Austin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Austin clear sky chart from 2005-11-05 to 2023-05-20.

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% 5% 2 4 4 2 4 4 5% 7% 46%	69888
	Night	13% 5% 1 3 3 2 3 3 4 7% 50%	69382
Transparency	Day	37% 4 9% 20% 18% 8%	69608
	Night	33% 4 11% 21% 18% 11%	69172
Seeing	Day	13% 5% 18% 26% 25% 9%	12731
	Night	15% 5% 23% 35% 18% 1	22702

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% 4 2 4 3 1 2 3 3 5% 53%	1599
	11th to 20th	Day	19% 6% 2 2 2 2 3 2 3 6% 48%	1618
	21st to end	Day	15% 5% 2 3 3 2 3 2 3 5% 52%	1822
February	1st to 10th	Day	20% 6% 2 4 3 1 2 3 3 5% 45%	1774
	11th to 20th	Day	21% 5% 2 3 3 2 3 3 4 6% 44%	1719
	21st to end	Day	20% 5% 2 3 3 2 3 2 2 4 48%	1472
March	1st to 10th	Day	21% 6% 2 5% 3 1 3 3 4 5% 40%	1977
	11th to 20th	Day	18% 5% 2 4 4 2 4 3 3 6% 43%	1945
	21st to end	Day	16% 6% 1 4 3 2 3 4 4 6% 47%	2164
April	1st to 10th	Day	15% 7% 3 5% 5% 1 4 4 4 5% 42%	1949
	11th to 20th	Day	19% 5% 2 5% 5% 2 3 4 4 5% 42%	1925
	21st to end	Day	15% 6% 3 5% 3 2 3 3 4 6% 45%	2280
May	1st to 10th	Day	16% 6% 3 5% 5% 2 4 4 4 6% 40%	2328
	11th to 20th	Day	15% 6% 2 6% 5% 3 4 5% 5% 6% 38%	2236
	21st to end	Day	15% 5% 2 5% 5% 3 6% 5% 5% 8% 33%	2330
June	1st to 10th	Day	7% 3 1 4 4 2 4 5% 6% 9% 49%	2210
	11th to 20th	Day	8% 4 2 4 6% 2 5% 5% 7% 9% 44%	2210
	21st to end	Day	7% 5% 2 5% 7% 4 6% 6% 7% 9% 35%	2192
July	1st to 10th	Day	9% 5% 3 4 6% 4 6% 5% 6% 8% 38%	2210
	11th to 20th	Day	5% 3 1 3 5% 3 5% 6% 7% 11% 47%	2179
	21st to end	Day	4 3 2 3 5% 3 4 5% 7% 10% 48%	2376
August	1st to 10th	Day	2 2 1 2 3 2 4 4 6% 10% 61%	2162
	11th to 20th	Day	6% 3 1 3 4 3 4 4 5% 9% 51%	2000
	21st to end	Day	5% 3 1 5% 5% 3 6% 7% 6% 11% 43%	2118
September	1st to 10th	Day	9% 5% 3 6% 6% 3 4 4 6% 8% 42%	1860
	11th to 20th	Day	11% 5% 3 6% 4 2 5% 6% 5% 7% 41%	1868
	21st to end	Day	8% 4 2 4 4 3 5% 5% 6% 7% 48%	1857
October	1st to 10th	Day	7% 3 1 3 3 2 4 3 4 7% 56%	1862
	11th to 20th	Day	14% 5% 1 3 3 2 3 3 4 6% 51%	1707
	21st to end	Day	11% 3 1 3 2 2 1 2 4 4 61%	1863
November	1st to 10th	Day	14% 6% 2 4 4 2 3 4 4 6% 47%	1756
	11th to 20th	Day	11% 5% 2 4 5% 1 4 3 4 4 51%	1699
	21st to end	Day	18% 6% 2 4 3 2 3 3 4 4 46%	1608
December	1st to 10th	Day	15% 7% 2 4 3 2 2 3 3 6% 47%	1612
	11th to 20th	Day	21% 8% 2 3 4 1 4 2 4 5% 41%	1620
	21st to end	Day	15% 6% 2 5% 3 2 3 3 4 5% 46%	1781
January	1st to 10th	Night	16% 5% 1 2 2 1 2 3 3 6% 54%	2314
	11th to 20th	Night	18% 5% 1 3 3 1 3 2 3 5% 50%	2330
	21st to end	Night	17% 5% 1 4 3 1 3 3 4 5% 50%	2470
February	1st to 10th	Night	19% 6% 1 4 3 1 2 2 3 5% 47%	2142
	11th to 20th	Night	20% 5% 2 3 2 2 2 2 3 5% 49%	2046
	21st to end	Night	21% 6% 1 3 3 1 3 3 3 5% 44%	1774
March	1st to 10th	Night	19% 6% 1 3 3 2 4 4 3 6% 42%	1980
	11th to 20th	Night	18% 7% 2 4 3 2 4 3 4 5% 42%	1961
	21st to end	Night	15% 5% 2 3 3 2 3 4 3 6% 48%	2172
April	1st to 10th	Night	14% 5% 2 4 4 1 3 3 4 7% 46%	1959
	11th to 20th	Night	19% 5% 2 4 3 2 3 4 3 5% 45%	1923
	21st to end	Night	17% 6% 2 3 3 1 3 3 4 6% 47%	1654
May	1st to 10th	Night	14% 5% 2 4 4 2 4 4 4 7% 42%	1612
	11th to 20th	Night	13% 5% 1 4 4 2 3 3 5% 7% 47%	1566
	21st to end	Night	13% 4 1 3 3 2 4 5% 6% 10% 44%	1599
June	1st to 10th	Night	5% 3 1 2 2 1 3 3 5% 9% 61%	1530
	11th to 20th	Night	4 2 1 3 3 2 4 4 4 8% 59%	1530
	21st to end	Night	6% 3 2 4 4 2 4 4 7% 8% 50%	1514
July	1st to 10th	Night	8% 4 2 3 4 2 4 5% 7% 9% 48%	1530
	11th to 20th	Night	3 2 3 3 2 3 3 6% 13% 57%	1506
	21st to end	Night	3 2 1 3 2 2 3 3 5% 10% 59%	1640
August	1st to 10th	Night	1 1 2 1 3 3 5% 9% 69%	1511
	11th to 20th	Night	5% 3 1 4 4 3 4 5% 6% 10% 50%	1599
	21st to end	Night	5% 2 1 4 4 2 5% 5% 6% 11% 49%	1969
September	1st to 10th	Night	8% 3 2 5% 4 2 4 4 5% 8% 50%	1868
	11th to 20th	Night	10% 4 3 5% 4 2 5% 4 5% 7% 46%	1862
	21st to end	Night	8% 4 1 3 4 2 4 4 6% 7% 52%	1852
October	1st to 10th	Night	6% 2 3 4 2 3 3 4 6% 62%	1867
	11th to 20th	Night	13% 4 1 3 3 1 3 4 4 7% 53%	1977
	21st to end	Night	14% 3 1 2 1 1 2 2 2 4 62%	2238
November	1st to 10th	Night	14% 4 1 4 3 2 2 3 3 6% 53%	2092
	11th to 20th	Night	9% 5% 1 4 3 2 2 3 4 5% 55%	2234
	21st to end	Night	20% 5% 1 3 3 2 3 3 3 5% 46%	2328
December	1st to 10th	Night	16% 6% 2 3 3 2 3 2 3 3 51%	2328
	11th to 20th	Night	20% 8% 2 4 3 2 3 2 3 4 44%	2340
	21st to end	Night	17% 6% 1 3 3 2 3 3 3 5% 48%	2565

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	34% 2 4 20% 23% 13%	1601
	11th to 20th	Day	38% 2 5% 17% 21% 14%	1619
	21st to end	Day	35% 3 5% 14% 25% 15%	1821
February	1st to 10th	Day	42% 3 5% 13% 20% 14%	1775
	11th to 20th	Day	42% 3 6% 17% 18% 11%	1721
	21st to end	Day	42% 2 5% 16% 17% 15%	1472
March	1st to 10th	Day	46% 3 8% 12% 19% 9%	1977
	11th to 20th	Day	43% 3 6% 12% 20% 13%	1969
	21st to end	Day	38% 3 8% 17% 20% 11%	2154
April	1st to 10th	Day	43% 4 7% 18% 15% 11%	1951
	11th to 20th	Day	43% 3 7% 15% 18% 11%	1926
	21st to end	Day	40% 4 5% 20% 20% 9%	2280
May	1st to 10th	Day	44% 4 8% 16% 18% 8%	2327
	11th to 20th	Day	44% 5% 9% 19% 17% 3	2244
	21st to end	Day	46% 6% 10% 19% 15% 1	2330
June	1st to 10th	Day	30% 5% 12% 26% 20% 4	2206
	11th to 20th	Day	32% 7% 11% 25% 18% 5%	2210
	21st to end	Day	41% 8% 9% 23% 15% 2	2195
July	1st to 10th	Day	39% 7% 15% 25% 10% 1	2123
	11th to 20th	Day	27% 6% 19% 26% 18% 1	2093
	21st to end	Day	25% 6% 22% 32% 12%	2232
August	1st to 10th	Day	18% 5% 16% 39% 18% 1	2153
	11th to 20th	Day	27% 6% 17% 32% 12% 2	2001
	21st to end	Day	32% 8% 16% 26% 13% 2	2120
September	1st to 10th	Day	38% 6% 11% 22% 14% 6%	1862
	11th to 20th	Day	40% 6% 10% 18% 18% 5%	1867
	21st to end	Day	32% 6% 8% 20% 18% 13%	1857
October	1st to 10th	Day	26% 4 8% 22% 25% 11%	1862
	11th to 20th	Day	33% 4 8% 16% 21% 15%	1709
	21st to end	Day	27% 2 4 17% 26% 21%	1862
November	1st to 10th	Day	38% 4 7% 18% 20% 9%	1756
	11th to 20th	Day	35% 3 7% 17% 21% 14%	1702
	21st to end	Day	41% 2 5% 16% 20% 13%	1611
December	1st to 10th	Day	40% 2 8% 19% 21% 6%	1619
	11th to 20th	Day	46% 1 6% 13% 16% 14%	1620
	21st to end	Day	39% 3 8% 16% 22% 9%	1781
January	1st to 10th	Night	32% 2 5% 18% 23% 17%	2315
	11th to 20th	Night	37% 2 6% 17% 21% 15%	2331
	21st to end	Night	37% 2 4 15% 21% 18%	2470
February	1st to 10th	Night	40% 3 5% 13% 19% 17%	2142
	11th to 20th	Night	39% 2 6% 16% 19% 15%	2055
	21st to end	Night	42% 2 5% 14% 16% 17%	1773
March	1st to 10th	Night	42% 3 9% 14% 18% 10%	1979
	11th to 20th	Night	43% 4 8% 11% 19% 13%	1969
	21st to end	Night	36% 4 10% 16% 19% 13%	2174
April	1st to 10th	Night	37% 3 9% 18% 17% 13%	1957
	11th to 20th	Night	40% 3 10% 14% 16% 14%	1923
	21st to end	Night	38% 3 9% 21% 18% 9%	1654
May	1st to 10th	Night	40% 4 10% 18% 17% 8%	1615
	11th to 20th	Night	36% 5% 11% 26% 16% 3	1568
	21st to end	Night	33% 5% 15% 29% 14% 1	1600
June	1st to 10th	Night	19% 6% 16% 30% 23% 3	1523
	11th to 20th	Night	23% 5% 14% 30% 20% 5%	1529
	21st to end	Night	27% 8% 16% 28% 15% 2	1515
July	1st to 10th	Night	27% 8% 22% 29% 10% 1	1476
	11th to 20th	Night	18% 6% 26% 30% 16%	1445
	21st to end	Night	18% 6% 26% 38% 9%	1542
August	1st to 10th	Night	11% 5% 25% 37% 18% 1	1501
	11th to 20th	Night	28% 7% 22% 28% 11% 1	1601
	21st to end	Night	27% 8% 22% 28% 11% 3	1968
September	1st to 10th	Night	31% 5% 16% 26% 14% 5%	1868
	11th to 20th	Night	35% 7% 14% 22% 14% 6%	1861
	21st to end	Night	29% 6% 12% 20% 18% 12%	1852
October	1st to 10th	Night	22% 4 10% 25% 23% 13%	1868
	11th to 20th	Night	31% 4 7% 18% 19% 18%	1977
	21st to end	Night	27% 2 5% 17% 24% 23%	2236
November	1st to 10th	Night	33% 4 8% 19% 21% 12%	2092
	11th to 20th	Night	30% 4 7% 20% 22% 15%	2234
	21st to end	Night	40% 3 7% 15% 18% 15%	2328
December	1st to 10th	Night	39% 2 7% 22% 18% 10%	2331
	11th to 20th	Night	44% 3 5% 13% 19% 14%	2340
	21st to end	Night	38% 2 6% 15% 24% 12%	2560

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% 8% 35% 25% 11% 1	240
	11th to 20th	Day	25% 9% 24% 29% 10% 2	240
	21st to end	Day	16% 9% 39% 25% 6% 1	261
February	1st to 10th	Day	26% 9% 32% 21% 9%	240
	11th to 20th	Day	25% 14% 31% 21% 6%	240
	21st to end	Day	26% 13% 37% 19% 3	198
March	1st to 10th	Day	24% 11% 34% 22% 6%	240
	11th to 20th	Day	19% 12% 33% 26% 6% 1	240
	21st to end	Day	16% 13% 34% 26% 7% 1	264
April	1st to 10th	Day	18% 12% 37% 23% 7%	237
	11th to 20th	Day	20% 8% 34% 21% 12% 1	229
	21st to end	Day	17% 9% 34% 25% 10% 1	543
May	1st to 10th	Day	16% 7% 32% 30% 12%	600
	11th to 20th	Day	17% 6% 23% 31% 17% 3	616
	21st to end	Day	15% 4 21% 34% 20% 3	602
June	1st to 10th	Day	8% 1 9% 36% 34% 9%	577
	11th to 20th	Day	8% 1 9% 42% 30% 7%	578
	21st to end	Day	6% 2 10% 29% 35% 15%	575
July	1st to 10th	Day	7% 1 7% 29% 37% 16%	566
	11th to 20th	Day	4 3 24% 52% 15%	561
	21st to end	Day	4 2 24% 51% 16%	622
August	1st to 10th	Day	3 4 18% 52% 19%	563
	11th to 20th	Day	6% 3 25% 46% 17%	432
	21st to end	Day	6% 1 4 18% 31% 37%	339
September	1st to 10th	Day	8% 3 17% 37% 32%	240
	11th to 20th	Day	7% 3 18% 35% 35%	240
	21st to end	Day	12% 8% 16% 34% 27%	240
October	1st to 10th	Day	5% 7% 26% 42% 19%	240
	11th to 20th	Day	12% 2 14% 33% 26% 11%	240
	21st to end	Day	18% 10% 20% 22% 21% 6%	264
November	1st to 10th	Day	19% 3 18% 32% 18% 7%	240
	11th to 20th	Day	17% 5% 24% 29% 19% 4	240
	21st to end	Day	21% 9% 32% 22% 11% 2	240
December	1st to 10th	Day	18% 5% 30% 26% 14% 5%	240
	11th to 20th	Day	22% 12% 31% 20% 13%	240
	21st to end	Day	20% 9% 28% 26% 12% 2	264
January	1st to 10th	Night	19% 7% 29% 33% 10%	890
	11th to 20th	Night	21% 8% 26% 34% 9%	897
	21st to end	Night	19% 7% 31% 33% 7%	905
February	1st to 10th	Night	23% 10% 30% 29% 6%	710
	11th to 20th	Night	25% 8% 36% 26% 3	687
	21st to end	Night	27% 10% 38% 21% 1	591
March	1st to 10th	Night	21% 10% 34% 29% 4	539
	11th to 20th	Night	20% 9% 30% 34% 5%	534
	21st to end	Night	15% 9% 40% 30% 3	594
April	1st to 10th	Night	16% 7% 40% 32% 3	535
	11th to 20th	Night	19% 8% 38% 27% 4	526
	21st to end	Night	16% 8% 39% 28% 7%	535
May	1st to 10th	Night	15% 9% 35% 31% 6%	538
	11th to 20th	Night	14% 5% 28% 38% 12%	523
	21st to end	Night	14% 2 30% 35% 16%	536
June	1st to 10th	Night	5% 2 14% 48% 27% 1	506
	11th to 20th	Night	5% 23% 51% 17% 1	507
	21st to end	Night	6% 1 14% 43% 30% 3	499
July	1st to 10th	Night	7% 1 9% 41% 35% 4	492
	11th to 20th	Night	5% 7% 47% 36% 3	488
	21st to end	Night	3 4 46% 40% 3	548
August	1st to 10th	Night	1 3 52% 38% 4	496
	11th to 20th	Night	7% 5% 44% 38% 5%	496
	21st to end	Night	5% 5% 34% 47% 6%	558
September	1st to 10th	Night	9% 5% 35% 43% 5%	510
	11th to 20th	Night	11% 1 4 31% 45% 5%	507
	21st to end	Night	10% 1 9% 33% 40% 4	501
October	1st to 10th	Night	6% 1 7% 44% 34% 5%	510
	11th to 20th	Night	14% 2 16% 37% 26% 2	625
	21st to end	Night	15% 4 23% 30% 23% 2	745
November	1st to 10th	Night	14% 2 18% 40% 22% 1	698
	11th to 20th	Night	13% 5% 25% 35% 18% 2	800
	21st to end	Night	22% 5% 27% 29% 13%	896
December	1st to 10th	Night	19% 6% 25% 36% 11%	895
	11th to 20th	Night	24% 8% 26% 33% 7%	900
	21st to end	Night	21% 6% 27% 35% 8%	985

Page generated at 2023-05-22 05:21:14. Version ac06

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