Brasstown Bald
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brasstown Bald clear sky chart from 2005-11-06 to 2026-03-18.

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	12% 8% 3 8% 5% 5% 5% 4 6% 7% 37%	131246
	Night	13% 8% 3 8% 5% 4 4 3 5% 7% 40%	130276
Transparency	Day	42% 7% 11% 18% 16% 5%	135009
	Night	41% 7% 12% 18% 17% 6%	134583
Seeing	Day	20% 14% 24% 20% 15% 8%	16662
	Night	18% 12% 20% 27% 19% 4	26780

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% 9% 3 7% 4 4 3 3 5% 5% 41%	5258
	11th to 20th	Day	10% 7% 2 6% 4 5% 3 2 3 5% 54%	5280
	21st to end	Day	18% 11% 4 8% 4 3 3 2 4 5% 36%	5816
February	1st to 10th	Day	15% 10% 3 6% 5% 4 4 4 4 6% 39%	2100
	11th to 20th	Day	18% 10% 4 7% 5% 4 4 3 4 6% 36%	2048
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 4 6% 37%	1730
March	1st to 10th	Day	18% 9% 3 8% 4 4 4 3 5% 6% 36%	4768
	11th to 20th	Day	11% 7% 2 6% 4 4 3 3 4 7% 50%	5057
	21st to end	Day	14% 10% 3 7% 4 3 4 3 4 5% 43%	5465
April	1st to 10th	Day	12% 7% 2 6% 6% 5% 4 5% 7% 6% 40%	2226
	11th to 20th	Day	14% 7% 3 7% 4 4 4 4 6% 6% 42%	2384
	21st to end	Day	12% 7% 2 6% 5% 4 5% 4 6% 8% 42%	2600
May	1st to 10th	Day	15% 9% 3 8% 5% 5% 6% 5% 6% 7% 30%	5862
	11th to 20th	Day	18% 10% 4 9% 6% 6% 6% 5% 6% 7% 24%	5861
	21st to end	Day	12% 8% 3 9% 5% 5% 5% 4 6% 8% 34%	6433
June	1st to 10th	Day	11% 7% 3 9% 7% 7% 6% 5% 7% 8% 30%	2600
	11th to 20th	Day	6% 6% 2 7% 6% 7% 6% 7% 9% 10% 33%	2600
	21st to end	Day	7% 5% 3 8% 6% 7% 7% 6% 8% 11% 33%	2600
July	1st to 10th	Day	5% 5% 3 9% 8% 7% 8% 6% 8% 10% 32%	5900
	11th to 20th	Day	7% 6% 3 10% 8% 8% 8% 6% 8% 11% 27%	5900
	21st to end	Day	10% 9% 4 12% 9% 8% 8% 5% 7% 8% 20%	6424
August	1st to 10th	Day	8% 7% 2 8% 7% 6% 6% 6% 9% 12% 29%	4234
	11th to 20th	Day	8% 5% 3 6% 6% 6% 7% 6% 9% 12% 32%	4052
	21st to end	Day	8% 5% 2 7% 5% 6% 6% 5% 6% 8% 43%	4289
September	1st to 10th	Day	11% 7% 3 9% 6% 6% 6% 5% 7% 7% 34%	2200
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 4 6% 7% 34%	2200
	21st to end	Day	13% 7% 2 8% 5% 5% 5% 3 6% 8% 39%	2200
October	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 5% 5% 51%	2200
	11th to 20th	Day	11% 6% 2 5% 3 4 4 3 4 5% 53%	2049
	21st to end	Day	13% 6% 2 5% 4 3 3 2 3 5% 53%	2200
November	1st to 10th	Day	11% 7% 2 4 3 3 4 2 4 5% 54%	1882
	11th to 20th	Day	13% 6% 2 5% 3 4 3 4 4 7% 50%	1890
	21st to end	Day	14% 7% 2 5% 4 4 4 4 5% 7% 44%	1890
December	1st to 10th	Day	18% 6% 2 5% 4 4 4 3 4 4 45%	3020
	11th to 20th	Day	15% 8% 4 9% 5% 5% 5% 4 4 5% 36%	3463
	21st to end	Day	16% 8% 4 8% 4 3 3 3 5% 7% 39%	4565
January	1st to 10th	Night	15% 10% 4 7% 5% 4 4 3 4 5% 42%	7635
	11th to 20th	Night	13% 9% 3 8% 4 3 3 2 3 5% 48%	7680
	21st to end	Night	18% 11% 3 7% 4 4 4 2 3 4 40%	8362
February	1st to 10th	Night	13% 8% 4 7% 5% 4 4 3 5% 7% 41%	2520
	11th to 20th	Night	19% 10% 3 7% 5% 4 3 3 4 4 37%	2458
	21st to end	Night	19% 9% 3 8% 4 4 4 3 5% 5% 35%	2076
March	1st to 10th	Night	18% 11% 5% 10% 5% 4 4 3 4 5% 31%	5305
	11th to 20th	Night	10% 6% 2 6% 3 3 4 3 6% 7% 49%	5058
	21st to end	Night	13% 8% 3 9% 4 4 4 3 4 6% 42%	5467
April	1st to 10th	Night	12% 8% 3 5% 4 3 4 3 5% 7% 45%	2190
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 7% 47%	1964
	21st to end	Night	10% 8% 3 6% 4 4 4 4 5% 5% 48%	1800
May	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 5% 6% 9% 32%	4033
	11th to 20th	Night	20% 10% 4 9% 6% 5% 5% 3 5% 7% 26%	4032
	21st to end	Night	11% 8% 4 8% 5% 5% 4 4 6% 9% 35%	4421
June	1st to 10th	Night	8% 7% 3 8% 7% 6% 5% 5% 8% 9% 35%	1800
	11th to 20th	Night	5% 5% 2 6% 5% 6% 6% 4 8% 12% 41%	1800
	21st to end	Night	7% 5% 2 5% 4 5% 5% 5% 7% 12% 42%	1800
July	1st to 10th	Night	7% 6% 3 10% 6% 6% 6% 4 7% 10% 34%	4058
	11th to 20th	Night	6% 7% 4 9% 6% 6% 6% 5% 9% 12% 31%	4057
	21st to end	Night	11% 10% 5% 11% 6% 6% 5% 5% 6% 7% 28%	4427
August	1st to 10th	Night	8% 7% 3 8% 7% 5% 5% 5% 8% 12% 32%	2915
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	2993
	21st to end	Night	7% 4 2 6% 4 4 5% 5% 7% 9% 46%	3586
September	1st to 10th	Night	10% 7% 2 8% 5% 6% 5% 4 7% 9% 37%	2189
	11th to 20th	Night	13% 7% 3 7% 4 5% 4 4 6% 8% 37%	2200
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2200
October	1st to 10th	Night	13% 6% 2 5% 3 2 4 3 4 5% 53%	2200
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 4 5% 51%	2350
	21st to end	Night	12% 7% 3 6% 4 3 3 2 4 5% 53%	2640
November	1st to 10th	Night	12% 5% 2 7% 4 4 3 3 4 6% 51%	2635
	11th to 20th	Night	12% 7% 3 5% 4 3 3 3 4 6% 49%	2730
	21st to end	Night	13% 8% 3 6% 4 4 4 4 5% 6% 42%	2730
December	1st to 10th	Night	17% 8% 3 7% 4 3 4 3 4 5% 44%	4380
	11th to 20th	Night	15% 11% 4 9% 5% 4 4 4 5% 5% 35%	4952
	21st to end	Night	16% 8% 4 8% 5% 5% 4 3 5% 6% 35%	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	43% 5% 8% 19% 20% 5%	5259
	11th to 20th	Day	32% 4 6% 13% 30% 15%	5280
	21st to end	Day	50% 4 6% 15% 16% 11%	5816
February	1st to 10th	Day	46% 5% 6% 19% 19% 5%	2100
	11th to 20th	Day	50% 4 6% 17% 18% 5%	2058
	21st to end	Day	48% 6% 8% 12% 20% 6%	1730
March	1st to 10th	Day	47% 5% 8% 13% 19% 8%	4768
	11th to 20th	Day	35% 5% 7% 15% 20% 19%	5057
	21st to end	Day	44% 4 7% 24% 17% 4	5465
April	1st to 10th	Day	40% 7% 10% 21% 18% 4	2226
	11th to 20th	Day	40% 6% 8% 17% 22% 5%	2384
	21st to end	Day	39% 6% 11% 26% 15% 3	2600
May	1st to 10th	Day	49% 8% 13% 17% 11% 1	5897
	11th to 20th	Day	55% 10% 12% 15% 7% 1	5865
	21st to end	Day	45% 8% 11% 20% 14% 1	6447
June	1st to 10th	Day	47% 10% 17% 20% 5% 1	2600
	11th to 20th	Day	39% 12% 18% 19% 10% 1	2600
	21st to end	Day	41% 12% 17% 17% 12% 2	2600
July	1st to 10th	Day	40% 13% 19% 21% 6%	5835
	11th to 20th	Day	44% 14% 24% 14% 3 1	5831
	21st to end	Day	56% 12% 15% 13% 4	6240
August	1st to 10th	Day	42% 11% 18% 23% 6%	4221
	11th to 20th	Day	38% 11% 22% 15% 12% 1	4091
	21st to end	Day	37% 9% 11% 28% 13% 1	4289
September	1st to 10th	Day	44% 10% 11% 16% 15% 3	2200
	11th to 20th	Day	46% 8% 13% 17% 16% 1	2200
	21st to end	Day	42% 6% 14% 15% 18% 5%	2200
October	1st to 10th	Day	26% 5% 7% 16% 35% 11%	3590
	11th to 20th	Day	22% 4 6% 17% 26% 25%	3315
	21st to end	Day	28% 4 8% 23% 24% 13%	3538
November	1st to 10th	Day	32% 4 8% 16% 29% 10%	1882
	11th to 20th	Day	34% 4 7% 19% 26% 10%	1890
	21st to end	Day	40% 5% 7% 17% 25% 6%	1890
December	1st to 10th	Day	42% 4 6% 16% 25% 7%	3020
	11th to 20th	Day	47% 5% 8% 16% 18% 6%	3460
	21st to end	Day	42% 6% 9% 26% 15% 2	4565
January	1st to 10th	Night	44% 4 12% 15% 22% 4	7636
	11th to 20th	Night	40% 3 5% 15% 26% 11%	7680
	21st to end	Night	47% 4 6% 15% 19% 10%	8362
February	1st to 10th	Night	43% 4 9% 19% 19% 5%	2520
	11th to 20th	Night	50% 5% 6% 16% 18% 5%	2459
	21st to end	Night	50% 5% 7% 15% 17% 6%	2076
March	1st to 10th	Night	50% 8% 7% 12% 18% 5%	5305
	11th to 20th	Night	33% 5% 8% 18% 21% 16%	5058
	21st to end	Night	43% 5% 8% 23% 15% 6%	5467
April	1st to 10th	Night	37% 6% 13% 19% 21% 5%	2190
	11th to 20th	Night	37% 4 10% 22% 21% 6%	1964
	21st to end	Night	36% 7% 13% 26% 16% 2	1800
May	1st to 10th	Night	45% 11% 16% 20% 8% 1	4060
	11th to 20th	Night	54% 10% 15% 15% 7%	4033
	21st to end	Night	41% 10% 15% 22% 11% 1	4429
June	1st to 10th	Night	42% 12% 18% 20% 8% 1	1800
	11th to 20th	Night	32% 12% 21% 24% 10% 1	1800
	21st to end	Night	32% 13% 19% 20% 13% 3	1800
July	1st to 10th	Night	42% 11% 20% 22% 5%	4015
	11th to 20th	Night	41% 15% 26% 15% 3 1	4006
	21st to end	Night	51% 12% 18% 15% 4	4297
August	1st to 10th	Night	39% 11% 26% 20% 5%	2904
	11th to 20th	Night	38% 12% 21% 16% 12%	3020
	21st to end	Night	31% 10% 17% 26% 15% 1	3586
September	1st to 10th	Night	39% 11% 16% 16% 15% 3	2189
	11th to 20th	Night	41% 10% 14% 19% 16% 1	2200
	21st to end	Night	37% 8% 13% 20% 17% 6%	2200
October	1st to 10th	Night	27% 4 10% 16% 35% 7%	3590
	11th to 20th	Night	22% 5% 7% 18% 28% 21%	3823
	21st to end	Night	28% 3 9% 21% 25% 14%	4252
November	1st to 10th	Night	35% 4 8% 19% 24% 10%	2635
	11th to 20th	Night	37% 4 6% 17% 25% 10%	2730
	21st to end	Night	41% 5% 7% 20% 22% 6%	2730
December	1st to 10th	Night	43% 4 6% 16% 23% 8%	4380
	11th to 20th	Night	47% 6% 9% 13% 19% 5%	4954
	21st to end	Night	44% 8% 11% 21% 14% 2	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	35% 27% 30% 7% 2	330
	11th to 20th	Day	41% 23% 22% 11% 3	330
	21st to end	Day	34% 28% 28% 8% 2	363
February	1st to 10th	Day	29% 26% 35% 8% 2	330
	11th to 20th	Day	43% 29% 23% 4 1	330
	21st to end	Day	40% 23% 30% 6% 1	273
March	1st to 10th	Day	31% 17% 31% 16% 5%	414
	11th to 20th	Day	30% 21% 27% 17% 4 1	528
	21st to end	Day	27% 23% 27% 18% 5% 1	550
April	1st to 10th	Day	25% 18% 27% 19% 9% 1	500
	11th to 20th	Day	17% 26% 25% 20% 11% 1	492
	21st to end	Day	19% 15% 26% 24% 12% 4	500
May	1st to 10th	Day	20% 20% 25% 18% 12% 5%	503
	11th to 20th	Day	17% 14% 22% 26% 11% 10%	527
	21st to end	Day	15% 11% 24% 21% 16% 12%	573
June	1st to 10th	Day	13% 7% 22% 27% 20% 10%	530
	11th to 20th	Day	8% 5% 25% 24% 24% 14%	530
	21st to end	Day	10% 4 23% 27% 21% 15%	530
July	1st to 10th	Day	9% 4 14% 26% 28% 18%	525
	11th to 20th	Day	9% 4 13% 26% 27% 23%	524
	21st to end	Day	8% 4 13% 27% 27% 21%	576
August	1st to 10th	Day	15% 7% 17% 23% 19% 18%	526
	11th to 20th	Day	11% 6% 16% 23% 28% 16%	519
	21st to end	Day	12% 6% 14% 23% 28% 17%	583
September	1st to 10th	Day	10% 6% 17% 26% 29% 12%	530
	11th to 20th	Day	17% 5% 17% 21% 31% 10%	530
	21st to end	Day	13% 7% 22% 26% 25% 7%	530
October	1st to 10th	Day	15% 7% 24% 29% 17% 7%	530
	11th to 20th	Day	17% 11% 26% 27% 17% 3	530
	21st to end	Day	20% 13% 27% 23% 14% 2	583
November	1st to 10th	Day	18% 19% 31% 22% 9% 2	360
	11th to 20th	Day	22% 23% 33% 16% 5%	330
	21st to end	Day	21% 25% 34% 14% 6% 1	330
December	1st to 10th	Day	34% 25% 26% 12% 3	330
	11th to 20th	Day	28% 18% 35% 13% 4 1	330
	21st to end	Day	28% 26% 30% 12% 3 1	363
January	1st to 10th	Night	28% 18% 28% 21% 5%	840
	11th to 20th	Night	25% 22% 24% 22% 7%	840
	21st to end	Night	24% 21% 30% 23% 3	924
February	1st to 10th	Night	21% 19% 26% 28% 5%	840
	11th to 20th	Night	29% 22% 28% 20% 2	823
	21st to end	Night	28% 21% 28% 19% 3	692
March	1st to 10th	Night	22% 18% 32% 24% 4	840
	11th to 20th	Night	22% 18% 26% 26% 7% 1	829
	21st to end	Night	20% 18% 28% 25% 9%	880
April	1st to 10th	Night	18% 18% 27% 26% 9% 1	790
	11th to 20th	Night	17% 15% 22% 30% 15% 1	593
	21st to end	Night	13% 11% 24% 34% 16% 2	600
May	1st to 10th	Night	15% 9% 20% 34% 20% 2	600
	11th to 20th	Night	15% 8% 18% 31% 23% 4	591
	21st to end	Night	13% 5% 12% 32% 31% 7%	650
June	1st to 10th	Night	10% 5% 12% 35% 33% 6%	600
	11th to 20th	Night	6% 3 15% 30% 34% 13%	600
	21st to end	Night	8% 2 10% 31% 40% 10%	600
July	1st to 10th	Night	9% 2 10% 24% 45% 10%	585
	11th to 20th	Night	9% 3 9% 20% 43% 14%	582
	21st to end	Night	10% 2 8% 23% 44% 14%	657
August	1st to 10th	Night	10% 5% 8% 23% 41% 12%	597
	11th to 20th	Night	12% 2 11% 26% 39% 9%	594
	21st to end	Night	12% 2 10% 25% 39% 11%	660
September	1st to 10th	Night	12% 3 15% 28% 34% 9%	789
	11th to 20th	Night	16% 5% 14% 27% 34% 4	800
	21st to end	Night	14% 6% 14% 32% 30% 3	800
October	1st to 10th	Night	14% 7% 20% 29% 23% 6%	800
	11th to 20th	Night	15% 10% 21% 32% 21% 2	800
	21st to end	Night	17% 14% 17% 35% 16% 2	880
November	1st to 10th	Night	14% 10% 25% 30% 18% 3	820
	11th to 20th	Night	19% 15% 23% 28% 13% 2	840
	21st to end	Night	21% 18% 20% 28% 13% 1	840
December	1st to 10th	Night	26% 18% 24% 25% 7% 1	840
	11th to 20th	Night	22% 16% 24% 30% 7% 1	840
	21st to end	Night	27% 16% 24% 27% 5%	924

Page generated at 2026-03-15 02:23:52. Version ac07

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