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New York City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New York City clear sky chart from 2005-11-06 to 2025-11-03.

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% 6% 2 6% 4 4 4 4 5% 7% 40%	126757
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	123291
Transparency	Day	41% 5% 12% 23% 16% 2	130284
	Night	42% 4 11% 22% 17% 3	127851
Seeing	Day	20% 12% 32% 23% 11% 3	16308
	Night	20% 10% 31% 28% 10% 1	25414

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% 2 4 3 3 4 3 5% 6% 51%	3597
	11th to 20th	Day	13% 8% 3 6% 5% 4 4 3 5% 6% 42%	3570
	21st to end	Day	18% 9% 4 7% 4 4 3 2 3 4 40%	4308
February	1st to 10th	Day	17% 8% 3 6% 4 3 4 4 5% 6% 40%	1817
	11th to 20th	Day	15% 8% 3 6% 5% 4 4 2 5% 6% 44%	1948
	21st to end	Day	20% 7% 2 6% 4 4 4 4 6% 6% 38%	1650
March	1st to 10th	Day	22% 6% 2 5% 3 3 3 3 5% 5% 43%	4476
	11th to 20th	Day	13% 8% 2 6% 4 4 5% 3 6% 7% 42%	4766
	21st to end	Day	18% 6% 3 6% 4 3 3 3 5% 6% 44%	5938
April	1st to 10th	Day	19% 8% 2 6% 4 3 4 3 6% 7% 38%	2400
	11th to 20th	Day	17% 6% 2 6% 4 5% 4 3 5% 8% 41%	2374
	21st to end	Day	18% 5% 2 6% 3 5% 4 4 6% 7% 41%	2424
May	1st to 10th	Day	28% 8% 2 6% 4 4 4 4 5% 8% 29%	5886
	11th to 20th	Day	24% 8% 2 6% 4 3 3 3 5% 6% 35%	6261
	21st to end	Day	21% 5% 2 5% 4 4 5% 4 5% 9% 36%	6949
June	1st to 10th	Day	16% 6% 2 5% 5% 4 6% 5% 6% 8% 38%	2800
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 4 6% 8% 37%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 11% 37%	6360
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 5% 8% 11% 33%	6360
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 9% 38%	6926
August	1st to 10th	Day	19% 5% 2 6% 5% 5% 5% 4 6% 9% 33%	4285
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 5% 8% 44%	3850
	21st to end	Day	10% 5% 2 5% 5% 4 5% 4 6% 8% 47%	4312
September	1st to 10th	Day	14% 6% 2 5% 3 4 5% 3 5% 7% 45%	2400
	11th to 20th	Day	12% 5% 2 4 4 3 4 3 5% 7% 51%	2310
	21st to end	Day	18% 6% 3 6% 5% 4 4 3 5% 6% 39%	2200
October	1st to 10th	Day	19% 5% 2 6% 3 3 4 3 4 6% 44%	2095
	11th to 20th	Day	16% 4 2 5% 4 4 4 3 5% 6% 48%	2000
	21st to end	Day	19% 5% 2 5% 3 3 4 3 4 7% 45%	2040
November	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 3 5% 53%	1779
	11th to 20th	Day	18% 4 2 5% 3 3 4 3 4 6% 49%	1800
	21st to end	Day	16% 6% 2 4 4 4 4 3 6% 6% 45%	1730
December	1st to 10th	Day	16% 6% 2 4 4 3 3 2 5% 7% 46%	2600
	11th to 20th	Day	22% 7% 2 4 3 2 3 2 4 6% 45%	2986
	21st to end	Day	18% 7% 2 7% 4 3 4 4 5% 7% 39%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 49%	6349
	11th to 20th	Night	14% 8% 3 6% 3 3 4 3 4 5% 48%	6315
	21st to end	Night	18% 9% 2 5% 4 4 4 3 5% 6% 40%	6646
February	1st to 10th	Night	17% 9% 3 6% 4 4 3 3 5% 5% 42%	2581
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 4 6% 41%	2338
	21st to end	Night	19% 8% 2 5% 4 4 3 3 5% 5% 41%	1980
March	1st to 10th	Night	20% 9% 2 5% 3 3 3 2 4 5% 43%	5364
	11th to 20th	Night	14% 10% 2 6% 3 3 3 3 5% 5% 45%	5177
	21st to end	Night	18% 9% 3 6% 4 3 3 3 4 5% 40%	4993
April	1st to 10th	Night	20% 7% 2 6% 4 4 5% 4 5% 7% 37%	2000
	11th to 20th	Night	18% 8% 2 6% 4 3 5% 3 4 7% 40%	1975
	21st to end	Night	19% 6% 2 5% 4 4 4 3 5% 7% 43%	1975
May	1st to 10th	Night	28% 9% 3 7% 4 4 4 3 4 7% 28%	4054
	11th to 20th	Night	23% 9% 3 6% 4 4 3 3 4 6% 35%	3675
	21st to end	Night	23% 7% 2 6% 4 4 4 3 5% 8% 35%	3926
June	1st to 10th	Night	16% 7% 2 5% 4 4 5% 4 6% 8% 40%	1600
	11th to 20th	Night	15% 7% 2 5% 4 4 4 4 6% 9% 40%	1600
	21st to end	Night	10% 4 2 6% 5% 4 5% 4 8% 9% 43%	1600
July	1st to 10th	Night	10% 6% 3 8% 5% 6% 5% 4 7% 8% 37%	3600
	11th to 20th	Night	15% 9% 3 7% 5% 5% 5% 4 7% 8% 33%	3600
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 43%	3926
August	1st to 10th	Night	23% 5% 2 6% 4 4 4 5% 6% 8% 33%	2827
	11th to 20th	Night	14% 6% 3 7% 4 5% 5% 4 6% 7% 40%	3197
	21st to end	Night	10% 5% 2 5% 3 3 4 3 5% 8% 52%	3586
September	1st to 10th	Night	15% 5% 2 7% 5% 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 7% 51%	2090
	21st to end	Night	18% 7% 2 6% 4 3 3 3 4 6% 43%	2200
October	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 5% 7% 42%	2302
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 5% 6% 50%	2400
	21st to end	Night	20% 7% 2 5% 3 3 3 3 4 5% 46%	2799
November	1st to 10th	Night	12% 5% 2 4 4 4 4 3 4 6% 52%	2564
	11th to 20th	Night	19% 6% 2 5% 3 3 3 2 4 5% 48%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 7% 46%	2668
December	1st to 10th	Night	15% 7% 3 5% 3 3 3 3 4 6% 47%	4580
	11th to 20th	Night	26% 7% 2 4 2 3 3 3 4 4 43%	5208
	21st to end	Night	19% 9% 3 6% 4 3 4 3 4 5% 40%	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	33% 3 8% 32% 21% 3	3598
	11th to 20th	Day	41% 5% 9% 23% 18% 5%	3600
	21st to end	Day	49% 3 10% 23% 14% 1	4308
February	1st to 10th	Day	45% 4 13% 24% 13% 2	1817
	11th to 20th	Day	43% 4 8% 26% 16% 2	1957
	21st to end	Day	45% 5% 11% 22% 14% 4	1650
March	1st to 10th	Day	41% 5% 11% 20% 15% 8%	4479
	11th to 20th	Day	38% 6% 13% 27% 12% 4	4766
	21st to end	Day	42% 4 9% 14% 25% 5%	5938
April	1st to 10th	Day	44% 5% 11% 20% 16% 4	2400
	11th to 20th	Day	40% 6% 12% 22% 17% 3	2374
	21st to end	Day	40% 8% 11% 20% 17% 4	2424
May	1st to 10th	Day	54% 5% 16% 14% 10% 1	5897
	11th to 20th	Day	50% 5% 11% 20% 14% 1	6265
	21st to end	Day	45% 6% 12% 22% 14% 1	6949
June	1st to 10th	Day	40% 8% 14% 21% 15% 2	2800
	11th to 20th	Day	42% 8% 13% 24% 12% 2	2800
	21st to end	Day	37% 9% 14% 23% 16% 1	2800
July	1st to 10th	Day	42% 8% 13% 22% 15% 1	6290
	11th to 20th	Day	43% 5% 20% 21% 10% 1	6285
	21st to end	Day	40% 6% 11% 22% 20% 1	6728
August	1st to 10th	Day	46% 7% 15% 22% 9% 1	4271
	11th to 20th	Day	37% 7% 13% 30% 11% 1	3886
	21st to end	Day	33% 4 12% 29% 20% 2	4312
September	1st to 10th	Day	37% 6% 12% 23% 19% 3	2400
	11th to 20th	Day	32% 5% 11% 25% 24% 2	2310
	21st to end	Day	45% 5% 11% 17% 19% 3	2200
October	1st to 10th	Day	35% 4 11% 21% 23% 5%	3407
	11th to 20th	Day	26% 3 11% 23% 31% 5%	3240
	21st to end	Day	28% 4 13% 26% 25% 3	3278
November	1st to 10th	Day	35% 3 14% 24% 22% 3	1779
	11th to 20th	Day	37% 4 10% 23% 22% 3	1800
	21st to end	Day	39% 4 14% 30% 11% 2	1730
December	1st to 10th	Day	39% 3 15% 28% 13% 2	2600
	11th to 20th	Day	43% 2 13% 23% 16% 2	2986
	21st to end	Day	44% 6% 9% 23% 16% 2	3960
January	1st to 10th	Night	36% 3 8% 26% 24% 4	6349
	11th to 20th	Night	40% 3 12% 22% 17% 6%	6360
	21st to end	Night	46% 3 9% 21% 17% 4	6646
February	1st to 10th	Night	45% 4 12% 24% 12% 2	2581
	11th to 20th	Night	45% 4 9% 19% 18% 5%	2340
	21st to end	Night	44% 4 8% 24% 17% 3	1980
March	1st to 10th	Night	43% 4 9% 21% 13% 9%	5374
	11th to 20th	Night	41% 5% 14% 23% 13% 4	5178
	21st to end	Night	47% 4 6% 14% 23% 5%	4993
April	1st to 10th	Night	47% 5% 10% 18% 17% 4	2000
	11th to 20th	Night	45% 6% 10% 17% 20% 2	1975
	21st to end	Night	41% 6% 9% 21% 19% 4	1975
May	1st to 10th	Night	57% 5% 13% 14% 10% 1	4060
	11th to 20th	Night	52% 5% 13% 14% 14% 2	3676
	21st to end	Night	49% 4 13% 22% 11% 2	3927
June	1st to 10th	Night	41% 6% 10% 20% 21% 2	1600
	11th to 20th	Night	40% 7% 15% 25% 12% 1	1600
	21st to end	Night	37% 8% 15% 24% 15% 2	1600
July	1st to 10th	Night	46% 7% 12% 20% 13% 2	3560
	11th to 20th	Night	49% 5% 14% 22% 10% 1	3552
	21st to end	Night	40% 5% 14% 22% 18% 1	3809
August	1st to 10th	Night	51% 6% 16% 17% 9% 1	2817
	11th to 20th	Night	43% 5% 12% 28% 10% 1	3227
	21st to end	Night	30% 5% 11% 32% 20% 2	3586
September	1st to 10th	Night	40% 7% 10% 23% 19% 2	2000
	11th to 20th	Night	33% 5% 11% 25% 23% 3	2090
	21st to end	Night	43% 5% 9% 22% 20% 2	2200
October	1st to 10th	Night	38% 4 12% 23% 21% 2	3770
	11th to 20th	Night	25% 3 10% 27% 30% 4	3899
	21st to end	Night	30% 3 12% 30% 23% 2	4511
November	1st to 10th	Night	34% 4 11% 24% 22% 4	2564
	11th to 20th	Night	40% 3 8% 24% 20% 4	2600
	21st to end	Night	38% 5% 12% 28% 16% 1	2668
December	1st to 10th	Night	39% 3 12% 30% 13% 2	4580
	11th to 20th	Night	46% 3 10% 23% 15% 3	5208
	21st to end	Night	45% 5% 11% 18% 18% 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	23% 25% 33% 16% 4 1	200
	11th to 20th	Day	21% 33% 32% 11% 4	200
	21st to end	Day	22% 22% 37% 13% 5% 2	297
February	1st to 10th	Day	24% 23% 36% 14% 3	317
	11th to 20th	Day	25% 19% 38% 16% 2	496
	21st to end	Day	25% 19% 36% 17% 3	414
March	1st to 10th	Day	22% 22% 31% 21% 4	500
	11th to 20th	Day	19% 21% 39% 16% 5% 1	500
	21st to end	Day	25% 19% 36% 14% 5% 1	550
April	1st to 10th	Day	25% 20% 33% 14% 7% 1	500
	11th to 20th	Day	24% 15% 36% 16% 9% 1	492
	21st to end	Day	25% 16% 34% 19% 5% 2	500
May	1st to 10th	Day	31% 14% 29% 18% 6% 2	503
	11th to 20th	Day	23% 10% 34% 24% 8% 1	527
	21st to end	Day	20% 5% 29% 26% 17% 3	573
June	1st to 10th	Day	18% 9% 31% 27% 13% 3	530
	11th to 20th	Day	16% 9% 34% 28% 12% 2	530
	21st to end	Day	14% 5% 33% 30% 16% 2	530
July	1st to 10th	Day	12% 4 26% 33% 21% 5%	525
	11th to 20th	Day	10% 4 27% 31% 23% 5%	524
	21st to end	Day	14% 5% 28% 35% 16% 3	576
August	1st to 10th	Day	13% 4 26% 33% 19% 6%	526
	11th to 20th	Day	14% 5% 20% 36% 21% 4	519
	21st to end	Day	12% 6% 27% 34% 15% 6%	583
September	1st to 10th	Day	16% 6% 30% 24% 17% 7%	530
	11th to 20th	Day	15% 3 28% 30% 16% 8%	530
	21st to end	Day	24% 8% 28% 24% 11% 4	530
October	1st to 10th	Day	23% 8% 26% 22% 15% 6%	530
	11th to 20th	Day	18% 15% 30% 26% 9% 2	530
	21st to end	Day	21% 13% 35% 21% 8% 2	495
November	1st to 10th	Day	13% 13% 35% 23% 13% 2	401
	11th to 20th	Day	20% 18% 33% 23% 5% 1	400
	21st to end	Day	19% 18% 34% 22% 6% 1	330
December	1st to 10th	Day	22% 22% 36% 15% 6% 1	200
	11th to 20th	Day	30% 23% 32% 12% 5%	200
	21st to end	Day	24% 14% 42% 10% 10%	220
January	1st to 10th	Night	19% 15% 42% 20% 3	800
	11th to 20th	Night	25% 17% 31% 24% 3	800
	21st to end	Night	19% 17% 40% 22% 2	880
February	1st to 10th	Night	23% 13% 38% 24% 2	800
	11th to 20th	Night	23% 18% 41% 17% 1	783
	21st to end	Night	22% 17% 36% 22% 3	660
March	1st to 10th	Night	21% 16% 37% 22% 5%	800
	11th to 20th	Night	22% 13% 39% 22% 5% 1	800
	21st to end	Night	21% 13% 39% 23% 4	880
April	1st to 10th	Night	23% 13% 36% 23% 5%	800
	11th to 20th	Night	21% 11% 35% 27% 5%	791
	21st to end	Night	21% 11% 35% 27% 6% 1	775
May	1st to 10th	Night	24% 10% 36% 23% 8% 1	600
	11th to 20th	Night	22% 7% 36% 26% 7% 1	442
	21st to end	Night	20% 3 21% 39% 15% 2	433
June	1st to 10th	Night	18% 6% 26% 36% 14% 1	400
	11th to 20th	Night	15% 4 25% 40% 17%	400
	21st to end	Night	12% 4 24% 47% 13% 1	400
July	1st to 10th	Night	13% 3 19% 44% 19% 2	390
	11th to 20th	Night	13% 3 18% 43% 20% 3	388
	21st to end	Night	12% 4 19% 44% 20% 1	438
August	1st to 10th	Night	14% 2 17% 45% 21% 1	535
	11th to 20th	Night	15% 3 18% 37% 26% 1	790
	21st to end	Night	14% 4 19% 39% 23% 3	880
September	1st to 10th	Night	15% 5% 24% 35% 19% 3	800
	11th to 20th	Night	16% 4 21% 35% 20% 5%	800
	21st to end	Night	22% 4 22% 34% 16% 2	800
October	1st to 10th	Night	20% 8% 25% 26% 18% 3	800
	11th to 20th	Night	18% 11% 28% 31% 11% 1	800
	21st to end	Night	23% 9% 35% 24% 9%	880
November	1st to 10th	Night	14% 10% 34% 29% 11% 1	789
	11th to 20th	Night	21% 14% 34% 24% 8%	800
	21st to end	Night	18% 15% 35% 25% 7% 1	800
December	1st to 10th	Night	25% 13% 34% 22% 6% 1	800
	11th to 20th	Night	23% 13% 36% 24% 4	800
	21st to end	Night	24% 13% 37% 24% 3	880

Page generated at 2025-10-31 02:02:40. Version ac07

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