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 2024-12-06.

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% 39%	101585
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 41%	98136
Transparency	Day	42% 7% 12% 22% 16% 2	105117
	Night	41% 6% 12% 23% 16% 2	102680
Seeing	Day	20% 15% 31% 22% 10% 3	15075
	Night	20% 11% 31% 28% 9% 1	24257

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% 7% 2 6% 3 3 4 3 4 6% 47%	2517
	11th to 20th	Day	15% 9% 3 7% 6% 6% 4 3 5% 6% 36%	2520
	21st to end	Day	22% 12% 4 7% 4 3 4 3 4 4 33%	3028
February	1st to 10th	Day	18% 8% 3 7% 4 3 4 3 5% 6% 40%	1710
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 3 5% 6% 44%	1848
	21st to end	Day	20% 8% 3 4 4 4 4 3 6% 6% 38%	1570
March	1st to 10th	Day	27% 8% 2 6% 3 3 4 3 4 5% 35%	3116
	11th to 20th	Day	10% 5% 1 5% 6% 4 5% 4 7% 8% 44%	3349
	21st to end	Day	21% 7% 2 5% 3 3 3 2 5% 6% 43%	4124
April	1st to 10th	Day	18% 8% 2 6% 4 4 4 4 5% 7% 39%	2280
	11th to 20th	Day	18% 5% 2 5% 5% 4 4 3 5% 7% 41%	2254
	21st to end	Day	20% 6% 2 5% 4 4 3 3 6% 7% 40%	2294
May	1st to 10th	Day	28% 8% 2 5% 4 3 4 3 5% 7% 30%	4106
	11th to 20th	Day	24% 8% 3 7% 5% 4 4 4 5% 6% 31%	4388
	21st to end	Day	14% 5% 2 5% 4 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	16% 5% 2 5% 5% 4 5% 4 8% 9% 37%	2660
	11th to 20th	Day	15% 7% 2 7% 4 5% 6% 4 7% 8% 36%	2660
	21st to end	Day	12% 5% 2 6% 6% 5% 5% 5% 7% 9% 39%	2660
July	1st to 10th	Day	9% 6% 3 7% 6% 6% 6% 5% 8% 11% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	4440
	21st to end	Day	13% 8% 3 8% 6% 5% 6% 4 6% 8% 31%	4814
August	1st to 10th	Day	20% 7% 2 6% 5% 5% 6% 4 6% 8% 31%	4158
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 43%	3730
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 5% 8% 46%	4180
September	1st to 10th	Day	14% 5% 3 5% 5% 4 5% 3 5% 7% 43%	2280
	11th to 20th	Day	14% 5% 1 5% 3 4 4 3 5% 8% 48%	2204
	21st to end	Day	18% 6% 2 6% 5% 5% 4 3 4 5% 40%	2090
October	1st to 10th	Day	20% 6% 2 5% 3 4 3 3 5% 7% 41%	1973
	11th to 20th	Day	16% 5% 2 5% 4 4 3 3 5% 6% 49%	1900
	21st to end	Day	20% 5% 2 5% 3 3 4 3 5% 5% 44%	1948
November	1st to 10th	Day	14% 6% 2 4 3 3 3 2 4 5% 52%	1761
	11th to 20th	Day	17% 5% 2 4 4 2 3 3 5% 6% 48%	1800
	21st to end	Day	16% 6% 2 5% 4 3 5% 3 5% 6% 45%	1708
December	1st to 10th	Day	18% 8% 2 6% 4 4 3 3 5% 8% 39%	1560
	11th to 20th	Day	22% 5% 2 4 3 3 3 4 5% 6% 44%	1906
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 5% 7% 31%	2772
January	1st to 10th	Night	16% 7% 2 4 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 4 5% 42%	4440
	21st to end	Night	25% 10% 3 5% 4 3 4 3 4 5% 34%	4624
February	1st to 10th	Night	17% 9% 2 5% 4 4 3 3 5% 5% 43%	2470
	11th to 20th	Night	17% 8% 3 6% 4 4 3 3 5% 5% 42%	2218
	21st to end	Night	19% 8% 2 5% 4 4 3 3 4 6% 41%	1884
March	1st to 10th	Night	24% 10% 2 6% 4 3 3 3 4 5% 37%	3724
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 47%	3607
	21st to end	Night	19% 9% 3 6% 3 3 3 3 4 5% 43%	3506
April	1st to 10th	Night	19% 7% 2 5% 5% 4 4 3 6% 6% 39%	1900
	11th to 20th	Night	18% 7% 2 5% 4 4 4 3 5% 7% 41%	1875
	21st to end	Night	19% 7% 3 6% 3 4 3 3 5% 7% 42%	1886
May	1st to 10th	Night	26% 10% 3 7% 4 3 4 3 5% 6% 29%	2834
	11th to 20th	Night	26% 9% 3 7% 5% 3 3 3 4 6% 33%	2533
	21st to end	Night	16% 7% 2 6% 4 3 4 3 6% 8% 41%	2738
June	1st to 10th	Night	16% 6% 3 4 4 5% 4 3 6% 8% 41%	1520
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 4 6% 9% 42%	1520
	21st to end	Night	11% 3 1 6% 5% 4 4 4 7% 10% 43%	1520
July	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 4 7% 9% 39%	2520
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 8% 9% 37%	2520
	21st to end	Night	17% 9% 2 6% 4 4 5% 4 7% 9% 35%	2739
August	1st to 10th	Night	22% 7% 2 6% 4 4 5% 4 6% 7% 33%	2721
	11th to 20th	Night	14% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	3097
	21st to end	Night	10% 5% 2 6% 3 4 4 3 5% 8% 52%	3476
September	1st to 10th	Night	15% 5% 3 6% 5% 5% 4 4 5% 6% 45%	1900
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 4 7% 52%	1975
	21st to end	Night	19% 6% 2 5% 4 4 3 2 4 6% 44%	2090
October	1st to 10th	Night	19% 6% 3 6% 3 4 3 3 4 6% 42%	2204
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 6% 51%	2280
	21st to end	Night	20% 7% 2 5% 3 3 3 3 4 5% 45%	2650
November	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 4 5% 53%	2537
	11th to 20th	Night	20% 6% 2 4 3 3 3 3 4 5% 48%	2600
	21st to end	Night	15% 5% 2 5% 4 3 4 4 5% 7% 46%	2690
December	1st to 10th	Night	18% 7% 3 5% 4 3 4 4 5% 6% 40%	2737
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 6% 5% 3 4 3 4 6% 36%	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	38% 3 11% 32% 13% 3	2518
	11th to 20th	Day	47% 6% 12% 21% 13% 2	2520
	21st to end	Day	54% 6% 8% 20% 10% 2	3028
February	1st to 10th	Day	45% 5% 13% 23% 12% 2	1710
	11th to 20th	Day	42% 5% 9% 24% 17% 3	1857
	21st to end	Day	46% 5% 11% 21% 14% 3	1570
March	1st to 10th	Day	50% 5% 11% 23% 9% 2	3119
	11th to 20th	Day	33% 9% 13% 29% 14% 2	3349
	21st to end	Day	43% 4 8% 16% 24% 5%	4124
April	1st to 10th	Day	44% 6% 10% 20% 16% 4	2280
	11th to 20th	Day	42% 5% 12% 21% 17% 3	2254
	21st to end	Day	43% 6% 10% 20% 18% 4	2294
May	1st to 10th	Day	52% 7% 12% 15% 12% 1	4120
	11th to 20th	Day	51% 9% 12% 18% 9% 1	4392
	21st to end	Day	35% 8% 11% 26% 18% 2	4837
June	1st to 10th	Day	40% 9% 13% 20% 15% 2	2660
	11th to 20th	Day	42% 9% 13% 23% 11% 2	2660
	21st to end	Day	39% 9% 13% 22% 16% 1	2660
July	1st to 10th	Day	41% 10% 12% 21% 15% 1	4370
	11th to 20th	Day	39% 8% 16% 22% 14% 1	4365
	21st to end	Day	48% 8% 11% 16% 15% 2	4661
August	1st to 10th	Day	48% 8% 14% 20% 9%	4144
	11th to 20th	Day	37% 7% 14% 28% 13% 1	3766
	21st to end	Day	35% 6% 10% 28% 19% 2	4180
September	1st to 10th	Day	39% 8% 10% 21% 19% 3	2280
	11th to 20th	Day	34% 5% 11% 23% 25% 3	2204
	21st to end	Day	45% 6% 8% 19% 19% 3	2090
October	1st to 10th	Day	39% 5% 10% 18% 23% 6%	3272
	11th to 20th	Day	26% 4 11% 24% 31% 5%	3140
	21st to end	Day	27% 4 14% 25% 26% 4	3186
November	1st to 10th	Day	35% 4 12% 23% 24% 3	1761
	11th to 20th	Day	38% 4 10% 24% 21% 4	1800
	21st to end	Day	39% 5% 13% 29% 11% 2	1708
December	1st to 10th	Day	45% 5% 14% 21% 14% 1	1560
	11th to 20th	Day	41% 5% 15% 24% 13% 3	1906
	21st to end	Day	50% 8% 11% 23% 8%	2772
January	1st to 10th	Night	38% 5% 11% 31% 12% 4	4429
	11th to 20th	Night	44% 5% 12% 25% 12% 2	4440
	21st to end	Night	51% 5% 9% 22% 12% 2	4624
February	1st to 10th	Night	44% 5% 12% 24% 12% 2	2470
	11th to 20th	Night	45% 4 9% 19% 18% 5%	2220
	21st to end	Night	44% 4 8% 24% 16% 4	1884
March	1st to 10th	Night	50% 5% 10% 21% 11% 3	3734
	11th to 20th	Night	35% 7% 14% 25% 16% 3	3608
	21st to end	Night	45% 4 8% 15% 22% 7%	3506
April	1st to 10th	Night	45% 6% 10% 19% 16% 4	1900
	11th to 20th	Night	44% 5% 10% 20% 19% 2	1875
	21st to end	Night	42% 6% 9% 21% 19% 4	1886
May	1st to 10th	Night	55% 7% 10% 17% 10% 1	2840
	11th to 20th	Night	53% 7% 14% 14% 10% 2	2534
	21st to end	Night	39% 8% 14% 24% 13% 3	2739
June	1st to 10th	Night	40% 7% 11% 21% 19% 2	1520
	11th to 20th	Night	39% 8% 13% 27% 12% 1	1520
	21st to end	Night	35% 9% 15% 25% 16% 1	1520
July	1st to 10th	Night	41% 9% 15% 18% 14% 2	2480
	11th to 20th	Night	41% 9% 14% 23% 12% 1	2472
	21st to end	Night	44% 8% 14% 15% 17% 2	2651
August	1st to 10th	Night	49% 9% 16% 16% 9% 1	2711
	11th to 20th	Night	42% 8% 13% 27% 10% 1	3127
	21st to end	Night	31% 6% 10% 32% 19% 1	3476
September	1st to 10th	Night	40% 7% 10% 23% 19% 1	1900
	11th to 20th	Night	33% 5% 11% 23% 24% 3	1975
	21st to end	Night	42% 5% 9% 22% 21% 2	2090
October	1st to 10th	Night	39% 5% 12% 22% 20% 2	3672
	11th to 20th	Night	24% 4 9% 28% 30% 4	3779
	21st to end	Night	30% 4 11% 30% 22% 2	4362
November	1st to 10th	Night	34% 5% 11% 24% 22% 4	2537
	11th to 20th	Night	39% 4 9% 24% 20% 4	2600
	21st to end	Night	38% 5% 13% 28% 15% 1	2690
December	1st to 10th	Night	43% 5% 13% 23% 14% 2	2737
	11th to 20th	Night	43% 5% 12% 20% 16% 4	3288
	21st to end	Night	47% 7% 13% 20% 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	21% 29% 29% 18% 3	180
	11th to 20th	Day	23% 31% 34% 10% 2	180
	21st to end	Day	19% 24% 38% 13% 4 2	270
February	1st to 10th	Day	27% 23% 37% 11% 2	270
	11th to 20th	Day	24% 21% 37% 16% 2	456
	21st to end	Day	27% 19% 34% 16% 4	382
March	1st to 10th	Day	23% 24% 29% 20% 4	460
	11th to 20th	Day	22% 22% 34% 16% 4 1	460
	21st to end	Day	27% 21% 32% 13% 6% 1	506
April	1st to 10th	Day	27% 22% 31% 13% 7% 1	460
	11th to 20th	Day	23% 21% 32% 15% 7% 2	452
	21st to end	Day	28% 17% 34% 16% 3 2	460
May	1st to 10th	Day	32% 18% 27% 16% 5% 2	463
	11th to 20th	Day	23% 13% 33% 23% 8% 1	487
	21st to end	Day	19% 8% 29% 27% 14% 2	529
June	1st to 10th	Day	16% 11% 32% 25% 12% 2	490
	11th to 20th	Day	16% 15% 31% 25% 12% 1	490
	21st to end	Day	14% 12% 33% 24% 15% 2	490
July	1st to 10th	Day	13% 6% 26% 31% 19% 5%	485
	11th to 20th	Day	10% 4 30% 31% 20% 4	484
	21st to end	Day	14% 8% 28% 33% 14% 2	532
August	1st to 10th	Day	13% 6% 24% 34% 16% 7%	486
	11th to 20th	Day	15% 6% 22% 33% 20% 4	479
	21st to end	Day	12% 8% 28% 30% 16% 7%	539
September	1st to 10th	Day	18% 10% 26% 23% 17% 7%	490
	11th to 20th	Day	16% 7% 28% 25% 14% 11%	490
	21st to end	Day	22% 12% 30% 21% 10% 5%	490
October	1st to 10th	Day	25% 9% 28% 20% 13% 5%	490
	11th to 20th	Day	18% 16% 30% 22% 11% 2	490
	21st to end	Day	24% 14% 32% 19% 9% 2	464
November	1st to 10th	Day	16% 14% 34% 22% 11% 3	395
	11th to 20th	Day	22% 19% 33% 22% 4 1	400
	21st to end	Day	19% 21% 34% 19% 6% 1	308
December	1st to 10th	Day	22% 26% 28% 17% 7%	190
	11th to 20th	Day	29% 22% 35% 12% 2	180
	21st to end	Day	27% 18% 35% 14% 6% 1	198
January	1st to 10th	Night	18% 16% 40% 21% 4	760
	11th to 20th	Night	25% 15% 33% 24% 3	760
	21st to end	Night	20% 16% 38% 24% 2	836
February	1st to 10th	Night	22% 12% 38% 26% 2	760
	11th to 20th	Night	22% 16% 42% 18% 1	743
	21st to end	Night	23% 17% 35% 21% 3	628
March	1st to 10th	Night	22% 15% 38% 21% 5%	760
	11th to 20th	Night	22% 15% 37% 21% 4 1	760
	21st to end	Night	22% 15% 37% 21% 5% 1	836
April	1st to 10th	Night	23% 16% 35% 21% 5%	760
	11th to 20th	Night	22% 15% 34% 24% 5%	751
	21st to end	Night	22% 13% 34% 26% 5% 1	746
May	1st to 10th	Night	23% 14% 35% 22% 7%	570
	11th to 20th	Night	23% 12% 32% 27% 7%	399
	21st to end	Night	20% 6% 21% 39% 13% 1	411
June	1st to 10th	Night	18% 6% 30% 35% 11%	380
	11th to 20th	Night	15% 4 29% 38% 13%	380
	21st to end	Night	10% 5% 26% 49% 10%	380
July	1st to 10th	Night	12% 5% 24% 39% 20% 1	370
	11th to 20th	Night	13% 4 21% 42% 19% 1	368
	21st to end	Night	15% 4 22% 45% 13% 1	416
August	1st to 10th	Night	12% 2 21% 43% 20% 2	502
	11th to 20th	Night	17% 3 17% 39% 23% 1	750
	21st to end	Night	15% 4 18% 40% 21% 2	836
September	1st to 10th	Night	15% 4 25% 35% 18% 3	760
	11th to 20th	Night	17% 5% 21% 34% 20% 4	760
	21st to end	Night	21% 4 25% 33% 15% 1	760
October	1st to 10th	Night	23% 8% 26% 26% 15% 3	760
	11th to 20th	Night	18% 9% 30% 31% 11% 1	760
	21st to end	Night	23% 10% 33% 25% 8%	836
November	1st to 10th	Night	15% 10% 33% 28% 12% 1	780
	11th to 20th	Night	22% 11% 35% 24% 7% 1	800
	21st to end	Night	18% 15% 35% 26% 6% 1	800
December	1st to 10th	Night	24% 13% 33% 24% 5% 1	783
	11th to 20th	Night	22% 12% 36% 27% 3	760
	21st to end	Night	23% 13% 36% 25% 2	836

Page generated at 2024-12-03 06:45:13. Version ac07

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