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 2025-11-18.

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 6% 4 4 5% 5% 7% 9% 43%	125823
	Night	10% 6% 2 6% 4 4 4 4 6% 8% 45%	124559
Transparency	Day	23% 39% 10% 13% 11% 5%	129636
	Night	24% 38% 9% 13% 12% 5%	128819
Seeing	Day	12% 7% 21% 26% 23% 11%	15631
	Night	12% 6% 20% 30% 26% 7%	25512

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	14% 4 1 5% 3 3 4 3 5% 7% 49%	4516
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 5% 6% 49%	4520
	21st to end	Day	19% 8% 3 6% 4 4 4 4 6% 7% 36%	4972
February	1st to 10th	Day	15% 8% 3 6% 5% 5% 4 2 4 6% 42%	2000
	11th to 20th	Day	15% 7% 2 5% 4 4 4 3 5% 8% 42%	1948
	21st to end	Day	14% 9% 4 7% 5% 4 6% 3 5% 6% 37%	1650
March	1st to 10th	Day	15% 9% 3 7% 5% 4 4 4 5% 6% 38%	4480
	11th to 20th	Day	12% 6% 2 5% 4 4 3 3 5% 7% 49%	4832
	21st to end	Day	14% 7% 3 7% 5% 4 4 4 4 6% 44%	5939
April	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 5% 6% 8% 45%	2400
	11th to 20th	Day	11% 6% 2 5% 4 4 4 5% 6% 8% 44%	2374
	21st to end	Day	7% 5% 1 5% 4 4 5% 4 6% 8% 51%	2400
May	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 5% 7% 10% 35%	5405
	11th to 20th	Day	9% 5% 2 5% 4 4 6% 5% 7% 10% 44%	5404
	21st to end	Day	6% 3 2 5% 4 4 5% 4 8% 12% 47%	6379
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 7% 9% 11% 35%	2600
	11th to 20th	Day	5% 4 1 6% 5% 5% 6% 6% 10% 12% 39%	2600
	21st to end	Day	7% 6% 3 7% 6% 5% 7% 7% 9% 14% 30%	2600
July	1st to 10th	Day	4 4 2 5% 5% 6% 8% 7% 11% 16% 31%	5488
	11th to 20th	Day	3 4 2 6% 5% 5% 6% 6% 10% 13% 41%	5440
	21st to end	Day	3 4 2 7% 6% 7% 8% 7% 11% 15% 31%	5922
August	1st to 10th	Day	3 2 1 4 4 5% 7% 6% 10% 13% 45%	3905
	11th to 20th	Day	5% 3 1 5% 4 5% 7% 6% 9% 13% 42%	3849
	21st to end	Day	5% 6% 3 8% 6% 6% 7% 6% 9% 8% 35%	4312
September	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 38%	2400
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 5% 7% 10% 43%	2251
	21st to end	Day	7% 3 2 5% 4 4 5% 4 7% 9% 50%	2200
October	1st to 10th	Day	7% 3 1 5% 4 3 4 4 6% 8% 55%	2200
	11th to 20th	Day	6% 3 1 4 3 3 4 4 5% 8% 60%	2085
	21st to end	Day	9% 4 2 5% 3 4 4 2 4 7% 57%	2200
November	1st to 10th	Day	8% 4 2 4 3 3 3 3 5% 6% 58%	1982
	11th to 20th	Day	10% 4 1 4 3 3 3 2 5% 6% 58%	1863
	21st to end	Day	11% 5% 2 7% 4 4 4 4 6% 6% 48%	1800
December	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 5% 6% 44%	2930
	11th to 20th	Day	9% 6% 2 6% 3 3 3 4 5% 8% 50%	3373
	21st to end	Day	16% 8% 3 6% 4 3 4 3 4 5% 44%	4604
January	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 4 6% 48%	5429
	11th to 20th	Night	18% 9% 3 5% 3 2 2 2 3 6% 45%	5440
	21st to end	Night	20% 8% 2 6% 4 4 4 3 5% 7% 38%	5984
February	1st to 10th	Night	14% 8% 2 6% 4 4 4 4 5% 6% 44%	2400
	11th to 20th	Night	18% 7% 3 5% 4 4 3 3 5% 6% 42%	2338
	21st to end	Night	15% 7% 3 7% 4 5% 4 4 5% 6% 40%	1980
March	1st to 10th	Night	19% 9% 3 7% 4 3 3 3 5% 7% 37%	5373
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 7% 49%	5169
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 6% 47%	4976
April	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 5% 5% 46%	2000
	11th to 20th	Night	11% 4 2 6% 4 4 4 4 5% 7% 47%	1975
	21st to end	Night	5% 4 1 4 4 3 4 3 6% 8% 58%	2000
May	1st to 10th	Night	13% 6% 3 6% 5% 5% 5% 4 6% 9% 38%	4490
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	4489
	21st to end	Night	4 4 2 5% 4 4 5% 4 7% 13% 46%	4470
June	1st to 10th	Night	7% 5% 2 6% 5% 5% 5% 5% 9% 11% 41%	1800
	11th to 20th	Night	4 3 2 5% 4 4 5% 6% 9% 14% 45%	1800
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 6% 9% 13% 37%	1800
July	1st to 10th	Night	3 4 2 7% 5% 6% 7% 7% 10% 13% 38%	4463
	11th to 20th	Night	1 3 1 5% 4 5% 5% 6% 8% 11% 48%	4517
	21st to end	Night	3 3 2 7% 6% 7% 8% 7% 11% 15% 33%	4929
August	1st to 10th	Night	2 2 1 4 3 4 5% 5% 8% 13% 53%	3244
	11th to 20th	Night	3 3 2 5% 4 4 5% 6% 8% 15% 45%	3200
	21st to end	Night	4 4 2 6% 6% 6% 6% 6% 8% 11% 40%	3586
September	1st to 10th	Night	7% 5% 2 7% 4 5% 7% 5% 8% 11% 39%	2000
	11th to 20th	Night	8% 6% 2 6% 4 4 5% 4 7% 9% 46%	2126
	21st to end	Night	6% 5% 2 5% 3 4 4 3 6% 9% 53%	2200
October	1st to 10th	Night	7% 4 1 5% 3 4 4 3 4 7% 56%	2200
	11th to 20th	Night	6% 4 1 4 3 3 2 2 5% 7% 63%	2310
	21st to end	Night	9% 4 2 5% 3 3 3 3 4 7% 56%	2640
November	1st to 10th	Night	8% 5% 1 6% 3 4 3 3 4 6% 56%	2533
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 4 6% 55%	2692
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 5% 7% 50%	2600
December	1st to 10th	Night	11% 6% 3 7% 4 5% 4 4 6% 7% 44%	4250
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 5% 6% 51%	4822
	21st to end	Night	16% 8% 3 7% 4 4 4 3 4 4 43%	6334

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	25% 27% 4 16% 21% 7%	4517
	11th to 20th	Day	27% 27% 2 14% 23% 8%	4520
	21st to end	Day	36% 28% 6% 11% 11% 8%	4972
February	1st to 10th	Day	20% 62% 3 5% 7% 4	2000
	11th to 20th	Day	16% 61% 4 8% 8% 2	1958
	21st to end	Day	17% 63% 3 5% 7% 4	1650
March	1st to 10th	Day	35% 30% 5% 13% 9% 7%	4480
	11th to 20th	Day	24% 30% 5% 12% 16% 12%	4832
	21st to end	Day	33% 30% 8% 13% 10% 7%	5941
April	1st to 10th	Day	16% 62% 3 7% 8% 4	2400
	11th to 20th	Day	15% 62% 4 8% 8% 3	2374
	21st to end	Day	12% 62% 6% 10% 7% 3	2400
May	1st to 10th	Day	32% 33% 12% 14% 7% 2	5440
	11th to 20th	Day	23% 29% 14% 23% 10%	5408
	21st to end	Day	21% 30% 15% 25% 8% 2	6393
June	1st to 10th	Day	16% 63% 8% 9% 5%	2600
	11th to 20th	Day	16% 64% 9% 7% 4	2600
	21st to end	Day	18% 61% 11% 7% 3	2600
July	1st to 10th	Day	27% 29% 27% 15% 2	5428
	11th to 20th	Day	27% 30% 32% 10%	5377
	21st to end	Day	30% 30% 21% 17% 1	5752
August	1st to 10th	Day	16% 37% 10% 21% 15% 2	3893
	11th to 20th	Day	18% 37% 13% 21% 10%	3885
	21st to end	Day	28% 39% 11% 12% 9% 1	4311
September	1st to 10th	Day	17% 59% 9% 7% 6% 2	2400
	11th to 20th	Day	11% 59% 7% 11% 10% 2	2251
	21st to end	Day	13% 58% 7% 14% 6% 2	2200
October	1st to 10th	Day	19% 36% 4 8% 10% 21%	3590
	11th to 20th	Day	5% 35% 3 14% 17% 26%	3377
	21st to end	Day	11% 35% 3 6% 30% 15%	3538
November	1st to 10th	Day	17% 53% 5% 11% 9% 5%	1982
	11th to 20th	Day	17% 55% 3 8% 12% 5%	1863
	21st to end	Day	16% 58% 3 9% 8% 6%	1800
December	1st to 10th	Day	29% 36% 5% 9% 17% 4	2930
	11th to 20th	Day	21% 31% 7% 16% 17% 9%	3370
	21st to end	Day	32% 27% 4 12% 21% 4	4604
January	1st to 10th	Night	30% 26% 3 14% 19% 8%	5429
	11th to 20th	Night	33% 26% 1 11% 24% 4	5440
	21st to end	Night	36% 28% 5% 11% 14% 7%	5984
February	1st to 10th	Night	17% 62% 3 7% 8% 4	2400
	11th to 20th	Night	18% 60% 3 7% 8% 3	2339
	21st to end	Night	17% 63% 4 5% 6% 4	1980
March	1st to 10th	Night	39% 30% 6% 9% 12% 5%	5373
	11th to 20th	Night	25% 31% 5% 10% 15% 13%	5169
	21st to end	Night	29% 29% 9% 15% 10% 8%	4976
April	1st to 10th	Night	17% 62% 3 5% 8% 5%	2000
	11th to 20th	Night	15% 63% 3 7% 8% 4	1975
	21st to end	Night	12% 62% 5% 9% 9% 3	2000
May	1st to 10th	Night	33% 32% 12% 12% 8% 2	4520
	11th to 20th	Night	29% 30% 12% 21% 9%	4490
	21st to end	Night	22% 30% 17% 24% 7% 1	4478
June	1st to 10th	Night	14% 63% 8% 9% 6%	1800
	11th to 20th	Night	13% 64% 10% 9% 4	1800
	21st to end	Night	15% 63% 12% 6% 4	1800
July	1st to 10th	Night	26% 30% 27% 16% 2	4415
	11th to 20th	Night	21% 32% 37% 10%	4460
	21st to end	Night	28% 35% 17% 20% 1	4785
August	1st to 10th	Night	13% 36% 11% 23% 15% 1	3232
	11th to 20th	Night	14% 37% 18% 24% 7%	3230
	21st to end	Night	22% 43% 12% 14% 8% 2	3586
September	1st to 10th	Night	16% 59% 9% 9% 6% 2	2000
	11th to 20th	Night	12% 58% 8% 10% 9% 3	2126
	21st to end	Night	12% 59% 7% 14% 6% 2	2200
October	1st to 10th	Night	24% 36% 5% 7% 14% 14%	3590
	11th to 20th	Night	7% 35% 2 13% 18% 25%	3757
	21st to end	Night	11% 35% 3 5% 33% 14%	4252
November	1st to 10th	Night	19% 53% 4 9% 10% 4	2533
	11th to 20th	Night	18% 55% 2 7% 13% 6%	2692
	21st to end	Night	15% 57% 3 9% 10% 6%	2600
December	1st to 10th	Night	29% 35% 5% 10% 15% 7%	4250
	11th to 20th	Night	22% 31% 5% 19% 14% 9%	4824
	21st to end	Night	35% 27% 4 12% 18% 4	6334

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% 16% 38% 20% 6%	300
	11th to 20th	Day	17% 17% 33% 25% 8% 1	300
	21st to end	Day	21% 19% 40% 16% 4	330
February	1st to 10th	Day	22% 19% 33% 19% 6% 1	300
	11th to 20th	Day	25% 19% 31% 20% 5%	300
	21st to end	Day	12% 23% 45% 16% 3	249
March	1st to 10th	Day	16% 18% 38% 25% 3	300
	11th to 20th	Day	18% 22% 33% 19% 7%	300
	21st to end	Day	15% 16% 33% 24% 12% 1	535
April	1st to 10th	Day	15% 14% 36% 24% 11% 1	500
	11th to 20th	Day	17% 13% 31% 24% 13% 2	492
	21st to end	Day	8% 7% 30% 32% 19% 4	500
May	1st to 10th	Day	12% 9% 27% 29% 18% 5%	503
	11th to 20th	Day	10% 5% 21% 33% 23% 8%	527
	21st to end	Day	7% 2 15% 38% 26% 12%	573
June	1st to 10th	Day	10% 2 13% 33% 27% 15%	530
	11th to 20th	Day	8% 3 12% 29% 29% 19%	530
	21st to end	Day	10% 1 10% 28% 28% 23%	530
July	1st to 10th	Day	7% 1 7% 21% 37% 27%	525
	11th to 20th	Day	8% 3 3 15% 40% 31%	524
	21st to end	Day	5% 1 7% 22% 39% 25%	576
August	1st to 10th	Day	5% 1 4 22% 38% 30%	526
	11th to 20th	Day	8% 5% 17% 36% 34%	519
	21st to end	Day	9% 3 9% 22% 34% 24%	583
September	1st to 10th	Day	8% 2 9% 25% 38% 18%	530
	11th to 20th	Day	10% 3 10% 26% 37% 14%	530
	21st to end	Day	8% 4 12% 30% 33% 12%	530
October	1st to 10th	Day	9% 4 18% 38% 25% 7%	530
	11th to 20th	Day	6% 5% 21% 32% 29% 7%	415
	21st to end	Day	14% 8% 26% 31% 17% 4	363
November	1st to 10th	Day	14% 7% 26% 32% 19% 2	330
	11th to 20th	Day	17% 8% 26% 31% 15% 2	321
	21st to end	Day	15% 11% 30% 28% 13% 3	300
December	1st to 10th	Day	17% 10% 35% 27% 10% 1	300
	11th to 20th	Day	19% 13% 36% 24% 7% 1	300
	21st to end	Day	25% 9% 32% 22% 9% 2	330
January	1st to 10th	Night	18% 11% 32% 33% 6%	800
	11th to 20th	Night	16% 11% 29% 35% 9%	800
	21st to end	Night	22% 10% 32% 30% 5%	880
February	1st to 10th	Night	17% 11% 33% 32% 8%	800
	11th to 20th	Night	22% 11% 32% 27% 8%	783
	21st to end	Night	18% 13% 37% 28% 4	660
March	1st to 10th	Night	16% 11% 32% 33% 9%	800
	11th to 20th	Night	15% 8% 31% 31% 14% 1	685
	21st to end	Night	13% 8% 27% 37% 15%	660
April	1st to 10th	Night	16% 9% 27% 32% 15% 1	600
	11th to 20th	Night	12% 6% 32% 30% 19% 1	593
	21st to end	Night	9% 5% 22% 37% 26% 2	600
May	1st to 10th	Night	10% 5% 17% 40% 26% 3	600
	11th to 20th	Night	7% 2 16% 39% 31% 5%	591
	21st to end	Night	6% 2 10% 34% 41% 8%	650
June	1st to 10th	Night	9% 2 5% 31% 43% 10%	600
	11th to 20th	Night	4 1 5% 25% 51% 14%	600
	21st to end	Night	8% 1 6% 22% 46% 18%	600
July	1st to 10th	Night	5% 2 3 17% 50% 23%	585
	11th to 20th	Night	3 1 2 11% 45% 38%	582
	21st to end	Night	5% 2 15% 51% 27%	657
August	1st to 10th	Night	2 2 15% 46% 35%	597
	11th to 20th	Night	7% 1 1 11% 49% 31%	594
	21st to end	Night	9% 1 4 18% 45% 22%	660
September	1st to 10th	Night	9% 1 7% 21% 45% 19%	600
	11th to 20th	Night	10% 2 7% 23% 47% 10%	726
	21st to end	Night	9% 1 10% 31% 42% 8%	800
October	1st to 10th	Night	9% 2 17% 37% 31% 4	800
	11th to 20th	Night	8% 4 18% 33% 31% 6%	800
	21st to end	Night	11% 6% 19% 38% 24% 3	880
November	1st to 10th	Night	11% 4 20% 40% 23% 4	820
	11th to 20th	Night	13% 6% 26% 36% 18% 1	829
	21st to end	Night	12% 8% 27% 35% 18% 1	800
December	1st to 10th	Night	14% 10% 30% 29% 16% 1	800
	11th to 20th	Night	18% 7% 29% 33% 13% 1	800
	21st to end	Night	23% 10% 29% 29% 9%	880

Page generated at 2025-11-14 23:55:56. Version ac07

Copyright © 2025 Attilla Danko.