Blue Ridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Ridge clear sky chart from 2005-11-06 to 2026-11-13.

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	6% 3 1 3 2 2 3 2 4 6% 67%	162135
	Night	7% 3 1 4 3 3 3 2 4 6% 63%	156469
Transparency	Day	20% 4 7% 18% 25% 26%	157052
	Night	23% 4 8% 17% 23% 25%	152541
Seeing	Day	8% 8% 22% 31% 24% 7%	17967
	Night	9% 4 19% 38% 26% 4	27223

By Month

Percentage Cloud Cover SW (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% 7% 3 5% 4 3 4 4 5% 7% 44%	4884
	11th to 20th	Day	10% 5% 2 5% 3 3 3 2 3 5% 59%	5340
	21st to end	Day	14% 6% 2 6% 4 3 5% 4 5% 8% 43%	5843
February	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 6% 5% 46%	1890
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 4 5% 8% 42%	1927
	21st to end	Day	12% 5% 2 6% 5% 4 4 3 6% 6% 47%	1730
March	1st to 10th	Day	10% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	4946
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 5% 7% 51%	5110
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 8% 39%	5709
April	1st to 10th	Day	10% 8% 2 4 4 4 5% 4 6% 7% 45%	2520
	11th to 20th	Day	9% 3 2 4 3 3 4 4 5% 7% 56%	2489
	21st to end	Day	4 4 2 3 3 4 3 3 5% 7% 62%	2520
May	1st to 10th	Day	4 3 1 3 2 2 2 2 3 5% 73%	7356
	11th to 20th	Day	1 1 1 1 1 2 2 3 6% 81%	7893
	21st to end	Day	1 1 2 1 1 2 2 4 6% 79%	8992
June	1st to 10th	Day	4 3 1 3 2 2 3 3 5% 7% 68%	2940
	11th to 20th	Day	1 1 1 2 2 2 4 6% 81%	2940
	21st to end	Day	1 1 1 1 1 2 2 3 5% 84%	2940
July	1st to 10th	Day	1 1 1 1 2 3 91%	8219
	11th to 20th	Day	2 2 1 2 2 1 2 1 2 3 82%	7879
	21st to end	Day	1 1 1 1 1 2 5% 87%	8304
August	1st to 10th	Day	1 1 1 1 1 1 2 3 4 85%	7547
	11th to 20th	Day	1 1 1 1 2 2 3 6% 83%	7245
	21st to end	Day	2 1 1 2 1 2 2 2 3 5% 78%	7750
September	1st to 10th	Day	1 1 1 1 1 2 2 1 2 5% 84%	2520
	11th to 20th	Day	2 1 1 3 2 2 2 3 4 7% 74%	2520
	21st to end	Day	2 2 1 2 2 2 1 2 3 4 78%	2228
October	1st to 10th	Day	1 3 1 4 2 2 2 2 3 4 76%	4660
	11th to 20th	Day	4 2 1 3 2 2 2 2 3 5% 75%	4639
	21st to end	Day	5% 5% 2 4 3 3 4 3 5% 7% 59%	5076
November	1st to 10th	Day	8% 4 1 3 2 3 4 2 6% 7% 59%	2081
	11th to 20th	Day	9% 6% 2 6% 5% 3 4 4 6% 6% 49%	1908
	21st to end	Day	11% 3 1 4 3 4 4 3 5% 6% 56%	1690
December	1st to 10th	Day	8% 4 2 3 3 2 3 3 7% 10% 55%	2700
	11th to 20th	Day	24% 8% 3 5% 4 3 4 3 6% 7% 33%	3108
	21st to end	Day	24% 10% 3 7% 3 3 3 3 5% 7% 31%	4092
January	1st to 10th	Night	17% 5% 2 4 3 3 3 3 5% 8% 46%	8001
	11th to 20th	Night	10% 4 2 4 2 3 3 3 4 5% 60%	7650
	21st to end	Night	12% 7% 3 6% 4 3 4 3 5% 7% 46%	8371
February	1st to 10th	Night	16% 5% 2 5% 3 4 4 3 5% 5% 50%	2730
	11th to 20th	Night	11% 5% 2 6% 4 3 5% 4 5% 7% 47%	2578
	21st to end	Night	11% 5% 2 5% 3 3 2 4 5% 7% 54%	2076
March	1st to 10th	Night	10% 7% 3 7% 4 4 4 4 6% 8% 44%	5153
	11th to 20th	Night	12% 4 1 4 3 3 4 3 5% 7% 55%	5110
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 8% 45%	5506
April	1st to 10th	Night	6% 5% 1 5% 5% 4 4 4 4 8% 54%	2100
	11th to 20th	Night	7% 4 1 4 3 3 3 4 5% 7% 59%	2079
	21st to end	Night	5% 3 1 2 3 2 3 3 5% 8% 64%	2100
May	1st to 10th	Night	4 3 1 3 3 2 2 1 3 7% 71%	5589
	11th to 20th	Night	1 1 1 1 2 2 2 1 3 6% 81%	4964
	21st to end	Night	1 1 1 1 1 1 2 3 5% 83%	5181
June	1st to 10th	Night	3 2 1 2 2 2 2 3 4 8% 70%	1680
	11th to 20th	Night	1 1 1 1 1 2 1 3 6% 83%	1680
	21st to end	Night	1 1 1 1 1 2 2 3 5% 83%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	4740
	11th to 20th	Night	3 2 1 2 1 1 1 1 2 3 82%	5094
	21st to end	Night	1 1 1 1 2 1 3 8% 82%	5806
August	1st to 10th	Night	1 1 1 1 1 1 1 3 5% 84%	5275
	11th to 20th	Night	1 1 2 2 2 4 9% 78%	5628
	21st to end	Night	1 1 1 2 2 2 2 2 4 6% 77%	6499
September	1st to 10th	Night	1 1 1 1 1 3 7% 83%	2100
	11th to 20th	Night	2 2 1 2 1 2 3 2 4 6% 75%	2100
	21st to end	Night	2 1 1 2 2 1 2 2 3 6% 79%	2388
October	1st to 10th	Night	2 1 1 2 2 2 2 2 4 5% 77%	5560
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 77%	5537
	21st to end	Night	5% 3 1 4 4 4 4 3 5% 6% 60%	6056
November	1st to 10th	Night	6% 3 1 4 3 3 3 3 6% 9% 58%	2656
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 8% 55%	2756
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 58%	2924
December	1st to 10th	Night	8% 3 2 4 3 4 3 3 5% 7% 58%	4700
	11th to 20th	Night	21% 7% 2 5% 4 4 5% 4 7% 8% 31%	5316
	21st to end	Night	23% 9% 2 7% 5% 4 4 3 4 5% 33%	7106

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% 8% 13% 23% 11% 6%	4885
	11th to 20th	Day	29% 4 5% 15% 25% 22%	5340
	21st to end	Day	40% 5% 8% 20% 10% 17%	5843
February	1st to 10th	Day	39% 5% 8% 20% 19% 9%	1890
	11th to 20th	Day	39% 6% 10% 19% 19% 7%	1936
	21st to end	Day	36% 4 11% 23% 17% 9%	1730
March	1st to 10th	Day	42% 6% 9% 19% 22% 4	4946
	11th to 20th	Day	31% 6% 13% 25% 16% 9%	5110
	21st to end	Day	36% 9% 15% 26% 12% 2	5709
April	1st to 10th	Day	35% 7% 12% 21% 20% 6%	2520
	11th to 20th	Day	26% 7% 13% 23% 22% 9%	2492
	21st to end	Day	21% 5% 14% 28% 26% 6%	2520
May	1st to 10th	Day	16% 3 6% 23% 31% 20%	7356
	11th to 20th	Day	7% 2 6% 25% 42% 19%	7896
	21st to end	Day	8% 4 8% 27% 43% 10%	8994
June	1st to 10th	Day	16% 5% 11% 26% 31% 11%	2940
	11th to 20th	Day	7% 2 10% 20% 35% 25%	2940
	21st to end	Day	6% 2 6% 16% 34% 37%	2940
July	1st to 10th	Day	3 1 2 7% 22% 66%	8151
	11th to 20th	Day	12% 1 2 5% 10% 69%	7805
	21st to end	Day	4 1 4 13% 24% 54%	8119
August	1st to 10th	Day	6% 2 3 8% 25% 56%	5976
	11th to 20th	Day	7% 2 3 20% 36% 32%	5716
	21st to end	Day	13% 2 4 10% 39% 33%	6077
September	1st to 10th	Day	6% 2 5% 11% 31% 46%	2520
	11th to 20th	Day	12% 3 9% 21% 38% 17%	2520
	21st to end	Day	12% 2 5% 17% 34% 29%	2228
October	1st to 10th	Day	14% 2 3 9% 20% 52%	4659
	11th to 20th	Day	13% 3 4 18% 29% 33%	4641
	21st to end	Day	25% 3 7% 24% 30% 11%	5074
November	1st to 10th	Day	24% 4 9% 28% 23% 11%	2081
	11th to 20th	Day	34% 6% 11% 23% 20% 7%	1908
	21st to end	Day	29% 4 10% 21% 24% 11%	1690
December	1st to 10th	Day	25% 4 7% 31% 25% 8%	2700
	11th to 20th	Day	50% 5% 9% 18% 15% 3	3108
	21st to end	Day	52% 6% 12% 17% 11% 2	4092
January	1st to 10th	Night	36% 8% 20% 20% 14% 3	8001
	11th to 20th	Night	27% 5% 7% 13% 28% 20%	7650
	21st to end	Night	38% 4 7% 16% 18% 16%	8371
February	1st to 10th	Night	36% 4 8% 19% 21% 11%	2730
	11th to 20th	Night	36% 5% 11% 21% 19% 10%	2580
	21st to end	Night	30% 4 11% 25% 22% 8%	2076
March	1st to 10th	Night	36% 8% 11% 17% 23% 6%	5153
	11th to 20th	Night	29% 4 14% 24% 18% 10%	5110
	21st to end	Night	35% 6% 15% 24% 17% 3	5506
April	1st to 10th	Night	29% 6% 14% 21% 22% 8%	2100
	11th to 20th	Night	24% 6% 13% 27% 18% 13%	2079
	21st to end	Night	18% 5% 11% 31% 28% 7%	2100
May	1st to 10th	Night	17% 3 7% 19% 33% 21%	5587
	11th to 20th	Night	8% 2 7% 21% 37% 26%	4964
	21st to end	Night	7% 2 8% 24% 37% 22%	5182
June	1st to 10th	Night	14% 5% 9% 24% 31% 15%	1680
	11th to 20th	Night	7% 2 7% 19% 35% 31%	1680
	21st to end	Night	6% 3 5% 14% 30% 42%	1680
July	1st to 10th	Night	4 1 2 6% 19% 70%	4700
	11th to 20th	Night	11% 1 2 5% 11% 71%	5045
	21st to end	Night	5% 1 3 14% 21% 56%	5679
August	1st to 10th	Night	8% 1 3 8% 17% 63%	4169
	11th to 20th	Night	9% 1 3 14% 29% 44%	4427
	21st to end	Night	11% 1 3 10% 36% 40%	5092
September	1st to 10th	Night	5% 1 5% 10% 29% 50%	2100
	11th to 20th	Night	11% 3 8% 20% 35% 24%	2100
	21st to end	Night	10% 3 7% 16% 29% 36%	2388
October	1st to 10th	Night	11% 2 4 8% 15% 60%	5560
	11th to 20th	Night	12% 2 5% 18% 26% 37%	5537
	21st to end	Night	25% 3 6% 20% 28% 18%	6057
November	1st to 10th	Night	23% 5% 10% 25% 23% 15%	2656
	11th to 20th	Night	28% 4 12% 26% 22% 9%	2756
	21st to end	Night	27% 5% 9% 21% 24% 14%	2924
December	1st to 10th	Night	27% 3 7% 22% 29% 13%	4700
	11th to 20th	Night	48% 6% 10% 17% 16% 3	5316
	21st to end	Night	52% 7% 11% 17% 11% 3	7106

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	30% 10% 25% 19% 13% 2	278
	11th to 20th	Day	15% 10% 20% 35% 15% 4	430
	21st to end	Day	15% 8% 21% 27% 23% 4	473
February	1st to 10th	Day	19% 13% 19% 26% 20% 4	430
	11th to 20th	Day	20% 15% 24% 23% 13% 4	469
	21st to end	Day	13% 11% 28% 30% 14% 3	446
March	1st to 10th	Day	18% 14% 26% 28% 10% 4	540
	11th to 20th	Day	19% 10% 23% 25% 17% 5%	540
	21st to end	Day	14% 14% 27% 26% 16% 2	594
April	1st to 10th	Day	14% 11% 27% 26% 17% 5%	540
	11th to 20th	Day	10% 12% 30% 23% 19% 6%	532
	21st to end	Day	5% 11% 26% 27% 23% 7%	540
May	1st to 10th	Day	6% 12% 29% 27% 21% 5%	543
	11th to 20th	Day	6% 9% 26% 30% 20% 8%	568
	21st to end	Day	2 7% 25% 34% 23% 9%	617
June	1st to 10th	Day	4 7% 25% 35% 23% 6%	570
	11th to 20th	Day	2 8% 24% 38% 26% 2	570
	21st to end	Day	1 4 23% 37% 28% 6%	570
July	1st to 10th	Day	1 2 17% 43% 30% 7%	566
	11th to 20th	Day	1 1 16% 39% 35% 8%	564
	21st to end	Day	1 16% 41% 32% 10%	619
August	1st to 10th	Day	2 2 15% 39% 32% 11%	567
	11th to 20th	Day	2 2 18% 33% 32% 13%	557
	21st to end	Day	1 2 13% 36% 36% 12%	627
September	1st to 10th	Day	2 3 14% 37% 32% 12%	570
	11th to 20th	Day	2 7% 17% 34% 29% 10%	570
	21st to end	Day	3 5% 20% 33% 28% 11%	570
October	1st to 10th	Day	3 8% 21% 29% 26% 13%	570
	11th to 20th	Day	7% 6% 22% 27% 27% 11%	570
	21st to end	Day	10% 8% 21% 29% 23% 10%	627
November	1st to 10th	Day	9% 9% 20% 26% 27% 8%	497
	11th to 20th	Day	12% 9% 23% 25% 24% 7%	336
	21st to end	Day	14% 6% 23% 33% 22% 2	225
December	1st to 10th	Day	15% 8% 24% 27% 19% 6%	220
	11th to 20th	Day	20% 7% 24% 28% 16% 5%	220
	21st to end	Day	24% 14% 21% 22% 16% 4	242
January	1st to 10th	Night	20% 5% 19% 32% 19% 5%	840
	11th to 20th	Night	15% 6% 17% 38% 20% 4	840
	21st to end	Night	16% 5% 18% 35% 23% 3	924
February	1st to 10th	Night	17% 7% 18% 35% 20% 3	840
	11th to 20th	Night	14% 8% 23% 31% 20% 4	824
	21st to end	Night	14% 7% 22% 38% 17% 2	692
March	1st to 10th	Night	16% 8% 23% 30% 21% 2	840
	11th to 20th	Night	16% 6% 20% 32% 24% 2	840
	21st to end	Night	13% 7% 24% 38% 17% 1	924
April	1st to 10th	Night	8% 6% 27% 38% 19% 2	840
	11th to 20th	Night	9% 7% 28% 33% 20% 3	831
	21st to end	Night	6% 5% 26% 39% 22% 3	840
May	1st to 10th	Night	5% 4 27% 36% 25% 3	729
	11th to 20th	Night	4 3 21% 42% 28% 2	511
	21st to end	Night	4 3 25% 44% 24% 1	455
June	1st to 10th	Night	3 2 23% 47% 23% 1	420
	11th to 20th	Night	1 2 25% 48% 23% 1	420
	21st to end	Night	1 1 20% 51% 27% 1	420
July	1st to 10th	Night	1 1 13% 56% 29%	410
	11th to 20th	Night	1 12% 50% 34% 3	527
	21st to end	Night	1 1 12% 48% 35% 3	690
August	1st to 10th	Night	1 1 13% 43% 37% 4	627
	11th to 20th	Night	1 14% 45% 34% 5%	739
	21st to end	Night	1 1 10% 44% 40% 4	924
September	1st to 10th	Night	2 11% 43% 39% 4	840
	11th to 20th	Night	2 3 17% 41% 33% 5%	840
	21st to end	Night	2 2 16% 40% 34% 6%	840
October	1st to 10th	Night	4 3 14% 40% 32% 6%	840
	11th to 20th	Night	5% 4 18% 35% 33% 5%	840
	21st to end	Night	7% 5% 18% 33% 29% 8%	924
November	1st to 10th	Night	7% 6% 18% 32% 32% 6%	860
	11th to 20th	Night	12% 4 18% 34% 28% 4	848
	21st to end	Night	10% 6% 17% 37% 24% 5%	840
December	1st to 10th	Night	15% 6% 20% 31% 23% 5%	840
	11th to 20th	Night	21% 5% 17% 32% 22% 3	840
	21st to end	Night	22% 8% 22% 30% 18%	924

Page generated at 2026-11-10 00:55:18. Version ac07

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