Battle Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Battle Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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 5% 2 5% 4 4 4 3 5% 7% 57%	104988
	Night	4 7% 2 6% 4 4 4 4 6% 8% 51%	102720
Transparency	Day	25% 7% 10% 17% 20% 22%	104732
	Night	29% 8% 12% 17% 18% 16%	102566
Seeing	Day	5% 5% 16% 30% 28% 15%	14767
	Night	7% 3 14% 44% 28% 4	24197

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	4 13% 6% 12% 6% 5% 6% 5% 6% 9% 26%	2539
	11th to 20th	Day	5% 12% 5% 11% 9% 7% 5% 5% 7% 8% 27%	2540
	21st to end	Day	5% 13% 5% 10% 8% 8% 7% 7% 9% 9% 18%	2794
February	1st to 10th	Day	6% 7% 3 8% 5% 5% 5% 4 7% 11% 37%	1882
	11th to 20th	Day	3 9% 4 7% 7% 5% 5% 5% 8% 12% 35%	1850
	21st to end	Day	2 8% 3 8% 5% 3 4 4 8% 11% 41%	1570
March	1st to 10th	Day	4 11% 4 10% 6% 6% 7% 5% 8% 13% 26%	3138
	11th to 20th	Day	2 7% 3 6% 3 3 3 4 8% 14% 46%	3325
	21st to end	Day	4 11% 5% 10% 7% 6% 7% 5% 7% 8% 32%	4041
April	1st to 10th	Day	5% 11% 3 7% 5% 4 5% 4 7% 10% 40%	2280
	11th to 20th	Day	4 7% 2 6% 5% 5% 4 4 5% 8% 49%	2249
	21st to end	Day	7% 7% 2 5% 4 4 4 3 5% 8% 51%	2422
May	1st to 10th	Day	3 5% 2 5% 3 3 4 3 6% 10% 55%	4110
	11th to 20th	Day	3 3 1 3 3 3 3 3 4 6% 68%	4071
	21st to end	Day	4 4 1 4 3 3 3 3 5% 6% 62%	4750
June	1st to 10th	Day	4 3 1 4 4 4 4 4 5% 9% 58%	2660
	11th to 20th	Day	4 3 1 3 2 2 4 3 4 5% 69%	2660
	21st to end	Day	2 2 1 2 3 2 3 2 4 5% 76%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 3 3 85%	4420
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 6% 73%	4420
	21st to end	Day	2 2 1 3 2 3 4 4 4 6% 70%	4790
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 6% 71%	4097
	11th to 20th	Day	1 1 1 2 1 2 2 2 2 3 83%	3817
	21st to end	Day	2 2 1 2 1 2 2 2 2 3 83%	4180
September	1st to 10th	Day	2 2 1 2 1 2 2 2 3 4 79%	2280
	11th to 20th	Day	1 3 1 4 3 3 3 2 4 5% 71%	2113
	21st to end	Day	3 3 1 3 2 2 3 2 3 4 73%	2090
October	1st to 10th	Day	2 3 1 3 3 2 3 2 4 6% 71%	3490
	11th to 20th	Day	4 4 1 3 2 2 3 2 3 4 71%	3177
	21st to end	Day	2 4 1 4 3 4 3 3 6% 8% 60%	3101
November	1st to 10th	Day	6% 7% 2 5% 5% 4 4 4 6% 7% 49%	1710
	11th to 20th	Day	5% 5% 2 6% 4 4 5% 4 7% 9% 49%	1710
	21st to end	Day	5% 8% 2 6% 5% 4 4 4 6% 9% 48%	1710
December	1st to 10th	Day	6% 9% 3 8% 5% 3 5% 4 5% 9% 43%	1620
	11th to 20th	Day	5% 12% 4 9% 7% 6% 6% 5% 7% 11% 29%	1928
	21st to end	Day	5% 10% 4 10% 6% 6% 5% 5% 6% 9% 33%	2794
January	1st to 10th	Night	4 13% 5% 11% 6% 5% 6% 5% 8% 9% 29%	4406
	11th to 20th	Night	5% 10% 4 14% 8% 7% 6% 5% 7% 8% 25%	4420
	21st to end	Night	6% 14% 4 9% 6% 7% 7% 6% 11% 9% 21%	4862
February	1st to 10th	Night	5% 10% 4 7% 5% 5% 3 3 6% 11% 40%	2295
	11th to 20th	Night	4 8% 4 8% 5% 4 5% 5% 7% 10% 40%	2218
	21st to end	Night	2 8% 4 9% 5% 5% 5% 4 8% 9% 39%	1884
March	1st to 10th	Night	3 12% 4 11% 5% 5% 6% 6% 9% 12% 27%	3736
	11th to 20th	Night	3 7% 4 7% 4 4 4 3 6% 12% 46%	3655
	21st to end	Night	6% 10% 3 7% 6% 5% 5% 4 6% 10% 37%	3595
April	1st to 10th	Night	4 9% 2 6% 5% 5% 5% 4 5% 10% 43%	1900
	11th to 20th	Night	5% 8% 2 5% 5% 4 4 4 6% 7% 52%	1879
	21st to end	Night	8% 8% 2 4 4 4 4 4 5% 7% 50%	1755
May	1st to 10th	Night	6% 7% 2 6% 4 3 3 3 5% 6% 54%	2860
	11th to 20th	Night	4 3 1 4 3 3 3 3 4 6% 67%	2834
	21st to end	Night	5% 4 2 6% 4 4 5% 3 5% 7% 55%	2810
June	1st to 10th	Night	4 3 1 4 4 4 5% 5% 5% 7% 57%	1520
	11th to 20th	Night	5% 3 1 3 3 3 3 3 3 6% 68%	1520
	21st to end	Night	1 2 1 3 3 2 4 3 5% 5% 72%	1520
July	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 80%	2540
	11th to 20th	Night	3 3 2 4 3 4 4 4 7% 6% 60%	2540
	21st to end	Night	4 3 2 4 4 5% 5% 4 6% 6% 58%	2761
August	1st to 10th	Night	3 3 1 4 3 3 4 3 5% 6% 64%	2839
	11th to 20th	Night	3 3 1 3 2 3 3 2 3 4 75%	3026
	21st to end	Night	2 3 1 3 2 2 2 2 3 3 78%	3498
September	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 74%	1900
	11th to 20th	Night	4 3 1 3 3 4 3 2 4 5% 69%	2066
	21st to end	Night	4 2 1 3 2 2 2 2 3 5% 74%	2090
October	1st to 10th	Night	3 3 1 2 2 3 2 2 4 4 73%	3490
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 5% 68%	3742
	21st to end	Night	3 3 1 5% 3 4 4 3 4 6% 64%	4457
November	1st to 10th	Night	6% 7% 2 5% 4 4 4 4 6% 7% 51%	2469
	11th to 20th	Night	5% 6% 2 5% 4 4 4 4 6% 7% 53%	2470
	21st to end	Night	4 7% 3 6% 5% 5% 4 4 5% 9% 48%	2470
December	1st to 10th	Night	6% 8% 3 8% 4 5% 5% 3 7% 7% 43%	2555
	11th to 20th	Night	6% 11% 4 9% 6% 5% 6% 5% 8% 11% 29%	3276
	21st to end	Night	6% 10% 4 10% 7% 6% 6% 5% 8% 10% 26%	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	47% 14% 17% 18% 4	2539
	11th to 20th	Day	47% 15% 19% 12% 6% 1	2540
	21st to end	Day	47% 22% 17% 9% 5% 1	2794
February	1st to 10th	Day	38% 11% 17% 24% 8% 1	1882
	11th to 20th	Day	38% 9% 18% 22% 12% 1	1860
	21st to end	Day	33% 10% 20% 25% 10% 2	1570
March	1st to 10th	Day	39% 14% 18% 20% 8% 1	3138
	11th to 20th	Day	25% 13% 24% 25% 11% 1	3325
	21st to end	Day	42% 14% 15% 18% 8% 2	4041
April	1st to 10th	Day	38% 6% 16% 22% 14% 4	2280
	11th to 20th	Day	31% 7% 13% 26% 18% 4	2252
	21st to end	Day	29% 6% 15% 28% 19% 3	2422
May	1st to 10th	Day	22% 8% 15% 26% 23% 7%	4110
	11th to 20th	Day	18% 4 9% 20% 38% 10%	4074
	21st to end	Day	21% 6% 9% 25% 34% 5%	4750
June	1st to 10th	Day	23% 6% 10% 20% 27% 13%	2660
	11th to 20th	Day	17% 4 6% 14% 33% 26%	2660
	21st to end	Day	12% 2 4 11% 27% 43%	2660
July	1st to 10th	Day	7% 1 3 5% 13% 70%	4351
	11th to 20th	Day	14% 3 2 6% 15% 60%	4345
	21st to end	Day	14% 4 4 8% 24% 45%	4639
August	1st to 10th	Day	15% 2 3 8% 19% 53%	4082
	11th to 20th	Day	9% 2 3 6% 17% 64%	3856
	21st to end	Day	10% 1 2 8% 28% 50%	4179
September	1st to 10th	Day	11% 3 3 8% 28% 47%	2280
	11th to 20th	Day	16% 4 6% 14% 28% 31%	2113
	21st to end	Day	16% 2 5% 16% 31% 31%	2090
October	1st to 10th	Day	17% 3 5% 11% 32% 33%	3490
	11th to 20th	Day	18% 3 5% 20% 36% 18%	3177
	21st to end	Day	22% 4 7% 31% 25% 11%	3101
November	1st to 10th	Day	31% 8% 11% 22% 21% 6%	1710
	11th to 20th	Day	29% 7% 15% 29% 19% 2	1710
	21st to end	Day	33% 7% 15% 26% 17% 3	1710
December	1st to 10th	Day	37% 8% 18% 23% 12% 3	1620
	11th to 20th	Day	45% 13% 15% 16% 10% 1	1928
	21st to end	Day	43% 10% 18% 18% 10% 1	2794
January	1st to 10th	Night	44% 15% 18% 17% 5% 1	4406
	11th to 20th	Night	50% 14% 19% 9% 6% 1	4420
	21st to end	Night	43% 21% 18% 11% 5% 1	4862
February	1st to 10th	Night	38% 7% 17% 27% 9% 1	2295
	11th to 20th	Night	35% 9% 17% 24% 13% 1	2219
	21st to end	Night	35% 9% 18% 25% 11% 2	1884
March	1st to 10th	Night	40% 14% 18% 19% 9% 2	3736
	11th to 20th	Night	29% 11% 22% 24% 14% 2	3655
	21st to end	Night	35% 13% 23% 22% 6% 2	3595
April	1st to 10th	Night	34% 7% 19% 22% 14% 3	1900
	11th to 20th	Night	30% 7% 15% 29% 15% 5%	1879
	21st to end	Night	31% 7% 13% 26% 19% 4	1755
May	1st to 10th	Night	26% 9% 13% 20% 25% 7%	2860
	11th to 20th	Night	18% 5% 8% 20% 38% 10%	2835
	21st to end	Night	25% 7% 12% 22% 30% 5%	2810
June	1st to 10th	Night	23% 8% 11% 19% 27% 12%	1520
	11th to 20th	Night	19% 3 5% 16% 34% 23%	1520
	21st to end	Night	14% 3 6% 10% 27% 41%	1520
July	1st to 10th	Night	11% 2 3 4 13% 67%	2500
	11th to 20th	Night	22% 4 4 6% 14% 49%	2492
	21st to end	Night	26% 4 5% 9% 19% 39%	2674
August	1st to 10th	Night	22% 3 5% 8% 14% 48%	2831
	11th to 20th	Night	16% 2 3 5% 15% 58%	3053
	21st to end	Night	14% 2 3 7% 20% 54%	3498
September	1st to 10th	Night	14% 3 4 7% 24% 47%	1900
	11th to 20th	Night	19% 3 5% 12% 25% 35%	2066
	21st to end	Night	16% 2 4 13% 27% 38%	2090
October	1st to 10th	Night	17% 2 3 11% 32% 35%	3490
	11th to 20th	Night	20% 3 4 14% 38% 21%	3742
	21st to end	Night	21% 3 6% 27% 33% 10%	4457
November	1st to 10th	Night	30% 6% 13% 20% 22% 8%	2469
	11th to 20th	Night	27% 6% 14% 27% 23% 3	2470
	21st to end	Night	31% 6% 14% 26% 20% 3	2470
December	1st to 10th	Night	37% 9% 15% 21% 13% 4	2555
	11th to 20th	Night	43% 10% 19% 19% 6% 2	3276
	21st to end	Night	45% 13% 18% 17% 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	9% 3 17% 37% 26% 8%	180
	11th to 20th	Day	6% 5% 10% 33% 31% 15%	180
	21st to end	Day	4 10% 34% 33% 19%	198
February	1st to 10th	Day	7% 3 17% 38% 25% 10%	451
	11th to 20th	Day	8% 5% 19% 37% 27% 5%	455
	21st to end	Day	4 5% 23% 38% 24% 6%	382
March	1st to 10th	Day	8% 7% 17% 38% 25% 4	460
	11th to 20th	Day	7% 6% 22% 33% 25% 7%	460
	21st to end	Day	7% 10% 21% 37% 21% 5%	506
April	1st to 10th	Day	8% 9% 16% 34% 22% 11%	460
	11th to 20th	Day	7% 8% 18% 36% 24% 7%	452
	21st to end	Day	8% 8% 15% 30% 26% 12%	460
May	1st to 10th	Day	5% 7% 20% 35% 23% 10%	463
	11th to 20th	Day	10% 6% 17% 24% 27% 17%	488
	21st to end	Day	8% 7% 15% 23% 28% 19%	529
June	1st to 10th	Day	4 6% 18% 26% 27% 19%	490
	11th to 20th	Day	5% 9% 21% 29% 22% 14%	490
	21st to end	Day	2 4 17% 32% 29% 18%	490
July	1st to 10th	Day	1 3 17% 31% 29% 19%	486
	11th to 20th	Day	2 3 13% 32% 30% 21%	484
	21st to end	Day	3 1 13% 26% 35% 23%	531
August	1st to 10th	Day	4 5% 13% 24% 32% 22%	487
	11th to 20th	Day	2 3 16% 27% 29% 23%	477
	21st to end	Day	3 3 13% 26% 35% 20%	539
September	1st to 10th	Day	2 2 16% 22% 33% 26%	490
	11th to 20th	Day	3 6% 15% 25% 30% 21%	490
	21st to end	Day	3 4 14% 27% 34% 18%	490
October	1st to 10th	Day	4 6% 16% 22% 30% 22%	490
	11th to 20th	Day	4 6% 15% 21% 35% 19%	451
	21st to end	Day	5% 4 16% 33% 29% 14%	330
November	1st to 10th	Day	10% 5% 16% 30% 28% 12%	282
	11th to 20th	Day	4 4 9% 34% 34% 15%	270
	21st to end	Day	8% 3 16% 29% 33% 12%	270
December	1st to 10th	Day	6% 2 16% 32% 28% 16%	228
	11th to 20th	Day	9% 2 13% 34% 32% 9%	180
	21st to end	Day	9% 3 15% 38% 23% 12%	198
January	1st to 10th	Night	8% 5% 16% 41% 25% 4	760
	11th to 20th	Night	9% 3 14% 43% 28% 4	760
	21st to end	Night	10% 3 12% 44% 24% 6%	836
February	1st to 10th	Night	8% 3 17% 44% 24% 3	760
	11th to 20th	Night	8% 2 16% 51% 22% 2	744
	21st to end	Night	5% 3 23% 48% 20% 2	628
March	1st to 10th	Night	8% 4 19% 46% 20% 2	760
	11th to 20th	Night	6% 3 15% 48% 25% 3	760
	21st to end	Night	9% 6% 21% 44% 18% 1	836
April	1st to 10th	Night	9% 5% 20% 44% 21% 2	760
	11th to 20th	Night	8% 5% 19% 43% 21% 4	751
	21st to end	Night	11% 5% 13% 40% 26% 4	615
May	1st to 10th	Night	6% 4 19% 43% 25% 2	570
	11th to 20th	Night	8% 4 14% 38% 32% 4	561
	21st to end	Night	9% 3 14% 37% 31% 5%	447
June	1st to 10th	Night	6% 2 14% 43% 31% 4	380
	11th to 20th	Night	6% 3 14% 46% 32% 1	380
	21st to end	Night	3 1 12% 54% 27% 3	380
July	1st to 10th	Night	3 2 7% 50% 37% 1	370
	11th to 20th	Night	2 9% 52% 36% 1	368
	21st to end	Night	4 2 6% 45% 40% 2	416
August	1st to 10th	Night	4 3 9% 48% 34% 1	559
	11th to 20th	Night	3 2 8% 47% 35% 5%	688
	21st to end	Night	3 1 7% 44% 41% 4	836
September	1st to 10th	Night	4 1 7% 43% 40% 5%	760
	11th to 20th	Night	5% 2 9% 38% 37% 9%	760
	21st to end	Night	5% 2 10% 38% 36% 9%	760
October	1st to 10th	Night	8% 1 11% 43% 33% 5%	760
	11th to 20th	Night	5% 2 12% 42% 33% 5%	760
	21st to end	Night	5% 2 14% 45% 28% 6%	836
November	1st to 10th	Night	8% 2 14% 44% 29% 4	760
	11th to 20th	Night	8% 2 12% 50% 23% 4	760
	21st to end	Night	6% 3 17% 42% 27% 5%	760
December	1st to 10th	Night	9% 3 16% 47% 20% 5%	760
	11th to 20th	Night	12% 4 14% 44% 23% 3	760
	21st to end	Night	13% 6% 19% 44% 15% 3	836

Page generated at 2024-11-02 23:11:18. Version ac07

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