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 2024-12-02.

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 8% 5% 5% 4 4 5% 7% 29%	101681
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 30%	97974
Transparency	Day	52% 6% 11% 20% 10% 1	105189
	Night	52% 6% 11% 19% 10% 1	102555
Seeing	Day	28% 16% 26% 18% 9% 3	14891
	Night	26% 16% 23% 24% 10% 1	24079

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	14% 15% 12% 14% 6% 3 3 3 4 4 22%	2517
	11th to 20th	Day	15% 16% 9% 14% 6% 6% 4 3 4 3 19%	2520
	21st to end	Day	22% 16% 9% 10% 6% 4 3 3 4 5% 18%	3031
February	1st to 10th	Day	15% 15% 6% 13% 9% 5% 4 3 5% 4 21%	1710
	11th to 20th	Day	13% 12% 5% 13% 7% 5% 4 3 5% 7% 26%	1774
	21st to end	Day	18% 15% 4 10% 7% 4 3 3 5% 5% 26%	1570
March	1st to 10th	Day	22% 17% 5% 10% 5% 3 2 2 3 4 27%	3116
	11th to 20th	Day	11% 16% 7% 11% 5% 4 4 3 5% 6% 28%	3436
	21st to end	Day	20% 13% 4 10% 5% 4 3 3 3 5% 32%	4066
April	1st to 10th	Day	18% 15% 3 9% 5% 4 4 3 4 5% 29%	2280
	11th to 20th	Day	17% 12% 3 7% 5% 5% 4 4 5% 6% 33%	2254
	21st to end	Day	19% 12% 4 7% 5% 4 4 3 5% 5% 32%	2281
May	1st to 10th	Day	27% 10% 3 6% 4 3 4 3 5% 6% 30%	4284
	11th to 20th	Day	20% 9% 3 8% 6% 6% 6% 5% 6% 7% 26%	4398
	21st to end	Day	14% 7% 2 5% 4 5% 6% 4 6% 8% 37%	4837
June	1st to 10th	Day	17% 7% 3 7% 6% 5% 5% 5% 6% 9% 30%	2660
	11th to 20th	Day	18% 8% 3 5% 6% 5% 5% 5% 7% 8% 29%	2660
	21st to end	Day	18% 8% 3 6% 6% 4 5% 4 7% 9% 30%	2660
July	1st to 10th	Day	11% 7% 2 8% 6% 6% 5% 5% 8% 9% 34%	4440
	11th to 20th	Day	10% 7% 3 6% 5% 5% 6% 5% 8% 11% 33%	4440
	21st to end	Day	15% 8% 3 8% 6% 5% 5% 5% 7% 8% 31%	4814
August	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	4210
	11th to 20th	Day	15% 8% 3 7% 5% 5% 6% 6% 7% 9% 29%	3795
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 7% 8% 36%	4180
September	1st to 10th	Day	18% 7% 2 6% 4 5% 4 4 4 7% 37%	2280
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 3 5% 7% 43%	2242
	21st to end	Day	20% 8% 2 7% 4 5% 4 3 6% 6% 34%	2090
October	1st to 10th	Day	19% 11% 3 8% 5% 4 4 4 4 5% 32%	1908
	11th to 20th	Day	17% 12% 3 6% 4 5% 5% 3 6% 5% 35%	1900
	21st to end	Day	24% 14% 3 7% 4 5% 3 3 4 6% 27%	1966
November	1st to 10th	Day	14% 12% 3 8% 5% 4 5% 3 5% 5% 38%	1761
	11th to 20th	Day	16% 16% 4 9% 5% 4 3 3 4 5% 31%	1795
	21st to end	Day	20% 15% 5% 9% 5% 4 4 4 5% 5% 26%	1600
December	1st to 10th	Day	18% 17% 6% 14% 5% 4 3 3 5% 5% 20%	1528
	11th to 20th	Day	21% 14% 8% 11% 4 3 3 3 4 5% 24%	1906
	21st to end	Day	20% 20% 8% 11% 6% 4 4 3 4 5% 16%	2772
January	1st to 10th	Night	16% 14% 9% 11% 4 4 5% 3 4 6% 24%	4429
	11th to 20th	Night	13% 19% 8% 15% 7% 5% 3 3 4 4 20%	4440
	21st to end	Night	21% 17% 6% 11% 9% 5% 4 3 3 4 18%	4624
February	1st to 10th	Night	14% 15% 5% 11% 9% 6% 5% 3 5% 5% 23%	2470
	11th to 20th	Night	12% 13% 5% 13% 8% 6% 5% 4 6% 6% 22%	2292
	21st to end	Night	17% 12% 5% 12% 5% 4 4 3 5% 5% 27%	1884
March	1st to 10th	Night	21% 16% 5% 8% 5% 3 3 3 4 4 27%	3724
	11th to 20th	Night	12% 16% 8% 11% 5% 4 3 3 5% 6% 27%	3520
	21st to end	Night	14% 16% 4 9% 5% 3 5% 3 4 5% 32%	3565
April	1st to 10th	Night	17% 15% 4 8% 5% 4 4 4 4 6% 28%	1900
	11th to 20th	Night	18% 12% 3 7% 4 5% 4 2 5% 6% 35%	1875
	21st to end	Night	19% 10% 4 8% 4 4 3 3 6% 5% 34%	1897
May	1st to 10th	Night	27% 10% 3 6% 4 3 3 3 4 6% 31%	2685
	11th to 20th	Night	19% 10% 3 8% 5% 4 3 4 6% 7% 31%	2495
	21st to end	Night	16% 9% 3 7% 4 5% 4 3 7% 7% 36%	2738
June	1st to 10th	Night	17% 7% 2 6% 5% 5% 4 3 6% 7% 38%	1520
	11th to 20th	Night	16% 8% 2 7% 3 4 4 3 6% 8% 40%	1520
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 7% 9% 41%	1520
July	1st to 10th	Night	13% 7% 3 8% 5% 4 4 4 6% 8% 37%	2520
	11th to 20th	Night	15% 7% 2 6% 4 4 5% 4 7% 9% 37%	2520
	21st to end	Night	17% 7% 3 6% 4 4 5% 4 6% 6% 38%	2739
August	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 5% 6% 32%	2715
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 4 6% 38%	3002
	21st to end	Night	13% 7% 3 6% 5% 4 4 3 4 7% 44%	3476
September	1st to 10th	Night	17% 8% 2 5% 3 4 4 4 5% 6% 43%	1900
	11th to 20th	Night	15% 6% 2 5% 5% 3 4 2 4 6% 49%	1938
	21st to end	Night	19% 7% 3 6% 5% 4 3 2 5% 6% 38%	2090
October	1st to 10th	Night	21% 9% 3 7% 4 4 3 3 4 7% 35%	2270
	11th to 20th	Night	20% 10% 2 7% 4 4 3 3 4 5% 38%	2280
	21st to end	Night	22% 14% 3 7% 4 4 3 3 4 6% 29%	2631
November	1st to 10th	Night	14% 11% 4 7% 4 4 3 3 5% 6% 39%	2537
	11th to 20th	Night	20% 12% 4 7% 5% 3 4 3 5% 6% 32%	2600
	21st to end	Night	15% 14% 5% 8% 6% 5% 4 4 6% 7% 28%	2800
December	1st to 10th	Night	19% 17% 6% 10% 6% 4 4 4 5% 5% 19%	2686
	11th to 20th	Night	20% 16% 6% 11% 5% 4 3 3 4 4 23%	3288
	21st to end	Night	23% 16% 8% 11% 5% 4 4 3 4 5% 18%	4884

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% 7% 8% 16% 5% 1	2518
	11th to 20th	Day	68% 6% 7% 13% 5% 2	2520
	21st to end	Day	68% 4 8% 14% 5% 1	3031
February	1st to 10th	Day	65% 6% 8% 15% 7%	1710
	11th to 20th	Day	57% 6% 7% 19% 11% 1	1783
	21st to end	Day	60% 5% 9% 18% 8% 1	1570
March	1st to 10th	Day	63% 3 9% 15% 9% 1	3119
	11th to 20th	Day	53% 8% 10% 19% 8% 1	3436
	21st to end	Day	55% 5% 5% 14% 17% 3	4066
April	1st to 10th	Day	56% 5% 7% 21% 9% 3	2280
	11th to 20th	Day	52% 5% 10% 19% 13% 2	2254
	21st to end	Day	53% 5% 8% 19% 12% 3	2281
May	1st to 10th	Day	55% 4 10% 18% 11% 2	4298
	11th to 20th	Day	57% 5% 11% 19% 7% 1	4402
	21st to end	Day	41% 7% 13% 25% 13% 1	4837
June	1st to 10th	Day	49% 6% 12% 20% 12%	2660
	11th to 20th	Day	49% 6% 13% 22% 9% 1	2660
	21st to end	Day	48% 7% 11% 24% 9%	2660
July	1st to 10th	Day	43% 8% 15% 23% 10% 1	4370
	11th to 20th	Day	40% 8% 18% 24% 10%	4365
	21st to end	Day	48% 7% 14% 20% 11% 1	4661
August	1st to 10th	Day	54% 5% 13% 19% 9%	4196
	11th to 20th	Day	46% 9% 15% 24% 5%	3833
	21st to end	Day	42% 7% 12% 30% 9% 1	4180
September	1st to 10th	Day	45% 6% 10% 25% 13% 1	2280
	11th to 20th	Day	40% 5% 10% 24% 21% 1	2242
	21st to end	Day	49% 5% 10% 20% 14% 2	2090
October	1st to 10th	Day	48% 7% 9% 21% 13% 1	3168
	11th to 20th	Day	44% 4 8% 23% 15% 6%	3140
	21st to end	Day	41% 5% 15% 26% 11% 2	3217
November	1st to 10th	Day	47% 6% 12% 20% 15% 2	1761
	11th to 20th	Day	54% 5% 10% 17% 11% 2	1795
	21st to end	Day	59% 4 13% 17% 5% 1	1600
December	1st to 10th	Day	66% 4 11% 12% 6% 1	1528
	11th to 20th	Day	63% 4 12% 15% 5% 1	1906
	21st to end	Day	72% 4 7% 11% 6%	2772
January	1st to 10th	Night	59% 6% 11% 15% 7% 1	4429
	11th to 20th	Night	63% 9% 8% 13% 6% 1	4440
	21st to end	Night	70% 4 7% 13% 5% 1	4624
February	1st to 10th	Night	61% 6% 10% 14% 8% 1	2470
	11th to 20th	Night	57% 9% 9% 15% 8% 1	2294
	21st to end	Night	57% 5% 9% 18% 9% 2	1884
March	1st to 10th	Night	60% 4 9% 16% 9% 1	3734
	11th to 20th	Night	54% 8% 12% 19% 7% 1	3521
	21st to end	Night	52% 7% 5% 16% 17% 2	3565
April	1st to 10th	Night	57% 4 8% 18% 11% 2	1900
	11th to 20th	Night	51% 4 10% 19% 15%	1875
	21st to end	Night	49% 5% 9% 20% 13% 3	1897
May	1st to 10th	Night	55% 4 9% 20% 9% 2	2691
	11th to 20th	Night	52% 7% 13% 19% 7% 1	2496
	21st to end	Night	45% 6% 13% 21% 13% 1	2739
June	1st to 10th	Night	44% 5% 12% 24% 14%	1520
	11th to 20th	Night	41% 6% 17% 25% 11% 1	1520
	21st to end	Night	37% 8% 16% 26% 13%	1520
July	1st to 10th	Night	44% 6% 16% 18% 15% 1	2480
	11th to 20th	Night	41% 7% 15% 25% 12%	2472
	21st to end	Night	43% 7% 13% 23% 13% 1	2651
August	1st to 10th	Night	52% 6% 14% 20% 6% 1	2705
	11th to 20th	Night	45% 6% 15% 24% 8%	3030
	21st to end	Night	38% 6% 12% 32% 11%	3476
September	1st to 10th	Night	42% 5% 12% 26% 15% 1	1900
	11th to 20th	Night	37% 5% 10% 25% 22% 1	1938
	21st to end	Night	48% 4 10% 21% 16% 1	2090
October	1st to 10th	Night	51% 7% 10% 21% 12% 1	3790
	11th to 20th	Night	42% 6% 13% 18% 16% 6%	3779
	21st to end	Night	42% 6% 15% 26% 10% 1	4330
November	1st to 10th	Night	45% 6% 9% 21% 17% 2	2537
	11th to 20th	Night	51% 6% 11% 18% 12% 2	2600
	21st to end	Night	53% 7% 14% 19% 7% 1	2800
December	1st to 10th	Night	64% 6% 10% 15% 4	2686
	11th to 20th	Night	62% 7% 10% 14% 7%	3288
	21st to end	Night	68% 6% 9% 12% 5%	4884

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	36% 19% 31% 12% 1 1	180
	11th to 20th	Day	47% 19% 22% 8% 3	180
	21st to end	Day	32% 26% 28% 11% 3	272
February	1st to 10th	Day	35% 30% 29% 6% 1	270
	11th to 20th	Day	37% 29% 25% 8% 1	382
	21st to end	Day	39% 20% 28% 11% 2	382
March	1st to 10th	Day	34% 22% 26% 15% 3	460
	11th to 20th	Day	36% 25% 22% 12% 3 1	460
	21st to end	Day	36% 25% 23% 9% 5% 2	506
April	1st to 10th	Day	39% 20% 25% 11% 4 1	460
	11th to 20th	Day	33% 22% 24% 12% 6% 3	452
	21st to end	Day	33% 18% 30% 11% 6% 2	460
May	1st to 10th	Day	39% 15% 24% 13% 6% 3	463
	11th to 20th	Day	25% 16% 29% 19% 6% 3	487
	21st to end	Day	22% 10% 29% 22% 12% 4	529
June	1st to 10th	Day	22% 13% 32% 20% 10% 2	490
	11th to 20th	Day	23% 11% 27% 24% 12% 2	490
	21st to end	Day	21% 15% 31% 20% 10% 2	490
July	1st to 10th	Day	15% 7% 30% 27% 16% 4	485
	11th to 20th	Day	14% 7% 29% 33% 15% 3	484
	21st to end	Day	17% 10% 34% 22% 13% 4	532
August	1st to 10th	Day	16% 10% 26% 25% 19% 6%	486
	11th to 20th	Day	19% 8% 25% 25% 16% 8%	479
	21st to end	Day	20% 8% 27% 22% 13% 9%	539
September	1st to 10th	Day	24% 10% 20% 21% 17% 8%	490
	11th to 20th	Day	16% 10% 24% 22% 14% 13%	490
	21st to end	Day	25% 10% 29% 19% 12% 4	490
October	1st to 10th	Day	30% 11% 22% 19% 13% 5%	490
	11th to 20th	Day	29% 16% 24% 20% 9% 2	490
	21st to end	Day	36% 15% 24% 18% 7%	473
November	1st to 10th	Day	28% 21% 20% 19% 10% 3	395
	11th to 20th	Day	31% 22% 23% 17% 5% 1	395
	21st to end	Day	37% 20% 32% 10% 2	200
December	1st to 10th	Day	36% 24% 25% 10% 5%	182
	11th to 20th	Day	41% 21% 29% 7% 3	180
	21st to end	Day	35% 27% 25% 11% 2 1	198
January	1st to 10th	Night	28% 24% 31% 13% 3	760
	11th to 20th	Night	31% 20% 25% 19% 3 1	760
	21st to end	Night	25% 25% 31% 17% 3	836
February	1st to 10th	Night	29% 22% 30% 18% 2	760
	11th to 20th	Night	29% 26% 30% 13% 2	743
	21st to end	Night	35% 21% 25% 16% 3	628
March	1st to 10th	Night	31% 21% 29% 16% 3	760
	11th to 20th	Night	31% 24% 24% 18% 3 1	760
	21st to end	Night	29% 22% 25% 17% 6%	836
April	1st to 10th	Night	31% 19% 27% 19% 4	760
	11th to 20th	Night	28% 18% 28% 19% 7% 1	751
	21st to end	Night	28% 18% 25% 22% 7%	757
May	1st to 10th	Night	33% 12% 22% 24% 8% 1	486
	11th to 20th	Night	20% 11% 28% 32% 7% 1	374
	21st to end	Night	19% 7% 20% 38% 16% 1	411
June	1st to 10th	Night	21% 8% 22% 33% 16% 1	380
	11th to 20th	Night	20% 6% 21% 36% 17%	380
	21st to end	Night	14% 6% 21% 41% 17% 1	380
July	1st to 10th	Night	16% 4 15% 42% 21% 2	370
	11th to 20th	Night	17% 2 17% 40% 23% 2	368
	21st to end	Night	17% 5% 15% 42% 21% 1	416
August	1st to 10th	Night	17% 2 16% 38% 24% 2	496
	11th to 20th	Night	21% 3 11% 36% 24% 5%	691
	21st to end	Night	20% 5% 14% 33% 27% 2	836
September	1st to 10th	Night	22% 6% 20% 28% 21% 3	760
	11th to 20th	Night	20% 5% 19% 27% 21% 7%	760
	21st to end	Night	24% 8% 21% 27% 17% 3	760
October	1st to 10th	Night	27% 12% 17% 24% 17% 3	760
	11th to 20th	Night	28% 11% 24% 28% 9% 1	760
	21st to end	Night	32% 16% 24% 22% 5%	836
November	1st to 10th	Night	22% 18% 26% 25% 9% 1	780
	11th to 20th	Night	30% 19% 23% 21% 6% 1	800
	21st to end	Night	26% 21% 26% 21% 5% 1	800
December	1st to 10th	Night	32% 23% 26% 14% 5%	768
	11th to 20th	Night	31% 22% 26% 18% 3	760
	21st to end	Night	33% 24% 22% 18% 2	836

Page generated at 2024-11-29 10:43:06. Version ac07

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