Seguin Outdoor Learning Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seguin Outdoor Learning Center clear sky chart from 2005-11-06 to 2025-11-03.

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 6% 7% 45%	126753
	Night	14% 6% 2 5% 3 3 3 3 5% 7% 48%	123593
Transparency	Day	37% 6% 10% 21% 17% 10%	130519
	Night	35% 5% 11% 20% 18% 12%	127877
Seeing	Day	13% 6% 19% 28% 25% 9%	16095
	Night	15% 6% 25% 36% 17% 1	25967

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	18% 9% 3 6% 3 2 3 2 3 4 47%	4077
	11th to 20th	Day	18% 5% 2 5% 2 3 3 2 4 5% 52%	4080
	21st to end	Day	28% 7% 2 4 3 2 2 3 4 6% 39%	4827
February	1st to 10th	Day	21% 8% 3 5% 3 3 3 2 3 5% 44%	2000
	11th to 20th	Day	20% 8% 3 5% 3 3 3 3 4 6% 43%	1949
	21st to end	Day	18% 8% 2 5% 3 2 4 2 4 6% 46%	1650
March	1st to 10th	Day	13% 7% 2 6% 4 3 3 3 4 6% 50%	4928
	11th to 20th	Day	14% 6% 2 7% 4 4 3 3 3 4 50%	4980
	21st to end	Day	19% 8% 3 6% 3 3 3 2 4 5% 44%	5462
April	1st to 10th	Day	14% 9% 2 6% 4 4 4 3 5% 6% 43%	2200
	11th to 20th	Day	18% 7% 2 6% 4 4 4 4 4 5% 42%	2176
	21st to end	Day	15% 8% 2 7% 5% 4 4 3 4 6% 42%	2508
May	1st to 10th	Day	19% 8% 2 7% 5% 5% 5% 3 6% 7% 33%	5862
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 6% 7% 45%	5862
	21st to end	Day	11% 6% 2 7% 4 5% 5% 5% 8% 10% 37%	6434
June	1st to 10th	Day	5% 4 2 5% 4 4 6% 5% 9% 10% 46%	2600
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	2600
	21st to end	Day	7% 6% 2 7% 6% 7% 6% 5% 9% 10% 37%	2600
July	1st to 10th	Day	11% 7% 3 8% 6% 5% 5% 4 6% 8% 36%	5900
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 6% 9% 12% 38%	5900
	21st to end	Day	7% 6% 2 7% 5% 5% 6% 4 8% 11% 38%	6422
August	1st to 10th	Day	1 2 1 3 3 3 3 3 6% 9% 66%	4234
	11th to 20th	Day	3 2 1 4 3 4 5% 4 8% 12% 53%	3846
	21st to end	Day	4 3 2 5% 5% 6% 6% 5% 8% 13% 44%	4090
September	1st to 10th	Day	8% 5% 3 8% 5% 6% 5% 5% 6% 7% 43%	2200
	11th to 20th	Day	9% 7% 3 7% 4 5% 5% 4 8% 8% 41%	2200
	21st to end	Day	8% 4 2 5% 4 4 5% 5% 6% 8% 49%	2200
October	1st to 10th	Day	6% 4 1 5% 4 4 5% 4 5% 8% 55%	2200
	11th to 20th	Day	12% 5% 2 4 3 3 4 4 4 6% 53%	2058
	21st to end	Day	10% 5% 2 4 3 4 3 3 4 6% 57%	2200
November	1st to 10th	Day	14% 7% 2 6% 4 3 4 4 5% 7% 44%	1978
	11th to 20th	Day	13% 5% 2 6% 4 4 3 3 4 6% 51%	1911
	21st to end	Day	18% 7% 2 6% 4 4 3 3 4 5% 44%	1800
December	1st to 10th	Day	29% 9% 2 6% 4 3 2 3 3 5% 35%	2940
	11th to 20th	Day	17% 8% 3 6% 4 4 3 4 4 5% 43%	3391
	21st to end	Day	14% 6% 2 5% 3 3 2 2 3 5% 55%	4488
January	1st to 10th	Night	21% 7% 2 4 2 2 2 2 4 5% 48%	5888
	11th to 20th	Night	13% 3 1 3 2 2 3 3 4 5% 61%	5900
	21st to end	Night	31% 6% 2 5% 3 2 3 2 4 5% 39%	6195
February	1st to 10th	Night	19% 7% 2 5% 3 3 3 3 5% 5% 46%	2400
	11th to 20th	Night	21% 7% 2 4 3 2 3 2 3 6% 47%	2338
	21st to end	Night	21% 7% 1 5% 3 2 3 2 4 6% 45%	1980
March	1st to 10th	Night	18% 7% 2 5% 3 4 4 3 4 5% 44%	4925
	11th to 20th	Night	17% 7% 2 5% 3 3 3 2 4 5% 48%	4980
	21st to end	Night	19% 9% 3 5% 4 3 3 3 4 5% 43%	5467
April	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2200
	11th to 20th	Night	16% 7% 3 6% 4 3 3 4 5% 6% 44%	2173
	21st to end	Night	16% 7% 2 5% 5% 4 3 3 4 6% 45%	1884
May	1st to 10th	Night	24% 8% 3 7% 4 4 3 3 5% 6% 33%	4053
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 6% 10% 46%	4053
	21st to end	Night	13% 7% 2 7% 5% 5% 5% 4 6% 10% 37%	4443
June	1st to 10th	Night	5% 4 1 4 3 3 4 3 5% 10% 57%	1800
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 10% 58%	1800
	21st to end	Night	5% 4 2 5% 5% 4 6% 4 7% 8% 50%	1800
July	1st to 10th	Night	8% 6% 3 6% 4 5% 5% 4 7% 10% 41%	4078
	11th to 20th	Night	4 3 2 5% 4 4 5% 4 8% 13% 47%	4077
	21st to end	Night	7% 6% 2 7% 5% 4 5% 5% 7% 9% 45%	4449
August	1st to 10th	Night	1 1 1 2 2 2 2 3 5% 6% 75%	2926
	11th to 20th	Night	3 2 1 3 2 4 4 4 7% 13% 56%	3207
	21st to end	Night	6% 3 1 4 3 3 4 4 7% 11% 54%	3811
September	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 6% 8% 49%	2200
	11th to 20th	Night	8% 6% 2 6% 5% 4 5% 4 5% 8% 48%	2200
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	2200
October	1st to 10th	Night	4 4 1 4 3 3 3 2 5% 7% 62%	2200
	11th to 20th	Night	13% 4 2 3 3 3 3 2 5% 5% 57%	2320
	21st to end	Night	12% 4 1 4 2 2 2 2 3 3 62%	2640
November	1st to 10th	Night	13% 6% 2 5% 4 2 3 2 4 6% 52%	2365
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 4 6% 55%	2485
	21st to end	Night	17% 6% 2 5% 4 2 4 3 4 6% 48%	2600
December	1st to 10th	Night	27% 9% 3 6% 4 3 3 2 3 4 35%	4250
	11th to 20th	Night	18% 9% 3 6% 3 3 3 3 3 5% 46%	4816
	21st to end	Night	17% 6% 2 4 2 2 2 2 3 4 56%	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	43% 3 4 18% 22% 10%	4078
	11th to 20th	Day	36% 2 5% 18% 20% 19%	4080
	21st to end	Day	48% 2 3 10% 24% 12%	4827
February	1st to 10th	Day	45% 4 4 12% 20% 16%	2000
	11th to 20th	Day	45% 3 7% 17% 18% 12%	1959
	21st to end	Day	40% 4 7% 16% 18% 14%	1650
March	1st to 10th	Day	37% 4 5% 20% 14% 20%	4928
	11th to 20th	Day	39% 5% 4 8% 18% 27%	4980
	21st to end	Day	42% 4 7% 20% 17% 10%	5464
April	1st to 10th	Day	41% 5% 9% 17% 16% 13%	2200
	11th to 20th	Day	44% 4 6% 16% 18% 12%	2176
	21st to end	Day	43% 5% 6% 20% 17% 9%	2508
May	1st to 10th	Day	48% 6% 10% 19% 14% 4	5900
	11th to 20th	Day	35% 7% 11% 20% 20% 8%	5866
	21st to end	Day	38% 7% 11% 29% 13% 1	6447
June	1st to 10th	Day	29% 9% 14% 27% 18% 2	2600
	11th to 20th	Day	32% 7% 13% 25% 19% 4	2600
	21st to end	Day	38% 9% 14% 25% 11% 2	2600
July	1st to 10th	Day	44% 7% 16% 27% 4 1	5836
	11th to 20th	Day	33% 9% 20% 27% 10% 1	5831
	21st to end	Day	37% 8% 17% 25% 12% 2	6240
August	1st to 10th	Day	15% 6% 11% 44% 23% 1	4220
	11th to 20th	Day	22% 7% 26% 34% 10% 2	3882
	21st to end	Day	30% 12% 18% 23% 16% 2	4089
September	1st to 10th	Day	39% 8% 10% 19% 17% 8%	2200
	11th to 20th	Day	38% 8% 12% 20% 17% 5%	2200
	21st to end	Day	30% 8% 10% 22% 17% 14%	2200
October	1st to 10th	Day	17% 4 7% 13% 23% 35%	3590
	11th to 20th	Day	23% 4 8% 20% 26% 20%	3324
	21st to end	Day	26% 4 6% 19% 28% 17%	3538
November	1st to 10th	Day	40% 5% 8% 18% 18% 12%	1978
	11th to 20th	Day	35% 4 9% 17% 20% 15%	1911
	21st to end	Day	43% 5% 7% 15% 19% 13%	1800
December	1st to 10th	Day	54% 3 5% 16% 15% 8%	2940
	11th to 20th	Day	42% 5% 8% 12% 20% 13%	3389
	21st to end	Day	34% 3 4 19% 25% 15%	4488
January	1st to 10th	Night	41% 3 5% 18% 20% 14%	5888
	11th to 20th	Night	29% 2 4 18% 28% 18%	5900
	21st to end	Night	50% 2 3 10% 20% 14%	6195
February	1st to 10th	Night	42% 4 6% 13% 19% 17%	2400
	11th to 20th	Night	42% 3 6% 17% 18% 14%	2338
	21st to end	Night	42% 4 6% 17% 17% 15%	1980
March	1st to 10th	Night	42% 5% 6% 16% 15% 16%	4925
	11th to 20th	Night	39% 4 7% 11% 14% 25%	4980
	21st to end	Night	44% 4 7% 17% 17% 10%	5467
April	1st to 10th	Night	37% 5% 10% 19% 16% 14%	2200
	11th to 20th	Night	41% 5% 10% 13% 16% 15%	2173
	21st to end	Night	41% 6% 8% 19% 16% 9%	1884
May	1st to 10th	Night	51% 5% 8% 18% 13% 5%	4080
	11th to 20th	Night	33% 7% 12% 21% 19% 9%	4054
	21st to end	Night	41% 7% 14% 28% 9% 1	4452
June	1st to 10th	Night	24% 6% 16% 30% 22% 2	1800
	11th to 20th	Night	22% 7% 13% 31% 22% 5%	1800
	21st to end	Night	29% 8% 18% 29% 14% 2	1800
July	1st to 10th	Night	37% 9% 23% 27% 4	4035
	11th to 20th	Night	27% 8% 25% 29% 10%	4026
	21st to end	Night	34% 8% 20% 24% 12% 2	4320
August	1st to 10th	Night	10% 5% 17% 47% 21%	2916
	11th to 20th	Night	18% 8% 33% 33% 7% 1	3237
	21st to end	Night	22% 12% 24% 27% 14% 2	3811
September	1st to 10th	Night	31% 8% 16% 22% 15% 7%	2200
	11th to 20th	Night	34% 8% 14% 24% 15% 5%	2200
	21st to end	Night	29% 7% 15% 21% 16% 12%	2200
October	1st to 10th	Night	15% 3 7% 17% 20% 37%	3590
	11th to 20th	Night	19% 4 9% 19% 28% 21%	3767
	21st to end	Night	22% 3 6% 22% 29% 17%	4252
November	1st to 10th	Night	35% 5% 8% 19% 20% 14%	2365
	11th to 20th	Night	31% 4 9% 18% 21% 16%	2485
	21st to end	Night	38% 3 8% 18% 19% 14%	2600
December	1st to 10th	Night	55% 3 5% 14% 13% 10%	4250
	11th to 20th	Night	42% 5% 7% 9% 20% 17%	4817
	21st to end	Night	34% 3 4 14% 29% 16%	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% 32% 28% 7% 1	300
	11th to 20th	Day	24% 12% 27% 27% 7% 2	300
	21st to end	Day	24% 11% 31% 24% 10%	330
February	1st to 10th	Day	27% 10% 27% 24% 12%	300
	11th to 20th	Day	25% 16% 32% 20% 6% 1	300
	21st to end	Day	23% 15% 36% 22% 3	249
March	1st to 10th	Day	20% 13% 37% 23% 6%	300
	11th to 20th	Day	15% 13% 43% 22% 5% 1	300
	21st to end	Day	18% 12% 35% 28% 6% 1	330
April	1st to 10th	Day	17% 15% 35% 24% 9%	300
	11th to 20th	Day	17% 16% 32% 24% 10% 1	294
	21st to end	Day	18% 13% 35% 26% 8% 1	608
May	1st to 10th	Day	17% 10% 34% 28% 10% 1	703
	11th to 20th	Day	15% 7% 27% 33% 16% 2	725
	21st to end	Day	14% 5% 24% 37% 19% 2	789
June	1st to 10th	Day	7% 2 12% 39% 32% 8%	730
	11th to 20th	Day	9% 1 11% 42% 30% 6%	730
	21st to end	Day	8% 2 10% 32% 36% 13%	730
July	1st to 10th	Day	8% 2 8% 29% 39% 16%	721
	11th to 20th	Day	6% 1 6% 26% 47% 15%	718
	21st to end	Day	4 1 6% 27% 44% 18%	794
August	1st to 10th	Day	3 3 21% 48% 24%	726
	11th to 20th	Day	4 3 27% 42% 23%	517
	21st to end	Day	6% 1 6% 18% 38% 31%	452
September	1st to 10th	Day	9% 8% 22% 37% 24%	330
	11th to 20th	Day	6% 1 4 21% 42% 27%	330
	21st to end	Day	10% 1 7% 22% 38% 24%	330
October	1st to 10th	Day	5% 1 11% 25% 38% 20%	330
	11th to 20th	Day	9% 4 15% 32% 28% 13%	330
	21st to end	Day	15% 10% 17% 28% 22% 8%	363
November	1st to 10th	Day	17% 6% 24% 29% 19% 5%	306
	11th to 20th	Day	17% 5% 24% 29% 20% 5%	300
	21st to end	Day	22% 10% 33% 20% 12% 4	300
December	1st to 10th	Day	22% 8% 27% 27% 12% 5%	300
	11th to 20th	Day	22% 13% 26% 24% 14% 1	300
	21st to end	Day	18% 9% 32% 28% 12% 2	330
January	1st to 10th	Night	22% 7% 29% 32% 9% 1	1000
	11th to 20th	Night	21% 9% 30% 31% 9%	1000
	21st to end	Night	24% 7% 29% 34% 6%	974
February	1st to 10th	Night	26% 9% 28% 31% 6%	800
	11th to 20th	Night	27% 10% 32% 28% 3	784
	21st to end	Night	25% 11% 37% 24% 2	660
March	1st to 10th	Night	21% 14% 35% 28% 3	606
	11th to 20th	Night	21% 10% 38% 27% 5%	600
	21st to end	Night	18% 10% 39% 29% 3	660
April	1st to 10th	Night	14% 10% 44% 29% 3	600
	11th to 20th	Night	17% 10% 38% 29% 5%	593
	21st to end	Night	16% 10% 40% 27% 7%	600
May	1st to 10th	Night	15% 9% 42% 28% 6%	600
	11th to 20th	Night	15% 5% 35% 35% 10% 1	591
	21st to end	Night	10% 4 35% 39% 13%	650
June	1st to 10th	Night	7% 2 20% 49% 21% 1	600
	11th to 20th	Night	5% 1 29% 46% 17% 1	600
	21st to end	Night	7% 2 15% 45% 28% 4	600
July	1st to 10th	Night	9% 2 11% 45% 31% 2	585
	11th to 20th	Night	3 1 11% 47% 36% 2	582
	21st to end	Night	3 2 9% 46% 38% 3	657
August	1st to 10th	Night	2 7% 49% 39% 4	597
	11th to 20th	Night	5% 1 7% 46% 37% 5%	594
	21st to end	Night	7% 4 38% 43% 7%	660
September	1st to 10th	Night	8% 1 9% 36% 41% 6%	600
	11th to 20th	Night	10% 1 6% 37% 43% 3	600
	21st to end	Night	9% 1 13% 33% 41% 3	600
October	1st to 10th	Night	5% 2 10% 46% 34% 4	600
	11th to 20th	Night	13% 2 18% 42% 22% 2	720
	21st to end	Night	12% 6% 25% 35% 19% 2	880
November	1st to 10th	Night	15% 5% 19% 40% 19% 1	789
	11th to 20th	Night	12% 6% 25% 39% 17% 1	885
	21st to end	Night	19% 9% 26% 31% 14% 1	1000
December	1st to 10th	Night	21% 7% 23% 37% 11% 1	1000
	11th to 20th	Night	25% 9% 25% 32% 9%	1000
	21st to end	Night	21% 7% 28% 35% 9%	1100

Page generated at 2025-10-31 01:02:37. Version ac07

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