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 2024-01-15.

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	4 5% 2 5% 5% 3 4 4 5% 8% 55%	74872
	Night	5% 6% 3 5% 5% 3 4 5% 6% 8% 50%	74932
Transparency	Day	27% 6% 11% 18% 19% 18%	74576
	Night	30% 7% 13% 19% 17% 14%	74750
Seeing	Day	5% 5% 16% 30% 28% 15%	13641
	Night	7% 3 14% 44% 28% 4	23201

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	6% 10% 3 7% 8% 4 6% 6% 7% 11% 32%	1519
	11th to 20th	Day	5% 9% 4 7% 8% 5% 5% 5% 7% 9% 35%	1475
	21st to end	Day	4 9% 4 8% 10% 5% 7% 7% 7% 9% 30%	1584
February	1st to 10th	Day	6% 7% 4 6% 6% 4 6% 4 7% 12% 38%	1783
	11th to 20th	Day	4 8% 3 7% 7% 4 5% 5% 8% 13% 36%	1750
	21st to end	Day	3 7% 4 8% 6% 3 4 6% 8% 11% 42%	1480
March	1st to 10th	Day	6% 10% 4 7% 7% 4 5% 5% 7% 10% 36%	1800
	11th to 20th	Day	4 9% 4 6% 6% 3 5% 6% 9% 11% 37%	1880
	21st to end	Day	5% 8% 4 6% 7% 4 6% 5% 8% 8% 38%	2304
April	1st to 10th	Day	5% 11% 3 7% 6% 3 6% 5% 7% 10% 39%	2160
	11th to 20th	Day	5% 6% 3 6% 5% 3 4 5% 5% 8% 48%	2129
	21st to end	Day	7% 7% 2 4 4 3 4 4 5% 8% 52%	2294
May	1st to 10th	Day	4 4 2 3 4 3 5% 5% 7% 8% 55%	2340
	11th to 20th	Day	6% 5% 2 5% 5% 3 5% 6% 6% 8% 49%	2301
	21st to end	Day	7% 6% 2 5% 5% 3 5% 5% 6% 7% 48%	2686
June	1st to 10th	Day	4 3 2 3 4 2 4 5% 5% 9% 58%	2520
	11th to 20th	Day	4 2 1 3 3 2 3 4 4 5% 68%	2520
	21st to end	Day	2 2 1 2 3 2 2 3 4 5% 75%	2520
July	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 5% 75%	2520
	11th to 20th	Day	2 2 1 2 3 1 2 4 3 5% 74%	2520
	21st to end	Day	3 2 1 3 4 2 4 5% 5% 6% 65%	2741
August	1st to 10th	Day	4 2 1 4 3 2 3 4 4 6% 66%	2333
	11th to 20th	Day	1 2 1 2 3 2 3 3 3 5% 76%	2179
	21st to end	Day	1 1 1 2 1 3 2 3 4 80%	2376
September	1st to 10th	Day	2 2 1 1 2 1 2 3 3 4 79%	2160
	11th to 20th	Day	1 2 1 3 4 1 3 3 4 5% 72%	2002
	21st to end	Day	3 3 1 3 2 2 3 3 3 5% 72%	1980
October	1st to 10th	Day	4 4 1 4 5% 2 3 4 4 6% 62%	1980
	11th to 20th	Day	4 5% 1 3 3 2 4 3 4 6% 66%	1818
	21st to end	Day	3 3 1 3 3 3 3 4 5% 7% 64%	1782
November	1st to 10th	Day	6% 7% 2 5% 6% 3 4 5% 5% 7% 50%	1674
	11th to 20th	Day	5% 5% 2 6% 4 3 5% 4 7% 9% 50%	1710
	21st to end	Day	5% 8% 3 5% 6% 3 4 4 6% 9% 48%	1710
December	1st to 10th	Day	6% 7% 4 7% 6% 2 5% 5% 5% 8% 44%	1620
	11th to 20th	Day	5% 11% 4 8% 7% 4 6% 7% 7% 11% 29%	1928
	21st to end	Day	6% 9% 4 9% 8% 5% 6% 6% 6% 9% 33%	2794
January	1st to 10th	Night	5% 9% 4 8% 6% 4 5% 6% 7% 10% 35%	2646
	11th to 20th	Night	4 7% 3 8% 8% 4 6% 6% 9% 10% 35%	2590
	21st to end	Night	6% 12% 4 6% 6% 3 5% 6% 8% 10% 33%	2772
February	1st to 10th	Night	5% 9% 4 6% 5% 4 4 4 6% 12% 42%	2174
	11th to 20th	Night	4 7% 4 7% 5% 3 5% 5% 7% 10% 41%	2098
	21st to end	Night	3 7% 4 8% 6% 3 6% 6% 7% 9% 40%	1776
March	1st to 10th	Night	5% 10% 3 8% 6% 3 6% 6% 7% 10% 37%	2160
	11th to 20th	Night	3 6% 2 6% 5% 4 6% 6% 7% 11% 43%	2080
	21st to end	Night	7% 9% 3 5% 6% 3 5% 5% 6% 10% 42%	2048
April	1st to 10th	Night	5% 9% 3 5% 6% 3 6% 5% 5% 10% 43%	1800
	11th to 20th	Night	6% 7% 2 4 5% 3 4 4 6% 7% 53%	1779
	21st to end	Night	9% 7% 2 4 4 3 4 5% 5% 7% 51%	1663
May	1st to 10th	Night	6% 4 2 5% 5% 4 4 5% 6% 8% 54%	1620
	11th to 20th	Night	7% 5% 2 6% 5% 3 5% 5% 5% 9% 50%	1594
	21st to end	Night	9% 5% 2 5% 5% 3 5% 5% 6% 8% 48%	1586
June	1st to 10th	Night	4 3 1 4 4 3 6% 5% 5% 8% 57%	1440
	11th to 20th	Night	5% 3 2 3 3 2 3 3 3 6% 68%	1440
	21st to end	Night	1 2 1 2 3 2 4 4 4 6% 72%	1440
July	1st to 10th	Night	3 2 1 3 3 2 4 5% 5% 7% 65%	1440
	11th to 20th	Night	2 3 2 3 4 2 3 4 6% 6% 66%	1440
	21st to end	Night	4 3 1 4 3 3 4 4 6% 7% 61%	1576
August	1st to 10th	Night	4 4 2 4 4 2 4 5% 6% 7% 57%	1603
	11th to 20th	Night	3 3 1 3 3 3 3 4 3 6% 69%	1719
	21st to end	Night	2 2 2 2 2 3 3 4 5% 73%	1980
September	1st to 10th	Night	3 2 1 2 2 2 2 2 4 4 75%	1800
	11th to 20th	Night	4 3 1 3 3 2 3 3 4 5% 70%	1957
	21st to end	Night	4 2 1 2 3 2 2 3 3 5% 73%	1980
October	1st to 10th	Night	5% 4 2 3 4 2 3 3 4 4 65%	1980
	11th to 20th	Night	4 4 1 4 3 2 3 4 4 5% 65%	2139
	21st to end	Night	4 3 1 3 3 2 3 3 4 6% 67%	2574
November	1st to 10th	Night	7% 6% 2 4 4 3 4 5% 5% 8% 52%	2405
	11th to 20th	Night	6% 5% 2 4 5% 3 5% 4 6% 8% 54%	2470
	21st to end	Night	4 7% 3 6% 5% 4 4 5% 5% 9% 48%	2470
December	1st to 10th	Night	6% 8% 4 7% 5% 3 6% 4 6% 8% 43%	2555
	11th to 20th	Night	6% 10% 4 8% 6% 4 6% 7% 8% 11% 29%	3276
	21st to end	Night	7% 9% 5% 9% 9% 5% 6% 6% 8% 10% 27%	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	43% 11% 21% 20% 4 1	1519
	11th to 20th	Day	41% 13% 18% 16% 10% 2	1475
	21st to end	Day	46% 12% 17% 15% 8% 2	1584
February	1st to 10th	Day	37% 11% 17% 25% 8% 1	1783
	11th to 20th	Day	38% 8% 17% 23% 13% 1	1760
	21st to end	Day	34% 8% 20% 25% 11% 2	1480
March	1st to 10th	Day	41% 7% 17% 24% 9% 1	1800
	11th to 20th	Day	37% 9% 17% 23% 11% 2	1880
	21st to end	Day	40% 10% 18% 22% 7% 3	2304
April	1st to 10th	Day	39% 6% 15% 21% 14% 4	2160
	11th to 20th	Day	33% 7% 13% 25% 18% 4	2132
	21st to end	Day	30% 6% 14% 28% 19% 4	2294
May	1st to 10th	Day	25% 6% 10% 25% 28% 6%	2340
	11th to 20th	Day	31% 7% 13% 21% 20% 8%	2304
	21st to end	Day	34% 7% 12% 21% 20% 7%	2686
June	1st to 10th	Day	23% 6% 10% 19% 27% 14%	2520
	11th to 20th	Day	18% 4 6% 15% 31% 26%	2520
	21st to end	Day	13% 2 4 12% 27% 42%	2520
July	1st to 10th	Day	12% 3 6% 10% 23% 47%	2451
	11th to 20th	Day	14% 2 3 9% 18% 54%	2445
	21st to end	Day	18% 5% 6% 9% 20% 43%	2589
August	1st to 10th	Day	20% 3 5% 11% 20% 42%	2317
	11th to 20th	Day	12% 2 5% 10% 24% 48%	2179
	21st to end	Day	10% 1 3 11% 28% 46%	2376
September	1st to 10th	Day	11% 3 3 8% 27% 48%	2160
	11th to 20th	Day	16% 4 6% 14% 28% 32%	2002
	21st to end	Day	17% 2 5% 16% 31% 29%	1980
October	1st to 10th	Day	24% 4 8% 18% 28% 19%	1980
	11th to 20th	Day	20% 4 7% 23% 31% 15%	1818
	21st to end	Day	20% 4 11% 31% 25% 9%	1782
November	1st to 10th	Day	31% 8% 11% 22% 22% 7%	1674
	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	41% 12% 20% 20% 5% 1	2646
	11th to 20th	Night	39% 13% 20% 15% 10% 2	2590
	21st to end	Night	42% 10% 17% 19% 9% 2	2772
February	1st to 10th	Night	37% 7% 18% 28% 10% 1	2174
	11th to 20th	Night	35% 9% 17% 25% 13% 1	2099
	21st to end	Night	36% 8% 18% 25% 12% 2	1776
March	1st to 10th	Night	39% 9% 17% 23% 9% 3	2160
	11th to 20th	Night	32% 10% 18% 24% 14% 3	2080
	21st to end	Night	36% 9% 19% 25% 8% 3	2048
April	1st to 10th	Night	35% 7% 17% 23% 14% 3	1800
	11th to 20th	Night	31% 6% 13% 29% 16% 5%	1779
	21st to end	Night	31% 6% 13% 26% 20% 4	1663
May	1st to 10th	Night	27% 6% 12% 20% 28% 7%	1620
	11th to 20th	Night	32% 6% 10% 21% 23% 7%	1595
	21st to end	Night	34% 7% 14% 22% 20% 5%	1586
June	1st to 10th	Night	23% 8% 10% 19% 27% 13%	1440
	11th to 20th	Night	19% 3 5% 16% 33% 23%	1440
	21st to end	Night	14% 3 6% 11% 28% 39%	1440
July	1st to 10th	Night	19% 4 6% 8% 23% 40%	1400
	11th to 20th	Night	18% 3 5% 8% 16% 50%	1392
	21st to end	Night	22% 3 5% 10% 18% 41%	1488
August	1st to 10th	Night	24% 3 8% 11% 17% 37%	1595
	11th to 20th	Night	17% 3 5% 9% 22% 44%	1719
	21st to end	Night	16% 2 5% 9% 21% 47%	1980
September	1st to 10th	Night	14% 3 4 8% 24% 47%	1800
	11th to 20th	Night	18% 3 6% 12% 24% 37%	1957
	21st to end	Night	17% 3 5% 13% 27% 36%	1980
October	1st to 10th	Night	23% 3 6% 17% 27% 23%	1980
	11th to 20th	Night	22% 4 6% 19% 30% 19%	2139
	21st to end	Night	19% 3 10% 28% 28% 11%	2574
November	1st to 10th	Night	29% 6% 13% 20% 22% 9%	2405
	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	7% 4 11% 33% 30% 15%	169
	21st to end	Day	4 10% 35% 32% 19%	176
February	1st to 10th	Day	7% 3 17% 38% 25% 10%	412
	11th to 20th	Day	9% 4 20% 37% 26% 5%	415
	21st to end	Day	4 5% 23% 38% 23% 6%	346
March	1st to 10th	Day	8% 7% 17% 37% 26% 5%	420
	11th to 20th	Day	8% 7% 21% 32% 25% 6%	420
	21st to end	Day	8% 10% 21% 35% 20% 5%	462
April	1st to 10th	Day	9% 10% 17% 34% 21% 10%	420
	11th to 20th	Day	8% 9% 19% 35% 22% 6%	412
	21st to end	Day	9% 8% 16% 31% 24% 13%	420
May	1st to 10th	Day	4 8% 20% 32% 24% 11%	423
	11th to 20th	Day	11% 6% 18% 24% 27% 14%	448
	21st to end	Day	9% 7% 15% 23% 27% 19%	485
June	1st to 10th	Day	4 7% 19% 26% 26% 18%	450
	11th to 20th	Day	5% 9% 21% 29% 22% 14%	450
	21st to end	Day	2 4 16% 31% 28% 19%	450
July	1st to 10th	Day	1 3 17% 30% 30% 19%	446
	11th to 20th	Day	2 3 13% 32% 30% 20%	444
	21st to end	Day	3 1 13% 26% 35% 22%	487
August	1st to 10th	Day	4 6% 12% 24% 32% 21%	447
	11th to 20th	Day	2 3 14% 27% 30% 25%	437
	21st to end	Day	2 3 13% 26% 35% 20%	495
September	1st to 10th	Day	2 2 16% 22% 32% 26%	450
	11th to 20th	Day	3 5% 15% 25% 30% 22%	450
	21st to end	Day	3 4 14% 28% 33% 18%	450
October	1st to 10th	Day	4 6% 17% 22% 29% 21%	450
	11th to 20th	Day	4 7% 15% 21% 35% 19%	414
	21st to end	Day	5% 3 15% 32% 30% 15%	297
November	1st to 10th	Day	10% 4 16% 29% 29% 12%	270
	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	8% 2 15% 43% 28% 4	740
	21st to end	Night	10% 3 12% 44% 25% 6%	792
February	1st to 10th	Night	8% 3 16% 45% 25% 3	720
	11th to 20th	Night	8% 2 15% 50% 23% 2	704
	21st to end	Night	5% 3 23% 48% 19% 2	592
March	1st to 10th	Night	8% 3 19% 47% 21% 2	720
	11th to 20th	Night	6% 3 15% 48% 25% 3	720
	21st to end	Night	9% 6% 21% 44% 18% 1	792
April	1st to 10th	Night	9% 5% 19% 44% 22% 2	720
	11th to 20th	Night	8% 6% 20% 42% 21% 4	711
	21st to end	Night	11% 5% 14% 40% 26% 4	583
May	1st to 10th	Night	6% 4 18% 43% 26% 3	540
	11th to 20th	Night	9% 4 14% 37% 32% 4	531
	21st to end	Night	9% 3 15% 36% 31% 6%	424
June	1st to 10th	Night	6% 2 14% 42% 31% 5%	360
	11th to 20th	Night	6% 3 14% 44% 34% 1	360
	21st to end	Night	3 1 12% 53% 28% 3	360
July	1st to 10th	Night	3 2 6% 50% 37% 1	350
	11th to 20th	Night	2 9% 52% 36% 1	348
	21st to end	Night	4 2 6% 46% 40% 2	394
August	1st to 10th	Night	5% 3 9% 47% 35% 2	529
	11th to 20th	Night	3 2 7% 47% 37% 5%	651
	21st to end	Night	2 1 7% 45% 41% 4	792
September	1st to 10th	Night	4 1 7% 41% 41% 5%	720
	11th to 20th	Night	4 2 8% 37% 38% 10%	720
	21st to end	Night	5% 2 11% 37% 36% 9%	720
October	1st to 10th	Night	8% 1 11% 42% 33% 5%	720
	11th to 20th	Night	6% 2 12% 41% 34% 5%	720
	21st to end	Night	5% 2 13% 44% 29% 6%	792
November	1st to 10th	Night	8% 2 14% 43% 30% 4	740
	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 2024-01-12 13:17:41. Version ac07

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