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 2025-04-11.

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	2 4 2 5% 4 4 4 3 5% 7% 61%	117342
	Night	3 5% 2 6% 4 4 4 4 6% 7% 56%	119786
Transparency	Day	24% 3 8% 21% 23% 20%	117083
	Night	28% 4 9% 22% 22% 15%	119634
Seeing	Day	7% 10% 23% 29% 23% 8%	15338
	Night	6% 5% 20% 40% 25% 4	24774

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	2 7% 3 10% 7% 7% 6% 5% 7% 9% 36%	3639
	11th to 20th	Day	2 6% 3 9% 6% 5% 5% 4 6% 8% 46%	3640
	21st to end	Day	3 7% 3 11% 7% 5% 5% 3 5% 7% 42%	4349
February	1st to 10th	Day	3 5% 3 8% 6% 6% 5% 5% 7% 9% 43%	1803
	11th to 20th	Day	3 4 2 8% 6% 7% 6% 5% 8% 9% 43%	1950
	21st to end	Day	1 6% 2 6% 6% 6% 6% 5% 8% 8% 47%	1650
March	1st to 10th	Day	4 9% 3 7% 6% 6% 7% 6% 8% 10% 35%	4518
	11th to 20th	Day	1 4 2 5% 4 4 5% 4 5% 9% 56%	4794
	21st to end	Day	3 6% 3 6% 5% 5% 5% 4 7% 8% 49%	5917
April	1st to 10th	Day	2 5% 3 7% 5% 5% 5% 4 7% 7% 49%	2400
	11th to 20th	Day	3 6% 2 5% 4 4 5% 4 6% 8% 53%	2251
	21st to end	Day	3 4 2 5% 4 4 4 4 6% 6% 58%	2292
May	1st to 10th	Day	2 5% 2 4 2 2 2 3 4 6% 66%	4110
	11th to 20th	Day	2 3 1 3 2 3 3 2 3 5% 73%	4337
	21st to end	Day	3 3 2 4 3 3 4 3 5% 5% 65%	4813
June	1st to 10th	Day	3 3 2 5% 4 4 4 4 5% 8% 59%	2660
	11th to 20th	Day	2 3 1 3 2 3 3 3 5% 5% 71%	2660
	21st to end	Day	1 2 1 2 2 2 2 2 4 5% 77%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 3 87%	4420
	11th to 20th	Day	1 2 1 1 2 2 2 2 4 4 79%	4420
	21st to end	Day	1 1 1 2 2 2 3 2 4 5% 78%	4790
August	1st to 10th	Day	2 2 1 2 2 2 3 3 4 6% 74%	4165
	11th to 20th	Day	1 1 1 1 1 1 2 1 2 3 85%	3724
	21st to end	Day	1 1 2 1 1 1 1 2 3 85%	4180
September	1st to 10th	Day	1 1 2 1 1 3 2 2 4 83%	2280
	11th to 20th	Day	2 2 1 2 2 2 3 2 3 6% 75%	2223
	21st to end	Day	2 2 1 3 2 2 2 2 4 5% 75%	2090
October	1st to 10th	Day	2 2 1 3 3 2 2 2 3 5% 73%	3286
	11th to 20th	Day	4 3 1 3 2 3 3 2 4 6% 69%	3161
	21st to end	Day	2 2 1 4 3 3 4 3 6% 8% 63%	3237
November	1st to 10th	Day	4 5% 2 5% 4 4 4 4 6% 7% 53%	1764
	11th to 20th	Day	2 4 2 5% 5% 5% 6% 5% 7% 11% 48%	1800
	21st to end	Day	1 5% 2 7% 6% 6% 5% 5% 8% 9% 47%	1707
December	1st to 10th	Day	2 5% 2 5% 4 5% 5% 4 6% 8% 54%	2620
	11th to 20th	Day	3 7% 3 11% 9% 10% 9% 6% 8% 9% 24%	3028
	21st to end	Day	4 7% 3 10% 7% 7% 8% 6% 8% 9% 30%	4004
January	1st to 10th	Night	3 6% 2 8% 7% 7% 7% 5% 8% 10% 37%	6306
	11th to 20th	Night	2 6% 2 9% 6% 5% 5% 4 6% 6% 47%	6320
	21st to end	Night	4 8% 3 8% 7% 5% 5% 3 5% 6% 45%	6621
February	1st to 10th	Night	2 5% 2 6% 6% 6% 6% 5% 8% 8% 47%	2595
	11th to 20th	Night	2 6% 2 7% 6% 6% 6% 4 7% 8% 47%	2338
	21st to end	Night	2 6% 2 7% 7% 6% 5% 6% 6% 9% 44%	1980
March	1st to 10th	Night	3 9% 3 7% 5% 6% 6% 5% 6% 8% 41%	5376
	11th to 20th	Night	1 4 2 5% 4 4 5% 4 6% 9% 55%	5203
	21st to end	Night	3 6% 3 8% 5% 5% 6% 5% 8% 9% 43%	5056
April	1st to 10th	Night	3 5% 2 6% 4 4 5% 4 7% 9% 51%	2000
	11th to 20th	Night	3 6% 2 5% 4 4 4 4 6% 7% 56%	1883
	21st to end	Night	4 6% 2 5% 3 3 3 3 5% 6% 61%	1886
May	1st to 10th	Night	3 5% 1 4 3 3 4 3 5% 7% 62%	2860
	11th to 20th	Night	4 3 1 3 3 2 3 2 4 5% 71%	2553
	21st to end	Night	4 4 1 4 3 3 4 3 5% 7% 62%	2762
June	1st to 10th	Night	3 5% 2 4 4 4 3 3 4 8% 60%	1520
	11th to 20th	Night	4 2 1 3 3 3 3 3 4 5% 71%	1520
	21st to end	Night	2 2 1 3 3 2 2 3 4 4 74%	1520
July	1st to 10th	Night	1 1 1 1 2 2 2 3 4 85%	2540
	11th to 20th	Night	3 2 1 3 2 2 2 2 4 5% 74%	2540
	21st to end	Night	3 1 1 3 2 2 3 3 5% 6% 72%	2761
August	1st to 10th	Night	3 2 1 3 3 3 3 3 4 5% 70%	2769
	11th to 20th	Night	1 1 1 2 2 1 1 2 3 4 83%	3126
	21st to end	Night	2 2 2 1 1 1 1 2 4 83%	3498
September	1st to 10th	Night	2 2 2 2 1 2 2 3 4 80%	1900
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 5% 75%	1957
	21st to end	Night	2 2 1 2 2 2 3 2 5% 6% 75%	2090
October	1st to 10th	Night	3 2 1 3 1 2 2 2 3 4 77%	3691
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 5% 74%	3777
	21st to end	Night	3 2 1 3 3 4 4 4 6% 7% 64%	4325
November	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 6% 8% 53%	2535
	11th to 20th	Night	3 4 2 5% 4 4 4 5% 6% 10% 53%	2600
	21st to end	Night	2 4 2 6% 4 5% 5% 5% 6% 8% 52%	2690
December	1st to 10th	Night	3 5% 2 5% 3 3 4 3 4 6% 60%	4560
	11th to 20th	Night	3 7% 3 10% 8% 7% 7% 6% 9% 10% 29%	5176
	21st to end	Night	4 8% 4 11% 8% 8% 7% 6% 7% 8% 30%	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	41% 9% 19% 25% 6%	3639
	11th to 20th	Day	36% 5% 16% 27% 16%	3640
	21st to end	Day	42% 3 11% 17% 21% 4	4349
February	1st to 10th	Day	35% 6% 16% 27% 13% 3	1803
	11th to 20th	Day	34% 6% 17% 27% 16% 1	1960
	21st to end	Day	32% 6% 16% 27% 15% 4	1650
March	1st to 10th	Day	44% 3 11% 23% 15% 4	4518
	11th to 20th	Day	26% 3 13% 35% 20% 2	4794
	21st to end	Day	34% 4 13% 25% 21% 3	5917
April	1st to 10th	Day	33% 5% 12% 27% 19% 3	2400
	11th to 20th	Day	29% 5% 9% 26% 24% 6%	2254
	21st to end	Day	27% 3 10% 31% 24% 5%	2292
May	1st to 10th	Day	21% 3 7% 33% 31% 6%	4110
	11th to 20th	Day	16% 2 4 17% 42% 18%	4340
	21st to end	Day	22% 3 6% 29% 33% 7%	4814
June	1st to 10th	Day	25% 3 7% 22% 32% 12%	2660
	11th to 20th	Day	16% 3 4 19% 33% 25%	2660
	21st to end	Day	13% 2 1 12% 33% 39%	2660
July	1st to 10th	Day	6% 1 1 6% 13% 74%	4351
	11th to 20th	Day	10% 1 2 5% 15% 67%	4345
	21st to end	Day	11% 2 1 6% 25% 55%	4639
August	1st to 10th	Day	14% 2 1 7% 20% 56%	4149
	11th to 20th	Day	7% 2 1 5% 28% 57%	3760
	21st to end	Day	8% 1 1 9% 37% 45%	4179
September	1st to 10th	Day	9% 2 1 8% 28% 53%	2280
	11th to 20th	Day	13% 2 4 18% 33% 29%	2223
	21st to end	Day	13% 2 4 23% 32% 27%	2090
October	1st to 10th	Day	16% 2 3 14% 33% 32%	3286
	11th to 20th	Day	19% 2 4 26% 37% 11%	3161
	21st to end	Day	20% 3 9% 33% 28% 7%	3237
November	1st to 10th	Day	28% 5% 12% 30% 22% 4	1764
	11th to 20th	Day	28% 7% 16% 31% 17%	1800
	21st to end	Day	30% 6% 13% 31% 18% 2	1707
December	1st to 10th	Day	27% 6% 9% 32% 25% 1	2620
	11th to 20th	Day	53% 7% 16% 19% 5%	3028
	21st to end	Day	47% 6% 19% 22% 5%	4004
January	1st to 10th	Night	38% 8% 21% 26% 7%	6306
	11th to 20th	Night	35% 5% 13% 26% 17% 3	6320
	21st to end	Night	40% 4 11% 19% 23% 4	6621
February	1st to 10th	Night	32% 7% 15% 27% 17% 3	2595
	11th to 20th	Night	33% 6% 15% 28% 18% 1	2339
	21st to end	Night	35% 6% 13% 26% 16% 4	1980
March	1st to 10th	Night	41% 4 11% 23% 16% 5%	5376
	11th to 20th	Night	27% 4 13% 36% 20% 1	5203
	21st to end	Night	36% 5% 17% 28% 13% 1	5056
April	1st to 10th	Night	30% 4 14% 30% 18% 4	2000
	11th to 20th	Night	29% 4 12% 30% 19% 7%	1883
	21st to end	Night	26% 3 12% 34% 21% 4	1886
May	1st to 10th	Night	21% 3 6% 33% 29% 7%	2860
	11th to 20th	Night	17% 3 4 19% 44% 13%	2553
	21st to end	Night	22% 3 6% 31% 33% 5%	2762
June	1st to 10th	Night	25% 4 7% 27% 27% 10%	1520
	11th to 20th	Night	16% 3 5% 18% 39% 18%	1520
	21st to end	Night	13% 3 3 12% 28% 40%	1520
July	1st to 10th	Night	7% 1 1 5% 15% 71%	2500
	11th to 20th	Night	15% 1 1 6% 14% 63%	2492
	21st to end	Night	14% 3 2 6% 28% 48%	2674
August	1st to 10th	Night	18% 2 2 7% 18% 53%	2761
	11th to 20th	Night	9% 2 1 5% 23% 60%	3156
	21st to end	Night	10% 1 1 9% 32% 47%	3498
September	1st to 10th	Night	10% 3 1 6% 25% 55%	1900
	11th to 20th	Night	15% 2 3 17% 30% 34%	1957
	21st to end	Night	12% 3 3 17% 30% 34%	2090
October	1st to 10th	Night	15% 1 2 12% 33% 36%	3691
	11th to 20th	Night	14% 3 4 24% 41% 14%	3777
	21st to end	Night	21% 3 7% 32% 28% 10%	4325
November	1st to 10th	Night	30% 5% 12% 25% 22% 7%	2535
	11th to 20th	Night	28% 5% 15% 28% 24% 1	2600
	21st to end	Night	29% 5% 12% 30% 20% 3	2690
December	1st to 10th	Night	25% 4 8% 28% 33% 1	4560
	11th to 20th	Night	46% 8% 15% 24% 7%	5176
	21st to end	Night	50% 7% 14% 20% 8%	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	10% 11% 32% 31% 13% 4	200
	11th to 20th	Day	8% 8% 27% 31% 21% 7%	200
	21st to end	Day	7% 9% 22% 31% 25% 6%	370
February	1st to 10th	Day	8% 12% 26% 32% 20% 2	403
	11th to 20th	Day	9% 15% 30% 29% 15% 2	495
	21st to end	Day	9% 14% 28% 35% 14% 2	414
March	1st to 10th	Day	12% 15% 31% 25% 13% 3	500
	11th to 20th	Day	11% 17% 27% 22% 20% 3	500
	21st to end	Day	12% 19% 30% 23% 14% 3	550
April	1st to 10th	Day	9% 19% 27% 26% 14% 5%	500
	11th to 20th	Day	12% 21% 26% 24% 13% 4	453
	21st to end	Day	10% 15% 25% 26% 20% 5%	460
May	1st to 10th	Day	8% 17% 28% 25% 15% 7%	463
	11th to 20th	Day	7% 17% 25% 26% 18% 8%	488
	21st to end	Day	10% 9% 19% 27% 26% 9%	529
June	1st to 10th	Day	6% 13% 19% 28% 24% 11%	490
	11th to 20th	Day	7% 13% 28% 25% 20% 7%	490
	21st to end	Day	2 10% 20% 32% 27% 8%	490
July	1st to 10th	Day	1 5% 21% 34% 29% 10%	486
	11th to 20th	Day	1 5% 17% 37% 30% 9%	484
	21st to end	Day	1 2 18% 37% 31% 11%	531
August	1st to 10th	Day	5% 5% 17% 29% 32% 12%	487
	11th to 20th	Day	1 6% 16% 29% 31% 17%	477
	21st to end	Day	3 4 20% 29% 29% 14%	539
September	1st to 10th	Day	2 5% 17% 29% 32% 15%	490
	11th to 20th	Day	6% 7% 19% 27% 26% 15%	490
	21st to end	Day	3 6% 17% 34% 30% 10%	490
October	1st to 10th	Day	7% 8% 17% 27% 29% 13%	490
	11th to 20th	Day	7% 8% 18% 24% 33% 10%	490
	21st to end	Day	6% 8% 21% 30% 26% 8%	416
November	1st to 10th	Day	8% 9% 21% 32% 24% 6%	300
	11th to 20th	Day	3 6% 26% 33% 24% 7%	300
	21st to end	Day	5% 6% 23% 32% 27% 6%	253
December	1st to 10th	Day	8% 6% 24% 28% 21% 14%	200
	11th to 20th	Day	9% 4 25% 33% 24% 6%	200
	21st to end	Day	13% 10% 26% 30% 18% 3	220
January	1st to 10th	Night	9% 5% 25% 37% 21% 4	800
	11th to 20th	Night	6% 6% 22% 43% 20% 4	800
	21st to end	Night	10% 4 18% 42% 22% 3	880
February	1st to 10th	Night	7% 7% 22% 43% 19% 2	800
	11th to 20th	Night	6% 7% 25% 39% 21% 3	784
	21st to end	Night	6% 7% 25% 43% 17% 2	660
March	1st to 10th	Night	8% 8% 27% 38% 17% 2	800
	11th to 20th	Night	6% 9% 23% 38% 22% 2	800
	21st to end	Night	8% 12% 26% 37% 16% 1	880
April	1st to 10th	Night	6% 10% 27% 38% 19% 1	800
	11th to 20th	Night	7% 10% 25% 36% 19% 3	753
	21st to end	Night	7% 8% 23% 36% 22% 4	746
May	1st to 10th	Night	7% 10% 27% 37% 18% 2	570
	11th to 20th	Night	9% 4 20% 37% 26% 4	398
	21st to end	Night	8% 5% 15% 41% 27% 4	411
June	1st to 10th	Night	6% 5% 21% 39% 26% 3	380
	11th to 20th	Night	5% 6% 18% 47% 22% 2	380
	21st to end	Night	3 2 17% 51% 25% 2	380
July	1st to 10th	Night	2 1 19% 52% 26% 1	370
	11th to 20th	Night	1 1 18% 52% 27% 1	368
	21st to end	Night	3 1 12% 45% 37% 2	416
August	1st to 10th	Night	5% 2 12% 47% 31% 4	514
	11th to 20th	Night	3 2 14% 42% 36% 3	752
	21st to end	Night	2 1 12% 45% 35% 4	836
September	1st to 10th	Night	2 2 12% 41% 38% 5%	760
	11th to 20th	Night	3 3 12% 39% 34% 8%	760
	21st to end	Night	3 4 15% 34% 35% 9%	760
October	1st to 10th	Night	6% 3 13% 43% 28% 7%	760
	11th to 20th	Night	3 6% 13% 38% 34% 6%	760
	21st to end	Night	5% 4 16% 39% 27% 9%	836
November	1st to 10th	Night	7% 4 21% 36% 25% 6%	780
	11th to 20th	Night	5% 4 22% 44% 22% 4	800
	21st to end	Night	5% 6% 20% 39% 27% 4	800
December	1st to 10th	Night	9% 5% 18% 41% 23% 4	800
	11th to 20th	Night	9% 6% 22% 37% 23% 3	800
	21st to end	Night	11% 8% 25% 41% 14% 1	880

Page generated at 2025-04-08 06:17:28. Version ac07

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