Cat Island (South)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cat Island (South) clear sky chart from 2005-11-06 to 2025-09-19.

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
Transparency	Day	30% 13% 24% 23% 9% 1	129785
	Night	30% 12% 24% 24% 10% 1	127352
Seeing	Day	6% 2 9% 27% 41% 15%	18554
	Night	7% 2 9% 26% 41% 16%	28917

By Month

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	26% 11% 19% 33% 12%	4516
	11th to 20th	Day	26% 12% 23% 31% 8% 1	4520
	21st to end	Day	29% 10% 14% 28% 18% 1	4972
February	1st to 10th	Day	28% 7% 15% 27% 21% 1	2000
	11th to 20th	Day	26% 7% 14% 24% 27% 3	1957
	21st to end	Day	23% 6% 15% 27% 25% 5%	1698
March	1st to 10th	Day	25% 11% 21% 22% 19% 2	4935
	11th to 20th	Day	18% 7% 13% 31% 23% 8%	4980
	21st to end	Day	25% 9% 17% 29% 18% 3	5641
April	1st to 10th	Day	20% 7% 17% 41% 13% 2	2400
	11th to 20th	Day	26% 9% 23% 25% 14% 3	2374
	21st to end	Day	31% 11% 17% 27% 14% 1	2400
May	1st to 10th	Day	19% 9% 22% 36% 13% 2	5437
	11th to 20th	Day	27% 8% 24% 37% 3	5408
	21st to end	Day	29% 13% 26% 26% 6%	5944
June	1st to 10th	Day	58% 13% 18% 9% 1	2400
	11th to 20th	Day	44% 15% 23% 17% 2	2400
	21st to end	Day	41% 19% 32% 8%	2400
July	1st to 10th	Day	27% 16% 46% 10%	5380
	11th to 20th	Day	28% 18% 42% 12%	5376
	21st to end	Day	24% 17% 35% 22% 2	5754
August	1st to 10th	Day	30% 18% 39% 12% 1	3894
	11th to 20th	Day	21% 15% 34% 28% 2	3886
	21st to end	Day	38% 18% 32% 12%	4312
September	1st to 10th	Day	36% 16% 33% 14%	2400
	11th to 20th	Day	34% 19% 30% 15% 1	2313
	21st to end	Day	39% 21% 24% 15%	2090
October	1st to 10th	Day	39% 14% 26% 14% 6%	3480
	11th to 20th	Day	47% 20% 21% 9% 4	3154
	21st to end	Day	38% 10% 16% 25% 8% 2	3428
November	1st to 10th	Day	42% 9% 15% 20% 13% 1	1957
	11th to 20th	Day	44% 11% 14% 18% 13% 1	2000
	21st to end	Day	35% 10% 16% 24% 14% 2	2000
December	1st to 10th	Day	24% 8% 16% 38% 15%	3260
	11th to 20th	Day	34% 12% 18% 23% 10% 3	3747
	21st to end	Day	37% 13% 23% 18% 9% 1	4972
January	1st to 10th	Night	27% 9% 16% 35% 12%	5430
	11th to 20th	Night	25% 11% 23% 32% 9% 1	5440
	21st to end	Night	31% 10% 14% 24% 20% 1	5984
February	1st to 10th	Night	29% 8% 15% 27% 18% 2	2400
	11th to 20th	Night	23% 7% 14% 27% 28% 1	2340
	21st to end	Night	21% 5% 13% 28% 25% 8%	1925
March	1st to 10th	Night	24% 10% 21% 24% 17% 4	4918
	11th to 20th	Night	18% 6% 14% 31% 26% 5%	4980
	21st to end	Night	28% 7% 15% 28% 19% 3	5289
April	1st to 10th	Night	18% 8% 19% 35% 17% 2	2000
	11th to 20th	Night	28% 8% 18% 29% 14% 4	1975
	21st to end	Night	28% 9% 19% 27% 16% 1	2000
May	1st to 10th	Night	21% 11% 20% 34% 13% 1	4520
	11th to 20th	Night	28% 8% 22% 36% 7%	4491
	21st to end	Night	27% 10% 25% 32% 6%	4931
June	1st to 10th	Night	56% 13% 20% 10% 1	2000
	11th to 20th	Night	37% 18% 27% 17% 1	2000
	21st to end	Night	34% 18% 36% 12%	2000
July	1st to 10th	Night	27% 18% 43% 11%	4471
	11th to 20th	Night	26% 16% 44% 14%	4460
	21st to end	Night	23% 16% 37% 23% 1	4785
August	1st to 10th	Night	29% 16% 39% 15% 1	3231
	11th to 20th	Night	19% 13% 36% 30% 2	3227
	21st to end	Night	30% 16% 38% 15%	3586
September	1st to 10th	Night	30% 15% 34% 19% 1	2000
	11th to 20th	Night	30% 20% 32% 17% 2	2043
	21st to end	Night	35% 20% 25% 18% 2	2090
October	1st to 10th	Night	35% 14% 29% 16% 6%	3480
	11th to 20th	Night	48% 18% 22% 9% 3	3744
	21st to end	Night	43% 10% 16% 21% 8% 2	4120
November	1st to 10th	Night	44% 11% 13% 20% 11% 1	2341
	11th to 20th	Night	43% 11% 16% 18% 11% 1	2400
	21st to end	Night	37% 7% 18% 24% 12% 1	2400
December	1st to 10th	Night	26% 8% 15% 38% 13%	3920
	11th to 20th	Night	36% 11% 20% 22% 8% 2	4447
	21st to end	Night	43% 10% 19% 20% 7% 1	5984

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	7% 4 13% 38% 33% 6%	500
	11th to 20th	Day	8% 4 17% 38% 30% 3	500
	21st to end	Day	6% 5% 17% 42% 28% 3	550
February	1st to 10th	Day	3 6% 15% 36% 38% 2	500
	11th to 20th	Day	5% 2 15% 36% 38% 5%	496
	21st to end	Day	6% 4 14% 34% 38% 5%	414
March	1st to 10th	Day	4 3 22% 41% 28% 2	500
	11th to 20th	Day	4 2 14% 45% 34% 1	500
	21st to end	Day	5% 3 14% 43% 33% 3	550
April	1st to 10th	Day	4 1 7% 43% 40% 4	500
	11th to 20th	Day	4 2 13% 43% 36% 2	492
	21st to end	Day	6% 1 9% 45% 37% 2	500
May	1st to 10th	Day	6% 3 5% 34% 44% 9%	503
	11th to 20th	Day	13% 3 9% 29% 41% 5%	527
	21st to end	Day	10% 1 7% 19% 46% 18%	573
June	1st to 10th	Day	15% 5% 6% 18% 41% 15%	530
	11th to 20th	Day	8% 4 10% 47% 30%	530
	21st to end	Day	3 1 2 11% 53% 29%	530
July	1st to 10th	Day	1 1 10% 57% 31%	525
	11th to 20th	Day	1 2 13% 57% 26%	524
	21st to end	Day	5% 1 11% 53% 29%	576
August	1st to 10th	Day	2 2 11% 56% 28%	526
	11th to 20th	Day	2 2 8% 55% 33%	519
	21st to end	Day	5% 1 3 12% 50% 29%	583
September	1st to 10th	Day	6% 2 2 10% 37% 42%	530
	11th to 20th	Day	4 1 8% 41% 45%	522
	21st to end	Day	7% 3 13% 40% 38%	490
October	1st to 10th	Day	11% 1 4 17% 45% 22%	490
	11th to 20th	Day	12% 3 4 19% 41% 21%	490
	21st to end	Day	9% 2 8% 29% 42% 9%	539
November	1st to 10th	Day	9% 2 14% 30% 36% 8%	495
	11th to 20th	Day	7% 3 13% 30% 40% 8%	500
	21st to end	Day	7% 1 12% 40% 33% 8%	500
December	1st to 10th	Day	4 1 13% 35% 40% 8%	500
	11th to 20th	Day	7% 4 10% 35% 40% 4	500
	21st to end	Day	7% 3 18% 32% 34% 6%	550
January	1st to 10th	Night	6% 3 13% 34% 40% 5%	800
	11th to 20th	Night	8% 4 13% 39% 34% 3	800
	21st to end	Night	5% 3 15% 44% 31% 2	880
February	1st to 10th	Night	5% 4 16% 35% 39% 1	800
	11th to 20th	Night	6% 3 14% 39% 34% 4	783
	21st to end	Night	5% 2 12% 36% 40% 5%	660
March	1st to 10th	Night	7% 3 20% 36% 32% 3	800
	11th to 20th	Night	4 1 15% 42% 36% 2	800
	21st to end	Night	5% 2 14% 42% 34% 4	880
April	1st to 10th	Night	3 1 6% 45% 43% 2	800
	11th to 20th	Night	5% 2 10% 42% 37% 5%	791
	21st to end	Night	5% 1 10% 42% 41% 1	800
May	1st to 10th	Night	7% 1 7% 34% 45% 7%	800
	11th to 20th	Night	14% 3 6% 33% 38% 5%	789
	21st to end	Night	10% 3 8% 22% 44% 13%	866
June	1st to 10th	Night	15% 4 6% 19% 40% 16%	800
	11th to 20th	Night	7% 1 4 11% 47% 30%	800
	21st to end	Night	6% 1 3 10% 50% 31%	800
July	1st to 10th	Night	3 1 2 10% 50% 35%	781
	11th to 20th	Night	6% 3 11% 51% 29%	776
	21st to end	Night	3 2 10% 50% 35%	875
August	1st to 10th	Night	4 2 14% 51% 29%	797
	11th to 20th	Night	3 1 10% 44% 42%	790
	21st to end	Night	5% 1 3 10% 50% 31%	880
September	1st to 10th	Night	6% 1 3 8% 35% 46%	800
	11th to 20th	Night	5% 1 1 8% 35% 51%	793
	21st to end	Night	5% 3 13% 41% 38%	760
October	1st to 10th	Night	10% 1 5% 16% 44% 23%	760
	11th to 20th	Night	9% 2 6% 17% 42% 25%	760
	21st to end	Night	15% 2 9% 25% 36% 12%	836
November	1st to 10th	Night	11% 2 14% 31% 37% 6%	780
	11th to 20th	Night	8% 3 12% 26% 43% 8%	800
	21st to end	Night	9% 3 12% 35% 35% 6%	800
December	1st to 10th	Night	6% 3 12% 31% 41% 7%	800
	11th to 20th	Night	8% 4 11% 33% 40% 5%	800
	21st to end	Night	9% 3 14% 30% 37% 6%	880

Page generated at 2025-09-16 01:49:13. Version ac07

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