Bryan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bryan clear sky chart from 2005-11-06 to 2026-02-16.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	131169
	Night	14% 6% 2 5% 3 3 4 3 5% 7% 49%	129974
Transparency	Day	37% 4 11% 21% 18% 8%	134860
	Night	35% 4 10% 21% 20% 11%	134347
Seeing	Day	14% 6% 20% 26% 25% 9%	16567
	Night	15% 6% 25% 35% 17% 2	26566

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	17% 9% 2 5% 3 3 3 3 4 6% 46%	5289
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 6% 53%	5310
	21st to end	Day	27% 8% 2 7% 5% 3 2 2 3 5% 35%	5812
February	1st to 10th	Day	21% 8% 2 7% 4 3 3 3 4 6% 40%	2054
	11th to 20th	Day	22% 8% 2 5% 4 4 3 2 3 6% 40%	1999
	21st to end	Day	20% 7% 2 5% 4 3 3 3 4 5% 43%	1743
March	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 41%	4936
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 4 6% 48%	4980
	21st to end	Day	17% 8% 2 7% 4 3 4 3 5% 6% 40%	5462
April	1st to 10th	Day	13% 10% 3 7% 5% 3 5% 4 5% 6% 39%	2200
	11th to 20th	Day	14% 8% 2 7% 5% 4 4 3 5% 6% 40%	2273
	21st to end	Day	13% 7% 3 6% 5% 4 4 4 5% 7% 44%	2400
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 6% 7% 34%	5862
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	5862
	21st to end	Day	10% 6% 2 8% 5% 6% 7% 5% 8% 10% 33%	6434
June	1st to 10th	Day	6% 4 2 5% 5% 5% 6% 5% 8% 11% 44%	2600
	11th to 20th	Day	6% 4 1 5% 5% 5% 6% 5% 7% 11% 47%	2600
	21st to end	Day	5% 5% 2 7% 6% 5% 7% 6% 10% 10% 38%	2600
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 4 4 7% 11% 39%	5900
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 5% 8% 12% 42%	5900
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	6422
August	1st to 10th	Day	2 1 1 2 2 3 3 3 5% 8% 70%	4234
	11th to 20th	Day	3 1 1 3 3 4 4 4 7% 12% 57%	4153
	21st to end	Day	5% 4 1 5% 4 6% 5% 5% 8% 11% 46%	4052
September	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 5% 7% 8% 45%	2200
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 7% 44%	2200
	21st to end	Day	6% 4 1 5% 4 4 6% 5% 6% 6% 52%	2200
October	1st to 10th	Day	5% 3 2 5% 4 3 4 3 4 7% 61%	2136
	11th to 20th	Day	12% 5% 2 3 3 3 4 3 4 5% 57%	2000
	21st to end	Day	13% 6% 2 4 3 3 3 2 3 4 58%	2200
November	1st to 10th	Day	11% 6% 2 5% 3 4 4 4 4 8% 48%	2058
	11th to 20th	Day	11% 6% 3 5% 3 3 3 2 4 6% 53%	2100
	21st to end	Day	18% 6% 3 6% 5% 3 3 4 5% 5% 43%	1900
December	1st to 10th	Day	22% 7% 2 5% 3 3 3 2 4 5% 42%	3030
	11th to 20th	Day	20% 7% 2 6% 3 4 3 4 5% 7% 40%	3481
	21st to end	Day	15% 7% 3 7% 3 3 4 2 4 5% 47%	4587
January	1st to 10th	Night	18% 6% 2 4 3 3 3 2 3 5% 51%	7634
	11th to 20th	Night	12% 4 1 3 2 3 4 3 4 5% 58%	7680
	21st to end	Night	29% 7% 2 6% 4 3 3 3 4 5% 35%	8402
February	1st to 10th	Night	20% 7% 3 5% 3 3 3 2 4 5% 46%	2583
	11th to 20th	Night	21% 7% 3 4 3 3 3 3 4 5% 45%	2398
	21st to end	Night	22% 7% 2 5% 3 3 3 2 5% 5% 43%	1885
March	1st to 10th	Night	18% 8% 2 6% 4 4 3 3 4 7% 41%	4919
	11th to 20th	Night	16% 7% 2 6% 4 3 3 2 4 5% 48%	4980
	21st to end	Night	19% 10% 2 6% 3 3 3 2 4 5% 43%	5467
April	1st to 10th	Night	13% 6% 2 6% 4 4 5% 3 5% 7% 46%	2200
	11th to 20th	Night	13% 5% 2 6% 4 4 4 3 5% 8% 46%	2075
	21st to end	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	1995
May	1st to 10th	Night	19% 9% 3 8% 4 4 4 3 5% 8% 33%	4053
	11th to 20th	Night	10% 5% 2 7% 5% 5% 5% 4 6% 7% 44%	4053
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 7% 10% 37%	4443
June	1st to 10th	Night	5% 4 1 4 3 3 4 3 8% 12% 55%	1800
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 60%	1800
	21st to end	Night	4 3 2 4 5% 4 4 4 7% 11% 50%	1800
July	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 4 7% 13% 41%	4078
	11th to 20th	Night	3 4 1 4 3 3 4 4 6% 12% 56%	4077
	21st to end	Night	8% 5% 2 6% 3 4 5% 4 7% 10% 46%	4449
August	1st to 10th	Night	1 1 2 1 2 3 2 5% 9% 74%	2926
	11th to 20th	Night	3 2 1 3 2 3 4 4 7% 12% 60%	2903
	21st to end	Night	3 4 1 4 3 4 5% 4 8% 12% 52%	3840
September	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 5% 9% 50%	2200
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 4 5% 7% 48%	2200
	21st to end	Night	6% 4 1 5% 2 3 4 3 6% 8% 58%	2200
October	1st to 10th	Night	4 3 1 4 3 3 3 3 4 7% 64%	2241
	11th to 20th	Night	11% 4 1 3 3 3 2 2 4 5% 61%	2400
	21st to end	Night	13% 4 1 3 3 2 3 2 3 4 61%	2640
November	1st to 10th	Night	12% 5% 1 5% 3 3 3 3 4 6% 56%	2460
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 4 6% 54%	2520
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 6% 47%	2714
December	1st to 10th	Night	22% 8% 2 6% 4 3 3 2 4 6% 41%	4380
	11th to 20th	Night	19% 8% 2 6% 3 3 3 2 4 4 45%	4946
	21st to end	Night	16% 6% 2 4 3 2 3 2 3 4 54%	6633

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	41% 2 6% 25% 19% 7%	5290
	11th to 20th	Day	34% 3 4 19% 28% 12%	5310
	21st to end	Day	55% 2 3 12% 17% 12%	5812
February	1st to 10th	Day	48% 2 5% 14% 20% 12%	2054
	11th to 20th	Day	48% 2 7% 17% 18% 9%	2009
	21st to end	Day	45% 3 6% 17% 17% 13%	1743
March	1st to 10th	Day	44% 3 6% 15% 20% 12%	4936
	11th to 20th	Day	38% 3 7% 11% 18% 23%	4980
	21st to end	Day	45% 4 8% 20% 18% 6%	5464
April	1st to 10th	Day	45% 5% 7% 18% 15% 11%	2200
	11th to 20th	Day	45% 3 8% 16% 18% 10%	2273
	21st to end	Day	39% 4 9% 20% 22% 6%	2400
May	1st to 10th	Day	48% 5% 10% 21% 12% 3	5900
	11th to 20th	Day	38% 4 13% 18% 23% 3	5866
	21st to end	Day	43% 6% 11% 26% 13% 2	6447
June	1st to 10th	Day	31% 6% 14% 30% 16% 2	2600
	11th to 20th	Day	30% 6% 14% 28% 18% 4	2600
	21st to end	Day	36% 7% 15% 27% 14% 2	2600
July	1st to 10th	Day	38% 5% 26% 27% 4	5836
	11th to 20th	Day	32% 6% 22% 28% 11% 1	5831
	21st to end	Day	37% 6% 18% 27% 13% 1	6240
August	1st to 10th	Day	13% 4 14% 42% 26% 1	4220
	11th to 20th	Day	19% 5% 29% 36% 10% 2	4192
	21st to end	Day	31% 8% 21% 25% 14% 1	4051
September	1st to 10th	Day	34% 7% 11% 23% 17% 8%	2200
	11th to 20th	Day	38% 6% 13% 20% 18% 5%	2200
	21st to end	Day	29% 6% 10% 23% 18% 14%	2200
October	1st to 10th	Day	15% 2 6% 13% 22% 41%	3474
	11th to 20th	Day	20% 2 6% 18% 35% 20%	3240
	21st to end	Day	25% 3 4 22% 31% 15%	3538
November	1st to 10th	Day	35% 3 8% 19% 23% 11%	2058
	11th to 20th	Day	34% 3 7% 20% 22% 14%	2100
	21st to end	Day	44% 3 7% 17% 20% 10%	1900
December	1st to 10th	Day	45% 2 7% 17% 21% 8%	3030
	11th to 20th	Day	44% 3 7% 12% 23% 10%	3479
	21st to end	Day	41% 3 5% 14% 28% 9%	4587
January	1st to 10th	Night	38% 2 6% 21% 22% 10%	7635
	11th to 20th	Night	29% 2 4 18% 30% 16%	7680
	21st to end	Night	54% 2 3 12% 17% 12%	8402
February	1st to 10th	Night	43% 3 6% 12% 21% 16%	2583
	11th to 20th	Night	44% 3 6% 16% 19% 13%	2398
	21st to end	Night	44% 3 7% 14% 17% 15%	1885
March	1st to 10th	Night	44% 3 6% 14% 21% 11%	4919
	11th to 20th	Night	40% 3 6% 15% 14% 22%	4980
	21st to end	Night	46% 3 7% 16% 19% 9%	5467
April	1st to 10th	Night	38% 4 9% 19% 18% 13%	2200
	11th to 20th	Night	37% 4 11% 17% 18% 14%	2075
	21st to end	Night	38% 4 9% 20% 22% 7%	1995
May	1st to 10th	Night	50% 5% 9% 23% 10% 4	4080
	11th to 20th	Night	39% 4 13% 20% 20% 4	4054
	21st to end	Night	41% 5% 14% 26% 12% 1	4452
June	1st to 10th	Night	22% 5% 19% 31% 21% 2	1800
	11th to 20th	Night	19% 6% 17% 34% 19% 5%	1800
	21st to end	Night	27% 6% 19% 30% 17% 2	1800
July	1st to 10th	Night	34% 6% 30% 25% 4	4035
	11th to 20th	Night	23% 6% 24% 37% 11%	4026
	21st to end	Night	32% 7% 21% 27% 11% 2	4320
August	1st to 10th	Night	9% 4 15% 41% 28% 2	2916
	11th to 20th	Night	17% 5% 30% 35% 11% 1	2930
	21st to end	Night	23% 10% 23% 29% 13% 2	3840
September	1st to 10th	Night	29% 7% 18% 22% 16% 8%	2200
	11th to 20th	Night	35% 7% 14% 22% 17% 7%	2200
	21st to end	Night	25% 4 14% 24% 20% 14%	2200
October	1st to 10th	Night	13% 3 6% 16% 20% 42%	3670
	11th to 20th	Night	16% 2 4 21% 33% 25%	3899
	21st to end	Night	21% 3 4 23% 32% 17%	4252
November	1st to 10th	Night	31% 3 9% 20% 24% 13%	2460
	11th to 20th	Night	32% 3 8% 20% 22% 15%	2520
	21st to end	Night	39% 3 8% 18% 19% 13%	2714
December	1st to 10th	Night	47% 2 4 17% 21% 8%	4380
	11th to 20th	Night	45% 2 7% 9% 23% 14%	4947
	21st to end	Night	36% 2 4 16% 30% 12%	6633

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% 12% 30% 24% 7% 2	330
	11th to 20th	Day	23% 12% 33% 24% 7% 1	330
	21st to end	Day	25% 13% 37% 18% 8% 1	363
February	1st to 10th	Day	27% 13% 32% 21% 7%	330
	11th to 20th	Day	30% 16% 30% 18% 5%	315
	21st to end	Day	29% 16% 34% 17% 4	249
March	1st to 10th	Day	23% 15% 36% 19% 7%	300
	11th to 20th	Day	22% 15% 38% 20% 4 2	300
	21st to end	Day	20% 12% 41% 19% 8% 1	330
April	1st to 10th	Day	22% 15% 35% 23% 4 1	300
	11th to 20th	Day	25% 12% 30% 24% 9% 2	391
	21st to end	Day	19% 9% 34% 27% 10% 2	500
May	1st to 10th	Day	17% 7% 37% 29% 10% 1	703
	11th to 20th	Day	14% 7% 27% 32% 16% 4	725
	21st to end	Day	12% 5% 25% 35% 19% 4	789
June	1st to 10th	Day	7% 2 14% 37% 30% 10%	730
	11th to 20th	Day	7% 2 12% 41% 31% 6%	730
	21st to end	Day	6% 3 9% 27% 40% 15%	730
July	1st to 10th	Day	9% 3 6% 29% 38% 16%	721
	11th to 20th	Day	4 2 4 29% 43% 20%	718
	21st to end	Day	6% 2 4 23% 47% 18%	794
August	1st to 10th	Day	4 1 2 21% 53% 21%	726
	11th to 20th	Day	5% 1 2 21% 52% 20%	710
	21st to end	Day	9% 3 3 17% 39% 29%	427
September	1st to 10th	Day	5% 1 7% 23% 35% 29%	330
	11th to 20th	Day	8% 4 25% 39% 25%	330
	21st to end	Day	8% 2 7% 29% 35% 18%	330
October	1st to 10th	Day	4 1 12% 33% 39% 12%	330
	11th to 20th	Day	11% 4 23% 28% 25% 9%	330
	21st to end	Day	24% 7% 23% 22% 19% 5%	363
November	1st to 10th	Day	17% 5% 20% 32% 19% 7%	330
	11th to 20th	Day	17% 6% 25% 34% 15% 3	330
	21st to end	Day	23% 13% 29% 21% 12% 2	330
December	1st to 10th	Day	23% 5% 33% 21% 12% 5%	330
	11th to 20th	Day	27% 9% 31% 22% 9% 2	330
	21st to end	Day	22% 8% 34% 25% 10% 1	363
January	1st to 10th	Night	22% 9% 31% 32% 7%	1050
	11th to 20th	Night	21% 12% 30% 29% 8%	1050
	21st to end	Night	22% 9% 31% 32% 6%	1155
February	1st to 10th	Night	23% 11% 34% 27% 4	903
	11th to 20th	Night	27% 10% 32% 27% 4	804
	21st to end	Night	26% 11% 40% 20% 3	565
March	1st to 10th	Night	23% 9% 40% 24% 5%	600
	11th to 20th	Night	19% 9% 38% 27% 7%	600
	21st to end	Night	16% 8% 43% 27% 5%	660
April	1st to 10th	Night	16% 10% 39% 31% 5%	600
	11th to 20th	Night	15% 11% 36% 31% 7%	593
	21st to end	Night	18% 8% 37% 28% 9%	600
May	1st to 10th	Night	15% 9% 38% 31% 6% 1	600
	11th to 20th	Night	14% 4 31% 37% 12% 2	591
	21st to end	Night	10% 2 29% 42% 16% 1	650
June	1st to 10th	Night	6% 2 17% 47% 26% 3	600
	11th to 20th	Night	4 1 23% 48% 22% 2	600
	21st to end	Night	5% 1 11% 47% 32% 5%	600
July	1st to 10th	Night	6% 2 6% 45% 36% 6%	585
	11th to 20th	Night	3 1 8% 48% 36% 4	582
	21st to end	Night	4 1 6% 47% 37% 5%	657
August	1st to 10th	Night	2 1 5% 49% 40% 4	597
	11th to 20th	Night	4 1 3 48% 37% 6%	594
	21st to end	Night	4 2 5% 35% 48% 6%	660
September	1st to 10th	Night	6% 2 8% 37% 40% 7%	600
	11th to 20th	Night	11% 1 5% 35% 43% 6%	600
	21st to end	Night	7% 1 12% 36% 38% 6%	600
October	1st to 10th	Night	5% 1 12% 45% 32% 5%	641
	11th to 20th	Night	13% 3 20% 42% 21% 2	800
	21st to end	Night	14% 7% 26% 32% 18% 3	880
November	1st to 10th	Night	14% 4 24% 37% 20% 1	820
	11th to 20th	Night	13% 7% 26% 40% 13% 1	840
	21st to end	Night	20% 9% 29% 29% 13% 1	1034
December	1st to 10th	Night	22% 7% 29% 31% 11%	1050
	11th to 20th	Night	23% 9% 27% 33% 7%	1050
	21st to end	Night	22% 7% 30% 32% 9% 1	1155

Page generated at 2026-02-13 00:42:14. Version ac07

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