South Llano River State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Llano River State Park clear sky chart from 2005-11-06 to 2025-01-22.

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	8% 5% 2 5% 4 4 4 3 5% 7% 54%	105189
	Night	8% 5% 2 4 3 3 3 3 5% 7% 58%	104312
Transparency	Day	29% 5% 9% 22% 22% 12%	109085
	Night	26% 5% 10% 22% 22% 14%	108544
Seeing	Day	10% 8% 24% 32% 20% 5%	15078
	Night	10% 7% 31% 38% 13% 1	25153

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	9% 6% 2 4 3 2 3 2 3 6% 60%	2937
	11th to 20th	Day	7% 7% 1 4 2 2 3 3 5% 6% 60%	3021
	21st to end	Day	11% 5% 2 5% 4 3 3 2 4 7% 52%	3497
February	1st to 10th	Day	10% 7% 2 5% 3 3 3 4 4 5% 54%	1900
	11th to 20th	Day	11% 6% 2 4 4 4 4 3 5% 5% 52%	1849
	21st to end	Day	11% 5% 2 3 2 3 4 3 5% 5% 56%	1570
March	1st to 10th	Day	12% 6% 2 7% 4 3 3 3 4 5% 49%	3213
	11th to 20th	Day	16% 9% 3 8% 4 4 4 3 5% 6% 40%	3480
	21st to end	Day	7% 6% 2 5% 4 4 4 4 5% 7% 52%	3814
April	1st to 10th	Day	9% 5% 2 5% 4 3 3 3 5% 6% 54%	2109
	11th to 20th	Day	11% 6% 2 5% 4 4 3 3 5% 6% 51%	2254
	21st to end	Day	9% 6% 2 5% 4 4 3 4 3 5% 56%	2304
May	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 6% 44%	4082
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 4 6% 49%	4082
	21st to end	Day	8% 5% 2 6% 4 5% 4 4 6% 9% 47%	4477
June	1st to 10th	Day	4 3 1 4 4 4 5% 3 6% 8% 57%	2470
	11th to 20th	Day	4 3 1 4 4 4 4 4 6% 9% 56%	2470
	21st to end	Day	6% 4 1 4 5% 5% 6% 5% 8% 8% 48%	2470
July	1st to 10th	Day	4 3 2 5% 5% 4 5% 4 7% 8% 53%	4120
	11th to 20th	Day	2 2 1 4 3 4 5% 4 7% 8% 59%	4120
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 9% 49%	4448
August	1st to 10th	Day	1 2 1 3 2 3 3 3 5% 8% 70%	3785
	11th to 20th	Day	3 3 1 3 3 3 3 3 5% 8% 65%	3726
	21st to end	Day	4 4 2 5% 5% 5% 6% 5% 6% 9% 49%	4180
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 3 4 7% 47%	2103
	11th to 20th	Day	10% 5% 2 7% 4 4 4 5% 6% 8% 45%	2090
	21st to end	Day	9% 4 2 4 4 4 4 4 5% 6% 54%	2090
October	1st to 10th	Day	5% 4 1 4 3 4 4 3 5% 7% 59%	2090
	11th to 20th	Day	10% 5% 2 5% 3 3 3 2 4 5% 58%	2076
	21st to end	Day	10% 4 2 4 2 2 3 2 3 5% 63%	2090
November	1st to 10th	Day	12% 6% 2 4 3 2 3 3 5% 5% 55%	1853
	11th to 20th	Day	7% 6% 2 4 3 2 3 3 5% 6% 60%	1800
	21st to end	Day	11% 6% 2 5% 3 3 2 3 4 7% 54%	1800
December	1st to 10th	Day	19% 8% 3 5% 3 2 3 2 4 5% 45%	2940
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 5% 5% 49%	3391
	21st to end	Day	8% 5% 2 4 3 2 2 2 3 4 65%	4488
January	1st to 10th	Night	11% 5% 2 5% 2 2 3 2 3 6% 59%	4238
	11th to 20th	Night	8% 5% 1 2 2 2 2 2 3 4 69%	4184
	21st to end	Night	15% 6% 2 5% 3 2 3 2 4 7% 51%	4192
February	1st to 10th	Night	10% 7% 2 4 3 3 3 3 4 6% 56%	2280
	11th to 20th	Night	12% 6% 1 5% 2 3 2 2 5% 6% 55%	2218
	21st to end	Night	10% 6% 1 4 3 3 4 3 5% 7% 54%	1884
March	1st to 10th	Night	8% 6% 2 4 3 3 4 4 5% 7% 54%	3646
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 5% 5% 44%	3480
	21st to end	Night	7% 7% 2 6% 4 3 4 3 5% 6% 54%	3817
April	1st to 10th	Night	6% 4 2 4 3 4 4 4 5% 7% 57%	2066
	11th to 20th	Night	10% 5% 2 5% 3 4 3 3 4 6% 55%	1877
	21st to end	Night	10% 5% 1 4 3 3 2 3 4 5% 59%	1875
May	1st to 10th	Night	14% 8% 2 4 3 3 3 2 4 8% 49%	2823
	11th to 20th	Night	8% 5% 2 4 4 3 3 3 5% 7% 55%	2823
	21st to end	Night	8% 4 2 5% 3 4 3 4 6% 9% 52%	3090
June	1st to 10th	Night	2 2 1 3 3 3 3 4 6% 11% 63%	1710
	11th to 20th	Night	2 1 1 2 3 3 4 4 6% 9% 65%	1710
	21st to end	Night	4 3 1 4 4 3 3 4 5% 9% 61%	1710
July	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 9% 59%	2850
	11th to 20th	Night	2 2 1 2 2 2 2 3 6% 9% 70%	2850
	21st to end	Night	3 3 1 4 4 4 4 4 7% 9% 56%	3098
August	1st to 10th	Night	1 1 1 3 2 2 3 2 4 6% 75%	3154
	11th to 20th	Night	2 3 1 2 2 3 3 3 7% 10% 65%	3113
	21st to end	Night	4 4 1 4 4 3 4 4 7% 11% 54%	3487
September	1st to 10th	Night	7% 5% 2 4 4 4 3 3 6% 8% 54%	2076
	11th to 20th	Night	8% 5% 2 4 4 4 5% 5% 6% 7% 51%	2090
	21st to end	Night	8% 4 2 4 3 3 4 3 6% 7% 57%	2090
October	1st to 10th	Night	4 2 2 3 2 2 3 3 5% 7% 67%	2090
	11th to 20th	Night	10% 4 1 4 3 3 3 3 4 5% 61%	2090
	21st to end	Night	11% 4 1 4 3 2 2 2 3 4 63%	2503
November	1st to 10th	Night	10% 4 2 4 3 2 3 2 4 6% 61%	2442
	11th to 20th	Night	7% 3 1 3 3 3 4 3 5% 6% 62%	2600
	21st to end	Night	11% 5% 2 4 3 4 4 3 4 6% 54%	2600
December	1st to 10th	Night	19% 7% 2 4 3 3 4 3 4 5% 45%	4250
	11th to 20th	Night	12% 6% 2 6% 4 3 3 3 4 5% 52%	4816
	21st to end	Night	9% 5% 2 4 3 2 2 2 3 5% 63%	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	28% 2 5% 16% 24% 25%	2938
	11th to 20th	Day	27% 3 6% 15% 32% 18%	3021
	21st to end	Day	33% 4 6% 15% 30% 12%	3497
February	1st to 10th	Day	32% 4 7% 14% 22% 21%	1900
	11th to 20th	Day	33% 4 6% 19% 21% 17%	1859
	21st to end	Day	30% 4 7% 14% 26% 20%	1570
March	1st to 10th	Day	37% 4 6% 13% 20% 20%	3213
	11th to 20th	Day	45% 5% 8% 12% 18% 12%	3480
	21st to end	Day	30% 6% 8% 16% 20% 21%	3814
April	1st to 10th	Day	30% 5% 9% 19% 20% 17%	2109
	11th to 20th	Day	35% 5% 6% 17% 22% 15%	2254
	21st to end	Day	32% 4 7% 21% 22% 14%	2304
May	1st to 10th	Day	39% 7% 9% 14% 20% 11%	4120
	11th to 20th	Day	36% 6% 7% 17% 22% 11%	4086
	21st to end	Day	32% 8% 12% 26% 16% 7%	4489
June	1st to 10th	Day	24% 6% 12% 31% 23% 4	2470
	11th to 20th	Day	23% 7% 13% 27% 24% 7%	2470
	21st to end	Day	29% 9% 13% 24% 20% 6%	2470
July	1st to 10th	Day	27% 8% 17% 38% 10% 1	4056
	11th to 20th	Day	20% 7% 14% 35% 20% 3	4051
	21st to end	Day	27% 8% 17% 29% 17% 2	4308
August	1st to 10th	Day	13% 5% 10% 39% 32% 1	3772
	11th to 20th	Day	19% 6% 16% 42% 15% 2	3762
	21st to end	Day	28% 10% 16% 23% 20% 2	4179
September	1st to 10th	Day	36% 8% 10% 19% 18% 9%	2103
	11th to 20th	Day	36% 8% 10% 20% 20% 6%	2090
	21st to end	Day	29% 6% 10% 23% 20% 12%	2090
October	1st to 10th	Day	14% 4 6% 14% 27% 35%	3480
	11th to 20th	Day	24% 5% 6% 18% 22% 25%	3432
	21st to end	Day	20% 3 5% 18% 41% 13%	3428
November	1st to 10th	Day	31% 4 8% 21% 22% 13%	1853
	11th to 20th	Day	26% 5% 7% 19% 22% 20%	1800
	21st to end	Day	33% 3 5% 19% 25% 16%	1800
December	1st to 10th	Day	43% 3 5% 17% 21% 11%	2940
	11th to 20th	Day	36% 5% 7% 13% 25% 15%	3389
	21st to end	Day	25% 3 3 18% 27% 23%	4488
January	1st to 10th	Night	29% 3 5% 13% 29% 22%	4238
	11th to 20th	Night	21% 2 4 19% 26% 28%	4184
	21st to end	Night	35% 3 5% 13% 29% 15%	4192
February	1st to 10th	Night	30% 4 8% 15% 23% 20%	2280
	11th to 20th	Night	32% 3 6% 18% 22% 19%	2218
	21st to end	Night	30% 4 6% 14% 23% 22%	1884
March	1st to 10th	Night	28% 6% 9% 17% 25% 16%	3646
	11th to 20th	Night	40% 6% 8% 15% 18% 14%	3480
	21st to end	Night	30% 6% 9% 18% 17% 20%	3817
April	1st to 10th	Night	26% 6% 10% 21% 18% 20%	2066
	11th to 20th	Night	31% 5% 10% 17% 19% 18%	1877
	21st to end	Night	26% 5% 10% 24% 22% 13%	1875
May	1st to 10th	Night	34% 5% 9% 21% 19% 12%	2850
	11th to 20th	Night	28% 7% 11% 23% 19% 12%	2824
	21st to end	Night	27% 9% 14% 28% 14% 9%	3099
June	1st to 10th	Night	14% 7% 18% 35% 23% 3	1710
	11th to 20th	Night	15% 6% 16% 31% 25% 7%	1710
	21st to end	Night	21% 6% 17% 30% 20% 6%	1710
July	1st to 10th	Night	19% 9% 22% 39% 10% 1	2805
	11th to 20th	Night	11% 6% 18% 40% 22% 3	2796
	21st to end	Night	19% 7% 20% 36% 17% 1	2999
August	1st to 10th	Night	11% 5% 13% 37% 33% 1	3144
	11th to 20th	Night	15% 6% 21% 42% 14% 2	3143
	21st to end	Night	22% 10% 22% 25% 19% 2	3487
September	1st to 10th	Night	27% 7% 12% 25% 20% 10%	2076
	11th to 20th	Night	29% 9% 16% 22% 18% 7%	2090
	21st to end	Night	26% 6% 13% 22% 20% 14%	2090
October	1st to 10th	Night	12% 4 8% 17% 23% 37%	3480
	11th to 20th	Night	19% 4 10% 16% 29% 23%	3460
	21st to end	Night	19% 3 6% 23% 33% 17%	4115
November	1st to 10th	Night	26% 4 9% 20% 25% 16%	2442
	11th to 20th	Night	23% 5% 9% 22% 22% 20%	2600
	21st to end	Night	32% 4 8% 17% 23% 16%	2600
December	1st to 10th	Night	41% 4 7% 17% 17% 13%	4250
	11th to 20th	Night	34% 4 6% 15% 23% 18%	4817
	21st to end	Night	25% 3 4 19% 29% 19%	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	12% 16% 42% 22% 7% 1	300
	11th to 20th	Day	16% 15% 31% 29% 9% 1	300
	21st to end	Day	10% 17% 40% 24% 8%	300
February	1st to 10th	Day	20% 15% 37% 21% 7% 1	270
	11th to 20th	Day	19% 15% 39% 23% 4	270
	21st to end	Day	17% 17% 44% 20% 3	225
March	1st to 10th	Day	14% 19% 41% 21% 4	270
	11th to 20th	Day	16% 16% 40% 19% 8%	270
	21st to end	Day	15% 19% 45% 14% 6% 1	297
April	1st to 10th	Day	15% 20% 40% 22% 2	289
	11th to 20th	Day	14% 20% 42% 21% 3	452
	21st to end	Day	11% 19% 41% 24% 5%	484
May	1st to 10th	Day	11% 12% 42% 28% 6%	653
	11th to 20th	Day	15% 9% 34% 30% 10% 2	675
	21st to end	Day	11% 9% 30% 38% 11% 1	734
June	1st to 10th	Day	4 4 20% 48% 21% 3	680
	11th to 20th	Day	4 1 25% 49% 18% 3	680
	21st to end	Day	4 1 16% 42% 33% 5%	680
July	1st to 10th	Day	7% 2 9% 37% 37% 9%	671
	11th to 20th	Day	2 5% 44% 41% 7%	668
	21st to end	Day	4 1 5% 39% 39% 12%	734
August	1st to 10th	Day	2 6% 35% 43% 13%	487
	11th to 20th	Day	6% 1 7% 35% 38% 13%	477
	21st to end	Day	6% 1 6% 30% 40% 18%	539
September	1st to 10th	Day	13% 1 4 27% 35% 20%	313
	11th to 20th	Day	6% 1 8% 24% 42% 19%	300
	21st to end	Day	13% 2 4 35% 33% 14%	300
October	1st to 10th	Day	5% 3 11% 35% 36% 10%	300
	11th to 20th	Day	10% 4 21% 41% 20% 3	300
	21st to end	Day	15% 12% 25% 27% 17% 4	330
November	1st to 10th	Day	17% 9% 26% 30% 16% 2	300
	11th to 20th	Day	14% 12% 31% 23% 13% 7%	300
	21st to end	Day	17% 17% 33% 20% 10% 2	300
December	1st to 10th	Day	16% 9% 30% 32% 10% 3	300
	11th to 20th	Day	13% 17% 35% 24% 9% 2	300
	21st to end	Day	13% 15% 35% 27% 9%	330
January	1st to 10th	Night	15% 8% 37% 32% 8%	1000
	11th to 20th	Night	14% 9% 36% 34% 7%	960
	21st to end	Night	16% 9% 38% 31% 7%	840
February	1st to 10th	Night	15% 11% 38% 32% 4	760
	11th to 20th	Night	16% 13% 42% 26% 3	744
	21st to end	Night	13% 16% 46% 24% 1	628
March	1st to 10th	Night	15% 14% 44% 25% 3	711
	11th to 20th	Night	13% 10% 43% 29% 5%	570
	21st to end	Night	8% 14% 53% 24% 2	627
April	1st to 10th	Night	7% 13% 53% 24% 3	570
	11th to 20th	Night	10% 14% 51% 23% 2	563
	21st to end	Night	10% 11% 53% 21% 5%	570
May	1st to 10th	Night	8% 11% 50% 28% 4	570
	11th to 20th	Night	10% 6% 41% 35% 8%	561
	21st to end	Night	8% 7% 41% 35% 8%	617
June	1st to 10th	Night	2 2 32% 51% 13%	570
	11th to 20th	Night	2 1 37% 50% 9%	570
	21st to end	Night	3 2 22% 52% 20% 1	570
July	1st to 10th	Night	5% 1 10% 56% 25% 3	555
	11th to 20th	Night	3 1 13% 59% 24% 1	552
	21st to end	Night	2 1 8% 59% 29% 1	624
August	1st to 10th	Night	1 1 5% 63% 27% 2	567
	11th to 20th	Night	5% 1 6% 53% 32% 3	564
	21st to end	Night	4 1 8% 46% 36% 5%	627
September	1st to 10th	Night	6% 2 9% 46% 34% 3	570
	11th to 20th	Night	9% 1 8% 44% 36% 2	570
	21st to end	Night	9% 1 14% 46% 29% 1	570
October	1st to 10th	Night	5% 1 14% 51% 28%	570
	11th to 20th	Night	10% 5% 24% 45% 15% 1	570
	21st to end	Night	11% 9% 29% 34% 16% 1	831
November	1st to 10th	Night	12% 5% 27% 40% 15% 1	882
	11th to 20th	Night	10% 6% 33% 35% 15% 2	1000
	21st to end	Night	13% 9% 34% 32% 11% 1	1000
December	1st to 10th	Night	14% 7% 30% 39% 9%	1000
	11th to 20th	Night	17% 10% 32% 35% 6%	1000
	21st to end	Night	11% 10% 37% 35% 7%	1100

Page generated at 2025-01-19 02:06:47. Version ac07

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