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 2024-05-13.

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 3 5% 7% 46%	84054
	Night	15% 6% 2 4 3 3 3 3 5% 7% 50%	85519
Transparency	Day	38% 4 9% 20% 20% 9%	83779
	Night	35% 4 10% 20% 20% 11%	85314
Seeing	Day	13% 5% 19% 27% 25% 10%	14135
	Night	16% 6% 24% 36% 18% 2	24193

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	15% 8% 2 5% 3 2 3 2 4 6% 50%	2847
	11th to 20th	Day	18% 5% 1 3 2 2 2 2 4 6% 56%	2850
	21st to end	Day	20% 8% 3 5% 3 3 3 2 4 7% 43%	3292
February	1st to 10th	Day	21% 7% 2 5% 3 3 2 3 4 5% 45%	1900
	11th to 20th	Day	20% 7% 2 4 4 3 3 3 4 6% 44%	1849
	21st to end	Day	19% 6% 2 4 3 3 3 2 3 4 49%	1570
March	1st to 10th	Day	16% 7% 3 7% 4 4 3 3 5% 5% 42%	3433
	11th to 20th	Day	22% 9% 3 6% 5% 5% 4 3 4 6% 32%	3480
	21st to end	Day	16% 8% 2 5% 3 3 4 3 5% 7% 44%	3814
April	1st to 10th	Day	16% 8% 3 6% 5% 3 4 3 5% 6% 42%	2090
	11th to 20th	Day	19% 6% 2 6% 4 3 4 3 5% 5% 42%	2066
	21st to end	Day	15% 7% 3 6% 4 3 4 3 5% 6% 44%	2414
May	1st to 10th	Day	17% 8% 2 6% 5% 4 4 4 5% 6% 39%	2470
	11th to 20th	Day	16% 7% 3 7% 4 5% 4 4 6% 6% 38%	2330
	21st to end	Day	16% 7% 2 6% 5% 6% 6% 4 6% 9% 33%	2531
June	1st to 10th	Day	7% 4 1 6% 4 4 4 4 7% 9% 50%	2340
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 4 7% 9% 46%	2340
	21st to end	Day	7% 6% 2 6% 7% 6% 6% 5% 8% 10% 37%	2340
July	1st to 10th	Day	9% 7% 3 6% 6% 6% 6% 4 6% 9% 38%	2340
	11th to 20th	Day	5% 3 1 4 5% 4 5% 5% 8% 11% 49%	2340
	21st to end	Day	4 4 2 4 5% 5% 4 5% 7% 10% 50%	2546
August	1st to 10th	Day	2 2 1 3 3 3 3 4 6% 10% 63%	2328
	11th to 20th	Day	6% 3 2 4 4 4 4 4 6% 9% 53%	2175
	21st to end	Day	5% 3 1 6% 5% 5% 7% 5% 7% 11% 44%	2258
September	1st to 10th	Day	8% 6% 2 8% 5% 4 4 4 6% 8% 46%	1980
	11th to 20th	Day	12% 5% 3 8% 4 4 5% 5% 5% 7% 41%	1980
	21st to end	Day	8% 4 2 5% 3 5% 6% 4 7% 7% 49%	1980
October	1st to 10th	Day	7% 4 2 5% 3 4 4 3 5% 8% 54%	1980
	11th to 20th	Day	14% 5% 2 4 3 4 3 3 4 6% 52%	1832
	21st to end	Day	13% 5% 1 4 2 3 2 3 4 5% 59%	1980
November	1st to 10th	Day	15% 6% 2 5% 4 3 3 3 5% 7% 46%	1858
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 4 5% 50%	1805
	21st to end	Day	18% 7% 3 5% 4 3 3 3 4 4 45%	1710
December	1st to 10th	Day	15% 8% 2 5% 3 4 3 3 4 6% 48%	1710
	11th to 20th	Day	18% 8% 2 4 4 3 4 3 5% 5% 44%	2161
	21st to end	Day	18% 6% 2 4 2 2 3 2 4 4 53%	3135
January	1st to 10th	Night	20% 7% 2 3 2 2 2 2 3 6% 52%	4108
	11th to 20th	Night	15% 4 1 3 2 2 2 2 3 4 64%	4120
	21st to end	Night	21% 7% 2 6% 3 3 2 3 4 6% 43%	4404
February	1st to 10th	Night	20% 7% 2 5% 3 3 3 2 4 5% 47%	2280
	11th to 20th	Night	21% 6% 2 4 2 3 3 2 4 5% 49%	2218
	21st to end	Night	21% 7% 2 4 3 3 3 3 4 5% 45%	1884
March	1st to 10th	Night	19% 8% 2 5% 4 4 4 4 4 6% 39%	3419
	11th to 20th	Night	26% 9% 3 6% 3 4 4 3 4 5% 32%	3480
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 5% 43%	3817
April	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 5% 7% 46%	2090
	11th to 20th	Night	20% 6% 2 5% 3 4 3 4 4 6% 44%	2063
	21st to end	Night	19% 7% 2 4 3 3 3 2 4 7% 46%	1760
May	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 42%	1710
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 7% 47%	1620
	21st to end	Night	14% 5% 1 4 3 4 4 4 7% 10% 44%	1745
June	1st to 10th	Night	5% 3 1 3 3 3 3 4 6% 9% 60%	1620
	11th to 20th	Night	5% 3 1 5% 3 3 5% 4 5% 9% 59%	1620
	21st to end	Night	6% 4 2 4 5% 3 4 5% 7% 8% 52%	1620
July	1st to 10th	Night	8% 5% 1 4 4 3 5% 4 8% 9% 48%	1620
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 13% 59%	1620
	21st to end	Night	3 3 1 4 3 3 4 3 6% 10% 59%	1772
August	1st to 10th	Night	1 1 1 2 2 2 3 3 6% 9% 70%	1611
	11th to 20th	Night	5% 4 2 5% 3 4 4 4 6% 10% 52%	1720
	21st to end	Night	5% 3 1 5% 4 4 6% 5% 7% 11% 50%	2096
September	1st to 10th	Night	8% 4 2 6% 4 4 4 3 5% 8% 52%	1980
	11th to 20th	Night	10% 5% 3 6% 5% 4 4 4 6% 7% 46%	1980
	21st to end	Night	8% 5% 2 4 3 4 4 3 6% 8% 53%	1980
October	1st to 10th	Night	7% 3 1 4 4 3 3 3 5% 6% 61%	1980
	11th to 20th	Night	14% 5% 1 4 3 2 3 3 4 7% 53%	2108
	21st to end	Night	16% 4 2 3 2 2 3 2 3 5% 60%	2376
November	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 4 6% 53%	2220
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 4 6% 54%	2370
	21st to end	Night	20% 5% 2 5% 3 3 3 3 4 6% 45%	2470
December	1st to 10th	Night	15% 6% 2 4 3 3 4 2 4 4 51%	2470
	11th to 20th	Night	17% 9% 2 5% 3 3 3 2 4 5% 46%	3036
	21st to end	Night	20% 6% 1 3 2 3 2 2 3 5% 53%	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	37% 3 3 19% 24% 13%	2848
	11th to 20th	Day	32% 2 6% 17% 29% 14%	2850
	21st to end	Day	43% 3 4 11% 28% 11%	3292
February	1st to 10th	Day	44% 3 5% 13% 21% 14%	1900
	11th to 20th	Day	42% 3 7% 17% 19% 12%	1859
	21st to end	Day	42% 2 5% 18% 18% 15%	1570
March	1st to 10th	Day	43% 4 7% 15% 21% 10%	3433
	11th to 20th	Day	54% 3 9% 10% 16% 8%	3480
	21st to end	Day	40% 3 10% 16% 23% 8%	3814
April	1st to 10th	Day	44% 4 7% 17% 15% 13%	2090
	11th to 20th	Day	45% 3 7% 15% 19% 11%	2066
	21st to end	Day	41% 4 5% 21% 20% 9%	2414
May	1st to 10th	Day	46% 4 8% 16% 18% 8%	2470
	11th to 20th	Day	45% 5% 9% 19% 17% 4	2334
	21st to end	Day	47% 6% 11% 20% 15% 2	2531
June	1st to 10th	Day	30% 5% 14% 27% 20% 4	2340
	11th to 20th	Day	31% 7% 12% 27% 18% 5%	2340
	21st to end	Day	40% 8% 10% 23% 16% 3	2340
July	1st to 10th	Day	40% 8% 15% 25% 11% 2	2276
	11th to 20th	Day	26% 6% 18% 27% 20% 2	2271
	21st to end	Day	24% 6% 23% 33% 13% 1	2405
August	1st to 10th	Day	18% 5% 16% 39% 20% 1	2314
	11th to 20th	Day	26% 6% 17% 32% 14% 5%	2175
	21st to end	Day	31% 8% 16% 27% 15% 3	2258
September	1st to 10th	Day	37% 6% 11% 22% 16% 9%	1980
	11th to 20th	Day	41% 6% 11% 19% 18% 5%	1980
	21st to end	Day	32% 7% 9% 22% 18% 13%	1980
October	1st to 10th	Day	28% 5% 10% 22% 24% 12%	1980
	11th to 20th	Day	33% 4 8% 16% 22% 17%	1832
	21st to end	Day	30% 3 5% 17% 25% 20%	1980
November	1st to 10th	Day	39% 4 8% 19% 21% 10%	1858
	11th to 20th	Day	37% 3 8% 18% 21% 14%	1805
	21st to end	Day	43% 3 5% 16% 20% 13%	1710
December	1st to 10th	Day	39% 3 8% 20% 22% 8%	1710
	11th to 20th	Day	43% 3 7% 12% 22% 13%	2159
	21st to end	Day	36% 3 5% 15% 27% 13%	3135
January	1st to 10th	Night	35% 3 4 17% 23% 18%	4108
	11th to 20th	Night	27% 2 4 17% 32% 18%	4120
	21st to end	Night	44% 2 4 13% 25% 11%	4404
February	1st to 10th	Night	41% 3 5% 13% 20% 17%	2280
	11th to 20th	Night	40% 3 6% 17% 20% 15%	2218
	21st to end	Night	43% 3 6% 15% 17% 17%	1884
March	1st to 10th	Night	46% 4 8% 15% 18% 9%	3419
	11th to 20th	Night	54% 4 10% 10% 13% 8%	3480
	21st to end	Night	43% 4 9% 14% 20% 9%	3817
April	1st to 10th	Night	39% 3 9% 18% 17% 14%	2090
	11th to 20th	Night	42% 3 10% 14% 16% 15%	2063
	21st to end	Night	40% 3 9% 21% 18% 9%	1760
May	1st to 10th	Night	41% 4 10% 19% 17% 8%	1710
	11th to 20th	Night	37% 5% 11% 26% 17% 4	1621
	21st to end	Night	34% 5% 16% 29% 14% 1	1746
June	1st to 10th	Night	20% 6% 18% 30% 23% 4	1620
	11th to 20th	Night	24% 5% 15% 31% 20% 5%	1620
	21st to end	Night	28% 8% 17% 28% 16% 3	1620
July	1st to 10th	Night	29% 8% 22% 29% 11% 1	1575
	11th to 20th	Night	18% 6% 25% 31% 19% 1	1566
	21st to end	Night	19% 6% 25% 39% 10% 1	1673
August	1st to 10th	Night	11% 5% 24% 38% 20% 1	1601
	11th to 20th	Night	27% 7% 21% 29% 13% 3	1720
	21st to end	Night	26% 8% 22% 29% 12% 4	2096
September	1st to 10th	Night	30% 6% 16% 26% 16% 7%	1980
	11th to 20th	Night	36% 7% 14% 22% 14% 6%	1980
	21st to end	Night	28% 6% 14% 22% 18% 12%	1980
October	1st to 10th	Night	24% 5% 10% 25% 22% 13%	1980
	11th to 20th	Night	32% 5% 7% 18% 19% 19%	2108
	21st to end	Night	30% 2 6% 16% 23% 22%	2376
November	1st to 10th	Night	33% 4 9% 18% 22% 13%	2220
	11th to 20th	Night	33% 4 8% 20% 21% 15%	2370
	21st to end	Night	41% 3 7% 16% 18% 15%	2470
December	1st to 10th	Night	38% 2 7% 22% 19% 11%	2470
	11th to 20th	Night	42% 3 5% 12% 21% 17%	3037
	21st to end	Night	36% 2 5% 14% 29% 13%	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	17% 11% 36% 24% 10% 1	270
	11th to 20th	Day	24% 10% 27% 28% 9% 2	270
	21st to end	Day	20% 9% 37% 25% 9% 1	297
February	1st to 10th	Day	27% 12% 30% 21% 9% 1	270
	11th to 20th	Day	23% 15% 32% 23% 6% 1	270
	21st to end	Day	25% 13% 41% 17% 3	225
March	1st to 10th	Day	22% 11% 35% 24% 6% 1	270
	11th to 20th	Day	20% 13% 35% 26% 6% 1	270
	21st to end	Day	18% 14% 36% 25% 7% 1	297
April	1st to 10th	Day	19% 14% 37% 23% 6% 1	270
	11th to 20th	Day	20% 10% 36% 22% 11% 1	264
	21st to end	Day	18% 10% 34% 27% 10% 1	594
May	1st to 10th	Day	18% 8% 32% 29% 12%	653
	11th to 20th	Day	18% 6% 24% 31% 17% 3	637
	21st to end	Day	16% 4 20% 33% 23% 4	679
June	1st to 10th	Day	8% 2 10% 37% 33% 10%	630
	11th to 20th	Day	8% 1 11% 44% 29% 7%	630
	21st to end	Day	6% 3 10% 30% 36% 15%	630
July	1st to 10th	Day	8% 1 9% 30% 38% 15%	621
	11th to 20th	Day	4 1 3 26% 51% 15%	618
	21st to end	Day	4 1 2 24% 51% 17%	684
August	1st to 10th	Day	3 4 21% 53% 19%	626
	11th to 20th	Day	6% 3 24% 48% 19%	489
	21st to end	Day	6% 1 5% 18% 32% 38%	377
September	1st to 10th	Day	8% 3 17% 38% 34%	270
	11th to 20th	Day	8% 4 20% 36% 31%	270
	21st to end	Day	11% 1 9% 16% 36% 27%	270
October	1st to 10th	Day	6% 1 10% 28% 39% 17%	270
	11th to 20th	Day	13% 2 17% 32% 26% 10%	270
	21st to end	Day	20% 9% 23% 22% 20% 6%	297
November	1st to 10th	Day	20% 3 20% 31% 19% 7%	270
	11th to 20th	Day	19% 6% 24% 28% 19% 4	270
	21st to end	Day	20% 11% 32% 23% 11% 3	270
December	1st to 10th	Day	17% 6% 31% 27% 14% 6%	270
	11th to 20th	Day	22% 11% 30% 23% 13% 1	270
	21st to end	Day	20% 9% 31% 26% 12% 2	297
January	1st to 10th	Night	20% 8% 30% 33% 9% 1	950
	11th to 20th	Night	21% 9% 28% 33% 9%	950
	21st to end	Night	21% 8% 31% 34% 7%	969
February	1st to 10th	Night	23% 11% 29% 30% 6%	760
	11th to 20th	Night	25% 9% 36% 27% 3	744
	21st to end	Night	27% 11% 39% 22% 2	628
March	1st to 10th	Night	22% 11% 35% 29% 4	570
	11th to 20th	Night	22% 9% 31% 33% 5%	570
	21st to end	Night	16% 10% 41% 30% 3	627
April	1st to 10th	Night	18% 7% 40% 32% 4	570
	11th to 20th	Night	21% 9% 39% 27% 4	563
	21st to end	Night	18% 9% 38% 28% 7%	570
May	1st to 10th	Night	18% 9% 35% 32% 6%	570
	11th to 20th	Night	15% 6% 28% 38% 12% 1	540
	21st to end	Night	15% 3 28% 36% 18%	584
June	1st to 10th	Night	6% 2 15% 48% 28% 1	540
	11th to 20th	Night	5% 1 25% 51% 16% 1	540
	21st to end	Night	6% 1 14% 45% 29% 4	540
July	1st to 10th	Night	8% 2 9% 43% 34% 5%	525
	11th to 20th	Night	5% 8% 49% 35% 3	522
	21st to end	Night	4 1 6% 47% 40% 3	591
August	1st to 10th	Night	1 4 53% 37% 4	537
	11th to 20th	Night	7% 5% 45% 38% 5%	534
	21st to end	Night	5% 5% 36% 47% 6%	594
September	1st to 10th	Night	9% 1 6% 38% 42% 5%	540
	11th to 20th	Night	11% 2 5% 33% 44% 5%	540
	21st to end	Night	9% 1 11% 35% 40% 4	540
October	1st to 10th	Night	6% 2 9% 44% 33% 5%	540
	11th to 20th	Night	15% 3 17% 38% 25% 2	668
	21st to end	Night	16% 6% 23% 30% 22% 2	792
November	1st to 10th	Night	14% 3 19% 41% 22% 1	740
	11th to 20th	Night	14% 6% 25% 35% 18% 2	850
	21st to end	Night	22% 6% 27% 31% 13% 1	950
December	1st to 10th	Night	18% 7% 26% 36% 12% 1	950
	11th to 20th	Night	24% 8% 26% 35% 7% 1	950
	21st to end	Night	22% 6% 29% 35% 8%	1045

Page generated at 2024-05-10 11:39:05. Version ac07

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