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 2026-10-29.

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	16% 7% 2 6% 4 4 4 3 5% 7% 42%	149071
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	142984
Transparency	Day	29% 34% 9% 16% 11% 1	152618
	Night	30% 34% 8% 15% 11% 2	147526
Seeing	Day	18% 9% 25% 29% 16% 3	17710
	Night	20% 11% 27% 27% 13% 2	26648

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	12% 8% 3 6% 4 4 4 3 6% 6% 44%	4661
	11th to 20th	Day	17% 7% 2 6% 4 3 4 3 4 5% 46%	4650
	21st to end	Day	17% 8% 3 6% 3 4 4 3 4 5% 44%	5199
February	1st to 10th	Day	17% 8% 3 6% 5% 4 5% 4 6% 7% 36%	2037
	11th to 20th	Day	15% 7% 2 6% 5% 4 4 3 5% 5% 43%	2048
	21st to end	Day	19% 9% 2 5% 3 3 3 4 5% 7% 39%	1730
March	1st to 10th	Day	20% 8% 2 5% 3 2 2 2 4 6% 45%	4576
	11th to 20th	Day	13% 10% 2 5% 3 3 3 3 6% 7% 46%	4798
	21st to end	Day	20% 10% 2 5% 4 4 4 3 5% 5% 39%	6026
April	1st to 10th	Day	19% 8% 2 5% 4 3 4 4 4 7% 41%	2520
	11th to 20th	Day	18% 7% 2 4 4 3 3 3 5% 7% 44%	2494
	21st to end	Day	18% 6% 2 5% 4 4 4 4 6% 6% 42%	2667
May	1st to 10th	Day	24% 10% 3 6% 4 3 3 3 4 7% 33%	7639
	11th to 20th	Day	18% 10% 2 6% 3 3 3 2 4 6% 42%	7716
	21st to end	Day	21% 9% 2 6% 3 3 4 3 5% 8% 35%	9060
June	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 6% 9% 42%	2940
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 9% 42%	2940
	21st to end	Day	12% 6% 1 5% 4 4 4 4 6% 9% 44%	2940
July	1st to 10th	Day	15% 8% 3 7% 4 4 4 4 6% 9% 37%	8280
	11th to 20th	Day	10% 7% 3 6% 4 4 4 4 7% 9% 41%	8280
	21st to end	Day	16% 6% 2 5% 3 3 3 3 5% 7% 45%	8993
August	1st to 10th	Day	14% 6% 3 7% 4 5% 4 4 7% 10% 36%	6072
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 5% 9% 48%	5607
	21st to end	Day	10% 4 2 5% 4 5% 5% 4 6% 8% 48%	6080
September	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 6% 8% 47%	2520
	11th to 20th	Day	12% 5% 2 5% 2 3 3 3 4 7% 53%	2335
	21st to end	Day	20% 7% 2 5% 4 4 5% 4 4 6% 39%	2310
October	1st to 10th	Day	20% 5% 2 4 3 3 3 4 4 6% 46%	2310
	11th to 20th	Day	16% 5% 2 5% 3 3 3 2 5% 7% 47%	2081
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 6% 44%	2052
November	1st to 10th	Day	15% 6% 1 5% 4 4 4 3 4 6% 48%	1851
	11th to 20th	Day	15% 6% 2 4 4 3 4 4 5% 6% 47%	1890
	21st to end	Day	16% 8% 2 6% 4 3 4 4 5% 6% 41%	1890
December	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 4 6% 45%	2765
	11th to 20th	Day	21% 8% 3 5% 3 2 2 2 4 5% 45%	3066
	21st to end	Day	19% 11% 4 8% 4 4 3 2 4 5% 37%	4048
January	1st to 10th	Night	14% 8% 3 6% 4 3 3 3 4 6% 46%	8234
	11th to 20th	Night	17% 9% 3 7% 4 4 4 3 4 4 42%	8235
	21st to end	Night	16% 9% 3 7% 5% 4 5% 4 6% 6% 36%	8979
February	1st to 10th	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 38%	2581
	11th to 20th	Night	19% 8% 2 5% 4 4 3 3 6% 7% 38%	2458
	21st to end	Night	20% 7% 3 6% 5% 4 4 4 6% 5% 38%	2076
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 6% 40%	5484
	11th to 20th	Night	16% 10% 3 6% 4 3 4 3 4 6% 41%	5380
	21st to end	Night	21% 9% 2 5% 3 5% 5% 3 5% 6% 36%	5132
April	1st to 10th	Night	20% 7% 3 5% 4 3 4 3 5% 6% 38%	2100
	11th to 20th	Night	16% 8% 3 6% 4 3 4 3 4 6% 43%	2075
	21st to end	Night	20% 8% 2 6% 4 3 3 3 5% 7% 39%	1953
May	1st to 10th	Night	23% 11% 4 7% 4 3 3 3 4 7% 32%	5259
	11th to 20th	Night	21% 10% 3 6% 3 4 4 3 5% 8% 34%	5199
	21st to end	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 29%	5114
June	1st to 10th	Night	17% 7% 2 6% 5% 4 4 3 5% 6% 40%	1680
	11th to 20th	Night	18% 6% 2 4 4 3 4 3 6% 9% 40%	1680
	21st to end	Night	13% 7% 3 7% 4 4 3 4 6% 9% 39%	1680
July	1st to 10th	Night	17% 11% 4 7% 4 4 4 4 6% 8% 31%	4680
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 5% 6% 8% 36%	4680
	21st to end	Night	14% 6% 2 6% 5% 4 4 4 5% 8% 42%	5084
August	1st to 10th	Night	17% 7% 2 7% 4 5% 5% 5% 6% 8% 32%	4018
	11th to 20th	Night	10% 6% 3 6% 5% 4 5% 4 7% 9% 41%	4434
	21st to end	Night	11% 4 2 5% 4 4 4 4 6% 8% 49%	5045
September	1st to 10th	Night	15% 7% 3 5% 4 4 5% 4 5% 6% 42%	2100
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 4 7% 50%	2284
	21st to end	Night	19% 7% 3 8% 4 5% 4 3 4 6% 37%	2310
October	1st to 10th	Night	19% 7% 2 5% 4 3 4 2 3 6% 43%	2310
	11th to 20th	Night	16% 6% 2 5% 3 3 3 4 5% 7% 47%	2532
	21st to end	Night	19% 7% 3 7% 4 3 4 3 4 6% 42%	2965
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 6% 46%	2667
	11th to 20th	Night	18% 7% 3 5% 3 4 4 3 4 6% 43%	2730
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 7% 44%	2730
December	1st to 10th	Night	15% 8% 4 7% 5% 4 4 3 4 5% 40%	4618
	11th to 20th	Night	24% 9% 2 6% 3 3 3 2 4 5% 40%	5348
	21st to end	Night	18% 9% 3 6% 4 3 3 2 4 6% 41%	7150

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% 22% 9% 20% 15% 1	4662
	11th to 20th	Day	30% 22% 8% 18% 16% 6%	4680
	21st to end	Day	34% 23% 10% 19% 13%	5199
February	1st to 10th	Day	20% 60% 7% 7% 5%	2037
	11th to 20th	Day	20% 58% 4 10% 8% 1	2057
	21st to end	Day	18% 60% 6% 10% 6% 2	1730
March	1st to 10th	Day	32% 29% 9% 11% 11% 8%	4579
	11th to 20th	Day	26% 30% 12% 23% 9% 1	4798
	21st to end	Day	36% 29% 7% 10% 15% 4	6026
April	1st to 10th	Day	21% 59% 5% 7% 7% 1	2520
	11th to 20th	Day	16% 59% 5% 9% 10%	2494
	21st to end	Day	17% 59% 4 10% 8% 1	2667
May	1st to 10th	Day	43% 25% 11% 12% 8% 1	7651
	11th to 20th	Day	37% 23% 10% 19% 10% 1	7720
	21st to end	Day	40% 24% 10% 17% 9%	9061
June	1st to 10th	Day	17% 60% 4 10% 9% 1	2940
	11th to 20th	Day	17% 59% 5% 10% 8% 1	2940
	21st to end	Day	15% 59% 6% 11% 10% 1	2940
July	1st to 10th	Day	37% 26% 11% 14% 11% 1	8210
	11th to 20th	Day	32% 25% 12% 21% 9%	8205
	21st to end	Day	31% 22% 10% 19% 17% 1	8795
August	1st to 10th	Day	34% 30% 16% 14% 6%	6058
	11th to 20th	Day	24% 29% 15% 28% 4	5645
	21st to end	Day	23% 29% 12% 24% 11%	6080
September	1st to 10th	Day	18% 56% 6% 13% 7%	2520
	11th to 20th	Day	16% 55% 5% 11% 11% 1	2335
	21st to end	Day	25% 55% 5% 8% 6%	2310
October	1st to 10th	Day	20% 35% 8% 15% 18% 4	3700
	11th to 20th	Day	15% 36% 7% 17% 24% 2	3297
	21st to end	Day	17% 36% 11% 20% 14% 2	3252
November	1st to 10th	Day	19% 54% 7% 10% 9% 1	1851
	11th to 20th	Day	16% 54% 5% 11% 12% 2	1890
	21st to end	Day	19% 54% 5% 15% 6% 1	1890
December	1st to 10th	Day	26% 36% 10% 20% 8%	2765
	11th to 20th	Day	30% 31% 8% 13% 15% 3	3066
	21st to end	Day	38% 27% 5% 17% 11% 2	4048
January	1st to 10th	Night	31% 21% 9% 23% 14% 2	8234
	11th to 20th	Night	35% 22% 9% 16% 14% 4	8280
	21st to end	Night	39% 25% 8% 14% 12% 2	8979
February	1st to 10th	Night	19% 61% 5% 10% 4 1	2581
	11th to 20th	Night	19% 58% 3 10% 8% 1	2460
	21st to end	Night	21% 59% 3 9% 6% 2	2076
March	1st to 10th	Night	36% 29% 8% 13% 9% 6%	5494
	11th to 20th	Night	32% 30% 10% 18% 9% 2	5381
	21st to end	Night	38% 30% 4 7% 17% 4	5132
April	1st to 10th	Night	21% 59% 4 7% 7% 2	2100
	11th to 20th	Night	16% 60% 7% 8% 9% 1	2075
	21st to end	Night	20% 59% 4 8% 8% 1	1953
May	1st to 10th	Night	41% 25% 12% 13% 8% 1	5265
	11th to 20th	Night	39% 25% 11% 17% 6% 2	5200
	21st to end	Night	45% 25% 9% 15% 6%	5115
June	1st to 10th	Night	17% 59% 3 10% 10% 1	1680
	11th to 20th	Night	17% 59% 5% 11% 7% 1	1680
	21st to end	Night	17% 58% 4 12% 7% 1	1680
July	1st to 10th	Night	43% 23% 8% 16% 10%	4640
	11th to 20th	Night	36% 25% 11% 20% 9%	4632
	21st to end	Night	33% 23% 12% 18% 14%	4967
August	1st to 10th	Night	38% 30% 13% 12% 6%	4008
	11th to 20th	Night	27% 31% 15% 23% 4	4462
	21st to end	Night	22% 28% 11% 25% 13%	5045
September	1st to 10th	Night	19% 56% 5% 13% 6% 1	2100
	11th to 20th	Night	18% 55% 5% 10% 11% 2	2284
	21st to end	Night	27% 56% 3 8% 6%	2310
October	1st to 10th	Night	24% 36% 7% 19% 12% 2	3700
	11th to 20th	Night	13% 35% 6% 16% 26% 4	4055
	21st to end	Night	16% 36% 10% 19% 18% 2	4715
November	1st to 10th	Night	19% 54% 6% 11% 9% 1	2667
	11th to 20th	Night	18% 55% 4 9% 11% 3	2730
	21st to end	Night	18% 55% 7% 14% 6% 1	2730
December	1st to 10th	Night	27% 35% 8% 20% 8% 1	4618
	11th to 20th	Night	34% 31% 6% 17% 10% 1	5348
	21st to end	Night	33% 27% 8% 14% 14% 3	7150

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	19% 21% 32% 23% 5%	220
	11th to 20th	Day	19% 25% 36% 18% 3	220
	21st to end	Day	20% 15% 42% 15% 7% 1	255
February	1st to 10th	Day	20% 14% 38% 24% 5%	477
	11th to 20th	Day	24% 18% 35% 21% 2	536
	21st to end	Day	23% 15% 33% 26% 3	446
March	1st to 10th	Day	20% 14% 35% 25% 5%	540
	11th to 20th	Day	16% 14% 39% 25% 6% 1	540
	21st to end	Day	21% 13% 38% 21% 7% 1	594
April	1st to 10th	Day	24% 12% 32% 23% 9% 1	540
	11th to 20th	Day	19% 11% 30% 31% 9% 1	532
	21st to end	Day	21% 9% 28% 34% 8% 1	540
May	1st to 10th	Day	24% 9% 27% 29% 9% 1	543
	11th to 20th	Day	19% 5% 27% 34% 14% 1	567
	21st to end	Day	18% 5% 20% 32% 20% 5%	617
June	1st to 10th	Day	15% 4 20% 34% 23% 4	570
	11th to 20th	Day	14% 4 20% 38% 21% 4	570
	21st to end	Day	14% 3 17% 37% 25% 4	570
July	1st to 10th	Day	15% 3 13% 34% 30% 6%	565
	11th to 20th	Day	9% 3 11% 39% 29% 9%	564
	21st to end	Day	13% 2 16% 40% 26% 3	620
August	1st to 10th	Day	12% 4 12% 32% 33% 7%	566
	11th to 20th	Day	13% 3 10% 35% 31% 8%	559
	21st to end	Day	10% 3 17% 35% 25% 10%	627
September	1st to 10th	Day	18% 4 17% 31% 22% 9%	570
	11th to 20th	Day	14% 3 20% 28% 26% 9%	570
	21st to end	Day	24% 5% 22% 29% 17% 3	570
October	1st to 10th	Day	21% 6% 19% 26% 19% 8%	570
	11th to 20th	Day	19% 8% 26% 29% 15% 3	540
	21st to end	Day	22% 10% 27% 26% 11% 4	486
November	1st to 10th	Day	15% 12% 28% 30% 13% 3	425
	11th to 20th	Day	20% 17% 32% 24% 8%	430
	21st to end	Day	19% 18% 30% 23% 8% 1	430
December	1st to 10th	Day	19% 17% 35% 20% 8%	279
	11th to 20th	Day	24% 21% 31% 20% 4	220
	21st to end	Day	22% 17% 32% 20% 8% 2	242
January	1st to 10th	Night	20% 20% 37% 18% 5%	840
	11th to 20th	Night	27% 18% 31% 20% 3	840
	21st to end	Night	20% 19% 38% 20% 3	924
February	1st to 10th	Night	22% 14% 39% 23% 3	840
	11th to 20th	Night	25% 19% 36% 17% 3	823
	21st to end	Night	23% 18% 34% 20% 5%	692
March	1st to 10th	Night	22% 14% 33% 24% 6%	840
	11th to 20th	Night	20% 11% 36% 26% 6% 1	840
	21st to end	Night	20% 11% 36% 24% 8% 1	924
April	1st to 10th	Night	24% 9% 30% 29% 7% 1	840
	11th to 20th	Night	19% 9% 31% 32% 9% 1	831
	21st to end	Night	21% 4 29% 33% 11% 1	693
May	1st to 10th	Night	22% 8% 26% 31% 11% 2	630
	11th to 20th	Night	21% 6% 28% 34% 10% 1	612
	21st to end	Night	24% 2 16% 33% 23% 3	455
June	1st to 10th	Night	18% 3 20% 34% 24% 2	420
	11th to 20th	Night	20% 3 16% 36% 23% 1	420
	21st to end	Night	16% 3 14% 38% 27% 1	420
July	1st to 10th	Night	14% 4 13% 37% 29% 3	410
	11th to 20th	Night	12% 4 13% 38% 28% 5%	408
	21st to end	Night	14% 2 13% 43% 25% 3	460
August	1st to 10th	Night	11% 1 12% 43% 29% 4	575
	11th to 20th	Night	12% 3 11% 38% 32% 5%	770
	21st to end	Night	13% 2 13% 35% 29% 7%	924
September	1st to 10th	Night	16% 3 18% 32% 25% 6%	840
	11th to 20th	Night	15% 4 16% 32% 24% 9%	840
	21st to end	Night	22% 5% 23% 29% 19% 3	840
October	1st to 10th	Night	22% 6% 23% 25% 18% 6%	840
	11th to 20th	Night	21% 9% 27% 28% 13% 3	840
	21st to end	Night	23% 9% 31% 23% 11% 2	913
November	1st to 10th	Night	16% 12% 30% 27% 13% 2	820
	11th to 20th	Night	22% 18% 30% 21% 9% 1	840
	21st to end	Night	17% 19% 29% 26% 7% 1	840
December	1st to 10th	Night	24% 17% 32% 21% 5% 1	840
	11th to 20th	Night	23% 21% 30% 21% 4	840
	21st to end	Night	24% 18% 34% 20% 4	924

Page generated at 2026-10-26 04:37:47. Version ac07

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