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 2024-04-10.

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% 3 5% 6% 4 5% 5% 5% 7% 41%	83251
	Night	13% 6% 3 5% 5% 3 5% 5% 5% 7% 43%	85528
Transparency	Day	41% 8% 12% 21% 15% 3	82968
	Night	38% 8% 12% 23% 16% 3	85330
Seeing	Day	20% 15% 26% 22% 13% 4	14104
	Night	17% 12% 26% 30% 13% 1	23902

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	15% 7% 4 6% 6% 3 4 4 5% 6% 41%	2772
	11th to 20th	Day	12% 10% 4 7% 9% 3 4 5% 4 5% 37%	2840
	21st to end	Day	15% 9% 3 7% 6% 4 4 4 5% 6% 37%	3124
February	1st to 10th	Day	11% 9% 3 7% 5% 4 6% 5% 5% 7% 39%	1710
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 5% 5% 6% 39%	1663
	21st to end	Day	15% 9% 3 6% 4 3 4 5% 4 6% 41%	1603
March	1st to 10th	Day	19% 10% 3 6% 6% 3 4 4 4 5% 36%	3435
	11th to 20th	Day	9% 5% 2 4 5% 3 4 4 5% 7% 51%	3480
	21st to end	Day	17% 8% 3 6% 5% 3 4 5% 5% 7% 38%	3815
April	1st to 10th	Day	10% 6% 3 6% 6% 4 5% 5% 6% 8% 41%	2243
	11th to 20th	Day	12% 6% 3 5% 5% 2 5% 4 5% 7% 47%	2134
	21st to end	Day	17% 6% 2 5% 6% 3 5% 4 5% 7% 39%	2209
May	1st to 10th	Day	15% 6% 2 6% 6% 3 5% 5% 6% 8% 37%	2340
	11th to 20th	Day	19% 6% 3 6% 6% 3 4 5% 5% 8% 35%	2301
	21st to end	Day	13% 5% 3 5% 6% 3 6% 5% 7% 8% 39%	2725
June	1st to 10th	Day	12% 5% 2 5% 5% 4 6% 5% 6% 9% 41%	2520
	11th to 20th	Day	10% 5% 3 6% 6% 5% 6% 6% 7% 10% 38%	2520
	21st to end	Day	9% 4 2 4 6% 4 6% 6% 7% 9% 42%	2520
July	1st to 10th	Day	9% 4 3 6% 7% 4 6% 6% 7% 9% 39%	2493
	11th to 20th	Day	6% 4 2 5% 6% 4 7% 6% 7% 12% 39%	2340
	21st to end	Day	11% 6% 3 6% 6% 5% 7% 8% 7% 8% 35%	2547
August	1st to 10th	Day	10% 6% 3 7% 7% 5% 7% 7% 7% 8% 33%	2327
	11th to 20th	Day	12% 5% 2 5% 7% 4 6% 7% 7% 9% 36%	2275
	21st to end	Day	11% 5% 2 6% 5% 4 6% 6% 6% 8% 40%	2376
September	1st to 10th	Day	15% 5% 2 6% 5% 4 5% 4 6% 6% 43%	2160
	11th to 20th	Day	13% 6% 2 4 5% 3 4 5% 5% 7% 46%	2098
	21st to end	Day	19% 6% 2 5% 6% 4 5% 4 4 6% 40%	1913
October	1st to 10th	Day	16% 5% 2 5% 4 2 5% 4 6% 8% 45%	1800
	11th to 20th	Day	15% 6% 2 5% 5% 4 3 4 5% 6% 47%	1800
	21st to end	Day	14% 6% 2 4 5% 3 4 3 6% 6% 48%	1980
November	1st to 10th	Day	10% 5% 2 5% 4 3 4 4 5% 6% 52%	1857
	11th to 20th	Day	13% 7% 3 5% 4 3 4 4 5% 6% 47%	1609
	21st to end	Day	14% 4 2 4 4 3 5% 5% 4 6% 48%	1520
December	1st to 10th	Day	14% 8% 3 6% 4 4 5% 5% 5% 7% 39%	1520
	11th to 20th	Day	13% 7% 3 5% 5% 3 4 4 4 7% 44%	1910
	21st to end	Day	16% 7% 2 4 6% 4 6% 5% 6% 8% 34%	2772
January	1st to 10th	Night	10% 8% 3 5% 5% 4 5% 5% 5% 7% 44%	4169
	11th to 20th	Night	15% 9% 3 4 4 2 4 4 5% 6% 44%	4120
	21st to end	Night	16% 9% 3 6% 5% 3 4 4 5% 6% 40%	4532
February	1st to 10th	Night	12% 7% 3 6% 6% 3 6% 5% 6% 6% 41%	2470
	11th to 20th	Night	16% 8% 3 5% 5% 3 5% 6% 6% 6% 39%	2403
	21st to end	Night	14% 9% 3 7% 6% 3 3 4 5% 6% 39%	1846
March	1st to 10th	Night	19% 7% 3 6% 5% 3 5% 4 5% 6% 36%	3418
	11th to 20th	Night	10% 6% 3 5% 4 3 4 4 5% 6% 49%	3480
	21st to end	Night	13% 6% 2 6% 5% 2 4 4 4 6% 48%	3817
April	1st to 10th	Night	12% 7% 3 6% 6% 3 4 6% 5% 7% 41%	1925
	11th to 20th	Night	11% 5% 2 6% 5% 3 5% 4 6% 8% 45%	1775
	21st to end	Night	16% 5% 2 4 5% 3 5% 4 4 7% 44%	1764
May	1st to 10th	Night	15% 6% 2 6% 5% 4 5% 4 4 8% 41%	1620
	11th to 20th	Night	15% 6% 3 7% 5% 3 4 4 6% 7% 40%	1592
	21st to end	Night	12% 5% 2 5% 5% 3 5% 5% 6% 10% 42%	1550
June	1st to 10th	Night	10% 5% 2 5% 4 3 5% 5% 6% 9% 46%	1440
	11th to 20th	Night	11% 5% 3 4 5% 4 6% 5% 7% 9% 42%	1440
	21st to end	Night	8% 3 2 6% 6% 3 4 6% 9% 10% 44%	1440
July	1st to 10th	Night	10% 5% 2 6% 5% 4 6% 6% 6% 9% 42%	1463
	11th to 20th	Night	6% 4 2 4 6% 3 5% 5% 7% 11% 47%	1620
	21st to end	Night	7% 4 2 5% 5% 3 6% 6% 8% 12% 42%	1771
August	1st to 10th	Night	8% 4 2 6% 6% 4 7% 6% 6% 9% 42%	1611
	11th to 20th	Night	10% 5% 3 6% 5% 5% 5% 5% 6% 9% 41%	1606
	21st to end	Night	10% 5% 2 5% 5% 3 5% 5% 8% 11% 41%	1980
September	1st to 10th	Night	14% 6% 2 5% 5% 3 5% 4 5% 7% 45%	1800
	11th to 20th	Night	12% 4 2 5% 4 3 3 4 5% 8% 50%	1859
	21st to end	Night	17% 6% 2 5% 5% 3 4 3 4 6% 45%	2047
October	1st to 10th	Night	18% 4 2 4 4 2 4 4 4 7% 46%	2160
	11th to 20th	Night	14% 5% 2 4 4 2 4 4 5% 6% 51%	2160
	21st to end	Night	15% 5% 2 3 4 3 4 4 5% 6% 51%	2376
November	1st to 10th	Night	9% 6% 3 5% 4 2 4 4 4 6% 52%	2221
	11th to 20th	Night	12% 6% 3 5% 4 2 4 4 5% 7% 48%	2564
	21st to end	Night	12% 5% 2 5% 5% 3 5% 4 5% 7% 45%	2660
December	1st to 10th	Night	13% 8% 3 6% 6% 3 4 5% 5% 6% 41%	2660
	11th to 20th	Night	14% 6% 2 6% 5% 2 5% 5% 6% 6% 43%	3285
	21st to end	Night	16% 6% 3 6% 5% 3 6% 6% 6% 8% 36%	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	41% 6% 10% 25% 15% 3	2773
	11th to 20th	Day	48% 7% 10% 16% 15% 5%	2840
	21st to end	Day	47% 7% 10% 21% 13% 2	3124
February	1st to 10th	Day	45% 7% 12% 21% 13% 2	1710
	11th to 20th	Day	45% 6% 11% 21% 16% 2	1672
	21st to end	Day	44% 6% 12% 18% 15% 4	1603
March	1st to 10th	Day	49% 6% 9% 19% 13% 3	3435
	11th to 20th	Day	32% 7% 8% 28% 21% 3	3480
	21st to end	Day	45% 9% 11% 19% 14% 3	3815
April	1st to 10th	Day	39% 9% 12% 18% 16% 5%	2243
	11th to 20th	Day	38% 6% 10% 21% 20% 5%	2134
	21st to end	Day	44% 8% 11% 19% 14% 4	2209
May	1st to 10th	Day	44% 8% 13% 20% 13% 2	2340
	11th to 20th	Day	48% 10% 11% 19% 11% 2	2305
	21st to end	Day	42% 9% 14% 23% 10% 1	2725
June	1st to 10th	Day	39% 9% 13% 23% 14% 1	2520
	11th to 20th	Day	40% 12% 15% 19% 13% 2	2520
	21st to end	Day	35% 11% 15% 24% 13% 2	2520
July	1st to 10th	Day	39% 11% 13% 20% 14% 2	2424
	11th to 20th	Day	35% 12% 15% 23% 13% 2	2271
	21st to end	Day	40% 11% 13% 19% 15% 2	2405
August	1st to 10th	Day	44% 12% 15% 19% 9%	2314
	11th to 20th	Day	41% 12% 15% 19% 12% 1	2275
	21st to end	Day	39% 11% 15% 22% 11% 2	2376
September	1st to 10th	Day	40% 8% 13% 17% 18% 3	2160
	11th to 20th	Day	36% 7% 10% 25% 18% 3	2098
	21st to end	Day	45% 7% 10% 20% 17% 2	1913
October	1st to 10th	Day	37% 8% 12% 23% 16% 4	1800
	11th to 20th	Day	39% 6% 10% 23% 19% 3	1800
	21st to end	Day	37% 5% 9% 24% 21% 4	1980
November	1st to 10th	Day	32% 6% 11% 24% 23% 4	1857
	11th to 20th	Day	37% 6% 11% 19% 22% 5%	1609
	21st to end	Day	37% 5% 12% 26% 18% 2	1520
December	1st to 10th	Day	45% 7% 12% 22% 12% 2	1520
	11th to 20th	Day	39% 6% 13% 29% 11% 4	1906
	21st to end	Day	42% 8% 16% 22% 10% 1	2772
January	1st to 10th	Night	36% 8% 12% 24% 18% 3	4169
	11th to 20th	Night	41% 6% 11% 23% 15% 4	4120
	21st to end	Night	44% 7% 9% 25% 13% 1	4532
February	1st to 10th	Night	42% 7% 12% 24% 14% 1	2470
	11th to 20th	Night	44% 7% 9% 21% 15% 4	2405
	21st to end	Night	46% 6% 11% 20% 12% 5%	1846
March	1st to 10th	Night	45% 8% 11% 24% 10% 2	3418
	11th to 20th	Night	32% 8% 12% 26% 20% 2	3480
	21st to end	Night	35% 8% 10% 24% 19% 3	3817
April	1st to 10th	Night	41% 9% 11% 20% 17% 3	1925
	11th to 20th	Night	36% 9% 11% 21% 18% 5%	1775
	21st to end	Night	39% 8% 11% 25% 13% 3	1764
May	1st to 10th	Night	42% 9% 13% 21% 12% 4	1620
	11th to 20th	Night	44% 8% 14% 19% 13% 1	1593
	21st to end	Night	37% 10% 17% 24% 10% 1	1551
June	1st to 10th	Night	34% 10% 12% 28% 14% 1	1440
	11th to 20th	Night	37% 11% 16% 22% 13% 1	1440
	21st to end	Night	33% 9% 17% 23% 16% 2	1440
July	1st to 10th	Night	36% 12% 18% 18% 12% 3	1422
	11th to 20th	Night	31% 11% 18% 24% 14% 2	1566
	21st to end	Night	29% 13% 19% 24% 14%	1672
August	1st to 10th	Night	36% 12% 16% 23% 12% 1	1600
	11th to 20th	Night	38% 9% 14% 25% 13%	1606
	21st to end	Night	35% 11% 15% 24% 12% 2	1980
September	1st to 10th	Night	38% 8% 13% 20% 17% 4	1800
	11th to 20th	Night	32% 7% 14% 27% 19% 2	1859
	21st to end	Night	41% 7% 11% 22% 18% 2	2047
October	1st to 10th	Night	39% 6% 12% 23% 18% 2	2160
	11th to 20th	Night	33% 6% 11% 26% 21% 2	2160
	21st to end	Night	35% 7% 9% 24% 23% 3	2376
November	1st to 10th	Night	33% 6% 11% 24% 21% 5%	2221
	11th to 20th	Night	36% 6% 9% 24% 21% 5%	2564
	21st to end	Night	38% 6% 12% 23% 18% 3	2660
December	1st to 10th	Night	45% 6% 11% 24% 12% 2	2660
	11th to 20th	Night	40% 7% 11% 22% 17% 3	3288
	21st to end	Night	42% 8% 17% 19% 13% 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	31% 29% 23% 13% 3	252
	11th to 20th	Day	32% 26% 29% 11% 3	270
	21st to end	Day	29% 27% 30% 11% 2	297
February	1st to 10th	Day	27% 29% 31% 11% 1	270
	11th to 20th	Day	41% 29% 26% 4	270
	21st to end	Day	33% 23% 28% 15% 2	363
March	1st to 10th	Day	27% 24% 25% 21% 3	460
	11th to 20th	Day	28% 23% 27% 15% 6% 1	460
	21st to end	Day	24% 23% 30% 17% 4 1	506
April	1st to 10th	Day	23% 25% 27% 18% 6% 1	457
	11th to 20th	Day	19% 18% 28% 21% 10% 4	412
	21st to end	Day	26% 16% 30% 16% 9% 1	420
May	1st to 10th	Day	24% 18% 28% 17% 10% 4	423
	11th to 20th	Day	22% 15% 29% 21% 10% 3	447
	21st to end	Day	18% 7% 25% 26% 18% 5%	485
June	1st to 10th	Day	15% 10% 26% 27% 18% 4	450
	11th to 20th	Day	15% 9% 30% 24% 16% 5%	450
	21st to end	Day	11% 9% 28% 31% 17% 3	450
July	1st to 10th	Day	9% 4 22% 31% 23% 10%	445
	11th to 20th	Day	5% 3 21% 33% 28% 9%	444
	21st to end	Day	13% 4 21% 32% 22% 8%	488
August	1st to 10th	Day	10% 7% 22% 26% 24% 11%	446
	11th to 20th	Day	12% 3 21% 31% 23% 11%	439
	21st to end	Day	8% 4 23% 28% 23% 14%	495
September	1st to 10th	Day	16% 8% 18% 24% 23% 11%	450
	11th to 20th	Day	14% 4 21% 28% 22% 11%	450
	21st to end	Day	24% 11% 22% 23% 15% 4	450
October	1st to 10th	Day	18% 8% 21% 28% 20% 5%	450
	11th to 20th	Day	18% 15% 26% 25% 13% 2	450
	21st to end	Day	17% 20% 31% 21% 9% 3	495
November	1st to 10th	Day	19% 12% 30% 24% 11% 3	455
	11th to 20th	Day	20% 18% 29% 22% 9% 1	267
	21st to end	Day	24% 17% 36% 18% 4	180
December	1st to 10th	Day	24% 24% 34% 12% 4 1	180
	11th to 20th	Day	25% 23% 29% 17% 6%	180
	21st to end	Day	22% 21% 31% 20% 6% 1	198
January	1st to 10th	Night	19% 21% 34% 22% 4	760
	11th to 20th	Night	22% 19% 29% 26% 3	760
	21st to end	Night	19% 18% 38% 23% 1	836
February	1st to 10th	Night	17% 19% 33% 29% 2	760
	11th to 20th	Night	26% 25% 31% 17% 1	743
	21st to end	Night	25% 19% 35% 19% 2	628
March	1st to 10th	Night	20% 18% 36% 23% 4	760
	11th to 20th	Night	25% 21% 28% 21% 5% 1	760
	21st to end	Night	18% 19% 35% 22% 5% 1	836
April	1st to 10th	Night	18% 22% 33% 22% 5%	760
	11th to 20th	Night	15% 16% 33% 25% 10% 1	711
	21st to end	Night	19% 12% 30% 31% 8%	684
May	1st to 10th	Night	19% 10% 26% 29% 14% 1	540
	11th to 20th	Night	17% 6% 27% 36% 14% 1	531
	21st to end	Night	13% 4 22% 35% 24% 2	389
June	1st to 10th	Night	11% 3 24% 38% 22% 1	360
	11th to 20th	Night	9% 6% 20% 42% 21% 2	360
	21st to end	Night	7% 4 20% 48% 20% 1	360
July	1st to 10th	Night	10% 2 17% 41% 25% 5%	372
	11th to 20th	Night	8% 1 11% 39% 38% 4	522
	21st to end	Night	8% 1 13% 45% 28% 4	591
August	1st to 10th	Night	8% 2 11% 46% 30% 3	537
	11th to 20th	Night	9% 2 12% 43% 30% 4	542
	21st to end	Night	10% 4 14% 39% 30% 4	792
September	1st to 10th	Night	15% 3 14% 33% 29% 5%	720
	11th to 20th	Night	10% 5% 18% 33% 30% 5%	720
	21st to end	Night	20% 5% 21% 32% 21% 1	720
October	1st to 10th	Night	19% 8% 18% 29% 22% 3	720
	11th to 20th	Night	16% 13% 25% 32% 13% 1	720
	21st to end	Night	18% 12% 28% 31% 11% 1	792
November	1st to 10th	Night	14% 11% 28% 34% 12% 1	740
	11th to 20th	Night	17% 16% 30% 28% 8% 1	760
	21st to end	Night	17% 17% 28% 30% 7% 1	760
December	1st to 10th	Night	20% 17% 31% 26% 6%	760
	11th to 20th	Night	18% 12% 35% 32% 3	760
	21st to end	Night	17% 16% 30% 34% 2	836

Page generated at 2024-04-07 09:28:15. Version ac07

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