Deep Sky West Remote Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Sky West Remote Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	2 3 1 4 3 4 4 4 6% 8% 61%	156865
	Night	3 4 2 5% 3 4 4 4 6% 8% 59%	152138
Transparency	Day	19% 5% 10% 21% 27% 18%	151899
	Night	21% 5% 10% 20% 27% 17%	148123
Seeing	Day	7% 15% 28% 28% 17% 4	17702
	Night	5% 11% 32% 35% 16% 1	27716

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	1 7% 3 6% 3 4 3 3 4 7% 58%	5140
	11th to 20th	Day	1 3 2 3 2 1 2 1 3 4 78%	5340
	21st to end	Day	2 6% 2 5% 4 3 4 4 5% 6% 60%	5844
February	1st to 10th	Day	1 5% 1 4 3 3 3 3 6% 7% 62%	1958
	11th to 20th	Day	2 5% 2 5% 2 4 3 3 5% 8% 62%	2049
	21st to end	Day	2 4 1 3 3 3 3 2 5% 7% 67%	1730
March	1st to 10th	Day	1 4 1 3 2 3 3 3 5% 6% 68%	4775
	11th to 20th	Day	2 4 2 5% 4 4 4 3 5% 7% 59%	5110
	21st to end	Day	1 3 1 4 3 3 4 3 6% 8% 63%	5831
April	1st to 10th	Day	3 3 1 3 2 3 4 4 7% 7% 65%	2520
	11th to 20th	Day	2 4 2 4 3 3 3 3 4 7% 65%	2491
	21st to end	Day	3 3 1 3 3 3 3 3 5% 8% 68%	2520
May	1st to 10th	Day	3 3 2 4 3 4 4 4 6% 7% 60%	7057
	11th to 20th	Day	3 2 1 3 2 3 3 3 5% 6% 71%	7281
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 66%	9026
June	1st to 10th	Day	2 2 1 4 4 4 5% 5% 6% 9% 60%	2940
	11th to 20th	Day	2 2 1 3 2 3 3 4 5% 6% 69%	2940
	21st to end	Day	5% 4 1 4 4 3 4 4 7% 8% 56%	2940
July	1st to 10th	Day	2 3 1 5% 4 5% 5% 4 6% 8% 57%	8249
	11th to 20th	Day	2 2 1 5% 4 6% 7% 6% 9% 12% 46%	7651
	21st to end	Day	4 3 1 6% 6% 6% 7% 7% 9% 10% 41%	8304
August	1st to 10th	Day	2 1 1 4 3 5% 6% 6% 8% 9% 55%	7241
	11th to 20th	Day	2 2 1 5% 4 6% 6% 5% 7% 9% 52%	7003
	21st to end	Day	2 2 1 5% 4 6% 7% 6% 9% 11% 46%	7751
September	1st to 10th	Day	5% 4 2 6% 4 5% 4 4 6% 8% 51%	2520
	11th to 20th	Day	6% 3 1 4 3 4 4 4 6% 7% 57%	2520
	21st to end	Day	5% 2 1 3 3 3 3 3 4 6% 68%	2281
October	1st to 10th	Day	4 2 1 3 2 2 2 2 3 4 73%	3270
	11th to 20th	Day	4 3 1 4 3 4 3 3 5% 5% 65%	3250
	21st to end	Day	2 2 2 1 1 2 2 3 5% 79%	3548
November	1st to 10th	Day	2 3 1 2 2 2 3 3 5% 8% 71%	1969
	11th to 20th	Day	2 3 1 3 2 2 3 3 4 7% 70%	1890
	21st to end	Day	4 5% 1 3 3 2 3 3 4 7% 65%	1890
December	1st to 10th	Day	1 2 1 3 2 2 2 2 3 6% 77%	2838
	11th to 20th	Day	2 2 2 6% 3 3 3 2 3 7% 68%	3106
	21st to end	Day	2 4 1 3 2 2 3 3 5% 6% 70%	4092
January	1st to 10th	Night	1 6% 3 8% 5% 4 4 3 5% 7% 55%	7823
	11th to 20th	Night	1 2 1 3 2 3 3 2 4 4 74%	7650
	21st to end	Night	2 5% 2 5% 3 3 4 3 5% 7% 60%	8370
February	1st to 10th	Night	2 5% 2 5% 2 3 3 3 5% 7% 64%	2660
	11th to 20th	Night	3 5% 1 4 3 3 3 3 5% 6% 62%	2458
	21st to end	Night	3 4 1 4 3 2 3 2 4 7% 68%	2076
March	1st to 10th	Night	2 3 1 3 3 3 3 3 5% 6% 69%	5323
	11th to 20th	Night	3 5% 2 6% 4 4 4 3 4 5% 60%	5110
	21st to end	Night	2 2 1 3 3 3 3 3 4 7% 69%	5362
April	1st to 10th	Night	2 3 1 3 3 3 3 2 4 7% 66%	2100
	11th to 20th	Night	3 4 2 4 3 3 3 3 5% 7% 65%	2077
	21st to end	Night	3 3 1 4 3 2 3 3 5% 6% 67%	2100
May	1st to 10th	Night	5% 5% 2 4 3 4 4 3 6% 7% 56%	5890
	11th to 20th	Night	4 3 2 3 2 3 3 3 5% 6% 65%	5589
	21st to end	Night	4 3 2 5% 4 4 4 3 5% 6% 62%	5181
June	1st to 10th	Night	3 3 2 5% 4 4 4 4 8% 9% 54%	1680
	11th to 20th	Night	3 2 1 3 3 3 3 3 4 8% 67%	1680
	21st to end	Night	5% 4 2 5% 4 4 6% 4 7% 9% 50%	1680
July	1st to 10th	Night	3 4 1 6% 5% 7% 6% 4 7% 8% 48%	4740
	11th to 20th	Night	3 3 1 5% 4 4 7% 6% 10% 14% 43%	5333
	21st to end	Night	5% 4 2 6% 4 6% 7% 6% 10% 13% 36%	5805
August	1st to 10th	Night	2 3 1 7% 6% 7% 7% 6% 9% 11% 40%	5569
	11th to 20th	Night	3 3 2 6% 5% 5% 7% 6% 9% 12% 39%	5853
	21st to end	Night	4 4 2 8% 7% 7% 7% 7% 11% 13% 31%	6465
September	1st to 10th	Night	5% 4 2 5% 4 5% 5% 5% 7% 9% 50%	2100
	11th to 20th	Night	5% 4 2 5% 3 4 5% 4 6% 8% 56%	2100
	21st to end	Night	5% 4 1 3 3 3 4 3 4 6% 63%	2289
October	1st to 10th	Night	5% 2 1 3 2 2 2 2 3 4 73%	3920
	11th to 20th	Night	5% 3 1 4 2 3 2 2 5% 6% 67%	3898
	21st to end	Night	3 1 2 2 2 2 2 4 6% 76%	4252
November	1st to 10th	Night	2 2 1 2 2 2 3 2 4 6% 73%	2528
	11th to 20th	Night	1 2 1 3 2 3 2 3 4 6% 72%	2730
	21st to end	Night	4 5% 1 3 3 3 3 3 4 6% 65%	2730
December	1st to 10th	Night	2 2 1 3 2 2 3 2 3 6% 74%	4568
	11th to 20th	Night	1 2 1 3 3 3 3 3 5% 7% 69%	5321
	21st to end	Night	2 4 2 4 3 3 3 2 4 7% 67%	7128

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	23% 5% 7% 30% 30% 5%	5143
	11th to 20th	Day	11% 4 7% 24% 35% 19%	5340
	21st to end	Day	23% 5% 6% 15% 36% 15%	5844
February	1st to 10th	Day	20% 3 9% 23% 30% 15%	1958
	11th to 20th	Day	21% 4 7% 24% 29% 15%	2059
	21st to end	Day	17% 3 5% 17% 34% 24%	1730
March	1st to 10th	Day	16% 3 5% 11% 34% 30%	4775
	11th to 20th	Day	18% 6% 8% 18% 32% 18%	5110
	21st to end	Day	17% 3 7% 26% 37% 10%	5831
April	1st to 10th	Day	17% 4 7% 18% 35% 19%	2520
	11th to 20th	Day	20% 3 6% 17% 30% 23%	2494
	21st to end	Day	15% 3 8% 19% 38% 17%	2520
May	1st to 10th	Day	21% 5% 9% 18% 29% 17%	7057
	11th to 20th	Day	13% 4 8% 14% 30% 32%	7284
	21st to end	Day	16% 5% 10% 15% 18% 37%	9027
June	1st to 10th	Day	17% 6% 12% 20% 23% 22%	2940
	11th to 20th	Day	13% 4 7% 14% 23% 40%	2940
	21st to end	Day	24% 4 11% 17% 20% 23%	2940
July	1st to 10th	Day	21% 7% 11% 14% 19% 27%	8181
	11th to 20th	Day	24% 9% 21% 29% 12% 5%	7581
	21st to end	Day	30% 9% 21% 27% 12% 2	8120
August	1st to 10th	Day	22% 9% 17% 26% 18% 7%	5736
	11th to 20th	Day	23% 7% 17% 26% 18% 9%	5519
	21st to end	Day	27% 8% 19% 30% 14% 2	6078
September	1st to 10th	Day	29% 6% 12% 20% 23% 10%	2520
	11th to 20th	Day	25% 5% 10% 19% 23% 17%	2520
	21st to end	Day	19% 4 6% 22% 31% 18%	2281
October	1st to 10th	Day	15% 3 5% 13% 32% 32%	3270
	11th to 20th	Day	20% 5% 7% 15% 29% 24%	3250
	21st to end	Day	10% 2 4 16% 41% 27%	3548
November	1st to 10th	Day	13% 3 7% 19% 41% 18%	1969
	11th to 20th	Day	15% 2 7% 22% 39% 15%	1890
	21st to end	Day	19% 3 7% 20% 33% 19%	1890
December	1st to 10th	Day	11% 3 6% 26% 37% 17%	2838
	11th to 20th	Day	17% 4 7% 24% 37% 11%	3104
	21st to end	Day	14% 3 9% 27% 34% 14%	4092
January	1st to 10th	Night	26% 6% 7% 26% 27% 8%	7824
	11th to 20th	Night	12% 4 6% 24% 38% 16%	7650
	21st to end	Night	20% 5% 6% 16% 38% 14%	8370
February	1st to 10th	Night	19% 4 9% 23% 31% 15%	2660
	11th to 20th	Night	21% 5% 8% 23% 29% 14%	2458
	21st to end	Night	17% 2 4 17% 36% 24%	2076
March	1st to 10th	Night	15% 3 6% 10% 38% 28%	5323
	11th to 20th	Night	22% 7% 7% 17% 32% 16%	5110
	21st to end	Night	14% 3 9% 24% 38% 12%	5362
April	1st to 10th	Night	18% 3 7% 19% 31% 22%	2100
	11th to 20th	Night	18% 4 7% 18% 28% 25%	2077
	21st to end	Night	16% 5% 8% 19% 34% 17%	2100
May	1st to 10th	Night	24% 5% 12% 20% 22% 18%	5888
	11th to 20th	Night	16% 5% 9% 14% 26% 30%	5590
	21st to end	Night	19% 6% 12% 10% 13% 40%	5182
June	1st to 10th	Night	23% 8% 14% 16% 17% 21%	1680
	11th to 20th	Night	17% 4 7% 14% 20% 38%	1680
	21st to end	Night	28% 6% 13% 16% 15% 22%	1680
July	1st to 10th	Night	28% 9% 11% 17% 15% 20%	4700
	11th to 20th	Night	26% 9% 26% 24% 10% 5%	5280
	21st to end	Night	34% 9% 23% 23% 10% 1	5677
August	1st to 10th	Night	33% 9% 17% 22% 14% 5%	4409
	11th to 20th	Night	32% 9% 19% 20% 14% 6%	4613
	21st to end	Night	36% 10% 22% 22% 6% 3	5069
September	1st to 10th	Night	28% 7% 15% 21% 21% 9%	2100
	11th to 20th	Night	25% 6% 12% 18% 23% 17%	2100
	21st to end	Night	21% 4 9% 17% 30% 18%	2289
October	1st to 10th	Night	15% 4 5% 16% 29% 30%	3920
	11th to 20th	Night	19% 4 8% 14% 28% 27%	3898
	21st to end	Night	11% 2 5% 17% 39% 26%	4252
November	1st to 10th	Night	12% 2 6% 20% 41% 19%	2528
	11th to 20th	Night	13% 3 6% 21% 40% 17%	2730
	21st to end	Night	21% 3 6% 20% 30% 19%	2730
December	1st to 10th	Night	13% 3 6% 30% 33% 16%	4568
	11th to 20th	Night	15% 3 6% 23% 40% 14%	5322
	21st to end	Night	17% 5% 8% 23% 38% 10%	7128

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	11% 28% 31% 23% 6% 1	330
	11th to 20th	Day	12% 23% 35% 19% 7% 2	330
	21st to end	Day	4 20% 42% 24% 9% 1	363
February	1st to 10th	Day	6% 31% 35% 22% 5% 1	330
	11th to 20th	Day	11% 31% 38% 16% 4	330
	21st to end	Day	12% 32% 37% 16% 3	273
March	1st to 10th	Day	10% 28% 33% 22% 6%	401
	11th to 20th	Day	16% 29% 30% 17% 7% 1	540
	21st to end	Day	12% 32% 34% 16% 5% 1	594
April	1st to 10th	Day	10% 27% 37% 18% 7% 1	540
	11th to 20th	Day	11% 32% 36% 15% 4	532
	21st to end	Day	10% 29% 37% 21% 3 1	540
May	1st to 10th	Day	8% 24% 42% 21% 4 1	543
	11th to 20th	Day	9% 15% 37% 26% 12% 2	635
	21st to end	Day	5% 11% 38% 32% 13% 1	844
June	1st to 10th	Day	3 8% 26% 39% 22% 3	780
	11th to 20th	Day	3 8% 29% 36% 22% 2	780
	21st to end	Day	5% 6% 26% 35% 22% 6%	780
July	1st to 10th	Day	5% 2 15% 36% 35% 7%	771
	11th to 20th	Day	4 1 7% 36% 37% 15%	564
	21st to end	Day	4 9% 32% 41% 14%	619
August	1st to 10th	Day	4 2 12% 37% 34% 11%	567
	11th to 20th	Day	2 2 14% 38% 34% 10%	557
	21st to end	Day	4 1 15% 40% 31% 9%	627
September	1st to 10th	Day	6% 2 16% 42% 27% 7%	570
	11th to 20th	Day	5% 3 28% 41% 18% 5%	570
	21st to end	Day	8% 7% 29% 32% 18% 6%	356
October	1st to 10th	Day	7% 14% 29% 27% 18% 6%	330
	11th to 20th	Day	10% 16% 29% 28% 14% 3	330
	21st to end	Day	10% 15% 31% 26% 13% 3	363
November	1st to 10th	Day	6% 25% 35% 24% 8% 2	330
	11th to 20th	Day	7% 16% 36% 29% 11% 2	330
	21st to end	Day	11% 24% 33% 23% 9% 1	330
December	1st to 10th	Day	8% 25% 35% 23% 8% 2	330
	11th to 20th	Day	8% 23% 40% 24% 5% 1	330
	21st to end	Day	12% 32% 33% 17% 4 1	363
January	1st to 10th	Night	4 16% 39% 30% 11%	919
	11th to 20th	Night	5% 14% 41% 29% 9% 1	840
	21st to end	Night	5% 14% 41% 30% 10% 1	924
February	1st to 10th	Night	4 15% 43% 31% 7%	840
	11th to 20th	Night	7% 18% 43% 27% 6%	824
	21st to end	Night	7% 18% 50% 22% 3	692
March	1st to 10th	Night	5% 17% 42% 30% 6% 1	840
	11th to 20th	Night	7% 17% 35% 32% 9%	840
	21st to end	Night	5% 15% 43% 32% 6%	818
April	1st to 10th	Night	5% 20% 41% 28% 5%	630
	11th to 20th	Night	4 19% 40% 30% 6%	623
	21st to end	Night	5% 17% 40% 32% 5%	630
May	1st to 10th	Night	4 12% 38% 37% 8%	630
	11th to 20th	Night	6% 10% 31% 38% 14% 1	621
	21st to end	Night	5% 9% 37% 37% 11%	683
June	1st to 10th	Night	2 6% 27% 45% 20%	630
	11th to 20th	Night	2 3 30% 48% 15% 1	630
	21st to end	Night	5% 4 20% 44% 25% 1	630
July	1st to 10th	Night	6% 2 11% 45% 34% 2	615
	11th to 20th	Night	4 1 7% 38% 46% 5%	612
	21st to end	Night	5% 2 7% 33% 47% 6%	690
August	1st to 10th	Night	4 1 9% 35% 44% 7%	627
	11th to 20th	Night	3 3 8% 41% 41% 4	624
	21st to end	Night	3 1 9% 43% 39% 5%	693
September	1st to 10th	Night	5% 3 13% 45% 33% 3	630
	11th to 20th	Night	5% 3 14% 49% 26% 2	630
	21st to end	Night	5% 4 23% 45% 21% 2	628
October	1st to 10th	Night	8% 5% 22% 45% 19% 2	800
	11th to 20th	Night	5% 8% 31% 40% 14% 2	800
	21st to end	Night	4 9% 32% 35% 17% 3	880
November	1st to 10th	Night	4 10% 33% 39% 13% 2	888
	11th to 20th	Night	3 11% 37% 36% 11% 2	1050
	21st to end	Night	6% 15% 33% 33% 11% 2	1050
December	1st to 10th	Night	6% 16% 39% 31% 8% 1	1050
	11th to 20th	Night	5% 18% 40% 30% 8%	1050
	21st to end	Night	8% 18% 44% 27% 4	1155

Page generated at 2026-09-26 02:18:41. Version ac07

Copyright © 2026 Attilla Danko.