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 2026-09-14.

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	16% 6% 2 6% 4 4 4 4 6% 8% 40%	149116
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	141936
Transparency	Day	28% 34% 8% 16% 12% 2	152644
	Night	28% 34% 8% 16% 12% 2	146496
Seeing	Day	21% 15% 29% 21% 10% 3	17413
	Night	19% 12% 31% 28% 9% 1	26573

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 6% 4 4 4 3 4 6% 48%	4661
	11th to 20th	Day	15% 7% 3 7% 4 4 3 2 4 5% 45%	4667
	21st to end	Day	16% 6% 3 5% 4 4 5% 4 5% 6% 41%	5780
February	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 5% 7% 41%	1890
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 3 4 6% 40%	2030
	21st to end	Day	18% 9% 3 7% 4 3 4 4 5% 6% 38%	1730
March	1st to 10th	Day	21% 6% 2 5% 3 4 4 3 4 5% 44%	4576
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 7% 44%	4996
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 6% 43%	5979
April	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 6% 6% 40%	2520
	11th to 20th	Day	15% 6% 2 5% 4 4 4 5% 6% 8% 41%	2494
	21st to end	Day	16% 5% 2 6% 4 5% 4 4 6% 6% 41%	2520
May	1st to 10th	Day	23% 7% 2 6% 4 4 4 3 5% 7% 33%	7538
	11th to 20th	Day	19% 7% 3 6% 4 4 4 4 5% 6% 39%	8221
	21st to end	Day	24% 7% 2 6% 4 4 4 4 5% 7% 34%	9060
June	1st to 10th	Day	13% 5% 2 5% 5% 4 5% 5% 7% 9% 39%	2940
	11th to 20th	Day	13% 7% 2 5% 5% 5% 4 5% 6% 8% 39%	2940
	21st to end	Day	12% 6% 3 5% 4 5% 5% 4 6% 9% 40%	2940
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 9% 37%	8280
	11th to 20th	Day	9% 7% 3 7% 5% 5% 6% 5% 7% 11% 35%	8280
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 4 7% 9% 39%	8993
August	1st to 10th	Day	15% 7% 2 8% 6% 6% 6% 5% 7% 10% 29%	5956
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 4 6% 10% 42%	5488
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 43%	6080
September	1st to 10th	Day	13% 6% 2 6% 4 4 3 3 6% 7% 44%	2520
	11th to 20th	Day	12% 5% 2 4 4 4 4 3 5% 9% 49%	2381
	21st to end	Day	18% 8% 3 7% 4 4 4 4 5% 6% 38%	2200
October	1st to 10th	Day	17% 6% 3 5% 3 3 4 3 5% 6% 44%	2041
	11th to 20th	Day	16% 6% 2 5% 3 4 3 3 5% 7% 48%	2000
	21st to end	Day	18% 7% 2 5% 3 2 3 3 4 6% 47%	2095
November	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 5% 7% 51%	1851
	11th to 20th	Day	16% 6% 3 4 2 3 4 3 4 6% 47%	1890
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 7% 45%	1785
December	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 6% 7% 45%	2680
	11th to 20th	Day	21% 8% 2 3 3 3 3 3 4 5% 44%	3066
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 6% 8% 39%	4048
January	1st to 10th	Night	12% 8% 3 6% 4 4 3 3 4 6% 47%	8234
	11th to 20th	Night	15% 7% 2 6% 4 3 3 3 4 6% 47%	8203
	21st to end	Night	15% 8% 2 5% 4 4 4 3 4 6% 45%	8401
February	1st to 10th	Night	16% 9% 3 6% 3 4 4 3 6% 6% 41%	2730
	11th to 20th	Night	18% 9% 3 5% 4 3 4 3 5% 5% 41%	2474
	21st to end	Night	18% 8% 3 6% 4 4 3 4 5% 5% 42%	2076
March	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 5% 44%	5484
	11th to 20th	Night	12% 9% 3 5% 3 4 3 3 4 5% 49%	5165
	21st to end	Night	16% 8% 3 7% 4 4 4 3 5% 6% 42%	5195
April	1st to 10th	Night	18% 7% 3 6% 4 4 4 4 5% 6% 40%	2100
	11th to 20th	Night	16% 6% 2 7% 4 4 4 4 6% 6% 41%	2075
	21st to end	Night	18% 6% 1 5% 3 3 4 3 5% 7% 44%	2100
May	1st to 10th	Night	19% 9% 3 8% 4 4 5% 4 6% 8% 31%	5363
	11th to 20th	Night	19% 8% 3 6% 5% 4 4 3 5% 8% 35%	4663
	21st to end	Night	25% 8% 3 7% 4 4 4 3 5% 7% 32%	5114
June	1st to 10th	Night	14% 7% 2 5% 4 4 5% 4 6% 7% 43%	1680
	11th to 20th	Night	12% 6% 2 7% 5% 5% 4 5% 6% 8% 40%	1680
	21st to end	Night	10% 5% 2 6% 6% 4 4 4 8% 11% 40%	1680
July	1st to 10th	Night	11% 6% 3 8% 4 5% 6% 4 7% 9% 37%	4680
	11th to 20th	Night	11% 7% 4 7% 5% 5% 5% 5% 7% 10% 34%	4680
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 6% 9% 41%	5084
August	1st to 10th	Night	19% 6% 3 8% 5% 5% 5% 4 7% 8% 30%	4141
	11th to 20th	Night	13% 7% 2 6% 4 5% 6% 4 6% 8% 39%	4557
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 7% 46%	5045
September	1st to 10th	Night	15% 6% 3 6% 5% 4 4 4 4 6% 45%	2100
	11th to 20th	Night	12% 5% 1 5% 4 4 4 3 5% 7% 51%	2086
	21st to end	Night	19% 7% 2 6% 4 4 3 3 5% 7% 40%	2200
October	1st to 10th	Night	17% 6% 2 6% 4 4 3 3 5% 6% 46%	2355
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 4 6% 51%	2400
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 5% 47%	2745
November	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 5% 6% 53%	2667
	11th to 20th	Night	17% 6% 2 6% 4 3 3 3 4 4 48%	2730
	21st to end	Night	13% 7% 2 5% 5% 4 4 3 6% 6% 45%	2831
December	1st to 10th	Night	13% 8% 3 5% 3 3 3 3 5% 6% 47%	4720
	11th to 20th	Night	23% 7% 2 5% 3 3 4 3 4 5% 42%	5348
	21st to end	Night	20% 8% 2 6% 4 4 3 3 5% 5% 41%	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	30% 22% 6% 23% 17% 2	4662
	11th to 20th	Day	32% 22% 6% 19% 16% 6%	4697
	21st to end	Day	34% 24% 10% 18% 13% 1	5780
February	1st to 10th	Day	19% 60% 6% 9% 4 1	1890
	11th to 20th	Day	20% 58% 3 10% 8% 1	2039
	21st to end	Day	19% 60% 4 10% 6% 1	1730
March	1st to 10th	Day	32% 29% 7% 14% 11% 7%	4579
	11th to 20th	Day	26% 30% 9% 21% 10% 4	4996
	21st to end	Day	30% 29% 8% 10% 18% 5%	5979
April	1st to 10th	Day	20% 60% 4 8% 6% 2	2520
	11th to 20th	Day	16% 61% 6% 10% 7%	2494
	21st to end	Day	18% 59% 4 10% 7% 1	2520
May	1st to 10th	Day	40% 25% 10% 14% 11%	7549
	11th to 20th	Day	36% 24% 7% 20% 12% 1	8225
	21st to end	Day	41% 24% 6% 18% 10% 1	9061
June	1st to 10th	Day	16% 60% 4 10% 9% 1	2940
	11th to 20th	Day	17% 60% 5% 10% 8% 1	2940
	21st to end	Day	17% 59% 5% 10% 9% 1	2940
July	1st to 10th	Day	35% 25% 11% 15% 14% 1	8210
	11th to 20th	Day	34% 25% 12% 19% 10%	8205
	21st to end	Day	31% 23% 8% 18% 19% 1	8795
August	1st to 10th	Day	38% 31% 12% 13% 5%	5942
	11th to 20th	Day	26% 29% 13% 24% 8%	5524
	21st to end	Day	25% 28% 7% 22% 15% 1	6080
September	1st to 10th	Day	17% 55% 7% 12% 8% 1	2520
	11th to 20th	Day	17% 57% 5% 11% 9% 2	2381
	21st to end	Day	24% 58% 4 8% 6%	2200
October	1st to 10th	Day	22% 37% 7% 9% 20% 5%	3327
	11th to 20th	Day	11% 36% 7% 16% 24% 6%	3240
	21st to end	Day	11% 35% 9% 19% 22% 4	3359
November	1st to 10th	Day	17% 54% 6% 11% 10% 2	1851
	11th to 20th	Day	16% 54% 4 12% 13% 2	1890
	21st to end	Day	17% 54% 7% 15% 6% 1	1785
December	1st to 10th	Day	26% 35% 10% 19% 9% 2	2680
	11th to 20th	Day	31% 31% 6% 21% 9% 2	3066
	21st to end	Day	31% 29% 7% 18% 13% 2	4048
January	1st to 10th	Night	31% 22% 10% 19% 15% 4	8234
	11th to 20th	Night	32% 21% 8% 18% 15% 7%	8248
	21st to end	Night	33% 22% 6% 18% 17% 3	8401
February	1st to 10th	Night	18% 59% 6% 11% 3 2	2730
	11th to 20th	Night	19% 58% 3 9% 10% 2	2476
	21st to end	Night	18% 59% 4 9% 7% 2	2076
March	1st to 10th	Night	33% 29% 5% 16% 8% 9%	5494
	11th to 20th	Night	25% 30% 12% 20% 10% 3	5166
	21st to end	Night	33% 29% 5% 11% 18% 4	5195
April	1st to 10th	Night	20% 59% 3 9% 7% 1	2100
	11th to 20th	Night	17% 60% 5% 9% 8% 1	2075
	21st to end	Night	17% 59% 4 9% 9% 1	2100
May	1st to 10th	Night	40% 26% 9% 16% 8% 1	5369
	11th to 20th	Night	38% 25% 10% 18% 9%	4664
	21st to end	Night	43% 25% 8% 16% 8% 1	5115
June	1st to 10th	Night	16% 60% 3 10% 10% 1	1680
	11th to 20th	Night	17% 60% 4 11% 7%	1680
	21st to end	Night	17% 59% 6% 11% 7% 1	1680
July	1st to 10th	Night	35% 24% 12% 17% 11% 1	4640
	11th to 20th	Night	36% 24% 13% 19% 8%	4632
	21st to end	Night	33% 22% 11% 18% 16% 1	4967
August	1st to 10th	Night	40% 30% 12% 12% 6%	4131
	11th to 20th	Night	30% 29% 11% 24% 6%	4587
	21st to end	Night	26% 28% 7% 24% 16%	5045
September	1st to 10th	Night	18% 56% 6% 12% 8% 1	2100
	11th to 20th	Night	15% 57% 4 9% 11% 2	2086
	21st to end	Night	23% 58% 4 8% 7% 1	2200
October	1st to 10th	Night	24% 37% 7% 14% 16% 2	3849
	11th to 20th	Night	11% 36% 5% 20% 23% 4	3899
	21st to end	Night	13% 36% 7% 23% 18% 2	4431
November	1st to 10th	Night	17% 54% 6% 12% 9% 3	2667
	11th to 20th	Night	16% 54% 4 11% 12% 3	2730
	21st to end	Night	16% 55% 7% 13% 8% 1	2831
December	1st to 10th	Night	25% 35% 7% 23% 8% 1	4720
	11th to 20th	Night	32% 31% 6% 17% 11% 3	5348
	21st to end	Night	35% 27% 7% 15% 13% 3	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	27% 25% 30% 15% 2 1	220
	11th to 20th	Day	37% 26% 28% 8% 1	223
	21st to end	Day	23% 29% 32% 11% 4	363
February	1st to 10th	Day	27% 25% 35% 10% 3	330
	11th to 20th	Day	31% 23% 33% 11% 1	518
	21st to end	Day	28% 22% 33% 14% 3	446
March	1st to 10th	Day	30% 19% 31% 17% 3	540
	11th to 20th	Day	25% 25% 32% 13% 4 1	540
	21st to end	Day	27% 25% 31% 13% 5% 1	594
April	1st to 10th	Day	29% 22% 32% 10% 6% 1	540
	11th to 20th	Day	23% 22% 32% 13% 8% 2	532
	21st to end	Day	26% 20% 31% 17% 4 2	540
May	1st to 10th	Day	30% 20% 30% 13% 6% 1	543
	11th to 20th	Day	21% 15% 34% 21% 8% 1	567
	21st to end	Day	24% 11% 26% 24% 13% 2	617
June	1st to 10th	Day	17% 11% 29% 27% 12% 3	570
	11th to 20th	Day	19% 14% 28% 26% 11% 3	570
	21st to end	Day	15% 11% 32% 28% 12% 2	570
July	1st to 10th	Day	12% 7% 22% 33% 21% 5%	565
	11th to 20th	Day	10% 5% 27% 30% 21% 7%	564
	21st to end	Day	13% 7% 31% 30% 16% 3	620
August	1st to 10th	Day	13% 5% 25% 34% 16% 6%	566
	11th to 20th	Day	14% 5% 22% 33% 20% 6%	559
	21st to end	Day	12% 8% 27% 30% 16% 8%	627
September	1st to 10th	Day	15% 10% 28% 25% 15% 7%	570
	11th to 20th	Day	15% 6% 26% 30% 15% 8%	542
	21st to end	Day	24% 13% 22% 26% 10% 5%	530
October	1st to 10th	Day	22% 8% 26% 22% 14% 7%	530
	11th to 20th	Day	19% 17% 27% 25% 10% 3	530
	21st to end	Day	21% 17% 30% 20% 10% 2	525
November	1st to 10th	Day	20% 12% 32% 23% 11% 2	425
	11th to 20th	Day	24% 18% 32% 20% 6%	430
	21st to end	Day	24% 16% 36% 16% 6%	325
December	1st to 10th	Day	27% 24% 33% 10% 7%	220
	11th to 20th	Day	35% 21% 25% 12% 5%	220
	21st to end	Day	29% 18% 31% 15% 7% 1	242
January	1st to 10th	Night	19% 20% 38% 20% 3	840
	11th to 20th	Night	23% 17% 36% 20% 3	840
	21st to end	Night	19% 20% 40% 21% 1	924
February	1st to 10th	Night	22% 15% 38% 23% 2	840
	11th to 20th	Night	26% 21% 35% 17% 1	823
	21st to end	Night	23% 18% 39% 18% 2	692
March	1st to 10th	Night	23% 19% 33% 21% 3	840
	11th to 20th	Night	24% 17% 35% 19% 4	840
	21st to end	Night	21% 15% 42% 19% 4	924
April	1st to 10th	Night	22% 19% 37% 18% 4	840
	11th to 20th	Night	19% 16% 38% 23% 4	831
	21st to end	Night	21% 13% 36% 26% 4	840
May	1st to 10th	Night	22% 16% 33% 23% 5%	669
	11th to 20th	Night	20% 10% 37% 27% 5%	426
	21st to end	Night	18% 7% 27% 36% 11% 1	455
June	1st to 10th	Night	15% 7% 30% 36% 11%	420
	11th to 20th	Night	13% 7% 30% 39% 11%	420
	21st to end	Night	11% 4 27% 43% 14%	420
July	1st to 10th	Night	11% 3 24% 43% 18% 1	410
	11th to 20th	Night	10% 3 24% 43% 19% 1	408
	21st to end	Night	11% 3 25% 43% 17%	460
August	1st to 10th	Night	14% 1 17% 44% 20% 2	620
	11th to 20th	Night	14% 3 20% 37% 24% 2	830
	21st to end	Night	14% 5% 19% 41% 20% 2	924
September	1st to 10th	Night	17% 4 26% 34% 17% 2	840
	11th to 20th	Night	15% 5% 21% 35% 21% 4	813
	21st to end	Night	21% 6% 22% 34% 16% 1	800
October	1st to 10th	Night	21% 8% 25% 26% 17% 3	800
	11th to 20th	Night	17% 12% 28% 33% 11%	800
	21st to end	Night	21% 11% 33% 27% 8%	880
November	1st to 10th	Night	15% 10% 34% 29% 11% 1	820
	11th to 20th	Night	19% 17% 31% 25% 7%	840
	21st to end	Night	18% 15% 35% 25% 7%	840
December	1st to 10th	Night	24% 17% 33% 20% 5% 1	840
	11th to 20th	Night	21% 15% 36% 24% 4	840
	21st to end	Night	23% 15% 33% 26% 3	924

Page generated at 2026-09-11 04:11:56. Version ac07

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