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 2024-11-04.

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%	105044
	Night	5% 9% 2 4 3 3 3 3 4 5% 60%	102668
Transparency	Day	24% 4 8% 18% 25% 21%	104792
	Night	26% 4 8% 19% 25% 18%	102510
Seeing	Day	15% 19% 34% 21% 9% 2	15143
	Night	12% 10% 25% 33% 18% 3	24513

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	7% 18% 4 4 3 3 4 2 5% 5% 45%	2539
	11th to 20th	Day	7% 16% 3 6% 4 5% 4 3 5% 7% 39%	2676
	21st to end	Day	8% 17% 5% 6% 3 4 4 3 4 8% 37%	3146
February	1st to 10th	Day	9% 13% 5% 5% 3 2 3 4 5% 5% 47%	1724
	11th to 20th	Day	6% 14% 4 5% 3 3 4 2 4 6% 48%	1850
	21st to end	Day	7% 15% 6% 8% 3 4 2 3 4 4 44%	1570
March	1st to 10th	Day	6% 18% 9% 12% 4 4 4 3 4 6% 30%	3138
	11th to 20th	Day	5% 14% 4 4 2 3 2 2 4 4 56%	3458
	21st to end	Day	6% 22% 7% 7% 4 4 3 3 4 5% 34%	4061
April	1st to 10th	Day	8% 13% 3 5% 3 3 3 2 5% 7% 47%	2280
	11th to 20th	Day	7% 14% 3 4 3 3 3 3 4 5% 50%	2249
	21st to end	Day	7% 10% 2 3 3 3 2 3 5% 7% 55%	2280
May	1st to 10th	Day	6% 7% 2 3 2 2 2 2 3 5% 68%	3924
	11th to 20th	Day	4 6% 1 2 2 2 2 2 3 5% 70%	4270
	21st to end	Day	5% 6% 1 3 2 2 2 2 4 5% 66%	4813
June	1st to 10th	Day	7% 5% 1 4 3 3 3 3 5% 6% 61%	2660
	11th to 20th	Day	3 3 1 2 2 2 2 2 3 5% 76%	2660
	21st to end	Day	3 2 1 2 2 2 2 2 3 4 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 90%	4420
	11th to 20th	Day	3 2 1 3 2 3 3 3 4 5% 74%	4420
	21st to end	Day	1 1 1 2 1 1 2 2 2 4 82%	4595
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%	1701
	11th to 20th	Day	7% 6% 2 3 4 3 3 4 4 5% 59%	1710
	21st to end	Day	6% 8% 3 4 2 3 3 2 5% 7% 56%	1677
December	1st to 10th	Day	10% 9% 3 5% 2 3 4 3 5% 7% 50%	1520
	11th to 20th	Day	13% 16% 4 7% 4 4 4 3 4 5% 35%	1928
	21st to end	Day	7% 10% 3 6% 3 3 4 3 7% 9% 45%	2794
January	1st to 10th	Night	6% 11% 4 7% 3 3 3 3 5% 7% 48%	4406
	11th to 20th	Night	8% 17% 3 6% 4 4 5% 5% 6% 6% 35%	4286
	21st to end	Night	6% 19% 4 6% 3 4 4 4 5% 6% 37%	4521
February	1st to 10th	Night	8% 13% 3 5% 3 3 2 3 5% 6% 48%	2453
	11th to 20th	Night	4 13% 4 6% 3 3 3 4 6% 8% 46%	2218
	21st to end	Night	6% 13% 4 9% 3 3 3 2 4 4 48%	1884
March	1st to 10th	Night	5% 20% 9% 10% 3 3 3 3 4 5% 35%	3736
	11th to 20th	Night	5% 14% 3 4 2 1 3 2 3 5% 57%	3508
	21st to end	Night	6% 22% 6% 7% 4 3 4 3 5% 5% 35%	3591
April	1st to 10th	Night	7% 11% 3 5% 4 4 3 4 5% 8% 48%	1900
	11th to 20th	Night	6% 12% 2 5% 2 3 3 2 4 7% 53%	1879
	21st to end	Night	4 10% 1 3 2 2 4 3 5% 6% 59%	1900
May	1st to 10th	Night	2 4 3 5% 2 2 2 2 4 5% 69%	3036
	11th to 20th	Night	2 4 1 3 2 2 2 2 4 5% 73%	2622
	21st to end	Night	2 5% 1 2 2 2 2 2 4 6% 72%	2762
June	1st to 10th	Night	5% 4 1 3 3 3 3 3 4 6% 66%	1520
	11th to 20th	Night	1 2 1 1 2 2 2 2 4 82%	1520
	21st to end	Night	3 2 1 2 2 2 1 1 2 4 80%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 92%	2540
	11th to 20th	Night	4 3 1 3 2 3 2 2 3 3 74%	2540
	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% 9% 2 2 3 2 3 2 5% 7% 57%	2450
	11th to 20th	Night	6% 6% 1 2 2 4 4 3 5% 8% 59%	2470
	21st to end	Night	6% 8% 2 4 3 2 3 3 4 6% 57%	2498
December	1st to 10th	Night	11% 10% 2 3 3 3 4 3 5% 6% 49%	2660
	11th to 20th	Night	13% 18% 3 5% 3 3 4 4 5% 7% 35%	3276
	21st to end	Night	6% 12% 5% 7% 4 5% 5% 4 5% 9% 38%	4862

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	39% 9% 9% 19% 19% 5%	2539
	11th to 20th	Day	46% 7% 9% 16% 14% 8%	2676
	21st to end	Day	45% 8% 9% 19% 13% 5%	3146
February	1st to 10th	Day	39% 4 10% 18% 19% 12%	1724
	11th to 20th	Day	37% 4 9% 20% 22% 8%	1860
	21st to end	Day	45% 4 7% 18% 21% 5%	1570
March	1st to 10th	Day	53% 7% 11% 13% 11% 5%	3138
	11th to 20th	Day	29% 7% 11% 29% 19% 5%	3458
	21st to end	Day	49% 6% 13% 21% 8% 2	4061
April	1st to 10th	Day	38% 6% 14% 20% 18% 5%	2280
	11th to 20th	Day	35% 6% 12% 24% 17% 6%	2252
	21st to end	Day	28% 5% 16% 28% 18% 4	2280
May	1st to 10th	Day	20% 4 11% 30% 21% 13%	3924
	11th to 20th	Day	17% 3 11% 28% 33% 8%	4273
	21st to end	Day	20% 4 10% 36% 27% 3	4814
June	1st to 10th	Day	24% 5% 11% 24% 28% 8%	2660
	11th to 20th	Day	13% 3 8% 26% 34% 16%	2660
	21st to end	Day	11% 3 6% 15% 34% 31%	2660
July	1st to 10th	Day	4 1 2 7% 16% 69%	4351
	11th to 20th	Day	11% 4 5% 10% 17% 53%	4345
	21st to end	Day	8% 2 5% 9% 30% 47%	4450
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	30% 5% 9% 20% 23% 13%	1701
	11th to 20th	Day	27% 4 11% 19% 28% 12%	1710
	21st to end	Day	29% 4 9% 19% 27% 13%	1677
December	1st to 10th	Day	33% 6% 9% 19% 21% 13%	1520
	11th to 20th	Day	52% 4 6% 14% 14% 9%	1928
	21st to end	Day	34% 8% 13% 21% 17% 7%	2794
January	1st to 10th	Night	34% 8% 12% 26% 16% 5%	4406
	11th to 20th	Night	46% 7% 8% 15% 16% 9%	4286
	21st to end	Night	45% 7% 11% 16% 14% 7%	4521
February	1st to 10th	Night	37% 4 8% 18% 19% 14%	2453
	11th to 20th	Night	34% 6% 9% 21% 21% 9%	2219
	21st to end	Night	39% 3 9% 22% 21% 6%	1884
March	1st to 10th	Night	49% 5% 11% 16% 14% 6%	3736
	11th to 20th	Night	31% 4 10% 28% 22% 5%	3508
	21st to end	Night	47% 7% 12% 19% 12% 3	3591
April	1st to 10th	Night	34% 8% 14% 21% 19% 5%	1900
	11th to 20th	Night	31% 6% 14% 23% 19% 7%	1879
	21st to end	Night	25% 6% 13% 35% 18% 4	1900
May	1st to 10th	Night	17% 4 12% 32% 25% 10%	3036
	11th to 20th	Night	13% 4 9% 27% 35% 12%	2622
	21st to end	Night	14% 3 12% 42% 25% 3	2762
June	1st to 10th	Night	20% 6% 11% 23% 30% 9%	1520
	11th to 20th	Night	8% 3 7% 28% 34% 19%	1520
	21st to end	Night	11% 2 4 16% 35% 33%	1520
July	1st to 10th	Night	3 1 2 6% 18% 69%	2500
	11th to 20th	Night	16% 2 4 9% 16% 53%	2492
	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% 5% 8% 21% 25% 15%	2450
	11th to 20th	Night	24% 5% 8% 21% 29% 12%	2470
	21st to end	Night	29% 4 6% 21% 25% 14%	2498
December	1st to 10th	Night	34% 5% 8% 18% 21% 14%	2660
	11th to 20th	Night	48% 6% 7% 13% 19% 8%	3276
	21st to end	Night	41% 7% 11% 16% 18% 7%	4862

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% 20% 23% 16% 4	180
	11th to 20th	Day	24% 19% 27% 19% 9% 2	264
	21st to end	Day	22% 18% 28% 21% 10% 1	407
February	1st to 10th	Day	29% 20% 26% 17% 7% 1	376
	11th to 20th	Day	24% 25% 28% 17% 6%	455
	21st to end	Day	24% 25% 33% 15% 3	382
March	1st to 10th	Day	32% 27% 26% 12% 3 1	460
	11th to 20th	Day	28% 23% 26% 16% 7% 1	460
	21st to end	Day	26% 29% 30% 13% 2	506
April	1st to 10th	Day	21% 26% 31% 15% 7%	460
	11th to 20th	Day	29% 22% 29% 15% 5%	452
	21st to end	Day	15% 24% 30% 22% 7% 2	460
May	1st to 10th	Day	18% 26% 32% 16% 7% 1	463
	11th to 20th	Day	18% 22% 28% 21% 10% 1	488
	21st to end	Day	18% 16% 29% 26% 9% 3	529
June	1st to 10th	Day	12% 19% 36% 21% 9% 3	490
	11th to 20th	Day	11% 21% 40% 19% 8% 2	490
	21st to end	Day	4 16% 43% 24% 10% 3	490
July	1st to 10th	Day	3 16% 46% 22% 10% 3	486
	11th to 20th	Day	2 10% 48% 26% 11% 3	484
	21st to end	Day	2 11% 45% 26% 12% 5%	531
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% 21% 25% 15% 4	279
	11th to 20th	Day	15% 14% 30% 26% 12% 4	270
	21st to end	Day	14% 19% 29% 25% 11% 1	255
December	1st to 10th	Day	22% 16% 27% 16% 13% 6%	180
	11th to 20th	Day	19% 28% 25% 14% 12% 1	180
	21st to end	Day	27% 19% 24% 20% 8% 2	198
January	1st to 10th	Night	21% 16% 25% 20% 14% 5%	760
	11th to 20th	Night	16% 13% 33% 26% 8% 3	760
	21st to end	Night	18% 16% 28% 23% 13% 2	836
February	1st to 10th	Night	21% 12% 28% 24% 13% 2	760
	11th to 20th	Night	17% 16% 26% 25% 13% 3	744
	21st to end	Night	22% 14% 26% 27% 9% 2	628
March	1st to 10th	Night	25% 14% 28% 22% 10% 2	760
	11th to 20th	Night	19% 14% 25% 23% 17% 2	760
	21st to end	Night	18% 16% 31% 25% 9% 1	836
April	1st to 10th	Night	16% 12% 29% 31% 11% 1	760
	11th to 20th	Night	14% 16% 28% 28% 12% 2	751
	21st to end	Night	11% 10% 31% 28% 17% 3	760
May	1st to 10th	Night	9% 14% 28% 31% 16% 3	681
	11th to 20th	Night	6% 9% 25% 38% 20% 2	441
	21st to end	Night	9% 6% 24% 32% 27% 2	411
June	1st to 10th	Night	7% 5% 24% 38% 24% 2	380
	11th to 20th	Night	3 5% 26% 43% 22% 1	380
	21st to end	Night	2 3 22% 46% 25% 2	380
July	1st to 10th	Night	1 1 16% 48% 32% 2	370
	11th to 20th	Night	3 2 15% 45% 32% 2	368
	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	13% 9% 21% 34% 18% 4	754
	11th to 20th	Night	11% 13% 26% 32% 14% 4	760
	21st to end	Night	13% 15% 28% 27% 14% 3	760
December	1st to 10th	Night	21% 11% 28% 26% 10% 4	760
	11th to 20th	Night	22% 14% 26% 25% 11% 2	760
	21st to end	Night	23% 17% 26% 26% 7% 1	836

Page generated at 2024-11-01 19:47:36. Version ac07

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