Mission Tejas State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mission Tejas State Park clear sky chart from 2005-11-06 to 2025-09-19.

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	13% 6% 2 6% 4 4 4 4 5% 7% 45%	126245
	Night	13% 6% 2 5% 3 3 4 3 5% 7% 49%	123069
Transparency	Day	38% 4 11% 21% 19% 7%	129881
	Night	35% 4 10% 20% 21% 10%	127496
Seeing	Day	14% 8% 23% 27% 21% 6%	16232
	Night	15% 8% 25% 32% 17% 2	25986

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	16% 10% 3 5% 3 3 3 2 3 5% 47%	4077
	11th to 20th	Day	15% 5% 2 4 2 2 2 2 5% 7% 53%	4080
	21st to end	Day	28% 10% 2 5% 2 2 2 1 2 4 42%	4488
February	1st to 10th	Day	22% 9% 3 7% 4 3 3 2 2 5% 40%	1825
	11th to 20th	Day	22% 9% 3 6% 4 3 4 2 3 5% 40%	1949
	21st to end	Day	21% 7% 3 6% 4 3 3 2 4 4 43%	1815
March	1st to 10th	Day	18% 11% 3 7% 4 4 3 3 4 4 39%	4936
	11th to 20th	Day	16% 5% 2 5% 3 3 4 3 4 6% 50%	4980
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	5462
April	1st to 10th	Day	15% 8% 3 7% 5% 4 4 4 5% 6% 42%	2200
	11th to 20th	Day	15% 7% 3 6% 4 5% 5% 4 6% 7% 40%	2364
	21st to end	Day	12% 7% 2 5% 4 4 5% 4 5% 6% 45%	2400
May	1st to 10th	Day	18% 7% 3 8% 5% 4 5% 4 6% 8% 34%	5668
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 7% 41%	5862
	21st to end	Day	11% 7% 2 7% 5% 5% 6% 5% 7% 9% 36%	6434
June	1st to 10th	Day	6% 5% 2 6% 5% 6% 6% 5% 8% 10% 39%	2600
	11th to 20th	Day	5% 4 2 5% 6% 6% 6% 5% 8% 11% 42%	2600
	21st to end	Day	6% 5% 2 6% 6% 5% 6% 6% 8% 11% 40%	2600
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 6% 9% 12% 34%	5900
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 7% 11% 48%	5900
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	6422
August	1st to 10th	Day	3 1 1 2 3 3 2 3 5% 9% 69%	4234
	11th to 20th	Day	3 2 1 3 3 4 4 3 7% 10% 58%	4049
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 7% 11% 43%	4312
September	1st to 10th	Day	7% 6% 2 7% 5% 5% 6% 4 6% 7% 45%	2226
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 7% 7% 44%	2178
	21st to end	Day	7% 3 2 5% 4 4 5% 3 6% 8% 53%	2090
October	1st to 10th	Day	7% 3 1 4 3 4 4 3 4 6% 62%	1952
	11th to 20th	Day	13% 5% 2 3 2 3 4 3 4 5% 57%	1900
	21st to end	Day	14% 5% 2 4 3 3 3 2 3 5% 56%	2090
November	1st to 10th	Day	13% 7% 2 5% 4 3 4 4 5% 6% 47%	1958
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 6% 53%	2000
	21st to end	Day	17% 7% 2 7% 4 3 3 3 5% 4 45%	1875
December	1st to 10th	Day	21% 5% 2 5% 4 3 3 2 4 5% 46%	2940
	11th to 20th	Day	18% 9% 2 6% 4 4 4 3 5% 5% 41%	3391
	21st to end	Day	16% 9% 3 7% 3 3 3 3 4 5% 45%	4488
January	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 3 5% 53%	5888
	11th to 20th	Night	14% 6% 1 4 2 2 3 2 4 5% 58%	5900
	21st to end	Night	27% 10% 2 5% 3 2 2 2 3 5% 39%	6490
February	1st to 10th	Night	18% 8% 3 5% 3 3 4 2 4 5% 45%	2593
	11th to 20th	Night	20% 9% 3 5% 3 3 4 2 4 4 44%	2337
	21st to end	Night	20% 7% 2 5% 3 3 3 3 4 5% 45%	1815
March	1st to 10th	Night	21% 9% 2 4 4 3 3 3 4 5% 42%	4919
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 6% 50%	4980
	21st to end	Night	18% 8% 3 6% 4 3 3 3 4 4 44%	5467
April	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 48%	2200
	11th to 20th	Night	13% 6% 2 6% 3 3 4 3 5% 7% 46%	1983
	21st to end	Night	13% 5% 2 5% 4 4 4 3 4 6% 51%	2000
May	1st to 10th	Night	16% 10% 3 6% 4 4 4 4 6% 7% 35%	4235
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 4 6% 7% 42%	4053
	21st to end	Night	11% 6% 2 5% 4 4 5% 4 7% 10% 41%	4443
June	1st to 10th	Night	5% 3 1 6% 4 3 4 4 6% 11% 54%	1800
	11th to 20th	Night	4 3 2 3 2 3 3 3 7% 9% 62%	1800
	21st to end	Night	6% 4 1 4 4 4 4 4 7% 11% 50%	1800
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 9% 12% 40%	4078
	11th to 20th	Night	3 3 1 4 3 4 4 4 6% 12% 56%	4077
	21st to end	Night	8% 6% 2 5% 3 4 4 4 7% 10% 48%	4449
August	1st to 10th	Night	2 1 1 1 2 2 3 4 9% 75%	2926
	11th to 20th	Night	3 2 1 3 3 3 4 4 6% 12% 59%	3003
	21st to end	Night	5% 3 1 4 5% 5% 5% 5% 8% 10% 48%	3586
September	1st to 10th	Night	6% 5% 2 5% 5% 4 5% 3 5% 9% 51%	2169
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 3 6% 7% 50%	2178
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 7% 59%	2090
October	1st to 10th	Night	5% 3 1 4 3 2 3 3 5% 6% 65%	2206
	11th to 20th	Night	12% 4 1 3 3 2 3 3 4 5% 60%	2280
	21st to end	Night	15% 4 1 3 3 2 2 2 3 4 60%	2508
November	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 55%	2340
	11th to 20th	Night	10% 6% 2 4 3 3 3 4 4 6% 55%	2400
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 5% 48%	2520
December	1st to 10th	Night	19% 7% 2 5% 3 3 3 3 4 5% 45%	4250
	11th to 20th	Night	17% 9% 2 6% 4 4 4 2 4 5% 44%	4816
	21st to end	Night	14% 8% 2 5% 3 3 3 2 3 4 52%	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	41% 3 4 26% 22% 4	4078
	11th to 20th	Day	33% 2 4 23% 28% 12%	4080
	21st to end	Day	50% 1 3 15% 17% 14%	4488
February	1st to 10th	Day	50% 2 4 14% 20% 10%	1825
	11th to 20th	Day	50% 2 6% 15% 18% 9%	1959
	21st to end	Day	47% 2 7% 14% 18% 12%	1815
March	1st to 10th	Day	49% 3 5% 11% 19% 12%	4936
	11th to 20th	Day	37% 3 7% 15% 20% 19%	4980
	21st to end	Day	44% 4 9% 21% 17% 5%	5464
April	1st to 10th	Day	44% 4 9% 19% 16% 8%	2200
	11th to 20th	Day	43% 4 10% 15% 20% 8%	2364
	21st to end	Day	39% 5% 9% 20% 24% 5%	2400
May	1st to 10th	Day	48% 5% 11% 22% 11% 3	5703
	11th to 20th	Day	42% 5% 13% 16% 22% 1	5866
	21st to end	Day	42% 5% 14% 21% 16% 2	6447
June	1st to 10th	Day	38% 7% 15% 25% 15% 1	2600
	11th to 20th	Day	34% 6% 14% 28% 16% 3	2600
	21st to end	Day	36% 9% 14% 25% 14% 2	2600
July	1st to 10th	Day	38% 9% 26% 21% 5%	5836
	11th to 20th	Day	29% 6% 20% 34% 10%	5831
	21st to end	Day	39% 7% 15% 28% 11%	6240
August	1st to 10th	Day	15% 4 13% 36% 30% 2	4220
	11th to 20th	Day	21% 5% 21% 42% 10% 1	4088
	21st to end	Day	35% 9% 19% 23% 13% 2	4311
September	1st to 10th	Day	36% 6% 13% 18% 17% 9%	2226
	11th to 20th	Day	38% 6% 13% 18% 18% 7%	2178
	21st to end	Day	30% 4 9% 22% 21% 13%	2090
October	1st to 10th	Day	15% 3 6% 13% 23% 41%	3238
	11th to 20th	Day	19% 2 4 23% 30% 22%	3140
	21st to end	Day	26% 3 4 18% 37% 12%	3428
November	1st to 10th	Day	37% 4 8% 19% 22% 10%	1958
	11th to 20th	Day	35% 3 6% 20% 24% 13%	2000
	21st to end	Day	43% 3 6% 18% 21% 9%	1875
December	1st to 10th	Day	42% 2 6% 17% 25% 7%	2940
	11th to 20th	Day	45% 3 6% 13% 22% 11%	3389
	21st to end	Day	44% 3 5% 14% 28% 6%	4488
January	1st to 10th	Night	36% 3 5% 23% 26% 6%	5888
	11th to 20th	Night	31% 2 4 18% 34% 11%	5900
	21st to end	Night	52% 2 3 13% 16% 14%	6490
February	1st to 10th	Night	43% 3 5% 15% 18% 15%	2593
	11th to 20th	Night	45% 3 6% 16% 19% 11%	2337
	21st to end	Night	43% 3 7% 13% 17% 16%	1815
March	1st to 10th	Night	46% 2 5% 13% 21% 13%	4919
	11th to 20th	Night	36% 3 8% 14% 18% 21%	4980
	21st to end	Night	45% 3 8% 16% 20% 8%	5467
April	1st to 10th	Night	39% 4 9% 20% 17% 12%	2200
	11th to 20th	Night	37% 3 11% 20% 17% 12%	1983
	21st to end	Night	35% 4 11% 18% 25% 7%	2000
May	1st to 10th	Night	47% 4 12% 22% 12% 3	4265
	11th to 20th	Night	42% 5% 13% 17% 21% 2	4054
	21st to end	Night	38% 5% 17% 26% 12% 3	4452
June	1st to 10th	Night	26% 6% 18% 30% 19% 1	1800
	11th to 20th	Night	19% 5% 18% 33% 20% 5%	1800
	21st to end	Night	27% 6% 16% 29% 20% 2	1800
July	1st to 10th	Night	35% 8% 28% 25% 4	4035
	11th to 20th	Night	22% 7% 25% 34% 12%	4026
	21st to end	Night	32% 7% 19% 30% 11% 1	4320
August	1st to 10th	Night	10% 3 16% 34% 33% 4	2916
	11th to 20th	Night	18% 5% 21% 44% 10% 2	3030
	21st to end	Night	29% 9% 20% 24% 16% 2	3586
September	1st to 10th	Night	32% 5% 15% 21% 17% 10%	2169
	11th to 20th	Night	33% 6% 14% 21% 18% 8%	2178
	21st to end	Night	26% 3 11% 21% 26% 12%	2090
October	1st to 10th	Night	13% 3 5% 15% 19% 44%	3687
	11th to 20th	Night	17% 2 3 19% 33% 26%	3779
	21st to end	Night	24% 3 4 16% 36% 17%	4120
November	1st to 10th	Night	33% 4 9% 19% 25% 11%	2340
	11th to 20th	Night	32% 3 7% 19% 25% 14%	2400
	21st to end	Night	39% 3 8% 17% 22% 11%	2520
December	1st to 10th	Night	43% 2 6% 16% 27% 6%	4250
	11th to 20th	Night	44% 3 7% 12% 22% 12%	4817
	21st to end	Night	38% 2 6% 14% 31% 9%	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	26% 15% 40% 16% 3 1	300
	11th to 20th	Day	27% 16% 34% 16% 5% 1	300
	21st to end	Day	30% 17% 36% 14% 3	330
February	1st to 10th	Day	27% 19% 35% 15% 3	300
	11th to 20th	Day	38% 20% 29% 12% 1	300
	21st to end	Day	28% 27% 35% 8% 3	249
March	1st to 10th	Day	30% 18% 32% 17% 4	300
	11th to 20th	Day	24% 27% 34% 12% 3	300
	21st to end	Day	23% 17% 41% 16% 4	330
April	1st to 10th	Day	25% 15% 43% 15% 2	300
	11th to 20th	Day	23% 18% 27% 22% 9% 1	482
	21st to end	Day	14% 13% 40% 26% 6% 1	500
May	1st to 10th	Day	17% 11% 38% 26% 7% 1	610
	11th to 20th	Day	15% 10% 28% 31% 14% 2	725
	21st to end	Day	12% 9% 29% 31% 16% 4	789
June	1st to 10th	Day	8% 4 18% 37% 26% 8%	730
	11th to 20th	Day	7% 2 19% 41% 25% 5%	730
	21st to end	Day	7% 2 14% 34% 31% 12%	730
July	1st to 10th	Day	8% 1 12% 30% 37% 12%	721
	11th to 20th	Day	3 2 8% 33% 43% 11%	718
	21st to end	Day	5% 2 9% 32% 41% 11%	794
August	1st to 10th	Day	4 1 4 30% 46% 14%	726
	11th to 20th	Day	6% 1 3 29% 46% 15%	645
	21st to end	Day	11% 2 9% 17% 42% 18%	583
September	1st to 10th	Day	5% 1 9% 32% 37% 16%	356
	11th to 20th	Day	8% 1 11% 29% 35% 16%	324
	21st to end	Day	10% 2 13% 32% 29% 14%	300
October	1st to 10th	Day	6% 3 20% 40% 24% 7%	300
	11th to 20th	Day	10% 6% 32% 34% 14% 5%	300
	21st to end	Day	23% 10% 26% 22% 15% 3	330
November	1st to 10th	Day	18% 8% 29% 30% 12% 3	300
	11th to 20th	Day	18% 13% 32% 27% 8% 2	300
	21st to end	Day	22% 18% 29% 22% 7% 2	300
December	1st to 10th	Day	21% 11% 34% 22% 10% 2	300
	11th to 20th	Day	28% 14% 34% 19% 5% 1	300
	21st to end	Day	25% 14% 40% 16% 5% 1	330
January	1st to 10th	Night	22% 12% 33% 26% 6%	1000
	11th to 20th	Night	25% 15% 29% 25% 6%	1000
	21st to end	Night	23% 12% 34% 28% 3	1100
February	1st to 10th	Night	23% 14% 36% 24% 3	993
	11th to 20th	Night	29% 15% 32% 22% 3	783
	21st to end	Night	27% 14% 36% 21% 2	495
March	1st to 10th	Night	24% 13% 34% 23% 7%	600
	11th to 20th	Night	20% 15% 35% 24% 6%	600
	21st to end	Night	17% 12% 40% 26% 4	660
April	1st to 10th	Night	14% 14% 39% 27% 6%	600
	11th to 20th	Night	17% 14% 35% 24% 10%	593
	21st to end	Night	13% 12% 39% 26% 9% 1	600
May	1st to 10th	Night	12% 10% 41% 29% 8% 1	600
	11th to 20th	Night	13% 7% 33% 33% 12% 2	591
	21st to end	Night	10% 4 29% 39% 15% 3	650
June	1st to 10th	Night	6% 2 16% 42% 31% 3	600
	11th to 20th	Night	3 2 20% 50% 23% 2	600
	21st to end	Night	7% 2 12% 44% 29% 6%	600
July	1st to 10th	Night	5% 1 9% 43% 36% 6%	585
	11th to 20th	Night	3 2 9% 45% 36% 6%	582
	21st to end	Night	6% 2 7% 41% 39% 5%	657
August	1st to 10th	Night	3 1 6% 44% 39% 6%	597
	11th to 20th	Night	6% 1 7% 42% 39% 6%	594
	21st to end	Night	7% 1 7% 35% 42% 8%	660
September	1st to 10th	Night	8% 1 10% 37% 38% 6%	600
	11th to 20th	Night	11% 2 10% 28% 42% 7%	594
	21st to end	Night	9% 2 9% 38% 37% 5%	570
October	1st to 10th	Night	6% 2 15% 40% 31% 5%	686
	11th to 20th	Night	13% 6% 22% 39% 18% 2	760
	21st to end	Night	18% 8% 25% 30% 18% 2	836
November	1st to 10th	Night	16% 5% 25% 34% 18% 2	780
	11th to 20th	Night	14% 10% 26% 38% 12%	800
	21st to end	Night	19% 12% 29% 27% 13% 1	920
December	1st to 10th	Night	22% 9% 32% 29% 9% 1	1000
	11th to 20th	Night	25% 11% 28% 30% 5%	1000
	21st to end	Night	22% 13% 29% 28% 8%	1100

Page generated at 2025-09-16 00:49:16. Version ac07

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