Black Rock Desert
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Rock Desert clear sky chart from 2005-11-06 to 2024-02-20.

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	3 4 2 5% 5% 3 5% 5% 5% 7% 57%	78393
	Night	3 5% 2 5% 6% 3 5% 5% 6% 7% 52%	80821
Transparency	Day	27% 4 9% 21% 21% 17%	78097
	Night	31% 4 11% 22% 19% 13%	80638
Seeing	Day	7% 10% 22% 29% 24% 8%	13841
	Night	6% 5% 19% 41% 25% 4	23296

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	3 9% 4 10% 10% 5% 6% 7% 6% 9% 30%	2539
	11th to 20th	Day	4 8% 4 11% 9% 6% 8% 7% 7% 10% 27%	2540
	21st to end	Day	5% 9% 5% 11% 11% 5% 5% 6% 6% 9% 28%	3027
February	1st to 10th	Day	3 5% 3 7% 6% 4 6% 6% 7% 9% 44%	1712
	11th to 20th	Day	3 4 3 6% 7% 5% 6% 7% 7% 9% 42%	1841
	21st to end	Day	1 5% 3 6% 6% 4 6% 7% 8% 8% 46%	1480
March	1st to 10th	Day	4 7% 3 6% 6% 5% 8% 7% 8% 9% 38%	1800
	11th to 20th	Day	3 5% 3 7% 7% 4 6% 5% 6% 11% 43%	1891
	21st to end	Day	3 5% 3 5% 6% 4 5% 5% 6% 10% 47%	2350
April	1st to 10th	Day	3 5% 3 7% 6% 4 6% 6% 6% 7% 48%	2160
	11th to 20th	Day	3 5% 2 5% 4 3 5% 5% 6% 8% 54%	2129
	21st to end	Day	4 4 2 4 5% 3 4 5% 5% 6% 58%	2171
May	1st to 10th	Day	2 4 2 4 3 2 3 5% 5% 8% 62%	2340
	11th to 20th	Day	4 4 1 4 4 3 6% 5% 4 8% 56%	2450
	21st to end	Day	5% 5% 3 5% 6% 4 4 5% 6% 6% 51%	2723
June	1st to 10th	Day	3 3 2 5% 4 2 5% 4 5% 8% 59%	2520
	11th to 20th	Day	2 2 1 2 3 2 3 3 5% 5% 70%	2520
	21st to end	Day	2 2 1 2 2 2 2 3 3 5% 77%	2520
July	1st to 10th	Day	1 1 1 1 2 1 3 3 3 5% 79%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 4 83%	2520
	21st to end	Day	2 2 1 2 2 2 3 3 4 5% 75%	2741
August	1st to 10th	Day	3 2 1 2 2 2 3 3 4 5% 73%	2376
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 81%	2122
	21st to end	Day	1 1 1 1 1 1 1 2 2 4 85%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 2 4 83%	2160
	11th to 20th	Day	1 1 1 2 3 1 3 3 3 6% 76%	2106
	21st to end	Day	2 2 1 2 2 2 2 3 4 6% 74%	1980
October	1st to 10th	Day	4 3 2 4 4 3 4 3 4 5% 65%	1867
	11th to 20th	Day	2 3 1 3 3 2 4 3 4 7% 68%	1800
	21st to end	Day	2 2 1 4 4 2 4 5% 5% 8% 63%	1864
November	1st to 10th	Day	4 5% 3 5% 5% 2 5% 5% 6% 7% 53%	1674
	11th to 20th	Day	3 4 2 4 5% 3 5% 6% 7% 12% 49%	1710
	21st to end	Day	2 4 2 5% 6% 4 6% 6% 8% 9% 47%	1622
December	1st to 10th	Day	3 7% 4 8% 6% 4 6% 5% 7% 9% 39%	1520
	11th to 20th	Day	4 8% 4 10% 10% 7% 10% 9% 7% 7% 23%	1928
	21st to end	Day	5% 8% 4 10% 10% 5% 8% 6% 8% 9% 28%	2794
January	1st to 10th	Night	3 7% 3 8% 9% 5% 7% 6% 7% 9% 35%	4406
	11th to 20th	Night	3 8% 4 11% 10% 5% 6% 6% 9% 8% 29%	4420
	21st to end	Night	6% 11% 5% 9% 10% 5% 6% 5% 6% 7% 30%	4635
February	1st to 10th	Night	2 5% 3 5% 6% 4 6% 6% 8% 8% 48%	2466
	11th to 20th	Night	3 6% 2 6% 7% 5% 6% 5% 7% 8% 47%	2211
	21st to end	Night	3 5% 3 6% 7% 5% 5% 7% 7% 9% 43%	1776
March	1st to 10th	Night	3 7% 3 7% 6% 4 8% 6% 6% 8% 42%	2160
	11th to 20th	Night	2 5% 3 6% 6% 4 5% 6% 7% 10% 46%	2066
	21st to end	Night	4 5% 3 6% 5% 4 6% 6% 7% 8% 47%	2004
April	1st to 10th	Night	3 5% 2 5% 5% 3 6% 5% 7% 10% 51%	1800
	11th to 20th	Night	3 5% 3 4 4 3 5% 5% 5% 8% 56%	1779
	21st to end	Night	4 5% 2 4 4 2 3 3 4 6% 61%	1787
May	1st to 10th	Night	4 3 2 3 3 3 3 5% 6% 8% 60%	1620
	11th to 20th	Night	6% 4 2 3 5% 2 4 4 6% 8% 55%	1439
	21st to end	Night	6% 6% 2 5% 5% 3 5% 5% 5% 7% 51%	1552
June	1st to 10th	Night	3 4 2 4 4 3 4 4 4 8% 61%	1440
	11th to 20th	Night	4 1 1 3 3 2 2 4 4 5% 70%	1440
	21st to end	Night	2 2 1 2 3 1 3 4 4 5% 74%	1440
July	1st to 10th	Night	1 1 2 2 2 2 4 4 7% 75%	1440
	11th to 20th	Night	1 1 2 2 1 2 2 3 6% 80%	1440
	21st to end	Night	2 1 1 2 2 2 2 3 5% 6% 74%	1576
August	1st to 10th	Night	4 2 2 3 3 3 3 3 4 5% 67%	1560
	11th to 20th	Night	1 2 1 2 3 1 2 3 4 5% 77%	1780
	21st to end	Night	2 1 1 2 1 2 2 3 4 83%	1980
September	1st to 10th	Night	2 1 1 2 1 2 2 3 4 81%	1800
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 77%	1854
	21st to end	Night	2 2 1 2 2 2 3 2 5% 6% 74%	1980
October	1st to 10th	Night	5% 4 2 3 2 2 3 3 3 4 69%	2090
	11th to 20th	Night	2 2 1 3 3 2 4 3 4 6% 69%	2160
	21st to end	Night	3 3 1 2 3 2 2 4 5% 7% 68%	2492
November	1st to 10th	Night	5% 4 2 4 5% 3 4 5% 6% 8% 53%	2405
	11th to 20th	Night	3 4 2 4 5% 3 5% 6% 6% 10% 54%	2470
	21st to end	Night	3 4 3 6% 5% 3 5% 6% 6% 8% 53%	2555
December	1st to 10th	Night	5% 7% 3 7% 6% 3 4 5% 5% 8% 46%	2660
	11th to 20th	Night	5% 8% 4 10% 11% 6% 8% 7% 7% 9% 27%	3276
	21st to end	Night	4 8% 4 10% 11% 6% 7% 7% 7% 8% 28%	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	48% 7% 17% 23% 4	2539
	11th to 20th	Day	51% 6% 21% 15% 6%	2540
	21st to end	Day	53% 5% 16% 21% 5%	3027
February	1st to 10th	Day	35% 7% 16% 27% 12% 3	1712
	11th to 20th	Day	34% 6% 17% 27% 15% 1	1851
	21st to end	Day	33% 6% 17% 26% 15% 3	1480
March	1st to 10th	Day	42% 5% 13% 26% 13% 2	1800
	11th to 20th	Day	37% 5% 13% 26% 17% 2	1891
	21st to end	Day	33% 5% 17% 30% 13% 3	2350
April	1st to 10th	Day	35% 5% 12% 25% 19% 3	2160
	11th to 20th	Day	30% 5% 8% 26% 25% 7%	2132
	21st to end	Day	27% 3 11% 30% 25% 5%	2171
May	1st to 10th	Day	21% 4 7% 29% 33% 7%	2340
	11th to 20th	Day	28% 4 7% 23% 29% 9%	2453
	21st to end	Day	34% 4 9% 25% 22% 6%	2724
June	1st to 10th	Day	25% 3 6% 21% 32% 12%	2520
	11th to 20th	Day	17% 3 4 20% 33% 23%	2520
	21st to end	Day	13% 2 2 12% 33% 38%	2520
July	1st to 10th	Day	10% 2 2 10% 22% 53%	2451
	11th to 20th	Day	7% 2 2 7% 24% 59%	2445
	21st to end	Day	13% 3 1 6% 22% 55%	2589
August	1st to 10th	Day	15% 2 2 11% 25% 45%	2359
	11th to 20th	Day	9% 3 1 9% 28% 51%	2122
	21st to end	Day	7% 1 1 10% 31% 50%	2376
September	1st to 10th	Day	9% 2 1 8% 28% 52%	2160
	11th to 20th	Day	12% 2 4 18% 33% 30%	2106
	21st to end	Day	14% 2 4 23% 32% 25%	1980
October	1st to 10th	Day	24% 2 6% 23% 27% 18%	1867
	11th to 20th	Day	18% 3 7% 28% 31% 14%	1800
	21st to end	Day	21% 3 11% 32% 25% 9%	1864
November	1st to 10th	Day	29% 5% 11% 29% 22% 4	1674
	11th to 20th	Day	27% 7% 16% 31% 18%	1710
	21st to end	Day	30% 6% 13% 31% 18% 2	1622
December	1st to 10th	Day	39% 8% 14% 25% 13% 2	1520
	11th to 20th	Day	55% 7% 13% 19% 6%	1928
	21st to end	Day	50% 5% 19% 20% 6%	2794
January	1st to 10th	Night	42% 6% 24% 22% 5% 1	4406
	11th to 20th	Night	50% 6% 17% 17% 9% 1	4420
	21st to end	Night	51% 5% 15% 22% 7%	4635
February	1st to 10th	Night	32% 7% 15% 28% 16% 2	2466
	11th to 20th	Night	33% 6% 15% 27% 18% 1	2212
	21st to end	Night	35% 6% 14% 27% 16% 3	1776
March	1st to 10th	Night	39% 6% 15% 26% 12% 3	2160
	11th to 20th	Night	33% 5% 13% 25% 20% 2	2066
	21st to end	Night	35% 6% 17% 27% 13% 3	2004
April	1st to 10th	Night	31% 4 14% 29% 18% 4	1800
	11th to 20th	Night	29% 4 12% 29% 20% 7%	1779
	21st to end	Night	26% 3 12% 33% 22% 4	1787
May	1st to 10th	Night	23% 4 7% 26% 33% 7%	1620
	11th to 20th	Night	28% 3 7% 30% 25% 7%	1439
	21st to end	Night	33% 4 10% 28% 20% 4	1552
June	1st to 10th	Night	25% 4 7% 27% 26% 11%	1440
	11th to 20th	Night	17% 4 5% 19% 39% 16%	1440
	21st to end	Night	13% 4 4 13% 28% 38%	1440
July	1st to 10th	Night	12% 3 2 9% 26% 49%	1400
	11th to 20th	Night	10% 1 1 7% 23% 57%	1392
	21st to end	Night	12% 3 1 7% 22% 53%	1488
August	1st to 10th	Night	20% 3 2 11% 23% 41%	1552
	11th to 20th	Night	12% 3 1 9% 25% 50%	1780
	21st to end	Night	9% 2 1 9% 29% 51%	1980
September	1st to 10th	Night	10% 3 1 7% 26% 54%	1800
	11th to 20th	Night	13% 2 3 17% 30% 36%	1854
	21st to end	Night	13% 3 3 18% 30% 33%	1980
October	1st to 10th	Night	21% 2 4 21% 29% 23%	2090
	11th to 20th	Night	18% 3 5% 24% 30% 21%	2160
	21st to end	Night	18% 3 9% 30% 26% 14%	2492
November	1st to 10th	Night	30% 5% 11% 25% 22% 7%	2405
	11th to 20th	Night	28% 5% 15% 28% 24% 1	2470
	21st to end	Night	29% 4 12% 30% 20% 4	2555
December	1st to 10th	Night	37% 6% 13% 25% 18% 2	2660
	11th to 20th	Night	51% 6% 13% 20% 9%	3276
	21st to end	Night	52% 5% 14% 20% 10%	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	11% 10% 32% 29% 14% 4	180
	11th to 20th	Day	9% 8% 27% 28% 21% 6%	180
	21st to end	Day	7% 8% 24% 30% 25% 6%	340
February	1st to 10th	Day	6% 10% 27% 33% 21% 2	372
	11th to 20th	Day	9% 16% 28% 29% 16% 2	452
	21st to end	Day	8% 14% 29% 34% 14% 1	346
March	1st to 10th	Day	12% 15% 30% 27% 13% 3	420
	11th to 20th	Day	10% 15% 27% 24% 21% 3	420
	21st to end	Day	12% 20% 29% 23% 15% 2	462
April	1st to 10th	Day	10% 20% 26% 27% 13% 4	420
	11th to 20th	Day	12% 22% 26% 24% 12% 4	412
	21st to end	Day	10% 15% 25% 25% 20% 5%	420
May	1st to 10th	Day	6% 17% 27% 26% 16% 7%	423
	11th to 20th	Day	8% 17% 25% 25% 17% 8%	448
	21st to end	Day	11% 10% 18% 27% 26% 9%	485
June	1st to 10th	Day	7% 13% 20% 27% 23% 10%	450
	11th to 20th	Day	8% 14% 27% 25% 20% 6%	450
	21st to end	Day	2 10% 20% 33% 28% 8%	450
July	1st to 10th	Day	2 5% 22% 33% 28% 10%	446
	11th to 20th	Day	1 5% 17% 37% 31% 8%	444
	21st to end	Day	1 2 19% 35% 32% 11%	487
August	1st to 10th	Day	5% 6% 16% 28% 33% 12%	447
	11th to 20th	Day	1 6% 13% 29% 32% 18%	437
	21st to end	Day	2 4 21% 30% 29% 14%	495
September	1st to 10th	Day	2 5% 17% 28% 32% 15%	450
	11th to 20th	Day	4 7% 19% 26% 28% 16%	450
	21st to end	Day	4 7% 17% 35% 28% 10%	450
October	1st to 10th	Day	7% 8% 17% 27% 28% 12%	450
	11th to 20th	Day	6% 8% 18% 25% 33% 10%	450
	21st to end	Day	6% 8% 21% 29% 27% 9%	379
November	1st to 10th	Day	9% 9% 19% 33% 24% 7%	270
	11th to 20th	Day	3 6% 23% 34% 27% 7%	270
	21st to end	Day	5% 5% 24% 32% 28% 7%	228
December	1st to 10th	Day	9% 7% 26% 27% 21% 11%	180
	11th to 20th	Day	8% 4 23% 35% 23% 6%	180
	21st to end	Day	12% 9% 25% 31% 20% 4	198
January	1st to 10th	Night	9% 4 23% 37% 22% 4	760
	11th to 20th	Night	6% 6% 21% 43% 20% 4	760
	21st to end	Night	10% 4 17% 42% 23% 3	836
February	1st to 10th	Night	6% 6% 22% 44% 20% 2	760
	11th to 20th	Night	6% 7% 23% 39% 22% 3	742
	21st to end	Night	7% 7% 26% 43% 16% 2	592
March	1st to 10th	Night	7% 8% 25% 39% 18% 3	720
	11th to 20th	Night	5% 8% 22% 40% 23% 2	720
	21st to end	Night	8% 11% 26% 37% 17% 1	792
April	1st to 10th	Night	6% 11% 27% 37% 19% 1	720
	11th to 20th	Night	7% 11% 25% 36% 19% 3	711
	21st to end	Night	7% 8% 23% 35% 23% 4	707
May	1st to 10th	Night	7% 10% 25% 37% 19% 2	540
	11th to 20th	Night	9% 5% 21% 36% 26% 4	377
	21st to end	Night	8% 5% 15% 40% 28% 4	389
June	1st to 10th	Night	6% 5% 21% 38% 26% 3	360
	11th to 20th	Night	5% 6% 19% 46% 23% 2	360
	21st to end	Night	3 2 16% 51% 26% 2	360
July	1st to 10th	Night	2 1 19% 50% 27% 1	350
	11th to 20th	Night	1 1 18% 53% 27% 1	348
	21st to end	Night	3 1 12% 44% 38% 2	394
August	1st to 10th	Night	5% 1 12% 47% 31% 4	486
	11th to 20th	Night	3 2 12% 43% 38% 3	712
	21st to end	Night	2 1 12% 46% 35% 4	792
September	1st to 10th	Night	2 2 11% 41% 38% 6%	720
	11th to 20th	Night	3 3 11% 39% 35% 9%	720
	21st to end	Night	3 4 15% 34% 34% 9%	720
October	1st to 10th	Night	6% 3 13% 43% 28% 7%	720
	11th to 20th	Night	3 6% 13% 37% 35% 6%	720
	21st to end	Night	5% 4 15% 38% 28% 10%	792
November	1st to 10th	Night	7% 4 20% 36% 26% 6%	740
	11th to 20th	Night	5% 4 20% 45% 23% 4	760
	21st to end	Night	5% 6% 19% 39% 27% 4	760
December	1st to 10th	Night	9% 5% 18% 42% 21% 4	760
	11th to 20th	Night	9% 6% 21% 38% 23% 3	760
	21st to end	Night	11% 7% 24% 42% 15% 1	836

Page generated at 2024-02-17 03:28:41. Version ac07

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