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 2024-11-02.

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%	101148
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	97840
Transparency	Day	45% 5% 11% 22% 15% 2	100906
	Night	46% 4 11% 22% 14% 2	97702
Seeing	Day	24% 18% 32% 18% 7% 2	15097
	Night	22% 15% 32% 23% 7% 1	24030

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	15% 8% 2 6% 3 4 5% 3 4 4 45%	2517
	11th to 20th	Day	18% 8% 2 6% 5% 4 4 4 4 5% 39%	2520
	21st to end	Day	23% 13% 3 6% 4 3 3 3 4 4 35%	2772
February	1st to 10th	Day	19% 8% 3 6% 4 4 5% 4 5% 7% 37%	1819
	11th to 20th	Day	14% 7% 3 5% 5% 5% 5% 3 5% 6% 42%	1848
	21st to end	Day	21% 10% 3 6% 3 4 3 2 4 6% 37%	1570
March	1st to 10th	Day	25% 13% 2 7% 3 3 3 2 4 5% 33%	3116
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 6% 8% 45%	3310
	21st to end	Day	21% 10% 3 6% 4 3 4 4 5% 5% 35%	4065
April	1st to 10th	Day	20% 9% 2 6% 4 4 3 4 4 6% 38%	2280
	11th to 20th	Day	19% 7% 2 5% 4 4 3 3 5% 7% 41%	2254
	21st to end	Day	22% 7% 2 5% 4 4 5% 3 5% 6% 37%	2449
May	1st to 10th	Day	27% 10% 3 7% 4 3 3 3 5% 7% 28%	4106
	11th to 20th	Day	23% 9% 3 8% 5% 4 3 3 4 7% 32%	4132
	21st to end	Day	16% 5% 1 5% 3 4 4 4 6% 8% 44%	4837
June	1st to 10th	Day	19% 6% 2 6% 4 4 4 5% 7% 8% 34%	2660
	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	16% 6% 2 5% 4 4 4 3 4 5% 47%	1681
	11th to 20th	Day	17% 6% 2 5% 2 3 3 3 5% 6% 47%	1710
	21st to end	Day	17% 7% 2 6% 4 4 3 3 4 5% 45%	1710
December	1st to 10th	Day	20% 7% 2 6% 5% 4 3 3 5% 7% 37%	1569
	11th to 20th	Day	21% 7% 2 4 4 2 3 2 4 5% 46%	1906
	21st to end	Day	20% 11% 3 8% 4 4 3 2 4 4 37%	2772
January	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 6% 48%	4429
	11th to 20th	Night	17% 10% 3 8% 4 3 3 3 3 4 41%	4440
	21st to end	Night	22% 12% 4 8% 4 4 3 3 4 5% 31%	4884
February	1st to 10th	Night	16% 9% 4 6% 4 3 3 3 4 6% 41%	2354
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 3 4 6% 41%	2218
	21st to end	Night	18% 10% 3 5% 4 4 3 3 4 5% 40%	1884
March	1st to 10th	Night	27% 12% 2 4 4 3 3 2 4 6% 34%	3724
	11th to 20th	Night	11% 7% 3 6% 4 4 5% 3 5% 7% 43%	3649
	21st to end	Night	24% 9% 2 5% 4 3 4 4 5% 5% 35%	3564
April	1st to 10th	Night	18% 10% 2 6% 5% 4 4 3 5% 6% 37%	1900
	11th to 20th	Night	19% 8% 2 7% 4 4 4 3 5% 6% 39%	1875
	21st to end	Night	21% 7% 3 6% 4 3 3 3 4 6% 40%	1729
May	1st to 10th	Night	25% 9% 4 9% 5% 4 4 3 4 7% 27%	2834
	11th to 20th	Night	23% 10% 3 8% 5% 5% 4 3 6% 7% 25%	2790
	21st to end	Night	17% 7% 2 5% 4 4 5% 4 6% 7% 38%	2738
June	1st to 10th	Night	18% 8% 2 6% 3 4 4 3 6% 8% 38%	1520
	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	14% 6% 2 6% 4 4 3 3 4 6% 48%	2431
	11th to 20th	Night	18% 8% 3 5% 4 3 3 3 4 5% 45%	2470
	21st to end	Night	16% 7% 2 5% 4 4 4 2 5% 7% 46%	2470
December	1st to 10th	Night	20% 8% 3 6% 3 4 4 3 4 5% 40%	2607
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 4 6% 42%	3288
	21st to end	Night	20% 12% 3 7% 4 3 3 2 4 5% 38%	4884

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 8% 29% 15% 2	2518
	11th to 20th	Day	48% 5% 9% 25% 12% 2	2520
	21st to end	Day	54% 3 7% 22% 13% 2	2772
February	1st to 10th	Day	46% 4 13% 20% 14% 3	1819
	11th to 20th	Day	44% 4 9% 24% 16% 4	1857
	21st to end	Day	49% 3 10% 20% 14% 3	1570
March	1st to 10th	Day	56% 3 10% 17% 12% 3	3119
	11th to 20th	Day	35% 4 10% 34% 15% 2	3310
	21st to end	Day	51% 4 5% 18% 17% 6%	4065
April	1st to 10th	Day	47% 5% 9% 20% 17% 3	2280
	11th to 20th	Day	44% 4 9% 21% 19% 3	2254
	21st to end	Day	47% 4 9% 21% 15% 4	2449
May	1st to 10th	Day	57% 4 13% 15% 10% 2	4120
	11th to 20th	Day	54% 3 13% 17% 10% 2	4136
	21st to end	Day	38% 5% 12% 24% 19% 2	4837
June	1st to 10th	Day	46% 6% 12% 23% 12% 1	2660
	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	45% 3 10% 21% 17% 4	2090
	11th to 20th	Day	37% 4 10% 28% 19% 2	1872
	21st to end	Day	43% 4 11% 22% 16% 4	1881
November	1st to 10th	Day	41% 4 12% 20% 20% 2	1681
	11th to 20th	Day	40% 5% 10% 21% 21% 3	1710
	21st to end	Day	42% 4 10% 28% 13% 3	1710
December	1st to 10th	Day	47% 4 12% 18% 17% 2	1569
	11th to 20th	Day	44% 3 12% 19% 18% 5%	1906
	21st to end	Day	52% 3 9% 24% 11% 1	2772
January	1st to 10th	Night	39% 3 10% 32% 12% 4	4429
	11th to 20th	Night	47% 4 11% 23% 12% 3	4440
	21st to end	Night	57% 3 8% 18% 12% 2	4884
February	1st to 10th	Night	46% 4 12% 23% 13% 2	2354
	11th to 20th	Night	45% 4 9% 20% 17% 5%	2220
	21st to end	Night	46% 4 7% 23% 16% 4	1884
March	1st to 10th	Night	54% 3 8% 21% 12% 2	3734
	11th to 20th	Night	40% 4 15% 22% 17% 2	3650
	21st to end	Night	51% 4 5% 14% 21% 6%	3564
April	1st to 10th	Night	47% 4 9% 21% 16% 3	1900
	11th to 20th	Night	46% 4 9% 20% 19% 2	1875
	21st to end	Night	47% 4 9% 21% 15% 5%	1729
May	1st to 10th	Night	58% 4 12% 15% 9% 1	2840
	11th to 20th	Night	58% 5% 12% 14% 8% 2	2791
	21st to end	Night	43% 8% 13% 22% 13% 1	2739
June	1st to 10th	Night	45% 6% 12% 22% 14% 1	1520
	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	46% 5% 9% 22% 15% 4	2090
	11th to 20th	Night	37% 4 12% 28% 18% 1	2304
	21st to end	Night	44% 3 12% 22% 16% 2	2717
November	1st to 10th	Night	38% 5% 11% 22% 20% 4	2431
	11th to 20th	Night	42% 3 8% 23% 19% 4	2470
	21st to end	Night	40% 3 14% 28% 14% 2	2470
December	1st to 10th	Night	47% 4 11% 22% 15% 1	2607
	11th to 20th	Night	43% 4 12% 20% 18% 2	3288
	21st to end	Night	51% 3 8% 24% 14% 1	4884

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	26% 27% 31% 15% 2	180
	11th to 20th	Day	31% 27% 32% 6% 5%	180
	21st to end	Day	24% 30% 34% 8% 4 1	198
February	1st to 10th	Day	31% 24% 31% 13% 1	394
	11th to 20th	Day	30% 30% 30% 8% 1	456
	21st to end	Day	31% 22% 33% 10% 3	382
March	1st to 10th	Day	30% 22% 31% 15% 2	460
	11th to 20th	Day	27% 27% 30% 12% 2 1	460
	21st to end	Day	31% 22% 31% 11% 3 2	506
April	1st to 10th	Day	33% 24% 26% 11% 6%	460
	11th to 20th	Day	29% 24% 32% 12% 3	452
	21st to end	Day	31% 20% 30% 13% 3 2	460
May	1st to 10th	Day	33% 24% 28% 12% 3	463
	11th to 20th	Day	24% 17% 43% 13% 3 1	487
	21st to end	Day	20% 14% 34% 25% 5% 1	529
June	1st to 10th	Day	21% 16% 36% 20% 7% 1	490
	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% 31% 20% 7% 1	429
November	1st to 10th	Day	20% 17% 32% 21% 8% 2	369
	11th to 20th	Day	26% 22% 29% 16% 6%	370
	21st to end	Day	24% 21% 31% 18% 6% 1	370
December	1st to 10th	Day	23% 29% 31% 13% 4	229
	11th to 20th	Day	32% 29% 28% 7% 4	180
	21st to end	Day	27% 24% 32% 11% 4 2	198
January	1st to 10th	Night	23% 21% 35% 19% 3	760
	11th to 20th	Night	30% 19% 33% 16% 3	760
	21st to end	Night	21% 25% 33% 19% 2	836
February	1st to 10th	Night	23% 19% 35% 21% 2	760
	11th to 20th	Night	26% 22% 38% 12% 2	743
	21st to end	Night	27% 22% 31% 17% 3	628
March	1st to 10th	Night	25% 19% 35% 17% 4	760
	11th to 20th	Night	22% 21% 35% 19% 3	760
	21st to end	Night	27% 20% 32% 17% 3 1	836
April	1st to 10th	Night	25% 21% 32% 19% 3	760
	11th to 20th	Night	23% 17% 36% 20% 4	751
	21st to end	Night	24% 18% 33% 19% 5% 1	589
May	1st to 10th	Night	28% 14% 31% 22% 5% 1	570
	11th to 20th	Night	24% 16% 38% 20% 3	552
	21st to end	Night	20% 8% 33% 30% 7% 1	411
June	1st to 10th	Night	20% 8% 27% 35% 9%	380
	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	17% 15% 32% 23% 11% 1	748
	11th to 20th	Night	24% 17% 34% 18% 7% 1	760
	21st to end	Night	22% 19% 33% 21% 6% 1	760
December	1st to 10th	Night	26% 18% 32% 19% 4 1	760
	11th to 20th	Night	25% 19% 34% 18% 3	760
	21st to end	Night	25% 18% 37% 17% 3	836

Page generated at 2024-10-30 13:19:23. Version ac07

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