Innerarity Island Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Innerarity Island Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	109164
	Night	10% 6% 2 5% 4 4 4 4 6% 9% 46%	109853
Transparency	Day	34% 7% 16% 20% 17% 7%	113082
	Night	34% 6% 14% 19% 19% 8%	114062
Seeing	Day	11% 3 14% 26% 30% 16%	14897
	Night	11% 4 17% 26% 29% 12%	24930

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	12% 4 2 5% 4 4 4 3 5% 7% 51%	4332
	11th to 20th	Day	13% 6% 3 5% 4 3 3 3 6% 6% 47%	4520
	21st to end	Day	20% 7% 3 6% 3 4 4 3 5% 8% 36%	4972
February	1st to 10th	Day	14% 9% 2 6% 5% 4 3 3 5% 6% 43%	2000
	11th to 20th	Day	14% 6% 2 5% 4 5% 4 3 6% 7% 44%	1948
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 7% 42%	1650
March	1st to 10th	Day	20% 10% 3 7% 4 4 4 3 4 6% 36%	3220
	11th to 20th	Day	11% 4 2 6% 4 4 5% 4 6% 9% 43%	3288
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 7% 45%	4119
April	1st to 10th	Day	12% 6% 1 5% 4 4 4 3 6% 7% 48%	2280
	11th to 20th	Day	11% 5% 2 6% 4 3 4 4 7% 8% 46%	2254
	21st to end	Day	6% 4 1 4 4 3 3 3 6% 7% 58%	2280
May	1st to 10th	Day	7% 5% 2 5% 3 4 6% 5% 7% 11% 45%	3765
	11th to 20th	Day	12% 5% 2 6% 4 3 4 4 5% 9% 45%	4006
	21st to end	Day	3 3 1 5% 3 5% 4 4 7% 12% 52%	4476
June	1st to 10th	Day	7% 6% 2 7% 5% 4 5% 5% 8% 13% 38%	2470
	11th to 20th	Day	5% 3 1 6% 6% 5% 6% 4 9% 13% 42%	2470
	21st to end	Day	7% 5% 1 6% 5% 4 6% 6% 10% 13% 37%	2470
July	1st to 10th	Day	6% 5% 3 6% 6% 6% 6% 6% 9% 14% 34%	4120
	11th to 20th	Day	4 4 2 6% 6% 5% 7% 7% 10% 11% 37%	3847
	21st to end	Day	3 4 2 6% 6% 7% 8% 8% 10% 17% 30%	4118
August	1st to 10th	Day	4 3 1 4 3 4 5% 5% 8% 14% 49%	3785
	11th to 20th	Day	5% 3 2 4 5% 5% 5% 5% 9% 11% 48%	3729
	21st to end	Day	6% 4 2 7% 5% 6% 7% 6% 9% 12% 37%	4180
September	1st to 10th	Day	9% 6% 2 6% 3 5% 6% 5% 8% 11% 39%	2252
	11th to 20th	Day	10% 7% 1 7% 4 4 5% 4 7% 10% 41%	2090
	21st to end	Day	8% 3 2 6% 3 4 4 4 5% 8% 53%	2090
October	1st to 10th	Day	8% 4 1 4 3 3 4 4 7% 8% 56%	2090
	11th to 20th	Day	7% 3 1 3 3 3 3 3 5% 8% 61%	2090
	21st to end	Day	9% 4 2 6% 4 3 3 3 4 6% 55%	2122
November	1st to 10th	Day	9% 3 2 5% 4 2 3 3 5% 6% 57%	1762
	11th to 20th	Day	9% 4 2 5% 3 3 4 3 5% 7% 56%	1800
	21st to end	Day	10% 5% 2 5% 3 5% 4 4 6% 8% 48%	1800
December	1st to 10th	Day	12% 7% 2 6% 3 4 3 3 6% 7% 47%	2930
	11th to 20th	Day	10% 7% 2 6% 5% 4 4 4 4 6% 47%	3373
	21st to end	Day	15% 8% 2 7% 4 3 3 3 4 6% 45%	4466
January	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 5% 6% 48%	5595
	11th to 20th	Night	17% 8% 3 7% 3 3 3 3 4 5% 43%	5440
	21st to end	Night	16% 8% 2 5% 4 4 4 4 5% 8% 40%	5984
February	1st to 10th	Night	14% 7% 2 6% 4 4 3 3 5% 6% 46%	2400
	11th to 20th	Night	17% 6% 2 5% 3 3 4 4 4 6% 45%	2338
	21st to end	Night	13% 8% 3 7% 4 4 4 3 4 6% 44%	1980
March	1st to 10th	Night	20% 10% 3 8% 4 3 4 4 4 6% 34%	3853
	11th to 20th	Night	8% 7% 2 5% 5% 5% 5% 4 6% 10% 43%	3700
	21st to end	Night	12% 6% 2 5% 4 3 4 4 5% 8% 46%	3540
April	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 6% 8% 47%	1900
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 5% 8% 48%	1875
	21st to end	Night	5% 4 1 3 5% 3 4 3 5% 6% 61%	1900
May	1st to 10th	Night	7% 5% 2 6% 4 4 5% 4 7% 9% 47%	3130
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 5% 8% 46%	2886
	21st to end	Night	3 3 1 5% 3 4 4 4 7% 12% 54%	3079
June	1st to 10th	Night	6% 6% 2 6% 6% 5% 4 4 8% 11% 42%	1710
	11th to 20th	Night	4 3 1 4 4 5% 5% 5% 8% 12% 49%	1710
	21st to end	Night	5% 5% 2 5% 5% 4 5% 6% 10% 12% 41%	1710
July	1st to 10th	Night	3 4 2 5% 4 5% 7% 5% 12% 17% 36%	2840
	11th to 20th	Night	2 2 1 4 4 4 5% 5% 9% 13% 50%	3094
	21st to end	Night	2 2 1 5% 6% 6% 7% 7% 12% 18% 34%	3435
August	1st to 10th	Night	2 2 1 3 4 5% 5% 5% 8% 14% 50%	3144
	11th to 20th	Night	4 3 1 4 3 3 4 4 8% 13% 52%	3100
	21st to end	Night	4 4 2 6% 5% 6% 6% 5% 8% 14% 40%	3476
September	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 5% 7% 13% 37%	1909
	11th to 20th	Night	9% 7% 2 7% 5% 5% 6% 5% 6% 9% 40%	2090
	21st to end	Night	8% 4 2 5% 4 4 4 4 5% 8% 52%	2090
October	1st to 10th	Night	7% 5% 2 4 4 4 4 4 6% 8% 53%	2090
	11th to 20th	Night	6% 4 2 3 4 3 3 3 5% 6% 61%	2090
	21st to end	Night	8% 5% 2 5% 5% 4 4 3 4 5% 55%	2467
November	1st to 10th	Night	9% 6% 2 3 3 3 3 3 5% 7% 55%	2536
	11th to 20th	Night	11% 6% 2 5% 3 4 4 2 4 7% 53%	2600
	21st to end	Night	10% 5% 1 6% 4 4 4 4 5% 7% 50%	2600
December	1st to 10th	Night	10% 6% 2 5% 4 4 4 4 6% 6% 49%	4250
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 50%	4822
	21st to end	Night	16% 8% 3 6% 4 4 3 2 4 5% 45%	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	34% 4 6% 20% 28% 8%	4333
	11th to 20th	Day	37% 4 7% 17% 27% 9%	4520
	21st to end	Day	47% 5% 8% 15% 16% 9%	4972
February	1st to 10th	Day	43% 4 8% 16% 19% 10%	2000
	11th to 20th	Day	39% 6% 9% 18% 19% 9%	1958
	21st to end	Day	39% 8% 10% 19% 16% 8%	1650
March	1st to 10th	Day	49% 4 10% 19% 14% 4	3220
	11th to 20th	Day	35% 6% 16% 18% 20% 4	3288
	21st to end	Day	39% 5% 13% 18% 17% 9%	4119
April	1st to 10th	Day	35% 5% 13% 19% 19% 8%	2280
	11th to 20th	Day	35% 5% 10% 23% 20% 7%	2254
	21st to end	Day	25% 4 13% 27% 22% 8%	2280
May	1st to 10th	Day	28% 8% 19% 25% 15% 4	3800
	11th to 20th	Day	36% 6% 16% 24% 17% 1	4010
	21st to end	Day	23% 8% 20% 35% 12% 2	4489
June	1st to 10th	Day	34% 9% 20% 27% 8% 1	2470
	11th to 20th	Day	29% 11% 21% 27% 11% 1	2470
	21st to end	Day	33% 12% 25% 19% 10% 1	2470
July	1st to 10th	Day	36% 14% 36% 12% 2	4055
	11th to 20th	Day	35% 15% 39% 8% 2	3782
	21st to end	Day	35% 18% 31% 14% 2	3987
August	1st to 10th	Day	24% 10% 22% 30% 13% 2	3773
	11th to 20th	Day	26% 10% 25% 27% 12%	3765
	21st to end	Day	36% 13% 23% 16% 10% 1	4179
September	1st to 10th	Day	36% 12% 20% 19% 11% 3	2252
	11th to 20th	Day	38% 9% 16% 17% 15% 5%	2090
	21st to end	Day	29% 8% 12% 21% 22% 7%	2090
October	1st to 10th	Day	29% 4 8% 14% 18% 26%	3480
	11th to 20th	Day	15% 4 6% 23% 24% 30%	3458
	21st to end	Day	22% 4 6% 13% 38% 18%	3460
November	1st to 10th	Day	28% 4 10% 22% 23% 12%	1762
	11th to 20th	Day	30% 5% 8% 18% 27% 12%	1800
	21st to end	Day	33% 6% 9% 22% 20% 10%	1800
December	1st to 10th	Day	36% 5% 12% 17% 23% 6%	2930
	11th to 20th	Day	38% 5% 8% 20% 21% 9%	3370
	21st to end	Day	41% 5% 7% 15% 29% 3	4466
January	1st to 10th	Night	37% 4 6% 15% 27% 10%	5595
	11th to 20th	Night	44% 3 5% 14% 29% 6%	5440
	21st to end	Night	43% 4 9% 16% 18% 9%	5984
February	1st to 10th	Night	39% 4 7% 17% 23% 10%	2400
	11th to 20th	Night	41% 5% 8% 15% 20% 12%	2339
	21st to end	Night	41% 5% 10% 18% 15% 11%	1980
March	1st to 10th	Night	51% 5% 10% 16% 14% 5%	3853
	11th to 20th	Night	35% 6% 15% 19% 18% 8%	3700
	21st to end	Night	37% 4 11% 20% 19% 9%	3540
April	1st to 10th	Night	35% 5% 14% 16% 19% 11%	1900
	11th to 20th	Night	34% 4 10% 22% 21% 9%	1875
	21st to end	Night	24% 4 10% 29% 25% 8%	1900
May	1st to 10th	Night	31% 6% 20% 22% 18% 4	3160
	11th to 20th	Night	36% 7% 16% 23% 17% 2	2887
	21st to end	Night	21% 6% 18% 36% 17% 2	3087
June	1st to 10th	Night	33% 7% 23% 25% 10% 1	1710
	11th to 20th	Night	25% 10% 24% 27% 13% 1	1710
	21st to end	Night	30% 12% 27% 20% 9% 1	1710
July	1st to 10th	Night	30% 14% 41% 13% 3	2795
	11th to 20th	Night	22% 14% 52% 10% 2	3037
	21st to end	Night	30% 21% 32% 15% 2	3325
August	1st to 10th	Night	22% 10% 28% 26% 13% 1	3132
	11th to 20th	Night	22% 10% 27% 34% 7%	3130
	21st to end	Night	34% 13% 24% 18% 10% 2	3476
September	1st to 10th	Night	37% 8% 24% 16% 12% 3	1909
	11th to 20th	Night	39% 8% 16% 17% 14% 5%	2090
	21st to end	Night	30% 7% 13% 24% 19% 8%	2090
October	1st to 10th	Night	35% 5% 8% 13% 18% 22%	3480
	11th to 20th	Night	15% 3 5% 19% 28% 29%	3461
	21st to end	Night	21% 3 5% 11% 45% 15%	4067
November	1st to 10th	Night	29% 4 8% 20% 26% 12%	2536
	11th to 20th	Night	34% 3 5% 19% 27% 11%	2600
	21st to end	Night	34% 5% 10% 20% 21% 12%	2600
December	1st to 10th	Night	35% 4 9% 19% 22% 9%	4250
	11th to 20th	Night	35% 4 8% 24% 19% 10%	4824
	21st to end	Night	43% 4 6% 18% 25% 4	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	13% 10% 30% 35% 11% 1	300
	11th to 20th	Day	10% 8% 28% 38% 15% 1	300
	21st to end	Day	25% 8% 28% 30% 8%	330
February	1st to 10th	Day	19% 7% 28% 30% 14% 2	300
	11th to 20th	Day	21% 5% 31% 32% 11%	300
	21st to end	Day	9% 6% 32% 39% 12% 1	249
March	1st to 10th	Day	13% 8% 30% 35% 14% 1	300
	11th to 20th	Day	14% 5% 27% 36% 17% 1	339
	21st to end	Day	14% 6% 26% 36% 17% 2	506
April	1st to 10th	Day	15% 6% 25% 35% 17% 2	460
	11th to 20th	Day	12% 7% 24% 30% 25% 3	452
	21st to end	Day	8% 4 16% 37% 31% 4	460
May	1st to 10th	Day	7% 5% 12% 39% 32% 5%	463
	11th to 20th	Day	7% 2 9% 32% 37% 13%	487
	21st to end	Day	5% 1 6% 28% 43% 17%	529
June	1st to 10th	Day	11% 1 7% 22% 41% 19%	490
	11th to 20th	Day	8% 2 6% 21% 39% 24%	490
	21st to end	Day	8% 1 6% 18% 37% 30%	490
July	1st to 10th	Day	8% 1 5% 9% 37% 40%	485
	11th to 20th	Day	7% 4 7% 31% 50%	484
	21st to end	Day	7% 1 4 10% 38% 40%	532
August	1st to 10th	Day	9% 1 2 7% 35% 47%	486
	11th to 20th	Day	7% 4 9% 35% 44%	479
	21st to end	Day	11% 1 6% 12% 40% 32%	539
September	1st to 10th	Day	13% 1 5% 11% 37% 33%	490
	11th to 20th	Day	13% 2 7% 20% 40% 18%	490
	21st to end	Day	12% 1 6% 23% 42% 17%	490
October	1st to 10th	Day	9% 1 12% 34% 37% 7%	490
	11th to 20th	Day	6% 2 11% 32% 35% 14%	490
	21st to end	Day	13% 4 13% 30% 31% 8%	367
November	1st to 10th	Day	12% 1 14% 32% 37% 4	300
	11th to 20th	Day	13% 4 18% 36% 25% 4	300
	21st to end	Day	12% 5% 18% 38% 24% 3	300
December	1st to 10th	Day	18% 3 21% 35% 20% 3	300
	11th to 20th	Day	20% 4 27% 29% 17% 2	300
	21st to end	Day	22% 7% 19% 34% 17% 2	330
January	1st to 10th	Night	16% 9% 32% 29% 12% 1	800
	11th to 20th	Night	16% 9% 27% 32% 16% 1	800
	21st to end	Night	18% 9% 32% 32% 9%	880
February	1st to 10th	Night	16% 8% 27% 34% 14% 1	800
	11th to 20th	Night	19% 8% 28% 29% 16%	783
	21st to end	Night	15% 7% 31% 35% 12%	660
March	1st to 10th	Night	14% 7% 28% 34% 18% 1	800
	11th to 20th	Night	11% 5% 26% 32% 21% 4	767
	21st to end	Night	12% 5% 22% 35% 24% 2	675
April	1st to 10th	Night	11% 7% 22% 37% 21% 2	570
	11th to 20th	Night	12% 4 21% 33% 26% 3	563
	21st to end	Night	6% 3 17% 35% 33% 6%	570
May	1st to 10th	Night	9% 3 12% 32% 35% 8%	570
	11th to 20th	Night	8% 2 10% 32% 37% 11%	561
	21st to end	Night	6% 1 6% 23% 48% 17%	617
June	1st to 10th	Night	9% 1 6% 21% 47% 17%	570
	11th to 20th	Night	4 2 3 16% 51% 25%	570
	21st to end	Night	8% 1 4 12% 47% 28%	570
July	1st to 10th	Night	5% 1 4 7% 45% 38%	555
	11th to 20th	Night	4 4 5% 36% 51%	552
	21st to end	Night	3 2 8% 45% 42%	624
August	1st to 10th	Night	4 2 5% 41% 47%	567
	11th to 20th	Night	8% 3 7% 39% 43%	564
	21st to end	Night	9% 2 6% 12% 42% 30%	627
September	1st to 10th	Night	10% 2 4 13% 40% 31%	579
	11th to 20th	Night	12% 1 9% 19% 43% 16%	760
	21st to end	Night	11% 1 7% 24% 44% 14%	760
October	1st to 10th	Night	10% 2 13% 31% 37% 7%	760
	11th to 20th	Night	7% 3 14% 30% 35% 10%	760
	21st to end	Night	11% 4 16% 31% 34% 5%	836
November	1st to 10th	Night	12% 3 17% 34% 28% 5%	780
	11th to 20th	Night	14% 7% 19% 35% 23% 2	800
	21st to end	Night	13% 5% 26% 33% 20% 4	800
December	1st to 10th	Night	13% 6% 26% 30% 20% 6%	800
	11th to 20th	Night	17% 6% 26% 29% 19% 3	800
	21st to end	Night	21% 7% 25% 30% 15% 1	880

Page generated at 2025-03-09 07:08:42. Version ac07

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