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 2024-03-18.

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 2 4 3 2 4 4 5% 7% 58%	79176
	Night	7% 4 1 3 3 2 3 4 5% 7% 61%	80686
Transparency	Day	26% 5% 9% 22% 26% 12%	78901
	Night	24% 5% 9% 21% 27% 15%	80481
Seeing	Day	8% 7% 25% 31% 21% 7%	14128
	Night	8% 7% 35% 36% 12% 1	24251

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	7% 6% 2 5% 4 2 3 3 3 5% 60%	2847
	11th to 20th	Day	6% 5% 2 3 2 1 3 3 4 6% 66%	2850
	21st to end	Day	13% 8% 2 4 3 2 3 3 4 5% 54%	3423
February	1st to 10th	Day	10% 5% 2 4 3 2 3 4 5% 5% 58%	1900
	11th to 20th	Day	9% 8% 2 5% 3 3 3 3 4 5% 55%	1849
	21st to end	Day	12% 7% 3 3 3 2 3 2 3 4 59%	1570
March	1st to 10th	Day	11% 5% 1 5% 3 3 4 4 6% 7% 50%	1939
	11th to 20th	Day	11% 4 2 4 4 2 4 3 4 6% 56%	2057
	21st to end	Day	6% 5% 3 4 3 2 4 4 4 6% 58%	2178
April	1st to 10th	Day	7% 3 2 4 3 3 4 4 5% 7% 58%	2029
	11th to 20th	Day	9% 5% 2 4 4 2 3 4 4 7% 57%	2134
	21st to end	Day	8% 4 2 4 4 2 4 4 4 6% 59%	2240
May	1st to 10th	Day	8% 4 2 4 4 2 4 4 5% 8% 56%	2340
	11th to 20th	Day	11% 4 2 3 4 3 4 4 6% 7% 52%	2302
	21st to end	Day	6% 3 2 4 5% 3 5% 5% 6% 9% 51%	2531
June	1st to 10th	Day	5% 3 2 3 3 2 4 4 5% 8% 61%	2340
	11th to 20th	Day	3 2 1 2 3 2 5% 4 6% 8% 65%	2340
	21st to end	Day	6% 2 1 3 4 3 4 5% 6% 8% 60%	2340
July	1st to 10th	Day	6% 3 2 4 5% 4 5% 7% 8% 11% 46%	2340
	11th to 20th	Day	4 2 1 3 3 3 4 4 5% 8% 64%	2340
	21st to end	Day	2 2 1 3 4 3 5% 5% 6% 10% 59%	2546
August	1st to 10th	Day	2 2 1 2 3 3 5% 4 5% 8% 65%	2254
	11th to 20th	Day	6% 4 1 5% 5% 2 5% 6% 7% 10% 48%	2123
	21st to end	Day	4 3 1 3 4 3 4 6% 6% 9% 56%	2376
September	1st to 10th	Day	9% 3 2 4 4 4 3 5% 5% 7% 54%	2012
	11th to 20th	Day	11% 5% 2 4 4 3 4 4 5% 7% 51%	1980
	21st to end	Day	9% 4 1 3 3 2 3 4 4 6% 61%	1980
October	1st to 10th	Day	4 3 1 3 3 2 4 3 4 7% 65%	1980
	11th to 20th	Day	8% 3 2 3 2 1 3 3 4 5% 67%	1929
	21st to end	Day	11% 4 1 3 3 2 2 2 3 4 65%	1980
November	1st to 10th	Day	7% 3 1 2 3 2 3 3 4 6% 65%	1701
	11th to 20th	Day	5% 4 1 3 3 2 3 4 5% 7% 65%	1710
	21st to end	Day	11% 5% 2 3 3 2 3 3 4 6% 59%	1710
December	1st to 10th	Day	11% 6% 1 4 3 3 3 4 4 6% 56%	1710
	11th to 20th	Day	7% 5% 2 3 4 2 4 6% 6% 7% 55%	2161
	21st to end	Day	9% 6% 2 4 4 2 3 3 3 4 62%	3135
January	1st to 10th	Night	7% 5% 1 4 3 2 2 3 4 6% 62%	4108
	11th to 20th	Night	8% 4 2 3 2 2 2 3 3 5% 66%	4120
	21st to end	Night	9% 8% 2 4 3 2 3 4 4 5% 56%	4272
February	1st to 10th	Night	9% 6% 2 4 4 2 3 3 3 6% 59%	2280
	11th to 20th	Night	11% 6% 2 4 3 2 4 3 4 6% 55%	2218
	21st to end	Night	9% 5% 1 4 2 2 2 4 4 5% 62%	1884
March	1st to 10th	Night	9% 5% 3 5% 4 3 4 5% 5% 6% 53%	2239
	11th to 20th	Night	11% 5% 2 4 3 2 3 3 3 5% 57%	2068
	21st to end	Night	5% 3 2 3 3 2 4 4 5% 7% 62%	2178
April	1st to 10th	Night	5% 3 2 3 4 2 3 4 5% 7% 62%	1926
	11th to 20th	Night	8% 3 2 3 3 3 4 3 5% 7% 59%	1777
	21st to end	Night	7% 3 1 3 3 1 2 3 4 7% 65%	1720
May	1st to 10th	Night	5% 3 2 4 4 3 4 3 4 7% 61%	1620
	11th to 20th	Night	8% 4 2 3 4 3 4 4 6% 10% 52%	1593
	21st to end	Night	5% 3 1 4 3 3 2 5% 7% 11% 57%	1745
June	1st to 10th	Night	3 2 1 2 3 3 3 5% 8% 10% 60%	1620
	11th to 20th	Night	2 1 1 2 3 3 4 4 6% 10% 63%	1620
	21st to end	Night	4 3 1 3 3 2 3 3 4 8% 67%	1620
July	1st to 10th	Night	5% 3 1 3 3 3 5% 5% 6% 11% 55%	1620
	11th to 20th	Night	3 1 1 2 2 2 3 4 4 9% 69%	1620
	21st to end	Night	1 2 1 2 3 2 4 4 6% 12% 63%	1772
August	1st to 10th	Night	1 1 1 2 3 2 3 3 5% 10% 70%	1681
	11th to 20th	Night	4 3 1 4 4 4 5% 4 6% 9% 56%	1778
	21st to end	Night	3 2 1 3 2 2 4 4 6% 10% 62%	1980
September	1st to 10th	Night	7% 2 1 4 4 3 4 4 5% 6% 58%	1948
	11th to 20th	Night	10% 3 2 5% 5% 2 4 5% 6% 8% 52%	1980
	21st to end	Night	8% 3 1 2 4 2 4 4 4 6% 61%	1980
October	1st to 10th	Night	4 2 2 2 3 2 4 4 5% 7% 66%	1980
	11th to 20th	Night	7% 2 1 3 3 1 2 3 3 5% 70%	2011
	21st to end	Night	9% 4 1 3 2 2 3 3 3 5% 66%	2376
November	1st to 10th	Night	7% 3 1 3 3 2 2 3 4 4 67%	2374
	11th to 20th	Night	4 2 1 3 3 2 3 4 5% 6% 66%	2470
	21st to end	Night	12% 3 2 4 4 2 4 4 4 6% 56%	2470
December	1st to 10th	Night	9% 4 1 3 3 2 3 2 4 7% 62%	2470
	11th to 20th	Night	7% 4 2 5% 5% 2 4 4 4 7% 57%	3036
	21st to end	Night	8% 5% 2 4 4 2 3 3 4 5% 60%	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	27% 3 6% 15% 31% 17%	2848
	11th to 20th	Day	21% 3 7% 18% 35% 15%	2850
	21st to end	Day	33% 4 6% 18% 28% 10%	3423
February	1st to 10th	Day	28% 4 6% 17% 26% 18%	1900
	11th to 20th	Day	34% 3 5% 19% 24% 16%	1859
	21st to end	Day	31% 3 4 12% 28% 22%	1570
March	1st to 10th	Day	33% 4 8% 15% 26% 14%	1939
	11th to 20th	Day	31% 5% 8% 16% 26% 14%	2057
	21st to end	Day	28% 4 9% 21% 24% 15%	2178
April	1st to 10th	Day	26% 6% 9% 20% 23% 17%	2029
	11th to 20th	Day	29% 5% 9% 14% 25% 19%	2134
	21st to end	Day	27% 5% 7% 18% 30% 12%	2240
May	1st to 10th	Day	29% 5% 9% 21% 23% 13%	2340
	11th to 20th	Day	32% 6% 12% 20% 22% 8%	2306
	21st to end	Day	30% 8% 13% 24% 20% 5%	2531
June	1st to 10th	Day	21% 7% 14% 28% 23% 7%	2340
	11th to 20th	Day	17% 6% 13% 31% 24% 9%	2340
	21st to end	Day	22% 7% 11% 26% 25% 10%	2340
July	1st to 10th	Day	29% 10% 17% 27% 14% 3	2276
	11th to 20th	Day	18% 6% 12% 31% 28% 6%	2271
	21st to end	Day	17% 7% 16% 35% 22% 2	2405
August	1st to 10th	Day	17% 5% 13% 32% 27% 5%	2240
	11th to 20th	Day	29% 8% 15% 26% 18% 4	2123
	21st to end	Day	22% 9% 14% 26% 24% 5%	2376
September	1st to 10th	Day	30% 5% 11% 21% 25% 8%	2012
	11th to 20th	Day	33% 8% 9% 21% 22% 7%	1980
	21st to end	Day	26% 5% 8% 18% 29% 14%	1980
October	1st to 10th	Day	20% 6% 12% 23% 27% 13%	1980
	11th to 20th	Day	22% 4 7% 17% 29% 21%	1929
	21st to end	Day	26% 2 5% 21% 28% 18%	1980
November	1st to 10th	Day	22% 4 8% 24% 27% 16%	1701
	11th to 20th	Day	19% 4 10% 22% 29% 16%	1710
	21st to end	Day	29% 3 5% 20% 28% 15%	1710
December	1st to 10th	Day	30% 4 5% 19% 30% 11%	1710
	11th to 20th	Day	26% 6% 9% 16% 26% 16%	2159
	21st to end	Day	27% 3 4 20% 28% 17%	3135
January	1st to 10th	Night	22% 4 5% 18% 36% 14%	4108
	11th to 20th	Night	21% 3 7% 20% 29% 20%	4120
	21st to end	Night	30% 5% 7% 16% 29% 14%	4272
February	1st to 10th	Night	29% 3 7% 16% 25% 20%	2280
	11th to 20th	Night	31% 4 7% 16% 24% 19%	2218
	21st to end	Night	26% 4 5% 14% 26% 25%	1884
March	1st to 10th	Night	32% 5% 7% 14% 24% 18%	2239
	11th to 20th	Night	32% 3 7% 19% 22% 16%	2068
	21st to end	Night	22% 5% 10% 20% 27% 16%	2178
April	1st to 10th	Night	22% 6% 10% 22% 20% 20%	1926
	11th to 20th	Night	25% 5% 12% 16% 22% 19%	1777
	21st to end	Night	21% 5% 10% 22% 29% 13%	1720
May	1st to 10th	Night	24% 6% 9% 21% 24% 17%	1620
	11th to 20th	Night	28% 8% 14% 20% 21% 9%	1594
	21st to end	Night	21% 8% 18% 25% 22% 6%	1746
June	1st to 10th	Night	17% 7% 18% 31% 22% 6%	1620
	11th to 20th	Night	15% 6% 13% 30% 26% 10%	1620
	21st to end	Night	17% 5% 11% 30% 25% 12%	1620
July	1st to 10th	Night	23% 9% 13% 32% 20% 4	1575
	11th to 20th	Night	14% 4 11% 30% 31% 11%	1566
	21st to end	Night	12% 6% 15% 34% 30% 2	1673
August	1st to 10th	Night	12% 4 10% 32% 34% 7%	1671
	11th to 20th	Night	23% 6% 14% 28% 21% 7%	1778
	21st to end	Night	17% 8% 15% 26% 27% 8%	1980
September	1st to 10th	Night	25% 7% 9% 23% 24% 12%	1948
	11th to 20th	Night	30% 5% 14% 21% 21% 8%	1980
	21st to end	Night	24% 5% 7% 20% 27% 17%	1980
October	1st to 10th	Night	18% 5% 13% 23% 26% 16%	1980
	11th to 20th	Night	20% 3 6% 18% 28% 26%	2011
	21st to end	Night	23% 3 5% 20% 28% 20%	2376
November	1st to 10th	Night	22% 4 8% 22% 26% 19%	2374
	11th to 20th	Night	19% 5% 7% 20% 29% 19%	2470
	21st to end	Night	30% 5% 5% 15% 30% 16%	2470
December	1st to 10th	Night	24% 4 8% 21% 26% 16%	2470
	11th to 20th	Night	28% 4 6% 19% 25% 18%	3037
	21st to end	Night	26% 5% 4 17% 28% 19%	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	6% 16% 42% 29% 6% 1	270
	11th to 20th	Day	14% 16% 30% 30% 9% 2	270
	21st to end	Day	13% 13% 38% 27% 8% 1	297
February	1st to 10th	Day	15% 13% 41% 24% 6%	270
	11th to 20th	Day	17% 13% 44% 21% 4	270
	21st to end	Day	21% 16% 46% 13% 4	225
March	1st to 10th	Day	13% 14% 41% 27% 4	270
	11th to 20th	Day	18% 11% 41% 23% 6% 1	261
	21st to end	Day	9% 17% 46% 22% 5%	264
April	1st to 10th	Day	9% 12% 49% 22% 7%	289
	11th to 20th	Day	11% 16% 50% 18% 3 1	412
	21st to end	Day	9% 18% 41% 24% 7% 1	500
May	1st to 10th	Day	8% 11% 41% 33% 6% 1	603
	11th to 20th	Day	12% 8% 31% 32% 12% 5%	625
	21st to end	Day	7% 6% 36% 35% 13% 3	679
June	1st to 10th	Day	5% 3 19% 46% 22% 5%	630
	11th to 20th	Day	2 1 21% 51% 20% 5%	630
	21st to end	Day	3 2 12% 39% 35% 8%	630
July	1st to 10th	Day	5% 2 8% 35% 36% 14%	621
	11th to 20th	Day	3 4 37% 44% 12%	618
	21st to end	Day	3 3 31% 44% 19%	684
August	1st to 10th	Day	3 1 3 32% 46% 16%	552
	11th to 20th	Day	6% 2 7% 28% 42% 16%	437
	21st to end	Day	3 1 7% 32% 40% 17%	495
September	1st to 10th	Day	9% 4 25% 40% 21%	302
	11th to 20th	Day	4 1 5% 29% 43% 17%	270
	21st to end	Day	14% 1 9% 26% 36% 15%	270
October	1st to 10th	Day	5% 3 16% 34% 34% 8%	270
	11th to 20th	Day	8% 6% 33% 35% 14% 4	270
	21st to end	Day	18% 5% 28% 30% 15% 2	297
November	1st to 10th	Day	13% 6% 30% 32% 16% 2	270
	11th to 20th	Day	10% 11% 31% 31% 14% 3	270
	21st to end	Day	15% 18% 33% 22% 9% 3	270
December	1st to 10th	Day	16% 9% 36% 28% 10% 1	270
	11th to 20th	Day	6% 16% 43% 27% 8%	270
	21st to end	Day	16% 12% 39% 28% 4	297
January	1st to 10th	Night	9% 11% 40% 31% 8%	950
	11th to 20th	Night	12% 12% 36% 32% 8%	950
	21st to end	Night	11% 11% 40% 32% 6%	889
February	1st to 10th	Night	11% 12% 46% 27% 5%	760
	11th to 20th	Night	14% 13% 43% 27% 4	744
	21st to end	Night	12% 15% 52% 18% 3	628
March	1st to 10th	Night	11% 13% 48% 25% 4	719
	11th to 20th	Night	14% 13% 40% 28% 4	564
	21st to end	Night	6% 13% 55% 24% 2	594
April	1st to 10th	Night	6% 11% 57% 22% 4	540
	11th to 20th	Night	8% 13% 52% 24% 2	533
	21st to end	Night	7% 11% 54% 23% 5%	540
May	1st to 10th	Night	5% 9% 56% 26% 4	540
	11th to 20th	Night	8% 5% 46% 30% 10% 1	531
	21st to end	Night	5% 6% 44% 36% 8% 1	584
June	1st to 10th	Night	3 2 34% 44% 16% 1	540
	11th to 20th	Night	2 1 39% 52% 6%	540
	21st to end	Night	5% 1 25% 48% 19% 1	540
July	1st to 10th	Night	5% 1 13% 53% 27% 2	525
	11th to 20th	Night	2 1 11% 57% 27% 2	522
	21st to end	Night	2 1 6% 60% 31% 1	591
August	1st to 10th	Night	1 6% 61% 30% 1	537
	11th to 20th	Night	4 10% 46% 36% 2	534
	21st to end	Night	3 1 8% 46% 38% 4	594
September	1st to 10th	Night	8% 1 11% 50% 26% 4	540
	11th to 20th	Night	11% 1 14% 47% 27% 1	540
	21st to end	Night	10% 1 19% 48% 22% 1	540
October	1st to 10th	Night	4 2 32% 43% 17% 1	540
	11th to 20th	Night	8% 5% 34% 40% 13% 1	571
	21st to end	Night	11% 7% 32% 35% 13% 1	792
November	1st to 10th	Night	9% 5% 35% 37% 14% 1	894
	11th to 20th	Night	5% 10% 37% 37% 10% 1	950
	21st to end	Night	13% 9% 38% 30% 10%	950
December	1st to 10th	Night	11% 9% 37% 36% 7%	950
	11th to 20th	Night	11% 10% 41% 33% 5%	950
	21st to end	Night	10% 10% 43% 31% 7%	1045

Page generated at 2024-03-15 13:01:42. Version ac07

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