Nassau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nassau clear sky chart from 2005-11-06 to 2024-11-28.

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	35% 11% 22% 22% 9% 1	104902
	Night	35% 10% 21% 23% 9% 1	102680
Seeing	Day	7% 2 9% 25% 38% 19%	17374
	Night	8% 2 9% 26% 39% 17%	27454

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	33% 11% 17% 26% 12% 1	3156
	11th to 20th	Day	45% 9% 16% 22% 7% 1	3160
	21st to end	Day	36% 10% 14% 23% 15% 2	3476
February	1st to 10th	Day	30% 6% 11% 31% 20% 2	1900
	11th to 20th	Day	27% 6% 15% 28% 22% 3	1977
	21st to end	Day	22% 4 10% 30% 29% 4	1727
March	1st to 10th	Day	35% 14% 16% 22% 12% 1	3435
	11th to 20th	Day	18% 6% 22% 41% 11% 2	3480
	21st to end	Day	24% 7% 11% 31% 24% 4	3815
April	1st to 10th	Day	20% 6% 19% 40% 13% 2	2206
	11th to 20th	Day	28% 7% 22% 28% 13% 1	2254
	21st to end	Day	27% 7% 19% 29% 16% 2	2280
May	1st to 10th	Day	16% 9% 17% 38% 20% 2	3800
	11th to 20th	Day	31% 12% 27% 27% 3	3768
	21st to end	Day	30% 11% 19% 32% 8%	4140
June	1st to 10th	Day	60% 11% 19% 8% 1	2280
	11th to 20th	Day	47% 14% 22% 15% 1	2280
	21st to end	Day	44% 15% 32% 9%	2370
July	1st to 10th	Day	32% 13% 41% 14%	3997
	11th to 20th	Day	36% 14% 38% 13%	3736
	21st to end	Day	27% 16% 44% 13%	3988
August	1st to 10th	Day	39% 14% 33% 13% 1	3774
	11th to 20th	Day	28% 13% 35% 23% 1	3766
	21st to end	Day	43% 17% 31% 9% 1	4180
September	1st to 10th	Day	42% 16% 29% 11% 1	2280
	11th to 20th	Day	39% 16% 27% 16% 2	2278
	21st to end	Day	46% 13% 23% 15% 3	1981
October	1st to 10th	Day	43% 9% 28% 17% 3	3160
	11th to 20th	Day	53% 12% 13% 17% 6%	3140
	21st to end	Day	37% 6% 13% 28% 12% 2	3428
November	1st to 10th	Day	37% 7% 13% 26% 16% 2	1957
	11th to 20th	Day	44% 7% 14% 21% 11% 3	2000
	21st to end	Day	33% 9% 16% 24% 16% 2	1970
December	1st to 10th	Day	30% 6% 17% 31% 16%	1900
	11th to 20th	Day	38% 7% 11% 22% 18% 5%	2387
	21st to end	Day	40% 10% 15% 19% 14% 1	3476
January	1st to 10th	Night	36% 9% 14% 26% 15% 1	3790
	11th to 20th	Night	44% 9% 17% 22% 7% 1	3800
	21st to end	Night	43% 11% 12% 22% 11% 1	4180
February	1st to 10th	Night	30% 7% 12% 31% 18% 2	2280
	11th to 20th	Night	29% 6% 12% 28% 21% 4	2095
	21st to end	Night	22% 6% 12% 29% 27% 4	1727
March	1st to 10th	Night	35% 11% 16% 23% 14% 1	3418
	11th to 20th	Night	19% 7% 19% 41% 13% 1	3480
	21st to end	Night	24% 7% 10% 34% 22% 4	3817
April	1st to 10th	Night	19% 7% 18% 40% 14% 3	1971
	11th to 20th	Night	29% 7% 21% 26% 15% 2	1875
	21st to end	Night	30% 7% 14% 30% 16% 3	1900
May	1st to 10th	Night	19% 8% 18% 34% 19% 2	3160
	11th to 20th	Night	29% 9% 24% 32% 5%	3131
	21st to end	Night	30% 9% 21% 31% 9%	3435
June	1st to 10th	Night	57% 11% 20% 10% 3	1900
	11th to 20th	Night	46% 14% 24% 15% 1	1900
	21st to end	Night	39% 13% 35% 13%	1807
July	1st to 10th	Night	31% 15% 39% 16% 1	2795
	11th to 20th	Night	31% 13% 40% 16%	3096
	21st to end	Night	21% 15% 45% 18% 1	3326
August	1st to 10th	Night	36% 14% 35% 13% 2	3131
	11th to 20th	Night	26% 13% 32% 26% 2	3127
	21st to end	Night	38% 15% 37% 9% 1	3476
September	1st to 10th	Night	37% 15% 31% 15% 1	1900
	11th to 20th	Night	38% 13% 31% 16% 2	1900
	21st to end	Night	45% 14% 24% 15% 3	2191
October	1st to 10th	Night	39% 10% 28% 20% 2 1	3800
	11th to 20th	Night	55% 11% 14% 15% 5% 1	3779
	21st to end	Night	41% 7% 11% 26% 13% 2	4120
November	1st to 10th	Night	42% 9% 12% 23% 13% 1	2341
	11th to 20th	Night	49% 7% 11% 20% 11% 3	2400
	21st to end	Night	37% 10% 14% 21% 16% 2	2365
December	1st to 10th	Night	33% 8% 14% 28% 16%	2280
	11th to 20th	Night	42% 8% 10% 23% 16% 2	2807
	21st to end	Night	49% 8% 13% 18% 11% 1	4180

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 16% 32% 35% 6%	460
	11th to 20th	Day	9% 6% 19% 33% 28% 5%	460
	21st to end	Day	5% 6% 19% 44% 25% 1	506
February	1st to 10th	Day	6% 5% 16% 37% 35% 2	460
	11th to 20th	Day	5% 2 16% 36% 36% 6%	456
	21st to end	Day	6% 2 13% 34% 38% 6%	382
March	1st to 10th	Day	4 3 22% 43% 25% 3	460
	11th to 20th	Day	4 2 17% 38% 36% 3	460
	21st to end	Day	5% 2 15% 37% 35% 7%	506
April	1st to 10th	Day	4 2 9% 45% 37% 3	460
	11th to 20th	Day	6% 2 10% 47% 32% 2	452
	21st to end	Day	5% 2 7% 42% 40% 3	460
May	1st to 10th	Day	6% 1 6% 30% 49% 7%	463
	11th to 20th	Day	13% 1 8% 33% 40% 6%	487
	21st to end	Day	9% 3 4 17% 48% 19%	529
June	1st to 10th	Day	13% 2 5% 21% 43% 16%	490
	11th to 20th	Day	9% 1 4 14% 36% 36%	490
	21st to end	Day	3 1 3 7% 41% 45%	490
July	1st to 10th	Day	3 1 2 8% 41% 46%	485
	11th to 20th	Day	4 7% 47% 41%	484
	21st to end	Day	3 1 3 8% 41% 44%	532
August	1st to 10th	Day	5% 1 6% 49% 39%	486
	11th to 20th	Day	3 2 6% 39% 49%	479
	21st to end	Day	8% 3 12% 42% 36%	539
September	1st to 10th	Day	6% 1 4 7% 35% 47%	490
	11th to 20th	Day	5% 1 1 9% 30% 53%	490
	21st to end	Day	8% 1 4 12% 38% 37%	490
October	1st to 10th	Day	10% 1 5% 21% 43% 19%	490
	11th to 20th	Day	12% 2 6% 22% 38% 20%	490
	21st to end	Day	12% 2 9% 28% 40% 9%	539
November	1st to 10th	Day	6% 2 12% 29% 39% 11%	495
	11th to 20th	Day	8% 3 10% 29% 39% 10%	500
	21st to end	Day	6% 2 14% 34% 36% 8%	488
December	1st to 10th	Day	7% 2 12% 32% 39% 9%	460
	11th to 20th	Day	10% 3 13% 29% 40% 7%	460
	21st to end	Day	8% 3 15% 31% 37% 6%	506
January	1st to 10th	Night	8% 3 13% 33% 37% 6%	760
	11th to 20th	Night	10% 3 14% 38% 33% 2	760
	21st to end	Night	6% 5% 19% 38% 31% 2	836
February	1st to 10th	Night	7% 4 14% 41% 32% 2	760
	11th to 20th	Night	5% 4 16% 38% 34% 3	743
	21st to end	Night	4 2 10% 38% 42% 4	628
March	1st to 10th	Night	6% 3 20% 41% 28% 3	760
	11th to 20th	Night	3 2 12% 42% 36% 4	760
	21st to end	Night	6% 1 13% 41% 33% 5%	836
April	1st to 10th	Night	2 1 8% 45% 42% 3	760
	11th to 20th	Night	6% 2 10% 40% 40% 2	751
	21st to end	Night	5% 1 9% 46% 38% 1	760
May	1st to 10th	Night	5% 1 6% 31% 47% 10%	760
	11th to 20th	Night	12% 2 9% 35% 38% 5%	749
	21st to end	Night	12% 3 6% 16% 47% 15%	822
June	1st to 10th	Night	14% 3 5% 19% 43% 15%	760
	11th to 20th	Night	7% 1 3 11% 45% 33%	760
	21st to end	Night	5% 3 9% 45% 37%	667
July	1st to 10th	Night	5% 1 2 6% 44% 43%	555
	11th to 20th	Night	7% 2 9% 44% 37%	732
	21st to end	Night	3 1 7% 39% 49%	831
August	1st to 10th	Night	5% 1 2 8% 44% 40%	757
	11th to 20th	Night	3 2 9% 39% 47%	750
	21st to end	Night	8% 1 3 11% 44% 34%	836
September	1st to 10th	Night	5% 1 4 8% 33% 49%	760
	11th to 20th	Night	5% 1 2 8% 33% 51%	760
	21st to end	Night	8% 1 3 13% 37% 38%	760
October	1st to 10th	Night	13% 1 5% 16% 43% 22%	760
	11th to 20th	Night	13% 2 6% 22% 39% 20%	760
	21st to end	Night	14% 2 10% 27% 35% 11%	836
November	1st to 10th	Night	10% 3 15% 30% 35% 8%	780
	11th to 20th	Night	12% 3 11% 29% 38% 8%	800
	21st to end	Night	8% 2 14% 35% 35% 6%	789
December	1st to 10th	Night	7% 1 10% 31% 45% 6%	760
	11th to 20th	Night	11% 2 13% 29% 39% 6%	760
	21st to end	Night	8% 4 14% 31% 35% 8%	836

Page generated at 2024-11-25 00:22:21. Version ac07

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