Huntsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Huntsville 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	5% 10% 3 6% 4 4 4 3 5% 6% 50%	124171
	Night	6% 10% 3 7% 4 4 4 3 5% 6% 49%	123859
Transparency	Day	35% 4 8% 21% 20% 12%	123937
	Night	36% 4 10% 22% 19% 9%	123680
Seeing	Day	12% 15% 32% 29% 11% 2	16173
	Night	12% 7% 26% 38% 17% 1	26244

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	4 19% 7% 11% 4 4 5% 4 5% 6% 30%	4098
	11th to 20th	Day	4 16% 8% 13% 5% 4 5% 3 4 4 34%	4100
	21st to end	Day	5% 15% 5% 8% 4 4 4 2 3 5% 45%	4510
February	1st to 10th	Day	8% 18% 5% 12% 4 5% 4 4 4 4 30%	1800
	11th to 20th	Day	7% 20% 6% 12% 5% 3 4 3 4 5% 30%	1806
	21st to end	Day	5% 19% 7% 13% 5% 5% 4 4 4 5% 29%	1650
March	1st to 10th	Day	5% 23% 7% 9% 5% 4 4 2 3 4 34%	4821
	11th to 20th	Day	4 12% 6% 8% 5% 5% 5% 4 5% 6% 41%	5000
	21st to end	Day	8% 21% 5% 11% 6% 5% 4 3 5% 5% 27%	5486
April	1st to 10th	Day	9% 14% 4 7% 5% 5% 5% 4 5% 7% 36%	2230
	11th to 20th	Day	8% 14% 4 7% 5% 4 5% 4 5% 6% 39%	2533
	21st to end	Day	8% 11% 3 8% 5% 4 3 3 6% 7% 42%	2600
May	1st to 10th	Day	7% 12% 2 5% 4 4 4 4 6% 7% 45%	5880
	11th to 20th	Day	8% 8% 2 6% 5% 4 5% 4 5% 8% 47%	5841
	21st to end	Day	5% 5% 2 5% 4 3 4 4 6% 7% 55%	6423
June	1st to 10th	Day	4 4 2 5% 3 4 4 4 7% 7% 55%	2795
	11th to 20th	Day	6% 4 2 4 3 3 3 3 5% 7% 60%	2800
	21st to end	Day	3 2 1 4 3 2 3 2 3 5% 72%	2893
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 5% 77%	4309
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 7% 67%	4240
	21st to end	Day	3 3 1 3 3 3 3 3 5% 7% 66%	4455
August	1st to 10th	Day	3 2 1 4 4 3 3 3 4 6% 68%	4092
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 67%	4028
	21st to end	Day	2 2 1 3 2 2 3 2 4 6% 74%	4495
September	1st to 10th	Day	4 3 1 2 2 2 3 2 4 6% 70%	2161
	11th to 20th	Day	5% 3 1 4 3 3 4 3 5% 6% 64%	2090
	21st to end	Day	6% 4 1 3 2 3 3 2 3 5% 68%	2090
October	1st to 10th	Day	6% 4 1 3 3 2 4 3 4 4 67%	3312
	11th to 20th	Day	8% 5% 2 4 3 4 4 3 6% 5% 57%	3150
	21st to end	Day	7% 8% 2 5% 3 3 3 2 4 6% 56%	3396
November	1st to 10th	Day	9% 10% 3 7% 5% 4 4 3 6% 6% 43%	1764
	11th to 20th	Day	10% 11% 4 6% 4 3 3 3 4 8% 43%	1797
	21st to end	Day	7% 13% 4 8% 5% 5% 3 3 5% 5% 42%	1600
December	1st to 10th	Day	5% 8% 3 8% 4 3 3 2 4 5% 55%	2620
	11th to 20th	Day	7% 14% 6% 10% 5% 5% 5% 4 5% 8% 31%	3026
	21st to end	Day	7% 16% 6% 11% 6% 5% 5% 4 6% 6% 28%	4280
January	1st to 10th	Night	5% 15% 8% 12% 4 4 4 3 4 6% 35%	5867
	11th to 20th	Night	5% 17% 6% 13% 5% 5% 5% 4 4 5% 31%	5880
	21st to end	Night	5% 15% 5% 8% 4 3 3 2 4 5% 47%	6468
February	1st to 10th	Night	10% 15% 5% 8% 5% 5% 5% 4 4 6% 32%	2600
	11th to 20th	Night	7% 16% 4 9% 5% 3 4 3 4 5% 39%	2477
	21st to end	Night	5% 15% 5% 11% 6% 5% 4 4 5% 5% 34%	1980
March	1st to 10th	Night	8% 19% 4 8% 4 4 4 4 5% 5% 34%	5072
	11th to 20th	Night	5% 11% 3 8% 5% 5% 5% 5% 6% 8% 40%	5000
	21st to end	Night	7% 15% 4 8% 4 4 4 3 5% 6% 38%	5489
April	1st to 10th	Night	9% 14% 3 6% 4 4 4 3 5% 5% 44%	2170
	11th to 20th	Night	6% 11% 4 7% 5% 5% 4 4 5% 5% 45%	1811
	21st to end	Night	8% 9% 2 7% 5% 3 4 4 6% 6% 47%	1800
May	1st to 10th	Night	8% 9% 2 5% 4 3 4 3 5% 6% 51%	4100
	11th to 20th	Night	8% 5% 2 4 3 3 4 4 6% 7% 55%	4074
	21st to end	Night	6% 5% 2 6% 4 4 4 3 5% 7% 55%	4474
June	1st to 10th	Night	5% 4 2 5% 4 3 4 4 5% 7% 57%	1600
	11th to 20th	Night	5% 3 2 3 3 3 3 2 4 6% 65%	1600
	21st to end	Night	2 3 1 4 2 2 3 3 4 6% 71%	1481
July	1st to 10th	Night	2 2 1 3 2 2 2 3 4 5% 74%	2851
	11th to 20th	Night	2 3 1 4 4 4 5% 4 6% 8% 59%	2950
	21st to end	Night	3 3 2 4 4 3 4 4 6% 7% 61%	3109
August	1st to 10th	Night	2 3 1 5% 4 4 4 4 5% 7% 61%	2847
	11th to 20th	Night	2 3 1 5% 4 5% 5% 3 5% 6% 60%	2811
	21st to end	Night	2 2 1 3 2 3 4 3 5% 5% 71%	3172
September	1st to 10th	Night	4 3 1 4 3 3 2 2 5% 5% 67%	2016
	11th to 20th	Night	6% 3 1 4 3 3 3 3 5% 5% 64%	2090
	21st to end	Night	6% 3 1 3 2 2 3 2 3 5% 70%	2090
October	1st to 10th	Night	5% 4 1 3 2 3 2 2 3 5% 70%	3662
	11th to 20th	Night	7% 6% 1 5% 3 3 3 3 5% 6% 58%	3778
	21st to end	Night	7% 7% 2 4 3 4 4 4 5% 7% 55%	4149
November	1st to 10th	Night	9% 8% 3 5% 4 4 3 3 5% 6% 49%	2535
	11th to 20th	Night	8% 8% 3 6% 5% 4 4 4 6% 8% 45%	2600
	21st to end	Night	6% 12% 4 6% 5% 4 5% 4 5% 6% 45%	2779
December	1st to 10th	Night	4 8% 3 7% 4 3 3 3 3 6% 55%	4570
	11th to 20th	Night	9% 13% 4 7% 4 4 4 3 5% 7% 40%	5181
	21st to end	Night	9% 13% 5% 11% 6% 5% 4 3 5% 7% 30%	6726

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	55% 3 15% 15% 10% 1	4099
	11th to 20th	Day	53% 5% 11% 19% 8% 4	4100
	21st to end	Day	43% 5% 13% 22% 16% 1	4510
February	1st to 10th	Day	56% 6% 13% 14% 10% 1	1800
	11th to 20th	Day	57% 5% 12% 17% 9% 1	1815
	21st to end	Day	56% 5% 10% 17% 10% 2	1650
March	1st to 10th	Day	53% 4 7% 21% 10% 4	4821
	11th to 20th	Day	43% 4 8% 34% 11% 1	5000
	21st to end	Day	59% 4 14% 19% 5% 1	5486
April	1st to 10th	Day	47% 6% 12% 20% 13% 3	2230
	11th to 20th	Day	45% 5% 9% 23% 17% 2	2536
	21st to end	Day	41% 5% 10% 26% 18% 1	2600
May	1st to 10th	Day	36% 5% 10% 25% 22% 3	5880
	11th to 20th	Day	34% 5% 6% 28% 23% 4	5844
	21st to end	Day	26% 4 6% 29% 31% 3	6424
June	1st to 10th	Day	25% 4 10% 24% 31% 6%	2795
	11th to 20th	Day	24% 3 6% 19% 29% 19%	2800
	21st to end	Day	16% 3 2 13% 33% 32%	2893
July	1st to 10th	Day	12% 3 3 8% 16% 58%	4245
	11th to 20th	Day	15% 3 4 10% 27% 42%	4171
	21st to end	Day	17% 3 4 10% 30% 34%	4315
August	1st to 10th	Day	19% 3 4 15% 30% 29%	4078
	11th to 20th	Day	17% 3 4 16% 35% 25%	4067
	21st to end	Day	13% 3 4 15% 36% 29%	4494
September	1st to 10th	Day	16% 3 5% 18% 31% 27%	2161
	11th to 20th	Day	20% 4 8% 18% 33% 18%	2090
	21st to end	Day	20% 3 6% 23% 36% 12%	2090
October	1st to 10th	Day	22% 3 5% 17% 33% 20%	3312
	11th to 20th	Day	28% 3 7% 29% 25% 8%	3150
	21st to end	Day	31% 3 10% 33% 20% 3	3396
November	1st to 10th	Day	41% 5% 13% 22% 17% 2	1764
	11th to 20th	Day	40% 4 15% 25% 14%	1797
	21st to end	Day	43% 5% 13% 23% 14% 1	1600
December	1st to 10th	Day	32% 5% 12% 40% 9% 2	2620
	11th to 20th	Day	52% 4 17% 20% 7%	3024
	21st to end	Day	55% 5% 11% 18% 10%	4280
January	1st to 10th	Night	52% 5% 11% 19% 13% 1	5867
	11th to 20th	Night	54% 6% 11% 21% 7% 2	5880
	21st to end	Night	41% 4 13% 23% 17% 1	6468
February	1st to 10th	Night	51% 7% 13% 19% 9% 1	2600
	11th to 20th	Night	46% 5% 12% 20% 15% 2	2478
	21st to end	Night	49% 6% 11% 20% 12% 2	1980
March	1st to 10th	Night	49% 7% 6% 22% 12% 5%	5072
	11th to 20th	Night	40% 5% 10% 30% 15% 1	5000
	21st to end	Night	47% 5% 16% 23% 9% 1	5489
April	1st to 10th	Night	41% 5% 12% 22% 14% 6%	2170
	11th to 20th	Night	39% 6% 10% 22% 21% 2	1811
	21st to end	Night	36% 6% 11% 27% 19% 1	1800
May	1st to 10th	Night	33% 5% 10% 23% 26% 3	4097
	11th to 20th	Night	27% 4 6% 29% 29% 5%	4075
	21st to end	Night	28% 5% 5% 27% 34% 1	4474
June	1st to 10th	Night	24% 6% 9% 23% 31% 7%	1600
	11th to 20th	Night	21% 3 7% 20% 30% 19%	1600
	21st to end	Night	16% 3 2 13% 30% 35%	1481
July	1st to 10th	Night	13% 3 3 8% 14% 58%	2806
	11th to 20th	Night	22% 3 2 10% 30% 33%	2896
	21st to end	Night	21% 4 5% 9% 29% 32%	3011
August	1st to 10th	Night	23% 3 4 11% 31% 28%	2838
	11th to 20th	Night	25% 3 5% 13% 27% 26%	2838
	21st to end	Night	15% 3 5% 10% 30% 37%	3172
September	1st to 10th	Night	20% 3 4 15% 26% 31%	2016
	11th to 20th	Night	21% 4 6% 18% 30% 22%	2090
	21st to end	Night	19% 3 6% 19% 36% 17%	2090
October	1st to 10th	Night	19% 3 4 18% 37% 19%	3662
	11th to 20th	Night	29% 2 5% 30% 26% 8%	3778
	21st to end	Night	29% 3 8% 36% 21% 3	4149
November	1st to 10th	Night	36% 5% 10% 24% 21% 4	2535
	11th to 20th	Night	36% 4 15% 28% 15% 2	2600
	21st to end	Night	40% 5% 12% 27% 14% 3	2779
December	1st to 10th	Night	32% 3 12% 39% 12% 2	4570
	11th to 20th	Night	44% 5% 21% 22% 8%	5182
	21st to end	Night	53% 4 15% 17% 10%	6726

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	21% 14% 32% 23% 8% 1	300
	11th to 20th	Day	15% 12% 37% 24% 11% 1	300
	21st to end	Day	11% 15% 36% 30% 8% 1	330
February	1st to 10th	Day	22% 20% 35% 19% 5%	300
	11th to 20th	Day	18% 20% 37% 19% 5% 1	351
	21st to end	Day	16% 22% 39% 17% 5% 1	414
March	1st to 10th	Day	18% 23% 34% 19% 5% 1	500
	11th to 20th	Day	17% 21% 36% 21% 6%	500
	21st to end	Day	22% 23% 33% 18% 3	550
April	1st to 10th	Day	19% 22% 28% 24% 8%	500
	11th to 20th	Day	20% 25% 32% 18% 4	492
	21st to end	Day	16% 23% 29% 24% 7% 1	500
May	1st to 10th	Day	18% 22% 31% 22% 6% 1	503
	11th to 20th	Day	15% 19% 32% 26% 7% 1	528
	21st to end	Day	14% 15% 30% 26% 12% 2	573
June	1st to 10th	Day	5% 14% 29% 35% 15% 2	725
	11th to 20th	Day	10% 12% 34% 32% 10% 1	730
	21st to end	Day	5% 11% 33% 36% 13% 1	672
July	1st to 10th	Day	4 9% 36% 40% 10% 2	526
	11th to 20th	Day	4 7% 36% 36% 13% 3	524
	21st to end	Day	4 3 33% 42% 15% 2	532
August	1st to 10th	Day	4 7% 40% 31% 16% 1	487
	11th to 20th	Day	4 8% 30% 39% 18% 1	477
	21st to end	Day	4 9% 29% 39% 18% 1	539
September	1st to 10th	Day	5% 8% 32% 32% 20% 3	490
	11th to 20th	Day	7% 13% 32% 32% 14% 2	490
	21st to end	Day	7% 13% 29% 32% 16% 3	490
October	1st to 10th	Day	12% 14% 22% 30% 19% 3	390
	11th to 20th	Day	9% 16% 25% 26% 20% 4	300
	21st to end	Day	13% 15% 29% 31% 11% 1	330
November	1st to 10th	Day	18% 15% 25% 29% 9% 4	300
	11th to 20th	Day	15% 12% 33% 30% 9% 2	300
	21st to end	Day	14% 11% 27% 32% 14% 2	300
December	1st to 10th	Day	13% 11% 32% 28% 12% 5%	300
	11th to 20th	Day	15% 12% 38% 28% 7% 1	300
	21st to end	Day	22% 15% 32% 25% 6% 1	330
January	1st to 10th	Night	17% 7% 30% 32% 14% 1	800
	11th to 20th	Night	17% 7% 27% 34% 14% 2	800
	21st to end	Night	14% 8% 31% 35% 10% 2	880
February	1st to 10th	Night	19% 7% 35% 31% 8% 1	800
	11th to 20th	Night	14% 7% 32% 36% 10%	784
	21st to end	Night	11% 9% 38% 33% 9%	660
March	1st to 10th	Night	16% 10% 30% 34% 9% 1	800
	11th to 20th	Night	10% 10% 30% 37% 12% 1	800
	21st to end	Night	17% 11% 28% 35% 9% 1	880
April	1st to 10th	Night	17% 10% 27% 36% 10% 1	770
	11th to 20th	Night	12% 12% 32% 33% 11%	593
	21st to end	Night	11% 9% 25% 38% 17% 1	600
May	1st to 10th	Night	13% 7% 30% 35% 15%	600
	11th to 20th	Night	13% 4 25% 35% 22% 2	591
	21st to end	Night	10% 6% 19% 39% 23% 2	650
June	1st to 10th	Night	6% 8% 19% 41% 25% 2	600
	11th to 20th	Night	7% 7% 23% 45% 18%	600
	21st to end	Night	4 3 20% 44% 27% 2	431
July	1st to 10th	Night	4 3 20% 42% 30% 2	525
	11th to 20th	Night	5% 2 16% 48% 29% 1	582
	21st to end	Night	4 1 11% 48% 34% 1	624
August	1st to 10th	Night	4 2 15% 51% 27% 1	567
	11th to 20th	Night	4 1 18% 46% 30% 1	564
	21st to end	Night	5% 3 17% 44% 30% 1	627
September	1st to 10th	Night	5% 4 18% 44% 26% 2	686
	11th to 20th	Night	8% 3 20% 42% 24% 4	760
	21st to end	Night	8% 4 19% 40% 24% 6%	760
October	1st to 10th	Night	11% 6% 20% 41% 22% 1	760
	11th to 20th	Night	11% 5% 22% 38% 22% 1	760
	21st to end	Night	11% 5% 25% 39% 18% 2	836
November	1st to 10th	Night	12% 7% 23% 41% 15% 2	780
	11th to 20th	Night	11% 5% 32% 39% 11% 2	800
	21st to end	Night	12% 9% 27% 36% 14% 2	979
December	1st to 10th	Night	13% 7% 33% 34% 12% 1	1000
	11th to 20th	Night	18% 7% 33% 32% 9% 1	1000
	21st to end	Night	19% 11% 33% 31% 6% 1	995

Page generated at 2025-07-17 23:10:00. Version ac07

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