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 2024-03-28.

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% 6% 3 5% 5% 3 5% 5% 6% 8% 40%	79381
	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 44%	80572
Transparency	Day	41% 7% 10% 20% 17% 4	79104
	Night	39% 6% 10% 20% 19% 5%	80368
Seeing	Day	16% 11% 21% 23% 20% 10%	13809
	Night	16% 7% 21% 30% 22% 4	23790

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	17% 12% 3 6% 4 3 4 4 6% 6% 34%	2836
	11th to 20th	Day	21% 7% 4 9% 4 2 3 3 3 4 39%	2852
	21st to end	Day	24% 10% 4 5% 4 2 4 3 4 6% 36%	3476
February	1st to 10th	Day	21% 8% 4 6% 4 3 3 4 4 7% 37%	1900
	11th to 20th	Day	22% 8% 4 5% 5% 3 4 3 4 5% 37%	1848
	21st to end	Day	24% 8% 3 5% 4 2 4 4 5% 5% 36%	1570
March	1st to 10th	Day	16% 8% 3 5% 5% 3 4 5% 5% 6% 39%	1900
	11th to 20th	Day	19% 8% 4 6% 4 3 4 4 5% 6% 36%	2009
	21st to end	Day	15% 7% 3 6% 6% 3 5% 5% 6% 8% 36%	2352
April	1st to 10th	Day	14% 5% 2 5% 4 3 4 4 6% 8% 44%	2160
	11th to 20th	Day	15% 6% 2 5% 5% 3 4 5% 4 8% 45%	2134
	21st to end	Day	11% 5% 3 5% 5% 3 5% 5% 6% 8% 44%	2168
May	1st to 10th	Day	15% 4 2 5% 5% 3 5% 4 5% 7% 45%	2340
	11th to 20th	Day	12% 6% 3 6% 6% 3 7% 5% 4 7% 41%	2301
	21st to end	Day	9% 5% 3 6% 6% 4 5% 5% 6% 9% 42%	2531
June	1st to 10th	Day	10% 5% 3 5% 6% 5% 6% 7% 7% 10% 36%	2340
	11th to 20th	Day	6% 4 2 4 5% 3 7% 6% 8% 10% 45%	2340
	21st to end	Day	7% 5% 2 5% 6% 3 6% 6% 8% 11% 40%	2428
July	1st to 10th	Day	9% 5% 4 7% 7% 4 7% 6% 9% 11% 30%	2404
	11th to 20th	Day	9% 5% 2 5% 7% 4 7% 8% 9% 11% 33%	2340
	21st to end	Day	8% 5% 2 6% 7% 4 7% 9% 9% 10% 33%	2547
August	1st to 10th	Day	7% 5% 2 6% 8% 6% 8% 7% 9% 10% 32%	2171
	11th to 20th	Day	9% 5% 3 6% 7% 5% 6% 8% 7% 9% 35%	2125
	21st to end	Day	12% 6% 3 7% 6% 4 6% 6% 7% 9% 34%	2376
September	1st to 10th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 9% 41%	2116
	11th to 20th	Day	10% 5% 3 5% 5% 4 5% 5% 7% 8% 43%	1980
	21st to end	Day	10% 4 2 4 4 3 5% 4 4 7% 52%	1980
October	1st to 10th	Day	9% 5% 2 4 5% 3 5% 3 4 4 56%	1980
	11th to 20th	Day	11% 4 2 4 4 3 4 4 5% 6% 53%	1980
	21st to end	Day	15% 5% 2 4 5% 2 4 4 4 6% 50%	1818
November	1st to 10th	Day	12% 5% 2 3 3 2 5% 4 4 5% 56%	1672
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 3 5% 7% 49%	1710
	21st to end	Day	16% 7% 3 5% 5% 3 4 5% 4 6% 44%	1710
December	1st to 10th	Day	21% 7% 3 6% 5% 3 5% 4 6% 5% 35%	1710
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 4 5% 39%	2153
	21st to end	Day	18% 10% 5% 6% 7% 3 4 5% 5% 6% 30%	3124
January	1st to 10th	Night	19% 13% 2 4 4 2 3 3 4 5% 40%	4109
	11th to 20th	Night	21% 8% 4 6% 4 2 3 4 4 5% 40%	4092
	21st to end	Night	22% 13% 2 5% 3 2 3 4 3 4 37%	4180
February	1st to 10th	Night	20% 8% 3 4 4 2 3 4 4 7% 40%	2280
	11th to 20th	Night	22% 8% 3 5% 4 2 4 4 4 4 40%	2218
	21st to end	Night	24% 7% 3 5% 5% 3 4 4 4 6% 35%	1884
March	1st to 10th	Night	18% 5% 3 5% 4 3 4 3 5% 7% 41%	2280
	11th to 20th	Night	16% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	2170
	21st to end	Night	15% 7% 2 6% 5% 3 5% 3 5% 6% 43%	2173
April	1st to 10th	Night	12% 4 2 5% 4 2 4 5% 5% 9% 47%	1800
	11th to 20th	Night	14% 5% 2 4 3 2 3 3 5% 8% 50%	1775
	21st to end	Night	12% 5% 3 4 5% 2 4 4 5% 7% 51%	1788
May	1st to 10th	Night	10% 4 2 4 4 3 4 5% 5% 8% 52%	1620
	11th to 20th	Night	10% 5% 2 4 5% 3 6% 6% 6% 10% 43%	1592
	21st to end	Night	6% 4 2 3 5% 3 6% 6% 8% 10% 46%	1744
June	1st to 10th	Night	7% 5% 2 7% 7% 4 5% 5% 6% 10% 42%	1620
	11th to 20th	Night	4 2 1 4 4 4 5% 6% 7% 11% 52%	1620
	21st to end	Night	7% 3 2 4 5% 3 5% 5% 6% 13% 48%	1510
July	1st to 10th	Night	9% 5% 3 6% 6% 5% 6% 6% 7% 9% 39%	1538
	11th to 20th	Night	7% 3 2 5% 4 4 7% 7% 8% 11% 43%	1620
	21st to end	Night	7% 5% 3 5% 5% 3 5% 7% 8% 14% 38%	1771
August	1st to 10th	Night	5% 3 2 4 5% 4 5% 7% 9% 13% 43%	1762
	11th to 20th	Night	9% 4 2 5% 6% 4 5% 6% 9% 10% 41%	1776
	21st to end	Night	9% 5% 3 6% 5% 4 6% 5% 6% 8% 43%	1980
September	1st to 10th	Night	8% 5% 1 5% 5% 3 4 4 6% 9% 50%	1826
	11th to 20th	Night	8% 6% 3 6% 6% 3 5% 5% 5% 9% 45%	1980
	21st to end	Night	8% 4 2 5% 4 3 4 4 5% 7% 54%	1980
October	1st to 10th	Night	10% 4 2 3 4 2 4 4 4 5% 60%	1980
	11th to 20th	Night	13% 6% 2 4 5% 3 3 4 4 5% 52%	1980
	21st to end	Night	15% 6% 2 4 3 2 3 3 4 5% 52%	2534
November	1st to 10th	Night	12% 5% 2 3 4 2 4 4 4 6% 54%	2406
	11th to 20th	Night	12% 5% 3 4 4 2 4 4 4 5% 52%	2470
	21st to end	Night	16% 7% 3 4 5% 2 4 3 4 6% 46%	2470
December	1st to 10th	Night	20% 7% 3 5% 4 3 4 5% 5% 7% 38%	2470
	11th to 20th	Night	17% 7% 3 4 4 2 3 4 3 6% 46%	3042
	21st to end	Night	18% 10% 4 7% 6% 3 4 5% 5% 7% 30%	4532

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	49% 4 5% 17% 22% 2	2837
	11th to 20th	Day	49% 4 6% 18% 21% 2	2852
	21st to end	Day	50% 4 7% 20% 17% 2	3476
February	1st to 10th	Day	49% 3 6% 20% 19% 3	1900
	11th to 20th	Day	51% 4 5% 19% 16% 5%	1858
	21st to end	Day	50% 4 7% 15% 18% 6%	1570
March	1st to 10th	Day	45% 5% 7% 15% 19% 8%	1900
	11th to 20th	Day	49% 5% 10% 16% 16% 4	2009
	21st to end	Day	45% 6% 12% 22% 13% 1	2352
April	1st to 10th	Day	38% 6% 11% 24% 16% 5%	2160
	11th to 20th	Day	39% 5% 7% 20% 23% 5%	2134
	21st to end	Day	37% 6% 9% 28% 18% 2	2168
May	1st to 10th	Day	39% 6% 11% 25% 15% 4	2340
	11th to 20th	Day	41% 8% 13% 23% 14%	2305
	21st to end	Day	36% 8% 13% 25% 15% 2	2531
June	1st to 10th	Day	39% 10% 13% 21% 16% 1	2340
	11th to 20th	Day	31% 9% 17% 25% 16% 2	2340
	21st to end	Day	35% 10% 18% 19% 14% 4	2428
July	1st to 10th	Day	41% 11% 16% 20% 9% 2	2339
	11th to 20th	Day	38% 14% 19% 18% 9% 2	2271
	21st to end	Day	39% 12% 18% 22% 8% 1	2405
August	1st to 10th	Day	40% 12% 18% 20% 9% 1	2158
	11th to 20th	Day	41% 10% 15% 19% 13% 1	2125
	21st to end	Day	43% 12% 12% 19% 11% 3	2376
September	1st to 10th	Day	38% 8% 15% 18% 17% 4	2116
	11th to 20th	Day	37% 9% 11% 18% 21% 4	1980
	21st to end	Day	33% 6% 9% 23% 21% 8%	1980
October	1st to 10th	Day	32% 6% 7% 21% 27% 7%	1980
	11th to 20th	Day	31% 5% 8% 22% 25% 9%	1980
	21st to end	Day	37% 4 4 18% 29% 8%	1818
November	1st to 10th	Day	32% 4 7% 20% 30% 8%	1672
	11th to 20th	Day	37% 3 6% 21% 25% 8%	1710
	21st to end	Day	41% 5% 5% 20% 23% 6%	1710
December	1st to 10th	Day	50% 4 6% 17% 18% 4	1710
	11th to 20th	Day	47% 5% 6% 20% 19% 4	2150
	21st to end	Day	52% 5% 9% 20% 12% 3	3124
January	1st to 10th	Night	48% 3 5% 19% 23% 2	4109
	11th to 20th	Night	48% 4 6% 19% 18% 6%	4092
	21st to end	Night	51% 3 5% 19% 19% 3	4180
February	1st to 10th	Night	45% 4 8% 20% 20% 4	2280
	11th to 20th	Night	49% 3 7% 17% 17% 7%	2219
	21st to end	Night	50% 5% 5% 15% 17% 7%	1884
March	1st to 10th	Night	43% 4 8% 17% 20% 9%	2280
	11th to 20th	Night	44% 6% 9% 18% 18% 5%	2170
	21st to end	Night	43% 4 10% 23% 18% 2	2173
April	1st to 10th	Night	35% 5% 12% 23% 20% 5%	1800
	11th to 20th	Night	34% 4 8% 21% 22% 11%	1775
	21st to end	Night	34% 5% 10% 27% 19% 4	1788
May	1st to 10th	Night	30% 7% 11% 23% 25% 3	1620
	11th to 20th	Night	35% 9% 17% 20% 17% 1	1593
	21st to end	Night	30% 10% 16% 24% 17% 3	1745
June	1st to 10th	Night	36% 9% 14% 21% 18% 2	1620
	11th to 20th	Night	23% 9% 18% 29% 19% 3	1620
	21st to end	Night	29% 8% 17% 24% 17% 4	1510
July	1st to 10th	Night	38% 12% 16% 20% 10% 3	1493
	11th to 20th	Night	29% 14% 21% 22% 12% 4	1566
	21st to end	Night	34% 12% 20% 24% 11% 1	1672
August	1st to 10th	Night	27% 12% 23% 24% 13% 1	1751
	11th to 20th	Night	34% 11% 20% 19% 13% 3	1776
	21st to end	Night	37% 9% 15% 23% 11% 4	1980
September	1st to 10th	Night	31% 8% 17% 22% 17% 5%	1826
	11th to 20th	Night	35% 8% 13% 16% 24% 3	1980
	21st to end	Night	29% 7% 8% 23% 23% 10%	1980
October	1st to 10th	Night	27% 6% 6% 23% 29% 9%	1980
	11th to 20th	Night	35% 5% 6% 21% 22% 11%	1980
	21st to end	Night	35% 4 4 19% 29% 9%	2534
November	1st to 10th	Night	32% 5% 6% 21% 25% 11%	2406
	11th to 20th	Night	34% 5% 6% 18% 27% 10%	2470
	21st to end	Night	41% 3 6% 20% 24% 6%	2470
December	1st to 10th	Night	47% 4 8% 19% 18% 3	2470
	11th to 20th	Night	40% 4 5% 19% 26% 5%	3044
	21st to end	Night	51% 6% 8% 19% 14% 2	4532

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% 14% 4	270
	11th to 20th	Day	27% 26% 29% 12% 6% 1	270
	21st to end	Day	20% 29% 32% 16% 2	297
February	1st to 10th	Day	26% 24% 30% 16% 4	270
	11th to 20th	Day	35% 20% 31% 10% 3 1	270
	21st to end	Day	36% 23% 30% 10% 1	225
March	1st to 10th	Day	25% 21% 33% 15% 5% 1	270
	11th to 20th	Day	23% 20% 29% 21% 6% 1	379
	21st to end	Day	25% 18% 31% 19% 6% 1	490
April	1st to 10th	Day	19% 17% 27% 23% 14% 1	420
	11th to 20th	Day	20% 16% 23% 28% 12% 2	412
	21st to end	Day	16% 15% 27% 27% 13% 3	420
May	1st to 10th	Day	16% 11% 27% 26% 14% 6%	423
	11th to 20th	Day	12% 7% 23% 27% 19% 12%	447
	21st to end	Day	12% 6% 14% 30% 22% 16%	485
June	1st to 10th	Day	12% 4 14% 26% 29% 15%	450
	11th to 20th	Day	8% 2 13% 26% 26% 26%	450
	21st to end	Day	11% 3 16% 24% 29% 16%	538
July	1st to 10th	Day	10% 3 10% 21% 33% 23%	509
	11th to 20th	Day	9% 2 10% 20% 31% 29%	444
	21st to end	Day	8% 3 9% 19% 34% 26%	488
August	1st to 10th	Day	11% 2 10% 21% 34% 23%	446
	11th to 20th	Day	13% 2 10% 24% 38% 14%	439
	21st to end	Day	15% 3 10% 21% 32% 19%	495
September	1st to 10th	Day	11% 3 9% 26% 35% 16%	450
	11th to 20th	Day	11% 3 13% 25% 31% 17%	450
	21st to end	Day	14% 4 13% 26% 35% 9%	450
October	1st to 10th	Day	11% 5% 23% 28% 23% 10%	450
	11th to 20th	Day	12% 10% 24% 34% 16% 3	450
	21st to end	Day	21% 14% 23% 28% 12% 3	305
November	1st to 10th	Day	19% 9% 27% 26% 16% 2	270
	11th to 20th	Day	13% 17% 38% 26% 6%	270
	21st to end	Day	17% 21% 27% 21% 11% 2	270
December	1st to 10th	Day	28% 20% 27% 16% 8%	270
	11th to 20th	Day	22% 19% 34% 15% 10%	270
	21st to end	Day	26% 20% 33% 18% 4	297
January	1st to 10th	Night	24% 14% 32% 25% 5% 1	760
	11th to 20th	Night	26% 15% 29% 23% 7%	760
	21st to end	Night	20% 14% 32% 30% 4	836
February	1st to 10th	Night	24% 10% 31% 30% 6%	760
	11th to 20th	Night	27% 14% 28% 28% 2	743
	21st to end	Night	28% 16% 29% 25% 2	628
March	1st to 10th	Night	21% 13% 30% 31% 5%	760
	11th to 20th	Night	19% 10% 33% 29% 8% 1	760
	21st to end	Night	19% 11% 30% 28% 11%	738
April	1st to 10th	Night	14% 9% 30% 33% 14%	540
	11th to 20th	Night	15% 8% 30% 31% 14% 1	533
	21st to end	Night	14% 7% 26% 37% 16% 1	540
May	1st to 10th	Night	13% 4 25% 35% 20% 3	540
	11th to 20th	Night	13% 3 20% 33% 27% 4	531
	21st to end	Night	7% 3 10% 38% 37% 6%	584
June	1st to 10th	Night	9% 2 12% 32% 39% 6%	540
	11th to 20th	Night	4 1 8% 32% 44% 11%	540
	21st to end	Night	8% 2 6% 32% 44% 8%	540
July	1st to 10th	Night	10% 1 7% 27% 41% 14%	525
	11th to 20th	Night	8% 1 6% 22% 45% 18%	522
	21st to end	Night	9% 1 7% 25% 46% 12%	591
August	1st to 10th	Night	5% 4 23% 55% 12%	537
	11th to 20th	Night	10% 2 6% 29% 46% 7%	534
	21st to end	Night	11% 2 7% 26% 44% 11%	594
September	1st to 10th	Night	10% 2 7% 27% 45% 8%	566
	11th to 20th	Night	10% 3 13% 31% 37% 7%	720
	21st to end	Night	10% 2 13% 33% 40% 3	720
October	1st to 10th	Night	11% 4 17% 31% 30% 6%	720
	11th to 20th	Night	15% 6% 24% 32% 21% 2	720
	21st to end	Night	17% 8% 21% 33% 19% 3	792
November	1st to 10th	Night	15% 7% 19% 34% 21% 3	740
	11th to 20th	Night	14% 9% 29% 34% 13% 1	760
	21st to end	Night	20% 10% 24% 32% 14% 1	760
December	1st to 10th	Night	23% 11% 27% 30% 7% 1	760
	11th to 20th	Night	23% 10% 26% 31% 10%	760
	21st to end	Night	25% 11% 29% 29% 5%	836

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