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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 2024-05-13.

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% 41%	83473
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	86028
Transparency	Day	30% 34% 8% 16% 11% 2	83178
	Night	31% 33% 8% 16% 11% 2	85857
Seeing	Day	19% 12% 31% 24% 11% 3	14330
	Night	19% 10% 31% 28% 10% 1	23617

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	23% 7% 2 6% 4 4 4 3 5% 7% 34%	2470
	11th to 20th	Day	20% 6% 2 5% 4 4 4 4 6% 8% 36%	2479
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 9% 41%	2725
June	1st to 10th	Day	16% 6% 2 5% 5% 4 5% 5% 6% 8% 37%	2520
	11th to 20th	Day	14% 8% 2 7% 5% 4 5% 4 6% 8% 36%	2520
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	2520
July	1st to 10th	Day	10% 5% 2 7% 6% 5% 6% 5% 7% 10% 38%	2520
	11th to 20th	Day	10% 4 2 5% 5% 4 5% 6% 7% 10% 42%	2520
	21st to end	Day	11% 6% 2 7% 6% 5% 6% 6% 7% 8% 36%	2744
August	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 8% 10% 38%	2362
	11th to 20th	Day	12% 6% 2 6% 5% 4 6% 5% 6% 9% 40%	2126
	21st to end	Day	12% 7% 2 5% 6% 3 5% 4 6% 7% 42%	2376
September	1st to 10th	Day	14% 6% 2 5% 3 5% 5% 4 6% 8% 43%	2160
	11th to 20th	Day	13% 5% 2 4 4 3 4 3 4 8% 51%	2080
	21st to end	Day	17% 6% 3 5% 5% 4 4 3 5% 6% 42%	1980
October	1st to 10th	Day	21% 6% 2 6% 3 3 4 3 4 7% 42%	1886
	11th to 20th	Day	16% 4 2 5% 4 4 4 3 5% 6% 46%	1800
	21st to end	Day	21% 5% 2 5% 4 4 4 3 4 7% 42%	1836
November	1st to 10th	Day	14% 6% 2 5% 4 3 3 3 3 5% 52%	1671
	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	22% 8% 3 7% 5% 4 3 3 4 6% 35%	1710
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 4 6% 38%	1485
	21st to end	Night	17% 6% 2 6% 5% 4 4 3 5% 9% 40%	1550
June	1st to 10th	Night	16% 7% 2 6% 4 4 5% 3 6% 8% 40%	1440
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 7% 9% 40%	1440
	21st to end	Night	9% 4 2 6% 5% 4 5% 4 8% 9% 45%	1440
July	1st to 10th	Night	12% 5% 2 7% 5% 5% 5% 4 8% 8% 39%	1440
	11th to 20th	Night	11% 6% 2 4 5% 5% 6% 5% 7% 8% 40%	1440
	21st to end	Night	10% 5% 2 5% 5% 4 5% 5% 7% 10% 42%	1574
August	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 6% 7% 9% 42%	1554
	11th to 20th	Night	12% 5% 3 8% 5% 5% 5% 4 7% 9% 37%	1774
	21st to end	Night	13% 6% 2 7% 4 4 5% 3 5% 9% 41%	1980
September	1st to 10th	Night	15% 5% 2 7% 5% 4 4 3 5% 6% 43%	1800
	11th to 20th	Night	15% 5% 2 5% 2 3 3 3 4 7% 52%	1880
	21st to end	Night	17% 6% 2 6% 5% 3 3 3 4 6% 45%	1980
October	1st to 10th	Night	20% 6% 3 6% 3 4 4 3 5% 6% 41%	2071
	11th to 20th	Night	15% 5% 2 6% 4 3 4 3 5% 6% 49%	2160
	21st to end	Night	21% 7% 3 5% 3 3 3 3 5% 4 44%	2519
November	1st to 10th	Night	13% 5% 2 4 4 4 4 3 4 5% 51%	2407
	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	30% 24% 8% 26% 11% 1	2518
	11th to 20th	Day	37% 26% 8% 18% 10% 1	2520
	21st to end	Day	47% 22% 6% 17% 6% 1	3008
February	1st to 10th	Day	29% 33% 7% 18% 11% 1	1726
	11th to 20th	Day	28% 35% 7% 18% 11% 1	1857
	21st to end	Day	32% 34% 6% 15% 10% 2	1570
March	1st to 10th	Day	41% 24% 8% 20% 7% 1	3119
	11th to 20th	Day	27% 24% 9% 27% 12% 1	3336
	21st to end	Day	34% 22% 6% 13% 21% 4	4148
April	1st to 10th	Day	29% 34% 7% 15% 11% 3	2280
	11th to 20th	Day	30% 35% 8% 14% 12% 3	2254
	21st to end	Day	28% 35% 7% 14% 13% 3	2303
May	1st to 10th	Day	33% 35% 6% 13% 12% 1	2470
	11th to 20th	Day	29% 37% 7% 14% 11% 2	2483
	21st to end	Day	25% 38% 11% 15% 10% 2	2725
June	1st to 10th	Day	27% 38% 10% 14% 9% 1	2520
	11th to 20th	Day	29% 38% 9% 16% 5% 2	2520
	21st to end	Day	27% 39% 9% 16% 9% 1	2520
July	1st to 10th	Day	27% 40% 9% 14% 9% 1	2450
	11th to 20th	Day	22% 39% 10% 17% 10% 2	2445
	21st to end	Day	26% 41% 9% 13% 11% 1	2591
August	1st to 10th	Day	26% 39% 11% 15% 9%	2348
	11th to 20th	Day	26% 38% 8% 16% 11% 1	2126
	21st to end	Day	30% 37% 7% 12% 11% 2	2376
September	1st to 10th	Day	26% 37% 7% 14% 13% 3	2160
	11th to 20th	Day	21% 37% 8% 17% 16% 2	2080
	21st to end	Day	28% 37% 5% 13% 14% 3	1980
October	1st to 10th	Day	27% 36% 7% 18% 12%	1886
	11th to 20th	Day	26% 37% 8% 18% 10% 2	1800
	21st to end	Day	29% 37% 6% 15% 11% 2	1836
November	1st to 10th	Day	20% 40% 7% 17% 15% 1	1671
	11th to 20th	Day	26% 39% 7% 15% 11% 2	1710
	21st to end	Day	27% 39% 7% 18% 8% 1	1644
December	1st to 10th	Day	27% 39% 10% 16% 7% 1	1520
	11th to 20th	Day	30% 32% 11% 16% 11% 1	1906
	21st to end	Day	38% 28% 9% 19% 6%	2772
January	1st to 10th	Night	31% 25% 8% 27% 8% 2	4429
	11th to 20th	Night	35% 25% 8% 19% 10% 2	4440
	21st to end	Night	44% 22% 6% 19% 8% 1	4646
February	1st to 10th	Night	30% 34% 8% 17% 11% 1	2452
	11th to 20th	Night	31% 35% 6% 13% 12% 3	2220
	21st to end	Night	30% 34% 4 18% 12% 2	1884
March	1st to 10th	Night	42% 23% 7% 19% 8% 1	3734
	11th to 20th	Night	30% 23% 11% 20% 13% 2	3622
	21st to end	Night	37% 23% 4 12% 19% 5%	3483
April	1st to 10th	Night	31% 35% 7% 12% 12% 3	1900
	11th to 20th	Night	34% 34% 5% 12% 14% 1	1875
	21st to end	Night	27% 36% 6% 13% 14% 3	1876
May	1st to 10th	Night	35% 35% 6% 11% 11% 2	1710
	11th to 20th	Night	30% 37% 7% 10% 13% 3	1486
	21st to end	Night	26% 38% 10% 14% 10% 2	1551
June	1st to 10th	Night	28% 37% 8% 13% 12% 1	1440
	11th to 20th	Night	26% 38% 11% 17% 7% 1	1440
	21st to end	Night	24% 39% 11% 16% 9%	1440
July	1st to 10th	Night	29% 38% 9% 13% 9% 2	1400
	11th to 20th	Night	25% 40% 8% 16% 10% 1	1392
	21st to end	Night	21% 41% 12% 13% 11% 2	1486
August	1st to 10th	Night	26% 39% 11% 15% 10% 1	1544
	11th to 20th	Night	29% 37% 7% 18% 8% 1	1774
	21st to end	Night	30% 39% 8% 12% 11% 1	1980
September	1st to 10th	Night	29% 37% 6% 13% 13% 1	1800
	11th to 20th	Night	21% 37% 6% 18% 16% 2	1880
	21st to end	Night	26% 36% 5% 15% 16% 1	1980
October	1st to 10th	Night	27% 37% 7% 16% 12% 1	2071
	11th to 20th	Night	27% 36% 9% 16% 10% 1	2160
	21st to end	Night	30% 37% 7% 14% 11% 1	2519
November	1st to 10th	Night	20% 40% 6% 15% 15% 3	2407
	11th to 20th	Night	27% 39% 5% 17% 11% 2	2470
	21st to end	Night	26% 39% 7% 17% 10% 1	2534
December	1st to 10th	Night	26% 39% 9% 15% 9% 1	2660
	11th to 20th	Night	30% 32% 8% 13% 14% 2	3288
	21st to end	Night	38% 27% 10% 15% 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	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	21% 9% 35% 25% 7% 2	456
	21st to end	Day	20% 4 27% 27% 19% 3	485
June	1st to 10th	Day	18% 8% 31% 27% 13% 3	450
	11th to 20th	Day	14% 9% 34% 28% 12% 2	450
	21st to end	Day	13% 5% 32% 30% 16% 2	450
July	1st to 10th	Day	12% 4 23% 34% 22% 5%	445
	11th to 20th	Day	11% 3 24% 32% 25% 5%	444
	21st to end	Day	14% 5% 26% 34% 17% 4	488
August	1st to 10th	Day	11% 4 23% 36% 20% 6%	446
	11th to 20th	Day	14% 4 18% 37% 22% 4	439
	21st to end	Day	13% 4 25% 35% 16% 6%	495
September	1st to 10th	Day	16% 5% 28% 25% 18% 8%	450
	11th to 20th	Day	16% 4 28% 28% 16% 8%	450
	21st to end	Day	22% 9% 28% 24% 12% 5%	450
October	1st to 10th	Day	26% 7% 25% 23% 15% 4	450
	11th to 20th	Day	17% 13% 30% 28% 10% 2	450
	21st to end	Day	23% 13% 35% 21% 8% 2	423
November	1st to 10th	Day	14% 13% 33% 24% 14% 2	365
	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	21% 7% 37% 27% 7% 1	406
	21st to end	Night	19% 3 20% 40% 16% 2	389
June	1st to 10th	Night	18% 6% 24% 35% 15% 1	360
	11th to 20th	Night	14% 4 24% 40% 18%	360
	21st to end	Night	10% 3 24% 50% 13% 1	360
July	1st to 10th	Night	14% 3 20% 43% 20% 1	350
	11th to 20th	Night	12% 2 18% 44% 21% 3	348
	21st to end	Night	11% 5% 20% 43% 20% 1	394
August	1st to 10th	Night	12% 2 18% 45% 21% 2	480
	11th to 20th	Night	15% 3 17% 37% 27% 1	710
	21st to end	Night	14% 4 17% 39% 24% 3	792
September	1st to 10th	Night	16% 4 23% 35% 19% 3	720
	11th to 20th	Night	16% 4 22% 33% 20% 5%	720
	21st to end	Night	21% 5% 23% 34% 17% 2	720
October	1st to 10th	Night	22% 8% 24% 25% 17% 3	720
	11th to 20th	Night	18% 11% 27% 33% 11% 1	720
	21st to end	Night	24% 9% 35% 23% 8%	792
November	1st to 10th	Night	15% 9% 34% 29% 12% 1	740
	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 2024-05-10 12:39:02. Version ac07

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