Villard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Villard clear sky chart from 2005-11-06 to 2024-01-15.

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	12% 8% 3 7% 6% 3 5% 5% 6% 8% 37%	74759
	Night	11% 9% 4 7% 6% 3 5% 5% 6% 7% 38%	75032
Transparency	Day	45% 5% 14% 25% 10% 1	74455
	Night	45% 4 14% 24% 12% 1	74856
Seeing	Day	15% 9% 31% 28% 14% 3	14877
	Night	15% 9% 33% 32% 11% 1	24915

By Month

Percentage Cloud Cover SE (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	7% 10% 6% 11% 8% 6% 7% 6% 6% 8% 24%	1328
	11th to 20th	Day	9% 13% 6% 12% 9% 4 5% 7% 5% 6% 24%	1423
	21st to end	Day	8% 13% 6% 13% 10% 6% 7% 7% 6% 7% 17%	1782
February	1st to 10th	Day	8% 10% 6% 8% 7% 4 7% 5% 6% 10% 28%	1620
	11th to 20th	Day	6% 11% 5% 8% 10% 5% 6% 6% 6% 8% 29%	1574
	21st to end	Day	9% 12% 6% 10% 10% 6% 5% 6% 6% 8% 23%	1381
March	1st to 10th	Day	13% 9% 5% 9% 8% 5% 4 5% 6% 7% 30%	1944
	11th to 20th	Day	12% 11% 5% 9% 6% 3 5% 4 5% 8% 33%	1980
	21st to end	Day	16% 11% 5% 10% 7% 3 4 5% 6% 7% 27%	2178
April	1st to 10th	Day	16% 10% 3 5% 6% 3 4 5% 5% 8% 35%	2110
	11th to 20th	Day	17% 13% 4 7% 4 3 3 4 6% 7% 32%	2271
	21st to end	Day	23% 11% 3 5% 5% 2 4 5% 4 6% 33%	2340
May	1st to 10th	Day	17% 9% 4 6% 5% 4 5% 5% 5% 6% 35%	2354
	11th to 20th	Day	16% 8% 3 6% 5% 3 5% 5% 5% 8% 37%	2479
	21st to end	Day	15% 6% 3 5% 6% 3 4 5% 7% 9% 38%	2725
June	1st to 10th	Day	12% 5% 2 6% 4 4 5% 5% 6% 9% 43%	2658
	11th to 20th	Day	13% 6% 3 6% 6% 3 4 6% 6% 8% 39%	2700
	21st to end	Day	9% 5% 3 4 5% 3 5% 6% 7% 11% 43%	2700
July	1st to 10th	Day	5% 3 2 3 4 3 5% 6% 7% 10% 51%	2700
	11th to 20th	Day	7% 4 2 4 5% 3 5% 4 6% 8% 53%	2692
	21st to end	Day	5% 3 1 4 4 3 5% 5% 7% 9% 53%	2621
August	1st to 10th	Day	8% 5% 3 5% 5% 4 5% 6% 7% 9% 43%	2328
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 4 6% 9% 44%	2301
	21st to end	Day	9% 4 2 4 4 2 4 4 4 9% 53%	2556
September	1st to 10th	Day	11% 4 2 4 4 2 5% 4 6% 7% 51%	2160
	11th to 20th	Day	11% 6% 2 5% 5% 3 5% 5% 5% 7% 46%	2020
	21st to end	Day	16% 6% 3 4 4 2 4 4 5% 8% 46%	1967
October	1st to 10th	Day	17% 8% 2 5% 4 3 4 4 5% 8% 40%	1800
	11th to 20th	Day	16% 11% 3 5% 4 2 4 4 5% 6% 40%	1800
	21st to end	Day	17% 9% 4 7% 5% 3 4 4 4 6% 37%	1928
November	1st to 10th	Day	14% 12% 4 7% 5% 3 3 5% 6% 6% 36%	1546
	11th to 20th	Day	10% 12% 5% 13% 9% 4 5% 4 4 6% 27%	1520
	21st to end	Day	13% 10% 5% 9% 7% 4 5% 4 5% 8% 31%	1520
December	1st to 10th	Day	8% 11% 6% 11% 10% 4 8% 6% 5% 6% 25%	1520
	11th to 20th	Day	10% 12% 6% 11% 8% 4 6% 5% 5% 7% 26%	1791
	21st to end	Day	20% 13% 5% 12% 10% 3 3 3 4 6% 20%	2442
January	1st to 10th	Night	7% 8% 5% 10% 9% 5% 7% 6% 7% 8% 29%	2837
	11th to 20th	Night	8% 14% 5% 10% 9% 5% 7% 5% 6% 7% 23%	2623
	21st to end	Night	9% 13% 6% 11% 8% 4 6% 5% 7% 7% 24%	2574
February	1st to 10th	Night	5% 10% 5% 7% 8% 5% 5% 6% 6% 9% 32%	2340
	11th to 20th	Night	6% 10% 5% 7% 6% 3 7% 5% 6% 7% 37%	2273
	21st to end	Night	11% 10% 4 7% 7% 5% 6% 6% 6% 8% 32%	1892
March	1st to 10th	Night	12% 8% 4 9% 7% 4 5% 6% 6% 6% 33%	2016
	11th to 20th	Night	12% 10% 4 8% 5% 3 4 4 5% 7% 39%	1980
	21st to end	Night	16% 9% 4 8% 5% 3 4 5% 6% 7% 32%	2178
April	1st to 10th	Night	15% 8% 4 6% 4 2 5% 4 5% 7% 40%	1850
	11th to 20th	Night	17% 10% 5% 7% 4 3 4 3 5% 5% 36%	1636
	21st to end	Night	17% 9% 4 7% 5% 2 5% 4 5% 5% 38%	1620
May	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 4 7% 39%	1603
	11th to 20th	Night	13% 7% 2 5% 6% 4 4 5% 6% 7% 41%	1416
	21st to end	Night	12% 6% 2 5% 5% 3 4 6% 6% 9% 44%	1551
June	1st to 10th	Night	10% 4 2 3 4 4 4 4 5% 9% 50%	1298
	11th to 20th	Night	9% 4 3 4 4 3 5% 5% 7% 10% 47%	1260
	21st to end	Night	8% 5% 2 3 4 2 5% 4 7% 9% 53%	1260
July	1st to 10th	Night	3 3 2 2 3 3 4 5% 6% 10% 59%	1260
	11th to 20th	Night	4 3 2 3 3 2 3 5% 5% 8% 62%	1264
	21st to end	Night	4 2 1 3 3 3 3 4 7% 9% 59%	1694
August	1st to 10th	Night	7% 4 2 3 4 4 5% 5% 7% 9% 51%	1611
	11th to 20th	Night	10% 4 3 4 5% 2 2 4 5% 8% 55%	1600
	21st to end	Night	7% 4 2 3 4 1 3 4 4 7% 61%	1800
September	1st to 10th	Night	9% 4 2 3 4 2 3 4 6% 8% 56%	1800
	11th to 20th	Night	10% 5% 2 5% 4 3 4 4 4 5% 53%	1938
	21st to end	Night	11% 6% 2 5% 4 3 3 4 4 7% 52%	1980
October	1st to 10th	Night	14% 7% 2 6% 5% 3 3 4 5% 6% 45%	2155
	11th to 20th	Night	14% 9% 2 5% 5% 3 4 4 4 7% 43%	2160
	21st to end	Night	16% 10% 4 7% 5% 3 4 4 5% 7% 37%	2425
November	1st to 10th	Night	11% 8% 3 6% 6% 3 5% 5% 7% 6% 39%	2532
	11th to 20th	Night	11% 12% 5% 11% 7% 3 4 4 5% 7% 32%	2660
	21st to end	Night	10% 9% 4 7% 7% 3 4 4 6% 7% 38%	2660
December	1st to 10th	Night	9% 12% 5% 9% 9% 4 5% 4 7% 7% 29%	2660
	11th to 20th	Night	10% 11% 4 10% 9% 4 6% 5% 6% 7% 26%	3401
	21st to end	Night	19% 15% 5% 10% 9% 4 4 4 5% 6% 18%	5225

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	56% 6% 13% 18% 6% 1	1329
	11th to 20th	Day	59% 4 12% 17% 7%	1423
	21st to end	Day	64% 4 12% 13% 6%	1782
February	1st to 10th	Day	51% 5% 13% 20% 10% 1	1620
	11th to 20th	Day	52% 4 14% 23% 6% 2	1583
	21st to end	Day	58% 4 9% 17% 10%	1381
March	1st to 10th	Day	54% 5% 15% 19% 7% 1	1944
	11th to 20th	Day	50% 3 14% 24% 9%	1980
	21st to end	Day	57% 4 13% 20% 5%	2178
April	1st to 10th	Day	47% 5% 11% 23% 12% 1	2110
	11th to 20th	Day	53% 4 12% 18% 13% 1	2271
	21st to end	Day	53% 5% 12% 21% 9% 1	2340
May	1st to 10th	Day	50% 5% 12% 23% 10% 1	2354
	11th to 20th	Day	46% 5% 13% 25% 11% 1	2483
	21st to end	Day	42% 6% 14% 26% 10% 2	2725
June	1st to 10th	Day	37% 5% 17% 29% 11% 1	2658
	11th to 20th	Day	43% 6% 15% 22% 14% 1	2700
	21st to end	Day	33% 6% 21% 29% 11% 1	2700
July	1st to 10th	Day	26% 6% 18% 33% 17% 1	2626
	11th to 20th	Day	29% 5% 17% 30% 17% 3	2611
	21st to end	Day	26% 6% 17% 32% 16% 2	2475
August	1st to 10th	Day	36% 6% 16% 30% 10% 3	2314
	11th to 20th	Day	37% 5% 17% 29% 10% 1	2301
	21st to end	Day	29% 4 14% 36% 15% 2	2556
September	1st to 10th	Day	32% 5% 15% 34% 13% 1	2160
	11th to 20th	Day	37% 5% 18% 31% 9% 1	2020
	21st to end	Day	39% 3 13% 33% 11% 1	1967
October	1st to 10th	Day	43% 4 14% 27% 12% 1	1800
	11th to 20th	Day	46% 3 12% 25% 11% 2	1800
	21st to end	Day	50% 3 12% 26% 9% 1	1928
November	1st to 10th	Day	48% 5% 11% 21% 12% 2	1546
	11th to 20th	Day	60% 4 11% 16% 8% 1	1520
	21st to end	Day	53% 2 16% 20% 6% 2	1520
December	1st to 10th	Day	58% 5% 15% 15% 6%	1520
	11th to 20th	Day	59% 2 16% 18% 4	1788
	21st to end	Day	68% 3 9% 14% 6%	2442
January	1st to 10th	Night	52% 4 12% 23% 9%	2837
	11th to 20th	Night	60% 5% 13% 14% 8% 1	2623
	21st to end	Night	57% 4 12% 18% 9% 1	2574
February	1st to 10th	Night	47% 5% 13% 22% 12% 1	2340
	11th to 20th	Night	45% 5% 14% 22% 12% 1	2274
	21st to end	Night	50% 5% 11% 21% 12% 2	1892
March	1st to 10th	Night	50% 5% 16% 22% 8%	2016
	11th to 20th	Night	46% 3 13% 25% 12% 1	1980
	21st to end	Night	50% 6% 12% 23% 7% 2	2178
April	1st to 10th	Night	45% 4 12% 25% 13% 1	1850
	11th to 20th	Night	51% 3 5% 24% 15% 2	1636
	21st to end	Night	49% 4 11% 23% 13% 2	1620
May	1st to 10th	Night	44% 5% 11% 26% 12% 1	1603
	11th to 20th	Night	41% 6% 12% 24% 14% 3	1417
	21st to end	Night	37% 6% 14% 26% 14% 3	1552
June	1st to 10th	Night	33% 5% 15% 31% 14% 1	1298
	11th to 20th	Night	31% 5% 18% 27% 15% 3	1260
	21st to end	Night	27% 6% 18% 30% 17% 3	1260
July	1st to 10th	Night	21% 6% 17% 36% 19% 1	1225
	11th to 20th	Night	21% 5% 15% 37% 17% 5%	1222
	21st to end	Night	22% 5% 16% 37% 16% 5%	1600
August	1st to 10th	Night	30% 5% 17% 31% 14% 4	1601
	11th to 20th	Night	29% 5% 19% 32% 14% 1	1600
	21st to end	Night	23% 5% 14% 34% 21% 4	1800
September	1st to 10th	Night	27% 4 18% 33% 17% 1	1800
	11th to 20th	Night	33% 4 15% 31% 16%	1938
	21st to end	Night	34% 3 13% 34% 16% 1	1980
October	1st to 10th	Night	41% 3 11% 29% 15% 2	2155
	11th to 20th	Night	42% 3 12% 28% 13% 2	2160
	21st to end	Night	48% 3 13% 24% 12% 1	2425
November	1st to 10th	Night	43% 5% 13% 24% 13% 2	2532
	11th to 20th	Night	53% 4 13% 18% 11% 1	2660
	21st to end	Night	46% 4 18% 23% 7% 2	2660
December	1st to 10th	Night	54% 4 16% 19% 7%	2660
	11th to 20th	Night	57% 3 16% 17% 6% 1	3403
	21st to end	Night	68% 3 10% 14% 6%	5225

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	13% 14% 31% 27% 11% 3	270
	11th to 20th	Day	13% 13% 31% 34% 8% 1	252
	21st to end	Day	12% 12% 39% 24% 13% 1	264
February	1st to 10th	Day	15% 16% 40% 26% 3	240
	11th to 20th	Day	15% 17% 35% 24% 8% 1	240
	21st to end	Day	15% 13% 36% 30% 6%	198
March	1st to 10th	Day	17% 12% 38% 24% 9%	240
	11th to 20th	Day	18% 8% 35% 26% 12% 2	240
	21st to end	Day	23% 13% 25% 21% 15% 3	264
April	1st to 10th	Day	24% 15% 31% 21% 9%	370
	11th to 20th	Day	27% 14% 24% 23% 10% 1	549
	21st to end	Day	26% 11% 31% 20% 11% 3	600
May	1st to 10th	Day	19% 12% 33% 24% 9% 2	603
	11th to 20th	Day	20% 12% 29% 25% 12% 3	625
	21st to end	Day	17% 7% 32% 28% 14% 2	679
June	1st to 10th	Day	11% 5% 27% 32% 21% 4	630
	11th to 20th	Day	15% 8% 35% 29% 12% 2	630
	21st to end	Day	12% 7% 32% 28% 18% 3	630
July	1st to 10th	Day	6% 4 24% 35% 25% 6%	621
	11th to 20th	Day	8% 6% 30% 32% 18% 5%	618
	21st to end	Day	6% 4 24% 38% 23% 6%	684
August	1st to 10th	Day	8% 2 23% 35% 26% 5%	626
	11th to 20th	Day	13% 4 22% 32% 23% 7%	615
	21st to end	Day	9% 7% 26% 31% 22% 5%	675
September	1st to 10th	Day	11% 6% 31% 31% 16% 4	450
	11th to 20th	Day	13% 4 33% 32% 14% 5%	310
	21st to end	Day	19% 13% 33% 21% 11% 2	270
October	1st to 10th	Day	19% 11% 31% 24% 11% 4	270
	11th to 20th	Day	14% 19% 35% 22% 9% 1	270
	21st to end	Day	23% 14% 37% 17% 7% 1	297
November	1st to 10th	Day	24% 11% 29% 29% 6% 1	270
	11th to 20th	Day	17% 16% 44% 19% 4	270
	21st to end	Day	19% 16% 37% 23% 4	270
December	1st to 10th	Day	10% 11% 44% 26% 8% 1	270
	11th to 20th	Day	18% 14% 36% 26% 5%	270
	21st to end	Day	28% 10% 35% 21% 5%	297
January	1st to 10th	Night	11% 11% 39% 29% 9% 2	950
	11th to 20th	Night	14% 10% 37% 30% 8% 1	921
	21st to end	Night	16% 11% 40% 26% 6%	990
February	1st to 10th	Night	10% 11% 39% 31% 8% 1	900
	11th to 20th	Night	12% 11% 42% 25% 8% 1	879
	21st to end	Night	16% 12% 32% 29% 10% 2	708
March	1st to 10th	Night	16% 9% 37% 29% 9% 1	576
	11th to 20th	Night	18% 6% 39% 30% 5% 1	540
	21st to end	Night	20% 10% 28% 29% 12% 2	594
April	1st to 10th	Night	18% 11% 36% 29% 6%	540
	11th to 20th	Night	23% 10% 31% 28% 8% 1	533
	21st to end	Night	21% 8% 32% 29% 8% 2	540
May	1st to 10th	Night	16% 9% 35% 30% 9% 1	540
	11th to 20th	Night	17% 8% 31% 33% 10% 1	531
	21st to end	Night	16% 7% 29% 37% 11%	584
June	1st to 10th	Night	12% 5% 28% 37% 17% 1	540
	11th to 20th	Night	9% 4 34% 43% 9%	540
	21st to end	Night	9% 5% 24% 48% 14% 1	540
July	1st to 10th	Night	4 2 24% 45% 24% 2	525
	11th to 20th	Night	6% 3 29% 45% 16% 1	522
	21st to end	Night	5% 3 26% 44% 20% 2	591
August	1st to 10th	Night	7% 3 19% 47% 21% 2	537
	11th to 20th	Night	10% 5% 19% 39% 25% 3	534
	21st to end	Night	9% 4 26% 37% 24% 1	594
September	1st to 10th	Night	11% 3 29% 39% 16% 2	540
	11th to 20th	Night	12% 6% 27% 35% 18% 1	540
	21st to end	Night	13% 7% 34% 32% 11% 1	540
October	1st to 10th	Night	19% 10% 32% 29% 10% 1	715
	11th to 20th	Night	19% 11% 34% 27% 9%	720
	21st to end	Night	22% 11% 32% 29% 5%	841
November	1st to 10th	Night	15% 11% 33% 32% 8%	925
	11th to 20th	Night	17% 13% 36% 25% 8% 1	950
	21st to end	Night	14% 13% 40% 25% 7%	950
December	1st to 10th	Night	14% 11% 36% 30% 8% 1	950
	11th to 20th	Night	19% 10% 36% 29% 5% 1	950
	21st to end	Night	24% 10% 34% 26% 6% 1	1045

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