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 2025-03-27.

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	6% 4 1 4 3 3 3 3 5% 6% 61%	113531
	Night	6% 4 2 4 3 3 3 3 5% 7% 61%	114618
Transparency	Day	23% 5% 8% 22% 27% 15%	113295
	Night	22% 5% 9% 21% 28% 16%	114444
Seeing	Day	9% 8% 28% 32% 19% 4	15711
	Night	8% 8% 29% 39% 15% 1	25832

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	7% 7% 2 6% 3 4 4 3 4 5% 56%	4077
	11th to 20th	Day	3 4 1 4 3 2 2 2 3 5% 71%	4080
	21st to end	Day	8% 5% 2 6% 4 3 3 2 4 6% 59%	4966
February	1st to 10th	Day	5% 6% 2 4 3 2 3 3 5% 6% 61%	2000
	11th to 20th	Day	6% 7% 2 5% 3 2 3 2 4 6% 59%	1949
	21st to end	Day	4 6% 2 3 3 3 3 3 4 6% 64%	1650
March	1st to 10th	Day	7% 3 1 2 2 3 3 3 4 7% 64%	3230
	11th to 20th	Day	9% 5% 2 4 4 3 3 2 4 5% 59%	3485
	21st to end	Day	5% 5% 2 7% 4 4 4 3 5% 7% 54%	3975
April	1st to 10th	Day	6% 4 1 4 3 2 3 2 4 5% 66%	2280
	11th to 20th	Day	9% 5% 2 4 2 2 3 2 5% 6% 59%	2251
	21st to end	Day	8% 3 1 3 3 2 4 3 5% 5% 63%	2318
May	1st to 10th	Day	11% 4 1 3 3 3 3 3 4 7% 59%	4120
	11th to 20th	Day	11% 5% 1 4 3 3 3 3 5% 6% 57%	4082
	21st to end	Day	9% 4 1 3 3 3 3 3 5% 6% 60%	4489
June	1st to 10th	Day	6% 4 1 4 4 5% 4 4 7% 8% 53%	2470
	11th to 20th	Day	5% 4 1 3 3 3 3 3 5% 8% 62%	2470
	21st to end	Day	4 3 1 4 3 3 4 4 6% 8% 61%	2470
July	1st to 10th	Day	8% 5% 2 5% 3 5% 5% 4 6% 8% 48%	4120
	11th to 20th	Day	3 2 1 4 4 4 4 4 6% 8% 61%	4120
	21st to end	Day	2 2 1 4 4 4 5% 4 6% 10% 58%	4466
August	1st to 10th	Day	3 3 1 4 3 3 4 3 7% 8% 61%	3883
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 8% 62%	3726
	21st to end	Day	6% 3 1 3 2 4 4 4 6% 8% 59%	4180
September	1st to 10th	Day	7% 4 1 4 3 4 4 3 6% 6% 57%	2237
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 5% 7% 54%	2090
	21st to end	Day	8% 3 1 3 2 2 3 3 4 6% 64%	2090
October	1st to 10th	Day	6% 2 1 3 2 1 2 1 2 4 76%	3480
	11th to 20th	Day	11% 4 1 3 2 2 3 2 4 5% 63%	3458
	21st to end	Day	6% 3 1 2 2 1 2 2 3 4 74%	3137
November	1st to 10th	Day	6% 4 1 3 2 2 2 2 4 6% 68%	1763
	11th to 20th	Day	3 3 1 3 3 2 2 3 4 5% 72%	1800
	21st to end	Day	8% 6% 2 4 2 2 2 2 5% 6% 63%	1800
December	1st to 10th	Day	4 3 1 3 3 2 3 2 4 6% 67%	2940
	11th to 20th	Day	5% 3 1 4 3 3 4 4 4 5% 65%	3391
	21st to end	Day	6% 8% 2 4 3 2 3 3 4 5% 62%	4488
January	1st to 10th	Night	6% 7% 3 5% 3 3 3 3 5% 6% 57%	5888
	11th to 20th	Night	2 3 2 4 2 3 3 3 5% 5% 68%	5900
	21st to end	Night	5% 7% 3 8% 3 3 3 3 4 6% 56%	6056
February	1st to 10th	Night	6% 6% 2 4 3 3 3 3 4 6% 61%	2400
	11th to 20th	Night	7% 6% 2 5% 4 3 3 4 4 6% 57%	2338
	21st to end	Night	6% 4 1 4 3 3 3 3 6% 6% 62%	1980
March	1st to 10th	Night	4 5% 2 4 3 2 3 2 4 6% 66%	3854
	11th to 20th	Night	7% 4 2 4 3 4 4 3 4 6% 60%	3696
	21st to end	Night	4 5% 3 5% 4 4 4 3 6% 7% 55%	3780
April	1st to 10th	Night	5% 4 1 3 2 3 3 3 5% 6% 65%	1900
	11th to 20th	Night	9% 4 1 2 3 3 3 3 5% 6% 61%	1877
	21st to end	Night	8% 3 1 3 2 3 3 3 5% 7% 61%	1862
May	1st to 10th	Night	13% 5% 2 3 3 3 3 2 3 6% 58%	2850
	11th to 20th	Night	10% 6% 1 5% 3 3 4 3 5% 6% 54%	2823
	21st to end	Night	9% 5% 2 3 3 2 3 3 4 5% 61%	3098
June	1st to 10th	Night	6% 4 1 3 3 3 5% 5% 6% 10% 54%	1710
	11th to 20th	Night	3 3 1 3 3 3 3 4 6% 9% 61%	1710
	21st to end	Night	3 3 1 3 2 3 4 4 8% 10% 59%	1710
July	1st to 10th	Night	6% 3 2 5% 4 4 5% 4 6% 10% 50%	2850
	11th to 20th	Night	3 3 1 5% 3 5% 4 5% 7% 11% 52%	2850
	21st to end	Night	3 3 1 4 2 3 4 4 7% 12% 59%	3097
August	1st to 10th	Night	3 2 1 3 3 3 5% 4 8% 12% 57%	3051
	11th to 20th	Night	4 3 1 4 3 4 5% 4 7% 12% 53%	3113
	21st to end	Night	3 3 1 4 3 3 3 3 6% 11% 59%	3487
September	1st to 10th	Night	6% 4 2 5% 4 3 4 3 5% 7% 57%	1943
	11th to 20th	Night	9% 5% 2 6% 3 3 4 3 5% 7% 54%	2090
	21st to end	Night	7% 3 1 3 2 2 3 2 5% 5% 67%	2090
October	1st to 10th	Night	5% 3 1 2 1 2 2 1 3 4 77%	3480
	11th to 20th	Night	11% 3 2 3 2 2 2 2 4 4 65%	3460
	21st to end	Night	4 2 1 2 2 2 2 2 3 5% 74%	4384
November	1st to 10th	Night	7% 3 1 2 2 2 2 2 3 5% 71%	2535
	11th to 20th	Night	4 4 1 2 2 2 2 2 4 6% 71%	2600
	21st to end	Night	8% 4 1 4 3 2 3 3 4 6% 63%	2600
December	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 7% 67%	4250
	11th to 20th	Night	4 4 1 3 2 3 3 3 5% 7% 66%	4816
	21st to end	Night	5% 6% 2 4 3 3 3 3 4 6% 61%	6490

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 7% 25% 25% 10%	4078
	11th to 20th	Day	18% 3 6% 21% 33% 19%	4080
	21st to end	Day	27% 4 5% 20% 31% 13%	4966
February	1st to 10th	Day	24% 2 8% 25% 26% 15%	2000
	11th to 20th	Day	28% 3 6% 23% 24% 15%	1959
	21st to end	Day	23% 3 5% 19% 31% 20%	1650
March	1st to 10th	Day	20% 3 5% 13% 28% 30%	3230
	11th to 20th	Day	26% 5% 7% 22% 29% 11%	3485
	21st to end	Day	28% 5% 8% 23% 24% 13%	3975
April	1st to 10th	Day	21% 4 6% 17% 27% 24%	2280
	11th to 20th	Day	27% 4 7% 19% 23% 20%	2254
	21st to end	Day	23% 4 9% 24% 29% 11%	2318
May	1st to 10th	Day	25% 6% 8% 18% 21% 22%	4120
	11th to 20th	Day	28% 5% 9% 21% 22% 15%	4086
	21st to end	Day	25% 6% 9% 15% 21% 24%	4489
June	1st to 10th	Day	26% 7% 15% 27% 15% 10%	2470
	11th to 20th	Day	20% 6% 10% 23% 27% 15%	2470
	21st to end	Day	19% 5% 13% 30% 20% 12%	2470
July	1st to 10th	Day	31% 8% 11% 25% 21% 5%	4056
	11th to 20th	Day	19% 6% 11% 30% 27% 7%	4051
	21st to end	Day	19% 7% 12% 29% 27% 6%	4325
August	1st to 10th	Day	19% 7% 12% 25% 25% 12%	3870
	11th to 20th	Day	19% 6% 11% 22% 29% 13%	3762
	21st to end	Day	21% 6% 12% 26% 28% 7%	4179
September	1st to 10th	Day	26% 7% 11% 21% 22% 13%	2237
	11th to 20th	Day	29% 7% 9% 21% 28% 6%	2090
	21st to end	Day	21% 4 8% 21% 31% 14%	2090
October	1st to 10th	Day	15% 3 5% 13% 37% 27%	3480
	11th to 20th	Day	25% 3 6% 20% 24% 22%	3458
	21st to end	Day	16% 2 4 24% 38% 15%	3137
November	1st to 10th	Day	18% 3 8% 19% 33% 20%	1763
	11th to 20th	Day	15% 4 6% 25% 33% 17%	1800
	21st to end	Day	24% 3 5% 16% 33% 19%	1800
December	1st to 10th	Day	19% 3 6% 31% 28% 12%	2940
	11th to 20th	Day	21% 2 6% 16% 38% 17%	3389
	21st to end	Day	26% 3 6% 21% 32% 12%	4488
January	1st to 10th	Night	28% 4 7% 30% 24% 6%	5888
	11th to 20th	Night	17% 4 10% 18% 33% 18%	5900
	21st to end	Night	30% 5% 6% 17% 29% 13%	6056
February	1st to 10th	Night	26% 3 7% 18% 28% 17%	2400
	11th to 20th	Night	29% 4 7% 20% 24% 17%	2338
	21st to end	Night	22% 3 5% 18% 28% 24%	1980
March	1st to 10th	Night	20% 5% 5% 15% 24% 31%	3854
	11th to 20th	Night	23% 5% 8% 24% 21% 19%	3696
	21st to end	Night	26% 6% 9% 24% 20% 15%	3780
April	1st to 10th	Night	19% 5% 9% 19% 25% 24%	1900
	11th to 20th	Night	24% 5% 9% 19% 25% 18%	1877
	21st to end	Night	21% 6% 12% 22% 24% 15%	1862
May	1st to 10th	Night	27% 6% 8% 18% 17% 24%	2850
	11th to 20th	Night	29% 7% 11% 16% 24% 12%	2824
	21st to end	Night	25% 6% 10% 13% 16% 30%	3099
June	1st to 10th	Night	23% 8% 18% 27% 16% 8%	1710
	11th to 20th	Night	19% 5% 12% 23% 26% 14%	1710
	21st to end	Night	18% 7% 15% 26% 22% 13%	1710
July	1st to 10th	Night	27% 7% 14% 32% 17% 3	2805
	11th to 20th	Night	23% 7% 12% 22% 28% 8%	2796
	21st to end	Night	17% 6% 12% 26% 32% 7%	2999
August	1st to 10th	Night	17% 5% 12% 27% 24% 14%	3041
	11th to 20th	Night	23% 7% 12% 21% 28% 9%	3143
	21st to end	Night	20% 5% 14% 27% 27% 7%	3487
September	1st to 10th	Night	27% 6% 10% 23% 23% 12%	1943
	11th to 20th	Night	30% 5% 11% 19% 27% 8%	2090
	21st to end	Night	19% 5% 8% 20% 32% 17%	2090
October	1st to 10th	Night	14% 3 6% 12% 35% 29%	3480
	11th to 20th	Night	25% 3 5% 17% 30% 20%	3460
	21st to end	Night	14% 3 4 21% 41% 18%	4384
November	1st to 10th	Night	18% 2 7% 21% 32% 20%	2535
	11th to 20th	Night	15% 3 6% 23% 35% 19%	2600
	21st to end	Night	23% 4 5% 18% 32% 19%	2600
December	1st to 10th	Night	17% 3 8% 30% 34% 9%	4250
	11th to 20th	Night	18% 3 4 17% 40% 18%	4817
	21st to end	Night	24% 4 7% 23% 30% 12%	6490

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% 40% 28% 8% 1	300
	11th to 20th	Day	11% 18% 34% 26% 10% 1	300
	21st to end	Day	10% 11% 42% 28% 8% 1	330
February	1st to 10th	Day	10% 13% 39% 30% 9%	300
	11th to 20th	Day	14% 11% 44% 23% 5% 2	300
	21st to end	Day	11% 17% 40% 27% 5%	249
March	1st to 10th	Day	10% 12% 44% 28% 5%	300
	11th to 20th	Day	18% 16% 39% 19% 7% 2	300
	21st to end	Day	13% 15% 40% 23% 8% 1	372
April	1st to 10th	Day	9% 21% 46% 19% 5%	460
	11th to 20th	Day	13% 19% 44% 21% 2	452
	21st to end	Day	11% 17% 39% 24% 7% 1	498
May	1st to 10th	Day	10% 12% 36% 32% 10% 1	653
	11th to 20th	Day	11% 9% 31% 31% 15% 3	675
	21st to end	Day	10% 9% 33% 32% 14% 2	734
June	1st to 10th	Day	7% 6% 24% 40% 20% 4	680
	11th to 20th	Day	6% 3 29% 40% 19% 3	680
	21st to end	Day	5% 2 20% 41% 27% 5%	680
July	1st to 10th	Day	7% 1 12% 33% 34% 13%	671
	11th to 20th	Day	3 1 9% 42% 37% 8%	668
	21st to end	Day	2 1 8% 36% 44% 9%	739
August	1st to 10th	Day	4 1 14% 42% 33% 6%	547
	11th to 20th	Day	8% 1 15% 35% 30% 11%	477
	21st to end	Day	8% 13% 40% 32% 7%	539
September	1st to 10th	Day	6% 1 15% 39% 31% 8%	447
	11th to 20th	Day	4 2 18% 40% 31% 5%	300
	21st to end	Day	12% 4 18% 35% 24% 7%	300
October	1st to 10th	Day	12% 2 26% 34% 21% 4	300
	11th to 20th	Day	6% 11% 26% 37% 17% 3	300
	21st to end	Day	18% 7% 33% 22% 16% 5%	330
November	1st to 10th	Day	13% 8% 32% 29% 15% 3	300
	11th to 20th	Day	9% 8% 35% 34% 10% 4	300
	21st to end	Day	14% 17% 32% 22% 13% 3	300
December	1st to 10th	Day	7% 11% 40% 32% 9% 1	300
	11th to 20th	Day	8% 11% 36% 35% 8% 2	300
	21st to end	Day	16% 16% 37% 23% 6% 2	330
January	1st to 10th	Night	7% 11% 33% 41% 9%	1000
	11th to 20th	Night	8% 10% 33% 39% 10% 1	1000
	21st to end	Night	7% 8% 35% 41% 8%	913
February	1st to 10th	Night	10% 11% 35% 37% 7% 1	800
	11th to 20th	Night	10% 12% 39% 33% 6%	784
	21st to end	Night	9% 13% 40% 35% 3	660
March	1st to 10th	Night	9% 16% 35% 36% 4	800
	11th to 20th	Night	13% 12% 35% 32% 7%	667
	21st to end	Night	9% 13% 42% 32% 4	647
April	1st to 10th	Night	7% 13% 41% 35% 3	570
	11th to 20th	Night	10% 13% 46% 29% 2	563
	21st to end	Night	9% 12% 35% 37% 6%	570
May	1st to 10th	Night	10% 10% 38% 37% 6%	570
	11th to 20th	Night	11% 9% 32% 36% 12% 1	561
	21st to end	Night	8% 4 39% 38% 10% 1	617
June	1st to 10th	Night	6% 4 30% 44% 15%	570
	11th to 20th	Night	5% 3 37% 44% 10%	570
	21st to end	Night	5% 2 22% 49% 22% 1	570
July	1st to 10th	Night	7% 1 14% 43% 33% 2	555
	11th to 20th	Night	4 1 13% 43% 37% 2	552
	21st to end	Night	3 1 7% 45% 43% 2	624
August	1st to 10th	Night	3 1 12% 43% 40% 1	567
	11th to 20th	Night	6% 2 11% 45% 36% 1	564
	21st to end	Night	4 10% 41% 41% 2	627
September	1st to 10th	Night	7% 2 13% 42% 34% 2	570
	11th to 20th	Night	11% 2 15% 47% 24% 1	570
	21st to end	Night	8% 3 21% 41% 27% 1	570
October	1st to 10th	Night	10% 4 22% 44% 19% 1	570
	11th to 20th	Night	11% 6% 29% 41% 13% 1	570
	21st to end	Night	8% 9% 27% 34% 20% 1	986
November	1st to 10th	Night	8% 7% 27% 43% 13% 1	975
	11th to 20th	Night	6% 10% 32% 39% 13%	1000
	21st to end	Night	10% 10% 28% 37% 13% 1	1000
December	1st to 10th	Night	8% 10% 31% 41% 10%	1000
	11th to 20th	Night	11% 10% 35% 35% 8%	1000
	21st to end	Night	11% 11% 33% 36% 8% 1	1100

Page generated at 2025-03-24 08:04:25. Version ac07

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