Sierra La Sal Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sierra La Sal Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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% 4 4 4 4 6% 7% 55%	105093
	Night	4 6% 2 5% 4 4 4 4 5% 7% 56%	103179
Transparency	Day	23% 8% 11% 20% 23% 15%	104858
	Night	24% 7% 11% 21% 23% 14%	103003
Seeing	Day	8% 13% 28% 30% 18% 4	15171
	Night	7% 7% 22% 35% 25% 4	25450

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	3 6% 3 7% 5% 5% 5% 4 7% 8% 48%	2858
	11th to 20th	Day	3 6% 2 7% 5% 4 4 4 6% 8% 51%	2860
	21st to end	Day	5% 9% 3 5% 3 3 4 4 4 6% 53%	3146
February	1st to 10th	Day	4 9% 2 8% 5% 4 3 3 6% 8% 49%	1710
	11th to 20th	Day	5% 7% 3 6% 5% 5% 4 3 5% 8% 50%	1665
	21st to end	Day	5% 10% 3 4 4 4 4 3 5% 6% 51%	1621
March	1st to 10th	Day	3 9% 3 6% 4 4 4 4 6% 8% 49%	3444
	11th to 20th	Day	4 10% 4 9% 6% 6% 5% 4 6% 7% 39%	3490
	21st to end	Day	5% 12% 3 8% 6% 5% 5% 4 5% 6% 40%	3825
April	1st to 10th	Day	4 6% 3 6% 4 4 3 3 5% 8% 54%	2210
	11th to 20th	Day	3 6% 2 6% 4 4 5% 5% 6% 8% 51%	2251
	21st to end	Day	4 4 2 6% 4 4 5% 4 5% 7% 53%	2359
May	1st to 10th	Day	5% 5% 2 6% 4 4 5% 4 5% 8% 53%	4110
	11th to 20th	Day	3 4 2 4 4 4 4 4 6% 7% 57%	4071
	21st to end	Day	3 4 1 5% 4 4 5% 4 5% 8% 57%	4568
June	1st to 10th	Day	3 3 1 3 3 2 4 3 5% 8% 64%	2660
	11th to 20th	Day	3 4 1 3 2 3 3 2 4 6% 70%	2660
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 66%	2636
July	1st to 10th	Day	3 3 1 3 3 3 3 3 4 6% 69%	4110
	11th to 20th	Day	2 2 1 4 4 4 5% 6% 10% 14% 48%	4110
	21st to end	Day	2 3 1 4 4 5% 5% 5% 7% 8% 56%	4454
August	1st to 10th	Day	3 3 1 5% 6% 6% 8% 7% 10% 11% 39%	4092
	11th to 20th	Day	3 3 1 5% 5% 5% 6% 5% 7% 8% 52%	4028
	21st to end	Day	4 3 1 4 3 5% 6% 4 7% 10% 53%	4211
September	1st to 10th	Day	5% 3 1 4 3 4 5% 3 6% 7% 58%	2280
	11th to 20th	Day	4 3 1 5% 3 4 5% 4 5% 7% 60%	2137
	21st to end	Day	5% 3 2 3 2 3 3 2 4 6% 67%	2077
October	1st to 10th	Day	4 2 1 3 2 2 2 2 4 4 75%	3170
	11th to 20th	Day	7% 4 2 5% 3 3 4 4 6% 8% 54%	3150
	21st to end	Day	4 3 1 4 2 2 4 3 4 5% 68%	3438
November	1st to 10th	Day	4 5% 2 4 3 2 3 3 4 5% 66%	1959
	11th to 20th	Day	4 5% 2 4 2 3 3 2 4 5% 67%	1775
	21st to end	Day	6% 5% 1 3 4 3 3 2 5% 6% 61%	1576
December	1st to 10th	Day	5% 8% 3 6% 4 4 4 3 6% 6% 52%	1520
	11th to 20th	Day	5% 9% 3 7% 4 5% 6% 4 6% 7% 43%	1926
	21st to end	Day	5% 8% 3 7% 4 4 4 4 5% 6% 50%	2936
January	1st to 10th	Night	4 7% 4 7% 4 4 4 3 4 7% 51%	4097
	11th to 20th	Night	4 8% 3 7% 5% 4 4 3 5% 7% 50%	4110
	21st to end	Night	5% 10% 3 7% 4 4 4 3 5% 6% 51%	4521
February	1st to 10th	Night	3 8% 3 5% 3 3 4 4 6% 6% 55%	2470
	11th to 20th	Night	4 6% 2 5% 3 4 4 5% 6% 6% 54%	2402
	21st to end	Night	3 10% 3 6% 5% 5% 4 3 5% 5% 51%	1829
March	1st to 10th	Night	3 8% 2 6% 4 5% 4 4 5% 7% 52%	3430
	11th to 20th	Night	4 10% 3 8% 5% 4 5% 4 6% 8% 43%	3490
	21st to end	Night	4 11% 3 8% 6% 4 5% 5% 6% 6% 42%	3828
April	1st to 10th	Night	3 8% 2 6% 5% 4 4 4 5% 6% 53%	1969
	11th to 20th	Night	4 5% 3 7% 4 4 4 3 4 7% 53%	1877
	21st to end	Night	5% 4 2 5% 4 4 3 4 5% 8% 56%	1818
May	1st to 10th	Night	4 6% 2 5% 4 4 5% 4 6% 6% 54%	2860
	11th to 20th	Night	3 4 1 5% 4 4 5% 5% 7% 9% 53%	2834
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 6% 64%	3014
June	1st to 10th	Night	3 1 1 4 3 3 3 4 6% 7% 65%	1520
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 6% 66%	1520
	21st to end	Night	3 2 1 3 2 2 4 4 6% 6% 66%	1536
July	1st to 10th	Night	1 2 1 2 3 3 3 3 4 6% 70%	2860
	11th to 20th	Night	1 2 1 4 5% 5% 7% 6% 10% 13% 46%	2860
	21st to end	Night	2 3 2 5% 4 5% 5% 4 7% 9% 54%	3109
August	1st to 10th	Night	3 3 2 8% 6% 7% 8% 7% 9% 11% 36%	2847
	11th to 20th	Night	3 3 1 5% 4 5% 5% 5% 7% 8% 53%	2811
	21st to end	Night	3 4 2 5% 4 4 4 4 7% 10% 53%	3456
September	1st to 10th	Night	4 4 1 4 3 3 4 4 5% 7% 60%	1900
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 7% 63%	2039
	21st to end	Night	5% 3 1 3 3 2 2 2 3 4 71%	2102
October	1st to 10th	Night	4 2 1 2 2 2 2 2 3 6% 74%	3800
	11th to 20th	Night	5% 5% 2 6% 3 4 4 3 4 6% 56%	3778
	21st to end	Night	4 4 1 4 2 3 2 2 3 6% 68%	4120
November	1st to 10th	Night	3 5% 2 4 2 3 3 3 4 6% 65%	2340
	11th to 20th	Night	4 3 1 4 2 3 3 3 5% 5% 68%	2597
	21st to end	Night	5% 6% 2 5% 3 2 2 3 5% 6% 61%	2759
December	1st to 10th	Night	6% 6% 2 4 3 3 4 3 4 7% 57%	2660
	11th to 20th	Night	6% 7% 2 7% 5% 5% 4 4 6% 8% 47%	3271
	21st to end	Night	6% 9% 3 5% 4 3 3 3 6% 8% 50%	4745

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	28% 10% 19% 30% 12% 2	2859
	11th to 20th	Day	25% 11% 22% 29% 11% 2	2860
	21st to end	Day	31% 9% 13% 30% 14% 4	3146
February	1st to 10th	Day	31% 9% 18% 20% 19% 4	1710
	11th to 20th	Day	32% 6% 12% 24% 21% 4	1674
	21st to end	Day	31% 7% 11% 22% 25% 5%	1621
March	1st to 10th	Day	26% 8% 15% 25% 23% 3	3444
	11th to 20th	Day	33% 13% 14% 25% 12% 3	3490
	21st to end	Day	33% 13% 14% 20% 18% 3	3825
April	1st to 10th	Day	26% 5% 9% 21% 26% 12%	2210
	11th to 20th	Day	26% 7% 10% 23% 23% 11%	2254
	21st to end	Day	25% 7% 12% 20% 28% 8%	2359
May	1st to 10th	Day	21% 8% 11% 17% 30% 14%	4110
	11th to 20th	Day	19% 8% 10% 19% 30% 14%	4074
	21st to end	Day	17% 8% 9% 15% 37% 15%	4568
June	1st to 10th	Day	16% 4 7% 17% 31% 25%	2660
	11th to 20th	Day	17% 4 5% 9% 24% 41%	2660
	21st to end	Day	14% 5% 7% 12% 23% 39%	2636
July	1st to 10th	Day	16% 4 7% 9% 12% 52%	4046
	11th to 20th	Day	20% 9% 11% 22% 24% 14%	4041
	21st to end	Day	20% 9% 13% 20% 13% 25%	4314
August	1st to 10th	Day	30% 10% 17% 18% 10% 14%	4078
	11th to 20th	Day	25% 9% 11% 14% 22% 18%	4067
	21st to end	Day	23% 8% 12% 19% 21% 16%	4210
September	1st to 10th	Day	24% 7% 9% 12% 23% 25%	2280
	11th to 20th	Day	22% 6% 10% 15% 20% 26%	2137
	21st to end	Day	19% 4 6% 15% 34% 21%	2077
October	1st to 10th	Day	14% 3 6% 12% 29% 36%	3170
	11th to 20th	Day	26% 5% 5% 24% 31% 9%	3150
	21st to end	Day	16% 6% 7% 29% 36% 6%	3438
November	1st to 10th	Day	19% 3 11% 27% 30% 10%	1959
	11th to 20th	Day	20% 4 8% 32% 33% 4	1775
	21st to end	Day	22% 4 13% 26% 28% 6%	1576
December	1st to 10th	Day	30% 6% 17% 25% 17% 5%	1520
	11th to 20th	Day	33% 10% 17% 24% 14% 1	1924
	21st to end	Day	32% 9% 13% 15% 25% 7%	2936
January	1st to 10th	Night	28% 9% 16% 30% 16% 1	4097
	11th to 20th	Night	27% 13% 18% 29% 12% 2	4110
	21st to end	Night	33% 7% 13% 30% 15% 3	4521
February	1st to 10th	Night	26% 7% 16% 27% 19% 4	2470
	11th to 20th	Night	26% 7% 15% 24% 23% 5%	2403
	21st to end	Night	30% 6% 11% 24% 24% 5%	1829
March	1st to 10th	Night	24% 9% 13% 23% 25% 6%	3430
	11th to 20th	Night	31% 11% 12% 24% 18% 4	3490
	21st to end	Night	32% 12% 13% 20% 20% 2	3828
April	1st to 10th	Night	28% 7% 9% 20% 24% 12%	1969
	11th to 20th	Night	27% 7% 9% 19% 26% 12%	1877
	21st to end	Night	23% 7% 9% 22% 29% 10%	1818
May	1st to 10th	Night	20% 9% 10% 17% 32% 12%	2860
	11th to 20th	Night	18% 9% 11% 19% 33% 11%	2835
	21st to end	Night	17% 6% 8% 17% 31% 20%	3014
June	1st to 10th	Night	15% 4 7% 16% 30% 28%	1520
	11th to 20th	Night	17% 5% 7% 11% 19% 42%	1520
	21st to end	Night	15% 4 6% 12% 22% 41%	1536
July	1st to 10th	Night	15% 5% 8% 8% 10% 54%	2815
	11th to 20th	Night	20% 7% 11% 21% 22% 20%	2806
	21st to end	Night	22% 7% 13% 17% 15% 26%	3011
August	1st to 10th	Night	34% 10% 16% 14% 11% 15%	2838
	11th to 20th	Night	23% 9% 14% 15% 17% 22%	2838
	21st to end	Night	24% 8% 11% 16% 22% 20%	3456
September	1st to 10th	Night	21% 6% 10% 12% 20% 30%	1900
	11th to 20th	Night	18% 6% 11% 17% 21% 27%	2039
	21st to end	Night	17% 3 6% 13% 35% 25%	2102
October	1st to 10th	Night	13% 3 6% 12% 27% 40%	3800
	11th to 20th	Night	27% 5% 7% 16% 33% 12%	3778
	21st to end	Night	18% 4 5% 30% 36% 7%	4120
November	1st to 10th	Night	20% 4 8% 24% 32% 13%	2340
	11th to 20th	Night	17% 5% 8% 28% 36% 6%	2597
	21st to end	Night	23% 6% 9% 23% 30% 10%	2759
December	1st to 10th	Night	26% 7% 14% 26% 21% 6%	2660
	11th to 20th	Night	30% 10% 15% 25% 19% 1	3272
	21st to end	Night	30% 9% 14% 17% 23% 7%	4745

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	16% 12% 31% 26% 12% 3	270
	11th to 20th	Day	13% 12% 33% 27% 12% 3	270
	21st to end	Day	7% 11% 31% 35% 14% 2	297
February	1st to 10th	Day	10% 19% 36% 23% 11%	270
	11th to 20th	Day	10% 18% 39% 23% 9%	270
	21st to end	Day	11% 24% 36% 23% 6% 1	329
March	1st to 10th	Day	13% 22% 32% 23% 11%	460
	11th to 20th	Day	11% 17% 33% 25% 11% 2	460
	21st to end	Day	14% 27% 34% 18% 6% 2	506
April	1st to 10th	Day	12% 21% 35% 21% 8% 3	460
	11th to 20th	Day	14% 23% 36% 18% 7% 1	452
	21st to end	Day	13% 23% 31% 22% 10% 1	460
May	1st to 10th	Day	10% 21% 38% 22% 8% 1	463
	11th to 20th	Day	9% 15% 31% 28% 14% 3	488
	21st to end	Day	8% 18% 27% 26% 17% 4	581
June	1st to 10th	Day	4 9% 25% 35% 24% 3	680
	11th to 20th	Day	6% 10% 27% 35% 18% 4	680
	21st to end	Day	3 7% 28% 39% 19% 3	656
July	1st to 10th	Day	4 4 23% 40% 25% 4	486
	11th to 20th	Day	3 2 17% 35% 36% 7%	484
	21st to end	Day	5% 2 11% 39% 35% 8%	531
August	1st to 10th	Day	6% 3 15% 42% 28% 7%	487
	11th to 20th	Day	5% 4 23% 35% 27% 6%	477
	21st to end	Day	5% 3 20% 38% 29% 6%	539
September	1st to 10th	Day	5% 5% 18% 36% 29% 8%	490
	11th to 20th	Day	5% 10% 30% 34% 17% 4	490
	21st to end	Day	7% 12% 22% 34% 18% 6%	477
October	1st to 10th	Day	9% 14% 22% 23% 22% 10%	300
	11th to 20th	Day	7% 14% 26% 29% 18% 5%	300
	21st to end	Day	7% 15% 26% 30% 19% 2	330
November	1st to 10th	Day	9% 15% 29% 31% 15% 2	300
	11th to 20th	Day	6% 15% 35% 26% 16% 2	300
	21st to end	Day	11% 14% 28% 29% 16% 1	291
December	1st to 10th	Day	11% 17% 28% 25% 16% 2	270
	11th to 20th	Day	8% 14% 34% 29% 12% 4	270
	21st to end	Day	13% 14% 34% 30% 8% 1	297
January	1st to 10th	Night	9% 6% 23% 36% 22% 5%	760
	11th to 20th	Night	9% 6% 23% 36% 23% 3	760
	21st to end	Night	9% 6% 24% 39% 18% 4	836
February	1st to 10th	Night	7% 9% 30% 36% 15% 3	760
	11th to 20th	Night	8% 8% 29% 37% 15% 2	744
	21st to end	Night	10% 11% 30% 37% 12% 1	628
March	1st to 10th	Night	7% 11% 29% 36% 15% 2	760
	11th to 20th	Night	6% 10% 23% 33% 26% 2	760
	21st to end	Night	9% 11% 27% 36% 15% 2	836
April	1st to 10th	Night	7% 13% 31% 35% 13% 1	639
	11th to 20th	Night	8% 15% 28% 34% 13% 2	563
	21st to end	Night	7% 12% 31% 27% 18% 4	570
May	1st to 10th	Night	8% 11% 28% 37% 14% 2	570
	11th to 20th	Night	6% 7% 21% 37% 24% 5%	561
	21st to end	Night	7% 11% 24% 30% 24% 3	617
June	1st to 10th	Night	4 4 21% 38% 31% 2	570
	11th to 20th	Night	5% 7% 21% 39% 25% 4	570
	21st to end	Night	3 2 18% 41% 31% 5%	570
July	1st to 10th	Night	3 3 12% 32% 44% 6%	555
	11th to 20th	Night	3 1 9% 31% 46% 10%	552
	21st to end	Night	4 7% 29% 50% 9%	624
August	1st to 10th	Night	4 3 9% 31% 47% 6%	567
	11th to 20th	Night	4 2 10% 37% 40% 7%	564
	21st to end	Night	4 4 9% 35% 38% 10%	627
September	1st to 10th	Night	6% 1 11% 37% 37% 8%	570
	11th to 20th	Night	4 3 17% 33% 36% 7%	709
	21st to end	Night	6% 5% 16% 31% 34% 9%	760
October	1st to 10th	Night	7% 6% 20% 34% 28% 5%	760
	11th to 20th	Night	4 6% 21% 38% 27% 5%	760
	21st to end	Night	7% 6% 22% 35% 24% 6%	836
November	1st to 10th	Night	6% 6% 21% 37% 26% 4	780
	11th to 20th	Night	6% 5% 26% 39% 19% 5%	857
	21st to end	Night	9% 9% 23% 33% 21% 5%	986
December	1st to 10th	Night	9% 7% 24% 38% 19% 2	950
	11th to 20th	Night	12% 6% 27% 34% 18% 2	950
	21st to end	Night	13% 10% 24% 39% 12% 2	969

Page generated at 2024-11-24 22:22:21. Version ac07

Copyright © 2024 Attilla Danko.