Lyndon B. Johnson State Park & Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lyndon B. Johnson State Park & Historic Site 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	10% 5% 2 5% 4 4 4 4 5% 7% 49%	105248
	Night	10% 6% 2 5% 3 3 3 3 5% 7% 53%	104259
Transparency	Day	33% 6% 10% 21% 20% 10%	109092
	Night	31% 5% 10% 20% 20% 13%	108542
Seeing	Day	12% 9% 24% 31% 20% 5%	15076
	Night	12% 8% 29% 35% 14% 1	25130

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	11% 9% 2 4 2 3 3 2 4 5% 54%	2937
	11th to 20th	Day	14% 6% 1 4 2 2 2 2 4 5% 57%	2940
	21st to end	Day	15% 7% 2 6% 4 3 2 3 4 7% 47%	3432
February	1st to 10th	Day	14% 8% 2 5% 4 4 3 2 4 6% 47%	1900
	11th to 20th	Day	14% 8% 2 5% 3 3 4 2 5% 6% 47%	1849
	21st to end	Day	15% 6% 1 4 3 2 3 3 5% 5% 51%	1570
March	1st to 10th	Day	14% 8% 3 8% 4 4 3 3 5% 6% 44%	3342
	11th to 20th	Day	17% 10% 3 9% 5% 4 4 4 5% 5% 35%	3480
	21st to end	Day	11% 6% 2 6% 4 4 4 4 5% 7% 46%	3814
April	1st to 10th	Day	11% 7% 3 7% 4 3 3 3 5% 7% 46%	2090
	11th to 20th	Day	17% 7% 2 5% 4 4 4 3 5% 5% 44%	2125
	21st to end	Day	13% 6% 2 6% 4 4 4 3 4 6% 47%	2392
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 5% 5% 7% 34%	4082
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 3 4 6% 45%	4082
	21st to end	Day	11% 5% 2 7% 5% 5% 6% 5% 7% 9% 38%	4477
June	1st to 10th	Day	5% 4 2 5% 5% 4 5% 6% 7% 8% 49%	2470
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 6% 9% 50%	2470
	21st to end	Day	7% 5% 2 7% 6% 5% 5% 5% 8% 9% 43%	2470
July	1st to 10th	Day	6% 4 2 5% 5% 4 5% 4 7% 10% 49%	4120
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 11% 54%	4120
	21st to end	Day	8% 4 1 6% 4 5% 6% 5% 8% 10% 42%	4465
August	1st to 10th	Day	1 1 2 2 3 3 2 6% 8% 71%	3995
	11th to 20th	Day	4 2 1 4 3 3 4 4 6% 9% 61%	3726
	21st to end	Day	4 3 1 6% 5% 5% 6% 5% 7% 11% 48%	4062
September	1st to 10th	Day	11% 6% 3 7% 5% 4 4 4 5% 6% 46%	2090
	11th to 20th	Day	10% 6% 2 7% 6% 5% 6% 4 6% 7% 42%	2090
	21st to end	Day	9% 4 1 5% 5% 4 4 4 6% 7% 51%	2090
October	1st to 10th	Day	7% 4 1 4 3 4 4 3 5% 7% 57%	2090
	11th to 20th	Day	11% 5% 2 5% 3 4 3 4 4 5% 54%	1995
	21st to end	Day	11% 4 2 4 3 3 3 3 3 5% 58%	2090
November	1st to 10th	Day	13% 6% 2 7% 4 4 4 3 5% 6% 47%	1958
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 4 7% 52%	1816
	21st to end	Day	15% 6% 2 5% 4 3 3 3 3 6% 49%	1800
December	1st to 10th	Day	22% 8% 3 7% 3 3 2 2 4 5% 41%	2940
	11th to 20th	Day	10% 7% 3 7% 5% 4 4 4 6% 6% 45%	3391
	21st to end	Day	10% 5% 2 4 3 3 3 2 3 4 60%	4488
January	1st to 10th	Night	14% 6% 3 5% 2 2 2 2 4 5% 54%	4238
	11th to 20th	Night	12% 3 1 3 2 2 2 2 3 4 66%	4250
	21st to end	Night	17% 7% 2 6% 4 4 3 3 4 6% 44%	4288
February	1st to 10th	Night	14% 5% 3 6% 4 2 3 3 5% 5% 50%	2280
	11th to 20th	Night	15% 6% 2 4 4 3 3 3 4 5% 51%	2218
	21st to end	Night	13% 7% 1 6% 5% 3 3 3 4 5% 49%	1884
March	1st to 10th	Night	11% 8% 2 8% 5% 4 4 3 5% 7% 44%	3515
	11th to 20th	Night	16% 10% 3 6% 5% 4 5% 4 6% 5% 36%	3480
	21st to end	Night	10% 8% 2 6% 5% 4 5% 4 5% 5% 46%	3817
April	1st to 10th	Night	9% 7% 2 5% 5% 3 4 3 6% 7% 49%	2090
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 4 6% 47%	2000
	21st to end	Night	14% 7% 2 5% 4 3 3 3 4 6% 49%	1786
May	1st to 10th	Night	19% 11% 3 5% 3 3 3 3 4 6% 40%	2823
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 5% 7% 51%	2823
	21st to end	Night	11% 5% 1 5% 3 4 5% 4 6% 9% 45%	3090
June	1st to 10th	Night	3 3 2 3 4 3 4 3 5% 8% 61%	1710
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 9% 61%	1710
	21st to end	Night	6% 4 1 4 3 3 3 5% 6% 9% 56%	1710
July	1st to 10th	Night	5% 4 1 3 3 3 4 4 6% 10% 57%	2850
	11th to 20th	Night	3 2 1 4 3 3 4 4 5% 9% 62%	2850
	21st to end	Night	4 5% 2 6% 4 5% 6% 5% 8% 10% 46%	3098
August	1st to 10th	Night	1 1 1 2 1 2 3 2 4 7% 75%	2925
	11th to 20th	Night	3 2 1 3 2 2 4 3 7% 10% 63%	3113
	21st to end	Night	4 3 1 4 3 4 4 4 6% 11% 56%	3601
September	1st to 10th	Night	8% 4 2 4 3 4 5% 4 6% 7% 53%	2090
	11th to 20th	Night	8% 6% 2 6% 4 5% 4 3 6% 8% 47%	2090
	21st to end	Night	7% 4 1 5% 4 4 4 4 6% 8% 54%	2090
October	1st to 10th	Night	5% 3 1 3 3 2 3 3 5% 7% 64%	2090
	11th to 20th	Night	11% 4 2 4 3 3 4 3 5% 6% 55%	2166
	21st to end	Night	12% 4 2 4 3 3 2 2 3 4 61%	2508
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 6% 54%	2340
	11th to 20th	Night	8% 6% 2 3 3 3 3 2 5% 6% 58%	2580
	21st to end	Night	14% 5% 2 5% 4 4 3 3 5% 6% 50%	2600
December	1st to 10th	Night	19% 8% 3 6% 3 3 3 3 4 5% 43%	4250
	11th to 20th	Night	11% 8% 3 7% 4 4 4 3 4 5% 48%	4816
	21st to end	Night	11% 6% 2 4 3 2 3 2 3 5% 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	34% 3 3 18% 25% 17%	2938
	11th to 20th	Day	31% 3 6% 13% 30% 16%	2940
	21st to end	Day	38% 3 5% 12% 29% 12%	3432
February	1st to 10th	Day	40% 4 5% 13% 21% 17%	1900
	11th to 20th	Day	39% 4 7% 18% 19% 15%	1859
	21st to end	Day	36% 3 6% 17% 21% 17%	1570
March	1st to 10th	Day	41% 5% 6% 13% 21% 14%	3342
	11th to 20th	Day	50% 9% 6% 10% 16% 10%	3480
	21st to end	Day	35% 7% 9% 16% 19% 14%	3814
April	1st to 10th	Day	39% 5% 8% 17% 18% 13%	2090
	11th to 20th	Day	42% 5% 7% 16% 19% 11%	2125
	21st to end	Day	39% 5% 6% 21% 19% 10%	2392
May	1st to 10th	Day	48% 8% 8% 14% 16% 6%	4120
	11th to 20th	Day	40% 7% 8% 16% 21% 8%	4086
	21st to end	Day	39% 9% 11% 28% 11% 3	4489
June	1st to 10th	Day	29% 8% 13% 26% 20% 4	2470
	11th to 20th	Day	30% 8% 11% 27% 19% 5%	2470
	21st to end	Day	35% 9% 11% 23% 17% 4	2470
July	1st to 10th	Day	29% 7% 18% 37% 8% 1	4056
	11th to 20th	Day	23% 6% 17% 34% 17% 3	4051
	21st to end	Day	31% 9% 17% 31% 11% 1	4325
August	1st to 10th	Day	13% 4 12% 40% 31% 1	3981
	11th to 20th	Day	20% 5% 22% 39% 12% 3	3762
	21st to end	Day	28% 9% 20% 24% 18% 2	4061
September	1st to 10th	Day	38% 8% 10% 19% 17% 9%	2090
	11th to 20th	Day	39% 9% 11% 18% 18% 6%	2090
	21st to end	Day	31% 7% 9% 22% 18% 13%	2090
October	1st to 10th	Day	16% 4 7% 11% 25% 37%	3480
	11th to 20th	Day	23% 3 8% 19% 24% 23%	3300
	21st to end	Day	25% 3 5% 17% 36% 14%	3428
November	1st to 10th	Day	38% 5% 8% 18% 20% 12%	1958
	11th to 20th	Day	33% 4 7% 17% 21% 17%	1816
	21st to end	Day	38% 4 5% 17% 22% 14%	1800
December	1st to 10th	Day	48% 3 5% 17% 17% 10%	2940
	11th to 20th	Day	40% 5% 7% 12% 22% 15%	3389
	21st to end	Day	29% 3 4 16% 28% 20%	4488
January	1st to 10th	Night	34% 3 4 14% 25% 20%	4238
	11th to 20th	Night	25% 2 4 17% 28% 24%	4250
	21st to end	Night	41% 5% 5% 12% 25% 13%	4288
February	1st to 10th	Night	38% 4 6% 13% 22% 18%	2280
	11th to 20th	Night	36% 4 6% 17% 20% 17%	2218
	21st to end	Night	38% 4 7% 13% 21% 18%	1884
March	1st to 10th	Night	39% 7% 7% 15% 21% 11%	3515
	11th to 20th	Night	47% 8% 9% 11% 14% 11%	3480
	21st to end	Night	37% 8% 9% 16% 18% 12%	3817
April	1st to 10th	Night	34% 6% 9% 19% 17% 15%	2090
	11th to 20th	Night	39% 6% 9% 14% 18% 16%	2000
	21st to end	Night	38% 6% 8% 20% 19% 10%	1786
May	1st to 10th	Night	46% 7% 9% 17% 13% 9%	2850
	11th to 20th	Night	32% 8% 11% 22% 18% 9%	2824
	21st to end	Night	33% 9% 14% 29% 11% 4	3099
June	1st to 10th	Night	20% 9% 15% 32% 21% 3	1710
	11th to 20th	Night	20% 6% 15% 30% 23% 6%	1710
	21st to end	Night	24% 8% 17% 30% 18% 4	1710
July	1st to 10th	Night	22% 8% 26% 37% 6% 1	2805
	11th to 20th	Night	20% 7% 21% 35% 17% 1	2796
	21st to end	Night	29% 8% 24% 31% 8%	2999
August	1st to 10th	Night	10% 4 15% 42% 28% 1	2915
	11th to 20th	Night	17% 6% 30% 33% 11% 2	3143
	21st to end	Night	22% 10% 22% 26% 18% 2	3601
September	1st to 10th	Night	30% 8% 15% 21% 18% 8%	2090
	11th to 20th	Night	34% 8% 13% 23% 16% 5%	2090
	21st to end	Night	28% 7% 12% 21% 19% 13%	2090
October	1st to 10th	Night	14% 4 8% 15% 22% 38%	3480
	11th to 20th	Night	20% 4 9% 16% 30% 20%	3587
	21st to end	Night	22% 3 4 21% 34% 16%	4120
November	1st to 10th	Night	32% 5% 8% 19% 22% 14%	2340
	11th to 20th	Night	28% 4 8% 21% 21% 18%	2580
	21st to end	Night	36% 4 8% 16% 19% 16%	2600
December	1st to 10th	Night	45% 3 7% 16% 17% 12%	4250
	11th to 20th	Night	40% 3 5% 12% 21% 18%	4817
	21st to end	Night	30% 3 4 17% 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	20% 15% 41% 20% 4 1	300
	11th to 20th	Day	20% 16% 36% 21% 6% 1	300
	21st to end	Day	17% 18% 39% 21% 5% 1	300
February	1st to 10th	Day	26% 15% 32% 24% 3	270
	11th to 20th	Day	24% 23% 36% 16% 1	270
	21st to end	Day	25% 23% 38% 14%	225
March	1st to 10th	Day	18% 20% 39% 20% 3	270
	11th to 20th	Day	19% 19% 36% 21% 5%	270
	21st to end	Day	17% 19% 45% 15% 4	297
April	1st to 10th	Day	18% 22% 40% 17% 4	270
	11th to 20th	Day	19% 22% 36% 20% 4	323
	21st to end	Day	17% 15% 41% 22% 5%	572
May	1st to 10th	Day	14% 16% 40% 24% 6%	653
	11th to 20th	Day	18% 11% 30% 30% 9% 2	675
	21st to end	Day	16% 7% 29% 34% 14% 1	734
June	1st to 10th	Day	6% 3 21% 42% 24% 4	680
	11th to 20th	Day	7% 2 19% 49% 19% 4	680
	21st to end	Day	6% 2 14% 41% 29% 7%	680
July	1st to 10th	Day	8% 2 13% 36% 33% 9%	671
	11th to 20th	Day	4 1 7% 40% 42% 7%	668
	21st to end	Day	3 1 8% 39% 39% 10%	739
August	1st to 10th	Day	2 4 41% 41% 11%	619
	11th to 20th	Day	6% 7% 36% 39% 12%	477
	21st to end	Day	4 1 7% 28% 43% 18%	473
September	1st to 10th	Day	10% 10% 26% 35% 18%	300
	11th to 20th	Day	5% 2 5% 31% 43% 14%	300
	21st to end	Day	10% 1 8% 33% 36% 12%	300
October	1st to 10th	Day	6% 14% 39% 30% 10%	300
	11th to 20th	Day	10% 5% 25% 38% 18% 4	300
	21st to end	Day	17% 14% 26% 27% 15% 2	330
November	1st to 10th	Day	18% 8% 29% 33% 9% 4	300
	11th to 20th	Day	17% 11% 32% 25% 13% 3	300
	21st to end	Day	20% 19% 33% 18% 8% 2	300
December	1st to 10th	Day	18% 11% 33% 27% 8% 3	300
	11th to 20th	Day	15% 19% 35% 23% 7% 1	300
	21st to end	Day	15% 14% 38% 26% 5% 1	330
January	1st to 10th	Night	16% 11% 35% 31% 7%	1000
	11th to 20th	Night	17% 13% 35% 30% 5%	1000
	21st to end	Night	18% 12% 34% 30% 7%	897
February	1st to 10th	Night	19% 13% 37% 26% 5%	760
	11th to 20th	Night	19% 14% 40% 24% 2	744
	21st to end	Night	19% 17% 45% 17% 1	628
March	1st to 10th	Night	17% 14% 39% 28% 2	632
	11th to 20th	Night	18% 11% 36% 31% 4	570
	21st to end	Night	14% 15% 44% 24% 4	627
April	1st to 10th	Night	10% 15% 46% 27% 3	570
	11th to 20th	Night	15% 14% 42% 26% 2	563
	21st to end	Night	15% 12% 45% 22% 6%	570
May	1st to 10th	Night	12% 14% 43% 27% 4	570
	11th to 20th	Night	11% 8% 39% 32% 10% 1	561
	21st to end	Night	12% 7% 35% 35% 11% 1	617
June	1st to 10th	Night	3 2 26% 47% 21% 1	570
	11th to 20th	Night	5% 2 33% 46% 14% 1	570
	21st to end	Night	5% 2 19% 51% 21% 3	570
July	1st to 10th	Night	8% 3 11% 51% 25% 2	555
	11th to 20th	Night	4 1 12% 52% 29% 2	552
	21st to end	Night	3 1 11% 54% 28% 3	624
August	1st to 10th	Night	1 1 8% 56% 31% 3	567
	11th to 20th	Night	6% 1 6% 52% 31% 4	564
	21st to end	Night	5% 1 7% 45% 36% 5%	627
September	1st to 10th	Night	9% 9% 44% 32% 6%	570
	11th to 20th	Night	10% 1 10% 39% 35% 4	570
	21st to end	Night	8% 1 15% 43% 31% 2	570
October	1st to 10th	Night	6% 1 15% 46% 28% 3	570
	11th to 20th	Night	12% 5% 23% 42% 16% 2	646
	21st to end	Night	13% 9% 29% 28% 19% 1	836
November	1st to 10th	Night	12% 6% 25% 40% 16% 1	780
	11th to 20th	Night	11% 8% 29% 36% 14% 1	980
	21st to end	Night	16% 11% 34% 29% 10% 1	1000
December	1st to 10th	Night	17% 9% 30% 35% 8% 1	1000
	11th to 20th	Night	18% 11% 32% 33% 6%	1000
	21st to end	Night	15% 11% 35% 31% 7%	1100

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

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