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 2026-04-17.

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% 46%	131072
	Night	14% 6% 2 5% 3 3 4 3 5% 6% 50%	131319
Transparency	Day	38% 3 10% 25% 19% 5%	134678
	Night	35% 3 10% 25% 21% 6%	135790
Seeing	Day	18% 11% 25% 25% 16% 5%	17287
	Night	17% 11% 25% 29% 16% 2	27212

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% 7% 2 5% 4 4 4 3 4 5% 47%	5289
	11th to 20th	Day	9% 8% 2 5% 4 3 3 2 4 4 56%	5310
	21st to end	Day	20% 6% 2 5% 2 2 2 3 4 4 51%	5812
February	1st to 10th	Day	21% 8% 2 6% 4 3 3 2 3 5% 43%	1890
	11th to 20th	Day	17% 7% 3 6% 4 4 4 3 4 6% 42%	1967
	21st to end	Day	17% 8% 3 8% 3 4 3 3 3 6% 41%	1763
March	1st to 10th	Day	21% 9% 3 6% 4 3 4 3 4 5% 38%	5046
	11th to 20th	Day	11% 6% 2 5% 3 3 4 4 5% 6% 53%	5090
	21st to end	Day	16% 8% 3 6% 4 3 3 3 4 6% 43%	5614
April	1st to 10th	Day	16% 7% 2 5% 4 4 5% 4 5% 5% 43%	2520
	11th to 20th	Day	16% 6% 2 7% 5% 4 4 3 4 6% 42%	2446
	21st to end	Day	19% 8% 2 6% 4 5% 4 3 5% 5% 39%	2400
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 5% 6% 34%	5422
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	5862
	21st to end	Day	20% 7% 3 7% 4 5% 5% 4 5% 7% 34%	6612
June	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 5% 6% 8% 43%	2800
	11th to 20th	Day	7% 4 2 6% 6% 5% 6% 5% 8% 9% 44%	2800
	21st to end	Day	4 4 2 4 4 5% 5% 5% 8% 10% 49%	2768
July	1st to 10th	Day	8% 5% 2 6% 4 5% 6% 5% 8% 11% 41%	5900
	11th to 20th	Day	5% 3 1 4 3 4 4 4 6% 9% 57%	5900
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	6422
August	1st to 10th	Day	4 3 1 4 3 3 4 3 5% 8% 61%	4234
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 43%	3894
	21st to end	Day	6% 3 1 4 4 4 5% 5% 6% 9% 53%	4312
September	1st to 10th	Day	11% 5% 2 5% 5% 4 4 5% 5% 7% 47%	2400
	11th to 20th	Day	11% 5% 2 7% 4 4 5% 4 6% 7% 46%	2400
	21st to end	Day	10% 5% 2 4 4 4 4 3 5% 7% 51%	2090
October	1st to 10th	Day	10% 4 2 4 4 3 3 3 5% 7% 57%	2000
	11th to 20th	Day	14% 4 2 4 2 2 3 2 3 5% 58%	2000
	21st to end	Day	19% 5% 3 4 3 3 3 3 3 4 49%	2200
November	1st to 10th	Day	14% 5% 2 4 3 2 2 2 3 5% 56%	2058
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 4 7% 53%	1965
	21st to end	Day	20% 6% 2 6% 2 2 3 3 4 5% 46%	1806
December	1st to 10th	Day	16% 7% 2 4 3 2 3 2 4 4 52%	2690
	11th to 20th	Day	18% 7% 2 6% 4 4 3 2 4 4 47%	3088
	21st to end	Day	21% 11% 3 7% 4 4 3 3 4 5% 36%	4302
January	1st to 10th	Night	17% 7% 2 6% 3 3 3 3 4 5% 47%	7634
	11th to 20th	Night	9% 5% 2 4 3 2 3 2 3 4 63%	7680
	21st to end	Night	21% 7% 3 6% 3 2 3 3 4 5% 44%	8402
February	1st to 10th	Night	20% 7% 2 5% 4 3 4 3 4 5% 42%	2730
	11th to 20th	Night	18% 8% 3 5% 3 3 3 3 4 6% 45%	2538
	21st to end	Night	17% 7% 1 6% 3 3 4 3 4 6% 48%	2060
March	1st to 10th	Night	21% 8% 3 6% 3 3 3 3 3 4 42%	5029
	11th to 20th	Night	12% 7% 2 5% 3 3 4 3 4 6% 52%	5090
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 7% 46%	5555
April	1st to 10th	Night	13% 6% 2 6% 3 4 3 2 5% 7% 48%	2100
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 5% 6% 48%	2035
	21st to end	Night	16% 7% 2 5% 3 3 4 3 5% 7% 44%	2000
May	1st to 10th	Night	20% 7% 2 5% 3 4 4 3 5% 7% 40%	4457
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 6% 8% 36%	4053
	21st to end	Night	20% 7% 2 6% 4 4 4 3 5% 7% 37%	4260
June	1st to 10th	Night	7% 4 2 5% 3 3 3 3 7% 10% 52%	1600
	11th to 20th	Night	5% 4 1 4 3 3 4 3 7% 10% 57%	1600
	21st to end	Night	4 3 1 3 3 3 3 4 6% 10% 60%	1625
July	1st to 10th	Night	7% 4 2 6% 4 5% 5% 5% 7% 10% 46%	4078
	11th to 20th	Night	4 3 1 3 2 3 4 3 6% 10% 62%	4077
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 9% 49%	4449
August	1st to 10th	Night	2 2 1 3 2 4 4 4 5% 9% 64%	2926
	11th to 20th	Night	5% 3 1 5% 3 4 4 4 6% 10% 54%	3154
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 8% 57%	3586
September	1st to 10th	Night	7% 4 2 4 4 3 4 3 6% 8% 55%	2000
	11th to 20th	Night	9% 6% 2 5% 3 4 4 4 5% 7% 51%	2000
	21st to end	Night	9% 5% 1 3 4 3 3 3 5% 6% 59%	2284
October	1st to 10th	Night	7% 3 2 4 2 3 3 3 4 7% 62%	2400
	11th to 20th	Night	12% 4 1 5% 2 3 2 2 3 5% 60%	2400
	21st to end	Night	18% 6% 1 5% 3 3 3 2 3 4 52%	2640
November	1st to 10th	Night	11% 6% 2 5% 3 2 3 3 4 5% 56%	2460
	11th to 20th	Night	13% 4 1 4 3 3 3 3 4 6% 57%	2651
	21st to end	Night	17% 6% 1 5% 4 2 3 3 4 5% 51%	2809
December	1st to 10th	Night	14% 7% 2 4 3 3 4 3 4 5% 53%	4720
	11th to 20th	Night	21% 6% 2 5% 4 4 3 2 3 4 47%	5339
	21st to end	Night	23% 7% 3 6% 4 4 4 3 4 5% 38%	6898

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	42% 2 8% 30% 17% 2	5290
	11th to 20th	Day	33% 2 6% 24% 30% 6%	5310
	21st to end	Day	39% 1 6% 21% 25% 8%	5812
February	1st to 10th	Day	47% 2 9% 23% 16% 3	1890
	11th to 20th	Day	45% 3 7% 22% 18% 4	1976
	21st to end	Day	46% 2 7% 18% 18% 8%	1763
March	1st to 10th	Day	50% 2 5% 18% 13% 13%	5046
	11th to 20th	Day	33% 2 8% 22% 23% 13%	5090
	21st to end	Day	43% 2 9% 27% 18% 1	5616
April	1st to 10th	Day	41% 4 9% 21% 21% 3	2520
	11th to 20th	Day	44% 2 9% 22% 16% 7%	2446
	21st to end	Day	47% 3 9% 22% 17% 2	2400
May	1st to 10th	Day	50% 4 11% 20% 14% 1	5457
	11th to 20th	Day	47% 4 13% 24% 12% 1	5866
	21st to end	Day	49% 3 10% 20% 15% 2	6626
June	1st to 10th	Day	37% 6% 13% 26% 17% 1	2800
	11th to 20th	Day	33% 5% 16% 28% 16% 3	2800
	21st to end	Day	27% 5% 16% 30% 18% 4	2768
July	1st to 10th	Day	34% 6% 15% 30% 14% 2	5836
	11th to 20th	Day	24% 5% 15% 37% 17% 2	5831
	21st to end	Day	37% 6% 14% 30% 12% 1	6240
August	1st to 10th	Day	21% 4 16% 34% 20% 5%	4220
	11th to 20th	Day	37% 5% 14% 30% 13% 1	3930
	21st to end	Day	26% 5% 13% 35% 17% 3	4311
September	1st to 10th	Day	36% 4 10% 25% 18% 7%	2400
	11th to 20th	Day	36% 4 11% 23% 22% 4	2400
	21st to end	Day	32% 4 7% 23% 29% 4	2090
October	1st to 10th	Day	17% 2 5% 16% 40% 20%	3260
	11th to 20th	Day	20% 1 3 23% 39% 14%	3240
	21st to end	Day	34% 2 6% 30% 22% 5%	3538
November	1st to 10th	Day	34% 2 7% 26% 24% 7%	2058
	11th to 20th	Day	32% 3 7% 25% 24% 9%	1965
	21st to end	Day	42% 2 7% 21% 24% 4	1806
December	1st to 10th	Day	38% 2 7% 29% 22% 3	2690
	11th to 20th	Day	42% 2 7% 25% 21% 3	3085
	21st to end	Day	52% 3 7% 21% 14% 3	4302
January	1st to 10th	Night	42% 2 8% 31% 16% 3	7635
	11th to 20th	Night	28% 1 7% 21% 36% 8%	7680
	21st to end	Night	44% 2 7% 19% 22% 5%	8402
February	1st to 10th	Night	46% 2 7% 23% 18% 3	2730
	11th to 20th	Night	42% 2 8% 24% 18% 5%	2539
	21st to end	Night	40% 2 7% 20% 22% 9%	2060
March	1st to 10th	Night	47% 2 6% 15% 17% 13%	5029
	11th to 20th	Night	35% 2 7% 26% 19% 11%	5090
	21st to end	Night	39% 3 9% 29% 18% 2	5555
April	1st to 10th	Night	37% 3 10% 24% 20% 6%	2100
	11th to 20th	Night	38% 3 8% 23% 20% 8%	2035
	21st to end	Night	40% 3 12% 24% 18% 3	2000
May	1st to 10th	Night	45% 4 14% 24% 11% 2	4487
	11th to 20th	Night	47% 4 14% 23% 11% 2	4054
	21st to end	Night	48% 4 11% 20% 12% 4	4268
June	1st to 10th	Night	27% 4 13% 32% 22% 2	1600
	11th to 20th	Night	23% 4 15% 35% 20% 3	1600
	21st to end	Night	20% 4 15% 32% 22% 6%	1625
July	1st to 10th	Night	31% 6% 17% 25% 20% 1	4035
	11th to 20th	Night	19% 5% 17% 39% 17% 2	4026
	21st to end	Night	32% 6% 15% 32% 15%	4320
August	1st to 10th	Night	17% 4 17% 37% 22% 2	2916
	11th to 20th	Night	25% 5% 21% 31% 16% 1	3184
	21st to end	Night	24% 4 12% 35% 22% 3	3586
September	1st to 10th	Night	28% 4 11% 29% 20% 8%	2000
	11th to 20th	Night	32% 5% 13% 22% 24% 5%	2000
	21st to end	Night	27% 4 7% 23% 32% 7%	2284
October	1st to 10th	Night	14% 2 7% 15% 36% 26%	3920
	11th to 20th	Night	18% 1 4 17% 40% 20%	3899
	21st to end	Night	31% 2 5% 26% 28% 9%	4252
November	1st to 10th	Night	32% 2 8% 25% 26% 8%	2460
	11th to 20th	Night	30% 2 5% 28% 26% 9%	2651
	21st to end	Night	38% 2 7% 24% 24% 5%	2809
December	1st to 10th	Night	36% 2 8% 34% 17% 3	4720
	11th to 20th	Night	42% 3 6% 21% 21% 7%	5341
	21st to end	Night	50% 3 7% 24% 13% 3	6898

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	28% 21% 33% 14% 3	330
	11th to 20th	Day	29% 25% 33% 11% 2	330
	21st to end	Day	26% 25% 34% 12% 3	363
February	1st to 10th	Day	31% 20% 35% 11% 3 1	330
	11th to 20th	Day	34% 26% 28% 10% 2	330
	21st to end	Day	33% 25% 28% 10% 4	273
March	1st to 10th	Day	31% 18% 34% 14% 3	330
	11th to 20th	Day	35% 18% 33% 12% 1	330
	21st to end	Day	28% 24% 38% 8% 3	369
April	1st to 10th	Day	26% 18% 30% 18% 6% 1	540
	11th to 20th	Day	27% 17% 34% 17% 5% 1	516
	21st to end	Day	25% 17% 34% 16% 8%	500
May	1st to 10th	Day	22% 17% 33% 19% 8%	507
	11th to 20th	Day	20% 11% 29% 25% 12% 3	725
	21st to end	Day	14% 8% 33% 29% 14% 3	789
June	1st to 10th	Day	11% 6% 21% 33% 23% 5%	730
	11th to 20th	Day	8% 4 21% 41% 22% 5%	730
	21st to end	Day	6% 3 26% 37% 23% 6%	730
July	1st to 10th	Day	9% 3 15% 35% 29% 10%	721
	11th to 20th	Day	5% 3 16% 36% 29% 11%	718
	21st to end	Day	7% 3 12% 33% 32% 13%	794
August	1st to 10th	Day	6% 3 13% 40% 30% 8%	726
	11th to 20th	Day	14% 3 11% 32% 28% 11%	552
	21st to end	Day	10% 2 13% 30% 31% 15%	583
September	1st to 10th	Day	12% 3 13% 33% 32% 7%	530
	11th to 20th	Day	10% 4 15% 30% 28% 12%	530
	21st to end	Day	14% 7% 25% 29% 20% 6%	345
October	1st to 10th	Day	9% 8% 24% 38% 15% 5%	330
	11th to 20th	Day	16% 12% 35% 24% 10% 2	330
	21st to end	Day	29% 15% 31% 19% 6% 1	363
November	1st to 10th	Day	20% 14% 34% 23% 9% 1	330
	11th to 20th	Day	19% 16% 38% 19% 7% 1	330
	21st to end	Day	30% 15% 30% 18% 5% 2	330
December	1st to 10th	Day	26% 20% 29% 19% 4 2	330
	11th to 20th	Day	27% 19% 35% 13% 6% 1	330
	21st to end	Day	31% 17% 37% 12% 1 1	363
January	1st to 10th	Night	25% 17% 33% 21% 4	1050
	11th to 20th	Night	23% 20% 34% 19% 3 1	1050
	21st to end	Night	22% 17% 35% 23% 3	1155
February	1st to 10th	Night	28% 17% 29% 23% 3	1050
	11th to 20th	Night	26% 21% 32% 19% 2	903
	21st to end	Night	25% 19% 32% 22% 1	676
March	1st to 10th	Night	23% 16% 30% 29% 3	630
	11th to 20th	Night	23% 16% 30% 27% 4	630
	21st to end	Night	22% 15% 35% 21% 6%	693
April	1st to 10th	Night	18% 17% 35% 23% 7%	630
	11th to 20th	Night	19% 16% 30% 26% 8%	611
	21st to end	Night	19% 12% 36% 24% 8% 1	600
May	1st to 10th	Night	18% 9% 30% 35% 9%	600
	11th to 20th	Night	19% 7% 26% 29% 16% 3	591
	21st to end	Night	13% 4 25% 34% 19% 4	650
June	1st to 10th	Night	8% 5% 17% 35% 33% 4	600
	11th to 20th	Night	6% 3 16% 44% 29% 3	600
	21st to end	Night	5% 1 16% 39% 35% 5%	600
July	1st to 10th	Night	5% 3 10% 33% 42% 7%	585
	11th to 20th	Night	4 2 8% 35% 41% 9%	582
	21st to end	Night	7% 2 7% 36% 38% 10%	657
August	1st to 10th	Night	5% 1 9% 41% 39% 6%	597
	11th to 20th	Night	8% 1 11% 37% 36% 6%	594
	21st to end	Night	7% 1 9% 37% 41% 6%	660
September	1st to 10th	Night	9% 2 10% 36% 40% 3	600
	11th to 20th	Night	12% 2 11% 35% 34% 6%	600
	21st to end	Night	11% 5% 16% 34% 31% 4	704
October	1st to 10th	Night	9% 5% 17% 38% 29% 3	800
	11th to 20th	Night	14% 9% 29% 31% 17%	800
	21st to end	Night	21% 13% 28% 28% 11% 1	880
November	1st to 10th	Night	15% 11% 31% 30% 14% 1	820
	11th to 20th	Night	18% 11% 32% 31% 9%	840
	21st to end	Night	22% 15% 28% 25% 9%	919
December	1st to 10th	Night	22% 14% 33% 25% 6%	1050
	11th to 20th	Night	24% 13% 28% 30% 5%	1050
	21st to end	Night	27% 16% 28% 24% 5%	1155

Page generated at 2026-04-14 01:44:30. Version ac07

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