Holly Mountain Airpark
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holly Mountain Airpark clear sky chart from 2005-11-06 to 2024-12-24.

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% 4 4 4 3 5% 7% 45%	101198
	Night	13% 6% 2 5% 3 3 4 3 5% 6% 50%	98975
Transparency	Day	38% 3 10% 25% 19% 5%	104843
	Night	35% 3 10% 25% 22% 6%	103470
Seeing	Day	17% 10% 25% 26% 16% 5%	15565
	Night	17% 11% 25% 29% 16% 2	25425

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	16% 9% 3 5% 4 3 4 2 3 4 47%	2847
	11th to 20th	Day	12% 10% 3 6% 4 3 3 2 3 4 50%	2850
	21st to end	Day	26% 6% 2 4 2 2 2 3 4 4 47%	3135
February	1st to 10th	Day	21% 8% 3 6% 4 3 3 2 3 5% 43%	1710
	11th to 20th	Day	17% 8% 3 7% 4 4 4 3 4 5% 42%	1775
	21st to end	Day	19% 9% 3 8% 4 4 3 3 3 6% 39%	1599
March	1st to 10th	Day	23% 9% 3 6% 4 3 4 3 3 4 38%	3436
	11th to 20th	Day	14% 7% 2 5% 4 3 4 3 4 6% 49%	3480
	21st to end	Day	17% 8% 3 7% 4 3 3 3 4 5% 42%	3831
April	1st to 10th	Day	15% 7% 2 5% 4 4 5% 4 5% 5% 43%	2280
	11th to 20th	Day	17% 6% 2 7% 5% 5% 4 3 4 6% 42%	2254
	21st to end	Day	19% 7% 2 7% 4 5% 4 3 5% 5% 40%	2280
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 5% 36%	3782
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 40%	4082
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	4599
June	1st to 10th	Day	9% 6% 2 6% 4 6% 6% 5% 6% 8% 42%	2660
	11th to 20th	Day	6% 3 2 6% 5% 5% 6% 5% 8% 9% 45%	2660
	21st to end	Day	4 4 2 4 5% 5% 5% 5% 8% 10% 48%	2630
July	1st to 10th	Day	9% 5% 2 5% 4 5% 5% 4 8% 9% 43%	4120
	11th to 20th	Day	6% 4 2 4 3 4 4 3 6% 8% 57%	4120
	21st to end	Day	10% 7% 3 9% 5% 6% 5% 4 7% 9% 34%	4465
August	1st to 10th	Day	4 3 1 4 3 3 4 4 6% 8% 61%	4104
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 43%	3772
	21st to end	Day	6% 3 1 5% 4 4 5% 5% 6% 9% 53%	4180
September	1st to 10th	Day	11% 5% 2 5% 5% 4 4 5% 5% 7% 47%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 46%	2280
	21st to end	Day	10% 5% 2 4 3 4 5% 3 5% 6% 52%	1985
October	1st to 10th	Day	10% 4 2 3 3 3 3 3 5% 7% 56%	1900
	11th to 20th	Day	15% 4 2 4 3 2 3 3 3 5% 57%	1900
	21st to end	Day	19% 5% 3 4 3 3 3 3 3 4 49%	2090
November	1st to 10th	Day	15% 5% 2 4 3 2 2 2 3 5% 55%	1958
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 7% 53%	1872
	21st to end	Day	21% 6% 3 6% 2 3 3 3 4 5% 46%	1720
December	1st to 10th	Day	19% 6% 2 4 3 2 3 2 4 5% 49%	1600
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 4 4 46%	1998
	21st to end	Day	16% 10% 3 8% 5% 4 4 3 4 5% 37%	2964
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 4 5% 45%	4108
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 3 5% 54%	4120
	21st to end	Night	24% 7% 2 5% 3 2 2 2 3 4 46%	4532
February	1st to 10th	Night	21% 8% 2 5% 4 3 4 3 4 5% 41%	2470
	11th to 20th	Night	16% 8% 3 6% 3 3 3 3 4 6% 46%	2291
	21st to end	Night	19% 7% 2 6% 3 3 3 3 4 6% 46%	1870
March	1st to 10th	Night	21% 8% 3 6% 3 3 3 3 4 5% 40%	3419
	11th to 20th	Night	15% 7% 2 5% 3 3 3 2 4 5% 50%	3480
	21st to end	Night	14% 6% 3 6% 4 4 4 3 5% 7% 45%	3798
April	1st to 10th	Night	12% 6% 2 7% 3 4 3 2 5% 6% 49%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 4 5% 49%	1875
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 8% 44%	1900
May	1st to 10th	Night	19% 7% 2 5% 3 4 3 3 5% 7% 41%	3110
	11th to 20th	Night	15% 6% 3 6% 3 3 3 3 6% 9% 43%	2823
	21st to end	Night	16% 7% 2 5% 5% 4 4 4 6% 8% 40%	2963
June	1st to 10th	Night	7% 4 2 5% 3 3 3 3 7% 10% 52%	1520
	11th to 20th	Night	4 3 1 3 3 3 4 3 7% 10% 59%	1520
	21st to end	Night	4 3 1 3 3 3 3 4 6% 10% 60%	1543
July	1st to 10th	Night	7% 4 2 5% 4 4 5% 5% 7% 9% 50%	2850
	11th to 20th	Night	5% 2 1 3 2 3 3 3 5% 8% 64%	2850
	21st to end	Night	9% 7% 3 7% 5% 5% 5% 4 6% 8% 41%	3098
August	1st to 10th	Night	2 2 1 3 2 4 4 4 5% 9% 64%	2836
	11th to 20th	Night	5% 3 1 5% 3 4 4 4 6% 10% 54%	3056
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 8% 57%	3476
September	1st to 10th	Night	7% 4 2 4 3 3 4 3 5% 8% 55%	1900
	11th to 20th	Night	9% 6% 2 5% 3 4 4 4 5% 7% 51%	1900
	21st to end	Night	9% 5% 1 3 4 2 3 3 5% 6% 59%	2170
October	1st to 10th	Night	8% 3 2 4 2 3 3 3 4 7% 61%	2280
	11th to 20th	Night	13% 4 1 5% 2 3 2 2 3 5% 60%	2280
	21st to end	Night	18% 6% 1 5% 3 3 2 2 3 4 52%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 2 3 3 4 5% 55%	2340
	11th to 20th	Night	13% 4 1 4 3 2 3 3 4 6% 57%	2525
	21st to end	Night	16% 6% 1 5% 4 2 3 3 4 5% 51%	2675
December	1st to 10th	Night	17% 6% 2 5% 4 3 3 3 4 5% 48%	2800
	11th to 20th	Night	18% 5% 2 6% 4 4 3 2 4 5% 46%	3419
	21st to end	Night	18% 8% 3 7% 5% 4 4 3 4 5% 38%	4770

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	44% 2 5% 27% 19% 4	2848
	11th to 20th	Day	40% 2 9% 25% 21% 3	2850
	21st to end	Day	43% 1 8% 19% 22% 6%	3135
February	1st to 10th	Day	47% 2 9% 22% 16% 3	1710
	11th to 20th	Day	45% 3 7% 21% 18% 5%	1784
	21st to end	Day	49% 2 7% 18% 15% 8%	1599
March	1st to 10th	Day	51% 2 6% 16% 15% 10%	3436
	11th to 20th	Day	39% 2 10% 25% 19% 5%	3480
	21st to end	Day	46% 2 10% 22% 20% 1	3831
April	1st to 10th	Day	41% 4 8% 21% 21% 4	2280
	11th to 20th	Day	45% 2 8% 22% 17% 7%	2254
	21st to end	Day	47% 3 8% 23% 17% 2	2280
May	1st to 10th	Day	50% 3 11% 19% 15% 2	3817
	11th to 20th	Day	43% 4 14% 26% 13% 1	4086
	21st to end	Day	47% 4 12% 23% 12% 2	4612
June	1st to 10th	Day	37% 6% 13% 26% 17% 1	2660
	11th to 20th	Day	32% 5% 16% 29% 16% 3	2660
	21st to end	Day	28% 5% 16% 29% 18% 4	2630
July	1st to 10th	Day	34% 5% 16% 30% 13% 2	4056
	11th to 20th	Day	25% 4 10% 35% 24% 3	4051
	21st to end	Day	45% 6% 15% 26% 8% 1	4325
August	1st to 10th	Day	21% 4 17% 33% 20% 6%	4090
	11th to 20th	Day	37% 5% 15% 29% 13% 1	3808
	21st to end	Day	26% 5% 13% 35% 17% 3	4179
September	1st to 10th	Day	36% 4 10% 24% 18% 8%	2280
	11th to 20th	Day	36% 4 11% 22% 23% 5%	2280
	21st to end	Day	32% 4 7% 24% 29% 4	1985
October	1st to 10th	Day	17% 2 5% 15% 40% 20%	3160
	11th to 20th	Day	20% 1 3 23% 39% 14%	3140
	21st to end	Day	34% 3 6% 31% 22% 5%	3428
November	1st to 10th	Day	34% 2 7% 25% 24% 8%	1958
	11th to 20th	Day	32% 3 6% 24% 24% 10%	1872
	21st to end	Day	42% 2 6% 21% 24% 4	1720
December	1st to 10th	Day	39% 3 8% 27% 19% 5%	1600
	11th to 20th	Day	44% 2 5% 23% 22% 4	1995
	21st to end	Day	50% 3 9% 18% 16% 5%	2964
January	1st to 10th	Night	43% 2 5% 23% 24% 3	4108
	11th to 20th	Night	36% 2 10% 25% 22% 4	4120
	21st to end	Night	45% 2 9% 20% 20% 4	4532
February	1st to 10th	Night	47% 3 7% 22% 18% 4	2470
	11th to 20th	Night	41% 3 8% 24% 19% 5%	2292
	21st to end	Night	41% 2 7% 21% 20% 8%	1870
March	1st to 10th	Night	48% 2 8% 16% 16% 10%	3419
	11th to 20th	Night	38% 2 8% 28% 19% 4	3480
	21st to end	Night	41% 3 9% 29% 17% 1	3798
April	1st to 10th	Night	36% 3 10% 23% 22% 6%	1900
	11th to 20th	Night	38% 3 7% 23% 21% 8%	1875
	21st to end	Night	39% 3 12% 25% 18% 3	1900
May	1st to 10th	Night	45% 3 13% 23% 13% 2	3140
	11th to 20th	Night	39% 3 17% 26% 13% 2	2824
	21st to end	Night	43% 4 13% 25% 13% 2	2971
June	1st to 10th	Night	27% 4 14% 33% 21% 2	1520
	11th to 20th	Night	21% 4 14% 37% 21% 3	1520
	21st to end	Night	21% 4 15% 32% 22% 7%	1543
July	1st to 10th	Night	29% 6% 19% 26% 19% 1	2805
	11th to 20th	Night	19% 4 12% 39% 24% 3	2796
	21st to end	Night	40% 5% 14% 28% 12%	2999
August	1st to 10th	Night	17% 4 17% 37% 22% 2	2826
	11th to 20th	Night	25% 5% 21% 31% 17% 1	3086
	21st to end	Night	23% 4 12% 35% 22% 3	3476
September	1st to 10th	Night	28% 4 11% 29% 20% 9%	1900
	11th to 20th	Night	32% 4 12% 20% 25% 5%	1900
	21st to end	Night	27% 4 8% 23% 32% 7%	2170
October	1st to 10th	Night	14% 2 7% 15% 36% 27%	3800
	11th to 20th	Night	18% 1 3 17% 40% 21%	3779
	21st to end	Night	30% 2 5% 27% 27% 9%	4120
November	1st to 10th	Night	32% 2 8% 25% 25% 8%	2340
	11th to 20th	Night	30% 3 5% 27% 27% 9%	2525
	21st to end	Night	37% 2 7% 24% 25% 5%	2675
December	1st to 10th	Night	41% 2 8% 24% 20% 5%	2800
	11th to 20th	Night	41% 3 6% 22% 23% 5%	3421
	21st to end	Night	47% 4 8% 21% 17% 3	4770

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	30% 19% 34% 15% 3	270
	11th to 20th	Day	32% 24% 31% 11% 3	270
	21st to end	Day	26% 24% 34% 13% 3	297
February	1st to 10th	Day	31% 20% 35% 10% 4 1	270
	11th to 20th	Day	32% 26% 28% 11% 3	270
	21st to end	Day	37% 24% 28% 8% 3	225
March	1st to 10th	Day	29% 16% 34% 16% 4	270
	11th to 20th	Day	38% 14% 33% 13% 1	270
	21st to end	Day	30% 24% 34% 8% 4	302
April	1st to 10th	Day	25% 19% 30% 17% 7% 1	460
	11th to 20th	Day	26% 17% 33% 18% 5% 1	452
	21st to end	Day	25% 17% 34% 16% 8%	460
May	1st to 10th	Day	22% 17% 33% 20% 9%	467
	11th to 20th	Day	18% 10% 30% 26% 13% 3	675
	21st to end	Day	12% 7% 33% 30% 14% 4	734
June	1st to 10th	Day	11% 5% 20% 34% 25% 6%	680
	11th to 20th	Day	7% 3 20% 41% 23% 5%	680
	21st to end	Day	6% 3 27% 35% 23% 6%	680
July	1st to 10th	Day	9% 3 16% 35% 28% 10%	671
	11th to 20th	Day	5% 3 15% 35% 29% 11%	668
	21st to end	Day	7% 3 13% 33% 31% 13%	739
August	1st to 10th	Day	7% 3 13% 39% 30% 9%	676
	11th to 20th	Day	15% 4 11% 32% 28% 10%	510
	21st to end	Day	9% 2 10% 30% 32% 16%	539
September	1st to 10th	Day	12% 2 13% 32% 33% 8%	490
	11th to 20th	Day	11% 5% 15% 30% 28% 12%	490
	21st to end	Day	13% 7% 26% 28% 21% 5%	314
October	1st to 10th	Day	10% 9% 24% 37% 15% 6%	300
	11th to 20th	Day	17% 12% 37% 23% 9% 2	300
	21st to end	Day	28% 15% 31% 19% 6% 1	330
November	1st to 10th	Day	21% 13% 32% 23% 10% 1	300
	11th to 20th	Day	19% 16% 38% 20% 6% 1	300
	21st to end	Day	30% 14% 32% 19% 4 2	300
December	1st to 10th	Day	26% 20% 29% 19% 4 2	300
	11th to 20th	Day	28% 18% 34% 13% 6%	300
	21st to end	Day	30% 18% 37% 13% 2 1	306
January	1st to 10th	Night	25% 17% 33% 21% 4	950
	11th to 20th	Night	24% 21% 33% 19% 3 1	950
	21st to end	Night	22% 18% 34% 23% 3	1045
February	1st to 10th	Night	29% 17% 28% 23% 3	950
	11th to 20th	Night	24% 21% 33% 20% 2	816
	21st to end	Night	26% 20% 33% 20% 1	614
March	1st to 10th	Night	22% 15% 30% 30% 4	570
	11th to 20th	Night	23% 15% 31% 27% 4	570
	21st to end	Night	23% 15% 35% 21% 7%	627
April	1st to 10th	Night	17% 18% 36% 22% 7%	570
	11th to 20th	Night	19% 16% 30% 26% 8% 1	563
	21st to end	Night	18% 12% 37% 24% 8% 1	570
May	1st to 10th	Night	18% 9% 29% 35% 9%	570
	11th to 20th	Night	19% 7% 25% 29% 17% 3	561
	21st to end	Night	12% 3 25% 35% 20% 4	617
June	1st to 10th	Night	8% 4 16% 34% 34% 4	570
	11th to 20th	Night	5% 3 15% 45% 29% 3	570
	21st to end	Night	5% 1 16% 39% 34% 5%	570
July	1st to 10th	Night	4 3 10% 34% 41% 7%	555
	11th to 20th	Night	4 2 9% 36% 40% 10%	552
	21st to end	Night	7% 2 8% 38% 36% 10%	624
August	1st to 10th	Night	4 1 9% 39% 40% 7%	567
	11th to 20th	Night	8% 1 12% 38% 34% 6%	564
	21st to end	Night	7% 1 9% 35% 42% 6%	627
September	1st to 10th	Night	9% 2 10% 36% 40% 4	570
	11th to 20th	Night	13% 2 11% 35% 32% 6%	570
	21st to end	Night	11% 5% 16% 34% 30% 4	669
October	1st to 10th	Night	9% 5% 18% 36% 29% 3	760
	11th to 20th	Night	15% 9% 30% 30% 16%	760
	21st to end	Night	20% 13% 28% 27% 11% 1	836
November	1st to 10th	Night	15% 11% 31% 30% 14% 1	780
	11th to 20th	Night	18% 11% 32% 30% 9%	800
	21st to end	Night	21% 15% 28% 25% 10%	875
December	1st to 10th	Night	23% 14% 33% 24% 6%	1000
	11th to 20th	Night	25% 13% 28% 30% 5%	1000
	21st to end	Night	25% 17% 29% 24% 5%	1063

Page generated at 2024-12-21 03:13:49. Version ac07

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