Lake Brownwood State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Brownwood State Park clear sky chart from 2005-11-06 to 2025-12-18.

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	9% 5% 2 5% 3 3 4 3 5% 7% 56%	127107
	Night	8% 5% 2 4 3 3 3 3 5% 7% 59%	124239
Transparency	Day	28% 5% 9% 22% 24% 12%	130912
	Night	26% 4 9% 22% 25% 15%	128497
Seeing	Day	9% 7% 23% 29% 24% 9%	16490
	Night	9% 6% 30% 38% 15% 1	26435

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% 7% 3 5% 3 3 2 2 4 5% 56%	4077
	11th to 20th	Day	7% 6% 1 3 2 2 3 2 4 5% 65%	4080
	21st to end	Day	17% 7% 2 5% 2 2 3 2 3 4 51%	4828
February	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 4 7% 53%	2000
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 4 5% 52%	1949
	21st to end	Day	13% 6% 2 5% 3 3 3 2 2 5% 56%	1650
March	1st to 10th	Day	10% 7% 2 5% 3 3 3 3 4 5% 55%	4710
	11th to 20th	Day	11% 5% 2 4 3 3 3 3 4 6% 57%	4980
	21st to end	Day	7% 4 2 5% 4 4 4 4 5% 7% 54%	5462
April	1st to 10th	Day	8% 7% 2 5% 3 4 4 4 5% 7% 52%	2200
	11th to 20th	Day	11% 5% 2 5% 4 3 3 2 5% 6% 53%	2334
	21st to end	Day	9% 6% 2 5% 4 3 3 3 5% 6% 55%	2527
May	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 5% 6% 50%	5862
	11th to 20th	Day	11% 6% 2 5% 4 4 3 3 5% 6% 51%	5862
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 7% 46%	6434
June	1st to 10th	Day	5% 3 1 3 3 3 5% 3 6% 7% 59%	2600
	11th to 20th	Day	3 3 1 4 4 4 4 3 6% 8% 60%	2600
	21st to end	Day	5% 3 1 4 4 4 4 3 6% 8% 59%	2600
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 5% 7% 44%	5900
	11th to 20th	Day	3 2 1 3 3 3 3 3 6% 10% 61%	5900
	21st to end	Day	3 3 1 3 3 3 4 4 6% 10% 60%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 3 4 7% 73%	4179
	11th to 20th	Day	5% 2 1 3 2 3 3 3 5% 9% 63%	3846
	21st to end	Day	2 2 1 5% 4 4 4 4 6% 9% 59%	4280
September	1st to 10th	Day	9% 5% 2 5% 5% 4 4 4 4 5% 54%	2200
	11th to 20th	Day	9% 4 2 6% 3 4 5% 3 5% 8% 51%	2200
	21st to end	Day	7% 4 1 5% 3 3 3 4 4 6% 59%	2200
October	1st to 10th	Day	5% 3 1 3 3 3 3 3 5% 6% 66%	2200
	11th to 20th	Day	9% 3 1 3 2 3 2 3 3 5% 66%	2104
	21st to end	Day	10% 5% 2 3 2 2 2 2 3 4 64%	2200
November	1st to 10th	Day	10% 4 2 4 3 3 2 2 4 5% 60%	1969
	11th to 20th	Day	5% 4 2 4 2 3 3 2 5% 8% 62%	1890
	21st to end	Day	13% 6% 2 5% 3 2 3 3 4 5% 54%	1890
December	1st to 10th	Day	14% 7% 2 5% 4 4 3 3 4 5% 48%	3030
	11th to 20th	Day	10% 5% 2 6% 3 4 5% 4 5% 5% 51%	3454
	21st to end	Day	11% 5% 1 4 2 2 3 2 3 4 61%	4488
January	1st to 10th	Night	12% 6% 2 4 3 2 3 2 4 5% 57%	5888
	11th to 20th	Night	7% 4 1 3 2 2 2 2 3 4 71%	5900
	21st to end	Night	17% 8% 2 4 3 3 3 3 4 4 48%	6191
February	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 5% 56%	2400
	11th to 20th	Night	13% 6% 2 5% 2 3 3 3 3 6% 53%	2338
	21st to end	Night	11% 7% 2 4 3 3 2 2 4 5% 56%	1980
March	1st to 10th	Night	8% 6% 2 5% 3 3 3 3 5% 5% 57%	5151
	11th to 20th	Night	11% 5% 2 4 2 2 3 3 5% 6% 58%	4980
	21st to end	Night	7% 6% 2 4 4 3 4 3 5% 7% 56%	5467
April	1st to 10th	Night	6% 4 2 4 4 3 3 4 7% 7% 56%	2200
	11th to 20th	Night	10% 5% 1 5% 4 4 4 4 5% 6% 53%	2011
	21st to end	Night	7% 4 2 4 3 3 2 3 5% 6% 60%	1870
May	1st to 10th	Night	15% 6% 2 4 3 3 3 3 4 6% 51%	4053
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 5% 6% 53%	4053
	21st to end	Night	9% 5% 2 5% 3 4 4 4 6% 10% 48%	4443
June	1st to 10th	Night	3 2 1 3 3 3 5% 3 6% 9% 62%	1800
	11th to 20th	Night	3 2 1 2 2 3 3 3 6% 9% 66%	1800
	21st to end	Night	3 3 1 3 3 2 3 3 6% 8% 65%	1800
July	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 5% 9% 50%	4078
	11th to 20th	Night	2 1 1 2 2 2 3 3 5% 9% 70%	4077
	21st to end	Night	2 2 1 3 3 3 4 4 6% 9% 63%	4449
August	1st to 10th	Night	1 1 1 2 2 2 2 1 5% 6% 76%	2975
	11th to 20th	Night	3 2 1 3 2 3 3 2 5% 9% 67%	3213
	21st to end	Night	2 2 2 3 3 4 4 4 6% 9% 62%	3625
September	1st to 10th	Night	6% 5% 2 5% 4 4 4 3 5% 8% 56%	2200
	11th to 20th	Night	9% 5% 2 4 4 3 3 4 6% 8% 54%	2200
	21st to end	Night	7% 3 1 3 3 3 4 3 5% 8% 60%	2200
October	1st to 10th	Night	5% 3 1 3 2 2 3 2 4 6% 69%	2200
	11th to 20th	Night	8% 3 1 3 2 3 2 2 4 5% 66%	2275
	21st to end	Night	11% 4 1 3 2 2 2 2 4 5% 64%	2640
November	1st to 10th	Night	9% 4 1 3 3 3 3 2 4 4 63%	2544
	11th to 20th	Night	6% 3 1 4 2 2 4 3 4 7% 65%	2730
	21st to end	Night	14% 5% 2 4 3 3 3 3 5% 6% 54%	2730
December	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 5% 5% 53%	4380
	11th to 20th	Night	10% 6% 2 6% 3 3 4 3 4 5% 53%	4908
	21st to end	Night	11% 5% 2 4 3 3 3 2 4 6% 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	32% 2 5% 22% 27% 11%	4078
	11th to 20th	Day	23% 2 5% 21% 34% 15%	4080
	21st to end	Day	38% 2 5% 13% 25% 17%	4828
February	1st to 10th	Day	32% 4 6% 17% 23% 19%	2000
	11th to 20th	Day	36% 3 7% 20% 20% 14%	1959
	21st to end	Day	34% 3 4 12% 26% 21%	1650
March	1st to 10th	Day	32% 3 6% 10% 25% 24%	4710
	11th to 20th	Day	30% 4 9% 10% 18% 29%	4980
	21st to end	Day	29% 5% 9% 20% 24% 13%	5464
April	1st to 10th	Day	31% 6% 9% 20% 18% 16%	2200
	11th to 20th	Day	33% 5% 8% 16% 23% 15%	2334
	21st to end	Day	30% 5% 8% 19% 28% 10%	2527
May	1st to 10th	Day	35% 6% 8% 18% 22% 11%	5900
	11th to 20th	Day	35% 5% 7% 15% 29% 9%	5866
	21st to end	Day	35% 7% 11% 24% 15% 7%	6447
June	1st to 10th	Day	23% 7% 14% 29% 22% 4	2600
	11th to 20th	Day	22% 6% 13% 30% 22% 7%	2600
	21st to end	Day	23% 7% 13% 26% 22% 8%	2600
July	1st to 10th	Day	39% 6% 13% 30% 11% 1	5836
	11th to 20th	Day	19% 5% 20% 34% 20% 2	5831
	21st to end	Day	20% 6% 15% 35% 22% 2	6240
August	1st to 10th	Day	13% 4 10% 33% 36% 4	4165
	11th to 20th	Day	19% 4 15% 34% 23% 4	3882
	21st to end	Day	21% 8% 16% 29% 22% 4	4279
September	1st to 10th	Day	32% 5% 10% 20% 23% 10%	2200
	11th to 20th	Day	32% 6% 11% 21% 24% 7%	2200
	21st to end	Day	25% 5% 9% 21% 25% 15%	2200
October	1st to 10th	Day	12% 3 7% 13% 33% 32%	3590
	11th to 20th	Day	17% 3 6% 22% 28% 23%	3409
	21st to end	Day	19% 3 3 22% 38% 15%	3538
November	1st to 10th	Day	29% 3 7% 20% 27% 14%	1969
	11th to 20th	Day	22% 4 8% 22% 27% 18%	1890
	21st to end	Day	34% 3 5% 20% 25% 13%	1890
December	1st to 10th	Day	39% 3 5% 16% 27% 10%	3030
	11th to 20th	Day	35% 4 7% 12% 26% 15%	3452
	21st to end	Day	27% 3 4 21% 28% 16%	4488
January	1st to 10th	Night	31% 2 6% 19% 30% 12%	5888
	11th to 20th	Night	20% 2 4 18% 35% 22%	5900
	21st to end	Night	41% 3 4 13% 21% 18%	6191
February	1st to 10th	Night	31% 4 7% 16% 22% 20%	2400
	11th to 20th	Night	33% 3 7% 16% 23% 17%	2338
	21st to end	Night	31% 4 5% 14% 22% 23%	1980
March	1st to 10th	Night	27% 3 6% 16% 26% 22%	5151
	11th to 20th	Night	28% 4 9% 14% 15% 30%	4980
	21st to end	Night	29% 4 9% 19% 26% 13%	5467
April	1st to 10th	Night	25% 6% 11% 19% 19% 20%	2200
	11th to 20th	Night	32% 6% 9% 15% 22% 16%	2011
	21st to end	Night	24% 5% 13% 21% 26% 10%	1870
May	1st to 10th	Night	35% 5% 8% 23% 18% 11%	4080
	11th to 20th	Night	32% 6% 9% 18% 20% 15%	4054
	21st to end	Night	32% 7% 13% 26% 15% 8%	4452
June	1st to 10th	Night	20% 6% 17% 32% 22% 4	1800
	11th to 20th	Night	16% 4 14% 34% 23% 8%	1800
	21st to end	Night	18% 6% 13% 30% 26% 8%	1800
July	1st to 10th	Night	32% 6% 14% 33% 14% 2	4035
	11th to 20th	Night	12% 4 16% 36% 29% 3	4026
	21st to end	Night	17% 7% 15% 35% 24% 2	4320
August	1st to 10th	Night	10% 2 11% 32% 39% 5%	2965
	11th to 20th	Night	15% 4 17% 38% 22% 3	3243
	21st to end	Night	17% 7% 21% 29% 22% 4	3625
September	1st to 10th	Night	27% 6% 10% 23% 23% 11%	2200
	11th to 20th	Night	28% 6% 13% 22% 22% 8%	2200
	21st to end	Night	22% 4 9% 23% 25% 17%	2200
October	1st to 10th	Night	11% 3 7% 16% 27% 36%	3590
	11th to 20th	Night	17% 3 7% 17% 32% 23%	3696
	21st to end	Night	19% 2 4 23% 37% 15%	4252
November	1st to 10th	Night	25% 4 8% 20% 25% 19%	2544
	11th to 20th	Night	21% 4 7% 23% 27% 19%	2730
	21st to end	Night	33% 3 6% 17% 25% 15%	2730
December	1st to 10th	Night	34% 3 6% 20% 25% 13%	4380
	11th to 20th	Night	34% 3 5% 14% 27% 16%	4909
	21st to end	Night	28% 3 5% 20% 24% 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	11% 15% 40% 27% 6% 1	300
	11th to 20th	Day	14% 15% 30% 31% 8% 2	300
	21st to end	Day	12% 12% 40% 25% 9% 1	330
February	1st to 10th	Day	15% 15% 37% 23% 10%	300
	11th to 20th	Day	21% 14% 38% 21% 5% 1	300
	21st to end	Day	18% 13% 43% 23% 2 2	249
March	1st to 10th	Day	13% 17% 38% 25% 6%	300
	11th to 20th	Day	16% 14% 38% 24% 7% 1	300
	21st to end	Day	9% 14% 47% 22% 8%	330
April	1st to 10th	Day	12% 17% 42% 20% 9%	300
	11th to 20th	Day	13% 15% 47% 21% 4	452
	21st to end	Day	10% 13% 43% 25% 8% 1	627
May	1st to 10th	Day	9% 12% 37% 34% 7%	703
	11th to 20th	Day	13% 8% 30% 31% 14% 3	725
	21st to end	Day	10% 6% 30% 34% 18% 2	789
June	1st to 10th	Day	6% 2 17% 43% 26% 6%	730
	11th to 20th	Day	3 2 18% 45% 26% 5%	730
	21st to end	Day	3 1 10% 36% 38% 11%	730
July	1st to 10th	Day	6% 2 7% 31% 40% 14%	721
	11th to 20th	Day	3 4 27% 47% 17%	718
	21st to end	Day	2 1 5% 26% 46% 21%	794
August	1st to 10th	Day	1 1 3 26% 47% 22%	697
	11th to 20th	Day	7% 2 5% 25% 42% 19%	517
	21st to end	Day	3 1 4 27% 38% 28%	564
September	1st to 10th	Day	11% 1 6% 19% 37% 26%	330
	11th to 20th	Day	4 1 6% 23% 41% 25%	330
	21st to end	Day	10% 2 7% 27% 33% 22%	330
October	1st to 10th	Day	3 3 10% 35% 34% 16%	330
	11th to 20th	Day	9% 2 28% 30% 26% 5%	330
	21st to end	Day	16% 10% 25% 22% 23% 4	363
November	1st to 10th	Day	14% 7% 28% 30% 16% 6%	330
	11th to 20th	Day	8% 12% 26% 31% 18% 5%	330
	21st to end	Day	15% 14% 30% 26% 12% 3	330
December	1st to 10th	Day	15% 9% 31% 30% 12% 3	330
	11th to 20th	Day	9% 13% 39% 26% 11% 1	321
	21st to end	Day	22% 8% 34% 28% 8% 1	330
January	1st to 10th	Night	12% 8% 37% 35% 7%	1000
	11th to 20th	Night	13% 10% 34% 36% 7%	1000
	21st to end	Night	14% 11% 35% 34% 6%	970
February	1st to 10th	Night	14% 9% 41% 31% 5%	800
	11th to 20th	Night	16% 10% 41% 29% 3	784
	21st to end	Night	16% 12% 47% 23% 3	660
March	1st to 10th	Night	13% 12% 42% 28% 4	707
	11th to 20th	Night	13% 10% 45% 28% 5%	600
	21st to end	Night	9% 11% 47% 30% 3	660
April	1st to 10th	Night	7% 11% 53% 26% 4	600
	11th to 20th	Night	11% 10% 50% 26% 3	593
	21st to end	Night	7% 9% 53% 24% 7%	600
May	1st to 10th	Night	9% 10% 44% 32% 4	600
	11th to 20th	Night	8% 6% 40% 35% 11%	591
	21st to end	Night	8% 4 39% 38% 11% 1	650
June	1st to 10th	Night	3 2 27% 49% 18% 1	600
	11th to 20th	Night	4 1 25% 56% 14%	600
	21st to end	Night	3 1 15% 54% 25% 1	600
July	1st to 10th	Night	7% 2 8% 50% 30% 3	585
	11th to 20th	Night	4 7% 54% 34% 1	582
	21st to end	Night	2 5% 51% 40% 2	657
August	1st to 10th	Night	1 6% 51% 40% 2	597
	11th to 20th	Night	6% 1 5% 46% 39% 3	594
	21st to end	Night	3 1 5% 42% 45% 5%	660
September	1st to 10th	Night	7% 1 10% 48% 32% 4	600
	11th to 20th	Night	10% 1 8% 45% 35% 1	600
	21st to end	Night	7% 1 13% 46% 31% 2	600
October	1st to 10th	Night	5% 1 19% 48% 26% 2	600
	11th to 20th	Night	9% 4 26% 43% 17% 1	675
	21st to end	Night	12% 8% 27% 35% 17% 1	880
November	1st to 10th	Night	10% 5% 28% 42% 14%	904
	11th to 20th	Night	6% 6% 32% 43% 13%	1050
	21st to end	Night	16% 8% 34% 33% 10% 1	1050
December	1st to 10th	Night	11% 7% 35% 39% 7%	1050
	11th to 20th	Night	14% 8% 33% 37% 8%	1036
	21st to end	Night	12% 8% 37% 34% 8%	1100

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