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 2025-09-04.

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	14% 7% 3 6% 5% 4 5% 4 6% 8% 39%	126100
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	122596
Transparency	Day	40% 6% 11% 21% 17% 4	129837
	Night	39% 5% 10% 21% 19% 6%	126929
Seeing	Day	16% 11% 21% 23% 19% 9%	15781
	Night	16% 7% 21% 30% 21% 4	25564

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	18% 9% 5% 7% 3 3 4 2 5% 5% 39%	4056
	11th to 20th	Day	17% 6% 5% 9% 3 2 3 2 3 5% 45%	4086
	21st to end	Day	21% 11% 4 6% 4 3 4 3 4 6% 36%	4972
February	1st to 10th	Day	20% 9% 3 6% 3 4 3 3 4 7% 37%	2000
	11th to 20th	Day	22% 9% 3 6% 4 4 4 2 4 5% 35%	1948
	21st to end	Day	22% 8% 3 6% 3 3 4 3 5% 5% 38%	1650
March	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 4 5% 5% 33%	4480
	11th to 20th	Day	13% 8% 2 6% 3 4 4 3 5% 6% 46%	4791
	21st to end	Day	13% 7% 2 8% 5% 4 4 3 5% 7% 42%	5724
April	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 7% 8% 43%	2400
	11th to 20th	Day	14% 7% 2 6% 4 3 4 3 4 8% 45%	2374
	21st to end	Day	11% 6% 2 6% 5% 4 4 4 6% 8% 43%	2410
May	1st to 10th	Day	18% 6% 2 6% 4 5% 5% 4 7% 9% 32%	5862
	11th to 20th	Day	15% 8% 3 8% 6% 6% 6% 5% 6% 8% 29%	5861
	21st to end	Day	16% 7% 3 7% 5% 4 4 3 6% 7% 39%	6433
June	1st to 10th	Day	10% 5% 2 6% 6% 6% 6% 6% 7% 10% 36%	2600
	11th to 20th	Day	6% 5% 1 5% 5% 5% 7% 5% 8% 10% 44%	2600
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 5% 9% 11% 39%	2699
July	1st to 10th	Day	7% 4 2 7% 5% 6% 6% 5% 9% 12% 36%	6048
	11th to 20th	Day	8% 5% 2 6% 6% 6% 6% 7% 10% 14% 32%	5900
	21st to end	Day	12% 7% 3 8% 6% 6% 6% 6% 8% 11% 26%	6424
August	1st to 10th	Day	5% 3 2 5% 5% 5% 6% 4 8% 10% 48%	3943
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 5% 6% 9% 43%	3849
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 5% 8% 52%	4312
September	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	2269
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 7% 43%	2090
	21st to end	Day	12% 4 2 5% 4 4 5% 3 5% 7% 49%	2090
October	1st to 10th	Day	8% 4 2 5% 4 4 4 3 4 5% 57%	2090
	11th to 20th	Day	11% 4 1 5% 3 4 3 3 5% 6% 55%	2090
	21st to end	Day	14% 5% 2 4 4 3 3 3 4 6% 51%	1918
November	1st to 10th	Day	12% 6% 2 4 3 4 4 3 4 5% 53%	1762
	11th to 20th	Day	13% 5% 2 6% 4 3 4 2 5% 7% 48%	1800
	21st to end	Day	15% 7% 2 5% 5% 3 4 3 5% 6% 44%	1800
December	1st to 10th	Day	18% 6% 3 6% 4 4 3 3 5% 4 44%	2930
	11th to 20th	Day	21% 9% 4 7% 5% 4 4 3 4 5% 34%	3373
	21st to end	Day	20% 9% 5% 7% 5% 4 4 3 5% 7% 32%	4466
January	1st to 10th	Night	17% 12% 3 7% 3 3 3 2 4 5% 41%	5889
	11th to 20th	Night	19% 9% 3 7% 3 2 2 3 3 4 44%	5858
	21st to end	Night	19% 10% 2 5% 3 3 3 3 4 5% 41%	5984
February	1st to 10th	Night	20% 9% 3 5% 4 3 3 3 4 7% 40%	2400
	11th to 20th	Night	22% 9% 3 6% 4 3 3 3 4 4 39%	2338
	21st to end	Night	22% 7% 3 5% 4 4 4 3 4 6% 36%	1980
March	1st to 10th	Night	24% 8% 3 8% 4 4 4 3 4 6% 32%	5373
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 5% 7% 48%	5168
	21st to end	Night	16% 7% 3 7% 5% 4 4 3 4 4 42%	5247
April	1st to 10th	Night	12% 4 2 6% 4 4 4 4 6% 8% 46%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 6% 8% 49%	1975
	21st to end	Night	12% 6% 2 5% 5% 3 4 3 5% 7% 49%	1986
May	1st to 10th	Night	14% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	4033
	11th to 20th	Night	17% 10% 4 9% 5% 5% 5% 4 5% 7% 30%	4032
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 7% 8% 39%	4421
June	1st to 10th	Night	7% 6% 2 8% 6% 5% 5% 4 7% 10% 41%	1800
	11th to 20th	Night	5% 3 1 4 4 5% 5% 6% 8% 10% 50%	1800
	21st to end	Night	7% 4 1 5% 5% 4 4 4 6% 11% 48%	1677
July	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 5% 7% 9% 39%	3872
	11th to 20th	Night	8% 6% 3 6% 5% 5% 6% 6% 8% 12% 36%	4057
	21st to end	Night	9% 7% 3 8% 5% 5% 7% 5% 8% 12% 30%	4427
August	1st to 10th	Night	3 2 2 4 3 4 4 4 7% 12% 56%	3201
	11th to 20th	Night	6% 3 1 4 4 4 4 4 8% 10% 51%	3200
	21st to end	Night	5% 3 1 4 3 4 4 3 5% 7% 59%	3586
September	1st to 10th	Night	8% 6% 1 6% 4 4 4 4 6% 9% 49%	1958
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 4 5% 9% 44%	2090
	21st to end	Night	9% 4 2 6% 3 4 4 3 5% 7% 53%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 5% 60%	2090
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 4 54%	2090
	21st to end	Night	14% 6% 2 4 3 3 3 3 4 5% 54%	2676
November	1st to 10th	Night	12% 6% 2 4 3 3 4 3 4 6% 52%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 4 6% 52%	2600
	21st to end	Night	16% 7% 2 5% 4 3 3 3 4 6% 47%	2600
December	1st to 10th	Night	21% 7% 2 4 3 3 3 3 4 6% 45%	4250
	11th to 20th	Night	23% 9% 3 5% 3 3 3 3 3 5% 41%	4822
	21st to end	Night	19% 10% 4 7% 4 4 4 3 5% 6% 34%	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	47% 4 7% 21% 20% 2	4057
	11th to 20th	Day	43% 4 5% 22% 24% 1	4086
	21st to end	Day	49% 4 7% 19% 18% 3	4972
February	1st to 10th	Day	49% 3 6% 20% 18% 3	2000
	11th to 20th	Day	52% 4 5% 18% 15% 5%	1958
	21st to end	Day	49% 4 7% 16% 19% 6%	1650
March	1st to 10th	Day	52% 4 6% 14% 16% 8%	4480
	11th to 20th	Day	39% 4 6% 20% 20% 11%	4791
	21st to end	Day	42% 5% 10% 25% 17% 2	5726
April	1st to 10th	Day	39% 6% 10% 24% 16% 5%	2400
	11th to 20th	Day	38% 5% 7% 22% 23% 6%	2374
	21st to end	Day	38% 6% 10% 27% 16% 3	2410
May	1st to 10th	Day	46% 7% 15% 20% 10% 2	5897
	11th to 20th	Day	50% 8% 14% 19% 9%	5865
	21st to end	Day	43% 6% 9% 23% 16% 2	6447
June	1st to 10th	Day	39% 10% 13% 21% 16% 2	2600
	11th to 20th	Day	32% 8% 17% 24% 17% 2	2600
	21st to end	Day	35% 10% 18% 19% 14% 4	2699
July	1st to 10th	Day	36% 8% 19% 26% 10% 1	5983
	11th to 20th	Day	37% 10% 27% 21% 4 1	5831
	21st to end	Day	48% 8% 23% 16% 4	6240
August	1st to 10th	Day	28% 9% 13% 34% 15% 1	3930
	11th to 20th	Day	34% 8% 15% 27% 13% 3	3885
	21st to end	Day	30% 8% 12% 23% 25% 3	4311
September	1st to 10th	Day	38% 8% 15% 17% 17% 5%	2269
	11th to 20th	Day	37% 9% 11% 18% 21% 3	2090
	21st to end	Day	34% 6% 10% 23% 20% 7%	2090
October	1st to 10th	Day	20% 5% 5% 16% 36% 18%	3480
	11th to 20th	Day	21% 3 5% 18% 31% 22%	3458
	21st to end	Day	27% 4 6% 23% 32% 9%	3130
November	1st to 10th	Day	33% 4 7% 19% 28% 7%	1762
	11th to 20th	Day	36% 4 6% 20% 26% 7%	1800
	21st to end	Day	40% 5% 6% 21% 24% 6%	1800
December	1st to 10th	Day	44% 3 5% 21% 24% 4	2930
	11th to 20th	Day	53% 4 6% 20% 14% 4	3370
	21st to end	Day	51% 4 10% 22% 11% 2	4466
January	1st to 10th	Night	47% 3 7% 20% 20% 3	5889
	11th to 20th	Night	45% 3 6% 17% 23% 5%	5858
	21st to end	Night	46% 3 5% 18% 22% 6%	5984
February	1st to 10th	Night	45% 3 8% 20% 20% 4	2400
	11th to 20th	Night	50% 3 7% 17% 16% 7%	2339
	21st to end	Night	49% 5% 5% 16% 19% 7%	1980
March	1st to 10th	Night	53% 4 5% 14% 18% 5%	5373
	11th to 20th	Night	35% 4 7% 18% 22% 14%	5168
	21st to end	Night	46% 3 7% 20% 19% 4	5247
April	1st to 10th	Night	36% 5% 12% 22% 20% 5%	2000
	11th to 20th	Night	34% 4 8% 21% 22% 11%	1975
	21st to end	Night	35% 5% 11% 27% 18% 4	1986
May	1st to 10th	Night	46% 8% 13% 19% 13% 1	4060
	11th to 20th	Night	53% 7% 13% 18% 9% 1	4033
	21st to end	Night	39% 8% 13% 23% 16% 1	4429
June	1st to 10th	Night	36% 8% 14% 21% 18% 2	1800
	11th to 20th	Night	25% 9% 18% 27% 19% 3	1800
	21st to end	Night	29% 8% 18% 25% 17% 4	1677
July	1st to 10th	Night	39% 9% 19% 23% 9% 2	3829
	11th to 20th	Night	35% 11% 27% 20% 5% 1	4006
	21st to end	Night	45% 9% 25% 17% 5%	4297
August	1st to 10th	Night	19% 8% 14% 37% 21% 1	3190
	11th to 20th	Night	26% 8% 21% 28% 16% 2	3230
	21st to end	Night	24% 6% 14% 24% 28% 3	3586
September	1st to 10th	Night	31% 8% 17% 22% 16% 6%	1958
	11th to 20th	Night	37% 8% 13% 17% 23% 3	2090
	21st to end	Night	31% 7% 9% 23% 22% 9%	2090
October	1st to 10th	Night	19% 5% 5% 18% 35% 19%	3480
	11th to 20th	Night	21% 3 4 17% 32% 23%	3461
	21st to end	Night	23% 3 4 26% 29% 14%	4414
November	1st to 10th	Night	33% 5% 7% 21% 24% 10%	2536
	11th to 20th	Night	34% 5% 6% 18% 28% 10%	2600
	21st to end	Night	40% 3 6% 21% 24% 6%	2600
December	1st to 10th	Night	43% 3 5% 20% 25% 3	4250
	11th to 20th	Night	48% 3 4 19% 22% 3	4824
	21st to end	Night	50% 5% 7% 24% 12% 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	25% 28% 29% 15% 3	300
	11th to 20th	Day	26% 25% 30% 13% 5% 1	300
	21st to end	Day	19% 28% 33% 17% 2	330
February	1st to 10th	Day	25% 23% 32% 16% 3	300
	11th to 20th	Day	36% 20% 31% 10% 2 1	300
	21st to end	Day	33% 22% 31% 12% 2	249
March	1st to 10th	Day	26% 22% 32% 14% 4 1	300
	11th to 20th	Day	24% 20% 30% 20% 6% 1	415
	21st to end	Day	24% 17% 33% 19% 6% 1	550
April	1st to 10th	Day	22% 18% 27% 20% 12% 1	500
	11th to 20th	Day	20% 16% 26% 27% 10% 1	492
	21st to end	Day	16% 14% 27% 27% 13% 2	500
May	1st to 10th	Day	16% 12% 28% 25% 14% 5%	503
	11th to 20th	Day	12% 10% 24% 27% 17% 10%	527
	21st to end	Day	13% 8% 18% 28% 19% 13%	573
June	1st to 10th	Day	12% 5% 16% 28% 26% 13%	530
	11th to 20th	Day	8% 2 15% 26% 25% 23%	530
	21st to end	Day	10% 3 15% 24% 31% 17%	629
July	1st to 10th	Day	10% 3 11% 24% 32% 22%	595
	11th to 20th	Day	9% 2 9% 19% 30% 30%	524
	21st to end	Day	10% 3 9% 20% 34% 24%	576
August	1st to 10th	Day	10% 2 10% 23% 35% 20%	526
	11th to 20th	Day	11% 3 11% 24% 37% 14%	519
	21st to end	Day	13% 3 11% 22% 33% 18%	583
September	1st to 10th	Day	11% 3 11% 28% 32% 14%	502
	11th to 20th	Day	12% 3 14% 26% 30% 16%	490
	21st to end	Day	16% 4 14% 26% 33% 9%	490
October	1st to 10th	Day	10% 4 23% 30% 22% 10%	490
	11th to 20th	Day	11% 11% 24% 34% 17% 3	490
	21st to end	Day	19% 13% 22% 30% 14% 3	338
November	1st to 10th	Day	20% 8% 29% 26% 16% 2	300
	11th to 20th	Day	13% 16% 38% 26% 6% 1	300
	21st to end	Day	17% 22% 27% 22% 11% 2	300
December	1st to 10th	Day	26% 20% 31% 15% 7%	300
	11th to 20th	Day	24% 19% 32% 16% 9%	300
	21st to end	Day	26% 19% 32% 18% 5% 1	330
January	1st to 10th	Night	23% 14% 32% 25% 5% 1	800
	11th to 20th	Night	25% 15% 29% 24% 7%	800
	21st to end	Night	20% 14% 33% 30% 4	880
February	1st to 10th	Night	24% 10% 31% 30% 6%	800
	11th to 20th	Night	27% 15% 28% 27% 2	783
	21st to end	Night	27% 15% 30% 26% 2	660
March	1st to 10th	Night	21% 13% 30% 31% 5%	800
	11th to 20th	Night	19% 10% 34% 29% 8% 1	800
	21st to end	Night	19% 11% 31% 29% 11%	789
April	1st to 10th	Night	15% 11% 30% 31% 12%	600
	11th to 20th	Night	14% 9% 32% 31% 13% 1	593
	21st to end	Night	14% 7% 27% 37% 15% 1	600
May	1st to 10th	Night	14% 4 26% 34% 20% 3	600
	11th to 20th	Night	15% 4 20% 33% 25% 4	591
	21st to end	Night	8% 4 12% 38% 33% 5%	650
June	1st to 10th	Night	9% 2 13% 33% 38% 5%	600
	11th to 20th	Night	5% 1 9% 32% 44% 10%	600
	21st to end	Night	8% 2 6% 30% 46% 8%	600
July	1st to 10th	Night	9% 2 7% 28% 42% 13%	585
	11th to 20th	Night	9% 1 6% 21% 45% 18%	582
	21st to end	Night	10% 1 7% 24% 46% 12%	657
August	1st to 10th	Night	6% 5% 25% 53% 11%	597
	11th to 20th	Night	9% 3 7% 29% 45% 8%	594
	21st to end	Night	10% 2 8% 27% 43% 10%	660
September	1st to 10th	Night	10% 1 8% 29% 43% 8%	607
	11th to 20th	Night	11% 3 13% 30% 36% 6%	760
	21st to end	Night	11% 2 13% 32% 39% 3	760
October	1st to 10th	Night	11% 4 17% 32% 30% 6%	760
	11th to 20th	Night	14% 6% 24% 33% 21% 2	760
	21st to end	Night	16% 8% 21% 34% 20% 3	836
November	1st to 10th	Night	15% 8% 20% 34% 21% 3	780
	11th to 20th	Night	14% 9% 28% 33% 13% 1	800
	21st to end	Night	20% 10% 25% 32% 13% 1	800
December	1st to 10th	Night	24% 11% 27% 30% 7% 1	800
	11th to 20th	Night	24% 10% 25% 31% 9%	800
	21st to end	Night	25% 11% 29% 29% 5%	880

Page generated at 2025-09-01 00:51:05. Version ac07

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