Stokesville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stokesville Observatory clear sky chart from 2005-11-06 to 2025-04-11.

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	12% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	113364
	Night	12% 6% 2 5% 4 4 4 4 6% 7% 46%	114892
Transparency	Day	39% 6% 11% 22% 17% 5%	117014
	Night	36% 6% 12% 23% 18% 5%	119381
Seeing	Day	17% 12% 25% 25% 16% 6%	15468
	Night	16% 8% 26% 33% 15% 2	25418

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% 6% 2 5% 5% 5% 4 4 4 5% 49%	4056
	11th to 20th	Day	11% 8% 2 7% 5% 4 4 3 4 5% 48%	4060
	21st to end	Day	12% 8% 3 6% 4 4 4 3 5% 5% 46%	4466
February	1st to 10th	Day	11% 8% 3 7% 5% 5% 5% 4 6% 6% 41%	1800
	11th to 20th	Day	14% 8% 3 7% 4 3 4 5% 5% 7% 41%	1753
	21st to end	Day	14% 8% 2 6% 4 4 4 4 5% 7% 42%	1717
March	1st to 10th	Day	14% 7% 2 5% 4 4 5% 5% 6% 6% 42%	4935
	11th to 20th	Day	8% 6% 2 5% 4 3 4 3 6% 7% 53%	4980
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 4 5% 6% 41%	5465
April	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 4 6% 6% 45%	2330
	11th to 20th	Day	13% 5% 2 5% 5% 4 4 4 5% 7% 46%	2254
	21st to end	Day	16% 6% 2 6% 5% 5% 4 3 5% 7% 41%	2369
May	1st to 10th	Day	16% 7% 3 8% 6% 6% 6% 4 7% 8% 29%	4082
	11th to 20th	Day	22% 7% 3 7% 5% 4 5% 3 5% 6% 34%	4081
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	4601
June	1st to 10th	Day	11% 4 2 6% 5% 6% 6% 4 7% 9% 41%	2660
	11th to 20th	Day	9% 5% 2 6% 6% 5% 6% 6% 7% 10% 36%	2660
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 5% 7% 11% 41%	2660
July	1st to 10th	Day	6% 5% 2 6% 6% 5% 6% 5% 7% 10% 41%	4124
	11th to 20th	Day	8% 5% 2 6% 6% 6% 7% 5% 9% 11% 35%	4120
	21st to end	Day	11% 8% 3 9% 6% 6% 6% 5% 7% 9% 29%	4466
August	1st to 10th	Day	12% 4 2 8% 6% 6% 6% 6% 8% 10% 32%	4104
	11th to 20th	Day	8% 4 2 7% 5% 6% 7% 5% 9% 9% 37%	4026
	21st to end	Day	8% 4 2 5% 5% 5% 5% 5% 6% 10% 45%	4180
September	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 5% 6% 45%	2280
	11th to 20th	Day	14% 7% 2 5% 4 5% 5% 4 5% 7% 43%	2148
	21st to end	Day	23% 5% 2 6% 4 4 4 4 6% 6% 37%	2054
October	1st to 10th	Day	15% 5% 2 5% 3 4 4 4 5% 7% 45%	1900
	11th to 20th	Day	15% 4 1 5% 3 4 4 3 5% 6% 50%	1900
	21st to end	Day	13% 5% 2 4 5% 3 4 4 3 6% 52%	2090
November	1st to 10th	Day	10% 6% 2 4 3 4 3 3 5% 6% 54%	1957
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 6% 6% 50%	1770
	21st to end	Day	12% 5% 2 5% 4 4 3 3 5% 6% 49%	1600
December	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 5% 6% 52%	2600
	11th to 20th	Day	18% 5% 1 5% 4 3 3 3 5% 7% 46%	2990
	21st to end	Day	17% 6% 2 7% 4 5% 5% 4 6% 7% 37%	4126
January	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 5% 5% 52%	5889
	11th to 20th	Night	11% 7% 2 5% 3 3 4 2 5% 5% 53%	5900
	21st to end	Night	13% 7% 2 5% 3 3 3 3 4 5% 52%	6490
February	1st to 10th	Night	11% 7% 2 6% 4 4 5% 5% 5% 8% 44%	2600
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 40%	2533
	21st to end	Night	13% 7% 2 6% 4 4 4 4 6% 9% 43%	1909
March	1st to 10th	Night	15% 5% 2 5% 3 3 3 3 5% 5% 48%	4918
	11th to 20th	Night	9% 3 1 4 4 4 4 3 6% 8% 53%	4980
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 7% 46%	5467
April	1st to 10th	Night	14% 7% 2 4 4 5% 5% 4 6% 6% 43%	2068
	11th to 20th	Night	11% 4 2 5% 4 5% 4 3 7% 8% 47%	1882
	21st to end	Night	16% 4 2 5% 4 4 4 4 6% 7% 44%	1826
May	1st to 10th	Night	18% 7% 2 6% 5% 5% 5% 4 6% 9% 33%	2813
	11th to 20th	Night	23% 7% 3 6% 4 3 4 4 5% 6% 35%	2812
	21st to end	Night	10% 5% 1 6% 4 4 5% 5% 6% 11% 44%	2935
June	1st to 10th	Night	9% 5% 2 5% 5% 3 4 4 8% 12% 43%	1520
	11th to 20th	Night	10% 5% 2 5% 4 4 6% 5% 7% 10% 44%	1520
	21st to end	Night	8% 4 2 5% 4 3 6% 5% 7% 10% 46%	1520
July	1st to 10th	Night	6% 4 1 5% 5% 4 5% 4 8% 11% 45%	2829
	11th to 20th	Night	7% 7% 3 6% 5% 5% 6% 5% 8% 11% 38%	2840
	21st to end	Night	9% 8% 3 9% 7% 6% 5% 4 6% 10% 34%	3087
August	1st to 10th	Night	15% 5% 2 6% 5% 5% 4 5% 7% 10% 37%	2825
	11th to 20th	Night	9% 6% 3 7% 5% 5% 6% 5% 7% 8% 39%	2785
	21st to end	Night	9% 4 2 6% 4 4 4 4 6% 9% 48%	3460
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 4 7% 49%	1900
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 5% 7% 46%	2028
	21st to end	Night	23% 6% 2 5% 3 3 4 3 5% 6% 40%	2125
October	1st to 10th	Night	16% 6% 2 5% 4 4 4 2 4 6% 46%	2280
	11th to 20th	Night	13% 5% 1 5% 4 3 4 3 5% 6% 51%	2280
	21st to end	Night	13% 3 1 4 4 3 4 3 5% 6% 52%	2508
November	1st to 10th	Night	11% 6% 3 4 3 4 4 3 4 5% 53%	2341
	11th to 20th	Night	12% 6% 1 5% 3 3 4 3 4 7% 51%	2625
	21st to end	Night	13% 5% 2 5% 4 4 4 4 6% 6% 49%	2800
December	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 5% 7% 53%	4580
	11th to 20th	Night	14% 8% 2 6% 4 4 4 3 5% 6% 43%	5205
	21st to end	Night	15% 5% 2 5% 4 4 5% 5% 7% 9% 39%	6812

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	37% 3 6% 20% 24% 10%	4057
	11th to 20th	Day	39% 3 6% 16% 22% 14%	4060
	21st to end	Day	40% 3 6% 23% 22% 5%	4466
February	1st to 10th	Day	43% 5% 10% 22% 17% 4	1800
	11th to 20th	Day	43% 5% 10% 19% 18% 5%	1762
	21st to end	Day	42% 5% 11% 18% 18% 6%	1717
March	1st to 10th	Day	41% 4 8% 19% 17% 11%	4935
	11th to 20th	Day	31% 5% 7% 26% 21% 9%	4980
	21st to end	Day	44% 6% 9% 16% 18% 7%	5465
April	1st to 10th	Day	38% 6% 11% 19% 18% 8%	2330
	11th to 20th	Day	37% 6% 11% 21% 20% 5%	2254
	21st to end	Day	43% 7% 11% 22% 14% 4	2369
May	1st to 10th	Day	50% 9% 10% 20% 10% 1	4120
	11th to 20th	Day	51% 7% 10% 21% 10% 1	4085
	21st to end	Day	36% 9% 15% 21% 16% 3	4615
June	1st to 10th	Day	38% 8% 14% 24% 15% 1	2660
	11th to 20th	Day	40% 10% 15% 20% 14% 2	2660
	21st to end	Day	36% 8% 15% 25% 13% 2	2660
July	1st to 10th	Day	36% 10% 17% 21% 9% 6%	4059
	11th to 20th	Day	38% 10% 16% 27% 8% 1	4051
	21st to end	Day	49% 9% 11% 21% 10% 1	4324
August	1st to 10th	Day	44% 10% 17% 22% 7%	4091
	11th to 20th	Day	37% 9% 13% 28% 12% 1	4065
	21st to end	Day	33% 9% 16% 27% 12% 1	4180
September	1st to 10th	Day	39% 7% 13% 18% 19% 4	2280
	11th to 20th	Day	40% 5% 8% 24% 19% 4	2148
	21st to end	Day	47% 7% 9% 18% 17% 3	2054
October	1st to 10th	Day	32% 5% 7% 21% 28% 8%	3160
	11th to 20th	Day	26% 3 7% 28% 22% 13%	3140
	21st to end	Day	23% 3 10% 29% 21% 14%	3428
November	1st to 10th	Day	32% 4 9% 24% 26% 5%	1957
	11th to 20th	Day	35% 5% 9% 20% 23% 9%	1770
	21st to end	Day	36% 4 10% 24% 23% 3	1600
December	1st to 10th	Day	33% 5% 9% 26% 20% 7%	2600
	11th to 20th	Day	39% 5% 12% 21% 18% 5%	2986
	21st to end	Day	44% 6% 13% 19% 15% 2	4126
January	1st to 10th	Night	33% 4 8% 21% 25% 10%	5889
	11th to 20th	Night	34% 3 6% 22% 23% 11%	5900
	21st to end	Night	37% 3 7% 25% 22% 6%	6490
February	1st to 10th	Night	38% 6% 12% 25% 17% 2	2600
	11th to 20th	Night	44% 5% 8% 19% 17% 6%	2535
	21st to end	Night	39% 6% 12% 22% 15% 7%	1909
March	1st to 10th	Night	38% 5% 7% 21% 19% 9%	4918
	11th to 20th	Night	28% 4 10% 25% 26% 7%	4980
	21st to end	Night	38% 5% 12% 19% 20% 5%	5467
April	1st to 10th	Night	41% 7% 10% 19% 19% 4	2068
	11th to 20th	Night	33% 6% 16% 21% 20% 5%	1882
	21st to end	Night	38% 6% 12% 25% 15% 3	1826
May	1st to 10th	Night	47% 9% 13% 19% 10% 2	2840
	11th to 20th	Night	48% 9% 11% 23% 9% 1	2813
	21st to end	Night	33% 10% 19% 26% 9% 3	2942
June	1st to 10th	Night	33% 9% 16% 27% 14%	1520
	11th to 20th	Night	34% 10% 18% 23% 13% 2	1520
	21st to end	Night	30% 10% 18% 22% 17% 2	1520
July	1st to 10th	Night	31% 11% 22% 20% 14% 3	2784
	11th to 20th	Night	38% 9% 19% 23% 9% 1	2786
	21st to end	Night	45% 9% 17% 20% 9%	2988
August	1st to 10th	Night	42% 9% 18% 25% 6% 1	2814
	11th to 20th	Night	39% 8% 14% 25% 13%	2812
	21st to end	Night	33% 7% 17% 32% 10% 2	3460
September	1st to 10th	Night	35% 7% 14% 20% 18% 4	1900
	11th to 20th	Night	39% 5% 9% 26% 18% 3	2028
	21st to end	Night	46% 6% 9% 20% 17% 2	2125
October	1st to 10th	Night	41% 4 8% 19% 22% 5%	3800
	11th to 20th	Night	25% 4 10% 21% 28% 12%	3779
	21st to end	Night	21% 3 11% 30% 27% 9%	4120
November	1st to 10th	Night	34% 4 8% 23% 24% 7%	2341
	11th to 20th	Night	34% 4 8% 22% 25% 6%	2625
	21st to end	Night	35% 5% 11% 24% 21% 5%	2800
December	1st to 10th	Night	31% 4 11% 29% 23% 3	4580
	11th to 20th	Night	42% 4 12% 17% 17% 7%	5208
	21st to end	Night	39% 7% 13% 21% 18% 1	6812

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% 30% 28% 16% 4 1	300
	11th to 20th	Day	25% 30% 29% 15% 2	300
	21st to end	Day	24% 26% 32% 16% 2	330
February	1st to 10th	Day	23% 26% 33% 15% 3	300
	11th to 20th	Day	34% 25% 32% 7% 1	300
	21st to end	Day	26% 19% 34% 18% 4	363
March	1st to 10th	Day	18% 23% 30% 22% 6%	500
	11th to 20th	Day	19% 22% 32% 19% 6% 2	500
	21st to end	Day	20% 18% 33% 22% 6% 1	550
April	1st to 10th	Day	22% 22% 26% 19% 9% 1	500
	11th to 20th	Day	17% 15% 28% 24% 13% 4	452
	21st to end	Day	23% 14% 28% 22% 10% 3	460
May	1st to 10th	Day	19% 15% 28% 22% 11% 4	463
	11th to 20th	Day	23% 9% 25% 23% 15% 5%	487
	21st to end	Day	16% 6% 21% 26% 21% 10%	529
June	1st to 10th	Day	13% 4 25% 28% 22% 8%	490
	11th to 20th	Day	12% 7% 20% 30% 19% 12%	490
	21st to end	Day	8% 5% 26% 34% 21% 6%	490
July	1st to 10th	Day	11% 3 17% 25% 30% 13%	485
	11th to 20th	Day	4 2 16% 32% 31% 14%	484
	21st to end	Day	12% 3 15% 33% 24% 13%	532
August	1st to 10th	Day	12% 5% 16% 28% 23% 16%	486
	11th to 20th	Day	13% 3 17% 27% 26% 14%	479
	21st to end	Day	10% 2 12% 30% 29% 18%	539
September	1st to 10th	Day	15% 5% 15% 27% 22% 17%	490
	11th to 20th	Day	15% 4 15% 26% 29% 12%	490
	21st to end	Day	27% 7% 18% 24% 18% 5%	490
October	1st to 10th	Day	19% 6% 20% 28% 22% 5%	490
	11th to 20th	Day	14% 12% 26% 28% 17% 3	490
	21st to end	Day	15% 11% 30% 31% 10% 2	539
November	1st to 10th	Day	16% 9% 29% 30% 13% 3	495
	11th to 20th	Day	18% 14% 34% 22% 10% 1	318
	21st to end	Day	19% 20% 31% 21% 9% 1	200
December	1st to 10th	Day	19% 21% 33% 23% 5% 1	200
	11th to 20th	Day	23% 18% 28% 22% 9% 1	200
	21st to end	Day	20% 20% 33% 16% 9% 1	257
January	1st to 10th	Night	17% 18% 38% 25% 3	800
	11th to 20th	Night	18% 15% 34% 29% 4	800
	21st to end	Night	16% 13% 42% 26% 3	880
February	1st to 10th	Night	15% 14% 39% 29% 3	800
	11th to 20th	Night	24% 15% 39% 22% 1	783
	21st to end	Night	20% 15% 37% 25% 3	660
March	1st to 10th	Night	16% 13% 38% 29% 4	800
	11th to 20th	Night	19% 15% 33% 25% 7% 1	800
	21st to end	Night	20% 11% 34% 29% 6% 1	880
April	1st to 10th	Night	19% 15% 33% 27% 6%	800
	11th to 20th	Night	14% 10% 33% 30% 12% 1	754
	21st to end	Night	19% 6% 29% 36% 9% 1	686
May	1st to 10th	Night	17% 6% 24% 36% 16% 1	570
	11th to 20th	Night	20% 4 23% 34% 17% 2	561
	21st to end	Night	15% 2 15% 38% 28% 2	537
June	1st to 10th	Night	10% 1 16% 48% 23% 2	380
	11th to 20th	Night	10% 3 14% 46% 26% 2	380
	21st to end	Night	9% 1 18% 45% 26% 2	380
July	1st to 10th	Night	12% 2 8% 37% 36% 5%	544
	11th to 20th	Night	6% 1 7% 39% 39% 7%	552
	21st to end	Night	8% 2 10% 41% 34% 5%	624
August	1st to 10th	Night	13% 1 8% 43% 31% 4	567
	11th to 20th	Night	12% 2 11% 38% 32% 5%	564
	21st to end	Night	12% 2 13% 34% 35% 5%	820
September	1st to 10th	Night	13% 1 11% 37% 30% 8%	760
	11th to 20th	Night	17% 2 11% 34% 31% 6%	760
	21st to end	Night	26% 3 17% 32% 21% 2	760
October	1st to 10th	Night	18% 5% 18% 32% 23% 4	760
	11th to 20th	Night	15% 8% 28% 32% 16% 1	760
	21st to end	Night	16% 9% 24% 37% 13% 2	836
November	1st to 10th	Night	15% 5% 26% 38% 13% 2	780
	11th to 20th	Night	16% 10% 29% 35% 9% 1	800
	21st to end	Night	17% 11% 31% 33% 8% 1	800
December	1st to 10th	Night	18% 11% 34% 31% 6%	800
	11th to 20th	Night	15% 10% 35% 35% 6%	800
	21st to end	Night	18% 11% 31% 35% 5%	880

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