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 2026-02-16.

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 5% 4 5% 6% 46%	140000
	Night	11% 8% 3 8% 5% 4 5% 4 5% 6% 41%	138158
Transparency	Day	23% 39% 8% 15% 10% 4	134738
	Night	26% 39% 9% 15% 8% 3	134421
Seeing	Day	16% 18% 29% 22% 12% 3	16027
	Night	16% 12% 24% 31% 16% 2	25160

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	21% 19% 7% 17% 8% 6% 5% 4 4 3 6%	4722
	11th to 20th	Day	13% 9% 3 9% 6% 6% 6% 5% 6% 6% 32%	4740
	21st to end	Day	20% 13% 5% 12% 6% 5% 4 3 5% 5% 24%	5405
February	1st to 10th	Day	16% 15% 5% 9% 6% 6% 7% 4 7% 6% 20%	1890
	11th to 20th	Day	14% 11% 4 8% 6% 6% 6% 5% 7% 7% 25%	1801
	21st to end	Day	10% 12% 3 11% 7% 6% 7% 5% 7% 7% 25%	1627
March	1st to 10th	Day	8% 10% 3 9% 6% 6% 7% 6% 8% 9% 27%	4549
	11th to 20th	Day	10% 11% 3 9% 5% 6% 5% 4 6% 6% 35%	5000
	21st to end	Day	10% 10% 4 11% 7% 8% 8% 6% 8% 9% 21%	5741
April	1st to 10th	Day	10% 9% 3 9% 6% 7% 6% 6% 8% 8% 29%	2400
	11th to 20th	Day	7% 9% 2 7% 6% 6% 6% 4 7% 6% 38%	2369
	21st to end	Day	5% 5% 3 7% 5% 5% 6% 5% 8% 9% 42%	2550
May	1st to 10th	Day	8% 5% 1 5% 4 4 4 4 5% 6% 53%	6320
	11th to 20th	Day	4 5% 2 5% 4 5% 5% 4 6% 9% 51%	6277
	21st to end	Day	6% 5% 1 5% 5% 4 5% 4 6% 8% 51%	6902
June	1st to 10th	Day	7% 6% 2 6% 4 4 5% 5% 6% 8% 47%	2800
	11th to 20th	Day	4 4 2 6% 4 5% 5% 4 7% 9% 51%	2800
	21st to end	Day	3 2 1 4 3 4 4 3 5% 7% 65%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 3 4 84%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 3 85%	6320
	21st to end	Day	2 1 1 2 2 1 2 2 3 5% 80%	6880
August	1st to 10th	Day	2 3 1 3 2 2 3 3 4 5% 71%	6067
	11th to 20th	Day	1 2 1 3 2 3 3 3 4 6% 71%	5796
	21st to end	Day	5% 5% 1 4 3 3 3 3 5% 7% 61%	6028
September	1st to 10th	Day	2 1 1 3 2 3 2 3 5% 7% 71%	2400
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 5% 7% 59%	2400
	21st to end	Day	7% 4 2 5% 4 3 4 3 4 6% 57%	2138
October	1st to 10th	Day	5% 4 1 5% 4 3 4 4 6% 7% 56%	3280
	11th to 20th	Day	6% 6% 3 8% 6% 6% 6% 4 7% 9% 39%	3261
	21st to end	Day	12% 7% 3 10% 7% 6% 7% 5% 7% 8% 29%	3342
November	1st to 10th	Day	15% 11% 4 10% 6% 7% 5% 5% 6% 7% 23%	1816
	11th to 20th	Day	15% 14% 4 13% 8% 7% 6% 4 6% 6% 16%	1680
	21st to end	Day	15% 13% 4 10% 7% 7% 6% 4 6% 7% 20%	1680
December	1st to 10th	Day	12% 11% 4 16% 8% 6% 6% 4 4 5% 23%	2700
	11th to 20th	Day	24% 19% 8% 15% 6% 6% 4 3 4 4 7%	3108
	21st to end	Day	21% 18% 6% 16% 8% 6% 5% 3 4 4 7%	4092
January	1st to 10th	Night	24% 18% 6% 14% 7% 5% 5% 4 4 4 8%	8172
	11th to 20th	Night	14% 9% 3 8% 4 4 5% 3 5% 6% 38%	8220
	21st to end	Night	20% 13% 4 10% 5% 4 3 2 4 5% 30%	8784
February	1st to 10th	Night	15% 13% 4 10% 6% 5% 6% 5% 6% 7% 24%	2730
	11th to 20th	Night	14% 11% 3 9% 6% 5% 5% 4 6% 7% 30%	2597
	21st to end	Night	11% 13% 5% 7% 6% 5% 6% 5% 7% 8% 27%	2001
March	1st to 10th	Night	7% 8% 3 9% 7% 7% 7% 6% 8% 10% 28%	5342
	11th to 20th	Night	9% 9% 4 9% 6% 5% 6% 4 5% 6% 37%	5000
	21st to end	Night	11% 8% 3 10% 8% 7% 7% 5% 8% 9% 22%	5233
April	1st to 10th	Night	10% 8% 3 7% 5% 5% 6% 5% 8% 9% 35%	2000
	11th to 20th	Night	7% 6% 4 6% 6% 4 5% 4 6% 8% 44%	1979
	21st to end	Night	6% 6% 2 6% 4 4 6% 5% 9% 10% 43%	1844
May	1st to 10th	Night	9% 6% 2 5% 3 2 3 3 4 6% 57%	3640
	11th to 20th	Night	3 5% 2 5% 4 4 4 4 7% 7% 55%	3616
	21st to end	Night	6% 3 1 6% 3 3 5% 5% 7% 9% 51%	3972
June	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 5% 5% 7% 47%	1600
	11th to 20th	Night	4 4 2 4 3 3 5% 4 5% 9% 58%	1600
	21st to end	Night	2 3 1 3 3 4 4 3 4 6% 67%	1600
July	1st to 10th	Night	1 1 1 1 2 2 2 3 4 82%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 86%	3640
	21st to end	Night	2 2 1 1 1 1 1 4 5% 82%	3970
August	1st to 10th	Night	3 2 1 3 3 3 3 3 4 7% 69%	3716
	11th to 20th	Night	3 2 1 3 3 3 3 3 4 5% 70%	4052
	21st to end	Night	3 3 1 4 3 3 3 3 5% 6% 66%	4969
September	1st to 10th	Night	2 2 1 3 2 2 3 2 3 6% 74%	2000
	11th to 20th	Night	4 4 1 4 3 3 4 3 5% 6% 63%	2000
	21st to end	Night	6% 3 1 4 3 3 3 4 5% 6% 61%	2260
October	1st to 10th	Night	5% 3 2 4 3 3 4 3 5% 8% 60%	3920
	11th to 20th	Night	7% 4 2 6% 5% 5% 6% 5% 7% 9% 44%	3897
	21st to end	Night	11% 7% 3 8% 6% 7% 6% 4 7% 7% 34%	4460
November	1st to 10th	Night	16% 9% 3 9% 6% 5% 6% 4 7% 7% 29%	2702
	11th to 20th	Night	17% 11% 4 10% 7% 6% 6% 5% 6% 6% 23%	2940
	21st to end	Night	13% 11% 4 10% 7% 5% 6% 5% 6% 7% 26%	2940
December	1st to 10th	Night	11% 10% 3 12% 6% 6% 6% 5% 6% 7% 30%	4700
	11th to 20th	Night	26% 17% 6% 15% 7% 6% 5% 3 4 4 8%	5316
	21st to end	Night	23% 17% 6% 12% 6% 5% 6% 3 4 5% 12%	7106

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	62% 26% 7% 4 1	4723
	11th to 20th	Day	31% 27% 13% 20% 8% 2	4740
	21st to end	Day	47% 24% 5% 15% 8%	5405
February	1st to 10th	Day	28% 62% 7% 3 1	1890
	11th to 20th	Day	26% 62% 6% 4 1	1810
	21st to end	Day	22% 65% 6% 2 5%	1627
March	1st to 10th	Day	31% 36% 11% 12% 9%	4549
	11th to 20th	Day	31% 32% 10% 22% 5%	5000
	21st to end	Day	38% 37% 13% 10% 2	5741
April	1st to 10th	Day	17% 65% 8% 8% 2	2400
	11th to 20th	Day	15% 64% 8% 8% 5%	2372
	21st to end	Day	12% 64% 8% 11% 5% 1	2550
May	1st to 10th	Day	19% 31% 8% 22% 18% 2	6320
	11th to 20th	Day	19% 33% 12% 24% 11% 1	6280
	21st to end	Day	15% 36% 18% 24% 6%	6904
June	1st to 10th	Day	8% 63% 6% 14% 8% 1	2800
	11th to 20th	Day	9% 62% 5% 15% 8% 1	2800
	21st to end	Day	7% 61% 7% 14% 9% 2	2800
July	1st to 10th	Day	5% 24% 4 19% 24% 24%	6251
	11th to 20th	Day	4 25% 2 12% 26% 31%	6245
	21st to end	Day	8% 25% 7% 28% 22% 9%	6681
August	1st to 10th	Day	10% 36% 3 10% 22% 19%	4415
	11th to 20th	Day	11% 37% 9% 30% 11% 3	4195
	21st to end	Day	17% 36% 7% 15% 20% 4	4343
September	1st to 10th	Day	7% 58% 8% 15% 10% 3	2400
	11th to 20th	Day	12% 58% 7% 12% 8% 2	2400
	21st to end	Day	12% 58% 8% 13% 9% 1	2138
October	1st to 10th	Day	15% 37% 8% 25% 15% 1	3280
	11th to 20th	Day	27% 38% 12% 15% 7%	3261
	21st to end	Day	31% 42% 7% 16% 4	3342
November	1st to 10th	Day	26% 56% 8% 9% 1	1816
	11th to 20th	Day	30% 57% 6% 5% 2	1680
	21st to end	Day	27% 57% 7% 5% 4	1680
December	1st to 10th	Day	37% 41% 10% 10% 2	2700
	11th to 20th	Day	58% 35% 5% 3 1	3108
	21st to end	Day	57% 33% 5% 4 1	4092
January	1st to 10th	Night	60% 28% 7% 4 1	8172
	11th to 20th	Night	28% 26% 13% 23% 8% 1	8220
	21st to end	Night	44% 25% 5% 17% 10%	8784
February	1st to 10th	Night	27% 61% 7% 4 1	2730
	11th to 20th	Night	24% 62% 5% 6% 2	2599
	21st to end	Night	19% 64% 6% 7% 3	2001
March	1st to 10th	Night	27% 38% 12% 15% 7% 1	5342
	11th to 20th	Night	30% 34% 11% 21% 5%	5000
	21st to end	Night	36% 39% 13% 12% 1	5233
April	1st to 10th	Night	15% 65% 9% 9% 2	2000
	11th to 20th	Night	12% 63% 8% 10% 6%	1979
	21st to end	Night	10% 65% 7% 12% 5%	1844
May	1st to 10th	Night	18% 30% 5% 21% 24% 1	3637
	11th to 20th	Night	15% 32% 16% 27% 10% 1	3616
	21st to end	Night	13% 35% 26% 20% 5%	3972
June	1st to 10th	Night	9% 62% 6% 16% 5% 1	1600
	11th to 20th	Night	6% 62% 6% 16% 9% 1	1600
	21st to end	Night	7% 61% 6% 15% 10% 1	1600
July	1st to 10th	Night	6% 25% 5% 16% 25% 23%	3600
	11th to 20th	Night	5% 24% 3 9% 31% 27%	3592
	21st to end	Night	6% 24% 8% 28% 23% 10%	3857
August	1st to 10th	Night	9% 36% 3 10% 24% 19%	2698
	11th to 20th	Night	10% 37% 12% 28% 10% 3	2929
	21st to end	Night	12% 37% 9% 17% 20% 5%	3575
September	1st to 10th	Night	7% 57% 8% 14% 11% 3	2000
	11th to 20th	Night	12% 58% 6% 13% 7% 3	2000
	21st to end	Night	11% 58% 6% 15% 10% 1	2260
October	1st to 10th	Night	11% 38% 7% 27% 17%	3920
	11th to 20th	Night	23% 39% 14% 16% 8%	3897
	21st to end	Night	31% 41% 7% 17% 4	4460
November	1st to 10th	Night	25% 56% 7% 9% 3	2702
	11th to 20th	Night	28% 57% 6% 6% 3	2940
	21st to end	Night	24% 56% 7% 8% 4 1	2940
December	1st to 10th	Night	29% 39% 10% 20% 2	4700
	11th to 20th	Night	55% 36% 5% 3 1	5316
	21st to end	Night	51% 34% 8% 6% 1	7106

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	35% 19% 20% 16% 9%	220
	11th to 20th	Day	29% 13% 25% 24% 8% 2	220
	21st to end	Day	23% 14% 26% 25% 12%	318
February	1st to 10th	Day	29% 19% 23% 22% 7% 1	430
	11th to 20th	Day	28% 20% 27% 20% 4 1	411
	21st to end	Day	24% 23% 26% 19% 7%	403
March	1st to 10th	Day	24% 22% 29% 18% 6% 1	500
	11th to 20th	Day	23% 22% 24% 21% 8% 2	500
	21st to end	Day	24% 24% 28% 18% 5% 1	550
April	1st to 10th	Day	25% 24% 28% 13% 8% 3	500
	11th to 20th	Day	20% 28% 28% 13% 8% 2	492
	21st to end	Day	16% 25% 31% 19% 6% 2	500
May	1st to 10th	Day	17% 22% 29% 21% 9% 3	503
	11th to 20th	Day	21% 18% 31% 16% 10% 4	528
	21st to end	Day	13% 18% 32% 23% 12% 3	573
June	1st to 10th	Day	15% 20% 30% 20% 13% 3	530
	11th to 20th	Day	16% 27% 33% 15% 8% 1	530
	21st to end	Day	8% 17% 34% 26% 13% 3	530
July	1st to 10th	Day	5% 10% 46% 25% 11% 2	526
	11th to 20th	Day	4 14% 39% 27% 14% 2	524
	21st to end	Day	3 11% 37% 26% 17% 5%	575
August	1st to 10th	Day	5% 9% 33% 28% 18% 7%	527
	11th to 20th	Day	3 10% 32% 27% 22% 6%	517
	21st to end	Day	8% 14% 27% 26% 19% 5%	583
September	1st to 10th	Day	4 10% 31% 28% 21% 6%	530
	11th to 20th	Day	8% 13% 32% 27% 18% 2	530
	21st to end	Day	12% 15% 26% 28% 16% 4	530
October	1st to 10th	Day	13% 17% 26% 23% 17% 4	530
	11th to 20th	Day	18% 18% 22% 24% 14% 5%	530
	21st to end	Day	21% 20% 24% 20% 11% 4	455
November	1st to 10th	Day	24% 20% 20% 25% 10% 1	310
	11th to 20th	Day	28% 20% 20% 21% 9% 2	220
	21st to end	Day	23% 18% 20% 27% 12%	220
December	1st to 10th	Day	26% 15% 19% 22% 15% 4	220
	11th to 20th	Day	35% 17% 25% 17% 5%	220
	21st to end	Day	26% 21% 23% 21% 9%	242
January	1st to 10th	Night	28% 16% 22% 24% 10% 1	840
	11th to 20th	Night	28% 10% 20% 29% 12% 1	840
	21st to end	Night	22% 11% 19% 31% 15% 2	924
February	1st to 10th	Night	25% 13% 20% 29% 12% 1	840
	11th to 20th	Night	21% 15% 22% 28% 13% 1	804
	21st to end	Night	23% 16% 22% 29% 10%	660
March	1st to 10th	Night	19% 15% 23% 31% 12% 1	800
	11th to 20th	Night	15% 17% 22% 33% 13% 1	800
	21st to end	Night	18% 16% 30% 26% 9% 1	880
April	1st to 10th	Night	17% 16% 26% 27% 12% 1	800
	11th to 20th	Night	14% 20% 27% 23% 14% 2	791
	21st to end	Night	10% 18% 30% 29% 13%	644
May	1st to 10th	Night	11% 13% 30% 31% 15% 2	400
	11th to 20th	Night	11% 12% 24% 32% 19% 2	394
	21st to end	Night	7% 9% 32% 35% 16% 2	433
June	1st to 10th	Night	11% 14% 30% 29% 15% 1	400
	11th to 20th	Night	9% 19% 33% 28% 11%	400
	21st to end	Night	5% 13% 29% 35% 19% 1	400
July	1st to 10th	Night	3 9% 30% 38% 20% 1	390
	11th to 20th	Night	2 6% 37% 39% 15% 1	388
	21st to end	Night	2 7% 28% 39% 23% 1	438
August	1st to 10th	Night	2 6% 23% 42% 24% 3	456
	11th to 20th	Night	3 4 19% 34% 32% 8%	594
	21st to end	Night	3 10% 27% 34% 21% 4	860
September	1st to 10th	Night	3 8% 24% 33% 28% 4	800
	11th to 20th	Night	5% 8% 26% 28% 27% 5%	800
	21st to end	Night	8% 9% 21% 32% 28% 3	800
October	1st to 10th	Night	11% 9% 20% 38% 19% 3	800
	11th to 20th	Night	15% 11% 19% 32% 21% 3	800
	21st to end	Night	19% 10% 23% 30% 15% 3	880
November	1st to 10th	Night	20% 12% 21% 34% 11% 1	820
	11th to 20th	Night	27% 13% 23% 25% 12% 1	840
	21st to end	Night	16% 10% 23% 33% 15% 2	840
December	1st to 10th	Night	24% 10% 20% 29% 15% 2	840
	11th to 20th	Night	29% 12% 18% 28% 12%	840
	21st to end	Night	28% 16% 23% 26% 8%	924

Page generated at 2026-02-12 22:42:11. Version ac07

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