Grayson Highlands
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grayson Highlands clear sky chart from 2005-11-06 to 2024-11-04.

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	12% 8% 3 8% 6% 6% 6% 4 6% 8% 34%	101223
	Night	12% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	97751
Transparency	Day	23% 49% 7% 11% 7% 3	104926
	Night	21% 50% 8% 11% 7% 3	102187
Seeing	Day	22% 18% 24% 19% 11% 5%	15144
	Night	20% 16% 22% 24% 15% 2	25203

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% 10% 4 8% 5% 4 5% 3 6% 9% 32%	2836
	11th to 20th	Day	10% 10% 6% 12% 6% 7% 5% 4 5% 5% 31%	2840
	21st to end	Day	15% 11% 5% 10% 4 4 4 3 4 5% 35%	3124
February	1st to 10th	Day	11% 11% 4 8% 6% 5% 5% 5% 5% 5% 36%	1710
	11th to 20th	Day	14% 10% 3 9% 6% 4 4 3 5% 6% 35%	1823
	21st to end	Day	17% 9% 4 8% 4 4 4 3 6% 6% 34%	1570
March	1st to 10th	Day	19% 7% 3 7% 5% 4 5% 3 5% 6% 36%	3435
	11th to 20th	Day	10% 7% 3 7% 5% 4 4 3 5% 7% 46%	3480
	21st to end	Day	16% 9% 2 6% 5% 4 4 3 6% 7% 38%	3815
April	1st to 10th	Day	10% 8% 3 7% 5% 4 4 5% 6% 7% 40%	2090
	11th to 20th	Day	15% 9% 3 6% 5% 4 5% 3 6% 6% 39%	2281
	21st to end	Day	14% 8% 3 7% 7% 5% 4 5% 5% 7% 36%	2470
May	1st to 10th	Day	13% 9% 4 11% 6% 7% 6% 5% 6% 7% 27%	4082
	11th to 20th	Day	16% 8% 4 9% 6% 7% 6% 5% 7% 7% 26%	4081
	21st to end	Day	8% 6% 2 7% 7% 7% 7% 6% 9% 10% 32%	4476
June	1st to 10th	Day	11% 7% 3 8% 7% 6% 6% 5% 7% 9% 31%	2470
	11th to 20th	Day	9% 7% 3 8% 6% 7% 7% 5% 8% 10% 32%	2470
	21st to end	Day	10% 6% 3 8% 7% 6% 6% 6% 9% 8% 32%	2470
July	1st to 10th	Day	6% 5% 2 7% 7% 8% 9% 6% 8% 9% 32%	4120
	11th to 20th	Day	9% 6% 2 8% 6% 7% 7% 5% 8% 11% 31%	4120
	21st to end	Day	15% 10% 4 12% 7% 8% 9% 5% 7% 7% 16%	4466
August	1st to 10th	Day	12% 7% 3 9% 7% 7% 7% 6% 8% 11% 24%	4104
	11th to 20th	Day	9% 5% 2 8% 7% 8% 7% 6% 9% 10% 28%	4044
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 4 7% 11% 41%	4340
September	1st to 10th	Day	13% 7% 2 7% 6% 5% 4 5% 6% 8% 37%	2095
	11th to 20th	Day	16% 8% 4 7% 6% 5% 5% 4 6% 8% 32%	2090
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 3 6% 7% 33%	2090
October	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 6% 43%	1990
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 5% 7% 46%	1900
	21st to end	Day	12% 6% 3 8% 5% 3 3 3 4 7% 47%	2090
November	1st to 10th	Day	9% 6% 2 5% 4 4 4 3 5% 6% 50%	1844
	11th to 20th	Day	10% 7% 2 6% 5% 4 4 4 6% 7% 45%	1710
	21st to end	Day	12% 8% 2 7% 4 4 4 3 6% 5% 44%	1710
December	1st to 10th	Day	15% 11% 4 9% 6% 5% 5% 3 6% 7% 31%	1710
	11th to 20th	Day	13% 6% 4 7% 5% 3 6% 3 6% 8% 39%	2153
	21st to end	Day	16% 8% 5% 8% 5% 5% 6% 4 7% 7% 31%	3124
January	1st to 10th	Night	12% 11% 5% 11% 7% 6% 5% 4 6% 6% 27%	4109
	11th to 20th	Night	10% 10% 3 10% 6% 6% 4 3 4 5% 38%	4120
	21st to end	Night	15% 10% 5% 8% 5% 4 4 3 5% 6% 34%	4532
February	1st to 10th	Night	10% 8% 3 8% 6% 4 4 4 7% 7% 38%	2470
	11th to 20th	Night	14% 11% 3 8% 5% 4 5% 4 6% 6% 34%	2241
	21st to end	Night	13% 7% 3 10% 7% 5% 5% 5% 7% 7% 33%	1884
March	1st to 10th	Night	19% 11% 4 11% 6% 5% 4 3 4 4 29%	3418
	11th to 20th	Night	10% 7% 2 8% 6% 4 5% 4 5% 6% 44%	3480
	21st to end	Night	13% 8% 2 5% 5% 4 4 4 6% 6% 42%	3817
April	1st to 10th	Night	9% 8% 3 8% 5% 5% 4 4 6% 9% 39%	2090
	11th to 20th	Night	11% 8% 2 6% 5% 3 5% 5% 6% 9% 40%	1862
	21st to end	Night	12% 7% 2 7% 5% 5% 4 4 5% 8% 42%	1710
May	1st to 10th	Night	13% 9% 3 9% 6% 6% 5% 4 6% 8% 30%	2813
	11th to 20th	Night	17% 9% 3 8% 6% 5% 4 4 6% 7% 31%	2812
	21st to end	Night	8% 6% 3 7% 5% 6% 5% 5% 8% 10% 37%	3079
June	1st to 10th	Night	7% 6% 2 7% 5% 4 6% 5% 7% 11% 38%	1710
	11th to 20th	Night	7% 6% 1 5% 4 5% 6% 5% 8% 12% 40%	1710
	21st to end	Night	6% 6% 2 6% 6% 6% 4 4 10% 12% 39%	1710
July	1st to 10th	Night	6% 6% 3 6% 5% 5% 6% 6% 10% 12% 37%	2840
	11th to 20th	Night	7% 4 2 5% 4 5% 5% 5% 9% 13% 41%	2840
	21st to end	Night	8% 10% 4 10% 7% 6% 6% 6% 9% 10% 24%	3087
August	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 5% 8% 11% 31%	2825
	11th to 20th	Night	8% 5% 2 7% 4 6% 6% 5% 8% 11% 36%	2785
	21st to end	Night	6% 4 1 4 4 3 5% 4 6% 9% 54%	3282
September	1st to 10th	Night	10% 7% 3 7% 6% 4 5% 4 7% 7% 42%	2080
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 6% 7% 40%	2090
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 6% 38%	2090
October	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 5% 7% 45%	2188
	11th to 20th	Night	12% 8% 3 5% 4 4 4 3 5% 6% 46%	2280
	21st to end	Night	11% 6% 3 6% 4 3 4 3 4 7% 49%	2508
November	1st to 10th	Night	11% 7% 2 6% 4 4 4 4 4 6% 48%	2305
	11th to 20th	Night	11% 6% 3 7% 4 4 4 3 5% 8% 45%	2470
	21st to end	Night	11% 7% 3 6% 4 4 5% 4 7% 6% 43%	2470
December	1st to 10th	Night	14% 9% 4 8% 6% 5% 5% 4 6% 7% 31%	2470
	11th to 20th	Night	13% 7% 3 12% 5% 5% 4 3 5% 7% 35%	3042
	21st to end	Night	16% 8% 4 9% 5% 5% 6% 5% 6% 8% 26%	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	23% 45% 8% 8% 13% 3	2837
	11th to 20th	Day	28% 44% 7% 7% 12% 1	2840
	21st to end	Day	31% 44% 6% 7% 11% 2	3124
February	1st to 10th	Day	18% 66% 3 5% 6% 2	1710
	11th to 20th	Day	19% 66% 3 4 7% 1	1833
	21st to end	Day	18% 66% 3 4 7% 2	1570
March	1st to 10th	Day	29% 46% 9% 8% 6% 2	3435
	11th to 20th	Day	17% 43% 5% 17% 12% 6%	3480
	21st to end	Day	24% 42% 6% 15% 9% 3	3815
April	1st to 10th	Day	16% 67% 4 7% 5% 1	2090
	11th to 20th	Day	16% 67% 4 7% 4 1	2281
	21st to end	Day	16% 67% 4 8% 5% 1	2470
May	1st to 10th	Day	33% 47% 5% 11% 3 1	4120
	11th to 20th	Day	31% 45% 7% 13% 3	4085
	21st to end	Day	21% 46% 11% 12% 7% 2	4489
June	1st to 10th	Day	16% 68% 5% 6% 4	2470
	11th to 20th	Day	15% 69% 6% 6% 4	2470
	21st to end	Day	18% 66% 5% 7% 3	2470
July	1st to 10th	Day	27% 43% 13% 11% 4 2	4055
	11th to 20th	Day	27% 40% 14% 18% 1	4051
	21st to end	Day	44% 39% 7% 7% 2	4324
August	1st to 10th	Day	33% 40% 13% 11% 2	4091
	11th to 20th	Day	23% 42% 14% 14% 4 2	4083
	21st to end	Day	17% 40% 15% 21% 7% 1	4340
September	1st to 10th	Day	16% 61% 6% 8% 5% 3	2095
	11th to 20th	Day	21% 62% 4 6% 6%	2090
	21st to end	Day	21% 62% 6% 7% 3	2090
October	1st to 10th	Day	15% 39% 5% 11% 21% 8%	3302
	11th to 20th	Day	12% 38% 4 18% 9% 20%	3140
	21st to end	Day	13% 38% 6% 21% 9% 14%	3428
November	1st to 10th	Day	17% 59% 5% 8% 8% 2	1844
	11th to 20th	Day	15% 61% 4 6% 11% 4	1710
	21st to end	Day	15% 63% 4 8% 10% 1	1710
December	1st to 10th	Day	23% 62% 3 6% 3 2	1710
	11th to 20th	Day	17% 52% 6% 7% 14% 3	2150
	21st to end	Day	29% 42% 9% 13% 7% 1	3124
January	1st to 10th	Night	28% 48% 8% 6% 6% 5%	4109
	11th to 20th	Night	26% 42% 4 9% 14% 5%	4120
	21st to end	Night	30% 44% 5% 8% 10% 2	4532
February	1st to 10th	Night	15% 67% 4 6% 6% 1	2470
	11th to 20th	Night	18% 67% 4 5% 5% 1	2242
	21st to end	Night	16% 68% 3 7% 4 2	1884
March	1st to 10th	Night	34% 48% 6% 7% 4 1	3418
	11th to 20th	Night	17% 43% 7% 16% 10% 7%	3480
	21st to end	Night	22% 43% 8% 15% 10% 3	3817
April	1st to 10th	Night	16% 68% 5% 7% 4 1	2090
	11th to 20th	Night	15% 68% 5% 7% 4 1	1862
	21st to end	Night	13% 66% 6% 10% 5%	1710
May	1st to 10th	Night	28% 49% 7% 13% 2	2840
	11th to 20th	Night	29% 46% 9% 14% 2	2813
	21st to end	Night	18% 49% 12% 14% 5% 1	3087
June	1st to 10th	Night	13% 69% 7% 7% 4	1710
	11th to 20th	Night	10% 70% 8% 10% 2 1	1710
	21st to end	Night	13% 67% 7% 8% 4	1710
July	1st to 10th	Night	23% 44% 15% 15% 3	2795
	11th to 20th	Night	19% 39% 21% 19% 2	2786
	21st to end	Night	38% 41% 9% 9% 2	2988
August	1st to 10th	Night	30% 41% 18% 10% 2	2814
	11th to 20th	Night	19% 43% 18% 17% 3	2812
	21st to end	Night	13% 39% 13% 28% 7%	3282
September	1st to 10th	Night	15% 62% 8% 8% 6% 1	2080
	11th to 20th	Night	18% 61% 6% 9% 6%	2090
	21st to end	Night	20% 62% 5% 10% 2	2090
October	1st to 10th	Night	16% 39% 6% 15% 14% 9%	3656
	11th to 20th	Night	12% 38% 5% 14% 13% 18%	3779
	21st to end	Night	14% 37% 6% 16% 12% 14%	4120
November	1st to 10th	Night	19% 59% 5% 9% 7% 1	2305
	11th to 20th	Night	14% 62% 3 7% 10% 5%	2470
	21st to end	Night	15% 62% 5% 9% 8% 1	2470
December	1st to 10th	Night	23% 63% 4 5% 4 2	2470
	11th to 20th	Night	20% 55% 4 7% 12% 2	3044
	21st to end	Night	31% 45% 8% 9% 6% 1	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	43% 27% 22% 7% 1 1	270
	11th to 20th	Day	41% 26% 25% 7%	270
	21st to end	Day	36% 37% 18% 8% 1	297
February	1st to 10th	Day	35% 33% 24% 7% 1	270
	11th to 20th	Day	49% 27% 20% 3	270
	21st to end	Day	44% 32% 22% 2	225
March	1st to 10th	Day	30% 28% 25% 13% 4	460
	11th to 20th	Day	36% 29% 20% 11% 3 1	460
	21st to end	Day	30% 29% 24% 14% 3 1	506
April	1st to 10th	Day	28% 27% 25% 12% 6% 1	460
	11th to 20th	Day	29% 22% 24% 15% 7% 2	452
	21st to end	Day	25% 24% 24% 15% 9% 2	460
May	1st to 10th	Day	24% 26% 28% 14% 4 5%	463
	11th to 20th	Day	20% 19% 27% 20% 9% 5%	487
	21st to end	Day	18% 12% 25% 22% 14% 9%	529
June	1st to 10th	Day	14% 12% 30% 22% 15% 7%	490
	11th to 20th	Day	10% 10% 28% 28% 17% 6%	490
	21st to end	Day	12% 16% 28% 24% 13% 6%	490
July	1st to 10th	Day	11% 8% 20% 28% 21% 11%	485
	11th to 20th	Day	9% 8% 19% 35% 19% 9%	484
	21st to end	Day	11% 7% 27% 25% 20% 9%	532
August	1st to 10th	Day	15% 8% 25% 26% 15% 11%	486
	11th to 20th	Day	10% 8% 26% 23% 22% 11%	479
	21st to end	Day	12% 5% 20% 27% 19% 17%	539
September	1st to 10th	Day	12% 6% 21% 25% 23% 12%	490
	11th to 20th	Day	17% 8% 17% 26% 22% 10%	490
	21st to end	Day	26% 11% 21% 22% 15% 4	490
October	1st to 10th	Day	20% 12% 22% 22% 17% 6%	490
	11th to 20th	Day	19% 21% 22% 22% 14% 2	490
	21st to end	Day	21% 19% 27% 22% 9% 3	539
November	1st to 10th	Day	19% 19% 29% 20% 9% 3	424
	11th to 20th	Day	32% 21% 24% 17% 6%	270
	21st to end	Day	26% 26% 29% 16% 3 1	270
December	1st to 10th	Day	33% 30% 28% 8% 1	270
	11th to 20th	Day	30% 24% 31% 10% 3	270
	21st to end	Day	31% 28% 27% 9% 4	297
January	1st to 10th	Night	32% 26% 23% 15% 3 1	760
	11th to 20th	Night	29% 26% 26% 17% 2	760
	21st to end	Night	27% 29% 25% 17% 2	836
February	1st to 10th	Night	25% 23% 31% 19% 2	760
	11th to 20th	Night	35% 32% 21% 11% 1	743
	21st to end	Night	26% 32% 28% 12% 2	628
March	1st to 10th	Night	24% 24% 30% 19% 3	760
	11th to 20th	Night	29% 24% 24% 16% 6%	760
	21st to end	Night	21% 22% 32% 19% 6%	836
April	1st to 10th	Night	24% 22% 28% 20% 6%	760
	11th to 20th	Night	21% 21% 26% 22% 9% 1	723
	21st to end	Night	16% 20% 24% 32% 7% 1	570
May	1st to 10th	Night	18% 16% 29% 23% 13% 1	570
	11th to 20th	Night	16% 11% 25% 31% 15% 2	561
	21st to end	Night	16% 7% 19% 29% 24% 5%	617
June	1st to 10th	Night	10% 6% 22% 35% 24% 4	570
	11th to 20th	Night	9% 6% 18% 32% 30% 4	570
	21st to end	Night	7% 7% 18% 37% 27% 4	570
July	1st to 10th	Night	10% 4 14% 32% 34% 6%	555
	11th to 20th	Night	7% 4 12% 35% 36% 6%	552
	21st to end	Night	5% 5% 13% 35% 36% 6%	624
August	1st to 10th	Night	13% 4 12% 30% 37% 4	567
	11th to 20th	Night	13% 4 11% 34% 33% 5%	564
	21st to end	Night	11% 3 13% 30% 36% 8%	720
September	1st to 10th	Night	12% 6% 15% 29% 32% 7%	760
	11th to 20th	Night	18% 5% 16% 28% 28% 5%	760
	21st to end	Night	21% 9% 17% 28% 24% 2	760
October	1st to 10th	Night	18% 11% 17% 26% 23% 5%	760
	11th to 20th	Night	19% 17% 23% 23% 14% 3	760
	21st to end	Night	21% 15% 23% 29% 11% 2	836
November	1st to 10th	Night	17% 15% 25% 24% 15% 3	755
	11th to 20th	Night	25% 16% 23% 27% 9% 1	760
	21st to end	Night	24% 18% 25% 22% 11% 1	760
December	1st to 10th	Night	27% 23% 25% 20% 5%	760
	11th to 20th	Night	25% 24% 25% 21% 5%	760
	21st to end	Night	27% 22% 27% 20% 4	836

Page generated at 2024-11-01 22:47:46. Version ac07

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