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 2025-07-06.

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% 6% 2 5% 4 4 4 3 5% 6% 56%	123481
	Night	7% 7% 2 6% 4 4 4 3 5% 7% 51%	124107
Transparency	Day	27% 5% 11% 21% 21% 15%	123226
	Night	32% 6% 12% 21% 18% 11%	123950
Seeing	Day	8% 9% 24% 29% 22% 8%	15327
	Night	10% 6% 22% 39% 21% 2	24722

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 10% 6% 5% 6% 5% 6% 7% 27%	3639
	11th to 20th	Day	7% 11% 3 10% 5% 5% 5% 3 5% 6% 39%	3640
	21st to end	Day	9% 9% 2 7% 5% 5% 4 4 4 6% 45%	4004
February	1st to 10th	Day	9% 10% 3 8% 5% 5% 4 4 7% 7% 39%	1821
	11th to 20th	Day	8% 10% 3 7% 5% 5% 4 4 5% 7% 40%	1950
	21st to end	Day	5% 11% 4 7% 5% 4 5% 4 6% 9% 40%	1650
March	1st to 10th	Day	6% 9% 4 10% 6% 6% 5% 4 5% 7% 38%	4518
	11th to 20th	Day	5% 7% 3 6% 4 3 4 4 5% 6% 53%	4864
	21st to end	Day	6% 8% 3 8% 6% 6% 6% 5% 7% 8% 37%	5651
April	1st to 10th	Day	7% 7% 3 5% 5% 4 5% 4 7% 9% 44%	2400
	11th to 20th	Day	4 7% 2 6% 5% 3 4 3 7% 7% 51%	2427
	21st to end	Day	6% 5% 2 4 4 5% 4 4 6% 8% 52%	2600
May	1st to 10th	Day	5% 6% 2 5% 3 4 3 3 4 6% 58%	5880
	11th to 20th	Day	4 3 2 4 3 3 4 3 4 6% 64%	5841
	21st to end	Day	3 3 1 3 3 3 4 3 6% 7% 63%	6902
June	1st to 10th	Day	5% 5% 1 5% 4 4 4 4 6% 8% 53%	2800
	11th to 20th	Day	4 4 1 3 3 3 4 3 5% 6% 65%	2800
	21st to end	Day	2 2 1 3 2 2 2 3 5% 6% 74%	2800
July	1st to 10th	Day	1 1 2 2 2 2 2 3 4 82%	4491
	11th to 20th	Day	2 1 1 2 2 2 3 3 3 5% 76%	4420
	21st to end	Day	2 2 1 3 2 3 3 2 4 5% 73%	4790
August	1st to 10th	Day	3 3 1 4 3 3 3 4 5% 7% 65%	4128
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 4 79%	4028
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4221
September	1st to 10th	Day	2 2 1 1 2 2 2 3 3 5% 77%	2268
	11th to 20th	Day	4 3 1 4 3 3 3 3 4 5% 68%	2090
	21st to end	Day	5% 3 1 3 2 2 2 3 3 5% 70%	2090
October	1st to 10th	Day	3 3 1 4 3 2 2 2 3 4 71%	3490
	11th to 20th	Day	4 5% 2 4 3 3 3 3 4 7% 62%	3085
	21st to end	Day	4 4 2 4 3 4 4 4 6% 9% 57%	3101
November	1st to 10th	Day	9% 7% 2 6% 5% 4 4 4 5% 9% 46%	1764
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 43%	1800
	21st to end	Day	9% 9% 3 7% 4 4 4 4 6% 8% 41%	1800
December	1st to 10th	Day	7% 5% 2 5% 3 3 3 3 6% 8% 55%	2696
	11th to 20th	Day	13% 10% 3 9% 5% 5% 5% 4 7% 8% 31%	3028
	21st to end	Day	12% 11% 5% 10% 6% 4 5% 4 6% 6% 32%	4004
January	1st to 10th	Night	11% 14% 5% 12% 6% 5% 5% 4 6% 7% 26%	6306
	11th to 20th	Night	10% 13% 4 10% 6% 5% 4 3 4 6% 35%	6320
	21st to end	Night	8% 8% 3 9% 4 4 4 3 5% 6% 46%	6952
February	1st to 10th	Night	13% 10% 3 7% 5% 5% 4 5% 6% 7% 36%	2572
	11th to 20th	Night	9% 8% 3 7% 4 4 5% 4 6% 7% 45%	2338
	21st to end	Night	7% 11% 2 5% 4 4 5% 4 7% 8% 42%	1980
March	1st to 10th	Night	8% 9% 3 7% 5% 4 4 4 5% 7% 43%	5376
	11th to 20th	Night	8% 7% 3 7% 5% 4 4 4 5% 6% 48%	5135
	21st to end	Night	6% 7% 3 7% 5% 5% 5% 4 6% 9% 43%	5319
April	1st to 10th	Night	8% 7% 2 6% 5% 5% 5% 4 6% 6% 45%	2000
	11th to 20th	Night	7% 7% 2 5% 5% 4 5% 4 6% 7% 50%	1921
	21st to end	Night	6% 5% 2 6% 4 4 4 3 7% 9% 51%	1800
May	1st to 10th	Night	8% 6% 2 5% 3 3 3 3 5% 6% 57%	4100
	11th to 20th	Night	5% 5% 2 6% 4 3 4 3 5% 7% 55%	4056
	21st to end	Night	3 4 1 3 3 3 3 3 4 6% 66%	3972
June	1st to 10th	Night	5% 5% 2 6% 5% 6% 5% 4 6% 7% 51%	1600
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 7% 64%	1600
	21st to end	Night	1 2 2 2 3 3 3 4 6% 73%	1600
July	1st to 10th	Night	1 1 2 2 2 3 2 3 4 81%	2580
	11th to 20th	Night	1 1 2 2 2 3 3 4 4 77%	2540
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 68%	2761
August	1st to 10th	Night	4 3 1 4 2 3 4 3 6% 7% 63%	2807
	11th to 20th	Night	1 1 1 1 2 3 3 3 5% 78%	2811
	21st to end	Night	2 3 1 3 2 2 2 2 3 4 77%	3452
September	1st to 10th	Night	2 2 1 2 2 2 2 2 4 4 75%	1910
	11th to 20th	Night	4 3 1 3 3 3 4 3 4 6% 66%	2090
	21st to end	Night	6% 2 1 3 2 3 2 2 4 5% 71%	2090
October	1st to 10th	Night	4 3 1 4 2 2 3 2 4 4 72%	3490
	11th to 20th	Night	5% 4 2 4 3 3 3 3 5% 5% 63%	3828
	21st to end	Night	6% 4 2 6% 5% 3 5% 4 5% 7% 54%	4457
November	1st to 10th	Night	10% 7% 2 7% 4 4 4 4 5% 6% 48%	2535
	11th to 20th	Night	12% 7% 3 7% 4 4 4 4 5% 8% 43%	2600
	21st to end	Night	8% 7% 2 6% 5% 5% 5% 4 5% 7% 46%	2600
December	1st to 10th	Night	7% 6% 2 5% 3 3 3 3 5% 11% 52%	4481
	11th to 20th	Night	13% 12% 4 9% 5% 4 5% 4 6% 9% 28%	5176
	21st to end	Night	12% 9% 3 9% 5% 6% 6% 4 6% 8% 32%	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	52% 11% 20% 15% 2	3639
	11th to 20th	Day	43% 9% 19% 23% 5%	3640
	21st to end	Day	40% 8% 17% 24% 10%	4004
February	1st to 10th	Day	43% 7% 20% 22% 6% 1	1821
	11th to 20th	Day	42% 8% 18% 23% 9% 1	1960
	21st to end	Day	41% 6% 17% 24% 11% 1	1650
March	1st to 10th	Day	42% 7% 11% 27% 10% 2	4518
	11th to 20th	Day	30% 6% 12% 35% 17% 1	4864
	21st to end	Day	40% 9% 19% 21% 10% 1	5651
April	1st to 10th	Day	35% 6% 16% 24% 16% 4	2400
	11th to 20th	Day	30% 6% 13% 26% 20% 5%	2430
	21st to end	Day	29% 5% 12% 28% 22% 4	2600
May	1st to 10th	Day	25% 4 10% 21% 32% 8%	5880
	11th to 20th	Day	21% 4 7% 26% 31% 11%	5844
	21st to end	Day	19% 4 11% 26% 29% 11%	6904
June	1st to 10th	Day	28% 6% 11% 25% 26% 5%	2800
	11th to 20th	Day	19% 4 8% 21% 34% 13%	2800
	21st to end	Day	13% 3 5% 17% 35% 27%	2800
July	1st to 10th	Day	8% 2 3 9% 18% 60%	4422
	11th to 20th	Day	11% 2 3 8% 19% 58%	4345
	21st to end	Day	13% 2 4 8% 28% 45%	4639
August	1st to 10th	Day	19% 3 4 12% 24% 38%	4112
	11th to 20th	Day	10% 2 4 12% 35% 38%	4067
	21st to end	Day	13% 2 3 12% 37% 34%	4220
September	1st to 10th	Day	12% 3 5% 13% 33% 34%	2268
	11th to 20th	Day	19% 4 7% 24% 26% 20%	2090
	21st to end	Day	19% 2 6% 21% 37% 15%	2090
October	1st to 10th	Day	18% 3 6% 18% 39% 16%	3490
	11th to 20th	Day	24% 4 9% 31% 26% 6%	3085
	21st to end	Day	24% 5% 12% 31% 23% 4	3101
November	1st to 10th	Day	36% 7% 14% 27% 14% 2	1764
	11th to 20th	Day	37% 7% 20% 28% 7% 1	1800
	21st to end	Day	40% 7% 20% 27% 6%	1800
December	1st to 10th	Day	27% 9% 25% 33% 5%	2696
	11th to 20th	Day	48% 10% 22% 18% 1	3028
	21st to end	Day	51% 6% 17% 22% 3	4004
January	1st to 10th	Night	55% 9% 19% 14% 2	6306
	11th to 20th	Night	49% 8% 17% 21% 6%	6320
	21st to end	Night	39% 8% 15% 25% 11% 1	6952
February	1st to 10th	Night	46% 8% 19% 22% 4 1	2572
	11th to 20th	Night	37% 7% 19% 25% 11% 1	2339
	21st to end	Night	38% 7% 17% 26% 11% 1	1980
March	1st to 10th	Night	37% 6% 12% 30% 14% 1	5376
	11th to 20th	Night	35% 5% 10% 30% 18% 2	5135
	21st to end	Night	36% 7% 18% 27% 10% 2	5319
April	1st to 10th	Night	38% 5% 13% 24% 17% 4	2000
	11th to 20th	Night	32% 5% 11% 25% 23% 4	1921
	21st to end	Night	29% 5% 12% 29% 22% 4	1800
May	1st to 10th	Night	26% 4 10% 20% 33% 8%	4097
	11th to 20th	Night	26% 4 8% 20% 32% 10%	4057
	21st to end	Night	20% 4 8% 22% 35% 10%	3972
June	1st to 10th	Night	32% 6% 10% 23% 25% 5%	1600
	11th to 20th	Night	20% 4 9% 20% 35% 13%	1600
	21st to end	Night	12% 3 6% 16% 31% 31%	1600
July	1st to 10th	Night	9% 2 3 7% 19% 61%	2540
	11th to 20th	Night	11% 2 2 7% 16% 62%	2492
	21st to end	Night	15% 3 3 8% 28% 43%	2674
August	1st to 10th	Night	20% 3 4 10% 21% 42%	2799
	11th to 20th	Night	9% 2 4 11% 29% 45%	2838
	21st to end	Night	14% 1 3 11% 32% 38%	3452
September	1st to 10th	Night	13% 3 4 11% 31% 39%	1910
	11th to 20th	Night	20% 4 6% 19% 26% 26%	2090
	21st to end	Night	18% 2 5% 21% 33% 21%	2090
October	1st to 10th	Night	17% 3 5% 15% 34% 26%	3490
	11th to 20th	Night	23% 3 6% 27% 33% 6%	3828
	21st to end	Night	29% 5% 10% 32% 21% 3	4457
November	1st to 10th	Night	36% 6% 11% 26% 18% 2	2535
	11th to 20th	Night	38% 6% 13% 30% 12% 1	2600
	21st to end	Night	37% 6% 16% 33% 8%	2600
December	1st to 10th	Night	29% 8% 26% 31% 5%	4481
	11th to 20th	Night	51% 9% 20% 18% 1	5176
	21st to end	Night	48% 9% 19% 18% 5%	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	14% 16% 27% 30% 13% 2	200
	11th to 20th	Day	12% 9% 31% 28% 18% 3	200
	21st to end	Day	13% 7% 22% 34% 20% 4	220
February	1st to 10th	Day	15% 15% 31% 23% 15% 1	336
	11th to 20th	Day	13% 12% 33% 24% 15% 2	495
	21st to end	Day	12% 16% 30% 29% 11% 1	414
March	1st to 10th	Day	11% 15% 33% 28% 12% 2	500
	11th to 20th	Day	10% 12% 30% 31% 14% 3	500
	21st to end	Day	11% 14% 33% 27% 12% 2	550
April	1st to 10th	Day	13% 16% 23% 26% 16% 6%	500
	11th to 20th	Day	11% 14% 33% 26% 11% 5%	492
	21st to end	Day	9% 15% 31% 25% 16% 4	500
May	1st to 10th	Day	6% 14% 29% 29% 16% 7%	503
	11th to 20th	Day	12% 11% 22% 29% 21% 6%	528
	21st to end	Day	8% 8% 16% 30% 24% 14%	573
June	1st to 10th	Day	6% 6% 24% 28% 24% 12%	530
	11th to 20th	Day	6% 9% 29% 31% 18% 7%	530
	21st to end	Day	3 6% 24% 34% 24% 10%	530
July	1st to 10th	Day	1 3 23% 34% 28% 10%	507
	11th to 20th	Day	1 3 22% 34% 28% 12%	484
	21st to end	Day	2 2 13% 34% 37% 11%	531
August	1st to 10th	Day	5% 3 17% 33% 31% 11%	487
	11th to 20th	Day	2 4 15% 31% 31% 18%	477
	21st to end	Day	2 5% 18% 28% 30% 17%	539
September	1st to 10th	Day	3 3 17% 22% 38% 17%	490
	11th to 20th	Day	8% 5% 16% 29% 31% 12%	490
	21st to end	Day	6% 7% 20% 29% 28% 10%	490
October	1st to 10th	Day	6% 8% 17% 29% 28% 14%	490
	11th to 20th	Day	8% 8% 22% 25% 25% 11%	366
	21st to end	Day	10% 6% 23% 37% 18% 5%	330
November	1st to 10th	Day	14% 9% 23% 29% 22% 2	300
	11th to 20th	Day	12% 8% 31% 29% 16% 4	300
	21st to end	Day	14% 8% 20% 34% 19% 4	300
December	1st to 10th	Day	16% 7% 18% 32% 17% 10%	225
	11th to 20th	Day	16% 13% 30% 28% 10% 5%	200
	21st to end	Day	17% 7% 26% 32% 12% 5%	220
January	1st to 10th	Night	15% 8% 25% 35% 16% 2	800
	11th to 20th	Night	14% 5% 26% 36% 17% 2	800
	21st to end	Night	13% 6% 21% 37% 20% 3	880
February	1st to 10th	Night	18% 8% 27% 35% 12%	800
	11th to 20th	Night	12% 6% 27% 40% 15% 1	784
	21st to end	Night	12% 6% 33% 36% 13%	660
March	1st to 10th	Night	11% 8% 34% 36% 11% 1	800
	11th to 20th	Night	11% 8% 25% 39% 17% 2	800
	21st to end	Night	13% 10% 25% 38% 14% 1	880
April	1st to 10th	Night	11% 7% 25% 39% 16% 2	800
	11th to 20th	Night	9% 9% 28% 36% 15% 2	733
	21st to end	Night	7% 7% 30% 39% 16% 2	600
May	1st to 10th	Night	9% 9% 28% 36% 17% 2	600
	11th to 20th	Night	8% 7% 21% 38% 23% 3	586
	21st to end	Night	9% 6% 20% 33% 29% 3	433
June	1st to 10th	Night	6% 6% 18% 40% 27% 3	400
	11th to 20th	Night	6% 7% 24% 39% 22% 2	400
	21st to end	Night	1 3 24% 46% 26% 1	400
July	1st to 10th	Night	2 1 16% 54% 26% 1	380
	11th to 20th	Night	2 2 17% 53% 26%	368
	21st to end	Night	2 1 9% 53% 32% 2	416
August	1st to 10th	Night	5% 3 14% 49% 28% 1	539
	11th to 20th	Night	1 2 14% 50% 32% 1	564
	21st to end	Night	2 3 15% 42% 33% 4	803
September	1st to 10th	Night	3 2 12% 45% 33% 5%	760
	11th to 20th	Night	6% 3 11% 39% 35% 6%	760
	21st to end	Night	7% 4 15% 36% 29% 8%	760
October	1st to 10th	Night	8% 5% 16% 41% 26% 3	760
	11th to 20th	Night	8% 5% 18% 38% 26% 5%	760
	21st to end	Night	7% 6% 23% 39% 21% 5%	836
November	1st to 10th	Night	11% 6% 20% 39% 21% 2	780
	11th to 20th	Night	15% 7% 23% 38% 15% 1	800
	21st to end	Night	12% 5% 23% 38% 19% 3	800
December	1st to 10th	Night	14% 6% 23% 37% 19% 2	800
	11th to 20th	Night	19% 7% 22% 36% 15% 2	800
	21st to end	Night	21% 9% 27% 33% 9% 1	880

Page generated at 2025-07-02 23:30:15. Version ac07

Copyright © 2025 Attilla Danko.