Valier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Valier clear sky chart from 2005-11-06 to 2024-12-06.

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	7% 7% 3 7% 5% 4 5% 4 6% 8% 46%	105708
	Night	6% 8% 3 7% 5% 4 4 4 6% 7% 46%	102661
Transparency	Day	35% 6% 14% 24% 16% 5%	105435
	Night	35% 6% 15% 25% 14% 4	102524
Seeing	Day	12% 12% 27% 28% 16% 5%	15495
	Night	11% 12% 30% 33% 13% 1	24795

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 8% 3 12% 7% 6% 5% 4 6% 9% 37%	2219
	11th to 20th	Day	5% 11% 4 11% 6% 6% 8% 6% 6% 7% 31%	2348
	21st to end	Day	3 8% 3 9% 5% 4 5% 4 6% 9% 44%	2794
February	1st to 10th	Day	6% 13% 5% 9% 6% 6% 5% 5% 7% 8% 29%	1681
	11th to 20th	Day	6% 14% 6% 8% 5% 4 4 4 6% 8% 35%	1665
	21st to end	Day	3 9% 5% 10% 7% 6% 6% 4 6% 7% 37%	1501
March	1st to 10th	Day	3 8% 3 8% 6% 6% 5% 3 5% 9% 44%	3226
	11th to 20th	Day	3 6% 2 6% 4 4 4 5% 7% 10% 48%	3490
	21st to end	Day	9% 16% 7% 15% 8% 5% 4 3 6% 6% 21%	3825
April	1st to 10th	Day	8% 13% 4 9% 6% 5% 5% 4 6% 7% 33%	2284
	11th to 20th	Day	11% 12% 4 8% 6% 5% 4 3 6% 7% 34%	2437
	21st to end	Day	11% 12% 3 7% 4 4 6% 4 6% 7% 36%	2470
May	1st to 10th	Day	15% 15% 4 8% 4 4 4 3 5% 6% 32%	4136
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 5% 8% 9% 38%	4495
	21st to end	Day	14% 8% 2 6% 5% 5% 5% 4 6% 8% 37%	5161
June	1st to 10th	Day	14% 5% 3 7% 4 5% 4 4 7% 8% 39%	2850
	11th to 20th	Day	14% 6% 3 7% 6% 5% 5% 4 6% 7% 37%	2850
	21st to end	Day	6% 3 1 4 4 4 5% 4 6% 9% 54%	2850
July	1st to 10th	Day	3 2 1 5% 4 4 4 4 6% 7% 58%	4740
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 7% 70%	4740
	21st to end	Day	2 1 1 2 2 3 3 3 5% 7% 71%	4932
August	1st to 10th	Day	8% 5% 2 4 3 4 4 4 7% 8% 51%	4161
	11th to 20th	Day	4 3 1 4 3 4 5% 5% 7% 9% 53%	4028
	21st to end	Day	5% 4 1 4 3 3 4 3 5% 7% 61%	4521
September	1st to 10th	Day	9% 4 2 5% 3 3 4 3 5% 6% 57%	2322
	11th to 20th	Day	10% 6% 2 5% 5% 5% 4 3 5% 6% 49%	2090
	21st to end	Day	12% 6% 2 3 4 3 3 3 5% 6% 53%	2090
October	1st to 10th	Day	7% 5% 2 5% 3 3 3 3 6% 9% 52%	3276
	11th to 20th	Day	5% 6% 2 5% 4 5% 5% 4 6% 7% 52%	3130
	21st to end	Day	6% 8% 3 9% 5% 4 4 4 6% 7% 45%	3101
November	1st to 10th	Day	8% 12% 4 8% 4 4 4 3 4 7% 40%	1646
	11th to 20th	Day	3 9% 3 8% 5% 5% 5% 5% 8% 8% 40%	1600
	21st to end	Day	5% 10% 4 7% 4 4 4 4 6% 9% 42%	1557
December	1st to 10th	Day	3 9% 4 8% 7% 5% 5% 5% 6% 8% 40%	1365
	11th to 20th	Day	4 11% 4 9% 6% 4 7% 4 7% 8% 36%	1685
	21st to end	Day	4 9% 3 7% 5% 5% 5% 4 5% 7% 46%	2442
January	1st to 10th	Night	3 8% 3 10% 6% 6% 6% 5% 7% 9% 38%	4726
	11th to 20th	Night	5% 12% 4 10% 7% 7% 6% 4 5% 6% 34%	4640
	21st to end	Night	3 9% 4 8% 5% 5% 5% 4 6% 8% 42%	4862
February	1st to 10th	Night	7% 12% 4 9% 6% 4 4 4 6% 7% 36%	2498
	11th to 20th	Night	4 13% 4 10% 7% 7% 6% 4 6% 7% 33%	2402
	21st to end	Night	4 10% 4 12% 7% 5% 5% 4 5% 7% 37%	1951
March	1st to 10th	Night	2 7% 4 9% 7% 7% 6% 5% 7% 8% 39%	3648
	11th to 20th	Night	3 6% 2 6% 4 4 5% 3 6% 8% 52%	3490
	21st to end	Night	11% 18% 5% 14% 7% 5% 4 3 4 6% 24%	3828
April	1st to 10th	Night	8% 11% 3 8% 5% 5% 4 4 7% 8% 38%	1893
	11th to 20th	Night	10% 13% 3 8% 5% 5% 6% 4 5% 6% 34%	1691
	21st to end	Night	10% 10% 4 6% 4 4 4 4 6% 8% 40%	1710
May	1st to 10th	Night	14% 14% 4 7% 4 5% 4 3 5% 5% 34%	2833
	11th to 20th	Night	7% 4 2 5% 4 5% 5% 4 8% 9% 47%	2402
	21st to end	Night	17% 7% 2 6% 4 4 4 5% 7% 8% 36%	2414
June	1st to 10th	Night	12% 5% 2 7% 4 4 4 4 7% 9% 43%	1330
	11th to 20th	Night	12% 6% 2 6% 6% 4 4 4 6% 7% 41%	1330
	21st to end	Night	6% 3 1 4 3 4 3 4 7% 9% 56%	1330
July	1st to 10th	Night	4 2 1 4 4 3 4 3 5% 7% 64%	2220
	11th to 20th	Night	3 2 3 2 3 3 2 3 5% 75%	2220
	21st to end	Night	3 2 1 3 2 2 2 3 4 5% 72%	2602
August	1st to 10th	Night	9% 4 2 4 4 3 4 3 5% 7% 55%	2774
	11th to 20th	Night	4 3 1 5% 4 5% 6% 5% 7% 10% 51%	2811
	21st to end	Night	7% 4 2 4 4 3 3 3 4 6% 60%	3146
September	1st to 10th	Night	10% 4 1 4 3 3 4 3 5% 6% 57%	1855
	11th to 20th	Night	11% 7% 2 4 3 4 4 3 4 7% 53%	2090
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 6% 55%	2090
October	1st to 10th	Night	8% 6% 2 5% 3 3 3 3 5% 6% 56%	3697
	11th to 20th	Night	6% 7% 2 6% 3 4 4 3 6% 7% 51%	3798
	21st to end	Night	3 6% 3 6% 4 4 4 4 6% 8% 51%	4457
November	1st to 10th	Night	9% 10% 3 7% 5% 5% 5% 4 6% 8% 39%	2631
	11th to 20th	Night	4 8% 3 7% 6% 4 5% 5% 6% 9% 43%	2800
	21st to end	Night	4 10% 4 8% 5% 4 5% 4 6% 8% 42%	2840
December	1st to 10th	Night	3 10% 4 8% 6% 5% 5% 5% 6% 9% 40%	2932
	11th to 20th	Night	3 9% 4 10% 6% 4 4 4 7% 9% 40%	3506
	21st to end	Night	3 10% 3 8% 4 4 4 4 6% 7% 48%	5214

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	41% 7% 16% 26% 8% 1	2219
	11th to 20th	Day	49% 7% 17% 13% 10% 5%	2348
	21st to end	Day	34% 8% 24% 26% 7% 1	2794
February	1st to 10th	Day	49% 7% 18% 18% 7% 1	1681
	11th to 20th	Day	46% 7% 17% 21% 8% 1	1674
	21st to end	Day	45% 7% 14% 21% 11% 2	1501
March	1st to 10th	Day	35% 7% 16% 23% 19% 1	3226
	11th to 20th	Day	28% 7% 28% 28% 8% 1	3490
	21st to end	Day	60% 7% 15% 13% 5%	3825
April	1st to 10th	Day	48% 6% 15% 21% 9% 1	2284
	11th to 20th	Day	47% 6% 13% 22% 11% 1	2440
	21st to end	Day	46% 6% 15% 23% 10% 1	2470
May	1st to 10th	Day	51% 5% 11% 25% 7% 1	4136
	11th to 20th	Day	36% 9% 15% 26% 12% 2	4499
	21st to end	Day	41% 8% 15% 23% 12% 1	5162
June	1st to 10th	Day	41% 8% 17% 22% 12% 1	2850
	11th to 20th	Day	43% 7% 12% 17% 17% 4	2850
	21st to end	Day	25% 6% 14% 34% 18% 3	2850
July	1st to 10th	Day	23% 4 9% 28% 24% 12%	4666
	11th to 20th	Day	14% 4 7% 19% 29% 27%	4659
	21st to end	Day	12% 4 6% 21% 32% 25%	4776
August	1st to 10th	Day	29% 5% 12% 21% 25% 8%	4145
	11th to 20th	Day	24% 6% 13% 34% 20% 3	4067
	21st to end	Day	22% 5% 10% 30% 27% 6%	4520
September	1st to 10th	Day	27% 5% 11% 26% 20% 11%	2322
	11th to 20th	Day	34% 6% 12% 27% 17% 5%	2090
	21st to end	Day	31% 5% 11% 30% 16% 6%	2090
October	1st to 10th	Day	28% 4 10% 33% 22% 3	3276
	11th to 20th	Day	31% 5% 13% 30% 18% 3	3130
	21st to end	Day	37% 6% 11% 27% 17% 2	3101
November	1st to 10th	Day	44% 5% 16% 22% 10% 3	1646
	11th to 20th	Day	35% 9% 18% 24% 12% 1	1600
	21st to end	Day	36% 6% 21% 26% 10% 2	1557
December	1st to 10th	Day	40% 7% 19% 23% 8% 4	1365
	11th to 20th	Day	43% 9% 22% 20% 6% 1	1684
	21st to end	Day	35% 7% 14% 25% 14% 5%	2442
January	1st to 10th	Night	37% 9% 20% 23% 10% 1	4726
	11th to 20th	Night	48% 7% 14% 17% 12% 3	4640
	21st to end	Night	37% 9% 20% 26% 8% 1	4862
February	1st to 10th	Night	46% 6% 18% 18% 10% 2	2498
	11th to 20th	Night	47% 7% 17% 19% 9% 1	2403
	21st to end	Night	44% 6% 16% 22% 10% 2	1951
March	1st to 10th	Night	35% 10% 15% 28% 12%	3648
	11th to 20th	Night	27% 7% 25% 29% 10%	3490
	21st to end	Night	60% 7% 13% 15% 4 1	3828
April	1st to 10th	Night	42% 7% 16% 25% 10% 1	1893
	11th to 20th	Night	47% 7% 12% 23% 10% 1	1691
	21st to end	Night	41% 7% 17% 25% 9% 1	1710
May	1st to 10th	Night	50% 5% 13% 24% 7% 1	2833
	11th to 20th	Night	28% 9% 17% 29% 17% 1	2403
	21st to end	Night	42% 8% 15% 25% 9%	2414
June	1st to 10th	Night	36% 5% 20% 26% 12% 1	1330
	11th to 20th	Night	39% 7% 14% 24% 14% 3	1330
	21st to end	Night	22% 6% 16% 34% 19% 2	1330
July	1st to 10th	Night	18% 4 10% 31% 27% 9%	2185
	11th to 20th	Night	13% 3 6% 23% 32% 23%	2178
	21st to end	Night	14% 3 7% 21% 31% 24%	2520
August	1st to 10th	Night	28% 3 12% 22% 24% 10%	2766
	11th to 20th	Night	26% 6% 13% 33% 18% 4	2838
	21st to end	Night	25% 3 9% 31% 24% 8%	3146
September	1st to 10th	Night	27% 5% 11% 27% 19% 12%	1855
	11th to 20th	Night	31% 4 13% 30% 16% 6%	2090
	21st to end	Night	31% 4 13% 30% 18% 5%	2090
October	1st to 10th	Night	29% 3 12% 31% 22% 4	3697
	11th to 20th	Night	32% 4 11% 32% 19% 2	3798
	21st to end	Night	30% 6% 12% 29% 21% 3	4457
November	1st to 10th	Night	40% 7% 18% 21% 11% 3	2631
	11th to 20th	Night	35% 7% 20% 24% 13% 1	2800
	21st to end	Night	38% 6% 20% 21% 11% 3	2840
December	1st to 10th	Night	39% 8% 18% 23% 9% 3	2932
	11th to 20th	Night	38% 8% 25% 22% 6% 1	3507
	21st to end	Night	33% 6% 15% 25% 14% 6%	5214

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	7% 14% 29% 24% 17% 9%	180
	11th to 20th	Day	8% 16% 27% 28% 16% 5%	180
	21st to end	Day	13% 16% 35% 23% 11% 2	198
February	1st to 10th	Day	20% 19% 30% 24% 6% 1	256
	11th to 20th	Day	14% 19% 30% 23% 9% 5%	270
	21st to end	Day	6% 20% 42% 23% 8% 1	313
March	1st to 10th	Day	14% 14% 31% 28% 10% 3	460
	11th to 20th	Day	10% 15% 30% 27% 14% 4	460
	21st to end	Day	13% 17% 30% 29% 8% 3	506
April	1st to 10th	Day	16% 18% 31% 25% 8% 2	460
	11th to 20th	Day	18% 15% 33% 22% 10% 3	452
	21st to end	Day	18% 18% 26% 20% 14% 4	460
May	1st to 10th	Day	16% 12% 22% 26% 16% 8%	476
	11th to 20th	Day	20% 9% 19% 26% 20% 6%	675
	21st to end	Day	21% 9% 18% 24% 22% 6%	734
June	1st to 10th	Day	13% 13% 24% 26% 18% 6%	680
	11th to 20th	Day	17% 17% 27% 24% 13% 3	680
	21st to end	Day	7% 8% 25% 34% 20% 6%	680
July	1st to 10th	Day	4 5% 23% 36% 25% 7%	671
	11th to 20th	Day	6% 7% 24% 39% 20% 3	668
	21st to end	Day	3 4 26% 38% 22% 7%	621
August	1st to 10th	Day	10% 5% 21% 35% 21% 7%	487
	11th to 20th	Day	6% 4 21% 32% 24% 12%	477
	21st to end	Day	6% 7% 26% 32% 21% 7%	539
September	1st to 10th	Day	10% 12% 26% 25% 21% 7%	490
	11th to 20th	Day	10% 11% 26% 30% 17% 6%	490
	21st to end	Day	17% 11% 27% 23% 16% 6%	490
October	1st to 10th	Day	16% 9% 22% 29% 17% 6%	367
	11th to 20th	Day	13% 13% 25% 23% 17% 9%	300
	21st to end	Day	15% 17% 32% 23% 9% 4	330
November	1st to 10th	Day	20% 14% 33% 23% 9% 1	300
	11th to 20th	Day	11% 17% 38% 25% 7% 1	300
	21st to end	Day	12% 18% 31% 25% 11% 4	277
December	1st to 10th	Day	9% 16% 35% 23% 13% 4	190
	11th to 20th	Day	18% 18% 29% 22% 10% 3	180
	21st to end	Day	12% 15% 26% 24% 18% 5%	198
January	1st to 10th	Night	8% 18% 36% 28% 10% 1	950
	11th to 20th	Night	10% 18% 36% 26% 8% 2	889
	21st to end	Night	9% 17% 39% 25% 8% 2	836
February	1st to 10th	Night	13% 18% 32% 25% 10% 3	760
	11th to 20th	Night	9% 16% 35% 29% 10% 1	744
	21st to end	Night	8% 14% 33% 30% 13% 2	628
March	1st to 10th	Night	6% 11% 36% 33% 11% 2	760
	11th to 20th	Night	8% 12% 33% 34% 11% 2	760
	21st to end	Night	13% 11% 31% 32% 13% 1	836
April	1st to 10th	Night	14% 11% 33% 30% 11% 1	675
	11th to 20th	Night	13% 10% 34% 31% 10% 1	563
	21st to end	Night	15% 8% 30% 32% 14%	570
May	1st to 10th	Night	15% 8% 28% 31% 17% 1	570
	11th to 20th	Night	14% 8% 19% 38% 20% 2	499
	21st to end	Night	21% 6% 21% 30% 19% 3	411
June	1st to 10th	Night	15% 6% 25% 38% 15% 2	380
	11th to 20th	Night	14% 11% 29% 31% 14%	380
	21st to end	Night	8% 5% 21% 44% 22% 1	380
July	1st to 10th	Night	7% 3 20% 44% 26%	370
	11th to 20th	Night	4 3 22% 55% 14% 1	368
	21st to end	Night	5% 3 18% 53% 20% 1	416
August	1st to 10th	Night	7% 3 20% 46% 22% 1	519
	11th to 20th	Night	6% 3 22% 43% 23% 2	564
	21st to end	Night	8% 6% 22% 44% 19% 1	627
September	1st to 10th	Night	11% 3 20% 44% 19% 3	615
	11th to 20th	Night	13% 5% 19% 39% 22% 3	760
	21st to end	Night	14% 6% 27% 32% 17% 4	760
October	1st to 10th	Night	16% 6% 23% 34% 19% 1	760
	11th to 20th	Night	11% 12% 29% 32% 13% 3	760
	21st to end	Night	10% 14% 34% 31% 9% 1	836
November	1st to 10th	Night	14% 15% 34% 31% 6%	876
	11th to 20th	Night	9% 18% 39% 26% 7% 1	1000
	21st to end	Night	8% 16% 37% 30% 8% 1	1000
December	1st to 10th	Night	10% 16% 33% 28% 12% 2	978
	11th to 20th	Night	9% 16% 36% 29% 9% 1	950
	21st to end	Night	10% 17% 35% 28% 10% 1	1045

Page generated at 2024-12-03 04:45:13. Version ac07

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