Fenton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fenton clear sky chart from 2005-11-06 to 2025-07-21.

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	14% 11% 4 9% 5% 5% 4 4 5% 7% 33%	119263
	Night	14% 12% 4 9% 5% 4 4 3 5% 6% 33%	119902
Transparency	Day	50% 5% 12% 20% 12% 1	122861
	Night	50% 5% 11% 20% 12% 1	124442
Seeing	Day	19% 12% 29% 22% 13% 5%	16435
	Night	20% 11% 29% 28% 11% 1	26294

By Month

Percentage Cloud Cover SE (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	11% 20% 7% 18% 5% 4 4 3 3 4 22%	3617
	11th to 20th	Day	13% 19% 6% 20% 9% 9% 4 2 4 4 10%	3620
	21st to end	Day	22% 18% 7% 14% 6% 4 5% 2 3 3 16%	4289
February	1st to 10th	Day	13% 15% 6% 13% 7% 5% 5% 3 5% 6% 22%	1800
	11th to 20th	Day	14% 14% 7% 14% 8% 6% 4 3 4 5% 23%	1901
	21st to end	Day	13% 17% 6% 12% 7% 4 3 4 4 5% 25%	1650
March	1st to 10th	Day	14% 12% 4 10% 6% 4 4 4 5% 6% 31%	4561
	11th to 20th	Day	12% 13% 5% 8% 5% 4 4 3 5% 7% 33%	4980
	21st to end	Day	18% 16% 4 9% 5% 4 4 3 4 5% 29%	5465
April	1st to 10th	Day	17% 13% 4 8% 6% 4 5% 3 5% 6% 30%	2350
	11th to 20th	Day	17% 11% 3 7% 4 4 4 4 6% 6% 35%	2526
	21st to end	Day	17% 8% 3 8% 5% 5% 4 3 4 7% 35%	2600
May	1st to 10th	Day	20% 10% 3 7% 4 4 4 4 5% 6% 34%	5862
	11th to 20th	Day	15% 9% 3 7% 5% 4 5% 4 5% 7% 36%	5861
	21st to end	Day	15% 7% 2 7% 4 4 4 3 5% 7% 42%	6525
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	2815
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 4 6% 9% 40%	2976
	21st to end	Day	11% 6% 2 6% 5% 6% 5% 5% 7% 9% 38%	2800
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	4580
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 48%	4580
	21st to end	Day	8% 5% 2 7% 5% 6% 6% 5% 7% 9% 42%	4606
August	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 6% 8% 41%	4104
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 5% 7% 8% 41%	4044
	21st to end	Day	8% 6% 2 7% 5% 6% 5% 4 6% 9% 40%	4452
September	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	2163
	11th to 20th	Day	10% 6% 2 5% 3 3 4 4 6% 8% 48%	2090
	21st to end	Day	16% 7% 2 6% 4 5% 5% 5% 6% 8% 35%	2090
October	1st to 10th	Day	14% 7% 3 7% 4 4 4 4 5% 6% 42%	2048
	11th to 20th	Day	18% 12% 3 7% 5% 4 5% 4 4 7% 32%	1900
	21st to end	Day	21% 11% 3 7% 5% 4 4 3 5% 7% 28%	1910
November	1st to 10th	Day	12% 11% 3 8% 5% 4 3 4 6% 6% 36%	1762
	11th to 20th	Day	14% 15% 5% 8% 6% 5% 5% 4 5% 6% 28%	1800
	21st to end	Day	18% 16% 6% 8% 5% 5% 4 3 5% 6% 25%	1714
December	1st to 10th	Day	13% 17% 8% 12% 6% 5% 4 4 5% 5% 20%	2600
	11th to 20th	Day	16% 21% 8% 11% 6% 4 4 4 4 4 18%	2667
	21st to end	Day	24% 21% 7% 13% 5% 3 3 3 3 4 13%	3955
January	1st to 10th	Night	14% 14% 7% 15% 6% 4 4 3 4 5% 24%	6348
	11th to 20th	Night	12% 16% 8% 17% 9% 7% 5% 4 4 4 14%	6360
	21st to end	Night	17% 17% 9% 11% 5% 5% 5% 3 4 5% 20%	6660
February	1st to 10th	Night	15% 17% 5% 11% 8% 6% 4 3 4 5% 22%	2600
	11th to 20th	Night	13% 15% 6% 12% 7% 5% 4 4 5% 5% 25%	2383
	21st to end	Night	17% 13% 4 10% 6% 4 4 3 5% 6% 28%	1980
March	1st to 10th	Night	14% 12% 4 8% 5% 4 4 3 5% 7% 35%	5292
	11th to 20th	Night	10% 10% 3 7% 4 4 4 4 6% 8% 40%	4980
	21st to end	Night	17% 11% 3 8% 5% 4 4 3 4 6% 36%	5467
April	1st to 10th	Night	17% 12% 3 6% 4 5% 4 3 5% 6% 36%	2066
	11th to 20th	Night	18% 10% 2 6% 4 3 4 3 6% 6% 37%	1822
	21st to end	Night	17% 8% 3 7% 4 4 4 4 5% 6% 38%	1800
May	1st to 10th	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 33%	4033
	11th to 20th	Night	17% 9% 3 7% 4 3 4 3 4 6% 41%	4032
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 7% 44%	4317
June	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 6% 9% 46%	1570
	11th to 20th	Night	11% 6% 2 5% 5% 4 3 4 7% 9% 44%	1406
	21st to end	Night	10% 6% 2 5% 4 3 3 3 6% 9% 48%	1600
July	1st to 10th	Night	9% 4 2 5% 4 4 5% 4 7% 11% 46%	2610
	11th to 20th	Night	10% 4 2 4 4 4 4 3 5% 8% 53%	2610
	21st to end	Night	6% 4 2 6% 5% 5% 5% 5% 7% 9% 48%	2951
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 7% 8% 48%	2825
	11th to 20th	Night	11% 6% 1 5% 4 4 5% 3 5% 7% 49%	2785
	21st to end	Night	9% 5% 2 6% 5% 4 4 3 4 8% 50%	3188
September	1st to 10th	Night	10% 6% 2 6% 5% 3 4 3 6% 7% 48%	1996
	11th to 20th	Night	10% 5% 2 4 3 3 4 3 4 7% 54%	2090
	21st to end	Night	15% 6% 3 5% 4 4 5% 4 5% 6% 42%	2090
October	1st to 10th	Night	15% 6% 3 6% 4 3 4 3 5% 6% 45%	2131
	11th to 20th	Night	19% 11% 3 7% 5% 4 4 3 5% 5% 34%	2280
	21st to end	Night	21% 10% 3 7% 5% 5% 4 3 5% 6% 31%	2684
November	1st to 10th	Night	14% 10% 3 6% 4 4 4 3 5% 6% 41%	2536
	11th to 20th	Night	15% 13% 4 7% 5% 6% 5% 4 5% 6% 29%	2600
	21st to end	Night	20% 16% 4 8% 5% 4 3 3 5% 6% 26%	2682
December	1st to 10th	Night	12% 17% 8% 14% 6% 5% 5% 3 5% 6% 21%	4580
	11th to 20th	Night	14% 22% 6% 13% 7% 4 3 3 4 4 18%	5534
	21st to end	Night	23% 21% 7% 11% 5% 4 3 3 3 5% 15%	7014

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	67% 3 12% 13% 5% 1	3618
	11th to 20th	Day	79% 4 9% 4 3	3620
	21st to end	Day	75% 3 10% 7% 4	4289
February	1st to 10th	Day	62% 5% 11% 14% 7%	1800
	11th to 20th	Day	64% 4 8% 15% 8% 1	1911
	21st to end	Day	62% 4 11% 15% 7% 2	1650
March	1st to 10th	Day	53% 4 14% 18% 9% 2	4561
	11th to 20th	Day	49% 5% 15% 21% 8% 1	4980
	21st to end	Day	59% 4 10% 16% 10% 2	5465
April	1st to 10th	Day	55% 5% 10% 19% 10% 1	2350
	11th to 20th	Day	48% 5% 11% 21% 12% 2	2526
	21st to end	Day	48% 5% 13% 18% 14% 1	2600
May	1st to 10th	Day	49% 6% 10% 19% 13% 3	5897
	11th to 20th	Day	47% 6% 12% 21% 13% 1	5865
	21st to end	Day	42% 4 10% 22% 19% 3	6539
June	1st to 10th	Day	37% 7% 13% 26% 15% 2	2815
	11th to 20th	Day	41% 6% 12% 24% 16% 2	2976
	21st to end	Day	39% 7% 13% 23% 16% 1	2800
July	1st to 10th	Day	41% 7% 14% 20% 16% 2	4511
	11th to 20th	Day	31% 6% 13% 33% 16% 2	4505
	21st to end	Day	36% 7% 15% 19% 21% 2	4460
August	1st to 10th	Day	39% 7% 13% 24% 16% 1	4091
	11th to 20th	Day	38% 7% 11% 32% 12% 1	4083
	21st to end	Day	38% 6% 14% 28% 13% 1	4451
September	1st to 10th	Day	40% 8% 13% 25% 12% 2	2163
	11th to 20th	Day	33% 6% 13% 32% 15% 2	2090
	21st to end	Day	43% 7% 13% 25% 12%	2090
October	1st to 10th	Day	33% 5% 10% 32% 20% 1	3399
	11th to 20th	Day	42% 4 11% 26% 17%	3140
	21st to end	Day	47% 4 13% 24% 11% 1	3122
November	1st to 10th	Day	45% 6% 14% 23% 11% 1	1762
	11th to 20th	Day	55% 5% 14% 17% 9% 1	1800
	21st to end	Day	61% 5% 12% 16% 6% 1	1714
December	1st to 10th	Day	65% 5% 17% 11% 3	2600
	11th to 20th	Day	70% 4 9% 12% 5%	2663
	21st to end	Day	76% 3 8% 8% 5%	3955
January	1st to 10th	Night	63% 4 9% 16% 6% 2	6348
	11th to 20th	Night	72% 5% 11% 8% 5%	6360
	21st to end	Night	67% 4 11% 13% 5%	6660
February	1st to 10th	Night	64% 6% 10% 12% 7% 1	2600
	11th to 20th	Night	60% 6% 8% 17% 8% 1	2384
	21st to end	Night	57% 4 12% 17% 8% 1	1980
March	1st to 10th	Night	50% 4 14% 22% 10% 1	5292
	11th to 20th	Night	40% 5% 14% 26% 14% 1	4980
	21st to end	Night	49% 5% 12% 19% 13% 1	5467
April	1st to 10th	Night	49% 5% 10% 21% 13% 2	2066
	11th to 20th	Night	46% 5% 11% 18% 17% 2	1822
	21st to end	Night	45% 5% 12% 19% 16% 2	1800
May	1st to 10th	Night	51% 5% 10% 16% 13% 5%	4060
	11th to 20th	Night	45% 5% 10% 25% 11% 4	4033
	21st to end	Night	40% 5% 11% 23% 16% 5%	4325
June	1st to 10th	Night	34% 6% 10% 29% 19% 3	1570
	11th to 20th	Night	35% 6% 13% 25% 18% 2	1406
	21st to end	Night	33% 6% 14% 26% 19% 1	1600
July	1st to 10th	Night	32% 5% 13% 28% 15% 6%	2570
	11th to 20th	Night	30% 5% 12% 30% 22% 1	2562
	21st to end	Night	31% 8% 17% 19% 22% 2	2857
August	1st to 10th	Night	34% 6% 14% 28% 17% 1	2814
	11th to 20th	Night	34% 6% 11% 36% 11% 2	2812
	21st to end	Night	35% 6% 12% 32% 15% 1	3188
September	1st to 10th	Night	34% 7% 12% 28% 16% 2	1996
	11th to 20th	Night	31% 5% 11% 30% 21% 2	2090
	21st to end	Night	41% 5% 12% 27% 14% 1	2090
October	1st to 10th	Night	26% 4 10% 34% 25% 1	3560
	11th to 20th	Night	45% 4 11% 23% 17% 1	3779
	21st to end	Night	42% 4 11% 30% 12%	4422
November	1st to 10th	Night	43% 6% 10% 26% 14% 1	2536
	11th to 20th	Night	54% 6% 13% 18% 8% 1	2600
	21st to end	Night	58% 5% 12% 18% 6% 1	2682
December	1st to 10th	Night	65% 5% 14% 13% 3	4580
	11th to 20th	Night	69% 5% 9% 12% 5% 1	5537
	21st to end	Night	74% 3 9% 7% 6%	7014

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	22% 18% 38% 16% 6%	300
	11th to 20th	Day	23% 18% 43% 13% 3 1	300
	21st to end	Day	30% 18% 31% 15% 5% 1	330
February	1st to 10th	Day	28% 23% 34% 13% 1 1	300
	11th to 20th	Day	27% 21% 37% 14% 1	300
	21st to end	Day	27% 27% 35% 9% 2	249
March	1st to 10th	Day	26% 21% 37% 13% 3	329
	11th to 20th	Day	23% 13% 35% 22% 7%	500
	21st to end	Day	29% 14% 31% 19% 5% 1	550
April	1st to 10th	Day	20% 18% 32% 22% 7% 1	500
	11th to 20th	Day	26% 18% 31% 15% 5% 5%	492
	21st to end	Day	22% 13% 32% 21% 9% 2	500
May	1st to 10th	Day	26% 15% 27% 20% 10% 2	503
	11th to 20th	Day	20% 11% 28% 20% 14% 6%	527
	21st to end	Day	18% 8% 22% 27% 17% 8%	613
June	1st to 10th	Day	13% 9% 30% 28% 16% 4	730
	11th to 20th	Day	13% 9% 31% 26% 16% 5%	730
	21st to end	Day	12% 9% 28% 31% 15% 5%	730
July	1st to 10th	Day	10% 5% 23% 31% 21% 10%	721
	11th to 20th	Day	11% 6% 28% 28% 18% 8%	718
	21st to end	Day	8% 5% 24% 31% 22% 9%	620
August	1st to 10th	Day	12% 3 22% 24% 25% 14%	486
	11th to 20th	Day	14% 4 18% 28% 24% 12%	479
	21st to end	Day	12% 6% 20% 26% 24% 12%	539
September	1st to 10th	Day	13% 7% 24% 24% 21% 11%	490
	11th to 20th	Day	12% 3 20% 22% 29% 14%	490
	21st to end	Day	19% 11% 21% 22% 19% 8%	490
October	1st to 10th	Day	17% 9% 28% 22% 16% 7%	490
	11th to 20th	Day	21% 17% 26% 28% 7% 1	490
	21st to end	Day	30% 15% 36% 15% 4	359
November	1st to 10th	Day	18% 23% 33% 17% 7% 1	300
	11th to 20th	Day	24% 21% 32% 16% 6% 1	300
	21st to end	Day	30% 21% 33% 12% 4	256
December	1st to 10th	Day	25% 22% 32% 15% 7%	200
	11th to 20th	Day	25% 24% 38% 10% 3 1	200
	21st to end	Day	27% 25% 34% 14% 1	324
January	1st to 10th	Night	22% 16% 37% 20% 5% 1	1000
	11th to 20th	Night	25% 16% 34% 21% 4 1	1000
	21st to end	Night	22% 13% 34% 25% 6%	959
February	1st to 10th	Night	26% 13% 35% 23% 2	800
	11th to 20th	Night	22% 16% 35% 24% 4	783
	21st to end	Night	25% 17% 35% 19% 3	660
March	1st to 10th	Night	21% 16% 34% 23% 6% 1	800
	11th to 20th	Night	17% 16% 35% 26% 5% 1	800
	21st to end	Night	24% 12% 30% 27% 6% 1	880
April	1st to 10th	Night	22% 17% 35% 22% 4 1	666
	11th to 20th	Night	21% 12% 34% 24% 7% 2	593
	21st to end	Night	21% 9% 34% 30% 7%	600
May	1st to 10th	Night	21% 6% 34% 32% 7% 1	600
	11th to 20th	Night	22% 6% 29% 31% 12% 1	591
	21st to end	Night	13% 4 25% 39% 16% 2	650
June	1st to 10th	Night	12% 5% 26% 43% 13%	570
	11th to 20th	Night	11% 6% 28% 41% 14%	406
	21st to end	Night	12% 4 24% 44% 15% 2	600
July	1st to 10th	Night	9% 2 18% 41% 27% 3	585
	11th to 20th	Night	12% 2 20% 41% 22% 3	582
	21st to end	Night	6% 3 19% 48% 22% 2	624
August	1st to 10th	Night	9% 3 15% 43% 28% 2	567
	11th to 20th	Night	10% 2 21% 36% 26% 5%	564
	21st to end	Night	11% 4 17% 37% 29% 3	627
September	1st to 10th	Night	12% 4 21% 35% 24% 4	666
	11th to 20th	Night	12% 4 17% 35% 28% 4	760
	21st to end	Night	17% 7% 20% 32% 20% 4	760
October	1st to 10th	Night	18% 7% 26% 30% 17% 2	760
	11th to 20th	Night	26% 12% 27% 27% 8% 1	760
	21st to end	Night	26% 11% 35% 24% 4	836
November	1st to 10th	Night	20% 13% 29% 27% 9% 1	780
	11th to 20th	Night	23% 17% 32% 22% 6% 1	800
	21st to end	Night	28% 12% 34% 21% 4	800
December	1st to 10th	Night	23% 18% 35% 19% 5% 1	800
	11th to 20th	Night	24% 15% 39% 20% 2	965
	21st to end	Night	32% 15% 35% 17% 2	1100

Page generated at 2025-07-18 01:10:00. Version ac07

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