Atlantic City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atlantic City clear sky chart from 2005-11-06 to 2024-02-15.

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	14% 6% 2 5% 5% 3 4 5% 5% 8% 43%	78307
	Night	16% 7% 3 5% 5% 3 4 4 5% 7% 43%	80761
Transparency	Day	41% 4 13% 25% 16% 3	78013
	Night	43% 3 11% 24% 17% 3	80589
Seeing	Day	17% 6% 20% 31% 21% 5%	14091
	Night	18% 8% 26% 30% 16% 3	23478

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% 8% 2 5% 4 2 4 4 4 6% 47%	2517
	11th to 20th	Day	16% 7% 2 6% 5% 3 4 5% 4 6% 42%	2552
	21st to end	Day	20% 10% 4 6% 5% 3 4 4 4 5% 36%	3124
February	1st to 10th	Day	15% 8% 3 5% 5% 3 4 4 6% 8% 39%	1738
	11th to 20th	Day	18% 6% 3 5% 4 3 4 5% 4 5% 43%	1788
	21st to end	Day	17% 10% 3 4 5% 3 4 5% 4 6% 39%	1480
March	1st to 10th	Day	14% 5% 3 5% 4 2 4 5% 4 6% 49%	1797
	11th to 20th	Day	16% 6% 2 5% 4 2 5% 4 5% 9% 43%	1926
	21st to end	Day	19% 6% 2 5% 5% 3 4 4 5% 6% 40%	2340
April	1st to 10th	Day	16% 7% 3 5% 5% 2 4 4 4 7% 43%	2160
	11th to 20th	Day	14% 6% 2 4 4 2 4 5% 5% 7% 46%	2134
	21st to end	Day	16% 5% 2 5% 4 3 6% 5% 5% 7% 40%	2160
May	1st to 10th	Day	17% 7% 2 5% 5% 3 6% 4 5% 7% 38%	2299
	11th to 20th	Day	18% 6% 2 5% 5% 4 4 4 6% 7% 39%	2419
	21st to end	Day	13% 7% 3 4 5% 3 4 5% 5% 9% 42%	2725
June	1st to 10th	Day	13% 6% 2 4 5% 3 5% 5% 7% 11% 39%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 4 5% 5% 7% 10% 40%	2520
	21st to end	Day	8% 3 2 5% 4 3 5% 6% 8% 11% 45%	2520
July	1st to 10th	Day	9% 4 2 5% 5% 3 5% 6% 6% 10% 44%	2520
	11th to 20th	Day	6% 4 2 4 5% 3 5% 6% 8% 12% 46%	2520
	21st to end	Day	9% 5% 3 4 5% 3 6% 6% 8% 10% 40%	2735
August	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 5% 6% 10% 44%	2263
	11th to 20th	Day	11% 5% 2 4 5% 3 6% 4 6% 9% 44%	2126
	21st to end	Day	11% 6% 2 4 4 3 4 6% 6% 9% 44%	2376
September	1st to 10th	Day	16% 5% 2 3 4 3 4 4 6% 7% 47%	2160
	11th to 20th	Day	11% 7% 2 4 4 2 4 4 5% 7% 50%	2093
	21st to end	Day	18% 7% 2 5% 5% 3 4 4 5% 7% 40%	1980
October	1st to 10th	Day	20% 5% 2 5% 4 3 4 3 4 6% 44%	1868
	11th to 20th	Day	16% 5% 2 4 4 3 3 3 5% 6% 50%	1800
	21st to end	Day	16% 6% 2 4 5% 3 4 4 5% 6% 44%	1886
November	1st to 10th	Day	15% 5% 2 5% 4 2 4 3 5% 6% 50%	1671
	11th to 20th	Day	16% 5% 2 5% 6% 2 4 3 5% 6% 47%	1710
	21st to end	Day	14% 5% 3 5% 5% 3 4 4 4 7% 48%	1682
December	1st to 10th	Day	17% 8% 2 5% 4 2 5% 4 5% 7% 40%	1520
	11th to 20th	Day	17% 7% 3 4 4 2 4 3 4 5% 47%	1906
	21st to end	Day	15% 7% 3 5% 4 3 4 5% 6% 9% 39%	2772
January	1st to 10th	Night	16% 7% 2 4 4 2 3 4 5% 6% 47%	4429
	11th to 20th	Night	20% 8% 2 5% 4 2 3 3 4 5% 45%	4406
	21st to end	Night	20% 10% 3 6% 4 3 4 4 4 6% 38%	4532
February	1st to 10th	Night	18% 6% 2 5% 5% 3 4 4 4 6% 43%	2441
	11th to 20th	Night	19% 7% 3 5% 4 3 4 4 4 5% 42%	2153
	21st to end	Night	18% 6% 3 5% 5% 2 4 4 5% 5% 44%	1776
March	1st to 10th	Night	15% 6% 2 4 3 3 3 4 4 7% 49%	2150
	11th to 20th	Night	17% 7% 3 5% 4 3 4 4 4 5% 44%	2029
	21st to end	Night	18% 7% 3 6% 5% 3 4 3 3 5% 42%	2016
April	1st to 10th	Night	17% 10% 3 5% 4 2 4 4 5% 6% 41%	1800
	11th to 20th	Night	14% 7% 3 5% 6% 3 4 3 3 6% 46%	1775
	21st to end	Night	18% 7% 2 6% 5% 3 4 4 5% 7% 39%	1800
May	1st to 10th	Night	17% 9% 4 6% 6% 3 5% 4 5% 7% 35%	1661
	11th to 20th	Night	18% 7% 3 7% 5% 3 4 4 5% 6% 38%	1488
	21st to end	Night	17% 9% 3 6% 5% 3 4 4 5% 8% 37%	1550
June	1st to 10th	Night	16% 7% 2 5% 6% 4 5% 5% 5% 7% 39%	1440
	11th to 20th	Night	12% 5% 3 5% 6% 3 5% 6% 5% 9% 40%	1440
	21st to end	Night	8% 5% 2 5% 5% 4 5% 6% 8% 10% 43%	1440
July	1st to 10th	Night	9% 5% 3 5% 6% 4 7% 6% 6% 9% 40%	1440
	11th to 20th	Night	5% 5% 3 6% 7% 3 5% 6% 8% 10% 42%	1440
	21st to end	Night	9% 5% 2 5% 7% 4 6% 6% 7% 9% 41%	1579
August	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 6% 7% 9% 40%	1655
	11th to 20th	Night	9% 5% 2 6% 5% 3 6% 5% 7% 8% 44%	1774
	21st to end	Night	10% 6% 2 5% 6% 3 6% 5% 6% 9% 43%	1980
September	1st to 10th	Night	15% 7% 2 5% 4 3 5% 4 5% 7% 43%	1800
	11th to 20th	Night	12% 5% 2 4 3 2 3 5% 6% 8% 49%	1865
	21st to end	Night	19% 8% 3 5% 4 3 4 4 5% 5% 39%	1980
October	1st to 10th	Night	20% 6% 2 5% 5% 3 3 4 4 6% 42%	2088
	11th to 20th	Night	18% 5% 2 4 3 2 3 4 4 7% 49%	2160
	21st to end	Night	17% 6% 2 5% 4 3 4 4 4 6% 45%	2469
November	1st to 10th	Night	13% 6% 3 4 4 2 4 3 5% 6% 51%	2407
	11th to 20th	Night	16% 7% 3 4 4 2 4 3 4 6% 47%	2470
	21st to end	Night	13% 5% 2 4 4 3 4 4 6% 7% 48%	2496
December	1st to 10th	Night	18% 8% 3 5% 4 3 3 4 5% 7% 40%	2660
	11th to 20th	Night	17% 5% 2 5% 5% 3 4 4 5% 8% 43%	3288
	21st to end	Night	15% 7% 3 5% 5% 3 4 4 5% 8% 40%	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	41% 2 8% 29% 17% 4	2518
	11th to 20th	Day	46% 2 10% 22% 15% 5%	2552
	21st to end	Day	52% 1 10% 22% 12% 3	3124
February	1st to 10th	Day	44% 3 14% 25% 13% 1	1738
	11th to 20th	Day	45% 2 8% 26% 15% 4	1797
	21st to end	Day	46% 3 8% 23% 14% 5%	1480
March	1st to 10th	Day	39% 3 11% 28% 17% 3	1800
	11th to 20th	Day	41% 3 10% 24% 18% 4	1926
	21st to end	Day	46% 3 9% 21% 16% 4	2340
April	1st to 10th	Day	43% 3 10% 20% 18% 6%	2160
	11th to 20th	Day	39% 4 13% 24% 17% 4	2134
	21st to end	Day	42% 4 11% 20% 17% 5%	2160
May	1st to 10th	Day	46% 3 12% 22% 14% 3	2299
	11th to 20th	Day	45% 3 14% 23% 14% 2	2423
	21st to end	Day	40% 4 17% 25% 12% 1	2725
June	1st to 10th	Day	40% 6% 15% 23% 14% 2	2520
	11th to 20th	Day	39% 7% 14% 26% 12% 2	2520
	21st to end	Day	32% 6% 17% 26% 18% 1	2520
July	1st to 10th	Day	36% 6% 18% 24% 15% 1	2450
	11th to 20th	Day	30% 7% 17% 32% 13% 2	2445
	21st to end	Day	35% 7% 14% 28% 15% 2	2582
August	1st to 10th	Day	35% 5% 17% 28% 15% 1	2250
	11th to 20th	Day	38% 4 17% 25% 14% 1	2126
	21st to end	Day	36% 5% 16% 23% 16% 3	2376
September	1st to 10th	Day	37% 4 17% 23% 18% 3	2160
	11th to 20th	Day	35% 4 9% 26% 23% 3	2093
	21st to end	Day	46% 4 9% 20% 18% 3	1980
October	1st to 10th	Day	43% 3 11% 24% 17% 2	1868
	11th to 20th	Day	37% 2 10% 25% 23% 2	1800
	21st to end	Day	42% 3 10% 24% 19% 2	1886
November	1st to 10th	Day	38% 2 11% 29% 17% 4	1671
	11th to 20th	Day	40% 2 10% 22% 23% 3	1710
	21st to end	Day	39% 3 10% 30% 15% 3	1682
December	1st to 10th	Day	44% 3 15% 22% 14% 2	1520
	11th to 20th	Day	42% 2 10% 28% 15% 3	1906
	21st to end	Day	44% 2 14% 25% 15% 1	2772
January	1st to 10th	Night	40% 1 8% 31% 16% 4	4429
	11th to 20th	Night	45% 1 10% 26% 15% 2	4406
	21st to end	Night	51% 1 6% 26% 14% 2	4532
February	1st to 10th	Night	44% 2 13% 25% 14% 2	2441
	11th to 20th	Night	46% 3 8% 20% 18% 6%	2155
	21st to end	Night	44% 1 8% 23% 19% 5%	1776
March	1st to 10th	Night	38% 2 12% 25% 20% 4	2160
	11th to 20th	Night	44% 3 9% 21% 19% 5%	2030
	21st to end	Night	48% 2 8% 19% 18% 6%	2016
April	1st to 10th	Night	45% 3 8% 21% 18% 5%	1800
	11th to 20th	Night	42% 1 10% 22% 20% 5%	1775
	21st to end	Night	46% 3 8% 19% 19% 5%	1800
May	1st to 10th	Night	51% 3 8% 20% 16% 2	1661
	11th to 20th	Night	49% 3 11% 16% 19% 2	1489
	21st to end	Night	47% 4 14% 21% 12% 1	1551
June	1st to 10th	Night	45% 5% 10% 20% 19% 1	1440
	11th to 20th	Night	41% 5% 13% 25% 14% 2	1440
	21st to end	Night	36% 5% 15% 27% 15% 3	1440
July	1st to 10th	Night	42% 5% 17% 24% 10% 3	1400
	11th to 20th	Night	36% 6% 17% 27% 14% 2	1392
	21st to end	Night	38% 6% 13% 26% 16% 1	1491
August	1st to 10th	Night	39% 6% 17% 23% 14% 1	1644
	11th to 20th	Night	37% 5% 15% 26% 15% 1	1774
	21st to end	Night	36% 6% 15% 22% 17% 3	1980
September	1st to 10th	Night	43% 3 12% 22% 16% 4	1800
	11th to 20th	Night	33% 4 11% 27% 23% 3	1865
	21st to end	Night	47% 4 6% 22% 19% 2	1980
October	1st to 10th	Night	45% 3 10% 22% 18% 2	2088
	11th to 20th	Night	38% 2 11% 28% 18% 3	2160
	21st to end	Night	42% 2 8% 26% 18% 3	2469
November	1st to 10th	Night	35% 3 10% 27% 19% 5%	2407
	11th to 20th	Night	41% 2 10% 22% 21% 5%	2470
	21st to end	Night	37% 3 12% 27% 19% 2	2496
December	1st to 10th	Night	46% 3 12% 24% 14% 2	2660
	11th to 20th	Night	42% 3 12% 21% 20% 3	3288
	21st to end	Night	46% 2 14% 25% 12% 1	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	14% 12% 33% 29% 10% 2	180
	11th to 20th	Day	14% 16% 34% 28% 7% 1	189
	21st to end	Day	21% 9% 33% 25% 12% 1	297
February	1st to 10th	Day	20% 7% 32% 31% 9% 1	298
	11th to 20th	Day	25% 12% 35% 23% 5%	432
	21st to end	Day	25% 11% 33% 26% 5%	346
March	1st to 10th	Day	15% 9% 37% 32% 7%	420
	11th to 20th	Day	19% 6% 33% 32% 7% 2	420
	21st to end	Day	21% 8% 31% 31% 9% 1	462
April	1st to 10th	Day	17% 10% 32% 29% 10% 1	420
	11th to 20th	Day	16% 8% 27% 38% 11% 1	412
	21st to end	Day	23% 5% 25% 35% 11% 1	420
May	1st to 10th	Day	23% 4 23% 35% 13% 2	423
	11th to 20th	Day	22% 3 19% 36% 18% 2	447
	21st to end	Day	20% 2 11% 28% 31% 8%	485
June	1st to 10th	Day	18% 3 11% 35% 28% 5%	450
	11th to 20th	Day	13% 4 13% 38% 28% 4	450
	21st to end	Day	10% 1 11% 40% 34% 3	450
July	1st to 10th	Day	12% 1 5% 34% 35% 12%	445
	11th to 20th	Day	5% 3 7% 32% 43% 10%	444
	21st to end	Day	10% 2 9% 38% 34% 7%	488
August	1st to 10th	Day	12% 2 7% 36% 37% 7%	446
	11th to 20th	Day	12% 2 6% 31% 40% 9%	439
	21st to end	Day	11% 3 9% 33% 31% 13%	495
September	1st to 10th	Day	18% 2 12% 26% 31% 12%	450
	11th to 20th	Day	16% 2 11% 30% 32% 8%	450
	21st to end	Day	25% 5% 16% 31% 20% 3	450
October	1st to 10th	Day	24% 4 14% 27% 23% 8%	450
	11th to 20th	Day	18% 5% 19% 28% 25% 5%	450
	21st to end	Day	18% 6% 28% 29% 15% 4	448
November	1st to 10th	Day	16% 8% 24% 28% 21% 4	365
	11th to 20th	Day	13% 12% 34% 26% 15% 1	370
	21st to end	Day	16% 11% 28% 27% 15% 2	342
December	1st to 10th	Day	24% 9% 29% 24% 13% 1	180
	11th to 20th	Day	21% 8% 32% 28% 11%	180
	21st to end	Day	22% 9% 27% 26% 15% 2	198
January	1st to 10th	Night	19% 18% 34% 23% 6%	760
	11th to 20th	Night	23% 14% 32% 25% 6%	760
	21st to end	Night	19% 13% 37% 28% 3	836
February	1st to 10th	Night	21% 12% 34% 28% 5%	760
	11th to 20th	Night	22% 12% 43% 20% 2	722
	21st to end	Night	22% 12% 36% 27% 3	592
March	1st to 10th	Night	19% 9% 38% 28% 6%	720
	11th to 20th	Night	21% 9% 31% 30% 7% 2	720
	21st to end	Night	21% 6% 32% 31% 8% 1	792
April	1st to 10th	Night	22% 8% 33% 29% 8% 1	720
	11th to 20th	Night	16% 5% 27% 38% 13% 1	711
	21st to end	Night	21% 4 27% 35% 11% 1	720
May	1st to 10th	Night	21% 5% 23% 35% 14% 3	581
	11th to 20th	Night	22% 4 23% 35% 16% 1	427
	21st to end	Night	22% 1 11% 29% 30% 6%	389
June	1st to 10th	Night	20% 4 13% 34% 26% 3	360
	11th to 20th	Night	15% 1 13% 38% 31% 2	360
	21st to end	Night	8% 2 10% 45% 31% 4	360
July	1st to 10th	Night	10% 3 8% 41% 32% 6%	350
	11th to 20th	Night	7% 3 7% 34% 44% 6%	348
	21st to end	Night	10% 2 11% 37% 36% 5%	399
August	1st to 10th	Night	11% 3 7% 37% 38% 5%	581
	11th to 20th	Night	10% 3 10% 34% 34% 9%	710
	21st to end	Night	12% 2 9% 33% 35% 9%	792
September	1st to 10th	Night	18% 3 11% 30% 29% 9%	720
	11th to 20th	Night	14% 3 12% 31% 31% 8%	720
	21st to end	Night	23% 3 17% 30% 24% 3	720
October	1st to 10th	Night	23% 4 19% 26% 21% 8%	720
	11th to 20th	Night	19% 8% 21% 33% 18% 1	720
	21st to end	Night	20% 7% 31% 28% 12% 2	792
November	1st to 10th	Night	16% 9% 27% 29% 15% 3	740
	11th to 20th	Night	19% 11% 30% 28% 11% 1	760
	21st to end	Night	16% 12% 33% 27% 10% 1	760
December	1st to 10th	Night	23% 12% 33% 22% 8% 2	760
	11th to 20th	Night	19% 12% 38% 25% 6% 1	760
	21st to end	Night	19% 10% 36% 29% 6%	836

Page generated at 2024-02-12 06:35:35. Version ac07

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