Trenton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trenton clear sky chart from 2005-11-06 to 2025-02-21.

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% 9% 3 7% 5% 4 4 4 5% 7% 36%	108757
	Night	16% 10% 3 8% 5% 4 4 4 5% 7% 34%	109813
Transparency	Day	46% 7% 13% 22% 11% 1	112359
	Night	49% 7% 12% 20% 12% 1	114374
Seeing	Day	19% 13% 30% 23% 11% 4	14748
	Night	20% 11% 30% 27% 11% 1	24155

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% 12% 4 9% 5% 4 5% 5% 5% 7% 31%	3597
	11th to 20th	Day	11% 18% 8% 13% 7% 6% 5% 4 5% 6% 16%	3595
	21st to end	Day	15% 18% 6% 12% 5% 5% 4 4 5% 5% 21%	4466
February	1st to 10th	Day	13% 15% 5% 12% 8% 5% 4 4 5% 5% 25%	1800
	11th to 20th	Day	14% 11% 4 12% 6% 6% 5% 4 5% 5% 28%	1753
	21st to end	Day	19% 12% 3 10% 5% 4 4 4 5% 4 28%	1513
March	1st to 10th	Day	21% 11% 3 8% 4 4 4 3 5% 5% 32%	3307
	11th to 20th	Day	10% 15% 4 9% 6% 6% 4 4 4 6% 33%	3480
	21st to end	Day	14% 8% 3 6% 4 3 4 3 4 6% 44%	3898
April	1st to 10th	Day	18% 11% 3 7% 5% 4 4 4 4 6% 33%	2280
	11th to 20th	Day	20% 7% 3 6% 4 4 3 3 4 6% 39%	2254
	21st to end	Day	20% 9% 2 7% 5% 5% 5% 4 5% 6% 34%	2433
May	1st to 10th	Day	19% 7% 3 7% 4 4 4 4 5% 7% 35%	4295
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 5% 9% 35%	4398
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 9% 46%	4837
June	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 4 7% 9% 35%	2660
	11th to 20th	Day	12% 6% 2 5% 4 4 5% 5% 6% 9% 42%	2660
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 9% 40%	2660
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	4440
	11th to 20th	Day	11% 4 1 4 3 4 4 4 7% 9% 47%	4440
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	4766
August	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 8% 40%	4104
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 7% 9% 41%	4044
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 8% 45%	4222
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 6% 9% 46%	2280
	11th to 20th	Day	10% 5% 1 6% 4 3 3 3 6% 7% 51%	2280
	21st to end	Day	15% 5% 2 7% 5% 4 5% 3 5% 7% 41%	1985
October	1st to 10th	Day	17% 7% 3 7% 4 4 5% 4 6% 7% 36%	1900
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	1900
	21st to end	Day	24% 9% 3 8% 5% 4 5% 3 5% 6% 28%	2053
November	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 6% 7% 37%	1711
	11th to 20th	Day	14% 10% 3 7% 6% 5% 3 4 6% 8% 32%	1600
	21st to end	Day	20% 14% 4 6% 6% 5% 4 3 5% 6% 27%	1600
December	1st to 10th	Day	19% 14% 4 10% 6% 5% 5% 4 5% 6% 22%	2600
	11th to 20th	Day	18% 15% 5% 10% 4 4 4 3 5% 5% 28%	2986
	21st to end	Day	26% 12% 4 9% 5% 5% 4 3 4 5% 24%	3960
January	1st to 10th	Night	15% 14% 6% 11% 6% 5% 5% 3 5% 5% 26%	6349
	11th to 20th	Night	14% 13% 5% 15% 8% 6% 6% 4 5% 6% 18%	6287
	21st to end	Night	17% 14% 6% 11% 5% 5% 5% 3 4 6% 23%	6490
February	1st to 10th	Night	15% 15% 4 10% 6% 5% 5% 4 5% 5% 25%	2600
	11th to 20th	Night	14% 15% 4 8% 5% 5% 4 4 6% 6% 29%	2533
	21st to end	Night	16% 10% 4 7% 5% 5% 5% 4 6% 7% 31%	1942
March	1st to 10th	Night	18% 11% 3 9% 5% 5% 4 3 4 5% 32%	3532
	11th to 20th	Night	17% 13% 4 8% 5% 4 4 3 5% 6% 31%	3479
	21st to end	Night	16% 8% 3 5% 3 3 2 3 4 6% 46%	3732
April	1st to 10th	Night	19% 9% 3 6% 4 4 5% 4 6% 6% 34%	1900
	11th to 20th	Night	18% 8% 3 7% 5% 5% 4 3 5% 5% 38%	1875
	21st to end	Night	19% 7% 3 7% 3 4 3 5% 6% 7% 36%	1762
May	1st to 10th	Night	21% 9% 3 7% 4 4 4 4 5% 6% 35%	2644
	11th to 20th	Night	16% 8% 2 6% 5% 5% 4 4 6% 7% 36%	2495
	21st to end	Night	10% 5% 2 5% 4 5% 5% 4 6% 8% 46%	2738
June	1st to 10th	Night	13% 6% 3 7% 6% 4 5% 5% 6% 8% 37%	1520
	11th to 20th	Night	9% 6% 2 7% 4 5% 5% 5% 6% 9% 43%	1520
	21st to end	Night	12% 6% 3 7% 6% 4 5% 4 5% 7% 41%	1520
July	1st to 10th	Night	8% 5% 2 5% 5% 5% 6% 4 7% 8% 43%	2520
	11th to 20th	Night	12% 5% 2 4 4 4 4 3 5% 8% 49%	2520
	21st to end	Night	10% 5% 2 4 4 3 3 4 6% 9% 50%	2784
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 6% 9% 46%	2825
	11th to 20th	Night	12% 6% 2 6% 3 4 4 3 5% 8% 47%	2785
	21st to end	Night	9% 3 2 4 4 4 5% 4 6% 9% 49%	3402
September	1st to 10th	Night	11% 6% 3 6% 3 3 3 4 7% 7% 47%	1900
	11th to 20th	Night	12% 4 1 4 4 3 4 4 5% 7% 52%	1900
	21st to end	Night	17% 6% 2 5% 5% 4 4 4 5% 7% 42%	2189
October	1st to 10th	Night	16% 7% 3 6% 5% 4 4 4 6% 6% 38%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 4 4 4 5% 6% 33%	2280
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 5% 7% 31%	2543
November	1st to 10th	Night	17% 8% 2 5% 4 4 4 3 5% 7% 40%	2583
	11th to 20th	Night	16% 9% 3 7% 5% 5% 4 4 6% 8% 33%	2800
	21st to end	Night	22% 11% 3 7% 4 4 5% 5% 7% 6% 28%	2800
December	1st to 10th	Night	20% 14% 4 7% 5% 5% 5% 4 6% 7% 23%	4580
	11th to 20th	Night	19% 14% 4 9% 4 5% 4 3 5% 7% 27%	5208
	21st to end	Night	27% 14% 4 9% 4 3 4 4 4 5% 21%	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	51% 8% 11% 19% 10% 1	3598
	11th to 20th	Day	68% 7% 10% 8% 6% 1	3625
	21st to end	Day	64% 6% 9% 11% 9% 1	4466
February	1st to 10th	Day	61% 7% 11% 16% 4 1	1800
	11th to 20th	Day	56% 8% 9% 15% 10% 1	1762
	21st to end	Day	58% 6% 11% 15% 9% 1	1513
March	1st to 10th	Day	53% 6% 13% 18% 9% 1	3310
	11th to 20th	Day	50% 6% 18% 15% 10% 2	3480
	21st to end	Day	40% 5% 10% 26% 16% 3	3898
April	1st to 10th	Day	51% 5% 11% 20% 11% 3	2280
	11th to 20th	Day	47% 4 10% 22% 16% 2	2254
	21st to end	Day	50% 6% 10% 18% 13% 2	2433
May	1st to 10th	Day	47% 8% 10% 22% 12% 2	4307
	11th to 20th	Day	46% 8% 15% 21% 10% 1	4402
	21st to end	Day	34% 8% 15% 26% 15% 3	4837
June	1st to 10th	Day	44% 8% 13% 20% 13% 1	2660
	11th to 20th	Day	37% 7% 14% 25% 14% 2	2660
	21st to end	Day	40% 7% 15% 24% 13% 1	2660
July	1st to 10th	Day	35% 6% 14% 30% 14% 1	4370
	11th to 20th	Day	31% 7% 16% 36% 10%	4365
	21st to end	Day	34% 8% 16% 29% 13%	4614
August	1st to 10th	Day	43% 6% 15% 23% 13% 1	4091
	11th to 20th	Day	37% 8% 16% 29% 10%	4083
	21st to end	Day	35% 6% 14% 34% 10% 1	4222
September	1st to 10th	Day	35% 8% 14% 30% 12% 1	2280
	11th to 20th	Day	31% 6% 15% 32% 15% 1	2280
	21st to end	Day	41% 8% 14% 27% 9%	1985
October	1st to 10th	Day	37% 7% 13% 29% 13% 1	3160
	11th to 20th	Day	39% 6% 18% 24% 12%	3140
	21st to end	Day	49% 6% 14% 21% 9%	3367
November	1st to 10th	Day	46% 7% 15% 21% 11% 1	1711
	11th to 20th	Day	49% 9% 16% 16% 10% 1	1600
	21st to end	Day	58% 7% 12% 15% 7%	1600
December	1st to 10th	Day	63% 6% 17% 11% 4	2600
	11th to 20th	Day	60% 6% 10% 15% 8%	2986
	21st to end	Day	63% 7% 8% 15% 7%	3960
January	1st to 10th	Night	59% 7% 11% 15% 8%	6349
	11th to 20th	Night	65% 9% 11% 9% 5% 1	6332
	21st to end	Night	62% 8% 8% 11% 10% 1	6490
February	1st to 10th	Night	59% 7% 12% 16% 5% 1	2600
	11th to 20th	Night	55% 6% 11% 18% 9% 1	2535
	21st to end	Night	51% 7% 13% 20% 8% 1	1942
March	1st to 10th	Night	54% 6% 8% 21% 10% 1	3542
	11th to 20th	Night	51% 7% 14% 16% 11% 1	3480
	21st to end	Night	38% 4 11% 23% 21% 3	3732
April	1st to 10th	Night	49% 5% 10% 20% 13% 3	1900
	11th to 20th	Night	47% 6% 10% 18% 18% 1	1875
	21st to end	Night	45% 7% 11% 18% 16% 3	1762
May	1st to 10th	Night	50% 6% 12% 16% 14% 2	2651
	11th to 20th	Night	44% 8% 15% 21% 10% 2	2496
	21st to end	Night	34% 8% 13% 21% 21% 2	2739
June	1st to 10th	Night	43% 8% 11% 22% 14% 2	1520
	11th to 20th	Night	36% 7% 13% 21% 21% 3	1520
	21st to end	Night	42% 6% 13% 22% 15% 2	1520
July	1st to 10th	Night	36% 7% 13% 23% 20% 1	2480
	11th to 20th	Night	34% 6% 13% 33% 15%	2472
	21st to end	Night	31% 7% 16% 32% 12% 2	2695
August	1st to 10th	Night	36% 6% 13% 28% 15% 2	2814
	11th to 20th	Night	36% 5% 17% 29% 12% 2	2812
	21st to end	Night	31% 7% 13% 36% 12% 1	3402
September	1st to 10th	Night	34% 9% 15% 27% 14% 2	1900
	11th to 20th	Night	30% 7% 13% 32% 17% 1	1900
	21st to end	Night	42% 6% 11% 26% 14% 1	2189
October	1st to 10th	Night	37% 5% 10% 27% 21% 1	3800
	11th to 20th	Night	42% 5% 14% 30% 9%	3779
	21st to end	Night	45% 6% 14% 26% 10%	4179
November	1st to 10th	Night	44% 6% 14% 22% 13% 1	2583
	11th to 20th	Night	48% 7% 14% 19% 10% 1	2800
	21st to end	Night	54% 10% 15% 15% 5% 1	2800
December	1st to 10th	Night	60% 6% 14% 16% 4	4580
	11th to 20th	Night	59% 6% 11% 13% 10% 1	5208
	21st to end	Night	65% 6% 9% 11% 9%	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	23% 22% 34% 14% 8% 1	200
	11th to 20th	Day	24% 21% 34% 16% 3 1	207
	21st to end	Day	24% 20% 34% 17% 4 1	330
February	1st to 10th	Day	29% 25% 30% 13% 3	300
	11th to 20th	Day	27% 24% 37% 11% 1	300
	21st to end	Day	31% 20% 34% 13% 1	325
March	1st to 10th	Day	22% 18% 37% 18% 5%	460
	11th to 20th	Day	24% 20% 32% 21% 3	460
	21st to end	Day	27% 16% 34% 14% 8% 1	506
April	1st to 10th	Day	23% 20% 33% 18% 7% 1	460
	11th to 20th	Day	25% 20% 25% 17% 9% 4	452
	21st to end	Day	24% 15% 35% 17% 7% 2	460
May	1st to 10th	Day	22% 11% 32% 21% 10% 4	463
	11th to 20th	Day	17% 11% 28% 28% 13% 4	487
	21st to end	Day	13% 8% 30% 29% 15% 4	529
June	1st to 10th	Day	19% 11% 29% 28% 12% 2	490
	11th to 20th	Day	11% 10% 30% 28% 17% 3	490
	21st to end	Day	19% 10% 27% 27% 13% 4	490
July	1st to 10th	Day	8% 6% 27% 30% 24% 5%	485
	11th to 20th	Day	13% 6% 27% 28% 20% 6%	484
	21st to end	Day	9% 6% 31% 36% 13% 5%	532
August	1st to 10th	Day	13% 6% 23% 31% 19% 8%	486
	11th to 20th	Day	11% 3 25% 31% 23% 7%	479
	21st to end	Day	12% 6% 28% 31% 16% 8%	539
September	1st to 10th	Day	12% 7% 27% 29% 16% 8%	490
	11th to 20th	Day	10% 7% 22% 27% 21% 14%	490
	21st to end	Day	16% 8% 29% 27% 17% 4	490
October	1st to 10th	Day	21% 12% 26% 19% 16% 6%	490
	11th to 20th	Day	19% 18% 31% 23% 8% 2	490
	21st to end	Day	28% 18% 25% 21% 7%	519
November	1st to 10th	Day	26% 16% 27% 22% 8% 1	345
	11th to 20th	Day	20% 21% 37% 18% 4 1	200
	21st to end	Day	31% 16% 33% 15% 5% 1	200
December	1st to 10th	Day	25% 20% 33% 15% 7% 1	200
	11th to 20th	Day	30% 25% 30% 12% 3 1	200
	21st to end	Day	34% 16% 32% 14% 3	220
January	1st to 10th	Night	26% 18% 32% 19% 5%	800
	11th to 20th	Night	29% 16% 30% 20% 5%	800
	21st to end	Night	22% 15% 33% 25% 5%	880
February	1st to 10th	Night	23% 17% 40% 18% 2	800
	11th to 20th	Night	23% 17% 37% 20% 4	783
	21st to end	Night	24% 17% 35% 21% 3	629
March	1st to 10th	Night	22% 12% 36% 26% 4 1	760
	11th to 20th	Night	24% 15% 34% 23% 4 1	760
	21st to end	Night	19% 11% 36% 26% 7% 1	836
April	1st to 10th	Night	22% 12% 36% 26% 4	760
	11th to 20th	Night	22% 13% 33% 21% 10% 1	751
	21st to end	Night	22% 10% 30% 27% 11% 1	622
May	1st to 10th	Night	21% 6% 29% 28% 14% 1	459
	11th to 20th	Night	15% 4 31% 36% 14%	374
	21st to end	Night	12% 5% 29% 36% 17% 2	411
June	1st to 10th	Night	13% 3 33% 36% 14% 1	380
	11th to 20th	Night	11% 3 29% 39% 17% 1	380
	21st to end	Night	13% 7% 27% 38% 14% 1	380
July	1st to 10th	Night	7% 3 26% 43% 21% 1	370
	11th to 20th	Night	11% 4 21% 40% 22% 2	368
	21st to end	Night	10% 2 22% 46% 19% 2	437
August	1st to 10th	Night	9% 3 19% 40% 25% 4	567
	11th to 20th	Night	9% 4 18% 37% 27% 4	564
	21st to end	Night	10% 5% 23% 37% 24% 2	788
September	1st to 10th	Night	12% 6% 24% 33% 21% 3	760
	11th to 20th	Night	13% 5% 17% 30% 28% 6%	760
	21st to end	Night	18% 7% 22% 29% 19% 5%	760
October	1st to 10th	Night	19% 9% 28% 25% 18% 3	760
	11th to 20th	Night	23% 11% 29% 27% 8% 1	760
	21st to end	Night	26% 13% 31% 24% 6%	836
November	1st to 10th	Night	22% 14% 27% 27% 10% 1	780
	11th to 20th	Night	22% 15% 34% 21% 6% 1	800
	21st to end	Night	29% 14% 30% 20% 7%	800
December	1st to 10th	Night	29% 17% 32% 19% 4	800
	11th to 20th	Night	26% 16% 36% 18% 4	800
	21st to end	Night	33% 14% 33% 18% 3	880

Page generated at 2025-02-18 03:26:26. Version ac07

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