Trenton (NJ)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trenton (NJ) clear sky chart from 2005-11-06 to 2025-05-11.

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	16% 7% 2 6% 4 4 4 4 5% 7% 41%	113721
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	115194
Transparency	Day	24% 43% 7% 14% 11% 2	117296
	Night	25% 41% 7% 14% 11% 3	119783
Seeing	Day	21% 15% 29% 21% 10% 3	15613
	Night	19% 12% 32% 27% 9% 1	24965

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% 3 3 4 3 4 6% 51%	3597
	11th to 20th	Day	13% 8% 3 8% 5% 4 4 3 5% 5% 42%	3587
	21st to end	Day	19% 8% 3 6% 5% 3 4 3 4 5% 41%	4466
February	1st to 10th	Day	16% 7% 3 8% 4 4 4 3 5% 7% 40%	1800
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 3 4 6% 41%	1931
	21st to end	Day	18% 8% 3 7% 4 3 4 4 5% 5% 38%	1650
March	1st to 10th	Day	21% 5% 2 4 3 4 4 3 4 5% 44%	4476
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 7% 44%	4888
	21st to end	Day	19% 5% 2 6% 4 4 4 3 5% 6% 43%	5850
April	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 6% 6% 39%	2400
	11th to 20th	Day	16% 6% 2 5% 4 4 4 4 6% 7% 41%	2374
	21st to end	Day	16% 5% 2 6% 4 5% 4 4 6% 6% 41%	2400
May	1st to 10th	Day	27% 8% 2 6% 4 4 4 3 5% 7% 29%	4188
	11th to 20th	Day	24% 8% 3 8% 5% 5% 4 4 5% 6% 29%	4398
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	4837
June	1st to 10th	Day	13% 5% 2 5% 5% 5% 5% 5% 8% 9% 38%	2660
	11th to 20th	Day	12% 7% 2 5% 5% 5% 5% 5% 6% 9% 38%	2660
	21st to end	Day	11% 6% 2 5% 4 5% 5% 5% 6% 9% 41%	2660
July	1st to 10th	Day	8% 6% 3 7% 6% 6% 7% 5% 8% 10% 35%	4440
	11th to 20th	Day	10% 7% 2 6% 5% 5% 6% 5% 7% 10% 38%	4440
	21st to end	Day	12% 9% 3 8% 5% 5% 5% 5% 7% 8% 32%	4814
August	1st to 10th	Day	18% 7% 2 8% 5% 5% 5% 4 6% 8% 32%	4061
	11th to 20th	Day	13% 6% 3 6% 4 5% 4 4 6% 9% 41%	3730
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 9% 47%	4180
September	1st to 10th	Day	14% 6% 2 7% 4 4 3 3 6% 7% 44%	2280
	11th to 20th	Day	12% 5% 2 4 4 4 4 3 5% 9% 49%	2228
	21st to end	Day	18% 7% 3 6% 4 4 4 4 4 6% 39%	2090
October	1st to 10th	Day	17% 7% 3 5% 3 3 4 3 5% 6% 43%	1939
	11th to 20th	Day	15% 6% 2 5% 3 4 3 3 5% 6% 49%	1900
	21st to end	Day	18% 7% 2 5% 3 3 3 3 5% 6% 46%	1990
November	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 5% 7% 52%	1761
	11th to 20th	Day	16% 6% 3 4 2 3 4 3 4 6% 48%	1800
	21st to end	Day	16% 6% 2 5% 4 3 3 3 5% 8% 46%	1700
December	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 6% 7% 45%	2600
	11th to 20th	Day	22% 8% 2 3 3 3 3 3 3 5% 44%	2986
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 6% 8% 40%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 4 3 3 4 6% 51%	6349
	11th to 20th	Night	15% 7% 2 6% 4 3 3 3 4 6% 48%	6297
	21st to end	Night	18% 9% 2 5% 4 4 4 3 4 6% 41%	6490
February	1st to 10th	Night	17% 9% 2 5% 3 4 4 3 6% 6% 41%	2600
	11th to 20th	Night	18% 9% 3 5% 4 3 3 3 5% 5% 42%	2353
	21st to end	Night	18% 8% 3 6% 4 4 2 4 5% 5% 42%	1980
March	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 6% 45%	5364
	11th to 20th	Night	12% 9% 3 5% 3 4 3 3 4 5% 49%	5053
	21st to end	Night	16% 8% 3 7% 4 4 4 3 5% 5% 42%	5082
April	1st to 10th	Night	17% 7% 3 6% 4 4 4 4 5% 6% 40%	2000
	11th to 20th	Night	17% 6% 2 7% 4 5% 4 3 5% 6% 41%	1975
	21st to end	Night	18% 6% 1 5% 3 3 4 3 5% 8% 44%	2000
May	1st to 10th	Night	22% 10% 4 7% 4 3 4 4 5% 7% 30%	2974
	11th to 20th	Night	23% 9% 3 7% 5% 4 3 3 5% 7% 31%	2512
	21st to end	Night	14% 7% 2 5% 3 4 4 4 6% 9% 42%	2738
June	1st to 10th	Night	15% 7% 2 5% 4 4 4 4 6% 7% 43%	1520
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 4 5% 8% 42%	1520
	21st to end	Night	9% 5% 2 6% 6% 4 4 4 8% 11% 41%	1520
July	1st to 10th	Night	7% 6% 3 8% 5% 5% 6% 5% 8% 9% 37%	2520
	11th to 20th	Night	12% 5% 3 6% 5% 5% 5% 5% 7% 10% 37%	2520
	21st to end	Night	15% 7% 3 7% 5% 4 5% 5% 7% 8% 35%	2739
August	1st to 10th	Night	23% 6% 2 7% 4 4 4 4 7% 8% 31%	2831
	11th to 20th	Night	13% 7% 2 6% 4 5% 5% 4 6% 7% 40%	3097
	21st to end	Night	10% 5% 2 5% 4 3 3 3 6% 9% 49%	3476
September	1st to 10th	Night	15% 6% 3 6% 5% 3 4 4 4 5% 45%	1900
	11th to 20th	Night	12% 5% 1 4 3 4 4 3 5% 7% 52%	1952
	21st to end	Night	19% 7% 2 6% 4 3 3 3 5% 7% 41%	2090
October	1st to 10th	Night	18% 6% 2 6% 4 4 3 3 4 6% 44%	2237
	11th to 20th	Night	14% 4 2 5% 3 3 4 3 4 7% 51%	2280
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 5% 46%	2608
November	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 5% 6% 53%	2537
	11th to 20th	Night	17% 6% 2 6% 4 3 3 3 4 4 48%	2600
	21st to end	Night	13% 7% 2 5% 5% 4 4 3 6% 6% 45%	2696
December	1st to 10th	Night	13% 8% 3 5% 3 3 3 3 5% 6% 47%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 4 3 4 5% 41%	5208
	21st to end	Night	20% 8% 2 6% 4 4 3 3 5% 5% 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	25% 27% 6% 21% 19% 3	3598
	11th to 20th	Day	31% 28% 6% 18% 13% 5%	3617
	21st to end	Day	35% 29% 8% 15% 11% 1	4466
February	1st to 10th	Day	19% 63% 6% 8% 4 1	1800
	11th to 20th	Day	18% 60% 3 9% 8% 2	1940
	21st to end	Day	17% 63% 4 9% 5% 1	1650
March	1st to 10th	Day	31% 30% 7% 14% 11% 7%	4479
	11th to 20th	Day	25% 31% 9% 21% 10% 4	4888
	21st to end	Day	30% 29% 7% 10% 19% 5%	5850
April	1st to 10th	Day	20% 62% 4 7% 6% 2	2400
	11th to 20th	Day	16% 64% 5% 8% 7%	2374
	21st to end	Day	16% 62% 4 9% 7% 1	2400
May	1st to 10th	Day	37% 41% 8% 10% 4	4202
	11th to 20th	Day	36% 42% 8% 11% 2	4402
	21st to end	Day	21% 43% 7% 18% 11% 1	4837
June	1st to 10th	Day	15% 66% 4 9% 6%	2660
	11th to 20th	Day	14% 66% 4 9% 7%	2660
	21st to end	Day	14% 65% 4 9% 8%	2660
July	1st to 10th	Day	27% 42% 10% 11% 8% 1	4370
	11th to 20th	Day	27% 40% 11% 13% 9%	4365
	21st to end	Day	32% 38% 7% 12% 10% 1	4661
August	1st to 10th	Day	34% 40% 8% 13% 5%	4047
	11th to 20th	Day	23% 39% 8% 20% 8%	3766
	21st to end	Day	17% 38% 7% 21% 17% 1	4180
September	1st to 10th	Day	16% 60% 6% 10% 7% 1	2280
	11th to 20th	Day	15% 61% 5% 9% 9% 2	2228
	21st to end	Day	22% 60% 3 8% 7%	2090
October	1st to 10th	Day	23% 38% 7% 8% 20% 5%	3225
	11th to 20th	Day	10% 37% 7% 15% 25% 6%	3140
	21st to end	Day	11% 36% 10% 18% 21% 4	3254
November	1st to 10th	Day	16% 56% 6% 10% 9% 2	1761
	11th to 20th	Day	14% 57% 4 11% 13% 2	1800
	21st to end	Day	15% 57% 7% 15% 5% 2	1700
December	1st to 10th	Day	25% 36% 10% 19% 9% 2	2600
	11th to 20th	Day	31% 32% 6% 21% 9% 2	2986
	21st to end	Day	30% 30% 7% 18% 13% 2	3960
January	1st to 10th	Night	25% 27% 6% 18% 18% 5%	6349
	11th to 20th	Night	28% 27% 8% 18% 13% 6%	6342
	21st to end	Night	34% 28% 7% 14% 13% 3	6490
February	1st to 10th	Night	17% 62% 6% 11% 3 1	2600
	11th to 20th	Night	17% 61% 2 8% 10% 2	2355
	21st to end	Night	17% 62% 4 7% 7% 3	1980
March	1st to 10th	Night	32% 30% 5% 16% 8% 9%	5374
	11th to 20th	Night	24% 31% 12% 19% 10% 3	5054
	21st to end	Night	33% 30% 4 11% 19% 4	5082
April	1st to 10th	Night	19% 62% 3 8% 7% 1	2000
	11th to 20th	Night	16% 63% 5% 8% 8% 1	1975
	21st to end	Night	16% 62% 4 8% 9% 1	2000
May	1st to 10th	Night	35% 42% 7% 13% 3	2980
	11th to 20th	Night	36% 42% 10% 8% 3	2513
	21st to end	Night	22% 43% 10% 14% 9% 2	2739
June	1st to 10th	Night	14% 65% 3 9% 8%	1520
	11th to 20th	Night	13% 66% 4 10% 6%	1520
	21st to end	Night	13% 64% 5% 11% 6% 1	1520
July	1st to 10th	Night	26% 41% 13% 11% 7% 1	2480
	11th to 20th	Night	27% 39% 12% 16% 6%	2472
	21st to end	Night	33% 37% 9% 10% 10% 1	2651
August	1st to 10th	Night	36% 40% 12% 8% 4	2821
	11th to 20th	Night	25% 39% 8% 21% 7%	3127
	21st to end	Night	16% 38% 6% 24% 16%	3476
September	1st to 10th	Night	15% 61% 6% 10% 7% 1	1900
	11th to 20th	Night	14% 61% 4 9% 11% 2	1952
	21st to end	Night	21% 60% 3 8% 6%	2090
October	1st to 10th	Night	24% 38% 7% 14% 16% 1	3731
	11th to 20th	Night	10% 37% 5% 20% 23% 4	3779
	21st to end	Night	13% 37% 7% 23% 18% 3	4294
November	1st to 10th	Night	16% 56% 6% 11% 8% 2	2537
	11th to 20th	Night	15% 57% 3 10% 11% 3	2600
	21st to end	Night	15% 57% 7% 13% 7% 1	2696
December	1st to 10th	Night	24% 36% 7% 23% 8% 1	4580
	11th to 20th	Night	32% 32% 6% 17% 10% 3	5208
	21st to end	Night	35% 27% 7% 15% 14% 3	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	28% 27% 28% 15% 2 1	200
	11th to 20th	Day	36% 25% 29% 8% 1	203
	21st to end	Day	24% 26% 33% 12% 5%	330
February	1st to 10th	Day	28% 25% 34% 10% 2	300
	11th to 20th	Day	32% 24% 32% 11% 1	479
	21st to end	Day	29% 22% 32% 14% 3	414
March	1st to 10th	Day	30% 20% 30% 17% 3	500
	11th to 20th	Day	24% 25% 32% 13% 5% 1	500
	21st to end	Day	27% 23% 31% 13% 5% 1	550
April	1st to 10th	Day	29% 22% 32% 10% 6% 1	500
	11th to 20th	Day	24% 22% 32% 13% 8% 2	492
	21st to end	Day	26% 20% 31% 17% 4 2	500
May	1st to 10th	Day	30% 18% 30% 14% 7% 1	503
	11th to 20th	Day	22% 16% 33% 20% 8% 1	487
	21st to end	Day	20% 9% 26% 27% 16% 2	529
June	1st to 10th	Day	17% 11% 31% 26% 12% 3	490
	11th to 20th	Day	18% 13% 28% 27% 12% 3	490
	21st to end	Day	15% 11% 33% 28% 11% 3	490
July	1st to 10th	Day	11% 7% 23% 33% 20% 6%	485
	11th to 20th	Day	9% 4 27% 32% 22% 6%	484
	21st to end	Day	14% 7% 31% 29% 16% 3	532
August	1st to 10th	Day	14% 5% 25% 34% 16% 7%	486
	11th to 20th	Day	13% 6% 22% 33% 21% 6%	479
	21st to end	Day	13% 7% 25% 29% 17% 9%	539
September	1st to 10th	Day	16% 10% 26% 24% 16% 8%	490
	11th to 20th	Day	15% 6% 28% 28% 15% 9%	490
	21st to end	Day	24% 13% 23% 24% 10% 6%	490
October	1st to 10th	Day	24% 8% 26% 22% 13% 7%	490
	11th to 20th	Day	17% 16% 28% 26% 10% 3	490
	21st to end	Day	21% 16% 29% 21% 10% 2	486
November	1st to 10th	Day	19% 11% 33% 23% 12% 3	395
	11th to 20th	Day	24% 16% 33% 21% 6% 1	400
	21st to end	Day	24% 15% 36% 17% 7%	300
December	1st to 10th	Day	27% 24% 32% 10% 7%	200
	11th to 20th	Day	36% 21% 26% 12% 6%	200
	21st to end	Day	27% 17% 32% 15% 7% 1	220
January	1st to 10th	Night	20% 20% 38% 20% 3	800
	11th to 20th	Night	23% 17% 36% 21% 3	800
	21st to end	Night	19% 19% 40% 21% 1	880
February	1st to 10th	Night	22% 15% 38% 23% 2	800
	11th to 20th	Night	26% 22% 35% 16% 1	783
	21st to end	Night	24% 18% 38% 18% 2	660
March	1st to 10th	Night	23% 19% 33% 21% 3	800
	11th to 20th	Night	24% 17% 35% 19% 4	800
	21st to end	Night	20% 15% 41% 19% 4	880
April	1st to 10th	Night	22% 19% 37% 18% 4	800
	11th to 20th	Night	20% 15% 38% 23% 5%	791
	21st to end	Night	21% 13% 36% 26% 5%	800
May	1st to 10th	Night	24% 16% 31% 24% 5%	637
	11th to 20th	Night	21% 9% 37% 27% 5%	387
	21st to end	Night	16% 6% 26% 39% 12% 1	411
June	1st to 10th	Night	15% 7% 29% 37% 11% 1	380
	11th to 20th	Night	12% 6% 31% 40% 12%	380
	21st to end	Night	11% 3 28% 45% 13%	380
July	1st to 10th	Night	10% 4 25% 42% 18% 1	370
	11th to 20th	Night	9% 3 24% 44% 19% 1	368
	21st to end	Night	12% 3 26% 43% 16%	416
August	1st to 10th	Night	14% 1 19% 45% 19% 2	560
	11th to 20th	Night	14% 3 20% 36% 24% 3	750
	21st to end	Night	14% 5% 17% 41% 21% 2	836
September	1st to 10th	Night	17% 3 26% 34% 18% 2	760
	11th to 20th	Night	15% 4 21% 34% 21% 4	760
	21st to end	Night	22% 6% 22% 33% 17% 1	760
October	1st to 10th	Night	22% 8% 26% 26% 16% 3	760
	11th to 20th	Night	16% 11% 28% 33% 12%	760
	21st to end	Night	21% 11% 32% 27% 8%	836
November	1st to 10th	Night	14% 10% 34% 29% 12% 1	780
	11th to 20th	Night	20% 16% 31% 25% 8%	800
	21st to end	Night	18% 15% 36% 25% 7% 1	800
December	1st to 10th	Night	25% 17% 32% 20% 6% 1	800
	11th to 20th	Night	21% 15% 36% 24% 4	800
	21st to end	Night	22% 15% 34% 26% 3	880

Page generated at 2025-05-08 09:33:54. Version ac07

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