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 2025-02-25.

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% 7% 2 6% 4 4 4 4 6% 8% 42%	108518
	Night	15% 7% 2 6% 4 4 4 3 5% 6% 43%	110129
Transparency	Day	40% 4 12% 25% 16% 3	112107
	Night	41% 3 11% 24% 18% 3	114691
Seeing	Day	17% 6% 21% 31% 21% 4	15437
	Night	18% 8% 26% 30% 16% 3	24808

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 3 3 4 6% 53%	3597
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 4 5% 47%	3616
	21st to end	Day	17% 8% 3 7% 4 4 4 3 4 5% 42%	4466
February	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 6% 8% 39%	1830
	11th to 20th	Day	18% 7% 3 5% 4 4 3 4 5% 5% 42%	1948
	21st to end	Day	16% 11% 2 5% 4 3 4 4 4 5% 40%	1610
March	1st to 10th	Day	25% 7% 3 4 3 3 3 3 3 5% 40%	3116
	11th to 20th	Day	10% 4 2 5% 3 4 4 3 6% 9% 51%	3384
	21st to end	Day	20% 8% 2 5% 3 3 3 3 5% 5% 42%	4102
April	1st to 10th	Day	16% 8% 2 6% 4 3 4 3 5% 7% 42%	2280
	11th to 20th	Day	13% 8% 2 5% 4 4 4 4 5% 7% 45%	2254
	21st to end	Day	16% 5% 2 5% 4 4 5% 4 6% 7% 41%	2280
May	1st to 10th	Day	22% 12% 3 9% 5% 4 4 3 5% 6% 26%	4037
	11th to 20th	Day	26% 9% 2 6% 4 4 3 3 5% 6% 32%	4297
	21st to end	Day	11% 7% 2 6% 4 4 4 4 6% 11% 41%	4837
June	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 8% 10% 40%	2660
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 7% 10% 41%	2660
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 8% 10% 44%	2660
July	1st to 10th	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 11% 39%	4440
	11th to 20th	Day	10% 6% 2 5% 4 4 6% 5% 8% 10% 40%	4440
	21st to end	Day	9% 7% 3 7% 6% 5% 7% 5% 8% 9% 35%	4792
August	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 7% 11% 37%	3985
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 3 6% 9% 43%	3730
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	4180
September	1st to 10th	Day	16% 5% 1 4 3 3 4 3 6% 7% 48%	2280
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 5% 7% 50%	2209
	21st to end	Day	20% 7% 2 6% 4 4 4 3 5% 6% 38%	2090
October	1st to 10th	Day	19% 5% 2 5% 4 3 4 2 4 6% 45%	1971
	11th to 20th	Day	15% 5% 2 4 3 3 3 2 5% 6% 51%	1900
	21st to end	Day	16% 5% 2 5% 4 4 4 3 5% 6% 46%	1990
November	1st to 10th	Day	14% 5% 2 5% 4 3 3 2 4 6% 51%	1761
	11th to 20th	Day	15% 5% 2 6% 5% 3 3 3 5% 6% 47%	1800
	21st to end	Day	14% 5% 2 5% 5% 4 3 3 4 7% 48%	1770
December	1st to 10th	Day	12% 6% 1 4 3 4 4 4 6% 7% 50%	2600
	11th to 20th	Day	19% 8% 3 5% 3 2 2 2 4 4 47%	2986
	21st to end	Day	13% 7% 3 5% 3 3 4 4 6% 8% 44%	3960
January	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 5% 52%	6349
	11th to 20th	Night	16% 7% 2 5% 4 3 3 2 4 5% 51%	6253
	21st to end	Night	15% 9% 2 6% 4 3 3 3 5% 6% 44%	6490
February	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 42%	2569
	11th to 20th	Night	20% 7% 2 6% 3 3 4 3 4 5% 43%	2338
	21st to end	Night	17% 7% 3 6% 4 3 4 3 4 5% 44%	1939
March	1st to 10th	Night	22% 11% 3 6% 3 3 3 2 4 5% 38%	3724
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 5% 5% 48%	3557
	21st to end	Night	20% 10% 3 6% 4 3 3 2 3 4 42%	3530
April	1st to 10th	Night	17% 10% 3 6% 3 3 4 3 5% 6% 40%	1900
	11th to 20th	Night	13% 8% 3 5% 5% 4 4 2 4 6% 45%	1875
	21st to end	Night	17% 7% 2 7% 4 4 4 3 5% 7% 40%	1900
May	1st to 10th	Night	19% 12% 5% 9% 5% 4 4 3 4 6% 28%	2903
	11th to 20th	Night	26% 9% 3 7% 4 3 4 3 5% 5% 31%	2624
	21st to end	Night	14% 10% 3 7% 4 4 3 4 5% 8% 38%	2738
June	1st to 10th	Night	16% 7% 1 6% 5% 4 5% 4 5% 8% 39%	1520
	11th to 20th	Night	12% 6% 2 5% 5% 5% 4 4 5% 9% 41%	1520
	21st to end	Night	8% 5% 2 5% 5% 6% 5% 5% 8% 10% 42%	1520
July	1st to 10th	Night	8% 8% 3 8% 5% 6% 6% 5% 6% 9% 36%	2520
	11th to 20th	Night	9% 6% 2 7% 6% 4 5% 4 7% 10% 39%	2520
	21st to end	Night	15% 9% 3 8% 6% 5% 5% 4 6% 7% 33%	2757
August	1st to 10th	Night	18% 8% 3 7% 4 5% 5% 4 6% 9% 31%	2911
	11th to 20th	Night	9% 5% 2 7% 5% 5% 5% 4 7% 8% 45%	3097
	21st to end	Night	8% 4 1 5% 4 3 4 4 5% 8% 53%	3476
September	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 43%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 6% 8% 49%	1969
	21st to end	Night	20% 8% 3 6% 4 4 4 3 5% 5% 38%	2090
October	1st to 10th	Night	19% 6% 2 5% 4 4 3 3 4 6% 43%	2204
	11th to 20th	Night	17% 5% 1 5% 2 3 3 2 4 7% 51%	2280
	21st to end	Night	16% 5% 2 5% 3 4 4 3 4 6% 46%	2607
November	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 5% 6% 52%	2537
	11th to 20th	Night	16% 8% 2 5% 3 4 3 3 4 6% 47%	2600
	21st to end	Night	13% 6% 2 4 4 4 3 4 6% 7% 47%	2628
December	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 7% 50%	4580
	11th to 20th	Night	22% 6% 2 5% 3 3 3 3 5% 7% 42%	5208
	21st to end	Night	14% 8% 3 6% 4 4 4 3 5% 7% 42%	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	35% 2 6% 27% 28% 3	3598
	11th to 20th	Day	41% 2 8% 23% 18% 7%	3646
	21st to end	Day	46% 1 10% 26% 13% 3	4466
February	1st to 10th	Day	44% 3 14% 24% 13% 1	1830
	11th to 20th	Day	45% 2 8% 25% 16% 4	1957
	21st to end	Day	46% 3 10% 23% 14% 5%	1610
March	1st to 10th	Day	49% 2 6% 27% 12% 3	3119
	11th to 20th	Day	32% 2 9% 34% 20% 3	3384
	21st to end	Day	46% 2 9% 18% 20% 5%	4102
April	1st to 10th	Day	43% 3 10% 21% 18% 6%	2280
	11th to 20th	Day	40% 3 13% 24% 17% 4	2254
	21st to end	Day	41% 4 11% 21% 18% 5%	2280
May	1st to 10th	Day	62% 2 9% 17% 8% 2	4051
	11th to 20th	Day	54% 2 14% 20% 8% 1	4301
	21st to end	Day	42% 3 12% 24% 18% 1	4837
June	1st to 10th	Day	40% 6% 15% 23% 15% 2	2660
	11th to 20th	Day	37% 6% 14% 28% 12% 2	2660
	21st to end	Day	32% 6% 17% 26% 18% 1	2660
July	1st to 10th	Day	39% 9% 18% 21% 12% 1	4370
	11th to 20th	Day	38% 6% 20% 26% 9% 1	4365
	21st to end	Day	42% 7% 14% 23% 13% 1	4639
August	1st to 10th	Day	41% 5% 21% 24% 9%	3972
	11th to 20th	Day	38% 4 16% 31% 11% 1	3766
	21st to end	Day	31% 5% 14% 31% 17% 2	4180
September	1st to 10th	Day	37% 4 16% 22% 19% 3	2280
	11th to 20th	Day	35% 4 9% 26% 23% 3	2209
	21st to end	Day	48% 4 8% 20% 17% 2	2090
October	1st to 10th	Day	35% 3 9% 24% 25% 5%	3270
	11th to 20th	Day	26% 2 8% 26% 31% 7%	3140
	21st to end	Day	27% 3 13% 28% 24% 6%	3254
November	1st to 10th	Day	37% 2 11% 29% 17% 4	1761
	11th to 20th	Day	39% 2 10% 22% 23% 3	1800
	21st to end	Day	39% 3 11% 30% 15% 2	1770
December	1st to 10th	Day	34% 3 19% 25% 17% 3	2600
	11th to 20th	Day	44% 2 10% 28% 14% 3	2986
	21st to end	Day	39% 3 13% 24% 19% 1	3960
January	1st to 10th	Night	36% 2 6% 25% 24% 8%	6349
	11th to 20th	Night	39% 2 8% 25% 19% 7%	6298
	21st to end	Night	44% 1 8% 26% 18% 2	6490
February	1st to 10th	Night	45% 2 13% 25% 14% 2	2569
	11th to 20th	Night	45% 3 8% 21% 18% 5%	2340
	21st to end	Night	44% 1 9% 23% 18% 5%	1939
March	1st to 10th	Night	51% 1 8% 23% 14% 2	3734
	11th to 20th	Night	40% 2 10% 26% 17% 5%	3558
	21st to end	Night	49% 1 5% 17% 22% 5%	3530
April	1st to 10th	Night	46% 3 8% 21% 18% 5%	1900
	11th to 20th	Night	43% 1 9% 22% 20% 5%	1875
	21st to end	Night	45% 3 8% 20% 19% 5%	1900
May	1st to 10th	Night	59% 2 8% 21% 10% 1	2909
	11th to 20th	Night	58% 3 10% 18% 11% 1	2625
	21st to end	Night	48% 3 12% 19% 17% 2	2739
June	1st to 10th	Night	44% 5% 10% 21% 19% 1	1520
	11th to 20th	Night	40% 5% 12% 27% 14% 2	1520
	21st to end	Night	36% 5% 15% 27% 15% 3	1520
July	1st to 10th	Night	45% 6% 16% 21% 10% 1	2480
	11th to 20th	Night	39% 5% 20% 26% 8% 1	2472
	21st to end	Night	50% 4 14% 17% 14% 1	2669
August	1st to 10th	Night	50% 5% 18% 19% 8%	2900
	11th to 20th	Night	36% 5% 13% 34% 11% 1	3127
	21st to end	Night	29% 5% 12% 31% 21% 2	3476
September	1st to 10th	Night	42% 3 11% 22% 18% 4	1900
	11th to 20th	Night	33% 4 10% 27% 22% 3	1969
	21st to end	Night	49% 4 6% 21% 18% 2	2090
October	1st to 10th	Night	39% 3 10% 24% 21% 2	3672
	11th to 20th	Night	25% 2 11% 25% 30% 6%	3779
	21st to end	Night	27% 2 11% 31% 24% 5%	4293
November	1st to 10th	Night	34% 3 10% 27% 21% 5%	2537
	11th to 20th	Night	41% 2 9% 22% 21% 5%	2600
	21st to end	Night	37% 3 12% 26% 20% 2	2628
December	1st to 10th	Night	35% 2 13% 27% 19% 4	4580
	11th to 20th	Night	44% 2 12% 22% 16% 3	5208
	21st to end	Night	44% 2 13% 21% 18% 2	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	14% 14% 36% 26% 9% 2	200
	11th to 20th	Day	14% 17% 36% 27% 6%	210
	21st to end	Day	20% 9% 35% 24% 11% 1	330
February	1st to 10th	Day	20% 9% 32% 30% 8% 1	330
	11th to 20th	Day	25% 14% 34% 22% 5%	496
	21st to end	Day	23% 11% 32% 26% 7% 1	398
March	1st to 10th	Day	17% 9% 35% 30% 8% 1	460
	11th to 20th	Day	17% 7% 34% 32% 8% 2	460
	21st to end	Day	21% 8% 30% 32% 9% 1	506
April	1st to 10th	Day	18% 10% 31% 30% 10% 1	460
	11th to 20th	Day	15% 9% 27% 37% 11% 1	452
	21st to end	Day	22% 5% 24% 37% 12% 1	460
May	1st to 10th	Day	24% 4 22% 36% 13% 2	463
	11th to 20th	Day	22% 4 18% 36% 19% 2	487
	21st to end	Day	18% 2 11% 29% 32% 8%	529
June	1st to 10th	Day	17% 3 11% 37% 28% 5%	490
	11th to 20th	Day	12% 4 12% 39% 29% 4	490
	21st to end	Day	10% 2 12% 40% 32% 3	490
July	1st to 10th	Day	11% 1 6% 36% 34% 11%	485
	11th to 20th	Day	6% 3 7% 33% 41% 9%	484
	21st to end	Day	11% 3 9% 38% 33% 6%	532
August	1st to 10th	Day	13% 2 8% 35% 35% 7%	486
	11th to 20th	Day	11% 2 8% 31% 39% 9%	479
	21st to end	Day	11% 3 9% 33% 31% 12%	539
September	1st to 10th	Day	18% 3 13% 27% 29% 11%	490
	11th to 20th	Day	15% 2 11% 32% 32% 8%	490
	21st to end	Day	26% 5% 17% 30% 19% 3	490
October	1st to 10th	Day	23% 4 15% 27% 23% 8%	490
	11th to 20th	Day	17% 5% 20% 28% 24% 6%	490
	21st to end	Day	17% 6% 27% 29% 16% 5%	486
November	1st to 10th	Day	15% 8% 25% 30% 19% 4	395
	11th to 20th	Day	13% 12% 35% 26% 14% 1	400
	21st to end	Day	16% 12% 29% 26% 14% 2	370
December	1st to 10th	Day	23% 10% 31% 24% 13% 1	200
	11th to 20th	Day	23% 9% 32% 27% 11%	200
	21st to end	Day	20% 9% 27% 27% 15% 2	220
January	1st to 10th	Night	18% 20% 34% 22% 6%	800
	11th to 20th	Night	22% 16% 32% 24% 6%	800
	21st to end	Night	19% 14% 37% 27% 3	880
February	1st to 10th	Night	21% 12% 35% 28% 5%	800
	11th to 20th	Night	23% 14% 41% 20% 2	783
	21st to end	Night	21% 13% 35% 27% 4 1	647
March	1st to 10th	Night	19% 9% 38% 27% 6% 1	760
	11th to 20th	Night	21% 9% 32% 29% 7% 2	760
	21st to end	Night	21% 7% 32% 31% 8% 1	836
April	1st to 10th	Night	21% 8% 33% 29% 8% 1	760
	11th to 20th	Night	16% 5% 28% 38% 13% 1	751
	21st to end	Night	21% 4 27% 35% 12% 1	760
May	1st to 10th	Night	20% 5% 22% 36% 14% 2	613
	11th to 20th	Night	22% 5% 22% 35% 16% 1	451
	21st to end	Night	22% 1 11% 30% 30% 6%	411
June	1st to 10th	Night	20% 4 14% 34% 26% 3	380
	11th to 20th	Night	14% 1 13% 38% 31% 2	380
	21st to end	Night	8% 3 11% 44% 30% 4	380
July	1st to 10th	Night	10% 2 8% 41% 32% 6%	370
	11th to 20th	Night	7% 3 7% 35% 43% 6%	368
	21st to end	Night	11% 2 11% 36% 35% 5%	422
August	1st to 10th	Night	12% 3 7% 36% 37% 5%	614
	11th to 20th	Night	10% 3 11% 34% 33% 9%	750
	21st to end	Night	12% 2 9% 34% 35% 9%	836
September	1st to 10th	Night	18% 3 12% 30% 28% 9%	760
	11th to 20th	Night	15% 3 11% 31% 31% 8%	760
	21st to end	Night	24% 3 17% 30% 23% 3	760
October	1st to 10th	Night	22% 4 19% 26% 21% 8%	760
	11th to 20th	Night	18% 9% 22% 32% 18% 1	760
	21st to end	Night	19% 7% 30% 28% 14% 2	836
November	1st to 10th	Night	16% 9% 27% 30% 15% 3	780
	11th to 20th	Night	19% 12% 31% 28% 11% 1	800
	21st to end	Night	16% 13% 33% 27% 10% 1	800
December	1st to 10th	Night	22% 13% 34% 22% 8% 2	800
	11th to 20th	Night	19% 12% 37% 25% 6% 1	800
	21st to end	Night	18% 10% 36% 29% 6%	880

Page generated at 2025-02-22 06:51:37. Version ac07

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