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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 2024-11-06.

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	16% 6% 2 6% 4 4 4 4 5% 7% 40%	101324
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	97759
Transparency	Day	41% 6% 13% 23% 16% 2	104869
	Night	42% 5% 12% 23% 16% 2	102303
Seeing	Day	19% 12% 31% 24% 11% 3	15025
	Night	19% 10% 31% 28% 10% 1	24155

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	15% 7% 2 5% 3 3 3 3 5% 5% 48%	2517
	11th to 20th	Day	15% 9% 3 6% 6% 5% 4 3 5% 7% 36%	2520
	21st to end	Day	22% 11% 4 8% 4 4 3 2 4 4 33%	3008
February	1st to 10th	Day	17% 8% 3 6% 5% 3 4 3 5% 6% 39%	1726
	11th to 20th	Day	14% 7% 3 6% 5% 4 4 3 5% 6% 45%	1848
	21st to end	Day	20% 7% 2 6% 4 4 4 4 6% 6% 37%	1570
March	1st to 10th	Day	27% 8% 3 5% 3 3 3 3 4 5% 36%	3116
	11th to 20th	Day	10% 5% 2 5% 5% 5% 6% 4 7% 8% 44%	3336
	21st to end	Day	20% 6% 3 5% 4 3 3 2 4 5% 44%	4148
April	1st to 10th	Day	18% 8% 2 6% 4 3 4 3 6% 7% 39%	2280
	11th to 20th	Day	17% 6% 2 6% 4 5% 4 3 5% 8% 42%	2254
	21st to end	Day	18% 5% 2 6% 3 5% 4 4 6% 6% 40%	2303
May	1st to 10th	Day	27% 9% 2 6% 4 4 3 3 5% 7% 30%	4106
	11th to 20th	Day	23% 7% 3 7% 5% 4 4 3 6% 7% 31%	4355
	21st to end	Day	14% 5% 2 5% 4 3 4 4 5% 9% 44%	4837
June	1st to 10th	Day	16% 6% 2 5% 5% 4 6% 5% 6% 8% 38%	2660
	11th to 20th	Day	14% 7% 2 6% 5% 4 5% 4 6% 9% 37%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	2660
July	1st to 10th	Day	9% 5% 2 8% 6% 5% 6% 5% 7% 10% 36%	4440
	11th to 20th	Day	11% 5% 2 6% 5% 4 6% 5% 7% 10% 39%	4440
	21st to end	Day	14% 7% 3 8% 6% 6% 6% 5% 7% 8% 31%	4814
August	1st to 10th	Day	20% 5% 2 6% 5% 5% 5% 4 7% 9% 32%	4154
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 5% 9% 44%	3730
	21st to end	Day	10% 5% 2 6% 5% 4 5% 4 6% 8% 46%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 5% 4 5% 7% 44%	2280
	11th to 20th	Day	13% 5% 2 4 3 3 4 3 5% 8% 51%	2195
	21st to end	Day	19% 7% 3 5% 4 4 4 3 5% 6% 40%	2090
October	1st to 10th	Day	20% 6% 2 6% 3 3 4 3 4 7% 42%	1990
	11th to 20th	Day	15% 4 2 5% 4 4 4 3 5% 6% 49%	1900
	21st to end	Day	20% 5% 2 5% 3 3 4 3 4 7% 44%	1938
November	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 3 5% 52%	1717
	11th to 20th	Day	18% 4 2 5% 3 3 4 3 4 6% 47%	1710
	21st to end	Day	16% 6% 2 4 5% 4 4 3 6% 6% 45%	1644
December	1st to 10th	Day	19% 8% 3 5% 4 3 4 2 5% 7% 39%	1520
	11th to 20th	Day	22% 6% 2 4 3 3 3 3 4 6% 45%	1906
	21st to end	Day	18% 8% 3 8% 6% 4 5% 5% 5% 7% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	17% 9% 3 5% 3 4 4 3 4 5% 43%	4440
	21st to end	Night	25% 10% 3 5% 4 3 4 3 4 5% 34%	4646
February	1st to 10th	Night	17% 9% 3 6% 4 4 3 3 4 5% 42%	2452
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 4 5% 41%	2218
	21st to end	Night	20% 8% 2 5% 4 4 3 3 5% 5% 41%	1884
March	1st to 10th	Night	23% 10% 3 6% 4 3 3 2 4 5% 37%	3724
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 6% 46%	3621
	21st to end	Night	20% 9% 3 6% 3 3 3 3 4 5% 42%	3483
April	1st to 10th	Night	19% 7% 2 6% 4 4 5% 4 5% 7% 37%	1900
	11th to 20th	Night	18% 7% 2 6% 4 3 5% 3 4 7% 40%	1875
	21st to end	Night	19% 7% 2 5% 3 4 4 3 5% 6% 42%	1876
May	1st to 10th	Night	25% 10% 4 7% 4 4 3 3 4 7% 30%	2834
	11th to 20th	Night	25% 8% 3 7% 5% 4 3 3 4 6% 33%	2567
	21st to end	Night	16% 7% 2 6% 4 4 4 3 5% 9% 40%	2738
June	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 6% 8% 40%	1520
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 6% 9% 42%	1520
	21st to end	Night	10% 4 2 6% 5% 4 5% 4 8% 9% 43%	1520
July	1st to 10th	Night	10% 6% 3 8% 6% 6% 5% 4 7% 8% 38%	2520
	11th to 20th	Night	13% 6% 2 5% 5% 5% 6% 5% 7% 8% 37%	2520
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 6% 7% 35%	2739
August	1st to 10th	Night	23% 5% 2 6% 4 4 5% 5% 6% 8% 32%	2740
	11th to 20th	Night	14% 6% 3 7% 4 5% 4 4 6% 7% 40%	3097
	21st to end	Night	10% 5% 2 5% 3 3 4 3 5% 8% 52%	3476
September	1st to 10th	Night	14% 5% 2 7% 5% 4 4 3 5% 6% 44%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 7% 52%	1985
	21st to end	Night	18% 7% 2 6% 4 3 3 3 4 6% 44%	2090
October	1st to 10th	Night	19% 6% 3 6% 3 3 4 3 6% 7% 41%	2187
	11th to 20th	Night	15% 5% 1 5% 4 3 3 3 5% 6% 50%	2280
	21st to end	Night	20% 7% 2 5% 3 3 2 3 5% 5% 45%	2659
November	1st to 10th	Night	13% 5% 2 4 4 4 4 3 4 5% 52%	2483
	11th to 20th	Night	19% 6% 2 5% 3 3 3 2 4 5% 48%	2470
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 7% 46%	2534
December	1st to 10th	Night	20% 7% 3 6% 4 3 3 4 5% 6% 39%	2660
	11th to 20th	Night	20% 7% 2 5% 3 4 4 3 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 6% 4 4 4 4 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	38% 3 11% 30% 14% 3	2518
	11th to 20th	Day	44% 6% 11% 23% 13% 1	2520
	21st to end	Day	54% 4 10% 21% 9% 2	3008
February	1st to 10th	Day	45% 4 13% 23% 13% 2	1726
	11th to 20th	Day	42% 4 9% 26% 17% 3	1857
	21st to end	Day	46% 5% 11% 21% 14% 4	1570
March	1st to 10th	Day	47% 7% 11% 23% 10% 2	3119
	11th to 20th	Day	32% 9% 13% 30% 14% 2	3336
	21st to end	Day	43% 4 8% 16% 24% 5%	4148
April	1st to 10th	Day	43% 5% 11% 21% 16% 4	2280
	11th to 20th	Day	40% 6% 12% 22% 17% 3	2254
	21st to end	Day	40% 8% 11% 20% 17% 4	2303
May	1st to 10th	Day	53% 6% 14% 14% 12% 1	4120
	11th to 20th	Day	50% 7% 14% 18% 9% 1	4359
	21st to end	Day	35% 7% 14% 24% 18% 2	4837
June	1st to 10th	Day	39% 9% 14% 21% 15% 2	2660
	11th to 20th	Day	41% 8% 13% 24% 12% 2	2660
	21st to end	Day	36% 9% 14% 23% 17% 1	2660
July	1st to 10th	Day	42% 9% 13% 20% 15% 1	4370
	11th to 20th	Day	40% 6% 18% 22% 13% 1	4365
	21st to end	Day	46% 7% 12% 17% 15% 1	4661
August	1st to 10th	Day	46% 7% 16% 22% 9%	4140
	11th to 20th	Day	37% 7% 13% 30% 11% 1	3766
	21st to end	Day	33% 4 12% 29% 20% 2	4180
September	1st to 10th	Day	37% 7% 13% 22% 19% 3	2280
	11th to 20th	Day	32% 5% 11% 25% 24% 2	2195
	21st to end	Day	44% 6% 10% 18% 20% 3	2090
October	1st to 10th	Day	36% 4 12% 21% 23% 5%	3302
	11th to 20th	Day	25% 4 11% 23% 32% 5%	3140
	21st to end	Day	28% 4 14% 26% 25% 3	3176
November	1st to 10th	Day	35% 3 14% 24% 22% 2	1717
	11th to 20th	Day	38% 5% 10% 23% 21% 3	1710
	21st to end	Day	38% 4 13% 30% 11% 2	1644
December	1st to 10th	Day	45% 4 15% 21% 14% 1	1520
	11th to 20th	Day	42% 4 15% 23% 15% 2	1906
	21st to end	Day	48% 8% 12% 24% 8%	2772
January	1st to 10th	Night	39% 4 11% 30% 12% 4	4429
	11th to 20th	Night	44% 4 12% 24% 13% 2	4440
	21st to end	Night	52% 4 8% 22% 12% 1	4646
February	1st to 10th	Night	44% 4 12% 24% 12% 2	2452
	11th to 20th	Night	45% 5% 9% 18% 18% 5%	2220
	21st to end	Night	43% 4 8% 24% 17% 4	1884
March	1st to 10th	Night	50% 5% 9% 22% 11% 3	3734
	11th to 20th	Night	36% 6% 14% 24% 16% 3	3622
	21st to end	Night	46% 5% 7% 15% 22% 6%	3483
April	1st to 10th	Night	46% 5% 10% 19% 17% 4	1900
	11th to 20th	Night	44% 6% 10% 18% 20% 2	1875
	21st to end	Night	42% 6% 9% 21% 18% 4	1876
May	1st to 10th	Night	55% 6% 11% 16% 10% 1	2840
	11th to 20th	Night	53% 6% 15% 14% 10% 2	2568
	21st to end	Night	41% 6% 15% 22% 14% 3	2739
June	1st to 10th	Night	41% 7% 10% 21% 20% 2	1520
	11th to 20th	Night	38% 7% 15% 26% 12% 1	1520
	21st to end	Night	36% 8% 15% 24% 15% 1	1520
July	1st to 10th	Night	46% 8% 13% 19% 13% 2	2480
	11th to 20th	Night	42% 6% 15% 25% 11% 1	2472
	21st to end	Night	46% 6% 14% 15% 17% 2	2651
August	1st to 10th	Night	51% 6% 17% 17% 9% 1	2730
	11th to 20th	Night	44% 5% 12% 28% 10% 1	3127
	21st to end	Night	31% 5% 11% 32% 20% 1	3476
September	1st to 10th	Night	40% 7% 11% 22% 19% 2	1900
	11th to 20th	Night	32% 5% 12% 24% 23% 3	1985
	21st to end	Night	43% 5% 8% 22% 21% 2	2090
October	1st to 10th	Night	38% 4 12% 22% 21% 2	3655
	11th to 20th	Night	24% 3 10% 27% 31% 4	3779
	21st to end	Night	30% 3 12% 30% 23% 2	4371
November	1st to 10th	Night	35% 4 11% 24% 21% 4	2483
	11th to 20th	Night	40% 3 9% 24% 19% 4	2470
	21st to end	Night	37% 5% 13% 28% 15% 2	2534
December	1st to 10th	Night	45% 5% 13% 22% 14% 2	2660
	11th to 20th	Night	42% 5% 12% 20% 17% 3	3288
	21st to end	Night	46% 7% 12% 21% 13%	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	19% 25% 33% 17% 4 1	180
	11th to 20th	Day	19% 34% 31% 12% 4	180
	21st to end	Day	21% 20% 37% 15% 6% 2	267
February	1st to 10th	Day	24% 21% 36% 15% 3	286
	11th to 20th	Day	23% 18% 40% 17% 2	456
	21st to end	Day	26% 18% 35% 18% 3	382
March	1st to 10th	Day	21% 21% 31% 22% 4	460
	11th to 20th	Day	17% 21% 40% 16% 5% 1	460
	21st to end	Day	25% 18% 36% 14% 5% 1	506
April	1st to 10th	Day	23% 20% 34% 15% 7% 1	460
	11th to 20th	Day	22% 15% 35% 17% 9% 2	452
	21st to end	Day	25% 15% 34% 19% 5% 2	460
May	1st to 10th	Day	30% 14% 29% 19% 5% 2	463
	11th to 20th	Day	22% 9% 34% 25% 8% 1	487
	21st to end	Day	19% 4 29% 28% 18% 3	529
June	1st to 10th	Day	17% 9% 31% 27% 13% 3	490
	11th to 20th	Day	13% 9% 34% 29% 12% 2	490
	21st to end	Day	14% 5% 33% 30% 16% 2	490
July	1st to 10th	Day	12% 4 25% 33% 21% 5%	485
	11th to 20th	Day	11% 4 26% 31% 24% 5%	484
	21st to end	Day	14% 5% 27% 34% 16% 4	532
August	1st to 10th	Day	13% 3 24% 34% 20% 6%	486
	11th to 20th	Day	14% 5% 18% 36% 22% 4	479
	21st to end	Day	12% 5% 26% 34% 16% 6%	539
September	1st to 10th	Day	16% 6% 29% 25% 17% 8%	490
	11th to 20th	Day	15% 3 28% 29% 16% 9%	490
	21st to end	Day	25% 8% 28% 23% 11% 4	490
October	1st to 10th	Day	25% 8% 26% 22% 14% 5%	490
	11th to 20th	Day	16% 14% 31% 27% 10% 2	490
	21st to end	Day	21% 12% 34% 22% 9% 2	459
November	1st to 10th	Day	14% 13% 35% 23% 13% 2	381
	11th to 20th	Day	21% 19% 32% 23% 5% 1	370
	21st to end	Day	18% 16% 35% 24% 6% 1	304
December	1st to 10th	Day	21% 23% 36% 14% 7% 1	180
	11th to 20th	Day	28% 22% 34% 11% 5%	180
	21st to end	Day	26% 14% 40% 11% 9% 1	198
January	1st to 10th	Night	19% 14% 42% 21% 3	760
	11th to 20th	Night	25% 16% 31% 24% 3	760
	21st to end	Night	19% 17% 39% 22% 2	836
February	1st to 10th	Night	22% 13% 38% 25% 2	760
	11th to 20th	Night	21% 18% 42% 17% 1	743
	21st to end	Night	22% 17% 35% 22% 4	628
March	1st to 10th	Night	21% 15% 37% 22% 5%	760
	11th to 20th	Night	22% 13% 39% 21% 4 1	760
	21st to end	Night	21% 12% 38% 24% 5%	836
April	1st to 10th	Night	22% 13% 36% 24% 5%	760
	11th to 20th	Night	20% 11% 36% 28% 5%	751
	21st to end	Night	21% 11% 35% 26% 6% 1	736
May	1st to 10th	Night	23% 9% 36% 23% 8% 1	570
	11th to 20th	Night	22% 7% 37% 26% 7% 1	420
	21st to end	Night	18% 3 21% 40% 16% 2	411
June	1st to 10th	Night	18% 6% 25% 35% 14% 1	380
	11th to 20th	Night	13% 4 25% 41% 18%	380
	21st to end	Night	10% 4 24% 49% 12% 1	380
July	1st to 10th	Night	13% 3 20% 44% 19% 2	370
	11th to 20th	Night	12% 2 18% 43% 21% 3	368
	21st to end	Night	13% 5% 20% 43% 20% 1	416
August	1st to 10th	Night	13% 2 18% 44% 21% 2	508
	11th to 20th	Night	16% 3 17% 36% 26% 1	750
	21st to end	Night	14% 4 17% 39% 23% 3	836
September	1st to 10th	Night	16% 4 24% 34% 19% 3	760
	11th to 20th	Night	16% 4 21% 34% 20% 5%	760
	21st to end	Night	22% 4 23% 33% 16% 2	760
October	1st to 10th	Night	21% 8% 25% 26% 17% 3	760
	11th to 20th	Night	17% 11% 29% 32% 11% 1	760
	21st to end	Night	22% 9% 34% 25% 9%	836
November	1st to 10th	Night	15% 10% 34% 29% 12% 1	764
	11th to 20th	Night	21% 14% 34% 23% 8%	760
	21st to end	Night	17% 14% 35% 26% 7% 1	760
December	1st to 10th	Night	25% 13% 35% 21% 6% 1	760
	11th to 20th	Night	22% 13% 37% 24% 4	760
	21st to end	Night	24% 13% 38% 24% 2	836

Page generated at 2024-11-03 13:19:04. Version ac07

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