Ketchum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ketchum clear sky chart from 2005-11-06 to 2025-10-04.

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	3 7% 2 6% 4 4 4 4 5% 7% 53%	134453
	Night	3 7% 2 5% 3 3 4 4 5% 7% 56%	132248
Transparency	Day	29% 6% 10% 22% 22% 11%	129199
	Night	28% 5% 11% 24% 22% 10%	128502
Seeing	Day	12% 19% 33% 24% 10% 2	15865
	Night	8% 8% 28% 37% 16% 3	25442

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	1 8% 4 9% 5% 6% 6% 5% 8% 8% 40%	3639
	11th to 20th	Day	1 9% 3 9% 5% 3 3 3 4 7% 52%	3640
	21st to end	Day	2 12% 3 6% 3 3 3 3 4 6% 54%	4078
February	1st to 10th	Day	3 11% 4 8% 4 4 4 5% 5% 8% 45%	1800
	11th to 20th	Day	3 12% 4 8% 7% 6% 5% 5% 6% 7% 37%	1900
	21st to end	Day	3 15% 4 13% 5% 5% 5% 4 5% 7% 34%	1650
March	1st to 10th	Day	2 11% 5% 11% 5% 5% 4 3 5% 7% 42%	4518
	11th to 20th	Day	3 15% 4 8% 5% 4 4 3 4 5% 45%	4995
	21st to end	Day	4 16% 3 10% 7% 5% 6% 5% 7% 7% 30%	5486
April	1st to 10th	Day	5% 12% 4 11% 6% 5% 5% 4 6% 7% 35%	2388
	11th to 20th	Day	4 10% 4 8% 6% 5% 5% 4 5% 8% 41%	2504
	21st to end	Day	6% 11% 4 8% 5% 4 5% 4 6% 8% 39%	2600
May	1st to 10th	Day	4 8% 3 7% 5% 5% 4 4 6% 7% 48%	5880
	11th to 20th	Day	5% 7% 3 8% 5% 5% 5% 5% 6% 7% 45%	5841
	21st to end	Day	4 8% 2 6% 4 5% 5% 4 5% 7% 51%	6772
June	1st to 10th	Day	8% 6% 3 7% 5% 4 5% 5% 7% 9% 40%	2860
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 8% 51%	3000
	21st to end	Day	2 3 1 4 3 4 3 4 5% 6% 65%	2829
July	1st to 10th	Day	1 2 1 3 2 3 3 3 4 5% 73%	6319
	11th to 20th	Day	1 2 1 2 3 3 3 3 5% 7% 69%	6320
	21st to end	Day	2 3 1 3 3 3 4 3 6% 8% 63%	6804
August	1st to 10th	Day	2 2 1 4 3 4 5% 4 7% 9% 59%	5779
	11th to 20th	Day	1 1 1 2 2 3 3 3 4 5% 74%	5798
	21st to end	Day	4 4 2 5% 3 4 4 3 4 5% 62%	6301
September	1st to 10th	Day	3 3 2 3 2 4 4 3 4 6% 67%	2335
	11th to 20th	Day	6% 4 1 5% 4 3 3 3 5% 7% 57%	2200
	21st to end	Day	7% 4 1 4 3 2 3 3 5% 5% 63%	2200
October	1st to 10th	Day	5% 5% 2 3 3 3 4 3 4 4 65%	3507
	11th to 20th	Day	3 4 2 3 3 3 4 3 6% 6% 63%	3097
	21st to end	Day	3 6% 2 4 3 3 4 3 6% 8% 57%	3101
November	1st to 10th	Day	7% 10% 2 6% 4 3 5% 4 5% 8% 46%	1764
	11th to 20th	Day	4 8% 3 6% 4 5% 5% 4 8% 8% 45%	1800
	21st to end	Day	2 9% 3 7% 3 4 4 4 6% 8% 50%	1708
December	1st to 10th	Day	2 7% 2 4 4 3 3 3 4 5% 65%	2460
	11th to 20th	Day	3 16% 4 7% 5% 4 4 4 7% 10% 35%	2645
	21st to end	Day	2 15% 3 7% 4 5% 5% 4 6% 8% 42%	3935
January	1st to 10th	Night	2 8% 3 9% 6% 4 5% 5% 7% 9% 42%	6306
	11th to 20th	Night	2 8% 3 9% 4 3 3 3 5% 7% 54%	6320
	21st to end	Night	2 13% 3 6% 3 3 3 2 4 6% 55%	6867
February	1st to 10th	Night	3 10% 3 8% 4 5% 5% 5% 7% 8% 43%	2600
	11th to 20th	Night	2 11% 4 7% 4 4 5% 4 5% 9% 46%	2385
	21st to end	Night	3 12% 3 10% 5% 4 4 4 5% 7% 43%	1980
March	1st to 10th	Night	2 13% 4 9% 4 3 3 3 4 6% 49%	5376
	11th to 20th	Night	3 13% 3 6% 3 3 3 4 5% 6% 50%	5005
	21st to end	Night	2 11% 3 6% 4 4 5% 5% 7% 9% 43%	5489
April	1st to 10th	Night	4 9% 3 6% 3 4 5% 4 6% 9% 48%	2010
	11th to 20th	Night	3 8% 3 6% 3 4 5% 4 7% 8% 50%	1843
	21st to end	Night	3 7% 2 5% 4 4 5% 5% 6% 9% 51%	1800
May	1st to 10th	Night	4 6% 2 5% 3 3 4 3 5% 7% 58%	4100
	11th to 20th	Night	4 6% 2 4 4 4 5% 4 7% 7% 53%	4074
	21st to end	Night	3 4 1 3 2 3 4 4 7% 8% 61%	4090
June	1st to 10th	Night	6% 3 2 5% 4 5% 5% 5% 6% 9% 51%	1530
	11th to 20th	Night	7% 4 1 4 4 4 4 3 5% 7% 59%	1400
	21st to end	Night	2 2 1 2 3 3 3 2 6% 7% 70%	1558
July	1st to 10th	Night	1 1 1 2 2 2 3 3 4 4 77%	3640
	11th to 20th	Night	1 1 1 2 2 2 3 2 4 5% 77%	3640
	21st to end	Night	1 2 1 3 3 3 4 3 6% 10% 65%	4049
August	1st to 10th	Night	1 3 1 4 3 3 4 3 5% 7% 66%	4033
	11th to 20th	Night	1 1 2 2 2 3 3 4 7% 76%	4051
	21st to end	Night	4 2 1 4 2 3 3 3 5% 6% 67%	4682
September	1st to 10th	Night	3 2 1 2 2 3 2 2 3 6% 73%	2065
	11th to 20th	Night	5% 3 1 4 3 3 3 3 5% 7% 64%	2200
	21st to end	Night	6% 3 1 3 3 3 2 2 4 5% 68%	2200
October	1st to 10th	Night	4 2 1 2 2 2 2 2 4 5% 74%	3537
	11th to 20th	Night	4 4 1 4 3 4 4 3 5% 6% 60%	3828
	21st to end	Night	4 4 1 4 3 4 4 4 6% 8% 56%	4457
November	1st to 10th	Night	7% 8% 2 5% 3 3 4 3 7% 8% 50%	2535
	11th to 20th	Night	4 9% 2 4 3 4 5% 5% 9% 8% 47%	2600
	21st to end	Night	2 8% 2 6% 4 4 4 4 6% 7% 52%	2667
December	1st to 10th	Night	2 5% 1 4 3 3 3 3 4 6% 66%	4723
	11th to 20th	Night	3 15% 4 9% 5% 5% 5% 4 6% 8% 35%	5546
	21st to end	Night	3 13% 3 8% 4 4 5% 5% 6% 7% 41%	7062

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	37% 10% 16% 19% 17% 1	3639
	11th to 20th	Day	32% 6% 13% 28% 15% 6%	3640
	21st to end	Day	32% 5% 13% 23% 19% 7%	4078
February	1st to 10th	Day	37% 8% 18% 23% 9% 5%	1800
	11th to 20th	Day	44% 7% 16% 19% 12% 3	1910
	21st to end	Day	46% 10% 12% 19% 11% 3	1650
March	1st to 10th	Day	41% 6% 10% 23% 15% 5%	4518
	11th to 20th	Day	39% 6% 10% 27% 15% 2	4995
	21st to end	Day	47% 11% 14% 22% 5% 1	5486
April	1st to 10th	Day	46% 7% 13% 19% 12% 2	2388
	11th to 20th	Day	40% 7% 13% 23% 15% 2	2507
	21st to end	Day	40% 7% 13% 25% 13% 1	2600
May	1st to 10th	Day	31% 8% 9% 30% 19% 2	5880
	11th to 20th	Day	36% 7% 7% 25% 18% 7%	5844
	21st to end	Day	28% 7% 7% 34% 21% 3	6773
June	1st to 10th	Day	36% 7% 13% 28% 14% 2	2860
	11th to 20th	Day	29% 6% 9% 22% 26% 9%	3000
	21st to end	Day	19% 4 6% 22% 40% 10%	2829
July	1st to 10th	Day	12% 2 4 11% 26% 44%	6251
	11th to 20th	Day	12% 2 5% 11% 29% 41%	6245
	21st to end	Day	17% 3 5% 11% 42% 22%	6606
August	1st to 10th	Day	22% 3 7% 15% 33% 20%	4208
	11th to 20th	Day	13% 3 5% 19% 41% 19%	4197
	21st to end	Day	20% 3 4 21% 32% 20%	4544
September	1st to 10th	Day	19% 4 5% 19% 33% 19%	2335
	11th to 20th	Day	26% 5% 8% 25% 25% 11%	2200
	21st to end	Day	23% 4 8% 28% 29% 8%	2200
October	1st to 10th	Day	23% 3 8% 21% 33% 11%	3507
	11th to 20th	Day	22% 4 12% 31% 23% 8%	3097
	21st to end	Day	25% 5% 14% 29% 25% 2	3101
November	1st to 10th	Day	38% 5% 15% 21% 19% 3	1764
	11th to 20th	Day	33% 7% 19% 26% 12% 2	1800
	21st to end	Day	31% 6% 16% 25% 17% 5%	1708
December	1st to 10th	Day	23% 4 20% 29% 21% 3	2460
	11th to 20th	Day	43% 6% 19% 21% 9% 1	2644
	21st to end	Day	40% 6% 13% 20% 16% 5%	3935
January	1st to 10th	Night	37% 9% 12% 26% 16% 1	6306
	11th to 20th	Night	31% 5% 13% 24% 20% 7%	6320
	21st to end	Night	32% 5% 11% 26% 19% 7%	6867
February	1st to 10th	Night	37% 8% 18% 22% 12% 4	2600
	11th to 20th	Night	36% 6% 16% 25% 15% 3	2386
	21st to end	Night	39% 7% 14% 24% 12% 4	1980
March	1st to 10th	Night	36% 5% 10% 22% 19% 8%	5376
	11th to 20th	Night	33% 4 12% 26% 23% 2	5005
	21st to end	Night	33% 8% 19% 29% 10% 1	5489
April	1st to 10th	Night	32% 8% 14% 27% 16% 3	2010
	11th to 20th	Night	30% 7% 13% 29% 18% 2	1843
	21st to end	Night	29% 5% 18% 31% 17%	1800
May	1st to 10th	Night	24% 6% 9% 36% 18% 6%	4097
	11th to 20th	Night	27% 7% 11% 30% 21% 4	4075
	21st to end	Night	19% 6% 8% 35% 28% 4	4090
June	1st to 10th	Night	28% 6% 16% 32% 17% 1	1530
	11th to 20th	Night	24% 5% 9% 24% 28% 10%	1400
	21st to end	Night	15% 4 6% 22% 37% 16%	1558
July	1st to 10th	Night	12% 2 4 10% 26% 46%	3600
	11th to 20th	Night	10% 2 4 10% 26% 48%	3592
	21st to end	Night	16% 3 4 12% 40% 25%	3935
August	1st to 10th	Night	23% 3 6% 13% 31% 24%	2928
	11th to 20th	Night	12% 4 3 18% 38% 25%	2928
	21st to end	Night	14% 3 5% 19% 37% 23%	3366
September	1st to 10th	Night	15% 4 5% 19% 36% 22%	2065
	11th to 20th	Night	20% 4 8% 28% 26% 14%	2200
	21st to end	Night	21% 3 7% 27% 31% 11%	2200
October	1st to 10th	Night	15% 2 7% 24% 37% 15%	3537
	11th to 20th	Night	25% 4 11% 26% 27% 7%	3828
	21st to end	Night	25% 6% 14% 30% 22% 3	4457
November	1st to 10th	Night	31% 6% 15% 23% 22% 4	2535
	11th to 20th	Night	31% 7% 17% 29% 14% 3	2600
	21st to end	Night	30% 6% 15% 25% 19% 5%	2667
December	1st to 10th	Night	20% 5% 23% 31% 18% 3	4723
	11th to 20th	Night	45% 7% 16% 21% 11% 1	5547
	21st to end	Night	40% 6% 13% 21% 15% 5%	7062

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	16% 15% 30% 26% 10% 3	200
	11th to 20th	Day	9% 21% 35% 22% 10% 5%	200
	21st to end	Day	9% 17% 38% 21% 12% 3	237
February	1st to 10th	Day	22% 22% 34% 14% 6% 1	300
	11th to 20th	Day	13% 27% 37% 15% 7% 1	445
	21st to end	Day	15% 23% 37% 19% 5%	414
March	1st to 10th	Day	14% 25% 41% 16% 4	500
	11th to 20th	Day	16% 23% 31% 22% 7% 1	500
	21st to end	Day	17% 27% 32% 20% 4	550
April	1st to 10th	Day	18% 23% 29% 21% 8% 2	500
	11th to 20th	Day	15% 29% 31% 18% 4 2	492
	21st to end	Day	15% 24% 32% 19% 9% 1	500
May	1st to 10th	Day	13% 23% 30% 22% 10% 1	503
	11th to 20th	Day	21% 20% 28% 21% 8% 2	528
	21st to end	Day	14% 17% 29% 24% 12% 3	573
June	1st to 10th	Day	9% 21% 29% 25% 12% 3	590
	11th to 20th	Day	15% 23% 30% 20% 11% 2	730
	21st to end	Day	7% 17% 37% 26% 11% 2	559
July	1st to 10th	Day	4 19% 38% 26% 11% 2	526
	11th to 20th	Day	3 18% 42% 28% 8% 1	524
	21st to end	Day	4 13% 41% 27% 14% 2	575
August	1st to 10th	Day	7% 16% 33% 28% 13% 2	527
	11th to 20th	Day	2 15% 34% 30% 16% 3	517
	21st to end	Day	8% 17% 32% 27% 12% 3	583
September	1st to 10th	Day	5% 13% 32% 32% 13% 5%	530
	11th to 20th	Day	12% 14% 31% 28% 13% 2	530
	21st to end	Day	9% 15% 33% 28% 12% 3	530
October	1st to 10th	Day	12% 17% 30% 26% 13% 2	499
	11th to 20th	Day	13% 16% 25% 27% 14% 5%	300
	21st to end	Day	13% 18% 37% 25% 6%	330
November	1st to 10th	Day	15% 20% 34% 19% 10% 1	300
	11th to 20th	Day	10% 17% 37% 29% 6% 2	300
	21st to end	Day	8% 13% 36% 31% 11% 1	300
December	1st to 10th	Day	13% 11% 30% 26% 13% 6%	253
	11th to 20th	Day	12% 21% 35% 24% 8% 1	200
	21st to end	Day	16% 18% 32% 24% 8% 2	220
January	1st to 10th	Night	8% 10% 31% 34% 15% 2	800
	11th to 20th	Night	9% 11% 30% 33% 14% 4	800
	21st to end	Night	6% 9% 33% 34% 15% 2	880
February	1st to 10th	Night	11% 12% 36% 30% 10% 2	800
	11th to 20th	Night	10% 10% 36% 33% 10% 2	784
	21st to end	Night	10% 10% 33% 34% 11% 2	660
March	1st to 10th	Night	9% 9% 34% 36% 10% 2	800
	11th to 20th	Night	12% 12% 27% 36% 12% 2	800
	21st to end	Night	11% 13% 29% 37% 10% 1	880
April	1st to 10th	Night	8% 14% 28% 36% 12% 3	800
	11th to 20th	Night	7% 12% 38% 32% 10% 2	655
	21st to end	Night	7% 11% 32% 35% 14% 2	600
May	1st to 10th	Night	7% 10% 31% 33% 17% 2	600
	11th to 20th	Night	7% 9% 30% 30% 21% 4	591
	21st to end	Night	10% 6% 25% 34% 20% 5%	487
June	1st to 10th	Night	9% 6% 24% 38% 20% 3	400
	11th to 20th	Night	9% 6% 29% 40% 15% 1	400
	21st to end	Night	2 1 22% 48% 23% 4	400
July	1st to 10th	Night	2 1 22% 44% 26% 5%	390
	11th to 20th	Night	1 2 26% 48% 22% 1	388
	21st to end	Night	2 1 19% 45% 28% 5%	467
August	1st to 10th	Night	4 2 19% 47% 24% 4	597
	11th to 20th	Night	2 2 19% 47% 27% 3	594
	21st to end	Night	4 3 20% 47% 23% 4	729
September	1st to 10th	Night	5% 2 17% 44% 26% 6%	800
	11th to 20th	Night	6% 3 16% 43% 26% 7%	800
	21st to end	Night	9% 3 22% 36% 22% 9%	800
October	1st to 10th	Night	8% 5% 25% 40% 17% 6%	772
	11th to 20th	Night	10% 6% 23% 36% 20% 5%	760
	21st to end	Night	8% 8% 31% 36% 12% 5%	836
November	1st to 10th	Night	9% 9% 28% 36% 13% 3	780
	11th to 20th	Night	11% 8% 34% 34% 12% 2	800
	21st to end	Night	7% 10% 36% 30% 13% 4	867
December	1st to 10th	Night	10% 7% 33% 37% 11% 2	1000
	11th to 20th	Night	11% 10% 33% 33% 11% 2	1000
	21st to end	Night	11% 12% 33% 34% 8% 2	925

Page generated at 2025-09-30 23:39:08. Version ac07

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