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 2026-10-29.

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	10% 6% 2 5% 4 4 4 3 5% 7% 50%	149181
	Night	11% 6% 2 5% 3 3 3 3 5% 7% 53%	143334
Transparency	Day	34% 4 10% 23% 20% 11%	152999
	Night	32% 4 10% 21% 20% 13%	147583
Seeing	Day	12% 8% 22% 31% 21% 6%	17482
	Night	13% 8% 26% 37% 15% 1	27326

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	10% 6% 2 4 3 4 4 3 4 5% 56%	5289
	11th to 20th	Day	11% 7% 2 4 3 3 2 3 4 5% 57%	5310
	21st to end	Day	20% 6% 2 5% 4 3 3 2 4 6% 45%	6426
February	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 4 5% 50%	2100
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 5% 6% 48%	2049
	21st to end	Day	13% 6% 2 5% 2 2 3 2 4 5% 53%	1730
March	1st to 10th	Day	11% 6% 2 4 3 3 3 3 5% 6% 54%	4864
	11th to 20th	Day	12% 7% 2 6% 3 3 3 2 3 5% 54%	5090
	21st to end	Day	11% 6% 2 5% 4 4 3 3 4 6% 50%	5583
April	1st to 10th	Day	13% 7% 3 6% 4 4 3 3 5% 6% 45%	2310
	11th to 20th	Day	17% 6% 2 6% 5% 4 3 4 4 6% 44%	2389
	21st to end	Day	13% 7% 2 6% 5% 4 4 3 4 5% 47%	2620
May	1st to 10th	Day	18% 8% 2 6% 4 4 4 4 6% 7% 39%	7617
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 43%	7627
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	8392
June	1st to 10th	Day	6% 4 2 6% 5% 4 5% 4 7% 9% 48%	2730
	11th to 20th	Day	6% 5% 2 5% 5% 5% 4 4 7% 9% 48%	2730
	21st to end	Day	6% 4 2 5% 5% 5% 6% 6% 7% 9% 45%	2730
July	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 9% 44%	7680
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 9% 42%	7680
	21st to end	Day	5% 3 1 4 3 4 5% 4 6% 9% 55%	8337
August	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 8% 71%	5782
	11th to 20th	Day	3 2 1 2 2 3 3 3 6% 10% 64%	5483
	21st to end	Day	3 3 1 4 4 4 5% 4 7% 9% 56%	5962
September	1st to 10th	Day	10% 6% 2 7% 5% 4 4 4 4 6% 47%	2310
	11th to 20th	Day	9% 5% 2 7% 6% 4 5% 4 6% 9% 43%	2310
	21st to end	Day	8% 4 1 5% 5% 4 4 4 7% 7% 49%	2310
October	1st to 10th	Day	7% 4 1 5% 3 3 4 4 5% 7% 57%	2310
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 4 5% 55%	2226
	21st to end	Day	10% 4 2 4 4 3 3 3 4 5% 59%	2280
November	1st to 10th	Day	13% 7% 2 5% 3 3 3 3 5% 4 50%	2047
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 5% 6% 54%	1890
	21st to end	Day	15% 7% 2 5% 4 3 3 3 3 6% 49%	1890
December	1st to 10th	Day	21% 9% 3 6% 3 3 3 2 4 4 43%	3030
	11th to 20th	Day	12% 8% 3 7% 4 4 4 3 4 6% 45%	3481
	21st to end	Day	10% 6% 2 5% 3 2 3 2 3 4 61%	4587
January	1st to 10th	Night	11% 5% 2 5% 3 2 3 2 3 5% 58%	7634
	11th to 20th	Night	8% 3 2 3 2 2 2 2 5% 5% 66%	7680
	21st to end	Night	25% 7% 2 5% 3 3 3 2 4 5% 42%	7829
February	1st to 10th	Night	13% 7% 2 5% 4 3 3 2 3 5% 53%	2520
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 5% 6% 50%	2458
	21st to end	Night	14% 8% 2 4 4 3 3 2 5% 5% 51%	2076
March	1st to 10th	Night	10% 8% 2 5% 4 3 3 3 6% 8% 48%	5217
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 4 5% 53%	5090
	21st to end	Night	13% 10% 2 5% 3 3 3 3 4 6% 49%	5588
April	1st to 10th	Night	10% 7% 3 5% 4 4 3 3 6% 6% 48%	2310
	11th to 20th	Night	15% 8% 2 5% 4 3 3 3 3 6% 47%	2175
	21st to end	Night	16% 7% 2 5% 3 3 3 3 4 6% 48%	1999
May	1st to 10th	Night	20% 9% 3 6% 3 3 4 3 4 6% 39%	5266
	11th to 20th	Night	8% 6% 3 6% 5% 4 5% 4 6% 8% 46%	5265
	21st to end	Night	13% 7% 2 6% 4 4 4 4 6% 11% 39%	5793
June	1st to 10th	Night	4 3 1 4 3 3 4 4 5% 10% 58%	1890
	11th to 20th	Night	6% 4 1 4 3 4 3 3 6% 8% 59%	1890
	21st to end	Night	6% 4 1 3 4 4 4 4 6% 8% 56%	1890
July	1st to 10th	Night	7% 5% 2 5% 3 4 5% 4 6% 10% 50%	5308
	11th to 20th	Night	8% 4 1 5% 3 4 4 4 6% 10% 49%	5307
	21st to end	Night	3 4 2 4 3 4 4 3 6% 9% 59%	5770
August	1st to 10th	Night	1 2 1 2 1 2 2 2 3 6% 77%	4382
	11th to 20th	Night	2 2 1 3 2 3 3 3 6% 11% 65%	4583
	21st to end	Night	3 4 1 3 3 3 3 3 6% 9% 62%	5181
September	1st to 10th	Night	8% 4 2 6% 3 4 5% 3 5% 8% 51%	2310
	11th to 20th	Night	8% 5% 3 5% 5% 4 5% 3 5% 9% 47%	2310
	21st to end	Night	6% 5% 2 5% 4 4 4 4 5% 9% 52%	2310
October	1st to 10th	Night	6% 4 1 4 3 2 3 2 5% 6% 64%	2310
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 6% 57%	2371
	21st to end	Night	12% 5% 2 4 3 2 3 1 3 4 62%	2737
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 3 5% 57%	2466
	11th to 20th	Night	8% 6% 2 4 3 3 3 3 4 6% 59%	2730
	21st to end	Night	16% 6% 2 5% 3 3 3 2 4 6% 50%	2730
December	1st to 10th	Night	19% 8% 3 5% 3 3 4 3 5% 5% 42%	4380
	11th to 20th	Night	14% 11% 2 6% 3 3 3 2 3 4 49%	4946
	21st to end	Night	13% 6% 2 4 2 2 3 2 3 4 59%	6633

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 22% 26% 12%	5290
	11th to 20th	Day	32% 2 3 15% 27% 21%	5310
	21st to end	Day	43% 2 4 14% 25% 12%	6426
February	1st to 10th	Day	38% 3 6% 12% 23% 19%	2100
	11th to 20th	Day	38% 4 6% 19% 19% 14%	2059
	21st to end	Day	34% 3 5% 17% 24% 17%	1730
March	1st to 10th	Day	33% 3 4 16% 18% 26%	4864
	11th to 20th	Day	36% 4 5% 8% 15% 32%	5090
	21st to end	Day	36% 4 8% 18% 21% 13%	5585
April	1st to 10th	Day	40% 4 8% 17% 17% 14%	2310
	11th to 20th	Day	42% 4 8% 16% 18% 12%	2389
	21st to end	Day	40% 5% 8% 20% 18% 10%	2620
May	1st to 10th	Day	45% 4 10% 20% 17% 5%	7655
	11th to 20th	Day	39% 4 10% 17% 22% 9%	7631
	21st to end	Day	43% 6% 11% 26% 12% 2	8405
June	1st to 10th	Day	30% 7% 13% 29% 19% 3	2730
	11th to 20th	Day	32% 6% 11% 26% 20% 5%	2730
	21st to end	Day	34% 7% 12% 25% 18% 4	2730
July	1st to 10th	Day	36% 4 18% 36% 6%	7616
	11th to 20th	Day	36% 4 18% 27% 13% 2	7611
	21st to end	Day	25% 4 13% 34% 22% 2	8155
August	1st to 10th	Day	13% 3 11% 41% 27% 5%	5768
	11th to 20th	Day	17% 3 22% 42% 14% 2	5519
	21st to end	Day	24% 5% 14% 30% 23% 3	5961
September	1st to 10th	Day	38% 6% 10% 19% 18% 8%	2310
	11th to 20th	Day	36% 7% 13% 22% 18% 5%	2310
	21st to end	Day	33% 5% 10% 21% 18% 13%	2310
October	1st to 10th	Day	18% 3 6% 11% 27% 35%	3700
	11th to 20th	Day	25% 2 7% 20% 25% 21%	3544
	21st to end	Day	27% 3 4 19% 35% 13%	3618
November	1st to 10th	Day	38% 4 7% 17% 21% 13%	2047
	11th to 20th	Day	33% 4 7% 17% 21% 18%	1890
	21st to end	Day	40% 3 5% 16% 22% 14%	1890
December	1st to 10th	Day	48% 2 5% 16% 18% 10%	3030
	11th to 20th	Day	41% 3 7% 12% 22% 15%	3479
	21st to end	Day	30% 2 3 16% 28% 21%	4587
January	1st to 10th	Night	32% 1 5% 18% 29% 15%	7635
	11th to 20th	Night	23% 1 3 17% 30% 25%	7680
	21st to end	Night	47% 2 3 10% 23% 15%	7829
February	1st to 10th	Night	36% 3 5% 12% 24% 19%	2520
	11th to 20th	Night	36% 4 6% 18% 20% 16%	2458
	21st to end	Night	37% 3 6% 13% 22% 18%	2076
March	1st to 10th	Night	36% 3 5% 19% 20% 17%	5217
	11th to 20th	Night	35% 4 6% 11% 16% 29%	5090
	21st to end	Night	37% 4 7% 18% 19% 14%	5588
April	1st to 10th	Night	36% 5% 10% 18% 16% 16%	2310
	11th to 20th	Night	40% 4 9% 14% 17% 16%	2175
	21st to end	Night	41% 4 9% 19% 18% 10%	1999
May	1st to 10th	Night	48% 3 10% 18% 14% 8%	5293
	11th to 20th	Night	36% 4 11% 17% 19% 11%	5266
	21st to end	Night	40% 5% 17% 26% 9% 3	5805
June	1st to 10th	Night	22% 7% 16% 34% 18% 3	1890
	11th to 20th	Night	24% 6% 14% 29% 21% 5%	1890
	21st to end	Night	26% 6% 17% 30% 18% 4	1890
July	1st to 10th	Night	30% 5% 24% 34% 6%	5265
	11th to 20th	Night	31% 5% 26% 27% 10% 1	5256
	21st to end	Night	23% 4 17% 35% 18% 2	5641
August	1st to 10th	Night	11% 2 14% 46% 22% 4	4372
	11th to 20th	Night	16% 3 31% 38% 10% 1	4613
	21st to end	Night	20% 7% 17% 31% 23% 1	5181
September	1st to 10th	Night	32% 6% 13% 23% 18% 8%	2310
	11th to 20th	Night	33% 7% 16% 24% 15% 5%	2310
	21st to end	Night	30% 5% 13% 22% 17% 13%	2310
October	1st to 10th	Night	15% 3 8% 14% 23% 37%	3700
	11th to 20th	Night	22% 3 9% 18% 29% 19%	3779
	21st to end	Night	25% 2 4 20% 33% 15%	4349
November	1st to 10th	Night	32% 4 6% 19% 24% 14%	2466
	11th to 20th	Night	28% 4 8% 21% 21% 18%	2730
	21st to end	Night	37% 3 8% 17% 20% 16%	2730
December	1st to 10th	Night	46% 2 7% 16% 17% 12%	4380
	11th to 20th	Night	42% 2 5% 11% 21% 19%	4947
	21st to end	Night	32% 2 3 16% 28% 18%	6633

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% 23% 6% 1	330
	11th to 20th	Day	18% 16% 33% 23% 8% 1	330
	21st to end	Day	17% 14% 39% 23% 6%	363
February	1st to 10th	Day	20% 13% 35% 23% 8%	330
	11th to 20th	Day	22% 14% 39% 23% 2	330
	21st to end	Day	21% 14% 42% 19% 5%	273
March	1st to 10th	Day	18% 18% 38% 22% 3	330
	11th to 20th	Day	17% 16% 39% 21% 6% 1	330
	21st to end	Day	16% 13% 41% 23% 5% 2	363
April	1st to 10th	Day	18% 17% 38% 23% 4	330
	11th to 20th	Day	21% 19% 36% 21% 4	427
	21st to end	Day	18% 15% 40% 22% 5%	640
May	1st to 10th	Day	16% 14% 37% 27% 6%	753
	11th to 20th	Day	17% 10% 33% 28% 10% 2	775
	21st to end	Day	17% 9% 26% 33% 14% 1	844
June	1st to 10th	Day	7% 4 19% 42% 23% 5%	780
	11th to 20th	Day	7% 4 16% 49% 20% 4	780
	21st to end	Day	7% 4 12% 38% 32% 8%	780
July	1st to 10th	Day	10% 4 8% 36% 32% 11%	771
	11th to 20th	Day	5% 2 7% 35% 42% 9%	768
	21st to end	Day	4 2 4 36% 41% 13%	849
August	1st to 10th	Day	2 1 3 39% 42% 14%	674
	11th to 20th	Day	7% 1 3 34% 40% 14%	557
	21st to end	Day	6% 1 4 26% 42% 20%	575
September	1st to 10th	Day	10% 2 4 27% 35% 21%	360
	11th to 20th	Day	5% 1 3 29% 45% 16%	360
	21st to end	Day	9% 2 6% 32% 37% 14%	360
October	1st to 10th	Day	8% 3 11% 33% 36% 11%	360
	11th to 20th	Day	8% 3 22% 39% 23% 5%	360
	21st to end	Day	16% 13% 25% 28% 15% 4	387
November	1st to 10th	Day	19% 8% 25% 32% 12% 4	330
	11th to 20th	Day	15% 10% 25% 31% 14% 5%	330
	21st to end	Day	20% 14% 34% 18% 11% 2	330
December	1st to 10th	Day	16% 12% 32% 26% 12% 2	330
	11th to 20th	Day	15% 17% 33% 23% 11% 2	330
	21st to end	Day	14% 12% 33% 29% 10% 1	363
January	1st to 10th	Night	16% 9% 33% 33% 8%	1050
	11th to 20th	Night	16% 11% 35% 32% 6%	1050
	21st to end	Night	20% 12% 32% 29% 7%	955
February	1st to 10th	Night	19% 13% 32% 29% 6%	840
	11th to 20th	Night	19% 15% 35% 28% 3	824
	21st to end	Night	20% 12% 44% 23% 1	692
March	1st to 10th	Night	19% 14% 36% 29% 2	719
	11th to 20th	Night	19% 10% 38% 28% 5%	630
	21st to end	Night	14% 12% 42% 29% 4	693
April	1st to 10th	Night	12% 11% 47% 26% 3	630
	11th to 20th	Night	18% 13% 39% 26% 3	623
	21st to end	Night	17% 11% 43% 23% 6%	630
May	1st to 10th	Night	17% 10% 41% 27% 4	630
	11th to 20th	Night	11% 9% 35% 36% 8% 1	621
	21st to end	Night	13% 7% 33% 35% 12%	683
June	1st to 10th	Night	5% 3 22% 49% 20% 1	630
	11th to 20th	Night	6% 2 26% 51% 14% 1	630
	21st to end	Night	7% 3 14% 50% 25% 2	630
July	1st to 10th	Night	8% 4 6% 50% 29% 3	615
	11th to 20th	Night	5% 2 9% 50% 31% 2	612
	21st to end	Night	3 1 7% 52% 32% 3	690
August	1st to 10th	Night	2 4 52% 38% 3	627
	11th to 20th	Night	5% 2 4 49% 36% 3	624
	21st to end	Night	6% 2 6% 40% 39% 7%	693
September	1st to 10th	Night	9% 2 5% 42% 37% 5%	630
	11th to 20th	Night	11% 1 6% 43% 36% 3	630
	21st to end	Night	9% 2 11% 44% 32% 3	630
October	1st to 10th	Night	7% 3 9% 49% 30% 2	630
	11th to 20th	Night	11% 4 20% 45% 18% 2	691
	21st to end	Night	15% 8% 25% 32% 19% 2	913
November	1st to 10th	Night	13% 8% 20% 42% 15% 1	826
	11th to 20th	Night	12% 8% 27% 37% 15% 1	1050
	21st to end	Night	18% 10% 29% 32% 10% 1	1050
December	1st to 10th	Night	16% 10% 29% 36% 8% 1	1050
	11th to 20th	Night	20% 10% 30% 31% 8%	1050
	21st to end	Night	15% 10% 31% 35% 8% 1	1155

Page generated at 2026-10-26 03:37:48. Version ac07

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