Texas A&M University Teaching Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Texas A&M University Teaching Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	126555
	Night	13% 6% 2 5% 3 3 4 3 5% 7% 49%	123423
Transparency	Day	36% 6% 12% 20% 18% 8%	130246
	Night	34% 6% 11% 20% 19% 10%	127782
Seeing	Day	13% 6% 19% 26% 25% 10%	16194
	Night	14% 6% 24% 35% 18% 2	26000

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	17% 10% 3 5% 3 3 3 3 4 5% 44%	4077
	11th to 20th	Day	14% 6% 2 6% 3 3 3 3 5% 6% 51%	4080
	21st to end	Day	29% 9% 3 5% 3 1 2 1 3 5% 38%	4488
February	1st to 10th	Day	22% 8% 3 7% 3 3 3 3 4 5% 39%	1960
	11th to 20th	Day	22% 7% 2 6% 4 4 2 3 3 6% 40%	1949
	21st to end	Day	21% 7% 2 5% 4 3 3 3 4 5% 43%	1745
March	1st to 10th	Day	15% 7% 3 8% 5% 4 4 3 5% 6% 41%	4936
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 48%	4980
	21st to end	Day	18% 8% 2 7% 4 4 4 3 5% 6% 40%	5462
April	1st to 10th	Day	14% 8% 4 7% 5% 4 4 3 5% 6% 39%	2200
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 3 5% 6% 40%	2271
	21st to end	Day	13% 6% 2 6% 3 4 5% 3 5% 6% 45%	2400
May	1st to 10th	Day	18% 7% 3 7% 5% 4 5% 4 7% 7% 33%	5857
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 7% 8% 43%	5862
	21st to end	Day	10% 6% 2 8% 5% 6% 7% 5% 8% 10% 33%	6434
June	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 6% 9% 9% 44%	2600
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 5% 8% 9% 47%	2600
	21st to end	Day	5% 5% 2 6% 6% 6% 7% 6% 8% 10% 38%	2600
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 11% 39%	5900
	11th to 20th	Day	5% 5% 2 6% 5% 5% 6% 5% 8% 13% 41%	5900
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 40%	6422
August	1st to 10th	Day	2 1 1 2 3 2 3 3 5% 8% 70%	4234
	11th to 20th	Day	3 2 1 3 3 4 4 5% 7% 13% 55%	4150
	21st to end	Day	5% 4 2 5% 5% 6% 6% 5% 7% 11% 45%	4049
September	1st to 10th	Day	6% 5% 2 7% 5% 6% 6% 5% 6% 8% 45%	2200
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 5% 6% 7% 42%	2200
	21st to end	Day	6% 4 1 5% 4 5% 6% 5% 5% 6% 53%	2200
October	1st to 10th	Day	5% 4 1 4 3 3 4 3 4 7% 61%	2137
	11th to 20th	Day	13% 4 2 4 3 3 3 3 4 6% 56%	1980
	21st to end	Day	13% 4 2 4 3 3 3 3 3 5% 58%	2090
November	1st to 10th	Day	11% 7% 2 5% 4 5% 5% 3 5% 7% 47%	1958
	11th to 20th	Day	11% 5% 2 6% 3 3 3 3 5% 6% 53%	2000
	21st to end	Day	18% 8% 2 5% 5% 3 4 3 5% 4 43%	1815
December	1st to 10th	Day	22% 7% 2 5% 4 3 3 3 4 6% 41%	2940
	11th to 20th	Day	20% 7% 2 6% 4 4 3 3 4 6% 41%	3391
	21st to end	Day	14% 8% 3 6% 3 3 3 3 4 5% 48%	4488
January	1st to 10th	Night	18% 7% 2 4 2 3 3 3 3 5% 49%	5888
	11th to 20th	Night	15% 5% 2 3 2 2 3 2 3 5% 57%	5900
	21st to end	Night	28% 8% 3 5% 3 3 2 2 3 5% 38%	6490
February	1st to 10th	Night	20% 7% 2 5% 4 3 3 2 4 5% 44%	2455
	11th to 20th	Night	21% 7% 3 5% 3 3 3 2 3 4 45%	2338
	21st to end	Night	22% 6% 2 5% 3 3 4 3 4 5% 43%	1883
March	1st to 10th	Night	17% 8% 2 7% 4 3 4 3 5% 7% 41%	4919
	11th to 20th	Night	16% 6% 2 6% 4 4 3 3 4 5% 47%	4980
	21st to end	Night	19% 9% 3 6% 4 3 3 2 4 5% 43%	5467
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 7% 47%	2200
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 5% 8% 45%	2075
	21st to end	Night	14% 7% 2 5% 4 3 3 3 5% 7% 46%	2000
May	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 5% 8% 33%	4053
	11th to 20th	Night	9% 6% 3 7% 5% 5% 6% 4 6% 7% 44%	4053
	21st to end	Night	10% 7% 3 6% 5% 5% 5% 5% 6% 11% 37%	4443
June	1st to 10th	Night	5% 3 2 4 3 3 4 3 7% 11% 56%	1800
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 60%	1800
	21st to end	Night	4 4 1 5% 4 5% 5% 4 8% 11% 50%	1800
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 13% 41%	4078
	11th to 20th	Night	3 4 2 4 4 3 4 4 7% 12% 54%	4077
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 7% 10% 46%	4449
August	1st to 10th	Night	1 1 2 2 2 2 2 5% 10% 74%	2926
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 12% 59%	2905
	21st to end	Night	3 3 2 4 3 4 5% 4 8% 12% 52%	3843
September	1st to 10th	Night	5% 5% 2 6% 4 4 4 4 6% 9% 50%	2200
	11th to 20th	Night	9% 5% 3 6% 4 5% 5% 4 6% 6% 48%	2200
	21st to end	Night	6% 4 1 4 3 3 4 3 6% 8% 58%	2200
October	1st to 10th	Night	4 3 1 4 3 3 3 3 4 7% 65%	2240
	11th to 20th	Night	11% 4 1 3 3 3 2 2 4 6% 62%	2377
	21st to end	Night	12% 5% 2 4 3 2 2 2 3 4 61%	2508
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 6% 54%	2340
	11th to 20th	Night	11% 5% 2 4 4 4 4 3 4 6% 54%	2400
	21st to end	Night	16% 7% 2 5% 4 3 4 3 5% 6% 47%	2580
December	1st to 10th	Night	22% 9% 3 6% 4 3 3 2 4 6% 40%	4250
	11th to 20th	Night	18% 9% 3 6% 3 3 3 2 4 4 45%	4816
	21st to end	Night	16% 5% 2 4 3 3 3 2 3 4 54%	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	42% 5% 6% 23% 17% 7%	4078
	11th to 20th	Day	35% 3 5% 19% 26% 11%	4080
	21st to end	Day	51% 3 3 11% 18% 15%	4488
February	1st to 10th	Day	48% 5% 6% 12% 18% 12%	1960
	11th to 20th	Day	48% 3 7% 16% 17% 9%	1959
	21st to end	Day	44% 5% 7% 15% 17% 12%	1745
March	1st to 10th	Day	42% 7% 7% 14% 19% 11%	4936
	11th to 20th	Day	36% 6% 7% 10% 18% 23%	4980
	21st to end	Day	44% 5% 9% 19% 17% 6%	5464
April	1st to 10th	Day	45% 7% 6% 16% 14% 11%	2200
	11th to 20th	Day	43% 6% 9% 14% 18% 9%	2271
	21st to end	Day	38% 6% 10% 18% 21% 6%	2400
May	1st to 10th	Day	45% 9% 11% 20% 11% 3	5895
	11th to 20th	Day	36% 7% 15% 18% 22% 3	5866
	21st to end	Day	40% 10% 12% 23% 12% 2	6447
June	1st to 10th	Day	31% 10% 15% 27% 15% 2	2600
	11th to 20th	Day	29% 9% 17% 24% 17% 4	2600
	21st to end	Day	36% 10% 16% 24% 12% 1	2600
July	1st to 10th	Day	38% 6% 28% 24% 3	5836
	11th to 20th	Day	31% 8% 23% 26% 10% 1	5831
	21st to end	Day	37% 8% 17% 25% 11% 1	6240
August	1st to 10th	Day	14% 5% 14% 40% 25% 1	4220
	11th to 20th	Day	19% 7% 30% 34% 8% 2	4189
	21st to end	Day	31% 11% 20% 23% 13% 1	4048
September	1st to 10th	Day	34% 9% 12% 21% 16% 8%	2200
	11th to 20th	Day	38% 9% 13% 18% 17% 5%	2200
	21st to end	Day	29% 8% 11% 21% 17% 14%	2200
October	1st to 10th	Day	15% 4 7% 13% 22% 40%	3475
	11th to 20th	Day	20% 3 6% 17% 34% 19%	3220
	21st to end	Day	24% 5% 5% 21% 31% 15%	3428
November	1st to 10th	Day	35% 7% 9% 17% 21% 10%	1958
	11th to 20th	Day	33% 5% 9% 17% 22% 14%	2000
	21st to end	Day	43% 5% 7% 16% 19% 10%	1815
December	1st to 10th	Day	45% 4 7% 16% 21% 7%	2940
	11th to 20th	Day	43% 5% 8% 12% 23% 10%	3389
	21st to end	Day	40% 4 6% 13% 28% 9%	4488
January	1st to 10th	Night	37% 4 6% 22% 22% 9%	5888
	11th to 20th	Night	31% 3 5% 19% 29% 13%	5900
	21st to end	Night	50% 3 4 11% 17% 14%	6490
February	1st to 10th	Night	44% 4 5% 11% 19% 16%	2455
	11th to 20th	Night	43% 4 6% 15% 18% 13%	2338
	21st to end	Night	45% 4 7% 13% 16% 15%	1883
March	1st to 10th	Night	42% 6% 8% 13% 21% 10%	4919
	11th to 20th	Night	39% 5% 7% 14% 14% 22%	4980
	21st to end	Night	44% 5% 7% 16% 19% 9%	5467
April	1st to 10th	Night	36% 7% 10% 17% 17% 13%	2200
	11th to 20th	Night	37% 6% 11% 16% 17% 14%	2075
	21st to end	Night	37% 6% 11% 19% 21% 7%	2000
May	1st to 10th	Night	48% 8% 10% 21% 10% 4	4080
	11th to 20th	Night	37% 7% 13% 19% 20% 4	4054
	21st to end	Night	38% 9% 15% 24% 12% 1	4452
June	1st to 10th	Night	21% 8% 20% 29% 21% 2	1800
	11th to 20th	Night	19% 8% 18% 32% 19% 5%	1800
	21st to end	Night	27% 8% 20% 28% 16% 2	1800
July	1st to 10th	Night	34% 8% 30% 24% 4	4035
	11th to 20th	Night	23% 7% 24% 36% 10%	4026
	21st to end	Night	32% 8% 21% 26% 12% 1	4320
August	1st to 10th	Night	8% 5% 16% 42% 27% 2	2916
	11th to 20th	Night	17% 7% 30% 34% 10% 1	2932
	21st to end	Night	24% 11% 23% 28% 13% 1	3843
September	1st to 10th	Night	27% 10% 18% 22% 15% 8%	2200
	11th to 20th	Night	34% 8% 15% 21% 16% 7%	2200
	21st to end	Night	24% 6% 15% 22% 19% 14%	2200
October	1st to 10th	Night	13% 4 7% 16% 19% 41%	3656
	11th to 20th	Night	15% 3 4 21% 32% 24%	3876
	21st to end	Night	21% 3 5% 21% 32% 18%	4120
November	1st to 10th	Night	31% 6% 10% 20% 21% 12%	2340
	11th to 20th	Night	33% 5% 9% 18% 20% 15%	2400
	21st to end	Night	38% 4 9% 16% 19% 13%	2580
December	1st to 10th	Night	47% 4 5% 17% 21% 7%	4250
	11th to 20th	Night	44% 4 8% 8% 23% 14%	4817
	21st to end	Night	35% 4 5% 15% 30% 11%	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	25% 12% 30% 24% 7% 2	300
	11th to 20th	Day	23% 12% 33% 24% 6% 1	300
	21st to end	Day	23% 13% 38% 17% 8% 1	330
February	1st to 10th	Day	29% 12% 31% 21% 7%	300
	11th to 20th	Day	31% 16% 30% 19% 5%	300
	21st to end	Day	28% 18% 34% 14% 5%	249
March	1st to 10th	Day	22% 16% 36% 18% 8%	300
	11th to 20th	Day	18% 18% 40% 19% 4 2	300
	21st to end	Day	20% 12% 41% 18% 8% 1	330
April	1st to 10th	Day	20% 15% 39% 21% 4 1	300
	11th to 20th	Day	24% 15% 29% 22% 9% 2	389
	21st to end	Day	19% 9% 33% 27% 11% 1	500
May	1st to 10th	Day	16% 8% 35% 30% 9% 1	698
	11th to 20th	Day	13% 8% 28% 32% 15% 4	725
	21st to end	Day	11% 6% 25% 36% 19% 4	789
June	1st to 10th	Day	6% 2 14% 37% 30% 10%	730
	11th to 20th	Day	7% 2 12% 41% 31% 7%	730
	21st to end	Day	6% 2 10% 27% 38% 16%	730
July	1st to 10th	Day	8% 3 7% 28% 38% 16%	721
	11th to 20th	Day	4 1 5% 29% 42% 20%	718
	21st to end	Day	6% 2 5% 23% 46% 19%	794
August	1st to 10th	Day	3 1 3 19% 53% 21%	726
	11th to 20th	Day	6% 1 2 21% 50% 21%	707
	21st to end	Day	8% 3 4 17% 38% 31%	424
September	1st to 10th	Day	5% 1 5% 23% 37% 29%	330
	11th to 20th	Day	8% 5% 23% 38% 27%	330
	21st to end	Day	8% 2 8% 27% 37% 18%	330
October	1st to 10th	Day	4 1 11% 32% 37% 15%	330
	11th to 20th	Day	13% 3 19% 30% 25% 11%	324
	21st to end	Day	23% 8% 21% 20% 22% 6%	330
November	1st to 10th	Day	17% 6% 19% 34% 17% 7%	300
	11th to 20th	Day	16% 8% 24% 32% 17% 4	300
	21st to end	Day	22% 13% 29% 21% 11% 3	300
December	1st to 10th	Day	21% 6% 32% 22% 13% 6%	300
	11th to 20th	Day	25% 12% 31% 22% 7% 2	300
	21st to end	Day	23% 9% 34% 22% 10% 1	330
January	1st to 10th	Night	21% 9% 30% 33% 7%	1000
	11th to 20th	Night	23% 10% 29% 30% 8%	1000
	21st to end	Night	21% 9% 32% 32% 6%	1100
February	1st to 10th	Night	24% 11% 34% 27% 4	855
	11th to 20th	Night	27% 10% 32% 27% 4	784
	21st to end	Night	26% 12% 39% 20% 3	563
March	1st to 10th	Night	21% 10% 40% 25% 4	600
	11th to 20th	Night	19% 10% 37% 27% 7%	600
	21st to end	Night	16% 9% 43% 28% 5%	660
April	1st to 10th	Night	16% 9% 41% 30% 4	600
	11th to 20th	Night	15% 11% 35% 32% 7%	593
	21st to end	Night	18% 9% 37% 28% 8%	600
May	1st to 10th	Night	14% 9% 40% 31% 6% 1	600
	11th to 20th	Night	12% 6% 31% 37% 13% 1	591
	21st to end	Night	10% 3 29% 42% 15% 1	650
June	1st to 10th	Night	6% 2 16% 47% 26% 3	600
	11th to 20th	Night	4 1 23% 48% 22% 2	600
	21st to end	Night	4 2 11% 46% 33% 5%	600
July	1st to 10th	Night	5% 2 6% 44% 37% 6%	585
	11th to 20th	Night	3 1 8% 48% 36% 4	582
	21st to end	Night	4 1 6% 49% 37% 4	657
August	1st to 10th	Night	2 5% 49% 40% 3	597
	11th to 20th	Night	5% 1 3 47% 39% 6%	594
	21st to end	Night	4 1 5% 34% 49% 6%	660
September	1st to 10th	Night	6% 2 8% 37% 41% 7%	600
	11th to 20th	Night	11% 2 5% 34% 43% 6%	600
	21st to end	Night	8% 1 10% 37% 39% 5%	600
October	1st to 10th	Night	5% 1 13% 43% 33% 6%	640
	11th to 20th	Night	12% 3 20% 42% 23% 1	793
	21st to end	Night	14% 6% 26% 32% 19% 3	836
November	1st to 10th	Night	14% 4 23% 38% 19% 2	780
	11th to 20th	Night	12% 8% 26% 40% 13% 1	800
	21st to end	Night	19% 9% 28% 29% 14% 1	980
December	1st to 10th	Night	22% 6% 28% 32% 12% 1	1000
	11th to 20th	Night	24% 9% 27% 32% 7%	1000
	21st to end	Night	21% 7% 30% 33% 9% 1	1100

Page generated at 2025-10-16 00:50:25. Version ac07

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