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 2026-10-14.

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% 39%	148950
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	142797
Transparency	Day	44% 4 11% 22% 15% 3	152498
	Night	44% 4 11% 22% 16% 3	147338
Seeing	Day	24% 19% 32% 17% 6% 2	17616
	Night	23% 15% 32% 23% 7% 1	26487

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% 4 4 5% 3 5% 5% 44%	4661
	11th to 20th	Day	15% 9% 3 6% 4 3 3 3 4 5% 46%	4650
	21st to end	Day	16% 10% 2 4 3 3 3 3 4 6% 46%	5124
February	1st to 10th	Day	17% 8% 3 6% 4 5% 5% 4 5% 6% 38%	2013
	11th to 20th	Day	15% 7% 3 5% 5% 5% 5% 3 5% 6% 41%	2048
	21st to end	Day	20% 10% 3 5% 3 4 3 3 4 6% 39%	1730
March	1st to 10th	Day	22% 11% 2 5% 3 3 3 2 4 5% 39%	4576
	11th to 20th	Day	14% 9% 2 6% 4 4 4 3 5% 7% 42%	4844
	21st to end	Day	22% 10% 2 6% 4 4 4 4 5% 6% 32%	5956
April	1st to 10th	Day	20% 9% 2 5% 3 4 3 3 4 7% 38%	2520
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 7% 40%	2494
	21st to end	Day	21% 7% 2 6% 4 4 5% 3 5% 6% 38%	2707
May	1st to 10th	Day	26% 9% 3 7% 4 4 3 3 5% 7% 29%	7639
	11th to 20th	Day	20% 9% 3 8% 4 3 3 3 4 6% 37%	7718
	21st to end	Day	23% 8% 2 6% 4 4 4 4 6% 7% 31%	9060
June	1st to 10th	Day	18% 6% 2 6% 4 5% 5% 5% 7% 8% 35%	2940
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 9% 36%	2940
	21st to end	Day	16% 7% 2 6% 4 5% 4 4 6% 9% 37%	2940
July	1st to 10th	Day	18% 7% 3 6% 4 4 5% 4 6% 9% 34%	8280
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 7% 10% 40%	8280
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 8% 39%	8993
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 29%	6067
	11th to 20th	Day	12% 5% 3 6% 4 5% 5% 4 6% 9% 42%	5745
	21st to end	Day	11% 4 2 6% 5% 5% 6% 5% 7% 9% 41%	6080
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 3 4 6% 45%	2520
	11th to 20th	Day	14% 5% 2 5% 2 3 4 3 5% 6% 50%	2318
	21st to end	Day	21% 6% 3 5% 3 4 5% 4 4 5% 40%	2310
October	1st to 10th	Day	21% 7% 2 5% 3 2 4 2 4 5% 45%	2310
	11th to 20th	Day	17% 6% 2 5% 3 4 4 3 4 7% 46%	2003
	21st to end	Day	18% 6% 2 7% 4 3 3 2 5% 4 44%	1980
November	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 4 5% 48%	1851
	11th to 20th	Day	16% 6% 2 6% 2 3 3 3 5% 6% 48%	1890
	21st to end	Day	18% 7% 2 6% 4 3 3 3 4 5% 44%	1890
December	1st to 10th	Day	14% 8% 2 6% 4 3 3 3 5% 6% 46%	2759
	11th to 20th	Day	19% 7% 2 5% 3 2 3 2 3 5% 48%	3066
	21st to end	Day	19% 11% 3 7% 4 3 3 2 3 4 40%	4048
January	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 4 6% 49%	8234
	11th to 20th	Night	16% 9% 3 7% 4 3 4 3 4 5% 42%	8235
	21st to end	Night	15% 9% 3 6% 4 5% 5% 3 5% 5% 40%	9057
February	1st to 10th	Night	15% 9% 3 6% 4 4 3 3 4 6% 41%	2600
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 4 6% 40%	2458
	21st to end	Night	18% 11% 3 6% 5% 4 3 4 4 5% 39%	2076
March	1st to 10th	Night	22% 10% 2 4 4 3 3 3 4 6% 39%	5484
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 4 6% 40%	5334
	21st to end	Night	22% 10% 3 6% 4 4 4 4 5% 5% 34%	5215
April	1st to 10th	Night	19% 10% 2 5% 5% 3 4 4 5% 6% 37%	2100
	11th to 20th	Night	18% 9% 2 6% 3 4 4 3 5% 6% 39%	2075
	21st to end	Night	21% 7% 3 6% 4 3 3 3 4 6% 40%	1911
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 4 6% 31%	5259
	11th to 20th	Night	18% 10% 3 8% 4 4 4 3 6% 7% 33%	5184
	21st to end	Night	22% 9% 3 7% 5% 5% 4 4 5% 6% 29%	5114
June	1st to 10th	Night	17% 7% 2 6% 3 5% 4 3 6% 8% 39%	1680
	11th to 20th	Night	19% 8% 2 6% 3 4 4 4 6% 8% 38%	1680
	21st to end	Night	15% 7% 2 6% 4 3 3 3 7% 8% 41%	1680
July	1st to 10th	Night	21% 8% 3 6% 5% 4 5% 4 6% 8% 32%	4680
	11th to 20th	Night	16% 9% 3 6% 4 3 4 4 5% 7% 39%	4680
	21st to end	Night	17% 7% 2 5% 4 4 4 3 5% 7% 41%	5084
August	1st to 10th	Night	20% 7% 3 7% 5% 4 6% 5% 7% 8% 30%	4035
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 7% 8% 37%	4296
	21st to end	Night	12% 6% 2 5% 3 4 4 3 6% 7% 49%	5045
September	1st to 10th	Night	14% 7% 3 7% 4 4 5% 3 6% 6% 41%	2100
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 4 6% 51%	2301
	21st to end	Night	22% 8% 3 7% 3 4 4 3 4 4 38%	2310
October	1st to 10th	Night	18% 7% 2 6% 4 3 3 3 4 5% 44%	2310
	11th to 20th	Night	16% 6% 2 5% 3 4 3 3 5% 6% 47%	2459
	21st to end	Night	20% 7% 2 6% 3 3 3 2 5% 6% 41%	2860
November	1st to 10th	Night	13% 6% 2 6% 3 4 4 3 4 6% 48%	2667
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 5% 47%	2730
	21st to end	Night	16% 7% 2 5% 4 4 3 2 5% 7% 46%	2730
December	1st to 10th	Night	16% 8% 2 7% 3 3 3 2 3 4 49%	4636
	11th to 20th	Night	23% 8% 2 5% 3 3 3 3 4 4 41%	5348
	21st to end	Night	17% 11% 3 7% 4 3 3 2 4 5% 43%	7150

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	41% 3 10% 25% 19% 3	4662
	11th to 20th	Day	42% 3 8% 21% 17% 9%	4680
	21st to end	Day	41% 2 10% 24% 21% 2	5124
February	1st to 10th	Day	46% 4 13% 19% 15% 3	2013
	11th to 20th	Day	44% 4 9% 24% 16% 4	2057
	21st to end	Day	48% 3 9% 20% 15% 3	1730
March	1st to 10th	Day	49% 2 10% 16% 13% 11%	4579
	11th to 20th	Day	42% 4 10% 31% 12% 2	4844
	21st to end	Day	52% 4 6% 15% 16% 6%	5956
April	1st to 10th	Day	47% 4 10% 19% 18% 3	2520
	11th to 20th	Day	45% 4 10% 20% 19% 3	2494
	21st to end	Day	46% 4 8% 21% 16% 4	2707
May	1st to 10th	Day	56% 4 13% 15% 11% 1	7651
	11th to 20th	Day	50% 3 13% 21% 12% 1	7722
	21st to end	Day	51% 5% 12% 19% 12% 1	9061
June	1st to 10th	Day	45% 6% 12% 23% 14% 1	2940
	11th to 20th	Day	44% 5% 14% 22% 13% 2	2940
	21st to end	Day	42% 7% 14% 22% 14% 1	2940
July	1st to 10th	Day	46% 6% 14% 21% 12% 1	8210
	11th to 20th	Day	37% 5% 17% 28% 12% 1	8205
	21st to end	Day	43% 5% 10% 23% 18% 1	8795
August	1st to 10th	Day	48% 7% 17% 19% 9%	6053
	11th to 20th	Day	38% 6% 15% 32% 8%	5784
	21st to end	Day	38% 6% 13% 25% 16% 2	6080
September	1st to 10th	Day	40% 6% 10% 23% 19% 2	2520
	11th to 20th	Day	34% 4 10% 24% 24% 4	2318
	21st to end	Day	47% 4 7% 19% 21% 2	2310
October	1st to 10th	Day	38% 3 9% 22% 22% 5%	3700
	11th to 20th	Day	31% 3 7% 25% 30% 4	3219
	21st to end	Day	32% 3 13% 28% 20% 3	3180
November	1st to 10th	Day	40% 4 13% 20% 22% 2	1851
	11th to 20th	Day	38% 4 9% 22% 22% 4	1890
	21st to end	Day	43% 4 10% 28% 13% 3	1890
December	1st to 10th	Day	40% 3 13% 28% 16% 1	2759
	11th to 20th	Day	41% 2 12% 19% 20% 6%	3066
	21st to end	Day	50% 2 7% 22% 14% 5%	4048
January	1st to 10th	Night	39% 2 10% 29% 18% 2	8234
	11th to 20th	Night	46% 3 10% 20% 16% 6%	8280
	21st to end	Night	46% 2 8% 20% 19% 4	9057
February	1st to 10th	Night	45% 4 11% 23% 14% 2	2600
	11th to 20th	Night	45% 4 8% 22% 17% 5%	2460
	21st to end	Night	47% 4 7% 23% 15% 4	2076
March	1st to 10th	Night	48% 2 9% 18% 15% 7%	5494
	11th to 20th	Night	46% 3 15% 21% 12% 3	5335
	21st to end	Night	52% 3 5% 12% 22% 6%	5215
April	1st to 10th	Night	47% 4 9% 20% 16% 4	2100
	11th to 20th	Night	46% 4 9% 19% 19% 2	2075
	21st to end	Night	46% 4 9% 21% 16% 4	1911
May	1st to 10th	Night	55% 4 14% 15% 11% 1	5265
	11th to 20th	Night	50% 5% 14% 20% 9% 2	5185
	21st to end	Night	54% 6% 11% 20% 9%	5115
June	1st to 10th	Night	44% 6% 11% 23% 15% 1	1680
	11th to 20th	Night	45% 4 13% 25% 12% 1	1680
	21st to end	Night	41% 5% 14% 26% 13% 1	1680
July	1st to 10th	Night	50% 5% 12% 20% 11% 1	4640
	11th to 20th	Night	44% 5% 13% 25% 12% 1	4632
	21st to end	Night	43% 5% 12% 23% 17% 1	4967
August	1st to 10th	Night	50% 8% 16% 15% 11% 1	4025
	11th to 20th	Night	42% 7% 17% 28% 6%	4323
	21st to end	Night	34% 5% 15% 29% 16% 1	5045
September	1st to 10th	Night	43% 4 9% 24% 17% 2	2100
	11th to 20th	Night	35% 4 11% 23% 25% 3	2301
	21st to end	Night	50% 4 7% 17% 19% 3	2310
October	1st to 10th	Night	39% 4 11% 25% 19% 3	3700
	11th to 20th	Night	27% 3 8% 25% 32% 4	3982
	21st to end	Night	34% 3 11% 28% 21% 3	4610
November	1st to 10th	Night	37% 5% 12% 23% 21% 4	2667
	11th to 20th	Night	41% 3 8% 23% 21% 5%	2730
	21st to end	Night	40% 3 13% 28% 14% 2	2730
December	1st to 10th	Night	42% 2 11% 29% 16% 1	4636
	11th to 20th	Night	47% 3 11% 16% 20% 2	5348
	21st to end	Night	47% 3 7% 21% 19% 4	7150

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	29% 28% 29% 13% 1	220
	11th to 20th	Day	34% 27% 30% 5% 4	220
	21st to end	Day	31% 28% 31% 7% 3	242
February	1st to 10th	Day	29% 25% 33% 12% 1	468
	11th to 20th	Day	31% 29% 30% 8% 1	536
	21st to end	Day	30% 25% 32% 10% 3	446
March	1st to 10th	Day	31% 23% 30% 14% 2	540
	11th to 20th	Day	29% 26% 30% 12% 2 1	540
	21st to end	Day	34% 23% 29% 10% 3 1	594
April	1st to 10th	Day	36% 24% 24% 10% 5% 1	540
	11th to 20th	Day	31% 25% 30% 11% 3	532
	21st to end	Day	31% 20% 32% 12% 3 1	540
May	1st to 10th	Day	33% 24% 29% 10% 2	543
	11th to 20th	Day	25% 17% 42% 12% 3 1	567
	21st to end	Day	23% 16% 33% 23% 5% 1	617
June	1st to 10th	Day	20% 16% 36% 21% 6% 1	570
	11th to 20th	Day	19% 20% 36% 19% 5% 1	570
	21st to end	Day	20% 14% 36% 22% 6% 1	570
July	1st to 10th	Day	19% 10% 34% 26% 10% 1	565
	11th to 20th	Day	15% 12% 35% 26% 11% 2	564
	21st to end	Day	15% 13% 40% 24% 8% 1	620
August	1st to 10th	Day	14% 10% 37% 26% 11% 2	566
	11th to 20th	Day	15% 11% 34% 27% 9% 4	559
	21st to end	Day	12% 12% 37% 23% 11% 5%	627
September	1st to 10th	Day	19% 12% 30% 23% 12% 3	570
	11th to 20th	Day	17% 12% 32% 22% 11% 7%	570
	21st to end	Day	26% 13% 34% 17% 8% 3	570
October	1st to 10th	Day	28% 13% 27% 20% 9% 4	570
	11th to 20th	Day	22% 18% 30% 18% 9% 2	498
	21st to end	Day	26% 16% 30% 19% 7% 1	462
November	1st to 10th	Day	21% 17% 33% 20% 8% 2	425
	11th to 20th	Day	25% 26% 28% 16% 5%	430
	21st to end	Day	27% 22% 30% 16% 6% 1	430
December	1st to 10th	Day	24% 26% 33% 13% 4	273
	11th to 20th	Day	36% 26% 27% 7% 4	220
	21st to end	Day	29% 24% 30% 11% 4 2	242
January	1st to 10th	Night	23% 21% 35% 18% 3	840
	11th to 20th	Night	31% 19% 33% 15% 3	840
	21st to end	Night	21% 25% 33% 19% 2	924
February	1st to 10th	Night	23% 20% 35% 20% 2	840
	11th to 20th	Night	28% 21% 37% 13% 2	823
	21st to end	Night	27% 22% 32% 16% 3	692
March	1st to 10th	Night	26% 19% 34% 17% 3	840
	11th to 20th	Night	24% 20% 34% 19% 3	840
	21st to end	Night	27% 21% 32% 16% 3 1	924
April	1st to 10th	Night	27% 21% 31% 18% 3	840
	11th to 20th	Night	23% 18% 37% 18% 3	831
	21st to end	Night	24% 18% 34% 19% 4	651
May	1st to 10th	Night	28% 14% 31% 21% 5%	630
	11th to 20th	Night	23% 16% 39% 20% 3	610
	21st to end	Night	22% 8% 33% 29% 7% 1	455
June	1st to 10th	Night	19% 8% 28% 36% 9%	420
	11th to 20th	Night	23% 10% 28% 32% 7%	420
	21st to end	Night	19% 5% 31% 37% 7%	420
July	1st to 10th	Night	18% 6% 28% 35% 13% 1	410
	11th to 20th	Night	19% 3 24% 39% 14% 1	408
	21st to end	Night	16% 4 27% 43% 10%	460
August	1st to 10th	Night	14% 6% 32% 37% 10%	579
	11th to 20th	Night	15% 5% 27% 38% 14% 1	709
	21st to end	Night	15% 6% 26% 37% 15% 3	924
September	1st to 10th	Night	17% 6% 31% 30% 15% 2	840
	11th to 20th	Night	15% 7% 28% 32% 15% 3	840
	21st to end	Night	25% 9% 27% 26% 11% 2	840
October	1st to 10th	Night	23% 10% 28% 25% 12% 2	840
	11th to 20th	Night	19% 13% 33% 23% 10% 1	813
	21st to end	Night	25% 15% 32% 21% 8%	880
November	1st to 10th	Night	18% 15% 33% 23% 11% 1	820
	11th to 20th	Night	24% 18% 34% 18% 6% 1	840
	21st to end	Night	23% 18% 31% 21% 6%	840
December	1st to 10th	Night	26% 19% 32% 19% 4	840
	11th to 20th	Night	27% 18% 33% 18% 3	840
	21st to end	Night	26% 18% 35% 17% 3	924

Page generated at 2026-10-11 05:06:33. Version ac07

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