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 2024-01-15.

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	9% 7% 3 6% 6% 3 5% 5% 5% 7% 43%	74779
	Night	11% 8% 4 7% 6% 3 5% 5% 5% 7% 40%	75012
Transparency	Day	39% 9% 14% 20% 14% 4	74482
	Night	42% 10% 15% 19% 11% 3	74830
Seeing	Day	16% 18% 29% 22% 12% 3	13420
	Night	16% 12% 23% 31% 17% 2	22549

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% 18% 7% 13% 10% 5% 6% 5% 3 4 9%	1519
	11th to 20th	Day	19% 15% 7% 11% 9% 6% 8% 6% 4 5% 11%	1472
	21st to end	Day	15% 12% 6% 14% 10% 5% 6% 6% 5% 7% 14%	1649
February	1st to 10th	Day	17% 14% 5% 8% 7% 4 7% 6% 7% 6% 21%	1620
	11th to 20th	Day	13% 9% 4 7% 7% 5% 8% 7% 8% 7% 26%	1575
	21st to end	Day	10% 10% 4 10% 8% 5% 6% 7% 7% 7% 26%	1459
March	1st to 10th	Day	13% 11% 4 8% 8% 4 7% 8% 7% 9% 24%	1805
	11th to 20th	Day	12% 10% 4 9% 8% 5% 7% 7% 6% 8% 24%	1980
	21st to end	Day	10% 9% 5% 10% 7% 5% 8% 7% 7% 8% 24%	2278
April	1st to 10th	Day	11% 8% 3 8% 7% 5% 7% 7% 7% 9% 29%	2160
	11th to 20th	Day	8% 9% 3 7% 7% 5% 7% 6% 6% 7% 36%	2129
	21st to end	Day	5% 5% 2 6% 5% 4 6% 7% 8% 10% 41%	2294
May	1st to 10th	Day	6% 4 2 6% 6% 4 5% 6% 6% 7% 50%	2520
	11th to 20th	Day	8% 6% 2 6% 6% 3 6% 5% 6% 10% 42%	2477
	21st to end	Day	8% 5% 2 5% 6% 3 6% 5% 6% 9% 44%	2723
June	1st to 10th	Day	7% 5% 3 6% 5% 3 5% 6% 6% 9% 45%	2520
	11th to 20th	Day	4 4 2 5% 5% 3 6% 5% 6% 10% 50%	2520
	21st to end	Day	3 2 1 3 3 3 4 4 5% 7% 65%	2520
July	1st to 10th	Day	1 1 1 2 2 2 2 3 4 6% 75%	2520
	11th to 20th	Day	2 1 1 2 2 1 2 3 4 5% 76%	2520
	21st to end	Day	1 1 1 1 2 1 1 2 2 3 85%	2741
August	1st to 10th	Day	1 2 1 2 2 1 2 2 4 6% 77%	2453
	11th to 20th	Day	2 2 2 2 2 3 3 3 6% 77%	2298
	21st to end	Day	2 1 1 3 3 2 3 3 5% 6% 70%	2394
September	1st to 10th	Day	2 1 1 2 2 2 2 3 4 7% 73%	2160
	11th to 20th	Day	4 3 1 4 5% 3 5% 5% 5% 8% 58%	2160
	21st to end	Day	7% 5% 2 5% 6% 3 4 4 4 6% 55%	1925
October	1st to 10th	Day	7% 5% 3 5% 6% 3 5% 5% 6% 8% 48%	1800
	11th to 20th	Day	9% 6% 4 6% 6% 4 6% 5% 7% 9% 40%	1800
	21st to end	Day	14% 8% 3 8% 7% 4 5% 5% 6% 7% 33%	1866
November	1st to 10th	Day	15% 10% 5% 8% 7% 5% 7% 6% 6% 7% 24%	1640
	11th to 20th	Day	15% 14% 5% 11% 9% 6% 7% 5% 5% 7% 17%	1520
	21st to end	Day	15% 12% 4 10% 8% 6% 6% 5% 6% 7% 21%	1520
December	1st to 10th	Day	15% 14% 7% 11% 8% 4 5% 5% 4 5% 22%	1520
	11th to 20th	Day	21% 18% 10% 15% 7% 4 5% 3 4 4 9%	1928
	21st to end	Day	23% 20% 8% 14% 8% 3 4 3 4 4 10%	2794
January	1st to 10th	Night	19% 16% 7% 12% 8% 4 5% 5% 6% 5% 13%	2646
	11th to 20th	Night	20% 15% 7% 10% 8% 4 5% 5% 5% 6% 16%	2576
	21st to end	Night	16% 11% 5% 11% 8% 4 6% 5% 5% 7% 20%	2704
February	1st to 10th	Night	16% 12% 4 8% 7% 3 5% 5% 6% 8% 25%	2340
	11th to 20th	Night	13% 10% 4 7% 7% 3 6% 5% 6% 7% 33%	2272
	21st to end	Night	10% 12% 6% 7% 7% 3 6% 6% 7% 9% 27%	1795
March	1st to 10th	Night	13% 10% 3 7% 7% 4 7% 6% 7% 8% 28%	2152
	11th to 20th	Night	11% 7% 4 6% 8% 5% 6% 7% 7% 9% 31%	1980
	21st to end	Night	9% 9% 4 8% 8% 5% 7% 6% 7% 7% 30%	2077
April	1st to 10th	Night	10% 9% 3 7% 6% 4 6% 6% 7% 9% 34%	1800
	11th to 20th	Night	8% 6% 4 5% 7% 4 5% 5% 6% 7% 43%	1779
	21st to end	Night	7% 5% 2 5% 4 3 5% 6% 8% 10% 44%	1661
May	1st to 10th	Night	5% 3 2 5% 5% 3 5% 5% 6% 7% 53%	1440
	11th to 20th	Night	6% 5% 2 4 5% 3 4 5% 7% 8% 50%	1416
	21st to end	Night	4 5% 2 5% 5% 3 5% 7% 6% 11% 48%	1552
June	1st to 10th	Night	8% 5% 3 5% 5% 3 7% 5% 6% 8% 45%	1440
	11th to 20th	Night	4 4 2 4 4 2 5% 5% 5% 8% 57%	1440
	21st to end	Night	3 3 1 2 4 2 4 4 4 6% 67%	1440
July	1st to 10th	Night	2 1 1 2 2 2 2 3 4 5% 77%	1440
	11th to 20th	Night	1 1 1 1 2 2 1 3 4 5% 80%	1440
	21st to end	Night	1 1 1 1 1 1 2 2 4 86%	1576
August	1st to 10th	Night	2 1 1 2 2 1 2 2 3 6% 77%	1484
	11th to 20th	Night	2 1 1 2 3 2 2 3 3 4 78%	1602
	21st to end	Night	1 1 1 2 2 1 3 3 4 6% 75%	1962
September	1st to 10th	Night	2 2 1 2 2 1 3 3 3 5% 77%	1800
	11th to 20th	Night	4 3 2 3 4 2 4 4 5% 6% 62%	1800
	21st to end	Night	7% 3 1 3 5% 3 3 5% 5% 6% 59%	2034
October	1st to 10th	Night	8% 5% 2 5% 4 2 4 4 5% 6% 54%	2160
	11th to 20th	Night	10% 5% 2 5% 6% 3 5% 5% 5% 7% 46%	2160
	21st to end	Night	12% 8% 3 5% 4 4 4 4 7% 7% 42%	2488
November	1st to 10th	Night	16% 8% 3 7% 7% 4 6% 5% 7% 7% 30%	2438
	11th to 20th	Night	17% 11% 4 9% 7% 4 6% 6% 5% 7% 23%	2660
	21st to end	Night	12% 9% 5% 9% 8% 4 6% 6% 6% 8% 27%	2660
December	1st to 10th	Night	18% 13% 5% 9% 8% 4 5% 5% 5% 6% 22%	2660
	11th to 20th	Night	22% 16% 6% 14% 9% 4 6% 4 4 5% 10%	3276
	21st to end	Night	21% 20% 7% 10% 7% 3 5% 4 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	76% 10% 9% 5% 1	1519
	11th to 20th	Day	71% 9% 12% 7% 1 1	1472
	21st to end	Day	64% 11% 13% 9% 3	1649
February	1st to 10th	Day	59% 12% 16% 10% 2	1620
	11th to 20th	Day	50% 13% 18% 14% 4	1584
	21st to end	Day	53% 13% 16% 10% 7% 1	1459
March	1st to 10th	Day	53% 12% 16% 13% 6%	1805
	11th to 20th	Day	55% 10% 13% 18% 4	1980
	21st to end	Day	55% 13% 17% 13% 2	2278
April	1st to 10th	Day	49% 12% 18% 16% 7%	2160
	11th to 20th	Day	46% 10% 17% 15% 10% 2	2132
	21st to end	Day	35% 12% 19% 20% 11% 2	2294
May	1st to 10th	Day	31% 10% 18% 27% 14%	2520
	11th to 20th	Day	37% 9% 16% 24% 12% 1	2480
	21st to end	Day	34% 11% 20% 24% 9%	2724
June	1st to 10th	Day	35% 8% 16% 27% 11% 2	2520
	11th to 20th	Day	28% 8% 20% 33% 11% 1	2520
	21st to end	Day	19% 6% 16% 34% 19% 6%	2520
July	1st to 10th	Day	11% 5% 13% 29% 28% 13%	2451
	11th to 20th	Day	12% 4 9% 21% 36% 18%	2445
	21st to end	Day	7% 3 6% 24% 42% 19%	2589
August	1st to 10th	Day	10% 4 11% 28% 34% 12%	2436
	11th to 20th	Day	11% 4 11% 29% 33% 12%	2298
	21st to end	Day	15% 5% 12% 30% 31% 6%	2394
September	1st to 10th	Day	13% 3 12% 31% 28% 13%	2160
	11th to 20th	Day	25% 7% 15% 24% 21% 7%	2160
	21st to end	Day	29% 8% 15% 25% 18% 5%	1925
October	1st to 10th	Day	33% 9% 15% 25% 16% 2	1800
	11th to 20th	Day	39% 9% 17% 21% 13% 1	1800
	21st to end	Day	48% 11% 12% 20% 9%	1866
November	1st to 10th	Day	55% 11% 15% 16% 4	1640
	11th to 20th	Day	62% 13% 13% 8% 3 1	1520
	21st to end	Day	57% 11% 15% 10% 6% 1	1520
December	1st to 10th	Day	63% 8% 13% 12% 4	1520
	11th to 20th	Day	74% 10% 10% 5% 1	1928
	21st to end	Day	71% 11% 10% 7% 1	2794
January	1st to 10th	Night	70% 12% 10% 6% 1	2646
	11th to 20th	Night	65% 10% 13% 9% 3	2576
	21st to end	Night	58% 12% 15% 12% 2 1	2704
February	1st to 10th	Night	55% 11% 17% 13% 2	2340
	11th to 20th	Night	49% 11% 17% 18% 5% 1	2274
	21st to end	Night	50% 12% 16% 16% 5% 1	1795
March	1st to 10th	Night	49% 13% 16% 16% 5% 1	2152
	11th to 20th	Night	46% 13% 16% 19% 5% 1	1980
	21st to end	Night	50% 12% 18% 15% 4	2077
April	1st to 10th	Night	42% 13% 19% 17% 7% 1	1800
	11th to 20th	Night	38% 10% 21% 19% 10% 2	1779
	21st to end	Night	32% 14% 20% 22% 11% 2	1661
May	1st to 10th	Night	27% 9% 20% 29% 13% 1	1440
	11th to 20th	Night	30% 9% 21% 26% 11% 2	1416
	21st to end	Night	28% 12% 27% 24% 9%	1552
June	1st to 10th	Night	37% 8% 15% 30% 9% 1	1440
	11th to 20th	Night	24% 8% 23% 33% 11% 1	1440
	21st to end	Night	19% 5% 13% 37% 19% 6%	1440
July	1st to 10th	Night	11% 5% 15% 27% 28% 14%	1400
	11th to 20th	Night	9% 4 12% 23% 34% 18%	1392
	21st to end	Night	6% 2 7% 20% 44% 21%	1488
August	1st to 10th	Night	10% 4 10% 31% 32% 12%	1476
	11th to 20th	Night	11% 4 12% 29% 33% 11%	1602
	21st to end	Night	11% 5% 12% 32% 33% 7%	1962
September	1st to 10th	Night	12% 4 14% 30% 27% 14%	1800
	11th to 20th	Night	23% 8% 13% 27% 18% 12%	1800
	21st to end	Night	25% 7% 15% 26% 21% 6%	2034
October	1st to 10th	Night	31% 6% 12% 26% 23% 2	2160
	11th to 20th	Night	36% 9% 14% 24% 14% 2	2160
	21st to end	Night	39% 11% 13% 22% 15% 1	2488
November	1st to 10th	Night	48% 12% 13% 20% 6%	2438
	11th to 20th	Night	58% 11% 14% 13% 4	2660
	21st to end	Night	50% 13% 15% 15% 6% 1	2660
December	1st to 10th	Night	60% 10% 14% 13% 3	2660
	11th to 20th	Night	70% 13% 10% 5% 1	3276
	21st to end	Night	64% 14% 10% 10% 2	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	33% 14% 23% 22% 6% 2	168
	21st to end	Day	27% 13% 23% 26% 11%	241
February	1st to 10th	Day	31% 20% 20% 21% 7% 1	340
	11th to 20th	Day	29% 21% 26% 19% 4 1	335
	21st to end	Day	23% 24% 27% 18% 8%	337
March	1st to 10th	Day	26% 21% 29% 16% 6% 1	420
	11th to 20th	Day	24% 20% 26% 22% 7% 1	420
	21st to end	Day	25% 23% 27% 19% 5% 1	462
April	1st to 10th	Day	27% 22% 27% 13% 8% 2	420
	11th to 20th	Day	21% 29% 28% 12% 7% 3	412
	21st to end	Day	17% 26% 30% 19% 5% 2	420
May	1st to 10th	Day	15% 23% 30% 22% 8% 2	423
	11th to 20th	Day	22% 15% 31% 16% 11% 4	448
	21st to end	Day	13% 17% 33% 23% 12% 2	485
June	1st to 10th	Day	14% 22% 29% 19% 13% 3	450
	11th to 20th	Day	15% 26% 34% 15% 9% 1	450
	21st to end	Day	7% 17% 35% 26% 13% 2	450
July	1st to 10th	Day	5% 9% 47% 27% 11% 1	446
	11th to 20th	Day	5% 15% 38% 26% 14% 2	444
	21st to end	Day	3 11% 36% 26% 17% 6%	487
August	1st to 10th	Day	4 10% 33% 29% 18% 7%	447
	11th to 20th	Day	3 9% 30% 27% 24% 7%	437
	21st to end	Day	7% 15% 30% 25% 19% 5%	495
September	1st to 10th	Day	4 12% 31% 28% 20% 5%	450
	11th to 20th	Day	9% 13% 30% 27% 20% 2	450
	21st to end	Day	12% 16% 26% 28% 15% 3	450
October	1st to 10th	Day	13% 17% 27% 23% 17% 4	450
	11th to 20th	Day	17% 18% 20% 25% 15% 6%	450
	21st to end	Day	22% 19% 23% 20% 12% 4	381
November	1st to 10th	Day	22% 19% 22% 25% 11% 1	254
	11th to 20th	Day	27% 19% 19% 22% 11% 2	180
	21st to end	Day	25% 18% 17% 27% 13% 1	180
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	736
	21st to end	Night	23% 10% 18% 31% 16% 2	792
February	1st to 10th	Night	25% 13% 20% 28% 13% 1	720
	11th to 20th	Night	21% 14% 21% 29% 14% 1	704
	21st to end	Night	21% 16% 22% 29% 10%	592
March	1st to 10th	Night	20% 15% 22% 30% 13% 1	720
	11th to 20th	Night	15% 17% 22% 34% 13%	720
	21st to end	Night	18% 15% 30% 26% 9% 1	792
April	1st to 10th	Night	18% 15% 26% 28% 13% 1	720
	11th to 20th	Night	15% 20% 27% 22% 14% 3	711
	21st to end	Night	11% 16% 30% 28% 14% 1	581
May	1st to 10th	Night	11% 12% 30% 31% 15% 2	360
	11th to 20th	Night	11% 9% 24% 34% 20% 2	354
	21st to end	Night	6% 9% 31% 35% 17% 2	389
June	1st to 10th	Night	11% 14% 29% 30% 15% 1	360
	11th to 20th	Night	9% 18% 33% 29% 12%	360
	21st to end	Night	5% 13% 27% 36% 19% 1	360
July	1st to 10th	Night	3 8% 29% 39% 21% 1	350
	11th to 20th	Night	2 5% 36% 39% 16% 1	348
	21st to end	Night	2 7% 26% 39% 25% 2	394
August	1st to 10th	Night	3 5% 21% 42% 25% 3	410
	11th to 20th	Night	2 4 16% 35% 35% 8%	534
	21st to end	Night	3 10% 28% 33% 21% 4	774
September	1st to 10th	Night	3 8% 24% 34% 28% 4	720
	11th to 20th	Night	5% 7% 24% 29% 30% 6%	720
	21st to end	Night	8% 8% 21% 32% 28% 3	720
October	1st to 10th	Night	12% 8% 20% 37% 19% 4	720
	11th to 20th	Night	15% 9% 18% 32% 23% 3	720
	21st to end	Night	19% 10% 22% 29% 17% 3	792
November	1st to 10th	Night	19% 12% 22% 34% 12% 1	740
	11th to 20th	Night	27% 11% 22% 26% 13% 1	760
	21st to end	Night	16% 10% 24% 33% 15% 3	760
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 2024-01-11 19:33:47. Version ac07

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