Lady Bird Johnson Municipal Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lady Bird Johnson Municipal Park clear sky chart from 2005-11-06 to 2025-07-06.

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	11% 6% 2 5% 4 4 4 3 5% 7% 49%	120218
	Night	11% 6% 2 5% 3 3 3 3 5% 7% 53%	118859
Transparency	Day	34% 4 9% 21% 20% 12%	124078
	Night	32% 4 9% 20% 20% 14%	123129
Seeing	Day	13% 8% 23% 30% 21% 6%	15720
	Night	13% 8% 26% 36% 15% 1	25663

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	12% 8% 2 5% 3 4 3 3 3 4 54%	4077
	11th to 20th	Day	12% 7% 2 3 3 3 2 3 4 6% 56%	4080
	21st to end	Day	21% 6% 2 5% 3 2 2 2 3 6% 47%	4966
February	1st to 10th	Day	15% 7% 2 6% 3 3 3 3 4 5% 49%	2000
	11th to 20th	Day	14% 7% 2 5% 4 3 4 3 5% 5% 48%	1949
	21st to end	Day	14% 6% 2 5% 2 2 3 3 4 5% 52%	1650
March	1st to 10th	Day	11% 6% 2 4 3 3 3 3 5% 6% 55%	4758
	11th to 20th	Day	12% 7% 2 6% 3 3 3 2 3 5% 53%	4980
	21st to end	Day	12% 6% 2 5% 4 4 3 3 4 6% 50%	5462
April	1st to 10th	Day	12% 7% 3 6% 4 4 3 3 5% 6% 47%	2200
	11th to 20th	Day	17% 6% 2 5% 4 4 3 3 4 6% 46%	2274
	21st to end	Day	12% 7% 2 6% 5% 4 4 3 4 5% 48%	2495
May	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 6% 7% 38%	5862
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 46%	5862
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 4 6% 9% 36%	6434
June	1st to 10th	Day	6% 4 1 6% 4 4 5% 4 6% 9% 50%	2600
	11th to 20th	Day	6% 5% 2 5% 4 4 4 4 7% 9% 50%	2600
	21st to end	Day	7% 4 2 5% 5% 5% 6% 6% 7% 9% 44%	2600
July	1st to 10th	Day	7% 4 2 6% 4 5% 6% 4 7% 9% 46%	4186
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 10% 54%	4120
	21st to end	Day	8% 4 2 5% 4 5% 7% 5% 8% 10% 42%	4465
August	1st to 10th	Day	1 1 1 3 3 3 3 3 5% 9% 68%	3947
	11th to 20th	Day	4 3 1 3 3 3 3 4 6% 10% 60%	3726
	21st to end	Day	4 3 2 5% 5% 5% 7% 5% 8% 10% 46%	4094
September	1st to 10th	Day	10% 7% 2 7% 5% 4 4 3 4 6% 46%	2090
	11th to 20th	Day	10% 6% 2 7% 6% 4 5% 4 6% 8% 42%	2090
	21st to end	Day	9% 4 1 5% 5% 4 4 4 7% 7% 50%	2090
October	1st to 10th	Day	6% 4 1 5% 3 3 4 3 5% 7% 57%	2090
	11th to 20th	Day	12% 5% 2 4 3 3 4 3 4 5% 53%	2014
	21st to end	Day	11% 4 2 4 3 2 3 3 3 5% 59%	2090
November	1st to 10th	Day	14% 8% 2 6% 3 3 3 3 5% 5% 48%	1948
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 5% 6% 53%	1800
	21st to end	Day	15% 6% 2 5% 4 3 3 3 4 6% 50%	1800
December	1st to 10th	Day	21% 9% 3 6% 3 3 3 2 4 4 42%	2940
	11th to 20th	Day	12% 8% 3 7% 4 4 4 3 4 6% 45%	3391
	21st to end	Day	10% 6% 2 5% 3 2 3 2 3 4 61%	4488
January	1st to 10th	Night	14% 5% 2 5% 2 2 3 2 4 5% 55%	5888
	11th to 20th	Night	10% 3 1 3 2 2 2 2 4 6% 66%	5900
	21st to end	Night	26% 6% 2 5% 3 3 3 2 4 5% 42%	6053
February	1st to 10th	Night	13% 7% 2 5% 4 3 3 2 3 5% 52%	2400
	11th to 20th	Night	15% 7% 3 5% 3 3 3 2 4 5% 51%	2338
	21st to end	Night	15% 8% 2 4 4 3 3 2 5% 5% 49%	1980
March	1st to 10th	Night	10% 8% 2 5% 4 3 3 3 6% 8% 49%	5103
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 4 4 53%	4980
	21st to end	Night	13% 10% 2 5% 3 3 3 3 4 6% 49%	5467
April	1st to 10th	Night	10% 7% 3 5% 3 4 3 3 6% 6% 50%	2200
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 6% 49%	2070
	21st to end	Night	15% 7% 2 5% 3 3 3 3 4 6% 49%	1904
May	1st to 10th	Night	21% 9% 3 5% 3 3 3 3 4 6% 40%	4053
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 6% 7% 51%	4053
	21st to end	Night	14% 7% 2 5% 4 4 4 3 5% 11% 41%	4443
June	1st to 10th	Night	4 3 1 4 3 3 4 4 5% 10% 60%	1800
	11th to 20th	Night	5% 4 1 4 3 3 3 3 6% 8% 61%	1800
	21st to end	Night	6% 4 1 3 4 4 4 4 6% 8% 56%	1800
July	1st to 10th	Night	6% 4 1 4 3 4 5% 4 6% 10% 55%	2895
	11th to 20th	Night	3 3 1 4 3 3 3 4 6% 9% 61%	2850
	21st to end	Night	5% 7% 2 6% 4 4 4 4 6% 10% 47%	3098
August	1st to 10th	Night	1 2 1 2 2 2 3 3 4 6% 75%	2987
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 11% 62%	3113
	21st to end	Night	4 5% 2 4 3 3 4 4 7% 11% 54%	3570
September	1st to 10th	Night	9% 4 2 6% 3 4 5% 3 5% 8% 51%	2090
	11th to 20th	Night	9% 6% 3 5% 4 4 5% 3 5% 8% 47%	2090
	21st to end	Night	7% 5% 3 5% 4 4 4 3 5% 8% 54%	2090
October	1st to 10th	Night	5% 4 1 4 3 2 3 2 5% 6% 64%	2090
	11th to 20th	Night	12% 4 2 5% 3 3 4 2 5% 6% 56%	2145
	21st to end	Night	13% 5% 1 4 3 2 3 1 3 4 61%	2508
November	1st to 10th	Night	12% 6% 2 6% 3 3 3 2 4 6% 55%	2345
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 4 6% 59%	2600
	21st to end	Night	15% 5% 2 5% 3 3 3 3 4 6% 50%	2600
December	1st to 10th	Night	19% 8% 3 5% 3 3 4 3 5% 5% 42%	4250
	11th to 20th	Night	14% 11% 2 6% 3 3 3 2 3 4 48%	4816
	21st to end	Night	13% 6% 2 4 2 2 2 2 3 4 59%	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	37% 2 2 20% 23% 14%	4078
	11th to 20th	Day	32% 2 4 16% 27% 19%	4080
	21st to end	Day	42% 2 4 11% 26% 15%	4966
February	1st to 10th	Day	38% 3 5% 12% 23% 19%	2000
	11th to 20th	Day	38% 4 6% 19% 19% 14%	1959
	21st to end	Day	35% 4 5% 17% 22% 17%	1650
March	1st to 10th	Day	32% 3 4 17% 18% 26%	4758
	11th to 20th	Day	36% 4 5% 8% 15% 32%	4980
	21st to end	Day	37% 4 8% 18% 21% 14%	5464
April	1st to 10th	Day	39% 4 8% 17% 18% 14%	2200
	11th to 20th	Day	41% 4 7% 17% 19% 12%	2274
	21st to end	Day	39% 5% 7% 21% 19% 11%	2495
May	1st to 10th	Day	45% 5% 8% 18% 18% 6%	5900
	11th to 20th	Day	35% 4 12% 16% 22% 11%	5866
	21st to end	Day	43% 7% 9% 25% 13% 3	6447
June	1st to 10th	Day	29% 7% 13% 29% 20% 3	2600
	11th to 20th	Day	30% 7% 11% 26% 21% 5%	2600
	21st to end	Day	35% 7% 12% 25% 16% 4	2600
July	1st to 10th	Day	32% 6% 17% 38% 8% 1	4122
	11th to 20th	Day	25% 5% 15% 35% 17% 3	4051
	21st to end	Day	33% 6% 17% 31% 12% 1	4325
August	1st to 10th	Day	14% 4 11% 40% 30% 1	3933
	11th to 20th	Day	21% 4 22% 38% 13% 2	3762
	21st to end	Day	30% 7% 18% 24% 18% 2	4093
September	1st to 10th	Day	39% 7% 10% 18% 18% 9%	2090
	11th to 20th	Day	38% 7% 11% 20% 18% 5%	2090
	21st to end	Day	33% 6% 9% 21% 19% 13%	2090
October	1st to 10th	Day	17% 3 6% 11% 26% 36%	3480
	11th to 20th	Day	25% 3 7% 19% 24% 22%	3332
	21st to end	Day	27% 3 3 18% 36% 13%	3428
November	1st to 10th	Day	39% 5% 7% 18% 20% 12%	1948
	11th to 20th	Day	33% 4 7% 17% 21% 18%	1800
	21st to end	Day	39% 4 5% 17% 22% 15%	1800
December	1st to 10th	Day	49% 2 5% 16% 18% 10%	2940
	11th to 20th	Day	41% 3 7% 13% 22% 14%	3389
	21st to end	Day	30% 2 3 16% 28% 21%	4488
January	1st to 10th	Night	35% 1 4 18% 27% 15%	5888
	11th to 20th	Night	23% 1 3 20% 27% 25%	5900
	21st to end	Night	46% 2 3 10% 21% 17%	6053
February	1st to 10th	Night	38% 3 5% 11% 23% 20%	2400
	11th to 20th	Night	37% 4 6% 17% 20% 17%	2338
	21st to end	Night	39% 3 6% 12% 21% 19%	1980
March	1st to 10th	Night	36% 3 5% 19% 20% 17%	5103
	11th to 20th	Night	35% 5% 6% 10% 15% 29%	4980
	21st to end	Night	38% 4 7% 18% 19% 14%	5467
April	1st to 10th	Night	35% 5% 9% 18% 16% 17%	2200
	11th to 20th	Night	38% 4 9% 15% 18% 16%	2070
	21st to end	Night	39% 4 9% 19% 19% 10%	1904
May	1st to 10th	Night	47% 3 7% 18% 14% 10%	4080
	11th to 20th	Night	32% 5% 12% 19% 18% 14%	4054
	21st to end	Night	39% 5% 14% 27% 11% 4	4452
June	1st to 10th	Night	20% 8% 16% 34% 19% 3	1800
	11th to 20th	Night	22% 7% 14% 30% 22% 6%	1800
	21st to end	Night	26% 6% 18% 29% 17% 4	1800
July	1st to 10th	Night	25% 7% 24% 37% 6% 1	2850
	11th to 20th	Night	20% 6% 20% 36% 17% 1	2796
	21st to end	Night	32% 5% 23% 31% 8%	2999
August	1st to 10th	Night	12% 3 14% 44% 26% 1	2977
	11th to 20th	Night	18% 5% 30% 35% 11% 2	3143
	21st to end	Night	25% 10% 21% 25% 19% 2	3570
September	1st to 10th	Night	32% 7% 13% 21% 19% 8%	2090
	11th to 20th	Night	34% 8% 15% 22% 16% 6%	2090
	21st to end	Night	30% 6% 12% 21% 18% 14%	2090
October	1st to 10th	Night	14% 3 8% 14% 22% 37%	3480
	11th to 20th	Night	22% 3 9% 17% 30% 19%	3553
	21st to end	Night	25% 2 4 20% 34% 15%	4120
November	1st to 10th	Night	33% 4 7% 20% 22% 14%	2345
	11th to 20th	Night	28% 4 8% 21% 21% 18%	2600
	21st to end	Night	37% 3 8% 16% 20% 16%	2600
December	1st to 10th	Night	46% 2 7% 16% 16% 12%	4250
	11th to 20th	Night	42% 2 5% 11% 21% 19%	4817
	21st to end	Night	32% 2 3 16% 28% 18%	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	19% 12% 39% 24% 5% 1	300
	11th to 20th	Day	19% 15% 33% 24% 8% 1	300
	21st to end	Day	17% 14% 38% 24% 7%	330
February	1st to 10th	Day	21% 14% 35% 22% 8%	300
	11th to 20th	Day	22% 15% 40% 21% 2	300
	21st to end	Day	23% 14% 41% 18% 4	249
March	1st to 10th	Day	18% 19% 39% 21% 3	300
	11th to 20th	Day	19% 16% 39% 19% 6% 1	300
	21st to end	Day	17% 15% 44% 19% 4 2	330
April	1st to 10th	Day	17% 18% 40% 20% 4	300
	11th to 20th	Day	21% 18% 36% 21% 4	392
	21st to end	Day	17% 15% 40% 22% 6%	595
May	1st to 10th	Day	15% 14% 38% 27% 6%	703
	11th to 20th	Day	18% 9% 32% 29% 10% 2	725
	21st to end	Day	17% 9% 27% 32% 14% 1	789
June	1st to 10th	Day	6% 5% 18% 43% 24% 5%	730
	11th to 20th	Day	7% 4 17% 49% 19% 4	730
	21st to end	Day	7% 4 11% 36% 34% 8%	730
July	1st to 10th	Day	9% 4 8% 34% 33% 11%	697
	11th to 20th	Day	4 2 4 36% 43% 10%	668
	21st to end	Day	5% 1 4 35% 41% 13%	739
August	1st to 10th	Day	2 1 2 39% 41% 14%	584
	11th to 20th	Day	8% 2 3 32% 40% 14%	477
	21st to end	Day	7% 1 4 26% 42% 20%	492
September	1st to 10th	Day	10% 1 5% 29% 32% 23%	300
	11th to 20th	Day	6% 1 4 27% 43% 19%	300
	21st to end	Day	10% 3 4 28% 40% 15%	300
October	1st to 10th	Day	5% 3 12% 33% 37% 10%	300
	11th to 20th	Day	9% 4 22% 40% 22% 4	300
	21st to end	Day	18% 13% 25% 26% 15% 3	330
November	1st to 10th	Day	20% 8% 26% 33% 9% 4	300
	11th to 20th	Day	16% 11% 26% 28% 13% 5%	300
	21st to end	Day	21% 14% 35% 19% 9% 3	300
December	1st to 10th	Day	16% 12% 31% 26% 13% 2	300
	11th to 20th	Day	15% 18% 34% 23% 10% 1	300
	21st to end	Day	15% 14% 34% 26% 11% 1	330
January	1st to 10th	Night	17% 9% 33% 32% 8% 1	1000
	11th to 20th	Night	17% 11% 35% 32% 6%	1000
	21st to end	Night	20% 11% 33% 29% 7%	910
February	1st to 10th	Night	20% 13% 32% 29% 6%	800
	11th to 20th	Night	20% 15% 35% 27% 3	784
	21st to end	Night	20% 13% 45% 21% 1	660
March	1st to 10th	Night	18% 14% 36% 29% 2	685
	11th to 20th	Night	19% 10% 38% 28% 5%	600
	21st to end	Night	14% 12% 43% 27% 4	660
April	1st to 10th	Night	12% 12% 47% 27% 3	600
	11th to 20th	Night	17% 13% 40% 27% 3	593
	21st to end	Night	16% 11% 44% 23% 6%	600
May	1st to 10th	Night	16% 11% 41% 28% 4	600
	11th to 20th	Night	11% 9% 35% 37% 8% 1	591
	21st to end	Night	13% 7% 34% 34% 11%	650
June	1st to 10th	Night	4 3 22% 50% 20% 1	600
	11th to 20th	Night	6% 2 26% 51% 14% 1	600
	21st to end	Night	6% 3 13% 50% 26% 2	600
July	1st to 10th	Night	9% 4 6% 50% 29% 3	570
	11th to 20th	Night	4 1 7% 52% 33% 3	552
	21st to end	Night	4 1 6% 53% 32% 4	624
August	1st to 10th	Night	2 1 4 51% 39% 3	567
	11th to 20th	Night	5% 2 4 48% 38% 3	564
	21st to end	Night	6% 3 6% 39% 39% 7%	627
September	1st to 10th	Night	10% 2 6% 42% 36% 5%	570
	11th to 20th	Night	12% 2 6% 41% 37% 3	570
	21st to end	Night	9% 2 11% 42% 33% 3	570
October	1st to 10th	Night	6% 3 9% 51% 28% 2	570
	11th to 20th	Night	12% 4 20% 46% 16% 2	625
	21st to end	Night	16% 8% 25% 30% 19% 2	836
November	1st to 10th	Night	14% 8% 20% 41% 15% 1	785
	11th to 20th	Night	12% 8% 28% 36% 15% 1	1000
	21st to end	Night	18% 11% 30% 31% 10% 1	1000
December	1st to 10th	Night	16% 11% 27% 37% 9% 1	1000
	11th to 20th	Night	21% 11% 30% 31% 7%	1000
	21st to end	Night	15% 10% 31% 35% 7%	1100

Page generated at 2025-07-03 00:30:12. Version ac07

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