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 2025-02-25.

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	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	109278
	Night	16% 14% 5% 10% 5% 4 4 3 4 6% 28%	109290
Transparency	Day	54% 6% 11% 19% 9% 1	112900
	Night	56% 6% 10% 17% 9% 1	113833
Seeing	Day	24% 16% 30% 19% 8% 3	15183
	Night	24% 13% 29% 24% 9% 1	24165

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	12% 17% 9% 13% 6% 6% 3 3 4 4 23%	3389
	11th to 20th	Day	10% 22% 10% 16% 8% 7% 5% 3 4 3 13%	3690
	21st to end	Day	14% 20% 9% 15% 7% 6% 4 3 3 3 16%	4466
February	1st to 10th	Day	12% 20% 7% 16% 7% 5% 3 3 3 4 19%	1800
	11th to 20th	Day	14% 16% 7% 14% 6% 4 4 3 5% 5% 23%	1753
	21st to end	Day	16% 19% 6% 13% 6% 5% 4 3 3 4 21%	1458
March	1st to 10th	Day	18% 18% 5% 8% 5% 4 4 3 5% 6% 26%	3432
	11th to 20th	Day	10% 18% 6% 12% 6% 5% 4 3 6% 5% 24%	3480
	21st to end	Day	13% 12% 5% 8% 5% 4 4 3 5% 5% 36%	3815
April	1st to 10th	Day	20% 15% 4 8% 4 4 4 3 5% 6% 27%	2266
	11th to 20th	Day	22% 12% 3 6% 4 4 3 3 4 5% 34%	2347
	21st to end	Day	21% 13% 3 7% 5% 3 3 3 4 4 33%	2470
May	1st to 10th	Day	20% 8% 3 8% 5% 4 4 4 5% 7% 32%	4222
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 6% 9% 37%	4398
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 6% 41%	4837
June	1st to 10th	Day	21% 8% 3 6% 6% 5% 4 4 5% 7% 32%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 6% 8% 37%	2842
	21st to end	Day	21% 8% 2 7% 5% 4 4 4 6% 7% 33%	2850
July	1st to 10th	Day	16% 6% 3 7% 5% 5% 5% 4 7% 9% 34%	4760
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 41%	4509
	21st to end	Day	11% 6% 2 5% 4 4 5% 3 5% 8% 46%	4675
August	1st to 10th	Day	14% 7% 3 7% 5% 6% 6% 5% 6% 8% 34%	4104
	11th to 20th	Day	18% 7% 2 7% 4 4 5% 4 6% 8% 34%	4044
	21st to end	Day	10% 5% 2 6% 4 5% 6% 5% 7% 8% 42%	4380
September	1st to 10th	Day	16% 7% 2 6% 4 4 5% 5% 5% 6% 39%	2280
	11th to 20th	Day	16% 6% 2 5% 4 4 4 3 5% 8% 42%	2195
	21st to end	Day	20% 9% 3 7% 4 5% 4 3 5% 6% 34%	2036
October	1st to 10th	Day	21% 8% 3 8% 5% 4 5% 3 5% 6% 33%	1900
	11th to 20th	Day	26% 14% 3 8% 5% 5% 5% 3 5% 6% 22%	1900
	21st to end	Day	32% 11% 4 9% 4 3 4 3 4 5% 20%	2090
November	1st to 10th	Day	19% 14% 3 8% 6% 4 4 3 5% 7% 27%	1596
	11th to 20th	Day	18% 20% 5% 10% 4 5% 5% 3 4 5% 21%	1600
	21st to end	Day	21% 22% 7% 10% 6% 5% 5% 2 4 4 14%	1600
December	1st to 10th	Day	18% 24% 7% 12% 5% 4 4 4 4 4 13%	2600
	11th to 20th	Day	19% 24% 6% 12% 6% 3 3 2 3 4 18%	2986
	21st to end	Day	22% 22% 6% 15% 4 3 3 2 3 3 16%	3848
January	1st to 10th	Night	13% 19% 9% 13% 7% 5% 4 3 4 5% 17%	6522
	11th to 20th	Night	10% 19% 8% 22% 8% 6% 4 3 4 4 11%	6181
	21st to end	Night	12% 20% 9% 15% 6% 8% 4 3 4 3 15%	6490
February	1st to 10th	Night	12% 19% 6% 14% 8% 5% 4 4 4 5% 19%	2600
	11th to 20th	Night	12% 17% 7% 13% 7% 6% 4 3 4 4 24%	2533
	21st to end	Night	15% 18% 6% 12% 6% 5% 4 3 4 5% 21%	2088
March	1st to 10th	Night	16% 13% 6% 9% 5% 4 4 4 5% 6% 29%	3408
	11th to 20th	Night	12% 17% 7% 10% 5% 4 4 4 5% 5% 27%	3479
	21st to end	Night	14% 10% 5% 7% 6% 5% 5% 4 5% 5% 35%	3817
April	1st to 10th	Night	21% 14% 4 7% 4 5% 3 3 5% 5% 29%	1914
	11th to 20th	Night	19% 11% 4 5% 5% 3 4 4 4 6% 36%	1797
	21st to end	Night	21% 10% 3 8% 5% 4 4 4 4 6% 31%	1710
May	1st to 10th	Night	18% 7% 2 8% 4 4 4 4 6% 7% 36%	2719
	11th to 20th	Night	15% 9% 2 7% 4 4 3 4 5% 8% 39%	2495
	21st to end	Night	11% 7% 2 6% 4 4 4 4 6% 9% 41%	2738
June	1st to 10th	Night	16% 9% 3 6% 6% 4 4 5% 6% 7% 35%	1520
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 6% 8% 44%	1332
	21st to end	Night	16% 8% 3 6% 5% 3 4 5% 7% 7% 37%	1330
July	1st to 10th	Night	11% 7% 3 8% 5% 4 3 3 5% 7% 44%	2210
	11th to 20th	Night	17% 6% 2 5% 4 3 3 3 5% 6% 47%	2448
	21st to end	Night	10% 6% 2 5% 3 4 5% 3 6% 7% 51%	2861
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 5% 8% 46%	2825
	11th to 20th	Night	17% 7% 2 6% 3 3 4 3 5% 7% 43%	2785
	21st to end	Night	16% 5% 1 4 3 4 4 3 5% 7% 48%	3243
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 6% 8% 45%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 4 4 5% 8% 47%	1982
	21st to end	Night	18% 7% 2 7% 4 4 4 3 4 5% 42%	2142
October	1st to 10th	Night	19% 9% 3 7% 4 4 4 4 5% 6% 36%	2280
	11th to 20th	Night	25% 11% 3 8% 5% 4 4 3 5% 6% 26%	2280
	21st to end	Night	27% 15% 5% 9% 5% 4 4 3 4 3 23%	2508
November	1st to 10th	Night	21% 14% 4 6% 5% 3 4 3 5% 5% 30%	2698
	11th to 20th	Night	18% 17% 4 7% 5% 5% 5% 3 5% 7% 25%	2800
	21st to end	Night	22% 20% 5% 10% 7% 4 4 3 4 5% 16%	2800
December	1st to 10th	Night	19% 24% 7% 13% 6% 4 4 3 4 5% 12%	4580
	11th to 20th	Night	17% 23% 7% 16% 6% 4 4 3 3 5% 13%	5208
	21st to end	Night	22% 22% 7% 14% 5% 4 3 2 3 4 14%	7067

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	65% 5% 7% 17% 6%	3390
	11th to 20th	Day	77% 3 5% 9% 6% 1	3720
	21st to end	Day	72% 4 6% 9% 7% 1	4466
February	1st to 10th	Day	71% 4 6% 13% 5% 1	1800
	11th to 20th	Day	64% 6% 9% 12% 9% 2	1762
	21st to end	Day	68% 5% 8% 12% 7%	1458
March	1st to 10th	Day	59% 7% 13% 10% 11% 1	3435
	11th to 20th	Day	59% 7% 12% 14% 7% 1	3480
	21st to end	Day	48% 6% 10% 22% 12% 2	3815
April	1st to 10th	Day	57% 6% 9% 17% 9% 2	2266
	11th to 20th	Day	53% 5% 7% 21% 12% 1	2347
	21st to end	Day	55% 5% 8% 17% 13% 3	2470
May	1st to 10th	Day	50% 7% 10% 21% 10% 2	4234
	11th to 20th	Day	43% 8% 13% 26% 10% 1	4402
	21st to end	Day	42% 7% 13% 18% 16% 4	4837
June	1st to 10th	Day	51% 7% 10% 20% 12%	2660
	11th to 20th	Day	44% 7% 11% 22% 15% 1	2842
	21st to end	Day	49% 7% 13% 20% 10% 1	2850
July	1st to 10th	Day	45% 7% 15% 23% 10% 1	4686
	11th to 20th	Day	40% 7% 15% 29% 9%	4431
	21st to end	Day	36% 6% 11% 31% 16%	4526
August	1st to 10th	Day	46% 8% 13% 24% 8% 1	4091
	11th to 20th	Day	45% 8% 14% 25% 7%	4083
	21st to end	Day	36% 8% 13% 32% 10% 1	4380
September	1st to 10th	Day	43% 7% 13% 25% 11% 1	2280
	11th to 20th	Day	40% 7% 13% 27% 12% 1	2195
	21st to end	Day	51% 6% 11% 24% 8%	2036
October	1st to 10th	Day	48% 7% 12% 23% 9% 1	3160
	11th to 20th	Day	53% 8% 11% 21% 6%	3140
	21st to end	Day	63% 6% 12% 16% 4	3428
November	1st to 10th	Day	56% 8% 13% 17% 5%	1596
	11th to 20th	Day	66% 7% 9% 13% 5% 1	1600
	21st to end	Day	73% 6% 9% 9% 3 1	1600
December	1st to 10th	Day	75% 6% 9% 8% 2	2600
	11th to 20th	Day	72% 4 5% 12% 6% 1	2986
	21st to end	Day	74% 4 4 12% 6%	3848
January	1st to 10th	Night	70% 5% 6% 14% 5%	6522
	11th to 20th	Night	76% 7% 6% 5% 6% 1	6226
	21st to end	Night	73% 6% 5% 7% 8% 1	6490
February	1st to 10th	Night	66% 6% 9% 13% 5% 1	2600
	11th to 20th	Night	64% 5% 8% 16% 7% 1	2535
	21st to end	Night	67% 5% 8% 14% 6% 1	2088
March	1st to 10th	Night	55% 6% 13% 14% 11% 1	3418
	11th to 20th	Night	57% 6% 13% 15% 7% 1	3480
	21st to end	Night	48% 7% 10% 22% 12% 2	3817
April	1st to 10th	Night	56% 5% 9% 18% 10% 2	1914
	11th to 20th	Night	49% 6% 6% 23% 14% 2	1797
	21st to end	Night	54% 6% 8% 14% 15% 2	1710
May	1st to 10th	Night	43% 8% 13% 24% 10% 2	2726
	11th to 20th	Night	41% 9% 13% 24% 12% 1	2496
	21st to end	Night	37% 9% 11% 24% 16% 2	2739
June	1st to 10th	Night	47% 8% 10% 20% 13% 2	1520
	11th to 20th	Night	37% 7% 13% 24% 19%	1332
	21st to end	Night	43% 8% 15% 21% 11% 1	1330
July	1st to 10th	Night	39% 6% 14% 24% 15% 2	2175
	11th to 20th	Night	38% 6% 12% 33% 10% 1	2403
	21st to end	Night	33% 6% 10% 33% 17% 1	2770
August	1st to 10th	Night	36% 6% 16% 25% 14% 2	2814
	11th to 20th	Night	41% 7% 18% 23% 10% 1	2812
	21st to end	Night	35% 7% 12% 33% 12% 1	3243
September	1st to 10th	Night	37% 8% 17% 25% 13% 1	1900
	11th to 20th	Night	35% 7% 15% 30% 13%	1982
	21st to end	Night	44% 6% 13% 27% 11%	2142
October	1st to 10th	Night	40% 6% 10% 27% 16%	3800
	11th to 20th	Night	51% 6% 15% 20% 8%	3779
	21st to end	Night	60% 5% 15% 13% 6%	4120
November	1st to 10th	Night	55% 6% 12% 20% 6%	2698
	11th to 20th	Night	59% 7% 12% 15% 6% 1	2800
	21st to end	Night	69% 7% 10% 11% 3	2800
December	1st to 10th	Night	75% 6% 11% 6% 2	4580
	11th to 20th	Night	75% 5% 6% 9% 6%	5208
	21st to end	Night	75% 5% 5% 10% 6%	7067

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	20% 24% 37% 13% 6% 1	200
	11th to 20th	Day	25% 19% 36% 16% 4 1	227
	21st to end	Day	29% 15% 35% 16% 5%	330
February	1st to 10th	Day	28% 31% 32% 6% 3 1	300
	11th to 20th	Day	30% 25% 36% 8% 1	300
	21st to end	Day	35% 27% 31% 7%	246
March	1st to 10th	Day	25% 20% 36% 16% 2	460
	11th to 20th	Day	22% 23% 35% 15% 5% 1	460
	21st to end	Day	30% 16% 32% 16% 5% 1	506
April	1st to 10th	Day	28% 20% 29% 16% 6% 1	460
	11th to 20th	Day	37% 20% 20% 13% 8% 3	452
	21st to end	Day	32% 15% 32% 13% 6% 1	460
May	1st to 10th	Day	26% 15% 30% 20% 6% 3	463
	11th to 20th	Day	20% 17% 30% 20% 10% 3	487
	21st to end	Day	21% 18% 29% 19% 9% 3	529
June	1st to 10th	Day	22% 15% 33% 23% 5% 1	490
	11th to 20th	Day	18% 15% 31% 25% 10% 2	672
	21st to end	Day	23% 13% 35% 19% 8% 2	680
July	1st to 10th	Day	13% 10% 33% 30% 11% 2	671
	11th to 20th	Day	17% 11% 28% 29% 12% 4	524
	21st to end	Day	14% 11% 32% 28% 11% 5%	532
August	1st to 10th	Day	16% 8% 27% 29% 13% 6%	486
	11th to 20th	Day	17% 5% 26% 28% 14% 9%	479
	21st to end	Day	17% 11% 28% 25% 15% 5%	539
September	1st to 10th	Day	18% 11% 30% 23% 12% 6%	490
	11th to 20th	Day	16% 8% 24% 24% 18% 9%	490
	21st to end	Day	22% 15% 24% 25% 11% 3	490
October	1st to 10th	Day	25% 16% 26% 18% 12% 4	490
	11th to 20th	Day	29% 18% 32% 15% 4 1	490
	21st to end	Day	36% 18% 29% 14% 3	539
November	1st to 10th	Day	33% 19% 30% 15% 1	221
	11th to 20th	Day	30% 25% 32% 9% 6%	200
	21st to end	Day	33% 23% 36% 7% 2 1	200
December	1st to 10th	Day	31% 21% 33% 13% 2 1	200
	11th to 20th	Day	39% 24% 22% 13% 3 1	200
	21st to end	Day	33% 25% 26% 13% 2 1	220
January	1st to 10th	Night	28% 17% 34% 17% 4	883
	11th to 20th	Night	30% 16% 32% 18% 4 1	800
	21st to end	Night	20% 13% 35% 23% 8% 1	880
February	1st to 10th	Night	23% 20% 34% 19% 4	800
	11th to 20th	Night	24% 16% 35% 21% 5%	783
	21st to end	Night	24% 23% 28% 21% 4	647
March	1st to 10th	Night	23% 18% 34% 21% 4	760
	11th to 20th	Night	21% 19% 34% 21% 4 1	760
	21st to end	Night	22% 14% 31% 26% 7%	836
April	1st to 10th	Night	28% 14% 32% 22% 5%	760
	11th to 20th	Night	25% 14% 29% 22% 9% 1	673
	21st to end	Night	25% 11% 28% 25% 10% 1	570
May	1st to 10th	Night	22% 6% 26% 33% 11% 1	508
	11th to 20th	Night	20% 9% 30% 32% 9%	374
	21st to end	Night	11% 8% 35% 35% 9%	411
June	1st to 10th	Night	18% 8% 32% 32% 9% 1	380
	11th to 20th	Night	16% 9% 24% 38% 13%	380
	21st to end	Night	20% 8% 24% 35% 13%	380
July	1st to 10th	Night	11% 6% 21% 45% 17% 1	370
	11th to 20th	Night	14% 7% 24% 37% 18% 1	368
	21st to end	Night	10% 5% 21% 42% 20% 1	489
August	1st to 10th	Night	15% 4 18% 36% 25% 2	567
	11th to 20th	Night	13% 5% 17% 38% 24% 3	564
	21st to end	Night	20% 6% 23% 28% 20% 2	694
September	1st to 10th	Night	16% 6% 27% 31% 17% 3	760
	11th to 20th	Night	15% 7% 25% 27% 23% 4	760
	21st to end	Night	23% 9% 21% 27% 18% 2	760
October	1st to 10th	Night	23% 12% 27% 24% 13% 1	760
	11th to 20th	Night	30% 11% 29% 21% 8% 1	760
	21st to end	Night	35% 14% 31% 16% 4	836
November	1st to 10th	Night	32% 11% 26% 23% 7% 1	780
	11th to 20th	Night	28% 19% 28% 19% 7%	800
	21st to end	Night	35% 15% 26% 19% 5%	800
December	1st to 10th	Night	32% 18% 30% 14% 5% 1	800
	11th to 20th	Night	29% 19% 34% 14% 4 1	800
	21st to end	Night	34% 15% 30% 17% 4	912

Page generated at 2025-02-22 06:51:39. Version ac07

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