Shired Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shired Island clear sky chart from 2005-11-06 to 2025-07-21.

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	9% 5% 2 5% 4 4 5% 4 7% 10% 45%	120291
	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	118820
Transparency	Day	34% 9% 16% 20% 16% 6%	124119
	Night	34% 7% 15% 20% 17% 7%	123129
Seeing	Day	11% 8% 23% 27% 20% 10%	16181
	Night	11% 7% 21% 31% 24% 7%	26201

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	11% 6% 2 4 3 3 3 3 5% 7% 54%	4056
	11th to 20th	Day	19% 9% 3 8% 4 3 3 3 4 6% 37%	4060
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 9% 48%	4862
February	1st to 10th	Day	14% 8% 3 7% 5% 4 4 3 4 6% 42%	2000
	11th to 20th	Day	13% 6% 2 5% 4 3 3 3 4 6% 51%	1948
	21st to end	Day	12% 5% 3 6% 4 4 4 3 6% 7% 47%	1650
March	1st to 10th	Day	14% 7% 2 6% 4 3 4 3 5% 9% 43%	4884
	11th to 20th	Day	9% 5% 2 4 3 3 3 3 6% 8% 56%	4980
	21st to end	Day	12% 4 2 4 3 3 4 4 6% 8% 51%	5465
April	1st to 10th	Day	7% 4 2 5% 4 3 4 4 6% 10% 52%	2200
	11th to 20th	Day	9% 4 2 5% 4 5% 5% 4 6% 8% 50%	2176
	21st to end	Day	5% 2 1 3 3 4 4 4 6% 9% 59%	2529
May	1st to 10th	Day	6% 4 1 4 3 4 4 4 7% 10% 52%	5862
	11th to 20th	Day	11% 4 2 5% 4 4 4 4 5% 9% 48%	5861
	21st to end	Day	4 3 1 3 3 4 4 4 7% 12% 56%	6433
June	1st to 10th	Day	8% 6% 2 6% 5% 4 6% 6% 9% 13% 34%	2600
	11th to 20th	Day	5% 4 2 6% 5% 6% 7% 6% 9% 13% 36%	2600
	21st to end	Day	8% 5% 2 6% 5% 6% 7% 6% 10% 11% 35%	2600
July	1st to 10th	Day	5% 4 2 6% 4 6% 7% 8% 13% 17% 28%	4250
	11th to 20th	Day	4 3 2 7% 6% 7% 9% 6% 10% 13% 34%	4250
	21st to end	Day	4 4 2 6% 6% 7% 8% 8% 12% 16% 28%	4466
August	1st to 10th	Day	11% 4 2 6% 5% 5% 6% 7% 10% 13% 32%	4021
	11th to 20th	Day	6% 4 1 6% 5% 6% 6% 5% 9% 13% 39%	3729
	21st to end	Day	7% 5% 2 7% 5% 5% 7% 6% 9% 13% 35%	3961
September	1st to 10th	Day	10% 6% 2 7% 7% 8% 8% 6% 9% 10% 26%	2090
	11th to 20th	Day	8% 5% 3 7% 6% 6% 7% 6% 9% 11% 32%	2090
	21st to end	Day	8% 5% 2 8% 5% 5% 5% 4 6% 9% 43%	2090
October	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 43%	2090
	11th to 20th	Day	5% 3 1 4 3 3 3 3 6% 8% 61%	1977
	21st to end	Day	6% 3 2 5% 4 3 4 3 6% 9% 55%	2090
November	1st to 10th	Day	7% 4 2 4 4 3 4 4 7% 7% 55%	1957
	11th to 20th	Day	8% 5% 3 6% 4 3 4 4 5% 7% 51%	1895
	21st to end	Day	10% 5% 2 6% 4 4 4 3 4 8% 50%	1800
December	1st to 10th	Day	5% 4 2 5% 3 4 4 4 6% 7% 57%	2930
	11th to 20th	Day	9% 5% 2 5% 4 4 3 3 6% 7% 53%	3373
	21st to end	Day	15% 9% 3 6% 3 3 3 3 4 6% 44%	4466
January	1st to 10th	Night	10% 6% 2 4 3 3 3 3 4 7% 56%	5889
	11th to 20th	Night	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	5900
	21st to end	Night	15% 7% 2 6% 4 3 4 3 6% 8% 42%	6076
February	1st to 10th	Night	12% 7% 2 7% 4 3 4 3 5% 6% 44%	2400
	11th to 20th	Night	12% 7% 4 5% 4 3 3 3 5% 6% 47%	2338
	21st to end	Night	12% 7% 3 6% 3 4 4 3 5% 6% 48%	1980
March	1st to 10th	Night	14% 7% 3 7% 4 4 5% 3 5% 6% 42%	4967
	11th to 20th	Night	6% 5% 1 5% 3 3 3 3 7% 9% 55%	4980
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 7% 49%	5467
April	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 5% 8% 49%	2200
	11th to 20th	Night	7% 4 2 6% 4 4 4 3 6% 7% 52%	2173
	21st to end	Night	5% 3 1 4 3 3 4 3 6% 8% 58%	1884
May	1st to 10th	Night	4 3 1 4 3 4 4 4 6% 10% 55%	4033
	11th to 20th	Night	10% 4 2 5% 3 4 3 3 6% 10% 50%	4032
	21st to end	Night	3 3 1 3 3 3 4 4 6% 10% 60%	4421
June	1st to 10th	Night	9% 6% 3 7% 5% 4 4 5% 7% 11% 40%	1800
	11th to 20th	Night	5% 4 1 4 4 5% 5% 6% 10% 17% 39%	1800
	21st to end	Night	6% 5% 2 6% 5% 6% 5% 6% 8% 13% 38%	1800
July	1st to 10th	Night	5% 4 2 8% 7% 8% 9% 8% 11% 16% 23%	2930
	11th to 20th	Night	2 3 2 6% 5% 5% 7% 6% 10% 14% 39%	2930
	21st to end	Night	3 4 3 8% 7% 7% 8% 7% 12% 14% 27%	3087
August	1st to 10th	Night	7% 4 2 6% 4 6% 9% 6% 9% 14% 33%	2902
	11th to 20th	Night	3 3 1 5% 4 4 6% 5% 9% 16% 44%	3100
	21st to end	Night	6% 5% 3 9% 7% 6% 8% 6% 9% 11% 29%	3660
September	1st to 10th	Night	7% 7% 3 8% 6% 8% 7% 6% 8% 12% 29%	2090
	11th to 20th	Night	10% 7% 4 8% 5% 6% 6% 6% 8% 10% 30%	2090
	21st to end	Night	9% 5% 2 7% 5% 6% 5% 4 6% 10% 42%	2090
October	1st to 10th	Night	9% 5% 2 7% 4 4 5% 3 6% 8% 45%	2090
	11th to 20th	Night	6% 4 2 4 4 4 4 3 5% 6% 58%	2200
	21st to end	Night	7% 4 2 5% 4 4 4 4 5% 8% 53%	2508
November	1st to 10th	Night	6% 4 2 5% 4 4 4 4 5% 7% 54%	2341
	11th to 20th	Night	9% 5% 3 6% 4 3 4 3 6% 7% 52%	2500
	21st to end	Night	8% 7% 2 5% 5% 4 4 4 5% 7% 49%	2600
December	1st to 10th	Night	9% 5% 2 4 3 3 4 3 4 8% 55%	4250
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 4 7% 50%	4822
	21st to end	Night	12% 8% 3 7% 5% 4 4 4 6% 8% 40%	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	29% 4 9% 16% 27% 15%	4057
	11th to 20th	Day	48% 4 5% 13% 19% 11%	4060
	21st to end	Day	31% 6% 13% 21% 18% 10%	4862
February	1st to 10th	Day	41% 5% 9% 13% 20% 12%	2000
	11th to 20th	Day	34% 4 9% 18% 23% 11%	1958
	21st to end	Day	34% 4 12% 16% 22% 12%	1650
March	1st to 10th	Day	37% 6% 11% 17% 20% 9%	4884
	11th to 20th	Day	26% 5% 12% 19% 22% 16%	4980
	21st to end	Day	30% 6% 10% 26% 19% 9%	5465
April	1st to 10th	Day	29% 7% 14% 21% 19% 11%	2200
	11th to 20th	Day	33% 6% 10% 21% 21% 10%	2176
	21st to end	Day	22% 7% 13% 26% 23% 9%	2529
May	1st to 10th	Day	26% 9% 21% 27% 13% 3	5897
	11th to 20th	Day	33% 7% 16% 32% 12% 1	5865
	21st to end	Day	22% 7% 20% 33% 16% 1	6447
June	1st to 10th	Day	39% 11% 21% 22% 6%	2600
	11th to 20th	Day	36% 13% 24% 21% 6%	2600
	21st to end	Day	40% 13% 24% 17% 6% 1	2600
July	1st to 10th	Day	38% 18% 33% 9% 1	4185
	11th to 20th	Day	39% 17% 34% 8% 2	4181
	21st to end	Day	40% 20% 31% 8% 1	4324
August	1st to 10th	Day	40% 15% 26% 15% 4	4008
	11th to 20th	Day	33% 13% 29% 17% 7% 1	3765
	21st to end	Day	42% 14% 23% 17% 4	3961
September	1st to 10th	Day	48% 15% 18% 12% 6%	2090
	11th to 20th	Day	44% 14% 20% 13% 7% 1	2090
	21st to end	Day	38% 9% 14% 20% 14% 5%	2090
October	1st to 10th	Day	49% 8% 10% 13% 12% 7%	3480
	11th to 20th	Day	15% 4 7% 20% 39% 15%	3269
	21st to end	Day	19% 5% 9% 25% 31% 10%	3428
November	1st to 10th	Day	27% 6% 12% 20% 21% 13%	1957
	11th to 20th	Day	33% 5% 9% 19% 23% 11%	1895
	21st to end	Day	33% 4 10% 23% 23% 8%	1800
December	1st to 10th	Day	26% 5% 14% 19% 24% 12%	2930
	11th to 20th	Day	32% 6% 10% 22% 21% 9%	3370
	21st to end	Day	41% 5% 8% 20% 22% 5%	4466
January	1st to 10th	Night	29% 3 7% 15% 31% 15%	5889
	11th to 20th	Night	50% 4 6% 16% 18% 6%	5900
	21st to end	Night	40% 5% 10% 17% 19% 10%	6076
February	1st to 10th	Night	39% 4 10% 16% 20% 12%	2400
	11th to 20th	Night	37% 5% 8% 18% 21% 11%	2339
	21st to end	Night	36% 4 10% 18% 22% 10%	1980
March	1st to 10th	Night	42% 6% 9% 16% 17% 10%	4967
	11th to 20th	Night	26% 5% 12% 19% 22% 16%	4980
	21st to end	Night	33% 5% 9% 23% 20% 10%	5467
April	1st to 10th	Night	33% 5% 14% 20% 18% 10%	2200
	11th to 20th	Night	30% 5% 9% 25% 22% 9%	2173
	21st to end	Night	23% 5% 13% 30% 22% 7%	1884
May	1st to 10th	Night	23% 9% 21% 32% 12% 3	4060
	11th to 20th	Night	31% 6% 17% 29% 16% 2	4033
	21st to end	Night	19% 7% 18% 39% 16% 1	4429
June	1st to 10th	Night	36% 8% 24% 25% 7% 1	1800
	11th to 20th	Night	28% 12% 31% 23% 5%	1800
	21st to end	Night	35% 12% 25% 22% 6% 1	1800
July	1st to 10th	Night	45% 14% 30% 9% 2	2885
	11th to 20th	Night	30% 16% 43% 9% 1	2876
	21st to end	Night	41% 16% 33% 9% 1	2988
August	1st to 10th	Night	36% 14% 32% 13% 4	2891
	11th to 20th	Night	25% 11% 33% 26% 6%	3130
	21st to end	Night	43% 14% 25% 14% 4	3660
September	1st to 10th	Night	45% 15% 22% 13% 5%	2090
	11th to 20th	Night	45% 11% 21% 17% 5% 1	2090
	21st to end	Night	36% 9% 17% 20% 14% 4	2090
October	1st to 10th	Night	50% 8% 11% 13% 11% 7%	3480
	11th to 20th	Night	20% 4 6% 23% 33% 14%	3647
	21st to end	Night	21% 5% 7% 22% 35% 10%	4120
November	1st to 10th	Night	29% 6% 10% 23% 21% 12%	2341
	11th to 20th	Night	33% 4 8% 20% 22% 13%	2500
	21st to end	Night	34% 6% 10% 20% 21% 10%	2600
December	1st to 10th	Night	29% 5% 10% 20% 20% 16%	4250
	11th to 20th	Night	36% 6% 11% 18% 19% 10%	4824
	21st to end	Night	41% 5% 10% 20% 18% 6%	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	12% 21% 48% 15% 4	300
	11th to 20th	Day	16% 15% 45% 17% 6% 2	300
	21st to end	Day	17% 24% 43% 13% 2	330
February	1st to 10th	Day	13% 17% 40% 21% 8% 1	300
	11th to 20th	Day	18% 16% 41% 19% 4 1	300
	21st to end	Day	10% 22% 45% 18% 5% 1	249
March	1st to 10th	Day	13% 20% 35% 21% 10% 1	473
	11th to 20th	Day	15% 15% 35% 22% 12% 2	500
	21st to end	Day	12% 16% 33% 28% 10% 1	550
April	1st to 10th	Day	14% 14% 34% 25% 13% 1	500
	11th to 20th	Day	14% 11% 32% 29% 13% 1	492
	21st to end	Day	6% 6% 32% 36% 15% 6%	500
May	1st to 10th	Day	6% 9% 31% 31% 17% 7%	503
	11th to 20th	Day	9% 5% 21% 35% 18% 11%	527
	21st to end	Day	8% 3 16% 32% 28% 14%	573
June	1st to 10th	Day	11% 3 16% 32% 24% 15%	530
	11th to 20th	Day	6% 3 15% 30% 26% 19%	530
	21st to end	Day	7% 2 8% 31% 31% 22%	530
July	1st to 10th	Day	7% 1 8% 25% 30% 29%	525
	11th to 20th	Day	6% 1 3 26% 36% 27%	524
	21st to end	Day	7% 2 6% 23% 36% 25%	532
August	1st to 10th	Day	14% 3 5% 23% 31% 24%	486
	11th to 20th	Day	10% 2 5% 19% 37% 28%	479
	21st to end	Day	9% 2 6% 27% 33% 23%	539
September	1st to 10th	Day	14% 5% 7% 23% 33% 19%	490
	11th to 20th	Day	11% 3 11% 33% 29% 13%	490
	21st to end	Day	10% 3 12% 28% 35% 13%	490
October	1st to 10th	Day	14% 5% 26% 30% 19% 6%	490
	11th to 20th	Day	5% 7% 22% 36% 23% 6%	490
	21st to end	Day	8% 5% 26% 40% 18% 3	539
November	1st to 10th	Day	10% 5% 29% 35% 18% 3	495
	11th to 20th	Day	14% 8% 33% 31% 13% 2	395
	21st to end	Day	9% 11% 40% 29% 10% 1	300
December	1st to 10th	Day	9% 18% 37% 24% 10% 3	300
	11th to 20th	Day	15% 13% 38% 25% 9%	300
	21st to end	Day	14% 10% 41% 24% 10% 2	330
January	1st to 10th	Night	16% 15% 32% 28% 9% 1	800
	11th to 20th	Night	13% 12% 27% 33% 15% 1	800
	21st to end	Night	20% 12% 33% 28% 7%	880
February	1st to 10th	Night	15% 10% 29% 33% 12% 1	800
	11th to 20th	Night	15% 12% 31% 31% 9% 1	783
	21st to end	Night	14% 11% 28% 40% 6%	660
March	1st to 10th	Night	11% 12% 34% 33% 10% 1	800
	11th to 20th	Night	13% 10% 26% 36% 15% 1	800
	21st to end	Night	10% 10% 31% 36% 13% 1	880
April	1st to 10th	Night	13% 9% 26% 36% 16% 1	800
	11th to 20th	Night	9% 9% 28% 37% 16%	791
	21st to end	Night	6% 4 24% 40% 24% 2	615
May	1st to 10th	Night	7% 4 18% 43% 25% 3	600
	11th to 20th	Night	8% 3 18% 37% 29% 5%	591
	21st to end	Night	6% 2 10% 34% 40% 8%	650
June	1st to 10th	Night	12% 2 9% 33% 35% 9%	600
	11th to 20th	Night	5% 2 7% 28% 37% 22%	600
	21st to end	Night	8% 2 7% 21% 41% 22%	600
July	1st to 10th	Night	5% 2 5% 17% 43% 28%	585
	11th to 20th	Night	5% 2 2 12% 47% 32%	582
	21st to end	Night	4 1 2 16% 51% 26%	624
August	1st to 10th	Night	9% 2 2 16% 47% 24%	567
	11th to 20th	Night	5% 2 2 13% 51% 26%	564
	21st to end	Night	9% 3 6% 25% 40% 17%	733
September	1st to 10th	Night	10% 4 7% 22% 39% 17%	760
	11th to 20th	Night	12% 5% 10% 30% 34% 10%	760
	21st to end	Night	12% 3 12% 31% 35% 8%	760
October	1st to 10th	Night	13% 4 19% 37% 24% 3	760
	11th to 20th	Night	7% 5% 21% 37% 26% 3	760
	21st to end	Night	9% 4 24% 39% 21% 2	836
November	1st to 10th	Night	9% 6% 28% 37% 17% 3	780
	11th to 20th	Night	11% 7% 30% 37% 15% 1	800
	21st to end	Night	11% 7% 30% 36% 16% 1	800
December	1st to 10th	Night	13% 7% 27% 32% 18% 2	800
	11th to 20th	Night	15% 11% 26% 33% 15% 1	800
	21st to end	Night	13% 10% 30% 32% 14% 1	880

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