Blue Ridge Regional Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Ridge Regional Park clear sky chart from 2005-11-06 to 2026-05-02.

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% 6% 2 6% 4 4 5% 4 6% 8% 41%	131789
	Night	13% 6% 2 6% 4 4 5% 4 6% 7% 42%	130682
Transparency	Day	39% 6% 12% 24% 16% 3	135387
	Night	39% 5% 12% 24% 17% 4	135154
Seeing	Day	19% 13% 26% 23% 13% 5%	16816
	Night	18% 11% 29% 29% 12% 1	26509

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 2 6% 4 5% 5% 4 5% 7% 44%	4959
	11th to 20th	Day	12% 8% 3 6% 4 3 3 3 4 5% 48%	5280
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 7% 40%	5780
February	1st to 10th	Day	13% 8% 3 6% 5% 5% 5% 4 6% 6% 40%	1890
	11th to 20th	Day	18% 7% 3 6% 5% 4 4 3 4 7% 38%	1857
	21st to end	Day	16% 9% 3 7% 4 3 4 2 5% 6% 40%	1739
March	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 4 6% 41%	5045
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 5% 7% 49%	5090
	21st to end	Day	15% 7% 2 7% 5% 4 5% 4 6% 6% 40%	5603
April	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	2520
	11th to 20th	Day	13% 7% 2 6% 4 5% 4 3 5% 7% 45%	2494
	21st to end	Day	16% 6% 3 6% 4 5% 3 3 6% 6% 41%	2533
May	1st to 10th	Day	18% 7% 2 7% 5% 5% 5% 5% 7% 9% 31%	5875
	11th to 20th	Day	23% 6% 2 6% 4 4 4 4 6% 9% 31%	6034
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 9% 38%	6934
June	1st to 10th	Day	11% 5% 1 6% 4 4 5% 5% 7% 9% 43%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 4 7% 9% 40%	2800
	21st to end	Day	9% 4 1 5% 5% 4 4 5% 6% 11% 45%	2800
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 4 7% 10% 44%	6360
	11th to 20th	Day	8% 5% 2 8% 6% 6% 7% 6% 9% 11% 32%	6003
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 10% 39%	6424
August	1st to 10th	Day	16% 5% 2 7% 5% 5% 6% 4 7% 9% 34%	4234
	11th to 20th	Day	8% 5% 2 7% 4 6% 6% 5% 7% 9% 41%	4057
	21st to end	Day	10% 5% 1 5% 4 4 5% 4 6% 8% 48%	4312
September	1st to 10th	Day	14% 5% 2 6% 3 4 4 3 4 6% 47%	2400
	11th to 20th	Day	13% 5% 2 6% 4 3 4 3 5% 8% 47%	2382
	21st to end	Day	21% 7% 2 7% 4 3 4 3 4 7% 36%	2095
October	1st to 10th	Day	16% 5% 2 5% 4 2 3 3 5% 7% 48%	2000
	11th to 20th	Day	15% 4 2 5% 4 4 4 4 5% 5% 49%	2000
	21st to end	Day	14% 5% 2 5% 3 3 4 3 4 7% 50%	2200
November	1st to 10th	Day	12% 5% 2 4 4 4 4 3 5% 8% 51%	1999
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 5% 6% 48%	1812
	21st to end	Day	15% 5% 2 5% 5% 5% 4 3 5% 6% 46%	1680
December	1st to 10th	Day	12% 6% 2 5% 4 4 4 4 5% 7% 48%	2680
	11th to 20th	Day	17% 8% 2 5% 4 5% 4 3 5% 6% 40%	3070
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 6% 9% 35%	4048
January	1st to 10th	Night	9% 7% 2 6% 5% 5% 6% 4 6% 7% 42%	7919
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 6% 49%	7680
	21st to end	Night	12% 7% 2 5% 3 4 4 4 5% 6% 47%	8401
February	1st to 10th	Night	13% 7% 3 6% 5% 4 5% 3 6% 7% 41%	2730
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	2647
	21st to end	Night	15% 9% 3 5% 4 5% 4 3 5% 7% 40%	2065
March	1st to 10th	Night	16% 7% 2 6% 4 3 3 3 4 6% 46%	5028
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 5% 7% 49%	5090
	21st to end	Night	11% 7% 2 6% 4 5% 5% 4 5% 6% 44%	5571
April	1st to 10th	Night	14% 8% 2 8% 4 4 4 5% 5% 6% 40%	2100
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 6% 7% 43%	2075
	21st to end	Night	15% 5% 2 5% 3 4 4 4 5% 8% 44%	2100
May	1st to 10th	Night	20% 8% 3 8% 5% 5% 5% 4 5% 8% 29%	4046
	11th to 20th	Night	24% 8% 2 6% 4 4 4 4 6% 8% 30%	3859
	21st to end	Night	17% 6% 3 6% 4 5% 5% 5% 7% 8% 35%	3920
June	1st to 10th	Night	11% 5% 2 5% 4 5% 5% 5% 6% 9% 43%	1600
	11th to 20th	Night	12% 5% 2 5% 5% 4 5% 5% 6% 9% 42%	1600
	21st to end	Night	8% 5% 1 6% 5% 4 5% 4 7% 10% 45%	1600
July	1st to 10th	Night	7% 6% 2 7% 5% 6% 6% 5% 8% 10% 39%	3598
	11th to 20th	Night	7% 7% 3 10% 7% 7% 6% 6% 9% 10% 29%	3936
	21st to end	Night	7% 6% 2 7% 4 5% 6% 5% 7% 9% 41%	4427
August	1st to 10th	Night	15% 5% 2 7% 5% 5% 5% 5% 7% 9% 33%	2915
	11th to 20th	Night	9% 7% 2 7% 5% 6% 6% 4 7% 9% 39%	2956
	21st to end	Night	13% 5% 2 4 3 4 5% 3 6% 8% 48%	3586
September	1st to 10th	Night	14% 5% 2 5% 4 4 4 4 6% 7% 45%	2000
	11th to 20th	Night	11% 6% 2 6% 4 4 3 2 4 7% 52%	2014
	21st to end	Night	20% 8% 2 6% 4 4 4 3 4 6% 39%	2305
October	1st to 10th	Night	19% 5% 2 5% 3 3 4 2 4 6% 47%	2400
	11th to 20th	Night	14% 4 2 5% 3 3 3 3 5% 5% 52%	2400
	21st to end	Night	14% 5% 1 5% 3 3 3 2 5% 6% 51%	2640
November	1st to 10th	Night	10% 6% 3 5% 3 3 3 3 5% 6% 53%	2515
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 49%	2804
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 8% 45%	2940
December	1st to 10th	Night	10% 5% 1 5% 3 4 4 3 6% 7% 51%	4720
	11th to 20th	Night	18% 7% 2 5% 4 4 4 3 5% 7% 39%	5345
	21st to end	Night	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 34%	7150

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	38% 4 9% 25% 18% 5%	4960
	11th to 20th	Day	39% 3 7% 21% 21% 10%	5280
	21st to end	Day	41% 4 10% 29% 13% 3	5780
February	1st to 10th	Day	42% 5% 13% 24% 13% 3	1890
	11th to 20th	Day	45% 5% 9% 22% 16% 2	1866
	21st to end	Day	45% 5% 11% 21% 14% 4	1739
March	1st to 10th	Day	42% 5% 8% 21% 16% 8%	5045
	11th to 20th	Day	33% 5% 10% 26% 20% 6%	5090
	21st to end	Day	43% 5% 11% 18% 18% 6%	5603
April	1st to 10th	Day	40% 6% 12% 19% 18% 4	2520
	11th to 20th	Day	37% 5% 12% 22% 19% 5%	2494
	21st to end	Day	43% 5% 10% 24% 15% 3	2533
May	1st to 10th	Day	47% 7% 15% 19% 10% 2	5910
	11th to 20th	Day	47% 7% 12% 24% 9% 1	6038
	21st to end	Day	39% 7% 15% 22% 16% 2	6949
June	1st to 10th	Day	35% 8% 15% 25% 17% 1	2800
	11th to 20th	Day	38% 9% 15% 23% 14% 2	2800
	21st to end	Day	32% 9% 16% 26% 16% 2	2800
July	1st to 10th	Day	34% 8% 17% 22% 16% 3	6290
	11th to 20th	Day	42% 8% 18% 24% 8% 1	5931
	21st to end	Day	38% 6% 10% 23% 22% 1	6240
August	1st to 10th	Day	44% 6% 16% 25% 8%	4221
	11th to 20th	Day	37% 7% 13% 28% 15% 1	4096
	21st to end	Day	33% 6% 15% 28% 17% 2	4312
September	1st to 10th	Day	38% 6% 11% 20% 21% 4	2400
	11th to 20th	Day	35% 5% 9% 27% 21% 3	2382
	21st to end	Day	48% 5% 10% 19% 17% 2	2095
October	1st to 10th	Day	36% 4 7% 21% 28% 5%	3260
	11th to 20th	Day	27% 3 8% 29% 23% 10%	3240
	21st to end	Day	23% 2 11% 29% 27% 6%	3538
November	1st to 10th	Day	33% 3 12% 25% 22% 4	1999
	11th to 20th	Day	37% 2 12% 23% 22% 5%	1812
	21st to end	Day	38% 5% 11% 28% 16% 2	1680
December	1st to 10th	Day	36% 4 12% 29% 14% 4	2680
	11th to 20th	Day	44% 4 14% 25% 10% 3	3066
	21st to end	Day	44% 6% 16% 20% 13% 1	4048
January	1st to 10th	Night	37% 5% 9% 25% 20% 3	7920
	11th to 20th	Night	37% 3 7% 22% 24% 7%	7680
	21st to end	Night	36% 3 9% 31% 18% 3	8401
February	1st to 10th	Night	42% 5% 13% 24% 15% 2	2730
	11th to 20th	Night	44% 4 10% 22% 15% 4	2649
	21st to end	Night	42% 4 11% 22% 15% 5%	2065
March	1st to 10th	Night	38% 5% 9% 25% 14% 8%	5028
	11th to 20th	Night	33% 5% 10% 27% 19% 6%	5090
	21st to end	Night	39% 4 11% 22% 20% 5%	5571
April	1st to 10th	Night	42% 5% 11% 20% 18% 4	2100
	11th to 20th	Night	37% 6% 12% 21% 18% 5%	2075
	21st to end	Night	37% 6% 14% 26% 13% 4	2100
May	1st to 10th	Night	53% 6% 12% 17% 8% 4	4073
	11th to 20th	Night	50% 7% 11% 21% 10% 1	3860
	21st to end	Night	43% 7% 15% 24% 8% 2	3927
June	1st to 10th	Night	35% 8% 12% 25% 17% 3	1600
	11th to 20th	Night	37% 8% 15% 24% 14% 2	1600
	21st to end	Night	32% 8% 16% 24% 18% 3	1600
July	1st to 10th	Night	39% 8% 17% 18% 14% 3	3560
	11th to 20th	Night	46% 9% 18% 16% 9% 1	3888
	21st to end	Night	36% 6% 15% 23% 19%	4297
August	1st to 10th	Night	46% 7% 15% 23% 8% 1	2904
	11th to 20th	Night	39% 7% 12% 26% 15% 1	2983
	21st to end	Night	35% 5% 13% 30% 16% 2	3586
September	1st to 10th	Night	37% 5% 12% 22% 19% 5%	2000
	11th to 20th	Night	34% 4 9% 28% 22% 3	2014
	21st to end	Night	47% 5% 10% 19% 16% 2	2305
October	1st to 10th	Night	40% 3 9% 22% 22% 4	3920
	11th to 20th	Night	25% 2 11% 23% 31% 7%	3899
	21st to end	Night	23% 3 10% 31% 26% 6%	4252
November	1st to 10th	Night	32% 4 10% 26% 23% 5%	2515
	11th to 20th	Night	36% 4 8% 25% 22% 6%	2804
	21st to end	Night	36% 4 12% 26% 19% 3	2940
December	1st to 10th	Night	32% 3 14% 30% 19% 2	4720
	11th to 20th	Night	44% 3 13% 20% 17% 4	5348
	21st to end	Night	43% 7% 16% 19% 14% 1	7150

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	32% 24% 27% 14% 3	275
	11th to 20th	Day	29% 27% 29% 12% 2	330
	21st to end	Day	23% 32% 30% 12% 3 1	363
February	1st to 10th	Day	23% 25% 35% 13% 3	330
	11th to 20th	Day	37% 26% 30% 5% 2	344
	21st to end	Day	29% 18% 34% 17% 2	446
March	1st to 10th	Day	24% 23% 29% 20% 4	540
	11th to 20th	Day	26% 22% 29% 17% 5% 2	540
	21st to end	Day	21% 21% 35% 17% 5% 1	594
April	1st to 10th	Day	24% 23% 26% 17% 8% 1	540
	11th to 20th	Day	18% 19% 28% 19% 12% 3	532
	21st to end	Day	24% 15% 30% 19% 10% 2	540
May	1st to 10th	Day	23% 16% 29% 19% 10% 3	507
	11th to 20th	Day	22% 11% 28% 21% 14% 4	527
	21st to end	Day	22% 8% 23% 23% 20% 5%	573
June	1st to 10th	Day	13% 8% 27% 26% 20% 6%	530
	11th to 20th	Day	16% 7% 25% 29% 17% 6%	530
	21st to end	Day	10% 6% 27% 31% 19% 8%	530
July	1st to 10th	Day	11% 5% 15% 31% 26% 12%	525
	11th to 20th	Day	7% 3 19% 31% 30% 10%	524
	21st to end	Day	12% 4 18% 33% 23% 10%	576
August	1st to 10th	Day	14% 4 17% 28% 23% 14%	526
	11th to 20th	Day	13% 4 19% 31% 22% 11%	519
	21st to end	Day	9% 4 21% 30% 22% 13%	583
September	1st to 10th	Day	17% 7% 17% 27% 21% 11%	530
	11th to 20th	Day	15% 4 18% 31% 21% 11%	530
	21st to end	Day	29% 8% 21% 24% 15% 3	530
October	1st to 10th	Day	18% 7% 21% 26% 20% 8%	530
	11th to 20th	Day	18% 14% 25% 28% 13% 3	530
	21st to end	Day	17% 14% 31% 25% 11% 3	583
November	1st to 10th	Day	16% 14% 32% 26% 10% 3	505
	11th to 20th	Day	22% 14% 34% 19% 9% 1	352
	21st to end	Day	23% 20% 31% 18% 6% 1	220
December	1st to 10th	Day	18% 22% 40% 15% 4 1	220
	11th to 20th	Day	22% 23% 29% 21% 5%	220
	21st to end	Day	22% 21% 32% 19% 6%	242
January	1st to 10th	Night	19% 21% 38% 19% 3	840
	11th to 20th	Night	23% 16% 33% 24% 4	840
	21st to end	Night	18% 17% 42% 20% 2	924
February	1st to 10th	Night	17% 16% 38% 26% 2	840
	11th to 20th	Night	24% 23% 34% 17% 2	823
	21st to end	Night	24% 16% 38% 18% 3	692
March	1st to 10th	Night	21% 17% 36% 22% 3	840
	11th to 20th	Night	24% 16% 33% 22% 5% 1	840
	21st to end	Night	19% 17% 39% 21% 4 1	924
April	1st to 10th	Night	19% 18% 37% 22% 4	840
	11th to 20th	Night	17% 12% 36% 27% 7% 1	831
	21st to end	Night	18% 12% 30% 31% 8%	840
May	1st to 10th	Night	22% 7% 25% 33% 12%	607
	11th to 20th	Night	21% 5% 25% 36% 12% 1	522
	21st to end	Night	15% 4 22% 39% 18% 1	433
June	1st to 10th	Night	12% 3 25% 40% 20%	400
	11th to 20th	Night	15% 5% 19% 39% 22% 1	400
	21st to end	Night	8% 3 22% 46% 20% 2	400
July	1st to 10th	Night	10% 3 13% 42% 28% 4	390
	11th to 20th	Night	7% 2 11% 41% 36% 3	529
	21st to end	Night	8% 3 14% 43% 28% 3	657
August	1st to 10th	Night	12% 3 9% 43% 29% 3	597
	11th to 20th	Night	11% 3 12% 39% 31% 3	636
	21st to end	Night	13% 2 16% 39% 26% 4	880
September	1st to 10th	Night	17% 2 16% 35% 25% 5%	800
	11th to 20th	Night	14% 3 17% 33% 29% 4	800
	21st to end	Night	25% 5% 20% 30% 20% 1	800
October	1st to 10th	Night	20% 5% 21% 28% 23% 3	800
	11th to 20th	Night	16% 11% 25% 33% 14% 1	800
	21st to end	Night	18% 9% 30% 31% 11% 1	880
November	1st to 10th	Night	14% 10% 33% 31% 11% 1	820
	11th to 20th	Night	18% 14% 31% 29% 7% 1	840
	21st to end	Night	16% 14% 35% 27% 7%	840
December	1st to 10th	Night	20% 15% 35% 23% 6%	840
	11th to 20th	Night	20% 12% 37% 28% 4	840
	21st to end	Night	19% 13% 36% 29% 3	924

Page generated at 2026-04-29 02:21:44. Version ac07

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