Abilene
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abilene clear sky chart from 2005-11-06 to 2025-06-10.

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% 4 1 4 3 3 3 3 5% 6% 59%	119807
	Night	7% 4 1 4 3 3 3 3 5% 7% 61%	118692
Transparency	Day	25% 4 8% 21% 27% 14%	123680
	Night	23% 4 8% 21% 27% 17%	122949
Seeing	Day	9% 7% 26% 31% 20% 6%	15833
	Night	8% 8% 35% 36% 12% 1	25820

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	8% 8% 3 5% 3 3 3 3 3 5% 56%	4077
	11th to 20th	Day	4 4 1 3 2 2 3 2 4 5% 70%	4080
	21st to end	Day	14% 7% 2 5% 3 2 3 2 4 5% 53%	4902
February	1st to 10th	Day	11% 5% 1 4 3 2 3 3 5% 5% 59%	2000
	11th to 20th	Day	9% 8% 2 6% 3 3 3 2 4 5% 54%	1949
	21st to end	Day	12% 7% 2 3 2 2 3 2 3 5% 60%	1650
March	1st to 10th	Day	9% 5% 1 4 3 3 3 3 5% 6% 59%	4601
	11th to 20th	Day	11% 4 1 4 3 3 3 3 4 6% 59%	4980
	21st to end	Day	4 5% 2 5% 3 4 5% 3 5% 7% 58%	5462
April	1st to 10th	Day	8% 4 2 4 3 3 4 4 5% 7% 57%	2255
	11th to 20th	Day	10% 5% 1 5% 3 3 3 3 4 6% 57%	2374
	21st to end	Day	8% 4 2 5% 3 3 3 3 4 6% 59%	2490
May	1st to 10th	Day	10% 5% 2 5% 3 4 3 3 5% 6% 54%	5862
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 54%	5862
	21st to end	Day	8% 4 2 6% 4 4 4 4 6% 7% 50%	6434
June	1st to 10th	Day	5% 4 1 4 3 3 4 3 5% 8% 61%	2588
	11th to 20th	Day	3 2 1 2 3 3 4 3 6% 7% 64%	2470
	21st to end	Day	5% 2 1 3 4 4 4 4 6% 7% 61%	2470
July	1st to 10th	Day	6% 4 2 4 4 4 4 4 6% 8% 55%	4120
	11th to 20th	Day	3 2 1 3 3 3 3 3 6% 9% 65%	4120
	21st to end	Day	3 3 1 3 3 3 4 3 5% 9% 63%	4465
August	1st to 10th	Day	1 2 1 2 2 3 3 3 4 7% 71%	3960
	11th to 20th	Day	3 3 1 3 2 2 3 3 5% 9% 65%	3726
	21st to end	Day	3 2 1 4 4 4 4 4 6% 8% 60%	4180
September	1st to 10th	Day	10% 4 2 4 3 5% 3 3 5% 6% 54%	2123
	11th to 20th	Day	10% 6% 2 5% 3 4 4 3 5% 6% 52%	2090
	21st to end	Day	9% 4 1 3 3 3 3 3 4 5% 62%	2090
October	1st to 10th	Day	4 3 1 3 3 3 3 3 4 7% 66%	2090
	11th to 20th	Day	7% 4 1 3 2 2 3 3 4 5% 67%	2036
	21st to end	Day	10% 4 1 3 2 2 2 2 3 3 66%	2090
November	1st to 10th	Day	8% 3 1 3 3 3 3 2 4 6% 64%	1792
	11th to 20th	Day	5% 4 1 3 2 2 3 3 5% 7% 66%	1800
	21st to end	Day	10% 6% 1 4 2 2 3 2 4 7% 59%	1800
December	1st to 10th	Day	11% 6% 2 6% 3 4 3 3 4 6% 53%	2940
	11th to 20th	Day	5% 4 1 4 3 4 4 4 4 6% 60%	3391
	21st to end	Day	8% 6% 2 4 3 2 2 2 3 4 65%	4488
January	1st to 10th	Night	8% 6% 2 5% 3 3 3 3 4 5% 60%	5888
	11th to 20th	Night	6% 3 1 3 2 2 2 2 3 5% 70%	5900
	21st to end	Night	13% 8% 2 4 3 2 2 3 4 6% 54%	6104
February	1st to 10th	Night	9% 6% 2 5% 3 3 3 2 3 5% 60%	2400
	11th to 20th	Night	11% 6% 1 5% 3 3 4 2 4 6% 54%	2338
	21st to end	Night	8% 5% 1 4 2 2 3 3 4 5% 62%	1980
March	1st to 10th	Night	6% 8% 2 4 3 3 3 3 4 5% 59%	5266
	11th to 20th	Night	9% 5% 1 3 2 2 2 3 4 7% 61%	4980
	21st to end	Night	4 5% 1 5% 3 3 4 3 4 6% 61%	5467
April	1st to 10th	Night	6% 4 2 4 3 3 3 3 5% 6% 61%	2140
	11th to 20th	Night	8% 4 1 4 2 4 3 3 6% 6% 59%	1977
	21st to end	Night	8% 4 1 3 2 3 2 3 5% 7% 63%	1910
May	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 4 6% 56%	4053
	11th to 20th	Night	6% 4 2 4 3 3 5% 4 6% 7% 56%	4053
	21st to end	Night	7% 4 1 5% 3 4 4 4 6% 9% 53%	4443
June	1st to 10th	Night	3 2 1 3 3 4 4 4 7% 11% 59%	1796
	11th to 20th	Night	2 2 1 3 3 4 4 3 6% 10% 63%	1710
	21st to end	Night	4 3 1 3 3 2 3 3 4 8% 67%	1710
July	1st to 10th	Night	5% 3 1 3 3 3 4 3 5% 9% 61%	2850
	11th to 20th	Night	2 1 1 2 2 2 3 3 5% 11% 69%	2850
	21st to end	Night	2 2 1 3 2 3 3 3 5% 8% 67%	3098
August	1st to 10th	Night	1 1 1 2 2 2 2 2 5% 9% 74%	2962
	11th to 20th	Night	2 2 1 2 2 3 3 2 4 9% 69%	3113
	21st to end	Night	3 2 1 3 3 3 4 3 6% 9% 63%	3487
September	1st to 10th	Night	8% 3 1 4 3 4 4 3 5% 6% 58%	2057
	11th to 20th	Night	9% 3 2 6% 4 3 4 4 6% 7% 54%	2090
	21st to end	Night	8% 3 1 3 3 3 3 3 4 6% 62%	2090
October	1st to 10th	Night	4 2 1 3 3 3 3 3 5% 6% 67%	2090
	11th to 20th	Night	7% 2 1 3 2 2 2 2 3 5% 70%	2123
	21st to end	Night	8% 4 1 3 2 2 2 2 3 4 67%	2508
November	1st to 10th	Night	8% 4 1 3 2 3 2 2 4 4 66%	2503
	11th to 20th	Night	4 2 1 4 3 3 3 3 5% 5% 67%	2600
	21st to end	Night	11% 3 1 5% 3 3 4 4 5% 6% 56%	2600
December	1st to 10th	Night	10% 6% 2 5% 3 3 3 2 4 5% 57%	4250
	11th to 20th	Night	5% 4 1 5% 4 3 4 3 4 6% 61%	4816
	21st to end	Night	7% 5% 2 5% 3 3 3 2 4 5% 62%	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	31% 2 7% 19% 27% 13%	4078
	11th to 20th	Day	18% 2 5% 21% 39% 14%	4080
	21st to end	Day	35% 3 5% 15% 25% 19%	4902
February	1st to 10th	Day	28% 4 6% 17% 26% 19%	2000
	11th to 20th	Day	35% 3 6% 19% 23% 15%	1959
	21st to end	Day	30% 3 4 12% 28% 23%	1650
March	1st to 10th	Day	28% 2 4 12% 25% 28%	4601
	11th to 20th	Day	28% 3 9% 9% 23% 28%	4980
	21st to end	Day	25% 4 8% 18% 29% 16%	5464
April	1st to 10th	Day	26% 5% 9% 18% 24% 17%	2255
	11th to 20th	Day	29% 5% 8% 15% 25% 18%	2374
	21st to end	Day	27% 5% 7% 18% 30% 12%	2490
May	1st to 10th	Day	31% 5% 7% 19% 24% 13%	5900
	11th to 20th	Day	32% 4 7% 14% 28% 15%	5866
	21st to end	Day	33% 6% 10% 25% 16% 11%	6447
June	1st to 10th	Day	21% 7% 13% 30% 23% 6%	2588
	11th to 20th	Day	18% 6% 12% 30% 25% 9%	2470
	21st to end	Day	21% 7% 11% 26% 25% 10%	2470
July	1st to 10th	Day	27% 6% 12% 33% 19% 4	4056
	11th to 20th	Day	17% 3 13% 34% 29% 4	4051
	21st to end	Day	18% 4 10% 31% 32% 5%	4325
August	1st to 10th	Day	14% 3 10% 27% 37% 8%	3946
	11th to 20th	Day	17% 5% 11% 34% 27% 6%	3762
	21st to end	Day	21% 6% 17% 26% 25% 5%	4179
September	1st to 10th	Day	31% 5% 10% 20% 24% 10%	2123
	11th to 20th	Day	32% 7% 9% 21% 24% 8%	2090
	21st to end	Day	25% 5% 8% 18% 30% 14%	2090
October	1st to 10th	Day	12% 3 7% 13% 35% 29%	3480
	11th to 20th	Day	19% 2 6% 24% 25% 24%	3367
	21st to end	Day	16% 1 3 27% 39% 14%	3428
November	1st to 10th	Day	23% 4 7% 23% 27% 16%	1792
	11th to 20th	Day	19% 4 9% 22% 29% 18%	1800
	21st to end	Day	29% 3 5% 20% 29% 15%	1800
December	1st to 10th	Day	35% 2 3 21% 28% 10%	2940
	11th to 20th	Day	26% 4 8% 17% 28% 18%	3389
	21st to end	Day	25% 2 4 23% 29% 16%	4488
January	1st to 10th	Night	27% 3 5% 22% 32% 10%	5888
	11th to 20th	Night	18% 2 5% 20% 34% 21%	5900
	21st to end	Night	33% 3 6% 15% 26% 17%	6104
February	1st to 10th	Night	28% 3 7% 15% 25% 22%	2400
	11th to 20th	Night	32% 3 8% 16% 23% 18%	2338
	21st to end	Night	25% 4 6% 14% 25% 26%	1980
March	1st to 10th	Night	28% 3 4 11% 25% 28%	5266
	11th to 20th	Night	25% 3 8% 15% 15% 34%	4980
	21st to end	Night	24% 4 7% 18% 30% 17%	5467
April	1st to 10th	Night	24% 5% 9% 20% 20% 22%	2140
	11th to 20th	Night	25% 5% 11% 17% 23% 19%	1977
	21st to end	Night	22% 4 10% 22% 28% 13%	1910
May	1st to 10th	Night	30% 6% 8% 20% 21% 15%	4080
	11th to 20th	Night	26% 6% 9% 16% 24% 20%	4054
	21st to end	Night	28% 6% 13% 21% 19% 13%	4452
June	1st to 10th	Night	18% 7% 17% 30% 22% 5%	1796
	11th to 20th	Night	16% 6% 13% 29% 27% 10%	1710
	21st to end	Night	17% 4 11% 30% 25% 12%	1710
July	1st to 10th	Night	22% 5% 11% 37% 21% 4	2805
	11th to 20th	Night	13% 2 8% 38% 32% 7%	2796
	21st to end	Night	16% 4 11% 32% 34% 3	2999
August	1st to 10th	Night	11% 2 8% 26% 44% 9%	2952
	11th to 20th	Night	14% 3 14% 34% 27% 8%	3143
	21st to end	Night	19% 5% 19% 26% 26% 5%	3487
September	1st to 10th	Night	25% 7% 8% 23% 23% 13%	2057
	11th to 20th	Night	29% 5% 13% 21% 23% 9%	2090
	21st to end	Night	24% 5% 7% 20% 27% 18%	2090
October	1st to 10th	Night	10% 3 7% 13% 33% 33%	3480
	11th to 20th	Night	14% 2 8% 20% 28% 27%	3518
	21st to end	Night	16% 2 3 24% 40% 15%	4120
November	1st to 10th	Night	22% 3 8% 21% 26% 20%	2503
	11th to 20th	Night	19% 5% 7% 20% 29% 20%	2600
	21st to end	Night	29% 4 5% 16% 31% 15%	2600
December	1st to 10th	Night	31% 2 5% 24% 25% 13%	4250
	11th to 20th	Night	25% 3 7% 19% 30% 17%	4817
	21st to end	Night	26% 4 4 24% 26% 18%	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	9% 15% 42% 28% 6% 1	300
	11th to 20th	Day	14% 16% 31% 29% 8% 2	300
	21st to end	Day	14% 14% 37% 26% 8% 1	330
February	1st to 10th	Day	15% 13% 43% 24% 6%	300
	11th to 20th	Day	19% 14% 44% 19% 4	300
	21st to end	Day	20% 16% 44% 14% 6%	249
March	1st to 10th	Day	15% 14% 40% 26% 4	300
	11th to 20th	Day	19% 11% 41% 22% 5% 1	300
	21st to end	Day	10% 17% 47% 22% 5%	330
April	1st to 10th	Day	12% 14% 47% 20% 7% 1	355
	11th to 20th	Day	12% 17% 50% 17% 3 1	492
	21st to end	Day	10% 17% 41% 25% 6% 1	590
May	1st to 10th	Day	9% 11% 41% 32% 6% 1	703
	11th to 20th	Day	12% 10% 33% 30% 11% 5%	725
	21st to end	Day	8% 6% 37% 34% 12% 2	789
June	1st to 10th	Day	5% 3 22% 45% 21% 4	726
	11th to 20th	Day	3 1 23% 49% 19% 5%	680
	21st to end	Day	3 2 12% 41% 34% 8%	680
July	1st to 10th	Day	5% 2 8% 37% 35% 13%	671
	11th to 20th	Day	3 5% 39% 41% 11%	668
	21st to end	Day	3 6% 32% 41% 18%	739
August	1st to 10th	Day	3 1 3 32% 46% 15%	597
	11th to 20th	Day	5% 2 6% 31% 41% 15%	477
	21st to end	Day	3 1 7% 33% 40% 16%	539
September	1st to 10th	Day	12% 1 5% 25% 39% 19%	333
	11th to 20th	Day	5% 1 5% 31% 41% 17%	300
	21st to end	Day	13% 1 9% 28% 34% 15%	300
October	1st to 10th	Day	5% 2 15% 35% 34% 9%	300
	11th to 20th	Day	8% 6% 33% 37% 13% 3	300
	21st to end	Day	16% 7% 30% 30% 15% 2	330
November	1st to 10th	Day	14% 8% 30% 31% 15% 2	300
	11th to 20th	Day	10% 12% 31% 30% 14% 3	300
	21st to end	Day	15% 18% 34% 21% 9% 4	300
December	1st to 10th	Day	17% 8% 36% 27% 10% 2	300
	11th to 20th	Day	6% 15% 42% 28% 9%	300
	21st to end	Day	17% 12% 38% 28% 5%	330
January	1st to 10th	Night	10% 11% 40% 31% 8%	1000
	11th to 20th	Night	12% 12% 37% 32% 8%	1000
	21st to end	Night	11% 12% 39% 32% 6%	935
February	1st to 10th	Night	11% 12% 46% 27% 5%	800
	11th to 20th	Night	15% 14% 42% 26% 4	784
	21st to end	Night	12% 15% 50% 20% 2	660
March	1st to 10th	Night	11% 13% 48% 24% 4	757
	11th to 20th	Night	14% 14% 40% 28% 4	600
	21st to end	Night	6% 13% 55% 24% 2	660
April	1st to 10th	Night	8% 12% 54% 23% 3	600
	11th to 20th	Night	9% 15% 52% 23% 2	593
	21st to end	Night	8% 11% 53% 23% 5%	600
May	1st to 10th	Night	6% 10% 55% 26% 4	600
	11th to 20th	Night	8% 7% 46% 29% 10% 1	591
	21st to end	Night	5% 7% 45% 35% 7% 1	650
June	1st to 10th	Night	3 3 36% 43% 15% 1	599
	11th to 20th	Night	3 1 41% 50% 6%	570
	21st to end	Night	5% 1 25% 49% 19% 1	570
July	1st to 10th	Night	5% 1 14% 54% 25% 2	555
	11th to 20th	Night	3 1 13% 56% 27% 1	552
	21st to end	Night	2 1 7% 60% 30% 1	624
August	1st to 10th	Night	1 6% 62% 29% 1	567
	11th to 20th	Night	4 11% 48% 34% 2	564
	21st to end	Night	4 9% 47% 36% 4	627
September	1st to 10th	Night	9% 1 11% 50% 26% 4	570
	11th to 20th	Night	10% 1 15% 48% 26% 1	570
	21st to end	Night	10% 1 19% 47% 22% 1	570
October	1st to 10th	Night	4 2 31% 44% 19% 1	570
	11th to 20th	Night	7% 5% 35% 39% 13% 1	603
	21st to end	Night	11% 8% 33% 35% 13% 1	836
November	1st to 10th	Night	9% 6% 35% 36% 13% 1	943
	11th to 20th	Night	5% 10% 37% 37% 10% 1	1000
	21st to end	Night	13% 10% 37% 30% 10%	1000
December	1st to 10th	Night	11% 9% 37% 36% 6%	1000
	11th to 20th	Night	11% 10% 41% 33% 6%	1000
	21st to end	Night	10% 10% 43% 31% 7%	1100

Page generated at 2025-06-07 09:28:15. Version ac07

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