Oak Mountain State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Mountain State Park clear sky chart from 2005-11-06 to 2026-02-01.

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% 3 6% 5% 5% 5% 4 6% 8% 41%	127242
	Night	12% 7% 2 6% 4 4 4 4 5% 7% 44%	124823
Transparency	Day	39% 7% 11% 20% 18% 6%	131022
	Night	37% 6% 10% 20% 20% 7%	129115
Seeing	Day	15% 10% 23% 25% 18% 9%	16126
	Night	14% 8% 23% 30% 21% 4	26151

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% 10% 5% 5% 4 3 3 3 4 4 44%	4146
	11th to 20th	Day	12% 6% 5% 6% 3 3 3 2 4 5% 51%	4362
	21st to end	Day	22% 9% 2 6% 4 3 3 3 3 6% 38%	5082
February	1st to 10th	Day	17% 10% 3 7% 4 4 4 3 4 6% 38%	2000
	11th to 20th	Day	23% 8% 2 5% 4 3 3 3 4 5% 39%	1948
	21st to end	Day	19% 8% 3 7% 5% 4 3 3 4 5% 38%	1650
March	1st to 10th	Day	19% 8% 3 7% 4 4 4 3 5% 5% 36%	4480
	11th to 20th	Day	12% 7% 3 6% 4 4 3 3 6% 6% 46%	4786
	21st to end	Day	15% 7% 3 7% 4 5% 5% 4 5% 7% 40%	5732
April	1st to 10th	Day	12% 7% 2 6% 5% 4 4 3 6% 8% 45%	2400
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 6% 7% 46%	2374
	21st to end	Day	8% 5% 1 5% 5% 4 5% 3 6% 8% 48%	2400
May	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 5% 7% 9% 35%	5763
	11th to 20th	Day	15% 8% 3 7% 5% 5% 6% 5% 6% 9% 31%	5861
	21st to end	Day	11% 6% 2 7% 5% 4 5% 4 7% 9% 41%	6433
June	1st to 10th	Day	9% 7% 3 7% 6% 7% 5% 6% 8% 10% 33%	2600
	11th to 20th	Day	6% 4 1 5% 6% 6% 6% 6% 8% 11% 41%	2600
	21st to end	Day	6% 5% 2 6% 6% 5% 6% 6% 8% 11% 39%	2600
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 7% 6% 9% 11% 31%	5900
	11th to 20th	Day	6% 5% 2 6% 6% 7% 8% 7% 11% 14% 29%	5900
	21st to end	Day	7% 6% 3 8% 7% 8% 8% 7% 10% 12% 23%	6249
August	1st to 10th	Day	4 3 2 4 3 5% 5% 6% 8% 11% 48%	3905
	11th to 20th	Day	6% 4 1 6% 5% 6% 6% 4 7% 9% 46%	3849
	21st to end	Day	6% 4 2 5% 5% 5% 6% 5% 8% 8% 46%	4312
September	1st to 10th	Day	9% 6% 2 8% 5% 5% 6% 4 6% 8% 41%	2348
	11th to 20th	Day	13% 7% 2 6% 5% 4 4 4 5% 7% 43%	2200
	21st to end	Day	9% 6% 2 6% 4 5% 4 4 5% 7% 49%	2200
October	1st to 10th	Day	9% 5% 2 6% 4 4 5% 3 5% 6% 53%	2200
	11th to 20th	Day	9% 4 2 5% 3 4 3 2 5% 7% 58%	2200
	21st to end	Day	12% 5% 2 5% 3 3 4 2 4 6% 54%	2082
November	1st to 10th	Day	12% 6% 2 4 4 3 3 3 3 6% 53%	1852
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 4 6% 53%	1890
	21st to end	Day	14% 7% 2 6% 3 4 4 3 4 7% 46%	1890
December	1st to 10th	Day	20% 7% 2 5% 3 3 3 2 5% 6% 43%	3020
	11th to 20th	Day	14% 8% 4 6% 5% 4 5% 3 4 5% 43%	3463
	21st to end	Day	19% 9% 3 6% 3 4 3 2 4 6% 41%	4565
January	1st to 10th	Night	16% 10% 4 6% 3 3 3 3 4 5% 45%	6019
	11th to 20th	Night	14% 9% 4 6% 3 3 3 3 4 5% 46%	5813
	21st to end	Night	19% 11% 2 5% 3 4 4 2 3 4 42%	6116
February	1st to 10th	Night	16% 8% 3 7% 4 3 4 3 4 5% 42%	2401
	11th to 20th	Night	20% 9% 3 6% 4 3 3 3 4 5% 41%	2338
	21st to end	Night	18% 6% 2 6% 4 4 4 3 5% 7% 41%	1980
March	1st to 10th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 34%	5373
	11th to 20th	Night	12% 7% 2 5% 3 3 4 3 5% 6% 51%	5174
	21st to end	Night	14% 6% 2 7% 5% 4 4 3 4 6% 44%	5238
April	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 47%	2000
	11th to 20th	Night	13% 5% 2 6% 3 3 3 3 5% 7% 50%	1975
	21st to end	Night	9% 5% 2 5% 4 5% 4 3 5% 7% 52%	2000
May	1st to 10th	Night	11% 7% 3 8% 5% 5% 5% 4 7% 8% 37%	4129
	11th to 20th	Night	16% 9% 3 8% 5% 4 5% 4 6% 7% 32%	4032
	21st to end	Night	9% 5% 2 5% 4 4 6% 5% 8% 11% 42%	4421
June	1st to 10th	Night	5% 6% 2 6% 5% 5% 8% 6% 8% 10% 38%	1800
	11th to 20th	Night	4 4 1 4 3 5% 6% 5% 9% 11% 48%	1800
	21st to end	Night	5% 4 1 6% 6% 4 5% 5% 9% 12% 43%	1800
July	1st to 10th	Night	6% 6% 2 8% 6% 5% 7% 5% 9% 11% 35%	4058
	11th to 20th	Night	6% 5% 3 7% 5% 6% 6% 6% 10% 14% 34%	4057
	21st to end	Night	6% 7% 3 9% 7% 6% 8% 7% 9% 11% 28%	4597
August	1st to 10th	Night	3 3 1 4 4 4 5% 4 7% 12% 53%	3244
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 5% 10% 52%	3200
	21st to end	Night	6% 3 1 5% 4 4 5% 4 7% 9% 52%	3586
September	1st to 10th	Night	8% 5% 2 7% 6% 5% 5% 4 7% 8% 43%	2030
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 46%	2200
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 6% 53%	2200
October	1st to 10th	Night	8% 5% 2 5% 3 3 3 3 4 5% 59%	2200
	11th to 20th	Night	10% 4 2 4 3 3 4 2 4 6% 59%	2200
	21st to end	Night	14% 6% 2 4 3 2 4 2 3 4 56%	2751
November	1st to 10th	Night	10% 5% 1 5% 3 3 3 3 5% 6% 57%	2666
	11th to 20th	Night	11% 6% 2 4 2 3 3 3 4 6% 55%	2730
	21st to end	Night	12% 6% 2 5% 4 4 4 3 6% 5% 48%	2730
December	1st to 10th	Night	19% 6% 2 5% 3 2 3 3 3 6% 48%	4380
	11th to 20th	Night	15% 8% 3 6% 3 3 4 3 4 5% 46%	4952
	21st to end	Night	19% 8% 3 6% 3 3 3 3 4 6% 41%	6633

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	43% 4 4 25% 21% 3	4147
	11th to 20th	Day	36% 3 5% 22% 29% 4	4362
	21st to end	Day	50% 2 6% 14% 18% 10%	5082
February	1st to 10th	Day	48% 3 7% 19% 18% 5%	2000
	11th to 20th	Day	48% 4 5% 17% 20% 7%	1958
	21st to end	Day	48% 5% 6% 13% 21% 8%	1650
March	1st to 10th	Day	49% 4 8% 13% 21% 6%	4480
	11th to 20th	Day	38% 4 6% 16% 20% 16%	4786
	21st to end	Day	44% 4 8% 18% 20% 5%	5734
April	1st to 10th	Day	37% 5% 10% 20% 20% 8%	2400
	11th to 20th	Day	38% 5% 7% 18% 24% 8%	2374
	21st to end	Day	32% 6% 11% 24% 24% 3	2400
May	1st to 10th	Day	42% 8% 13% 24% 12% 2	5799
	11th to 20th	Day	47% 7% 16% 21% 8% 1	5865
	21st to end	Day	38% 7% 13% 24% 16% 1	6447
June	1st to 10th	Day	42% 9% 15% 20% 14% 1	2600
	11th to 20th	Day	31% 10% 18% 24% 15% 2	2600
	21st to end	Day	34% 10% 19% 23% 11% 4	2600
July	1st to 10th	Day	39% 14% 18% 21% 8% 1	5835
	11th to 20th	Day	37% 15% 27% 16% 4	5831
	21st to end	Day	46% 14% 20% 17% 3	6068
August	1st to 10th	Day	25% 9% 13% 33% 19% 1	3893
	11th to 20th	Day	32% 9% 16% 26% 15% 2	3885
	21st to end	Day	31% 9% 15% 20% 21% 4	4311
September	1st to 10th	Day	39% 8% 13% 17% 17% 5%	2348
	11th to 20th	Day	39% 7% 10% 21% 19% 4	2200
	21st to end	Day	33% 7% 10% 21% 22% 7%	2200
October	1st to 10th	Day	24% 4 6% 13% 31% 22%	3590
	11th to 20th	Day	18% 2 5% 14% 31% 29%	3568
	21st to end	Day	25% 3 5% 18% 36% 12%	3332
November	1st to 10th	Day	34% 4 6% 17% 27% 11%	1852
	11th to 20th	Day	34% 3 6% 19% 27% 11%	1890
	21st to end	Day	39% 5% 7% 17% 24% 8%	1890
December	1st to 10th	Day	43% 4 5% 17% 27% 4	3020
	11th to 20th	Day	45% 4 7% 19% 19% 6%	3460
	21st to end	Day	46% 3 6% 23% 22% 2	4565
January	1st to 10th	Night	43% 3 5% 23% 23% 3	6019
	11th to 20th	Night	42% 3 3 19% 24% 9%	5813
	21st to end	Night	47% 2 4 15% 26% 6%	6116
February	1st to 10th	Night	44% 3 6% 18% 21% 8%	2401
	11th to 20th	Night	47% 4 5% 17% 18% 10%	2339
	21st to end	Night	43% 5% 8% 15% 20% 9%	1980
March	1st to 10th	Night	51% 3 6% 14% 17% 8%	5373
	11th to 20th	Night	34% 4 8% 15% 22% 17%	5174
	21st to end	Night	43% 3 6% 23% 18% 8%	5238
April	1st to 10th	Night	35% 6% 11% 21% 20% 8%	2000
	11th to 20th	Night	33% 5% 8% 20% 24% 11%	1975
	21st to end	Night	32% 5% 11% 24% 22% 6%	2000
May	1st to 10th	Night	41% 9% 13% 19% 15% 2	4157
	11th to 20th	Night	48% 8% 14% 20% 8% 1	4033
	21st to end	Night	33% 9% 14% 25% 17% 2	4429
June	1st to 10th	Night	35% 12% 14% 19% 18% 1	1800
	11th to 20th	Night	26% 8% 22% 26% 15% 3	1800
	21st to end	Night	30% 10% 18% 22% 16% 4	1800
July	1st to 10th	Night	38% 11% 21% 20% 8% 1	4015
	11th to 20th	Night	34% 14% 30% 17% 4 1	4006
	21st to end	Night	45% 14% 21% 16% 4	4464
August	1st to 10th	Night	21% 8% 14% 38% 17% 2	3232
	11th to 20th	Night	27% 8% 18% 29% 15% 3	3230
	21st to end	Night	27% 7% 15% 22% 25% 4	3586
September	1st to 10th	Night	36% 8% 16% 18% 16% 6%	2030
	11th to 20th	Night	35% 8% 11% 21% 21% 5%	2200
	21st to end	Night	29% 6% 11% 22% 24% 7%	2200
October	1st to 10th	Night	23% 4 6% 14% 28% 24%	3590
	11th to 20th	Night	18% 2 4 17% 29% 30%	3571
	21st to end	Night	23% 2 4 22% 32% 17%	4451
November	1st to 10th	Night	29% 4 9% 17% 27% 14%	2666
	11th to 20th	Night	31% 3 7% 18% 28% 13%	2730
	21st to end	Night	36% 5% 7% 19% 24% 9%	2730
December	1st to 10th	Night	39% 3 5% 21% 26% 5%	4380
	11th to 20th	Night	41% 4 9% 15% 25% 5%	4954
	21st to end	Night	44% 3 7% 24% 20% 2	6633

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	29% 21% 31% 15% 4	330
	11th to 20th	Day	25% 24% 30% 15% 6%	330
	21st to end	Day	26% 26% 34% 11% 2 1	363
February	1st to 10th	Day	25% 19% 39% 14% 3 1	300
	11th to 20th	Day	40% 17% 30% 12% 1	300
	21st to end	Day	25% 22% 43% 8% 2	249
March	1st to 10th	Day	28% 23% 31% 14% 4	300
	11th to 20th	Day	22% 18% 37% 16% 6% 1	410
	21st to end	Day	22% 19% 31% 19% 8%	550
April	1st to 10th	Day	21% 15% 31% 22% 10% 1	500
	11th to 20th	Day	17% 14% 33% 22% 11% 2	492
	21st to end	Day	12% 11% 31% 32% 13% 2	500
May	1st to 10th	Day	13% 10% 28% 31% 15% 4	503
	11th to 20th	Day	11% 6% 28% 28% 18% 9%	527
	21st to end	Day	12% 6% 20% 31% 17% 14%	573
June	1st to 10th	Day	12% 5% 16% 32% 22% 12%	530
	11th to 20th	Day	6% 4 17% 24% 29% 19%	530
	21st to end	Day	7% 4 11% 27% 33% 18%	530
July	1st to 10th	Day	8% 2 8% 26% 35% 22%	525
	11th to 20th	Day	7% 3 7% 21% 33% 29%	524
	21st to end	Day	6% 2 8% 25% 36% 23%	576
August	1st to 10th	Day	8% 2 7% 30% 30% 23%	526
	11th to 20th	Day	8% 2 8% 29% 34% 19%	519
	21st to end	Day	12% 4 11% 26% 29% 18%	583
September	1st to 10th	Day	8% 5% 12% 34% 28% 13%	530
	11th to 20th	Day	11% 6% 13% 27% 32% 11%	530
	21st to end	Day	11% 3 18% 30% 30% 8%	530
October	1st to 10th	Day	12% 7% 23% 33% 21% 5%	530
	11th to 20th	Day	10% 7% 26% 34% 21% 1	530
	21st to end	Day	19% 12% 24% 30% 13% 2	393
November	1st to 10th	Day	18% 9% 32% 28% 9% 3	330
	11th to 20th	Day	15% 14% 39% 24% 7%	330
	21st to end	Day	17% 18% 37% 19% 8% 1	330
December	1st to 10th	Day	29% 17% 30% 20% 3	330
	11th to 20th	Day	23% 19% 37% 15% 5% 1	330
	21st to end	Day	26% 19% 31% 20% 4	363
January	1st to 10th	Night	21% 15% 35% 23% 4	840
	11th to 20th	Night	22% 18% 29% 25% 7%	840
	21st to end	Night	19% 16% 35% 26% 3	924
February	1st to 10th	Night	21% 11% 35% 29% 4	801
	11th to 20th	Night	26% 14% 32% 25% 3	783
	21st to end	Night	21% 16% 36% 25% 2	660
March	1st to 10th	Night	20% 15% 30% 31% 5%	800
	11th to 20th	Night	17% 13% 35% 25% 9% 1	800
	21st to end	Night	17% 12% 34% 28% 10%	780
April	1st to 10th	Night	13% 12% 34% 29% 12%	600
	11th to 20th	Night	14% 10% 32% 29% 13% 2	593
	21st to end	Night	12% 8% 27% 35% 16% 2	600
May	1st to 10th	Night	9% 7% 28% 32% 21% 3	600
	11th to 20th	Night	11% 5% 23% 33% 25% 3	591
	21st to end	Night	9% 2 12% 35% 35% 6%	650
June	1st to 10th	Night	9% 2 10% 41% 33% 6%	600
	11th to 20th	Night	6% 1 10% 29% 42% 12%	600
	21st to end	Night	5% 1 8% 29% 44% 13%	600
July	1st to 10th	Night	7% 2 5% 25% 46% 15%	585
	11th to 20th	Night	7% 1 4 21% 47% 21%	582
	21st to end	Night	6% 1 6% 25% 48% 14%	657
August	1st to 10th	Night	5% 1 4 27% 47% 16%	597
	11th to 20th	Night	8% 2 7% 29% 45% 9%	594
	21st to end	Night	11% 3 7% 26% 40% 12%	660
September	1st to 10th	Night	9% 3 9% 33% 38% 9%	630
	11th to 20th	Night	13% 3 12% 29% 38% 5%	800
	21st to end	Night	9% 1 15% 33% 38% 4	800
October	1st to 10th	Night	10% 4 22% 33% 26% 5%	800
	11th to 20th	Night	11% 6% 23% 37% 22% 2	800
	21st to end	Night	16% 7% 21% 35% 20% 2	880
November	1st to 10th	Night	13% 7% 21% 37% 18% 3	820
	11th to 20th	Night	14% 9% 29% 34% 13% 1	840
	21st to end	Night	15% 10% 30% 33% 12% 1	840
December	1st to 10th	Night	22% 12% 27% 30% 8% 1	840
	11th to 20th	Night	23% 10% 28% 29% 9%	840
	21st to end	Night	24% 12% 30% 28% 7%	924

Page generated at 2026-01-29 00:21:47. Version ac07

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