Texas Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Texas Star Party 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	3 3 1 3 3 3 4 4 5% 7% 63%	123764
	Night	3 3 1 3 3 3 3 3 5% 7% 65%	123917
Transparency	Day	19% 5% 8% 17% 26% 25%	123551
	Night	18% 5% 8% 18% 26% 26%	123717
Seeing	Day	6% 9% 24% 30% 23% 8%	15489
	Night	5% 6% 23% 39% 25% 3	25629

By Month

Percentage Cloud Cover SW (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	3 3 1 2 2 2 3 3 6% 6% 70%	4537
	11th to 20th	Day	1 2 2 2 2 2 2 4 6% 75%	4540
	21st to end	Day	2 2 1 3 3 3 4 4 5% 6% 68%	4994
February	1st to 10th	Day	3 3 1 3 3 4 4 4 5% 6% 64%	2000
	11th to 20th	Day	3 3 2 4 3 4 3 3 5% 6% 65%	1949
	21st to end	Day	2 2 1 3 2 3 3 4 5% 8% 68%	1650
March	1st to 10th	Day	2 3 2 4 3 3 3 4 6% 8% 64%	4500
	11th to 20th	Day	4 4 1 3 2 2 3 3 5% 7% 65%	4852
	21st to end	Day	2 3 1 4 3 4 4 3 6% 7% 64%	5920
April	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 65%	2400
	11th to 20th	Day	2 4 1 4 3 3 4 3 4 6% 65%	2371
	21st to end	Day	2 3 1 3 2 2 2 3 4 6% 71%	2400
May	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 76%	5440
	11th to 20th	Day	3 3 1 3 2 3 3 3 5% 7% 67%	5405
	21st to end	Day	3 2 1 2 2 3 4 4 6% 7% 66%	6356
June	1st to 10th	Day	2 2 1 3 3 4 5% 5% 8% 8% 62%	2600
	11th to 20th	Day	2 2 1 4 3 4 5% 5% 8% 8% 59%	2600
	21st to end	Day	5% 5% 2 5% 5% 5% 5% 6% 8% 9% 48%	2600
July	1st to 10th	Day	5% 3 1 5% 4 6% 8% 6% 7% 10% 44%	3873
	11th to 20th	Day	3 2 1 3 3 5% 6% 6% 8% 9% 54%	3800
	21st to end	Day	5% 4 2 5% 5% 6% 7% 5% 8% 10% 43%	4118
August	1st to 10th	Day	3 2 1 4 4 5% 6% 5% 8% 10% 53%	3784
	11th to 20th	Day	4 3 2 5% 5% 5% 5% 5% 7% 10% 49%	3726
	21st to end	Day	5% 3 2 5% 4 5% 6% 5% 7% 9% 49%	4180
September	1st to 10th	Day	10% 6% 2 5% 6% 6% 6% 5% 6% 8% 41%	2280
	11th to 20th	Day	10% 6% 3 6% 5% 5% 6% 4 7% 8% 40%	2169
	21st to end	Day	8% 5% 2 5% 4 4 4 3 6% 7% 52%	2090
October	1st to 10th	Day	3 2 1 3 2 2 3 2 3 5% 74%	3480
	11th to 20th	Day	4 3 1 3 2 2 3 2 4 5% 70%	3243
	21st to end	Day	3 2 1 2 1 2 1 2 3 4 80%	3438
November	1st to 10th	Day	4 3 1 2 2 2 2 2 4 5% 72%	1894
	11th to 20th	Day	2 4 1 4 3 2 4 3 4 5% 68%	1800
	21st to end	Day	5% 4 2 4 3 3 3 2 5% 6% 64%	1800
December	1st to 10th	Day	4 11% 2 4 2 2 3 3 4 6% 58%	2940
	11th to 20th	Day	1 2 1 3 3 4 4 3 5% 6% 69%	3391
	21st to end	Day	2 2 1 2 1 2 2 2 4 5% 77%	4644
January	1st to 10th	Night	2 2 1 4 3 3 3 3 4 6% 69%	5428
	11th to 20th	Night	2 2 1 2 2 2 3 2 5% 6% 73%	5440
	21st to end	Night	2 3 1 3 3 3 4 3 5% 7% 64%	5984
February	1st to 10th	Night	3 3 1 3 2 3 3 3 5% 7% 66%	2400
	11th to 20th	Night	4 4 1 4 3 4 4 4 5% 6% 61%	2338
	21st to end	Night	3 3 1 3 2 3 3 5% 4 6% 66%	1980
March	1st to 10th	Night	2 2 1 3 3 3 3 3 6% 8% 65%	5374
	11th to 20th	Night	4 8% 2 3 2 2 2 2 4 5% 65%	5137
	21st to end	Night	2 3 1 3 3 3 4 3 5% 7% 66%	5034
April	1st to 10th	Night	5% 3 1 4 3 4 3 4 4 6% 64%	2000
	11th to 20th	Night	3 4 1 3 3 3 3 4 5% 6% 65%	1977
	21st to end	Night	2 3 1 2 2 3 3 3 4 5% 73%	2000
May	1st to 10th	Night	1 4 1 2 2 2 2 2 3 4 76%	4540
	11th to 20th	Night	5% 3 1 4 2 3 4 3 5% 7% 64%	4510
	21st to end	Night	3 3 1 4 3 4 4 4 6% 7% 62%	4523
June	1st to 10th	Night	2 2 1 4 4 3 4 5% 7% 10% 58%	1800
	11th to 20th	Night	3 2 2 4 3 3 5% 5% 9% 9% 55%	1800
	21st to end	Night	5% 3 1 5% 4 4 5% 4 7% 10% 52%	1800
July	1st to 10th	Night	4 3 2 5% 4 4 4 5% 8% 11% 50%	3186
	11th to 20th	Night	2 1 1 2 2 2 3 3 6% 11% 67%	3170
	21st to end	Night	4 3 2 4 3 3 5% 4 8% 12% 51%	3445
August	1st to 10th	Night	2 2 1 2 3 3 4 4 8% 15% 56%	3155
	11th to 20th	Night	2 2 1 3 3 4 4 4 9% 12% 55%	3113
	21st to end	Night	4 3 1 4 3 3 4 3 7% 11% 57%	3487
September	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 51%	1900
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 5% 7% 9% 47%	2009
	21st to end	Night	6% 4 2 5% 3 3 5% 4 7% 7% 54%	2090
October	1st to 10th	Night	2 2 1 2 3 2 2 3 4 5% 74%	3480
	11th to 20th	Night	4 3 1 3 2 2 3 3 4 5% 70%	3677
	21st to end	Night	2 2 1 2 2 1 2 1 2 3 82%	4120
November	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 72%	2380
	11th to 20th	Night	2 4 2 3 2 2 4 3 4 5% 69%	2600
	21st to end	Night	4 3 1 4 3 3 3 2 4 6% 65%	2600
December	1st to 10th	Night	6% 8% 2 4 4 4 4 3 4 5% 57%	4250
	11th to 20th	Night	1 3 1 4 3 2 2 2 4 7% 70%	4816
	21st to end	Night	2 3 1 2 2 2 2 2 3 5% 78%	6374

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	15% 3 4 16% 26% 36%	4538
	11th to 20th	Day	12% 3 3 18% 39% 26%	4540
	21st to end	Day	16% 4 5% 17% 32% 26%	4994
February	1st to 10th	Day	18% 4 6% 14% 24% 34%	2000
	11th to 20th	Day	21% 4 6% 15% 27% 28%	1959
	21st to end	Day	15% 3 5% 14% 29% 34%	1650
March	1st to 10th	Day	17% 3 4 8% 21% 47%	4500
	11th to 20th	Day	18% 4 5% 11% 22% 40%	4852
	21st to end	Day	18% 3 6% 7% 30% 36%	5920
April	1st to 10th	Day	17% 3 6% 13% 27% 34%	2400
	11th to 20th	Day	17% 6% 6% 10% 27% 34%	2374
	21st to end	Day	15% 3 5% 11% 33% 33%	2400
May	1st to 10th	Day	12% 3 4 13% 27% 41%	5440
	11th to 20th	Day	16% 4 6% 11% 28% 35%	5408
	21st to end	Day	15% 5% 8% 16% 18% 38%	6357
June	1st to 10th	Day	16% 7% 13% 22% 26% 17%	2600
	11th to 20th	Day	18% 6% 9% 18% 28% 22%	2600
	21st to end	Day	28% 7% 12% 22% 19% 12%	2600
July	1st to 10th	Day	29% 9% 17% 29% 15% 2	3814
	11th to 20th	Day	20% 8% 15% 32% 21% 3	3737
	21st to end	Day	30% 9% 14% 26% 18% 4	3988
August	1st to 10th	Day	20% 8% 13% 31% 26% 3	3772
	11th to 20th	Day	27% 8% 14% 25% 22% 4	3762
	21st to end	Day	28% 8% 15% 28% 18% 3	4179
September	1st to 10th	Day	36% 9% 13% 17% 15% 10%	2280
	11th to 20th	Day	35% 9% 13% 17% 18% 8%	2169
	21st to end	Day	29% 6% 9% 20% 23% 13%	2090
October	1st to 10th	Day	12% 5% 6% 13% 25% 39%	3480
	11th to 20th	Day	15% 3 8% 21% 21% 32%	3243
	21st to end	Day	10% 2 2 14% 46% 27%	3438
November	1st to 10th	Day	15% 3 7% 18% 30% 27%	1894
	11th to 20th	Day	18% 4 6% 21% 28% 24%	1800
	21st to end	Day	22% 3 6% 18% 29% 22%	1800
December	1st to 10th	Day	28% 3 4 18% 26% 20%	2940
	11th to 20th	Day	17% 3 4 18% 35% 24%	3389
	21st to end	Day	11% 2 3 12% 37% 35%	4644
January	1st to 10th	Night	17% 4 4 11% 33% 32%	5428
	11th to 20th	Night	13% 2 4 17% 30% 34%	5440
	21st to end	Night	19% 4 4 17% 32% 24%	5984
February	1st to 10th	Night	17% 3 6% 13% 24% 36%	2400
	11th to 20th	Night	23% 4 7% 12% 25% 29%	2338
	21st to end	Night	18% 3 5% 9% 27% 37%	1980
March	1st to 10th	Night	16% 3 4 8% 23% 46%	5374
	11th to 20th	Night	17% 9% 4 8% 22% 41%	5137
	21st to end	Night	18% 3 6% 8% 26% 39%	5034
April	1st to 10th	Night	22% 4 5% 12% 26% 32%	2000
	11th to 20th	Night	19% 4 7% 13% 24% 32%	1977
	21st to end	Night	13% 4 6% 15% 27% 34%	2000
May	1st to 10th	Night	12% 4 5% 14% 24% 41%	4537
	11th to 20th	Night	19% 5% 6% 15% 24% 31%	4511
	21st to end	Night	20% 5% 10% 14% 16% 36%	4524
June	1st to 10th	Night	17% 8% 14% 27% 23% 12%	1800
	11th to 20th	Night	20% 6% 11% 20% 26% 18%	1800
	21st to end	Night	25% 7% 14% 22% 21% 12%	1800
July	1st to 10th	Night	25% 8% 18% 37% 11% 2	3136
	11th to 20th	Night	12% 6% 16% 42% 22% 3	3110
	21st to end	Night	23% 7% 16% 35% 17% 2	3336
August	1st to 10th	Night	14% 6% 15% 35% 27% 3	3144
	11th to 20th	Night	19% 6% 21% 33% 19% 2	3143
	21st to end	Night	21% 7% 20% 32% 17% 3	3487
September	1st to 10th	Night	28% 9% 16% 21% 16% 10%	1900
	11th to 20th	Night	29% 10% 17% 20% 16% 8%	2009
	21st to end	Night	25% 7% 13% 21% 20% 13%	2090
October	1st to 10th	Night	13% 4 8% 12% 22% 40%	3480
	11th to 20th	Night	15% 4 11% 18% 19% 33%	3677
	21st to end	Night	10% 2 3 13% 42% 29%	4120
November	1st to 10th	Night	16% 3 6% 15% 33% 27%	2380
	11th to 20th	Night	16% 4 5% 20% 28% 27%	2600
	21st to end	Night	21% 4 6% 16% 30% 23%	2600
December	1st to 10th	Night	31% 3 5% 15% 27% 19%	4250
	11th to 20th	Night	16% 3 3 14% 35% 28%	4817
	21st to end	Night	13% 2 3 13% 38% 32%	6374

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	7% 20% 32% 29% 12% 1	300
	11th to 20th	Day	9% 16% 36% 27% 12% 1	300
	21st to end	Day	5% 21% 35% 28% 9% 3	330
February	1st to 10th	Day	7% 13% 33% 28% 17% 3	300
	11th to 20th	Day	10% 17% 40% 23% 10%	300
	21st to end	Day	8% 18% 45% 21% 6% 1	249
March	1st to 10th	Day	8% 17% 45% 20% 9% 1	300
	11th to 20th	Day	11% 19% 39% 21% 8% 2	430
	21st to end	Day	7% 21% 44% 22% 6% 1	550
April	1st to 10th	Day	7% 17% 45% 21% 9% 2	500
	11th to 20th	Day	6% 20% 45% 24% 5% 1	492
	21st to end	Day	5% 16% 43% 29% 6% 1	500
May	1st to 10th	Day	4 13% 44% 27% 10% 2	503
	11th to 20th	Day	5% 11% 35% 36% 10% 2	528
	21st to end	Day	4 4 33% 40% 17% 2	751
June	1st to 10th	Day	2 2 17% 44% 30% 4	730
	11th to 20th	Day	2 2 12% 44% 34% 5%	730
	21st to end	Day	6% 4 8% 31% 40% 12%	730
July	1st to 10th	Day	6% 2 4 27% 40% 22%	519
	11th to 20th	Day	5% 1 2 26% 43% 23%	484
	21st to end	Day	3 1 4 31% 42% 20%	531
August	1st to 10th	Day	3 2 2 21% 47% 25%	487
	11th to 20th	Day	5% 3 4 26% 42% 21%	477
	21st to end	Day	8% 2 3 22% 42% 22%	539
September	1st to 10th	Day	9% 2 6% 34% 35% 14%	490
	11th to 20th	Day	9% 3 6% 33% 33% 17%	379
	21st to end	Day	7% 2 10% 35% 30% 16%	300
October	1st to 10th	Day	8% 3 13% 33% 32% 11%	300
	11th to 20th	Day	7% 5% 22% 37% 23% 6%	300
	21st to end	Day	6% 11% 27% 28% 18% 10%	330
November	1st to 10th	Day	7% 9% 27% 32% 19% 6%	300
	11th to 20th	Day	5% 11% 26% 33% 17% 8%	300
	21st to end	Day	9% 18% 32% 24% 13% 4	300
December	1st to 10th	Day	12% 11% 27% 33% 15% 2	300
	11th to 20th	Day	5% 16% 38% 26% 13% 2	300
	21st to end	Day	5% 18% 38% 28% 11% 1	330
January	1st to 10th	Night	6% 9% 33% 38% 13% 1	800
	11th to 20th	Night	6% 8% 33% 36% 15% 2	800
	21st to end	Night	5% 10% 34% 38% 12% 1	880
February	1st to 10th	Night	5% 11% 29% 37% 17% 2	800
	11th to 20th	Night	7% 7% 37% 38% 11% 1	784
	21st to end	Night	5% 12% 41% 36% 5%	660
March	1st to 10th	Night	5% 11% 34% 37% 12% 1	800
	11th to 20th	Night	7% 12% 31% 34% 15% 2	800
	21st to end	Night	4 9% 40% 38% 9% 1	684
April	1st to 10th	Night	5% 10% 32% 40% 11% 1	600
	11th to 20th	Night	6% 9% 36% 41% 8%	593
	21st to end	Night	3 8% 36% 43% 9% 1	600
May	1st to 10th	Night	4 7% 34% 42% 14% 1	600
	11th to 20th	Night	7% 5% 28% 47% 13% 1	591
	21st to end	Night	4 3 25% 51% 17%	650
June	1st to 10th	Night	2 2 15% 55% 25% 1	600
	11th to 20th	Night	3 2 13% 53% 28% 2	600
	21st to end	Night	5% 2 8% 45% 38% 2	600
July	1st to 10th	Night	6% 1 5% 32% 53% 3	570
	11th to 20th	Night	3 2 36% 53% 6%	552
	21st to end	Night	2 3 33% 57% 4	624
August	1st to 10th	Night	3 1 1 23% 65% 7%	567
	11th to 20th	Night	4 1 1 23% 61% 10%	564
	21st to end	Night	5% 1 1 28% 59% 6%	627
September	1st to 10th	Night	8% 2 3 27% 54% 6%	570
	11th to 20th	Night	9% 1 4 35% 48% 4	570
	21st to end	Night	7% 1 7% 38% 42% 5%	570
October	1st to 10th	Night	5% 1 9% 45% 35% 3	570
	11th to 20th	Night	9% 2 16% 43% 27% 3	698
	21st to end	Night	4 5% 19% 40% 25% 7%	836
November	1st to 10th	Night	7% 2 20% 40% 25% 6%	820
	11th to 20th	Night	6% 5% 23% 43% 22% 2	1000
	21st to end	Night	7% 9% 26% 38% 17% 4	1000
December	1st to 10th	Night	8% 6% 27% 40% 16% 3	1000
	11th to 20th	Night	4 9% 32% 41% 13% 2	1000
	21st to end	Night	4 13% 31% 38% 12% 2	1049

Page generated at 2025-07-03 00:30:13. Version ac07

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