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Smokey Jack Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smokey Jack Observatory clear sky chart from 2005-11-06 to 2026-03-18.

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	2 4 2 4 3 4 4 4 6% 8% 58%	139889
	Night	2 4 1 4 3 3 3 3 5% 7% 64%	139124
Transparency	Day	20% 6% 11% 24% 26% 12%	134862
	Night	18% 6% 13% 27% 27% 10%	135159
Seeing	Day	9% 13% 30% 28% 16% 5%	17209
	Night	5% 10% 35% 33% 15% 2	27407

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 2 7% 4 3 3 3 4 7% 64%	4720
	11th to 20th	Day	2 1 4 3 3 2 2 4 6% 74%	5217
	21st to end	Day	5% 3 5% 3 3 3 3 5% 8% 63%	5844
February	1st to 10th	Day	5% 3 5% 3 2 3 3 6% 7% 63%	1890
	11th to 20th	Day	1 3 2 5% 3 2 3 3 5% 7% 66%	2043
	21st to end	Day	6% 3 6% 2 2 2 3 5% 8% 62%	1730
March	1st to 10th	Day	4 3 5% 3 3 3 3 5% 7% 64%	4642
	11th to 20th	Day	2 10% 5% 5% 5% 5% 5% 4 6% 7% 47%	5078
	21st to end	Day	1 5% 2 4 3 3 4 3 5% 9% 62%	5766
April	1st to 10th	Day	2 6% 1 4 4 4 4 4 6% 8% 58%	2400
	11th to 20th	Day	4 8% 2 5% 4 4 4 3 6% 7% 53%	2371
	21st to end	Day	4 7% 2 4 4 4 4 4 7% 9% 50%	2400
May	1st to 10th	Day	5% 10% 2 6% 4 4 4 4 6% 7% 48%	5525
	11th to 20th	Day	4 5% 1 4 4 4 4 4 7% 8% 55%	6196
	21st to end	Day	2 2 1 3 3 4 5% 5% 8% 11% 57%	6925
June	1st to 10th	Day	4 3 1 4 3 4 5% 5% 8% 11% 51%	2800
	11th to 20th	Day	3 3 1 2 3 4 5% 5% 7% 9% 59%	2800
	21st to end	Day	3 2 2 3 4 5% 6% 6% 9% 8% 52%	2800
July	1st to 10th	Day	3 2 1 3 3 4 4 4 6% 9% 61%	6339
	11th to 20th	Day	2 2 1 4 5% 6% 8% 7% 10% 10% 45%	6340
	21st to end	Day	4 3 2 6% 5% 6% 6% 6% 8% 9% 44%	6475
August	1st to 10th	Day	3 2 1 5% 5% 6% 7% 7% 10% 12% 42%	5720
	11th to 20th	Day	2 2 1 3 4 4 6% 5% 9% 11% 51%	5366
	21st to end	Day	4 4 2 6% 5% 5% 6% 5% 8% 10% 44%	5984
September	1st to 10th	Day	5% 4 1 4 4 4 5% 5% 7% 8% 54%	2400
	11th to 20th	Day	5% 2 1 3 2 4 3 4 6% 8% 62%	2394
	21st to end	Day	4 3 1 4 3 4 3 3 4 5% 67%	2195
October	1st to 10th	Day	3 2 2 2 2 3 2 3 4 75%	3270
	11th to 20th	Day	2 3 1 3 2 2 3 3 5% 9% 67%	3250
	21st to end	Day	2 3 1 2 1 2 2 2 3 6% 76%	3531
November	1st to 10th	Day	1 4 2 2 2 2 2 3 4 7% 72%	1853
	11th to 20th	Day	2 1 3 2 2 3 2 4 7% 73%	1890
	21st to end	Day	1 4 1 4 3 3 2 2 5% 6% 69%	1837
December	1st to 10th	Day	4 2 2 2 1 2 2 4 5% 76%	2700
	11th to 20th	Day	2 1 3 1 2 2 3 5% 8% 72%	3106
	21st to end	Day	3 2 4 3 3 4 3 6% 7% 65%	4092
January	1st to 10th	Night	3 2 7% 4 3 3 3 5% 7% 64%	8201
	11th to 20th	Night	1 1 1 2 2 3 2 5% 6% 77%	7830
	21st to end	Night	3 2 4 3 3 3 3 4 6% 69%	8370
February	1st to 10th	Night	4 3 5% 3 2 2 2 4 6% 68%	2730
	11th to 20th	Night	1 4 1 4 3 3 3 3 5% 7% 64%	2463
	21st to end	Night	4 2 5% 3 2 3 3 4 7% 68%	2076
March	1st to 10th	Night	1 6% 2 5% 2 3 3 2 4 5% 67%	5449
	11th to 20th	Night	1 7% 3 3 2 3 3 3 5% 6% 63%	5077
	21st to end	Night	1 4 2 3 3 3 3 3 5% 6% 68%	5196
April	1st to 10th	Night	1 5% 2 3 2 2 3 2 6% 8% 65%	2000
	11th to 20th	Night	3 7% 2 5% 3 2 3 3 5% 7% 60%	1977
	21st to end	Night	3 6% 2 5% 3 3 4 3 5% 7% 58%	2000
May	1st to 10th	Night	4 8% 2 7% 4 4 4 3 5% 7% 54%	4453
	11th to 20th	Night	5% 6% 1 3 2 2 3 3 5% 7% 62%	3715
	21st to end	Night	4 4 1 3 3 3 4 3 5% 7% 64%	3972
June	1st to 10th	Night	4 3 2 3 3 3 4 3 5% 8% 62%	1600
	11th to 20th	Night	2 3 1 3 2 3 3 2 4 8% 69%	1600
	21st to end	Night	3 4 1 4 4 4 4 6% 8% 8% 55%	1600
July	1st to 10th	Night	3 2 1 3 3 4 5% 4 7% 9% 58%	3640
	11th to 20th	Night	2 2 1 3 3 4 6% 7% 10% 14% 47%	3640
	21st to end	Night	3 3 1 5% 4 5% 6% 5% 9% 11% 47%	4380
August	1st to 10th	Night	3 3 1 5% 4 4 5% 5% 9% 11% 49%	4089
	11th to 20th	Night	2 2 1 3 3 3 5% 4 9% 14% 54%	4483
	21st to end	Night	4 5% 2 6% 5% 5% 6% 5% 9% 12% 41%	4993
September	1st to 10th	Night	4 5% 2 4 4 4 5% 4 6% 8% 55%	2000
	11th to 20th	Night	5% 4 1 3 3 3 3 3 5% 8% 63%	2005
	21st to end	Night	4 3 1 3 2 3 3 3 5% 6% 66%	2200
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 4 77%	3920
	11th to 20th	Night	3 2 1 3 3 2 3 3 5% 7% 68%	3898
	21st to end	Night	2 3 1 2 1 2 2 2 3 4 78%	4252
November	1st to 10th	Night	1 3 1 2 1 1 2 2 5% 6% 75%	2647
	11th to 20th	Night	1 2 1 2 1 2 3 2 5% 6% 76%	2730
	21st to end	Night	1 5% 2 2 2 2 2 2 5% 7% 69%	2779
December	1st to 10th	Night	2 1 4 2 2 2 2 3 5% 77%	4710
	11th to 20th	Night	1 2 1 3 2 2 2 2 5% 7% 74%	5321
	21st to end	Night	4 2 5% 3 3 4 3 6% 8% 63%	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	18% 5% 10% 29% 31% 8%	4723
	11th to 20th	Day	12% 4 11% 27% 32% 15%	5217
	21st to end	Day	19% 4 10% 24% 28% 14%	5844
February	1st to 10th	Day	20% 4 12% 30% 25% 10%	1890
	11th to 20th	Day	17% 4 11% 27% 31% 10%	2053
	21st to end	Day	21% 3 7% 23% 30% 16%	1730
March	1st to 10th	Day	16% 5% 7% 16% 38% 19%	4642
	11th to 20th	Day	30% 5% 8% 26% 24% 6%	5078
	21st to end	Day	18% 5% 9% 44% 20% 3	5766
April	1st to 10th	Day	23% 5% 11% 25% 24% 12%	2400
	11th to 20th	Day	29% 4 8% 27% 22% 10%	2374
	21st to end	Day	28% 6% 11% 28% 22% 6%	2400
May	1st to 10th	Day	31% 6% 10% 23% 19% 9%	5525
	11th to 20th	Day	23% 7% 11% 23% 24% 12%	6200
	21st to end	Day	16% 8% 10% 22% 31% 13%	6926
June	1st to 10th	Day	22% 9% 14% 23% 22% 10%	2800
	11th to 20th	Day	19% 6% 9% 17% 26% 23%	2800
	21st to end	Day	23% 8% 11% 22% 22% 14%	2800
July	1st to 10th	Day	17% 6% 10% 15% 24% 27%	6271
	11th to 20th	Day	24% 13% 18% 27% 13% 6%	6265
	21st to end	Day	28% 12% 17% 17% 16% 10%	6289
August	1st to 10th	Day	32% 12% 21% 19% 12% 4	4160
	11th to 20th	Day	22% 11% 17% 17% 22% 10%	3882
	21st to end	Day	27% 10% 17% 21% 20% 4	4311
September	1st to 10th	Day	25% 6% 12% 23% 23% 12%	2400
	11th to 20th	Day	19% 5% 12% 17% 31% 15%	2394
	21st to end	Day	19% 4 7% 25% 34% 11%	2195
October	1st to 10th	Day	13% 3 5% 18% 37% 23%	3270
	11th to 20th	Day	14% 5% 9% 32% 32% 9%	3250
	21st to end	Day	12% 2 5% 21% 44% 17%	3531
November	1st to 10th	Day	12% 3 8% 24% 39% 13%	1853
	11th to 20th	Day	12% 4 7% 35% 32% 10%	1890
	21st to end	Day	18% 3 7% 26% 31% 14%	1837
December	1st to 10th	Day	12% 3 10% 33% 33% 9%	2700
	11th to 20th	Day	10% 4 10% 33% 33% 11%	3104
	21st to end	Day	15% 7% 10% 28% 28% 13%	4092
January	1st to 10th	Night	19% 4 8% 35% 28% 6%	8202
	11th to 20th	Night	8% 2 11% 33% 30% 14%	7830
	21st to end	Night	15% 5% 12% 24% 30% 13%	8370
February	1st to 10th	Night	19% 2 12% 31% 24% 11%	2730
	11th to 20th	Night	19% 4 12% 29% 27% 8%	2463
	21st to end	Night	17% 3 7% 27% 33% 12%	2076
March	1st to 10th	Night	17% 3 7% 19% 40% 13%	5449
	11th to 20th	Night	21% 4 10% 25% 32% 7%	5077
	21st to end	Night	17% 5% 14% 43% 19% 2	5196
April	1st to 10th	Night	18% 4 13% 30% 27% 8%	2000
	11th to 20th	Night	25% 4 10% 27% 27% 7%	1977
	21st to end	Night	25% 4 13% 32% 20% 5%	2000
May	1st to 10th	Night	28% 8% 13% 26% 17% 7%	4450
	11th to 20th	Night	21% 5% 11% 30% 23% 10%	3716
	21st to end	Night	18% 8% 14% 21% 28% 11%	3972
June	1st to 10th	Night	21% 6% 18% 23% 19% 13%	1600
	11th to 20th	Night	15% 4 11% 23% 25% 21%	1600
	21st to end	Night	23% 7% 13% 21% 22% 14%	1600
July	1st to 10th	Night	19% 9% 15% 20% 24% 14%	3600
	11th to 20th	Night	20% 13% 30% 24% 10% 3	3592
	21st to end	Night	24% 15% 23% 17% 15% 6%	4255
August	1st to 10th	Night	32% 14% 24% 15% 10% 5%	2973
	11th to 20th	Night	19% 11% 29% 18% 18% 5%	3243
	21st to end	Night	28% 12% 19% 24% 14% 3	3597
September	1st to 10th	Night	25% 6% 14% 27% 21% 8%	2000
	11th to 20th	Night	20% 6% 12% 21% 27% 14%	2005
	21st to end	Night	19% 4 10% 26% 34% 8%	2200
October	1st to 10th	Night	12% 4 8% 25% 34% 16%	3920
	11th to 20th	Night	14% 6% 12% 29% 29% 10%	3898
	21st to end	Night	11% 3 5% 27% 39% 15%	4252
November	1st to 10th	Night	11% 3 9% 28% 36% 13%	2647
	11th to 20th	Night	10% 3 7% 35% 31% 13%	2730
	21st to end	Night	16% 3 10% 25% 33% 13%	2779
December	1st to 10th	Night	12% 3 10% 38% 30% 8%	4710
	11th to 20th	Night	11% 4 9% 29% 38% 9%	5322
	21st to end	Night	18% 6% 11% 25% 30% 11%	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	12% 18% 37% 21% 8% 4	330
	11th to 20th	Day	14% 16% 38% 25% 5% 1	330
	21st to end	Day	5% 16% 43% 25% 9% 2	363
February	1st to 10th	Day	10% 23% 43% 19% 4 1	330
	11th to 20th	Day	9% 30% 40% 17% 3 1	330
	21st to end	Day	16% 19% 38% 21% 5%	273
March	1st to 10th	Day	12% 21% 37% 22% 8% 1	346
	11th to 20th	Day	12% 23% 35% 21% 7% 1	529
	21st to end	Day	15% 26% 36% 18% 4 1	550
April	1st to 10th	Day	15% 24% 34% 20% 5% 1	500
	11th to 20th	Day	17% 27% 36% 15% 5% 1	492
	21st to end	Day	14% 23% 39% 16% 7% 1	500
May	1st to 10th	Day	14% 18% 36% 21% 9% 1	536
	11th to 20th	Day	12% 12% 27% 31% 15% 3	725
	21st to end	Day	8% 14% 30% 28% 16% 4	789
June	1st to 10th	Day	6% 9% 27% 31% 22% 7%	730
	11th to 20th	Day	5% 10% 32% 32% 17% 6%	730
	21st to end	Day	4 8% 29% 30% 23% 7%	730
July	1st to 10th	Day	7% 3 18% 37% 26% 9%	721
	11th to 20th	Day	4 2 13% 36% 35% 10%	718
	21st to end	Day	7% 3 12% 34% 32% 12%	610
August	1st to 10th	Day	6% 3 18% 37% 25% 11%	527
	11th to 20th	Day	5% 2 21% 38% 26% 9%	517
	21st to end	Day	8% 3 20% 37% 24% 8%	583
September	1st to 10th	Day	6% 5% 22% 33% 24% 9%	530
	11th to 20th	Day	5% 9% 31% 33% 18% 3	524
	21st to end	Day	6% 7% 22% 30% 28% 8%	330
October	1st to 10th	Day	8% 10% 26% 25% 23% 8%	330
	11th to 20th	Day	8% 17% 31% 27% 12% 5%	330
	21st to end	Day	11% 13% 31% 29% 13% 2	363
November	1st to 10th	Day	8% 19% 33% 26% 12% 2	330
	11th to 20th	Day	5% 19% 38% 25% 10% 4	330
	21st to end	Day	6% 16% 37% 32% 7% 2	330
December	1st to 10th	Day	10% 19% 37% 23% 9% 2	330
	11th to 20th	Day	8% 22% 40% 19% 9% 2	330
	21st to end	Day	10% 23% 44% 18% 4 1	363
January	1st to 10th	Night	4 16% 39% 28% 9% 2	1050
	11th to 20th	Night	5% 17% 41% 27% 8% 2	903
	21st to end	Night	3 11% 48% 31% 7% 1	924
February	1st to 10th	Night	3 12% 54% 25% 5%	840
	11th to 20th	Night	4 14% 53% 22% 6%	824
	21st to end	Night	3 13% 55% 27% 2	692
March	1st to 10th	Night	5% 16% 44% 28% 6% 1	840
	11th to 20th	Night	6% 7% 42% 33% 10% 1	828
	21st to end	Night	6% 12% 45% 32% 5%	755
April	1st to 10th	Night	8% 12% 46% 29% 6%	600
	11th to 20th	Night	9% 13% 41% 30% 6% 1	593
	21st to end	Night	8% 12% 36% 34% 10% 1	600
May	1st to 10th	Night	9% 10% 31% 39% 10% 1	600
	11th to 20th	Night	12% 6% 27% 37% 16% 2	591
	21st to end	Night	9% 10% 29% 34% 15% 2	650
June	1st to 10th	Night	6% 6% 21% 41% 24% 2	600
	11th to 20th	Night	3 6% 27% 45% 17% 2	600
	21st to end	Night	3 5% 20% 40% 29% 3	600
July	1st to 10th	Night	7% 2 10% 39% 36% 5%	585
	11th to 20th	Night	5% 1 5% 39% 41% 9%	582
	21st to end	Night	5% 2 4 33% 49% 6%	657
August	1st to 10th	Night	7% 2 8% 37% 38% 9%	597
	11th to 20th	Night	6% 1 10% 43% 34% 5%	594
	21st to end	Night	5% 3 11% 40% 35% 6%	660
September	1st to 10th	Night	5% 3 14% 43% 29% 7%	600
	11th to 20th	Night	7% 4 24% 39% 23% 5%	600
	21st to end	Night	5% 6% 25% 40% 21% 4	600
October	1st to 10th	Night	6% 6% 28% 40% 17% 3	800
	11th to 20th	Night	3 7% 36% 37% 15% 3	800
	21st to end	Night	5% 6% 38% 33% 15% 3	880
November	1st to 10th	Night	3 10% 39% 34% 12% 2	1007
	11th to 20th	Night	4 11% 43% 30% 10% 2	1050
	21st to end	Night	6% 10% 40% 34% 10% 1	1050
December	1st to 10th	Night	3 15% 42% 32% 7% 1	1050
	11th to 20th	Night	5% 14% 48% 25% 8% 1	1050
	21st to end	Night	5% 18% 46% 24% 5% 1	1155

Page generated at 2026-03-15 00:23:53. Version ac07

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