W. Alton Jones Campus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the W. Alton Jones Campus Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	18% 8% 2 6% 4 4 4 3 5% 7% 38%	119126
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	119107
Transparency	Day	45% 4 11% 21% 15% 3	122717
	Night	44% 4 11% 22% 16% 3	123677
Seeing	Day	24% 18% 32% 17% 6% 2	15822
	Night	22% 15% 32% 23% 7% 1	24838

By Month

Percentage Cloud Cover NE (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	11% 9% 3 7% 3 4 5% 3 5% 5% 47%	3597
	11th to 20th	Day	15% 8% 2 5% 4 3 3 4 4 5% 47%	3570
	21st to end	Day	18% 10% 2 6% 4 3 3 3 4 4 43%	3960
February	1st to 10th	Day	18% 8% 3 6% 4 5% 5% 4 5% 6% 37%	1916
	11th to 20th	Day	15% 7% 3 5% 5% 5% 5% 3 5% 6% 41%	1948
	21st to end	Day	20% 10% 3 5% 3 4 3 3 4 6% 38%	1650
March	1st to 10th	Day	22% 11% 2 5% 3 3 3 2 4 5% 39%	4476
	11th to 20th	Day	14% 9% 2 5% 4 4 4 3 5% 7% 42%	4740
	21st to end	Day	23% 10% 2 6% 4 4 4 4 5% 6% 32%	5827
April	1st to 10th	Day	21% 9% 2 6% 3 4 3 4 5% 6% 37%	2400
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 7% 40%	2374
	21st to end	Day	21% 7% 2 5% 4 4 5% 3 5% 7% 37%	2578
May	1st to 10th	Day	29% 10% 3 6% 4 4 3 3 5% 8% 25%	5886
	11th to 20th	Day	21% 9% 3 8% 5% 4 4 3 4 6% 33%	5940
	21st to end	Day	20% 7% 2 6% 4 4 4 4 6% 7% 35%	6949
June	1st to 10th	Day	19% 6% 2 6% 4 4 5% 5% 7% 8% 34%	2786
	11th to 20th	Day	16% 8% 2 6% 5% 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	15% 7% 2 6% 4 5% 4 4 5% 9% 37%	2660
July	1st to 10th	Day	15% 6% 3 6% 5% 5% 6% 4 6% 9% 34%	4440
	11th to 20th	Day	16% 5% 2 6% 5% 4 5% 4 7% 10% 37%	4440
	21st to end	Day	21% 7% 3 7% 4 4 5% 5% 6% 8% 30%	4814
August	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	4142
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 9% 38%	3898
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 7% 9% 44%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 3 6% 45%	2280
	11th to 20th	Day	14% 6% 2 5% 2 3 3 3 5% 6% 51%	2098
	21st to end	Day	20% 6% 3 5% 3 4 4 4 4 5% 42%	2090
October	1st to 10th	Day	22% 8% 2 6% 3 2 4 2 4 5% 42%	2090
	11th to 20th	Day	16% 5% 2 5% 3 4 3 3 4 7% 47%	1872
	21st to end	Day	18% 6% 3 7% 4 3 3 2 5% 4 44%	1881
November	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 4 5% 48%	1761
	11th to 20th	Day	16% 6% 2 5% 2 3 3 3 5% 5% 48%	1800
	21st to end	Day	18% 6% 2 6% 4 3 3 3 4 5% 45%	1800
December	1st to 10th	Day	14% 8% 2 6% 4 3 3 2 5% 6% 46%	2677
	11th to 20th	Day	19% 7% 2 5% 3 2 3 2 3 5% 48%	2986
	21st to end	Day	19% 11% 3 7% 4 3 3 2 3 4 40%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 7% 50%	6349
	11th to 20th	Night	15% 9% 3 8% 4 3 3 3 3 4 44%	6315
	21st to end	Night	17% 9% 3 7% 4 5% 4 3 5% 5% 37%	6996
February	1st to 10th	Night	16% 9% 4 7% 4 4 3 3 4 6% 41%	2477
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 4 6% 40%	2338
	21st to end	Night	18% 10% 3 6% 5% 4 3 4 4 5% 40%	1980
March	1st to 10th	Night	22% 10% 2 4 4 3 3 3 4 6% 39%	5364
	11th to 20th	Night	16% 10% 3 6% 4 4 4 3 4 6% 40%	5219
	21st to end	Night	22% 10% 3 5% 4 4 4 4 5% 5% 34%	5102
April	1st to 10th	Night	19% 10% 2 6% 5% 4 4 3 5% 6% 37%	2000
	11th to 20th	Night	19% 9% 2 6% 3 4 4 3 5% 6% 38%	1975
	21st to end	Night	21% 7% 3 6% 4 3 3 3 4 6% 40%	1820
May	1st to 10th	Night	28% 9% 3 8% 4 4 4 3 4 7% 26%	4054
	11th to 20th	Night	20% 10% 3 8% 5% 5% 4 3 6% 7% 28%	3996
	21st to end	Night	21% 9% 3 6% 5% 4 4 4 6% 6% 31%	3926
June	1st to 10th	Night	17% 8% 2 5% 3 5% 4 3 6% 8% 37%	1598
	11th to 20th	Night	19% 7% 2 6% 3 3 4 3 5% 7% 39%	1520
	21st to end	Night	16% 8% 2 6% 4 3 3 3 7% 8% 40%	1520
July	1st to 10th	Night	17% 7% 3 7% 6% 4 6% 4 6% 7% 31%	2520
	11th to 20th	Night	18% 7% 2 5% 4 3 4 4 6% 9% 37%	2520
	21st to end	Night	21% 9% 3 6% 5% 4 5% 4 5% 8% 31%	2739
August	1st to 10th	Night	24% 8% 2 6% 5% 4 5% 4 7% 7% 27%	2755
	11th to 20th	Night	9% 8% 3 8% 5% 5% 6% 5% 7% 8% 35%	2926
	21st to end	Night	8% 4 2 5% 3 3 4 3 5% 8% 55%	3476
September	1st to 10th	Night	14% 7% 3 7% 4 4 5% 3 5% 6% 42%	1900
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 4 6% 51%	2081
	21st to end	Night	20% 7% 3 7% 3 4 4 3 4 4 39%	2090
October	1st to 10th	Night	19% 7% 3 6% 5% 3 3 3 4 6% 41%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 5% 6% 48%	2304
	21st to end	Night	20% 7% 2 6% 3 3 3 2 5% 6% 41%	2717
November	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 4 6% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 4 3 3 2 4 5% 46%	2600
	21st to end	Night	16% 7% 2 5% 4 4 4 2 5% 7% 46%	2600
December	1st to 10th	Night	16% 8% 2 7% 3 3 3 2 3 4 49%	4499
	11th to 20th	Night	24% 8% 2 5% 3 3 3 3 4 4 41%	5208
	21st to end	Night	17% 11% 3 7% 4 3 3 2 4 5% 43%	6996

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	39% 2 7% 27% 21% 4	3598
	11th to 20th	Day	41% 4 9% 21% 17% 8%	3600
	21st to end	Day	47% 3 8% 22% 19% 2	3960
February	1st to 10th	Day	46% 4 13% 20% 14% 3	1916
	11th to 20th	Day	44% 4 9% 23% 16% 4	1957
	21st to end	Day	48% 3 10% 20% 15% 3	1650
March	1st to 10th	Day	48% 2 10% 16% 13% 11%	4479
	11th to 20th	Day	41% 4 10% 31% 12% 2	4740
	21st to end	Day	52% 4 6% 15% 17% 6%	5827
April	1st to 10th	Day	47% 4 9% 19% 17% 3	2400
	11th to 20th	Day	45% 4 9% 21% 19% 3	2374
	21st to end	Day	46% 4 9% 21% 16% 4	2578
May	1st to 10th	Day	59% 5% 14% 14% 8% 1	5897
	11th to 20th	Day	53% 4 13% 18% 11% 2	5944
	21st to end	Day	47% 5% 11% 21% 14% 1	6949
June	1st to 10th	Day	46% 6% 12% 23% 12% 1	2786
	11th to 20th	Day	44% 5% 14% 21% 14% 2	2660
	21st to end	Day	42% 7% 14% 23% 14% 1	2660
July	1st to 10th	Day	46% 6% 13% 20% 14% 1	4370
	11th to 20th	Day	42% 6% 16% 23% 11% 2	4365
	21st to end	Day	51% 6% 12% 18% 12% 2	4661
August	1st to 10th	Day	51% 6% 15% 20% 8%	4128
	11th to 20th	Day	41% 6% 14% 28% 10% 1	3937
	21st to end	Day	34% 6% 13% 26% 18% 2	4180
September	1st to 10th	Day	40% 6% 10% 22% 20% 2	2280
	11th to 20th	Day	35% 4 10% 24% 24% 3	2098
	21st to end	Day	45% 4 7% 20% 22% 2	2090
October	1st to 10th	Day	39% 4 9% 22% 21% 5%	3480
	11th to 20th	Day	30% 3 7% 25% 31% 4	3088
	21st to end	Day	32% 4 13% 28% 20% 3	3081
November	1st to 10th	Day	40% 4 13% 20% 21% 2	1761
	11th to 20th	Day	38% 4 9% 21% 23% 4	1800
	21st to end	Day	42% 4 10% 28% 13% 3	1800
December	1st to 10th	Day	40% 3 13% 28% 16% 1	2677
	11th to 20th	Day	41% 2 12% 19% 20% 6%	2986
	21st to end	Day	50% 2 7% 22% 14% 5%	3960
January	1st to 10th	Night	35% 3 9% 31% 19% 3	6349
	11th to 20th	Night	44% 3 11% 21% 15% 6%	6360
	21st to end	Night	49% 2 10% 18% 16% 4	6996
February	1st to 10th	Night	46% 4 11% 23% 13% 2	2477
	11th to 20th	Night	45% 4 9% 20% 18% 5%	2340
	21st to end	Night	47% 4 7% 23% 16% 4	1980
March	1st to 10th	Night	48% 3 10% 18% 15% 7%	5374
	11th to 20th	Night	46% 3 15% 21% 12% 3	5220
	21st to end	Night	52% 3 5% 12% 22% 6%	5102
April	1st to 10th	Night	47% 4 9% 20% 16% 4	2000
	11th to 20th	Night	46% 4 9% 19% 19% 2	1975
	21st to end	Night	46% 4 9% 21% 15% 5%	1820
May	1st to 10th	Night	59% 4 14% 13% 9% 1	4060
	11th to 20th	Night	54% 6% 13% 16% 8% 3	3997
	21st to end	Night	52% 7% 12% 19% 10% 1	3927
June	1st to 10th	Night	45% 6% 12% 22% 14% 1	1598
	11th to 20th	Night	44% 4 13% 25% 12% 1	1520
	21st to end	Night	41% 6% 15% 25% 13% 1	1520
July	1st to 10th	Night	49% 7% 11% 19% 11% 1	2480
	11th to 20th	Night	44% 6% 16% 24% 9% 1	2472
	21st to end	Night	52% 6% 13% 15% 13% 2	2651
August	1st to 10th	Night	54% 8% 13% 17% 8% 1	2745
	11th to 20th	Night	43% 7% 15% 27% 8%	2953
	21st to end	Night	27% 6% 16% 30% 21% 1	3476
September	1st to 10th	Night	43% 4 10% 23% 18% 2	1900
	11th to 20th	Night	35% 4 11% 23% 25% 3	2081
	21st to end	Night	48% 4 7% 18% 20% 3	2090
October	1st to 10th	Night	40% 4 11% 25% 18% 3	3480
	11th to 20th	Night	26% 3 8% 26% 33% 4	3827
	21st to end	Night	33% 3 12% 28% 21% 3	4467
November	1st to 10th	Night	37% 5% 12% 22% 21% 4	2537
	11th to 20th	Night	41% 3 8% 22% 20% 5%	2600
	21st to end	Night	40% 3 14% 28% 14% 2	2600
December	1st to 10th	Night	42% 2 11% 29% 16% 1	4499
	11th to 20th	Night	47% 3 12% 16% 20% 2	5208
	21st to end	Night	47% 3 7% 21% 18% 4	6996

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	30% 28% 28% 14% 2	200
	11th to 20th	Day	32% 27% 32% 5% 5%	200
	21st to end	Day	27% 29% 33% 7% 3	220
February	1st to 10th	Day	32% 25% 31% 12% 1	431
	11th to 20th	Day	32% 30% 29% 8% 1	496
	21st to end	Day	30% 24% 32% 10% 3	414
March	1st to 10th	Day	31% 23% 30% 14% 2	500
	11th to 20th	Day	28% 27% 30% 12% 2 1	500
	21st to end	Day	33% 22% 31% 11% 3 1	550
April	1st to 10th	Day	36% 24% 24% 10% 5%	500
	11th to 20th	Day	31% 24% 30% 11% 2	492
	21st to end	Day	31% 20% 31% 13% 3 2	500
May	1st to 10th	Day	34% 23% 29% 11% 3	503
	11th to 20th	Day	25% 17% 42% 12% 3 1	527
	21st to end	Day	22% 14% 34% 24% 5% 1	573
June	1st to 10th	Day	21% 16% 36% 20% 6% 1	526
	11th to 20th	Day	17% 20% 37% 20% 6% 1	490
	21st to end	Day	20% 14% 37% 22% 6% 2	490
July	1st to 10th	Day	19% 9% 33% 27% 11% 1	485
	11th to 20th	Day	16% 10% 34% 28% 11% 2	484
	21st to end	Day	14% 13% 39% 24% 8% 1	532
August	1st to 10th	Day	15% 11% 37% 25% 10% 3	486
	11th to 20th	Day	16% 10% 33% 26% 10% 4	479
	21st to end	Day	11% 11% 36% 24% 12% 6%	539
September	1st to 10th	Day	20% 12% 27% 24% 14% 3	490
	11th to 20th	Day	17% 12% 30% 21% 12% 8%	490
	21st to end	Day	23% 12% 35% 17% 8% 3	490
October	1st to 10th	Day	29% 11% 26% 20% 9% 4	490
	11th to 20th	Day	20% 18% 30% 19% 10% 2	450
	21st to end	Day	25% 16% 30% 20% 7% 1	429
November	1st to 10th	Day	20% 17% 33% 20% 8% 2	395
	11th to 20th	Day	26% 24% 30% 16% 5%	400
	21st to end	Day	25% 21% 31% 16% 6% 1	400
December	1st to 10th	Day	23% 27% 33% 14% 4	251
	11th to 20th	Day	35% 27% 27% 8% 4	200
	21st to end	Day	26% 25% 31% 12% 4 2	220
January	1st to 10th	Night	23% 22% 34% 18% 3	800
	11th to 20th	Night	30% 19% 33% 16% 3	800
	21st to end	Night	21% 25% 33% 19% 2	880
February	1st to 10th	Night	24% 20% 35% 21% 2	800
	11th to 20th	Night	28% 22% 37% 11% 2	783
	21st to end	Night	27% 22% 32% 17% 3	660
March	1st to 10th	Night	26% 20% 34% 17% 3	800
	11th to 20th	Night	23% 21% 34% 19% 3	800
	21st to end	Night	27% 21% 33% 16% 3 1	880
April	1st to 10th	Night	26% 21% 32% 19% 3	800
	11th to 20th	Night	24% 18% 36% 19% 4	791
	21st to end	Night	25% 18% 34% 19% 4	620
May	1st to 10th	Night	28% 13% 31% 22% 5% 1	600
	11th to 20th	Night	23% 16% 39% 19% 3	581
	21st to end	Night	21% 8% 33% 29% 7% 1	433
June	1st to 10th	Night	19% 9% 29% 35% 9%	400
	11th to 20th	Night	22% 9% 27% 34% 7%	380
	21st to end	Night	20% 5% 31% 36% 7%	380
July	1st to 10th	Night	16% 5% 29% 35% 14% 1	370
	11th to 20th	Night	19% 2 24% 40% 13% 1	368
	21st to end	Night	16% 4 26% 43% 10%	416
August	1st to 10th	Night	14% 6% 33% 37% 10%	523
	11th to 20th	Night	15% 5% 27% 37% 15% 1	641
	21st to end	Night	14% 5% 25% 38% 16% 3	836
September	1st to 10th	Night	18% 5% 31% 29% 15% 2	760
	11th to 20th	Night	16% 7% 27% 31% 15% 4	760
	21st to end	Night	23% 9% 29% 27% 11% 2	760
October	1st to 10th	Night	24% 10% 27% 24% 12% 2	760
	11th to 20th	Night	18% 13% 33% 24% 10% 2	760
	21st to end	Night	25% 14% 32% 21% 8%	836
November	1st to 10th	Night	16% 15% 33% 23% 11% 1	780
	11th to 20th	Night	24% 17% 35% 18% 6% 1	800
	21st to end	Night	23% 18% 32% 20% 6% 1	800
December	1st to 10th	Night	26% 19% 31% 19% 4 1	800
	11th to 20th	Night	26% 18% 33% 18% 3	800
	21st to end	Night	25% 18% 36% 18% 4	880

Page generated at 2025-06-07 10:28:13. Version ac07

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