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 2024-09-14.

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	15% 9% 3 7% 5% 4 4 4 5% 7% 37%	101003
	Night	17% 10% 3 7% 5% 4 4 4 5% 7% 35%	96898
Transparency	Day	46% 7% 13% 22% 11% 1	100761
	Night	48% 7% 12% 20% 11% 1	96759
Seeing	Day	19% 13% 30% 23% 11% 4	14296
	Night	20% 11% 30% 27% 11% 1	23518

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	16% 14% 5% 9% 5% 4 5% 4 4 6% 29%	2517
	11th to 20th	Day	12% 18% 7% 13% 6% 6% 5% 4 5% 7% 16%	2531
	21st to end	Day	19% 20% 6% 10% 6% 5% 4 3 4 4 20%	3124
February	1st to 10th	Day	13% 15% 5% 12% 8% 5% 4 5% 5% 5% 24%	1710
	11th to 20th	Day	14% 11% 5% 12% 6% 6% 5% 4 5% 5% 28%	1663
	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 7% 7% 52%	2198
	21st to end	Day	14% 5% 2 7% 5% 4 5% 4 6% 7% 41%	1882
October	1st to 10th	Day	18% 7% 3 8% 4 4 5% 4 6% 6% 35%	1800
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 33%	1800
	21st to end	Day	25% 10% 3 7% 5% 4 5% 3 4 6% 27%	1945
November	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 6% 7% 37%	1624
	11th to 20th	Day	15% 10% 3 8% 6% 5% 3 4 6% 8% 32%	1520
	21st to end	Day	20% 13% 3 6% 6% 5% 4 3 5% 6% 27%	1520
December	1st to 10th	Day	18% 15% 5% 10% 6% 5% 4 4 5% 6% 23%	1520
	11th to 20th	Day	18% 14% 5% 9% 5% 4 4 3 5% 5% 28%	1906
	21st to end	Day	29% 14% 4 8% 5% 4 4 3 4 4 21%	2772
January	1st to 10th	Night	19% 15% 5% 10% 5% 5% 4 3 5% 5% 24%	4429
	11th to 20th	Night	15% 12% 5% 13% 8% 6% 5% 4 5% 5% 20%	4426
	21st to end	Night	21% 15% 5% 9% 6% 4 5% 3 4 5% 23%	4532
February	1st to 10th	Night	15% 15% 4 10% 6% 5% 5% 4 5% 5% 25%	2470
	11th to 20th	Night	14% 15% 4 9% 5% 5% 4 4 6% 6% 29%	2403
	21st to end	Night	16% 10% 4 7% 5% 5% 5% 4 6% 7% 31%	1941
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%	1840
	21st to end	Night	16% 6% 2 5% 5% 4 4 4 5% 7% 43%	2073
October	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 4 6% 6% 37%	2160
	11th to 20th	Night	20% 8% 3 8% 5% 4 4 4 5% 6% 32%	2160
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 30%	2409
November	1st to 10th	Night	18% 8% 2 5% 4 4 4 3 5% 7% 40%	2450
	11th to 20th	Night	17% 9% 3 7% 5% 5% 5% 4 6% 8% 33%	2660
	21st to end	Night	22% 11% 3 7% 4 4 5% 5% 7% 6% 28%	2660
December	1st to 10th	Night	20% 14% 4 8% 6% 5% 5% 4 5% 6% 23%	2660
	11th to 20th	Night	19% 14% 4 8% 5% 5% 4 3 5% 6% 28%	3288
	21st to end	Night	31% 15% 4 8% 4 3 4 4 4 5% 17%	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	54% 11% 13% 13% 6% 2	2518
	11th to 20th	Day	67% 9% 11% 7% 6%	2531
	21st to end	Day	67% 7% 10% 11% 4 1	3124
February	1st to 10th	Day	61% 7% 12% 15% 4 1	1710
	11th to 20th	Day	56% 8% 10% 15% 10% 1	1672
	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	2198
	21st to end	Day	40% 9% 14% 28% 8%	1882
October	1st to 10th	Day	46% 8% 14% 19% 12% 1	1800
	11th to 20th	Day	49% 9% 16% 19% 7% 1	1800
	21st to end	Day	58% 7% 12% 15% 8% 1	1945
November	1st to 10th	Day	45% 7% 15% 21% 11% 1	1624
	11th to 20th	Day	50% 9% 16% 16% 9% 1	1520
	21st to end	Day	58% 8% 12% 14% 8%	1520
December	1st to 10th	Day	63% 8% 13% 12% 5%	1520
	11th to 20th	Day	58% 9% 13% 12% 7%	1906
	21st to end	Day	66% 7% 11% 12% 4	2772
January	1st to 10th	Night	60% 9% 13% 13% 5%	4429
	11th to 20th	Night	63% 11% 12% 9% 4 1	4426
	21st to end	Night	64% 10% 8% 12% 6%	4532
February	1st to 10th	Night	60% 7% 12% 16% 5% 1	2470
	11th to 20th	Night	54% 7% 11% 18% 9% 1	2405
	21st to end	Night	51% 7% 13% 20% 8% 1	1941
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% 31% 17% 1	1840
	21st to end	Night	41% 6% 12% 27% 13% 1	2073
October	1st to 10th	Night	47% 7% 11% 20% 14% 1	2160
	11th to 20th	Night	51% 8% 13% 20% 8%	2160
	21st to end	Night	54% 8% 13% 15% 11% 1	2409
November	1st to 10th	Night	45% 6% 14% 21% 12% 1	2450
	11th to 20th	Night	48% 7% 15% 18% 10% 1	2660
	21st to end	Night	54% 10% 16% 14% 5% 1	2660
December	1st to 10th	Night	61% 9% 12% 13% 4	2660
	11th to 20th	Night	58% 7% 12% 16% 6% 1	3288
	21st to end	Night	69% 7% 10% 10% 3	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	24% 20% 33% 14% 8% 1	180
	11th to 20th	Day	24% 22% 35% 16% 3 1	186
	21st to end	Day	23% 19% 35% 18% 5% 1	297
February	1st to 10th	Day	27% 25% 31% 13% 4	270
	11th to 20th	Day	25% 22% 40% 12% 1	270
	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% 23% 28% 20% 13%	463
	21st to end	Day	14% 9% 30% 26% 17% 5%	450
October	1st to 10th	Day	22% 12% 26% 19% 16% 6%	450
	11th to 20th	Day	20% 18% 31% 22% 8% 2	450
	21st to end	Day	30% 17% 25% 21% 7%	477
November	1st to 10th	Day	26% 16% 25% 23% 9% 1	318
	11th to 20th	Day	21% 21% 36% 18% 4 1	180
	21st to end	Day	28% 16% 34% 16% 5% 1	180
December	1st to 10th	Day	23% 21% 33% 16% 6% 1	180
	11th to 20th	Day	28% 26% 31% 13% 2 1	180
	21st to end	Day	35% 18% 33% 12% 3	198
January	1st to 10th	Night	27% 18% 30% 19% 5%	760
	11th to 20th	Night	29% 16% 30% 20% 5%	760
	21st to end	Night	22% 15% 33% 25% 5%	836
February	1st to 10th	Night	23% 17% 40% 18% 3	760
	11th to 20th	Night	23% 16% 38% 20% 4	743
	21st to end	Night	24% 17% 35% 21% 3	628
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	14% 5% 18% 30% 27% 6%	736
	21st to end	Night	17% 8% 22% 29% 19% 5%	720
October	1st to 10th	Night	19% 9% 28% 24% 17% 3	720
	11th to 20th	Night	23% 12% 30% 27% 8% 1	720
	21st to end	Night	27% 13% 30% 25% 5%	792
November	1st to 10th	Night	22% 13% 27% 28% 10% 1	740
	11th to 20th	Night	22% 15% 34% 22% 6% 1	760
	21st to end	Night	28% 13% 30% 21% 7%	760
December	1st to 10th	Night	29% 17% 31% 19% 4	760
	11th to 20th	Night	26% 15% 36% 18% 4	760
	21st to end	Night	33% 14% 33% 17% 3	836

Page generated at 2024-09-11 10:00:01. Version ac07

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