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 2024-04-03.

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	6% 8% 3 3 3 2 3 3 4 6% 59%	78937
	Night	6% 9% 3 4 3 2 3 4 4 6% 57%	81217
Transparency	Day	28% 4 9% 19% 24% 16%	78648
	Night	28% 5% 9% 19% 24% 15%	81028
Seeing	Day	15% 19% 34% 21% 8% 2	14289
	Night	12% 10% 25% 32% 18% 3	23818

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% 5% 4 4 2 3 3 4 5% 45%	2539
	11th to 20th	Day	7% 16% 3 5% 5% 4 5% 4 4 7% 39%	2676
	21st to end	Day	8% 17% 5% 5% 4 3 4 4 4 7% 38%	3146
February	1st to 10th	Day	9% 12% 5% 4 3 2 3 4 5% 6% 47%	1724
	11th to 20th	Day	6% 12% 5% 5% 4 2 4 3 4 6% 49%	1850
	21st to end	Day	8% 13% 7% 7% 4 3 3 3 4 4 44%	1570
March	1st to 10th	Day	8% 16% 7% 8% 4 3 4 4 4 7% 34%	1900
	11th to 20th	Day	8% 18% 4 5% 3 2 3 4 5% 6% 40%	2070
	21st to end	Day	8% 17% 6% 5% 4 3 4 4 4 6% 40%	2440
April	1st to 10th	Day	8% 12% 4 4 3 3 4 3 5% 7% 47%	2185
	11th to 20th	Day	9% 12% 4 3 4 2 4 4 4 5% 50%	2129
	21st to end	Day	8% 9% 2 3 3 2 3 4 4 7% 55%	2160
May	1st to 10th	Day	7% 8% 3 3 3 2 2 3 4 7% 57%	2232
	11th to 20th	Day	7% 9% 2 4 4 2 3 3 4 7% 56%	2409
	21st to end	Day	9% 9% 2 4 4 2 4 4 5% 6% 50%	2723
June	1st to 10th	Day	7% 5% 1 3 3 2 4 3 5% 6% 60%	2520
	11th to 20th	Day	3 3 1 2 2 1 2 3 3 5% 75%	2520
	21st to end	Day	3 2 1 2 2 2 3 3 3 4 76%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 3 83%	2520
	11th to 20th	Day	1 2 1 2 1 1 3 3 3 5% 78%	2520
	21st to end	Day	2 2 1 3 3 1 3 3 3 5% 75%	2634
August	1st to 10th	Day	2 2 1 2 2 2 2 3 4 4 77%	2289
	11th to 20th	Day	2 1 1 2 2 2 3 2 3 4 79%	2122
	21st to end	Day	1 1 2 2 1 2 1 2 3 85%	2376
September	1st to 10th	Day	2 1 1 1 2 2 2 3 4 82%	2160
	11th to 20th	Day	4 2 1 2 2 1 3 2 4 5% 72%	2134
	21st to end	Day	4 4 3 3 1 2 2 3 4 74%	1980
October	1st to 10th	Day	6% 5% 1 3 2 2 3 3 4 5% 66%	1828
	11th to 20th	Day	6% 3 1 2 2 2 3 3 3 5% 70%	1800
	21st to end	Day	6% 5% 1 3 3 2 3 3 3 6% 67%	1958
November	1st to 10th	Day	8% 8% 2 3 3 2 4 4 4 7% 55%	1674
	11th to 20th	Day	7% 6% 2 3 4 2 4 4 4 5% 59%	1710
	21st to end	Day	6% 8% 3 3 3 2 4 3 4 8% 56%	1677
December	1st to 10th	Day	11% 8% 3 4 2 2 4 4 5% 7% 50%	1520
	11th to 20th	Day	14% 15% 4 7% 5% 3 4 4 4 5% 35%	1928
	21st to end	Day	7% 10% 4 5% 4 2 4 5% 6% 10% 45%	2794
January	1st to 10th	Night	6% 11% 4 6% 4 2 3 3 5% 7% 48%	4406
	11th to 20th	Night	8% 17% 3 5% 4 3 5% 6% 6% 6% 36%	4286
	21st to end	Night	6% 19% 4 5% 4 3 5% 5% 5% 7% 38%	4521
February	1st to 10th	Night	9% 12% 3 5% 3 2 3 3 5% 7% 49%	2453
	11th to 20th	Night	4 12% 5% 5% 4 2 3 4 6% 8% 46%	2218
	21st to end	Night	7% 12% 4 8% 3 3 3 3 4 5% 48%	1884
March	1st to 10th	Night	7% 17% 7% 8% 3 2 3 4 3 5% 41%	2280
	11th to 20th	Night	7% 13% 5% 4 3 2 3 4 5% 7% 46%	2108
	21st to end	Night	7% 16% 5% 5% 4 2 3 4 4 6% 44%	2157
April	1st to 10th	Night	7% 10% 4 4 4 3 3 4 5% 8% 47%	1820
	11th to 20th	Night	7% 10% 3 4 3 2 3 3 4 7% 53%	1779
	21st to end	Night	5% 9% 2 3 3 2 3 4 5% 7% 59%	1800
May	1st to 10th	Night	4 5% 3 4 3 2 4 3 5% 6% 61%	1726
	11th to 20th	Night	3 7% 3 3 3 2 3 3 5% 8% 62%	1480
	21st to end	Night	4 8% 2 3 3 2 2 3 5% 8% 60%	1552
June	1st to 10th	Night	5% 4 1 3 2 2 3 4 3 5% 66%	1440
	11th to 20th	Night	1 2 1 1 2 1 2 3 2 4 81%	1440
	21st to end	Night	3 2 1 2 2 1 2 2 2 4 80%	1440
July	1st to 10th	Night	1 1 1 1 1 2 2 2 3 86%	1440
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 3 79%	1440
	21st to end	Night	4 2 1 2 3 2 2 3 3 4 73%	1681
August	1st to 10th	Night	2 2 1 3 2 1 3 3 4 4 76%	1647
	11th to 20th	Night	2 1 1 2 2 2 2 3 3 4 78%	1780
	21st to end	Night	2 1 1 1 2 1 1 1 2 3 85%	1980
September	1st to 10th	Night	1 1 1 1 2 1 1 1 1 3 87%	1800
	11th to 20th	Night	2 2 1 1 2 2 2 2 3 5% 79%	1824
	21st to end	Night	2 3 1 2 3 2 2 2 3 5% 76%	1980
October	1st to 10th	Night	5% 4 1 2 3 1 2 3 4 4 71%	2128
	11th to 20th	Night	4 3 1 3 2 1 3 3 3 6% 71%	2160
	21st to end	Night	5% 4 1 1 2 1 2 3 3 6% 72%	2396
November	1st to 10th	Night	8% 8% 2 2 3 2 3 3 4 7% 58%	2405
	11th to 20th	Night	6% 6% 1 2 3 2 4 4 5% 8% 59%	2470
	21st to end	Night	6% 8% 3 3 4 2 3 4 4 7% 57%	2498
December	1st to 10th	Night	12% 9% 3 3 4 2 4 4 5% 6% 50%	2660
	11th to 20th	Night	13% 18% 3 4 3 2 4 5% 5% 7% 36%	3276
	21st to end	Night	6% 11% 5% 6% 5% 4 5% 5% 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	51% 6% 9% 16% 14% 5%	1900
	11th to 20th	Day	44% 5% 10% 19% 16% 6%	2070
	21st to end	Day	46% 6% 14% 20% 11% 3	2440
April	1st to 10th	Day	38% 6% 14% 19% 19% 5%	2185
	11th to 20th	Day	36% 5% 12% 23% 17% 6%	2132
	21st to end	Day	29% 6% 16% 27% 18% 3	2160
May	1st to 10th	Day	26% 5% 13% 29% 21% 5%	2232
	11th to 20th	Day	30% 4 12% 28% 22% 4	2412
	21st to end	Day	33% 7% 12% 26% 18% 4	2724
June	1st to 10th	Day	24% 6% 11% 24% 27% 8%	2520
	11th to 20th	Day	14% 3 8% 26% 33% 16%	2520
	21st to end	Day	12% 3 6% 15% 35% 29%	2520
July	1st to 10th	Day	7% 2 4 12% 29% 46%	2451
	11th to 20th	Day	10% 4 6% 15% 26% 41%	2445
	21st to end	Day	13% 2 8% 11% 27% 39%	2488
August	1st to 10th	Day	12% 2 6% 13% 26% 41%	2273
	11th to 20th	Day	10% 1 6% 11% 37% 35%	2122
	21st to end	Day	8% 1 4 12% 39% 36%	2376
September	1st to 10th	Day	9% 2 4 12% 34% 39%	2160
	11th to 20th	Day	15% 3 7% 22% 34% 19%	2134
	21st to end	Day	17% 2 5% 21% 37% 19%	1980
October	1st to 10th	Day	21% 4 7% 16% 29% 23%	1828
	11th to 20th	Day	18% 3 7% 23% 28% 21%	1800
	21st to end	Day	20% 3 8% 20% 31% 19%	1958
November	1st to 10th	Day	30% 5% 9% 19% 23% 13%	1674
	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	45% 5% 9% 15% 19% 6%	2280
	11th to 20th	Night	38% 6% 10% 20% 18% 8%	2108
	21st to end	Night	40% 7% 13% 21% 14% 4	2157
April	1st to 10th	Night	35% 8% 13% 20% 19% 5%	1820
	11th to 20th	Night	31% 6% 13% 22% 20% 7%	1779
	21st to end	Night	26% 6% 13% 34% 17% 4	1800
May	1st to 10th	Night	23% 6% 12% 29% 25% 5%	1726
	11th to 20th	Night	21% 4 13% 32% 25% 5%	1480
	21st to end	Night	23% 5% 16% 31% 20% 5%	1552
June	1st to 10th	Night	21% 6% 11% 24% 30% 9%	1440
	11th to 20th	Night	9% 3 8% 28% 33% 19%	1440
	21st to end	Night	11% 2 4 17% 35% 31%	1440
July	1st to 10th	Night	6% 2 4 11% 33% 44%	1400
	11th to 20th	Night	11% 2 6% 14% 26% 41%	1392
	21st to end	Night	16% 2 5% 10% 28% 39%	1588
August	1st to 10th	Night	13% 2 6% 16% 26% 38%	1638
	11th to 20th	Night	10% 3 4 13% 35% 35%	1780
	21st to end	Night	9% 1 2 13% 36% 38%	1980
September	1st to 10th	Night	6% 2 4 10% 37% 41%	1800
	11th to 20th	Night	10% 4 5% 23% 36% 21%	1824
	21st to end	Night	13% 3 6% 23% 35% 21%	1980
October	1st to 10th	Night	18% 4 6% 19% 31% 21%	2128
	11th to 20th	Night	16% 4 6% 20% 33% 22%	2160
	21st to end	Night	15% 3 8% 20% 35% 19%	2396
November	1st to 10th	Night	26% 4 8% 21% 25% 16%	2405
	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% 28% 30% 13% 2	506
April	1st to 10th	Day	22% 26% 31% 14% 6%	429
	11th to 20th	Day	29% 23% 30% 13% 4	412
	21st to end	Day	16% 24% 31% 21% 7% 2	420
May	1st to 10th	Day	18% 25% 32% 16% 8% 1	423
	11th to 20th	Day	19% 23% 29% 18% 9% 1	448
	21st to end	Day	19% 17% 28% 25% 8% 3	485
June	1st to 10th	Day	12% 19% 36% 20% 9% 3	450
	11th to 20th	Day	12% 20% 41% 18% 7% 2	450
	21st to end	Day	5% 16% 42% 25% 9% 3	450
July	1st to 10th	Day	3 17% 48% 21% 9% 2	446
	11th to 20th	Day	2 10% 49% 26% 10% 3	444
	21st to end	Day	2 11% 45% 27% 11% 5%	487
August	1st to 10th	Day	3 19% 43% 22% 10% 3	447
	11th to 20th	Day	3 13% 44% 23% 11% 4	437
	21st to end	Day	3 10% 48% 25% 12% 2	495
September	1st to 10th	Day	3 12% 45% 28% 11% 1	450
	11th to 20th	Day	10% 18% 36% 29% 5% 2	450
	21st to end	Day	9% 15% 39% 30% 5% 2	450
October	1st to 10th	Day	8% 21% 32% 30% 7% 2	450
	11th to 20th	Day	10% 14% 36% 27% 11% 2	450
	21st to end	Day	13% 17% 29% 27% 11% 3	473
November	1st to 10th	Day	19% 15% 21% 25% 15% 4	270
	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	19% 16% 31% 25% 9% 1	836
April	1st to 10th	Night	16% 12% 29% 31% 11% 2	728
	11th to 20th	Night	14% 16% 28% 27% 12% 3	711
	21st to end	Night	11% 11% 30% 28% 17% 3	720
May	1st to 10th	Night	9% 12% 28% 31% 17% 3	646
	11th to 20th	Night	7% 9% 25% 38% 20% 2	418
	21st to end	Night	9% 6% 23% 31% 28% 2	389
June	1st to 10th	Night	8% 5% 24% 37% 25% 2	360
	11th to 20th	Night	3 5% 26% 43% 23% 1	360
	21st to end	Night	3 3 21% 46% 26% 2	360
July	1st to 10th	Night	1 15% 48% 33% 2	350
	11th to 20th	Night	2 1 16% 45% 33% 2	348
	21st to end	Night	3 1 13% 36% 40% 6%	499
August	1st to 10th	Night	3 1 16% 47% 31% 2	573
	11th to 20th	Night	1 1 19% 48% 27% 4	712
	21st to end	Night	2 2 15% 50% 28% 3	792
September	1st to 10th	Night	2 3 18% 46% 28% 3	720
	11th to 20th	Night	3 3 22% 39% 27% 6%	720
	21st to end	Night	4 6% 25% 34% 26% 5%	720
October	1st to 10th	Night	8% 8% 23% 37% 20% 3	720
	11th to 20th	Night	8% 9% 22% 38% 19% 4	720
	21st to end	Night	10% 9% 23% 29% 22% 7%	792
November	1st to 10th	Night	13% 9% 21% 35% 18% 4	740
	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 2024-03-31 03:08:53. Version ac07

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