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 2025-03-12.

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	7% 12% 4 8% 4 4 4 3 5% 6% 44%	113669
	Night	7% 14% 4 8% 4 3 3 3 5% 6% 43%	114203
Transparency	Day	40% 5% 10% 19% 17% 8%	113421
	Night	41% 5% 12% 20% 15% 6%	114040
Seeing	Day	15% 14% 27% 26% 14% 4	15998
	Night	15% 6% 20% 39% 18% 2	25777

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	5% 25% 10% 13% 4 4 3 3 6% 5% 22%	3886
	11th to 20th	Day	6% 17% 8% 19% 5% 3 3 2 3 3 30%	4100
	21st to end	Day	5% 22% 5% 9% 4 4 4 3 4 5% 35%	4510
February	1st to 10th	Day	11% 27% 7% 13% 5% 4 4 3 4 5% 20%	1800
	11th to 20th	Day	8% 24% 7% 13% 6% 4 3 4 4 4 24%	1755
	21st to end	Day	7% 23% 8% 17% 5% 4 4 3 4 4 22%	1615
March	1st to 10th	Day	6% 23% 6% 15% 5% 4 3 2 4 4 30%	3488
	11th to 20th	Day	7% 15% 5% 7% 4 4 3 3 4 5% 44%	3502
	21st to end	Day	9% 27% 7% 12% 5% 5% 5% 4 5% 5% 15%	3825
April	1st to 10th	Day	12% 18% 5% 9% 4 4 4 4 5% 6% 28%	2171
	11th to 20th	Day	10% 16% 5% 10% 6% 5% 5% 3 4 5% 31%	2389
	21st to end	Day	9% 17% 4 10% 6% 5% 4 4 5% 6% 31%	2470
May	1st to 10th	Day	11% 17% 4 9% 6% 4 5% 4 5% 6% 29%	4110
	11th to 20th	Day	5% 6% 2 6% 5% 5% 4 5% 7% 8% 47%	4120
	21st to end	Day	10% 12% 3 8% 5% 5% 5% 4 5% 6% 37%	4825
June	1st to 10th	Day	10% 7% 2 6% 4 4 4 4 7% 7% 44%	2660
	11th to 20th	Day	9% 7% 2 6% 4 4 5% 4 5% 7% 48%	2797
	21st to end	Day	3 2 1 4 3 3 4 3 5% 7% 65%	2850
July	1st to 10th	Day	2 2 1 2 2 2 2 3 3 6% 75%	4740
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 7% 67%	4170
	21st to end	Day	3 4 1 5% 3 4 4 4 5% 7% 60%	4454
August	1st to 10th	Day	3 3 1 5% 3 4 5% 4 6% 8% 57%	4092
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 6% 64%	4028
	21st to end	Day	4 3 1 3 2 3 4 3 4 6% 67%	4472
September	1st to 10th	Day	5% 4 2 5% 3 2 4 3 5% 6% 62%	2242
	11th to 20th	Day	7% 5% 2 5% 3 3 4 3 4 7% 58%	2090
	21st to end	Day	9% 4 2 4 3 2 2 2 3 5% 62%	2090
October	1st to 10th	Day	7% 6% 2 5% 3 3 3 2 4 3 63%	3244
	11th to 20th	Day	8% 8% 2 5% 3 3 3 3 3 4 57%	3150
	21st to end	Day	9% 14% 3 6% 3 4 3 4 6% 7% 42%	3392
November	1st to 10th	Day	14% 13% 6% 8% 3 3 3 2 4 5% 39%	1764
	11th to 20th	Day	12% 20% 4 8% 3 3 3 3 4 6% 35%	1618
	21st to end	Day	8% 18% 7% 8% 3 3 3 3 4 6% 38%	1600
December	1st to 10th	Day	6% 15% 4 10% 5% 3 2 1 3 4 45%	2620
	11th to 20th	Day	10% 25% 8% 9% 4 3 3 3 4 6% 25%	3026
	21st to end	Day	10% 19% 7% 12% 5% 4 4 4 6% 7% 22%	4004
January	1st to 10th	Night	5% 21% 9% 16% 5% 3 3 2 5% 6% 24%	6120
	11th to 20th	Night	6% 22% 7% 19% 7% 3 2 2 3 4 25%	5880
	21st to end	Night	6% 23% 5% 8% 3 3 3 3 4 5% 38%	6468
February	1st to 10th	Night	9% 25% 6% 13% 5% 4 4 3 4 4 22%	2600
	11th to 20th	Night	9% 23% 7% 11% 5% 3 3 3 4 4 29%	2532
	21st to end	Night	7% 25% 7% 14% 4 4 4 2 4 4 25%	2013
March	1st to 10th	Night	7% 21% 6% 13% 4 3 4 3 4 5% 30%	3606
	11th to 20th	Night	4 13% 4 6% 4 3 3 3 5% 8% 46%	3506
	21st to end	Night	9% 21% 5% 10% 5% 4 4 4 5% 5% 27%	3828
April	1st to 10th	Night	10% 17% 4 7% 5% 4 4 4 5% 6% 35%	2008
	11th to 20th	Night	9% 12% 4 9% 4 4 4 4 4 6% 38%	1737
	21st to end	Night	11% 11% 3 6% 3 4 3 3 5% 6% 44%	1710
May	1st to 10th	Night	11% 18% 3 6% 4 4 3 3 5% 6% 37%	2860
	11th to 20th	Night	5% 4 2 4 4 4 4 4 7% 9% 54%	2785
	21st to end	Night	9% 9% 2 6% 5% 4 5% 4 5% 7% 43%	2762
June	1st to 10th	Night	8% 6% 2 5% 4 4 5% 3 7% 9% 46%	1520
	11th to 20th	Night	7% 6% 2 4 3 4 3 5% 5% 8% 54%	1377
	21st to end	Night	3 2 1 3 2 2 2 4 4 6% 71%	1330
July	1st to 10th	Night	1 1 1 2 2 3 3 4 6% 6% 73%	2220
	11th to 20th	Night	1 1 1 2 2 3 4 3 6% 7% 71%	2778
	21st to end	Night	1 2 1 3 2 2 4 4 6% 8% 67%	3109
August	1st to 10th	Night	3 3 1 5% 3 4 3 4 7% 8% 60%	2847
	11th to 20th	Night	3 3 1 4 3 3 5% 4 6% 7% 62%	2811
	21st to end	Night	3 2 1 3 2 2 3 3 4 6% 72%	3194
September	1st to 10th	Night	5% 2 1 5% 2 2 2 3 5% 6% 67%	1933
	11th to 20th	Night	7% 5% 1 4 3 3 3 3 5% 6% 61%	2090
	21st to end	Night	9% 4 1 4 3 2 2 3 3 5% 65%	2090
October	1st to 10th	Night	7% 4 2 3 2 2 2 2 3 5% 67%	3728
	11th to 20th	Night	10% 8% 2 4 3 3 3 3 4 5% 54%	3778
	21st to end	Night	10% 11% 2 4 2 3 3 3 5% 7% 49%	4163
November	1st to 10th	Night	14% 14% 4 7% 4 3 3 3 4 6% 38%	2535
	11th to 20th	Night	11% 15% 3 7% 3 4 4 4 5% 5% 38%	2760
	21st to end	Night	8% 17% 5% 7% 4 4 4 3 4 6% 39%	2800
December	1st to 10th	Night	7% 14% 6% 10% 3 3 3 2 3 4 45%	4570
	11th to 20th	Night	11% 23% 7% 10% 4 4 3 2 3 5% 27%	5181
	21st to end	Night	12% 24% 7% 11% 4 3 3 3 5% 7% 21%	6974

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	62% 6% 11% 14% 7% 1	3887
	11th to 20th	Day	58% 5% 11% 13% 9% 3	4100
	21st to end	Day	50% 6% 10% 19% 13% 1	4510
February	1st to 10th	Day	68% 5% 10% 12% 5% 1	1800
	11th to 20th	Day	63% 6% 10% 13% 6% 2	1764
	21st to end	Day	65% 5% 8% 13% 5% 2	1615
March	1st to 10th	Day	58% 5% 9% 16% 12% 1	3488
	11th to 20th	Day	41% 5% 14% 29% 10% 1	3502
	21st to end	Day	67% 9% 12% 10% 2	3825
April	1st to 10th	Day	56% 6% 13% 16% 9% 2	2171
	11th to 20th	Day	54% 5% 11% 21% 8% 1	2392
	21st to end	Day	52% 6% 11% 23% 8%	2470
May	1st to 10th	Day	51% 5% 11% 20% 10% 2	4110
	11th to 20th	Day	29% 7% 12% 34% 15% 4	4123
	21st to end	Day	44% 7% 11% 27% 11%	4825
June	1st to 10th	Day	36% 7% 15% 26% 15% 2	2660
	11th to 20th	Day	34% 5% 11% 20% 20% 10%	2797
	21st to end	Day	17% 4 7% 22% 34% 16%	2850
July	1st to 10th	Day	11% 3 4 11% 34% 37%	4666
	11th to 20th	Day	17% 4 5% 11% 25% 39%	4098
	21st to end	Day	22% 5% 6% 13% 36% 20%	4314
August	1st to 10th	Day	22% 5% 7% 16% 31% 19%	4078
	11th to 20th	Day	20% 4 6% 20% 35% 16%	4067
	21st to end	Day	18% 3 6% 20% 30% 22%	4471
September	1st to 10th	Day	22% 4 8% 17% 30% 19%	2242
	11th to 20th	Day	26% 5% 9% 21% 28% 10%	2090
	21st to end	Day	26% 4 9% 27% 29% 6%	2090
October	1st to 10th	Day	28% 3 6% 19% 33% 11%	3244
	11th to 20th	Day	31% 4 9% 32% 17% 7%	3150
	21st to end	Day	42% 4 14% 26% 13%	3392
November	1st to 10th	Day	49% 4 14% 21% 10% 2	1764
	11th to 20th	Day	52% 5% 15% 17% 10% 1	1618
	21st to end	Day	50% 5% 15% 19% 10% 1	1600
December	1st to 10th	Day	43% 6% 23% 22% 5% 2	2620
	11th to 20th	Day	61% 5% 18% 14% 2	3024
	21st to end	Day	59% 6% 12% 13% 8% 2	4004
January	1st to 10th	Night	61% 6% 9% 18% 6%	6120
	11th to 20th	Night	64% 5% 9% 14% 5% 2	5880
	21st to end	Night	48% 6% 13% 20% 13% 1	6468
February	1st to 10th	Night	66% 6% 10% 13% 6%	2600
	11th to 20th	Night	59% 5% 10% 17% 9% 1	2533
	21st to end	Night	62% 5% 12% 13% 6% 2	2013
March	1st to 10th	Night	52% 8% 9% 20% 11% 1	3606
	11th to 20th	Night	34% 9% 17% 27% 11% 1	3506
	21st to end	Night	54% 10% 16% 17% 2 1	3828
April	1st to 10th	Night	48% 7% 16% 16% 11% 3	2008
	11th to 20th	Night	46% 6% 14% 22% 11% 1	1737
	21st to end	Night	39% 6% 16% 27% 11%	1710
May	1st to 10th	Night	45% 7% 11% 23% 13% 1	2860
	11th to 20th	Night	23% 7% 16% 35% 16% 3	2786
	21st to end	Night	33% 10% 13% 30% 12% 2	2762
June	1st to 10th	Night	32% 8% 16% 28% 15% 1	1520
	11th to 20th	Night	27% 5% 13% 25% 21% 10%	1377
	21st to end	Night	14% 4 8% 21% 38% 16%	1330
July	1st to 10th	Night	11% 3 7% 14% 30% 36%	2185
	11th to 20th	Night	11% 3 4 14% 31% 37%	2727
	21st to end	Night	13% 3 8% 17% 40% 18%	3011
August	1st to 10th	Night	21% 3 7% 14% 35% 19%	2838
	11th to 20th	Night	20% 4 6% 20% 32% 17%	2838
	21st to end	Night	14% 3 6% 21% 33% 23%	3194
September	1st to 10th	Night	18% 4 7% 17% 32% 21%	1933
	11th to 20th	Night	24% 5% 10% 20% 29% 12%	2090
	21st to end	Night	24% 2 9% 27% 32% 6%	2090
October	1st to 10th	Night	22% 3 7% 23% 37% 8%	3728
	11th to 20th	Night	33% 3 8% 31% 17% 6%	3778
	21st to end	Night	35% 4 13% 31% 15% 1	4163
November	1st to 10th	Night	46% 6% 13% 22% 11% 2	2535
	11th to 20th	Night	46% 5% 16% 22% 9% 1	2760
	21st to end	Night	47% 5% 15% 21% 10% 2	2800
December	1st to 10th	Night	44% 4 23% 22% 5% 1	4570
	11th to 20th	Night	61% 5% 16% 15% 3	5182
	21st to end	Night	61% 6% 10% 15% 7% 1	6974

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	23% 10% 20% 28% 15% 3	300
	11th to 20th	Day	19% 8% 25% 30% 14% 3	300
	21st to end	Day	15% 11% 24% 37% 11% 2	330
February	1st to 10th	Day	31% 18% 26% 19% 6% 1	300
	11th to 20th	Day	20% 19% 29% 21% 9% 2	300
	21st to end	Day	22% 23% 27% 20% 7% 1	379
March	1st to 10th	Day	24% 19% 27% 22% 6% 2	500
	11th to 20th	Day	14% 19% 32% 24% 9% 2	465
	21st to end	Day	23% 25% 31% 16% 4	506
April	1st to 10th	Day	28% 19% 25% 19% 7% 1	460
	11th to 20th	Day	25% 24% 28% 16% 5% 1	452
	21st to end	Day	24% 18% 24% 22% 9% 3	460
May	1st to 10th	Day	16% 22% 29% 24% 8% 1	463
	11th to 20th	Day	14% 17% 30% 23% 13% 2	511
	21st to end	Day	18% 12% 21% 26% 18% 5%	734
June	1st to 10th	Day	12% 12% 27% 26% 19% 4	680
	11th to 20th	Day	14% 17% 30% 26% 12% 2	680
	21st to end	Day	4 12% 28% 33% 18% 5%	680
July	1st to 10th	Day	3 9% 27% 33% 23% 5%	671
	11th to 20th	Day	3 10% 39% 28% 16% 3	515
	21st to end	Day	3 10% 30% 31% 20% 6%	531
August	1st to 10th	Day	6% 8% 36% 31% 17% 4	487
	11th to 20th	Day	3 11% 31% 30% 17% 8%	477
	21st to end	Day	7% 11% 27% 29% 19% 6%	539
September	1st to 10th	Day	5% 13% 27% 29% 18% 8%	490
	11th to 20th	Day	11% 16% 28% 23% 14% 8%	490
	21st to end	Day	10% 12% 24% 28% 18% 7%	490
October	1st to 10th	Day	12% 10% 24% 28% 17% 9%	348
	11th to 20th	Day	15% 12% 16% 27% 20% 9%	300
	21st to end	Day	20% 12% 25% 27% 14% 2	330
November	1st to 10th	Day	26% 9% 22% 25% 11% 7%	300
	11th to 20th	Day	21% 11% 28% 26% 11% 3	300
	21st to end	Day	16% 9% 25% 35% 12% 3	300
December	1st to 10th	Day	21% 9% 22% 28% 17% 3	300
	11th to 20th	Day	27% 14% 24% 24% 10% 1	300
	21st to end	Day	27% 11% 27% 21% 11% 4	330
January	1st to 10th	Night	19% 10% 22% 36% 13% 1	910
	11th to 20th	Night	20% 7% 24% 33% 14% 3	800
	21st to end	Night	20% 7% 23% 37% 11% 2	880
February	1st to 10th	Night	22% 9% 27% 35% 7% 1	800
	11th to 20th	Night	18% 8% 30% 33% 9% 1	784
	21st to end	Night	17% 10% 29% 34% 9%	660
March	1st to 10th	Night	17% 9% 28% 36% 9% 1	800
	11th to 20th	Night	13% 8% 23% 41% 16% 1	766
	21st to end	Night	16% 10% 24% 38% 12% 1	836
April	1st to 10th	Night	18% 10% 23% 36% 12% 1	678
	11th to 20th	Night	16% 10% 27% 37% 10%	563
	21st to end	Night	15% 8% 21% 35% 19% 1	570
May	1st to 10th	Night	15% 8% 21% 36% 19% 1	570
	11th to 20th	Night	12% 3 20% 37% 27% 1	561
	21st to end	Night	14% 6% 17% 38% 22% 2	617
June	1st to 10th	Night	9% 7% 20% 37% 25% 1	570
	11th to 20th	Night	10% 5% 23% 42% 20%	427
	21st to end	Night	4 1 11% 50% 30% 3	380
July	1st to 10th	Night	2 1 8% 48% 39% 2	370
	11th to 20th	Night	2 2 10% 53% 32% 1	534
	21st to end	Night	2 8% 48% 39% 2	624
August	1st to 10th	Night	5% 2 9% 47% 34% 2	567
	11th to 20th	Night	3 1 10% 49% 35% 2	564
	21st to end	Night	5% 3 12% 44% 33% 3	627
September	1st to 10th	Night	6% 3 10% 44% 34% 3	603
	11th to 20th	Night	8% 3 13% 40% 31% 5%	760
	21st to end	Night	11% 2 13% 40% 28% 5%	760
October	1st to 10th	Night	15% 5% 15% 40% 23% 3	760
	11th to 20th	Night	16% 5% 15% 37% 24% 3	760
	21st to end	Night	17% 3 17% 45% 15% 2	836
November	1st to 10th	Night	19% 7% 20% 37% 15% 2	780
	11th to 20th	Night	18% 9% 25% 37% 10% 1	960
	21st to end	Night	16% 7% 23% 39% 13% 2	1000
December	1st to 10th	Night	21% 7% 26% 35% 11% 1	1000
	11th to 20th	Night	22% 9% 25% 37% 8%	1000
	21st to end	Night	22% 11% 25% 31% 9% 2	1100

Page generated at 2025-03-09 06:08:46. Version ac07

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