George Washington National Forest Helicopter Landing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the George Washington National Forest Helicopter Landing Site clear sky chart from 2005-11-06 to 2024-11-05.

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% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	100984
	Night	13% 7% 2 6% 4 4 4 4 6% 7% 41%	97982
Transparency	Day	40% 8% 12% 22% 14% 3	104634
	Night	37% 8% 13% 24% 15% 3	102471
Seeing	Day	19% 14% 26% 23% 13% 5%	14949
	Night	16% 11% 27% 31% 13% 1	24707

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% 8% 3 8% 5% 4 4 3 5% 6% 40%	2836
	11th to 20th	Day	11% 12% 4 11% 6% 5% 4 3 4 4 36%	2840
	21st to end	Day	15% 12% 4 7% 4 4 4 3 5% 5% 37%	3124
February	1st to 10th	Day	11% 10% 4 8% 4 5% 4 4 7% 7% 37%	1710
	11th to 20th	Day	14% 8% 3 7% 5% 4 5% 3 5% 6% 38%	1663
	21st to end	Day	15% 8% 3 7% 4 4 4 3 5% 6% 39%	1621
March	1st to 10th	Day	17% 11% 4 8% 4 4 4 3 5% 7% 34%	3435
	11th to 20th	Day	10% 7% 2 5% 4 3 4 4 5% 6% 50%	3480
	21st to end	Day	16% 9% 3 7% 5% 5% 5% 4 5% 5% 36%	3815
April	1st to 10th	Day	10% 9% 3 7% 5% 5% 5% 4 6% 6% 40%	2220
	11th to 20th	Day	14% 7% 2 6% 4 4 3 3 5% 7% 44%	2254
	21st to end	Day	18% 8% 2 7% 5% 5% 4 4 5% 6% 38%	2374
May	1st to 10th	Day	18% 8% 3 9% 6% 6% 6% 4 6% 7% 27%	4082
	11th to 20th	Day	23% 9% 2 6% 4 4 4 4 5% 7% 32%	4081
	21st to end	Day	12% 5% 2 8% 5% 5% 7% 5% 7% 9% 36%	4661
June	1st to 10th	Day	14% 5% 2 5% 5% 5% 5% 5% 7% 9% 38%	2660
	11th to 20th	Day	12% 5% 3 7% 6% 6% 6% 5% 6% 10% 34%	2660
	21st to end	Day	9% 6% 2 7% 6% 5% 7% 5% 7% 9% 38%	2660
July	1st to 10th	Day	7% 5% 3 8% 6% 6% 6% 5% 7% 8% 38%	4194
	11th to 20th	Day	10% 5% 2 7% 6% 7% 7% 6% 8% 10% 33%	4120
	21st to end	Day	14% 8% 3 10% 7% 6% 6% 5% 6% 8% 28%	4466
August	1st to 10th	Day	13% 7% 2 8% 7% 6% 7% 5% 7% 9% 28%	4104
	11th to 20th	Day	9% 5% 3 8% 7% 6% 7% 6% 7% 9% 34%	4030
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 4 6% 8% 43%	4180
September	1st to 10th	Day	14% 6% 3 7% 4 4 5% 3 5% 7% 42%	2280
	11th to 20th	Day	14% 7% 2 7% 4 4 4 3 5% 8% 42%	2157
	21st to end	Day	23% 6% 3 6% 5% 4 4 4 5% 5% 35%	2050
October	1st to 10th	Day	17% 6% 2 6% 4 4 5% 3 5% 6% 43%	1900
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 4 5% 45%	1900
	21st to end	Day	14% 6% 2 5% 3 3 5% 3 5% 5% 48%	2090
November	1st to 10th	Day	10% 7% 2 5% 4 3 4 3 4 6% 52%	1898
	11th to 20th	Day	13% 8% 2 5% 4 3 4 3 5% 7% 47%	1649
	21st to end	Day	14% 7% 2 6% 4 5% 3 4 4 6% 45%	1520
December	1st to 10th	Day	15% 10% 3 7% 5% 5% 4 3 6% 7% 35%	1520
	11th to 20th	Day	14% 6% 2 6% 4 4 3 3 5% 7% 47%	1910
	21st to end	Day	16% 7% 2 8% 5% 6% 6% 5% 7% 8% 31%	2840
January	1st to 10th	Night	10% 11% 3 7% 4 4 5% 4 5% 7% 41%	4109
	11th to 20th	Night	13% 10% 3 8% 5% 3 3 3 5% 5% 42%	4120
	21st to end	Night	20% 9% 3 5% 4 4 4 3 4 6% 39%	4532
February	1st to 10th	Night	10% 9% 3 6% 5% 5% 5% 5% 6% 7% 40%	2470
	11th to 20th	Night	15% 8% 3 7% 4 5% 5% 5% 6% 6% 36%	2403
	21st to end	Night	14% 8% 3 7% 5% 4 5% 4 6% 7% 38%	1828
March	1st to 10th	Night	19% 10% 3 7% 4 4 4 4 6% 6% 34%	3418
	11th to 20th	Night	9% 6% 3 6% 3 4 5% 4 6% 7% 47%	3480
	21st to end	Night	14% 7% 3 6% 4 4 4 3 5% 6% 45%	3817
April	1st to 10th	Night	12% 9% 2 6% 5% 4 5% 4 5% 7% 41%	1958
	11th to 20th	Night	12% 6% 2 5% 5% 4 4 4 6% 8% 43%	1875
	21st to end	Night	16% 6% 2 5% 3 4 4 3 6% 7% 42%	1821
May	1st to 10th	Night	21% 8% 3 7% 5% 4 5% 4 6% 8% 30%	2813
	11th to 20th	Night	23% 10% 2 5% 4 3 4 3 4 5% 35%	2812
	21st to end	Night	11% 5% 2 5% 5% 4 5% 4 7% 10% 42%	2889
June	1st to 10th	Night	11% 5% 2 5% 5% 5% 4 4 7% 9% 45%	1520
	11th to 20th	Night	10% 5% 2 7% 4 5% 5% 5% 7% 9% 42%	1520
	21st to end	Night	8% 5% 2 5% 5% 4 4 6% 8% 10% 45%	1520
July	1st to 10th	Night	7% 5% 1 6% 5% 5% 5% 6% 8% 12% 41%	2760
	11th to 20th	Night	8% 6% 3 7% 4 5% 5% 6% 7% 10% 40%	2840
	21st to end	Night	9% 7% 3 9% 6% 7% 6% 5% 7% 9% 34%	3087
August	1st to 10th	Night	14% 5% 2 6% 5% 5% 5% 5% 7% 9% 36%	2825
	11th to 20th	Night	9% 8% 3 7% 6% 5% 5% 5% 5% 7% 38%	2785
	21st to end	Night	8% 6% 2 5% 4 5% 4 4 5% 9% 47%	3444
September	1st to 10th	Night	13% 5% 2 6% 4 4 4 2 5% 7% 48%	1900
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 5% 7% 45%	2019
	21st to end	Night	22% 7% 2 5% 3 3 4 3 5% 5% 41%	2129
October	1st to 10th	Night	18% 5% 2 5% 4 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 6% 50%	2280
	21st to end	Night	14% 6% 2 6% 4 4 3 4 5% 6% 48%	2508
November	1st to 10th	Night	11% 7% 3 5% 3 4 4 4 4 5% 50%	2280
	11th to 20th	Night	12% 6% 2 5% 4 4 3 4 6% 7% 47%	2524
	21st to end	Night	13% 5% 2 6% 4 5% 4 4 5% 6% 45%	2660
December	1st to 10th	Night	13% 9% 3 8% 4 5% 4 4 5% 7% 38%	2660
	11th to 20th	Night	14% 7% 3 6% 4 5% 4 4 6% 7% 41%	3285
	21st to end	Night	15% 7% 2 7% 5% 5% 5% 5% 7% 8% 34%	4811

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	43% 5% 8% 25% 16% 4	2837
	11th to 20th	Day	49% 5% 8% 16% 17% 5%	2840
	21st to end	Day	47% 5% 10% 21% 16% 2	3124
February	1st to 10th	Day	43% 6% 12% 21% 15% 3	1710
	11th to 20th	Day	45% 5% 9% 22% 17% 3	1672
	21st to end	Day	44% 5% 13% 18% 16% 4	1621
March	1st to 10th	Day	45% 8% 11% 20% 13% 3	3435
	11th to 20th	Day	32% 6% 9% 27% 23% 4	3480
	21st to end	Day	46% 7% 11% 19% 14% 3	3815
April	1st to 10th	Day	39% 7% 11% 21% 16% 6%	2220
	11th to 20th	Day	38% 6% 10% 20% 20% 5%	2254
	21st to end	Day	45% 6% 11% 22% 13% 4	2374
May	1st to 10th	Day	50% 11% 10% 19% 9% 1	4120
	11th to 20th	Day	49% 9% 11% 23% 8% 1	4085
	21st to end	Day	36% 12% 15% 20% 13% 3	4675
June	1st to 10th	Day	38% 10% 14% 23% 15% 1	2660
	11th to 20th	Day	40% 11% 16% 20% 12% 2	2660
	21st to end	Day	37% 9% 15% 24% 13% 2	2660
July	1st to 10th	Day	37% 13% 15% 20% 9% 5%	4129
	11th to 20th	Day	39% 12% 15% 25% 8% 1	4051
	21st to end	Day	49% 8% 11% 21% 11% 1	4324
August	1st to 10th	Day	45% 11% 16% 21% 7%	4091
	11th to 20th	Day	38% 11% 13% 26% 11% 1	4069
	21st to end	Day	35% 10% 15% 27% 12% 1	4180
September	1st to 10th	Day	40% 7% 13% 16% 19% 4	2280
	11th to 20th	Day	39% 6% 9% 25% 18% 3	2157
	21st to end	Day	47% 7% 9% 19% 15% 2	2050
October	1st to 10th	Day	32% 6% 9% 19% 26% 8%	3160
	11th to 20th	Day	27% 5% 9% 29% 17% 14%	3140
	21st to end	Day	24% 5% 9% 28% 23% 11%	3428
November	1st to 10th	Day	32% 5% 9% 26% 24% 4	1898
	11th to 20th	Day	36% 4 12% 20% 22% 6%	1649
	21st to end	Day	37% 4 11% 25% 20% 2	1520
December	1st to 10th	Day	46% 6% 12% 22% 12% 3	1520
	11th to 20th	Day	36% 4 11% 29% 16% 5%	1906
	21st to end	Day	43% 10% 15% 21% 10% 1	2840
January	1st to 10th	Night	37% 7% 13% 24% 17% 3	4109
	11th to 20th	Night	39% 6% 12% 23% 16% 5%	4120
	21st to end	Night	44% 6% 8% 25% 15% 2	4532
February	1st to 10th	Night	39% 7% 14% 24% 14% 2	2470
	11th to 20th	Night	43% 6% 11% 21% 15% 4	2405
	21st to end	Night	42% 8% 13% 20% 12% 5%	1828
March	1st to 10th	Night	46% 7% 10% 24% 10% 3	3418
	11th to 20th	Night	29% 6% 12% 28% 23% 2	3480
	21st to end	Night	36% 7% 12% 24% 18% 4	3817
April	1st to 10th	Night	39% 8% 12% 21% 17% 3	1958
	11th to 20th	Night	35% 6% 15% 21% 18% 4	1875
	21st to end	Night	37% 7% 14% 25% 14% 3	1821
May	1st to 10th	Night	48% 11% 13% 19% 9% 2	2840
	11th to 20th	Night	47% 10% 12% 24% 7%	2813
	21st to end	Night	33% 11% 20% 25% 8% 3	2896
June	1st to 10th	Night	33% 11% 15% 27% 14% 1	1520
	11th to 20th	Night	34% 11% 17% 24% 12% 1	1520
	21st to end	Night	30% 12% 18% 21% 17% 2	1520
July	1st to 10th	Night	32% 12% 23% 18% 12% 3	2715
	11th to 20th	Night	35% 12% 18% 25% 9% 1	2786
	21st to end	Night	41% 10% 17% 22% 10%	2988
August	1st to 10th	Night	40% 10% 18% 23% 7%	2814
	11th to 20th	Night	37% 12% 16% 22% 13%	2812
	21st to end	Night	32% 8% 17% 31% 11% 1	3444
September	1st to 10th	Night	36% 8% 16% 18% 18% 4	1900
	11th to 20th	Night	36% 6% 11% 28% 18% 2	2019
	21st to end	Night	44% 6% 11% 21% 16% 2	2129
October	1st to 10th	Night	38% 5% 9% 21% 22% 3	3800
	11th to 20th	Night	24% 6% 12% 21% 26% 12%	3779
	21st to end	Night	21% 4 12% 30% 23% 9%	4120
November	1st to 10th	Night	33% 5% 12% 23% 22% 5%	2280
	11th to 20th	Night	34% 6% 9% 25% 21% 5%	2524
	21st to end	Night	37% 5% 12% 23% 18% 4	2660
December	1st to 10th	Night	44% 6% 13% 22% 13% 3	2660
	11th to 20th	Night	38% 6% 11% 23% 21% 2	3288
	21st to end	Night	39% 11% 14% 23% 12% 1	4811

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	24% 30% 31% 11% 3	270
	11th to 20th	Day	27% 27% 29% 15% 2	270
	21st to end	Day	26% 29% 32% 11% 2	297
February	1st to 10th	Day	25% 29% 33% 10% 2	270
	11th to 20th	Day	35% 30% 28% 6% 1	270
	21st to end	Day	30% 25% 29% 14% 3	332
March	1st to 10th	Day	20% 27% 29% 21% 3	460
	11th to 20th	Day	23% 25% 29% 18% 5% 1	460
	21st to end	Day	22% 21% 31% 18% 7% 1	506
April	1st to 10th	Day	22% 25% 26% 18% 8%	460
	11th to 20th	Day	19% 20% 26% 22% 10% 3	452
	21st to end	Day	26% 16% 28% 18% 9% 2	460
May	1st to 10th	Day	21% 19% 27% 19% 10% 4	463
	11th to 20th	Day	23% 12% 28% 22% 11% 3	487
	21st to end	Day	18% 8% 25% 25% 17% 7%	529
June	1st to 10th	Day	13% 10% 25% 30% 15% 6%	490
	11th to 20th	Day	14% 8% 28% 26% 17% 7%	490
	21st to end	Day	10% 8% 30% 33% 16% 4	490
July	1st to 10th	Day	11% 5% 20% 29% 24% 11%	485
	11th to 20th	Day	6% 3 21% 34% 25% 11%	484
	21st to end	Day	14% 5% 19% 30% 24% 8%	532
August	1st to 10th	Day	13% 7% 21% 26% 20% 13%	486
	11th to 20th	Day	14% 4 22% 27% 23% 10%	479
	21st to end	Day	10% 4 19% 29% 24% 15%	539
September	1st to 10th	Day	17% 7% 20% 23% 21% 12%	490
	11th to 20th	Day	17% 4 18% 28% 24% 10%	490
	21st to end	Day	28% 10% 21% 22% 16% 4	490
October	1st to 10th	Day	20% 6% 24% 27% 19% 4	490
	11th to 20th	Day	16% 16% 24% 27% 14% 2	490
	21st to end	Day	17% 15% 34% 23% 8% 2	539
November	1st to 10th	Day	15% 13% 31% 27% 12% 2	472
	11th to 20th	Day	24% 18% 26% 23% 7% 1	269
	21st to end	Day	20% 20% 36% 19% 4 1	180
December	1st to 10th	Day	22% 22% 38% 13% 4 1	180
	11th to 20th	Day	26% 18% 35% 14% 7% 1	180
	21st to end	Day	20% 23% 36% 16% 5%	218
January	1st to 10th	Night	17% 22% 36% 22% 3	760
	11th to 20th	Night	19% 17% 34% 26% 4	760
	21st to end	Night	15% 17% 43% 23% 2	836
February	1st to 10th	Night	15% 18% 39% 26% 3	760
	11th to 20th	Night	23% 21% 36% 19% 1	743
	21st to end	Night	21% 17% 39% 20% 2	628
March	1st to 10th	Night	16% 18% 38% 25% 3	760
	11th to 20th	Night	21% 18% 32% 23% 5% 1	760
	21st to end	Night	20% 17% 34% 23% 6% 1	836
April	1st to 10th	Night	16% 22% 31% 24% 6%	760
	11th to 20th	Night	15% 16% 31% 27% 10% 1	751
	21st to end	Night	19% 11% 29% 34% 8%	681
May	1st to 10th	Night	18% 8% 27% 32% 14% 1	570
	11th to 20th	Night	19% 6% 24% 35% 14% 2	561
	21st to end	Night	14% 2 19% 41% 21% 2	504
June	1st to 10th	Night	10% 3 22% 41% 22% 1	380
	11th to 20th	Night	9% 6% 16% 47% 20% 2	380
	21st to end	Night	8% 3 18% 51% 19% 1	380
July	1st to 10th	Night	12% 2 12% 37% 31% 5%	501
	11th to 20th	Night	6% 2 12% 41% 34% 5%	552
	21st to end	Night	7% 2 13% 42% 31% 4	624
August	1st to 10th	Night	10% 2 12% 42% 31% 3	567
	11th to 20th	Night	11% 3 12% 39% 32% 3	564
	21st to end	Night	12% 3 15% 38% 29% 3	817
September	1st to 10th	Night	16% 3 16% 33% 28% 5%	760
	11th to 20th	Night	15% 4 14% 36% 26% 4	760
	21st to end	Night	24% 4 19% 32% 19% 2	760
October	1st to 10th	Night	18% 9% 19% 30% 20% 3	760
	11th to 20th	Night	16% 10% 30% 30% 14% 1	760
	21st to end	Night	16% 12% 27% 33% 11% 1	836
November	1st to 10th	Night	14% 9% 28% 37% 11% 2	760
	11th to 20th	Night	16% 15% 28% 31% 10% 1	760
	21st to end	Night	16% 15% 30% 30% 8% 1	760
December	1st to 10th	Night	17% 16% 35% 27% 4	760
	11th to 20th	Night	15% 13% 37% 31% 4	760
	21st to end	Night	16% 16% 33% 33% 3	836

Page generated at 2024-11-03 02:11:11. Version ac07

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