Oyster Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oyster Bay clear sky chart from 2005-11-06 to 2025-10-19.

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	15% 7% 2 6% 4 4 4 4 6% 8% 41%	126523
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	123167
Transparency	Day	42% 5% 12% 23% 16% 2	130050
	Night	43% 4 11% 23% 17% 3	127727
Seeing	Day	21% 15% 32% 22% 9% 2	16276
	Night	20% 13% 31% 26% 9% 1	25333

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% 6% 1 5% 4 3 3 3 5% 7% 50%	3597
	11th to 20th	Day	14% 9% 2 6% 4 4 4 4 4 6% 44%	3570
	21st to end	Day	18% 8% 3 8% 4 4 4 3 4 4 40%	4218
February	1st to 10th	Day	17% 7% 3 7% 4 4 3 4 5% 7% 39%	1845
	11th to 20th	Day	15% 6% 3 7% 4 4 4 3 5% 7% 44%	1948
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 40%	1650
March	1st to 10th	Day	20% 8% 2 5% 3 3 3 3 5% 5% 43%	4476
	11th to 20th	Day	11% 8% 3 5% 4 4 5% 4 6% 8% 43%	4709
	21st to end	Day	18% 6% 2 6% 4 3 4 3 5% 7% 42%	5970
April	1st to 10th	Day	18% 8% 2 6% 5% 3 3 3 6% 7% 39%	2400
	11th to 20th	Day	17% 6% 2 6% 4 3 4 4 5% 7% 42%	2374
	21st to end	Day	18% 5% 2 4 4 4 5% 3 5% 8% 42%	2455
May	1st to 10th	Day	26% 9% 2 5% 3 3 4 3 6% 8% 29%	5886
	11th to 20th	Day	20% 9% 3 6% 4 3 3 3 5% 7% 37%	6177
	21st to end	Day	20% 6% 2 5% 4 4 4 4 6% 9% 37%	6949
June	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 6% 9% 41%	2800
	11th to 20th	Day	14% 7% 2 5% 5% 4 5% 4 6% 9% 40%	2800
	21st to end	Day	10% 7% 2 6% 4 4 4 4 6% 9% 43%	2800
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 6% 5% 7% 10% 36%	6360
	11th to 20th	Day	8% 6% 3 7% 5% 5% 6% 5% 8% 11% 35%	6360
	21st to end	Day	12% 7% 2 6% 4 5% 5% 4 6% 8% 40%	6926
August	1st to 10th	Day	16% 6% 3 7% 5% 4 5% 4 7% 10% 34%	4319
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 9% 43%	3850
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 10% 48%	4312
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 3 5% 8% 47%	2400
	11th to 20th	Day	11% 6% 2 4 3 3 4 3 5% 7% 52%	2290
	21st to end	Day	18% 6% 3 7% 5% 4 4 3 5% 6% 40%	2200
October	1st to 10th	Day	19% 7% 2 4 2 4 3 3 4 7% 44%	2130
	11th to 20th	Day	14% 6% 2 5% 3 4 4 4 4 6% 47%	1980
	21st to end	Day	19% 6% 2 6% 4 3 4 3 4 6% 42%	1910
November	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 5% 5% 51%	1761
	11th to 20th	Day	16% 7% 2 5% 2 3 3 3 4 6% 49%	1800
	21st to end	Day	15% 7% 2 5% 4 2 5% 4 5% 7% 45%	1755
December	1st to 10th	Day	14% 8% 3 5% 4 3 4 3 6% 7% 43%	2600
	11th to 20th	Day	21% 7% 3 5% 3 2 3 2 4 6% 46%	2986
	21st to end	Day	17% 9% 3 7% 4 4 4 3 4 6% 38%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 49%	6349
	11th to 20th	Night	14% 8% 3 6% 3 4 3 3 5% 5% 46%	6315
	21st to end	Night	17% 9% 3 7% 4 4 4 3 5% 6% 38%	6720
February	1st to 10th	Night	17% 10% 2 5% 4 4 3 3 5% 5% 41%	2555
	11th to 20th	Night	18% 8% 3 5% 4 3 4 3 5% 7% 40%	2338
	21st to end	Night	19% 8% 2 5% 3 4 4 3 5% 5% 41%	1980
March	1st to 10th	Night	19% 9% 3 5% 4 3 4 3 4 5% 43%	5364
	11th to 20th	Night	14% 10% 2 6% 5% 4 3 3 5% 6% 43%	5247
	21st to end	Night	19% 9% 3 6% 4 4 3 3 5% 5% 38%	4962
April	1st to 10th	Night	19% 7% 2 6% 5% 5% 4 3 5% 6% 38%	2000
	11th to 20th	Night	19% 8% 2 6% 4 4 3 3 5% 7% 40%	1975
	21st to end	Night	18% 7% 3 6% 4 3 3 3 4 6% 43%	1942
May	1st to 10th	Night	26% 10% 3 7% 4 4 3 3 5% 7% 27%	4054
	11th to 20th	Night	22% 10% 3 6% 4 4 3 3 5% 6% 35%	3745
	21st to end	Night	22% 8% 2 5% 4 4 4 3 5% 7% 36%	3926
June	1st to 10th	Night	16% 7% 2 6% 4 3 4 4 5% 7% 41%	1600
	11th to 20th	Night	14% 7% 3 5% 4 3 5% 4 7% 8% 39%	1600
	21st to end	Night	10% 5% 2 5% 5% 5% 6% 5% 7% 9% 41%	1600
July	1st to 10th	Night	10% 9% 3 8% 6% 5% 6% 5% 6% 9% 35%	3600
	11th to 20th	Night	11% 9% 3 8% 5% 6% 6% 4 7% 9% 32%	3600
	21st to end	Night	12% 7% 3 6% 4 4 4 4 6% 9% 41%	3926
August	1st to 10th	Night	21% 7% 2 7% 5% 4 5% 4 7% 8% 32%	2782
	11th to 20th	Night	13% 7% 3 7% 4 5% 5% 4 6% 8% 38%	3197
	21st to end	Night	8% 4 2 5% 3 4 5% 3 6% 8% 51%	3586
September	1st to 10th	Night	13% 5% 2 6% 4 4 5% 4 6% 7% 44%	2000
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 6% 52%	2110
	21st to end	Night	17% 6% 2 6% 5% 4 4 3 4 7% 42%	2200
October	1st to 10th	Night	18% 8% 2 6% 4 4 3 3 3 6% 43%	2268
	11th to 20th	Night	15% 5% 2 5% 3 3 4 2 4 6% 49%	2377
	21st to end	Night	21% 6% 2 6% 4 3 4 3 4 6% 42%	2688
November	1st to 10th	Night	12% 5% 2 6% 3 4 4 3 5% 6% 50%	2537
	11th to 20th	Night	18% 7% 3 4 3 2 3 3 4 5% 48%	2600
	21st to end	Night	14% 6% 2 4 4 4 3 3 5% 6% 46%	2640
December	1st to 10th	Night	16% 7% 2 5% 3 3 3 3 5% 5% 48%	4580
	11th to 20th	Night	24% 8% 2 5% 3 3 3 3 3 4 42%	5208
	21st to end	Night	18% 9% 3 6% 4 3 4 3 5% 5% 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	34% 4 6% 33% 21% 2	3598
	11th to 20th	Day	42% 3 10% 24% 16% 6%	3600
	21st to end	Day	50% 3 9% 24% 14% 1	4218
February	1st to 10th	Day	45% 4 13% 23% 14% 1	1845
	11th to 20th	Day	43% 3 9% 26% 17% 2	1957
	21st to end	Day	47% 3 10% 22% 15% 3	1650
March	1st to 10th	Day	44% 4 10% 19% 15% 8%	4479
	11th to 20th	Day	39% 4 13% 28% 13% 3	4709
	21st to end	Day	44% 4 9% 14% 23% 6%	5970
April	1st to 10th	Day	46% 5% 8% 21% 16% 4	2400
	11th to 20th	Day	43% 4 10% 22% 17% 3	2374
	21st to end	Day	43% 4 9% 23% 17% 4	2455
May	1st to 10th	Day	54% 5% 16% 15% 10% 1	5897
	11th to 20th	Day	49% 4 11% 20% 14% 2	6181
	21st to end	Day	45% 5% 11% 23% 14% 1	6949
June	1st to 10th	Day	42% 4 13% 24% 15% 1	2800
	11th to 20th	Day	43% 5% 13% 25% 13% 2	2800
	21st to end	Day	38% 6% 16% 23% 15% 1	2800
July	1st to 10th	Day	43% 9% 12% 21% 15% 1	6290
	11th to 20th	Day	41% 8% 19% 21% 10% 1	6285
	21st to end	Day	40% 6% 11% 21% 19% 1	6728
August	1st to 10th	Day	46% 6% 15% 23% 9% 1	4305
	11th to 20th	Day	38% 5% 14% 32% 10% 1	3886
	21st to end	Day	32% 6% 13% 28% 20% 2	4312
September	1st to 10th	Day	38% 5% 13% 24% 19% 2	2400
	11th to 20th	Day	33% 4 11% 26% 25% 2	2290
	21st to end	Day	46% 4 10% 19% 19% 3	2200
October	1st to 10th	Day	35% 5% 11% 19% 25% 5%	3468
	11th to 20th	Day	27% 3 10% 23% 31% 5%	3220
	21st to end	Day	30% 3 15% 25% 24% 3	3122
November	1st to 10th	Day	36% 3 13% 23% 23% 2	1761
	11th to 20th	Day	38% 3 9% 23% 23% 3	1800
	21st to end	Day	39% 4 14% 29% 12% 2	1755
December	1st to 10th	Day	40% 3 15% 28% 12% 1	2600
	11th to 20th	Day	43% 3 13% 22% 18% 3	2986
	21st to end	Day	47% 3 10% 22% 15% 3	3960
January	1st to 10th	Night	36% 2 8% 26% 24% 4	6349
	11th to 20th	Night	40% 3 13% 22% 16% 5%	6360
	21st to end	Night	48% 2 9% 21% 17% 4	6720
February	1st to 10th	Night	45% 3 12% 25% 13% 2	2555
	11th to 20th	Night	45% 3 9% 21% 17% 5%	2340
	21st to end	Night	45% 3 7% 24% 18% 4	1980
March	1st to 10th	Night	45% 3 9% 21% 14% 9%	5374
	11th to 20th	Night	43% 4 12% 25% 12% 4	5248
	21st to end	Night	48% 3 6% 14% 24% 5%	4962
April	1st to 10th	Night	48% 4 9% 19% 17% 4	2000
	11th to 20th	Night	45% 4 9% 19% 21% 2	1975
	21st to end	Night	44% 3 8% 21% 19% 4	1942
May	1st to 10th	Night	58% 4 12% 14% 10% 1	4060
	11th to 20th	Night	53% 4 13% 15% 14% 2	3746
	21st to end	Night	49% 4 12% 22% 11% 2	3927
June	1st to 10th	Night	44% 4 9% 22% 20% 1	1600
	11th to 20th	Night	41% 6% 14% 27% 12% 1	1600
	21st to end	Night	38% 7% 13% 26% 13% 2	1600
July	1st to 10th	Night	47% 8% 11% 21% 11% 1	3560
	11th to 20th	Night	49% 6% 14% 21% 10% 1	3552
	21st to end	Night	39% 6% 15% 23% 17% 1	3809
August	1st to 10th	Night	50% 5% 17% 18% 10% 1	2772
	11th to 20th	Night	41% 6% 13% 29% 9% 1	3227
	21st to end	Night	30% 5% 12% 33% 18% 1	3586
September	1st to 10th	Night	39% 5% 10% 25% 19% 1	2000
	11th to 20th	Night	35% 3 10% 26% 23% 3	2110
	21st to end	Night	44% 5% 8% 21% 20% 2	2200
October	1st to 10th	Night	39% 4 10% 24% 20% 3	3710
	11th to 20th	Night	25% 3 10% 28% 31% 4	3876
	21st to end	Night	31% 3 12% 30% 21% 3	4426
November	1st to 10th	Night	36% 4 11% 24% 22% 4	2537
	11th to 20th	Night	40% 2 8% 25% 21% 5%	2600
	21st to end	Night	38% 3 13% 30% 15% 2	2640
December	1st to 10th	Night	40% 3 12% 30% 13% 2	4580
	11th to 20th	Night	47% 2 9% 24% 15% 3	5208
	21st to end	Night	46% 3 9% 21% 17% 4	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	29% 24% 31% 15% 3	200
	11th to 20th	Day	25% 29% 30% 14% 3	200
	21st to end	Day	23% 23% 36% 12% 4 1	277
February	1st to 10th	Day	28% 22% 37% 12% 2	345
	11th to 20th	Day	27% 21% 38% 13% 2	496
	21st to end	Day	28% 21% 34% 13% 4	414
March	1st to 10th	Day	24% 23% 33% 17% 3	500
	11th to 20th	Day	22% 22% 36% 16% 4 1	500
	21st to end	Day	30% 19% 33% 13% 4 1	550
April	1st to 10th	Day	28% 22% 31% 13% 5% 1	500
	11th to 20th	Day	26% 19% 32% 16% 6% 1	492
	21st to end	Day	28% 18% 33% 15% 4 1	500
May	1st to 10th	Day	30% 19% 30% 16% 5% 1	503
	11th to 20th	Day	21% 17% 35% 20% 6% 1	527
	21st to end	Day	20% 10% 31% 25% 12% 2	573
June	1st to 10th	Day	19% 11% 32% 27% 9% 2	530
	11th to 20th	Day	18% 11% 34% 27% 9% 2	530
	21st to end	Day	13% 10% 35% 28% 12% 2	530
July	1st to 10th	Day	12% 9% 26% 34% 14% 5%	525
	11th to 20th	Day	10% 6% 30% 34% 16% 4	524
	21st to end	Day	13% 10% 31% 30% 13% 3	576
August	1st to 10th	Day	13% 7% 28% 32% 14% 5%	526
	11th to 20th	Day	14% 5% 27% 35% 15% 4	519
	21st to end	Day	11% 8% 31% 30% 13% 6%	583
September	1st to 10th	Day	19% 7% 30% 24% 15% 4	530
	11th to 20th	Day	14% 7% 31% 25% 14% 9%	530
	21st to end	Day	23% 9% 30% 23% 11% 4	530
October	1st to 10th	Day	23% 10% 26% 21% 15% 5%	530
	11th to 20th	Day	19% 15% 31% 21% 12% 2	522
	21st to end	Day	21% 13% 36% 18% 9% 2	444
November	1st to 10th	Day	15% 15% 32% 26% 9% 2	395
	11th to 20th	Day	22% 23% 30% 19% 6% 1	400
	21st to end	Day	22% 18% 31% 21% 6% 1	355
December	1st to 10th	Day	25% 21% 34% 15% 5% 1	200
	11th to 20th	Day	34% 22% 32% 10% 4	200
	21st to end	Day	25% 17% 38% 13% 7%	220
January	1st to 10th	Night	21% 21% 37% 19% 3	800
	11th to 20th	Night	25% 19% 30% 24% 3	800
	21st to end	Night	19% 20% 38% 21% 2	880
February	1st to 10th	Night	22% 18% 36% 22% 2	800
	11th to 20th	Night	25% 21% 37% 16% 2	783
	21st to end	Night	23% 21% 35% 17% 3	660
March	1st to 10th	Night	24% 18% 34% 19% 5%	800
	11th to 20th	Night	22% 17% 38% 19% 4 1	800
	21st to end	Night	23% 17% 36% 20% 4	880
April	1st to 10th	Night	25% 18% 34% 19% 5%	800
	11th to 20th	Night	23% 15% 34% 24% 5%	791
	21st to end	Night	22% 15% 33% 24% 5% 1	742
May	1st to 10th	Night	25% 11% 33% 24% 7% 1	600
	11th to 20th	Night	23% 14% 33% 26% 4	473
	21st to end	Night	22% 6% 23% 35% 12% 1	433
June	1st to 10th	Night	19% 7% 28% 33% 12% 1	400
	11th to 20th	Night	15% 8% 25% 38% 13% 1	400
	21st to end	Night	12% 6% 27% 45% 10% 1	400
July	1st to 10th	Night	12% 4 24% 43% 15% 1	390
	11th to 20th	Night	15% 4 22% 41% 15% 2	388
	21st to end	Night	12% 5% 23% 43% 16%	438
August	1st to 10th	Night	12% 3 25% 42% 17% 1	516
	11th to 20th	Night	15% 4 21% 37% 21% 2	790
	21st to end	Night	14% 5% 20% 38% 21% 2	880
September	1st to 10th	Night	16% 6% 25% 34% 17% 2	800
	11th to 20th	Night	15% 5% 23% 33% 19% 5%	800
	21st to end	Night	21% 6% 26% 30% 16% 2	800
October	1st to 10th	Night	22% 9% 24% 27% 15% 3	800
	11th to 20th	Night	18% 13% 28% 28% 11% 1	793
	21st to end	Night	24% 12% 32% 24% 8%	836
November	1st to 10th	Night	15% 13% 34% 27% 11% 2	780
	11th to 20th	Night	22% 15% 34% 22% 7%	800
	21st to end	Night	19% 18% 31% 25% 7% 1	800
December	1st to 10th	Night	26% 17% 33% 19% 5% 1	800
	11th to 20th	Night	24% 16% 35% 21% 4	800
	21st to end	Night	24% 15% 36% 22% 3	880

Page generated at 2025-10-16 01:50:24. Version ac07

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