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 2024-11-05.

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 8% 3 6% 4 4 4 4 5% 7% 51%	104794
	Night	3 7% 2 6% 4 4 4 4 5% 7% 54%	102885
Transparency	Day	31% 6% 10% 22% 21% 11%	104539
	Night	29% 6% 11% 24% 21% 10%	102730
Seeing	Day	12% 19% 33% 24% 10% 2	14673
	Night	8% 8% 27% 37% 16% 3	24291

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 11% 5% 11% 5% 6% 5% 5% 8% 8% 35%	2539
	11th to 20th	Day	1 13% 4 11% 6% 4 4 3 5% 8% 41%	2540
	21st to end	Day	3 17% 4 8% 4 4 3 3 5% 7% 39%	2840
February	1st to 10th	Day	3 10% 4 7% 4 3 4 5% 5% 8% 46%	1710
	11th to 20th	Day	3 12% 4 8% 7% 6% 5% 5% 6% 7% 37%	1802
	21st to end	Day	3 16% 4 13% 5% 5% 5% 4 5% 7% 33%	1570
March	1st to 10th	Day	2 12% 6% 13% 6% 5% 4 4 6% 7% 36%	3138
	11th to 20th	Day	3 12% 3 7% 4 3 4 3 4 5% 52%	3485
	21st to end	Day	5% 17% 4 11% 8% 6% 6% 5% 7% 7% 24%	3825
April	1st to 10th	Day	5% 13% 4 11% 7% 5% 5% 4 6% 7% 34%	2268
	11th to 20th	Day	4 11% 4 9% 6% 5% 5% 4 5% 8% 40%	2377
	21st to end	Day	6% 12% 4 8% 5% 4 4 4 6% 8% 39%	2470
May	1st to 10th	Day	6% 11% 4 9% 6% 6% 5% 4 7% 7% 37%	4110
	11th to 20th	Day	5% 6% 2 6% 4 4 4 4 5% 6% 53%	4071
	21st to end	Day	6% 11% 3 8% 5% 5% 5% 4 6% 6% 41%	4722
June	1st to 10th	Day	9% 7% 3 7% 5% 4 5% 5% 7% 9% 39%	2717
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 3 6% 7% 51%	2850
	21st to end	Day	2 2 1 4 3 4 3 4 5% 6% 65%	2688
July	1st to 10th	Day	1 2 1 3 2 2 3 3 4 5% 74%	4420
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 7% 66%	4420
	21st to end	Day	3 3 1 4 3 4 4 3 6% 7% 61%	4740
August	1st to 10th	Day	3 3 1 5% 4 4 5% 4 7% 8% 56%	4092
	11th to 20th	Day	1 1 1 3 2 3 4 4 5% 6% 71%	4028
	21st to end	Day	2 3 1 4 3 3 3 2 3 5% 69%	4406
September	1st to 10th	Day	3 3 2 3 2 3 4 2 4 6% 68%	2218
	11th to 20th	Day	7% 5% 1 5% 4 3 3 3 5% 7% 57%	2090
	21st to end	Day	8% 4 1 4 3 2 3 3 5% 5% 63%	2090
October	1st to 10th	Day	4 5% 2 3 3 3 4 3 4 4 66%	3473
	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% 11% 2 6% 4 3 5% 4 5% 8% 45%	1710
	11th to 20th	Day	4 8% 2 5% 4 5% 5% 4 9% 8% 45%	1710
	21st to end	Day	2 9% 3 7% 3 4 4 4 5% 8% 50%	1623
December	1st to 10th	Day	4 12% 3 6% 6% 4 4 5% 5% 6% 46%	1430
	11th to 20th	Day	3 17% 4 7% 5% 5% 4 4 6% 9% 35%	1685
	21st to end	Day	3 12% 2 7% 4 5% 4 3 6% 8% 45%	2739
January	1st to 10th	Night	2 7% 3 10% 6% 5% 5% 5% 8% 9% 41%	4406
	11th to 20th	Night	3 12% 4 12% 4 3 3 3 5% 7% 44%	4420
	21st to end	Night	2 18% 4 8% 4 4 4 3 4 6% 42%	4803
February	1st to 10th	Night	3 9% 3 8% 4 5% 6% 5% 7% 9% 43%	2470
	11th to 20th	Night	2 11% 4 7% 4 4 5% 4 5% 9% 47%	2263
	21st to end	Night	3 12% 3 11% 5% 4 4 4 5% 7% 42%	1884
March	1st to 10th	Night	2 14% 5% 10% 4 3 3 4 5% 6% 43%	3736
	11th to 20th	Night	3 10% 2 5% 3 3 3 3 5% 5% 58%	3495
	21st to end	Night	3 12% 3 6% 5% 5% 5% 5% 8% 10% 38%	3828
April	1st to 10th	Night	4 9% 4 6% 3 4 5% 4 6% 9% 46%	1910
	11th to 20th	Night	4 8% 3 6% 4 4 5% 4 7% 8% 49%	1750
	21st to end	Night	4 7% 2 5% 4 4 4 5% 6% 9% 51%	1710
May	1st to 10th	Night	5% 8% 3 6% 4 4 4 3 4 7% 52%	2860
	11th to 20th	Night	3 3 1 3 3 3 4 3 7% 8% 60%	2834
	21st to end	Night	5% 5% 2 5% 3 4 4 4 8% 9% 52%	2838
June	1st to 10th	Night	6% 3 2 5% 4 5% 5% 5% 7% 9% 49%	1454
	11th to 20th	Night	7% 4 1 4 4 4 3 3 5% 6% 59%	1330
	21st to end	Night	2 2 1 2 3 3 3 2 6% 7% 70%	1480
July	1st to 10th	Night	1 1 1 1 2 2 2 2 3 4 81%	2540
	11th to 20th	Night	1 1 1 3 2 3 4 3 4 6% 73%	2540
	21st to end	Night	1 2 1 3 3 3 3 3 5% 7% 68%	2812
August	1st to 10th	Night	2 4 1 5% 4 4 5% 4 6% 7% 60%	2847
	11th to 20th	Night	2 1 2 2 2 3 3 4 6% 75%	2811
	21st to end	Night	2 1 1 2 2 3 3 3 4 5% 74%	3263
September	1st to 10th	Night	4 2 1 2 2 3 2 2 3 6% 73%	1962
	11th to 20th	Night	5% 3 1 4 2 3 3 3 5% 6% 64%	2090
	21st to end	Night	6% 4 1 3 3 2 2 2 3 5% 68%	2090
October	1st to 10th	Night	4 2 1 2 2 2 2 2 4 5% 75%	3504
	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% 49%	2469
	11th to 20th	Night	4 9% 2 4 3 4 4 5% 9% 8% 48%	2470
	21st to end	Night	2 8% 2 6% 4 4 4 4 6% 7% 52%	2533
December	1st to 10th	Night	4 8% 2 6% 5% 4 5% 5% 6% 9% 46%	2748
	11th to 20th	Night	4 14% 4 9% 5% 5% 4 4 5% 8% 37%	3506
	21st to end	Night	3 11% 3 8% 5% 4 5% 4 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	42% 10% 14% 21% 12% 1	2539
	11th to 20th	Day	41% 7% 14% 24% 8% 5%	2540
	21st to end	Day	43% 6% 16% 24% 8% 2	2840
February	1st to 10th	Day	36% 9% 19% 24% 9% 3	1710
	11th to 20th	Day	44% 6% 16% 19% 11% 3	1812
	21st to end	Day	47% 10% 12% 19% 10% 2	1570
March	1st to 10th	Day	44% 9% 11% 19% 15% 2	3138
	11th to 20th	Day	32% 7% 12% 30% 16% 2	3485
	21st to end	Day	52% 12% 13% 17% 6% 1	3825
April	1st to 10th	Day	47% 7% 14% 18% 12% 2	2268
	11th to 20th	Day	41% 7% 13% 23% 15% 2	2380
	21st to end	Day	40% 7% 14% 26% 13% 1	2470
May	1st to 10th	Day	40% 10% 8% 24% 14% 3	4110
	11th to 20th	Day	29% 7% 8% 29% 17% 9%	4074
	21st to end	Day	37% 8% 8% 30% 14% 3	4722
June	1st to 10th	Day	37% 8% 13% 27% 13% 2	2717
	11th to 20th	Day	30% 6% 9% 21% 25% 9%	2850
	21st to end	Day	19% 4 6% 22% 40% 10%	2688
July	1st to 10th	Day	11% 3 4 12% 21% 49%	4351
	11th to 20th	Day	15% 2 5% 10% 24% 44%	4345
	21st to end	Day	19% 4 5% 12% 33% 27%	4590
August	1st to 10th	Day	23% 3 7% 14% 33% 20%	4078
	11th to 20th	Day	13% 3 5% 19% 41% 19%	4067
	21st to end	Day	19% 3 4 21% 32% 20%	4405
September	1st to 10th	Day	18% 4 5% 19% 34% 20%	2218
	11th to 20th	Day	26% 5% 8% 24% 25% 11%	2090
	21st to end	Day	23% 4 8% 29% 28% 8%	2090
October	1st to 10th	Day	23% 3 8% 21% 34% 11%	3473
	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% 20% 19% 3	1710
	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	37% 10% 12% 26% 13% 1	4406
	11th to 20th	Night	42% 6% 13% 18% 16% 5%	4420
	21st to end	Night	42% 6% 14% 23% 12% 2	4803
February	1st to 10th	Night	36% 8% 19% 23% 11% 3	2470
	11th to 20th	Night	36% 6% 16% 25% 15% 3	2264
	21st to end	Night	40% 7% 14% 24% 11% 4	1884
March	1st to 10th	Night	40% 7% 11% 19% 19% 4	3736
	11th to 20th	Night	26% 4 13% 29% 25% 2	3495
	21st to end	Night	37% 8% 17% 29% 8% 1	3828
April	1st to 10th	Night	33% 8% 14% 27% 15% 3	1910
	11th to 20th	Night	31% 7% 14% 28% 18% 2	1750
	21st to end	Night	29% 4 18% 32% 16%	1710
May	1st to 10th	Night	29% 7% 8% 33% 17% 6%	2860
	11th to 20th	Night	18% 7% 10% 36% 23% 5%	2835
	21st to end	Night	26% 7% 11% 36% 18% 3	2838
June	1st to 10th	Night	30% 6% 17% 32% 15% 1	1454
	11th to 20th	Night	24% 6% 9% 24% 28% 9%	1330
	21st to end	Night	15% 4 6% 21% 36% 17%	1480
July	1st to 10th	Night	10% 2 3 11% 21% 53%	2500
	11th to 20th	Night	13% 2 4 10% 21% 50%	2492
	21st to end	Night	17% 3 3 13% 34% 30%	2724
August	1st to 10th	Night	23% 3 7% 12% 31% 25%	2838
	11th to 20th	Night	12% 4 4 18% 37% 25%	2838
	21st to end	Night	13% 3 5% 19% 37% 23%	3263
September	1st to 10th	Night	15% 3 4 18% 37% 23%	1962
	11th to 20th	Night	21% 4 8% 27% 26% 14%	2090
	21st to end	Night	21% 3 7% 28% 30% 11%	2090
October	1st to 10th	Night	15% 2 7% 24% 37% 15%	3504
	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	32% 6% 15% 23% 21% 4	2469
	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	18% 14% 26% 27% 11% 3	180
	11th to 20th	Day	10% 19% 34% 21% 11% 5%	180
	21st to end	Day	10% 17% 37% 20% 13% 3	213
February	1st to 10th	Day	19% 23% 35% 15% 7% 1	270
	11th to 20th	Day	14% 27% 36% 14% 7% 1	407
	21st to end	Day	16% 22% 38% 19% 5% 1	382
March	1st to 10th	Day	15% 25% 40% 16% 3	460
	11th to 20th	Day	15% 22% 32% 23% 7% 1	460
	21st to end	Day	16% 26% 34% 20% 4	506
April	1st to 10th	Day	19% 23% 30% 20% 7% 1	460
	11th to 20th	Day	15% 30% 31% 18% 3 2	452
	21st to end	Day	15% 24% 32% 19% 10% 1	460
May	1st to 10th	Day	14% 24% 30% 22% 10% 1	463
	11th to 20th	Day	20% 19% 28% 22% 9% 2	488
	21st to end	Day	14% 17% 29% 23% 12% 4	529
June	1st to 10th	Day	10% 20% 29% 26% 12% 3	547
	11th to 20th	Day	16% 22% 29% 20% 11% 2	680
	21st to end	Day	7% 17% 36% 27% 11% 2	518
July	1st to 10th	Day	5% 19% 37% 27% 11% 2	486
	11th to 20th	Day	4 18% 42% 28% 8% 1	484
	21st to end	Day	4 12% 41% 27% 14% 2	531
August	1st to 10th	Day	7% 15% 34% 29% 14% 2	487
	11th to 20th	Day	2 14% 33% 31% 16% 3	477
	21st to end	Day	8% 17% 32% 28% 12% 3	539
September	1st to 10th	Day	6% 13% 33% 31% 13% 4	490
	11th to 20th	Day	13% 14% 30% 28% 12% 2	490
	21st to end	Day	10% 15% 32% 28% 12% 2	490
October	1st to 10th	Day	12% 16% 30% 27% 14% 2	486
	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	16% 20% 33% 20% 10% 1	282
	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% 10% 29% 36% 15% 3	760
	11th to 20th	Night	9% 11% 28% 34% 14% 4	760
	21st to end	Night	7% 8% 32% 35% 16% 2	836
February	1st to 10th	Night	10% 12% 36% 31% 10% 2	760
	11th to 20th	Night	10% 10% 34% 33% 11% 2	744
	21st to end	Night	10% 10% 32% 34% 12% 2	628
March	1st to 10th	Night	10% 10% 32% 36% 10% 3	760
	11th to 20th	Night	12% 11% 26% 37% 13% 2	760
	21st to end	Night	11% 13% 28% 37% 11% 1	836
April	1st to 10th	Night	8% 13% 27% 36% 12% 3	760
	11th to 20th	Night	7% 12% 36% 32% 10% 2	622
	21st to end	Night	7% 11% 30% 35% 15% 2	570
May	1st to 10th	Night	7% 10% 31% 32% 17% 2	570
	11th to 20th	Night	7% 7% 30% 30% 22% 4	561
	21st to end	Night	11% 6% 24% 33% 20% 5%	462
June	1st to 10th	Night	9% 6% 23% 38% 21% 3	380
	11th to 20th	Night	10% 6% 27% 40% 16% 1	380
	21st to end	Night	2 1 21% 48% 24% 4	380
July	1st to 10th	Night	2 22% 44% 28% 5%	370
	11th to 20th	Night	1 2 25% 48% 23% 1	368
	21st to end	Night	2 2 19% 43% 30% 5%	443
August	1st to 10th	Night	4 2 18% 46% 26% 4	567
	11th to 20th	Night	2 2 18% 46% 29% 3	564
	21st to end	Night	3 3 20% 46% 24% 4	692
September	1st to 10th	Night	5% 2 17% 43% 27% 6%	760
	11th to 20th	Night	6% 3 16% 41% 27% 7%	760
	21st to end	Night	9% 3 22% 35% 22% 9%	760
October	1st to 10th	Night	7% 5% 24% 40% 17% 6%	760
	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	10% 9% 28% 36% 13% 3	760
	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

Page generated at 2024-11-03 00:11:18. Version ac07

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