Bruneau Dunes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bruneau Dunes Observatory clear sky chart from 2005-11-06 to 2026-10-29.

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% 5% 2 5% 3 3 4 3 5% 7% 58%	157907
	Night	6% 6% 2 6% 4 4 4 3 5% 7% 52%	151553
Transparency	Day	25% 5% 10% 21% 22% 16%	152713
	Night	30% 6% 12% 21% 18% 13%	147745
Seeing	Day	8% 9% 24% 30% 22% 8%	17053
	Night	10% 6% 22% 40% 21% 2	26368

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	9% 15% 4 9% 5% 4 5% 5% 7% 7% 29%	4722
	11th to 20th	Day	6% 9% 3 9% 5% 4 4 3 5% 7% 46%	4740
	21st to end	Day	7% 7% 2 8% 6% 6% 5% 4 5% 7% 42%	5187
February	1st to 10th	Day	9% 9% 3 8% 5% 5% 4 4 7% 7% 39%	1913
	11th to 20th	Day	8% 10% 3 7% 5% 5% 5% 4 6% 7% 40%	2050
	21st to end	Day	6% 11% 4 7% 5% 4 5% 4 6% 8% 41%	1730
March	1st to 10th	Day	6% 9% 4 9% 6% 5% 5% 4 5% 7% 38%	4618
	11th to 20th	Day	5% 7% 3 6% 4 3 4 4 5% 7% 53%	4971
	21st to end	Day	6% 8% 3 8% 6% 6% 6% 5% 7% 9% 37%	5776
April	1st to 10th	Day	7% 7% 2 5% 5% 4 5% 4 7% 9% 45%	2520
	11th to 20th	Day	4 7% 2 6% 5% 3 4 4 7% 7% 51%	2550
	21st to end	Day	6% 5% 2 4 4 4 4 4 6% 8% 52%	2730
May	1st to 10th	Day	4 5% 1 4 3 3 3 3 4 6% 63%	7626
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 6% 64%	7596
	21st to end	Day	3 2 1 3 3 3 4 4 6% 8% 61%	8992
June	1st to 10th	Day	5% 5% 1 5% 4 4 4 4 6% 8% 53%	2940
	11th to 20th	Day	4 4 1 3 3 3 3 3 5% 7% 65%	2940
	21st to end	Day	2 2 1 3 2 2 2 3 5% 6% 73%	2940
July	1st to 10th	Day	1 1 1 2 2 2 2 3 4 5% 77%	8219
	11th to 20th	Day	1 1 1 3 2 2 3 2 4 5% 76%	8220
	21st to end	Day	2 2 1 3 2 3 3 3 5% 7% 70%	8922
August	1st to 10th	Day	2 2 1 3 2 2 3 3 4 6% 73%	7611
	11th to 20th	Day	2 2 1 3 2 3 3 2 5% 6% 72%	7565
	21st to end	Day	5% 3 1 4 3 3 4 3 5% 6% 62%	7828
September	1st to 10th	Day	2 3 1 2 2 3 3 3 4 5% 74%	2506
	11th to 20th	Day	3 3 1 4 3 2 3 3 4 5% 68%	2310
	21st to end	Day	4 3 1 3 2 2 3 3 3 5% 69%	2310
October	1st to 10th	Day	3 3 1 4 3 2 2 2 3 5% 71%	3710
	11th to 20th	Day	5% 5% 2 4 3 3 3 3 4 7% 62%	3281
	21st to end	Day	4 4 2 4 3 3 4 4 6% 9% 57%	3272
November	1st to 10th	Day	9% 7% 2 6% 4 4 4 4 5% 9% 46%	1854
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 44%	1890
	21st to end	Day	9% 9% 3 7% 4 5% 4 4 6% 8% 42%	1890
December	1st to 10th	Day	7% 5% 2 5% 3 3 3 3 5% 8% 55%	2778
	11th to 20th	Day	13% 10% 3 9% 5% 5% 5% 4 7% 8% 31%	3108
	21st to end	Day	12% 11% 5% 10% 6% 4 5% 4 6% 6% 32%	4092
January	1st to 10th	Night	11% 14% 5% 12% 6% 5% 5% 4 6% 7% 25%	8172
	11th to 20th	Night	7% 10% 4 9% 5% 4 4 3 5% 10% 41%	8220
	21st to end	Night	7% 7% 3 8% 4 4 4 4 6% 8% 45%	8994
February	1st to 10th	Night	12% 10% 3 7% 5% 5% 4 5% 6% 7% 37%	2700
	11th to 20th	Night	9% 9% 3 7% 4 4 5% 4 6% 7% 44%	2458
	21st to end	Night	7% 11% 3 5% 4 4 5% 4 7% 8% 42%	2076
March	1st to 10th	Night	8% 9% 3 7% 4 4 4 3 5% 7% 44%	5496
	11th to 20th	Night	8% 7% 3 7% 5% 4 5% 3 5% 6% 48%	5248
	21st to end	Night	6% 7% 3 7% 5% 5% 5% 4 6% 9% 43%	5436
April	1st to 10th	Night	8% 7% 2 6% 5% 5% 5% 4 6% 6% 46%	2100
	11th to 20th	Night	7% 7% 2 5% 5% 4 5% 4 6% 7% 50%	2018
	21st to end	Night	6% 5% 2 6% 4 4 4 3 7% 9% 52%	1890
May	1st to 10th	Night	6% 4 1 4 2 3 3 3 5% 7% 61%	5321
	11th to 20th	Night	4 4 2 5% 3 3 4 3 5% 7% 59%	5278
	21st to end	Night	3 4 1 4 3 4 4 3 5% 7% 62%	5181
June	1st to 10th	Night	5% 5% 1 6% 5% 5% 5% 4 6% 7% 51%	1680
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 7% 65%	1680
	21st to end	Night	2 2 1 3 3 3 3 3 4 6% 71%	1680
July	1st to 10th	Night	2 1 2 2 2 2 3 4 4 77%	4740
	11th to 20th	Night	1 1 1 3 2 2 3 3 5% 5% 74%	4740
	21st to end	Night	2 2 1 4 2 3 4 4 6% 9% 62%	5153
August	1st to 10th	Night	2 2 1 3 2 2 2 3 4 5% 74%	5205
	11th to 20th	Night	1 1 1 2 2 3 4 4 5% 7% 70%	5291
	21st to end	Night	4 4 1 4 3 3 4 4 5% 7% 61%	6413
September	1st to 10th	Night	3 2 1 3 2 2 3 3 4 5% 73%	2112
	11th to 20th	Night	4 3 1 3 3 3 4 3 4 6% 65%	2310
	21st to end	Night	5% 2 1 3 2 3 2 2 4 5% 70%	2310
October	1st to 10th	Night	4 3 1 4 2 2 3 2 4 4 72%	3710
	11th to 20th	Night	5% 4 2 4 3 3 3 3 5% 5% 62%	4072
	21st to end	Night	6% 4 2 6% 4 3 5% 4 5% 7% 54%	4704
November	1st to 10th	Night	9% 7% 2 7% 4 4 4 4 5% 6% 48%	2665
	11th to 20th	Night	11% 7% 3 7% 4 4 4 4 6% 8% 42%	2730
	21st to end	Night	8% 7% 2 6% 5% 5% 5% 4 5% 7% 45%	2730
December	1st to 10th	Night	7% 6% 2 5% 3 3 3 3 5% 11% 52%	4618
	11th to 20th	Night	13% 12% 4 9% 5% 4 5% 4 6% 9% 29%	5316
	21st to end	Night	12% 9% 3 9% 5% 6% 6% 4 6% 8% 32%	7106

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	50% 11% 23% 15% 2	4723
	11th to 20th	Day	36% 8% 19% 30% 6%	4740
	21st to end	Day	41% 8% 18% 25% 8%	5187
February	1st to 10th	Day	42% 7% 21% 22% 6% 1	1913
	11th to 20th	Day	42% 8% 18% 23% 8% 1	2060
	21st to end	Day	41% 6% 17% 24% 12% 1	1730
March	1st to 10th	Day	42% 7% 11% 28% 10% 2	4618
	11th to 20th	Day	29% 6% 12% 35% 17% 1	4971
	21st to end	Day	39% 9% 19% 22% 10% 1	5776
April	1st to 10th	Day	34% 6% 15% 25% 16% 4	2520
	11th to 20th	Day	31% 6% 13% 25% 20% 5%	2553
	21st to end	Day	28% 5% 12% 28% 23% 4	2730
May	1st to 10th	Day	21% 3 8% 20% 37% 10%	7626
	11th to 20th	Day	20% 4 6% 26% 34% 12%	7599
	21st to end	Day	18% 5% 10% 26% 30% 11%	8994
June	1st to 10th	Day	28% 6% 10% 25% 26% 5%	2940
	11th to 20th	Day	19% 4 8% 21% 35% 14%	2940
	21st to end	Day	13% 3 6% 17% 35% 26%	2940
July	1st to 10th	Day	10% 2 3 11% 24% 50%	8151
	11th to 20th	Day	11% 2 2 9% 23% 53%	8145
	21st to end	Day	13% 3 4 13% 30% 38%	8723
August	1st to 10th	Day	14% 2 3 9% 21% 50%	6026
	11th to 20th	Day	16% 3 6% 17% 31% 28%	5964
	21st to end	Day	19% 3 3 16% 34% 25%	6143
September	1st to 10th	Day	13% 3 5% 15% 32% 32%	2506
	11th to 20th	Day	18% 4 7% 25% 27% 18%	2310
	21st to end	Day	19% 3 6% 21% 36% 15%	2310
October	1st to 10th	Day	18% 3 6% 19% 39% 16%	3710
	11th to 20th	Day	24% 4 8% 31% 26% 6%	3281
	21st to end	Day	24% 5% 13% 32% 22% 4	3272
November	1st to 10th	Day	36% 7% 14% 28% 14% 2	1854
	11th to 20th	Day	37% 7% 20% 28% 7% 1	1890
	21st to end	Day	40% 7% 21% 27% 6%	1890
December	1st to 10th	Day	28% 9% 25% 33% 5%	2778
	11th to 20th	Day	48% 9% 22% 19% 2	3108
	21st to end	Day	51% 6% 17% 23% 3	4092
January	1st to 10th	Night	56% 9% 20% 13% 2	8172
	11th to 20th	Night	39% 8% 19% 26% 7%	8220
	21st to end	Night	36% 10% 17% 26% 10% 1	8994
February	1st to 10th	Night	45% 8% 20% 22% 4 1	2700
	11th to 20th	Night	38% 7% 19% 25% 10% 1	2459
	21st to end	Night	38% 6% 17% 26% 11% 1	2076
March	1st to 10th	Night	37% 6% 12% 30% 13% 1	5496
	11th to 20th	Night	35% 4 10% 30% 18% 2	5248
	21st to end	Night	36% 7% 18% 27% 10% 2	5436
April	1st to 10th	Night	37% 5% 12% 25% 17% 4	2100
	11th to 20th	Night	32% 5% 11% 25% 23% 4	2018
	21st to end	Night	29% 5% 11% 29% 23% 4	1890
May	1st to 10th	Night	21% 3 8% 20% 38% 11%	5319
	11th to 20th	Night	22% 4 6% 19% 37% 11%	5279
	21st to end	Night	21% 5% 9% 22% 34% 9%	5182
June	1st to 10th	Night	32% 5% 9% 22% 25% 7%	1680
	11th to 20th	Night	19% 4 8% 19% 35% 15%	1680
	21st to end	Night	14% 3 5% 16% 31% 31%	1680
July	1st to 10th	Night	11% 2 3 11% 20% 54%	4700
	11th to 20th	Night	12% 2 3 8% 19% 56%	4692
	21st to end	Night	16% 3 4 13% 30% 34%	5040
August	1st to 10th	Night	14% 2 3 7% 18% 55%	4114
	11th to 20th	Night	15% 4 6% 14% 26% 36%	4168
	21st to end	Night	21% 3 4 15% 30% 28%	5019
September	1st to 10th	Night	14% 3 4 12% 30% 37%	2112
	11th to 20th	Night	20% 4 6% 20% 26% 24%	2310
	21st to end	Night	18% 2 5% 21% 33% 21%	2310
October	1st to 10th	Night	17% 3 5% 15% 34% 26%	3710
	11th to 20th	Night	24% 3 6% 27% 34% 6%	4072
	21st to end	Night	29% 5% 10% 33% 21% 3	4704
November	1st to 10th	Night	36% 6% 12% 27% 18% 2	2665
	11th to 20th	Night	39% 6% 14% 30% 11%	2730
	21st to end	Night	37% 7% 17% 32% 7%	2730
December	1st to 10th	Night	29% 8% 26% 31% 5%	4618
	11th to 20th	Night	51% 9% 20% 19% 2	5316
	21st to end	Night	48% 9% 19% 18% 5%	7106

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	13% 16% 26% 28% 15% 2	220
	11th to 20th	Day	11% 8% 28% 29% 20% 4	220
	21st to end	Day	12% 7% 21% 36% 20% 3	242
February	1st to 10th	Day	14% 15% 30% 22% 16% 3	368
	11th to 20th	Day	13% 13% 33% 25% 14% 2	535
	21st to end	Day	13% 16% 31% 29% 10% 1	446
March	1st to 10th	Day	12% 15% 33% 28% 11% 1	540
	11th to 20th	Day	10% 12% 30% 31% 14% 3	540
	21st to end	Day	11% 14% 32% 28% 13% 2	594
April	1st to 10th	Day	12% 15% 23% 27% 16% 7%	540
	11th to 20th	Day	10% 15% 32% 27% 11% 5%	532
	21st to end	Day	8% 15% 32% 24% 16% 5%	540
May	1st to 10th	Day	5% 14% 27% 30% 16% 7%	543
	11th to 20th	Day	11% 11% 23% 29% 20% 6%	568
	21st to end	Day	8% 8% 18% 29% 23% 13%	617
June	1st to 10th	Day	5% 8% 25% 27% 23% 12%	570
	11th to 20th	Day	6% 9% 28% 31% 19% 8%	570
	21st to end	Day	3 6% 25% 33% 24% 10%	570
July	1st to 10th	Day	1 2 23% 34% 29% 10%	566
	11th to 20th	Day	1 3 21% 34% 29% 12%	564
	21st to end	Day	3 2 14% 34% 35% 12%	619
August	1st to 10th	Day	4 3 18% 33% 30% 12%	567
	11th to 20th	Day	2 4 15% 32% 29% 17%	557
	21st to end	Day	4 5% 18% 29% 28% 17%	627
September	1st to 10th	Day	3 4 18% 23% 36% 16%	570
	11th to 20th	Day	6% 5% 17% 29% 30% 12%	570
	21st to end	Day	5% 7% 20% 30% 28% 10%	570
October	1st to 10th	Day	5% 8% 17% 27% 27% 16%	570
	11th to 20th	Day	9% 9% 22% 25% 25% 10%	432
	21st to end	Day	11% 6% 22% 36% 19% 5%	387
November	1st to 10th	Day	14% 9% 23% 30% 22% 2	330
	11th to 20th	Day	12% 7% 29% 30% 18% 5%	330
	21st to end	Day	13% 9% 21% 35% 19% 4	330
December	1st to 10th	Day	15% 7% 18% 32% 18% 9%	247
	11th to 20th	Day	16% 12% 27% 28% 11% 5%	220
	21st to end	Day	17% 8% 26% 31% 12% 5%	242
January	1st to 10th	Night	15% 8% 25% 35% 16% 2	840
	11th to 20th	Night	13% 5% 25% 36% 19% 2	840
	21st to end	Night	13% 6% 21% 38% 20% 2	924
February	1st to 10th	Night	17% 7% 26% 36% 13% 1	840
	11th to 20th	Night	12% 6% 27% 40% 14% 1	824
	21st to end	Night	12% 6% 33% 36% 12%	692
March	1st to 10th	Night	11% 8% 33% 36% 11% 1	840
	11th to 20th	Night	10% 8% 25% 40% 16% 2	840
	21st to end	Night	12% 10% 24% 39% 13% 1	924
April	1st to 10th	Night	11% 7% 24% 39% 17% 2	840
	11th to 20th	Night	9% 9% 28% 37% 15% 2	770
	21st to end	Night	7% 7% 29% 40% 15% 1	630
May	1st to 10th	Night	8% 9% 28% 36% 17% 2	630
	11th to 20th	Night	8% 8% 22% 37% 22% 3	616
	21st to end	Night	8% 5% 22% 33% 29% 3	455
June	1st to 10th	Night	6% 6% 18% 40% 26% 3	420
	11th to 20th	Night	6% 7% 24% 40% 22% 2	420
	21st to end	Night	2 2 23% 47% 25% 1	420
July	1st to 10th	Night	2 1 16% 54% 26% 1	410
	11th to 20th	Night	2 2 16% 54% 25%	408
	21st to end	Night	2 2 9% 54% 32% 2	460
August	1st to 10th	Night	4 3 15% 50% 27% 1	597
	11th to 20th	Night	1 2 14% 51% 31% 1	624
	21st to end	Night	3 4 15% 43% 32% 3	888
September	1st to 10th	Night	4 2 12% 45% 33% 5%	840
	11th to 20th	Night	5% 3 12% 40% 35% 5%	840
	21st to end	Night	7% 4 16% 37% 29% 7%	840
October	1st to 10th	Night	8% 5% 17% 41% 27% 3	840
	11th to 20th	Night	8% 6% 19% 38% 25% 4	840
	21st to end	Night	7% 6% 22% 39% 22% 4	912
November	1st to 10th	Night	11% 6% 20% 39% 22% 2	820
	11th to 20th	Night	15% 7% 22% 39% 16% 1	840
	21st to end	Night	11% 5% 23% 39% 20% 3	840
December	1st to 10th	Night	14% 6% 23% 38% 18% 2	840
	11th to 20th	Night	19% 7% 21% 36% 15% 2	840
	21st to end	Night	21% 9% 27% 32% 10% 1	924

Page generated at 2026-10-26 02:37:49. Version ac07

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