Lookout Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Mountain clear sky chart from 2005-11-06 to 2025-12-03.

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	5% 7% 3 7% 5% 5% 5% 4 6% 7% 48%	136230
	Night	5% 7% 3 7% 5% 5% 5% 4 6% 8% 46%	131791
Transparency	Day	35% 8% 14% 21% 16% 7%	130990
	Night	35% 10% 16% 19% 14% 6%	128029
Seeing	Day	14% 19% 30% 25% 11% 2	15903
	Night	12% 14% 28% 30% 15% 2	24907

By Month

Percentage Cloud Cover SW (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	7% 14% 6% 12% 8% 6% 7% 5% 7% 10% 18%	3639
	11th to 20th	Day	6% 11% 3 8% 6% 5% 5% 3 6% 7% 40%	3640
	21st to end	Day	4 12% 4 10% 6% 6% 6% 5% 6% 7% 34%	4234
February	1st to 10th	Day	7% 14% 4 9% 7% 5% 6% 5% 8% 8% 26%	1800
	11th to 20th	Day	7% 12% 4 8% 5% 5% 6% 7% 9% 9% 28%	1755
	21st to end	Day	6% 11% 5% 11% 7% 7% 5% 4 7% 8% 29%	1623
March	1st to 10th	Day	5% 10% 4 9% 6% 6% 7% 6% 8% 8% 30%	4578
	11th to 20th	Day	5% 13% 4 10% 6% 6% 5% 4 6% 7% 35%	5000
	21st to end	Day	5% 13% 5% 12% 8% 8% 8% 6% 7% 7% 21%	5719
April	1st to 10th	Day	8% 10% 3 10% 7% 7% 6% 5% 7% 9% 27%	2400
	11th to 20th	Day	7% 12% 4 10% 6% 6% 4 5% 6% 7% 33%	2369
	21st to end	Day	5% 9% 3 8% 6% 5% 6% 5% 7% 9% 37%	2533
May	1st to 10th	Day	7% 6% 2 6% 4 4 4 3 5% 6% 53%	6320
	11th to 20th	Day	5% 6% 2 6% 5% 4 4 3 5% 8% 51%	6277
	21st to end	Day	6% 6% 2 6% 5% 5% 5% 5% 7% 9% 44%	6902
June	1st to 10th	Day	8% 7% 3 7% 5% 4 5% 5% 6% 8% 42%	2800
	11th to 20th	Day	5% 5% 2 7% 5% 4 5% 4 7% 9% 46%	2800
	21st to end	Day	4 3 1 5% 4 3 4 3 5% 7% 60%	2800
July	1st to 10th	Day	2 2 1 1 1 1 2 2 3 4 82%	6319
	11th to 20th	Day	1 1 2 1 2 2 2 2 3 84%	6320
	21st to end	Day	3 2 1 2 2 2 2 2 3 5% 77%	6880
August	1st to 10th	Day	2 2 1 3 2 3 3 3 5% 6% 70%	6002
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 6% 67%	5796
	21st to end	Day	4 5% 2 4 3 3 4 3 5% 7% 59%	6030
September	1st to 10th	Day	3 2 1 3 2 3 4 3 4 7% 68%	2400
	11th to 20th	Day	4 4 2 5% 5% 4 5% 3 5% 8% 56%	2400
	21st to end	Day	6% 6% 2 5% 4 4 5% 3 5% 7% 54%	2134
October	1st to 10th	Day	6% 5% 2 4 3 4 5% 3 5% 6% 58%	3280
	11th to 20th	Day	4 5% 2 7% 6% 6% 6% 5% 7% 9% 43%	3261
	21st to end	Day	5% 8% 3 9% 6% 7% 7% 5% 7% 9% 35%	3374
November	1st to 10th	Day	7% 10% 4 10% 7% 6% 6% 4 7% 10% 28%	1817
	11th to 20th	Day	5% 12% 6% 11% 8% 7% 7% 6% 8% 8% 23%	1680
	21st to end	Day	5% 11% 5% 9% 6% 6% 5% 5% 9% 9% 31%	1680
December	1st to 10th	Day	5% 8% 3 7% 5% 4 4 3 5% 8% 48%	2636
	11th to 20th	Day	6% 14% 5% 12% 9% 7% 8% 5% 9% 9% 18%	3028
	21st to end	Day	6% 13% 5% 12% 8% 7% 6% 5% 7% 8% 24%	4004
January	1st to 10th	Night	7% 13% 4 11% 7% 7% 8% 6% 8% 9% 20%	6306
	11th to 20th	Night	6% 10% 4 8% 5% 4 3 4 5% 8% 43%	6320
	21st to end	Night	6% 10% 4 10% 6% 5% 5% 4 5% 6% 38%	6718
February	1st to 10th	Night	5% 12% 4 10% 6% 6% 6% 4 7% 9% 31%	2600
	11th to 20th	Night	7% 11% 3 8% 6% 5% 5% 4 7% 9% 35%	2532
	21st to end	Night	7% 9% 3 7% 6% 6% 5% 5% 8% 10% 33%	2005
March	1st to 10th	Night	3 6% 3 8% 7% 6% 7% 7% 9% 10% 35%	5315
	11th to 20th	Night	4 8% 4 9% 7% 5% 5% 4 7% 8% 40%	5000
	21st to end	Night	6% 8% 3 9% 7% 7% 7% 7% 11% 12% 24%	5255
April	1st to 10th	Night	7% 8% 3 8% 6% 6% 6% 5% 8% 10% 33%	2000
	11th to 20th	Night	6% 7% 2 6% 6% 7% 6% 4 8% 8% 41%	1979
	21st to end	Night	6% 7% 3 6% 4 5% 5% 4 7% 9% 42%	1864
May	1st to 10th	Night	8% 6% 2 4 3 2 3 2 4 6% 60%	3640
	11th to 20th	Night	4 5% 1 4 3 4 5% 5% 8% 8% 54%	3616
	21st to end	Night	6% 4 2 4 3 4 5% 4 8% 11% 50%	3972
June	1st to 10th	Night	9% 6% 2 7% 4 4 4 4 6% 9% 44%	1600
	11th to 20th	Night	6% 4 1 4 3 3 4 4 6% 9% 54%	1600
	21st to end	Night	3 3 1 5% 4 3 4 3 3 5% 67%	1600
July	1st to 10th	Night	1 1 2 2 2 3 3 3 4 80%	3640
	11th to 20th	Night	2 1 1 1 1 1 1 2 3 3 83%	3640
	21st to end	Night	2 1 1 1 1 2 2 4 5% 81%	3970
August	1st to 10th	Night	2 2 1 3 3 3 4 3 6% 8% 65%	3798
	11th to 20th	Night	5% 2 1 3 3 3 3 2 3 5% 70%	4052
	21st to end	Night	4 3 2 4 3 3 3 3 4 5% 66%	4965
September	1st to 10th	Night	2 2 1 3 2 2 2 2 5% 6% 72%	2000
	11th to 20th	Night	4 3 2 4 4 4 4 4 6% 7% 60%	2000
	21st to end	Night	4 5% 2 5% 3 3 4 3 6% 8% 58%	2262
October	1st to 10th	Night	4 3 1 4 2 3 3 3 6% 7% 63%	3920
	11th to 20th	Night	4 4 2 5% 4 6% 6% 5% 7% 10% 47%	3897
	21st to end	Night	6% 5% 2 7% 5% 5% 6% 6% 8% 10% 40%	4429
November	1st to 10th	Night	7% 8% 4 8% 6% 7% 7% 6% 7% 8% 33%	2700
	11th to 20th	Night	6% 9% 3 9% 7% 7% 6% 6% 8% 10% 29%	2940
	21st to end	Night	5% 7% 4 8% 7% 6% 7% 6% 7% 10% 34%	2940
December	1st to 10th	Night	4 6% 3 5% 4 4 5% 4 5% 7% 53%	4588
	11th to 20th	Night	6% 13% 5% 13% 9% 7% 7% 6% 8% 8% 19%	5176
	21st to end	Night	8% 10% 4 11% 6% 6% 6% 4 7% 8% 29%	6952

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	59% 14% 13% 11% 3	3639
	11th to 20th	Day	43% 10% 11% 18% 16% 2	3640
	21st to end	Day	47% 10% 11% 13% 12% 7%	4234
February	1st to 10th	Day	54% 13% 17% 13% 3	1800
	11th to 20th	Day	51% 11% 17% 15% 6% 1	1764
	21st to end	Day	53% 10% 14% 14% 7% 1	1623
March	1st to 10th	Day	47% 6% 15% 20% 9% 2	4578
	11th to 20th	Day	46% 9% 12% 24% 8%	5000
	21st to end	Day	56% 12% 16% 13% 3	5719
April	1st to 10th	Day	53% 8% 19% 16% 5%	2400
	11th to 20th	Day	49% 7% 16% 15% 11% 2	2372
	21st to end	Day	41% 9% 21% 18% 8% 2	2533
May	1st to 10th	Day	32% 4 13% 30% 18% 2	6320
	11th to 20th	Day	30% 9% 18% 28% 14% 2	6280
	21st to end	Day	32% 11% 24% 26% 6% 1	6904
June	1st to 10th	Day	40% 5% 19% 23% 11% 2	2800
	11th to 20th	Day	34% 6% 23% 23% 11% 3	2800
	21st to end	Day	23% 5% 15% 30% 20% 6%	2800
July	1st to 10th	Day	9% 2 7% 21% 28% 33%	6251
	11th to 20th	Day	8% 2 4 12% 33% 40%	6245
	21st to end	Day	11% 4 7% 30% 30% 18%	6681
August	1st to 10th	Day	15% 3 9% 18% 33% 22%	4373
	11th to 20th	Day	16% 5% 10% 37% 25% 7%	4195
	21st to end	Day	22% 5% 12% 24% 31% 7%	4345
September	1st to 10th	Day	16% 4 15% 26% 27% 13%	2400
	11th to 20th	Day	27% 5% 15% 25% 21% 7%	2400
	21st to end	Day	31% 5% 14% 24% 19% 7%	2134
October	1st to 10th	Day	27% 6% 10% 23% 28% 6%	3280
	11th to 20th	Day	36% 10% 15% 24% 13% 1	3261
	21st to end	Day	41% 11% 16% 21% 9% 1	3374
November	1st to 10th	Day	50% 9% 17% 18% 5% 1	1817
	11th to 20th	Day	57% 14% 15% 11% 4	1680
	21st to end	Day	48% 11% 16% 13% 11% 1	1680
December	1st to 10th	Day	36% 9% 13% 16% 21% 4	2636
	11th to 20th	Day	59% 14% 15% 10% 2	3028
	21st to end	Day	56% 11% 18% 12% 3	4004
January	1st to 10th	Night	56% 15% 13% 11% 4	6306
	11th to 20th	Night	41% 7% 15% 20% 15% 2	6320
	21st to end	Night	47% 10% 11% 10% 16% 6%	6718
February	1st to 10th	Night	48% 14% 19% 15% 4	2600
	11th to 20th	Night	45% 12% 20% 14% 8% 1	2534
	21st to end	Night	46% 11% 18% 17% 7% 1	2005
March	1st to 10th	Night	38% 10% 17% 24% 8% 3	5315
	11th to 20th	Night	40% 8% 20% 25% 7%	5000
	21st to end	Night	46% 18% 23% 12% 2	5255
April	1st to 10th	Night	43% 12% 24% 15% 5%	2000
	11th to 20th	Night	39% 8% 24% 17% 9% 3	1979
	21st to end	Night	37% 10% 23% 18% 10% 2	1864
May	1st to 10th	Night	28% 4 14% 30% 22% 2	3637
	11th to 20th	Night	23% 10% 20% 29% 16% 1	3616
	21st to end	Night	27% 12% 29% 25% 5% 2	3972
June	1st to 10th	Night	38% 7% 18% 24% 11% 2	1600
	11th to 20th	Night	27% 7% 26% 25% 11% 4	1600
	21st to end	Night	21% 5% 17% 29% 20% 8%	1600
July	1st to 10th	Night	10% 3 10% 14% 23% 40%	3600
	11th to 20th	Night	8% 4 6% 8% 29% 46%	3592
	21st to end	Night	7% 3 7% 28% 31% 24%	3857
August	1st to 10th	Night	14% 3 9% 14% 35% 24%	2755
	11th to 20th	Night	13% 6% 11% 33% 26% 11%	2929
	21st to end	Night	16% 5% 14% 25% 30% 11%	3571
September	1st to 10th	Night	14% 3 16% 26% 26% 14%	2000
	11th to 20th	Night	24% 6% 15% 22% 20% 11%	2000
	21st to end	Night	25% 5% 18% 24% 20% 9%	2262
October	1st to 10th	Night	21% 7% 12% 26% 29% 4	3920
	11th to 20th	Night	32% 9% 17% 25% 14% 2	3897
	21st to end	Night	34% 13% 21% 18% 13% 1	4429
November	1st to 10th	Night	48% 10% 17% 17% 6% 1	2700
	11th to 20th	Night	49% 14% 18% 13% 5%	2940
	21st to end	Night	43% 13% 18% 16% 9% 1	2940
December	1st to 10th	Night	32% 9% 13% 18% 24% 4	4588
	11th to 20th	Night	58% 14% 16% 9% 3	5176
	21st to end	Night	50% 15% 20% 12% 3	6952

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% 27% 29% 13% 9% 1	200
	11th to 20th	Day	22% 20% 31% 21% 6% 2	200
	21st to end	Day	14% 24% 30% 20% 10% 1	320
February	1st to 10th	Day	22% 24% 32% 16% 6% 1	400
	11th to 20th	Day	21% 29% 29% 18% 3	395
	21st to end	Day	24% 26% 26% 20% 4	401
March	1st to 10th	Day	18% 26% 36% 15% 4 1	500
	11th to 20th	Day	20% 24% 28% 20% 7%	500
	21st to end	Day	25% 24% 31% 15% 5%	550
April	1st to 10th	Day	21% 26% 25% 19% 8% 1	500
	11th to 20th	Day	18% 29% 30% 14% 7% 2	492
	21st to end	Day	13% 26% 32% 22% 6% 1	500
May	1st to 10th	Day	16% 21% 32% 19% 9% 2	503
	11th to 20th	Day	21% 16% 29% 21% 9% 4	528
	21st to end	Day	13% 16% 28% 29% 11% 3	573
June	1st to 10th	Day	11% 21% 24% 28% 12% 4	530
	11th to 20th	Day	12% 26% 30% 22% 8% 2	530
	21st to end	Day	6% 15% 30% 31% 15% 3	530
July	1st to 10th	Day	3 11% 34% 36% 13% 2	526
	11th to 20th	Day	3 12% 32% 34% 16% 3	524
	21st to end	Day	2 6% 31% 37% 18% 5%	575
August	1st to 10th	Day	3 9% 28% 33% 20% 7%	527
	11th to 20th	Day	3 8% 28% 34% 20% 6%	517
	21st to end	Day	6% 12% 32% 29% 15% 5%	583
September	1st to 10th	Day	3 10% 30% 36% 17% 3	530
	11th to 20th	Day	7% 12% 31% 35% 13% 2	530
	21st to end	Day	12% 16% 30% 30% 11% 1	530
October	1st to 10th	Day	16% 14% 32% 24% 14%	530
	11th to 20th	Day	15% 20% 28% 24% 12% 2	530
	21st to end	Day	18% 27% 28% 17% 10% 2	474
November	1st to 10th	Day	21% 21% 27% 24% 7%	311
	11th to 20th	Day	19% 24% 26% 20% 9% 2	220
	21st to end	Day	16% 17% 35% 24% 7% 1	220
December	1st to 10th	Day	17% 18% 27% 22% 12% 4	204
	11th to 20th	Day	19% 29% 33% 15% 4 1	200
	21st to end	Day	24% 25% 23% 20% 7% 1	220
January	1st to 10th	Night	20% 20% 27% 21% 12% 1	800
	11th to 20th	Night	16% 16% 29% 26% 12% 2	800
	21st to end	Night	15% 14% 27% 29% 13% 2	880
February	1st to 10th	Night	16% 18% 29% 25% 12% 1	800
	11th to 20th	Night	15% 19% 28% 25% 12% 1	784
	21st to end	Night	20% 16% 30% 26% 7% 1	660
March	1st to 10th	Night	13% 19% 30% 26% 11% 1	800
	11th to 20th	Night	11% 18% 30% 30% 11% 1	800
	21st to end	Night	16% 21% 29% 24% 8% 2	880
April	1st to 10th	Night	15% 17% 29% 26% 11% 2	800
	11th to 20th	Night	11% 19% 32% 22% 12% 3	791
	21st to end	Night	11% 16% 34% 25% 13% 1	664
May	1st to 10th	Night	8% 17% 30% 29% 15% 2	400
	11th to 20th	Night	8% 12% 25% 32% 19% 3	394
	21st to end	Night	8% 9% 27% 37% 16% 2	433
June	1st to 10th	Night	14% 11% 26% 33% 16% 1	400
	11th to 20th	Night	7% 15% 34% 32% 12% 1	400
	21st to end	Night	6% 6% 26% 44% 18% 1	400
July	1st to 10th	Night	3 3 29% 46% 18% 1	390
	11th to 20th	Night	2 2 35% 45% 14% 2	388
	21st to end	Night	2 3 24% 49% 20% 3	438
August	1st to 10th	Night	3 1 24% 43% 25% 5%	487
	11th to 20th	Night	3 3 16% 38% 31% 9%	594
	21st to end	Night	3 5% 25% 39% 23% 4	856
September	1st to 10th	Night	3 5% 22% 41% 26% 4	800
	11th to 20th	Night	5% 6% 22% 33% 29% 5%	800
	21st to end	Night	8% 8% 23% 33% 25% 3	800
October	1st to 10th	Night	10% 9% 28% 32% 19% 4	800
	11th to 20th	Night	10% 11% 26% 29% 19% 4	800
	21st to end	Night	13% 18% 25% 27% 14% 4	880
November	1st to 10th	Night	14% 15% 30% 31% 10%	820
	11th to 20th	Night	17% 22% 27% 24% 10% 1	840
	21st to end	Night	11% 16% 29% 29% 13% 2	840
December	1st to 10th	Night	14% 14% 28% 27% 16% 2	808
	11th to 20th	Night	17% 16% 32% 23% 11% 1	800
	21st to end	Night	19% 21% 31% 21% 8% 1	880

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