Walker County Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walker County Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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% 7% 3 7% 5% 5% 5% 4 6% 7% 41%	113897
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	114748
Transparency	Day	39% 7% 10% 21% 18% 4	117703
	Night	38% 6% 10% 22% 20% 5%	119080
Seeing	Day	17% 11% 23% 23% 18% 8%	15269
	Night	15% 8% 24% 30% 20% 3	25367

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	15% 9% 3 6% 4 3 3 3 4 5% 44%	4056
	11th to 20th	Day	13% 7% 5% 7% 4 4 3 3 3 5% 48%	4060
	21st to end	Day	20% 10% 3 6% 3 3 3 3 5% 6% 38%	4761
February	1st to 10th	Day	16% 10% 3 6% 4 4 4 4 5% 6% 38%	2000
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 3 4 5% 36%	1948
	21st to end	Day	20% 7% 3 7% 3 4 3 3 5% 6% 38%	1650
March	1st to 10th	Day	18% 9% 3 8% 4 5% 5% 4 6% 5% 33%	4480
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 5% 6% 49%	4970
	21st to end	Day	13% 7% 3 7% 5% 4 4 3 5% 6% 43%	5465
April	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	2380
	11th to 20th	Day	11% 7% 2 6% 5% 4 3 3 6% 6% 46%	2374
	21st to end	Day	11% 6% 2 6% 5% 5% 4 5% 6% 8% 44%	2443
May	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 7% 40%	4082
	11th to 20th	Day	13% 8% 3 7% 4 5% 5% 4 6% 8% 36%	4081
	21st to end	Day	9% 5% 2 7% 5% 5% 4 5% 7% 9% 41%	4476
June	1st to 10th	Day	9% 6% 3 7% 6% 6% 6% 5% 8% 10% 36%	2470
	11th to 20th	Day	4 3 2 6% 5% 6% 6% 6% 8% 12% 42%	2470
	21st to end	Day	6% 4 2 7% 6% 6% 6% 6% 7% 12% 38%	2470
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 8% 6% 9% 10% 31%	4120
	11th to 20th	Day	8% 6% 2 7% 6% 6% 7% 6% 8% 10% 34%	4120
	21st to end	Day	13% 10% 4 10% 8% 7% 7% 6% 8% 8% 19%	4466
August	1st to 10th	Day	4 4 1 6% 4 6% 6% 6% 8% 10% 44%	4049
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 11% 41%	3729
	21st to end	Day	8% 4 2 6% 5% 4 5% 5% 6% 8% 48%	4180
September	1st to 10th	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 8% 39%	2164
	11th to 20th	Day	14% 6% 2 5% 5% 5% 5% 4 5% 7% 41%	2090
	21st to end	Day	13% 6% 2 7% 4 3 4 4 5% 6% 48%	2090
October	1st to 10th	Day	11% 5% 2 4 4 3 4 3 4 5% 54%	2090
	11th to 20th	Day	10% 5% 3 5% 3 3 4 2 5% 5% 56%	2037
	21st to end	Day	14% 4 2 4 3 3 4 3 5% 6% 52%	1995
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 5% 5% 53%	1762
	11th to 20th	Day	12% 5% 2 6% 4 4 3 3 5% 7% 49%	1800
	21st to end	Day	15% 5% 2 5% 4 4 4 3 5% 7% 46%	1800
December	1st to 10th	Day	15% 8% 3 7% 4 4 3 3 4 4 46%	2930
	11th to 20th	Day	14% 11% 4 9% 5% 5% 4 3 4 5% 35%	3373
	21st to end	Day	18% 8% 3 7% 4 4 4 3 5% 7% 37%	4466
January	1st to 10th	Night	14% 7% 4 8% 5% 4 4 3 4 5% 43%	5889
	11th to 20th	Night	16% 7% 3 6% 4 3 3 3 4 5% 48%	5900
	21st to end	Night	16% 10% 2 6% 3 4 4 4 5% 5% 42%	6191
February	1st to 10th	Night	14% 8% 3 8% 4 4 4 3 5% 5% 43%	2400
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 3 4 5% 38%	2338
	21st to end	Night	19% 8% 3 6% 4 3 4 3 5% 6% 38%	1980
March	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 5% 6% 32%	5373
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 6% 7% 49%	4990
	21st to end	Night	13% 7% 3 8% 5% 5% 4 4 4 5% 42%	5467
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 7% 48%	2036
	11th to 20th	Night	11% 6% 2 5% 3 3 3 4 5% 7% 50%	1975
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 7% 49%	1851
May	1st to 10th	Night	10% 7% 3 8% 6% 5% 5% 4 6% 8% 39%	2813
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 4 7% 9% 39%	2812
	21st to end	Night	7% 4 2 6% 4 5% 5% 5% 8% 11% 43%	3079
June	1st to 10th	Night	5% 5% 2 8% 6% 6% 6% 4 7% 11% 40%	1710
	11th to 20th	Night	4 3 2 4 3 5% 4 4 7% 13% 51%	1710
	21st to end	Night	5% 4 2 5% 5% 4 5% 6% 8% 12% 45%	1710
July	1st to 10th	Night	7% 5% 2 8% 7% 6% 6% 5% 8% 11% 33%	2840
	11th to 20th	Night	9% 5% 2 5% 5% 4 5% 5% 7% 11% 42%	2840
	21st to end	Night	11% 9% 4 10% 6% 7% 7% 5% 7% 10% 25%	3087
August	1st to 10th	Night	4 3 2 4 4 5% 5% 5% 9% 10% 49%	2876
	11th to 20th	Night	6% 4 2 5% 4 5% 4 4 7% 9% 50%	3100
	21st to end	Night	7% 3 2 4 4 4 4 4 6% 8% 56%	3476
September	1st to 10th	Night	8% 6% 2 7% 5% 5% 4 5% 6% 10% 41%	1995
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 6% 8% 43%	2090
	21st to end	Night	11% 5% 2 6% 4 4 3 4 5% 7% 50%	2090
October	1st to 10th	Night	11% 4 2 4 3 3 3 2 4 6% 59%	2090
	11th to 20th	Night	11% 4 1 7% 3 4 3 2 4 4 55%	2142
	21st to end	Night	13% 5% 2 4 3 3 3 3 5% 6% 55%	2600
November	1st to 10th	Night	13% 6% 1 4 3 4 3 3 5% 6% 52%	2536
	11th to 20th	Night	12% 7% 2 6% 3 3 3 3 5% 6% 52%	2600
	21st to end	Night	14% 6% 2 6% 5% 4 4 3 4 5% 47%	2600
December	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 4 4 46%	4250
	11th to 20th	Night	18% 10% 3 6% 4 4 4 3 4 5% 41%	4822
	21st to end	Night	18% 7% 3 8% 4 5% 5% 4 5% 6% 36%	6490

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	41% 5% 8% 23% 22% 2	4057
	11th to 20th	Day	40% 4 6% 20% 28% 3	4060
	21st to end	Day	47% 3 8% 20% 19% 3	4761
February	1st to 10th	Day	46% 5% 8% 21% 17% 3	2000
	11th to 20th	Day	51% 5% 6% 18% 16% 4	1958
	21st to end	Day	46% 5% 8% 15% 20% 5%	1650
March	1st to 10th	Day	51% 5% 7% 11% 18% 7%	4480
	11th to 20th	Day	35% 5% 6% 18% 23% 13%	4970
	21st to end	Day	42% 4 9% 26% 17% 2	5465
April	1st to 10th	Day	39% 7% 10% 22% 17% 5%	2380
	11th to 20th	Day	38% 5% 8% 21% 23% 6%	2374
	21st to end	Day	37% 7% 11% 28% 16% 2	2443
May	1st to 10th	Day	40% 9% 13% 23% 14% 2	4120
	11th to 20th	Day	43% 9% 13% 23% 11% 1	4085
	21st to end	Day	36% 9% 11% 23% 19% 1	4489
June	1st to 10th	Day	39% 10% 16% 21% 12% 1	2470
	11th to 20th	Day	30% 11% 18% 25% 14% 2	2470
	21st to end	Day	36% 11% 17% 19% 13% 3	2470
July	1st to 10th	Day	40% 13% 20% 19% 7% 1	4055
	11th to 20th	Day	40% 11% 20% 20% 6% 2	4051
	21st to end	Day	58% 11% 12% 13% 5%	4324
August	1st to 10th	Day	30% 10% 13% 35% 11%	4036
	11th to 20th	Day	32% 9% 16% 25% 15% 2	3765
	21st to end	Day	31% 9% 11% 27% 20% 2	4179
September	1st to 10th	Day	39% 10% 13% 16% 16% 6%	2164
	11th to 20th	Day	41% 8% 10% 20% 18% 2	2090
	21st to end	Day	36% 6% 11% 19% 21% 7%	2090
October	1st to 10th	Day	25% 4 6% 15% 38% 12%	3480
	11th to 20th	Day	22% 4 5% 21% 32% 17%	3368
	21st to end	Day	27% 4 7% 25% 28% 9%	3271
November	1st to 10th	Day	34% 4 7% 19% 28% 7%	1762
	11th to 20th	Day	35% 4 7% 21% 26% 7%	1800
	21st to end	Day	39% 5% 7% 23% 23% 4	1800
December	1st to 10th	Day	42% 4 5% 20% 25% 4	2930
	11th to 20th	Day	53% 4 6% 19% 15% 4	3370
	21st to end	Day	46% 4 11% 26% 12% 2	4466
January	1st to 10th	Night	43% 4 8% 22% 21% 2	5889
	11th to 20th	Night	40% 4 6% 19% 25% 6%	5900
	21st to end	Night	44% 3 5% 21% 21% 6%	6191
February	1st to 10th	Night	43% 5% 9% 19% 20% 4	2400
	11th to 20th	Night	50% 5% 7% 17% 15% 6%	2339
	21st to end	Night	47% 5% 8% 17% 18% 6%	1980
March	1st to 10th	Night	52% 5% 6% 15% 18% 4	5373
	11th to 20th	Night	33% 5% 7% 19% 22% 14%	4990
	21st to end	Night	44% 4 7% 23% 18% 4	5467
April	1st to 10th	Night	33% 6% 12% 23% 21% 5%	2036
	11th to 20th	Night	33% 4 7% 24% 23% 9%	1975
	21st to end	Night	34% 6% 11% 27% 19% 2	1851
May	1st to 10th	Night	39% 10% 14% 22% 14% 2	2840
	11th to 20th	Night	39% 10% 16% 23% 12% 1	2813
	21st to end	Night	29% 11% 16% 25% 16% 2	3087
June	1st to 10th	Night	36% 10% 17% 21% 14% 3	1710
	11th to 20th	Night	23% 9% 21% 30% 16% 2	1710
	21st to end	Night	29% 10% 20% 21% 14% 5%	1710
July	1st to 10th	Night	41% 12% 18% 20% 7% 2	2795
	11th to 20th	Night	33% 10% 24% 23% 7% 2	2786
	21st to end	Night	53% 11% 15% 15% 6% 1	2988
August	1st to 10th	Night	27% 10% 15% 35% 13% 1	2865
	11th to 20th	Night	28% 8% 21% 27% 14% 1	3130
	21st to end	Night	26% 8% 14% 24% 26% 2	3476
September	1st to 10th	Night	36% 9% 17% 18% 14% 5%	1995
	11th to 20th	Night	37% 9% 12% 19% 20% 2	2090
	21st to end	Night	33% 6% 10% 22% 21% 7%	2090
October	1st to 10th	Night	21% 4 7% 20% 32% 16%	3480
	11th to 20th	Night	20% 3 5% 17% 35% 20%	3550
	21st to end	Night	24% 3 5% 27% 29% 12%	4274
November	1st to 10th	Night	33% 5% 7% 21% 23% 9%	2536
	11th to 20th	Night	34% 4 6% 20% 27% 9%	2600
	21st to end	Night	39% 5% 7% 23% 22% 5%	2600
December	1st to 10th	Night	42% 4 7% 20% 26% 2	4250
	11th to 20th	Night	46% 4 6% 19% 21% 3	4824
	21st to end	Night	46% 5% 10% 25% 13% 1	6490

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	28% 24% 29% 15% 3	300
	11th to 20th	Day	27% 23% 33% 11% 6% 1	300
	21st to end	Day	22% 25% 37% 14% 3	330
February	1st to 10th	Day	27% 19% 36% 13% 5%	300
	11th to 20th	Day	40% 22% 26% 10% 2	300
	21st to end	Day	34% 22% 31% 10% 3	249
March	1st to 10th	Day	28% 24% 29% 15% 3 1	300
	11th to 20th	Day	23% 20% 30% 20% 6% 1	490
	21st to end	Day	20% 18% 37% 18% 7%	550
April	1st to 10th	Day	19% 18% 32% 18% 11% 2	500
	11th to 20th	Day	16% 17% 32% 22% 12% 1	492
	21st to end	Day	17% 13% 33% 21% 13% 3	480
May	1st to 10th	Day	14% 11% 29% 26% 13% 6%	463
	11th to 20th	Day	13% 7% 23% 30% 18% 10%	487
	21st to end	Day	13% 5% 20% 27% 22% 13%	529
June	1st to 10th	Day	14% 4 18% 28% 22% 13%	490
	11th to 20th	Day	5% 3 13% 31% 27% 21%	490
	21st to end	Day	10% 3 18% 24% 25% 18%	490
July	1st to 10th	Day	10% 2 12% 25% 28% 23%	485
	11th to 20th	Day	11% 2 10% 24% 32% 21%	484
	21st to end	Day	9% 2 9% 28% 29% 23%	532
August	1st to 10th	Day	11% 3 12% 24% 32% 17%	486
	11th to 20th	Day	10% 2 15% 29% 29% 14%	479
	21st to end	Day	14% 3 10% 22% 32% 19%	539
September	1st to 10th	Day	9% 4 14% 29% 30% 15%	490
	11th to 20th	Day	18% 3 12% 23% 32% 13%	490
	21st to end	Day	17% 6% 16% 26% 30% 6%	490
October	1st to 10th	Day	14% 5% 20% 30% 22% 9%	490
	11th to 20th	Day	12% 11% 26% 30% 20% 2	490
	21st to end	Day	18% 9% 23% 29% 17% 4	444
November	1st to 10th	Day	22% 10% 27% 27% 12% 3	300
	11th to 20th	Day	17% 15% 35% 26% 6% 1	300
	21st to end	Day	15% 20% 35% 21% 8% 1	300
December	1st to 10th	Day	26% 19% 35% 16% 3 1	300
	11th to 20th	Day	19% 17% 37% 19% 6% 1	300
	21st to end	Day	29% 19% 28% 17% 5% 1	330
January	1st to 10th	Night	23% 15% 35% 23% 5%	800
	11th to 20th	Night	20% 15% 33% 27% 6%	800
	21st to end	Night	18% 14% 36% 29% 2	880
February	1st to 10th	Night	19% 13% 34% 30% 4	800
	11th to 20th	Night	25% 17% 34% 24% 1	783
	21st to end	Night	25% 16% 35% 21% 2	660
March	1st to 10th	Night	19% 14% 33% 29% 5%	800
	11th to 20th	Night	18% 15% 34% 25% 8% 1	800
	21st to end	Night	18% 12% 33% 28% 8%	880
April	1st to 10th	Night	13% 13% 32% 31% 10%	636
	11th to 20th	Night	13% 10% 35% 32% 9% 1	593
	21st to end	Night	13% 8% 27% 39% 12% 1	587
May	1st to 10th	Night	10% 8% 27% 34% 20% 2	570
	11th to 20th	Night	14% 5% 21% 33% 23% 4	561
	21st to end	Night	10% 2 12% 39% 33% 4	617
June	1st to 10th	Night	8% 2 14% 38% 33% 5%	570
	11th to 20th	Night	4 2 11% 36% 37% 10%	570
	21st to end	Night	6% 2 10% 31% 43% 8%	570
July	1st to 10th	Night	10% 2 8% 27% 41% 11%	555
	11th to 20th	Night	9% 2 6% 27% 44% 12%	552
	21st to end	Night	8% 1 8% 26% 46% 10%	624
August	1st to 10th	Night	7% 2 5% 25% 50% 11%	567
	11th to 20th	Night	11% 1 11% 30% 41% 6%	564
	21st to end	Night	13% 1 8% 25% 43% 9%	627
September	1st to 10th	Night	10% 2 11% 31% 39% 7%	665
	11th to 20th	Night	15% 3 11% 30% 37% 4	760
	21st to end	Night	14% 2 15% 32% 34% 3	760
October	1st to 10th	Night	13% 4 18% 30% 29% 7%	760
	11th to 20th	Night	14% 5% 27% 32% 21% 1	760
	21st to end	Night	15% 6% 21% 37% 18% 2	836
November	1st to 10th	Night	15% 9% 22% 34% 20% 1	780
	11th to 20th	Night	14% 9% 33% 31% 13% 1	800
	21st to end	Night	18% 11% 28% 32% 10% 1	800
December	1st to 10th	Night	22% 14% 28% 29% 8%	800
	11th to 20th	Night	20% 11% 30% 31% 8% 1	800
	21st to end	Night	22% 11% 30% 30% 7%	880

Page generated at 2025-04-23 09:25:01. Version ac07

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