North Jersey Astronomical Group
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Jersey Astronomical Group clear sky chart from 2005-11-06 to 2026-03-18.

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	17% 7% 2 6% 4 4 4 4 6% 7% 40%	131154
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	130353
Transparency	Day	41% 6% 11% 22% 17% 3	134668
	Night	41% 5% 11% 22% 17% 3	134913
Seeing	Day	21% 15% 31% 21% 10% 3	16659
	Night	20% 11% 31% 28% 9% 1	25936

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	12% 6% 2 6% 4 4 5% 3 5% 6% 48%	4661
	11th to 20th	Day	15% 8% 2 5% 5% 4 3 3 4 6% 44%	4650
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 5% 5% 42%	5614
February	1st to 10th	Day	16% 8% 2 7% 4 4 4 4 5% 6% 41%	1890
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 3 4 6% 43%	2048
	21st to end	Day	20% 8% 3 4 4 4 4 3 5% 6% 39%	1730
March	1st to 10th	Day	22% 6% 2 5% 3 3 4 3 5% 5% 42%	4576
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 4 6% 7% 42%	4866
	21st to end	Day	18% 6% 2 6% 4 3 4 3 5% 6% 43%	5914
April	1st to 10th	Day	19% 8% 2 7% 4 4 4 4 5% 7% 38%	2400
	11th to 20th	Day	18% 6% 2 5% 5% 4 4 3 5% 7% 40%	2374
	21st to end	Day	19% 6% 2 5% 4 4 3 3 6% 7% 40%	2415
May	1st to 10th	Day	29% 7% 2 5% 4 4 4 3 5% 8% 28%	5886
	11th to 20th	Day	24% 8% 3 6% 4 4 3 3 4 6% 35%	6308
	21st to end	Day	21% 6% 2 6% 4 4 4 4 6% 8% 36%	6949
June	1st to 10th	Day	16% 5% 2 6% 4 4 6% 4 8% 8% 37%	2800
	11th to 20th	Day	16% 7% 2 7% 4 4 5% 4 7% 7% 36%	2800
	21st to end	Day	12% 5% 3 6% 6% 4 5% 5% 7% 9% 39%	2800
July	1st to 10th	Day	10% 6% 3 7% 5% 6% 6% 4 7% 11% 36%	6360
	11th to 20th	Day	10% 7% 3 8% 5% 5% 6% 5% 8% 11% 32%	6360
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 6% 9% 39%	6926
August	1st to 10th	Day	20% 7% 2 6% 5% 5% 5% 4 6% 8% 32%	4290
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 43%	3850
	21st to end	Day	10% 6% 2 6% 3 4 5% 4 5% 8% 46%	4312
September	1st to 10th	Day	14% 5% 3 5% 5% 4 5% 3 5% 7% 43%	2400
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 8% 49%	2320
	21st to end	Day	18% 6% 3 7% 5% 5% 4 3 5% 5% 39%	2200
October	1st to 10th	Day	19% 6% 2 5% 3 4 3 3 5% 7% 42%	2077
	11th to 20th	Day	16% 5% 2 5% 4 4 3 3 5% 6% 48%	2000
	21st to end	Day	20% 4 2 5% 3 3 4 3 5% 6% 44%	2050
November	1st to 10th	Day	13% 6% 2 4 4 3 4 2 5% 6% 52%	1851
	11th to 20th	Day	17% 5% 2 4 4 3 3 3 5% 6% 47%	1890
	21st to end	Day	16% 6% 2 5% 4 3 5% 3 5% 6% 44%	1793
December	1st to 10th	Day	15% 7% 2 5% 4 3 4 3 5% 7% 45%	2680
	11th to 20th	Day	22% 7% 2 4 3 2 2 3 5% 6% 44%	3066
	21st to end	Day	18% 7% 3 7% 4 4 4 4 5% 7% 37%	4048
January	1st to 10th	Night	12% 8% 3 6% 4 4 4 3 5% 6% 46%	8234
	11th to 20th	Night	15% 8% 3 6% 4 3 4 3 4 5% 44%	8235
	21st to end	Night	15% 8% 2 5% 3 4 4 3 4 6% 44%	8563
February	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 5% 42%	2729
	11th to 20th	Night	18% 8% 3 6% 4 4 3 3 5% 6% 40%	2458
	21st to end	Night	18% 8% 2 6% 4 4 4 3 4 6% 41%	2076
March	1st to 10th	Night	20% 8% 2 5% 4 3 3 3 4 5% 43%	5484
	11th to 20th	Night	14% 9% 3 5% 3 3 3 3 4 6% 46%	5245
	21st to end	Night	18% 9% 3 7% 4 3 3 3 4 6% 41%	5016
April	1st to 10th	Night	20% 7% 2 6% 5% 4 4 3 6% 5% 38%	2000
	11th to 20th	Night	18% 7% 2 6% 3 4 4 3 5% 6% 40%	1975
	21st to end	Night	18% 6% 3 6% 3 4 3 3 5% 7% 42%	1985
May	1st to 10th	Night	28% 9% 3 7% 4 3 4 3 5% 6% 27%	4054
	11th to 20th	Night	24% 9% 3 7% 4 3 3 3 4 6% 34%	3627
	21st to end	Night	23% 7% 2 6% 4 3 4 3 5% 8% 35%	3926
June	1st to 10th	Night	16% 6% 3 4 4 5% 4 3 6% 8% 41%	1600
	11th to 20th	Night	15% 6% 2 5% 4 4 5% 4 6% 8% 41%	1600
	21st to end	Night	12% 4 1 6% 5% 4 4 4 7% 10% 43%	1600
July	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 7% 10% 37%	3600
	11th to 20th	Night	15% 8% 3 8% 4 5% 5% 4 7% 9% 32%	3600
	21st to end	Night	13% 7% 2 5% 4 4 5% 4 6% 8% 42%	3926
August	1st to 10th	Night	22% 7% 2 6% 4 4 5% 3 6% 7% 34%	2808
	11th to 20th	Night	14% 6% 2 7% 5% 5% 5% 4 6% 7% 39%	3197
	21st to end	Night	10% 5% 2 6% 3 4 4 3 5% 8% 52%	3586
September	1st to 10th	Night	15% 5% 3 6% 5% 4 4 4 4 6% 45%	2000
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 4 7% 51%	2079
	21st to end	Night	19% 7% 2 5% 4 4 3 2 4 7% 43%	2200
October	1st to 10th	Night	19% 6% 2 6% 3 4 3 3 4 6% 43%	2320
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 4 6% 50%	2400
	21st to end	Night	20% 7% 2 5% 3 3 3 3 4 5% 46%	2790
November	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 6% 52%	2667
	11th to 20th	Night	19% 6% 2 4 4 3 3 3 4 5% 49%	2730
	21st to end	Night	15% 5% 2 6% 4 3 4 4 5% 6% 46%	2825
December	1st to 10th	Night	14% 8% 2 6% 4 3 3 3 4 6% 47%	4720
	11th to 20th	Night	25% 7% 2 4 3 3 3 3 4 4 43%	5348
	21st to end	Night	20% 9% 2 6% 4 3 4 3 4 5% 40%	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	36% 4 9% 30% 18% 2	4662
	11th to 20th	Day	41% 4 9% 21% 18% 6%	4680
	21st to end	Day	43% 4 11% 24% 17% 1	5614
February	1st to 10th	Day	44% 5% 13% 23% 13% 2	1890
	11th to 20th	Day	43% 4 9% 25% 17% 3	2057
	21st to end	Day	45% 5% 11% 22% 14% 3	1730
March	1st to 10th	Day	43% 4 11% 20% 14% 8%	4579
	11th to 20th	Day	38% 7% 13% 27% 11% 4	4866
	21st to end	Day	42% 5% 10% 13% 25% 5%	5914
April	1st to 10th	Day	45% 6% 10% 19% 16% 5%	2400
	11th to 20th	Day	42% 5% 11% 21% 17% 3	2374
	21st to end	Day	42% 5% 10% 21% 18% 4	2415
May	1st to 10th	Day	54% 7% 13% 15% 10% 1	5897
	11th to 20th	Day	49% 7% 9% 20% 13% 1	6312
	21st to end	Day	44% 6% 10% 23% 14% 1	6949
June	1st to 10th	Day	40% 9% 13% 21% 15% 2	2800
	11th to 20th	Day	43% 8% 13% 22% 12% 2	2800
	21st to end	Day	39% 9% 13% 22% 16% 1	2800
July	1st to 10th	Day	41% 10% 12% 21% 15% 1	6290
	11th to 20th	Day	42% 8% 18% 21% 10% 1	6285
	21st to end	Day	41% 6% 11% 20% 20% 2	6728
August	1st to 10th	Day	47% 8% 14% 21% 10% 1	4276
	11th to 20th	Day	37% 7% 14% 28% 13% 1	3886
	21st to end	Day	35% 6% 10% 28% 20% 2	4312
September	1st to 10th	Day	39% 8% 10% 22% 19% 3	2400
	11th to 20th	Day	34% 5% 10% 24% 25% 2	2320
	21st to end	Day	46% 6% 9% 18% 18% 3	2200
October	1st to 10th	Day	38% 5% 9% 19% 24% 6%	3376
	11th to 20th	Day	26% 4 11% 24% 30% 5%	3240
	21st to end	Day	27% 4 13% 26% 26% 4	3288
November	1st to 10th	Day	34% 4 12% 23% 23% 3	1851
	11th to 20th	Day	38% 4 9% 24% 21% 4	1890
	21st to end	Day	39% 5% 13% 29% 11% 2	1793
December	1st to 10th	Day	40% 3 15% 28% 13% 2	2680
	11th to 20th	Day	42% 3 14% 24% 15% 3	3066
	21st to end	Day	45% 6% 9% 23% 15% 2	4048
January	1st to 10th	Night	39% 5% 11% 24% 18% 3	8234
	11th to 20th	Night	42% 4 11% 21% 16% 6%	8280
	21st to end	Night	42% 4 9% 22% 20% 4	8563
February	1st to 10th	Night	44% 5% 12% 25% 12% 2	2729
	11th to 20th	Night	45% 4 9% 20% 18% 4	2460
	21st to end	Night	45% 4 8% 25% 16% 3	2076
March	1st to 10th	Night	43% 5% 10% 21% 13% 8%	5494
	11th to 20th	Night	39% 5% 15% 24% 13% 4	5246
	21st to end	Night	46% 4 7% 15% 23% 5%	5016
April	1st to 10th	Night	46% 5% 10% 19% 16% 4	2000
	11th to 20th	Night	45% 5% 10% 20% 19% 2	1975
	21st to end	Night	41% 6% 9% 21% 19% 4	1985
May	1st to 10th	Night	57% 6% 12% 14% 10% 1	4060
	11th to 20th	Night	51% 6% 13% 14% 14% 2	3628
	21st to end	Night	47% 6% 13% 22% 10% 2	3927
June	1st to 10th	Night	41% 6% 11% 21% 20% 2	1600
	11th to 20th	Night	40% 8% 12% 26% 12% 1	1600
	21st to end	Night	36% 8% 15% 24% 16% 2	1600
July	1st to 10th	Night	43% 9% 13% 18% 15% 2	3560
	11th to 20th	Night	47% 8% 13% 20% 10% 1	3552
	21st to end	Night	38% 6% 13% 22% 19% 1	3809
August	1st to 10th	Night	48% 9% 15% 17% 9% 1	2798
	11th to 20th	Night	41% 8% 13% 27% 10% 1	3227
	21st to end	Night	31% 6% 10% 32% 20% 1	3586
September	1st to 10th	Night	40% 6% 10% 24% 18% 1	2000
	11th to 20th	Night	33% 5% 11% 22% 25% 3	2079
	21st to end	Night	43% 5% 9% 21% 21% 2	2200
October	1st to 10th	Night	38% 5% 12% 22% 21% 2	3788
	11th to 20th	Night	25% 4 9% 28% 29% 4	3899
	21st to end	Night	30% 4 11% 30% 22% 2	4502
November	1st to 10th	Night	34% 5% 11% 24% 22% 4	2667
	11th to 20th	Night	39% 4 8% 24% 20% 5%	2730
	21st to end	Night	38% 5% 12% 28% 16% 1	2825
December	1st to 10th	Night	39% 4 13% 30% 12% 2	4720
	11th to 20th	Night	46% 3 9% 22% 16% 4	5348
	21st to end	Night	46% 5% 11% 18% 17% 4	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	23% 28% 30% 16% 3	220
	11th to 20th	Day	25% 31% 34% 8% 2	220
	21st to end	Day	19% 26% 39% 12% 3 2	331
February	1st to 10th	Day	26% 21% 38% 12% 2	330
	11th to 20th	Day	25% 21% 36% 16% 2	536
	21st to end	Day	26% 20% 36% 15% 3	446
March	1st to 10th	Day	24% 24% 30% 18% 4	540
	11th to 20th	Day	24% 21% 34% 16% 5% 1	528
	21st to end	Day	28% 21% 32% 13% 6% 1	550
April	1st to 10th	Day	28% 23% 31% 12% 6% 1	500
	11th to 20th	Day	24% 22% 31% 14% 7% 2	492
	21st to end	Day	28% 17% 33% 18% 3 2	500
May	1st to 10th	Day	32% 18% 27% 16% 5% 2	503
	11th to 20th	Day	24% 13% 32% 21% 7% 1	527
	21st to end	Day	21% 9% 29% 26% 14% 2	573
June	1st to 10th	Day	17% 11% 31% 26% 12% 2	530
	11th to 20th	Day	18% 15% 30% 24% 12% 1	530
	21st to end	Day	14% 12% 32% 25% 15% 2	530
July	1st to 10th	Day	13% 6% 26% 31% 18% 5%	525
	11th to 20th	Day	10% 4 30% 31% 20% 4	524
	21st to end	Day	14% 7% 28% 34% 14% 2	576
August	1st to 10th	Day	13% 6% 25% 34% 16% 7%	526
	11th to 20th	Day	15% 6% 21% 34% 19% 4	519
	21st to end	Day	12% 8% 29% 30% 15% 6%	583
September	1st to 10th	Day	18% 10% 27% 23% 16% 6%	530
	11th to 20th	Day	16% 6% 27% 26% 14% 10%	530
	21st to end	Day	22% 11% 30% 22% 10% 5%	530
October	1st to 10th	Day	24% 8% 28% 20% 14% 6%	530
	11th to 20th	Day	20% 16% 29% 21% 11% 2	530
	21st to end	Day	24% 13% 33% 19% 9% 2	500
November	1st to 10th	Day	16% 15% 33% 23% 10% 3	425
	11th to 20th	Day	22% 20% 32% 21% 4 1	430
	21st to end	Day	20% 22% 34% 18% 5% 1	333
December	1st to 10th	Day	23% 25% 30% 15% 6%	220
	11th to 20th	Day	31% 21% 32% 13% 3	220
	21st to end	Day	27% 17% 36% 14% 6%	242
January	1st to 10th	Night	19% 17% 39% 21% 4	840
	11th to 20th	Night	24% 17% 32% 24% 3	840
	21st to end	Night	20% 16% 40% 23% 2	924
February	1st to 10th	Night	22% 13% 38% 25% 2	840
	11th to 20th	Night	23% 16% 41% 19% 1	823
	21st to end	Night	22% 17% 37% 21% 3	692
March	1st to 10th	Night	22% 15% 37% 21% 5%	840
	11th to 20th	Night	22% 15% 36% 22% 4	829
	21st to end	Night	22% 15% 38% 20% 4 1	880
April	1st to 10th	Night	24% 16% 35% 20% 5%	800
	11th to 20th	Night	23% 16% 34% 23% 5%	791
	21st to end	Night	22% 13% 34% 26% 5% 1	785
May	1st to 10th	Night	24% 13% 35% 22% 7%	600
	11th to 20th	Night	23% 12% 31% 28% 6%	420
	21st to end	Night	21% 6% 22% 38% 12% 1	433
June	1st to 10th	Night	18% 6% 30% 36% 11%	400
	11th to 20th	Night	16% 5% 29% 37% 13%	400
	21st to end	Night	11% 5% 26% 48% 10%	400
July	1st to 10th	Night	12% 5% 24% 39% 20% 1	390
	11th to 20th	Night	14% 4 20% 41% 19% 1	388
	21st to end	Night	14% 4 22% 46% 13% 1	438
August	1st to 10th	Night	12% 2 20% 44% 20% 2	529
	11th to 20th	Night	16% 3 16% 41% 23% 1	790
	21st to end	Night	15% 4 20% 40% 20% 2	880
September	1st to 10th	Night	15% 5% 25% 35% 18% 2	800
	11th to 20th	Night	16% 4 21% 36% 20% 3	800
	21st to end	Night	21% 4 24% 33% 15% 1	800
October	1st to 10th	Night	23% 7% 26% 26% 16% 3	800
	11th to 20th	Night	19% 10% 30% 30% 11% 1	800
	21st to end	Night	23% 10% 34% 25% 8%	880
November	1st to 10th	Night	16% 11% 32% 28% 12% 1	820
	11th to 20th	Night	21% 13% 35% 24% 7%	840
	21st to end	Night	18% 15% 34% 26% 6% 1	840
December	1st to 10th	Night	23% 14% 33% 24% 5% 1	840
	11th to 20th	Night	23% 13% 35% 25% 3	840
	21st to end	Night	23% 13% 36% 25% 3	924

Page generated at 2026-03-15 02:23:55. Version ac07

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