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 2024-03-23.

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% 6% 2 5% 4 3 4 4 5% 7% 42%	78581
	Night	18% 7% 3 5% 5% 3 4 4 5% 7% 40%	81297
Transparency	Day	41% 7% 13% 22% 15% 2	78286
	Night	45% 6% 12% 21% 13% 2	81126
Seeing	Day	18% 9% 26% 28% 15% 4	14254
	Night	20% 10% 27% 27% 13% 2	23408

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	17% 7% 3 4 5% 3 4 4 6% 5% 42%	2517
	11th to 20th	Day	19% 7% 2 5% 5% 3 4 5% 5% 6% 38%	2520
	21st to end	Day	23% 10% 4 7% 4 3 4 4 4 5% 33%	2805
February	1st to 10th	Day	18% 7% 3 5% 5% 3 5% 5% 6% 8% 36%	1843
	11th to 20th	Day	15% 6% 3 6% 6% 3 4 4 5% 6% 44%	1848
	21st to end	Day	20% 9% 3 4 3 2 3 5% 5% 7% 38%	1570
March	1st to 10th	Day	16% 6% 2 5% 4 3 3 4 4 9% 44%	1897
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 6% 7% 44%	1966
	21st to end	Day	18% 8% 3 5% 5% 3 4 4 4 5% 42%	2367
April	1st to 10th	Day	18% 7% 2 4 4 2 4 5% 4 7% 42%	2160
	11th to 20th	Day	17% 6% 2 3 4 2 3 4 5% 7% 45%	2134
	21st to end	Day	18% 6% 2 5% 5% 3 5% 4 5% 6% 41%	2286
May	1st to 10th	Day	23% 8% 3 5% 4 3 3 4 4 7% 38%	2340
	11th to 20th	Day	18% 6% 3 5% 4 3 4 3 5% 8% 43%	2322
	21st to end	Day	14% 6% 2 5% 4 2 3 4 6% 9% 43%	2725
June	1st to 10th	Day	17% 6% 3 5% 4 3 4 5% 6% 9% 40%	2520
	11th to 20th	Day	14% 6% 3 5% 4 3 5% 5% 6% 9% 41%	2520
	21st to end	Day	12% 6% 2 5% 4 3 4 5% 6% 9% 45%	2520
July	1st to 10th	Day	12% 5% 2 5% 4 3 4 4 6% 10% 46%	2520
	11th to 20th	Day	10% 6% 3 4 4 3 5% 5% 6% 8% 46%	2520
	21st to end	Day	12% 4 3 4 5% 3 5% 5% 6% 9% 44%	2744
August	1st to 10th	Day	11% 5% 2 4 4 3 4 5% 7% 10% 46%	2355
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 5% 8% 46%	2174
	21st to end	Day	12% 4 3 4 4 3 5% 5% 5% 7% 47%	2376
September	1st to 10th	Day	14% 5% 2 5% 5% 2 4 4 6% 8% 46%	2160
	11th to 20th	Day	13% 5% 2 4 3 2 3 4 4 7% 54%	2002
	21st to end	Day	19% 6% 2 4 4 3 4 5% 5% 6% 43%	1980
October	1st to 10th	Day	22% 5% 2 4 4 2 3 4 4 6% 43%	1980
	11th to 20th	Day	16% 5% 2 5% 5% 2 4 3 5% 7% 46%	1785
	21st to end	Day	18% 6% 2 5% 4 3 4 4 6% 6% 41%	1782
November	1st to 10th	Day	17% 6% 2 4 4 3 4 4 4 6% 47%	1671
	11th to 20th	Day	17% 6% 3 4 3 2 5% 4 4 7% 45%	1710
	21st to end	Day	16% 7% 2 5% 4 2 4 5% 5% 7% 41%	1710
December	1st to 10th	Day	20% 8% 3 6% 4 3 4 4 5% 7% 35%	1574
	11th to 20th	Day	22% 6% 3 4 3 2 3 3 5% 6% 43%	1906
	21st to end	Day	20% 11% 4 8% 5% 3 3 3 4 5% 33%	2772
January	1st to 10th	Night	18% 6% 2 4 4 3 3 3 5% 7% 44%	4429
	11th to 20th	Night	19% 10% 3 6% 4 2 4 3 4 5% 41%	4440
	21st to end	Night	24% 11% 4 6% 5% 3 4 3 5% 5% 29%	4848
February	1st to 10th	Night	17% 8% 3 7% 5% 3 4 4 4 7% 37%	2336
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 6% 7% 38%	2218
	21st to end	Night	21% 6% 3 5% 5% 3 4 5% 5% 6% 39%	1884
March	1st to 10th	Night	17% 7% 3 5% 5% 3 3 4 5% 6% 42%	2270
	11th to 20th	Night	17% 7% 2 6% 5% 2 4 4 5% 8% 40%	2212
	21st to end	Night	17% 9% 3 4 4 3 3 4 4 7% 43%	2032
April	1st to 10th	Night	20% 8% 3 5% 4 2 4 4 5% 6% 39%	1800
	11th to 20th	Night	16% 7% 3 5% 4 2 4 4 4 6% 43%	1775
	21st to end	Night	21% 8% 3 5% 4 2 3 4 4 8% 38%	1674
May	1st to 10th	Night	20% 9% 4 6% 5% 3 4 4 5% 7% 32%	1620
	11th to 20th	Night	19% 9% 2 4 6% 4 4 5% 4 9% 34%	1585
	21st to end	Night	18% 8% 2 6% 5% 2 6% 5% 5% 7% 35%	1550
June	1st to 10th	Night	18% 7% 3 6% 5% 4 5% 4 5% 6% 37%	1440
	11th to 20th	Night	18% 6% 2 4 4 3 4 5% 6% 9% 40%	1440
	21st to end	Night	13% 6% 3 6% 5% 3 4 5% 6% 9% 40%	1440
July	1st to 10th	Night	11% 6% 3 6% 5% 3 5% 6% 7% 9% 39%	1440
	11th to 20th	Night	13% 6% 2 4 5% 3 4 5% 7% 9% 40%	1440
	21st to end	Night	12% 6% 3 6% 6% 3 6% 5% 6% 8% 40%	1574
August	1st to 10th	Night	7% 5% 2 5% 6% 3 5% 7% 7% 9% 44%	1566
	11th to 20th	Night	11% 4 3 5% 6% 3 4 6% 7% 10% 40%	1722
	21st to end	Night	12% 5% 2 5% 4 3 5% 5% 6% 8% 46%	1980
September	1st to 10th	Night	15% 7% 3 4 5% 3 5% 5% 5% 6% 41%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 3 4 4 7% 50%	1957
	21st to end	Night	17% 7% 3 7% 5% 3 4 4 4 6% 41%	1980
October	1st to 10th	Night	21% 7% 2 5% 5% 2 4 3 3 6% 40%	1980
	11th to 20th	Night	17% 6% 2 5% 4 2 3 4 5% 7% 45%	2169
	21st to end	Night	21% 7% 3 6% 5% 2 4 4 4 5% 38%	2574
November	1st to 10th	Night	16% 6% 2 5% 5% 3 4 3 5% 6% 45%	2407
	11th to 20th	Night	19% 6% 3 5% 4 3 4 4 4 6% 42%	2470
	21st to end	Night	16% 5% 2 4 5% 3 4 5% 5% 7% 44%	2470
December	1st to 10th	Night	20% 9% 4 5% 6% 3 3 5% 5% 6% 35%	2603
	11th to 20th	Night	19% 7% 3 6% 5% 3 4 4 5% 7% 39%	3288
	21st to end	Night	20% 11% 3 5% 5% 3 4 3 4 6% 36%	4884

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	44% 5% 12% 27% 12% 1	2518
	11th to 20th	Day	46% 7% 13% 23% 10% 1	2520
	21st to end	Day	54% 5% 10% 20% 9% 1	2805
February	1st to 10th	Day	47% 6% 16% 19% 11% 1	1843
	11th to 20th	Day	42% 5% 11% 26% 14% 2	1857
	21st to end	Day	46% 6% 12% 19% 14% 4	1570
March	1st to 10th	Day	39% 6% 16% 22% 14% 3	1900
	11th to 20th	Day	39% 5% 13% 26% 16% 2	1966
	21st to end	Day	44% 5% 9% 20% 17% 5%	2367
April	1st to 10th	Day	42% 6% 11% 19% 18% 3	2160
	11th to 20th	Day	39% 5% 11% 21% 20% 3	2134
	21st to end	Day	43% 6% 9% 21% 17% 4	2286
May	1st to 10th	Day	49% 6% 10% 21% 13% 3	2340
	11th to 20th	Day	42% 7% 10% 22% 17% 3	2326
	21st to end	Day	40% 8% 16% 22% 13% 2	2725
June	1st to 10th	Day	42% 7% 14% 22% 14% 1	2520
	11th to 20th	Day	40% 8% 14% 23% 14% 1	2520
	21st to end	Day	36% 8% 15% 25% 14% 1	2520
July	1st to 10th	Day	36% 9% 16% 21% 17% 2	2450
	11th to 20th	Day	35% 9% 15% 28% 12% 2	2445
	21st to end	Day	35% 9% 13% 24% 16% 3	2591
August	1st to 10th	Day	33% 8% 19% 26% 15% 1	2341
	11th to 20th	Day	37% 10% 13% 26% 14% 2	2174
	21st to end	Day	35% 9% 14% 22% 19% 2	2376
September	1st to 10th	Day	38% 8% 13% 22% 18% 1	2160
	11th to 20th	Day	31% 6% 14% 23% 24% 2	2002
	21st to end	Day	43% 6% 10% 20% 19% 2	1980
October	1st to 10th	Day	42% 6% 12% 21% 17% 3	1980
	11th to 20th	Day	37% 5% 15% 25% 17% 1	1785
	21st to end	Day	44% 6% 13% 20% 14% 2	1782
November	1st to 10th	Day	39% 6% 15% 21% 17% 2	1671
	11th to 20th	Day	40% 6% 15% 22% 16% 2	1710
	21st to end	Day	43% 5% 14% 27% 9% 2	1710
December	1st to 10th	Day	49% 7% 14% 16% 12% 1	1574
	11th to 20th	Day	45% 5% 17% 15% 17% 2	1906
	21st to end	Day	53% 6% 12% 21% 8%	2772
January	1st to 10th	Night	41% 5% 12% 30% 9% 3	4429
	11th to 20th	Night	48% 4 13% 22% 11% 1	4440
	21st to end	Night	57% 6% 10% 17% 9% 1	4848
February	1st to 10th	Night	48% 6% 13% 21% 10% 2	2336
	11th to 20th	Night	47% 5% 10% 22% 13% 3	2220
	21st to end	Night	47% 4 9% 22% 15% 4	1884
March	1st to 10th	Night	43% 5% 13% 21% 14% 3	2280
	11th to 20th	Night	42% 6% 11% 23% 15% 4	2213
	21st to end	Night	42% 5% 10% 19% 19% 6%	2032
April	1st to 10th	Night	46% 5% 9% 20% 16% 4	1800
	11th to 20th	Night	42% 5% 11% 19% 20% 2	1775
	21st to end	Night	46% 4 11% 20% 14% 5%	1674
May	1st to 10th	Night	52% 6% 10% 17% 12% 3	1620
	11th to 20th	Night	48% 7% 10% 19% 13% 3	1586
	21st to end	Night	48% 7% 15% 17% 11% 2	1551
June	1st to 10th	Night	48% 7% 11% 18% 15% 1	1440
	11th to 20th	Night	41% 7% 13% 23% 14% 1	1440
	21st to end	Night	40% 8% 13% 24% 14% 1	1440
July	1st to 10th	Night	39% 11% 16% 19% 14% 1	1400
	11th to 20th	Night	37% 8% 16% 26% 12% 1	1392
	21st to end	Night	38% 9% 14% 23% 13% 2	1486
August	1st to 10th	Night	33% 9% 19% 24% 13% 1	1556
	11th to 20th	Night	37% 12% 15% 24% 12%	1722
	21st to end	Night	34% 8% 13% 24% 18% 2	1980
September	1st to 10th	Night	43% 6% 10% 23% 16% 2	1800
	11th to 20th	Night	35% 5% 13% 22% 23% 2	1957
	21st to end	Night	45% 6% 8% 18% 19% 3	1980
October	1st to 10th	Night	48% 6% 8% 20% 15% 3	1980
	11th to 20th	Night	39% 5% 14% 27% 14% 1	2169
	21st to end	Night	49% 6% 12% 19% 13% 1	2574
November	1st to 10th	Night	41% 7% 12% 21% 17% 3	2407
	11th to 20th	Night	44% 6% 12% 21% 15% 3	2470
	21st to end	Night	41% 6% 14% 25% 12% 2	2470
December	1st to 10th	Night	52% 7% 14% 16% 11% 1	2603
	11th to 20th	Night	47% 6% 14% 18% 15% 1	3288
	21st to end	Night	50% 6% 13% 21% 10%	4884

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	21% 21% 31% 22% 5% 1	180
	11th to 20th	Day	20% 26% 34% 17% 3	180
	21st to end	Day	22% 15% 38% 15% 9% 1	208
February	1st to 10th	Day	22% 14% 36% 23% 4	403
	11th to 20th	Day	24% 18% 36% 20% 2	456
	21st to end	Day	24% 16% 33% 22% 4 1	382
March	1st to 10th	Day	20% 14% 37% 24% 5%	460
	11th to 20th	Day	15% 14% 42% 22% 6% 1	460
	21st to end	Day	21% 13% 37% 20% 9% 1	470
April	1st to 10th	Day	23% 11% 33% 23% 10% 1	420
	11th to 20th	Day	19% 10% 29% 31% 10% 1	412
	21st to end	Day	23% 9% 29% 30% 7% 2	420
May	1st to 10th	Day	26% 8% 29% 26% 9% 1	423
	11th to 20th	Day	19% 4 31% 32% 13% 1	447
	21st to end	Day	18% 3 19% 30% 24% 7%	485
June	1st to 10th	Day	16% 3 22% 33% 22% 4	450
	11th to 20th	Day	14% 4 20% 36% 21% 4	450
	21st to end	Day	15% 3 17% 37% 24% 4	450
July	1st to 10th	Day	14% 3 13% 36% 28% 6%	445
	11th to 20th	Day	8% 2 11% 40% 30% 10%	444
	21st to end	Day	13% 2 17% 41% 25% 3	488
August	1st to 10th	Day	10% 4 14% 34% 32% 7%	446
	11th to 20th	Day	14% 3 12% 33% 31% 8%	439
	21st to end	Day	11% 3 18% 32% 25% 10%	495
September	1st to 10th	Day	19% 3 17% 28% 22% 10%	450
	11th to 20th	Day	15% 3 23% 27% 22% 9%	450
	21st to end	Day	23% 4 24% 29% 17% 4	450
October	1st to 10th	Day	25% 7% 19% 24% 18% 7%	450
	11th to 20th	Day	17% 8% 26% 28% 18% 3	428
	21st to end	Day	25% 11% 28% 24% 9% 2	396
November	1st to 10th	Day	17% 11% 25% 30% 14% 3	365
	11th to 20th	Day	22% 17% 30% 24% 8%	370
	21st to end	Day	18% 18% 29% 25% 9% 1	370
December	1st to 10th	Day	21% 17% 35% 17% 9%	234
	11th to 20th	Day	23% 22% 30% 21% 4	180
	21st to end	Day	24% 16% 33% 19% 6% 2	198
January	1st to 10th	Night	22% 19% 36% 18% 5%	760
	11th to 20th	Night	28% 17% 32% 20% 4	760
	21st to end	Night	21% 18% 37% 21% 3	836
February	1st to 10th	Night	22% 14% 39% 22% 2	760
	11th to 20th	Night	25% 19% 38% 16% 2	743
	21st to end	Night	24% 19% 33% 19% 6%	628
March	1st to 10th	Night	22% 14% 33% 23% 6%	760
	11th to 20th	Night	20% 11% 36% 26% 6% 1	760
	21st to end	Night	20% 10% 36% 24% 9% 1	801
April	1st to 10th	Night	23% 10% 30% 29% 7% 1	720
	11th to 20th	Night	19% 8% 30% 32% 10% 1	711
	21st to end	Night	23% 5% 29% 31% 11% 2	594
May	1st to 10th	Night	22% 7% 26% 31% 11% 2	540
	11th to 20th	Night	21% 5% 30% 34% 10% 1	524
	21st to end	Night	23% 1 15% 32% 26% 3	389
June	1st to 10th	Night	19% 3 19% 32% 24% 3	360
	11th to 20th	Night	20% 3 16% 35% 24% 1	360
	21st to end	Night	16% 3 14% 41% 25% 2	360
July	1st to 10th	Night	13% 3 14% 39% 27% 3	350
	11th to 20th	Night	12% 3 12% 38% 30% 5%	348
	21st to end	Night	14% 2 13% 45% 23% 3	394
August	1st to 10th	Night	8% 1 12% 46% 30% 4	492
	11th to 20th	Night	13% 2 12% 37% 32% 5%	658
	21st to end	Night	13% 3 13% 35% 28% 8%	792
September	1st to 10th	Night	17% 3 17% 33% 24% 7%	720
	11th to 20th	Night	16% 4 17% 32% 23% 8%	720
	21st to end	Night	20% 5% 23% 30% 19% 3	720
October	1st to 10th	Night	25% 6% 22% 24% 18% 5%	720
	11th to 20th	Night	22% 8% 27% 28% 13% 2	720
	21st to end	Night	25% 10% 32% 22% 10% 1	792
November	1st to 10th	Night	17% 11% 30% 26% 13% 3	740
	11th to 20th	Night	23% 17% 29% 22% 9% 1	760
	21st to end	Night	18% 19% 30% 25% 7% 1	760
December	1st to 10th	Night	26% 17% 30% 21% 5% 1	760
	11th to 20th	Night	23% 21% 30% 21% 5% 1	760
	21st to end	Night	25% 17% 34% 20% 3	836

Page generated at 2024-03-19 23:31:05. Version ac07

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