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 2026-07-01.

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	16% 12% 4 9% 5% 5% 4 3 5% 6% 31%	138887
	Night	16% 14% 5% 10% 5% 4 4 3 4 6% 28%	133366
Transparency	Day	53% 6% 10% 20% 10% 1	142463
	Night	56% 6% 10% 18% 9% 1	137880
Seeing	Day	24% 16% 30% 19% 8% 3	17002
	Night	24% 13% 29% 24% 9% 1	25789

By Month

Percentage Cloud Cover NE (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	14% 16% 8% 11% 5% 6% 4 3 5% 5% 24%	4390
	11th to 20th	Day	9% 24% 10% 17% 7% 7% 5% 3 4 3 11%	4812
	21st to end	Day	11% 16% 9% 18% 8% 6% 5% 3 4 4 17%	5780
February	1st to 10th	Day	12% 20% 7% 15% 7% 5% 4 3 3 4 19%	1890
	11th to 20th	Day	13% 17% 7% 14% 6% 4 4 3 5% 5% 23%	1843
	21st to end	Day	15% 19% 6% 13% 6% 5% 4 3 4 5% 20%	1568
March	1st to 10th	Day	18% 16% 5% 11% 5% 5% 3 3 4 5% 25%	5042
	11th to 20th	Day	12% 14% 5% 11% 6% 5% 5% 4 6% 6% 24%	5090
	21st to end	Day	17% 16% 6% 8% 4 4 3 3 4 4 31%	5586
April	1st to 10th	Day	20% 15% 4 8% 4 5% 4 3 5% 6% 27%	2504
	11th to 20th	Day	23% 12% 3 6% 4 4 3 3 4 5% 34%	2597
	21st to end	Day	22% 12% 3 7% 5% 3 3 3 4 4 34%	2730
May	1st to 10th	Day	17% 9% 3 7% 5% 5% 5% 4 6% 8% 32%	7838
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 5% 7% 36%	8221
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 6% 38%	9060
June	1st to 10th	Day	20% 8% 3 6% 6% 5% 4 4 5% 7% 33%	2940
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 7% 36%	3142
	21st to end	Day	20% 8% 2 7% 5% 4 4 4 6% 7% 33%	3150
July	1st to 10th	Day	16% 6% 2 6% 4 5% 5% 4 7% 9% 36%	6820
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 7% 45%	6457
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 5% 8% 48%	6731
August	1st to 10th	Day	13% 7% 3 7% 5% 6% 6% 5% 6% 8% 35%	4234
	11th to 20th	Day	18% 7% 2 6% 4 4 5% 4 6% 8% 34%	4174
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 8% 42%	4518
September	1st to 10th	Day	16% 7% 2 6% 4 4 5% 5% 5% 7% 39%	2400
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 8% 43%	2310
	21st to end	Day	20% 9% 3 7% 4 5% 4 3 5% 6% 34%	2143
October	1st to 10th	Day	21% 7% 2 8% 5% 4 5% 3 5% 7% 34%	2000
	11th to 20th	Day	25% 13% 3 7% 5% 5% 5% 3 5% 6% 23%	2000
	21st to end	Day	31% 12% 4 9% 4 3 4 3 4 5% 21%	2200
November	1st to 10th	Day	19% 15% 3 8% 6% 4 4 3 5% 7% 26%	1678
	11th to 20th	Day	18% 19% 6% 10% 4 5% 5% 3 4 5% 21%	1680
	21st to end	Day	21% 23% 7% 10% 5% 5% 5% 2 4 4 14%	1680
December	1st to 10th	Day	18% 25% 7% 12% 5% 4 4 3 4 4 13%	2680
	11th to 20th	Day	19% 24% 6% 12% 6% 3 3 2 3 4 18%	3066
	21st to end	Day	22% 22% 6% 15% 4 3 3 2 3 3 16%	3933
January	1st to 10th	Night	12% 19% 10% 15% 7% 5% 4 3 4 4 16%	8461
	11th to 20th	Night	10% 21% 9% 22% 8% 5% 4 3 3 4 12%	8059
	21st to end	Night	10% 17% 9% 16% 8% 7% 4 3 4 4 17%	8401
February	1st to 10th	Night	12% 18% 6% 13% 8% 5% 4 4 4 5% 20%	2730
	11th to 20th	Night	12% 17% 7% 13% 6% 6% 4 3 4 4 24%	2663
	21st to end	Night	15% 18% 7% 12% 7% 5% 4 3 4 5% 21%	2235
March	1st to 10th	Night	16% 14% 5% 10% 5% 4 3 3 5% 6% 28%	5018
	11th to 20th	Night	10% 14% 7% 11% 5% 5% 5% 4 6% 7% 26%	5089
	21st to end	Night	20% 12% 5% 7% 5% 4 4 3 4 5% 30%	5588
April	1st to 10th	Night	21% 14% 4 7% 4 5% 3 3 5% 5% 29%	2116
	11th to 20th	Night	18% 11% 4 5% 5% 3 4 4 4 6% 35%	1989
	21st to end	Night	19% 10% 3 8% 6% 4 4 4 4 6% 31%	1890
May	1st to 10th	Night	18% 7% 2 7% 4 5% 5% 4 6% 8% 35%	5061
	11th to 20th	Night	18% 7% 2 6% 4 4 3 3 5% 7% 42%	4639
	21st to end	Night	18% 7% 2 5% 4 4 4 3 5% 8% 40%	5114
June	1st to 10th	Night	16% 9% 3 6% 5% 4 4 5% 6% 7% 36%	1680
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 6% 8% 43%	1472
	21st to end	Night	16% 8% 3 6% 5% 3 4 5% 6% 7% 37%	1470
July	1st to 10th	Night	14% 7% 2 7% 5% 4 4 4 5% 8% 41%	3160
	11th to 20th	Night	16% 6% 2 5% 4 3 3 3 5% 6% 48%	3502
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 7% 52%	4104
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 7% 47%	2915
	11th to 20th	Night	17% 7% 2 6% 3 3 4 3 5% 7% 43%	2875
	21st to end	Night	16% 5% 1 5% 3 4 4 3 5% 7% 48%	3346
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	2000
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 8% 48%	2087
	21st to end	Night	18% 8% 2 7% 4 4 4 3 4 5% 41%	2255
October	1st to 10th	Night	18% 8% 3 7% 4 4 4 4 5% 6% 37%	2400
	11th to 20th	Night	25% 11% 3 8% 5% 4 4 3 5% 6% 27%	2400
	21st to end	Night	26% 14% 4 8% 5% 4 4 3 4 3 25%	2640
November	1st to 10th	Night	21% 15% 4 7% 5% 3 4 3 5% 5% 29%	2836
	11th to 20th	Night	18% 17% 4 8% 5% 4 4 3 5% 7% 25%	2940
	21st to end	Night	22% 21% 5% 10% 6% 4 4 3 4 5% 16%	2940
December	1st to 10th	Night	19% 24% 7% 13% 6% 4 4 3 4 5% 12%	4720
	11th to 20th	Night	17% 23% 7% 16% 6% 4 4 3 3 5% 13%	5348
	21st to end	Night	22% 22% 7% 14% 5% 4 3 2 3 4 15%	7223

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	63% 5% 8% 17% 6% 1	4391
	11th to 20th	Day	80% 3 4 7% 6% 1	4842
	21st to end	Day	71% 4 6% 10% 8% 1	5780
February	1st to 10th	Day	70% 4 6% 13% 5% 1	1890
	11th to 20th	Day	64% 6% 9% 12% 8% 1	1852
	21st to end	Day	68% 5% 8% 13% 7%	1568
March	1st to 10th	Day	61% 6% 11% 8% 13% 1	5045
	11th to 20th	Day	58% 6% 14% 14% 7% 1	5090
	21st to end	Day	56% 4 8% 20% 11% 2	5586
April	1st to 10th	Day	58% 6% 9% 17% 9% 2	2504
	11th to 20th	Day	54% 5% 7% 21% 12% 1	2597
	21st to end	Day	55% 5% 8% 18% 12% 3	2730
May	1st to 10th	Day	49% 7% 10% 21% 9% 4	7847
	11th to 20th	Day	46% 6% 10% 23% 14% 1	8225
	21st to end	Day	46% 5% 10% 21% 14% 2	9061
June	1st to 10th	Day	50% 6% 9% 20% 13%	2940
	11th to 20th	Day	45% 7% 10% 23% 14% 1	3142
	21st to end	Day	48% 7% 14% 20% 10% 1	3150
July	1st to 10th	Day	43% 7% 14% 25% 10% 1	6747
	11th to 20th	Day	37% 6% 12% 33% 12%	6379
	21st to end	Day	33% 6% 14% 33% 14%	6537
August	1st to 10th	Day	45% 8% 14% 25% 8% 1	4221
	11th to 20th	Day	45% 8% 14% 25% 7%	4213
	21st to end	Day	36% 8% 13% 32% 10% 1	4518
September	1st to 10th	Day	43% 7% 13% 25% 11% 1	2400
	11th to 20th	Day	39% 7% 12% 29% 12% 1	2310
	21st to end	Day	51% 6% 10% 24% 9%	2143
October	1st to 10th	Day	48% 7% 12% 24% 9% 1	3260
	11th to 20th	Day	53% 8% 11% 21% 7%	3240
	21st to end	Day	62% 6% 11% 16% 5%	3538
November	1st to 10th	Day	57% 8% 12% 17% 5%	1678
	11th to 20th	Day	65% 7% 9% 12% 5% 1	1680
	21st to end	Day	73% 6% 9% 9% 3	1680
December	1st to 10th	Day	75% 5% 9% 8% 2	2680
	11th to 20th	Day	72% 4 5% 12% 6%	3066
	21st to end	Day	74% 4 4 12% 6%	3933
January	1st to 10th	Night	71% 4 7% 13% 5%	8461
	11th to 20th	Night	77% 6% 5% 5% 7% 1	8104
	21st to end	Night	70% 5% 6% 9% 9% 1	8401
February	1st to 10th	Night	65% 6% 9% 14% 6% 1	2730
	11th to 20th	Night	64% 5% 8% 16% 7% 1	2665
	21st to end	Night	67% 5% 8% 14% 6% 1	2235
March	1st to 10th	Night	56% 5% 11% 12% 12% 4	5028
	11th to 20th	Night	56% 7% 14% 15% 8% 1	5090
	21st to end	Night	55% 5% 8% 19% 12% 2	5588
April	1st to 10th	Night	56% 5% 9% 18% 10% 2	2116
	11th to 20th	Night	49% 6% 7% 23% 14% 1	1989
	21st to end	Night	53% 6% 8% 16% 14% 2	1890
May	1st to 10th	Night	46% 6% 9% 24% 12% 3	5068
	11th to 20th	Night	41% 7% 11% 23% 17% 1	4640
	21st to end	Night	42% 6% 9% 27% 15% 1	5115
June	1st to 10th	Night	46% 8% 10% 20% 14% 2	1680
	11th to 20th	Night	38% 7% 12% 25% 17%	1472
	21st to end	Night	43% 8% 15% 21% 11% 1	1470
July	1st to 10th	Night	41% 6% 14% 27% 11% 1	3125
	11th to 20th	Night	37% 5% 11% 34% 12% 1	3457
	21st to end	Night	32% 6% 9% 39% 14%	3984
August	1st to 10th	Night	35% 6% 17% 26% 14% 2	2904
	11th to 20th	Night	41% 7% 18% 23% 10% 1	2902
	21st to end	Night	35% 6% 13% 33% 12% 1	3346
September	1st to 10th	Night	36% 8% 18% 25% 12% 1	2000
	11th to 20th	Night	34% 6% 15% 31% 14%	2087
	21st to end	Night	44% 6% 12% 26% 11%	2255
October	1st to 10th	Night	39% 6% 10% 28% 16%	3920
	11th to 20th	Night	51% 6% 14% 20% 8%	3899
	21st to end	Night	60% 5% 15% 14% 6%	4252
November	1st to 10th	Night	56% 6% 12% 20% 6%	2836
	11th to 20th	Night	59% 7% 12% 15% 6% 1	2940
	21st to end	Night	70% 6% 9% 11% 3	2940
December	1st to 10th	Night	75% 6% 10% 6% 3	4720
	11th to 20th	Night	75% 5% 6% 9% 6%	5348
	21st to end	Night	75% 5% 5% 10% 6%	7223

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% 23% 37% 12% 6% 1	220
	11th to 20th	Day	26% 18% 36% 15% 3 1	250
	21st to end	Day	28% 15% 36% 16% 5%	363
February	1st to 10th	Day	28% 28% 32% 8% 4 1	330
	11th to 20th	Day	30% 25% 37% 8% 1	330
	21st to end	Day	34% 26% 31% 8% 1	284
March	1st to 10th	Day	26% 21% 36% 15% 2	540
	11th to 20th	Day	25% 23% 33% 14% 4 1	540
	21st to end	Day	31% 17% 31% 15% 4 1	594
April	1st to 10th	Day	30% 21% 28% 15% 5% 1	540
	11th to 20th	Day	38% 19% 20% 13% 7% 3	532
	21st to end	Day	32% 15% 31% 14% 6% 1	540
May	1st to 10th	Day	26% 16% 30% 19% 5% 3	543
	11th to 20th	Day	20% 18% 31% 19% 9% 3	567
	21st to end	Day	23% 19% 29% 17% 9% 3	617
June	1st to 10th	Day	22% 15% 32% 24% 5% 2	570
	11th to 20th	Day	18% 16% 31% 25% 9% 2	772
	21st to end	Day	22% 13% 35% 20% 8% 2	780
July	1st to 10th	Day	13% 11% 33% 30% 11% 2	722
	11th to 20th	Day	16% 11% 28% 29% 11% 4	566
	21st to end	Day	13% 12% 33% 27% 11% 5%	576
August	1st to 10th	Day	15% 8% 27% 31% 14% 6%	526
	11th to 20th	Day	17% 5% 27% 29% 14% 8%	519
	21st to end	Day	16% 11% 28% 24% 15% 5%	583
September	1st to 10th	Day	18% 11% 29% 23% 13% 6%	530
	11th to 20th	Day	15% 8% 24% 25% 18% 10%	530
	21st to end	Day	22% 14% 24% 26% 11% 3	530
October	1st to 10th	Day	24% 15% 26% 19% 13% 4	530
	11th to 20th	Day	29% 18% 32% 15% 4 1	530
	21st to end	Day	35% 17% 30% 15% 3	583
November	1st to 10th	Day	35% 20% 29% 15% 1	243
	11th to 20th	Day	29% 24% 33% 9% 6%	220
	21st to end	Day	34% 22% 35% 7% 1	220
December	1st to 10th	Day	30% 20% 32% 14% 2 1	220
	11th to 20th	Day	39% 23% 22% 12% 3	220
	21st to end	Day	34% 24% 27% 12% 2 1	242
January	1st to 10th	Night	27% 17% 34% 18% 4	927
	11th to 20th	Night	30% 17% 32% 18% 3	840
	21st to end	Night	20% 14% 35% 23% 8% 1	924
February	1st to 10th	Night	22% 20% 33% 20% 4	840
	11th to 20th	Night	23% 17% 35% 21% 5%	823
	21st to end	Night	24% 22% 29% 22% 4	692
March	1st to 10th	Night	22% 18% 35% 21% 4	840
	11th to 20th	Night	22% 18% 35% 20% 4 1	840
	21st to end	Night	23% 14% 30% 25% 7%	924
April	1st to 10th	Night	28% 14% 32% 21% 4	840
	11th to 20th	Night	25% 15% 28% 22% 9% 1	745
	21st to end	Night	24% 11% 29% 26% 10%	630
May	1st to 10th	Night	22% 7% 26% 33% 11% 1	562
	11th to 20th	Night	21% 10% 30% 31% 8%	414
	21st to end	Night	13% 9% 34% 35% 9%	455
June	1st to 10th	Night	18% 9% 30% 33% 10%	420
	11th to 20th	Night	17% 9% 25% 37% 12%	420
	21st to end	Night	19% 8% 24% 37% 12%	420
July	1st to 10th	Night	11% 6% 21% 45% 17% 1	390
	11th to 20th	Night	14% 6% 23% 38% 18% 1	388
	21st to end	Night	10% 5% 22% 42% 20% 1	515
August	1st to 10th	Night	14% 4 17% 38% 25% 2	597
	11th to 20th	Night	13% 6% 17% 38% 23% 3	594
	21st to end	Night	19% 6% 24% 28% 20% 2	731
September	1st to 10th	Night	16% 7% 27% 31% 17% 3	800
	11th to 20th	Night	15% 6% 24% 28% 24% 4	800
	21st to end	Night	22% 9% 22% 27% 18% 2	800
October	1st to 10th	Night	22% 12% 27% 24% 14% 1	800
	11th to 20th	Night	31% 11% 30% 21% 7% 1	800
	21st to end	Night	34% 13% 31% 17% 4	880
November	1st to 10th	Night	32% 12% 26% 23% 7% 1	820
	11th to 20th	Night	27% 19% 28% 19% 7%	840
	21st to end	Night	35% 16% 26% 18% 4	840
December	1st to 10th	Night	31% 18% 31% 15% 5%	840
	11th to 20th	Night	28% 19% 34% 14% 4 1	840
	21st to end	Night	34% 15% 30% 17% 3	958

Page generated at 2026-06-28 02:10:45. Version ac07

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