Chuchupate Ranger Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chuchupate Ranger Station clear sky chart from 2005-11-06 to 2025-12-03.

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 3 2 2 3 3 4 6% 73%	135100
	Night	2 3 1 3 2 3 3 3 4 6% 70%	133097
Transparency	Day	13% 3 7% 17% 30% 31%	130181
	Night	13% 4 8% 17% 29% 29%	128988
Seeing	Day	7% 14% 30% 33% 13% 3	16969
	Night	5% 7% 22% 36% 25% 5%	26692

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	2 4 2 4 3 3 3 3 4 7% 66%	3639
	11th to 20th	Day	2 4 2 4 2 2 3 3 5% 8% 66%	4081
	21st to end	Day	3 7% 3 5% 3 3 4 4 6% 9% 53%	4662
February	1st to 10th	Day	3 6% 2 5% 4 3 4 4 5% 6% 57%	2000
	11th to 20th	Day	4 6% 2 6% 3 4 4 3 6% 9% 54%	1950
	21st to end	Day	4 8% 2 5% 4 4 4 4 5% 6% 55%	1650
March	1st to 10th	Day	4 8% 2 5% 5% 5% 4 4 5% 7% 51%	4518
	11th to 20th	Day	2 5% 2 5% 4 4 4 4 6% 7% 59%	4814
	21st to end	Day	2 6% 2 3 3 4 4 4 7% 9% 56%	5922
April	1st to 10th	Day	3 7% 2 3 3 3 4 3 6% 8% 58%	2400
	11th to 20th	Day	3 4 1 4 3 3 3 3 5% 6% 66%	2369
	21st to end	Day	2 3 1 3 2 3 4 3 6% 7% 66%	2400
May	1st to 10th	Day	2 2 1 2 2 3 3 2 4 5% 74%	5479
	11th to 20th	Day	1 1 1 1 1 2 2 2 4 5% 80%	5841
	21st to end	Day	1 1 2 1 1 2 2 3 4 82%	6439
June	1st to 10th	Day	1 2 1 3 2 2 3 3 5% 6% 73%	2800
	11th to 20th	Day	1 1 1 1 2 3 5% 86%	2800
	21st to end	Day	1 1 1 1 2 2 3 3 86%	2800
July	1st to 10th	Day	1 1 1 1 1 1 1 2 92%	6319
	11th to 20th	Day	1 1 2 1 2 2 2 3 4 83%	6246
	21st to end	Day	1 1 1 1 1 1 2 3 4 86%	6193
August	1st to 10th	Day	1 1 1 1 2 2 1 4 5% 82%	5346
	11th to 20th	Day	1 1 2 2 93%	5364
	21st to end	Day	1 1 1 1 1 2 2 3 5% 84%	5984
September	1st to 10th	Day	1 1 2 1 2 2 2 3 4 83%	2400
	11th to 20th	Day	1 1 1 1 2 2 1 3 4 84%	2305
	21st to end	Day	1 1 2 2 2 2 2 3 4 81%	2200
October	1st to 10th	Day	1 2 1 2 2 2 2 2 3 5% 81%	3546
	11th to 20th	Day	1 1 1 1 2 2 2 3 4 82%	3261
	21st to end	Day	1 2 1 2 3 2 3 3 5% 7% 72%	3558
November	1st to 10th	Day	1 4 1 3 2 3 3 3 5% 6% 70%	1859
	11th to 20th	Day	2 4 1 3 3 3 3 3 6% 7% 66%	1890
	21st to end	Day	2 5% 2 4 4 4 4 4 5% 7% 58%	1890
December	1st to 10th	Day	1 3 1 4 3 4 5% 4 6% 7% 63%	2968
	11th to 20th	Day	3 4 1 5% 4 4 4 4 6% 8% 57%	3203
	21st to end	Day	5% 6% 2 5% 4 4 5% 5% 7% 9% 48%	4004
January	1st to 10th	Night	2 4 3 5% 3 4 4 3 5% 7% 61%	6306
	11th to 20th	Night	1 2 2 4 3 4 4 3 4 7% 66%	5883
	21st to end	Night	3 7% 3 6% 3 3 4 4 6% 8% 53%	6319
February	1st to 10th	Night	3 7% 3 6% 4 3 5% 4 5% 7% 54%	2400
	11th to 20th	Night	3 6% 3 5% 3 3 4 4 5% 8% 56%	2338
	21st to end	Night	2 5% 2 6% 5% 3 5% 4 5% 7% 56%	1980
March	1st to 10th	Night	2 6% 2 6% 3 7% 4 4 7% 9% 50%	5376
	11th to 20th	Night	2 4 2 5% 5% 6% 5% 4 5% 6% 56%	5181
	21st to end	Night	2 4 3 7% 5% 5% 4 4 6% 8% 52%	5051
April	1st to 10th	Night	2 5% 2 5% 3 4 6% 3 5% 7% 57%	2000
	11th to 20th	Night	2 5% 2 3 3 3 3 3 4 7% 65%	1979
	21st to end	Night	2 4 2 3 2 2 4 2 5% 7% 67%	2000
May	1st to 10th	Night	2 3 1 2 2 3 3 2 3 4 77%	4519
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 4 82%	4074
	21st to end	Night	1 1 1 1 1 1 1 1 3 88%	4438
June	1st to 10th	Night	1 2 1 2 1 2 2 3 5% 5% 77%	1600
	11th to 20th	Night	1 1 1 1 1 1 2 3 89%	1600
	21st to end	Night	1 1 1 1 1 1 2 3 90%	1600
July	1st to 10th	Night	1 1 1 1 1 2 93%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 89%	3686
	21st to end	Night	1 1 1 1 1 1 2 3 90%	4689
August	1st to 10th	Night	1 1 1 1 1 1 3 5% 86%	4486
	11th to 20th	Night	1 1 1 1 1 1 94%	4506
	21st to end	Night	1 1 1 1 1 1 2 3 89%	5015
September	1st to 10th	Night	1 2 1 1 1 1 2 3 87%	2000
	11th to 20th	Night	1 1 1 1 2 2 1 2 4 86%	2094
	21st to end	Night	1 1 2 2 2 2 3 4 82%	2200
October	1st to 10th	Night	1 1 1 1 2 2 1 2 3 85%	3649
	11th to 20th	Night	1 1 2 1 2 2 2 4 6% 80%	3897
	21st to end	Night	1 3 1 2 2 2 3 2 3 5% 76%	4253
November	1st to 10th	Night	1 3 2 3 2 3 4 3 4 8% 67%	2657
	11th to 20th	Night	2 4 1 3 3 3 4 3 5% 7% 64%	2730
	21st to end	Night	3 4 1 4 3 4 4 4 7% 8% 58%	2730
December	1st to 10th	Night	1 3 1 4 3 3 4 3 6% 7% 64%	4266
	11th to 20th	Night	3 4 1 4 4 5% 6% 5% 8% 10% 51%	5003
	21st to end	Night	5% 5% 2 5% 5% 5% 5% 5% 8% 10% 45%	6952

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	15% 3 6% 31% 32% 12%	3639
	11th to 20th	Day	16% 4 12% 14% 21% 33%	4081
	21st to end	Day	24% 5% 9% 18% 24% 20%	4662
February	1st to 10th	Day	25% 4 7% 19% 25% 20%	2000
	11th to 20th	Day	23% 3 9% 22% 28% 14%	1960
	21st to end	Day	27% 4 8% 21% 28% 12%	1650
March	1st to 10th	Day	26% 6% 11% 18% 24% 15%	4518
	11th to 20th	Day	19% 5% 13% 32% 21% 10%	4814
	21st to end	Day	18% 8% 15% 33% 20% 5%	5922
April	1st to 10th	Day	21% 5% 11% 25% 26% 11%	2400
	11th to 20th	Day	17% 4 9% 27% 28% 14%	2372
	21st to end	Day	14% 4 12% 27% 35% 10%	2400
May	1st to 10th	Day	10% 5% 9% 20% 39% 17%	5479
	11th to 20th	Day	7% 2 7% 18% 45% 21%	5844
	21st to end	Day	8% 1 5% 16% 48% 22%	6440
June	1st to 10th	Day	11% 4 7% 19% 35% 25%	2800
	11th to 20th	Day	4 2 6% 14% 33% 42%	2800
	21st to end	Day	5% 1 3 6% 27% 57%	2800
July	1st to 10th	Day	3 1 1 3 15% 77%	6251
	11th to 20th	Day	7% 2 3 8% 25% 56%	6171
	21st to end	Day	4 1 4 15% 33% 42%	6014
August	1st to 10th	Day	7% 1 3 10% 31% 48%	3890
	11th to 20th	Day	3 1 2 5% 28% 61%	3880
	21st to end	Day	5% 1 2 8% 27% 57%	4311
September	1st to 10th	Day	6% 2 4 8% 29% 50%	2400
	11th to 20th	Day	6% 2 4 10% 37% 42%	2305
	21st to end	Day	8% 2 3 11% 39% 37%	2200
October	1st to 10th	Day	7% 2 4 10% 22% 54%	3546
	11th to 20th	Day	7% 1 4 15% 41% 31%	3261
	21st to end	Day	12% 2 5% 11% 35% 34%	3558
November	1st to 10th	Day	13% 3 6% 21% 32% 26%	1859
	11th to 20th	Day	17% 3 8% 19% 27% 26%	1890
	21st to end	Day	23% 4 9% 14% 25% 25%	1890
December	1st to 10th	Day	19% 5% 6% 13% 30% 27%	2968
	11th to 20th	Day	25% 4 8% 24% 28% 11%	3202
	21st to end	Day	27% 6% 12% 23% 23% 9%	4004
January	1st to 10th	Night	16% 5% 6% 26% 31% 16%	6306
	11th to 20th	Night	16% 5% 8% 16% 25% 29%	5883
	21st to end	Night	24% 5% 7% 18% 21% 26%	6319
February	1st to 10th	Night	24% 5% 10% 16% 24% 20%	2400
	11th to 20th	Night	22% 4 9% 22% 27% 16%	2339
	21st to end	Night	23% 6% 10% 20% 27% 14%	1980
March	1st to 10th	Night	21% 7% 12% 20% 26% 13%	5376
	11th to 20th	Night	19% 6% 14% 33% 19% 9%	5181
	21st to end	Night	18% 7% 16% 32% 21% 6%	5051
April	1st to 10th	Night	20% 4 15% 26% 24% 11%	2000
	11th to 20th	Night	15% 4 11% 23% 31% 15%	1979
	21st to end	Night	12% 4 11% 30% 35% 8%	2000
May	1st to 10th	Night	9% 5% 10% 20% 39% 16%	4516
	11th to 20th	Night	6% 2 6% 26% 44% 17%	4075
	21st to end	Night	6% 1 6% 18% 46% 24%	4438
June	1st to 10th	Night	9% 3 9% 21% 35% 22%	1600
	11th to 20th	Night	4 2 6% 14% 33% 42%	1600
	21st to end	Night	3 3 8% 29% 58%	1600
July	1st to 10th	Night	3 2 3 16% 77%	3600
	11th to 20th	Night	4 1 2 8% 21% 64%	3638
	21st to end	Night	3 1 3 13% 37% 43%	4556
August	1st to 10th	Night	6% 1 3 8% 37% 45%	3256
	11th to 20th	Night	3 1 2 5% 29% 60%	3256
	21st to end	Night	4 1 1 8% 30% 57%	3608
September	1st to 10th	Night	6% 1 3 8% 28% 54%	2000
	11th to 20th	Night	5% 2 4 10% 41% 38%	2094
	21st to end	Night	5% 2 4 14% 38% 38%	2200
October	1st to 10th	Night	6% 2 3 10% 20% 59%	3649
	11th to 20th	Night	7% 1 4 14% 40% 34%	3897
	21st to end	Night	8% 4 6% 9% 36% 36%	4253
November	1st to 10th	Night	12% 4 6% 19% 32% 26%	2657
	11th to 20th	Night	16% 4 9% 16% 27% 27%	2730
	21st to end	Night	20% 4 9% 16% 24% 26%	2730
December	1st to 10th	Night	17% 4 5% 12% 34% 28%	4266
	11th to 20th	Night	26% 5% 11% 20% 23% 15%	5003
	21st to end	Night	26% 6% 14% 22% 25% 7%	6952

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	15% 21% 32% 25% 7% 1	200
	11th to 20th	Day	11% 26% 30% 27% 5% 1	394
	21st to end	Day	14% 24% 34% 21% 6% 1	471
February	1st to 10th	Day	12% 24% 32% 24% 6% 2	500
	11th to 20th	Day	17% 20% 35% 20% 6% 1	495
	21st to end	Day	10% 27% 38% 21% 5%	414
March	1st to 10th	Day	16% 26% 34% 20% 5%	500
	11th to 20th	Day	15% 24% 31% 23% 6% 1	500
	21st to end	Day	12% 29% 34% 19% 5%	550
April	1st to 10th	Day	12% 19% 34% 24% 11% 1	500
	11th to 20th	Day	8% 22% 37% 25% 7% 1	492
	21st to end	Day	8% 19% 30% 27% 13% 3	500
May	1st to 10th	Day	9% 16% 35% 28% 11% 1	503
	11th to 20th	Day	6% 14% 33% 32% 11% 4	528
	21st to end	Day	7% 12% 33% 33% 12% 3	573
June	1st to 10th	Day	3 8% 32% 34% 18% 5%	530
	11th to 20th	Day	2 11% 29% 38% 16% 4	530
	21st to end	Day	2 5% 32% 38% 16% 6%	530
July	1st to 10th	Day	1 3 23% 44% 22% 7%	526
	11th to 20th	Day	2 1 14% 45% 26% 11%	524
	21st to end	Day	1 1 18% 43% 26% 9%	575
August	1st to 10th	Day	1 2 27% 45% 17% 8%	527
	11th to 20th	Day	1 3 21% 46% 21% 7%	517
	21st to end	Day	2 4 22% 48% 17% 7%	583
September	1st to 10th	Day	1 6% 28% 42% 19% 5%	530
	11th to 20th	Day	2 7% 33% 43% 14% 1	530
	21st to end	Day	2 11% 31% 38% 16% 2	530
October	1st to 10th	Day	4 10% 35% 39% 12% 1	530
	11th to 20th	Day	5% 11% 35% 35% 13% 1	530
	21st to end	Day	5% 13% 32% 35% 13% 2	583
November	1st to 10th	Day	6% 10% 32% 33% 17% 1	335
	11th to 20th	Day	11% 14% 30% 30% 12% 3	330
	21st to end	Day	7% 19% 32% 31% 9% 2	330
December	1st to 10th	Day	4 15% 40% 29% 11% 1	306
	11th to 20th	Day	9% 17% 32% 27% 14% 1	253
	21st to end	Day	16% 26% 29% 20% 7% 2	220
January	1st to 10th	Night	9% 10% 28% 32% 14% 7%	800
	11th to 20th	Night	5% 10% 30% 36% 16% 4	800
	21st to end	Night	9% 15% 28% 32% 13% 3	880
February	1st to 10th	Night	10% 11% 28% 30% 18% 4	800
	11th to 20th	Night	8% 13% 26% 31% 16% 6%	784
	21st to end	Night	7% 13% 31% 34% 12% 3	660
March	1st to 10th	Night	7% 16% 29% 34% 13% 2	800
	11th to 20th	Night	7% 12% 27% 32% 19% 4	800
	21st to end	Night	7% 14% 28% 32% 17% 2	880
April	1st to 10th	Night	7% 10% 32% 33% 15% 3	800
	11th to 20th	Night	5% 10% 29% 36% 18% 2	791
	21st to end	Night	5% 10% 30% 33% 18% 5%	800
May	1st to 10th	Night	3 9% 29% 35% 21% 3	785
	11th to 20th	Night	4 7% 24% 38% 26% 2	591
	21st to end	Night	3 9% 27% 33% 25% 3	640
June	1st to 10th	Night	2 4 19% 48% 25% 3	400
	11th to 20th	Night	1 5% 18% 43% 33% 2	400
	21st to end	Night	1 2 15% 43% 36% 4	400
July	1st to 10th	Night	1 1 9% 38% 47% 6%	390
	11th to 20th	Night	1 2 39% 48% 9%	408
	21st to end	Night	1 5% 33% 51% 10%	747
August	1st to 10th	Night	2 8% 39% 44% 7%	796
	11th to 20th	Night	9% 32% 49% 10%	792
	21st to end	Night	1 1 5% 34% 49% 10%	880
September	1st to 10th	Night	1 2 8% 37% 43% 9%	800
	11th to 20th	Night	2 2 11% 46% 32% 7%	800
	21st to end	Night	1 3 18% 39% 33% 7%	800
October	1st to 10th	Night	2 4 19% 48% 24% 3	800
	11th to 20th	Night	4 4 21% 40% 25% 7%	800
	21st to end	Night	2 6% 22% 36% 25% 9%	880
November	1st to 10th	Night	3 8% 21% 39% 21% 8%	820
	11th to 20th	Night	6% 6% 23% 37% 22% 6%	840
	21st to end	Night	5% 9% 29% 34% 19% 4	840
December	1st to 10th	Night	5% 10% 26% 38% 18% 3	808
	11th to 20th	Night	9% 9% 26% 38% 15% 3	800
	21st to end	Night	9% 13% 29% 31% 13% 4	880

Page generated at 2025-11-29 22:00:57. Version ac07

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