DVHS Espace Academy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DVHS Espace Academy clear sky chart from 2005-11-06 to 2025-12-03.

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	5% 3 1 3 2 2 2 2 4 6% 69%	135552
	Night	6% 3 1 3 3 3 3 3 4 6% 65%	132571
Transparency	Day	19% 3 7% 19% 26% 25%	130480
	Night	22% 4 9% 19% 23% 23%	128628
Seeing	Day	7% 9% 24% 32% 21% 7%	16730
	Night	7% 5% 21% 39% 24% 4	26064

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	13% 7% 3 7% 4 3 4 3 6% 8% 43%	3759
	11th to 20th	Day	11% 8% 3 7% 3 3 3 2 3 5% 51%	4100
	21st to end	Day	15% 8% 3 8% 5% 4 3 3 4 6% 41%	4510
February	1st to 10th	Day	13% 7% 3 7% 4 4 4 4 4 6% 45%	1800
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 3 6% 8% 46%	1859
	21st to end	Day	12% 4 2 4 4 4 4 5% 5% 7% 50%	1650
March	1st to 10th	Day	8% 7% 2 7% 6% 5% 6% 5% 7% 8% 40%	4798
	11th to 20th	Day	8% 4 1 5% 3 3 4 3 6% 7% 53%	5000
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 4 8% 9% 44%	5612
April	1st to 10th	Day	10% 6% 2 4 4 4 3 4 6% 7% 50%	2400
	11th to 20th	Day	7% 4 1 4 3 3 3 3 5% 7% 61%	2369
	21st to end	Day	4 3 1 3 2 3 3 3 5% 8% 65%	2400
May	1st to 10th	Day	3 1 1 2 1 1 1 1 3 4 81%	5572
	11th to 20th	Day	1 1 2 1 1 1 1 3 4 84%	6091
	21st to end	Day	1 1 1 1 1 1 1 3 5% 85%	6902
June	1st to 10th	Day	2 3 1 2 2 2 2 2 4 8% 71%	2800
	11th to 20th	Day	1 1 1 1 2 2 4 5% 83%	2800
	21st to end	Day	1 1 1 1 1 1 1 1 2 3 87%	2800
July	1st to 10th	Day	1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 91%	6060
	21st to end	Day	1 1 1 1 1 2 4 88%	6402
August	1st to 10th	Day	1 1 1 1 1 2 1 3 4 85%	5777
	11th to 20th	Day	1 1 1 3 92%	5490
	21st to end	Day	1 1 1 1 1 1 1 2 4 87%	5984
September	1st to 10th	Day	1 1 1 1 1 1 2 4 88%	2400
	11th to 20th	Day	2 1 1 2 1 1 2 3 4 6% 77%	2400
	21st to end	Day	2 2 1 2 1 2 2 2 2 4 80%	2134
October	1st to 10th	Day	1 2 1 3 2 2 2 2 3 6% 77%	3280
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 77%	3261
	21st to end	Day	3 2 1 3 2 3 3 3 5% 8% 67%	3558
November	1st to 10th	Day	6% 4 1 4 3 3 3 3 5% 8% 60%	1975
	11th to 20th	Day	8% 6% 3 5% 5% 4 4 4 6% 7% 47%	1890
	21st to end	Day	10% 6% 2 5% 3 3 3 3 6% 7% 53%	1732
December	1st to 10th	Day	6% 5% 2 5% 3 3 4 4 7% 11% 50%	2636
	11th to 20th	Day	18% 11% 6% 13% 7% 5% 4 3 5% 5% 23%	3028
	21st to end	Day	14% 11% 4 10% 5% 4 5% 4 7% 8% 29%	4004
January	1st to 10th	Night	9% 5% 2 5% 3 3 4 4 6% 9% 50%	6174
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 5% 52%	5880
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 6% 47%	6468
February	1st to 10th	Night	14% 5% 2 5% 4 4 4 3 4 5% 50%	2600
	11th to 20th	Night	11% 4 2 4 4 4 3 4 5% 8% 51%	2426
	21st to end	Night	11% 4 2 4 3 3 3 3 4 7% 57%	1980
March	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 6% 8% 46%	5079
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 4 6% 57%	5000
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 49%	5363
April	1st to 10th	Night	7% 4 2 4 4 4 4 3 5% 8% 55%	2000
	11th to 20th	Night	6% 3 1 4 3 3 4 3 4 6% 63%	1979
	21st to end	Night	4 2 1 2 2 2 3 3 6% 7% 68%	2000
May	1st to 10th	Night	1 1 1 2 1 1 2 1 3 5% 81%	4405
	11th to 20th	Night	1 1 1 2 2 2 3 5% 82%	3805
	21st to end	Night	1 1 1 1 1 1 2 4 87%	3972
June	1st to 10th	Night	2 2 2 2 2 2 2 4 8% 73%	1600
	11th to 20th	Night	1 1 1 1 1 2 2 4 86%	1600
	21st to end	Night	1 1 1 1 1 1 2 2 4 86%	1600
July	1st to 10th	Night	1 2 95%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 91%	3906
	21st to end	Night	1 1 1 1 1 2 2 3 5% 85%	4472
August	1st to 10th	Night	2 1 1 1 1 1 1 2 6% 85%	4035
	11th to 20th	Night	1 1 2 3 92%	4371
	21st to end	Night	1 1 1 1 1 2 1 2 4 86%	5015
September	1st to 10th	Night	1 1 1 1 2 1 3 5% 86%	2000
	11th to 20th	Night	1 2 1 1 1 2 2 1 4 8% 77%	2000
	21st to end	Night	1 1 2 2 2 2 2 3 4 82%	2261
October	1st to 10th	Night	2 1 1 2 1 2 2 2 4 5% 79%	3920
	11th to 20th	Night	2 1 1 2 2 2 2 2 4 6% 76%	3897
	21st to end	Night	4 1 1 3 2 3 3 4 5% 7% 68%	4253
November	1st to 10th	Night	5% 4 1 3 2 3 3 3 5% 8% 63%	2542
	11th to 20th	Night	9% 4 2 4 3 3 3 3 5% 8% 55%	2730
	21st to end	Night	8% 4 2 4 3 3 4 3 5% 7% 57%	2882
December	1st to 10th	Night	6% 4 2 4 3 4 3 3 5% 7% 59%	4588
	11th to 20th	Night	16% 7% 3 8% 6% 5% 5% 4 8% 8% 29%	5176
	21st to end	Night	17% 8% 3 8% 6% 5% 5% 4 5% 6% 34%	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	38% 6% 17% 20% 15% 3	3759
	11th to 20th	Day	37% 4 8% 16% 23% 12%	4100
	21st to end	Day	44% 4 8% 15% 17% 12%	4510
February	1st to 10th	Day	40% 5% 9% 21% 18% 7%	1800
	11th to 20th	Day	36% 6% 11% 19% 21% 6%	1868
	21st to end	Day	33% 6% 9% 24% 21% 7%	1650
March	1st to 10th	Day	40% 6% 9% 20% 21% 3	4798
	11th to 20th	Day	28% 5% 14% 30% 14% 8%	5000
	21st to end	Day	33% 7% 16% 31% 11% 2	5612
April	1st to 10th	Day	33% 6% 12% 22% 22% 5%	2400
	11th to 20th	Day	24% 5% 14% 26% 24% 8%	2372
	21st to end	Day	18% 4 13% 30% 29% 6%	2400
May	1st to 10th	Day	10% 2 5% 26% 34% 23%	5572
	11th to 20th	Day	7% 2 3 28% 44% 15%	6094
	21st to end	Day	6% 2 6% 29% 46% 12%	6904
June	1st to 10th	Day	14% 4 10% 25% 33% 14%	2800
	11th to 20th	Day	5% 2 7% 21% 37% 28%	2800
	21st to end	Day	7% 1 3 11% 33% 46%	2800
July	1st to 10th	Day	2 1 1 4 21% 71%	6251
	11th to 20th	Day	4 1 2 5% 10% 79%	5986
	21st to end	Day	4 1 3 13% 30% 49%	6217
August	1st to 10th	Day	7% 2 2 7% 27% 55%	4206
	11th to 20th	Day	2 1 1 8% 37% 51%	3972
	21st to end	Day	5% 1 3 9% 37% 46%	4311
September	1st to 10th	Day	5% 2 2 10% 31% 50%	2400
	11th to 20th	Day	9% 4 5% 22% 39% 21%	2400
	21st to end	Day	10% 2 4 19% 37% 28%	2134
October	1st to 10th	Day	11% 2 4 12% 27% 44%	3280
	11th to 20th	Day	11% 3 6% 27% 32% 21%	3261
	21st to end	Day	16% 2 7% 24% 36% 15%	3558
November	1st to 10th	Day	24% 5% 10% 27% 24% 10%	1975
	11th to 20th	Day	34% 4 12% 25% 19% 5%	1890
	21st to end	Day	32% 4 11% 21% 25% 7%	1732
December	1st to 10th	Day	26% 4 10% 32% 22% 5%	2636
	11th to 20th	Day	61% 5% 9% 13% 11% 2	3028
	21st to end	Day	50% 6% 15% 18% 10% 1	4004
January	1st to 10th	Night	30% 5% 23% 23% 15% 3	6174
	11th to 20th	Night	35% 5% 10% 15% 24% 11%	5880
	21st to end	Night	38% 5% 10% 14% 21% 13%	6468
February	1st to 10th	Night	36% 4 8% 20% 22% 10%	2600
	11th to 20th	Night	32% 5% 11% 22% 22% 8%	2428
	21st to end	Night	29% 4 11% 28% 21% 7%	1980
March	1st to 10th	Night	36% 6% 12% 19% 22% 5%	5079
	11th to 20th	Night	29% 5% 13% 28% 17% 9%	5000
	21st to end	Night	33% 7% 15% 28% 14% 3	5363
April	1st to 10th	Night	28% 6% 13% 23% 22% 8%	2000
	11th to 20th	Night	23% 5% 12% 29% 21% 11%	1979
	21st to end	Night	15% 5% 12% 31% 29% 8%	2000
May	1st to 10th	Night	10% 3 8% 25% 31% 23%	4402
	11th to 20th	Night	7% 2 5% 24% 42% 20%	3805
	21st to end	Night	5% 2 7% 26% 45% 16%	3972
June	1st to 10th	Night	13% 4 11% 23% 32% 16%	1600
	11th to 20th	Night	6% 2 7% 16% 33% 35%	1600
	21st to end	Night	5% 2 2 12% 30% 49%	1600
July	1st to 10th	Night	2 1 1 3 17% 77%	3600
	11th to 20th	Night	4 1 1 4 9% 81%	3857
	21st to end	Night	5% 1 2 13% 25% 54%	4345
August	1st to 10th	Night	8% 2 1 7% 21% 61%	2929
	11th to 20th	Night	2 1 1 7% 26% 62%	3158
	21st to end	Night	6% 1 2 8% 30% 52%	3608
September	1st to 10th	Night	4 2 3 9% 26% 57%	2000
	11th to 20th	Night	9% 5% 4 20% 34% 28%	2000
	21st to end	Night	8% 2 5% 18% 32% 34%	2261
October	1st to 10th	Night	10% 2 5% 12% 19% 53%	3920
	11th to 20th	Night	10% 3 6% 27% 27% 26%	3897
	21st to end	Night	16% 3 6% 22% 31% 22%	4253
November	1st to 10th	Night	21% 5% 10% 27% 22% 15%	2542
	11th to 20th	Night	27% 5% 12% 26% 22% 7%	2730
	21st to end	Night	27% 4 9% 23% 26% 10%	2882
December	1st to 10th	Night	25% 5% 8% 28% 25% 10%	4588
	11th to 20th	Night	48% 6% 13% 18% 13% 2	5176
	21st to end	Night	50% 5% 15% 18% 9% 3	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	24% 11% 23% 23% 16% 4	255
	11th to 20th	Day	15% 9% 21% 28% 21% 6%	400
	21st to end	Day	15% 7% 21% 26% 24% 8%	440
February	1st to 10th	Day	17% 15% 20% 22% 20% 7%	400
	11th to 20th	Day	14% 17% 25% 21% 19% 4	448
	21st to end	Day	11% 16% 22% 29% 19% 3	414
March	1st to 10th	Day	14% 15% 29% 27% 12% 4	500
	11th to 20th	Day	16% 15% 24% 23% 15% 6%	500
	21st to end	Day	12% 17% 30% 26% 13% 3	550
April	1st to 10th	Day	11% 17% 29% 23% 14% 6%	500
	11th to 20th	Day	9% 16% 33% 24% 13% 6%	492
	21st to end	Day	3 20% 27% 29% 16% 6%	500
May	1st to 10th	Day	5% 13% 35% 30% 14% 4	503
	11th to 20th	Day	5% 13% 33% 28% 19% 2	528
	21st to end	Day	3 10% 28% 36% 18% 5%	573
June	1st to 10th	Day	3 12% 29% 33% 19% 4	530
	11th to 20th	Day	1 11% 31% 38% 17% 3	530
	21st to end	Day	1 5% 27% 40% 20% 6%	530
July	1st to 10th	Day	2 25% 49% 19% 5%	526
	11th to 20th	Day	2 19% 45% 29% 6%	524
	21st to end	Day	1 1 21% 44% 26% 7%	575
August	1st to 10th	Day	1 3 24% 44% 20% 6%	527
	11th to 20th	Day	3 24% 40% 24% 9%	517
	21st to end	Day	1 2 17% 44% 28% 8%	583
September	1st to 10th	Day	1 4 19% 40% 29% 8%	530
	11th to 20th	Day	2 8% 22% 37% 22% 9%	530
	21st to end	Day	2 6% 21% 35% 26% 10%	530
October	1st to 10th	Day	3 8% 21% 28% 28% 13%	530
	11th to 20th	Day	5% 8% 18% 26% 28% 15%	530
	21st to end	Day	6% 8% 19% 27% 26% 13%	583
November	1st to 10th	Day	7% 9% 21% 21% 29% 13%	451
	11th to 20th	Day	9% 7% 18% 32% 23% 10%	330
	21st to end	Day	12% 4 19% 31% 28% 5%	247
December	1st to 10th	Day	15% 10% 18% 25% 21% 11%	204
	11th to 20th	Day	20% 11% 17% 21% 26% 7%	200
	21st to end	Day	17% 12% 25% 26% 16% 4	220
January	1st to 10th	Night	15% 6% 17% 34% 23% 6%	800
	11th to 20th	Night	12% 6% 17% 35% 25% 5%	800
	21st to end	Night	14% 5% 16% 35% 25% 4	880
February	1st to 10th	Night	16% 7% 17% 35% 22% 4	800
	11th to 20th	Night	11% 9% 21% 32% 22% 4	784
	21st to end	Night	11% 10% 21% 38% 18% 2	660
March	1st to 10th	Night	14% 10% 21% 33% 20% 2	800
	11th to 20th	Night	13% 10% 22% 33% 19% 3	800
	21st to end	Night	11% 9% 28% 34% 17% 1	880
April	1st to 10th	Night	9% 8% 27% 37% 17% 2	800
	11th to 20th	Night	7% 11% 32% 31% 17% 3	791
	21st to end	Night	5% 8% 33% 34% 18% 2	800
May	1st to 10th	Night	4 6% 32% 39% 16% 3	736
	11th to 20th	Night	2 4 26% 48% 20% 1	479
	21st to end	Night	2 6% 33% 44% 15%	433
June	1st to 10th	Night	2 4 32% 49% 13%	400
	11th to 20th	Night	1 5% 28% 53% 13% 1	400
	21st to end	Night	1 2 27% 52% 20%	400
July	1st to 10th	Night	1 23% 57% 19%	390
	11th to 20th	Night	1 1 16% 54% 27% 2	497
	21st to end	Night	2 1 17% 47% 32% 2	657
August	1st to 10th	Night	2 1 21% 44% 28% 4	597
	11th to 20th	Night	1 21% 50% 27% 1	732
	21st to end	Night	1 1 15% 50% 30% 3	880
September	1st to 10th	Night	1 2 18% 45% 31% 3	800
	11th to 20th	Night	2 3 21% 45% 26% 3	800
	21st to end	Night	2 4 16% 42% 32% 6%	800
October	1st to 10th	Night	3 4 18% 40% 30% 6%	800
	11th to 20th	Night	4 4 16% 38% 33% 5%	800
	21st to end	Night	5% 4 15% 36% 30% 9%	880
November	1st to 10th	Night	5% 4 15% 36% 32% 7%	820
	11th to 20th	Night	9% 3 16% 40% 28% 5%	840
	21st to end	Night	8% 4 17% 36% 30% 6%	840
December	1st to 10th	Night	12% 5% 15% 37% 24% 6%	808
	11th to 20th	Night	19% 6% 14% 34% 24% 4	800
	21st to end	Night	17% 8% 20% 34% 19% 2	880

Page generated at 2025-11-29 22:00:56. Version ac07

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