Valle Grande Entrance Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Valle Grande Entrance Station clear sky chart from 2005-11-06 to 2025-04-26.

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	3 5% 2 6% 4 4 5% 4 6% 7% 54%	117551
	Night	3 4 2 5% 4 4 4 4 6% 7% 58%	119987
Transparency	Day	24% 5% 9% 21% 27% 15%	117311
	Night	22% 4 8% 20% 29% 17%	119816
Seeing	Day	12% 19% 29% 25% 13% 3	15685
	Night	9% 13% 26% 32% 17% 2	25948

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 2 8% 4 4 4 3 5% 7% 59%	4052
	11th to 20th	Day	1 3 1 6% 3 2 3 3 6% 6% 65%	4100
	21st to end	Day	2 8% 4 6% 5% 4 4 3 5% 5% 55%	4510
February	1st to 10th	Day	1 5% 4 8% 5% 3 3 3 5% 8% 55%	1800
	11th to 20th	Day	2 6% 3 8% 4 4 5% 3 6% 7% 54%	1934
	21st to end	Day	1 8% 3 6% 3 3 4 3 4 7% 57%	1650
March	1st to 10th	Day	1 6% 3 7% 4 3 4 3 5% 7% 56%	4811
	11th to 20th	Day	2 12% 3 8% 5% 5% 6% 4 6% 6% 44%	5000
	21st to end	Day	1 5% 2 6% 4 4 5% 5% 8% 7% 53%	5617
April	1st to 10th	Day	2 4 2 5% 4 4 5% 4 6% 7% 57%	2400
	11th to 20th	Day	3 6% 2 5% 5% 3 4 4 6% 5% 57%	2371
	21st to end	Day	3 5% 2 5% 3 5% 3 5% 6% 7% 57%	2341
May	1st to 10th	Day	2 3 1 3 3 3 4 4 5% 6% 65%	3800
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 4 6% 7% 47%	3986
	21st to end	Day	3 3 1 4 3 3 3 3 5% 6% 67%	4825
June	1st to 10th	Day	2 3 1 4 4 4 4 5% 8% 8% 57%	2660
	11th to 20th	Day	2 2 1 4 3 3 3 4 6% 6% 65%	2660
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 7% 8% 49%	2660
July	1st to 10th	Day	3 4 2 5% 4 5% 6% 5% 8% 8% 49%	4336
	11th to 20th	Day	2 3 2 6% 6% 7% 11% 10% 11% 9% 34%	4110
	21st to end	Day	4 5% 3 9% 8% 8% 9% 8% 10% 10% 27%	4454
August	1st to 10th	Day	4 4 2 8% 8% 8% 10% 8% 9% 10% 29%	4045
	11th to 20th	Day	3 4 2 6% 5% 6% 6% 5% 8% 11% 43%	3726
	21st to end	Day	5% 4 2 8% 5% 7% 8% 6% 10% 11% 32%	4180
September	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 8% 44%	2280
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 7% 51%	2280
	21st to end	Day	5% 3 1 4 3 3 3 3 5% 7% 64%	2048
October	1st to 10th	Day	6% 4 2 5% 4 3 3 3 4 5% 63%	3170
	11th to 20th	Day	7% 7% 2 6% 3 3 4 3 4 6% 56%	3150
	21st to end	Day	2 3 1 3 2 2 2 2 4 5% 73%	3438
November	1st to 10th	Day	2 4 1 3 3 3 3 3 4 6% 68%	1922
	11th to 20th	Day	1 3 1 3 2 2 4 3 5% 7% 68%	1800
	21st to end	Day	4 5% 2 4 3 4 3 3 5% 5% 63%	1785
December	1st to 10th	Day	1 3 1 2 2 2 2 2 4 5% 75%	2620
	11th to 20th	Day	1 3 1 5% 4 4 3 3 5% 8% 62%	3026
	21st to end	Day	1 5% 2 5% 4 3 3 3 5% 7% 64%	4004
January	1st to 10th	Night	4 2 7% 5% 5% 5% 4 6% 6% 56%	5941
	11th to 20th	Night	1 2 1 5% 3 3 4 3 5% 7% 66%	5880
	21st to end	Night	1 4 2 6% 6% 6% 5% 4 6% 7% 54%	6468
February	1st to 10th	Night	1 6% 2 5% 3 3 3 3 5% 6% 62%	2600
	11th to 20th	Night	2 6% 2 5% 4 4 4 4 6% 7% 56%	2353
	21st to end	Night	2 7% 2 4 3 3 3 3 5% 6% 63%	1980
March	1st to 10th	Night	1 5% 2 6% 4 4 3 3 4 5% 62%	5073
	11th to 20th	Night	4 11% 3 5% 4 4 4 3 5% 6% 52%	5000
	21st to end	Night	1 4 2 5% 4 4 4 4 5% 7% 61%	5352
April	1st to 10th	Night	2 4 2 5% 4 3 4 4 6% 7% 59%	2000
	11th to 20th	Night	4 5% 2 5% 4 3 4 3 4 7% 59%	1977
	21st to end	Night	3 4 1 4 3 3 3 3 4 7% 63%	1955
May	1st to 10th	Night	3 7% 2 4 4 3 3 3 5% 6% 60%	3170
	11th to 20th	Night	7% 9% 2 6% 4 4 4 3 5% 6% 49%	2910
	21st to end	Night	3 2 1 3 2 3 3 3 5% 5% 70%	2762
June	1st to 10th	Night	2 4 2 4 4 5% 5% 4 7% 9% 54%	1520
	11th to 20th	Night	4 3 1 3 2 2 3 4 5% 7% 66%	1520
	21st to end	Night	6% 5% 2 6% 5% 4 5% 5% 5% 8% 49%	1520
July	1st to 10th	Night	3 4 2 6% 6% 5% 6% 5% 7% 6% 49%	2627
	11th to 20th	Night	3 4 3 8% 5% 5% 7% 7% 10% 12% 35%	2860
	21st to end	Night	7% 7% 2 7% 5% 5% 6% 5% 10% 10% 35%	3109
August	1st to 10th	Night	3 5% 3 9% 7% 8% 9% 7% 10% 12% 28%	2894
	11th to 20th	Night	4 4 2 6% 5% 6% 7% 5% 10% 13% 38%	3113
	21st to end	Night	4 5% 3 8% 7% 8% 8% 7% 10% 10% 30%	3487
September	1st to 10th	Night	5% 5% 3 6% 5% 5% 5% 3 6% 9% 49%	1900
	11th to 20th	Night	6% 3 2 5% 4 3 4 4 6% 7% 57%	1900
	21st to end	Night	5% 3 1 4 2 4 3 3 4 6% 65%	2128
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 72%	3800
	11th to 20th	Night	8% 5% 1 4 3 3 4 3 4 6% 60%	3778
	21st to end	Night	3 2 1 2 2 2 2 2 4 5% 77%	4120
November	1st to 10th	Night	2 2 1 2 2 3 3 3 4 5% 73%	2355
	11th to 20th	Night	2 1 3 2 3 3 3 5% 6% 73%	2600
	21st to end	Night	4 6% 1 4 3 3 3 4 5% 5% 62%	2610
December	1st to 10th	Night	1 2 1 2 2 2 3 3 4 6% 74%	4570
	11th to 20th	Night	2 3 1 3 3 3 3 4 6% 9% 64%	5181
	21st to end	Night	2 5% 2 5% 3 3 3 3 4 5% 65%	6974

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	24% 3 6% 25% 36% 6%	4053
	11th to 20th	Day	16% 2 9% 24% 27% 22%	4100
	21st to end	Day	28% 2 5% 20% 31% 14%	4510
February	1st to 10th	Day	26% 3 9% 23% 27% 12%	1800
	11th to 20th	Day	26% 5% 6% 25% 27% 12%	1944
	21st to end	Day	25% 3 3 18% 31% 20%	1650
March	1st to 10th	Day	23% 2 4 14% 38% 19%	4811
	11th to 20th	Day	32% 2 5% 21% 27% 13%	5000
	21st to end	Day	23% 3 5% 33% 30% 7%	5617
April	1st to 10th	Day	21% 5% 6% 21% 31% 16%	2400
	11th to 20th	Day	24% 3 5% 20% 32% 16%	2374
	21st to end	Day	22% 4 6% 24% 33% 12%	2341
May	1st to 10th	Day	19% 2 5% 18% 37% 20%	3800
	11th to 20th	Day	34% 3 6% 20% 25% 12%	3989
	21st to end	Day	17% 2 4 13% 27% 36%	4825
June	1st to 10th	Day	20% 4 9% 20% 28% 20%	2660
	11th to 20th	Day	17% 2 4 15% 26% 35%	2660
	21st to end	Day	28% 4 8% 19% 23% 19%	2660
July	1st to 10th	Day	25% 8% 12% 14% 17% 24%	4269
	11th to 20th	Day	31% 12% 18% 28% 7% 4	4041
	21st to end	Day	35% 13% 22% 20% 6% 3	4314
August	1st to 10th	Day	36% 12% 21% 17% 9% 5%	4031
	11th to 20th	Day	26% 8% 16% 24% 17% 8%	3762
	21st to end	Day	33% 11% 18% 21% 15% 3	4179
September	1st to 10th	Day	30% 6% 10% 24% 20% 9%	2280
	11th to 20th	Day	25% 5% 10% 19% 28% 14%	2280
	21st to end	Day	18% 3 6% 26% 34% 13%	2048
October	1st to 10th	Day	20% 3 7% 18% 29% 23%	3170
	11th to 20th	Day	25% 5% 6% 16% 30% 17%	3150
	21st to end	Day	12% 2 5% 18% 43% 20%	3438
November	1st to 10th	Day	16% 2 6% 24% 38% 15%	1922
	11th to 20th	Day	14% 3 6% 27% 38% 13%	1800
	21st to end	Day	21% 2 5% 22% 34% 16%	1785
December	1st to 10th	Day	11% 2 5% 30% 35% 16%	2620
	11th to 20th	Day	20% 3 6% 27% 36% 9%	3024
	21st to end	Day	18% 3 8% 26% 34% 12%	4004
January	1st to 10th	Night	25% 2 6% 22% 31% 14%	5941
	11th to 20th	Night	16% 1 5% 24% 30% 24%	5880
	21st to end	Night	24% 3 7% 20% 32% 15%	6468
February	1st to 10th	Night	21% 2 8% 24% 30% 15%	2600
	11th to 20th	Night	22% 4 6% 25% 28% 15%	2353
	21st to end	Night	19% 3 4 18% 34% 22%	1980
March	1st to 10th	Night	19% 2 4 13% 42% 20%	5073
	11th to 20th	Night	30% 2 3 18% 32% 14%	5000
	21st to end	Night	20% 2 5% 30% 34% 9%	5352
April	1st to 10th	Night	22% 4 5% 22% 31% 17%	2000
	11th to 20th	Night	23% 3 5% 18% 30% 20%	1977
	21st to end	Night	19% 3 7% 21% 37% 12%	1955
May	1st to 10th	Night	25% 2 4 13% 32% 23%	3170
	11th to 20th	Night	36% 2 6% 21% 20% 14%	2911
	21st to end	Night	17% 1 5% 11% 24% 42%	2762
June	1st to 10th	Night	24% 4 10% 20% 21% 21%	1520
	11th to 20th	Night	18% 3 4 14% 24% 38%	1520
	21st to end	Night	30% 5% 9% 15% 18% 23%	1520
July	1st to 10th	Night	29% 8% 10% 13% 13% 27%	2585
	11th to 20th	Night	31% 10% 22% 26% 6% 5%	2806
	21st to end	Night	36% 8% 21% 27% 8% 1	3011
August	1st to 10th	Night	38% 13% 19% 16% 9% 6%	2885
	11th to 20th	Night	28% 8% 20% 17% 15% 11%	3143
	21st to end	Night	38% 10% 19% 17% 12% 4	3487
September	1st to 10th	Night	28% 5% 13% 23% 20% 10%	1900
	11th to 20th	Night	24% 5% 10% 16% 26% 19%	1900
	21st to end	Night	19% 4 6% 19% 34% 18%	2128
October	1st to 10th	Night	16% 2 5% 15% 35% 26%	3800
	11th to 20th	Night	21% 4 6% 19% 27% 23%	3778
	21st to end	Night	10% 2 3 18% 39% 27%	4120
November	1st to 10th	Night	13% 2 3 25% 41% 15%	2355
	11th to 20th	Night	11% 3 5% 25% 40% 16%	2600
	21st to end	Night	21% 2 5% 20% 32% 19%	2610
December	1st to 10th	Night	12% 2 5% 30% 34% 18%	4570
	11th to 20th	Night	16% 2 6% 22% 37% 17%	5182
	21st to end	Night	20% 2 7% 22% 37% 13%	6974

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% 25% 32% 22% 5%	300
	11th to 20th	Day	24% 23% 27% 22% 4	300
	21st to end	Day	10% 23% 37% 19% 10% 1	330
February	1st to 10th	Day	17% 28% 32% 20% 3	300
	11th to 20th	Day	18% 31% 33% 15% 3	300
	21st to end	Day	24% 31% 29% 14% 3	249
March	1st to 10th	Day	17% 32% 33% 14% 3	430
	11th to 20th	Day	23% 30% 27% 14% 5% 1	500
	21st to end	Day	24% 34% 30% 8% 4	550
April	1st to 10th	Day	17% 33% 33% 13% 4 1	500
	11th to 20th	Day	19% 37% 32% 10% 1	492
	21st to end	Day	16% 33% 36% 12% 3	481
May	1st to 10th	Day	13% 30% 43% 12% 3	463
	11th to 20th	Day	11% 24% 36% 20% 7% 2	497
	21st to end	Day	12% 21% 31% 26% 9% 1	734
June	1st to 10th	Day	5% 11% 32% 33% 17% 1	680
	11th to 20th	Day	6% 15% 30% 29% 18% 2	680
	21st to end	Day	8% 12% 28% 30% 18% 4	680
July	1st to 10th	Day	7% 5% 23% 32% 29% 5%	618
	11th to 20th	Day	7% 3 12% 36% 35% 8%	484
	21st to end	Day	6% 2 11% 39% 33% 8%	531
August	1st to 10th	Day	8% 4 14% 37% 29% 8%	487
	11th to 20th	Day	8% 3 23% 41% 20% 5%	477
	21st to end	Day	7% 4 20% 39% 24% 6%	539
September	1st to 10th	Day	6% 7% 21% 39% 21% 6%	490
	11th to 20th	Day	8% 8% 32% 35% 13% 4	490
	21st to end	Day	8% 14% 29% 29% 15% 6%	343
October	1st to 10th	Day	10% 19% 26% 25% 15% 5%	300
	11th to 20th	Day	15% 16% 29% 24% 12% 4	300
	21st to end	Day	16% 16% 28% 27% 10% 2	330
November	1st to 10th	Day	15% 23% 33% 23% 6%	300
	11th to 20th	Day	10% 19% 35% 25% 11% 1	300
	21st to end	Day	14% 28% 29% 19% 10%	300
December	1st to 10th	Day	14% 21% 32% 25% 8% 1	300
	11th to 20th	Day	12% 25% 34% 23% 4 1	300
	21st to end	Day	25% 25% 31% 18% 2 1	330
January	1st to 10th	Night	8% 15% 29% 32% 14% 2	835
	11th to 20th	Night	11% 15% 29% 31% 11% 3	800
	21st to end	Night	8% 15% 33% 29% 13% 3	880
February	1st to 10th	Night	11% 16% 33% 29% 9% 1	800
	11th to 20th	Night	13% 17% 37% 25% 7% 1	784
	21st to end	Night	12% 24% 33% 27% 4	660
March	1st to 10th	Night	10% 22% 33% 26% 8% 1	800
	11th to 20th	Night	12% 19% 27% 30% 12% 1	800
	21st to end	Night	13% 20% 32% 27% 7%	820
April	1st to 10th	Night	12% 22% 39% 23% 4	600
	11th to 20th	Night	12% 25% 27% 27% 8%	593
	21st to end	Night	10% 23% 32% 28% 7%	587
May	1st to 10th	Night	9% 18% 34% 31% 8%	570
	11th to 20th	Night	10% 14% 29% 32% 15% 1	561
	21st to end	Night	7% 15% 32% 33% 13%	617
June	1st to 10th	Night	4 9% 26% 41% 19% 1	570
	11th to 20th	Night	6% 9% 29% 40% 15% 1	570
	21st to end	Night	7% 7% 23% 34% 27% 2	570
July	1st to 10th	Night	6% 2 18% 36% 35% 3	555
	11th to 20th	Night	4 2 7% 38% 44% 5%	552
	21st to end	Night	6% 1 6% 29% 50% 8%	624
August	1st to 10th	Night	5% 3 10% 29% 42% 10%	567
	11th to 20th	Night	8% 1 10% 41% 36% 4	564
	21st to end	Night	4 2 10% 38% 40% 6%	627
September	1st to 10th	Night	8% 2 14% 41% 30% 5%	570
	11th to 20th	Night	6% 3 20% 40% 26% 4	570
	21st to end	Night	7% 5% 21% 41% 24% 2	651
October	1st to 10th	Night	8% 9% 27% 39% 16% 2	760
	11th to 20th	Night	7% 9% 28% 38% 15% 3	760
	21st to end	Night	10% 11% 26% 33% 16% 5%	836
November	1st to 10th	Night	5% 12% 25% 36% 19% 2	795
	11th to 20th	Night	5% 12% 30% 34% 16% 3	1000
	21st to end	Night	13% 15% 24% 29% 16% 3	1000
December	1st to 10th	Night	8% 15% 31% 33% 11% 1	1000
	11th to 20th	Night	12% 16% 30% 30% 11% 1	1000
	21st to end	Night	15% 16% 31% 30% 8% 1	1100

Page generated at 2025-04-23 07:25:04. Version ac07

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