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 2025-01-07.

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	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	104822
	Night	14% 7% 2 6% 4 4 4 4 6% 7% 42%	104162
Transparency	Day	39% 6% 12% 24% 16% 3	108464
	Night	39% 5% 12% 24% 17% 3	108659
Seeing	Day	19% 13% 26% 23% 14% 5%	15094
	Night	18% 11% 28% 29% 13% 1	24759

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% 5% 1 5% 4 4 4 4 5% 6% 44%	2724
	11th to 20th	Day	13% 11% 3 7% 5% 4 4 4 4 5% 39%	2840
	21st to end	Day	16% 10% 3 8% 5% 4 5% 4 5% 6% 35%	3124
February	1st to 10th	Day	13% 8% 3 6% 5% 5% 5% 4 6% 5% 38%	1710
	11th to 20th	Day	17% 7% 3 6% 6% 4 3 3 5% 7% 39%	1675
	21st to end	Day	17% 9% 3 7% 4 3 4 2 5% 7% 39%	1578
March	1st to 10th	Day	20% 9% 3 7% 4 4 4 3 4 6% 35%	3435
	11th to 20th	Day	10% 5% 2 5% 5% 4 4 4 5% 7% 48%	3480
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 39%	3832
April	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	2280
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 46%	2254
	21st to end	Day	17% 6% 2 6% 4 5% 3 3 6% 6% 41%	2291
May	1st to 10th	Day	21% 7% 2 7% 5% 5% 5% 4 6% 8% 30%	4082
	11th to 20th	Day	24% 7% 3 6% 4 4 4 4 5% 8% 32%	4198
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 44%	4823
June	1st to 10th	Day	11% 5% 1 6% 4 4 5% 5% 7% 8% 43%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 4 7% 9% 40%	2660
	21st to end	Day	9% 4 1 5% 5% 4 4 5% 6% 11% 44%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 5% 8% 11% 43%	4440
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	4195
	21st to end	Day	10% 7% 3 7% 6% 5% 5% 4 6% 8% 37%	4466
August	1st to 10th	Day	16% 4 2 7% 5% 5% 6% 4 7% 9% 33%	4104
	11th to 20th	Day	8% 4 2 7% 5% 6% 6% 5% 7% 9% 41%	3930
	21st to end	Day	10% 5% 1 5% 4 4 5% 4 6% 8% 48%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Day	13% 5% 2 6% 4 3 3 3 5% 8% 47%	2263
	21st to end	Day	21% 6% 2 7% 4 4 5% 3 5% 7% 37%	1990
October	1st to 10th	Day	17% 6% 2 5% 4 3 3 3 5% 7% 46%	1900
	11th to 20th	Day	16% 4 2 5% 4 3 5% 4 4 5% 49%	1900
	21st to end	Day	14% 5% 2 5% 3 3 4 3 4 7% 51%	2090
November	1st to 10th	Day	12% 5% 2 4 4 3 4 3 5% 7% 51%	1902
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 6% 6% 48%	1726
	21st to end	Day	15% 5% 2 5% 5% 5% 4 3 5% 6% 46%	1600
December	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 5% 7% 48%	2600
	11th to 20th	Day	18% 8% 2 5% 4 5% 4 3 5% 6% 40%	2990
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 6% 9% 35%	3960
January	1st to 10th	Night	11% 8% 3 6% 4 4 4 3 5% 7% 44%	4352
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 5% 6% 44%	4120
	21st to end	Night	18% 10% 3 6% 4 4 4 4 4 5% 38%	4532
February	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 6% 6% 41%	2470
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 40%	2389
	21st to end	Night	16% 9% 3 5% 4 4 4 3 5% 7% 39%	1875
March	1st to 10th	Night	20% 8% 3 6% 4 4 4 4 5% 6% 37%	3418
	11th to 20th	Night	12% 5% 1 5% 4 4 4 3 6% 7% 49%	3480
	21st to end	Night	14% 8% 3 6% 4 3 3 3 4 5% 47%	3800
April	1st to 10th	Night	14% 8% 2 8% 4 3 5% 5% 5% 6% 40%	1900
	11th to 20th	Night	11% 6% 2 7% 4 4 4 4 6% 7% 44%	1875
	21st to end	Night	16% 5% 2 5% 3 4 4 5% 5% 8% 43%	1900
May	1st to 10th	Night	22% 8% 3 7% 5% 4 4 4 5% 8% 30%	2817
	11th to 20th	Night	23% 10% 3 7% 4 4 3 3 5% 6% 32%	2695
	21st to end	Night	11% 5% 2 5% 4 4 5% 5% 7% 10% 42%	2732
June	1st to 10th	Night	11% 5% 3 5% 4 4 5% 5% 6% 9% 43%	1520
	11th to 20th	Night	12% 5% 2 5% 5% 4 5% 5% 6% 9% 43%	1520
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 11% 45%	1520
July	1st to 10th	Night	6% 5% 2 7% 5% 6% 6% 6% 9% 10% 39%	2520
	11th to 20th	Night	6% 5% 2 7% 6% 6% 6% 5% 9% 10% 38%	2761
	21st to end	Night	10% 6% 2 8% 5% 5% 6% 5% 7% 9% 38%	3087
August	1st to 10th	Night	15% 5% 2 8% 5% 5% 6% 5% 7% 9% 33%	2825
	11th to 20th	Night	9% 7% 2 7% 5% 6% 6% 4 7% 9% 38%	2864
	21st to end	Night	13% 5% 2 4 3 4 5% 3 6% 8% 48%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 4 4 4 6% 6% 44%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 3 2 4 7% 52%	1913
	21st to end	Night	20% 8% 2 6% 4 3 3 3 4 6% 40%	2190
October	1st to 10th	Night	19% 5% 2 5% 3 4 4 2 4 7% 46%	2280
	11th to 20th	Night	14% 4 2 5% 3 3 3 3 5% 5% 52%	2280
	21st to end	Night	14% 6% 1 5% 3 3 3 2 5% 6% 51%	2508
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 53%	2392
	11th to 20th	Night	14% 7% 2 5% 3 4 3 3 5% 6% 49%	2670
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 8% 46%	2800
December	1st to 10th	Night	10% 5% 1 5% 3 4 4 3 5% 7% 51%	4580
	11th to 20th	Night	19% 7% 2 5% 4 4 4 4 5% 7% 39%	5205
	21st to end	Night	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 33%	6996

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% 5% 9% 30% 14% 4	2725
	11th to 20th	Day	46% 5% 10% 19% 15% 5%	2840
	21st to end	Day	48% 5% 11% 23% 12% 2	3124
February	1st to 10th	Day	44% 5% 13% 23% 11% 3	1710
	11th to 20th	Day	44% 5% 10% 23% 16% 3	1684
	21st to end	Day	45% 5% 12% 19% 15% 4	1578
March	1st to 10th	Day	48% 6% 10% 21% 13% 3	3435
	11th to 20th	Day	32% 6% 10% 28% 20% 4	3480
	21st to end	Day	44% 6% 11% 21% 15% 3	3832
April	1st to 10th	Day	40% 6% 13% 19% 18% 4	2280
	11th to 20th	Day	37% 5% 12% 22% 19% 5%	2254
	21st to end	Day	44% 5% 10% 22% 15% 4	2291
May	1st to 10th	Day	49% 9% 11% 20% 10% 1	4120
	11th to 20th	Day	48% 8% 13% 22% 8% 1	4202
	21st to end	Day	32% 9% 16% 24% 16% 2	4837
June	1st to 10th	Day	35% 8% 15% 25% 16% 1	2660
	11th to 20th	Day	37% 9% 16% 23% 14% 2	2660
	21st to end	Day	32% 9% 16% 26% 16% 2	2660
July	1st to 10th	Day	34% 8% 19% 23% 12% 4	4370
	11th to 20th	Day	35% 7% 16% 29% 11% 1	4123
	21st to end	Day	42% 7% 9% 23% 18% 1	4324
August	1st to 10th	Day	45% 6% 16% 25% 8%	4091
	11th to 20th	Day	36% 7% 13% 28% 15% 1	3969
	21st to end	Day	33% 6% 15% 27% 17% 2	4180
September	1st to 10th	Day	39% 7% 11% 19% 21% 4	2280
	11th to 20th	Day	35% 5% 9% 27% 21% 3	2263
	21st to end	Day	46% 5% 9% 19% 17% 2	1990
October	1st to 10th	Day	36% 4 7% 20% 28% 5%	3160
	11th to 20th	Day	26% 3 8% 29% 24% 10%	3140
	21st to end	Day	23% 2 11% 29% 27% 6%	3428
November	1st to 10th	Day	33% 3 12% 25% 22% 4	1902
	11th to 20th	Day	37% 2 12% 22% 22% 5%	1726
	21st to end	Day	38% 5% 11% 28% 16% 2	1600
December	1st to 10th	Day	36% 4 12% 29% 14% 4	2600
	11th to 20th	Day	44% 4 14% 25% 10% 2	2986
	21st to end	Day	44% 6% 17% 19% 14% 1	3960
January	1st to 10th	Night	36% 6% 11% 27% 17% 3	4352
	11th to 20th	Night	40% 4 11% 25% 17% 3	4120
	21st to end	Night	45% 4 10% 26% 13% 1	4532
February	1st to 10th	Night	42% 5% 13% 25% 14% 2	2470
	11th to 20th	Night	43% 5% 9% 22% 16% 4	2391
	21st to end	Night	44% 5% 11% 22% 14% 5%	1875
March	1st to 10th	Night	45% 6% 10% 26% 11% 2	3418
	11th to 20th	Night	32% 6% 10% 29% 20% 3	3480
	21st to end	Night	39% 5% 10% 24% 19% 5%	3800
April	1st to 10th	Night	42% 6% 10% 20% 18% 4	1900
	11th to 20th	Night	37% 6% 12% 20% 19% 6%	1875
	21st to end	Night	38% 6% 14% 25% 13% 4	1900
May	1st to 10th	Night	52% 7% 11% 18% 10% 3	2844
	11th to 20th	Night	50% 9% 11% 20% 9% 1	2696
	21st to end	Night	33% 9% 18% 25% 11% 3	2739
June	1st to 10th	Night	34% 8% 12% 26% 16% 2	1520
	11th to 20th	Night	36% 9% 15% 24% 14% 2	1520
	21st to end	Night	32% 7% 16% 24% 18% 3	1520
July	1st to 10th	Night	37% 7% 21% 18% 12% 5%	2480
	11th to 20th	Night	37% 8% 19% 22% 12% 1	2710
	21st to end	Night	40% 7% 16% 20% 16% 1	2988
August	1st to 10th	Night	46% 7% 15% 23% 8% 1	2814
	11th to 20th	Night	40% 7% 12% 26% 15% 1	2891
	21st to end	Night	35% 5% 14% 30% 16% 2	3476
September	1st to 10th	Night	38% 6% 12% 21% 19% 5%	1900
	11th to 20th	Night	34% 4 9% 28% 23% 3	1913
	21st to end	Night	45% 5% 10% 20% 17% 3	2190
October	1st to 10th	Night	41% 3 9% 22% 21% 4	3800
	11th to 20th	Night	24% 3 11% 23% 31% 7%	3779
	21st to end	Night	23% 3 10% 31% 26% 6%	4120
November	1st to 10th	Night	32% 4 10% 26% 22% 5%	2392
	11th to 20th	Night	36% 4 7% 25% 22% 6%	2670
	21st to end	Night	36% 5% 12% 25% 19% 3	2800
December	1st to 10th	Night	32% 3 13% 30% 19% 2	4580
	11th to 20th	Night	45% 3 13% 19% 16% 4	5208
	21st to end	Night	43% 7% 16% 19% 14% 1	6996

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	31% 24% 27% 13% 3	238
	11th to 20th	Day	29% 26% 29% 14% 1	270
	21st to end	Day	23% 34% 28% 12% 3 1	297
February	1st to 10th	Day	22% 25% 36% 13% 3	270
	11th to 20th	Day	33% 28% 32% 5% 2	282
	21st to end	Day	31% 19% 32% 16% 2	382
March	1st to 10th	Day	23% 23% 29% 21% 3	460
	11th to 20th	Day	25% 23% 30% 16% 4 2	460
	21st to end	Day	22% 21% 34% 17% 6% 1	506
April	1st to 10th	Day	23% 23% 27% 17% 8% 1	460
	11th to 20th	Day	17% 20% 27% 20% 13% 3	452
	21st to end	Day	24% 16% 29% 18% 10% 3	460
May	1st to 10th	Day	24% 17% 27% 19% 10% 4	463
	11th to 20th	Day	22% 10% 29% 21% 14% 4	487
	21st to end	Day	21% 6% 22% 25% 20% 5%	529
June	1st to 10th	Day	13% 8% 27% 26% 20% 6%	490
	11th to 20th	Day	15% 7% 26% 29% 16% 7%	490
	21st to end	Day	10% 7% 28% 31% 17% 7%	490
July	1st to 10th	Day	11% 5% 15% 31% 26% 12%	485
	11th to 20th	Day	7% 2 20% 32% 30% 9%	484
	21st to end	Day	13% 4 18% 33% 22% 9%	532
August	1st to 10th	Day	13% 4 17% 27% 24% 14%	486
	11th to 20th	Day	13% 4 20% 30% 22% 12%	479
	21st to end	Day	9% 4 21% 30% 22% 14%	539
September	1st to 10th	Day	18% 7% 17% 26% 21% 12%	490
	11th to 20th	Day	15% 4 18% 31% 19% 12%	490
	21st to end	Day	28% 9% 21% 25% 14% 3	490
October	1st to 10th	Day	19% 7% 21% 25% 21% 7%	490
	11th to 20th	Day	17% 14% 24% 28% 13% 3	490
	21st to end	Day	17% 12% 32% 25% 12% 3	539
November	1st to 10th	Day	17% 12% 31% 26% 11% 3	468
	11th to 20th	Day	21% 15% 34% 20% 10% 1	326
	21st to end	Day	23% 21% 32% 19% 6% 1	200
December	1st to 10th	Day	18% 22% 40% 16% 5% 1	200
	11th to 20th	Day	23% 24% 28% 21% 5%	200
	21st to end	Day	20% 21% 32% 20% 6%	220
January	1st to 10th	Night	19% 20% 38% 19% 3	785
	11th to 20th	Night	23% 15% 32% 25% 4	760
	21st to end	Night	19% 17% 41% 21% 2	836
February	1st to 10th	Night	17% 17% 37% 27% 2	760
	11th to 20th	Night	23% 23% 35% 17% 2	743
	21st to end	Night	25% 17% 37% 18% 3	628
March	1st to 10th	Night	20% 18% 37% 22% 3	760
	11th to 20th	Night	24% 16% 32% 22% 5% 1	760
	21st to end	Night	20% 16% 38% 21% 4 1	836
April	1st to 10th	Night	18% 18% 37% 22% 4	760
	11th to 20th	Night	17% 12% 36% 27% 8% 1	751
	21st to end	Night	19% 13% 31% 29% 8%	760
May	1st to 10th	Night	22% 7% 25% 33% 13%	574
	11th to 20th	Night	21% 5% 26% 35% 12% 1	496
	21st to end	Night	15% 4 21% 39% 19% 1	411
June	1st to 10th	Night	12% 2 26% 39% 20%	380
	11th to 20th	Night	13% 4 19% 39% 23% 1	380
	21st to end	Night	8% 3 22% 47% 19% 1	380
July	1st to 10th	Night	11% 3 13% 42% 28% 4	370
	11th to 20th	Night	7% 2 11% 41% 36% 4	502
	21st to end	Night	8% 3 15% 43% 27% 4	624
August	1st to 10th	Night	11% 3 10% 44% 30% 3	567
	11th to 20th	Night	11% 3 12% 39% 31% 3	604
	21st to end	Night	13% 2 15% 39% 26% 4	836
September	1st to 10th	Night	17% 2 16% 35% 26% 5%	760
	11th to 20th	Night	13% 3 18% 32% 29% 4	760
	21st to end	Night	24% 5% 20% 29% 21% 1	760
October	1st to 10th	Night	21% 5% 21% 28% 22% 3	760
	11th to 20th	Night	16% 11% 25% 33% 14% 1	760
	21st to end	Night	19% 9% 29% 30% 12% 1	836
November	1st to 10th	Night	14% 9% 33% 31% 11% 1	780
	11th to 20th	Night	18% 14% 31% 29% 8% 1	800
	21st to end	Night	16% 14% 35% 27% 7%	800
December	1st to 10th	Night	20% 16% 35% 23% 6%	800
	11th to 20th	Night	20% 12% 37% 28% 4	800
	21st to end	Night	19% 13% 34% 30% 3	880

Page generated at 2025-01-04 03:24:04. Version ac07

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