Austin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Austin clear sky chart from 2005-11-06 to 2025-11-03.

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	13% 6% 2 5% 4 4 4 4 5% 7% 46%	126739
	Night	15% 6% 2 5% 3 3 3 3 5% 7% 50%	123605
Transparency	Day	36% 4 10% 21% 19% 10%	130495
	Night	35% 4 10% 20% 19% 12%	127912
Seeing	Day	13% 6% 20% 27% 25% 9%	16186
	Night	16% 6% 24% 36% 17% 2	26040

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% 9% 2 6% 3 3 3 2 4 4 47%	4077
	11th to 20th	Day	15% 5% 2 4 2 2 2 3 5% 6% 54%	4080
	21st to end	Day	27% 7% 2 4 2 3 2 2 3 5% 42%	4715
February	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 4 5% 45%	2000
	11th to 20th	Day	20% 7% 2 5% 4 3 3 3 4 6% 44%	1949
	21st to end	Day	20% 6% 2 4 3 3 3 2 3 4 49%	1650
March	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 4 5% 51%	4933
	11th to 20th	Day	16% 7% 2 5% 4 3 3 2 4 5% 49%	4980
	21st to end	Day	17% 8% 2 5% 3 3 3 3 4 6% 44%	5462
April	1st to 10th	Day	16% 8% 3 6% 4 3 4 3 5% 6% 42%	2200
	11th to 20th	Day	18% 6% 2 6% 4 3 4 3 5% 5% 42%	2176
	21st to end	Day	15% 7% 3 6% 4 4 4 3 5% 6% 43%	2542
May	1st to 10th	Day	21% 8% 3 6% 4 4 4 4 6% 7% 32%	5862
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 45%	5862
	21st to end	Day	13% 7% 2 6% 5% 6% 6% 5% 7% 10% 34%	6434
June	1st to 10th	Day	7% 4 1 6% 4 4 4 4 7% 9% 49%	2600
	11th to 20th	Day	9% 4 2 5% 5% 4 6% 4 7% 9% 45%	2600
	21st to end	Day	6% 6% 2 6% 6% 6% 6% 5% 8% 10% 39%	2600
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	5900
	11th to 20th	Day	5% 4 2 5% 4 5% 6% 5% 8% 12% 43%	5900
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	6422
August	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 9% 72%	4234
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 11% 58%	3940
	21st to end	Day	4 3 1 5% 5% 4 6% 5% 8% 11% 48%	4089
September	1st to 10th	Day	9% 6% 2 8% 5% 4 4 3 6% 7% 46%	2200
	11th to 20th	Day	11% 5% 3 7% 4 4 5% 5% 6% 7% 43%	2200
	21st to end	Day	7% 4 2 5% 3 4 6% 4 7% 7% 50%	2200
October	1st to 10th	Day	7% 4 2 4 3 3 4 3 5% 7% 58%	2200
	11th to 20th	Day	13% 5% 1 4 3 4 3 3 5% 5% 55%	2035
	21st to end	Day	12% 5% 1 4 3 3 3 3 4 5% 59%	2200
November	1st to 10th	Day	15% 6% 2 6% 4 4 3 3 4 7% 46%	1978
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 4 5% 52%	1900
	21st to end	Day	18% 7% 2 5% 4 3 3 3 5% 5% 46%	1800
December	1st to 10th	Day	24% 7% 3 6% 4 3 3 2 3 6% 40%	2940
	11th to 20th	Day	18% 8% 2 5% 4 3 4 3 5% 5% 43%	3391
	21st to end	Day	15% 5% 2 4 2 2 3 2 3 4 56%	4488
January	1st to 10th	Night	20% 7% 2 4 2 2 2 2 3 5% 51%	5888
	11th to 20th	Night	13% 3 1 2 2 2 3 3 4 5% 64%	5900
	21st to end	Night	28% 6% 2 5% 3 2 2 2 4 5% 40%	6306
February	1st to 10th	Night	20% 7% 2 5% 3 3 3 2 4 5% 47%	2400
	11th to 20th	Night	21% 6% 2 5% 2 3 3 2 4 5% 48%	2338
	21st to end	Night	21% 7% 2 4 3 3 3 3 4 5% 45%	1980
March	1st to 10th	Night	17% 7% 2 4 3 4 4 3 5% 7% 45%	4919
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 5% 48%	4980
	21st to end	Night	20% 9% 2 5% 3 3 3 3 4 5% 42%	5467
April	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 5% 7% 46%	2200
	11th to 20th	Night	19% 6% 2 5% 3 4 3 4 4 6% 45%	2173
	21st to end	Night	19% 7% 2 4 3 3 3 2 4 7% 46%	1852
May	1st to 10th	Night	26% 8% 2 6% 3 3 4 3 5% 7% 33%	4053
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 8% 48%	4053
	21st to end	Night	15% 8% 2 6% 4 4 5% 4 6% 8% 38%	4443
June	1st to 10th	Night	6% 3 1 3 3 3 4 3 6% 9% 59%	1800
	11th to 20th	Night	6% 4 1 5% 3 3 5% 4 5% 9% 57%	1800
	21st to end	Night	6% 4 2 5% 5% 3 4 4 7% 8% 53%	1800
July	1st to 10th	Night	9% 6% 2 6% 4 5% 5% 4 7% 9% 42%	4078
	11th to 20th	Night	4 4 1 4 3 4 5% 4 7% 13% 51%	4077
	21st to end	Night	6% 6% 2 6% 4 4 5% 4 7% 9% 46%	4449
August	1st to 10th	Night	1 1 1 2 1 2 3 3 4 8% 75%	2926
	11th to 20th	Night	3 2 1 4 2 3 4 4 7% 11% 59%	3113
	21st to end	Night	4 3 1 4 3 3 5% 4 7% 11% 55%	3811
September	1st to 10th	Night	8% 4 2 6% 4 4 4 3 6% 8% 51%	2200
	11th to 20th	Night	10% 5% 3 6% 5% 4 4 4 6% 7% 47%	2200
	21st to end	Night	7% 4 2 5% 3 4 4 3 6% 8% 54%	2200
October	1st to 10th	Night	6% 3 1 4 4 3 3 3 4 6% 63%	2200
	11th to 20th	Night	13% 4 1 4 3 2 3 3 4 7% 57%	2343
	21st to end	Night	15% 4 2 3 2 2 3 2 3 5% 60%	2640
November	1st to 10th	Night	15% 5% 2 5% 3 3 3 3 4 6% 52%	2365
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 6% 56%	2495
	21st to end	Night	19% 5% 2 4 3 3 3 3 4 6% 47%	2600
December	1st to 10th	Night	22% 8% 3 6% 3 4 4 2 4 4 41%	4250
	11th to 20th	Night	21% 9% 2 5% 3 2 3 2 3 4 47%	4816
	21st to end	Night	19% 6% 1 3 2 2 2 2 3 4 56%	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	42% 2 3 23% 20% 10%	4078
	11th to 20th	Day	33% 2 5% 18% 25% 18%	4080
	21st to end	Day	48% 2 3 9% 24% 14%	4715
February	1st to 10th	Day	44% 3 5% 13% 21% 15%	2000
	11th to 20th	Day	43% 3 7% 17% 18% 11%	1959
	21st to end	Day	42% 2 5% 18% 18% 15%	1650
March	1st to 10th	Day	36% 3 5% 19% 17% 20%	4933
	11th to 20th	Day	39% 2 6% 9% 16% 28%	4980
	21st to end	Day	42% 3 8% 18% 21% 8%	5464
April	1st to 10th	Day	43% 4 7% 17% 15% 13%	2200
	11th to 20th	Day	44% 3 7% 15% 19% 11%	2176
	21st to end	Day	41% 5% 6% 20% 19% 9%	2542
May	1st to 10th	Day	49% 4 9% 20% 14% 4	5900
	11th to 20th	Day	38% 4 11% 19% 22% 7%	5866
	21st to end	Day	44% 5% 11% 25% 13% 2	6447
June	1st to 10th	Day	30% 5% 14% 27% 20% 4	2600
	11th to 20th	Day	32% 7% 11% 26% 19% 5%	2600
	21st to end	Day	37% 9% 11% 24% 17% 3	2600
July	1st to 10th	Day	40% 7% 17% 30% 5% 1	5836
	11th to 20th	Day	29% 8% 18% 30% 13% 1	5831
	21st to end	Day	34% 7% 17% 25% 15% 2	6240
August	1st to 10th	Day	11% 4 12% 42% 30% 1	4220
	11th to 20th	Day	19% 5% 21% 40% 12% 2	3979
	21st to end	Day	26% 9% 20% 25% 18% 2	4088
September	1st to 10th	Day	37% 6% 10% 21% 16% 10%	2200
	11th to 20th	Day	39% 6% 11% 20% 19% 5%	2200
	21st to end	Day	31% 6% 9% 22% 18% 14%	2200
October	1st to 10th	Day	16% 3 6% 13% 25% 37%	3590
	11th to 20th	Day	20% 3 8% 19% 30% 19%	3288
	21st to end	Day	27% 3 5% 20% 31% 15%	3538
November	1st to 10th	Day	39% 4 8% 18% 20% 11%	1978
	11th to 20th	Day	35% 3 7% 18% 21% 15%	1900
	21st to end	Day	41% 3 6% 17% 20% 13%	1800
December	1st to 10th	Day	48% 3 6% 17% 17% 9%	2940
	11th to 20th	Day	43% 3 7% 11% 23% 12%	3389
	21st to end	Day	34% 2 4 17% 27% 15%	4488
January	1st to 10th	Night	38% 3 4 20% 23% 13%	5888
	11th to 20th	Night	26% 1 4 18% 32% 19%	5900
	21st to end	Night	49% 2 3 11% 21% 15%	6306
February	1st to 10th	Night	41% 3 5% 13% 20% 18%	2400
	11th to 20th	Night	41% 3 6% 17% 19% 14%	2338
	21st to end	Night	43% 3 5% 15% 18% 16%	1980
March	1st to 10th	Night	39% 4 6% 17% 19% 15%	4919
	11th to 20th	Night	40% 3 8% 10% 14% 25%	4980
	21st to end	Night	45% 3 7% 17% 18% 10%	5467
April	1st to 10th	Night	39% 3 9% 18% 16% 15%	2200
	11th to 20th	Night	41% 3 10% 14% 16% 15%	2173
	21st to end	Night	40% 3 10% 20% 18% 9%	1852
May	1st to 10th	Night	51% 4 8% 19% 13% 5%	4080
	11th to 20th	Night	35% 4 12% 21% 19% 8%	4054
	21st to end	Night	43% 4 14% 26% 11% 2	4452
June	1st to 10th	Night	21% 6% 18% 30% 22% 3	1800
	11th to 20th	Night	25% 6% 14% 30% 20% 5%	1800
	21st to end	Night	27% 8% 18% 28% 17% 3	1800
July	1st to 10th	Night	36% 8% 24% 26% 5% 1	4035
	11th to 20th	Night	25% 7% 24% 32% 12% 1	4026
	21st to end	Night	32% 8% 20% 25% 12% 4	4320
August	1st to 10th	Night	10% 4 15% 45% 26% 1	2916
	11th to 20th	Night	19% 5% 30% 32% 12% 2	3140
	21st to end	Night	22% 10% 22% 27% 16% 2	3811
September	1st to 10th	Night	31% 6% 15% 24% 16% 8%	2200
	11th to 20th	Night	35% 7% 14% 23% 15% 6%	2200
	21st to end	Night	27% 6% 14% 23% 17% 13%	2200
October	1st to 10th	Night	16% 3 7% 16% 20% 38%	3590
	11th to 20th	Night	20% 3 8% 18% 31% 21%	3816
	21st to end	Night	25% 2 5% 20% 31% 17%	4252
November	1st to 10th	Night	34% 4 9% 18% 22% 13%	2365
	11th to 20th	Night	32% 4 8% 19% 21% 16%	2495
	21st to end	Night	39% 3 8% 17% 18% 15%	2600
December	1st to 10th	Night	49% 2 5% 18% 17% 10%	4250
	11th to 20th	Night	43% 3 6% 9% 23% 16%	4817
	21st to end	Night	35% 2 4 15% 29% 15%	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	18% 14% 35% 23% 9% 1	300
	11th to 20th	Day	23% 14% 26% 27% 8% 2	300
	21st to end	Day	22% 12% 34% 23% 8% 1	330
February	1st to 10th	Day	26% 12% 31% 21% 9% 1	300
	11th to 20th	Day	25% 15% 32% 21% 6% 1	300
	21st to end	Day	26% 14% 39% 18% 3	249
March	1st to 10th	Day	23% 13% 33% 24% 6% 1	300
	11th to 20th	Day	19% 15% 36% 23% 5% 1	300
	21st to end	Day	18% 15% 37% 22% 7% 1	330
April	1st to 10th	Day	19% 15% 37% 22% 6% 1	300
	11th to 20th	Day	21% 11% 36% 21% 10% 1	294
	21st to end	Day	19% 11% 34% 26% 9% 1	642
May	1st to 10th	Day	18% 9% 33% 28% 11%	703
	11th to 20th	Day	18% 9% 25% 31% 16% 3	725
	21st to end	Day	14% 5% 23% 33% 21% 3	789
June	1st to 10th	Day	8% 2 13% 37% 31% 9%	730
	11th to 20th	Day	9% 1 14% 42% 27% 7%	730
	21st to end	Day	6% 2 12% 31% 35% 14%	730
July	1st to 10th	Day	9% 2 10% 30% 36% 14%	721
	11th to 20th	Day	6% 2 4 28% 47% 14%	718
	21st to end	Day	5% 2 5% 25% 47% 16%	794
August	1st to 10th	Day	3 4 23% 51% 18%	726
	11th to 20th	Day	6% 1 3 27% 47% 17%	575
	21st to end	Day	5% 1 6% 21% 33% 34%	451
September	1st to 10th	Day	9% 1 8% 21% 34% 28%	330
	11th to 20th	Day	7% 1 5% 23% 38% 26%	330
	21st to end	Day	10% 1 9% 24% 32% 24%	330
October	1st to 10th	Day	5% 1 10% 31% 38% 16%	330
	11th to 20th	Day	10% 2 19% 34% 25% 10%	330
	21st to end	Day	18% 9% 23% 24% 20% 6%	363
November	1st to 10th	Day	20% 6% 22% 28% 18% 6%	306
	11th to 20th	Day	18% 6% 26% 28% 19% 4	300
	21st to end	Day	19% 13% 31% 23% 11% 3	300
December	1st to 10th	Day	19% 7% 30% 26% 13% 5%	300
	11th to 20th	Day	23% 11% 30% 23% 13% 1	300
	21st to end	Day	19% 10% 31% 26% 12% 2	330
January	1st to 10th	Night	20% 8% 30% 32% 9% 1	1000
	11th to 20th	Night	21% 10% 29% 32% 9%	1000
	21st to end	Night	22% 8% 31% 32% 7%	1020
February	1st to 10th	Night	24% 10% 30% 29% 6%	800
	11th to 20th	Night	27% 9% 35% 26% 3	784
	21st to end	Night	27% 12% 37% 23% 2	660
March	1st to 10th	Night	22% 11% 34% 29% 4	600
	11th to 20th	Night	21% 11% 32% 32% 5%	600
	21st to end	Night	17% 10% 40% 30% 3	660
April	1st to 10th	Night	19% 8% 39% 31% 4	600
	11th to 20th	Night	21% 9% 39% 26% 4	593
	21st to end	Night	18% 9% 38% 28% 7%	600
May	1st to 10th	Night	17% 10% 35% 31% 7%	600
	11th to 20th	Night	15% 6% 30% 37% 11% 1	591
	21st to end	Night	15% 4 31% 34% 16%	650
June	1st to 10th	Night	7% 2 17% 47% 26% 2	600
	11th to 20th	Night	7% 2 25% 49% 16% 1	600
	21st to end	Night	6% 2 16% 44% 29% 4	600
July	1st to 10th	Night	9% 2 9% 45% 31% 4	585
	11th to 20th	Night	5% 1 10% 48% 32% 3	582
	21st to end	Night	5% 1 8% 45% 38% 3	657
August	1st to 10th	Night	1 6% 52% 37% 4	597
	11th to 20th	Night	6% 7% 47% 35% 5%	594
	21st to end	Night	5% 5% 37% 46% 6%	660
September	1st to 10th	Night	9% 1 8% 38% 40% 5%	600
	11th to 20th	Night	11% 2 7% 33% 42% 5%	600
	21st to end	Night	9% 1 12% 37% 37% 4	600
October	1st to 10th	Night	6% 2 9% 45% 34% 5%	600
	11th to 20th	Night	13% 2 18% 39% 25% 2	743
	21st to end	Night	16% 7% 24% 30% 21% 2	880
November	1st to 10th	Night	15% 3 19% 40% 21% 1	789
	11th to 20th	Night	14% 6% 26% 36% 17% 2	895
	21st to end	Night	21% 7% 28% 30% 13% 1	1000
December	1st to 10th	Night	19% 8% 26% 36% 12% 1	1000
	11th to 20th	Night	25% 8% 25% 34% 7% 1	1000
	21st to end	Night	22% 6% 29% 35% 8%	1100

Page generated at 2025-10-31 01:02:38. Version ac07

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