Star Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Valley clear sky chart from 2005-11-06 to 2026-07-16.

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	6% 12% 3 7% 4 4 4 3 5% 6% 46%	147957
	Night	7% 13% 4 7% 3 3 3 3 5% 6% 45%	142261
Transparency	Day	38% 5% 10% 20% 18% 8%	142692
	Night	40% 5% 11% 21% 16% 6%	138546
Seeing	Day	15% 14% 27% 26% 14% 4	17926
	Night	15% 6% 21% 39% 18% 2	27479

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	7% 30% 9% 13% 4 3 4 3 5% 4 19%	5052
	11th to 20th	Day	5% 13% 6% 14% 4 3 3 2 3 5% 42%	5340
	21st to end	Day	4 19% 5% 9% 4 4 4 3 5% 5% 38%	5844
February	1st to 10th	Day	11% 26% 7% 12% 4 4 4 2 4 5% 21%	1890
	11th to 20th	Day	8% 23% 7% 13% 6% 4 3 3 4 4 24%	1845
	21st to end	Day	7% 22% 8% 17% 4 4 4 3 3 4 23%	1693
March	1st to 10th	Day	6% 22% 6% 13% 4 3 3 2 3 4 33%	4972
	11th to 20th	Day	7% 20% 6% 7% 4 3 3 2 4 5% 38%	5110
	21st to end	Day	8% 28% 6% 10% 5% 5% 5% 4 5% 5% 19%	5607
April	1st to 10th	Day	11% 17% 5% 9% 4 4 4 4 5% 6% 31%	2400
	11th to 20th	Day	9% 15% 5% 10% 6% 5% 5% 3 4 5% 32%	2644
	21st to end	Day	9% 17% 4 10% 5% 5% 4 4 5% 6% 30%	2730
May	1st to 10th	Day	7% 10% 2 6% 4 3 4 3 5% 7% 48%	7626
	11th to 20th	Day	7% 10% 2 6% 5% 5% 4 4 6% 8% 43%	7673
	21st to end	Day	9% 9% 2 7% 4 5% 5% 4 6% 7% 43%	9026
June	1st to 10th	Day	9% 7% 2 6% 4 4 4 4 7% 7% 46%	2940
	11th to 20th	Day	8% 6% 2 6% 3 4 5% 4 5% 6% 51%	3091
	21st to end	Day	3 2 1 4 3 3 4 3 5% 7% 64%	3150
July	1st to 10th	Day	2 2 1 3 2 2 3 3 4 6% 72%	6929
	11th to 20th	Day	1 2 1 3 3 3 4 3 4 6% 70%	6036
	21st to end	Day	3 3 1 4 3 3 4 4 5% 7% 63%	6401
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 7% 60%	5779
	11th to 20th	Day	2 2 1 4 3 3 4 3 5% 7% 66%	5798
	21st to end	Day	6% 4 2 5% 3 4 4 3 4 6% 60%	6393
September	1st to 10th	Day	4 4 2 4 3 2 4 3 5% 7% 63%	2360
	11th to 20th	Day	7% 5% 2 5% 3 3 4 3 5% 7% 57%	2200
	21st to end	Day	9% 4 2 5% 3 2 3 2 4 5% 62%	2200
October	1st to 10th	Day	7% 6% 2 5% 3 3 3 2 3 3 63%	3346
	11th to 20th	Day	8% 8% 2 5% 3 3 4 3 3 4 56%	3250
	21st to end	Day	8% 14% 3 6% 3 4 3 4 6% 7% 43%	3501
November	1st to 10th	Day	14% 13% 6% 7% 3 4 3 2 4 6% 39%	1854
	11th to 20th	Day	12% 20% 4 8% 3 3 3 3 4 6% 35%	1699
	21st to end	Day	8% 18% 7% 8% 3 3 3 3 4 5% 38%	1680
December	1st to 10th	Day	7% 16% 4 10% 5% 3 2 1 3 4 44%	2700
	11th to 20th	Day	11% 24% 8% 9% 4 3 3 3 4 6% 25%	3106
	21st to end	Day	10% 19% 7% 12% 5% 4 4 4 6% 7% 22%	4092
January	1st to 10th	Night	7% 26% 9% 15% 5% 4 3 2 5% 5% 19%	7924
	11th to 20th	Night	4 17% 5% 15% 6% 3 3 2 4 4 38%	7650
	21st to end	Night	5% 21% 5% 8% 3 3 3 3 4 6% 38%	8370
February	1st to 10th	Night	9% 24% 6% 13% 5% 3 4 3 4 5% 23%	2730
	11th to 20th	Night	9% 23% 7% 11% 5% 3 3 3 4 4 29%	2662
	21st to end	Night	8% 24% 7% 14% 4 4 4 2 4 5% 25%	2110
March	1st to 10th	Night	6% 22% 6% 12% 3 3 3 2 3 5% 35%	5142
	11th to 20th	Night	8% 17% 5% 6% 3 3 3 3 5% 7% 40%	5110
	21st to end	Night	10% 20% 5% 9% 5% 4 4 4 5% 5% 30%	5610
April	1st to 10th	Night	10% 17% 4 7% 5% 4 4 4 5% 6% 36%	2219
	11th to 20th	Night	9% 13% 4 9% 4 4 4 4 4 7% 38%	1921
	21st to end	Night	10% 11% 3 6% 3 4 3 3 5% 7% 43%	1890
May	1st to 10th	Night	8% 11% 2 4 3 4 3 2 5% 7% 51%	5321
	11th to 20th	Night	8% 7% 2 4 3 3 4 3 5% 7% 53%	5219
	21st to end	Night	8% 6% 2 4 4 4 5% 4 6% 8% 50%	5181
June	1st to 10th	Night	8% 6% 2 5% 4 4 5% 3 6% 9% 48%	1680
	11th to 20th	Night	7% 5% 2 3 3 3 3 4 6% 8% 56%	1521
	21st to end	Night	3 2 1 3 2 2 3 4 4 6% 70%	1470
July	1st to 10th	Night	1 1 1 2 2 3 3 4 5% 6% 71%	3250
	11th to 20th	Night	1 1 2 2 3 4 3 6% 6% 72%	4018
	21st to end	Night	1 1 1 3 2 3 3 4 6% 8% 69%	4472
August	1st to 10th	Night	3 3 1 4 3 4 3 3 6% 8% 63%	4033
	11th to 20th	Night	2 2 1 3 2 3 4 3 6% 7% 66%	4051
	21st to end	Night	6% 3 1 4 2 3 3 3 5% 6% 63%	4570
September	1st to 10th	Night	5% 2 1 5% 2 2 2 3 5% 7% 67%	2035
	11th to 20th	Night	7% 5% 1 4 3 3 3 3 5% 6% 60%	2200
	21st to end	Night	9% 4 1 3 3 2 3 3 3 5% 64%	2200
October	1st to 10th	Night	8% 4 2 3 2 2 2 2 3 5% 66%	3846
	11th to 20th	Night	11% 8% 2 4 3 3 3 3 4 5% 54%	3898
	21st to end	Night	10% 11% 2 4 2 3 3 3 5% 7% 50%	4296
November	1st to 10th	Night	13% 14% 3 7% 4 3 4 3 4 6% 39%	2665
	11th to 20th	Night	11% 15% 3 7% 3 4 5% 4 5% 5% 38%	2898
	21st to end	Night	7% 17% 5% 7% 3 4 4 3 4 6% 39%	2940
December	1st to 10th	Night	8% 15% 6% 10% 3 3 3 2 3 4 44%	4710
	11th to 20th	Night	11% 23% 7% 9% 4 4 3 2 3 5% 28%	5321
	21st to end	Night	12% 24% 6% 11% 4 3 3 3 5% 7% 21%	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	67% 5% 11% 11% 6%	5055
	11th to 20th	Day	46% 5% 18% 18% 10% 3	5340
	21st to end	Day	46% 6% 13% 21% 12% 1	5844
February	1st to 10th	Day	66% 5% 10% 13% 5% 1	1890
	11th to 20th	Day	63% 6% 10% 13% 6% 2	1854
	21st to end	Day	64% 5% 8% 14% 6% 2	1693
March	1st to 10th	Day	55% 5% 9% 17% 10% 4	4972
	11th to 20th	Day	49% 4 10% 26% 9% 1	5110
	21st to end	Day	63% 7% 12% 14% 3	5607
April	1st to 10th	Day	53% 6% 12% 19% 9% 1	2400
	11th to 20th	Day	52% 6% 10% 21% 10% 1	2647
	21st to end	Day	52% 6% 11% 22% 9%	2730
May	1st to 10th	Day	33% 5% 12% 29% 19% 2	7626
	11th to 20th	Day	36% 6% 9% 27% 18% 4	7676
	21st to end	Day	37% 6% 11% 29% 16% 1	9027
June	1st to 10th	Day	34% 7% 14% 26% 17% 2	2940
	11th to 20th	Day	32% 5% 10% 20% 24% 9%	3091
	21st to end	Day	18% 4 7% 22% 35% 14%	3150
July	1st to 10th	Day	13% 3 4 13% 32% 35%	6856
	11th to 20th	Day	15% 3 4 13% 31% 35%	5964
	21st to end	Day	19% 4 5% 13% 38% 21%	6217
August	1st to 10th	Day	22% 5% 6% 16% 31% 19%	4208
	11th to 20th	Day	20% 4 6% 20% 34% 16%	4197
	21st to end	Day	19% 3 6% 20% 30% 22%	4612
September	1st to 10th	Day	22% 4 8% 18% 30% 18%	2360
	11th to 20th	Day	26% 5% 9% 22% 28% 10%	2200
	21st to end	Day	26% 4 9% 26% 30% 6%	2200
October	1st to 10th	Day	28% 3 6% 19% 33% 11%	3346
	11th to 20th	Day	32% 4 9% 32% 16% 7%	3250
	21st to end	Day	41% 4 14% 27% 13%	3501
November	1st to 10th	Day	48% 4 14% 22% 10% 2	1854
	11th to 20th	Day	52% 5% 15% 17% 9% 1	1699
	21st to end	Day	49% 5% 15% 20% 10% 1	1680
December	1st to 10th	Day	44% 6% 22% 21% 5% 1	2700
	11th to 20th	Day	60% 5% 18% 14% 3	3104
	21st to end	Day	59% 6% 12% 14% 8% 2	4092
January	1st to 10th	Night	66% 5% 8% 15% 5%	7925
	11th to 20th	Night	51% 4 18% 20% 6% 2	7650
	21st to end	Night	46% 6% 12% 22% 13% 1	8370
February	1st to 10th	Night	64% 6% 11% 13% 5%	2730
	11th to 20th	Night	58% 5% 10% 17% 9% 1	2663
	21st to end	Night	61% 5% 11% 14% 6% 2	2110
March	1st to 10th	Night	50% 6% 9% 20% 11% 4	5142
	11th to 20th	Night	43% 7% 13% 26% 10% 1	5110
	21st to end	Night	52% 8% 17% 19% 4	5610
April	1st to 10th	Night	47% 7% 15% 17% 11% 2	2219
	11th to 20th	Night	46% 5% 14% 22% 12% 2	1921
	21st to end	Night	40% 6% 15% 28% 11%	1890
May	1st to 10th	Night	33% 5% 9% 28% 23% 2	5319
	11th to 20th	Night	28% 6% 11% 26% 23% 6%	5220
	21st to end	Night	27% 7% 13% 33% 17% 2	5182
June	1st to 10th	Night	31% 7% 15% 27% 17% 3	1680
	11th to 20th	Night	25% 5% 12% 24% 24% 10%	1521
	21st to end	Night	14% 5% 8% 22% 37% 15%	1470
July	1st to 10th	Night	13% 3 5% 15% 28% 36%	3215
	11th to 20th	Night	11% 3 4 14% 32% 36%	3967
	21st to end	Night	12% 4 6% 15% 41% 22%	4344
August	1st to 10th	Night	21% 3 7% 14% 36% 19%	2928
	11th to 20th	Night	20% 4 6% 21% 31% 17%	2928
	21st to end	Night	15% 3 6% 21% 32% 23%	3294
September	1st to 10th	Night	18% 4 8% 18% 33% 20%	2035
	11th to 20th	Night	24% 6% 10% 21% 29% 11%	2200
	21st to end	Night	24% 3 9% 27% 32% 6%	2200
October	1st to 10th	Night	22% 3 7% 24% 37% 7%	3846
	11th to 20th	Night	34% 3 8% 31% 17% 6%	3898
	21st to end	Night	35% 4 13% 32% 15% 1	4296
November	1st to 10th	Night	46% 5% 13% 23% 11% 2	2665
	11th to 20th	Night	47% 5% 17% 22% 8% 1	2898
	21st to end	Night	47% 5% 15% 21% 10% 2	2940
December	1st to 10th	Night	46% 4 22% 22% 5% 1	4710
	11th to 20th	Night	60% 5% 16% 15% 4	5322
	21st to end	Night	61% 6% 10% 15% 7% 1	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	24% 12% 22% 26% 14% 3	330
	11th to 20th	Day	17% 8% 26% 32% 15% 3	330
	21st to end	Day	14% 10% 25% 39% 10% 2	363
February	1st to 10th	Day	29% 17% 25% 20% 9% 1	330
	11th to 20th	Day	21% 19% 27% 23% 8% 2	330
	21st to end	Day	22% 23% 27% 20% 6% 1	409
March	1st to 10th	Day	25% 19% 28% 21% 6% 2	540
	11th to 20th	Day	17% 20% 31% 23% 8% 1	540
	21st to end	Day	23% 23% 31% 17% 5%	594
April	1st to 10th	Day	26% 18% 26% 20% 8% 2	540
	11th to 20th	Day	24% 24% 28% 17% 5% 2	532
	21st to end	Day	25% 18% 25% 21% 9% 3	540
May	1st to 10th	Day	15% 20% 28% 25% 10% 3	543
	11th to 20th	Day	16% 19% 27% 22% 13% 2	593
	21st to end	Day	16% 13% 22% 26% 18% 5%	844
June	1st to 10th	Day	11% 12% 28% 27% 18% 4	780
	11th to 20th	Day	12% 16% 31% 26% 13% 2	780
	21st to end	Day	5% 13% 29% 32% 18% 4	780
July	1st to 10th	Day	3 9% 27% 33% 24% 4	771
	11th to 20th	Day	3 10% 39% 29% 16% 3	579
	21st to end	Day	3 10% 32% 30% 19% 6%	575
August	1st to 10th	Day	5% 9% 36% 30% 17% 4	527
	11th to 20th	Day	3 11% 31% 30% 18% 8%	517
	21st to end	Day	7% 11% 27% 30% 18% 7%	583
September	1st to 10th	Day	4 12% 26% 31% 18% 9%	530
	11th to 20th	Day	11% 15% 27% 25% 15% 8%	530
	21st to end	Day	10% 11% 25% 28% 19% 8%	530
October	1st to 10th	Day	13% 10% 23% 28% 17% 9%	380
	11th to 20th	Day	16% 13% 18% 26% 18% 8%	330
	21st to end	Day	18% 12% 25% 27% 15% 3	363
November	1st to 10th	Day	25% 10% 23% 24% 12% 6%	330
	11th to 20th	Day	21% 10% 28% 26% 12% 3	330
	21st to end	Day	16% 10% 25% 35% 12% 4	330
December	1st to 10th	Day	23% 9% 22% 26% 16% 2	330
	11th to 20th	Day	28% 13% 24% 24% 10% 1	330
	21st to end	Day	28% 11% 26% 20% 12% 3	363
January	1st to 10th	Night	21% 9% 22% 36% 12% 1	955
	11th to 20th	Night	19% 7% 25% 34% 13% 2	840
	21st to end	Night	19% 7% 24% 38% 11% 2	924
February	1st to 10th	Night	21% 9% 27% 34% 8% 1	840
	11th to 20th	Night	18% 8% 30% 33% 9% 1	824
	21st to end	Night	18% 10% 30% 34% 8%	692
March	1st to 10th	Night	18% 9% 29% 34% 9% 1	840
	11th to 20th	Night	15% 8% 24% 39% 14% 1	840
	21st to end	Night	15% 9% 26% 38% 12% 1	924
April	1st to 10th	Night	18% 9% 23% 36% 12% 1	749
	11th to 20th	Night	15% 11% 28% 36% 10%	623
	21st to end	Night	15% 8% 22% 36% 18% 1	630
May	1st to 10th	Night	14% 8% 21% 36% 19% 1	630
	11th to 20th	Night	13% 4 21% 36% 24% 1	621
	21st to end	Night	13% 6% 18% 39% 21% 2	683
June	1st to 10th	Night	9% 7% 21% 39% 23% 1	630
	11th to 20th	Night	9% 5% 24% 43% 19%	471
	21st to end	Night	4 2 14% 49% 28% 3	420
July	1st to 10th	Night	2 1 8% 50% 38% 2	410
	11th to 20th	Night	2 2 11% 54% 31% 1	577
	21st to end	Night	2 9% 49% 38% 2	657
August	1st to 10th	Night	5% 2 9% 48% 33% 2	597
	11th to 20th	Night	3 1 10% 49% 35% 2	594
	21st to end	Night	6% 3 12% 44% 32% 3	660
September	1st to 10th	Night	6% 3 10% 44% 34% 3	635
	11th to 20th	Night	8% 2 13% 40% 32% 5%	800
	21st to end	Night	10% 2 13% 41% 29% 5%	800
October	1st to 10th	Night	15% 5% 16% 40% 22% 3	800
	11th to 20th	Night	17% 6% 17% 35% 23% 3	800
	21st to end	Night	16% 3 17% 46% 15% 2	880
November	1st to 10th	Night	19% 7% 21% 37% 15% 2	820
	11th to 20th	Night	18% 9% 25% 38% 9% 1	1008
	21st to end	Night	16% 7% 22% 39% 13% 2	1050
December	1st to 10th	Night	23% 7% 25% 34% 10%	1050
	11th to 20th	Night	22% 8% 26% 36% 7%	1050
	21st to end	Night	23% 11% 25% 30% 9% 2	1155

Page generated at 2026-07-13 01:14:52. Version ac07

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