Claude
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Claude clear sky chart from 2005-11-06 to 2026-07-31.

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% 4 1 4 3 3 3 3 5% 7% 60%	146955
	Night	6% 4 2 4 3 3 3 3 5% 7% 61%	143522
Transparency	Day	24% 4 8% 21% 27% 15%	142006
	Night	23% 4 8% 21% 27% 16%	139483
Seeing	Day	9% 8% 28% 32% 18% 4	17663
	Night	8% 8% 29% 39% 15% 1	27538

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	5% 6% 2 7% 4 4 4 3 4 5% 56%	5287
	11th to 20th	Day	2 4 1 4 3 2 2 2 3 4 74%	5310
	21st to end	Day	10% 5% 2 5% 4 3 3 2 4 6% 58%	6426
February	1st to 10th	Day	5% 5% 2 4 3 2 3 3 5% 6% 62%	2100
	11th to 20th	Day	6% 7% 2 5% 3 3 3 2 4 6% 59%	2049
	21st to end	Day	4 6% 2 3 3 2 3 3 3 6% 65%	1730
March	1st to 10th	Day	7% 4 1 3 3 3 3 3 4 6% 62%	4600
	11th to 20th	Day	7% 4 1 4 3 3 3 2 4 7% 61%	4946
	21st to end	Day	4 4 2 5% 4 3 4 3 5% 7% 59%	5725
April	1st to 10th	Day	6% 4 2 4 3 2 3 2 4 5% 65%	2520
	11th to 20th	Day	9% 5% 2 5% 2 2 3 2 5% 6% 59%	2491
	21st to end	Day	8% 3 1 3 3 2 4 3 5% 6% 62%	2562
May	1st to 10th	Day	13% 4 1 3 3 3 3 3 5% 7% 55%	7655
	11th to 20th	Day	8% 4 1 3 2 2 2 3 4 5% 66%	7627
	21st to end	Day	12% 6% 2 5% 3 4 4 3 5% 6% 50%	8404
June	1st to 10th	Day	6% 4 1 5% 4 5% 4 4 6% 8% 53%	2730
	11th to 20th	Day	5% 4 1 3 2 3 3 3 5% 8% 62%	2730
	21st to end	Day	4 3 1 4 3 3 4 4 7% 8% 59%	2730
July	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 5% 6% 8% 44%	6029
	11th to 20th	Day	3 2 1 4 3 4 3 4 7% 9% 61%	6030
	21st to end	Day	2 2 1 4 4 4 5% 4 6% 10% 60%	6555
August	1st to 10th	Day	4 3 1 4 3 3 4 3 6% 8% 60%	5488
	11th to 20th	Day	3 3 1 4 3 4 5% 5% 7% 10% 55%	5366
	21st to end	Day	7% 4 1 4 3 4 4 4 6% 8% 54%	5984
September	1st to 10th	Day	7% 4 1 4 3 4 4 3 6% 6% 57%	2355
	11th to 20th	Day	8% 4 1 5% 4 4 5% 3 5% 7% 54%	2200
	21st to end	Day	8% 3 1 3 2 2 3 3 4 6% 63%	2200
October	1st to 10th	Day	6% 2 1 2 2 1 2 1 2 4 76%	3590
	11th to 20th	Day	11% 4 1 3 2 2 3 2 4 5% 63%	3568
	21st to end	Day	6% 3 1 2 2 1 2 2 3 4 74%	3237
November	1st to 10th	Day	6% 4 1 2 2 2 2 2 4 6% 69%	1853
	11th to 20th	Day	3 3 1 2 2 2 2 3 4 5% 72%	1890
	21st to end	Day	7% 6% 2 4 2 2 2 2 4 6% 63%	1890
December	1st to 10th	Day	4 3 1 3 3 2 3 2 4 6% 68%	3030
	11th to 20th	Day	5% 2 1 3 3 3 4 3 4 5% 66%	3481
	21st to end	Day	6% 8% 2 4 3 2 3 3 4 5% 62%	4587
January	1st to 10th	Night	5% 6% 3 5% 3 3 4 4 5% 6% 55%	7634
	11th to 20th	Night	2 3 2 3 2 2 3 2 4 5% 73%	7680
	21st to end	Night	7% 7% 3 8% 3 3 3 3 4 5% 54%	7832
February	1st to 10th	Night	6% 6% 1 4 3 3 3 3 4 6% 62%	2520
	11th to 20th	Night	7% 6% 2 5% 3 3 3 3 4 6% 58%	2458
	21st to end	Night	5% 4 1 4 2 3 3 3 5% 6% 63%	2076
March	1st to 10th	Night	4 4 2 5% 3 3 3 3 4 6% 65%	5494
	11th to 20th	Night	5% 3 1 3 3 3 3 3 4 6% 65%	5238
	21st to end	Night	3 3 2 4 4 3 4 3 6% 8% 60%	5437
April	1st to 10th	Night	6% 4 1 3 2 3 3 3 5% 6% 64%	2100
	11th to 20th	Night	8% 4 1 3 3 4 3 3 5% 6% 61%	2077
	21st to end	Night	9% 3 1 3 2 3 4 3 5% 8% 60%	2058
May	1st to 10th	Night	12% 5% 1 4 3 3 3 3 4 6% 56%	5292
	11th to 20th	Night	6% 4 1 4 3 2 3 3 4 6% 65%	5265
	21st to end	Night	13% 6% 2 4 3 3 4 3 5% 6% 50%	5803
June	1st to 10th	Night	6% 4 1 3 3 3 5% 5% 7% 11% 53%	1890
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 9% 61%	1890
	21st to end	Night	4 4 1 3 2 3 4 4 8% 10% 57%	1890
July	1st to 10th	Night	9% 5% 2 5% 4 5% 5% 5% 6% 10% 44%	4170
	11th to 20th	Night	2 3 1 4 3 5% 5% 5% 8% 13% 51%	4170
	21st to end	Night	2 2 1 4 3 4 5% 4 7% 12% 56%	4539
August	1st to 10th	Night	4 2 1 3 2 3 4 4 7% 12% 59%	4319
	11th to 20th	Night	3 3 1 5% 4 5% 6% 5% 8% 12% 48%	4483
	21st to end	Night	7% 4 2 4 3 4 4 3 6% 10% 53%	4993
September	1st to 10th	Night	6% 4 1 4 4 3 4 4 6% 7% 56%	2045
	11th to 20th	Night	8% 5% 2 6% 3 3 4 3 5% 7% 54%	2200
	21st to end	Night	6% 4 1 3 2 3 3 3 5% 6% 66%	2200
October	1st to 10th	Night	5% 3 1 2 2 2 2 1 3 4 76%	3590
	11th to 20th	Night	11% 3 2 3 2 2 2 2 4 4 65%	3570
	21st to end	Night	4 2 1 2 2 2 2 2 3 5% 73%	4525
November	1st to 10th	Night	7% 2 1 2 2 2 2 2 3 5% 71%	2665
	11th to 20th	Night	3 4 1 2 2 2 2 2 4 6% 71%	2730
	21st to end	Night	8% 4 1 3 2 2 3 3 4 6% 64%	2730
December	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 7% 67%	4380
	11th to 20th	Night	4 3 1 3 2 3 3 3 5% 7% 66%	4946
	21st to end	Night	5% 6% 2 4 3 3 3 3 4 6% 61%	6633

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	30% 4 6% 22% 27% 13%	5290
	11th to 20th	Day	17% 2 6% 18% 36% 21%	5310
	21st to end	Day	29% 3 5% 17% 34% 12%	6426
February	1st to 10th	Day	23% 2 8% 24% 27% 15%	2100
	11th to 20th	Day	28% 3 6% 23% 25% 15%	2059
	21st to end	Day	22% 3 5% 19% 32% 20%	1730
March	1st to 10th	Day	23% 3 4 11% 27% 33%	4600
	11th to 20th	Day	23% 4 5% 16% 30% 22%	4946
	21st to end	Day	23% 4 9% 26% 27% 12%	5725
April	1st to 10th	Day	22% 4 6% 17% 28% 23%	2520
	11th to 20th	Day	26% 4 7% 19% 23% 20%	2494
	21st to end	Day	23% 4 10% 23% 28% 12%	2562
May	1st to 10th	Day	29% 5% 9% 21% 23% 14%	7655
	11th to 20th	Day	21% 4 5% 17% 26% 28%	7631
	21st to end	Day	34% 6% 10% 17% 15% 18%	8405
June	1st to 10th	Day	27% 7% 15% 28% 15% 9%	2730
	11th to 20th	Day	21% 5% 9% 24% 27% 14%	2730
	21st to end	Day	21% 5% 14% 30% 19% 11%	2730
July	1st to 10th	Day	35% 8% 10% 21% 22% 4	5966
	11th to 20th	Day	18% 6% 11% 33% 26% 6%	5961
	21st to end	Day	17% 7% 18% 30% 23% 5%	6371
August	1st to 10th	Day	19% 7% 12% 26% 25% 11%	3993
	11th to 20th	Day	19% 5% 12% 22% 29% 13%	3882
	21st to end	Day	22% 6% 12% 25% 28% 7%	4311
September	1st to 10th	Day	26% 7% 11% 22% 22% 12%	2355
	11th to 20th	Day	29% 7% 9% 22% 28% 6%	2200
	21st to end	Day	21% 5% 8% 21% 31% 14%	2200
October	1st to 10th	Day	16% 3 5% 13% 37% 26%	3590
	11th to 20th	Day	25% 3 6% 20% 24% 22%	3568
	21st to end	Day	17% 2 4 24% 38% 15%	3237
November	1st to 10th	Day	17% 2 7% 19% 34% 20%	1853
	11th to 20th	Day	15% 4 6% 25% 33% 18%	1890
	21st to end	Day	24% 3 5% 18% 32% 18%	1890
December	1st to 10th	Day	19% 3 6% 31% 29% 11%	3030
	11th to 20th	Day	21% 2 6% 16% 38% 17%	3479
	21st to end	Day	26% 3 6% 21% 31% 13%	4587
January	1st to 10th	Night	27% 3 6% 28% 28% 7%	7635
	11th to 20th	Night	14% 3 8% 19% 36% 18%	7680
	21st to end	Night	32% 4 5% 16% 30% 12%	7832
February	1st to 10th	Night	26% 3 7% 18% 29% 17%	2520
	11th to 20th	Night	28% 3 7% 21% 24% 17%	2458
	21st to end	Night	21% 3 5% 18% 29% 23%	2076
March	1st to 10th	Night	21% 4 4 14% 23% 35%	5494
	11th to 20th	Night	19% 4 6% 18% 18% 35%	5238
	21st to end	Night	21% 5% 9% 23% 28% 14%	5437
April	1st to 10th	Night	20% 4 9% 19% 25% 22%	2100
	11th to 20th	Night	25% 4 8% 19% 25% 18%	2077
	21st to end	Night	22% 6% 12% 22% 24% 14%	2058
May	1st to 10th	Night	29% 5% 9% 22% 21% 14%	5293
	11th to 20th	Night	20% 5% 7% 14% 28% 25%	5266
	21st to end	Night	33% 7% 13% 14% 12% 22%	5805
June	1st to 10th	Night	24% 8% 19% 26% 16% 7%	1890
	11th to 20th	Night	19% 6% 12% 25% 25% 13%	1890
	21st to end	Night	20% 7% 14% 25% 22% 12%	1890
July	1st to 10th	Night	33% 8% 14% 28% 15% 2	4125
	11th to 20th	Night	21% 6% 14% 28% 24% 6%	4116
	21st to end	Night	20% 6% 13% 30% 26% 5%	4410
August	1st to 10th	Night	17% 5% 12% 27% 25% 14%	3138
	11th to 20th	Night	23% 7% 12% 22% 27% 9%	3243
	21st to end	Night	20% 5% 14% 26% 27% 7%	3597
September	1st to 10th	Night	27% 6% 10% 23% 22% 11%	2045
	11th to 20th	Night	30% 5% 11% 21% 26% 8%	2200
	21st to end	Night	19% 5% 8% 21% 31% 17%	2200
October	1st to 10th	Night	14% 3 6% 13% 36% 29%	3590
	11th to 20th	Night	24% 3 6% 18% 30% 20%	3570
	21st to end	Night	14% 3 4 20% 40% 18%	4525
November	1st to 10th	Night	17% 2 7% 21% 32% 21%	2665
	11th to 20th	Night	15% 2 5% 22% 36% 19%	2730
	21st to end	Night	22% 4 5% 19% 32% 18%	2730
December	1st to 10th	Night	17% 3 7% 30% 34% 9%	4380
	11th to 20th	Night	18% 3 4 17% 40% 18%	4947
	21st to end	Night	24% 4 7% 23% 30% 12%	6633

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	10% 13% 41% 28% 8% 1	330
	11th to 20th	Day	11% 19% 32% 26% 11% 1	330
	21st to end	Day	11% 10% 42% 28% 8% 1	363
February	1st to 10th	Day	9% 13% 39% 29% 9%	330
	11th to 20th	Day	14% 12% 44% 23% 5% 2	330
	21st to end	Day	10% 15% 42% 27% 5%	273
March	1st to 10th	Day	10% 13% 44% 28% 5%	330
	11th to 20th	Day	17% 16% 38% 22% 6% 2	330
	21st to end	Day	12% 15% 40% 25% 8% 1	426
April	1st to 10th	Day	9% 20% 44% 21% 6%	540
	11th to 20th	Day	12% 20% 45% 20% 2	532
	21st to end	Day	12% 17% 39% 24% 7% 1	582
May	1st to 10th	Day	10% 13% 37% 31% 9% 1	753
	11th to 20th	Day	10% 11% 32% 30% 14% 3	775
	21st to end	Day	10% 9% 33% 32% 15% 2	844
June	1st to 10th	Day	7% 6% 25% 40% 19% 3	780
	11th to 20th	Day	6% 4 30% 39% 18% 3	780
	21st to end	Day	5% 2 24% 40% 24% 4	780
July	1st to 10th	Day	7% 2 15% 34% 32% 11%	771
	11th to 20th	Day	3 1 10% 41% 38% 8%	768
	21st to end	Day	2 1 7% 37% 44% 9%	845
August	1st to 10th	Day	4 1 15% 42% 32% 6%	590
	11th to 20th	Day	8% 1 15% 37% 29% 11%	517
	21st to end	Day	9% 13% 40% 31% 7%	583
September	1st to 10th	Day	7% 1 17% 39% 29% 7%	485
	11th to 20th	Day	3 2 19% 42% 29% 5%	330
	21st to end	Day	11% 4 19% 34% 25% 7%	330
October	1st to 10th	Day	12% 2 26% 35% 22% 4	330
	11th to 20th	Day	7% 11% 27% 36% 17% 3	330
	21st to end	Day	18% 8% 32% 22% 17% 4	363
November	1st to 10th	Day	12% 8% 32% 29% 16% 3	330
	11th to 20th	Day	9% 8% 32% 35% 12% 4	330
	21st to end	Day	14% 17% 33% 22% 12% 2	330
December	1st to 10th	Day	7% 11% 41% 32% 9% 1	330
	11th to 20th	Day	8% 11% 33% 37% 10% 2	330
	21st to end	Day	15% 15% 36% 25% 7% 1	363
January	1st to 10th	Night	7% 11% 34% 40% 8%	1050
	11th to 20th	Night	8% 10% 33% 39% 10%	1050
	21st to end	Night	8% 8% 35% 41% 8%	958
February	1st to 10th	Night	9% 11% 35% 38% 7% 1	840
	11th to 20th	Night	10% 12% 39% 33% 6%	824
	21st to end	Night	9% 12% 40% 35% 3	692
March	1st to 10th	Night	9% 15% 36% 35% 4	840
	11th to 20th	Night	13% 12% 35% 33% 7%	700
	21st to end	Night	9% 13% 42% 32% 4	693
April	1st to 10th	Night	8% 13% 39% 35% 4	630
	11th to 20th	Night	10% 14% 45% 29% 2	623
	21st to end	Night	10% 13% 36% 35% 5%	630
May	1st to 10th	Night	10% 10% 37% 37% 5%	630
	11th to 20th	Night	10% 9% 33% 36% 12%	621
	21st to end	Night	9% 4 37% 39% 10% 1	683
June	1st to 10th	Night	6% 4 30% 45% 14%	630
	11th to 20th	Night	5% 4 37% 44% 10%	630
	21st to end	Night	5% 2 24% 47% 21%	630
July	1st to 10th	Night	8% 1 15% 43% 31% 2	615
	11th to 20th	Night	4 1 13% 45% 37% 1	612
	21st to end	Night	2 1 7% 45% 43% 2	687
August	1st to 10th	Night	3 1 13% 44% 38% 1	597
	11th to 20th	Night	6% 2 11% 46% 35% 1	594
	21st to end	Night	6% 10% 41% 41% 2	660
September	1st to 10th	Night	8% 2 13% 43% 33% 2	600
	11th to 20th	Night	11% 2 15% 49% 23% 1	600
	21st to end	Night	7% 3 21% 42% 26% 1	600
October	1st to 10th	Night	10% 5% 22% 44% 19% 1	600
	11th to 20th	Night	10% 6% 29% 42% 13% 1	600
	21st to end	Night	8% 9% 27% 35% 20% 1	1039
November	1st to 10th	Night	8% 7% 27% 44% 13% 1	1025
	11th to 20th	Night	6% 9% 31% 40% 13%	1050
	21st to end	Night	10% 9% 29% 37% 13% 1	1050
December	1st to 10th	Night	8% 10% 32% 41% 10%	1050
	11th to 20th	Night	11% 10% 35% 36% 9%	1050
	21st to end	Night	11% 11% 34% 36% 8% 1	1155

Page generated at 2026-07-28 02:25:23. Version ac07

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