Bryan College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bryan College clear sky chart from 2005-11-06 to 2025-08-05.

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	13% 7% 3 6% 5% 5% 5% 4 6% 8% 39%	125427
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 42%	122664
Transparency	Day	42% 3 12% 23% 16% 3	129164
	Night	40% 3 10% 24% 18% 4	126995
Seeing	Day	17% 8% 21% 24% 20% 10%	15695
	Night	16% 7% 22% 32% 20% 3	25703

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	16% 11% 3 6% 3 3 4 4 5% 5% 41%	4056
	11th to 20th	Day	15% 7% 4 7% 5% 3 4 2 4 5% 45%	4060
	21st to end	Day	21% 8% 2 6% 3 3 3 3 5% 7% 38%	4647
February	1st to 10th	Day	18% 9% 3 7% 5% 4 4 3 5% 6% 36%	2000
	11th to 20th	Day	22% 8% 3 6% 4 4 3 3 5% 5% 35%	1948
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 6% 38%	1650
March	1st to 10th	Day	19% 9% 2 6% 4 5% 5% 4 5% 6% 34%	4498
	11th to 20th	Day	13% 6% 3 6% 4 3 4 3 5% 5% 49%	4980
	21st to end	Day	14% 6% 3 6% 4 4 4 3 5% 6% 43%	5465
April	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 7% 7% 42%	2356
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 6% 6% 45%	2374
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	2545
May	1st to 10th	Day	16% 9% 3 8% 5% 5% 6% 5% 7% 8% 30%	5862
	11th to 20th	Day	16% 8% 3 9% 5% 6% 5% 4 6% 7% 29%	5861
	21st to end	Day	15% 8% 3 7% 4 4 5% 4 5% 8% 38%	6433
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 8% 10% 39%	2600
	11th to 20th	Day	5% 4 2 5% 5% 6% 6% 6% 9% 12% 41%	2600
	21st to end	Day	6% 5% 2 5% 5% 5% 6% 5% 8% 12% 39%	2600
July	1st to 10th	Day	5% 4 2 6% 5% 6% 8% 6% 8% 11% 38%	5900
	11th to 20th	Day	8% 4 2 7% 7% 6% 7% 6% 9% 12% 31%	5900
	21st to end	Day	11% 8% 4 10% 7% 7% 8% 6% 8% 10% 22%	6424
August	1st to 10th	Day	6% 4 2 6% 5% 6% 7% 6% 10% 10% 40%	4156
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 5% 8% 10% 42%	3768
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 8% 49%	4180
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 8% 40%	2153
	11th to 20th	Day	14% 5% 2 6% 5% 4 5% 4 7% 8% 40%	2090
	21st to end	Day	14% 5% 2 5% 3 4 4 3 5% 7% 48%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 5% 55%	2090
	11th to 20th	Day	12% 5% 1 4 3 3 4 2 4 6% 56%	2008
	21st to end	Day	14% 5% 2 4 4 3 4 4 5% 7% 49%	2002
November	1st to 10th	Day	11% 5% 2 5% 4 3 4 4 4 4 54%	1762
	11th to 20th	Day	14% 5% 2 6% 4 3 4 3 5% 6% 47%	1800
	21st to end	Day	15% 6% 2 6% 3 4 4 4 4 6% 46%	1800
December	1st to 10th	Day	17% 7% 2 5% 4 3 4 3 4 4 46%	2930
	11th to 20th	Day	19% 10% 3 8% 6% 5% 4 4 4 4 32%	3373
	21st to end	Day	20% 7% 3 7% 4 4 4 3 6% 7% 34%	4466
January	1st to 10th	Night	15% 9% 2 7% 4 4 3 3 4 5% 43%	5889
	11th to 20th	Night	18% 7% 3 6% 4 3 3 3 5% 5% 43%	5900
	21st to end	Night	18% 9% 2 6% 4 3 3 3 5% 6% 41%	6306
February	1st to 10th	Night	16% 7% 3 6% 5% 5% 4 3 5% 7% 40%	2400
	11th to 20th	Night	22% 7% 4 7% 5% 4 4 4 4 4 36%	2338
	21st to end	Night	22% 8% 3 6% 3 4 3 3 5% 5% 36%	1980
March	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 5% 6% 35%	5355
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 50%	4980
	21st to end	Night	15% 6% 3 7% 4 5% 4 3 4 6% 42%	5467
April	1st to 10th	Night	12% 5% 1 5% 4 4 3 3 6% 7% 48%	2060
	11th to 20th	Night	13% 5% 2 6% 4 3 3 3 5% 6% 50%	1975
	21st to end	Night	11% 5% 2 5% 4 3 5% 4 6% 7% 48%	1854
May	1st to 10th	Night	12% 7% 3 8% 6% 5% 6% 5% 7% 9% 32%	4033
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 5% 8% 30%	4032
	21st to end	Night	15% 7% 2 6% 4 4 4 4 6% 8% 39%	4421
June	1st to 10th	Night	8% 6% 2 7% 5% 6% 7% 5% 6% 8% 41%	1800
	11th to 20th	Night	5% 3 1 3 4 4 5% 4 8% 13% 50%	1800
	21st to end	Night	6% 4 2 6% 4 5% 6% 5% 7% 11% 44%	1800
July	1st to 10th	Night	7% 5% 2 6% 5% 6% 6% 5% 8% 12% 38%	4058
	11th to 20th	Night	8% 4 2 5% 5% 5% 5% 5% 8% 13% 39%	4057
	21st to end	Night	10% 8% 3 9% 6% 6% 7% 5% 8% 12% 26%	4427
August	1st to 10th	Night	4 3 2 5% 4 5% 5% 4 8% 10% 48%	2861
	11th to 20th	Night	6% 4 2 5% 5% 4 4 4 6% 9% 50%	3057
	21st to end	Night	6% 3 1 4 4 4 5% 4 6% 9% 53%	3476
September	1st to 10th	Night	9% 6% 3 7% 5% 4 5% 4 6% 9% 43%	2006
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 5% 7% 43%	2090
	21st to end	Night	11% 5% 2 5% 3 3 4 3 5% 6% 51%	2090
October	1st to 10th	Night	11% 4 1 4 3 3 3 2 4 6% 59%	2090
	11th to 20th	Night	13% 4 2 5% 3 4 3 3 5% 5% 55%	2171
	21st to end	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2593
November	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 4 6% 52%	2536
	11th to 20th	Night	13% 6% 2 6% 4 3 3 3 4 7% 50%	2600
	21st to end	Night	17% 7% 2 5% 4 3 4 4 5% 6% 44%	2600
December	1st to 10th	Night	18% 8% 2 6% 4 4 4 3 4 5% 42%	4250
	11th to 20th	Night	21% 8% 3 7% 4 3 3 3 4 5% 39%	4822
	21st to end	Night	20% 6% 3 7% 4 5% 5% 4 6% 7% 32%	6490

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	46% 2 6% 25% 20% 1	4057
	11th to 20th	Day	44% 2 5% 21% 27% 2	4060
	21st to end	Day	47% 2 7% 25% 17% 3	4647
February	1st to 10th	Day	49% 3 8% 20% 17% 3	2000
	11th to 20th	Day	51% 3 7% 20% 16% 3	1958
	21st to end	Day	48% 2 8% 17% 19% 6%	1650
March	1st to 10th	Day	51% 2 7% 14% 18% 8%	4498
	11th to 20th	Day	38% 2 5% 22% 22% 11%	4980
	21st to end	Day	43% 2 7% 32% 14% 1	5465
April	1st to 10th	Day	40% 3 11% 24% 18% 3	2356
	11th to 20th	Day	39% 2 9% 21% 24% 5%	2374
	21st to end	Day	41% 3 11% 28% 15% 2	2545
May	1st to 10th	Day	51% 3 13% 21% 10% 1	5897
	11th to 20th	Day	53% 3 15% 20% 8%	5865
	21st to end	Day	45% 3 10% 22% 17% 3	6447
June	1st to 10th	Day	40% 5% 17% 23% 14% 2	2600
	11th to 20th	Day	32% 6% 20% 25% 14% 2	2600
	21st to end	Day	36% 7% 19% 20% 15% 3	2600
July	1st to 10th	Day	38% 6% 20% 22% 14% 1	5835
	11th to 20th	Day	42% 5% 28% 20% 4 1	5831
	21st to end	Day	55% 5% 18% 18% 4	6240
August	1st to 10th	Day	35% 6% 16% 33% 11% 1	4143
	11th to 20th	Day	33% 5% 18% 27% 15% 2	3805
	21st to end	Day	32% 4 13% 35% 16% 2	4179
September	1st to 10th	Day	41% 5% 13% 19% 17% 6%	2153
	11th to 20th	Day	41% 5% 11% 22% 18% 3	2090
	21st to end	Day	37% 3 12% 22% 20% 6%	2090
October	1st to 10th	Day	24% 2 5% 23% 33% 13%	3480
	11th to 20th	Day	23% 1 5% 26% 32% 12%	3313
	21st to end	Day	31% 1 8% 26% 25% 8%	3278
November	1st to 10th	Day	34% 3 8% 23% 26% 6%	1762
	11th to 20th	Day	38% 3 6% 25% 24% 5%	1800
	21st to end	Day	40% 2 8% 26% 19% 4	1800
December	1st to 10th	Day	42% 2 5% 26% 23% 2	2930
	11th to 20th	Day	56% 2 6% 21% 12% 3	3370
	21st to end	Day	49% 2 13% 25% 10% 2	4466
January	1st to 10th	Night	45% 2 7% 26% 19% 2	5889
	11th to 20th	Night	43% 2 5% 21% 24% 5%	5900
	21st to end	Night	46% 1 5% 23% 19% 6%	6306
February	1st to 10th	Night	45% 2 10% 23% 17% 3	2400
	11th to 20th	Night	52% 2 7% 19% 15% 5%	2339
	21st to end	Night	51% 3 6% 18% 18% 5%	1980
March	1st to 10th	Night	51% 2 6% 18% 19% 4	5355
	11th to 20th	Night	34% 2 7% 22% 22% 14%	4980
	21st to end	Night	45% 1 6% 28% 16% 3	5467
April	1st to 10th	Night	35% 3 11% 25% 22% 4	2060
	11th to 20th	Night	35% 3 8% 23% 24% 7%	1975
	21st to end	Night	36% 4 13% 29% 17% 2	1854
May	1st to 10th	Night	49% 3 16% 22% 10% 1	4060
	11th to 20th	Night	53% 3 15% 18% 10%	4033
	21st to end	Night	44% 3 12% 25% 15% 1	4429
June	1st to 10th	Night	39% 7% 14% 25% 13% 2	1800
	11th to 20th	Night	25% 6% 23% 29% 16% 2	1800
	21st to end	Night	32% 8% 17% 26% 14% 4	1800
July	1st to 10th	Night	37% 7% 20% 24% 11% 1	4015
	11th to 20th	Night	35% 4 31% 23% 5% 2	4006
	21st to end	Night	49% 7% 21% 17% 5% 1	4297
August	1st to 10th	Night	30% 5% 15% 36% 14% 1	2850
	11th to 20th	Night	30% 4 22% 28% 16% 1	3086
	21st to end	Night	27% 4 14% 36% 18% 1	3476
September	1st to 10th	Night	37% 5% 15% 21% 16% 6%	2006
	11th to 20th	Night	40% 5% 12% 20% 21% 1	2090
	21st to end	Night	35% 4 9% 23% 23% 6%	2090
October	1st to 10th	Night	21% 2 5% 25% 31% 16%	3480
	11th to 20th	Night	21% 1 5% 23% 34% 16%	3605
	21st to end	Night	27% 2 5% 28% 29% 10%	4267
November	1st to 10th	Night	34% 2 8% 23% 24% 8%	2536
	11th to 20th	Night	36% 2 5% 23% 26% 7%	2600
	21st to end	Night	42% 2 6% 25% 21% 4	2600
December	1st to 10th	Night	46% 2 6% 22% 23% 2	4250
	11th to 20th	Night	49% 2 5% 24% 19% 1	4824
	21st to end	Night	52% 2 11% 22% 12% 1	6490

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	25% 19% 30% 21% 4 1	300
	11th to 20th	Day	26% 20% 33% 14% 6% 2	300
	21st to end	Day	23% 13% 41% 19% 4	330
February	1st to 10th	Day	23% 18% 36% 17% 6%	300
	11th to 20th	Day	36% 14% 34% 12% 3 1	300
	21st to end	Day	35% 18% 33% 11% 4	249
March	1st to 10th	Day	25% 18% 32% 18% 6% 1	305
	11th to 20th	Day	24% 14% 30% 25% 7%	500
	21st to end	Day	21% 12% 33% 26% 7%	550
April	1st to 10th	Day	19% 16% 24% 28% 11% 3	500
	11th to 20th	Day	18% 10% 32% 24% 14% 1	492
	21st to end	Day	17% 7% 31% 28% 13% 4	500
May	1st to 10th	Day	17% 11% 27% 26% 14% 6%	503
	11th to 20th	Day	15% 6% 24% 25% 20% 10%	527
	21st to end	Day	15% 6% 17% 24% 20% 17%	573
June	1st to 10th	Day	12% 4 15% 27% 27% 14%	530
	11th to 20th	Day	7% 3 12% 27% 29% 22%	530
	21st to end	Day	9% 3 10% 28% 28% 22%	530
July	1st to 10th	Day	9% 3 7% 22% 31% 27%	525
	11th to 20th	Day	10% 2 7% 23% 30% 27%	524
	21st to end	Day	11% 2 6% 23% 34% 24%	576
August	1st to 10th	Day	12% 3 8% 23% 34% 20%	502
	11th to 20th	Day	13% 3 8% 29% 34% 13%	479
	21st to end	Day	14% 2 6% 21% 34% 24%	539
September	1st to 10th	Day	11% 2 8% 26% 33% 19%	490
	11th to 20th	Day	15% 2 9% 23% 32% 18%	490
	21st to end	Day	17% 2 13% 23% 32% 12%	490
October	1st to 10th	Day	13% 4 18% 24% 29% 11%	490
	11th to 20th	Day	12% 9% 22% 29% 22% 5%	490
	21st to end	Day	18% 6% 21% 32% 20% 4	451
November	1st to 10th	Day	19% 6% 25% 28% 16% 5%	300
	11th to 20th	Day	14% 12% 32% 33% 8% 1	300
	21st to end	Day	14% 12% 34% 25% 13% 1	300
December	1st to 10th	Day	29% 11% 28% 23% 8% 1	300
	11th to 20th	Day	20% 15% 29% 24% 11% 1	300
	21st to end	Day	29% 13% 25% 22% 9%	330
January	1st to 10th	Night	24% 11% 37% 24% 4	800
	11th to 20th	Night	23% 13% 33% 26% 6%	800
	21st to end	Night	21% 10% 35% 32% 2	880
February	1st to 10th	Night	20% 11% 33% 31% 5%	800
	11th to 20th	Night	26% 15% 33% 24% 2	783
	21st to end	Night	28% 12% 35% 24% 2	660
March	1st to 10th	Night	20% 12% 31% 33% 5%	800
	11th to 20th	Night	20% 10% 33% 29% 7% 1	800
	21st to end	Night	18% 11% 31% 33% 7% 1	880
April	1st to 10th	Night	15% 8% 31% 35% 9% 1	660
	11th to 20th	Night	16% 7% 30% 34% 12%	593
	21st to end	Night	13% 7% 26% 41% 13% 1	600
May	1st to 10th	Night	14% 4 26% 35% 19% 2	600
	11th to 20th	Night	15% 5% 19% 34% 22% 5%	591
	21st to end	Night	12% 2 14% 32% 34% 6%	650
June	1st to 10th	Night	11% 2 12% 35% 35% 5%	600
	11th to 20th	Night	6% 2 10% 35% 37% 11%	600
	21st to end	Night	6% 2 6% 34% 42% 10%	600
July	1st to 10th	Night	12% 3 5% 25% 44% 11%	585
	11th to 20th	Night	12% 2 5% 25% 44% 13%	582
	21st to end	Night	8% 3 6% 24% 47% 11%	657
August	1st to 10th	Night	7% 2 5% 28% 47% 11%	579
	11th to 20th	Night	12% 2 6% 34% 40% 6%	564
	21st to end	Night	12% 2 4 27% 45% 10%	627
September	1st to 10th	Night	10% 3 9% 29% 41% 8%	676
	11th to 20th	Night	15% 3 9% 27% 40% 6%	760
	21st to end	Night	14% 1 13% 34% 34% 3	760
October	1st to 10th	Night	12% 5% 15% 31% 29% 8%	760
	11th to 20th	Night	14% 5% 22% 36% 21% 2	760
	21st to end	Night	16% 5% 18% 42% 16% 3	836
November	1st to 10th	Night	15% 7% 20% 37% 19% 2	780
	11th to 20th	Night	15% 7% 31% 33% 12% 1	800
	21st to end	Night	19% 10% 27% 33% 12% 1	800
December	1st to 10th	Night	24% 12% 26% 30% 7%	800
	11th to 20th	Night	21% 8% 29% 35% 7%	800
	21st to end	Night	27% 9% 25% 33% 6%	880

Page generated at 2025-08-02 01:32:27. Version ac07

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