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 2024-01-12.

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	5% 8% 3 6% 5% 3 5% 5% 5% 7% 49%	74558
	Night	4 7% 3 5% 4 3 4 5% 6% 8% 53%	75147
Transparency	Day	33% 6% 12% 22% 19% 8%	74263
	Night	30% 6% 13% 24% 19% 8%	74964
Seeing	Day	12% 19% 33% 24% 10% 2	13545
	Night	8% 8% 27% 37% 17% 4	23301

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 12% 4 7% 6% 4 5% 6% 7% 9% 39%	1519
	11th to 20th	Day	2 10% 4 7% 6% 3 3 4 4 10% 46%	1448
	21st to end	Day	3 10% 4 7% 5% 3 5% 5% 6% 9% 45%	1616
February	1st to 10th	Day	3 8% 4 6% 5% 2 5% 5% 6% 9% 48%	1620
	11th to 20th	Day	3 12% 4 8% 7% 4 6% 6% 6% 7% 38%	1705
	21st to end	Day	3 13% 6% 12% 6% 4 6% 5% 6% 8% 33%	1480
March	1st to 10th	Day	4 13% 5% 10% 6% 4 5% 6% 6% 8% 33%	1800
	11th to 20th	Day	5% 14% 5% 7% 5% 3 5% 4 6% 7% 38%	1975
	21st to end	Day	7% 15% 4 9% 7% 3 5% 5% 6% 8% 32%	2178
April	1st to 10th	Day	6% 11% 5% 9% 9% 3 6% 5% 6% 7% 34%	2148
	11th to 20th	Day	5% 10% 5% 8% 7% 4 4 5% 5% 8% 39%	2250
	21st to end	Day	6% 11% 4 7% 6% 3 5% 5% 5% 8% 40%	2340
May	1st to 10th	Day	6% 9% 3 7% 7% 4 5% 4 6% 8% 40%	2340
	11th to 20th	Day	8% 9% 4 8% 7% 5% 6% 7% 6% 7% 34%	2301
	21st to end	Day	8% 11% 5% 9% 8% 5% 7% 6% 6% 6% 28%	2671
June	1st to 10th	Day	9% 6% 4 6% 6% 3 6% 6% 7% 9% 39%	2574
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 5% 6% 7% 50%	2700
	21st to end	Day	3 3 1 3 4 2 4 4 5% 6% 65%	2547
July	1st to 10th	Day	2 3 2 4 4 3 4 5% 5% 7% 63%	2520
	11th to 20th	Day	3 2 1 2 3 2 2 3 4 6% 73%	2520
	21st to end	Day	4 3 2 4 3 3 4 4 5% 6% 62%	2715
August	1st to 10th	Day	5% 4 1 4 5% 3 5% 5% 5% 6% 56%	2328
	11th to 20th	Day	2 2 1 2 3 2 4 4 5% 6% 69%	2299
	21st to end	Day	4 3 2 3 4 3 5% 3 4 5% 65%	2511
September	1st to 10th	Day	3 3 2 3 3 2 4 4 3 5% 68%	2102
	11th to 20th	Day	7% 4 2 4 4 2 3 4 4 7% 58%	1980
	21st to end	Day	8% 4 1 3 4 2 3 4 5% 5% 61%	1980
October	1st to 10th	Day	8% 7% 3 4 4 3 4 4 5% 6% 52%	1977
	11th to 20th	Day	5% 5% 2 3 4 3 5% 4 6% 6% 57%	1771
	21st to end	Day	5% 5% 2 5% 4 3 5% 3 6% 9% 53%	1782
November	1st to 10th	Day	7% 9% 3 5% 5% 3 4 5% 5% 8% 46%	1674
	11th to 20th	Day	4 7% 3 5% 4 4 5% 5% 9% 9% 45%	1710
	21st to end	Day	2 8% 4 7% 3 3 4 5% 5% 8% 50%	1623
December	1st to 10th	Day	4 11% 3 5% 6% 3 4 5% 5% 6% 46%	1430
	11th to 20th	Day	3 16% 4 6% 6% 4 4 5% 6% 9% 35%	1685
	21st to end	Day	3 11% 2 6% 5% 4 4 4 6% 8% 45%	2739
January	1st to 10th	Night	3 8% 4 7% 7% 3 5% 6% 7% 9% 43%	2646
	11th to 20th	Night	2 10% 3 5% 4 2 4 4 6% 8% 51%	2540
	21st to end	Night	2 10% 4 5% 5% 2 4 5% 6% 8% 49%	2739
February	1st to 10th	Night	2 7% 3 6% 5% 3 6% 6% 7% 9% 45%	2340
	11th to 20th	Night	2 9% 5% 7% 4 3 4 5% 5% 9% 48%	2140
	21st to end	Night	4 10% 4 10% 6% 3 5% 5% 5% 7% 41%	1776
March	1st to 10th	Night	4 9% 5% 7% 6% 3 5% 6% 6% 8% 43%	2160
	11th to 20th	Night	5% 10% 4 5% 5% 2 4 5% 7% 8% 45%	1985
	21st to end	Night	5% 11% 3 5% 5% 3 4 5% 6% 9% 42%	2178
April	1st to 10th	Night	4 9% 4 5% 4 3 5% 6% 7% 9% 46%	1810
	11th to 20th	Night	4 7% 4 6% 4 2 4 5% 7% 8% 48%	1657
	21st to end	Night	4 6% 2 4 4 3 4 6% 6% 9% 52%	1620
May	1st to 10th	Night	3 6% 2 4 3 3 5% 5% 5% 8% 57%	1620
	11th to 20th	Night	5% 5% 2 4 5% 3 6% 6% 9% 9% 47%	1594
	21st to end	Night	8% 7% 3 6% 4 3 4 6% 8% 10% 42%	1600
June	1st to 10th	Night	7% 3 2 4 4 3 5% 6% 6% 9% 50%	1378
	11th to 20th	Night	8% 4 1 3 4 3 4 4 5% 7% 58%	1260
	21st to end	Night	2 2 1 2 3 2 3 3 5% 7% 70%	1402
July	1st to 10th	Night	1 2 1 3 3 2 3 4 5% 7% 71%	1440
	11th to 20th	Night	1 1 1 2 2 2 4 3 3 5% 76%	1440
	21st to end	Night	2 2 1 3 3 2 4 3 3 7% 70%	1601
August	1st to 10th	Night	2 3 1 3 5% 2 4 5% 5% 7% 61%	1611
	11th to 20th	Night	2 1 2 3 2 2 2 4 7% 73%	1602
	21st to end	Night	2 2 1 2 3 2 3 4 5% 7% 69%	1843
September	1st to 10th	Night	4 2 1 2 3 2 2 3 2 6% 73%	1858
	11th to 20th	Night	5% 3 1 3 3 2 3 4 5% 6% 66%	1980
	21st to end	Night	6% 4 2 3 3 2 2 3 4 6% 66%	1980
October	1st to 10th	Night	6% 4 2 3 3 2 3 3 5% 6% 62%	1981
	11th to 20th	Night	6% 4 1 4 3 2 3 4 6% 8% 60%	2186
	21st to end	Night	4 4 2 4 4 3 4 5% 6% 9% 55%	2574
November	1st to 10th	Night	7% 7% 2 4 4 2 5% 4 7% 8% 50%	2405
	11th to 20th	Night	4 8% 3 3 4 3 4 6% 9% 8% 48%	2470
	21st to end	Night	3 7% 2 5% 5% 3 5% 5% 6% 7% 52%	2533
December	1st to 10th	Night	4 8% 3 5% 5% 3 5% 6% 6% 9% 47%	2748
	11th to 20th	Night	4 13% 4 8% 6% 4 5% 5% 5% 8% 37%	3506
	21st to end	Night	3 11% 3 6% 6% 3 5% 5% 5% 6% 45%	4944

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	39% 10% 21% 20% 9% 2	1519
	11th to 20th	Day	36% 7% 14% 25% 12% 5%	1448
	21st to end	Day	35% 8% 18% 26% 10% 4	1616
February	1st to 10th	Day	33% 9% 20% 25% 9% 4	1620
	11th to 20th	Day	44% 7% 16% 19% 11% 3	1715
	21st to end	Day	47% 10% 13% 19% 9% 3	1480
March	1st to 10th	Day	48% 8% 14% 22% 8% 2	1800
	11th to 20th	Day	41% 9% 16% 22% 11% 1	1975
	21st to end	Day	50% 9% 16% 17% 7% 1	2178
April	1st to 10th	Day	47% 7% 14% 17% 12% 2	2148
	11th to 20th	Day	42% 6% 13% 22% 15% 2	2253
	21st to end	Day	40% 7% 14% 25% 13% 1	2340
May	1st to 10th	Day	39% 8% 11% 24% 15% 2	2340
	11th to 20th	Day	45% 7% 13% 24% 10% 1	2304
	21st to end	Day	50% 7% 13% 21% 8% 2	2671
June	1st to 10th	Day	38% 8% 14% 26% 12% 2	2574
	11th to 20th	Day	31% 6% 9% 22% 23% 9%	2700
	21st to end	Day	19% 4 6% 22% 40% 9%	2547
July	1st to 10th	Day	18% 4 4 21% 33% 20%	2451
	11th to 20th	Day	13% 3 3 15% 30% 36%	2445
	21st to end	Day	21% 5% 4 13% 29% 28%	2564
August	1st to 10th	Day	25% 5% 6% 18% 27% 18%	2313
	11th to 20th	Day	14% 4 4 26% 34% 17%	2299
	21st to end	Day	21% 4 5% 21% 32% 18%	2511
September	1st to 10th	Day	19% 4 5% 18% 33% 21%	2102
	11th to 20th	Day	26% 5% 8% 24% 26% 12%	1980
	21st to end	Day	24% 4 8% 29% 28% 7%	1980
October	1st to 10th	Day	32% 5% 11% 27% 19% 5%	1977
	11th to 20th	Day	26% 6% 12% 33% 17% 5%	1771
	21st to end	Day	28% 6% 17% 27% 19% 3	1782
November	1st to 10th	Day	38% 5% 15% 20% 19% 3	1674
	11th to 20th	Day	33% 8% 19% 26% 12% 2	1710
	21st to end	Day	31% 6% 16% 24% 17% 5%	1623
December	1st to 10th	Day	38% 6% 16% 21% 13% 5%	1430
	11th to 20th	Day	46% 5% 19% 18% 10% 2	1684
	21st to end	Day	36% 6% 14% 21% 17% 7%	2739
January	1st to 10th	Night	38% 9% 18% 23% 10% 2	2646
	11th to 20th	Night	32% 7% 17% 21% 18% 5%	2540
	21st to end	Night	33% 6% 15% 28% 14% 4	2739
February	1st to 10th	Night	34% 8% 19% 23% 11% 3	2340
	11th to 20th	Night	35% 6% 15% 25% 15% 3	2141
	21st to end	Night	41% 7% 15% 23% 11% 4	1776
March	1st to 10th	Night	38% 8% 14% 25% 12% 2	2160
	11th to 20th	Night	35% 5% 16% 26% 15% 3	1985
	21st to end	Night	39% 8% 19% 24% 10% 1	2178
April	1st to 10th	Night	33% 8% 14% 25% 15% 4	1810
	11th to 20th	Night	33% 7% 14% 26% 18% 2	1657
	21st to end	Night	29% 4 18% 32% 16%	1620
May	1st to 10th	Night	25% 6% 11% 35% 19% 3	1620
	11th to 20th	Night	30% 7% 17% 31% 14% 1	1595
	21st to end	Night	36% 7% 17% 28% 10% 2	1600
June	1st to 10th	Night	30% 6% 17% 31% 15% 1	1378
	11th to 20th	Night	25% 6% 10% 25% 26% 9%	1260
	21st to end	Night	15% 4 6% 22% 36% 16%	1402
July	1st to 10th	Night	14% 4 5% 19% 35% 24%	1400
	11th to 20th	Night	13% 3 3 13% 27% 41%	1392
	21st to end	Night	17% 4 3 12% 28% 36%	1512
August	1st to 10th	Night	22% 5% 8% 17% 23% 25%	1602
	11th to 20th	Night	13% 4 3 20% 37% 23%	1602
	21st to end	Night	15% 4 7% 18% 32% 24%	1843
September	1st to 10th	Night	16% 3 4 17% 36% 24%	1858
	11th to 20th	Night	20% 3 8% 26% 28% 15%	1980
	21st to end	Night	22% 4 7% 27% 30% 10%	1980
October	1st to 10th	Night	25% 3 12% 30% 22% 8%	1981
	11th to 20th	Night	23% 5% 12% 34% 22% 5%	2186
	21st to end	Night	26% 6% 16% 29% 20% 3	2574
November	1st to 10th	Night	31% 6% 15% 23% 21% 4	2405
	11th to 20th	Night	30% 7% 16% 29% 14% 3	2470
	21st to end	Night	30% 6% 15% 24% 19% 6%	2533
December	1st to 10th	Night	33% 8% 19% 22% 14% 4	2748
	11th to 20th	Night	45% 6% 14% 21% 13% 1	3507
	21st to end	Night	38% 5% 13% 23% 14% 7%	4944

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	17% 14% 26% 28% 11% 3	180
	11th to 20th	Day	10% 19% 33% 23% 10% 6%	162
	21st to end	Day	11% 15% 39% 19% 14% 3	190
February	1st to 10th	Day	18% 23% 37% 14% 7% 1	240
	11th to 20th	Day	14% 26% 36% 15% 8% 1	370
	21st to end	Day	15% 23% 37% 20% 5% 1	346
March	1st to 10th	Day	14% 25% 41% 16% 4	420
	11th to 20th	Day	15% 22% 32% 24% 6%	420
	21st to end	Day	17% 27% 34% 18% 4	462
April	1st to 10th	Day	19% 23% 29% 20% 7% 1	420
	11th to 20th	Day	16% 32% 30% 17% 3 2	412
	21st to end	Day	16% 23% 32% 19% 9% 1	420
May	1st to 10th	Day	13% 22% 31% 22% 10% 1	423
	11th to 20th	Day	20% 18% 29% 22% 8% 2	448
	21st to end	Day	15% 17% 28% 24% 13% 4	485
June	1st to 10th	Day	10% 21% 28% 25% 13% 4	504
	11th to 20th	Day	15% 21% 29% 20% 12% 2	630
	21st to end	Day	6% 16% 36% 28% 11% 2	477
July	1st to 10th	Day	4 16% 38% 28% 12% 2	446
	11th to 20th	Day	4 17% 42% 28% 8% 1	444
	21st to end	Day	4 11% 41% 28% 14% 2	487
August	1st to 10th	Day	7% 14% 34% 30% 14% 2	447
	11th to 20th	Day	2 13% 33% 32% 17% 4	437
	21st to end	Day	7% 16% 32% 29% 13% 3	495
September	1st to 10th	Day	6% 14% 32% 32% 13% 4	450
	11th to 20th	Day	13% 15% 28% 28% 13% 2	450
	21st to end	Day	10% 15% 32% 29% 12% 2	450
October	1st to 10th	Day	12% 17% 28% 26% 15% 2	447
	11th to 20th	Day	13% 17% 25% 27% 12% 6%	270
	21st to end	Day	12% 18% 36% 27% 7%	297
November	1st to 10th	Day	16% 19% 33% 21% 11% 1	270
	11th to 20th	Day	10% 14% 36% 32% 6% 2	270
	21st to end	Day	8% 11% 36% 31% 12% 1	270
December	1st to 10th	Day	14% 11% 30% 26% 13% 5%	228
	11th to 20th	Day	12% 19% 36% 24% 7% 1	180
	21st to end	Day	15% 16% 34% 24% 9% 2	198
January	1st to 10th	Night	8% 9% 29% 36% 15% 3	760
	11th to 20th	Night	9% 10% 28% 34% 15% 4	726
	21st to end	Night	7% 8% 32% 34% 16% 2	792
February	1st to 10th	Night	9% 11% 36% 31% 11% 2	720
	11th to 20th	Night	10% 10% 33% 34% 11% 2	704
	21st to end	Night	10% 9% 31% 35% 12% 3	592
March	1st to 10th	Night	9% 9% 31% 37% 11% 3	720
	11th to 20th	Night	12% 10% 26% 37% 13% 2	720
	21st to end	Night	11% 13% 28% 36% 11% 1	792
April	1st to 10th	Night	8% 13% 27% 35% 13% 3	720
	11th to 20th	Night	7% 12% 35% 33% 11% 2	589
	21st to end	Night	7% 11% 29% 35% 15% 3	540
May	1st to 10th	Night	6% 10% 30% 33% 18% 2	540
	11th to 20th	Night	7% 7% 29% 29% 23% 4	531
	21st to end	Night	12% 7% 22% 33% 21% 5%	438
June	1st to 10th	Night	10% 6% 21% 38% 22% 4	360
	11th to 20th	Night	10% 6% 25% 41% 16% 1	360
	21st to end	Night	2 1 19% 48% 26% 4	360
July	1st to 10th	Night	2 20% 43% 29% 5%	350
	11th to 20th	Night	1 2 25% 46% 24% 1	348
	21st to end	Night	2 2 17% 42% 31% 5%	419
August	1st to 10th	Night	4 2 17% 46% 27% 4	537
	11th to 20th	Night	2 2 15% 47% 30% 3	534
	21st to end	Night	3 3 18% 47% 25% 4	655
September	1st to 10th	Night	6% 1 17% 43% 27% 6%	720
	11th to 20th	Night	6% 2 14% 42% 28% 8%	720
	21st to end	Night	9% 3 21% 35% 23% 10%	720
October	1st to 10th	Night	8% 5% 23% 40% 18% 6%	720
	11th to 20th	Night	10% 6% 23% 35% 21% 5%	720
	21st to end	Night	8% 7% 29% 38% 13% 5%	792
November	1st to 10th	Night	10% 9% 27% 37% 14% 3	740
	11th to 20th	Night	11% 7% 33% 36% 12% 2	760
	21st to end	Night	7% 10% 34% 31% 13% 5%	823
December	1st to 10th	Night	11% 8% 32% 37% 11% 2	950
	11th to 20th	Night	11% 10% 31% 34% 12% 2	950
	21st to end	Night	11% 12% 32% 35% 9% 2	879

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