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 2024-04-03.

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	7% 10% 4 6% 5% 3 4 4 5% 6% 47%	79172
	Night	7% 10% 4 7% 5% 3 4 4 5% 6% 46%	80988
Transparency	Day	37% 5% 10% 19% 19% 9%	78897
	Night	39% 5% 11% 20% 17% 8%	80784
Seeing	Day	12% 15% 33% 28% 10% 1	14359
	Night	12% 7% 26% 37% 17% 1	24589

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	6% 19% 8% 12% 6% 3 4 4 4 5% 30%	2858
	11th to 20th	Day	7% 21% 9% 12% 6% 3 4 3 4 4 27%	2860
	21st to end	Day	7% 19% 8% 8% 6% 3 4 3 3 5% 34%	3146
February	1st to 10th	Day	8% 16% 7% 11% 5% 4 4 5% 4 5% 31%	1710
	11th to 20th	Day	7% 19% 6% 11% 6% 2 4 4 4 5% 32%	1713
	21st to end	Day	5% 18% 8% 13% 6% 4 4 4 4 5% 28%	1570
March	1st to 10th	Day	7% 15% 8% 8% 6% 3 5% 4 5% 7% 32%	2028
	11th to 20th	Day	6% 13% 4 7% 6% 4 5% 6% 6% 8% 35%	2090
	21st to end	Day	11% 17% 5% 9% 6% 3 5% 4 5% 7% 28%	2299
April	1st to 10th	Day	10% 13% 4 7% 6% 3 5% 5% 4 7% 36%	2029
	11th to 20th	Day	8% 14% 5% 7% 6% 3 4 5% 4 5% 39%	2276
	21st to end	Day	8% 11% 3 7% 6% 3 3 4 5% 7% 43%	2340
May	1st to 10th	Day	8% 10% 3 6% 6% 4 5% 6% 6% 9% 38%	2340
	11th to 20th	Day	8% 8% 2 6% 6% 3 5% 5% 6% 10% 42%	2301
	21st to end	Day	11% 7% 3 6% 6% 3 5% 7% 6% 8% 38%	2530
June	1st to 10th	Day	5% 4 2 5% 4 3 4 5% 7% 8% 54%	2515
	11th to 20th	Day	7% 4 2 4 4 2 4 4 5% 7% 58%	2520
	21st to end	Day	3 2 1 3 3 2 3 3 3 5% 71%	2603
July	1st to 10th	Day	3 2 1 3 3 2 4 4 5% 7% 66%	2381
	11th to 20th	Day	4 3 1 3 3 2 4 4 5% 6% 66%	2340
	21st to end	Day	4 3 1 3 3 2 4 4 6% 8% 60%	2545
August	1st to 10th	Day	4 3 1 4 4 3 3 4 6% 7% 61%	2328
	11th to 20th	Day	3 3 1 3 3 2 4 4 5% 6% 67%	2299
	21st to end	Day	3 3 1 4 3 2 4 4 4 7% 66%	2561
September	1st to 10th	Day	4 3 1 2 2 2 3 3 4 6% 69%	2048
	11th to 20th	Day	5% 3 1 3 3 2 4 3 5% 6% 64%	1980
	21st to end	Day	6% 4 1 3 3 2 3 3 3 5% 67%	1980
October	1st to 10th	Day	11% 6% 2 4 4 2 4 5% 4 5% 53%	1886
	11th to 20th	Day	8% 5% 3 3 3 3 3 4 6% 6% 55%	1800
	21st to end	Day	6% 8% 2 4 4 2 4 4 4 6% 55%	1962
November	1st to 10th	Day	10% 10% 4 6% 6% 2 4 3 6% 6% 43%	1674
	11th to 20th	Day	11% 10% 3 6% 5% 2 3 4 4 8% 44%	1708
	21st to end	Day	7% 12% 5% 8% 5% 4 3 4 4 5% 42%	1520
December	1st to 10th	Day	8% 13% 6% 9% 6% 3 4 4 5% 5% 37%	1520
	11th to 20th	Day	10% 14% 7% 10% 7% 3 5% 4 5% 7% 29%	1926
	21st to end	Day	6% 13% 6% 9% 6% 3 5% 5% 6% 7% 34%	2986
January	1st to 10th	Night	6% 15% 9% 12% 6% 3 4 3 4 6% 32%	4097
	11th to 20th	Night	7% 22% 7% 12% 7% 3 4 4 4 5% 25%	4110
	21st to end	Night	8% 19% 6% 8% 5% 3 4 4 4 6% 32%	4521
February	1st to 10th	Night	10% 15% 5% 8% 6% 4 5% 5% 5% 6% 33%	2470
	11th to 20th	Night	7% 15% 4 8% 5% 3 4 4 4 6% 40%	2350
	21st to end	Night	6% 14% 7% 10% 7% 4 4 4 6% 5% 33%	1884
March	1st to 10th	Night	9% 15% 5% 8% 5% 3 5% 5% 5% 6% 34%	2151
	11th to 20th	Night	6% 10% 3 6% 7% 3 5% 5% 6% 8% 41%	2090
	21st to end	Night	8% 14% 4 7% 6% 3 5% 5% 5% 6% 37%	2299
April	1st to 10th	Night	10% 13% 3 5% 5% 3 4 4 5% 5% 44%	1976
	11th to 20th	Night	6% 11% 3 7% 6% 3 5% 4 5% 5% 45%	1629
	21st to end	Night	8% 8% 3 6% 4 3 3 4 5% 6% 49%	1620
May	1st to 10th	Night	9% 8% 3 6% 6% 4 4 6% 6% 7% 42%	1620
	11th to 20th	Night	9% 6% 2 4 5% 2 4 5% 6% 7% 49%	1594
	21st to end	Night	9% 7% 3 6% 6% 3 4 5% 6% 7% 44%	1746
June	1st to 10th	Night	5% 4 3 4 5% 2 4 5% 5% 7% 57%	1440
	11th to 20th	Night	6% 3 2 3 3 3 3 2 4 7% 65%	1440
	21st to end	Night	3 3 1 4 3 2 3 3 3 6% 71%	1333
July	1st to 10th	Night	3 3 2 4 4 2 4 5% 5% 9% 58%	1566
	11th to 20th	Night	4 3 2 4 5% 2 5% 4 5% 6% 59%	1620
	21st to end	Night	4 3 2 4 4 2 4 6% 5% 9% 57%	1773
August	1st to 10th	Night	4 4 1 4 4 3 4 5% 5% 8% 57%	1611
	11th to 20th	Night	3 3 2 4 3 3 5% 4 5% 7% 61%	1602
	21st to end	Night	3 3 2 4 4 3 5% 4 5% 6% 62%	1795
September	1st to 10th	Night	4 3 1 4 4 2 2 3 5% 5% 67%	1909
	11th to 20th	Night	6% 3 1 3 3 2 3 4 5% 5% 65%	1980
	21st to end	Night	6% 3 1 3 3 2 3 3 3 5% 69%	1980
October	1st to 10th	Night	9% 6% 2 4 4 2 3 3 4 6% 58%	2074
	11th to 20th	Night	9% 6% 1 4 3 2 3 3 4 6% 59%	2160
	21st to end	Night	6% 7% 2 4 4 2 3 4 4 6% 59%	2393
November	1st to 10th	Night	9% 8% 3 5% 4 3 4 4 5% 7% 49%	2405
	11th to 20th	Night	8% 7% 3 5% 6% 3 5% 4 5% 8% 46%	2470
	21st to end	Night	6% 12% 5% 5% 6% 3 5% 5% 4 6% 45%	2640
December	1st to 10th	Night	7% 12% 5% 9% 7% 3 4 4 4 7% 39%	2660
	11th to 20th	Night	11% 12% 5% 8% 6% 4 5% 5% 5% 7% 33%	3271
	21st to end	Night	8% 12% 6% 10% 7% 3 5% 4 5% 6% 35%	4709

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	57% 5% 13% 18% 6% 1	2859
	11th to 20th	Day	62% 6% 12% 13% 5% 1	2860
	21st to end	Day	53% 6% 17% 15% 8% 1	3146
February	1st to 10th	Day	56% 6% 14% 14% 9% 1	1710
	11th to 20th	Day	55% 5% 13% 17% 9% 1	1722
	21st to end	Day	58% 5% 11% 16% 9% 1	1570
March	1st to 10th	Day	51% 6% 12% 22% 9% 1	2028
	11th to 20th	Day	45% 6% 13% 24% 11% 2	2090
	21st to end	Day	55% 6% 13% 18% 6% 2	2299
April	1st to 10th	Day	48% 6% 11% 18% 14% 4	2029
	11th to 20th	Day	47% 5% 9% 22% 16% 2	2279
	21st to end	Day	41% 4 10% 25% 19% 1	2340
May	1st to 10th	Day	40% 6% 10% 23% 18% 2	2340
	11th to 20th	Day	37% 5% 9% 26% 19% 4	2304
	21st to end	Day	41% 6% 10% 26% 14% 2	2530
June	1st to 10th	Day	26% 5% 10% 24% 29% 6%	2515
	11th to 20th	Day	25% 4 7% 20% 27% 18%	2520
	21st to end	Day	16% 3 3 13% 32% 33%	2603
July	1st to 10th	Day	17% 4 6% 15% 25% 33%	2317
	11th to 20th	Day	18% 3 6% 13% 27% 33%	2271
	21st to end	Day	21% 5% 7% 13% 28% 26%	2404
August	1st to 10th	Day	21% 4 6% 18% 24% 26%	2313
	11th to 20th	Day	17% 5% 4 15% 34% 25%	2299
	21st to end	Day	19% 4 4 17% 34% 22%	2561
September	1st to 10th	Day	17% 4 5% 17% 29% 28%	2048
	11th to 20th	Day	20% 4 8% 18% 32% 18%	1980
	21st to end	Day	21% 3 7% 23% 36% 11%	1980
October	1st to 10th	Day	34% 5% 8% 24% 23% 7%	1886
	11th to 20th	Day	28% 5% 10% 30% 23% 5%	1800
	21st to end	Day	30% 5% 14% 30% 19% 2	1962
November	1st to 10th	Day	42% 5% 13% 22% 17% 2	1674
	11th to 20th	Day	40% 5% 15% 25% 15%	1708
	21st to end	Day	44% 5% 13% 23% 14% 1	1520
December	1st to 10th	Day	48% 7% 16% 17% 9% 3	1520
	11th to 20th	Day	55% 5% 13% 19% 8%	1924
	21st to end	Day	48% 6% 13% 18% 13% 1	2986
January	1st to 10th	Night	55% 6% 10% 20% 8% 1	4097
	11th to 20th	Night	61% 6% 13% 13% 5% 2	4110
	21st to end	Night	53% 6% 16% 16% 8% 2	4521
February	1st to 10th	Night	51% 7% 13% 20% 8% 1	2470
	11th to 20th	Night	45% 5% 12% 21% 15% 2	2351
	21st to end	Night	50% 6% 11% 20% 11% 2	1884
March	1st to 10th	Night	49% 6% 10% 24% 11%	2151
	11th to 20th	Night	40% 6% 13% 26% 15% 2	2090
	21st to end	Night	47% 6% 13% 24% 8% 2	2299
April	1st to 10th	Night	42% 6% 13% 21% 13% 6%	1976
	11th to 20th	Night	40% 6% 11% 23% 19% 2	1629
	21st to end	Night	35% 6% 11% 27% 21% 2	1620
May	1st to 10th	Night	39% 6% 9% 23% 20% 3	1620
	11th to 20th	Night	34% 5% 9% 27% 20% 6%	1595
	21st to end	Night	38% 6% 11% 27% 16% 2	1746
June	1st to 10th	Night	25% 6% 9% 23% 30% 6%	1440
	11th to 20th	Night	21% 3 7% 21% 29% 19%	1440
	21st to end	Night	16% 3 3 14% 30% 35%	1333
July	1st to 10th	Night	21% 5% 5% 14% 23% 31%	1521
	11th to 20th	Night	24% 4 4 14% 26% 28%	1566
	21st to end	Night	22% 6% 7% 14% 25% 26%	1674
August	1st to 10th	Night	24% 4 7% 16% 22% 27%	1602
	11th to 20th	Night	22% 5% 5% 14% 28% 26%	1602
	21st to end	Night	21% 5% 6% 13% 30% 25%	1795
September	1st to 10th	Night	20% 3 4 15% 25% 32%	1909
	11th to 20th	Night	21% 4 6% 17% 29% 23%	1980
	21st to end	Night	20% 3 6% 19% 36% 16%	1980
October	1st to 10th	Night	29% 4 7% 24% 28% 8%	2074
	11th to 20th	Night	28% 3 8% 31% 26% 5%	2160
	21st to end	Night	27% 5% 10% 33% 21% 4	2393
November	1st to 10th	Night	36% 5% 11% 23% 21% 5%	2405
	11th to 20th	Night	36% 5% 15% 27% 15% 2	2470
	21st to end	Night	40% 5% 12% 26% 14% 3	2640
December	1st to 10th	Night	47% 4 16% 20% 10% 3	2660
	11th to 20th	Night	50% 6% 14% 20% 10%	3272
	21st to end	Night	50% 4 15% 17% 13%	4709

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% 33% 22% 9% 1	270
	11th to 20th	Day	17% 13% 37% 23% 10%	270
	21st to end	Day	12% 15% 35% 30% 7% 1	297
February	1st to 10th	Day	20% 20% 37% 19% 5%	270
	11th to 20th	Day	18% 21% 37% 18% 5% 1	318
	21st to end	Day	16% 23% 40% 16% 4 1	382
March	1st to 10th	Day	19% 24% 34% 19% 4	460
	11th to 20th	Day	17% 20% 36% 21% 6%	460
	21st to end	Day	24% 24% 33% 17% 2	506
April	1st to 10th	Day	20% 22% 29% 23% 7%	429
	11th to 20th	Day	22% 27% 32% 16% 4	412
	21st to end	Day	17% 25% 26% 23% 7% 1	420
May	1st to 10th	Day	17% 22% 33% 22% 5%	423
	11th to 20th	Day	14% 18% 32% 27% 8% 1	448
	21st to end	Day	15% 15% 31% 26% 11% 2	485
June	1st to 10th	Day	6% 15% 29% 34% 15% 2	625
	11th to 20th	Day	11% 12% 34% 32% 10% 1	630
	21st to end	Day	4 11% 34% 37% 13% 1	578
July	1st to 10th	Day	3 9% 35% 41% 10% 2	446
	11th to 20th	Day	4 9% 39% 36% 11% 2	444
	21st to end	Day	5% 3 34% 42% 16% 1	487
August	1st to 10th	Day	4 7% 41% 31% 15% 1	447
	11th to 20th	Day	4 8% 28% 39% 19% 1	437
	21st to end	Day	3 9% 29% 40% 18% 1	495
September	1st to 10th	Day	6% 9% 33% 31% 19% 3	450
	11th to 20th	Day	8% 12% 31% 32% 14% 3	450
	21st to end	Day	8% 14% 29% 32% 16% 2	450
October	1st to 10th	Day	13% 15% 24% 28% 18% 2	356
	11th to 20th	Day	8% 18% 24% 27% 19% 4	270
	21st to end	Day	12% 16% 31% 30% 10% 1	297
November	1st to 10th	Day	20% 15% 24% 29% 8% 4	270
	11th to 20th	Day	14% 11% 33% 29% 10% 2	270
	21st to end	Day	14% 11% 28% 31% 14% 2	270
December	1st to 10th	Day	14% 11% 34% 28% 10% 3	270
	11th to 20th	Day	16% 12% 40% 27% 6% 1	270
	21st to end	Day	22% 14% 32% 24% 6% 1	297
January	1st to 10th	Night	18% 7% 29% 31% 15% 1	760
	11th to 20th	Night	17% 8% 28% 33% 13% 1	760
	21st to end	Night	15% 8% 30% 34% 11% 2	836
February	1st to 10th	Night	18% 7% 34% 32% 9% 1	760
	11th to 20th	Night	14% 7% 33% 35% 11%	744
	21st to end	Night	11% 9% 39% 32% 8%	628
March	1st to 10th	Night	16% 10% 31% 33% 9% 1	760
	11th to 20th	Night	10% 9% 30% 38% 12% 1	760
	21st to end	Night	17% 11% 28% 34% 9% 1	836
April	1st to 10th	Night	18% 10% 27% 35% 9% 1	702
	11th to 20th	Night	12% 12% 32% 32% 12%	533
	21st to end	Night	11% 9% 26% 36% 18% 1	540
May	1st to 10th	Night	13% 6% 31% 36% 14%	540
	11th to 20th	Night	13% 4 24% 33% 24% 2	531
	21st to end	Night	11% 7% 19% 38% 23% 2	584
June	1st to 10th	Night	7% 8% 20% 39% 25% 2	540
	11th to 20th	Night	8% 7% 23% 43% 19%	540
	21st to end	Night	4 3 21% 42% 28% 2	389
July	1st to 10th	Night	4 3 20% 40% 31% 2	471
	11th to 20th	Night	5% 2 17% 48% 27% 1	522
	21st to end	Night	4 1 10% 48% 35% 2	591
August	1st to 10th	Night	4 2 16% 50% 27% 1	537
	11th to 20th	Night	4 1 17% 46% 32% 1	534
	21st to end	Night	5% 3 16% 44% 31% 1	594
September	1st to 10th	Night	5% 4 18% 44% 25% 2	649
	11th to 20th	Night	7% 3 20% 41% 25% 4	720
	21st to end	Night	8% 4 20% 39% 23% 6%	720
October	1st to 10th	Night	11% 6% 20% 41% 20% 1	720
	11th to 20th	Night	12% 5% 22% 37% 23% 1	720
	21st to end	Night	11% 5% 26% 38% 19% 2	792
November	1st to 10th	Night	12% 7% 23% 40% 16% 2	740
	11th to 20th	Night	12% 5% 32% 38% 11% 2	760
	21st to end	Night	12% 10% 27% 36% 14% 2	930
December	1st to 10th	Night	13% 8% 34% 34% 11% 1	950
	11th to 20th	Night	18% 8% 33% 32% 9% 1	950
	21st to end	Night	19% 11% 33% 31% 6% 1	946

Page generated at 2024-03-31 04:08:54. Version ac07

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