Shangri-La Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shangri-La Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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	8% 7% 3 7% 5% 4 4 4 5% 6% 46%	105589
	Night	11% 9% 3 7% 5% 4 4 4 5% 7% 41%	102676
Transparency	Day	19% 48% 7% 12% 9% 5%	105332
	Night	21% 49% 8% 11% 7% 3	102522
Seeing	Day	16% 18% 29% 22% 12% 3	14592
	Night	16% 12% 24% 31% 16% 2	23612

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	20% 22% 6% 15% 8% 6% 5% 3 4 3 7%	2539
	11th to 20th	Day	24% 17% 5% 10% 6% 6% 6% 4 5% 5% 12%	2540
	21st to end	Day	31% 17% 6% 14% 7% 4 3 3 3 4 8%	2901
February	1st to 10th	Day	16% 15% 5% 9% 6% 6% 7% 5% 7% 6% 21%	1710
	11th to 20th	Day	14% 10% 4 8% 6% 7% 6% 5% 8% 7% 25%	1665
	21st to end	Day	10% 12% 3 11% 7% 6% 7% 6% 7% 7% 25%	1548
March	1st to 10th	Day	8% 11% 4 9% 7% 6% 7% 6% 8% 9% 25%	3156
	11th to 20th	Day	8% 8% 3 8% 5% 5% 5% 4 6% 6% 44%	3490
	21st to end	Day	10% 10% 4 10% 7% 7% 7% 6% 7% 8% 25%	4002
April	1st to 10th	Day	10% 9% 3 9% 6% 7% 6% 6% 8% 8% 29%	2280
	11th to 20th	Day	7% 10% 3 8% 6% 6% 6% 5% 7% 6% 36%	2249
	21st to end	Day	5% 6% 3 7% 5% 5% 6% 5% 8% 9% 41%	2422
May	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 6% 47%	4420
	11th to 20th	Day	5% 4 1 4 3 3 3 3 4 7% 63%	4377
	21st to end	Day	7% 6% 2 6% 6% 5% 7% 5% 7% 8% 40%	4813
June	1st to 10th	Day	8% 6% 2 7% 5% 4 5% 5% 6% 8% 45%	2660
	11th to 20th	Day	4 4 2 6% 4 5% 5% 4 6% 9% 50%	2660
	21st to end	Day	3 2 1 4 3 4 3 3 5% 7% 65%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 3 4 84%	4420
	11th to 20th	Day	1 1 1 1 2 1 2 2 2 4 83%	4420
	21st to end	Day	1 1 1 2 2 1 2 2 3 4 82%	4790
August	1st to 10th	Day	2 3 1 3 2 2 2 2 4 5% 75%	4294
	11th to 20th	Day	1 2 1 3 2 3 4 3 5% 7% 70%	4026
	21st to end	Day	4 4 1 4 3 3 3 2 4 5% 66%	4211
September	1st to 10th	Day	2 1 1 3 2 3 2 2 5% 7% 73%	2280
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 5% 8% 58%	2280
	21st to end	Day	7% 4 2 5% 5% 3 4 3 4 6% 56%	2031
October	1st to 10th	Day	5% 4 1 5% 4 3 4 4 6% 7% 56%	3180
	11th to 20th	Day	6% 6% 3 8% 5% 6% 6% 4 7% 9% 39%	3161
	21st to end	Day	12% 7% 3 10% 7% 6% 7% 5% 7% 8% 29%	3239
November	1st to 10th	Day	15% 11% 4 9% 6% 7% 5% 5% 6% 7% 24%	1728
	11th to 20th	Day	15% 14% 4 12% 8% 7% 6% 4 6% 6% 16%	1600
	21st to end	Day	14% 13% 4 10% 7% 7% 6% 4 6% 7% 21%	1595
December	1st to 10th	Day	15% 16% 6% 13% 7% 6% 4 4 4 5% 22%	1520
	11th to 20th	Day	21% 19% 10% 16% 6% 5% 4 2 4 4 9%	1928
	21st to end	Day	23% 21% 7% 16% 6% 4 3 3 4 4 10%	2794
January	1st to 10th	Night	21% 21% 7% 14% 7% 5% 4 4 5% 4 9%	4406
	11th to 20th	Night	25% 16% 5% 10% 6% 4 4 3 4 6% 16%	4420
	21st to end	Night	30% 16% 6% 13% 6% 4 4 2 3 4 11%	4755
February	1st to 10th	Night	16% 13% 4 10% 6% 4 5% 4 6% 7% 25%	2470
	11th to 20th	Night	14% 11% 3 9% 6% 5% 5% 4 6% 7% 31%	2402
	21st to end	Night	11% 13% 5% 7% 6% 5% 6% 5% 7% 9% 26%	1904
March	1st to 10th	Night	8% 10% 4 10% 7% 6% 7% 5% 8% 10% 26%	3715
	11th to 20th	Night	7% 6% 3 6% 5% 5% 5% 4 5% 7% 48%	3490
	21st to end	Night	9% 8% 3 10% 8% 7% 7% 5% 8% 8% 26%	3650
April	1st to 10th	Night	10% 9% 3 8% 5% 6% 6% 4 8% 8% 34%	1900
	11th to 20th	Night	7% 7% 4 6% 6% 5% 5% 4 6% 8% 43%	1879
	21st to end	Night	7% 6% 2 6% 4 4 5% 5% 9% 10% 42%	1752
May	1st to 10th	Night	10% 8% 2 6% 4 3 3 3 5% 5% 50%	2540
	11th to 20th	Night	4 3 1 3 3 3 2 3 6% 7% 64%	2516
	21st to end	Night	2 4 2 7% 4 4 6% 5% 8% 10% 48%	2762
June	1st to 10th	Night	8% 6% 2 6% 4 5% 6% 5% 6% 7% 45%	1520
	11th to 20th	Night	4 4 2 4 3 3 5% 4 5% 8% 58%	1520
	21st to end	Night	2 3 1 3 3 4 4 3 4 6% 67%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 86%	2540
	11th to 20th	Night	1 1 1 1 2 1 2 3 3 83%	2540
	21st to end	Night	1 1 1 1 1 2 2 2 4 85%	2761
August	1st to 10th	Night	3 1 1 2 2 2 3 2 3 6% 76%	2623
	11th to 20th	Night	1 1 1 2 3 3 3 3 4 6% 72%	2812
	21st to end	Night	2 2 1 3 2 3 3 3 4 5% 72%	3466
September	1st to 10th	Night	1 1 1 3 2 2 3 2 3 5% 76%	1900
	11th to 20th	Night	4 4 1 4 3 3 4 3 5% 6% 62%	1900
	21st to end	Night	6% 3 1 4 3 3 3 4 5% 6% 60%	2147
October	1st to 10th	Night	5% 3 2 4 3 3 4 3 6% 8% 60%	3800
	11th to 20th	Night	7% 4 2 6% 5% 5% 6% 5% 7% 9% 45%	3777
	21st to end	Night	11% 7% 3 8% 6% 6% 6% 4 7% 7% 34%	4321
November	1st to 10th	Night	16% 9% 3 8% 6% 5% 6% 4 7% 7% 30%	2570
	11th to 20th	Night	17% 11% 4 10% 6% 6% 6% 5% 6% 6% 23%	2800
	21st to end	Night	12% 11% 4 10% 6% 5% 6% 5% 7% 8% 26%	2800
December	1st to 10th	Night	17% 16% 4 10% 7% 6% 4 4 5% 6% 22%	2660
	11th to 20th	Night	22% 17% 6% 15% 8% 6% 5% 3 4 5% 10%	3276
	21st to end	Night	21% 20% 7% 12% 5% 4 4 3 5% 6% 14%	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	44% 43% 9% 3	2539
	11th to 20th	Day	46% 41% 8% 5%	2540
	21st to end	Day	54% 42% 2 1	2901
February	1st to 10th	Day	24% 67% 6% 2 1	1710
	11th to 20th	Day	23% 67% 6% 3 1	1674
	21st to end	Day	21% 68% 5% 2 4	1548
March	1st to 10th	Day	25% 49% 11% 12% 4	3156
	11th to 20th	Day	15% 43% 11% 26% 5%	3490
	21st to end	Day	28% 48% 12% 9% 3	4002
April	1st to 10th	Day	16% 68% 7% 6% 2	2280
	11th to 20th	Day	15% 67% 8% 4 5%	2252
	21st to end	Day	12% 67% 8% 9% 4 1	2422
May	1st to 10th	Day	18% 43% 9% 16% 13% 1	4420
	11th to 20th	Day	8% 39% 8% 27% 16% 2	4380
	21st to end	Day	17% 50% 17% 14% 2	4814
June	1st to 10th	Day	8% 66% 5% 13% 7% 1	2660
	11th to 20th	Day	8% 65% 6% 14% 6% 1	2660
	21st to end	Day	6% 64% 6% 13% 10% 2	2660
July	1st to 10th	Day	3 35% 3 7% 19% 34%	4351
	11th to 20th	Day	3 35% 2 6% 17% 37%	4345
	21st to end	Day	6% 36% 6% 14% 25% 13%	4639
August	1st to 10th	Day	10% 36% 3 9% 23% 19%	4278
	11th to 20th	Day	11% 38% 9% 29% 11% 2	4065
	21st to end	Day	17% 37% 7% 15% 20% 3	4210
September	1st to 10th	Day	5% 60% 7% 15% 10% 3	2280
	11th to 20th	Day	12% 61% 7% 10% 7% 2	2280
	21st to end	Day	11% 61% 8% 12% 7% 1	2031
October	1st to 10th	Day	14% 38% 8% 24% 16% 1	3180
	11th to 20th	Day	26% 39% 12% 15% 7%	3161
	21st to end	Day	31% 43% 7% 16% 4	3239
November	1st to 10th	Day	24% 58% 7% 9% 1	1728
	11th to 20th	Day	28% 60% 5% 4 2	1600
	21st to end	Day	25% 59% 6% 5% 4 1	1595
December	1st to 10th	Day	32% 60% 4 3 1	1520
	11th to 20th	Day	42% 51% 4 2 1	1928
	21st to end	Day	46% 43% 5% 5% 1	2794
January	1st to 10th	Night	43% 45% 8% 3 1	4406
	11th to 20th	Night	43% 43% 11% 3	4420
	21st to end	Night	52% 43% 3 2	4755
February	1st to 10th	Night	24% 67% 6% 3	2470
	11th to 20th	Night	22% 66% 5% 5% 1	2404
	21st to end	Night	18% 67% 6% 6% 2 1	1904
March	1st to 10th	Night	22% 50% 12% 13% 3	3715
	11th to 20th	Night	13% 43% 11% 27% 6%	3490
	21st to end	Night	25% 51% 12% 10% 1	3650
April	1st to 10th	Night	15% 68% 8% 7% 2	1900
	11th to 20th	Night	13% 66% 8% 8% 5%	1879
	21st to end	Night	9% 68% 7% 11% 4	1752
May	1st to 10th	Night	20% 43% 6% 18% 12% 1	2540
	11th to 20th	Night	5% 40% 10% 30% 14% 2	2516
	21st to end	Night	8% 48% 31% 11% 2	2762
June	1st to 10th	Night	9% 65% 6% 14% 4 1	1520
	11th to 20th	Night	6% 65% 7% 14% 8%	1520
	21st to end	Night	6% 63% 4 15% 10% 1	1520
July	1st to 10th	Night	3 34% 2 7% 22% 31%	2500
	11th to 20th	Night	5% 35% 3 8% 17% 33%	2492
	21st to end	Night	4 34% 6% 14% 26% 15%	2674
August	1st to 10th	Night	8% 37% 2 9% 24% 19%	2615
	11th to 20th	Night	9% 38% 12% 28% 10% 2	2839
	21st to end	Night	12% 38% 9% 17% 20% 4	3466
September	1st to 10th	Night	5% 60% 7% 14% 11% 3	1900
	11th to 20th	Night	12% 61% 6% 12% 5% 4	1900
	21st to end	Night	11% 61% 6% 13% 9% 1	2147
October	1st to 10th	Night	10% 40% 7% 26% 18%	3800
	11th to 20th	Night	22% 40% 14% 16% 8%	3777
	21st to end	Night	31% 42% 7% 17% 4	4321
November	1st to 10th	Night	23% 58% 6% 9% 3	2570
	11th to 20th	Night	27% 60% 6% 5% 3	2800
	21st to end	Night	21% 59% 7% 8% 4 1	2800
December	1st to 10th	Night	30% 62% 4 4 1	2660
	11th to 20th	Night	38% 55% 4 2 1	3276
	21st to end	Night	41% 44% 7% 7% 1	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	38% 19% 18% 16% 9% 1	180
	11th to 20th	Day	34% 14% 22% 22% 6% 2	180
	21st to end	Day	27% 14% 23% 26% 10%	266
February	1st to 10th	Day	29% 20% 22% 21% 7% 1	370
	11th to 20th	Day	28% 21% 25% 19% 5% 1	365
	21st to end	Day	23% 25% 26% 17% 8% 1	372
March	1st to 10th	Day	24% 22% 30% 17% 6% 1	460
	11th to 20th	Day	22% 20% 25% 23% 8% 2	460
	21st to end	Day	24% 24% 28% 19% 5% 1	506
April	1st to 10th	Day	26% 24% 27% 13% 8% 2	460
	11th to 20th	Day	20% 29% 28% 12% 8% 2	452
	21st to end	Day	17% 27% 30% 18% 6% 2	460
May	1st to 10th	Day	17% 23% 29% 21% 8% 2	463
	11th to 20th	Day	20% 16% 31% 17% 11% 4	488
	21st to end	Day	14% 17% 33% 22% 12% 2	529
June	1st to 10th	Day	16% 21% 29% 20% 12% 3	490
	11th to 20th	Day	16% 27% 32% 15% 9% 1	490
	21st to end	Day	7% 17% 34% 27% 13% 2	490
July	1st to 10th	Day	5% 10% 45% 26% 11% 2	486
	11th to 20th	Day	4 14% 38% 27% 14% 2	484
	21st to end	Day	3 11% 37% 26% 17% 6%	531
August	1st to 10th	Day	4 10% 32% 29% 18% 7%	487
	11th to 20th	Day	3 9% 31% 28% 22% 6%	477
	21st to end	Day	8% 15% 28% 25% 18% 5%	539
September	1st to 10th	Day	4 11% 31% 28% 21% 5%	490
	11th to 20th	Day	9% 13% 31% 26% 19% 2	490
	21st to end	Day	12% 15% 26% 28% 16% 3	490
October	1st to 10th	Day	13% 17% 26% 22% 18% 4	490
	11th to 20th	Day	17% 18% 21% 25% 15% 5%	490
	21st to end	Day	21% 20% 24% 20% 11% 4	418
November	1st to 10th	Day	23% 18% 21% 25% 11% 1	282
	11th to 20th	Day	29% 20% 20% 20% 10% 2	200
	21st to end	Day	23% 18% 19% 27% 13% 1	199
December	1st to 10th	Day	22% 17% 21% 20% 15% 5%	180
	11th to 20th	Day	33% 17% 25% 19% 6%	180
	21st to end	Day	26% 20% 23% 20% 10% 1	198
January	1st to 10th	Night	26% 16% 21% 25% 11% 1	760
	11th to 20th	Night	30% 10% 19% 27% 12% 2	760
	21st to end	Night	24% 11% 18% 30% 15% 2	836
February	1st to 10th	Night	25% 13% 20% 28% 12% 1	760
	11th to 20th	Night	21% 15% 22% 28% 13% 1	744
	21st to end	Night	23% 16% 22% 29% 10%	628
March	1st to 10th	Night	19% 15% 22% 30% 13% 1	760
	11th to 20th	Night	14% 16% 22% 33% 13% 1	760
	21st to end	Night	18% 15% 31% 26% 9% 1	836
April	1st to 10th	Night	18% 16% 26% 27% 12% 1	760
	11th to 20th	Night	14% 20% 28% 22% 14% 3	751
	21st to end	Night	10% 17% 30% 28% 14%	612
May	1st to 10th	Night	11% 13% 31% 30% 14% 2	380
	11th to 20th	Night	11% 10% 25% 33% 20% 2	374
	21st to end	Night	6% 9% 32% 35% 16% 2	411
June	1st to 10th	Night	12% 14% 29% 30% 14% 1	380
	11th to 20th	Night	9% 17% 33% 29% 11%	380
	21st to end	Night	5% 13% 27% 36% 19% 1	380
July	1st to 10th	Night	3 8% 29% 39% 20% 1	370
	11th to 20th	Night	2 5% 37% 39% 16% 1	368
	21st to end	Night	2 7% 27% 39% 24% 1	416
August	1st to 10th	Night	3 6% 22% 42% 24% 3	433
	11th to 20th	Night	2 4 18% 35% 33% 8%	564
	21st to end	Night	3 11% 28% 33% 21% 4	817
September	1st to 10th	Night	3 7% 24% 34% 28% 4	760
	11th to 20th	Night	5% 8% 26% 28% 28% 6%	760
	21st to end	Night	8% 8% 21% 32% 28% 3	760
October	1st to 10th	Night	11% 8% 20% 38% 19% 3	760
	11th to 20th	Night	14% 10% 19% 33% 22% 3	760
	21st to end	Night	19% 10% 23% 29% 16% 3	836
November	1st to 10th	Night	20% 12% 21% 34% 12% 1	780
	11th to 20th	Night	28% 12% 22% 25% 12% 1	800
	21st to end	Night	15% 10% 24% 33% 15% 2	800
December	1st to 10th	Night	23% 11% 21% 29% 15% 2	760
	11th to 20th	Night	28% 12% 19% 28% 13% 1	760
	21st to end	Night	28% 16% 22% 26% 8%	836

Page generated at 2024-11-27 14:30:51. Version ac07

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