Piney Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Piney Mountain clear sky chart from 2005-11-06 to 2025-07-06.

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	15% 6% 2 6% 4 4 5% 4 6% 8% 39%	120076
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 42%	118703
Transparency	Day	41% 7% 13% 23% 15% 3	123713
	Night	40% 6% 12% 23% 16% 3	123203
Seeing	Day	20% 17% 27% 20% 11% 4	15694
	Night	18% 16% 29% 26% 10% 1	25165

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% 7% 2 7% 4 4 4 5% 6% 6% 43%	3597
	11th to 20th	Day	12% 11% 4 9% 6% 5% 4 4 6% 6% 35%	4056
	21st to end	Day	14% 9% 3 7% 5% 5% 4 4 5% 7% 38%	4466
February	1st to 10th	Day	14% 9% 3 7% 5% 6% 6% 4 4 6% 36%	1800
	11th to 20th	Day	14% 9% 3 7% 5% 5% 6% 4 4 7% 36%	1781
	21st to end	Day	19% 8% 4 7% 4 4 4 4 4 6% 37%	1650
March	1st to 10th	Day	18% 6% 2 4 4 4 5% 4 5% 6% 42%	4837
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 5% 8% 44%	4980
	21st to end	Day	15% 8% 2 6% 4 4 5% 4 6% 6% 41%	5554
April	1st to 10th	Day	15% 8% 2 8% 6% 5% 4 4 5% 7% 36%	2400
	11th to 20th	Day	13% 8% 2 6% 5% 4 4 4 5% 7% 42%	2374
	21st to end	Day	18% 8% 2 6% 4 4 4 4 6% 6% 40%	2402
May	1st to 10th	Day	25% 6% 2 6% 4 4 5% 4 6% 9% 30%	5862
	11th to 20th	Day	25% 6% 3 6% 4 4 5% 3 5% 8% 31%	6262
	21st to end	Day	17% 5% 2 6% 4 5% 5% 5% 7% 9% 36%	6934
June	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 7% 10% 40%	2800
	11th to 20th	Day	14% 5% 2 7% 5% 4 5% 5% 7% 9% 38%	2800
	21st to end	Day	10% 4 2 5% 5% 4 5% 4 7% 11% 43%	2800
July	1st to 10th	Day	6% 4 2 6% 6% 5% 6% 5% 8% 9% 43%	4510
	11th to 20th	Day	8% 5% 2 5% 5% 5% 5% 5% 7% 10% 43%	4394
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	4466
August	1st to 10th	Day	18% 4 2 6% 5% 5% 6% 4 7% 9% 34%	4104
	11th to 20th	Day	13% 4 2 5% 4 4 6% 5% 7% 9% 41%	3921
	21st to end	Day	15% 4 1 5% 3 3 4 4 6% 8% 47%	4180
September	1st to 10th	Day	17% 5% 2 5% 3 4 4 3 6% 6% 45%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 4 6% 7% 47%	2280
	21st to end	Day	22% 6% 2 5% 4 3 4 3 5% 6% 39%	1994
October	1st to 10th	Day	16% 6% 2 5% 4 4 5% 3 5% 6% 45%	1900
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 5% 7% 45%	1900
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 7% 44%	2090
November	1st to 10th	Day	11% 6% 2 5% 3 3 4 3 5% 7% 51%	1825
	11th to 20th	Day	15% 6% 2 4 4 4 4 4 6% 7% 44%	1727
	21st to end	Day	15% 7% 2 5% 5% 5% 4 4 5% 8% 41%	1600
December	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 6% 8% 40%	2600
	11th to 20th	Day	19% 10% 3 6% 4 4 4 3 5% 7% 36%	2990
	21st to end	Day	16% 8% 3 8% 5% 5% 5% 4 7% 8% 31%	3960
January	1st to 10th	Night	11% 7% 2 6% 5% 4 3 3 5% 8% 46%	6349
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 46%	5900
	21st to end	Night	14% 8% 3 6% 4 4 4 3 6% 6% 43%	6490
February	1st to 10th	Night	16% 8% 2 7% 5% 4 5% 4 5% 6% 39%	2600
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 38%	2503
	21st to end	Night	16% 8% 2 7% 5% 4 5% 4 5% 6% 38%	1980
March	1st to 10th	Night	16% 6% 2 5% 4 4 3 3 5% 6% 46%	5012
	11th to 20th	Night	10% 5% 3 6% 4 4 4 3 5% 6% 50%	4980
	21st to end	Night	12% 8% 2 5% 4 4 4 3 5% 6% 46%	5376
April	1st to 10th	Night	17% 8% 3 7% 6% 4 5% 4 5% 7% 34%	2000
	11th to 20th	Night	14% 6% 2 7% 3 4 4 4 5% 9% 42%	1975
	21st to end	Night	18% 5% 2 5% 4 3 4 4 6% 7% 42%	2000
May	1st to 10th	Night	28% 7% 2 6% 4 4 4 3 5% 7% 29%	4047
	11th to 20th	Night	25% 7% 2 5% 4 3 3 4 6% 8% 33%	3631
	21st to end	Night	20% 6% 2 6% 4 4 5% 4 6% 8% 36%	3920
June	1st to 10th	Night	12% 6% 2 4 4 3 5% 4 5% 8% 47%	1600
	11th to 20th	Night	13% 5% 2 6% 5% 6% 5% 4 6% 9% 39%	1600
	21st to end	Night	10% 4 2 6% 3 5% 4 4 7% 10% 44%	1600
July	1st to 10th	Night	7% 4 2 6% 5% 5% 6% 4 7% 11% 43%	2560
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 11% 43%	2548
	21st to end	Night	13% 6% 2 6% 5% 4 4 3 6% 8% 42%	3087
August	1st to 10th	Night	18% 4 2 7% 4 5% 4 4 6% 9% 37%	2825
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 3 6% 8% 43%	2874
	21st to end	Night	16% 4 1 4 3 4 3 3 5% 8% 48%	3476
September	1st to 10th	Night	15% 4 2 6% 4 3 4 2 4 7% 48%	1900
	11th to 20th	Night	12% 5% 2 5% 3 3 4 2 5% 7% 53%	1900
	21st to end	Night	21% 6% 2 4 4 4 4 3 5% 6% 40%	2181
October	1st to 10th	Night	18% 7% 2 5% 3 3 3 3 4 6% 45%	2280
	11th to 20th	Night	14% 5% 2 5% 4 3 4 3 4 6% 49%	2280
	21st to end	Night	15% 6% 1 5% 3 4 4 3 6% 7% 46%	2508
November	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 6% 52%	2470
	11th to 20th	Night	14% 8% 2 5% 4 3 4 3 5% 7% 45%	2670
	21st to end	Night	14% 5% 2 5% 4 5% 4 4 6% 7% 43%	2800
December	1st to 10th	Night	10% 5% 2 5% 4 5% 6% 4 6% 8% 44%	4580
	11th to 20th	Night	20% 7% 2 5% 4 4 5% 4 6% 7% 37%	5205
	21st to end	Night	16% 9% 3 7% 5% 5% 6% 4 6% 7% 32%	6996

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	38% 6% 13% 24% 17% 3	3598
	11th to 20th	Day	49% 6% 10% 17% 15% 4	4056
	21st to end	Day	45% 7% 12% 22% 13% 1	4466
February	1st to 10th	Day	49% 5% 12% 22% 10% 2	1800
	11th to 20th	Day	48% 6% 11% 23% 11% 2	1790
	21st to end	Day	48% 5% 11% 21% 11% 4	1650
March	1st to 10th	Day	41% 6% 10% 23% 14% 6%	4837
	11th to 20th	Day	36% 6% 13% 26% 13% 5%	4980
	21st to end	Day	43% 6% 10% 19% 18% 4	5554
April	1st to 10th	Day	46% 6% 13% 17% 15% 3	2400
	11th to 20th	Day	41% 6% 12% 21% 17% 3	2374
	21st to end	Day	43% 6% 10% 22% 16% 3	2402
May	1st to 10th	Day	49% 8% 13% 18% 11% 1	5897
	11th to 20th	Day	50% 8% 10% 22% 9% 1	6266
	21st to end	Day	40% 8% 14% 21% 15% 1	6949
June	1st to 10th	Day	38% 7% 14% 23% 16% 1	2800
	11th to 20th	Day	40% 9% 15% 21% 13% 2	2800
	21st to end	Day	33% 9% 15% 27% 15% 1	2800
July	1st to 10th	Day	33% 11% 14% 26% 12% 3	4440
	11th to 20th	Day	33% 10% 17% 26% 13% 1	4319
	21st to end	Day	41% 8% 11% 21% 17% 1	4324
August	1st to 10th	Day	45% 9% 15% 23% 8%	4091
	11th to 20th	Day	36% 9% 13% 27% 15% 1	3960
	21st to end	Day	34% 6% 13% 28% 17% 2	4180
September	1st to 10th	Day	39% 6% 12% 19% 21% 4	2280
	11th to 20th	Day	33% 6% 12% 25% 20% 3	2280
	21st to end	Day	46% 5% 10% 18% 19% 2	1994
October	1st to 10th	Day	36% 4 9% 22% 24% 5%	3160
	11th to 20th	Day	26% 6% 14% 28% 20% 7%	3140
	21st to end	Day	27% 4 12% 30% 25% 2	3428
November	1st to 10th	Day	32% 5% 14% 24% 20% 4	1825
	11th to 20th	Day	38% 6% 12% 22% 18% 3	1727
	21st to end	Day	41% 6% 13% 28% 10% 2	1600
December	1st to 10th	Day	40% 8% 17% 26% 7% 3	2600
	11th to 20th	Day	48% 5% 14% 23% 8% 1	2986
	21st to end	Day	48% 9% 16% 15% 10% 1	3960
January	1st to 10th	Night	37% 6% 12% 26% 16% 3	6349
	11th to 20th	Night	38% 5% 14% 24% 14% 5%	5900
	21st to end	Night	41% 5% 12% 24% 15% 2	6490
February	1st to 10th	Night	45% 6% 13% 24% 11% 1	2600
	11th to 20th	Night	46% 5% 12% 19% 16% 2	2505
	21st to end	Night	46% 5% 11% 19% 14% 4	1980
March	1st to 10th	Night	39% 5% 10% 26% 12% 8%	5012
	11th to 20th	Night	35% 6% 13% 29% 12% 5%	4980
	21st to end	Night	38% 6% 11% 20% 23% 3	5376
April	1st to 10th	Night	49% 5% 10% 17% 15% 3	2000
	11th to 20th	Night	39% 7% 11% 21% 18% 4	1975
	21st to end	Night	39% 6% 12% 22% 16% 4	2000
May	1st to 10th	Night	55% 6% 9% 16% 11% 4	4074
	11th to 20th	Night	48% 8% 12% 22% 9% 1	3632
	21st to end	Night	44% 7% 13% 23% 11% 2	3927
June	1st to 10th	Night	35% 8% 11% 26% 17% 3	1600
	11th to 20th	Night	39% 9% 13% 22% 16% 2	1600
	21st to end	Night	34% 9% 13% 25% 17% 2	1600
July	1st to 10th	Night	35% 9% 17% 20% 14% 5%	2520
	11th to 20th	Night	34% 10% 16% 23% 15% 1	2500
	21st to end	Night	39% 7% 15% 18% 19% 1	2988
August	1st to 10th	Night	43% 9% 17% 22% 8% 1	2814
	11th to 20th	Night	37% 7% 12% 26% 16% 1	2901
	21st to end	Night	34% 7% 12% 29% 16% 2	3476
September	1st to 10th	Night	37% 5% 13% 21% 21% 4	1900
	11th to 20th	Night	32% 5% 10% 28% 23% 3	1900
	21st to end	Night	44% 5% 10% 20% 18% 2	2181
October	1st to 10th	Night	37% 6% 11% 23% 22% 1	3800
	11th to 20th	Night	26% 6% 10% 26% 26% 6%	3779
	21st to end	Night	26% 4 11% 32% 23% 4	4120
November	1st to 10th	Night	33% 5% 12% 25% 21% 4	2470
	11th to 20th	Night	38% 5% 10% 25% 18% 4	2670
	21st to end	Night	39% 6% 14% 25% 15% 2	2800
December	1st to 10th	Night	37% 8% 14% 31% 10% 1	4580
	11th to 20th	Night	44% 6% 15% 20% 12% 2	5208
	21st to end	Night	49% 8% 13% 18% 12%	6996

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	27% 34% 26% 11% 2 1	200
	11th to 20th	Day	33% 27% 31% 8% 2	298
	21st to end	Day	23% 37% 28% 9% 3	330
February	1st to 10th	Day	28% 32% 30% 9% 1	300
	11th to 20th	Day	35% 32% 28% 3 1	328
	21st to end	Day	31% 25% 28% 14% 2	414
March	1st to 10th	Day	27% 25% 28% 17% 3	500
	11th to 20th	Day	25% 30% 28% 13% 4 1	500
	21st to end	Day	28% 23% 31% 13% 3 1	550
April	1st to 10th	Day	27% 25% 30% 12% 5% 1	500
	11th to 20th	Day	21% 24% 28% 14% 10% 2	492
	21st to end	Day	25% 20% 32% 15% 6% 2	500
May	1st to 10th	Day	27% 20% 27% 16% 7% 3	503
	11th to 20th	Day	22% 19% 28% 19% 10% 2	527
	21st to end	Day	19% 10% 26% 24% 16% 5%	573
June	1st to 10th	Day	15% 16% 30% 18% 16% 4	530
	11th to 20th	Day	18% 12% 29% 24% 13% 4	530
	21st to end	Day	11% 11% 30% 28% 16% 4	530
July	1st to 10th	Day	11% 5% 25% 31% 18% 9%	505
	11th to 20th	Day	5% 6% 27% 30% 23% 8%	484
	21st to end	Day	12% 7% 25% 32% 20% 5%	532
August	1st to 10th	Day	11% 5% 22% 32% 22% 8%	486
	11th to 20th	Day	13% 7% 23% 31% 18% 8%	479
	21st to end	Day	12% 6% 22% 32% 18% 10%	539
September	1st to 10th	Day	18% 9% 20% 24% 18% 10%	490
	11th to 20th	Day	14% 5% 19% 32% 21% 9%	490
	21st to end	Day	27% 13% 23% 20% 12% 4	490
October	1st to 10th	Day	20% 11% 25% 22% 17% 5%	490
	11th to 20th	Day	18% 21% 26% 22% 11% 2	490
	21st to end	Day	17% 19% 36% 19% 10% 1	539
November	1st to 10th	Day	17% 18% 29% 23% 12% 2	428
	11th to 20th	Day	21% 25% 28% 19% 6% 1	327
	21st to end	Day	26% 24% 33% 13% 5%	200
December	1st to 10th	Day	25% 31% 29% 12% 4 1	200
	11th to 20th	Day	27% 27% 29% 13% 4	200
	21st to end	Day	21% 28% 29% 18% 5%	220
January	1st to 10th	Night	18% 30% 31% 18% 2	800
	11th to 20th	Night	22% 22% 31% 22% 2	800
	21st to end	Night	18% 25% 37% 19% 2	880
February	1st to 10th	Night	21% 23% 33% 23% 2	800
	11th to 20th	Night	24% 28% 35% 13% 1	783
	21st to end	Night	24% 25% 34% 15% 2	660
March	1st to 10th	Night	20% 23% 35% 19% 4	800
	11th to 20th	Night	23% 23% 31% 18% 6%	800
	21st to end	Night	20% 20% 38% 16% 5%	880
April	1st to 10th	Night	23% 25% 31% 17% 5%	800
	11th to 20th	Night	18% 19% 32% 24% 7% 1	791
	21st to end	Night	22% 15% 31% 25% 7%	800
May	1st to 10th	Night	23% 11% 28% 27% 10%	614
	11th to 20th	Night	19% 10% 33% 29% 9%	424
	21st to end	Night	16% 8% 23% 37% 15% 1	433
June	1st to 10th	Night	14% 4 28% 35% 19% 1	400
	11th to 20th	Night	15% 7% 26% 36% 16% 1	400
	21st to end	Night	10% 5% 26% 45% 14%	400
July	1st to 10th	Night	10% 4 23% 36% 24% 2	380
	11th to 20th	Night	6% 3 20% 45% 25% 2	383
	21st to end	Night	10% 3 20% 42% 24% 2	624
August	1st to 10th	Night	12% 2 14% 45% 25% 3	567
	11th to 20th	Night	12% 6% 15% 40% 24% 4	614
	21st to end	Night	14% 3 17% 37% 26% 3	836
September	1st to 10th	Night	16% 5% 21% 33% 22% 3	760
	11th to 20th	Night	13% 5% 18% 34% 26% 4	760
	21st to end	Night	24% 8% 21% 28% 19% 2	760
October	1st to 10th	Night	21% 9% 22% 27% 18% 3	760
	11th to 20th	Night	17% 14% 28% 30% 10% 1	760
	21st to end	Night	19% 15% 29% 27% 9%	836
November	1st to 10th	Night	13% 14% 34% 28% 10% 1	780
	11th to 20th	Night	18% 22% 30% 22% 7% 1	800
	21st to end	Night	17% 23% 31% 24% 5%	800
December	1st to 10th	Night	21% 20% 34% 19% 5% 1	800
	11th to 20th	Night	20% 21% 34% 22% 3	800
	21st to end	Night	18% 21% 34% 25% 3	880

Page generated at 2025-07-03 01:30:15. Version ac07

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