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 2024-03-08.

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% 7% 3 5% 5% 3 4 4 5% 7% 40%	78412
	Night	18% 8% 3 5% 5% 3 4 4 4 6% 41%	81138
Transparency	Day	44% 5% 11% 23% 15% 3	78117
	Night	45% 4 11% 23% 15% 3	80967
Seeing	Day	24% 18% 32% 18% 7% 2	14156
	Night	22% 15% 32% 23% 7% 1	23264

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% 3 5% 4 3 5% 4 4 4 45%	2517
	11th to 20th	Day	18% 8% 3 5% 6% 3 4 5% 4 5% 39%	2520
	21st to end	Day	23% 13% 3 5% 4 2 3 3 4 4 35%	2772
February	1st to 10th	Day	19% 7% 3 5% 3 3 5% 5% 5% 7% 38%	1819
	11th to 20th	Day	14% 7% 3 5% 6% 4 5% 4 4 6% 42%	1848
	21st to end	Day	21% 10% 3 5% 4 2 4 3 4 6% 37%	1570
March	1st to 10th	Day	18% 9% 2 4 4 2 4 4 5% 6% 42%	1867
	11th to 20th	Day	16% 7% 4 5% 4 3 4 5% 5% 7% 39%	1880
	21st to end	Day	19% 9% 3 5% 5% 2 4 4 4 5% 40%	2317
April	1st to 10th	Day	20% 7% 3 5% 4 3 4 5% 5% 6% 39%	2160
	11th to 20th	Day	19% 6% 2 5% 4 3 3 4 5% 7% 42%	2134
	21st to end	Day	23% 6% 2 5% 5% 3 4 5% 4 7% 36%	2320
May	1st to 10th	Day	25% 8% 3 5% 5% 2 4 3 4 8% 33%	2340
	11th to 20th	Day	19% 6% 2 5% 5% 3 3 3 5% 8% 40%	2324
	21st to end	Day	16% 6% 2 5% 4 2 4 4 5% 8% 44%	2725
June	1st to 10th	Day	19% 6% 3 5% 5% 3 4 5% 7% 8% 33%	2520
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 5% 6% 8% 35%	2520
	21st to end	Day	15% 6% 3 5% 5% 4 5% 5% 5% 9% 38%	2520
July	1st to 10th	Day	14% 6% 3 4 6% 3 6% 5% 5% 9% 40%	2520
	11th to 20th	Day	15% 5% 3 6% 6% 3 5% 5% 6% 9% 37%	2520
	21st to end	Day	14% 5% 3 6% 5% 3 6% 6% 6% 9% 38%	2744
August	1st to 10th	Day	13% 6% 3 5% 5% 3 6% 5% 7% 9% 37%	2350
	11th to 20th	Day	14% 6% 3 6% 6% 3 5% 5% 5% 9% 39%	2227
	21st to end	Day	12% 5% 2 6% 6% 3 6% 6% 6% 7% 41%	2376
September	1st to 10th	Day	16% 7% 2 5% 5% 2 5% 5% 3 6% 44%	2160
	11th to 20th	Day	15% 5% 2 4 3 2 4 3 5% 6% 51%	1988
	21st to end	Day	20% 5% 3 3 4 3 5% 4 4 5% 44%	1980
October	1st to 10th	Day	23% 8% 2 5% 4 1 3 3 4 5% 41%	1980
	11th to 20th	Day	17% 5% 2 4 4 3 3 4 4 7% 46%	1774
	21st to end	Day	19% 6% 3 6% 5% 3 3 3 5% 4 42%	1782
November	1st to 10th	Day	17% 6% 3 4 5% 3 4 3 4 5% 47%	1671
	11th to 20th	Day	17% 5% 2 5% 3 2 3 3 5% 6% 47%	1710
	21st to end	Day	17% 6% 2 5% 5% 3 3 4 4 5% 45%	1710
December	1st to 10th	Day	20% 7% 2 5% 6% 3 4 4 5% 7% 38%	1569
	11th to 20th	Day	21% 7% 2 4 4 2 3 3 3 5% 46%	1906
	21st to end	Day	20% 10% 4 6% 5% 3 4 3 4 4 37%	2772
January	1st to 10th	Night	17% 7% 2 4 3 2 3 3 4 6% 48%	4429
	11th to 20th	Night	17% 9% 3 7% 5% 2 3 4 3 4 42%	4440
	21st to end	Night	22% 12% 4 7% 5% 3 3 4 4 5% 31%	4884
February	1st to 10th	Night	16% 8% 4 6% 5% 2 3 4 4 6% 41%	2354
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 4 4 6% 41%	2218
	21st to end	Night	19% 9% 3 4 5% 3 3 4 4 5% 40%	1884
March	1st to 10th	Night	17% 7% 2 4 5% 2 4 4 5% 7% 42%	2241
	11th to 20th	Night	16% 8% 3 5% 6% 3 5% 4 4 7% 39%	2079
	21st to end	Night	18% 9% 3 5% 4 2 3 4 4 6% 41%	2036
April	1st to 10th	Night	18% 10% 2 5% 5% 3 4 5% 5% 6% 38%	1800
	11th to 20th	Night	19% 7% 3 6% 4 3 4 4 5% 6% 40%	1775
	21st to end	Night	22% 7% 3 5% 4 3 4 3 4 7% 39%	1638
May	1st to 10th	Night	23% 8% 3 7% 6% 3 4 4 5% 6% 32%	1620
	11th to 20th	Night	21% 7% 2 6% 6% 3 5% 3 5% 8% 36%	1584
	21st to end	Night	17% 8% 3 5% 5% 3 5% 5% 6% 7% 36%	1550
June	1st to 10th	Night	19% 7% 3 5% 4 3 5% 4 6% 8% 37%	1440
	11th to 20th	Night	20% 7% 2 5% 4 3 4 4 5% 7% 38%	1440
	21st to end	Night	15% 7% 3 5% 4 3 4 3 6% 9% 41%	1440
July	1st to 10th	Night	13% 6% 4 7% 6% 3 6% 6% 6% 7% 37%	1440
	11th to 20th	Night	15% 7% 3 5% 5% 2 6% 5% 6% 9% 36%	1440
	21st to end	Night	14% 6% 3 6% 6% 3 5% 4 5% 9% 40%	1574
August	1st to 10th	Night	9% 6% 3 5% 6% 3 6% 6% 7% 8% 41%	1569
	11th to 20th	Night	10% 7% 3 5% 6% 4 5% 6% 7% 8% 38%	1670
	21st to end	Night	13% 6% 2 5% 4 3 4 4 5% 7% 47%	1980
September	1st to 10th	Night	15% 7% 3 6% 5% 3 6% 4 5% 6% 41%	1800
	11th to 20th	Night	14% 5% 2 5% 4 2 3 4 4 7% 50%	1971
	21st to end	Night	19% 7% 3 6% 4 3 4 4 4 4 42%	1980
October	1st to 10th	Night	20% 7% 3 6% 5% 2 3 4 4 5% 41%	1980
	11th to 20th	Night	16% 6% 2 5% 5% 3 3 4 5% 7% 46%	2182
	21st to end	Night	21% 7% 2 5% 4 2 3 3 4 6% 40%	2574
November	1st to 10th	Night	14% 6% 2 5% 4 3 3 4 4 6% 48%	2407
	11th to 20th	Night	18% 7% 3 5% 4 2 3 3 4 6% 45%	2470
	21st to end	Night	16% 6% 2 4 4 2 4 3 5% 6% 46%	2470
December	1st to 10th	Night	20% 7% 3 5% 4 3 4 3 4 5% 40%	2607
	11th to 20th	Night	20% 6% 2 5% 4 3 4 4 4 6% 42%	3288
	21st to end	Night	21% 11% 3 6% 5% 2 3 3 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	44% 3 12% 23% 14% 5%	1870
	11th to 20th	Day	43% 4 10% 24% 16% 3	1880
	21st to end	Day	48% 4 8% 18% 17% 6%	2317
April	1st to 10th	Day	46% 5% 9% 20% 17% 3	2160
	11th to 20th	Day	43% 4 8% 22% 20% 3	2134
	21st to end	Day	48% 4 9% 20% 15% 4	2320
May	1st to 10th	Day	52% 4 9% 20% 12% 3	2340
	11th to 20th	Day	44% 5% 10% 22% 17% 3	2328
	21st to end	Day	39% 6% 16% 23% 13% 2	2725
June	1st to 10th	Day	47% 6% 12% 23% 11% 1	2520
	11th to 20th	Day	46% 6% 12% 21% 14% 1	2520
	21st to end	Day	42% 7% 14% 24% 13% 1	2520
July	1st to 10th	Day	42% 5% 12% 24% 15% 2	2450
	11th to 20th	Day	42% 5% 13% 27% 10% 2	2445
	21st to end	Day	40% 7% 14% 21% 15% 3	2591
August	1st to 10th	Day	41% 6% 16% 23% 13% 1	2336
	11th to 20th	Day	42% 6% 13% 24% 14% 1	2227
	21st to end	Day	40% 6% 10% 23% 19% 2	2376
September	1st to 10th	Day	41% 6% 10% 22% 19% 2	2160
	11th to 20th	Day	35% 4 10% 23% 24% 3	1988
	21st to end	Day	43% 4 7% 21% 23% 2	1980
October	1st to 10th	Day	46% 3 9% 21% 16% 4	1980
	11th to 20th	Day	38% 4 10% 29% 17% 2	1774
	21st to end	Day	44% 4 11% 21% 16% 4	1782
November	1st to 10th	Day	41% 4 13% 20% 20% 2	1671
	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	43% 4 10% 24% 16% 4	2251
	11th to 20th	Night	46% 4 9% 20% 18% 4	2080
	21st to end	Night	45% 4 7% 19% 19% 6%	2036
April	1st to 10th	Night	46% 4 9% 21% 17% 4	1800
	11th to 20th	Night	45% 4 9% 21% 19% 2	1775
	21st to end	Night	47% 4 9% 21% 14% 5%	1638
May	1st to 10th	Night	53% 5% 9% 17% 14% 3	1620
	11th to 20th	Night	48% 5% 10% 19% 14% 3	1585
	21st to end	Night	46% 9% 14% 18% 12% 1	1551
June	1st to 10th	Night	45% 6% 12% 22% 14% 1	1440
	11th to 20th	Night	46% 4 13% 25% 12% 1	1440
	21st to end	Night	40% 6% 15% 26% 13% 1	1440
July	1st to 10th	Night	44% 7% 13% 22% 13% 1	1400
	11th to 20th	Night	44% 6% 15% 26% 8% 1	1392
	21st to end	Night	41% 6% 15% 25% 12% 2	1486
August	1st to 10th	Night	38% 7% 17% 24% 12% 2	1559
	11th to 20th	Night	41% 7% 15% 25% 11% 1	1670
	21st to end	Night	35% 7% 11% 25% 20% 2	1980
September	1st to 10th	Night	45% 5% 10% 23% 16% 2	1800
	11th to 20th	Night	36% 4 11% 22% 26% 2	1971
	21st to end	Night	46% 4 7% 19% 21% 3	1980
October	1st to 10th	Night	46% 5% 9% 21% 14% 4	1980
	11th to 20th	Night	38% 4 12% 29% 15% 1	2182
	21st to end	Night	46% 3 12% 22% 15% 2	2574
November	1st to 10th	Night	38% 5% 11% 22% 20% 4	2407
	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% 21% 31% 15% 2	448
	11th to 20th	Day	27% 27% 30% 12% 2 1	420
	21st to end	Day	29% 22% 31% 12% 3 2	462
April	1st to 10th	Day	33% 24% 25% 11% 6%	420
	11th to 20th	Day	28% 24% 32% 13% 3	412
	21st to end	Day	33% 20% 30% 12% 3 1	420
May	1st to 10th	Day	34% 24% 28% 11% 3	423
	11th to 20th	Day	23% 17% 43% 13% 3 1	447
	21st to end	Day	21% 12% 33% 26% 6% 1	485
June	1st to 10th	Day	20% 15% 36% 20% 7% 1	450
	11th to 20th	Day	18% 20% 36% 19% 6% 1	450
	21st to end	Day	20% 13% 37% 23% 6% 2	450
July	1st to 10th	Day	19% 9% 32% 28% 12% 1	445
	11th to 20th	Day	15% 9% 34% 28% 12% 2	444
	21st to end	Day	12% 13% 40% 25% 9% 1	488
August	1st to 10th	Day	14% 11% 36% 26% 11% 2	446
	11th to 20th	Day	17% 10% 33% 27% 10% 4	439
	21st to end	Day	12% 10% 37% 23% 13% 6%	495
September	1st to 10th	Day	20% 11% 27% 24% 14% 3	450
	11th to 20th	Day	17% 12% 32% 21% 11% 6%	450
	21st to end	Day	22% 12% 35% 18% 9% 4	450
October	1st to 10th	Day	31% 11% 26% 19% 9% 4	450
	11th to 20th	Day	20% 18% 30% 20% 10% 2	414
	21st to end	Day	26% 17% 30% 19% 7% 1	396
November	1st to 10th	Day	19% 17% 32% 21% 8% 2	365
	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	26% 19% 35% 16% 4	751
	11th to 20th	Night	23% 20% 35% 19% 3	720
	21st to end	Night	25% 20% 33% 17% 3 1	792
April	1st to 10th	Night	25% 21% 31% 19% 3	720
	11th to 20th	Night	22% 16% 37% 20% 4	711
	21st to end	Night	25% 18% 32% 19% 4 1	558
May	1st to 10th	Night	28% 14% 31% 21% 5% 1	540
	11th to 20th	Night	24% 16% 37% 20% 3	523
	21st to end	Night	21% 8% 32% 30% 8% 1	389
June	1st to 10th	Night	20% 8% 28% 34% 10%	360
	11th to 20th	Night	23% 9% 26% 34% 8%	360
	21st to end	Night	19% 4 31% 38% 8%	360
July	1st to 10th	Night	15% 5% 29% 35% 14% 1	350
	11th to 20th	Night	19% 2 22% 41% 14% 1	348
	21st to end	Night	15% 4 27% 43% 10% 1	394
August	1st to 10th	Night	12% 6% 34% 38% 10%	495
	11th to 20th	Night	14% 5% 27% 38% 15% 1	606
	21st to end	Night	15% 5% 24% 37% 16% 3	792
September	1st to 10th	Night	18% 5% 31% 29% 15% 2	720
	11th to 20th	Night	16% 7% 28% 31% 14% 3	720
	21st to end	Night	21% 8% 29% 27% 12% 2	720
October	1st to 10th	Night	25% 10% 28% 23% 11% 2	720
	11th to 20th	Night	18% 13% 33% 25% 10% 2	720
	21st to end	Night	26% 14% 32% 20% 7%	792
November	1st to 10th	Night	17% 14% 32% 24% 12% 1	740
	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 2024-03-05 07:24:04. Version ac07

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