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 2024-11-06.

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%	101058
	Night	14% 6% 2 4 3 3 3 3 5% 7% 50%	98117
Transparency	Day	35% 5% 10% 22% 20% 9%	104853
	Night	34% 4 11% 21% 20% 11%	102449
Seeing	Day	13% 5% 19% 28% 25% 9%	14861
	Night	16% 6% 24% 36% 18% 2	24749

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	25% 9% 3 7% 4 4 4 4 5% 6% 30%	4082
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 5% 7% 42%	4082
	21st to end	Day	12% 6% 2 6% 5% 6% 6% 5% 7% 10% 35%	4477
June	1st to 10th	Day	7% 4 1 6% 4 4 4 4 7% 9% 49%	2470
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 4 7% 9% 45%	2470
	21st to end	Day	6% 6% 2 6% 7% 6% 5% 5% 8% 10% 39%	2470
July	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 6% 9% 49%	4120
	11th to 20th	Day	4 4 2 5% 4 4 5% 5% 8% 11% 48%	4120
	21st to end	Day	9% 6% 3 6% 5% 5% 5% 6% 7% 10% 37%	4465
August	1st to 10th	Day	1 2 1 2 2 2 3 3 5% 9% 72%	4104
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 11% 59%	3817
	21st to end	Day	4 3 1 5% 5% 4 6% 5% 8% 11% 48%	3964
September	1st to 10th	Day	8% 6% 3 8% 5% 4 4 4 6% 8% 45%	2090
	11th to 20th	Day	11% 5% 3 7% 4 4 5% 5% 5% 7% 42%	2090
	21st to end	Day	8% 4 2 5% 3 5% 6% 4 7% 7% 50%	2090
October	1st to 10th	Day	7% 4 2 5% 3 3 4 3 5% 8% 57%	2090
	11th to 20th	Day	13% 5% 1 4 3 4 3 3 5% 6% 53%	1933
	21st to end	Day	12% 4 1 4 3 3 3 3 4 5% 58%	2090
November	1st to 10th	Day	15% 7% 2 6% 4 4 3 4 5% 7% 45%	1908
	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	28% 8% 2 5% 3 3 3 3 4 6% 35%	2823
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 5% 7% 49%	2823
	21st to end	Night	15% 7% 2 4 3 4 4 4 6% 9% 42%	3090
June	1st to 10th	Night	5% 3 1 3 3 3 4 4 6% 9% 60%	1710
	11th to 20th	Night	5% 3 1 5% 3 3 5% 4 4 9% 58%	1710
	21st to end	Night	6% 4 2 4 5% 3 4 4 7% 8% 53%	1710
July	1st to 10th	Night	5% 3 1 4 3 3 5% 4 7% 9% 55%	2850
	11th to 20th	Night	4 3 1 4 3 4 5% 4 7% 12% 54%	2850
	21st to end	Night	8% 8% 3 6% 4 5% 5% 4 7% 9% 42%	3098
August	1st to 10th	Night	1 1 1 2 1 2 3 3 5% 8% 76%	2836
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 11% 60%	3016
	21st to end	Night	4 3 1 4 3 3 5% 4 6% 11% 55%	3694
September	1st to 10th	Night	8% 4 2 6% 4 4 4 3 5% 8% 52%	2090
	11th to 20th	Night	10% 5% 3 6% 5% 4 4 4 6% 7% 46%	2090
	21st to end	Night	8% 5% 2 4 3 4 4 3 6% 8% 54%	2090
October	1st to 10th	Night	6% 3 1 4 4 3 3 3 4 6% 62%	2090
	11th to 20th	Night	13% 5% 1 4 3 2 3 3 4 7% 55%	2226
	21st to end	Night	15% 4 2 3 2 2 3 2 3 5% 60%	2508
November	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 4 6% 52%	2292
	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	54% 4 9% 14% 13% 5%	4120
	11th to 20th	Day	42% 4 9% 18% 21% 5%	4086
	21st to end	Day	42% 6% 13% 27% 11% 1	4489
June	1st to 10th	Day	30% 5% 14% 27% 20% 4	2470
	11th to 20th	Day	32% 7% 12% 26% 18% 5%	2470
	21st to end	Day	38% 8% 10% 24% 17% 3	2470
July	1st to 10th	Day	29% 7% 17% 38% 8% 1	4056
	11th to 20th	Day	27% 7% 17% 31% 17% 2	4051
	21st to end	Day	38% 7% 18% 27% 9% 1	4325
August	1st to 10th	Day	11% 4 11% 42% 30% 2	4090
	11th to 20th	Day	19% 5% 21% 40% 12% 3	3856
	21st to end	Day	26% 9% 20% 25% 18% 2	3963
September	1st to 10th	Day	37% 6% 11% 21% 16% 10%	2090
	11th to 20th	Day	40% 6% 11% 19% 19% 5%	2090
	21st to end	Day	31% 6% 9% 21% 18% 14%	2090
October	1st to 10th	Day	17% 3 6% 13% 24% 38%	3480
	11th to 20th	Day	21% 3 8% 19% 30% 19%	3186
	21st to end	Day	26% 3 5% 20% 31% 15%	3428
November	1st to 10th	Day	40% 4 8% 18% 20% 10%	1908
	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	52% 3 9% 18% 14% 5%	2850
	11th to 20th	Night	36% 4 11% 24% 18% 7%	2824
	21st to end	Night	38% 5% 15% 30% 11% 2	3099
June	1st to 10th	Night	20% 6% 18% 30% 23% 3	1710
	11th to 20th	Night	24% 6% 14% 30% 20% 5%	1710
	21st to end	Night	27% 8% 16% 29% 17% 3	1710
July	1st to 10th	Night	23% 7% 25% 37% 7% 1	2805
	11th to 20th	Night	24% 7% 20% 33% 15% 1	2796
	21st to end	Night	37% 7% 22% 27% 7%	2999
August	1st to 10th	Night	9% 4 15% 45% 27% 1	2826
	11th to 20th	Night	19% 5% 30% 32% 12% 2	3043
	21st to end	Night	22% 10% 22% 27% 16% 2	3694
September	1st to 10th	Night	31% 6% 15% 25% 16% 7%	2090
	11th to 20th	Night	36% 7% 14% 22% 15% 6%	2090
	21st to end	Night	28% 6% 14% 22% 18% 13%	2090
October	1st to 10th	Night	16% 3 7% 16% 19% 39%	3480
	11th to 20th	Night	20% 3 8% 17% 30% 21%	3699
	21st to end	Night	25% 2 5% 20% 32% 17%	4120
November	1st to 10th	Night	34% 4 9% 18% 22% 13%	2292
	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% 7% 24% 32% 17% 3	675
	21st to end	Day	15% 5% 22% 33% 22% 4	734
June	1st to 10th	Day	8% 2 11% 37% 32% 10%	680
	11th to 20th	Day	9% 1 12% 43% 28% 7%	680
	21st to end	Day	6% 3 11% 30% 36% 14%	680
July	1st to 10th	Day	7% 1 9% 31% 37% 14%	671
	11th to 20th	Day	5% 1 3 27% 49% 15%	668
	21st to end	Day	5% 2 4 24% 48% 16%	739
August	1st to 10th	Day	3 4 22% 51% 19%	676
	11th to 20th	Day	6% 1 3 26% 47% 17%	532
	21st to end	Day	5% 1 6% 20% 32% 36%	414
September	1st to 10th	Day	8% 7% 19% 34% 31%	300
	11th to 20th	Day	8% 1 5% 22% 37% 28%	300
	21st to end	Day	10% 1 9% 21% 34% 25%	300
October	1st to 10th	Day	5% 1 10% 30% 39% 16%	300
	11th to 20th	Day	11% 2 18% 35% 25% 9%	300
	21st to end	Day	18% 9% 23% 23% 20% 6%	330
November	1st to 10th	Day	21% 5% 21% 29% 18% 7%	285
	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	17% 9% 35% 32% 6%	570
	11th to 20th	Night	15% 5% 29% 39% 12% 1	561
	21st to end	Night	15% 3 30% 35% 17%	617
June	1st to 10th	Night	6% 2 15% 48% 27% 2	570
	11th to 20th	Night	6% 2 25% 50% 16% 1	570
	21st to end	Night	6% 2 15% 44% 29% 4	570
July	1st to 10th	Night	8% 2 9% 45% 32% 4	555
	11th to 20th	Night	5% 9% 49% 34% 3	552
	21st to end	Night	5% 1 7% 46% 38% 3	624
August	1st to 10th	Night	1 4 53% 37% 5%	567
	11th to 20th	Night	6% 6% 47% 36% 5%	564
	21st to end	Night	5% 6% 36% 46% 6%	627
September	1st to 10th	Night	9% 1 8% 38% 40% 5%	570
	11th to 20th	Night	11% 2 6% 33% 43% 5%	570
	21st to end	Night	9% 1 11% 36% 38% 4	570
October	1st to 10th	Night	6% 2 9% 44% 34% 5%	570
	11th to 20th	Night	14% 3 18% 39% 25% 2	706
	21st to end	Night	16% 6% 23% 30% 22% 2	836
November	1st to 10th	Night	15% 3 19% 40% 21% 1	764
	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 2024-11-03 12:19:00. Version ac07

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