Atlantic City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atlantic City clear sky chart from 2005-11-05 to 2024-10-14.

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 4 6% 8% 41%	101010
	Night	16% 8% 3 6% 4 4 4 3 5% 7% 42%	97542
Transparency	Day	42% 4 13% 24% 15% 2	100767
	Night	44% 3 11% 24% 16% 3	97410
Seeing	Day	17% 6% 20% 32% 21% 4	15059
	Night	18% 8% 25% 30% 16% 3	24272

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% 3 4 3 3 4 6% 47%	2517
	11th to 20th	Day	16% 7% 2 7% 4 4 4 4 4 6% 41%	2552
	21st to end	Day	20% 10% 4 7% 4 4 4 3 4 5% 35%	3124
February	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 6% 8% 39%	1738
	11th to 20th	Day	17% 7% 3 5% 4 4 3 4 5% 5% 43%	1848
	21st to end	Day	16% 11% 3 5% 4 3 4 4 4 5% 39%	1570
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	16% 5% 2 4 3 3 3 2 5% 6% 50%	1830
	21st to end	Day	16% 6% 2 5% 4 4 4 3 6% 6% 44%	1886
November	1st to 10th	Day	15% 5% 2 5% 4 3 3 2 5% 6% 50%	1671
	11th to 20th	Day	15% 5% 2 5% 5% 3 4 3 5% 6% 47%	1710
	21st to end	Day	14% 5% 2 5% 5% 4 3 3 4 7% 47%	1682
December	1st to 10th	Day	17% 9% 1 6% 3 4 4 4 5% 7% 40%	1520
	11th to 20th	Day	17% 7% 3 5% 4 3 3 2 5% 5% 47%	1906
	21st to end	Day	15% 7% 3 5% 4 4 4 4 6% 8% 39%	2772
January	1st to 10th	Night	16% 7% 2 4 3 3 4 3 5% 6% 47%	4429
	11th to 20th	Night	20% 9% 2 5% 4 2 3 2 4 4 45%	4406
	21st to end	Night	20% 11% 3 6% 3 3 4 3 4 6% 37%	4532
February	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 42%	2441
	11th to 20th	Night	19% 7% 2 6% 3 3 4 3 4 5% 43%	2218
	21st to end	Night	18% 6% 3 6% 4 3 4 3 5% 5% 44%	1884
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% 50%	2203
	21st to end	Night	17% 6% 2 6% 3 4 5% 3 4 6% 45%	2469
November	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 51%	2407
	11th to 20th	Night	16% 7% 2 5% 4 4 3 2 4 6% 47%	2470
	21st to end	Night	13% 6% 2 4 4 4 3 3 6% 7% 47%	2496
December	1st to 10th	Night	18% 8% 3 6% 3 4 3 3 5% 7% 40%	2660
	11th to 20th	Night	17% 5% 2 6% 4 3 4 3 6% 8% 42%	3288
	21st to end	Night	15% 7% 3 6% 4 4 4 4 5% 7% 39%	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	44% 2 8% 26% 16% 4	1857
	21st to end	Day	47% 3 9% 22% 14% 5%	1570
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	41% 3 11% 24% 18% 2	1971
	11th to 20th	Day	37% 2 10% 26% 22% 2	1831
	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	45% 3 8% 21% 18% 5%	2220
	21st to end	Night	44% 1 9% 23% 18% 5%	1884
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	44% 3 10% 22% 18% 2	2204
	11th to 20th	Night	37% 2 11% 29% 18% 3	2207
	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	24% 12% 35% 24% 5%	456
	21st to end	Day	24% 11% 32% 26% 7% 1	382
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	18% 5% 19% 29% 24% 5%	462
	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% 13% 43% 20% 2	743
	21st to end	Night	21% 12% 35% 27% 4 1	628
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	19% 8% 21% 33% 18% 1	735
	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 2024-10-11 10:49:56. Version ac07

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