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 2026-02-01.

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	33% 10% 23% 24% 10% 1	131215
	Night	33% 9% 21% 25% 10% 1	128811
Seeing	Day	6% 2 9% 25% 38% 19%	19094
	Night	7% 2 9% 26% 39% 17%	29159

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	30% 9% 15% 32% 14%	4616
	11th to 20th	Day	39% 8% 18% 26% 7% 1	4620
	21st to end	Day	31% 8% 13% 32% 14% 1	5082
February	1st to 10th	Day	30% 6% 12% 31% 20% 2	2000
	11th to 20th	Day	26% 6% 14% 29% 23% 3	2084
	21st to end	Day	23% 5% 10% 30% 28% 4	1815
March	1st to 10th	Day	28% 10% 14% 26% 21% 1	4935
	11th to 20th	Day	16% 4 17% 33% 20% 9%	4980
	21st to end	Day	25% 7% 12% 34% 19% 3	5465
April	1st to 10th	Day	20% 6% 18% 39% 14% 3	2322
	11th to 20th	Day	27% 7% 21% 26% 15% 3	2374
	21st to end	Day	26% 7% 18% 30% 18% 2	2400
May	1st to 10th	Day	16% 8% 21% 37% 17% 1	5437
	11th to 20th	Day	29% 10% 25% 33% 4	5408
	21st to end	Day	24% 9% 26% 34% 7%	5944
June	1st to 10th	Day	59% 11% 20% 9% 1	2400
	11th to 20th	Day	45% 14% 23% 16% 2	2400
	21st to end	Day	43% 14% 33% 10%	2495
July	1st to 10th	Day	37% 14% 39% 10%	5749
	11th to 20th	Day	34% 14% 38% 14%	5376
	21st to end	Day	25% 13% 41% 19% 2	5754
August	1st to 10th	Day	38% 14% 33% 13% 1	3894
	11th to 20th	Day	27% 12% 35% 24% 1	3886
	21st to end	Day	42% 17% 32% 9% 1	4312
September	1st to 10th	Day	42% 16% 30% 11% 1	2400
	11th to 20th	Day	40% 16% 27% 15% 2	2398
	21st to end	Day	46% 14% 23% 14% 3	2085
October	1st to 10th	Day	43% 9% 28% 17% 3	3260
	11th to 20th	Day	52% 11% 13% 16% 6%	3240
	21st to end	Day	37% 6% 14% 28% 12% 3	3538
November	1st to 10th	Day	37% 7% 14% 25% 15% 2	2057
	11th to 20th	Day	43% 7% 14% 21% 13% 2	2100
	21st to end	Day	32% 8% 16% 25% 18% 2	2100
December	1st to 10th	Day	25% 5% 14% 38% 17%	3360
	11th to 20th	Day	41% 9% 14% 20% 13% 3	3847
	21st to end	Day	38% 10% 19% 20% 13% 1	5082
January	1st to 10th	Night	31% 8% 13% 33% 15% 1	5550
	11th to 20th	Night	38% 8% 18% 28% 7% 1	5560
	21st to end	Night	38% 10% 12% 27% 12% 1	6116
February	1st to 10th	Night	30% 6% 12% 32% 19% 2	2401
	11th to 20th	Night	28% 6% 12% 28% 22% 4	2208
	21st to end	Night	23% 6% 12% 28% 27% 4	1815
March	1st to 10th	Night	29% 9% 14% 26% 20% 2	4918
	11th to 20th	Night	17% 5% 14% 33% 24% 7%	4980
	21st to end	Night	27% 7% 10% 31% 21% 3	5467
April	1st to 10th	Night	18% 7% 17% 38% 16% 3	2075
	11th to 20th	Night	28% 7% 20% 25% 16% 4	1975
	21st to end	Night	29% 7% 13% 30% 18% 3	2000
May	1st to 10th	Night	17% 7% 22% 35% 17% 1	4520
	11th to 20th	Night	30% 8% 22% 36% 4	4491
	21st to end	Night	22% 7% 30% 33% 7%	4931
June	1st to 10th	Night	56% 10% 20% 11% 3	2000
	11th to 20th	Night	44% 14% 24% 16% 3	2000
	21st to end	Night	38% 13% 35% 13%	1902
July	1st to 10th	Night	32% 15% 40% 12%	4015
	11th to 20th	Night	28% 13% 42% 17%	4456
	21st to end	Night	19% 13% 42% 23% 2	4785
August	1st to 10th	Night	36% 14% 35% 14% 2	3231
	11th to 20th	Night	26% 13% 33% 27% 2	3227
	21st to end	Night	38% 15% 37% 9% 1	3586
September	1st to 10th	Night	37% 15% 31% 15% 1	2000
	11th to 20th	Night	38% 14% 31% 15% 2	2000
	21st to end	Night	45% 14% 23% 14% 3	2307
October	1st to 10th	Night	39% 10% 28% 20% 2 1	3920
	11th to 20th	Night	54% 11% 14% 14% 6% 1	3899
	21st to end	Night	40% 7% 11% 26% 14% 2	4252
November	1st to 10th	Night	42% 8% 12% 22% 14% 1	2461
	11th to 20th	Night	48% 6% 11% 20% 13% 2	2520
	21st to end	Night	36% 9% 14% 22% 16% 2	2520
December	1st to 10th	Night	25% 7% 13% 37% 17%	4040
	11th to 20th	Night	45% 10% 14% 20% 10% 1	4567
	21st to end	Night	44% 9% 17% 20% 9% 1	6116

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	6% 4 15% 33% 34% 7%	540
	11th to 20th	Day	9% 6% 19% 34% 27% 6%	540
	21st to end	Day	5% 6% 18% 45% 25% 1	594
February	1st to 10th	Day	6% 4 15% 34% 38% 3	500
	11th to 20th	Day	4 2 15% 34% 39% 6%	496
	21st to end	Day	6% 2 14% 35% 37% 6%	414
March	1st to 10th	Day	4 3 22% 43% 25% 3	500
	11th to 20th	Day	4 2 17% 39% 35% 3	500
	21st to end	Day	5% 2 15% 39% 34% 6%	550
April	1st to 10th	Day	4 2 9% 44% 38% 3	500
	11th to 20th	Day	6% 2 9% 48% 33% 2	492
	21st to end	Day	5% 2 7% 40% 42% 4	500
May	1st to 10th	Day	6% 1 5% 31% 50% 7%	503
	11th to 20th	Day	13% 1 7% 32% 41% 6%	527
	21st to end	Day	9% 3 4 16% 49% 20%	573
June	1st to 10th	Day	13% 2 5% 21% 42% 18%	530
	11th to 20th	Day	8% 1 3 14% 38% 35%	530
	21st to end	Day	3 1 3 7% 43% 43%	530
July	1st to 10th	Day	3 1 2 8% 41% 44%	525
	11th to 20th	Day	4 7% 48% 40%	524
	21st to end	Day	3 1 3 8% 41% 44%	576
August	1st to 10th	Day	5% 2 5% 48% 40%	526
	11th to 20th	Day	3 2 6% 40% 48%	519
	21st to end	Day	7% 3 11% 39% 39%	583
September	1st to 10th	Day	6% 1 4 7% 34% 48%	530
	11th to 20th	Day	5% 1 2 8% 31% 53%	530
	21st to end	Day	8% 1 5% 12% 36% 38%	530
October	1st to 10th	Day	10% 1 5% 20% 43% 22%	530
	11th to 20th	Day	12% 2 6% 22% 39% 20%	530
	21st to end	Day	11% 2 9% 30% 39% 9%	583
November	1st to 10th	Day	5% 3 12% 30% 40% 10%	535
	11th to 20th	Day	7% 3 10% 30% 39% 10%	540
	21st to end	Day	6% 2 13% 32% 38% 9%	540
December	1st to 10th	Day	6% 2 12% 31% 39% 10%	540
	11th to 20th	Day	9% 4 13% 31% 37% 6%	540
	21st to end	Day	7% 4 15% 32% 35% 7%	594
January	1st to 10th	Night	8% 3 13% 33% 37% 6%	840
	11th to 20th	Night	10% 4 14% 38% 33% 2	840
	21st to end	Night	6% 5% 18% 40% 30% 2	924
February	1st to 10th	Night	7% 4 13% 39% 34% 3	801
	11th to 20th	Night	5% 4 15% 37% 35% 3	783
	21st to end	Night	5% 2 10% 38% 40% 4	660
March	1st to 10th	Night	6% 3 20% 41% 28% 3	800
	11th to 20th	Night	3 2 13% 43% 36% 4	800
	21st to end	Night	6% 2 14% 42% 32% 4	880
April	1st to 10th	Night	2 1 8% 44% 43% 3	800
	11th to 20th	Night	5% 2 10% 40% 41% 2	791
	21st to end	Night	5% 1 9% 44% 41% 1	800
May	1st to 10th	Night	5% 1 6% 32% 47% 9%	800
	11th to 20th	Night	12% 2 8% 35% 38% 5%	789
	21st to end	Night	12% 3 6% 16% 49% 16%	866
June	1st to 10th	Night	14% 3 5% 19% 43% 16%	800
	11th to 20th	Night	7% 1 3 11% 46% 33%	800
	21st to end	Night	5% 3 9% 45% 36%	702
July	1st to 10th	Night	4 1 2 7% 44% 42%	585
	11th to 20th	Night	7% 2 9% 46% 37%	772
	21st to end	Night	4 1 7% 40% 48%	875
August	1st to 10th	Night	5% 1 2 7% 44% 41%	797
	11th to 20th	Night	3 2 9% 39% 47%	790
	21st to end	Night	8% 1 2 10% 42% 36%	880
September	1st to 10th	Night	5% 1 4 8% 32% 50%	800
	11th to 20th	Night	5% 1 2 8% 33% 52%	800
	21st to end	Night	7% 1 4 13% 37% 38%	800
October	1st to 10th	Night	12% 1 5% 16% 42% 24%	800
	11th to 20th	Night	12% 2 5% 21% 39% 20%	800
	21st to end	Night	14% 2 10% 29% 35% 11%	880
November	1st to 10th	Night	10% 3 14% 30% 36% 7%	820
	11th to 20th	Night	11% 3 11% 30% 38% 8%	840
	21st to end	Night	8% 2 13% 34% 37% 6%	840
December	1st to 10th	Night	7% 1 11% 30% 44% 7%	840
	11th to 20th	Night	11% 3 13% 30% 38% 5%	840
	21st to end	Night	8% 3 13% 32% 34% 9%	924

Page generated at 2026-01-29 01:21:46. Version ac07

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