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 2026-08-30.

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	3 4 2 6% 4 5% 5% 5% 7% 7% 53%	151879
	Night	3 4 2 5% 4 4 4 4 6% 7% 57%	147911
Transparency	Day	23% 5% 10% 21% 26% 15%	146861
	Night	22% 4 8% 20% 28% 17%	143937
Seeing	Day	13% 19% 29% 25% 12% 2	17583
	Night	9% 13% 27% 32% 16% 2	27656

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	4 2 9% 5% 4 4 4 5% 7% 55%	5259
	11th to 20th	Day	1 2 1 5% 2 2 3 3 4 5% 73%	5340
	21st to end	Day	1 8% 4 6% 4 4 4 3 5% 5% 57%	5844
February	1st to 10th	Day	1 5% 4 8% 5% 3 3 3 5% 8% 56%	1890
	11th to 20th	Day	2 6% 3 8% 4 4 5% 3 6% 7% 53%	2033
	21st to end	Day	1 7% 3 6% 3 3 4 3 4 7% 58%	1730
March	1st to 10th	Day	1 6% 3 7% 4 3 4 3 5% 7% 57%	4917
	11th to 20th	Day	2 11% 3 8% 5% 5% 6% 4 6% 6% 45%	5110
	21st to end	Day	1 5% 2 6% 4 4 5% 5% 8% 7% 53%	5741
April	1st to 10th	Day	2 4 2 5% 4 4 5% 4 6% 7% 57%	2520
	11th to 20th	Day	3 5% 2 5% 5% 3 4 4 6% 6% 57%	2491
	21st to end	Day	3 5% 2 5% 3 4 3 5% 6% 7% 58%	2520
May	1st to 10th	Day	5% 6% 2 6% 5% 5% 5% 4 6% 7% 50%	7057
	11th to 20th	Day	3 3 1 5% 4 5% 5% 4 5% 6% 59%	7423
	21st to end	Day	2 3 2 4 3 3 4 4 6% 6% 62%	9026
June	1st to 10th	Day	2 3 1 4 4 4 4 5% 8% 8% 56%	2940
	11th to 20th	Day	2 2 1 4 3 3 3 4 6% 6% 66%	2940
	21st to end	Day	5% 4 2 6% 4 5% 5% 4 7% 8% 51%	2940
July	1st to 10th	Day	2 3 1 5% 5% 6% 6% 5% 8% 8% 51%	8071
	11th to 20th	Day	2 2 1 6% 7% 8% 11% 9% 11% 10% 33%	7650
	21st to end	Day	3 4 3 8% 8% 9% 9% 7% 10% 11% 28%	8304
August	1st to 10th	Day	3 3 2 6% 7% 7% 9% 8% 9% 10% 37%	5849
	11th to 20th	Day	3 4 2 6% 6% 7% 8% 6% 9% 11% 39%	5486
	21st to end	Day	4 4 2 8% 6% 8% 8% 7% 11% 12% 32%	6093
September	1st to 10th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 44%	2400
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 7% 51%	2400
	21st to end	Day	5% 3 1 4 3 3 3 3 5% 7% 63%	2155
October	1st to 10th	Day	6% 4 2 5% 4 3 3 3 4 4 63%	3270
	11th to 20th	Day	8% 7% 2 6% 3 3 4 3 4 6% 56%	3250
	21st to end	Day	2 3 1 3 2 2 2 2 3 5% 73%	3548
November	1st to 10th	Day	2 4 1 3 3 3 3 3 4 5% 69%	2020
	11th to 20th	Day	1 3 1 3 3 2 4 3 5% 7% 67%	1890
	21st to end	Day	4 5% 1 4 3 4 3 3 5% 5% 63%	1874
December	1st to 10th	Day	1 3 1 2 2 2 2 2 4 5% 76%	2700
	11th to 20th	Day	1 3 1 5% 4 4 3 3 5% 8% 63%	3106
	21st to end	Day	1 5% 2 5% 4 3 3 3 5% 7% 64%	4092
January	1st to 10th	Night	5% 3 9% 6% 6% 5% 4 6% 6% 50%	7704
	11th to 20th	Night	1 2 1 4 2 2 3 3 5% 6% 72%	7650
	21st to end	Night	1 4 2 5% 5% 5% 5% 4 6% 8% 56%	8370
February	1st to 10th	Night	1 6% 2 5% 3 3 3 3 5% 6% 64%	2730
	11th to 20th	Night	2 6% 2 6% 4 4 4 4 6% 7% 54%	2473
	21st to end	Night	2 6% 2 3 3 3 3 3 5% 6% 64%	2076
March	1st to 10th	Night	1 5% 2 5% 4 4 3 3 4 5% 62%	5186
	11th to 20th	Night	4 11% 3 5% 4 3 4 3 5% 6% 53%	5110
	21st to end	Night	1 4 2 5% 4 4 4 4 5% 7% 62%	5470
April	1st to 10th	Night	2 4 2 5% 4 3 4 4 5% 7% 59%	2100
	11th to 20th	Night	4 5% 2 5% 4 3 4 3 4 7% 59%	2077
	21st to end	Night	3 4 1 4 3 3 4 3 5% 7% 62%	2100
May	1st to 10th	Night	5% 8% 2 6% 5% 4 5% 4 6% 6% 50%	5890
	11th to 20th	Night	4 6% 2 5% 4 4 4 3 4 6% 61%	5433
	21st to end	Night	3 3 2 4 3 4 4 3 5% 6% 62%	5181
June	1st to 10th	Night	2 4 2 5% 4 5% 5% 4 7% 9% 53%	1680
	11th to 20th	Night	3 3 1 3 3 2 3 4 5% 6% 66%	1680
	21st to end	Night	5% 5% 2 6% 5% 4 5% 5% 5% 8% 50%	1680
July	1st to 10th	Night	2 4 1 6% 5% 5% 5% 4 6% 7% 55%	4911
	11th to 20th	Night	3 4 2 7% 5% 6% 7% 6% 10% 11% 38%	5340
	21st to end	Night	4 6% 3 9% 6% 6% 8% 6% 11% 12% 28%	5805
August	1st to 10th	Night	3 4 2 8% 6% 7% 8% 6% 9% 11% 37%	4183
	11th to 20th	Night	3 4 2 7% 5% 6% 7% 6% 10% 14% 38%	4583
	21st to end	Night	5% 5% 3 9% 6% 7% 7% 6% 10% 11% 30%	5083
September	1st to 10th	Night	5% 5% 3 6% 5% 5% 5% 3 6% 9% 49%	2000
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 7% 57%	2000
	21st to end	Night	5% 3 1 4 3 4 3 3 4 6% 64%	2240
October	1st to 10th	Night	4 3 2 3 2 2 2 2 3 5% 71%	3920
	11th to 20th	Night	9% 5% 1 4 3 3 3 3 4 5% 60%	3898
	21st to end	Night	3 2 1 2 2 2 2 2 4 5% 77%	4252
November	1st to 10th	Night	2 2 1 2 2 3 3 3 4 5% 74%	2476
	11th to 20th	Night	1 2 1 3 2 3 3 3 5% 6% 72%	2730
	21st to end	Night	4 5% 1 4 4 3 3 4 5% 5% 62%	2741
December	1st to 10th	Night	1 2 1 3 2 2 3 3 4 6% 74%	4710
	11th to 20th	Night	2 3 1 3 3 3 3 4 6% 9% 65%	5321
	21st to end	Night	2 5% 2 5% 3 3 3 3 4 5% 65%	7128

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	23% 4 7% 29% 33% 5%	5262
	11th to 20th	Day	12% 1 7% 23% 33% 23%	5340
	21st to end	Day	26% 2 5% 18% 34% 15%	5844
February	1st to 10th	Day	25% 3 9% 22% 29% 12%	1890
	11th to 20th	Day	25% 5% 6% 25% 27% 12%	2043
	21st to end	Day	23% 3 3 19% 33% 19%	1730
March	1st to 10th	Day	22% 2 4 14% 38% 19%	4917
	11th to 20th	Day	32% 2 5% 21% 28% 13%	5110
	21st to end	Day	23% 3 5% 33% 29% 7%	5741
April	1st to 10th	Day	21% 5% 6% 22% 30% 17%	2520
	11th to 20th	Day	24% 4 5% 20% 32% 17%	2494
	21st to end	Day	21% 4 6% 23% 33% 14%	2520
May	1st to 10th	Day	27% 5% 9% 19% 29% 12%	7057
	11th to 20th	Day	21% 3 7% 16% 31% 22%	7426
	21st to end	Day	18% 5% 8% 16% 24% 30%	9027
June	1st to 10th	Day	21% 5% 9% 20% 27% 19%	2940
	11th to 20th	Day	17% 3 5% 15% 26% 35%	2940
	21st to end	Day	26% 4 9% 18% 23% 20%	2940
July	1st to 10th	Day	21% 8% 11% 14% 18% 28%	8005
	11th to 20th	Day	27% 15% 22% 23% 8% 6%	7581
	21st to end	Day	33% 15% 25% 18% 7% 2	8120
August	1st to 10th	Day	35% 12% 21% 18% 10% 5%	4289
	11th to 20th	Day	27% 8% 17% 24% 16% 8%	4002
	21st to end	Day	33% 11% 19% 20% 14% 3	4420
September	1st to 10th	Day	29% 7% 11% 25% 20% 8%	2400
	11th to 20th	Day	25% 5% 10% 19% 28% 13%	2400
	21st to end	Day	19% 4 6% 25% 34% 13%	2155
October	1st to 10th	Day	20% 3 7% 17% 30% 23%	3270
	11th to 20th	Day	25% 5% 6% 16% 30% 17%	3250
	21st to end	Day	12% 2 5% 18% 43% 20%	3548
November	1st to 10th	Day	15% 2 5% 24% 38% 15%	2020
	11th to 20th	Day	14% 3 7% 27% 38% 12%	1890
	21st to end	Day	20% 2 5% 23% 34% 15%	1874
December	1st to 10th	Day	11% 2 6% 30% 35% 16%	2700
	11th to 20th	Day	19% 3 5% 26% 37% 9%	3104
	21st to end	Day	17% 3 8% 26% 34% 12%	4092
January	1st to 10th	Night	26% 4 7% 24% 28% 11%	7705
	11th to 20th	Night	12% 1 5% 22% 38% 22%	7650
	21st to end	Night	22% 2 6% 17% 34% 18%	8370
February	1st to 10th	Night	21% 2 8% 24% 30% 16%	2730
	11th to 20th	Night	22% 4 7% 25% 28% 14%	2473
	21st to end	Night	19% 3 4 18% 36% 21%	2076
March	1st to 10th	Night	19% 2 4 13% 42% 20%	5186
	11th to 20th	Night	30% 2 3 19% 32% 14%	5110
	21st to end	Night	20% 2 5% 30% 34% 10%	5470
April	1st to 10th	Night	21% 4 5% 22% 31% 16%	2100
	11th to 20th	Night	23% 3 5% 18% 31% 20%	2077
	21st to end	Night	19% 3 7% 21% 36% 13%	2100
May	1st to 10th	Night	30% 5% 8% 17% 26% 14%	5888
	11th to 20th	Night	24% 3 5% 18% 27% 24%	5434
	21st to end	Night	20% 4 9% 13% 20% 35%	5182
June	1st to 10th	Night	24% 4 10% 19% 21% 21%	1680
	11th to 20th	Night	17% 3 5% 14% 23% 38%	1680
	21st to end	Night	29% 5% 8% 15% 17% 25%	1680
July	1st to 10th	Night	24% 7% 9% 11% 16% 33%	4869
	11th to 20th	Night	29% 11% 25% 21% 6% 8%	5286
	21st to end	Night	39% 10% 22% 20% 8% 1	5677
August	1st to 10th	Night	37% 12% 18% 16% 10% 7%	3067
	11th to 20th	Night	29% 8% 20% 18% 15% 10%	3343
	21st to end	Night	38% 10% 20% 17% 11% 4	3687
September	1st to 10th	Night	29% 6% 13% 22% 20% 10%	2000
	11th to 20th	Night	24% 5% 10% 16% 26% 19%	2000
	21st to end	Night	20% 4 6% 19% 34% 17%	2240
October	1st to 10th	Night	17% 2 5% 15% 35% 26%	3920
	11th to 20th	Night	21% 4 6% 19% 27% 23%	3898
	21st to end	Night	10% 2 3 18% 40% 27%	4252
November	1st to 10th	Night	12% 2 3 25% 42% 16%	2476
	11th to 20th	Night	12% 3 5% 25% 40% 15%	2730
	21st to end	Night	21% 2 5% 21% 32% 18%	2741
December	1st to 10th	Night	12% 2 5% 30% 34% 17%	4710
	11th to 20th	Night	15% 2 6% 22% 37% 17%	5322
	21st to end	Night	19% 2 7% 22% 37% 13%	7128

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	18% 25% 32% 21% 5%	330
	11th to 20th	Day	23% 23% 27% 23% 4	330
	21st to end	Day	11% 24% 37% 18% 9% 1	363
February	1st to 10th	Day	16% 26% 33% 20% 4	330
	11th to 20th	Day	22% 30% 31% 14% 3	330
	21st to end	Day	23% 32% 29% 14% 3	273
March	1st to 10th	Day	17% 33% 33% 13% 3 1	466
	11th to 20th	Day	23% 31% 26% 14% 5% 1	540
	21st to end	Day	24% 34% 30% 8% 3 1	594
April	1st to 10th	Day	17% 32% 33% 14% 4 1	540
	11th to 20th	Day	20% 37% 32% 9% 1	532
	21st to end	Day	21% 33% 33% 11% 2	540
May	1st to 10th	Day	16% 28% 41% 12% 3	543
	11th to 20th	Day	14% 26% 35% 18% 6% 1	578
	21st to end	Day	11% 22% 31% 26% 9% 1	844
June	1st to 10th	Day	5% 14% 32% 32% 16% 1	780
	11th to 20th	Day	6% 16% 32% 28% 16% 1	780
	21st to end	Day	7% 15% 29% 29% 16% 3	780
July	1st to 10th	Day	6% 6% 24% 33% 27% 4	712
	11th to 20th	Day	6% 2 13% 37% 34% 7%	564
	21st to end	Day	6% 3 13% 39% 32% 8%	619
August	1st to 10th	Day	7% 5% 16% 37% 27% 7%	567
	11th to 20th	Day	7% 4 22% 41% 22% 4	557
	21st to end	Day	6% 4 20% 40% 24% 6%	620
September	1st to 10th	Day	6% 7% 24% 37% 21% 5%	530
	11th to 20th	Day	7% 10% 32% 34% 12% 4	530
	21st to end	Day	8% 14% 31% 27% 14% 5%	375
October	1st to 10th	Day	10% 20% 26% 24% 14% 5%	330
	11th to 20th	Day	17% 19% 28% 22% 11% 4	330
	21st to end	Day	15% 18% 28% 25% 10% 2	363
November	1st to 10th	Day	14% 24% 33% 23% 6%	330
	11th to 20th	Day	11% 19% 35% 24% 11% 1	330
	21st to end	Day	14% 28% 31% 18% 9%	330
December	1st to 10th	Day	15% 22% 32% 23% 7% 1	330
	11th to 20th	Day	12% 26% 33% 23% 4 1	330
	21st to end	Day	25% 24% 32% 17% 2 1	363
January	1st to 10th	Night	8% 16% 29% 31% 13% 2	877
	11th to 20th	Night	11% 15% 30% 31% 11% 3	840
	21st to end	Night	9% 15% 33% 29% 12% 2	924
February	1st to 10th	Night	10% 16% 34% 30% 9% 1	840
	11th to 20th	Night	14% 17% 37% 25% 7%	824
	21st to end	Night	13% 24% 33% 27% 4	692
March	1st to 10th	Night	10% 22% 34% 26% 8% 1	840
	11th to 20th	Night	13% 18% 28% 29% 11% 1	840
	21st to end	Night	13% 20% 33% 27% 7%	861
April	1st to 10th	Night	13% 21% 37% 24% 4	630
	11th to 20th	Night	12% 25% 28% 27% 7%	623
	21st to end	Night	12% 23% 32% 27% 7%	630
May	1st to 10th	Night	10% 17% 34% 31% 8%	630
	11th to 20th	Night	12% 14% 28% 30% 14% 1	621
	21st to end	Night	7% 15% 33% 32% 12%	683
June	1st to 10th	Night	4 10% 27% 41% 17% 1	630
	11th to 20th	Night	6% 10% 30% 40% 14% 1	630
	21st to end	Night	7% 9% 24% 34% 25% 1	630
July	1st to 10th	Night	5% 3 19% 38% 33% 3	615
	11th to 20th	Night	4 2 9% 39% 42% 5%	612
	21st to end	Night	6% 2 8% 30% 47% 7%	690
August	1st to 10th	Night	5% 3 11% 32% 41% 9%	627
	11th to 20th	Night	7% 2 11% 42% 34% 4	624
	21st to end	Night	5% 2 11% 38% 39% 5%	687
September	1st to 10th	Night	8% 3 14% 43% 29% 5%	600
	11th to 20th	Night	6% 3 22% 40% 25% 4	600
	21st to end	Night	7% 6% 21% 41% 23% 2	685
October	1st to 10th	Night	8% 9% 27% 39% 15% 2	800
	11th to 20th	Night	9% 9% 27% 38% 15% 3	800
	21st to end	Night	10% 11% 27% 32% 15% 5%	880
November	1st to 10th	Night	6% 12% 25% 37% 18% 2	836
	11th to 20th	Night	6% 12% 30% 35% 15% 3	1050
	21st to end	Night	13% 15% 25% 29% 15% 3	1050
December	1st to 10th	Night	9% 16% 31% 32% 10% 1	1050
	11th to 20th	Night	12% 16% 30% 30% 11% 1	1050
	21st to end	Night	15% 16% 32% 29% 8% 1	1155

Page generated at 2026-08-27 02:07:11. Version ac07

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