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 2026-07-01.

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 3 5% 7% 43%	137721
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	134635
Transparency	Day	41% 4 12% 25% 16% 3	141263
	Night	41% 3 11% 24% 18% 4	139168
Seeing	Day	17% 6% 22% 31% 20% 4	17244
	Night	18% 8% 26% 30% 15% 3	26489

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 5% 4 4 3 3 4 5% 50%	4661
	11th to 20th	Day	15% 6% 2 6% 4 4 3 3 3 5% 49%	4710
	21st to end	Day	15% 7% 3 6% 4 4 4 3 4 6% 45%	5780
February	1st to 10th	Day	14% 8% 3 6% 4 4 4 4 6% 8% 40%	1922
	11th to 20th	Day	17% 7% 3 6% 4 4 3 4 5% 5% 41%	2048
	21st to end	Day	16% 11% 2 5% 4 4 4 4 4 5% 40%	1730
March	1st to 10th	Day	19% 6% 2 4 3 2 3 3 4 6% 48%	4576
	11th to 20th	Day	12% 9% 2 5% 3 4 3 3 5% 7% 46%	4949
	21st to end	Day	16% 7% 2 5% 3 4 3 3 5% 6% 44%	6008
April	1st to 10th	Day	17% 8% 2 6% 4 3 4 3 5% 7% 42%	2520
	11th to 20th	Day	14% 8% 2 5% 4 4 4 3 6% 7% 44%	2494
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 5% 8% 40%	2520
May	1st to 10th	Day	20% 9% 3 7% 4 4 5% 3 5% 6% 34%	7515
	11th to 20th	Day	20% 8% 2 6% 3 3 3 3 5% 6% 40%	8037
	21st to end	Day	23% 8% 2 6% 4 3 4 3 5% 8% 33%	9060
June	1st to 10th	Day	12% 7% 2 5% 4 4 4 4 7% 9% 41%	2940
	11th to 20th	Day	12% 5% 2 6% 4 5% 4 4 8% 10% 41%	2940
	21st to end	Day	8% 5% 2 6% 3 4 5% 5% 8% 10% 44%	2940
July	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 7% 10% 43%	6360
	11th to 20th	Day	11% 7% 3 6% 5% 5% 7% 5% 9% 10% 32%	6360
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 4 7% 10% 42%	6890
August	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 7% 11% 38%	4111
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 3 6% 9% 42%	3850
	21st to end	Day	9% 5% 2 4 4 4 4 4 6% 8% 50%	4312
September	1st to 10th	Day	16% 5% 1 4 3 3 4 3 6% 7% 48%	2400
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 5% 7% 49%	2325
	21st to end	Day	20% 7% 2 6% 5% 4 4 3 5% 6% 38%	2200
October	1st to 10th	Day	18% 4 2 5% 3 3 4 2 5% 6% 46%	2075
	11th to 20th	Day	16% 5% 2 4 3 3 3 2 5% 6% 51%	2000
	21st to end	Day	15% 5% 2 5% 4 3 4 3 6% 6% 46%	2095
November	1st to 10th	Day	14% 5% 2 5% 4 3 3 2 4 6% 51%	1851
	11th to 20th	Day	15% 5% 2 5% 5% 3 4 3 6% 7% 47%	1890
	21st to end	Day	14% 5% 2 5% 5% 3 3 3 4 7% 48%	1858
December	1st to 10th	Day	12% 6% 1 4 3 4 4 4 5% 7% 49%	2680
	11th to 20th	Day	19% 8% 3 5% 3 2 2 2 4 4 47%	3066
	21st to end	Day	13% 7% 3 5% 4 3 4 3 5% 8% 44%	4048
January	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 5% 6% 50%	8234
	11th to 20th	Night	16% 7% 2 5% 3 3 3 2 3 4 51%	8159
	21st to end	Night	14% 8% 2 6% 3 3 3 3 4 6% 47%	8401
February	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 42%	2697
	11th to 20th	Night	20% 7% 2 6% 3 4 4 3 4 5% 42%	2458
	21st to end	Night	17% 7% 3 6% 4 3 4 3 5% 5% 44%	2076
March	1st to 10th	Night	18% 9% 3 5% 3 3 3 2 3 5% 46%	5484
	11th to 20th	Night	12% 12% 3 5% 3 3 3 3 4 4 46%	5212
	21st to end	Night	16% 8% 2 6% 4 4 4 3 4 5% 43%	5166
April	1st to 10th	Night	17% 10% 3 6% 3 3 4 3 5% 6% 40%	2100
	11th to 20th	Night	13% 8% 2 5% 5% 4 4 2 4 6% 45%	2075
	21st to end	Night	16% 6% 2 7% 4 4 4 3 5% 7% 41%	2100
May	1st to 10th	Night	16% 9% 4 7% 4 4 5% 4 6% 8% 33%	5384
	11th to 20th	Night	19% 8% 3 7% 4 3 4 3 5% 6% 38%	4878
	21st to end	Night	26% 10% 3 7% 4 4 3 3 4 6% 32%	5114
June	1st to 10th	Night	15% 7% 1 6% 5% 5% 5% 4 5% 7% 40%	1680
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 5% 5% 9% 40%	1680
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	1680
July	1st to 10th	Night	9% 7% 3 8% 5% 6% 6% 5% 6% 9% 35%	3600
	11th to 20th	Night	12% 7% 3 9% 7% 6% 5% 4 7% 9% 30%	3600
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 4 7% 9% 38%	3958
August	1st to 10th	Night	18% 8% 3 7% 4 5% 5% 4 6% 9% 31%	3004
	11th to 20th	Night	10% 5% 2 7% 5% 4 4 4 7% 8% 44%	3197
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 8% 53%	3586
September	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 43%	2000
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 6% 8% 49%	2073
	21st to end	Night	20% 8% 3 5% 4 4 5% 3 6% 5% 37%	2200
October	1st to 10th	Night	18% 6% 2 5% 4 4 3 3 4 6% 44%	2320
	11th to 20th	Night	17% 5% 1 5% 3 3 3 2 4 7% 50%	2400
	21st to end	Night	16% 6% 2 5% 3 4 4 3 4 6% 47%	2744
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 52%	2667
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 4 6% 47%	2730
	21st to end	Night	13% 6% 2 4 4 4 4 3 6% 7% 47%	2760
December	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 7% 49%	4720
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 5% 7% 42%	5348
	21st to end	Night	14% 8% 3 6% 4 4 4 3 5% 7% 43%	7150

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% 2 6% 27% 24% 3	4662
	11th to 20th	Day	40% 2 7% 23% 21% 8%	4740
	21st to end	Day	42% 1 10% 31% 13% 3	5780
February	1st to 10th	Day	43% 3 14% 24% 14% 2	1922
	11th to 20th	Day	46% 2 8% 25% 16% 3	2057
	21st to end	Day	46% 3 9% 23% 15% 4	1730
March	1st to 10th	Day	40% 2 7% 25% 18% 8%	4579
	11th to 20th	Day	39% 2 8% 28% 18% 5%	4949
	21st to end	Day	42% 3 11% 17% 21% 7%	6008
April	1st to 10th	Day	43% 3 10% 20% 18% 6%	2520
	11th to 20th	Day	41% 3 12% 24% 16% 4	2494
	21st to end	Day	42% 4 11% 22% 18% 4	2520
May	1st to 10th	Day	53% 3 12% 20% 11% 1	7526
	11th to 20th	Day	45% 3 11% 28% 13% 1	8041
	21st to end	Day	52% 3 9% 22% 13% 1	9061
June	1st to 10th	Day	39% 5% 14% 23% 16% 2	2940
	11th to 20th	Day	37% 6% 14% 27% 12% 2	2940
	21st to end	Day	33% 6% 17% 26% 18% 1	2940
July	1st to 10th	Day	36% 9% 19% 22% 13% 1	6290
	11th to 20th	Day	44% 8% 20% 20% 6% 1	6285
	21st to end	Day	36% 7% 12% 25% 19% 1	6692
August	1st to 10th	Day	41% 5% 20% 24% 9%	4098
	11th to 20th	Day	39% 4 15% 30% 11% 1	3886
	21st to end	Day	31% 5% 14% 31% 18% 2	4312
September	1st to 10th	Day	36% 3 16% 23% 19% 2	2400
	11th to 20th	Day	35% 3 9% 27% 22% 3	2325
	21st to end	Day	48% 4 9% 19% 17% 2	2200
October	1st to 10th	Day	34% 3 9% 24% 25% 5%	3374
	11th to 20th	Day	27% 2 8% 26% 30% 7%	3240
	21st to end	Day	27% 3 13% 28% 24% 6%	3359
November	1st to 10th	Day	37% 2 11% 29% 17% 4	1851
	11th to 20th	Day	38% 3 10% 23% 23% 3	1890
	21st to end	Day	39% 3 10% 30% 15% 3	1858
December	1st to 10th	Day	35% 3 19% 25% 16% 3	2680
	11th to 20th	Day	43% 2 10% 28% 14% 3	3066
	21st to end	Day	40% 3 13% 24% 19% 1	4048
January	1st to 10th	Night	37% 2 10% 26% 19% 6%	8234
	11th to 20th	Night	38% 2 8% 24% 20% 8%	8204
	21st to end	Night	40% 1 8% 28% 19% 3	8401
February	1st to 10th	Night	45% 2 12% 24% 14% 2	2697
	11th to 20th	Night	45% 3 8% 21% 18% 5%	2460
	21st to end	Night	44% 2 9% 23% 18% 5%	2076
March	1st to 10th	Night	43% 2 9% 23% 14% 10%	5494
	11th to 20th	Night	43% 2 10% 23% 16% 6%	5213
	21st to end	Night	45% 3 8% 17% 24% 4	5166
April	1st to 10th	Night	46% 2 8% 20% 18% 5%	2100
	11th to 20th	Night	43% 1 10% 22% 20% 5%	2075
	21st to end	Night	44% 3 9% 20% 20% 5%	2100
May	1st to 10th	Night	49% 3 12% 23% 11% 2	5390
	11th to 20th	Night	48% 3 10% 24% 14% 1	4879
	21st to end	Night	57% 2 8% 18% 14% 1	5115
June	1st to 10th	Night	44% 5% 9% 21% 20% 2	1680
	11th to 20th	Night	41% 5% 13% 25% 14% 2	1680
	21st to end	Night	37% 5% 15% 26% 15% 2	1680
July	1st to 10th	Night	46% 7% 14% 21% 12% 1	3560
	11th to 20th	Night	49% 6% 17% 21% 6% 1	3552
	21st to end	Night	42% 5% 14% 21% 17%	3841
August	1st to 10th	Night	49% 5% 17% 19% 9%	2993
	11th to 20th	Night	37% 5% 13% 34% 10% 1	3227
	21st to end	Night	30% 5% 12% 31% 21% 2	3586
September	1st to 10th	Night	42% 3 11% 23% 17% 4	2000
	11th to 20th	Night	33% 4 10% 28% 22% 3	2073
	21st to end	Night	49% 5% 7% 20% 17% 2	2200
October	1st to 10th	Night	39% 3 10% 24% 22% 2	3788
	11th to 20th	Night	26% 2 11% 25% 30% 6%	3899
	21st to end	Night	27% 2 11% 31% 24% 5%	4430
November	1st to 10th	Night	34% 3 10% 27% 21% 5%	2667
	11th to 20th	Night	40% 2 9% 22% 22% 5%	2730
	21st to end	Night	37% 3 12% 26% 20% 2	2760
December	1st to 10th	Night	35% 2 14% 27% 18% 4	4720
	11th to 20th	Night	44% 2 11% 22% 17% 4	5348
	21st to end	Night	44% 2 13% 21% 18% 2	7150

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% 14% 34% 28% 9% 2	220
	11th to 20th	Day	15% 16% 37% 25% 6%	231
	21st to end	Day	19% 10% 39% 22% 10% 1	363
February	1st to 10th	Day	19% 9% 32% 30% 9% 1	362
	11th to 20th	Day	24% 14% 35% 23% 4	536
	21st to end	Day	22% 11% 33% 26% 6%	446
March	1st to 10th	Day	17% 11% 36% 28% 7% 1	540
	11th to 20th	Day	18% 9% 33% 31% 8% 2	540
	21st to end	Day	19% 9% 34% 30% 8% 1	594
April	1st to 10th	Day	19% 10% 32% 28% 10% 1	540
	11th to 20th	Day	16% 10% 27% 36% 10% 1	532
	21st to end	Day	20% 5% 25% 37% 12% 1	540
May	1st to 10th	Day	23% 5% 25% 34% 11% 2	543
	11th to 20th	Day	21% 4 19% 36% 18% 2	567
	21st to end	Day	22% 4 13% 27% 28% 7%	617
June	1st to 10th	Day	16% 3 12% 37% 27% 5%	570
	11th to 20th	Day	13% 4 16% 36% 26% 4	570
	21st to end	Day	11% 3 13% 39% 31% 4	570
July	1st to 10th	Day	11% 2 6% 36% 34% 11%	525
	11th to 20th	Day	6% 3 8% 34% 40% 9%	524
	21st to end	Day	10% 3 9% 38% 33% 6%	576
August	1st to 10th	Day	13% 2 9% 36% 33% 7%	526
	11th to 20th	Day	12% 2 8% 31% 39% 8%	519
	21st to end	Day	10% 3 11% 33% 31% 12%	583
September	1st to 10th	Day	18% 3 14% 27% 28% 10%	530
	11th to 20th	Day	16% 2 10% 33% 31% 7%	530
	21st to end	Day	26% 5% 17% 31% 18% 3	530
October	1st to 10th	Day	22% 5% 15% 26% 24% 8%	530
	11th to 20th	Day	18% 6% 21% 27% 22% 5%	530
	21st to end	Day	16% 7% 28% 28% 15% 5%	525
November	1st to 10th	Day	14% 8% 27% 29% 19% 3	425
	11th to 20th	Day	13% 13% 35% 26% 13% 1	430
	21st to end	Day	17% 12% 30% 26% 13% 2	398
December	1st to 10th	Day	24% 10% 30% 24% 12%	220
	11th to 20th	Day	21% 10% 33% 26% 10%	220
	21st to end	Day	20% 10% 29% 26% 14% 2	242
January	1st to 10th	Night	18% 19% 35% 21% 6%	840
	11th to 20th	Night	22% 17% 33% 23% 5%	840
	21st to end	Night	18% 16% 37% 26% 3	924
February	1st to 10th	Night	21% 12% 35% 27% 5%	840
	11th to 20th	Night	23% 13% 41% 20% 2	823
	21st to end	Night	21% 12% 36% 27% 4 1	692
March	1st to 10th	Night	19% 10% 37% 27% 6%	840
	11th to 20th	Night	20% 11% 32% 29% 7% 2	840
	21st to end	Night	20% 8% 33% 30% 7% 1	924
April	1st to 10th	Night	21% 9% 33% 28% 8% 1	840
	11th to 20th	Night	16% 6% 29% 36% 12%	831
	21st to end	Night	20% 4 27% 35% 12% 1	840
May	1st to 10th	Night	19% 6% 25% 35% 13% 2	677
	11th to 20th	Night	21% 5% 23% 35% 15% 1	499
	21st to end	Night	24% 2 13% 29% 27% 5%	455
June	1st to 10th	Night	19% 3 16% 34% 26% 3	420
	11th to 20th	Night	15% 2 15% 38% 29% 2	420
	21st to end	Night	9% 3 12% 43% 30% 4	420
July	1st to 10th	Night	11% 2 8% 41% 31% 6%	390
	11th to 20th	Night	8% 3 7% 34% 41% 6%	388
	21st to end	Night	10% 2 11% 36% 36% 4	445
August	1st to 10th	Night	12% 2 8% 36% 36% 5%	647
	11th to 20th	Night	11% 3 10% 34% 34% 9%	790
	21st to end	Night	12% 2 10% 34% 34% 9%	880
September	1st to 10th	Night	18% 3 13% 30% 28% 9%	800
	11th to 20th	Night	15% 3 11% 32% 31% 7%	800
	21st to end	Night	25% 3 17% 30% 22% 3	800
October	1st to 10th	Night	21% 4 19% 26% 21% 8%	800
	11th to 20th	Night	19% 10% 22% 31% 17% 1	800
	21st to end	Night	19% 7% 31% 28% 13% 2	880
November	1st to 10th	Night	15% 10% 28% 30% 14% 3	820
	11th to 20th	Night	18% 13% 31% 27% 10% 1	840
	21st to end	Night	15% 14% 33% 27% 10% 1	840
December	1st to 10th	Night	21% 13% 34% 22% 8% 2	840
	11th to 20th	Night	19% 13% 37% 24% 6%	840
	21st to end	Night	18% 11% 36% 28% 6%	924

Page generated at 2026-06-28 02:10:48. Version ac07

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