Mountain Home
Clear Sky Chart
History

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

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	12% 6% 2 6% 4 4 4 4 5% 7% 45%	131838
	Night	12% 6% 2 6% 4 3 4 3 5% 7% 49%	131556
Transparency	Day	37% 5% 10% 25% 19% 4	135445
	Night	35% 4 10% 25% 20% 5%	136026
Seeing	Day	16% 11% 25% 25% 18% 5%	17551
	Night	16% 9% 26% 31% 16% 2	27417

By Month

Percentage Cloud Cover SE (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	15% 9% 3 6% 4 4 3 3 4 5% 45%	5289
	11th to 20th	Day	7% 7% 2 6% 4 3 3 3 4 5% 55%	5310
	21st to end	Day	18% 7% 3 5% 3 3 3 2 3 5% 48%	5812
February	1st to 10th	Day	18% 9% 3 6% 5% 3 3 3 3 5% 42%	1890
	11th to 20th	Day	16% 7% 2 7% 3 3 4 4 5% 5% 43%	1953
	21st to end	Day	15% 10% 3 5% 5% 3 5% 3 5% 5% 41%	1748
March	1st to 10th	Day	16% 10% 2 6% 4 3 3 2 4 5% 44%	5046
	11th to 20th	Day	10% 4 2 5% 3 3 3 3 5% 7% 54%	5090
	21st to end	Day	14% 7% 3 7% 4 4 4 3 6% 8% 39%	5620
April	1st to 10th	Day	12% 6% 3 6% 5% 3 4 4 5% 6% 46%	2520
	11th to 20th	Day	15% 6% 3 7% 4 5% 4 4 5% 6% 41%	2494
	21st to end	Day	17% 9% 3 7% 4 4 4 4 4 6% 37%	2520
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 7% 8% 35%	5613
	11th to 20th	Day	12% 7% 3 8% 6% 5% 4 4 5% 7% 39%	5992
	21st to end	Day	19% 7% 3 7% 5% 4 5% 4 5% 7% 36%	6939
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 6% 9% 44%	2801
	11th to 20th	Day	6% 4 1 4 5% 5% 6% 5% 8% 11% 46%	2800
	21st to end	Day	4 3 1 5% 5% 5% 5% 5% 7% 10% 51%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	6022
	11th to 20th	Day	4 3 1 5% 5% 5% 5% 5% 7% 12% 47%	5900
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 8% 11% 42%	6422
August	1st to 10th	Day	4 3 1 4 3 4 4 3 5% 9% 60%	4234
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 7% 9% 44%	3925
	21st to end	Day	5% 3 2 5% 4 4 5% 5% 6% 8% 54%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 7% 48%	2400
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 45%	2400
	21st to end	Day	10% 4 2 5% 4 3 5% 3 5% 7% 53%	2093
October	1st to 10th	Day	8% 5% 2 5% 3 4 3 3 5% 6% 57%	2000
	11th to 20th	Day	14% 4 1 5% 2 3 2 2 3 7% 56%	2000
	21st to end	Day	19% 7% 2 5% 3 2 3 2 4 6% 48%	2200
November	1st to 10th	Day	12% 5% 2 4 3 3 2 3 3 5% 57%	2058
	11th to 20th	Day	11% 6% 2 6% 4 4 3 3 4 5% 52%	1921
	21st to end	Day	19% 7% 2 5% 3 3 3 2 4 5% 47%	1772
December	1st to 10th	Day	12% 7% 2 5% 4 4 3 2 4 5% 53%	2690
	11th to 20th	Day	14% 8% 3 7% 4 3 3 3 4 5% 45%	3088
	21st to end	Day	17% 15% 3 8% 4 4 4 3 4 5% 31%	4164
January	1st to 10th	Night	14% 7% 3 7% 4 4 4 3 5% 6% 44%	7634
	11th to 20th	Night	8% 5% 2 7% 3 3 3 3 4 5% 56%	7680
	21st to end	Night	18% 9% 3 6% 3 4 3 2 4 5% 44%	8402
February	1st to 10th	Night	16% 9% 2 6% 4 3 3 3 5% 6% 42%	2730
	11th to 20th	Night	16% 7% 3 7% 4 3 3 3 4 6% 44%	2553
	21st to end	Night	15% 8% 2 4 4 4 3 2 4 5% 49%	2076
March	1st to 10th	Night	18% 9% 2 6% 3 3 4 2 4 5% 43%	5029
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 4 6% 53%	5090
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 7% 44%	5549
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 4 6% 51%	2100
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 5% 6% 48%	2075
	21st to end	Night	17% 7% 2 6% 4 4 4 4 6% 6% 43%	2100
May	1st to 10th	Night	16% 7% 3 5% 4 3 5% 4 5% 7% 42%	4501
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 6% 8% 39%	4143
	21st to end	Night	18% 7% 3 7% 5% 4 4 3 5% 7% 38%	4176
June	1st to 10th	Night	8% 3 2 5% 4 3 3 4 6% 10% 51%	1600
	11th to 20th	Night	4 3 1 4 4 3 4 3 6% 11% 57%	1600
	21st to end	Night	3 3 2 3 4 3 4 3 6% 9% 60%	1600
July	1st to 10th	Night	7% 4 2 6% 5% 6% 5% 5% 7% 9% 45%	3936
	11th to 20th	Night	3 3 2 4 4 4 4 4 6% 9% 57%	4077
	21st to end	Night	4 4 2 5% 5% 4 4 4 7% 10% 49%	4449
August	1st to 10th	Night	2 3 1 3 3 3 4 4 5% 9% 64%	2926
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 6% 8% 52%	3126
	21st to end	Night	4 3 1 4 2 3 4 4 5% 8% 61%	3586
September	1st to 10th	Night	8% 4 2 4 2 3 3 4 6% 8% 55%	2000
	11th to 20th	Night	10% 5% 2 5% 4 5% 4 4 6% 7% 49%	2000
	21st to end	Night	7% 5% 2 5% 3 3 3 3 4 6% 58%	2280
October	1st to 10th	Night	7% 4 1 4 3 2 3 3 5% 6% 62%	2400
	11th to 20th	Night	12% 4 1 4 2 2 4 2 4 5% 59%	2400
	21st to end	Night	18% 6% 2 4 3 3 3 2 3 5% 51%	2640
November	1st to 10th	Night	12% 5% 2 4 3 2 3 3 4 5% 58%	2460
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 4 5% 57%	2695
	21st to end	Night	15% 7% 2 4 3 3 3 3 4 6% 48%	2846
December	1st to 10th	Night	12% 6% 2 5% 4 2 3 2 4 7% 52%	4720
	11th to 20th	Night	17% 8% 2 6% 3 3 3 2 3 4 47%	5339
	21st to end	Night	22% 11% 3 7% 4 4 4 3 4 5% 33%	7038

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	43% 3 8% 28% 16% 2	5290
	11th to 20th	Day	31% 3 7% 27% 26% 5%	5310
	21st to end	Day	41% 2 7% 20% 22% 7%	5812
February	1st to 10th	Day	46% 4 9% 24% 14% 3	1890
	11th to 20th	Day	43% 4 9% 23% 17% 4	1962
	21st to end	Day	45% 4 7% 20% 16% 8%	1748
March	1st to 10th	Day	44% 3 6% 20% 14% 12%	5046
	11th to 20th	Day	31% 3 7% 23% 24% 12%	5090
	21st to end	Day	42% 4 10% 28% 15% 1	5622
April	1st to 10th	Day	39% 5% 9% 25% 20% 3	2520
	11th to 20th	Day	42% 5% 12% 21% 15% 5%	2494
	21st to end	Day	47% 5% 10% 22% 14% 2	2520
May	1st to 10th	Day	45% 6% 12% 23% 13% 1	5648
	11th to 20th	Day	44% 6% 12% 23% 13% 2	5996
	21st to end	Day	48% 6% 9% 19% 15% 2	6953
June	1st to 10th	Day	35% 8% 15% 24% 17% 1	2801
	11th to 20th	Day	30% 7% 14% 28% 17% 3	2800
	21st to end	Day	26% 7% 16% 27% 19% 4	2800
July	1st to 10th	Day	35% 7% 13% 25% 17% 3	5958
	11th to 20th	Day	27% 8% 15% 31% 16% 2	5831
	21st to end	Day	33% 8% 16% 30% 13% 1	6240
August	1st to 10th	Day	21% 6% 17% 32% 21% 3	4220
	11th to 20th	Day	36% 6% 13% 31% 13% 1	3962
	21st to end	Day	26% 6% 13% 35% 16% 3	4311
September	1st to 10th	Day	34% 6% 10% 25% 18% 6%	2400
	11th to 20th	Day	36% 7% 8% 23% 23% 3	2400
	21st to end	Day	31% 6% 7% 25% 28% 3	2093
October	1st to 10th	Day	17% 3 5% 17% 45% 13%	3260
	11th to 20th	Day	20% 2 4 23% 39% 11%	3240
	21st to end	Day	31% 3 7% 32% 23% 4	3538
November	1st to 10th	Day	31% 3 8% 27% 24% 7%	2058
	11th to 20th	Day	34% 4 6% 25% 22% 8%	1921
	21st to end	Day	40% 3 9% 21% 23% 3	1772
December	1st to 10th	Day	35% 3 8% 31% 21% 2	2690
	11th to 20th	Day	41% 4 7% 26% 21% 1	3085
	21st to end	Day	53% 4 8% 22% 9% 3	4164
January	1st to 10th	Night	41% 4 10% 30% 13% 2	7635
	11th to 20th	Night	31% 3 8% 20% 33% 5%	7680
	21st to end	Night	45% 2 8% 20% 21% 4	8402
February	1st to 10th	Night	43% 4 9% 25% 15% 3	2730
	11th to 20th	Night	42% 4 9% 23% 19% 4	2554
	21st to end	Night	37% 4 9% 21% 20% 8%	2076
March	1st to 10th	Night	45% 3 7% 16% 17% 11%	5029
	11th to 20th	Night	34% 3 7% 26% 19% 11%	5090
	21st to end	Night	38% 4 10% 30% 17% 1	5549
April	1st to 10th	Night	35% 4 11% 23% 21% 6%	2100
	11th to 20th	Night	36% 4 10% 25% 19% 7%	2075
	21st to end	Night	40% 5% 10% 26% 15% 3	2100
May	1st to 10th	Night	42% 6% 14% 25% 12% 2	4531
	11th to 20th	Night	43% 5% 13% 24% 11% 4	4144
	21st to end	Night	46% 6% 11% 22% 12% 3	4184
June	1st to 10th	Night	27% 6% 13% 32% 20% 2	1600
	11th to 20th	Night	22% 5% 15% 35% 20% 4	1600
	21st to end	Night	20% 6% 16% 30% 21% 7%	1600
July	1st to 10th	Night	33% 8% 16% 22% 20% 2	3893
	11th to 20th	Night	23% 8% 17% 34% 17% 2	4026
	21st to end	Night	28% 7% 18% 31% 15%	4320
August	1st to 10th	Night	17% 6% 16% 38% 22% 2	2916
	11th to 20th	Night	29% 6% 18% 30% 16% 1	3155
	21st to end	Night	21% 5% 14% 34% 22% 3	3586
September	1st to 10th	Night	27% 6% 11% 30% 19% 8%	2000
	11th to 20th	Night	33% 6% 11% 23% 23% 5%	2000
	21st to end	Night	28% 4 9% 22% 32% 5%	2280
October	1st to 10th	Night	14% 3 7% 15% 41% 21%	3920
	11th to 20th	Night	19% 2 6% 17% 38% 19%	3899
	21st to end	Night	29% 3 6% 27% 28% 6%	4252
November	1st to 10th	Night	30% 3 9% 25% 26% 7%	2460
	11th to 20th	Night	30% 3 8% 26% 26% 8%	2695
	21st to end	Night	38% 4 8% 24% 23% 4	2846
December	1st to 10th	Night	34% 3 10% 35% 17% 2	4720
	11th to 20th	Night	42% 3 7% 23% 21% 4	5341
	21st to end	Night	53% 5% 9% 22% 9% 2	7038

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	29% 17% 33% 17% 4 1	330
	11th to 20th	Day	26% 20% 37% 14% 2	330
	21st to end	Day	24% 23% 35% 16% 2	363
February	1st to 10th	Day	26% 18% 37% 14% 5%	330
	11th to 20th	Day	30% 23% 32% 11% 4 1	330
	21st to end	Day	32% 23% 29% 12% 3	273
March	1st to 10th	Day	30% 20% 32% 15% 3	330
	11th to 20th	Day	32% 20% 32% 14% 2	330
	21st to end	Day	26% 23% 38% 10% 2	375
April	1st to 10th	Day	23% 18% 30% 21% 8% 1	540
	11th to 20th	Day	23% 19% 33% 19% 6% 1	532
	21st to end	Day	23% 15% 35% 20% 6% 1	540
May	1st to 10th	Day	19% 18% 32% 22% 9%	579
	11th to 20th	Day	17% 12% 32% 22% 14% 3	775
	21st to end	Day	14% 9% 33% 26% 15% 4	844
June	1st to 10th	Day	10% 5% 23% 28% 26% 8%	731
	11th to 20th	Day	7% 2 19% 37% 28% 5%	730
	21st to end	Day	5% 4 23% 35% 27% 7%	730
July	1st to 10th	Day	8% 2 14% 32% 33% 10%	721
	11th to 20th	Day	4 3 14% 35% 33% 13%	718
	21st to end	Day	7% 1 13% 31% 33% 15%	794
August	1st to 10th	Day	7% 3 13% 38% 32% 7%	726
	11th to 20th	Day	11% 3 12% 32% 32% 10%	571
	21st to end	Day	10% 2 10% 29% 34% 15%	583
September	1st to 10th	Day	11% 3 11% 32% 33% 10%	530
	11th to 20th	Day	12% 3 10% 31% 30% 14%	530
	21st to end	Day	11% 7% 21% 30% 24% 7%	350
October	1st to 10th	Day	9% 7% 25% 33% 21% 5%	330
	11th to 20th	Day	15% 15% 33% 24% 11% 2	330
	21st to end	Day	32% 14% 27% 20% 6% 1	363
November	1st to 10th	Day	17% 14% 32% 22% 11% 3	330
	11th to 20th	Day	21% 13% 35% 20% 10% 1	330
	21st to end	Day	30% 15% 27% 18% 8% 2	330
December	1st to 10th	Day	22% 24% 30% 14% 8% 3	330
	11th to 20th	Day	25% 21% 29% 18% 7%	330
	21st to end	Day	27% 20% 33% 15% 4	363
January	1st to 10th	Night	22% 16% 33% 25% 4	1050
	11th to 20th	Night	22% 17% 34% 23% 3 1	1050
	21st to end	Night	21% 15% 37% 25% 2	1155
February	1st to 10th	Night	22% 12% 37% 25% 4	1050
	11th to 20th	Night	24% 16% 37% 23% 1	919
	21st to end	Night	23% 18% 35% 22% 2	692
March	1st to 10th	Night	23% 14% 33% 27% 3	630
	11th to 20th	Night	23% 14% 32% 27% 4	630
	21st to end	Night	21% 14% 35% 26% 4	693
April	1st to 10th	Night	15% 15% 37% 28% 5%	630
	11th to 20th	Night	16% 17% 31% 29% 7%	623
	21st to end	Night	19% 10% 36% 27% 8% 1	630
May	1st to 10th	Night	15% 8% 30% 38% 8%	630
	11th to 20th	Night	17% 7% 27% 29% 18% 2	621
	21st to end	Night	13% 8% 22% 34% 20% 4	683
June	1st to 10th	Night	10% 3 15% 39% 32% 2	600
	11th to 20th	Night	5% 2 14% 46% 30% 3	600
	21st to end	Night	5% 1 17% 41% 33% 3	600
July	1st to 10th	Night	6% 2 10% 36% 39% 8%	585
	11th to 20th	Night	4 1 9% 38% 42% 7%	582
	21st to end	Night	5% 1 8% 37% 41% 8%	657
August	1st to 10th	Night	5% 2 9% 39% 39% 6%	597
	11th to 20th	Night	6% 1 12% 39% 37% 4	594
	21st to end	Night	8% 1 7% 35% 40% 7%	660
September	1st to 10th	Night	9% 2 11% 36% 39% 3	600
	11th to 20th	Night	12% 1 9% 37% 35% 7%	600
	21st to end	Night	9% 5% 16% 36% 31% 3	705
October	1st to 10th	Night	9% 3 18% 39% 28% 3	800
	11th to 20th	Night	14% 8% 28% 33% 17% 1	800
	21st to end	Night	23% 10% 27% 30% 10%	880
November	1st to 10th	Night	14% 8% 32% 32% 13%	820
	11th to 20th	Night	17% 10% 29% 35% 9%	840
	21st to end	Night	21% 12% 28% 29% 10%	956
December	1st to 10th	Night	22% 11% 31% 30% 6%	1050
	11th to 20th	Night	24% 13% 28% 30% 6%	1050
	21st to end	Night	24% 16% 29% 27% 4	1155

Page generated at 2026-05-29 00:53:28. Version ac07

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