Shenandoah County Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shenandoah County Park clear sky chart from 2005-11-06 to 2025-07-21.

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% 5% 5% 5% 4 6% 7% 41%	120080
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 43%	119014
Transparency	Day	39% 8% 11% 22% 16% 4	123724
	Night	38% 7% 12% 23% 17% 3	123507
Seeing	Day	20% 15% 27% 22% 13% 4	15819
	Night	17% 12% 27% 30% 12% 1	25471

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	13% 6% 3 6% 5% 4 4 3 5% 5% 45%	3964
	11th to 20th	Day	11% 9% 3 7% 6% 4 4 3 4 4 46%	4060
	21st to end	Day	13% 7% 3 7% 4 4 4 3 5% 6% 43%	4466
February	1st to 10th	Day	11% 10% 3 8% 4 5% 5% 4 5% 6% 39%	1800
	11th to 20th	Day	16% 8% 2 8% 5% 4 5% 3 5% 6% 38%	1753
	21st to end	Day	14% 9% 3 6% 4 4 4 4 4 5% 42%	1685
March	1st to 10th	Day	15% 8% 3 6% 4 4 4 3 4 6% 42%	4935
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 5% 7% 51%	4980
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 6% 6% 39%	5465
April	1st to 10th	Day	11% 8% 2 6% 5% 5% 5% 4 6% 7% 40%	2372
	11th to 20th	Day	11% 8% 2 6% 4 3 4 3 5% 6% 46%	2374
	21st to end	Day	16% 6% 2 6% 5% 5% 4 3 6% 7% 40%	2455
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 5% 8% 9% 30%	5862
	11th to 20th	Day	21% 7% 2 6% 4 4 5% 4 7% 9% 30%	5861
	21st to end	Day	15% 5% 2 6% 5% 5% 6% 4 7% 8% 37%	6934
June	1st to 10th	Day	11% 6% 2 5% 5% 5% 6% 4 6% 9% 41%	2800
	11th to 20th	Day	10% 5% 2 6% 5% 6% 6% 4 7% 10% 38%	2800
	21st to end	Day	9% 5% 1 5% 5% 5% 6% 5% 7% 9% 43%	2800
July	1st to 10th	Day	6% 4 2 7% 5% 6% 6% 5% 8% 10% 43%	4523
	11th to 20th	Day	8% 5% 2 6% 6% 6% 6% 5% 8% 12% 37%	4250
	21st to end	Day	10% 8% 3 7% 6% 6% 6% 5% 6% 8% 35%	4466
August	1st to 10th	Day	14% 6% 3 7% 5% 6% 6% 5% 8% 9% 31%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 7% 9% 40%	3988
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 47%	4180
September	1st to 10th	Day	14% 5% 2 6% 4 5% 5% 3 5% 6% 45%	2280
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 5% 7% 46%	2214
	21st to end	Day	21% 6% 2 5% 5% 5% 4 3 5% 5% 39%	2019
October	1st to 10th	Day	16% 5% 2 6% 3 3 4 3 6% 7% 45%	1900
	11th to 20th	Day	14% 6% 2 6% 4 5% 3 3 5% 5% 48%	1900
	21st to end	Day	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2090
November	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 5% 6% 52%	1957
	11th to 20th	Day	12% 7% 2 5% 4 4 4 4 5% 6% 46%	1693
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 4 6% 47%	1600
December	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 4 6% 51%	2600
	11th to 20th	Day	16% 9% 3 6% 4 4 4 3 4 6% 40%	2990
	21st to end	Day	14% 9% 3 6% 5% 5% 6% 4 6% 8% 34%	3960
January	1st to 10th	Night	9% 7% 2 6% 5% 5% 4 3 5% 6% 47%	5963
	11th to 20th	Night	12% 8% 3 5% 4 3 4 3 5% 5% 48%	5900
	21st to end	Night	12% 8% 3 7% 3 3 3 3 5% 5% 47%	6490
February	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 4 6% 6% 41%	2600
	11th to 20th	Night	15% 9% 2 6% 5% 4 5% 4 5% 6% 39%	2533
	21st to end	Night	13% 9% 3 7% 5% 4 3 4 6% 6% 40%	1939
March	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 5% 47%	4918
	11th to 20th	Night	8% 5% 2 5% 3 4 4 4 5% 8% 51%	4980
	21st to end	Night	10% 5% 2 8% 5% 4 5% 4 5% 6% 45%	5467
April	1st to 10th	Night	13% 8% 3 7% 5% 4 5% 4 6% 6% 40%	2026
	11th to 20th	Night	11% 6% 2 7% 5% 4 4 4 6% 8% 44%	1975
	21st to end	Night	14% 6% 2 5% 4 5% 4 4 5% 7% 44%	1960
May	1st to 10th	Night	17% 8% 3 8% 5% 5% 5% 4 5% 8% 31%	4033
	11th to 20th	Night	22% 8% 2 6% 5% 4 4 3 6% 7% 32%	4018
	21st to end	Night	15% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	3920
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 6% 8% 46%	1600
	11th to 20th	Night	11% 6% 3 5% 4 5% 5% 5% 7% 9% 41%	1600
	21st to end	Night	8% 4 2 7% 5% 4 5% 5% 9% 9% 43%	1600
July	1st to 10th	Night	6% 4 2 7% 5% 6% 6% 5% 8% 10% 41%	2653
	11th to 20th	Night	6% 5% 2 7% 6% 5% 6% 4 8% 11% 38%	2930
	21st to end	Night	8% 7% 3 8% 5% 5% 6% 5% 7% 9% 36%	3087
August	1st to 10th	Night	14% 5% 2 7% 5% 6% 6% 5% 6% 9% 35%	2825
	11th to 20th	Night	8% 6% 3 8% 6% 6% 5% 4 6% 9% 39%	2807
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 9% 48%	3476
September	1st to 10th	Night	13% 5% 2 6% 4 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 4 2 6% 4 4 3 3 6% 8% 49%	1963
	21st to end	Night	18% 7% 2 6% 4 4 4 2 4 6% 43%	2161
October	1st to 10th	Night	18% 5% 2 5% 3 3 4 3 4 7% 46%	2280
	11th to 20th	Night	13% 5% 2 4 4 3 3 3 5% 6% 52%	2280
	21st to end	Night	14% 5% 2 3 3 4 3 3 5% 6% 52%	2508
November	1st to 10th	Night	9% 7% 2 5% 3 3 4 3 4 6% 52%	2341
	11th to 20th	Night	12% 7% 3 5% 4 3 4 3 6% 7% 46%	2700
	21st to end	Night	12% 5% 2 6% 5% 4 5% 4 6% 7% 45%	2800
December	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 5% 7% 52%	4580
	11th to 20th	Night	15% 7% 3 8% 5% 4 4 4 6% 6% 39%	5205
	21st to end	Night	14% 7% 3 7% 4 6% 5% 5% 7% 8% 35%	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	39% 5% 7% 22% 21% 6%	3965
	11th to 20th	Day	41% 5% 8% 18% 18% 10%	4060
	21st to end	Day	41% 6% 8% 26% 15% 4	4466
February	1st to 10th	Day	45% 7% 12% 21% 13% 2	1800
	11th to 20th	Day	46% 6% 11% 20% 16% 2	1762
	21st to end	Day	43% 6% 11% 20% 16% 4	1685
March	1st to 10th	Day	43% 5% 7% 20% 16% 8%	4935
	11th to 20th	Day	32% 6% 9% 27% 21% 6%	4980
	21st to end	Day	43% 8% 10% 17% 18% 5%	5465
April	1st to 10th	Day	41% 8% 12% 18% 16% 5%	2372
	11th to 20th	Day	38% 7% 10% 21% 20% 5%	2374
	21st to end	Day	43% 8% 11% 21% 14% 3	2455
May	1st to 10th	Day	46% 10% 14% 19% 9% 2	5897
	11th to 20th	Day	49% 9% 10% 23% 8% 1	5865
	21st to end	Day	41% 10% 13% 20% 15% 2	6949
June	1st to 10th	Day	38% 10% 13% 23% 16% 1	2800
	11th to 20th	Day	39% 11% 15% 20% 13% 2	2800
	21st to end	Day	35% 10% 15% 24% 14% 2	2800
July	1st to 10th	Day	34% 11% 18% 22% 11% 5%	4454
	11th to 20th	Day	37% 11% 15% 28% 9% 1	4181
	21st to end	Day	44% 9% 9% 23% 15% 1	4324
August	1st to 10th	Day	45% 10% 16% 22% 7%	4091
	11th to 20th	Day	37% 10% 12% 26% 14% 1	4027
	21st to end	Day	33% 9% 15% 27% 15% 1	4180
September	1st to 10th	Day	39% 8% 13% 16% 20% 4	2280
	11th to 20th	Day	36% 7% 10% 25% 18% 3	2214
	21st to end	Day	47% 6% 9% 20% 16% 2	2019
October	1st to 10th	Day	32% 7% 9% 20% 27% 5%	3160
	11th to 20th	Day	27% 5% 8% 28% 22% 10%	3140
	21st to end	Day	25% 4 10% 29% 28% 5%	3428
November	1st to 10th	Day	32% 6% 11% 24% 23% 4	1957
	11th to 20th	Day	37% 6% 11% 19% 22% 5%	1693
	21st to end	Day	38% 5% 12% 25% 18% 2	1600
December	1st to 10th	Day	34% 6% 11% 27% 17% 4	2600
	11th to 20th	Day	44% 5% 13% 24% 11% 3	2986
	21st to end	Day	43% 8% 16% 18% 14% 1	3960
January	1st to 10th	Night	34% 7% 9% 22% 24% 3	5963
	11th to 20th	Night	37% 5% 8% 23% 19% 8%	5900
	21st to end	Night	38% 6% 8% 29% 17% 3	6490
February	1st to 10th	Night	42% 6% 13% 24% 14% 1	2600
	11th to 20th	Night	45% 6% 9% 21% 14% 4	2535
	21st to end	Night	45% 6% 11% 20% 14% 5%	1939
March	1st to 10th	Night	37% 6% 9% 25% 15% 8%	4918
	11th to 20th	Night	29% 7% 13% 27% 19% 5%	4980
	21st to end	Night	37% 8% 11% 21% 18% 4	5467
April	1st to 10th	Night	42% 9% 10% 20% 16% 3	2026
	11th to 20th	Night	37% 9% 11% 21% 18% 5%	1975
	21st to end	Night	39% 8% 11% 26% 14% 3	1960
May	1st to 10th	Night	50% 9% 14% 16% 9% 3	4060
	11th to 20th	Night	49% 9% 11% 22% 8% 1	4019
	21st to end	Night	44% 10% 14% 23% 7% 3	3927
June	1st to 10th	Night	34% 10% 12% 27% 15% 2	1600
	11th to 20th	Night	37% 11% 15% 23% 12% 1	1600
	21st to end	Night	33% 10% 16% 23% 17% 2	1600
July	1st to 10th	Night	33% 12% 22% 17% 13% 3	2612
	11th to 20th	Night	37% 11% 19% 23% 9% 1	2876
	21st to end	Night	39% 12% 15% 20% 13%	2988
August	1st to 10th	Night	43% 9% 16% 24% 7%	2814
	11th to 20th	Night	39% 10% 12% 24% 15%	2834
	21st to end	Night	33% 8% 15% 30% 13% 1	3476
September	1st to 10th	Night	38% 8% 12% 19% 18% 4	1900
	11th to 20th	Night	32% 7% 13% 27% 19% 2	1963
	21st to end	Night	43% 6% 11% 21% 17% 2	2161
October	1st to 10th	Night	38% 7% 10% 21% 21% 3	3800
	11th to 20th	Night	24% 5% 11% 23% 31% 7%	3779
	21st to end	Night	22% 4 10% 32% 27% 5%	4120
November	1st to 10th	Night	32% 6% 11% 24% 22% 5%	2341
	11th to 20th	Night	36% 6% 9% 24% 20% 5%	2700
	21st to end	Night	38% 6% 12% 23% 19% 3	2800
December	1st to 10th	Night	32% 5% 14% 28% 19% 2	4580
	11th to 20th	Night	44% 6% 12% 18% 16% 3	5208
	21st to end	Night	43% 8% 15% 19% 15% 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	34% 28% 23% 12% 3	280
	11th to 20th	Day	32% 27% 28% 10% 2	300
	21st to end	Day	28% 28% 30% 12% 2	330
February	1st to 10th	Day	30% 29% 29% 10% 1	300
	11th to 20th	Day	44% 28% 24% 4	300
	21st to end	Day	32% 23% 29% 14% 2	394
March	1st to 10th	Day	28% 24% 25% 21% 3	500
	11th to 20th	Day	28% 23% 28% 14% 6% 1	500
	21st to end	Day	25% 23% 31% 16% 4 1	550
April	1st to 10th	Day	26% 24% 27% 17% 5% 1	500
	11th to 20th	Day	20% 21% 28% 19% 9% 3	492
	21st to end	Day	25% 16% 31% 17% 9% 1	500
May	1st to 10th	Day	23% 19% 28% 17% 10% 3	503
	11th to 20th	Day	23% 15% 28% 20% 11% 3	527
	21st to end	Day	18% 9% 27% 24% 17% 4	573
June	1st to 10th	Day	14% 11% 28% 26% 16% 4	530
	11th to 20th	Day	15% 8% 28% 28% 16% 5%	530
	21st to end	Day	11% 9% 28% 30% 18% 4	530
July	1st to 10th	Day	9% 4 23% 33% 22% 8%	525
	11th to 20th	Day	7% 4 22% 34% 25% 9%	524
	21st to end	Day	13% 5% 21% 33% 20% 8%	532
August	1st to 10th	Day	10% 7% 24% 25% 23% 10%	486
	11th to 20th	Day	11% 3 24% 30% 22% 10%	479
	21st to end	Day	8% 4 22% 29% 24% 13%	539
September	1st to 10th	Day	16% 8% 19% 24% 22% 11%	490
	11th to 20th	Day	14% 5% 21% 28% 22% 10%	490
	21st to end	Day	28% 10% 22% 23% 14% 4	490
October	1st to 10th	Day	18% 8% 21% 29% 19% 4	490
	11th to 20th	Day	18% 14% 27% 25% 13% 2	490
	21st to end	Day	15% 19% 32% 22% 9% 3	539
November	1st to 10th	Day	18% 13% 31% 24% 11% 3	495
	11th to 20th	Day	19% 16% 32% 23% 8% 1	291
	21st to end	Day	28% 17% 36% 17% 4	200
December	1st to 10th	Day	25% 23% 36% 12% 4 1	200
	11th to 20th	Day	25% 22% 31% 17% 6%	200
	21st to end	Day	23% 20% 30% 21% 5% 1	220
January	1st to 10th	Night	20% 21% 35% 21% 4	800
	11th to 20th	Night	22% 19% 31% 26% 3	800
	21st to end	Night	19% 18% 38% 23% 1	880
February	1st to 10th	Night	18% 20% 33% 28% 2	800
	11th to 20th	Night	27% 24% 31% 17% 1	783
	21st to end	Night	25% 19% 35% 19% 2	660
March	1st to 10th	Night	20% 18% 36% 22% 3	800
	11th to 20th	Night	24% 21% 28% 21% 5% 1	800
	21st to end	Night	18% 20% 35% 22% 5% 1	880
April	1st to 10th	Night	18% 22% 33% 22% 5%	800
	11th to 20th	Night	16% 16% 34% 24% 9% 1	791
	21st to end	Night	18% 12% 30% 32% 7%	760
May	1st to 10th	Night	19% 11% 26% 29% 14% 1	600
	11th to 20th	Night	17% 7% 27% 35% 13% 1	590
	21st to end	Night	13% 4 24% 34% 23% 1	433
June	1st to 10th	Night	11% 4 27% 37% 20% 1	400
	11th to 20th	Night	10% 6% 20% 42% 21% 2	400
	21st to end	Night	7% 5% 20% 47% 21% 1	400
July	1st to 10th	Night	10% 2 18% 42% 24% 5%	416
	11th to 20th	Night	7% 2 12% 39% 36% 4	582
	21st to end	Night	9% 1 14% 45% 27% 4	624
August	1st to 10th	Night	9% 2 12% 46% 28% 3	567
	11th to 20th	Night	10% 3 12% 44% 28% 3	573
	21st to end	Night	10% 4 14% 39% 29% 4	836
September	1st to 10th	Night	15% 3 15% 33% 29% 5%	760
	11th to 20th	Night	11% 5% 17% 34% 29% 5%	760
	21st to end	Night	21% 5% 21% 31% 20% 1	760
October	1st to 10th	Night	20% 8% 19% 29% 22% 3	760
	11th to 20th	Night	15% 12% 26% 33% 13% 1	760
	21st to end	Night	17% 11% 28% 32% 10% 1	836
November	1st to 10th	Night	13% 11% 29% 34% 12% 1	780
	11th to 20th	Night	17% 16% 30% 28% 8% 1	800
	21st to end	Night	18% 16% 30% 29% 7% 1	800
December	1st to 10th	Night	20% 17% 32% 25% 6%	800
	11th to 20th	Night	18% 13% 34% 32% 3	800
	21st to end	Night	18% 16% 30% 34% 2	880

Page generated at 2025-07-18 01:09:58. Version ac07

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