Vale
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vale clear sky chart from 2005-11-06 to 2025-11-18.

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	6% 6% 2 6% 4 4 4 3 5% 6% 53%	135622
	Night	9% 8% 3 7% 4 4 4 3 5% 6% 48%	132040
Transparency	Day	30% 6% 10% 20% 20% 14%	130396
	Night	35% 7% 12% 20% 17% 10%	128276
Seeing	Day	9% 6% 17% 28% 27% 13%	15791
	Night	11% 3 20% 39% 23% 3	25013

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	15% 16% 5% 11% 8% 5% 5% 3 5% 5% 23%	3639
	11th to 20th	Day	12% 13% 4 9% 6% 6% 5% 3 5% 8% 30%	3640
	21st to end	Day	15% 12% 4 10% 5% 5% 6% 4 5% 6% 28%	4004
February	1st to 10th	Day	13% 13% 4 9% 6% 5% 4 3 5% 6% 30%	1737
	11th to 20th	Day	11% 9% 4 10% 7% 5% 5% 4 6% 7% 33%	1950
	21st to end	Day	8% 9% 4 7% 6% 6% 5% 4 7% 9% 36%	1650
March	1st to 10th	Day	6% 11% 4 10% 5% 5% 6% 4 7% 9% 34%	4518
	11th to 20th	Day	5% 7% 3 6% 4 4 5% 3 7% 7% 49%	4709
	21st to end	Day	7% 9% 3 9% 6% 6% 6% 5% 8% 8% 33%	5881
April	1st to 10th	Day	9% 8% 3 6% 5% 5% 5% 4 7% 7% 42%	2400
	11th to 20th	Day	6% 7% 3 7% 5% 4 5% 4 6% 7% 47%	2373
	21st to end	Day	7% 6% 2 6% 5% 4 5% 4 5% 8% 48%	2600
May	1st to 10th	Day	6% 5% 1 4 4 4 5% 4 5% 6% 57%	5880
	11th to 20th	Day	6% 4 2 4 3 3 3 4 5% 8% 60%	6228
	21st to end	Day	3 3 1 4 3 4 4 4 5% 8% 60%	6902
June	1st to 10th	Day	7% 5% 2 5% 6% 5% 5% 5% 7% 8% 47%	2800
	11th to 20th	Day	6% 4 1 4 4 4 3 3 6% 7% 58%	2800
	21st to end	Day	2 3 1 3 2 2 3 3 4 6% 71%	2800
July	1st to 10th	Day	2 2 1 2 1 1 2 2 4 4 80%	6319
	11th to 20th	Day	1 1 2 2 1 2 2 2 4 83%	6320
	21st to end	Day	2 2 1 2 2 3 3 3 5% 7% 72%	6880
August	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 8% 65%	6130
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	5677
	21st to end	Day	4 4 1 4 3 2 3 2 4 5% 70%	5984
September	1st to 10th	Day	3 2 1 2 2 2 3 2 4 6% 73%	2400
	11th to 20th	Day	3 3 1 4 3 4 4 3 5% 7% 63%	2263
	21st to end	Day	5% 3 1 4 3 3 4 2 4 6% 65%	2200
October	1st to 10th	Day	5% 4 1 4 3 3 2 2 3 5% 68%	3551
	11th to 20th	Day	7% 6% 3 5% 4 3 4 3 4 7% 56%	3138
	21st to end	Day	9% 6% 2 6% 3 4 5% 4 6% 8% 46%	3200
November	1st to 10th	Day	13% 8% 3 6% 5% 4 4 3 7% 7% 39%	1854
	11th to 20th	Day	12% 9% 4 9% 5% 4 5% 5% 6% 6% 35%	1863
	21st to end	Day	10% 8% 4 11% 6% 6% 4 5% 6% 6% 32%	1680
December	1st to 10th	Day	11% 9% 3 9% 7% 7% 6% 4 5% 7% 32%	2620
	11th to 20th	Day	19% 14% 6% 17% 7% 5% 4 3 5% 4 15%	3028
	21st to end	Day	15% 14% 4 11% 7% 6% 6% 4 6% 6% 21%	4004
January	1st to 10th	Night	18% 17% 6% 11% 5% 5% 5% 3 5% 5% 20%	6306
	11th to 20th	Night	15% 10% 3 8% 6% 5% 4 4 5% 6% 34%	6320
	21st to end	Night	15% 14% 4 9% 4 4 4 3 5% 6% 34%	6952
February	1st to 10th	Night	12% 12% 4 9% 6% 4 5% 5% 6% 7% 31%	2657
	11th to 20th	Night	11% 10% 3 8% 4 4 5% 4 6% 7% 37%	2338
	21st to end	Night	9% 10% 3 8% 6% 5% 6% 4 6% 7% 34%	1980
March	1st to 10th	Night	7% 11% 3 8% 5% 5% 5% 4 6% 8% 38%	5376
	11th to 20th	Night	8% 11% 3 7% 4 3 4 3 5% 6% 46%	5291
	21st to end	Night	7% 8% 3 9% 6% 6% 7% 5% 7% 9% 33%	5078
April	1st to 10th	Night	9% 7% 3 7% 5% 3 5% 4 5% 7% 45%	2000
	11th to 20th	Night	7% 7% 2 7% 5% 3 5% 4 5% 7% 48%	1974
	21st to end	Night	8% 5% 2 5% 3 3 4 4 6% 8% 51%	1800
May	1st to 10th	Night	8% 4 2 4 3 3 4 3 4 6% 59%	4100
	11th to 20th	Night	4 4 1 5% 4 3 3 3 6% 8% 58%	3663
	21st to end	Night	6% 5% 2 5% 3 3 3 3 5% 6% 59%	3972
June	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 4 5% 8% 49%	1600
	11th to 20th	Night	6% 4 2 4 4 3 4 3 5% 8% 58%	1600
	21st to end	Night	3 3 1 3 3 3 3 3 5% 7% 66%	1600
July	1st to 10th	Night	1 2 1 2 2 2 2 2 4 4 77%	3640
	11th to 20th	Night	1 1 1 1 2 4 4 84%	3640
	21st to end	Night	2 2 1 4 3 4 4 3 6% 8% 61%	3970
August	1st to 10th	Night	3 3 2 4 4 4 4 4 6% 7% 60%	3666
	11th to 20th	Night	1 2 1 2 2 2 2 2 4 4 77%	4161
	21st to end	Night	4 4 1 4 3 2 3 2 4 5% 68%	5015
September	1st to 10th	Night	4 2 1 3 2 2 2 2 4 6% 73%	2000
	11th to 20th	Night	4 2 1 4 4 4 3 3 5% 7% 64%	2136
	21st to end	Night	6% 3 1 3 2 3 4 3 4 6% 66%	2200
October	1st to 10th	Night	5% 3 2 4 2 2 2 2 3 5% 70%	3632
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 6% 61%	4014
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 7% 50%	4600
November	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 5% 7% 44%	2665
	11th to 20th	Night	14% 8% 3 7% 4 5% 5% 4 6% 7% 38%	2691
	21st to end	Night	12% 9% 3 6% 5% 4 4 3 5% 6% 43%	2715
December	1st to 10th	Night	10% 8% 2 8% 4 4 4 4 6% 9% 39%	4560
	11th to 20th	Night	17% 15% 7% 13% 5% 5% 5% 4 5% 5% 18%	5176
	21st to end	Night	16% 15% 4 10% 5% 5% 5% 4 6% 6% 26%	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	62% 9% 11% 15% 3	3639
	11th to 20th	Day	53% 8% 16% 19% 4	3640
	21st to end	Day	55% 10% 10% 17% 6% 2	4004
February	1st to 10th	Day	51% 11% 18% 14% 5% 1	1737
	11th to 20th	Day	46% 12% 16% 18% 7%	1960
	21st to end	Day	40% 10% 21% 19% 9% 1	1650
March	1st to 10th	Day	43% 9% 16% 23% 10% 1	4518
	11th to 20th	Day	33% 5% 14% 31% 16%	4709
	21st to end	Day	42% 10% 20% 19% 8% 2	5881
April	1st to 10th	Day	36% 9% 16% 24% 13% 2	2400
	11th to 20th	Day	33% 7% 13% 25% 17% 4	2376
	21st to end	Day	32% 7% 14% 27% 17% 3	2600
May	1st to 10th	Day	24% 5% 8% 25% 31% 6%	5880
	11th to 20th	Day	22% 4 7% 28% 28% 10%	6231
	21st to end	Day	19% 7% 11% 31% 26% 6%	6904
June	1st to 10th	Day	31% 8% 12% 25% 21% 3	2800
	11th to 20th	Day	23% 6% 10% 24% 26% 11%	2800
	21st to end	Day	15% 4 7% 20% 32% 21%	2800
July	1st to 10th	Day	10% 2 2 9% 27% 50%	6251
	11th to 20th	Day	9% 1 2 6% 21% 62%	6245
	21st to end	Day	13% 2 2 15% 34% 35%	6681
August	1st to 10th	Day	20% 3 4 10% 27% 35%	4466
	11th to 20th	Day	10% 2 3 15% 37% 32%	4112
	21st to end	Day	13% 2 4 22% 33% 26%	4311
September	1st to 10th	Day	14% 3 4 20% 32% 27%	2400
	11th to 20th	Day	21% 5% 9% 24% 28% 13%	2263
	21st to end	Day	20% 5% 9% 27% 31% 9%	2200
October	1st to 10th	Day	21% 4 7% 23% 37% 8%	3551
	11th to 20th	Day	29% 4 14% 29% 19% 4	3138
	21st to end	Day	33% 5% 14% 31% 15% 1	3200
November	1st to 10th	Day	41% 8% 20% 23% 9%	1854
	11th to 20th	Day	47% 10% 18% 19% 5% 1	1863
	21st to end	Day	48% 11% 18% 16% 6% 1	1680
December	1st to 10th	Day	49% 8% 20% 19% 3	2620
	11th to 20th	Day	72% 8% 11% 8% 2	3028
	21st to end	Day	60% 10% 16% 12% 3	4004
January	1st to 10th	Night	63% 11% 12% 11% 3	6306
	11th to 20th	Night	48% 8% 18% 18% 7%	6320
	21st to end	Night	51% 8% 14% 16% 9% 2	6952
February	1st to 10th	Night	49% 12% 18% 16% 4	2657
	11th to 20th	Night	44% 10% 18% 19% 9%	2339
	21st to end	Night	43% 11% 18% 19% 8% 1	1980
March	1st to 10th	Night	39% 9% 15% 25% 11% 1	5376
	11th to 20th	Night	39% 5% 9% 31% 16%	5291
	21st to end	Night	41% 10% 18% 23% 7%	5078
April	1st to 10th	Night	37% 7% 14% 23% 17% 2	2000
	11th to 20th	Night	33% 7% 12% 27% 17% 4	1974
	21st to end	Night	28% 7% 13% 27% 22% 3	1800
May	1st to 10th	Night	23% 6% 9% 23% 34% 5%	4097
	11th to 20th	Night	22% 5% 8% 29% 30% 6%	3663
	21st to end	Night	23% 6% 9% 33% 24% 4	3972
June	1st to 10th	Night	31% 8% 14% 23% 22% 3	1600
	11th to 20th	Night	25% 6% 10% 22% 29% 9%	1600
	21st to end	Night	18% 3 6% 21% 35% 17%	1600
July	1st to 10th	Night	12% 2 2 9% 23% 52%	3600
	11th to 20th	Night	6% 2 2 7% 23% 61%	3592
	21st to end	Night	22% 2 2 14% 29% 31%	3857
August	1st to 10th	Night	23% 3 5% 10% 25% 33%	2661
	11th to 20th	Night	12% 2 4 11% 31% 40%	3012
	21st to end	Night	14% 2 3 17% 32% 32%	3608
September	1st to 10th	Night	14% 2 5% 17% 29% 33%	2000
	11th to 20th	Night	21% 4 8% 20% 26% 21%	2136
	21st to end	Night	19% 4 6% 23% 31% 17%	2200
October	1st to 10th	Night	20% 2 6% 19% 33% 20%	3632
	11th to 20th	Night	24% 3 12% 29% 27% 4	4014
	21st to end	Night	32% 5% 12% 32% 18% 1	4600
November	1st to 10th	Night	40% 6% 15% 24% 14% 1	2665
	11th to 20th	Night	43% 9% 18% 22% 8%	2691
	21st to end	Night	41% 8% 19% 22% 9% 1	2715
December	1st to 10th	Night	39% 7% 25% 25% 4	4560
	11th to 20th	Night	66% 8% 14% 9% 2	5176
	21st to end	Night	56% 11% 16% 12% 6%	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	21% 5% 16% 33% 21% 5%	200
	11th to 20th	Day	19% 9% 14% 29% 22% 9%	200
	21st to end	Day	20% 2 15% 29% 25% 8%	220
February	1st to 10th	Day	19% 4 22% 29% 22% 4	322
	11th to 20th	Day	14% 5% 21% 36% 18% 5%	495
	21st to end	Day	11% 7% 29% 29% 20% 5%	414
March	1st to 10th	Day	13% 10% 25% 32% 18% 2	500
	11th to 20th	Day	12% 10% 24% 27% 21% 7%	500
	21st to end	Day	13% 11% 23% 29% 20% 4	550
April	1st to 10th	Day	11% 12% 22% 23% 21% 10%	500
	11th to 20th	Day	10% 13% 26% 26% 16% 10%	492
	21st to end	Day	7% 8% 27% 29% 22% 7%	500
May	1st to 10th	Day	5% 11% 23% 26% 23% 11%	503
	11th to 20th	Day	15% 8% 19% 27% 20% 11%	528
	21st to end	Day	7% 5% 16% 29% 25% 19%	573
June	1st to 10th	Day	6% 7% 18% 26% 25% 18%	530
	11th to 20th	Day	7% 8% 23% 29% 22% 10%	530
	21st to end	Day	2 2 18% 30% 31% 17%	530
July	1st to 10th	Day	3 1 11% 34% 35% 16%	526
	11th to 20th	Day	2 2 10% 35% 37% 14%	524
	21st to end	Day	3 1 9% 30% 38% 20%	575
August	1st to 10th	Day	6% 2 11% 29% 36% 17%	527
	11th to 20th	Day	2 1 10% 28% 36% 24%	517
	21st to end	Day	5% 2 12% 28% 29% 24%	583
September	1st to 10th	Day	4 2 9% 23% 35% 27%	530
	11th to 20th	Day	4 3 11% 25% 32% 24%	530
	21st to end	Day	6% 3 12% 27% 33% 20%	530
October	1st to 10th	Day	7% 4 16% 22% 29% 22%	530
	11th to 20th	Day	8% 3 16% 28% 27% 17%	458
	21st to end	Day	10% 7% 15% 28% 29% 10%	363
November	1st to 10th	Day	13% 8% 16% 27% 29% 6%	330
	11th to 20th	Day	15% 5% 17% 29% 26% 7%	321
	21st to end	Day	15% 4 13% 27% 33% 8%	240
December	1st to 10th	Day	20% 4 16% 27% 20% 15%	200
	11th to 20th	Day	25% 6% 18% 30% 20% 3	200
	21st to end	Day	20% 5% 17% 30% 23% 5%	220
January	1st to 10th	Night	19% 4 19% 34% 19% 4	800
	11th to 20th	Night	17% 5% 20% 34% 21% 4	800
	21st to end	Night	15% 1 19% 37% 23% 4	880
February	1st to 10th	Night	17% 4 23% 37% 17% 2	800
	11th to 20th	Night	15% 2 21% 41% 19% 2	784
	21st to end	Night	13% 3 26% 40% 16% 1	660
March	1st to 10th	Night	12% 4 25% 40% 17% 2	800
	11th to 20th	Night	12% 5% 22% 40% 19% 2	800
	21st to end	Night	13% 5% 27% 39% 15% 1	880
April	1st to 10th	Night	12% 6% 23% 36% 21% 2	800
	11th to 20th	Night	9% 6% 28% 36% 18% 2	786
	21st to end	Night	9% 4 27% 40% 18% 1	600
May	1st to 10th	Night	7% 7% 28% 40% 17% 1	600
	11th to 20th	Night	8% 4 22% 37% 25% 4	415
	21st to end	Night	8% 5% 21% 39% 23% 4	433
June	1st to 10th	Night	7% 5% 23% 39% 24% 2	400
	11th to 20th	Night	8% 7% 29% 36% 19% 2	400
	21st to end	Night	5% 4 24% 44% 23% 1	400
July	1st to 10th	Night	3 2 22% 52% 20% 1	390
	11th to 20th	Night	1 1 24% 59% 15%	388
	21st to end	Night	3 20% 52% 24% 1	438
August	1st to 10th	Night	4 1 20% 46% 27% 2	432
	11th to 20th	Night	2 2 15% 47% 32% 2	639
	21st to end	Night	4 2 14% 43% 33% 4	880
September	1st to 10th	Night	5% 2 12% 40% 37% 4	800
	11th to 20th	Night	4 2 12% 39% 37% 6%	800
	21st to end	Night	8% 2 15% 36% 32% 7%	800
October	1st to 10th	Night	10% 3 16% 38% 27% 6%	800
	11th to 20th	Night	7% 3 19% 36% 28% 6%	800
	21st to end	Night	9% 3 19% 39% 26% 3	880
November	1st to 10th	Night	14% 3 17% 39% 25% 2	820
	11th to 20th	Night	17% 3 18% 40% 19% 3	828
	21st to end	Night	16% 3 20% 34% 23% 5%	800
December	1st to 10th	Night	19% 3 18% 36% 21% 3	800
	11th to 20th	Night	22% 3 15% 40% 18% 2	800
	21st to end	Night	23% 5% 23% 36% 12% 2	880

Page generated at 2025-11-14 22:55:57. Version ac07

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