Greenbrier State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenbrier State Park clear sky chart from 2005-11-06 to 2024-03-28.

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% 3 5% 5% 3 5% 5% 6% 8% 39%	78812
	Night	14% 6% 2 5% 5% 3 5% 5% 6% 7% 41%	81188
Transparency	Day	40% 8% 13% 22% 14% 2	78522
	Night	39% 8% 13% 23% 14% 3	80997
Seeing	Day	18% 13% 26% 23% 15% 5%	14030
	Night	17% 10% 29% 31% 12% 1	23694

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% 6% 3 5% 6% 4 5% 5% 4 6% 40%	2590
	11th to 20th	Day	14% 11% 4 7% 6% 4 5% 4 5% 7% 33%	2840
	21st to end	Day	17% 11% 4 8% 6% 4 5% 4 5% 6% 31%	3124
February	1st to 10th	Day	15% 9% 3 6% 7% 3 5% 5% 4 7% 37%	1710
	11th to 20th	Day	15% 7% 3 6% 7% 3 4 4 5% 6% 38%	1682
	21st to end	Day	18% 9% 3 7% 5% 3 5% 4 5% 5% 38%	1570
March	1st to 10th	Day	14% 6% 2 5% 5% 3 5% 4 5% 7% 44%	2074
	11th to 20th	Day	15% 8% 3 5% 6% 3 4 5% 5% 7% 39%	2090
	21st to end	Day	18% 7% 3 7% 6% 3 4 4 5% 6% 37%	2273
April	1st to 10th	Day	13% 7% 3 6% 6% 4 5% 5% 6% 8% 38%	2160
	11th to 20th	Day	14% 6% 3 5% 6% 3 4 6% 4 8% 43%	2134
	21st to end	Day	18% 6% 2 5% 5% 3 5% 4 6% 6% 39%	2168
May	1st to 10th	Day	16% 7% 3 5% 5% 3 5% 5% 7% 8% 35%	2340
	11th to 20th	Day	19% 7% 3 5% 5% 3 5% 4 6% 8% 35%	2403
	21st to end	Day	13% 6% 3 5% 5% 3 5% 5% 6% 9% 39%	2725
June	1st to 10th	Day	12% 5% 2 4 5% 3 5% 5% 8% 10% 41%	2520
	11th to 20th	Day	12% 6% 3 5% 5% 4 7% 6% 6% 10% 38%	2520
	21st to end	Day	10% 4 2 4 5% 3 5% 5% 7% 10% 44%	2520
July	1st to 10th	Day	8% 4 2 5% 6% 3 7% 7% 7% 10% 41%	2520
	11th to 20th	Day	6% 4 2 5% 5% 4 6% 7% 7% 11% 42%	2443
	21st to end	Day	10% 6% 2 6% 6% 4 6% 6% 8% 9% 36%	2547
August	1st to 10th	Day	9% 5% 3 6% 7% 5% 7% 7% 7% 10% 36%	2327
	11th to 20th	Day	11% 5% 3 5% 5% 4 5% 6% 7% 9% 39%	2244
	21st to end	Day	10% 5% 2 6% 6% 3 5% 5% 7% 9% 41%	2376
September	1st to 10th	Day	16% 5% 3 4 5% 3 5% 4 5% 7% 43%	2160
	11th to 20th	Day	12% 4 2 4 5% 3 4 5% 6% 9% 46%	2160
	21st to end	Day	18% 7% 2 6% 6% 3 4 4 5% 7% 39%	1880
October	1st to 10th	Day	16% 5% 2 5% 5% 3 3 4 5% 8% 44%	1800
	11th to 20th	Day	17% 5% 2 4 4 3 5% 4 5% 6% 45%	1800
	21st to end	Day	14% 7% 3 6% 4 3 4 4 5% 6% 46%	1980
November	1st to 10th	Day	12% 6% 2 4 4 3 3 4 5% 8% 49%	1771
	11th to 20th	Day	16% 5% 2 3 5% 2 4 5% 4 7% 46%	1639
	21st to end	Day	16% 6% 2 6% 5% 2 5% 5% 5% 8% 41%	1520
December	1st to 10th	Day	17% 9% 3 5% 5% 3 4 5% 7% 6% 34%	1520
	11th to 20th	Day	17% 6% 2 6% 6% 3 5% 4 6% 7% 38%	1910
	21st to end	Day	17% 7% 3 6% 6% 4 6% 5% 6% 9% 31%	2772
January	1st to 10th	Night	12% 9% 2 7% 6% 3 5% 5% 6% 8% 38%	4352
	11th to 20th	Night	18% 7% 2 5% 5% 3 4 4 5% 6% 39%	4120
	21st to end	Night	19% 10% 4 6% 5% 3 5% 5% 5% 6% 33%	4532
February	1st to 10th	Night	14% 8% 2 6% 5% 3 4 5% 6% 7% 39%	2470
	11th to 20th	Night	17% 8% 3 6% 5% 3 4 5% 5% 6% 38%	2384
	21st to end	Night	17% 9% 3 6% 6% 4 5% 4 5% 7% 35%	1884
March	1st to 10th	Night	15% 6% 2 4 4 3 5% 5% 5% 7% 44%	2104
	11th to 20th	Night	17% 6% 2 5% 4 4 5% 4 5% 6% 41%	2090
	21st to end	Night	14% 7% 3 7% 5% 3 4 4 5% 7% 41%	2238
April	1st to 10th	Night	14% 7% 4 7% 6% 3 6% 5% 6% 6% 36%	1800
	11th to 20th	Night	13% 5% 3 6% 5% 3 4 5% 6% 9% 43%	1775
	21st to end	Night	17% 5% 2 4 5% 3 5% 5% 6% 8% 41%	1800
May	1st to 10th	Night	16% 7% 3 5% 5% 4 4 5% 5% 8% 38%	1626
	11th to 20th	Night	17% 6% 3 6% 5% 3 4 6% 6% 8% 36%	1487
	21st to end	Night	12% 5% 3 5% 5% 3 5% 6% 7% 8% 40%	1550
June	1st to 10th	Night	11% 4 3 4 4 4 4 4 6% 9% 47%	1440
	11th to 20th	Night	10% 5% 2 8% 6% 3 6% 4 7% 7% 40%	1440
	21st to end	Night	8% 5% 2 5% 6% 3 5% 6% 7% 9% 45%	1440
July	1st to 10th	Night	10% 5% 2 5% 7% 4 6% 6% 6% 9% 40%	1440
	11th to 20th	Night	5% 5% 2 5% 5% 3 6% 6% 7% 9% 47%	1514
	21st to end	Night	9% 4 2 3 4 3 6% 7% 10% 11% 41%	1771
August	1st to 10th	Night	9% 4 2 6% 6% 4 5% 6% 7% 9% 40%	1611
	11th to 20th	Night	10% 6% 2 6% 6% 5% 5% 7% 6% 7% 42%	1638
	21st to end	Night	10% 5% 2 5% 5% 3 4 5% 7% 9% 44%	1980
September	1st to 10th	Night	13% 6% 2 5% 5% 3 4 5% 5% 8% 45%	1800
	11th to 20th	Night	10% 6% 3 4 4 3 3 4 4 7% 52%	1800
	21st to end	Night	17% 6% 3 5% 4 3 5% 4 5% 6% 43%	2074
October	1st to 10th	Night	18% 6% 2 5% 5% 3 4 4 4 6% 43%	2160
	11th to 20th	Night	14% 5% 2 5% 4 3 4 4 5% 6% 49%	2160
	21st to end	Night	16% 6% 2 5% 3 2 4 4 5% 7% 46%	2376
November	1st to 10th	Night	11% 6% 2 5% 4 2 3 4 5% 6% 52%	2306
	11th to 20th	Night	15% 6% 2 4 4 3 4 5% 5% 7% 45%	2537
	21st to end	Night	14% 5% 3 5% 5% 3 5% 5% 6% 7% 43%	2660
December	1st to 10th	Night	17% 8% 3 6% 6% 3 4 5% 5% 6% 37%	2660
	11th to 20th	Night	17% 6% 2 5% 5% 4 6% 5% 5% 6% 38%	3285
	21st to end	Night	16% 7% 2 5% 6% 3 6% 7% 7% 9% 31%	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	40% 7% 12% 27% 10% 3	2591
	11th to 20th	Day	47% 7% 11% 19% 12% 3	2840
	21st to end	Day	49% 8% 10% 21% 9% 2	3124
February	1st to 10th	Day	46% 7% 14% 22% 10% 2	1710
	11th to 20th	Day	46% 5% 11% 23% 13% 2	1691
	21st to end	Day	48% 5% 11% 19% 13% 4	1570
March	1st to 10th	Day	39% 6% 12% 24% 17% 2	2074
	11th to 20th	Day	42% 6% 12% 19% 15% 5%	2090
	21st to end	Day	47% 6% 11% 19% 15% 3	2273
April	1st to 10th	Day	42% 7% 13% 18% 16% 4	2160
	11th to 20th	Day	39% 6% 12% 21% 18% 4	2134
	21st to end	Day	44% 7% 10% 20% 16% 3	2168
May	1st to 10th	Day	43% 9% 13% 19% 14% 2	2340
	11th to 20th	Day	46% 8% 12% 18% 13% 3	2407
	21st to end	Day	40% 8% 15% 23% 12% 1	2725
June	1st to 10th	Day	35% 9% 15% 23% 15% 1	2520
	11th to 20th	Day	38% 12% 14% 20% 13% 2	2520
	21st to end	Day	32% 9% 16% 26% 15% 1	2520
July	1st to 10th	Day	36% 11% 15% 20% 15% 3	2450
	11th to 20th	Day	32% 9% 16% 24% 16% 2	2368
	21st to end	Day	39% 10% 13% 20% 15% 2	2405
August	1st to 10th	Day	39% 11% 16% 23% 11% 1	2314
	11th to 20th	Day	38% 9% 15% 22% 14% 2	2244
	21st to end	Day	37% 7% 16% 24% 12% 3	2376
September	1st to 10th	Day	40% 7% 11% 20% 18% 4	2160
	11th to 20th	Day	33% 7% 13% 25% 20% 3	2160
	21st to end	Day	44% 6% 10% 19% 19% 2	1880
October	1st to 10th	Day	39% 7% 12% 23% 17% 2	1800
	11th to 20th	Day	38% 6% 12% 23% 20% 1	1800
	21st to end	Day	38% 6% 11% 25% 18% 2	1980
November	1st to 10th	Day	33% 5% 13% 25% 18% 4	1771
	11th to 20th	Day	36% 5% 14% 23% 19% 3	1639
	21st to end	Day	40% 6% 13% 28% 12% 1	1520
December	1st to 10th	Day	46% 8% 14% 22% 9% 1	1520
	11th to 20th	Day	41% 9% 13% 29% 7% 2	1906
	21st to end	Day	43% 12% 19% 18% 8%	2772
January	1st to 10th	Night	39% 9% 15% 24% 12% 2	4352
	11th to 20th	Night	41% 7% 14% 25% 11% 2	4120
	21st to end	Night	47% 7% 11% 25% 8% 1	4532
February	1st to 10th	Night	42% 8% 14% 24% 12% 1	2470
	11th to 20th	Night	44% 6% 11% 22% 16% 2	2386
	21st to end	Night	46% 6% 12% 20% 12% 5%	1884
March	1st to 10th	Night	38% 6% 11% 27% 15% 2	2104
	11th to 20th	Night	41% 6% 11% 23% 16% 3	2090
	21st to end	Night	42% 6% 12% 21% 15% 5%	2238
April	1st to 10th	Night	45% 7% 11% 19% 15% 4	1800
	11th to 20th	Night	37% 7% 11% 22% 17% 6%	1775
	21st to end	Night	40% 6% 13% 23% 14% 4	1800
May	1st to 10th	Night	43% 8% 11% 21% 13% 4	1626
	11th to 20th	Night	43% 9% 12% 18% 16% 2	1488
	21st to end	Night	37% 11% 16% 23% 12% 2	1551
June	1st to 10th	Night	33% 9% 12% 26% 17% 3	1440
	11th to 20th	Night	39% 11% 12% 23% 14% 2	1440
	21st to end	Night	33% 10% 14% 25% 17% 2	1440
July	1st to 10th	Night	39% 12% 16% 18% 12% 4	1400
	11th to 20th	Night	31% 10% 17% 23% 17% 3	1466
	21st to end	Night	29% 11% 21% 21% 16% 2	1672
August	1st to 10th	Night	36% 10% 18% 23% 12% 1	1600
	11th to 20th	Night	39% 9% 15% 20% 15% 1	1638
	21st to end	Night	35% 8% 15% 24% 15% 3	1980
September	1st to 10th	Night	38% 7% 13% 20% 18% 5%	1800
	11th to 20th	Night	32% 5% 11% 27% 22% 3	1800
	21st to end	Night	42% 6% 10% 21% 18% 3	2074
October	1st to 10th	Night	42% 6% 11% 23% 17% 2	2160
	11th to 20th	Night	35% 5% 11% 27% 19% 2	2160
	21st to end	Night	36% 6% 11% 26% 19% 2	2376
November	1st to 10th	Night	32% 5% 11% 27% 20% 4	2306
	11th to 20th	Night	36% 6% 11% 24% 19% 5%	2537
	21st to end	Night	37% 7% 13% 24% 16% 3	2660
December	1st to 10th	Night	46% 7% 12% 24% 11% 1	2660
	11th to 20th	Night	42% 7% 12% 23% 15% 2	3288
	21st to end	Night	41% 11% 19% 19% 8% 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	27% 25% 28% 16% 3	202
	11th to 20th	Day	29% 28% 27% 11% 4	270
	21st to end	Day	22% 28% 33% 13% 3 1	297
February	1st to 10th	Day	23% 24% 37% 13% 3	270
	11th to 20th	Day	32% 26% 32% 8% 1	289
	21st to end	Day	29% 20% 30% 18% 2	382
March	1st to 10th	Day	21% 23% 30% 21% 5%	460
	11th to 20th	Day	23% 23% 30% 17% 6% 1	460
	21st to end	Day	21% 19% 31% 21% 5% 1	490
April	1st to 10th	Day	19% 22% 28% 23% 6% 2	420
	11th to 20th	Day	17% 15% 32% 17% 14% 5%	412
	21st to end	Day	26% 15% 28% 20% 8% 2	420
May	1st to 10th	Day	23% 14% 30% 19% 11% 3	423
	11th to 20th	Day	20% 14% 26% 23% 13% 4	447
	21st to end	Day	16% 7% 23% 25% 22% 8%	485
June	1st to 10th	Day	15% 6% 28% 24% 19% 7%	450
	11th to 20th	Day	16% 8% 26% 25% 19% 6%	450
	21st to end	Day	10% 6% 24% 31% 23% 6%	450
July	1st to 10th	Day	10% 4 18% 28% 28% 13%	445
	11th to 20th	Day	5% 3 18% 31% 31% 12%	444
	21st to end	Day	12% 3 18% 32% 26% 8%	488
August	1st to 10th	Day	10% 3 17% 27% 29% 13%	446
	11th to 20th	Day	11% 3 18% 33% 23% 13%	439
	21st to end	Day	10% 3 17% 31% 24% 15%	495
September	1st to 10th	Day	18% 6% 17% 23% 24% 12%	450
	11th to 20th	Day	12% 4 20% 28% 26% 11%	450
	21st to end	Day	22% 9% 22% 25% 17% 5%	450
October	1st to 10th	Day	19% 7% 20% 25% 23% 6%	450
	11th to 20th	Day	17% 12% 26% 28% 14% 2	450
	21st to end	Day	15% 14% 33% 25% 10% 2	495
November	1st to 10th	Day	15% 13% 29% 27% 13% 3	414
	11th to 20th	Day	19% 17% 30% 20% 13% 1	299
	21st to end	Day	19% 20% 34% 19% 7% 1	180
December	1st to 10th	Day	22% 24% 31% 17% 4 2	180
	11th to 20th	Day	23% 23% 27% 20% 8%	180
	21st to end	Day	22% 16% 33% 20% 8% 1	198
January	1st to 10th	Night	18% 17% 42% 21% 3	760
	11th to 20th	Night	22% 16% 33% 27% 3	760
	21st to end	Night	18% 17% 39% 24% 1	836
February	1st to 10th	Night	18% 17% 33% 29% 2	760
	11th to 20th	Night	24% 20% 36% 19% 1	743
	21st to end	Night	23% 18% 38% 18% 3	628
March	1st to 10th	Night	20% 15% 38% 23% 4	760
	11th to 20th	Night	22% 18% 31% 24% 5%	760
	21st to end	Night	18% 15% 38% 24% 5%	821
April	1st to 10th	Night	18% 19% 34% 24% 5%	720
	11th to 20th	Night	15% 12% 35% 29% 9%	711
	21st to end	Night	21% 11% 32% 28% 7%	720
May	1st to 10th	Night	20% 8% 27% 33% 12%	546
	11th to 20th	Night	20% 5% 26% 37% 11%	426
	21st to end	Night	16% 3 22% 39% 19% 2	389
June	1st to 10th	Night	12% 3 25% 36% 24% 1	360
	11th to 20th	Night	11% 5% 21% 41% 20% 2	360
	21st to end	Night	9% 3 20% 50% 18%	360
July	1st to 10th	Night	11% 3 16% 39% 29% 3	350
	11th to 20th	Night	6% 2 15% 40% 34% 3	422
	21st to end	Night	10% 2 13% 43% 30% 3	591
August	1st to 10th	Night	12% 1 8% 46% 30% 2	537
	11th to 20th	Night	12% 3 13% 39% 30% 3	574
	21st to end	Night	12% 3 14% 40% 28% 4	792
September	1st to 10th	Night	17% 1 17% 35% 26% 3	720
	11th to 20th	Night	12% 3 19% 35% 28% 3	720
	21st to end	Night	20% 3 19% 35% 20% 2	720
October	1st to 10th	Night	20% 6% 21% 31% 20% 3	720
	11th to 20th	Night	15% 9% 30% 33% 12% 1	720
	21st to end	Night	19% 9% 32% 29% 10% 1	792
November	1st to 10th	Night	13% 8% 31% 37% 10% 1	740
	11th to 20th	Night	17% 14% 31% 29% 8% 1	760
	21st to end	Night	15% 14% 33% 30% 7%	760
December	1st to 10th	Night	22% 13% 36% 22% 6%	760
	11th to 20th	Night	18% 10% 40% 28% 4	760
	21st to end	Night	20% 11% 35% 32% 3	836

Page generated at 2024-03-24 23:37:04. Version ac07

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