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 2024-01-17.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 41%	74690
	Night	14% 6% 2 5% 5% 3 5% 5% 5% 7% 43%	75141
Transparency	Day	39% 6% 13% 23% 16% 3	74403
	Night	39% 6% 12% 23% 17% 3	74947
Seeing	Day	19% 13% 26% 23% 14% 5%	13815
	Night	18% 11% 29% 29% 13% 1	23504

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% 7% 2 5% 5% 3 5% 5% 4 6% 43%	1610
	11th to 20th	Day	15% 8% 3 6% 5% 3 4 5% 5% 7% 40%	1674
	21st to end	Day	15% 8% 3 6% 5% 2 5% 5% 5% 6% 40%	1782
February	1st to 10th	Day	14% 8% 4 5% 6% 4 6% 5% 6% 6% 37%	1620
	11th to 20th	Day	17% 6% 3 5% 6% 3 4 4 4 7% 39%	1585
	21st to end	Day	17% 8% 4 6% 5% 2 4 3 4 7% 39%	1487
March	1st to 10th	Day	12% 6% 2 5% 5% 3 4 4 4 7% 48%	1980
	11th to 20th	Day	16% 6% 3 5% 6% 3 4 5% 4 7% 40%	1980
	21st to end	Day	17% 7% 3 6% 6% 4 4 4 5% 7% 38%	2182
April	1st to 10th	Day	11% 6% 3 6% 5% 3 5% 4 6% 8% 41%	2160
	11th to 20th	Day	13% 5% 2 5% 5% 3 5% 4 5% 6% 46%	2134
	21st to end	Day	18% 6% 3 5% 5% 3 5% 4 6% 6% 40%	2170
May	1st to 10th	Day	16% 7% 2 5% 5% 3 6% 5% 6% 9% 37%	2340
	11th to 20th	Day	19% 6% 3 5% 5% 3 4 6% 5% 8% 36%	2362
	21st to end	Day	15% 5% 2 5% 5% 3 4 5% 6% 8% 40%	2725
June	1st to 10th	Day	12% 4 2 5% 5% 3 5% 5% 7% 9% 43%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 4 7% 5% 7% 9% 39%	2520
	21st to end	Day	10% 3 1 4 6% 3 5% 6% 6% 11% 44%	2520
July	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 7% 9% 41%	2520
	11th to 20th	Day	6% 3 2 5% 5% 4 7% 6% 8% 11% 42%	2387
	21st to end	Day	10% 5% 3 5% 7% 4 6% 6% 7% 10% 37%	2547
August	1st to 10th	Day	9% 5% 2 6% 6% 5% 8% 7% 8% 9% 36%	2327
	11th to 20th	Day	12% 5% 3 6% 5% 4 5% 6% 6% 9% 39%	2245
	21st to end	Day	11% 5% 2 5% 5% 4 6% 6% 7% 9% 42%	2376
September	1st to 10th	Day	15% 5% 2 5% 4 3 4 4 4 6% 45%	2160
	11th to 20th	Day	13% 5% 2 5% 4 2 4 4 5% 8% 47%	2144
	21st to end	Day	19% 6% 2 6% 4 3 5% 4 5% 7% 39%	1886
October	1st to 10th	Day	17% 5% 2 4 5% 2 3 4 5% 7% 46%	1800
	11th to 20th	Day	17% 4 2 4 5% 3 4 5% 4 5% 47%	1800
	21st to end	Day	15% 5% 2 4 5% 2 4 4 4 7% 49%	1980
November	1st to 10th	Day	13% 5% 2 3 4 3 4 3 4 7% 51%	1805
	11th to 20th	Day	14% 6% 2 4 3 3 4 4 5% 6% 48%	1640
	21st to end	Day	15% 5% 2 4 5% 4 4 4 4 7% 47%	1520
December	1st to 10th	Day	16% 8% 3 5% 5% 3 5% 4 5% 7% 38%	1520
	11th to 20th	Day	15% 5% 2 5% 5% 3 5% 4 6% 8% 42%	1910
	21st to end	Day	18% 6% 2 5% 5% 3 5% 6% 6% 8% 35%	2772
January	1st to 10th	Night	13% 7% 3 5% 4 3 4 5% 5% 7% 43%	2554
	11th to 20th	Night	18% 5% 2 6% 6% 3 4 5% 6% 8% 38%	2430
	21st to end	Night	14% 8% 3 5% 5% 3 5% 4 4 6% 43%	2574
February	1st to 10th	Night	15% 6% 3 5% 6% 3 5% 4 6% 7% 40%	2340
	11th to 20th	Night	16% 7% 3 5% 4 3 4 4 5% 6% 40%	2259
	21st to end	Night	17% 8% 3 4 6% 3 5% 3 5% 7% 39%	1768
March	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 5% 6% 48%	1980
	11th to 20th	Night	18% 6% 2 4 4 3 4 4 5% 6% 44%	1980
	21st to end	Night	16% 6% 3 6% 5% 3 4 5% 5% 6% 41%	2174
April	1st to 10th	Night	14% 7% 3 7% 5% 2 5% 5% 5% 6% 40%	1800
	11th to 20th	Night	12% 5% 3 6% 5% 3 4 5% 6% 7% 45%	1775
	21st to end	Night	17% 5% 2 5% 4 2 5% 5% 5% 8% 43%	1800
May	1st to 10th	Night	17% 6% 3 4 5% 3 5% 4 6% 8% 39%	1624
	11th to 20th	Night	16% 8% 3 7% 5% 3 5% 4 5% 8% 37%	1531
	21st to end	Night	13% 5% 3 5% 4 3 5% 5% 7% 10% 41%	1550
June	1st to 10th	Night	11% 4 2 5% 4 3 5% 6% 7% 9% 44%	1440
	11th to 20th	Night	12% 5% 2 4 5% 3 4 6% 6% 9% 42%	1440
	21st to end	Night	9% 4 2 5% 5% 3 5% 5% 7% 11% 45%	1440
July	1st to 10th	Night	9% 6% 2 6% 5% 4 6% 6% 7% 10% 39%	1440
	11th to 20th	Night	6% 4 2 4 6% 4 4 6% 8% 10% 45%	1569
	21st to end	Night	8% 4 2 5% 5% 3 7% 7% 7% 11% 42%	1771
August	1st to 10th	Night	9% 5% 3 5% 7% 4 6% 7% 7% 8% 40%	1611
	11th to 20th	Night	10% 6% 3 6% 5% 4 6% 6% 7% 9% 39%	1635
	21st to end	Night	11% 5% 2 5% 5% 3 7% 5% 7% 9% 42%	1980
September	1st to 10th	Night	15% 5% 2 5% 5% 4 4 5% 5% 7% 44%	1800
	11th to 20th	Night	11% 6% 2 5% 4 3 4 2 3 7% 52%	1812
	21st to end	Night	18% 7% 2 5% 5% 3 4 3 4 6% 42%	2074
October	1st to 10th	Night	19% 5% 2 4 4 3 4 4 4 7% 46%	2160
	11th to 20th	Night	15% 4 2 5% 4 3 3 4 5% 5% 51%	2160
	21st to end	Night	15% 6% 1 5% 4 2 3 3 5% 6% 50%	2376
November	1st to 10th	Night	11% 6% 3 5% 4 2 3 3 4 7% 53%	2269
	11th to 20th	Night	14% 6% 2 4 3 2 4 4 4 6% 49%	2536
	21st to end	Night	13% 5% 2 4 5% 2 5% 5% 5% 8% 46%	2660
December	1st to 10th	Night	16% 7% 2 6% 5% 3 5% 4 5% 6% 40%	2660
	11th to 20th	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 42%	3285
	21st to end	Night	16% 6% 2 5% 5% 4 6% 6% 7% 9% 35%	4884

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	42% 6% 10% 24% 16% 4	1611
	11th to 20th	Day	43% 5% 13% 23% 14% 2	1674
	21st to end	Day	44% 4 11% 23% 14% 3	1782
February	1st to 10th	Day	45% 5% 13% 22% 11% 3	1620
	11th to 20th	Day	44% 5% 9% 23% 15% 2	1594
	21st to end	Day	45% 5% 12% 19% 15% 4	1487
March	1st to 10th	Day	37% 5% 11% 25% 20% 2	1980
	11th to 20th	Day	43% 5% 11% 19% 17% 6%	1980
	21st to end	Day	45% 5% 11% 19% 16% 4	2182
April	1st to 10th	Day	39% 6% 13% 19% 19% 5%	2160
	11th to 20th	Day	37% 5% 12% 21% 20% 5%	2134
	21st to end	Day	44% 5% 10% 22% 15% 4	2170
May	1st to 10th	Day	42% 7% 13% 21% 15% 2	2340
	11th to 20th	Day	45% 8% 13% 19% 13% 2	2366
	21st to end	Day	40% 8% 14% 26% 11% 1	2725
June	1st to 10th	Day	35% 8% 15% 25% 16% 1	2520
	11th to 20th	Day	38% 9% 16% 21% 14% 2	2520
	21st to end	Day	32% 9% 16% 26% 15% 2	2520
July	1st to 10th	Day	37% 9% 13% 22% 17% 2	2450
	11th to 20th	Day	31% 9% 16% 26% 15% 2	2315
	21st to end	Day	38% 9% 13% 21% 17% 2	2405
August	1st to 10th	Day	40% 9% 16% 24% 11% 1	2314
	11th to 20th	Day	39% 9% 14% 22% 15% 1	2245
	21st to end	Day	35% 9% 16% 25% 13% 3	2376
September	1st to 10th	Day	39% 7% 11% 20% 19% 4	2160
	11th to 20th	Day	35% 6% 9% 27% 21% 3	2144
	21st to end	Day	44% 6% 10% 20% 18% 2	1886
October	1st to 10th	Day	39% 5% 10% 26% 16% 3	1800
	11th to 20th	Day	38% 5% 10% 24% 20% 3	1800
	21st to end	Day	36% 4 10% 26% 22% 3	1980
November	1st to 10th	Day	34% 3 12% 26% 21% 5%	1805
	11th to 20th	Day	37% 2 12% 23% 21% 5%	1640
	21st to end	Day	38% 5% 10% 28% 16% 2	1520
December	1st to 10th	Day	44% 6% 12% 25% 10% 2	1520
	11th to 20th	Day	38% 6% 12% 30% 11% 3	1906
	21st to end	Day	42% 8% 16% 23% 10% 1	2772
January	1st to 10th	Night	40% 4 10% 23% 18% 5%	2554
	11th to 20th	Night	44% 5% 13% 22% 15% 2	2430
	21st to end	Night	41% 4 10% 26% 17% 2	2574
February	1st to 10th	Night	43% 5% 13% 24% 13% 2	2340
	11th to 20th	Night	43% 5% 10% 22% 16% 5%	2261
	21st to end	Night	44% 4 11% 22% 14% 5%	1768
March	1st to 10th	Night	35% 6% 11% 28% 17% 3	1980
	11th to 20th	Night	41% 5% 11% 21% 19% 4	1980
	21st to end	Night	42% 6% 12% 20% 15% 5%	2174
April	1st to 10th	Night	42% 5% 10% 20% 18% 4	1800
	11th to 20th	Night	36% 6% 12% 20% 19% 6%	1775
	21st to end	Night	38% 6% 14% 25% 12% 5%	1800
May	1st to 10th	Night	42% 7% 13% 21% 13% 4	1624
	11th to 20th	Night	44% 7% 13% 19% 16% 2	1532
	21st to end	Night	37% 8% 18% 24% 12% 1	1551
June	1st to 10th	Night	34% 9% 12% 26% 16% 2	1440
	11th to 20th	Night	37% 9% 15% 22% 14% 2	1440
	21st to end	Night	32% 8% 17% 24% 18% 3	1440
July	1st to 10th	Night	38% 8% 17% 20% 13% 4	1400
	11th to 20th	Night	31% 10% 18% 22% 18% 2	1518
	21st to end	Night	31% 9% 19% 25% 15% 1	1672
August	1st to 10th	Night	38% 9% 16% 21% 13% 1	1600
	11th to 20th	Night	39% 9% 15% 23% 13% 2	1635
	21st to end	Night	37% 7% 15% 23% 15% 3	1980
September	1st to 10th	Night	39% 6% 12% 21% 18% 4	1800
	11th to 20th	Night	34% 4 10% 27% 22% 3	1812
	21st to end	Night	43% 5% 10% 21% 18% 3	2074
October	1st to 10th	Night	40% 4 10% 25% 18% 3	2160
	11th to 20th	Night	35% 4 10% 27% 22% 2	2160
	21st to end	Night	35% 4 10% 25% 23% 3	2376
November	1st to 10th	Night	33% 4 10% 26% 22% 5%	2269
	11th to 20th	Night	36% 4 7% 25% 22% 6%	2536
	21st to end	Night	35% 5% 12% 26% 19% 3	2660
December	1st to 10th	Night	44% 4 11% 26% 13% 2	2660
	11th to 20th	Night	41% 4 11% 23% 18% 3	3288
	21st to end	Night	40% 10% 17% 20% 12% 1	4884

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% 24% 28% 14% 4	225
	11th to 20th	Day	27% 26% 31% 14% 2	258
	21st to end	Day	24% 35% 26% 11% 3 1	264
February	1st to 10th	Day	24% 27% 36% 10% 3	240
	11th to 20th	Day	33% 28% 33% 5% 1	252
	21st to end	Day	30% 19% 33% 16% 2	346
March	1st to 10th	Day	22% 25% 29% 22% 3	420
	11th to 20th	Day	25% 22% 30% 17% 4 2	420
	21st to end	Day	21% 21% 34% 16% 6% 1	462
April	1st to 10th	Day	22% 23% 27% 19% 8% 1	420
	11th to 20th	Day	17% 17% 27% 21% 14% 4	412
	21st to end	Day	25% 15% 29% 19% 10% 2	420
May	1st to 10th	Day	23% 18% 27% 19% 10% 3	423
	11th to 20th	Day	21% 11% 30% 21% 14% 4	447
	21st to end	Day	22% 6% 21% 24% 21% 6%	485
June	1st to 10th	Day	13% 8% 26% 27% 20% 6%	450
	11th to 20th	Day	16% 8% 27% 28% 15% 6%	450
	21st to end	Day	10% 6% 28% 32% 18% 6%	450
July	1st to 10th	Day	12% 5% 14% 30% 26% 13%	445
	11th to 20th	Day	6% 2 19% 32% 31% 9%	444
	21st to end	Day	12% 5% 18% 33% 22% 10%	488
August	1st to 10th	Day	13% 4 18% 26% 24% 15%	446
	11th to 20th	Day	13% 4 17% 30% 23% 13%	439
	21st to end	Day	9% 4 22% 30% 22% 15%	495
September	1st to 10th	Day	19% 6% 17% 25% 20% 12%	450
	11th to 20th	Day	15% 5% 18% 31% 20% 12%	450
	21st to end	Day	24% 9% 21% 26% 16% 4	450
October	1st to 10th	Day	19% 6% 21% 26% 22% 7%	450
	11th to 20th	Day	18% 14% 24% 28% 13% 3	450
	21st to end	Day	18% 13% 32% 25% 9% 3	495
November	1st to 10th	Day	17% 12% 29% 26% 11% 3	431
	11th to 20th	Day	22% 15% 32% 19% 10% 1	300
	21st to end	Day	20% 21% 32% 19% 7% 1	180
December	1st to 10th	Day	18% 23% 38% 16% 5% 1	180
	11th to 20th	Day	22% 26% 26% 22% 4	180
	21st to end	Day	21% 21% 32% 18% 7% 1	198
January	1st to 10th	Night	19% 20% 38% 19% 3	760
	11th to 20th	Night	23% 15% 32% 26% 4	748
	21st to end	Night	19% 17% 42% 21% 2	792
February	1st to 10th	Night	18% 18% 37% 26% 2	720
	11th to 20th	Night	22% 23% 35% 18% 2	703
	21st to end	Night	26% 18% 37% 17% 3	592
March	1st to 10th	Night	19% 18% 37% 22% 3	720
	11th to 20th	Night	25% 16% 32% 22% 5% 1	720
	21st to end	Night	20% 15% 39% 21% 5% 1	792
April	1st to 10th	Night	18% 18% 37% 23% 4	720
	11th to 20th	Night	17% 12% 35% 28% 8% 1	711
	21st to end	Night	20% 12% 31% 29% 8%	720
May	1st to 10th	Night	21% 7% 25% 32% 13%	544
	11th to 20th	Night	20% 5% 26% 36% 12% 1	470
	21st to end	Night	16% 4 20% 40% 19% 1	389
June	1st to 10th	Night	12% 2 25% 40% 21%	360
	11th to 20th	Night	14% 4 20% 39% 22% 1	360
	21st to end	Night	8% 3 22% 47% 19% 1	360
July	1st to 10th	Night	11% 3 13% 41% 28% 4	350
	11th to 20th	Night	7% 2 12% 39% 36% 4	474
	21st to end	Night	8% 3 15% 43% 28% 4	591
August	1st to 10th	Night	11% 3 9% 44% 30% 3	537
	11th to 20th	Night	11% 4 12% 37% 32% 4	571
	21st to end	Night	14% 2 16% 38% 26% 4	792
September	1st to 10th	Night	18% 2 16% 34% 26% 5%	720
	11th to 20th	Night	13% 3 19% 32% 29% 4	720
	21st to end	Night	22% 5% 21% 30% 22% 1	720
October	1st to 10th	Night	21% 5% 21% 28% 22% 3	720
	11th to 20th	Night	17% 11% 25% 33% 14% 1	720
	21st to end	Night	20% 10% 31% 29% 11% 1	792
November	1st to 10th	Night	15% 9% 33% 30% 11% 1	740
	11th to 20th	Night	18% 14% 30% 29% 8% 1	760
	21st to end	Night	16% 14% 34% 28% 8%	760
December	1st to 10th	Night	21% 16% 35% 22% 7%	760
	11th to 20th	Night	19% 12% 39% 27% 4	760
	21st to end	Night	19% 14% 34% 30% 3	836

Page generated at 2024-01-14 09:54:58. Version ac07

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