29%	4343
	11th to 20th	Day	15% 8% 3 7% 5% 6% 6% 6% 7% 9% 30%	3917
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 7% 8% 36%	4312
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 4 7% 38%	2400
	11th to 20th	Day	14% 6% 2 6% 4 5% 4 4 5% 7% 42%	2360
	21st to end	Day	20% 8% 2 7% 4 5% 4 3 7% 6% 33%	2200
October	1st to 10th	Day	19% 10% 3 7% 4 4 4 4 4 5% 34%	2008
	11th to 20th	Day	17% 12% 3 6% 4 4 5% 3 6% 6% 34%	2000
	21st to end	Day	23% 15% 3 7% 3 5% 3 3 5% 6% 27%	2069
November	1st to 10th	Day	13% 12% 3 8% 5% 4 5% 3 5% 5% 37%	1851
	11th to 20th	Day	15% 17% 4 9% 5% 4 3 3 4 5% 30%	1885
	21st to end	Day	19% 17% 5% 9% 4 4 4 3 5% 5% 25%	1680
December	1st to 10th	Day	14% 19% 7% 22% 5% 4 3 3 4 4 16%	2680
	11th to 20th	Day	18% 16% 8% 11% 5% 3 3 2 3 4 25%	3066
	21st to end	Day	16% 19% 8% 12% 5% 3 4 3 4 5% 21%	4048
January	1st to 10th	Night	13% 14% 8% 23% 7% 4 4 3 3 4 17%	8234
	11th to 20th	Night	11% 16% 8% 22% 8% 5% 4 3 4 4 15%	8235
	21st to end	Night	12% 12% 5% 10% 10% 8% 7% 4 4 5% 22%	8549
February	1st to 10th	Night	13% 14% 5% 12% 8% 6% 5% 3 5% 5% 24%	2730
	11th to 20th	Night	12% 13% 6% 13% 9% 6% 5% 4 5% 6% 21%	2539
	21st to end	Night	16% 14% 5% 12% 6% 4 4 3 5% 5% 26%	2076
March	1st to 10th	Night	17% 13% 4 11% 7% 4 3 3 5% 5% 28%	5389
	11th to 20th	Night	13% 13% 6% 10% 5% 3 3 3 5% 6% 33%	5034
	21st to end	Night	15% 15% 4 10% 5% 4 4 2 4 5% 30%	5103
April	1st to 10th	Night	18% 14% 4 9% 5% 4 4 4 4 6% 27%	2000
	11th to 20th	Night	18% 13% 3 7% 4 5% 4 2 5% 6% 34%	1975
	21st to end	Night	19% 10% 4 8% 4 4 3 3 6% 5% 35%	1997
May	1st to 10th	Night	31% 12% 3 7% 4 3 3 3 4 5% 26%	3835
	11th to 20th	Night	21% 10% 3 8% 5% 4 4 4 5% 6% 30%	3575
	21st to end	Night	23% 12% 3 8% 4 4 3 3 5% 6% 29%	3926
June	1st to 10th	Night	18% 7% 2 6% 5% 5% 4 3 6% 7% 38%	1600
	11th to 20th	Night	17% 8% 2 7% 3 4 4 3 6% 7% 39%	1600
	21st to end	Night	13% 5% 2 6% 4 4 5% 4 7% 9% 42%	1600
July	1st to 10th	Night	13% 8% 3 9% 5% 4 4 4 6% 8% 38%	3600
	11th to 20th	Night	17% 8% 3 7% 5% 5% 5% 3 6% 8% 33%	3600
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 6% 44%	3926
August	1st to 10th	Night	23% 9% 3 7% 4 4 5% 3 5% 6% 32%	2802
	11th to 20th	Night	18% 8% 2 6% 4 4 4 3 4 6% 39%	3099
	21st to end	Night	13% 7% 3 6% 5% 4 4 3 4 7% 45%	3586
September	1st to 10th	Night	17% 8% 2 5% 3 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	14% 6% 2 5% 5% 3 4 2 4 6% 49%	2040
	21st to end	Night	19% 7% 3 7% 5% 4 4 3 5% 6% 37%	2200
October	1st to 10th	Night	20% 9% 3 6% 4 3 3 3 4 7% 37%	2390
	11th to 20th	Night	20% 10% 2 7% 3 4 4 3 4 5% 38%	2400
	21st to end	Night	22% 14% 3 8% 4 4 3 3 4 6% 29%	2770
November	1st to 10th	Night	14% 11% 4 7% 4 4 3 3 5% 6% 38%	2667
	11th to 20th	Night	19% 12% 4 8% 5% 3 4 3 5% 6% 30%	2730
	21st to end	Night	15% 15% 5% 9% 6% 5% 4 4 5% 6% 27%	2940
December	1st to 10th	Night	13% 18% 8% 16% 6% 4 4 3 4 5% 19%	4720
	11th to 20th	Night	22% 16% 6% 9% 4 3 3 2 3 3 28%	5348
	21st to end	Night	19% 18% 8% 11% 6% 4 3 3 3 4 21%	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	72% 5% 7% 12% 3	4662
	11th to 20th	Day	69% 6% 6% 11% 7% 1	4680
	21st to end	Day	59% 5% 9% 19% 7%	5617
February	1st to 10th	Day	63% 5% 8% 15% 8%	1890
	11th to 20th	Day	59% 6% 7% 17% 10% 1	1975
	21st to end	Day	60% 4 9% 18% 8% 1	1730
March	1st to 10th	Day	61% 4 10% 14% 10% 2	4499
	11th to 20th	Day	48% 7% 14% 21% 7% 4	4922
	21st to end	Day	55% 6% 6% 12% 18% 3	5828
April	1st to 10th	Day	57% 5% 6% 21% 9% 3	2400
	11th to 20th	Day	52% 5% 10% 19% 13% 2	2374
	21st to end	Day	52% 5% 9% 19% 12% 3	2401
May	1st to 10th	Day	61% 5% 9% 14% 9% 1	6145
	11th to 20th	Day	56% 5% 9% 19% 10% 1	6322
	21st to end	Day	52% 7% 11% 19% 10% 1	6949
June	1st to 10th	Day	49% 6% 12% 20% 12%	2800
	11th to 20th	Day	50% 6% 14% 21% 9% 1	2800
	21st to end	Day	48% 7% 11% 24% 10%	2800
July	1st to 10th	Day	44% 8% 14% 22% 10% 1	6290
	11th to 20th	Day	43% 9% 16% 23% 9%	6285
	21st to end	Day	42% 7% 12% 25% 13%	6728
August	1st to 10th	Day	53% 5% 13% 19% 9%	4329
	11th to 20th	Day	46% 9% 15% 24% 5%	3955
	21st to end	Day	42% 7% 12% 30% 9% 1	4312
September	1st to 10th	Day	44% 6% 10% 26% 13% 1	2400
	11th to 20th	Day	40% 5% 10% 24% 21% 1	2360
	21st to end	Day	49% 5% 11% 20% 14% 2	2200
October	1st to 10th	Day	47% 7% 9% 22% 14% 2	3268
	11th to 20th	Day	44% 4 8% 23% 14% 6%	3240
	21st to end	Day	41% 6% 14% 25% 12% 2	3320
November	1st to 10th	Day	47% 6% 11% 20% 14% 2	1851
	11th to 20th	Day	55% 5% 9% 17% 11% 2	1885
	21st to end	Day	61% 4 13% 17% 5% 1	1680
December	1st to 10th	Day	72% 4 9% 11% 4	2680
	11th to 20th	Day	63% 4 9% 14% 9%	3066
	21st to end	Day	66% 4 8% 12% 10% 2	4048
January	1st to 10th	Night	70% 5% 8% 11% 6% 1	8234
	11th to 20th	Night	69% 8% 8% 9% 6% 1	8280
	21st to end	Night	62% 6% 8% 13% 10% 1	8549
February	1st to 10th	Night	61% 6% 10% 15% 8% 1	2730
	11th to 20th	Night	59% 9% 9% 15% 8% 1	2541
	21st to end	Night	58% 5% 9% 18% 8% 2	2076
March	1st to 10th	Night	58% 4 12% 14% 10% 1	5399
	11th to 20th	Night	49% 7% 17% 16% 7% 3	5035
	21st to end	Night	54% 7% 5% 15% 17% 2	5103
April	1st to 10th	Night	58% 4 8% 18% 10% 2	2000
	11th to 20th	Night	52% 4 10% 19% 15%	1975
	21st to end	Night	49% 5% 9% 20% 14% 3	1997
May	1st to 10th	Night	62% 4 8% 15% 8% 2	3841
	11th to 20th	Night	53% 8% 12% 19% 8% 1	3576
	21st to end	Night	55% 6% 11% 18% 9% 1	3927
June	1st to 10th	Night	45% 5% 12% 23% 15%	1600
	11th to 20th	Night	43% 6% 16% 25% 10% 1	1600
	21st to end	Night	37% 8% 16% 25% 14% 1	1600
July	1st to 10th	Night	44% 6% 15% 19% 14% 1	3560
	11th to 20th	Night	46% 8% 13% 21% 11% 1	3552
	21st to end	Night	37% 7% 13% 29% 14% 1	3809
August	1st to 10th	Night	52% 6% 14% 20% 7% 1	2792
	11th to 20th	Night	45% 6% 16% 25% 8%	3127
	21st to end	Night	38% 6% 12% 32% 11%	3586
September	1st to 10th	Night	41% 5% 12% 26% 15% 1	2000
	11th to 20th	Night	36% 5% 10% 27% 21% 1	2040
	21st to end	Night	48% 5% 10% 21% 16% 2	2200
October	1st to 10th	Night	50% 7% 10% 21% 12% 1	3910
	11th to 20th	Night	42% 6% 13% 18% 16% 5%	3899
	21st to end	Night	42% 6% 15% 25% 11% 1	4469
November	1st to 10th	Night	45% 6% 10% 21% 16% 2	2667
	11th to 20th	Night	52% 6% 11% 18% 12% 2	2730
	21st to end	Night	54% 7% 14% 19% 6% 1	2940
December	1st to 10th	Night	65% 7% 9% 16% 3	4720
	11th to 20th	Night	61% 5% 10% 14% 11%	5348
	21st to end	Night	66% 5% 7% 10% 10% 2	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	39% 22% 27% 10% 1	220
	11th to 20th	Day	48% 22% 21% 6% 3	220
	21st to end	Day	37% 27% 24% 9% 3	333
February	1st to 10th	Day	38% 28% 28% 5% 1	330
	11th to 20th	Day	39% 28% 24% 7% 1	454
	21st to end	Day	37% 24% 27% 10% 1	446
March	1st to 10th	Day	35% 23% 25% 14% 3	508
	11th to 20th	Day	36% 26% 23% 12% 4 1	500
	21st to end	Day	36% 25% 24% 9% 5% 2	550
April	1st to 10th	Day	41% 20% 24% 11% 4 1	500
	11th to 20th	Day	34% 23% 23% 11% 5% 3	492
	21st to end	Day	33% 19% 29% 11% 6% 2	500
May	1st to 10th	Day	39% 16% 24% 13% 6% 3	503
	11th to 20th	Day	27% 17% 29% 18% 6% 3	527
	21st to end	Day	23% 11% 29% 21% 11% 4	573
June	1st to 10th	Day	23% 13% 31% 20% 10% 2	530
	11th to 20th	Day	25% 12% 27% 23% 12% 2	530
	21st to end	Day	21% 15% 32% 20% 9% 2	530
July	1st to 10th	Day	14% 7% 31% 28% 15% 4	525
	11th to 20th	Day	15% 7% 29% 32% 14% 3	524
	21st to end	Day	17% 10% 34% 22% 13% 4	576
August	1st to 10th	Day	15% 9% 26% 25% 18% 6%	526
	11th to 20th	Day	19% 7% 24% 26% 16% 7%	519
	21st to end	Day	20% 9% 28% 23% 13% 8%	583
September	1st to 10th	Day	23% 10% 21% 22% 17% 8%	530
	11th to 20th	Day	15% 10% 24% 22% 16% 13%	530
	21st to end	Day	25% 10% 29% 19% 12% 4	530
October	1st to 10th	Day	29% 11% 22% 20% 13% 6%	530
	11th to 20th	Day	30% 17% 23% 19% 9% 2	530
	21st to end	Day	36% 15% 24% 18% 6%	510
November	1st to 10th	Day	29% 22% 20% 18% 9% 2	425
	11th to 20th	Day	32% 23% 22% 17% 5% 1	425
	21st to end	Day	40% 20% 30% 9% 1	220
December	1st to 10th	Day	37% 25% 23% 11% 4	220
	11th to 20th	Day	42% 22% 26% 7% 3	220
	21st to end	Day	36% 25% 26% 10% 2	242
January	1st to 10th	Night	28% 26% 30% 13% 3	840
	11th to 20th	Night	32% 21% 25% 18% 3	840
	21st to end	Night	25% 27% 30% 16% 3	924
February	1st to 10th	Night	29% 23% 29% 17% 2	840
	11th to 20th	Night	30% 25% 30% 13% 1	823
	21st to end	Night	34% 21% 27% 15% 2	692
March	1st to 10th	Night	32% 22% 28% 16% 3	809
	11th to 20th	Night	31% 24% 24% 18% 3 1	800
	21st to end	Night	29% 21% 26% 17% 6%	880
April	1st to 10th	Night	32% 19% 26% 19% 4	800
	11th to 20th	Night	28% 19% 27% 19% 6% 1	791
	21st to end	Night	28% 18% 25% 22% 7%	797
May	1st to 10th	Night	34% 12% 22% 23% 8% 1	511
	11th to 20th	Night	21% 12% 27% 32% 7% 1	394
	21st to end	Night	20% 7% 21% 37% 15% 1	433
June	1st to 10th	Night	22% 8% 22% 33% 15% 1	400
	11th to 20th	Night	21% 6% 22% 35% 16%	400
	21st to end	Night	14% 7% 21% 42% 17% 1	400
July	1st to 10th	Night	16% 5% 15% 43% 20% 2	390
	11th to 20th	Night	18% 3 16% 40% 22% 2	388
	21st to end	Night	16% 5% 15% 43% 20% 1	438
August	1st to 10th	Night	17% 2 16% 38% 25% 2	523
	11th to 20th	Night	20% 4 12% 36% 25% 4	728
	21st to end	Night	20% 6% 15% 33% 26% 2	880
September	1st to 10th	Night	22% 7% 20% 29% 21% 3	800
	11th to 20th	Night	19% 5% 19% 28% 22% 7%	800
	21st to end	Night	24% 8% 22% 28% 17% 3	800
October	1st to 10th	Night	26% 12% 17% 24% 18% 3	800
	11th to 20th	Night	28% 11% 24% 28% 8% 1	800
	21st to end	Night	32% 16% 24% 23% 5%	880
November	1st to 10th	Night	23% 18% 26% 24% 8% 1	820
	11th to 20th	Night	31% 20% 22% 20% 6% 1	840
	21st to end	Night	27% 21% 25% 21% 4	840
December	1st to 10th	Night	32% 23% 26% 15% 4	840
	11th to 20th	Night	33% 21% 25% 18% 3	840
	21st to end	Night	34% 24% 22% 18% 2	924

Page generated at 2026-02-28 01:40:23. Version ac07

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