Glens of Grandfather Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glens of Grandfather Mountain clear sky chart from 2005-11-06 to 2024-11-02.

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% 7% 2 7% 5% 5% 5% 4 6% 8% 36%	101169
	Night	14% 7% 2 6% 4 4 4 4 6% 8% 40%	97760
Transparency	Day	41% 11% 13% 19% 13% 3	100982
	Night	38% 11% 15% 19% 13% 4	97617
Seeing	Day	19% 17% 25% 20% 12% 6%	15115
	Night	17% 16% 22% 25% 17% 3	25172

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% 5% 2 5% 4 5% 3 3 6% 8% 45%	2836
	11th to 20th	Day	13% 7% 3 6% 5% 6% 4 3 4 7% 43%	2840
	21st to end	Day	20% 7% 2 6% 4 4 4 3 5% 6% 40%	3124
February	1st to 10th	Day	11% 9% 3 6% 5% 5% 6% 5% 5% 7% 37%	1721
	11th to 20th	Day	16% 10% 3 6% 5% 4 4 3 5% 6% 38%	1848
	21st to end	Day	16% 7% 3 6% 5% 4 4 4 6% 7% 37%	1570
March	1st to 10th	Day	22% 6% 2 5% 4 4 5% 3 5% 6% 39%	3421
	11th to 20th	Day	11% 6% 2 5% 5% 4 4 3 5% 5% 50%	3480
	21st to end	Day	18% 7% 2 6% 5% 4 4 3 5% 7% 38%	3815
April	1st to 10th	Day	11% 6% 2 6% 4 5% 4 4 6% 8% 43%	2090
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 6% 8% 39%	2269
	21st to end	Day	15% 6% 3 7% 5% 4 5% 4 5% 6% 41%	2470
May	1st to 10th	Day	14% 7% 3 8% 6% 6% 6% 5% 7% 8% 31%	4082
	11th to 20th	Day	17% 8% 3 8% 6% 6% 6% 5% 7% 7% 27%	4081
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 5% 8% 11% 37%	4476
June	1st to 10th	Day	13% 6% 2 7% 7% 7% 6% 5% 6% 8% 31%	2470
	11th to 20th	Day	9% 7% 3 8% 6% 7% 6% 6% 8% 9% 32%	2470
	21st to end	Day	9% 7% 2 8% 6% 7% 7% 6% 9% 10% 31%	2470
July	1st to 10th	Day	8% 6% 2 8% 7% 7% 7% 6% 9% 10% 31%	4120
	11th to 20th	Day	10% 6% 3 9% 7% 8% 7% 5% 7% 9% 30%	4120
	21st to end	Day	14% 11% 4 11% 9% 8% 7% 5% 8% 8% 16%	4466
August	1st to 10th	Day	15% 8% 3 8% 6% 7% 7% 5% 9% 10% 23%	4104
	11th to 20th	Day	10% 7% 3 8% 6% 7% 8% 6% 7% 11% 27%	4044
	21st to end	Day	9% 5% 2 6% 5% 6% 7% 5% 7% 9% 39%	4286
September	1st to 10th	Day	13% 8% 3 8% 5% 5% 6% 4 6% 8% 34%	2090
	11th to 20th	Day	18% 9% 3 7% 5% 4 6% 4 7% 7% 30%	2090
	21st to end	Day	20% 7% 2 6% 5% 5% 4 5% 6% 7% 33%	2090
October	1st to 10th	Day	18% 5% 2 6% 3 3 4 3 5% 6% 45%	2012
	11th to 20th	Day	13% 6% 1 5% 3 4 4 3 4 6% 51%	1900
	21st to end	Day	15% 6% 1 5% 3 3 3 3 4 6% 50%	2090
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 4 4 7% 53%	1817
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 50%	1710
	21st to end	Day	14% 5% 2 6% 3 3 4 3 4 7% 48%	1710
December	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 4 4 7% 33%	1710
	11th to 20th	Day	13% 5% 2 5% 3 4 4 4 7% 8% 46%	2153
	21st to end	Day	18% 6% 2 5% 4 5% 5% 4 6% 7% 39%	3124
January	1st to 10th	Night	13% 6% 2 6% 4 5% 5% 5% 6% 6% 42%	4109
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 5% 6% 44%	4120
	21st to end	Night	19% 8% 2 5% 4 5% 4 3 5% 6% 40%	4532
February	1st to 10th	Night	12% 7% 2 6% 4 4 5% 5% 7% 8% 41%	2456
	11th to 20th	Night	17% 8% 2 5% 4 4 5% 4 6% 6% 40%	2218
	21st to end	Night	13% 7% 2 7% 6% 4 5% 4 8% 7% 36%	1884
March	1st to 10th	Night	21% 10% 3 7% 5% 5% 4 3 5% 5% 32%	3430
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	3480
	21st to end	Night	18% 6% 1 4 4 4 4 3 5% 8% 42%	3817
April	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 4 6% 9% 43%	2090
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 6% 8% 45%	1873
	21st to end	Night	12% 6% 2 5% 4 4 4 5% 6% 8% 44%	1710
May	1st to 10th	Night	14% 7% 2 7% 5% 6% 4 4 7% 9% 34%	2813
	11th to 20th	Night	20% 7% 2 6% 5% 4 4 3 7% 9% 32%	2812
	21st to end	Night	9% 5% 2 6% 4 4 5% 5% 7% 11% 42%	3079
June	1st to 10th	Night	10% 6% 3 7% 4 5% 6% 5% 8% 10% 35%	1710
	11th to 20th	Night	9% 6% 2 5% 5% 5% 5% 4 9% 10% 40%	1710
	21st to end	Night	7% 5% 2 5% 6% 4 6% 5% 9% 11% 39%	1710
July	1st to 10th	Night	9% 6% 2 6% 4 5% 7% 5% 9% 12% 34%	2840
	11th to 20th	Night	9% 5% 1 5% 4 4 5% 5% 8% 12% 43%	2840
	21st to end	Night	11% 9% 4 9% 7% 6% 7% 6% 8% 11% 22%	3087
August	1st to 10th	Night	14% 8% 2 7% 5% 4 5% 5% 7% 12% 31%	2825
	11th to 20th	Night	11% 7% 2 6% 4 5% 6% 4 7% 12% 35%	2785
	21st to end	Night	8% 5% 2 4 4 4 4 4 7% 10% 50%	3331
September	1st to 10th	Night	13% 8% 2 8% 4 4 5% 4 5% 7% 41%	2090
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 7% 37%	2090
	21st to end	Night	21% 8% 2 6% 3 4 4 3 4 5% 41%	2090
October	1st to 10th	Night	17% 6% 2 5% 3 4 3 3 5% 6% 46%	2166
	11th to 20th	Night	14% 6% 1 5% 4 3 3 3 5% 6% 51%	2280
	21st to end	Night	14% 5% 1 4 3 3 3 3 4 5% 54%	2508
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 2 5% 7% 49%	2291
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 5% 7% 50%	2470
	21st to end	Night	13% 6% 2 5% 4 4 3 4 6% 7% 47%	2470
December	1st to 10th	Night	15% 7% 3 6% 4 6% 5% 3 5% 7% 37%	2470
	11th to 20th	Night	13% 7% 2 6% 5% 5% 4 4 5% 7% 42%	3042
	21st to end	Night	20% 8% 2 6% 4 4 5% 4 6% 7% 33%	4532

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	33% 8% 13% 22% 20% 5%	2837
	11th to 20th	Day	39% 8% 11% 19% 20% 4	2840
	21st to end	Day	43% 6% 9% 19% 19% 4	3124
February	1st to 10th	Day	42% 10% 12% 17% 15% 4	1721
	11th to 20th	Day	44% 9% 10% 17% 16% 4	1858
	21st to end	Day	44% 10% 12% 15% 14% 6%	1570
March	1st to 10th	Day	42% 9% 11% 19% 16% 5%	3421
	11th to 20th	Day	33% 8% 11% 24% 15% 10%	3480
	21st to end	Day	43% 7% 12% 23% 12% 4	3815
April	1st to 10th	Day	36% 10% 12% 22% 17% 4	2090
	11th to 20th	Day	40% 8% 11% 19% 17% 5%	2269
	21st to end	Day	41% 11% 13% 21% 13% 2	2470
May	1st to 10th	Day	46% 13% 13% 19% 7% 1	4120
	11th to 20th	Day	49% 13% 12% 19% 6% 1	4085
	21st to end	Day	35% 13% 16% 20% 14% 2	4489
June	1st to 10th	Day	46% 13% 15% 17% 9% 1	2470
	11th to 20th	Day	43% 13% 15% 16% 12% 1	2470
	21st to end	Day	42% 13% 15% 17% 12% 1	2470
July	1st to 10th	Day	42% 17% 16% 16% 7% 1	4055
	11th to 20th	Day	45% 15% 19% 16% 5% 1	4051
	21st to end	Day	60% 14% 11% 11% 3 1	4324
August	1st to 10th	Day	48% 16% 17% 15% 3	4091
	11th to 20th	Day	41% 16% 20% 13% 6% 3	4083
	21st to end	Day	33% 14% 17% 29% 6% 2	4286
September	1st to 10th	Day	44% 11% 11% 18% 13% 3	2090
	11th to 20th	Day	47% 10% 11% 18% 13% 2	2090
	21st to end	Day	47% 8% 12% 16% 12% 4	2090
October	1st to 10th	Day	38% 7% 10% 19% 21% 5%	2012
	11th to 20th	Day	33% 6% 11% 23% 19% 8%	1900
	21st to end	Day	33% 7% 9% 25% 18% 8%	2090
November	1st to 10th	Day	31% 6% 10% 19% 27% 7%	1817
	11th to 20th	Day	32% 7% 9% 21% 23% 7%	1710
	21st to end	Day	35% 6% 10% 22% 22% 5%	1710
December	1st to 10th	Day	49% 7% 10% 17% 14% 4	1710
	11th to 20th	Day	33% 8% 12% 20% 21% 6%	2150
	21st to end	Day	41% 9% 10% 22% 16% 2	3124
January	1st to 10th	Night	34% 11% 14% 22% 13% 7%	4109
	11th to 20th	Night	37% 10% 10% 16% 20% 7%	4120
	21st to end	Night	45% 7% 10% 16% 16% 7%	4532
February	1st to 10th	Night	37% 10% 13% 20% 17% 3	2456
	11th to 20th	Night	43% 8% 12% 18% 15% 5%	2219
	21st to end	Night	42% 10% 13% 17% 13% 5%	1884
March	1st to 10th	Night	48% 12% 11% 14% 13% 3	3430
	11th to 20th	Night	31% 10% 13% 24% 14% 9%	3480
	21st to end	Night	38% 9% 12% 24% 11% 6%	3817
April	1st to 10th	Night	34% 10% 16% 20% 15% 4	2090
	11th to 20th	Night	35% 9% 12% 22% 16% 6%	1873
	21st to end	Night	35% 10% 15% 23% 15% 1	1710
May	1st to 10th	Night	44% 13% 16% 21% 6% 1	2840
	11th to 20th	Night	44% 14% 17% 19% 6%	2813
	21st to end	Night	32% 15% 21% 22% 9% 1	3087
June	1st to 10th	Night	40% 14% 17% 20% 8% 1	1710
	11th to 20th	Night	34% 13% 22% 22% 8% 1	1710
	21st to end	Night	33% 15% 18% 19% 11% 3	1710
July	1st to 10th	Night	38% 16% 21% 18% 6% 1	2795
	11th to 20th	Night	31% 14% 28% 22% 4 1	2786
	21st to end	Night	50% 18% 16% 12% 4	2988
August	1st to 10th	Night	43% 14% 25% 14% 5%	2814
	11th to 20th	Night	37% 16% 21% 17% 7% 1	2812
	21st to end	Night	27% 12% 20% 31% 7% 3	3331
September	1st to 10th	Night	41% 11% 14% 18% 14% 3	2090
	11th to 20th	Night	45% 10% 14% 17% 15% 1	2090
	21st to end	Night	45% 7% 12% 18% 15% 2	2090
October	1st to 10th	Night	36% 9% 12% 18% 21% 4	2166
	11th to 20th	Night	35% 6% 11% 23% 18% 7%	2280
	21st to end	Night	31% 7% 9% 23% 22% 9%	2508
November	1st to 10th	Night	35% 7% 10% 20% 22% 8%	2291
	11th to 20th	Night	32% 7% 10% 20% 22% 8%	2470
	21st to end	Night	34% 7% 10% 23% 21% 5%	2470
December	1st to 10th	Night	44% 8% 12% 18% 13% 5%	2470
	11th to 20th	Night	37% 10% 13% 15% 20% 5%	3044
	21st to end	Night	43% 11% 13% 19% 13% 2	4532

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	33% 35% 24% 7% 1	270
	11th to 20th	Day	30% 29% 32% 9% 1	270
	21st to end	Day	28% 36% 27% 7% 1	297
February	1st to 10th	Day	22% 34% 33% 10% 1	270
	11th to 20th	Day	41% 34% 21% 4	270
	21st to end	Day	36% 34% 25% 4	225
March	1st to 10th	Day	24% 28% 28% 15% 5%	446
	11th to 20th	Day	26% 33% 25% 13% 3 1	460
	21st to end	Day	27% 29% 26% 12% 5%	506
April	1st to 10th	Day	23% 27% 26% 16% 7% 1	460
	11th to 20th	Day	21% 27% 22% 19% 9% 2	452
	21st to end	Day	21% 20% 29% 15% 12% 4	460
May	1st to 10th	Day	17% 22% 34% 14% 8% 5%	463
	11th to 20th	Day	20% 13% 27% 22% 11% 7%	487
	21st to end	Day	18% 10% 24% 22% 16% 10%	529
June	1st to 10th	Day	15% 9% 28% 26% 15% 7%	490
	11th to 20th	Day	11% 7% 25% 30% 17% 10%	490
	21st to end	Day	10% 10% 31% 27% 14% 9%	490
July	1st to 10th	Day	9% 4 21% 29% 25% 13%	485
	11th to 20th	Day	9% 5% 17% 33% 24% 12%	484
	21st to end	Day	10% 6% 19% 31% 21% 13%	532
August	1st to 10th	Day	17% 8% 23% 23% 15% 14%	486
	11th to 20th	Day	11% 5% 24% 25% 23% 11%	479
	21st to end	Day	14% 4 16% 27% 21% 17%	539
September	1st to 10th	Day	14% 5% 18% 27% 25% 12%	490
	11th to 20th	Day	18% 9% 16% 23% 26% 10%	490
	21st to end	Day	23% 10% 23% 25% 15% 4	490
October	1st to 10th	Day	22% 11% 21% 22% 18% 6%	490
	11th to 20th	Day	17% 19% 24% 21% 16% 3	490
	21st to end	Day	18% 17% 27% 25% 10% 3	539
November	1st to 10th	Day	17% 18% 28% 23% 10% 3	409
	11th to 20th	Day	20% 28% 30% 18% 3 1	270
	21st to end	Day	18% 24% 34% 19% 4 1	270
December	1st to 10th	Day	26% 28% 33% 11% 2	270
	11th to 20th	Day	22% 23% 38% 13% 3	270
	21st to end	Day	26% 25% 35% 9% 5% 1	297
January	1st to 10th	Night	20% 29% 28% 20% 4	760
	11th to 20th	Night	21% 27% 27% 21% 4	760
	21st to end	Night	17% 31% 29% 20% 3	836
February	1st to 10th	Night	15% 26% 30% 26% 3	760
	11th to 20th	Night	25% 32% 26% 16% 1	743
	21st to end	Night	21% 30% 31% 17% 2	628
March	1st to 10th	Night	17% 26% 30% 23% 4	760
	11th to 20th	Night	22% 22% 30% 18% 8%	760
	21st to end	Night	20% 22% 29% 21% 7%	836
April	1st to 10th	Night	19% 24% 25% 25% 7%	760
	11th to 20th	Night	20% 19% 24% 23% 13% 1	709
	21st to end	Night	15% 16% 24% 32% 12% 1	570
May	1st to 10th	Night	16% 15% 30% 25% 14% 1	570
	11th to 20th	Night	15% 11% 23% 30% 18% 2	561
	21st to end	Night	17% 7% 16% 27% 27% 7%	617
June	1st to 10th	Night	11% 3 19% 34% 28% 5%	570
	11th to 20th	Night	11% 3 20% 27% 33% 7%	570
	21st to end	Night	7% 5% 19% 31% 34% 4	570
July	1st to 10th	Night	12% 2 12% 27% 42% 6%	555
	11th to 20th	Night	9% 3 11% 28% 41% 9%	552
	21st to end	Night	7% 3 12% 29% 40% 9%	624
August	1st to 10th	Night	16% 3 11% 26% 37% 7%	567
	11th to 20th	Night	14% 4 13% 30% 33% 7%	564
	21st to end	Night	14% 3 10% 27% 38% 9%	710
September	1st to 10th	Night	15% 5% 13% 27% 33% 7%	760
	11th to 20th	Night	23% 4 12% 24% 33% 5%	760
	21st to end	Night	23% 7% 14% 26% 26% 3	760
October	1st to 10th	Night	18% 11% 19% 23% 22% 7%	760
	11th to 20th	Night	19% 14% 23% 28% 14% 3	760
	21st to end	Night	17% 16% 21% 31% 11% 3	836
November	1st to 10th	Night	17% 14% 20% 32% 14% 3	748
	11th to 20th	Night	18% 19% 21% 31% 10% 2	760
	21st to end	Night	17% 19% 24% 28% 11% 1	760
December	1st to 10th	Night	21% 23% 25% 25% 7%	760
	11th to 20th	Night	18% 22% 25% 27% 6% 1	760
	21st to end	Night	25% 21% 26% 24% 5%	836

Page generated at 2024-10-30 13:19:21. Version ac07

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