Amagansett
Clear Sky Chart
History

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

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	17% 8% 2 6% 4 4 4 3 5% 7% 42%	119500
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	119274
Transparency	Day	26% 41% 8% 14% 10% 2	123090
	Night	27% 40% 7% 14% 10% 2	123845
Seeing	Day	18% 9% 25% 29% 15% 3	15967
	Night	20% 10% 27% 27% 13% 2	24981

By Month

Percentage Cloud Cover NE (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	13% 7% 2 5% 4 4 3 3 6% 6% 47%	3597
	11th to 20th	Day	17% 7% 2 5% 4 3 4 3 5% 5% 46%	3570
	21st to end	Day	19% 8% 3 7% 4 4 4 2 4 4 40%	4021
February	1st to 10th	Day	17% 8% 3 6% 5% 4 5% 4 6% 7% 35%	1940
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 3 5% 5% 43%	1948
	21st to end	Day	19% 9% 2 5% 3 3 3 4 5% 7% 39%	1650
March	1st to 10th	Day	20% 8% 2 5% 3 2 2 2 4 6% 46%	4476
	11th to 20th	Day	13% 10% 2 4 3 3 3 3 6% 7% 46%	4694
	21st to end	Day	21% 10% 2 5% 4 4 4 3 5% 5% 39%	5896
April	1st to 10th	Day	19% 8% 2 5% 4 3 4 4 4 7% 41%	2400
	11th to 20th	Day	18% 7% 2 4 4 3 3 3 5% 7% 44%	2374
	21st to end	Day	18% 6% 2 5% 4 4 4 4 6% 6% 42%	2540
May	1st to 10th	Day	26% 10% 3 6% 4 3 3 3 5% 8% 29%	5886
	11th to 20th	Day	20% 10% 3 7% 3 3 2 2 4 6% 39%	5938
	21st to end	Day	18% 9% 2 6% 3 3 3 3 5% 8% 38%	6949
June	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 6% 8% 40%	2800
	11th to 20th	Day	14% 7% 2 5% 3 4 4 4 6% 8% 42%	2800
	21st to end	Day	12% 6% 1 5% 4 4 4 4 6% 9% 44%	2800
July	1st to 10th	Day	13% 9% 3 8% 4 4 4 4 6% 8% 36%	4510
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 4 7% 9% 42%	4440
	21st to end	Day	18% 7% 3 6% 4 4 4 4 6% 7% 37%	4814
August	1st to 10th	Day	17% 6% 3 6% 4 4 4 3 6% 8% 37%	4147
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 5% 9% 46%	3804
	21st to end	Day	7% 3 2 5% 4 5% 5% 4 6% 8% 52%	4180
September	1st to 10th	Day	13% 6% 2 5% 4 3 3 3 5% 7% 47%	2280
	11th to 20th	Day	12% 5% 2 5% 2 3 3 3 4 7% 53%	2113
	21st to end	Day	20% 7% 2 5% 4 4 4 4 4 6% 41%	2090
October	1st to 10th	Day	21% 5% 2 4 3 3 3 4 4 6% 44%	2090
	11th to 20th	Day	15% 5% 2 6% 4 3 3 3 5% 7% 48%	1883
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 6% 42%	1881
November	1st to 10th	Day	16% 6% 1 5% 4 4 4 3 4 6% 48%	1761
	11th to 20th	Day	16% 7% 2 4 3 3 4 4 5% 6% 47%	1800
	21st to end	Day	16% 8% 2 6% 3 3 4 4 5% 6% 41%	1800
December	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 4 6% 45%	2682
	11th to 20th	Day	21% 8% 3 5% 3 2 2 2 4 5% 45%	2986
	21st to end	Day	19% 11% 4 8% 4 4 3 2 4 5% 37%	3960
January	1st to 10th	Night	14% 6% 2 6% 4 4 3 3 5% 6% 48%	6349
	11th to 20th	Night	16% 9% 3 7% 4 4 4 2 4 4 43%	6315
	21st to end	Night	18% 9% 4 7% 4 4 5% 3 6% 7% 34%	6932
February	1st to 10th	Night	17% 9% 3 7% 4 4 4 3 5% 6% 37%	2458
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 6% 7% 38%	2338
	21st to end	Night	20% 7% 2 6% 5% 4 4 4 6% 5% 38%	1980
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 6% 40%	5364
	11th to 20th	Night	16% 11% 3 6% 4 3 4 3 4 6% 40%	5264
	21st to end	Night	21% 9% 2 5% 3 4 5% 3 5% 6% 36%	5020
April	1st to 10th	Night	20% 7% 3 5% 4 4 5% 3 5% 6% 38%	2000
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 6% 42%	1975
	21st to end	Night	20% 9% 2 6% 4 3 3 3 5% 8% 39%	1860
May	1st to 10th	Night	25% 12% 4 7% 4 3 3 3 4 7% 27%	4054
	11th to 20th	Night	25% 11% 3 5% 3 4 4 3 5% 7% 31%	3997
	21st to end	Night	21% 10% 3 7% 4 4 4 4 6% 7% 31%	3926
June	1st to 10th	Night	17% 7% 3 6% 5% 4 4 4 5% 6% 38%	1600
	11th to 20th	Night	19% 6% 2 4 4 3 4 3 6% 9% 40%	1600
	21st to end	Night	13% 7% 3 7% 5% 4 3 5% 6% 9% 39%	1600
July	1st to 10th	Night	15% 12% 4 7% 4 4 4 4 7% 7% 31%	2560
	11th to 20th	Night	13% 7% 2 6% 6% 4 5% 5% 7% 10% 35%	2520
	21st to end	Night	19% 9% 3 6% 5% 5% 4 3 5% 7% 34%	2739
August	1st to 10th	Night	21% 8% 3 7% 4 5% 4 5% 6% 7% 30%	2752
	11th to 20th	Night	9% 5% 3 7% 5% 4 5% 5% 7% 9% 41%	3019
	21st to end	Night	8% 4 2 4 3 4 4 4 5% 8% 55%	3476
September	1st to 10th	Night	15% 7% 2 5% 4 4 5% 4 5% 6% 43%	1900
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 7% 50%	2066
	21st to end	Night	17% 7% 3 8% 4 5% 4 3 4 6% 39%	2090
October	1st to 10th	Night	20% 7% 2 6% 5% 3 4 2 3 6% 40%	2090
	11th to 20th	Night	16% 5% 2 6% 3 3 2 4 5% 7% 46%	2291
	21st to end	Night	20% 7% 3 7% 4 3 4 3 4 6% 40%	2717
November	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 5% 6% 46%	2537
	11th to 20th	Night	19% 7% 3 5% 3 4 4 3 4 6% 43%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 7% 44%	2600
December	1st to 10th	Night	16% 8% 4 7% 5% 4 4 3 4 5% 41%	4481
	11th to 20th	Night	24% 9% 2 6% 3 3 3 2 4 4 40%	5208
	21st to end	Night	18% 10% 3 6% 4 3 3 2 4 6% 41%	6996

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	28% 27% 6% 22% 17% 1	3598
	11th to 20th	Day	26% 29% 8% 17% 14% 6%	3600
	21st to end	Day	37% 29% 7% 15% 11% 1	4021
February	1st to 10th	Day	19% 63% 7% 7% 4	1940
	11th to 20th	Day	19% 60% 3 9% 8% 1	1957
	21st to end	Day	16% 62% 6% 8% 6% 2	1650
March	1st to 10th	Day	31% 30% 9% 10% 11% 9%	4479
	11th to 20th	Day	26% 30% 12% 22% 9% 1	4694
	21st to end	Day	36% 29% 7% 10% 15% 4	5896
April	1st to 10th	Day	20% 62% 4 7% 6% 1	2400
	11th to 20th	Day	15% 62% 4 9% 10%	2374
	21st to end	Day	16% 62% 4 9% 8% 1	2540
May	1st to 10th	Day	42% 32% 13% 8% 4 1	5897
	11th to 20th	Day	38% 29% 10% 14% 9% 1	5942
	21st to end	Day	35% 30% 8% 18% 9%	6949
June	1st to 10th	Day	17% 62% 4 9% 8% 1	2800
	11th to 20th	Day	16% 62% 4 10% 7% 1	2800
	21st to end	Day	13% 61% 5% 11% 9% 1	2800
July	1st to 10th	Day	33% 41% 6% 9% 11% 1	4440
	11th to 20th	Day	26% 40% 13% 13% 8%	4365
	21st to end	Day	32% 38% 9% 11% 9% 1	4661
August	1st to 10th	Day	32% 39% 11% 14% 4	4133
	11th to 20th	Day	22% 39% 11% 23% 4	3842
	21st to end	Day	14% 39% 11% 23% 12%	4180
September	1st to 10th	Day	16% 61% 5% 11% 7%	2280
	11th to 20th	Day	15% 61% 4 9% 10% 1	2113
	21st to end	Day	21% 60% 4 8% 6%	2090
October	1st to 10th	Day	20% 38% 8% 14% 17% 4	3480
	11th to 20th	Day	13% 38% 7% 16% 24% 2	3099
	21st to end	Day	17% 38% 11% 20% 13% 1	3081
November	1st to 10th	Day	18% 57% 7% 9% 8% 1	1761
	11th to 20th	Day	15% 57% 5% 11% 12% 2	1800
	21st to end	Day	17% 57% 6% 14% 5% 1	1800
December	1st to 10th	Day	25% 37% 10% 20% 8%	2682
	11th to 20th	Day	30% 32% 8% 13% 14% 3	2986
	21st to end	Day	38% 28% 5% 17% 10% 2	3960
January	1st to 10th	Night	26% 27% 7% 22% 16% 2	6349
	11th to 20th	Night	31% 27% 9% 15% 13% 4	6360
	21st to end	Night	38% 30% 8% 12% 10% 2	6932
February	1st to 10th	Night	18% 63% 5% 10% 3 1	2458
	11th to 20th	Night	18% 61% 3 9% 8% 1	2340
	21st to end	Night	19% 62% 3 8% 6% 2	1980
March	1st to 10th	Night	36% 30% 8% 12% 9% 6%	5374
	11th to 20th	Night	32% 30% 10% 18% 8% 2	5265
	21st to end	Night	37% 30% 4 7% 17% 4	5020
April	1st to 10th	Night	20% 62% 3 7% 6% 1	2000
	11th to 20th	Night	15% 63% 6% 7% 8% 1	1975
	21st to end	Night	19% 62% 3 8% 7% 1	1860
May	1st to 10th	Night	43% 31% 12% 9% 5% 1	4060
	11th to 20th	Night	41% 30% 10% 11% 5% 2	3998
	21st to end	Night	39% 32% 10% 14% 6% 1	3927
June	1st to 10th	Night	17% 62% 3 9% 9% 1	1600
	11th to 20th	Night	16% 62% 5% 10% 7%	1600
	21st to end	Night	16% 61% 4 11% 7% 1	1600
July	1st to 10th	Night	36% 39% 5% 11% 8%	2520
	11th to 20th	Night	27% 40% 12% 15% 5%	2472
	21st to end	Night	35% 37% 10% 8% 9%	2651
August	1st to 10th	Night	36% 40% 10% 10% 4 1	2742
	11th to 20th	Night	22% 41% 13% 18% 5%	3047
	21st to end	Night	12% 39% 10% 24% 15%	3476
September	1st to 10th	Night	15% 61% 5% 12% 6% 1	1900
	11th to 20th	Night	16% 60% 4 8% 10% 1	2066
	21st to end	Night	23% 61% 3 7% 6%	2090
October	1st to 10th	Night	24% 38% 7% 18% 11% 2	3480
	11th to 20th	Night	11% 37% 5% 16% 26% 4	3814
	21st to end	Night	16% 37% 10% 18% 17% 2	4467
November	1st to 10th	Night	18% 57% 6% 9% 9% 1	2537
	11th to 20th	Night	17% 57% 4 9% 10% 3	2600
	21st to end	Night	17% 57% 6% 13% 5% 1	2600
December	1st to 10th	Night	27% 36% 8% 20% 8% 1	4481
	11th to 20th	Night	34% 32% 6% 17% 10% 1	5208
	21st to end	Night	33% 28% 8% 14% 14% 3	6996

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	20% 23% 33% 20% 5% 1	200
	11th to 20th	Day	19% 25% 36% 18% 3	200
	21st to end	Day	21% 16% 39% 15% 8% 1	232
February	1st to 10th	Day	21% 15% 37% 23% 4	440
	11th to 20th	Day	25% 19% 35% 20% 2	496
	21st to end	Day	22% 16% 34% 24% 4	414
March	1st to 10th	Day	19% 15% 37% 24% 5%	500
	11th to 20th	Day	16% 14% 40% 24% 6% 1	500
	21st to end	Day	21% 13% 37% 20% 8% 1	550
April	1st to 10th	Day	24% 11% 32% 23% 8% 1	500
	11th to 20th	Day	20% 12% 31% 28% 9% 1	492
	21st to end	Day	21% 9% 28% 32% 9% 2	500
May	1st to 10th	Day	25% 9% 28% 28% 10% 1	503
	11th to 20th	Day	19% 5% 29% 34% 13% 1	527
	21st to end	Day	17% 5% 20% 31% 21% 6%	573
June	1st to 10th	Day	16% 4 20% 34% 22% 4	530
	11th to 20th	Day	15% 4 19% 37% 22% 4	530
	21st to end	Day	14% 3 17% 37% 24% 4	530
July	1st to 10th	Day	14% 3 13% 35% 29% 6%	505
	11th to 20th	Day	8% 4 10% 40% 30% 9%	484
	21st to end	Day	13% 2 17% 41% 24% 3	532
August	1st to 10th	Day	11% 4 14% 33% 31% 6%	486
	11th to 20th	Day	14% 3 11% 34% 30% 8%	479
	21st to end	Day	10% 3 18% 33% 26% 11%	539
September	1st to 10th	Day	19% 3 17% 29% 22% 10%	490
	11th to 20th	Day	14% 3 22% 26% 24% 10%	490
	21st to end	Day	24% 4 23% 30% 16% 3	490
October	1st to 10th	Day	24% 7% 19% 24% 19% 7%	490
	11th to 20th	Day	16% 8% 27% 29% 17% 3	465
	21st to end	Day	23% 10% 27% 27% 10% 3	429
November	1st to 10th	Day	16% 10% 27% 30% 14% 3	395
	11th to 20th	Day	21% 16% 30% 25% 8%	400
	21st to end	Day	19% 18% 30% 24% 9% 1	400
December	1st to 10th	Day	20% 17% 35% 19% 9%	256
	11th to 20th	Day	24% 21% 31% 21% 4	200
	21st to end	Day	23% 14% 33% 20% 9% 2	220
January	1st to 10th	Night	21% 20% 36% 18% 5%	800
	11th to 20th	Night	27% 17% 31% 20% 4	800
	21st to end	Night	20% 18% 38% 21% 3	880
February	1st to 10th	Night	22% 14% 39% 22% 2	800
	11th to 20th	Night	25% 20% 37% 16% 2	783
	21st to end	Night	23% 18% 34% 20% 6%	660
March	1st to 10th	Night	22% 15% 34% 23% 6%	800
	11th to 20th	Night	21% 11% 35% 26% 6% 2	800
	21st to end	Night	21% 11% 36% 24% 8% 1	880
April	1st to 10th	Night	24% 9% 30% 30% 6% 1	800
	11th to 20th	Night	20% 9% 31% 30% 9% 1	791
	21st to end	Night	21% 5% 30% 33% 11% 1	660
May	1st to 10th	Night	22% 8% 25% 32% 12% 2	600
	11th to 20th	Night	22% 5% 29% 33% 10% 1	582
	21st to end	Night	23% 2 15% 33% 24% 3	433
June	1st to 10th	Night	18% 4 20% 33% 23% 2	400
	11th to 20th	Night	20% 4 15% 35% 24% 2	400
	21st to end	Night	15% 3 15% 38% 27% 2	400
July	1st to 10th	Night	13% 4 14% 38% 29% 3	380
	11th to 20th	Night	12% 3 13% 38% 30% 5%	368
	21st to end	Night	15% 2 13% 44% 24% 3	416
August	1st to 10th	Night	9% 1 13% 45% 28% 4	520
	11th to 20th	Night	12% 2 11% 37% 32% 5%	696
	21st to end	Night	13% 3 13% 35% 29% 8%	836
September	1st to 10th	Night	16% 3 18% 32% 25% 6%	760
	11th to 20th	Night	16% 4 17% 31% 23% 9%	760
	21st to end	Night	20% 5% 23% 30% 18% 3	760
October	1st to 10th	Night	24% 6% 22% 25% 18% 5%	760
	11th to 20th	Night	21% 9% 27% 28% 13% 3	760
	21st to end	Night	24% 10% 31% 23% 11% 2	836
November	1st to 10th	Night	16% 11% 30% 27% 13% 3	780
	11th to 20th	Night	23% 16% 30% 22% 9% 1	800
	21st to end	Night	18% 19% 30% 26% 7% 1	800
December	1st to 10th	Night	25% 17% 31% 21% 6% 1	800
	11th to 20th	Night	24% 20% 30% 21% 5% 1	800
	21st to end	Night	24% 16% 34% 21% 4	880

Page generated at 2025-07-03 01:30:18. Version ac07

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