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 2024-07-05.

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	8% 8% 3 7% 5% 4 5% 4 6% 8% 43%	89435
	Night	6% 9% 3 7% 5% 5% 5% 4 6% 7% 43%	89943
Transparency	Day	37% 7% 15% 24% 14% 3	89122
	Night	37% 7% 16% 24% 13% 3	89778
Seeing	Day	13% 12% 27% 28% 16% 5%	14931
	Night	11% 12% 30% 33% 13% 1	24241

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	4 3 1 4 4 4 4 4 7% 7% 59%	2763
	11th to 20th	Day	4 3 1 4 3 4 3 4 5% 8% 60%	2700
	21st to end	Day	3 1 1 3 2 3 4 3 6% 8% 64%	2827
August	1st to 10th	Day	6% 4 2 3 2 4 3 4 7% 7% 58%	2372
	11th to 20th	Day	6% 4 1 4 3 3 4 3 6% 8% 58%	2299
	21st to end	Day	7% 4 2 4 3 4 4 4 6% 7% 56%	2574
September	1st to 10th	Day	9% 4 2 5% 3 4 4 3 5% 6% 56%	2201
	11th to 20th	Day	10% 5% 2 5% 5% 4 4 3 5% 6% 50%	1980
	21st to end	Day	13% 6% 2 3 4 3 3 3 5% 6% 52%	1980
October	1st to 10th	Day	12% 8% 2 6% 4 3 3 3 6% 8% 44%	1864
	11th to 20th	Day	8% 8% 3 7% 5% 5% 5% 3 5% 6% 44%	1792
	21st to end	Day	7% 9% 3 7% 5% 4 5% 4 7% 8% 40%	1782
November	1st to 10th	Day	8% 13% 5% 8% 4 4 4 4 4 7% 39%	1562
	11th to 20th	Day	3 9% 3 8% 5% 5% 5% 5% 8% 8% 40%	1520
	21st to end	Day	5% 10% 4 7% 4 4 4 4 7% 9% 43%	1480
December	1st to 10th	Day	3 9% 4 9% 7% 5% 5% 5% 6% 8% 39%	1330
	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	5% 3 1 3 3 3 3 3 4 8% 65%	1291
	11th to 20th	Night	4 3 4 2 4 4 2 5% 6% 65%	1260
	21st to end	Night	4 2 2 3 3 2 2 3 4 6% 70%	1487
August	1st to 10th	Night	6% 3 1 4 3 3 3 2 5% 7% 63%	1565
	11th to 20th	Night	5% 3 1 4 3 3 4 4 5% 9% 58%	1602
	21st to end	Night	7% 5% 2 4 4 4 4 3 5% 6% 56%	1782
September	1st to 10th	Night	10% 4 1 4 3 4 4 3 5% 6% 56%	1756
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 7% 54%	1980
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 6% 54%	1980
October	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 6% 7% 48%	2096
	11th to 20th	Night	8% 10% 3 7% 4 4 4 4 6% 6% 45%	2168
	21st to end	Night	5% 8% 4 7% 4 5% 5% 4 6% 7% 44%	2574
November	1st to 10th	Night	9% 10% 3 6% 4 5% 5% 4 6% 8% 39%	2496
	11th to 20th	Night	4 8% 3 7% 6% 4 5% 5% 6% 9% 44%	2660
	21st to end	Night	4 10% 4 8% 5% 4 4 4 5% 8% 43%	2698
December	1st to 10th	Night	4 11% 4 8% 6% 5% 5% 5% 6% 9% 39%	2850
	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	22% 5% 11% 30% 25% 6%	2689
	11th to 20th	Day	21% 5% 11% 25% 23% 15%	2619
	21st to end	Day	15% 6% 8% 27% 33% 12%	2670
August	1st to 10th	Day	23% 5% 12% 26% 25% 9%	2355
	11th to 20th	Day	23% 5% 12% 30% 25% 5%	2299
	21st to end	Day	25% 6% 11% 25% 23% 10%	2574
September	1st to 10th	Day	28% 5% 11% 27% 19% 11%	2201
	11th to 20th	Day	32% 6% 12% 27% 17% 5%	1980
	21st to end	Day	32% 5% 11% 30% 16% 5%	1980
October	1st to 10th	Day	38% 5% 15% 29% 13% 1	1864
	11th to 20th	Day	39% 5% 16% 23% 13% 3	1792
	21st to end	Day	39% 8% 15% 25% 11% 2	1782
November	1st to 10th	Day	45% 6% 16% 21% 9% 4	1562
	11th to 20th	Day	35% 9% 19% 25% 11% 1	1520
	21st to end	Day	35% 6% 20% 26% 10% 3	1480
December	1st to 10th	Day	41% 7% 19% 22% 8% 4	1330
	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	17% 5% 10% 33% 24% 10%	1256
	11th to 20th	Night	19% 5% 10% 28% 26% 12%	1218
	21st to end	Night	14% 4 9% 23% 36% 15%	1404
August	1st to 10th	Night	22% 3 11% 29% 25% 10%	1557
	11th to 20th	Night	22% 5% 11% 31% 24% 7%	1602
	21st to end	Night	27% 4 9% 25% 25% 9%	1782
September	1st to 10th	Night	28% 5% 11% 27% 19% 11%	1756
	11th to 20th	Night	30% 4 12% 30% 17% 6%	1980
	21st to end	Night	32% 4 13% 30% 17% 4	1980
October	1st to 10th	Night	35% 4 16% 29% 14% 2	2096
	11th to 20th	Night	37% 6% 14% 27% 13% 3	2168
	21st to end	Night	36% 8% 17% 24% 13% 2	2574
November	1st to 10th	Night	40% 7% 18% 21% 11% 3	2496
	11th to 20th	Night	34% 7% 20% 24% 14% 1	2660
	21st to end	Night	37% 6% 20% 22% 12% 3	2698
December	1st to 10th	Night	40% 8% 18% 23% 9% 3	2850
	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%	642
	11th to 20th	Day	7% 8% 24% 39% 19% 3	618
	21st to end	Day	3 4 25% 38% 22% 7%	573
August	1st to 10th	Day	9% 5% 22% 35% 21% 7%	447
	11th to 20th	Day	7% 5% 22% 32% 23% 11%	437
	21st to end	Day	6% 7% 26% 32% 21% 7%	495
September	1st to 10th	Day	10% 12% 28% 25% 20% 4	450
	11th to 20th	Day	10% 11% 25% 31% 18% 6%	450
	21st to end	Day	18% 11% 26% 23% 16% 6%	450
October	1st to 10th	Day	18% 8% 21% 30% 16% 7%	334
	11th to 20th	Day	14% 13% 25% 22% 17% 9%	270
	21st to end	Day	15% 18% 32% 23% 8% 4	297
November	1st to 10th	Day	21% 15% 33% 21% 10% 1	270
	11th to 20th	Day	11% 16% 39% 26% 7% 1	270
	21st to end	Day	11% 19% 32% 22% 12% 4	250
December	1st to 10th	Day	10% 17% 35% 24% 11% 3	180
	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 21% 43% 26%	359
	11th to 20th	Night	5% 3 23% 54% 14% 1	348
	21st to end	Night	4 4 18% 54% 20% 1	394
August	1st to 10th	Night	6% 4 20% 47% 22% 1	491
	11th to 20th	Night	6% 3 22% 44% 23% 2	534
	21st to end	Night	8% 6% 22% 45% 19% 1	594
September	1st to 10th	Night	12% 4 21% 44% 16% 3	582
	11th to 20th	Night	13% 4 18% 39% 23% 3	720
	21st to end	Night	15% 6% 27% 33% 17% 4	720
October	1st to 10th	Night	16% 6% 24% 33% 20% 1	720
	11th to 20th	Night	11% 12% 29% 31% 13% 3	720
	21st to end	Night	10% 14% 35% 30% 9% 2	792
November	1st to 10th	Night	14% 16% 34% 31% 5%	831
	11th to 20th	Night	10% 18% 39% 26% 7% 1	950
	21st to end	Night	8% 17% 37% 29% 8% 1	950
December	1st to 10th	Night	10% 16% 33% 28% 12% 2	950
	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 2024-07-02 04:41:29. Version ac07

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