Stark Bayou Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stark Bayou Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	10% 5% 2 5% 5% 3 5% 6% 7% 9% 42%	74697
	Night	10% 5% 2 5% 5% 3 5% 5% 6% 9% 46%	75025
Transparency	Day	37% 9% 13% 19% 16% 6%	74443
	Night	35% 7% 13% 19% 18% 8%	74798
Seeing	Day	12% 7% 19% 26% 24% 12%	13190
	Night	12% 5% 19% 30% 26% 8%	23177

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	13% 6% 2 5% 5% 3 4 5% 5% 7% 45%	1896
	11th to 20th	Day	13% 6% 3 6% 5% 2 3 4 5% 6% 48%	1816
	21st to end	Day	17% 6% 3 5% 5% 3 4 4 4 5% 44%	1980
February	1st to 10th	Day	16% 8% 3 5% 5% 3 3 3 3 6% 44%	1800
	11th to 20th	Day	15% 7% 2 4 4 3 4 4 4 9% 43%	1748
	21st to end	Day	14% 8% 4 6% 5% 4 6% 4 5% 7% 36%	1480
March	1st to 10th	Day	12% 6% 3 6% 6% 3 4 4 6% 8% 44%	1800
	11th to 20th	Day	13% 7% 2 5% 5% 4 4 5% 6% 8% 42%	1916
	21st to end	Day	10% 6% 2 5% 5% 2 4 5% 5% 7% 49%	2362
April	1st to 10th	Day	9% 5% 2 4 5% 4 4 6% 6% 9% 46%	2160
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 6% 6% 8% 43%	2134
	21st to end	Day	8% 4 2 4 4 3 5% 5% 5% 8% 52%	2160
May	1st to 10th	Day	10% 4 2 3 4 3 4 6% 6% 8% 51%	2160
	11th to 20th	Day	7% 5% 2 4 5% 4 5% 6% 7% 10% 45%	2124
	21st to end	Day	7% 4 2 4 5% 3 6% 6% 7% 11% 45%	2505
June	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 8% 9% 12% 34%	2340
	11th to 20th	Day	5% 3 2 5% 6% 3 7% 7% 10% 12% 40%	2340
	21st to end	Day	8% 6% 3 6% 6% 4 6% 8% 9% 15% 29%	2340
July	1st to 10th	Day	8% 5% 4 6% 7% 4 8% 8% 11% 14% 25%	2180
	11th to 20th	Day	6% 7% 4 7% 7% 5% 6% 8% 10% 13% 28%	2160
	21st to end	Day	6% 5% 3 6% 7% 4 7% 9% 10% 13% 31%	2350
August	1st to 10th	Day	5% 3 2 5% 5% 5% 8% 9% 10% 14% 33%	2148
	11th to 20th	Day	9% 5% 2 7% 7% 5% 8% 8% 9% 13% 28%	2125
	21st to end	Day	9% 6% 2 6% 6% 4 6% 8% 10% 10% 33%	2376
September	1st to 10th	Day	7% 6% 2 6% 7% 4 6% 7% 8% 11% 38%	2160
	11th to 20th	Day	9% 5% 3 5% 5% 4 5% 7% 7% 10% 41%	2027
	21st to end	Day	8% 3 2 4 5% 3 5% 5% 7% 9% 48%	1980
October	1st to 10th	Day	6% 3 1 4 5% 2 3 5% 6% 8% 56%	1980
	11th to 20th	Day	6% 3 2 4 4 2 5% 4 6% 8% 56%	1877
	21st to end	Day	9% 4 2 4 4 3 4 4 4 6% 56%	1980
November	1st to 10th	Day	8% 3 2 3 4 3 3 4 4 7% 60%	1790
	11th to 20th	Day	10% 4 2 4 3 2 4 3 4 6% 58%	1710
	21st to end	Day	11% 5% 3 5% 5% 3 4 4 6% 6% 47%	1710
December	1st to 10th	Day	12% 6% 3 6% 6% 3 4 4 4 7% 45%	1710
	11th to 20th	Day	13% 8% 4 7% 5% 2 4 5% 4 7% 42%	2153
	21st to end	Day	16% 8% 3 6% 6% 2 4 4 5% 6% 41%	3220
January	1st to 10th	Night	14% 6% 3 4 5% 3 4 4 5% 6% 47%	2269
	11th to 20th	Night	12% 7% 3 5% 4 3 3 4 4 7% 48%	2184
	21st to end	Night	19% 6% 2 4 4 2 4 4 4 4 45%	2376
February	1st to 10th	Night	15% 7% 3 5% 4 3 4 5% 4 7% 44%	2160
	11th to 20th	Night	17% 6% 2 4 5% 3 4 3 4 7% 44%	2098
	21st to end	Night	16% 7% 3 6% 5% 3 5% 4 5% 6% 39%	1776
March	1st to 10th	Night	12% 6% 3 5% 5% 3 3 5% 5% 7% 46%	2160
	11th to 20th	Night	12% 6% 3 5% 4 3 5% 5% 6% 10% 41%	2057
	21st to end	Night	10% 5% 2 4 4 3 4 4 5% 8% 52%	1994
April	1st to 10th	Night	12% 5% 2 5% 5% 3 5% 5% 5% 6% 47%	1800
	11th to 20th	Night	12% 4 2 5% 5% 2 5% 5% 5% 8% 46%	1775
	21st to end	Night	6% 4 1 3 4 2 3 4 5% 8% 60%	1800
May	1st to 10th	Night	10% 4 2 2 3 3 5% 4 4 9% 54%	1800
	11th to 20th	Night	5% 4 2 5% 6% 3 6% 6% 7% 10% 47%	1769
	21st to end	Night	5% 3 2 4 4 3 5% 6% 7% 12% 48%	1765
June	1st to 10th	Night	8% 5% 2 5% 6% 4 5% 6% 8% 12% 40%	1620
	11th to 20th	Night	4 2 2 5% 4 3 5% 7% 8% 14% 45%	1620
	21st to end	Night	6% 5% 3 6% 6% 4 6% 6% 8% 12% 38%	1620
July	1st to 10th	Night	5% 6% 3 7% 5% 4 6% 7% 8% 11% 39%	1773
	11th to 20th	Night	3 4 2 5% 5% 4 7% 9% 10% 13% 39%	1800
	21st to end	Night	5% 4 2 6% 5% 4 6% 7% 7% 14% 40%	1968
August	1st to 10th	Night	3 3 1 4 4 3 5% 6% 8% 15% 48%	1790
	11th to 20th	Night	5% 5% 3 5% 5% 4 6% 8% 10% 16% 34%	1776
	21st to end	Night	7% 5% 2 6% 6% 4 6% 6% 7% 11% 39%	1980
September	1st to 10th	Night	6% 5% 3 6% 5% 4 7% 7% 8% 10% 40%	1800
	11th to 20th	Night	8% 5% 2 5% 5% 3 5% 6% 7% 9% 45%	1912
	21st to end	Night	7% 5% 2 5% 3 3 5% 4 6% 9% 52%	1980
October	1st to 10th	Night	7% 4 1 4 4 3 4 4 4 7% 59%	1980
	11th to 20th	Night	7% 3 2 3 4 1 3 3 5% 7% 61%	2078
	21st to end	Night	10% 4 2 4 4 2 3 4 4 7% 55%	2376
November	1st to 10th	Night	8% 5% 1 5% 4 3 3 3 4 6% 57%	2285
	11th to 20th	Night	10% 4 2 4 4 2 4 4 4 6% 55%	2470
	21st to end	Night	10% 5% 2 5% 5% 3 5% 4 5% 7% 49%	2470
December	1st to 10th	Night	13% 6% 3 5% 5% 3 4 4 5% 7% 45%	2470
	11th to 20th	Night	14% 7% 3 5% 5% 3 5% 4 5% 6% 44%	3042
	21st to end	Night	16% 7% 4 6% 6% 3 5% 4 5% 5% 40%	4432

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% 5% 7% 17% 23% 9%	1897
	11th to 20th	Day	38% 5% 7% 17% 23% 10%	1816
	21st to end	Day	44% 5% 4 17% 22% 10%	1980
February	1st to 10th	Day	45% 4 9% 12% 20% 10%	1800
	11th to 20th	Day	41% 6% 8% 17% 19% 10%	1758
	21st to end	Day	44% 9% 8% 14% 16% 9%	1480
March	1st to 10th	Day	38% 6% 8% 20% 21% 8%	1800
	11th to 20th	Day	40% 8% 10% 15% 20% 7%	1916
	21st to end	Day	35% 7% 12% 20% 19% 7%	2362
April	1st to 10th	Day	34% 9% 12% 19% 18% 8%	2160
	11th to 20th	Day	38% 6% 9% 21% 19% 8%	2134
	21st to end	Day	29% 6% 10% 23% 23% 8%	2160
May	1st to 10th	Day	30% 7% 11% 24% 20% 8%	2160
	11th to 20th	Day	34% 10% 16% 21% 18% 2	2128
	21st to end	Day	33% 9% 16% 24% 15% 3	2505
June	1st to 10th	Day	41% 10% 17% 23% 9% 1	2340
	11th to 20th	Day	32% 12% 19% 25% 10% 2	2340
	21st to end	Day	42% 12% 21% 17% 8%	2340
July	1st to 10th	Day	46% 16% 20% 14% 4	2120
	11th to 20th	Day	44% 15% 23% 14% 3 1	2097
	21st to end	Day	41% 15% 21% 19% 4	2219
August	1st to 10th	Day	37% 15% 24% 19% 5%	2136
	11th to 20th	Day	45% 15% 19% 15% 5%	2125
	21st to end	Day	42% 13% 19% 17% 7% 2	2376
September	1st to 10th	Day	39% 12% 16% 16% 12% 4	2160
	11th to 20th	Day	38% 10% 14% 16% 16% 6%	2027
	21st to end	Day	33% 8% 11% 23% 18% 7%	1980
October	1st to 10th	Day	25% 7% 13% 20% 21% 13%	1980
	11th to 20th	Day	27% 5% 8% 21% 26% 13%	1877
	21st to end	Day	31% 4 7% 16% 26% 17%	1980
November	1st to 10th	Day	27% 5% 8% 22% 25% 13%	1790
	11th to 20th	Day	30% 3 7% 18% 29% 13%	1710
	21st to end	Day	36% 5% 9% 18% 20% 12%	1710
December	1st to 10th	Day	39% 7% 9% 18% 20% 7%	1710
	11th to 20th	Day	43% 5% 8% 15% 20% 10%	2150
	21st to end	Day	44% 5% 7% 19% 21% 5%	3220
January	1st to 10th	Night	39% 4 9% 15% 25% 9%	2269
	11th to 20th	Night	38% 4 7% 17% 24% 10%	2184
	21st to end	Night	43% 4 6% 12% 26% 10%	2376
February	1st to 10th	Night	40% 5% 7% 17% 19% 11%	2160
	11th to 20th	Night	42% 5% 5% 15% 20% 12%	2099
	21st to end	Night	46% 6% 10% 15% 11% 12%	1776
March	1st to 10th	Night	38% 5% 9% 16% 23% 9%	2160
	11th to 20th	Night	39% 8% 11% 16% 18% 7%	2057
	21st to end	Night	31% 5% 13% 20% 22% 8%	1994
April	1st to 10th	Night	38% 5% 11% 16% 19% 10%	1800
	11th to 20th	Night	36% 5% 9% 21% 20% 8%	1775
	21st to end	Night	24% 5% 11% 26% 26% 8%	1800
May	1st to 10th	Night	29% 4 12% 25% 24% 6%	1800
	11th to 20th	Night	30% 10% 17% 21% 19% 3	1770
	21st to end	Night	28% 8% 18% 26% 17% 2	1766
June	1st to 10th	Night	35% 9% 20% 25% 10% 1	1620
	11th to 20th	Night	26% 11% 24% 27% 12%	1620
	21st to end	Night	35% 12% 24% 19% 9% 1	1620
July	1st to 10th	Night	35% 13% 27% 20% 5%	1723
	11th to 20th	Night	30% 16% 31% 18% 3 1	1740
	21st to end	Night	30% 12% 31% 22% 4	1858
August	1st to 10th	Night	23% 12% 35% 24% 5%	1778
	11th to 20th	Night	32% 17% 29% 17% 5%	1776
	21st to end	Night	38% 11% 25% 17% 6% 3	1980
September	1st to 10th	Night	34% 10% 20% 17% 14% 5%	1800
	11th to 20th	Night	34% 10% 17% 17% 14% 8%	1912
	21st to end	Night	29% 8% 12% 24% 18% 8%	1980
October	1st to 10th	Night	26% 6% 11% 19% 22% 15%	1980
	11th to 20th	Night	25% 4 10% 22% 26% 14%	2078
	21st to end	Night	30% 5% 6% 15% 27% 17%	2376
November	1st to 10th	Night	30% 3 8% 18% 27% 15%	2285
	11th to 20th	Night	32% 4 6% 16% 29% 13%	2470
	21st to end	Night	35% 5% 7% 20% 21% 12%	2470
December	1st to 10th	Night	38% 6% 10% 19% 20% 6%	2470
	11th to 20th	Night	41% 5% 7% 13% 21% 13%	3044
	21st to end	Night	46% 5% 6% 19% 18% 5%	4432

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	19% 15% 37% 23% 7%	270
	11th to 20th	Day	18% 13% 31% 28% 9% 1	245
	21st to end	Day	20% 18% 42% 16% 4	264
February	1st to 10th	Day	24% 20% 33% 17% 6%	240
	11th to 20th	Day	24% 18% 30% 23% 6%	240
	21st to end	Day	13% 24% 43% 19% 2	198
March	1st to 10th	Day	13% 16% 40% 28% 4	240
	11th to 20th	Day	18% 18% 36% 20% 8%	240
	21st to end	Day	14% 15% 32% 25% 13% 1	448
April	1st to 10th	Day	13% 11% 36% 26% 12% 2	420
	11th to 20th	Day	19% 11% 29% 24% 14% 2	412
	21st to end	Day	9% 7% 28% 33% 20% 3	420
May	1st to 10th	Day	11% 8% 25% 31% 20% 5%	423
	11th to 20th	Day	9% 3 17% 36% 25% 10%	447
	21st to end	Day	7% 1 10% 38% 30% 14%	485
June	1st to 10th	Day	11% 2 10% 32% 28% 17%	450
	11th to 20th	Day	8% 3 11% 28% 31% 20%	450
	21st to end	Day	11% 2 10% 25% 29% 24%	450
July	1st to 10th	Day	8% 1 7% 17% 38% 29%	445
	11th to 20th	Day	9% 3 3 14% 41% 31%	444
	21st to end	Day	6% 1 8% 21% 40% 25%	488
August	1st to 10th	Day	5% 4 20% 38% 33%	446
	11th to 20th	Day	8% 5% 16% 36% 35%	439
	21st to end	Day	9% 2 8% 20% 35% 26%	495
September	1st to 10th	Day	6% 1 7% 23% 41% 22%	450
	11th to 20th	Day	10% 3 9% 25% 38% 14%	450
	21st to end	Day	9% 2 11% 29% 35% 13%	450
October	1st to 10th	Day	7% 3 16% 39% 27% 8%	450
	11th to 20th	Day	6% 4 17% 32% 33% 8%	347
	21st to end	Day	14% 8% 22% 32% 19% 4	297
November	1st to 10th	Day	13% 6% 23% 33% 22% 3	270
	11th to 20th	Day	17% 10% 26% 30% 17% 2	270
	21st to end	Day	15% 11% 28% 30% 13% 3	270
December	1st to 10th	Day	16% 10% 33% 29% 11% 1	270
	11th to 20th	Day	20% 12% 35% 25% 7%	270
	21st to end	Day	25% 9% 32% 21% 10% 2	297
January	1st to 10th	Night	18% 11% 31% 34% 6%	760
	11th to 20th	Night	15% 9% 29% 37% 10%	728
	21st to end	Night	22% 10% 31% 31% 6%	792
February	1st to 10th	Night	16% 12% 33% 32% 7%	720
	11th to 20th	Night	21% 9% 32% 28% 8%	703
	21st to end	Night	19% 12% 37% 29% 4	592
March	1st to 10th	Night	15% 10% 32% 34% 9%	720
	11th to 20th	Night	16% 7% 29% 31% 15% 1	617
	21st to end	Night	12% 8% 26% 37% 16%	594
April	1st to 10th	Night	14% 9% 27% 32% 17% 1	540
	11th to 20th	Night	13% 6% 30% 29% 20% 1	533
	21st to end	Night	8% 5% 22% 38% 25% 2	540
May	1st to 10th	Night	10% 4 16% 41% 26% 3	540
	11th to 20th	Night	6% 2 13% 40% 34% 5%	531
	21st to end	Night	5% 2 8% 33% 43% 9%	584
June	1st to 10th	Night	10% 1 4 29% 45% 11%	540
	11th to 20th	Night	4 1 4 25% 50% 15%	540
	21st to end	Night	8% 1 6% 22% 45% 18%	540
July	1st to 10th	Night	6% 2 4 16% 50% 23%	525
	11th to 20th	Night	3 1 3 10% 46% 38%	522
	21st to end	Night	5% 2 14% 49% 30%	591
August	1st to 10th	Night	2 2 13% 46% 36%	537
	11th to 20th	Night	7% 1 1 11% 50% 31%	534
	21st to end	Night	10% 1 4 17% 45% 24%	594
September	1st to 10th	Night	7% 1 6% 19% 46% 21%	540
	11th to 20th	Night	10% 2 8% 22% 47% 11%	652
	21st to end	Night	9% 9% 30% 43% 8%	720
October	1st to 10th	Night	8% 2 15% 38% 33% 5%	720
	11th to 20th	Night	8% 4 17% 32% 32% 7%	720
	21st to end	Night	12% 6% 19% 35% 25% 3	792
November	1st to 10th	Night	10% 4 18% 40% 23% 4	740
	11th to 20th	Night	12% 6% 27% 36% 18% 2	760
	21st to end	Night	12% 7% 26% 35% 18% 1	760
December	1st to 10th	Night	14% 10% 29% 29% 17% 1	760
	11th to 20th	Night	19% 7% 28% 33% 12% 1	760
	21st to end	Night	22% 11% 29% 29% 9%	836

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