Bear Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bear Valley clear sky chart from 2005-11-06 to 2025-07-21.

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	5% 8% 2 4 2 2 3 2 4 5% 63%	123932
	Night	5% 9% 2 4 2 3 3 3 4 5% 60%	124028
Transparency	Day	24% 4 8% 18% 26% 20%	123681
	Night	26% 4 8% 19% 25% 18%	123867
Seeing	Day	15% 19% 34% 21% 9% 2	16034
	Night	12% 10% 25% 32% 17% 3	25404

By Month

Percentage Cloud Cover SW (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	6% 13% 3 4 3 3 3 3 5% 6% 52%	3639
	11th to 20th	Day	5% 11% 2 4 3 4 3 2 3 5% 57%	3846
	21st to end	Day	7% 14% 4 4 3 3 4 3 4 6% 47%	4510
February	1st to 10th	Day	10% 13% 5% 5% 2 2 3 4 5% 5% 46%	1815
	11th to 20th	Day	6% 14% 5% 5% 3 3 4 3 4 6% 48%	1950
	21st to end	Day	7% 14% 6% 8% 3 3 3 3 4 4 45%	1650
March	1st to 10th	Day	5% 17% 9% 10% 3 3 4 3 5% 6% 35%	4518
	11th to 20th	Day	5% 16% 5% 5% 2 3 3 3 4 5% 49%	4955
	21st to end	Day	7% 23% 6% 6% 4 3 2 3 4 5% 38%	5826
April	1st to 10th	Day	8% 13% 3 5% 3 3 3 2 5% 7% 47%	2400
	11th to 20th	Day	7% 14% 3 4 3 3 3 3 4 5% 51%	2369
	21st to end	Day	7% 10% 2 3 3 3 3 3 5% 7% 54%	2400
May	1st to 10th	Day	5% 7% 2 3 2 2 2 2 3 5% 69%	5616
	11th to 20th	Day	3 7% 2 3 3 2 2 2 3 5% 68%	6118
	21st to end	Day	4 4 1 3 2 2 2 2 3 5% 71%	6902
June	1st to 10th	Day	6% 5% 1 4 3 3 3 3 5% 6% 61%	2800
	11th to 20th	Day	3 3 1 2 2 2 2 2 3 5% 76%	2800
	21st to end	Day	3 2 1 2 2 2 2 2 3 4 77%	2800
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 90%	4560
	11th to 20th	Day	3 2 1 3 2 3 3 3 4 4 74%	4560
	21st to end	Day	1 1 1 2 1 1 2 2 2 4 82%	4596
August	1st to 10th	Day	2 2 1 3 2 2 2 2 3 4 78%	4013
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	3724
	21st to end	Day	2 2 2 1 1 1 1 2 2 85%	4180
September	1st to 10th	Day	2 1 1 1 2 2 2 3 4 82%	2280
	11th to 20th	Day	4 2 1 3 2 2 2 2 4 5% 72%	2252
	21st to end	Day	4 4 3 2 2 2 1 3 4 75%	2090
October	1st to 10th	Day	4 4 1 3 2 2 2 2 5% 6% 70%	3221
	11th to 20th	Day	6% 2 1 2 1 2 2 2 3 3 76%	3161
	21st to end	Day	3 5% 1 3 3 3 3 3 4 6% 65%	3400
November	1st to 10th	Day	8% 8% 2 3 3 4 3 3 4 7% 55%	1764
	11th to 20th	Day	7% 6% 2 3 4 4 4 4 4 5% 59%	1800
	21st to end	Day	6% 9% 3 4 2 3 3 2 5% 7% 55%	1765
December	1st to 10th	Day	6% 5% 1 3 2 2 4 4 6% 8% 59%	2620
	11th to 20th	Day	13% 15% 4 5% 4 3 4 3 5% 6% 37%	3028
	21st to end	Day	11% 13% 3 5% 3 3 4 4 6% 9% 39%	4004
January	1st to 10th	Night	4 9% 3 5% 3 3 3 3 6% 8% 53%	6306
	11th to 20th	Night	5% 12% 2 4 3 3 4 3 4 5% 53%	6121
	21st to end	Night	4 14% 3 5% 3 4 4 3 5% 5% 50%	6468
February	1st to 10th	Night	9% 13% 3 5% 3 3 3 3 5% 6% 48%	2582
	11th to 20th	Night	4 13% 4 6% 4 3 3 3 6% 8% 46%	2338
	21st to end	Night	6% 13% 3 8% 3 3 3 2 4 5% 49%	1980
March	1st to 10th	Night	5% 17% 8% 10% 3 3 3 3 4 6% 38%	5376
	11th to 20th	Night	5% 17% 5% 7% 3 2 3 2 3 5% 48%	5031
	21st to end	Night	7% 21% 6% 6% 3 3 4 3 4 6% 37%	5148
April	1st to 10th	Night	7% 11% 3 5% 4 4 3 3 5% 7% 49%	2000
	11th to 20th	Night	5% 11% 2 5% 2 3 4 3 4 7% 53%	1979
	21st to end	Night	4 10% 2 3 2 2 3 3 5% 6% 59%	2000
May	1st to 10th	Night	2 3 2 4 2 2 2 2 4 5% 72%	4360
	11th to 20th	Night	2 6% 1 3 2 2 2 2 3 5% 73%	3764
	21st to end	Night	2 4 1 2 2 2 2 2 3 4 77%	3972
June	1st to 10th	Night	5% 4 1 3 3 3 3 3 4 6% 66%	1600
	11th to 20th	Night	1 2 1 1 2 2 2 2 4 82%	1600
	21st to end	Night	3 2 1 2 2 2 1 1 2 4 81%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	2620
	11th to 20th	Night	4 3 1 3 2 2 2 1 3 3 75%	2620
	21st to end	Night	2 1 1 2 1 2 2 1 2 3 82%	2947
August	1st to 10th	Night	2 2 1 3 2 2 2 2 4 4 76%	2926
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 87%	3126
	21st to end	Night	1 1 2 2 2 1 1 1 2 87%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 1 1 3 87%	1900
	11th to 20th	Night	2 2 1 2 2 2 2 1 3 5% 78%	1926
	21st to end	Night	2 3 1 2 2 2 1 2 3 5% 77%	2090
October	1st to 10th	Night	3 3 1 2 2 1 2 1 3 4 78%	3755
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	3777
	21st to end	Night	5% 5% 1 2 2 2 3 3 4 6% 67%	4165
November	1st to 10th	Night	7% 8% 2 2 2 2 3 3 5% 7% 58%	2535
	11th to 20th	Night	6% 7% 1 2 2 3 4 3 5% 8% 58%	2600
	21st to end	Night	7% 8% 3 4 3 2 3 3 4 6% 57%	2630
December	1st to 10th	Night	7% 6% 2 3 3 3 3 3 4 6% 62%	4560
	11th to 20th	Night	10% 16% 3 5% 3 4 3 4 7% 10% 34%	5176
	21st to end	Night	9% 13% 4 7% 4 5% 5% 4 5% 8% 35%	6952

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	32% 7% 13% 19% 20% 9%	3639
	11th to 20th	Day	32% 5% 7% 13% 26% 18%	3846
	21st to end	Day	37% 7% 7% 15% 18% 17%	4510
February	1st to 10th	Day	40% 4 9% 17% 18% 13%	1815
	11th to 20th	Day	38% 4 9% 20% 22% 8%	1960
	21st to end	Day	43% 4 7% 18% 20% 7%	1650
March	1st to 10th	Day	49% 6% 8% 13% 18% 6%	4518
	11th to 20th	Day	35% 7% 12% 27% 15% 4	4955
	21st to end	Day	47% 6% 12% 22% 10% 3	5826
April	1st to 10th	Day	37% 6% 14% 20% 19% 5%	2400
	11th to 20th	Day	35% 5% 12% 24% 17% 6%	2372
	21st to end	Day	29% 6% 16% 28% 19% 3	2400
May	1st to 10th	Day	19% 4 9% 31% 26% 11%	5616
	11th to 20th	Day	19% 4 11% 29% 31% 7%	6121
	21st to end	Day	15% 4 8% 30% 38% 6%	6904
June	1st to 10th	Day	23% 6% 11% 25% 28% 8%	2800
	11th to 20th	Day	13% 3 8% 24% 34% 18%	2800
	21st to end	Day	11% 3 5% 14% 36% 31%	2800
July	1st to 10th	Day	4 1 2 7% 17% 69%	4491
	11th to 20th	Day	11% 4 5% 9% 17% 54%	4485
	21st to end	Day	8% 2 5% 9% 30% 47%	4451
August	1st to 10th	Day	11% 2 4 9% 29% 45%	3998
	11th to 20th	Day	6% 1 3 7% 32% 51%	3760
	21st to end	Day	8% 2 3 9% 42% 35%	4179
September	1st to 10th	Day	8% 2 4 12% 36% 38%	2280
	11th to 20th	Day	15% 3 7% 21% 35% 18%	2252
	21st to end	Day	16% 2 5% 20% 37% 21%	2090
October	1st to 10th	Day	15% 3 4 10% 38% 29%	3221
	11th to 20th	Day	15% 2 4 19% 41% 18%	3161
	21st to end	Day	20% 4 6% 23% 35% 13%	3400
November	1st to 10th	Day	29% 5% 9% 20% 23% 13%	1764
	11th to 20th	Day	28% 4 11% 19% 27% 11%	1800
	21st to end	Day	30% 4 9% 18% 25% 14%	1765
December	1st to 10th	Day	22% 5% 8% 20% 27% 18%	2620
	11th to 20th	Day	48% 5% 8% 13% 16% 10%	3028
	21st to end	Day	41% 7% 13% 17% 16% 6%	4004
January	1st to 10th	Night	27% 7% 15% 24% 20% 7%	6306
	11th to 20th	Night	33% 5% 6% 13% 26% 18%	6121
	21st to end	Night	35% 6% 8% 13% 20% 18%	6468
February	1st to 10th	Night	38% 4 7% 17% 19% 15%	2582
	11th to 20th	Night	35% 6% 9% 20% 20% 9%	2339
	21st to end	Night	38% 3 9% 22% 20% 8%	1980
March	1st to 10th	Night	46% 5% 8% 15% 17% 9%	5376
	11th to 20th	Night	39% 5% 9% 27% 16% 4	5031
	21st to end	Night	47% 7% 14% 20% 11% 2	5148
April	1st to 10th	Night	34% 7% 13% 21% 20% 5%	2000
	11th to 20th	Night	30% 7% 13% 23% 19% 7%	1979
	21st to end	Night	26% 6% 12% 34% 18% 4	2000
May	1st to 10th	Night	16% 4 10% 35% 28% 8%	4357
	11th to 20th	Night	15% 3 10% 32% 31% 9%	3764
	21st to end	Night	12% 3 8% 31% 38% 7%	3972
June	1st to 10th	Night	20% 6% 11% 25% 30% 9%	1600
	11th to 20th	Night	8% 3 7% 27% 34% 21%	1600
	21st to end	Night	10% 2 4 16% 36% 33%	1600
July	1st to 10th	Night	3 1 2 6% 19% 69%	2580
	11th to 20th	Night	16% 2 4 9% 16% 54%	2572
	21st to end	Night	10% 2 3 10% 28% 48%	2855
August	1st to 10th	Night	12% 2 4 10% 32% 40%	2917
	11th to 20th	Night	6% 2 2 8% 30% 52%	3156
	21st to end	Night	9% 1 2 12% 41% 36%	3498
September	1st to 10th	Night	6% 1 4 10% 39% 40%	1900
	11th to 20th	Night	11% 4 5% 23% 37% 21%	1926
	21st to end	Night	12% 2 6% 22% 35% 22%	2090
October	1st to 10th	Night	13% 3 3 11% 39% 31%	3755
	11th to 20th	Night	11% 3 4 19% 44% 19%	3777
	21st to end	Night	19% 4 6% 20% 37% 15%	4165
November	1st to 10th	Night	26% 4 8% 22% 25% 16%	2535
	11th to 20th	Night	25% 5% 8% 22% 29% 12%	2600
	21st to end	Night	30% 4 6% 20% 24% 15%	2630
December	1st to 10th	Night	24% 4 7% 20% 22% 23%	4560
	11th to 20th	Night	43% 6% 8% 14% 22% 7%	5176
	21st to end	Night	45% 7% 10% 16% 16% 6%	6952

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% 18% 24% 16% 5%	200
	11th to 20th	Day	25% 19% 28% 18% 9% 2	289
	21st to end	Day	22% 19% 27% 20% 10% 2	440
February	1st to 10th	Day	32% 19% 25% 16% 6% 1	407
	11th to 20th	Day	25% 25% 28% 16% 5%	495
	21st to end	Day	22% 24% 33% 17% 4	414
March	1st to 10th	Day	30% 27% 26% 12% 3 1	500
	11th to 20th	Day	29% 22% 26% 15% 6% 1	500
	21st to end	Day	27% 28% 29% 13% 3	550
April	1st to 10th	Day	22% 24% 31% 16% 6% 1	500
	11th to 20th	Day	27% 22% 29% 15% 6% 1	492
	21st to end	Day	15% 23% 31% 22% 7% 2	500
May	1st to 10th	Day	18% 26% 32% 16% 7% 1	503
	11th to 20th	Day	19% 22% 28% 20% 9% 2	528
	21st to end	Day	16% 17% 31% 25% 9% 3	573
June	1st to 10th	Day	11% 18% 36% 22% 10% 3	530
	11th to 20th	Day	11% 21% 40% 19% 8% 2	530
	21st to end	Day	5% 16% 43% 23% 10% 3	530
July	1st to 10th	Day	3 18% 45% 21% 10% 3	526
	11th to 20th	Day	2 10% 49% 25% 12% 3	524
	21st to end	Day	2 11% 45% 26% 12% 5%	532
August	1st to 10th	Day	3 18% 44% 22% 11% 3	487
	11th to 20th	Day	4 15% 43% 23% 11% 4	477
	21st to end	Day	5% 10% 47% 24% 12% 2	539
September	1st to 10th	Day	3 13% 45% 27% 11% 1	490
	11th to 20th	Day	10% 20% 36% 28% 5% 2	490
	21st to end	Day	9% 14% 40% 30% 6% 1	490
October	1st to 10th	Day	8% 20% 32% 30% 8% 2	490
	11th to 20th	Day	11% 15% 35% 27% 11% 2	490
	21st to end	Day	13% 18% 30% 26% 10% 3	515
November	1st to 10th	Day	19% 16% 23% 24% 14% 4	300
	11th to 20th	Day	16% 14% 31% 24% 11% 4	300
	21st to end	Day	18% 18% 27% 24% 11% 1	283
December	1st to 10th	Day	20% 15% 26% 16% 17% 7%	200
	11th to 20th	Day	21% 27% 24% 16% 12% 2	200
	21st to end	Day	29% 19% 25% 19% 7% 2	220
January	1st to 10th	Night	21% 16% 25% 20% 13% 5%	800
	11th to 20th	Night	17% 13% 34% 26% 8% 3	800
	21st to end	Night	18% 16% 28% 24% 12% 2	880
February	1st to 10th	Night	23% 12% 29% 23% 12% 2	800
	11th to 20th	Night	17% 15% 27% 25% 12% 3	784
	21st to end	Night	21% 14% 28% 26% 9% 2	660
March	1st to 10th	Night	24% 14% 29% 22% 10% 2	800
	11th to 20th	Night	20% 14% 25% 22% 16% 2	800
	21st to end	Night	19% 15% 30% 26% 9% 1	880
April	1st to 10th	Night	16% 12% 29% 32% 10% 1	800
	11th to 20th	Night	13% 16% 30% 28% 11% 2	791
	21st to end	Night	11% 10% 31% 29% 16% 3	800
May	1st to 10th	Night	10% 14% 28% 30% 16% 3	717
	11th to 20th	Night	7% 9% 26% 38% 19% 2	464
	21st to end	Night	8% 6% 25% 33% 26% 2	433
June	1st to 10th	Night	7% 5% 24% 39% 24% 2	400
	11th to 20th	Night	3 5% 26% 45% 21% 1	400
	21st to end	Night	2 3 22% 47% 24% 2	400
July	1st to 10th	Night	1 1 17% 49% 30% 2	390
	11th to 20th	Night	3 2 15% 46% 32% 2	388
	21st to end	Night	3 1 14% 37% 39% 5%	527
August	1st to 10th	Night	3 1 16% 49% 29% 2	606
	11th to 20th	Night	1 1 20% 49% 25% 4	752
	21st to end	Night	2 3 15% 50% 27% 3	836
September	1st to 10th	Night	2 3 19% 47% 26% 3	760
	11th to 20th	Night	3 4 22% 39% 26% 5%	760
	21st to end	Night	4 6% 25% 36% 24% 5%	760
October	1st to 10th	Night	7% 8% 23% 39% 20% 3	760
	11th to 20th	Night	8% 9% 22% 38% 19% 4	760
	21st to end	Night	10% 9% 24% 29% 21% 7%	836
November	1st to 10th	Night	14% 9% 21% 34% 18% 4	780
	11th to 20th	Night	12% 13% 27% 31% 13% 4	800
	21st to end	Night	14% 15% 29% 26% 14% 2	800
December	1st to 10th	Night	20% 11% 29% 27% 10% 4	800
	11th to 20th	Night	22% 14% 27% 25% 11% 2	800
	21st to end	Night	24% 16% 28% 25% 6% 1	880

Page generated at 2025-07-17 22:10:05. Version ac07

Copyright © 2025 Attilla Danko.