Stephen F. Austin State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stephen F. Austin 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% 5% 5% 5% 4 6% 8% 41%	126137
	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	123179
Transparency	Day	39% 6% 12% 20% 16% 8%	129826
	Night	36% 5% 12% 20% 17% 9%	127553
Seeing	Day	13% 6% 17% 25% 26% 14%	16015
	Night	15% 5% 21% 34% 22% 3	25810

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	20% 10% 3 7% 3 3 3 2 3 4 41%	4077
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 3 5% 50%	4080
	21st to end	Day	31% 8% 2 5% 2 2 2 2 4 5% 35%	4488
February	1st to 10th	Day	22% 8% 3 6% 4 3 3 3 4 5% 38%	1965
	11th to 20th	Day	21% 8% 3 7% 5% 3 3 2 4 5% 39%	1949
	21st to end	Day	21% 8% 2 6% 4 3 3 2 4 5% 41%	1780
March	1st to 10th	Day	14% 6% 2 7% 6% 4 4 3 6% 8% 40%	4936
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 3 4 5% 47%	4980
	21st to end	Day	18% 7% 3 6% 4 4 4 3 5% 6% 40%	5462
April	1st to 10th	Day	15% 8% 3 8% 4 5% 4 4 5% 5% 39%	2200
	11th to 20th	Day	17% 7% 2 7% 4 5% 4 3 5% 6% 40%	2277
	21st to end	Day	13% 7% 2 7% 5% 3 5% 4 5% 7% 42%	2400
May	1st to 10th	Day	18% 6% 3 8% 5% 5% 4 5% 6% 8% 33%	5715
	11th to 20th	Day	11% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	5862
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 9% 36%	6434
June	1st to 10th	Day	5% 4 2 6% 5% 5% 6% 4 7% 10% 45%	2600
	11th to 20th	Day	6% 3 2 5% 6% 6% 6% 5% 7% 9% 44%	2600
	21st to end	Day	5% 6% 3 7% 7% 7% 8% 6% 9% 9% 31%	2600
July	1st to 10th	Day	8% 5% 2 8% 6% 6% 7% 6% 8% 11% 32%	5900
	11th to 20th	Day	5% 6% 3 7% 6% 6% 8% 6% 9% 13% 30%	5900
	21st to end	Day	10% 7% 3 6% 5% 5% 6% 5% 8% 11% 35%	6422
August	1st to 10th	Day	2 2 1 3 3 3 4 4 8% 10% 59%	4234
	11th to 20th	Day	3 2 1 4 4 5% 6% 6% 10% 13% 46%	4087
	21st to end	Day	6% 4 2 7% 6% 7% 7% 5% 8% 10% 38%	4057
September	1st to 10th	Day	7% 6% 3 7% 5% 6% 6% 5% 7% 10% 39%	2200
	11th to 20th	Day	11% 6% 3 7% 5% 6% 5% 4 7% 9% 38%	2178
	21st to end	Day	7% 6% 2 5% 5% 5% 6% 4 6% 8% 46%	2090
October	1st to 10th	Day	6% 4 1 5% 3 5% 4 3 5% 8% 56%	2021
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 4 6% 53%	1900
	21st to end	Day	12% 5% 2 5% 3 3 2 2 4 6% 54%	2090
November	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 7% 45%	1958
	11th to 20th	Day	11% 6% 3 5% 4 3 4 3 5% 6% 50%	2000
	21st to end	Day	16% 7% 2 6% 4 5% 4 3 6% 6% 42%	1876
December	1st to 10th	Day	25% 8% 3 5% 3 3 3 3 4 6% 36%	2940
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 3 4 5% 43%	3391
	21st to end	Day	15% 6% 2 6% 4 3 4 3 4 6% 47%	4488
January	1st to 10th	Night	20% 7% 2 5% 3 3 3 2 4 5% 46%	5888
	11th to 20th	Night	16% 7% 2 4 3 2 3 2 3 5% 52%	5900
	21st to end	Night	30% 7% 2 4 3 3 3 3 3 6% 36%	6490
February	1st to 10th	Night	20% 9% 3 6% 3 3 3 2 4 5% 40%	2450
	11th to 20th	Night	22% 8% 2 4 3 3 3 2 3 5% 44%	2338
	21st to end	Night	22% 8% 3 5% 4 3 4 3 4 5% 40%	1850
March	1st to 10th	Night	20% 9% 3 5% 3 3 4 3 5% 6% 39%	4919
	11th to 20th	Night	20% 7% 2 6% 3 3 3 2 4 4 45%	4980
	21st to end	Night	19% 9% 3 6% 4 3 3 3 4 5% 42%	5467
April	1st to 10th	Night	14% 7% 2 5% 4 4 4 4 7% 7% 42%	2200
	11th to 20th	Night	17% 7% 1 5% 3 3 4 3 5% 6% 45%	2070
	21st to end	Night	15% 6% 2 6% 4 4 4 4 4 7% 44%	2000
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 4 5% 7% 30%	4189
	11th to 20th	Night	11% 6% 2 6% 3 4 5% 4 6% 9% 44%	4053
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 5% 7% 10% 33%	4443
June	1st to 10th	Night	6% 3 2 5% 3 3 3 3 5% 11% 56%	1800
	11th to 20th	Night	5% 4 1 3 3 4 5% 4 6% 10% 55%	1800
	21st to end	Night	5% 4 2 5% 5% 6% 6% 5% 7% 11% 46%	1800
July	1st to 10th	Night	6% 5% 2 6% 4 5% 5% 5% 9% 12% 42%	4078
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 7% 11% 49%	4077
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 7% 10% 46%	4449
August	1st to 10th	Night	1 1 1 2 2 2 2 2 5% 10% 72%	2926
	11th to 20th	Night	1 2 1 3 3 3 4 4 8% 12% 59%	2968
	21st to end	Night	4 3 1 5% 4 5% 5% 5% 8% 12% 49%	3835
September	1st to 10th	Night	5% 5% 3 5% 4 5% 6% 4 7% 8% 48%	2200
	11th to 20th	Night	10% 5% 2 7% 4 4 4 4 5% 7% 47%	2178
	21st to end	Night	7% 3 1 5% 4 3 3 4 7% 9% 55%	2090
October	1st to 10th	Night	4 3 2 3 3 3 3 2 5% 9% 62%	2137
	11th to 20th	Night	10% 5% 1 3 3 3 3 3 4 6% 61%	2280
	21st to end	Night	11% 5% 2 3 3 2 2 3 4 4 61%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 52%	2340
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 4 4 53%	2400
	21st to end	Night	17% 7% 2 5% 3 3 3 3 4 6% 47%	2520
December	1st to 10th	Night	23% 11% 3 7% 4 3 3 3 4 5% 34%	4250
	11th to 20th	Night	17% 9% 3 6% 4 3 3 3 4 4 46%	4816
	21st to end	Night	16% 6% 2 5% 3 3 3 3 3 6% 51%	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	49% 3 5% 18% 18% 7%	4078
	11th to 20th	Day	38% 4 4 18% 22% 14%	4080
	21st to end	Day	52% 3 3 11% 16% 15%	4488
February	1st to 10th	Day	48% 4 6% 12% 17% 13%	1965
	11th to 20th	Day	49% 3 8% 14% 17% 9%	1959
	21st to end	Day	46% 4 8% 16% 16% 11%	1780
March	1st to 10th	Day	41% 5% 8% 17% 15% 13%	4936
	11th to 20th	Day	40% 5% 6% 9% 18% 22%	4980
	21st to end	Day	44% 5% 7% 19% 19% 6%	5464
April	1st to 10th	Day	46% 5% 6% 17% 15% 10%	2200
	11th to 20th	Day	45% 5% 8% 14% 18% 10%	2277
	21st to end	Day	42% 5% 8% 20% 19% 7%	2400
May	1st to 10th	Day	46% 7% 12% 20% 12% 3	5751
	11th to 20th	Day	38% 6% 11% 21% 21% 3	5866
	21st to end	Day	39% 9% 11% 29% 11% 1	6447
June	1st to 10th	Day	32% 8% 16% 27% 16% 2	2600
	11th to 20th	Day	33% 8% 15% 24% 17% 2	2600
	21st to end	Day	43% 12% 16% 20% 9% 1	2600
July	1st to 10th	Day	42% 8% 29% 19% 3	5836
	11th to 20th	Day	41% 8% 24% 20% 6%	5831
	21st to end	Day	40% 8% 19% 25% 8% 1	6240
August	1st to 10th	Day	18% 8% 14% 41% 18% 1	4220
	11th to 20th	Day	25% 9% 32% 27% 7% 1	4126
	21st to end	Day	38% 11% 17% 22% 12% 1	4056
September	1st to 10th	Day	40% 9% 13% 18% 14% 6%	2200
	11th to 20th	Day	41% 9% 11% 19% 17% 3	2178
	21st to end	Day	34% 7% 12% 17% 17% 13%	2090
October	1st to 10th	Day	18% 4 6% 15% 18% 39%	3359
	11th to 20th	Day	23% 4 7% 16% 35% 16%	3140
	21st to end	Day	28% 5% 5% 18% 32% 14%	3428
November	1st to 10th	Day	37% 4 9% 19% 21% 9%	1958
	11th to 20th	Day	35% 5% 10% 16% 21% 14%	2000
	21st to end	Day	43% 5% 8% 15% 17% 11%	1876
December	1st to 10th	Day	51% 3 6% 16% 19% 5%	2940
	11th to 20th	Day	42% 5% 8% 13% 22% 10%	3389
	21st to end	Day	39% 4 5% 17% 24% 12%	4488
January	1st to 10th	Night	41% 4 6% 19% 19% 10%	5888
	11th to 20th	Night	37% 3 4 20% 24% 13%	5900
	21st to end	Night	51% 3 4 12% 17% 12%	6490
February	1st to 10th	Night	48% 4 6% 11% 17% 14%	2450
	11th to 20th	Night	44% 4 7% 16% 17% 12%	2338
	21st to end	Night	48% 4 7% 13% 16% 13%	1850
March	1st to 10th	Night	46% 4 8% 16% 16% 11%	4919
	11th to 20th	Night	43% 4 6% 13% 15% 19%	4980
	21st to end	Night	45% 4 8% 15% 19% 8%	5467
April	1st to 10th	Night	40% 6% 9% 19% 15% 10%	2200
	11th to 20th	Night	40% 5% 10% 17% 15% 14%	2070
	21st to end	Night	40% 5% 9% 20% 18% 7%	2000
May	1st to 10th	Night	53% 6% 10% 19% 9% 3	4218
	11th to 20th	Night	35% 6% 12% 25% 16% 5%	4054
	21st to end	Night	43% 8% 16% 25% 7% 1	4452
June	1st to 10th	Night	22% 7% 19% 33% 19% 1	1800
	11th to 20th	Night	24% 6% 18% 31% 17% 4	1800
	21st to end	Night	30% 9% 22% 26% 12% 1	1800
July	1st to 10th	Night	33% 7% 34% 22% 3	4035
	11th to 20th	Night	28% 7% 27% 31% 7%	4026
	21st to end	Night	33% 9% 21% 28% 9%	4320
August	1st to 10th	Night	9% 5% 19% 49% 18%	2916
	11th to 20th	Night	16% 7% 36% 35% 6% 1	2995
	21st to end	Night	26% 13% 23% 27% 10% 1	3835
September	1st to 10th	Night	30% 10% 20% 21% 15% 5%	2200
	11th to 20th	Night	35% 7% 14% 24% 15% 4	2178
	21st to end	Night	26% 6% 16% 22% 18% 12%	2090
October	1st to 10th	Night	14% 4 8% 18% 17% 39%	3566
	11th to 20th	Night	15% 3 7% 23% 33% 19%	3779
	21st to end	Night	20% 3 5% 22% 33% 17%	4120
November	1st to 10th	Night	33% 5% 11% 20% 22% 10%	2340
	11th to 20th	Night	35% 4 10% 18% 20% 14%	2400
	21st to end	Night	40% 4 9% 17% 18% 12%	2520
December	1st to 10th	Night	54% 4 5% 14% 17% 6%	4250
	11th to 20th	Night	42% 4 10% 10% 20% 15%	4817
	21st to end	Night	36% 4 5% 16% 28% 10%	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	22% 10% 35% 26% 6% 2	300
	11th to 20th	Day	22% 10% 29% 29% 9%	300
	21st to end	Day	25% 12% 33% 22% 9%	330
February	1st to 10th	Day	30% 12% 24% 25% 9% 1	300
	11th to 20th	Day	26% 16% 28% 24% 6% 1	300
	21st to end	Day	29% 10% 37% 19% 6%	249
March	1st to 10th	Day	21% 13% 36% 21% 9%	300
	11th to 20th	Day	18% 14% 40% 22% 5% 1	300
	21st to end	Day	22% 10% 32% 25% 10% 1	330
April	1st to 10th	Day	16% 15% 35% 24% 9%	300
	11th to 20th	Day	24% 10% 29% 26% 10% 1	395
	21st to end	Day	16% 9% 31% 29% 14% 2	500
May	1st to 10th	Day	14% 9% 35% 28% 13% 1	632
	11th to 20th	Day	12% 5% 26% 34% 20% 3	725
	21st to end	Day	12% 4 21% 37% 22% 4	789
June	1st to 10th	Day	7% 3 8% 35% 34% 14%	730
	11th to 20th	Day	7% 3 8% 35% 36% 12%	730
	21st to end	Day	7% 2 7% 24% 38% 22%	730
July	1st to 10th	Day	8% 3 6% 20% 38% 25%	721
	11th to 20th	Day	3 3 1 18% 42% 33%	718
	21st to end	Day	7% 1 2 20% 42% 28%	794
August	1st to 10th	Day	3 1 1 16% 45% 33%	726
	11th to 20th	Day	4 2 2 14% 44% 34%	670
	21st to end	Day	9% 1 3 12% 34% 41%	432
September	1st to 10th	Day	8% 3 3 19% 38% 28%	330
	11th to 20th	Day	8% 1 4 19% 37% 31%	324
	21st to end	Day	10% 1 4 20% 41% 24%	300
October	1st to 10th	Day	6% 3 7% 29% 38% 18%	300
	11th to 20th	Day	9% 3 13% 31% 30% 15%	300
	21st to end	Day	19% 8% 18% 24% 22% 10%	330
November	1st to 10th	Day	16% 4 16% 34% 24% 6%	300
	11th to 20th	Day	14% 5% 24% 32% 20% 4	300
	21st to end	Day	20% 12% 30% 23% 12% 4	300
December	1st to 10th	Day	21% 5% 30% 22% 17% 4	300
	11th to 20th	Day	19% 11% 29% 31% 8% 2	300
	21st to end	Day	19% 7% 34% 28% 10% 2	330
January	1st to 10th	Night	23% 9% 28% 32% 9%	1000
	11th to 20th	Night	22% 11% 26% 33% 8%	1000
	21st to end	Night	25% 8% 29% 32% 7%	1100
February	1st to 10th	Night	26% 11% 28% 30% 6%	850
	11th to 20th	Night	27% 9% 28% 31% 5%	784
	21st to end	Night	26% 9% 35% 27% 3	530
March	1st to 10th	Night	22% 8% 37% 29% 4	600
	11th to 20th	Night	22% 8% 33% 32% 5%	600
	21st to end	Night	17% 7% 36% 32% 7% 1	660
April	1st to 10th	Night	16% 8% 36% 36% 4	600
	11th to 20th	Night	22% 7% 31% 31% 8%	593
	21st to end	Night	19% 8% 33% 32% 9% 1	600
May	1st to 10th	Night	17% 5% 35% 36% 8%	600
	11th to 20th	Night	14% 2 28% 43% 12% 2	591
	21st to end	Night	10% 2 27% 40% 20% 1	650
June	1st to 10th	Night	5% 3 10% 49% 31% 2	600
	11th to 20th	Night	4 3 11% 52% 28% 2	600
	21st to end	Night	5% 2 8% 34% 43% 8%	600
July	1st to 10th	Night	6% 2 3 35% 46% 8%	585
	11th to 20th	Night	4 1 3 30% 55% 7%	582
	21st to end	Night	2 1 3 37% 50% 7%	657
August	1st to 10th	Night	2 1 1 35% 55% 6%	597
	11th to 20th	Night	3 1 1 30% 57% 8%	594
	21st to end	Night	4 1 3 25% 57% 10%	660
September	1st to 10th	Night	5% 3 4 28% 51% 9%	600
	11th to 20th	Night	10% 2 3 31% 47% 6%	594
	21st to end	Night	9% 1 8% 32% 44% 7%	570
October	1st to 10th	Night	6% 1 8% 38% 42% 5%	617
	11th to 20th	Night	11% 2 17% 43% 25% 3	760
	21st to end	Night	13% 5% 21% 38% 21% 3	836
November	1st to 10th	Night	12% 3 18% 41% 23% 2	780
	11th to 20th	Night	16% 6% 20% 38% 20% 1	800
	21st to end	Night	21% 6% 25% 33% 13% 1	920
December	1st to 10th	Night	23% 6% 24% 31% 15% 1	1000
	11th to 20th	Night	24% 9% 24% 34% 9% 1	1000
	21st to end	Night	21% 7% 29% 32% 10%	1100

Page generated at 2025-09-16 00:49:17. Version ac07

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