Chimney Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chimney Rock clear sky chart from 2005-11-06 to 2026-02-01.

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	4 5% 2 5% 4 4 4 4 6% 7% 55%	135939
	Night	5% 6% 2 6% 4 4 4 3 5% 6% 55%	133561
Transparency	Day	25% 6% 10% 22% 25% 12%	130873
	Night	28% 5% 9% 22% 24% 11%	129630
Seeing	Day	10% 11% 28% 31% 17% 4	16825
	Night	9% 4 20% 44% 21% 2	27083

By Month

Percentage Cloud Cover SW (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	2 8% 4 8% 4 3 3 3 5% 6% 52%	4119
	11th to 20th	Day	3 7% 2 4 3 3 3 4 5% 7% 59%	4190
	21st to end	Day	4 10% 3 6% 3 3 4 3 4 5% 55%	4609
February	1st to 10th	Day	4 9% 3 5% 5% 4 3 3 4 6% 54%	1800
	11th to 20th	Day	6% 10% 2 7% 4 4 4 3 5% 6% 49%	1845
	21st to end	Day	5% 12% 4 7% 4 4 3 3 4 6% 49%	1650
March	1st to 10th	Day	4 9% 2 6% 4 4 4 3 5% 8% 50%	4908
	11th to 20th	Day	4 14% 5% 8% 5% 4 5% 4 6% 7% 39%	5000
	21st to end	Day	4 8% 3 8% 5% 5% 4 4 5% 8% 46%	5543
April	1st to 10th	Day	5% 6% 2 4 4 5% 5% 4 6% 7% 53%	2400
	11th to 20th	Day	4 6% 2 4 5% 5% 5% 4 6% 7% 53%	2371
	21st to end	Day	5% 5% 2 5% 4 4 4 4 6% 7% 55%	2400
May	1st to 10th	Day	6% 5% 2 6% 4 4 5% 4 6% 7% 52%	5604
	11th to 20th	Day	3 4 1 4 4 5% 5% 5% 6% 8% 55%	5873
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 67%	6925
June	1st to 10th	Day	4 2 1 3 3 3 4 4 7% 7% 62%	2800
	11th to 20th	Day	2 2 1 3 2 3 3 3 5% 6% 71%	2800
	21st to end	Day	2 2 1 4 4 4 5% 4 7% 7% 60%	2800
July	1st to 10th	Day	2 2 1 4 4 3 4 4 6% 6% 64%	6215
	11th to 20th	Day	1 2 1 4 4 7% 8% 7% 11% 11% 44%	5880
	21st to end	Day	3 3 2 5% 5% 6% 7% 6% 8% 9% 47%	6401
August	1st to 10th	Day	4 3 1 5% 5% 6% 7% 5% 8% 10% 47%	5779
	11th to 20th	Day	2 2 1 4 3 5% 6% 5% 8% 9% 55%	5503
	21st to end	Day	5% 3 1 6% 5% 6% 7% 6% 9% 11% 41%	5984
September	1st to 10th	Day	7% 4 2 5% 4 4 5% 4 6% 7% 52%	2400
	11th to 20th	Day	8% 3 1 5% 3 3 5% 4 5% 7% 56%	2400
	21st to end	Day	9% 3 1 3 3 3 3 3 3 5% 64%	2115
October	1st to 10th	Day	6% 2 1 3 2 2 3 3 4 5% 70%	3270
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 3 5% 55%	3250
	21st to end	Day	6% 4 2 4 2 3 3 2 3 5% 67%	3548
November	1st to 10th	Day	4 4 1 3 2 2 3 3 4 5% 69%	2037
	11th to 20th	Day	3 3 1 4 2 2 3 2 5% 7% 68%	1890
	21st to end	Day	7% 7% 2 4 3 2 2 2 4 5% 60%	1732
December	1st to 10th	Day	4 5% 2 2 2 1 2 2 4 7% 70%	2700
	11th to 20th	Day	4 6% 2 4 3 3 3 3 5% 7% 60%	3106
	21st to end	Day	4 9% 3 6% 3 3 3 3 5% 5% 56%	4092
January	1st to 10th	Night	3 9% 5% 8% 4 4 4 3 5% 5% 51%	6109
	11th to 20th	Night	2 7% 3 4 3 4 4 4 5% 5% 60%	6010
	21st to end	Night	4 10% 3 8% 4 3 3 2 4 5% 52%	6611
February	1st to 10th	Night	6% 10% 3 5% 2 2 3 2 3 6% 59%	2600
	11th to 20th	Night	7% 10% 2 6% 3 3 3 3 4 6% 54%	2441
	21st to end	Night	6% 11% 2 5% 3 3 3 2 4 5% 56%	1980
March	1st to 10th	Night	3 14% 3 7% 4 4 4 3 4 5% 49%	4971
	11th to 20th	Night	7% 11% 3 6% 4 3 4 4 5% 7% 47%	5000
	21st to end	Night	6% 7% 2 6% 5% 5% 5% 3 5% 6% 50%	5427
April	1st to 10th	Night	6% 8% 2 4 4 3 4 3 5% 6% 55%	2000
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 5% 5% 54%	1977
	21st to end	Night	6% 7% 2 4 3 3 4 3 4 5% 59%	2000
May	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 5% 7% 52%	4373
	11th to 20th	Night	4 3 1 4 3 4 4 4 6% 8% 60%	4038
	21st to end	Night	5% 3 1 4 3 3 3 3 4 6% 65%	3972
June	1st to 10th	Night	3 3 2 4 3 3 4 4 4 6% 65%	1600
	11th to 20th	Night	3 3 1 3 3 2 3 3 4 5% 70%	1600
	21st to end	Night	4 3 1 3 4 5% 5% 4 7% 7% 58%	1600
July	1st to 10th	Night	3 3 1 5% 4 5% 5% 4 5% 5% 59%	3732
	11th to 20th	Night	2 3 1 5% 5% 6% 6% 6% 11% 14% 42%	4100
	21st to end	Night	4 4 2 7% 6% 6% 7% 6% 9% 10% 39%	4472
August	1st to 10th	Night	4 4 2 8% 5% 5% 6% 5% 8% 10% 42%	4033
	11th to 20th	Night	3 3 2 6% 5% 5% 6% 5% 8% 11% 46%	4343
	21st to end	Night	7% 6% 3 9% 6% 7% 7% 5% 9% 11% 30%	4993
September	1st to 10th	Night	6% 3 1 8% 5% 5% 5% 5% 8% 9% 46%	2000
	11th to 20th	Night	6% 4 1 6% 4 4 4 3 5% 6% 57%	2000
	21st to end	Night	8% 3 1 4 3 3 3 2 5% 6% 63%	2279
October	1st to 10th	Night	7% 3 1 3 2 2 3 2 3 5% 69%	3920
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 6% 53%	3898
	21st to end	Night	6% 4 2 4 2 2 2 2 3 4 68%	4252
November	1st to 10th	Night	5% 5% 1 3 2 2 2 2 4 6% 68%	2460
	11th to 20th	Night	3 4 1 2 2 2 2 3 3 4 73%	2729
	21st to end	Night	8% 9% 2 4 2 2 3 2 4 4 59%	2882
December	1st to 10th	Night	4 5% 1 3 2 2 2 2 3 5% 71%	4710
	11th to 20th	Night	5% 7% 2 4 3 2 3 3 4 6% 62%	5321
	21st to end	Night	6% 9% 3 6% 4 4 3 3 4 5% 55%	7128

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	31% 4 13% 31% 18% 3	4120
	11th to 20th	Day	23% 6% 14% 22% 24% 13%	4190
	21st to end	Day	31% 4 7% 26% 23% 8%	4609
February	1st to 10th	Day	31% 5% 14% 25% 21% 5%	1800
	11th to 20th	Day	36% 4 8% 27% 21% 3	1854
	21st to end	Day	37% 4 6% 16% 29% 7%	1650
March	1st to 10th	Day	28% 6% 6% 20% 31% 8%	4908
	11th to 20th	Day	40% 7% 7% 25% 18% 4	5000
	21st to end	Day	33% 7% 9% 28% 20% 3	5543
April	1st to 10th	Day	28% 5% 7% 22% 27% 11%	2400
	11th to 20th	Day	28% 5% 6% 21% 27% 13%	2374
	21st to end	Day	26% 6% 7% 22% 31% 9%	2400
May	1st to 10th	Day	28% 6% 11% 20% 23% 13%	5604
	11th to 20th	Day	21% 8% 8% 19% 33% 10%	5876
	21st to end	Day	14% 5% 6% 15% 42% 19%	6926
June	1st to 10th	Day	18% 6% 7% 21% 28% 20%	2800
	11th to 20th	Day	13% 4 5% 13% 27% 38%	2800
	21st to end	Day	19% 6% 7% 15% 25% 28%	2800
July	1st to 10th	Day	18% 6% 8% 10% 18% 40%	6149
	11th to 20th	Day	24% 9% 17% 28% 15% 7%	5811
	21st to end	Day	26% 8% 18% 21% 18% 9%	6217
August	1st to 10th	Day	34% 10% 19% 17% 12% 8%	4208
	11th to 20th	Day	24% 9% 14% 19% 19% 15%	3985
	21st to end	Day	30% 9% 15% 19% 20% 7%	4311
September	1st to 10th	Day	28% 7% 10% 18% 24% 13%	2400
	11th to 20th	Day	25% 7% 8% 17% 27% 17%	2400
	21st to end	Day	22% 4 4 18% 37% 14%	2115
October	1st to 10th	Day	17% 4 4 16% 32% 26%	3270
	11th to 20th	Day	30% 4 4 21% 30% 11%	3250
	21st to end	Day	21% 3 5% 23% 42% 6%	3548
November	1st to 10th	Day	18% 3 7% 31% 34% 7%	2037
	11th to 20th	Day	17% 3 8% 33% 34% 6%	1890
	21st to end	Day	27% 3 6% 30% 25% 9%	1732
December	1st to 10th	Day	17% 2 12% 31% 33% 6%	2700
	11th to 20th	Day	25% 4 8% 39% 21% 2	3104
	21st to end	Day	29% 4 12% 24% 26% 5%	4092
January	1st to 10th	Night	34% 4 9% 29% 19% 5%	6109
	11th to 20th	Night	24% 5% 13% 23% 24% 11%	6010
	21st to end	Night	32% 6% 7% 27% 20% 8%	6611
February	1st to 10th	Night	29% 3 12% 28% 20% 8%	2600
	11th to 20th	Night	33% 4 9% 26% 23% 6%	2442
	21st to end	Night	32% 3 7% 18% 32% 8%	1980
March	1st to 10th	Night	34% 6% 5% 18% 30% 8%	4971
	11th to 20th	Night	35% 5% 6% 22% 24% 7%	5000
	21st to end	Night	30% 8% 7% 30% 21% 4	5427
April	1st to 10th	Night	31% 3 7% 19% 27% 13%	2000
	11th to 20th	Night	30% 5% 6% 17% 28% 14%	1977
	21st to end	Night	28% 4 5% 20% 31% 11%	2000
May	1st to 10th	Night	29% 6% 12% 17% 26% 10%	4370
	11th to 20th	Night	21% 6% 9% 24% 25% 15%	4039
	21st to end	Night	19% 5% 7% 15% 31% 23%	3972
June	1st to 10th	Night	20% 5% 8% 17% 25% 25%	1600
	11th to 20th	Night	17% 3 5% 13% 20% 43%	1600
	21st to end	Night	21% 6% 8% 14% 22% 29%	1600
July	1st to 10th	Night	25% 6% 9% 7% 15% 39%	3690
	11th to 20th	Night	27% 8% 19% 28% 7% 11%	4046
	21st to end	Night	35% 9% 17% 16% 15% 7%	4344
August	1st to 10th	Night	41% 10% 18% 11% 12% 9%	2928
	11th to 20th	Night	32% 8% 18% 12% 15% 15%	3137
	21st to end	Night	39% 9% 13% 19% 13% 6%	3597
September	1st to 10th	Night	30% 7% 13% 17% 17% 15%	2000
	11th to 20th	Night	27% 5% 8% 15% 24% 21%	2000
	21st to end	Night	22% 5% 5% 15% 37% 16%	2279
October	1st to 10th	Night	19% 4 5% 12% 37% 24%	3920
	11th to 20th	Night	31% 4 5% 17% 32% 11%	3898
	21st to end	Night	21% 3 5% 23% 40% 8%	4252
November	1st to 10th	Night	19% 3 6% 29% 36% 8%	2460
	11th to 20th	Night	16% 3 6% 33% 35% 7%	2729
	21st to end	Night	30% 2 6% 25% 29% 7%	2882
December	1st to 10th	Night	19% 2 9% 41% 25% 5%	4710
	11th to 20th	Night	25% 3 7% 35% 27% 2	5322
	21st to end	Night	32% 5% 11% 24% 25% 3	7128

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	18% 5% 31% 31% 13% 2	330
	11th to 20th	Day	18% 7% 32% 32% 10% 2	330
	21st to end	Day	8% 7% 33% 39% 10% 3	363
February	1st to 10th	Day	9% 13% 35% 35% 6% 2	300
	11th to 20th	Day	17% 13% 35% 29% 5% 1	300
	21st to end	Day	17% 19% 33% 23% 8%	249
March	1st to 10th	Day	16% 21% 28% 25% 10%	478
	11th to 20th	Day	17% 17% 32% 23% 7% 3	500
	21st to end	Day	17% 26% 30% 21% 5% 1	550
April	1st to 10th	Day	12% 24% 37% 19% 7% 1	500
	11th to 20th	Day	17% 30% 30% 16% 6%	492
	21st to end	Day	12% 27% 35% 19% 6% 1	500
May	1st to 10th	Day	14% 21% 39% 18% 7% 1	503
	11th to 20th	Day	11% 16% 35% 25% 12% 2	534
	21st to end	Day	8% 14% 30% 31% 16% 1	789
June	1st to 10th	Day	5% 7% 24% 38% 22% 3	730
	11th to 20th	Day	4 9% 32% 30% 20% 4	730
	21st to end	Day	3 10% 26% 32% 23% 5%	730
July	1st to 10th	Day	3 5% 20% 36% 30% 6%	677
	11th to 20th	Day	4 2 19% 35% 29% 11%	524
	21st to end	Day	7% 3 12% 37% 33% 8%	575
August	1st to 10th	Day	6% 6% 18% 37% 26% 7%	527
	11th to 20th	Day	5% 3 22% 37% 25% 8%	517
	21st to end	Day	7% 3 22% 37% 25% 7%	583
September	1st to 10th	Day	7% 4 23% 34% 25% 8%	530
	11th to 20th	Day	7% 5% 28% 39% 18% 3	530
	21st to end	Day	11% 7% 24% 33% 19% 6%	418
October	1st to 10th	Day	12% 8% 19% 31% 22% 8%	330
	11th to 20th	Day	13% 11% 26% 28% 16% 5%	330
	21st to end	Day	11% 10% 25% 31% 19% 4	363
November	1st to 10th	Day	9% 12% 27% 34% 16% 2	330
	11th to 20th	Day	5% 8% 32% 34% 18% 4	330
	21st to end	Day	15% 6% 29% 28% 19% 3	330
December	1st to 10th	Day	12% 8% 30% 33% 12% 5%	330
	11th to 20th	Day	9% 8% 28% 37% 14% 4	330
	21st to end	Day	18% 9% 28% 35% 9% 1	363
January	1st to 10th	Night	12% 3 25% 42% 15% 3	887
	11th to 20th	Night	9% 3 26% 45% 15% 3	840
	21st to end	Night	11% 3 24% 45% 14% 3	924
February	1st to 10th	Night	12% 3 30% 43% 11% 2	800
	11th to 20th	Night	12% 5% 30% 41% 11% 1	784
	21st to end	Night	15% 3 32% 44% 6%	660
March	1st to 10th	Night	10% 6% 27% 45% 11%	800
	11th to 20th	Night	11% 5% 23% 43% 17% 1	800
	21st to end	Night	11% 8% 26% 43% 12% 1	856
April	1st to 10th	Night	12% 8% 30% 43% 8%	600
	11th to 20th	Night	12% 8% 25% 43% 12%	593
	21st to end	Night	10% 9% 25% 43% 13%	600
May	1st to 10th	Night	9% 7% 26% 43% 15%	600
	11th to 20th	Night	10% 3 24% 45% 18% 1	591
	21st to end	Night	10% 7% 19% 44% 19% 2	650
June	1st to 10th	Night	5% 3 16% 50% 26% 1	600
	11th to 20th	Night	4 3 18% 50% 25% 1	600
	21st to end	Night	5% 2 13% 48% 32% 1	600
July	1st to 10th	Night	4 2 9% 49% 35% 1	585
	11th to 20th	Night	4 2 6% 37% 44% 7%	582
	21st to end	Night	6% 2 6% 33% 44% 8%	657
August	1st to 10th	Night	5% 1 6% 34% 48% 5%	597
	11th to 20th	Night	6% 2 6% 40% 42% 4	594
	21st to end	Night	7% 2 6% 40% 41% 4	660
September	1st to 10th	Night	7% 1 7% 44% 37% 3	600
	11th to 20th	Night	8% 2 12% 47% 30% 2	600
	21st to end	Night	9% 2 12% 44% 31% 2	769
October	1st to 10th	Night	13% 3 14% 47% 22% 2	800
	11th to 20th	Night	10% 2 16% 50% 20% 3	800
	21st to end	Night	8% 2 17% 49% 19% 5%	880
November	1st to 10th	Night	7% 2 17% 51% 20% 3	820
	11th to 20th	Night	6% 4 22% 48% 17% 3	1049
	21st to end	Night	14% 4 21% 38% 20% 3	1050
December	1st to 10th	Night	11% 4 24% 45% 13% 2	1050
	11th to 20th	Night	13% 5% 23% 43% 15% 1	1050
	21st to end	Night	13% 5% 25% 45% 10% 1	1155

Page generated at 2026-01-28 23:21:41. Version ac07

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