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 2026-10-29.

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% 40%	149699
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 42%	142369
Transparency	Day	40% 7% 13% 23% 15% 2	153295
	Night	39% 7% 12% 24% 15% 3	146844
Seeing	Day	20% 18% 27% 20% 11% 3	17452
	Night	18% 16% 29% 26% 10% 1	26853

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% 6% 2 7% 4 5% 5% 4 5% 6% 43%	4661
	11th to 20th	Day	11% 11% 4 9% 5% 5% 4 3 5% 6% 37%	5276
	21st to end	Day	13% 8% 2 6% 5% 5% 5% 4 6% 7% 39%	5780
February	1st to 10th	Day	14% 9% 3 7% 5% 5% 6% 3 4 6% 37%	1890
	11th to 20th	Day	14% 10% 3 7% 5% 5% 6% 4 4 7% 35%	1873
	21st to end	Day	18% 8% 4 8% 4 4 4 4 4 6% 38%	1730
March	1st to 10th	Day	18% 7% 2 4 3 4 5% 4 5% 6% 42%	4945
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 5% 8% 44%	5090
	21st to end	Day	15% 8% 2 6% 4 4 5% 4 6% 7% 41%	5677
April	1st to 10th	Day	15% 8% 2 8% 6% 5% 4 4 5% 7% 37%	2520
	11th to 20th	Day	13% 8% 2 6% 4 4 4 4 5% 7% 42%	2494
	21st to end	Day	18% 8% 2 6% 4 4 4 4 6% 6% 40%	2522
May	1st to 10th	Day	23% 5% 2 6% 4 4 5% 4 6% 8% 33%	7616
	11th to 20th	Day	21% 5% 2 6% 4 4 5% 4 6% 8% 37%	8139
	21st to end	Day	22% 6% 2 6% 4 4 4 4 5% 7% 36%	9045
June	1st to 10th	Day	12% 5% 2 6% 5% 4 5% 4 7% 9% 41%	2940
	11th to 20th	Day	13% 5% 2 7% 5% 4 5% 5% 7% 9% 39%	2940
	21st to end	Day	11% 4 2 5% 5% 4 5% 4 6% 11% 43%	2940
July	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 43%	8280
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 8% 12% 37%	8206
	21st to end	Day	10% 4 2 6% 5% 5% 5% 4 6% 10% 42%	8340
August	1st to 10th	Day	16% 5% 2 7% 6% 6% 7% 5% 8% 10% 29%	6014
	11th to 20th	Day	14% 4 2 5% 4 4 6% 5% 7% 10% 38%	5769
	21st to end	Day	12% 3 1 5% 3 4 5% 4 6% 10% 48%	6080
September	1st to 10th	Day	15% 5% 2 5% 3 4 4 3 6% 7% 47%	2520
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 7% 47%	2520
	21st to end	Day	23% 7% 2 6% 4 3 4 3 4 6% 37%	2203
October	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 5% 6% 47%	2100
	11th to 20th	Day	15% 5% 2 5% 3 3 4 3 5% 7% 46%	2100
	21st to end	Day	13% 7% 2 5% 4 4 3 4 5% 7% 46%	2280
November	1st to 10th	Day	11% 6% 2 5% 3 3 4 4 5% 7% 51%	1918
	11th to 20th	Day	15% 6% 2 4 5% 4 4 4 6% 7% 44%	1813
	21st to end	Day	15% 7% 2 5% 5% 4 4 4 5% 8% 41%	1680
December	1st to 10th	Day	13% 6% 3 6% 5% 4 5% 4 6% 8% 39%	2680
	11th to 20th	Day	18% 10% 3 6% 4 4 4 3 5% 7% 36%	3070
	21st to end	Day	16% 8% 3 8% 5% 5% 5% 4 7% 8% 31%	4048
January	1st to 10th	Night	10% 6% 3 6% 5% 4 4 4 6% 8% 43%	8233
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 5% 6% 46%	7680
	21st to end	Night	12% 7% 2 5% 4 4 4 3 6% 8% 45%	8401
February	1st to 10th	Night	15% 8% 2 6% 5% 4 5% 4 6% 7% 39%	2730
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 4 5% 7% 38%	2631
	21st to end	Night	15% 8% 2 7% 5% 4 5% 4 5% 6% 39%	2076
March	1st to 10th	Night	16% 6% 2 5% 4 4 3 3 4 6% 45%	5124
	11th to 20th	Night	11% 5% 3 6% 4 4 4 3 5% 6% 49%	5090
	21st to end	Night	11% 8% 2 5% 4 4 5% 4 5% 6% 46%	5495
April	1st to 10th	Night	17% 8% 3 6% 6% 4 5% 4 5% 6% 36%	2100
	11th to 20th	Night	14% 6% 2 7% 3 4 4 4 5% 9% 42%	2075
	21st to end	Night	18% 5% 2 5% 4 3 4 4 6% 7% 42%	2100
May	1st to 10th	Night	24% 6% 2 6% 4 4 4 3 5% 7% 34%	5265
	11th to 20th	Night	20% 6% 2 5% 3 3 4 4 6% 9% 38%	4721
	21st to end	Night	25% 6% 2 6% 4 4 4 3 5% 7% 34%	5108
June	1st to 10th	Night	12% 5% 2 4 4 3 5% 3 5% 8% 48%	1680
	11th to 20th	Night	13% 5% 2 6% 5% 6% 6% 4 6% 9% 39%	1680
	21st to end	Night	10% 4 2 6% 3 5% 4 4 6% 10% 44%	1680
July	1st to 10th	Night	13% 5% 2 6% 4 5% 5% 4 6% 9% 42%	4678
	11th to 20th	Night	9% 6% 2 7% 5% 6% 6% 5% 7% 10% 38%	4733
	21st to end	Night	10% 5% 2 5% 4 4 4 4 7% 9% 47%	5736
August	1st to 10th	Night	16% 5% 2 8% 5% 5% 5% 5% 7% 9% 32%	4135
	11th to 20th	Night	12% 5% 2 6% 5% 4 5% 3 7% 9% 42%	4229
	21st to end	Night	14% 4 1 5% 4 4 4 4 5% 8% 47%	5045
September	1st to 10th	Night	14% 4 2 6% 4 3 4 3 4 7% 49%	2100
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 5% 7% 52%	2100
	21st to end	Night	21% 6% 2 5% 4 4 4 3 6% 6% 38%	2411
October	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 47%	2520
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 4 6% 50%	2520
	21st to end	Night	15% 5% 1 5% 3 4 4 3 5% 7% 48%	2737
November	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 6% 52%	2597
	11th to 20th	Night	14% 8% 2 5% 4 3 4 3 5% 7% 45%	2804
	21st to end	Night	13% 5% 2 6% 4 5% 4 4 6% 7% 43%	2940
December	1st to 10th	Night	10% 5% 2 5% 4 5% 6% 4 6% 8% 44%	4720
	11th to 20th	Night	20% 7% 2 5% 4 4 5% 4 6% 7% 38%	5345
	21st to end	Night	16% 9% 3 7% 5% 5% 6% 4 6% 7% 32%	7150

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	40% 6% 13% 24% 15% 2	4662
	11th to 20th	Day	46% 6% 10% 18% 15% 6%	5276
	21st to end	Day	42% 7% 13% 25% 12% 1	5780
February	1st to 10th	Day	47% 5% 12% 22% 11% 2	1890
	11th to 20th	Day	48% 6% 11% 22% 11% 2	1882
	21st to end	Day	48% 5% 11% 22% 11% 4	1730
March	1st to 10th	Day	41% 6% 10% 23% 14% 6%	4945
	11th to 20th	Day	36% 6% 13% 26% 13% 5%	5090
	21st to end	Day	42% 6% 10% 19% 18% 4	5677
April	1st to 10th	Day	45% 6% 13% 17% 15% 3	2520
	11th to 20th	Day	40% 6% 13% 21% 17% 3	2494
	21st to end	Day	43% 6% 10% 22% 15% 3	2522
May	1st to 10th	Day	46% 8% 11% 21% 12% 1	7651
	11th to 20th	Day	44% 8% 11% 26% 11% 1	8143
	21st to end	Day	45% 7% 11% 19% 16% 1	9061
June	1st to 10th	Day	38% 7% 14% 23% 18% 1	2940
	11th to 20th	Day	39% 9% 15% 22% 13% 2	2940
	21st to end	Day	34% 8% 15% 27% 15% 1	2940
July	1st to 10th	Day	37% 10% 12% 23% 15% 2	8210
	11th to 20th	Day	36% 11% 15% 27% 10% 1	8131
	21st to end	Day	36% 8% 12% 24% 19% 1	8156
August	1st to 10th	Day	47% 11% 15% 19% 8%	6001
	11th to 20th	Day	37% 10% 16% 25% 11% 1	5808
	21st to end	Day	31% 7% 15% 29% 16% 1	6080
September	1st to 10th	Day	36% 7% 13% 20% 21% 3	2520
	11th to 20th	Day	34% 6% 12% 26% 19% 3	2520
	21st to end	Day	48% 5% 10% 17% 18% 2	2203
October	1st to 10th	Day	35% 4 9% 23% 24% 5%	3360
	11th to 20th	Day	26% 6% 14% 28% 20% 7%	3340
	21st to end	Day	26% 4 12% 30% 25% 3	3618
November	1st to 10th	Day	31% 5% 15% 24% 20% 4	1918
	11th to 20th	Day	39% 6% 12% 22% 19% 3	1813
	21st to end	Day	41% 6% 13% 28% 10% 2	1680
December	1st to 10th	Day	40% 8% 17% 25% 6% 3	2680
	11th to 20th	Day	48% 5% 14% 24% 8% 1	3066
	21st to end	Day	48% 9% 16% 15% 10% 1	4048
January	1st to 10th	Night	39% 6% 14% 25% 13% 2	8234
	11th to 20th	Night	38% 5% 12% 23% 17% 5%	7680
	21st to end	Night	36% 5% 12% 29% 15% 2	8401
February	1st to 10th	Night	44% 6% 13% 24% 12% 1	2730
	11th to 20th	Night	46% 5% 12% 19% 16% 2	2633
	21st to end	Night	46% 5% 11% 20% 14% 4	2076
March	1st to 10th	Night	40% 5% 10% 26% 12% 8%	5124
	11th to 20th	Night	35% 6% 13% 29% 12% 5%	5090
	21st to end	Night	38% 6% 11% 20% 23% 3	5495
April	1st to 10th	Night	48% 5% 10% 18% 16% 3	2100
	11th to 20th	Night	39% 7% 12% 21% 18% 4	2075
	21st to end	Night	39% 6% 13% 22% 16% 4	2100
May	1st to 10th	Night	50% 7% 10% 18% 13% 3	5292
	11th to 20th	Night	42% 8% 15% 25% 10% 1	4722
	21st to end	Night	49% 6% 10% 21% 11% 2	5115
June	1st to 10th	Night	34% 8% 11% 26% 19% 3	1680
	11th to 20th	Night	39% 9% 12% 22% 16% 2	1680
	21st to end	Night	34% 9% 13% 26% 17% 1	1680
July	1st to 10th	Night	39% 8% 14% 20% 15% 3	4640
	11th to 20th	Night	40% 10% 14% 22% 13% 1	4688
	21st to end	Night	32% 9% 15% 23% 20% 1	5606
August	1st to 10th	Night	46% 10% 15% 19% 9%	4124
	11th to 20th	Night	38% 8% 16% 25% 12% 1	4256
	21st to end	Night	35% 8% 12% 30% 15% 1	5045
September	1st to 10th	Night	36% 6% 13% 22% 20% 4	2100
	11th to 20th	Night	32% 5% 10% 28% 22% 2	2100
	21st to end	Night	46% 6% 10% 19% 17% 2	2411
October	1st to 10th	Night	37% 6% 11% 23% 22% 2	4040
	11th to 20th	Night	27% 6% 10% 26% 25% 6%	4019
	21st to end	Night	25% 4 11% 31% 24% 4	4349
November	1st to 10th	Night	33% 5% 12% 25% 21% 4	2597
	11th to 20th	Night	38% 5% 10% 25% 18% 4	2804
	21st to end	Night	39% 6% 13% 25% 15% 2	2940
December	1st to 10th	Night	37% 8% 14% 31% 10% 1	4720
	11th to 20th	Night	44% 6% 15% 20% 13% 2	5348
	21st to end	Night	49% 8% 13% 18% 12%	7150

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% 35% 25% 11% 2	220
	11th to 20th	Day	35% 28% 28% 7% 2	328
	21st to end	Day	25% 39% 26% 8% 2	363
February	1st to 10th	Day	28% 31% 30% 9% 1	330
	11th to 20th	Day	36% 31% 29% 4 1	360
	21st to end	Day	30% 26% 28% 14% 2	446
March	1st to 10th	Day	28% 25% 28% 16% 3	540
	11th to 20th	Day	27% 28% 27% 12% 4 1	540
	21st to end	Day	28% 24% 31% 13% 3 1	594
April	1st to 10th	Day	27% 25% 29% 13% 5% 1	540
	11th to 20th	Day	21% 24% 29% 14% 9% 2	532
	21st to end	Day	25% 19% 33% 15% 6% 2	540
May	1st to 10th	Day	28% 22% 26% 15% 6% 3	543
	11th to 20th	Day	22% 19% 28% 20% 10% 2	567
	21st to end	Day	22% 10% 26% 23% 15% 5%	617
June	1st to 10th	Day	14% 16% 30% 20% 16% 4	570
	11th to 20th	Day	19% 13% 29% 24% 12% 4	570
	21st to end	Day	12% 12% 30% 26% 16% 4	570
July	1st to 10th	Day	11% 6% 25% 31% 19% 8%	565
	11th to 20th	Day	6% 6% 28% 30% 22% 7%	564
	21st to end	Day	11% 7% 25% 32% 20% 5%	620
August	1st to 10th	Day	11% 7% 21% 32% 20% 8%	566
	11th to 20th	Day	13% 8% 23% 31% 17% 7%	559
	21st to end	Day	11% 7% 25% 32% 17% 10%	627
September	1st to 10th	Day	16% 9% 23% 25% 18% 9%	570
	11th to 20th	Day	14% 5% 19% 32% 22% 8%	570
	21st to end	Day	28% 13% 25% 20% 11% 4	570
October	1st to 10th	Day	19% 11% 26% 23% 16% 5%	570
	11th to 20th	Day	19% 21% 26% 21% 11% 2	570
	21st to end	Day	16% 18% 35% 20% 9% 1	615
November	1st to 10th	Day	18% 19% 28% 22% 11% 2	461
	11th to 20th	Day	23% 24% 28% 19% 6% 1	353
	21st to end	Day	27% 24% 33% 12% 5%	220
December	1st to 10th	Day	25% 33% 28% 10% 3 1	220
	11th to 20th	Day	27% 28% 29% 13% 4	220
	21st to end	Day	24% 27% 29% 16% 4	242
January	1st to 10th	Night	18% 30% 32% 18% 2	840
	11th to 20th	Night	23% 23% 31% 21% 2	840
	21st to end	Night	18% 25% 36% 19% 2	924
February	1st to 10th	Night	21% 23% 33% 22% 2	840
	11th to 20th	Night	24% 28% 35% 12% 1	823
	21st to end	Night	23% 25% 34% 15% 2	692
March	1st to 10th	Night	20% 22% 35% 19% 3	840
	11th to 20th	Night	24% 22% 30% 19% 5%	840
	21st to end	Night	20% 20% 39% 16% 5%	924
April	1st to 10th	Night	23% 24% 31% 17% 5%	840
	11th to 20th	Night	17% 19% 32% 24% 7%	831
	21st to end	Night	21% 15% 31% 25% 7%	840
May	1st to 10th	Night	22% 12% 29% 26% 10%	645
	11th to 20th	Night	18% 9% 35% 29% 9%	446
	21st to end	Night	18% 8% 22% 36% 14% 1	455
June	1st to 10th	Night	13% 5% 29% 34% 19%	420
	11th to 20th	Night	15% 7% 27% 35% 15%	420
	21st to end	Night	10% 5% 26% 45% 13%	420
July	1st to 10th	Night	11% 5% 23% 36% 24% 2	410
	11th to 20th	Night	6% 3 20% 45% 24% 1	425
	21st to end	Night	10% 3 20% 42% 24% 2	690
August	1st to 10th	Night	11% 3 14% 44% 25% 3	627
	11th to 20th	Night	11% 6% 16% 41% 23% 3	680
	21st to end	Night	14% 4 19% 37% 24% 3	924
September	1st to 10th	Night	15% 5% 21% 34% 23% 3	840
	11th to 20th	Night	13% 5% 18% 35% 26% 3	840
	21st to end	Night	23% 8% 21% 28% 18% 2	840
October	1st to 10th	Night	20% 8% 23% 29% 17% 3	840
	11th to 20th	Night	18% 15% 27% 29% 10% 1	840
	21st to end	Night	18% 15% 29% 28% 9%	913
November	1st to 10th	Night	14% 14% 33% 28% 9% 1	820
	11th to 20th	Night	19% 23% 30% 22% 6% 1	840
	21st to end	Night	18% 23% 30% 23% 5%	840
December	1st to 10th	Night	21% 20% 35% 19% 5%	840
	11th to 20th	Night	20% 21% 34% 22% 3	840
	21st to end	Night	18% 22% 34% 24% 3	924

Page generated at 2026-10-26 04:37:51. Version ac07

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