Wears Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wears Valley clear sky chart from 2005-11-06 to 2024-10-20.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	100884
	Night	13% 9% 3 7% 5% 4 4 4 6% 7% 38%	97744
Transparency	Day	46% 8% 12% 19% 13% 3	100697
	Night	44% 8% 13% 18% 14% 3	97601
Seeing	Day	19% 14% 25% 23% 14% 6%	14843
	Night	18% 11% 22% 29% 18% 3	24864

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	12% 11% 7% 10% 5% 4 4 4 7% 6% 29%	2836
	11th to 20th	Day	12% 14% 6% 10% 5% 6% 5% 3 4 4 31%	2840
	21st to end	Day	15% 15% 5% 8% 4 3 3 3 5% 6% 32%	3124
February	1st to 10th	Day	15% 13% 5% 8% 5% 5% 5% 3 5% 4 32%	1866
	11th to 20th	Day	17% 12% 4 11% 4 4 3 3 4 6% 31%	1848
	21st to end	Day	18% 11% 4 8% 5% 4 4 3 5% 5% 34%	1570
March	1st to 10th	Day	19% 11% 5% 6% 4 4 4 3 4 6% 34%	3262
	11th to 20th	Day	13% 10% 3 6% 4 3 4 3 4 5% 47%	3480
	21st to end	Day	15% 11% 2 7% 5% 4 4 3 5% 5% 37%	3815
April	1st to 10th	Day	10% 9% 3 6% 5% 5% 5% 4 7% 7% 40%	2118
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 6% 42%	2288
	21st to end	Day	15% 6% 2 6% 5% 5% 4 4 5% 6% 40%	2470
May	1st to 10th	Day	15% 8% 4 7% 6% 6% 5% 5% 6% 7% 32%	4082
	11th to 20th	Day	16% 8% 3 9% 6% 5% 5% 5% 6% 6% 30%	4081
	21st to end	Day	10% 6% 2 8% 5% 5% 6% 5% 8% 10% 35%	4476
June	1st to 10th	Day	10% 6% 3 7% 7% 7% 7% 6% 7% 9% 32%	2470
	11th to 20th	Day	5% 6% 3 8% 7% 6% 6% 6% 9% 10% 34%	2470
	21st to end	Day	9% 6% 3 7% 6% 6% 6% 6% 8% 10% 34%	2470
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 7% 9% 13% 31%	4120
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 9% 35%	4120
	21st to end	Day	13% 10% 5% 12% 9% 9% 7% 5% 7% 7% 16%	4466
August	1st to 10th	Day	9% 6% 3 8% 6% 6% 7% 6% 8% 11% 32%	4104
	11th to 20th	Day	9% 7% 3 7% 5% 6% 6% 5% 8% 11% 33%	3997
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 7% 7% 45%	4160
September	1st to 10th	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 8% 37%	2090
	11th to 20th	Day	15% 7% 2 7% 5% 6% 5% 4 6% 8% 36%	2090
	21st to end	Day	15% 5% 2 6% 4 5% 4 4 7% 7% 41%	2090
October	1st to 10th	Day	11% 5% 2 5% 4 4 5% 3 5% 5% 51%	2090
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 5% 52%	1918
	21st to end	Day	14% 6% 2 4 4 3 4 3 6% 5% 49%	1980
November	1st to 10th	Day	11% 7% 1 5% 3 3 3 3 4 7% 53%	1686
	11th to 20th	Day	10% 10% 2 6% 5% 3 4 4 6% 5% 46%	1710
	21st to end	Day	11% 9% 3 8% 4 4 3 4 5% 6% 43%	1710
December	1st to 10th	Day	16% 12% 4 8% 4 4 5% 4 5% 6% 33%	1710
	11th to 20th	Day	12% 13% 4 7% 5% 4 4 4 5% 7% 35%	2153
	21st to end	Day	11% 12% 5% 8% 6% 5% 4 3 5% 6% 34%	3124
January	1st to 10th	Night	14% 17% 6% 10% 5% 4 4 3 3 5% 30%	4109
	11th to 20th	Night	17% 12% 4 8% 5% 5% 4 3 5% 5% 33%	4120
	21st to end	Night	16% 13% 4 8% 5% 4 4 3 4 4 34%	4532
February	1st to 10th	Night	14% 12% 3 8% 4 4 4 4 6% 6% 35%	2309
	11th to 20th	Night	18% 13% 4 9% 5% 4 4 3 3 4 32%	2218
	21st to end	Night	18% 12% 3 8% 5% 4 4 4 6% 6% 31%	1884
March	1st to 10th	Night	19% 14% 4 8% 4 4 3 3 4 7% 30%	3589
	11th to 20th	Night	13% 8% 3 6% 4 3 4 3 5% 7% 44%	3480
	21st to end	Night	14% 8% 3 7% 5% 5% 4 4 5% 6% 40%	3817
April	1st to 10th	Night	13% 10% 2 4 4 4 4 3 6% 7% 43%	2078
	11th to 20th	Night	13% 8% 3 6% 5% 3 3 3 5% 7% 44%	1839
	21st to end	Night	14% 6% 2 6% 5% 4 4 4 6% 7% 43%	1710
May	1st to 10th	Night	12% 8% 3 8% 6% 5% 6% 4 6% 9% 33%	2813
	11th to 20th	Night	17% 7% 3 7% 4 4 5% 4 6% 7% 34%	2812
	21st to end	Night	10% 6% 2 6% 4 5% 6% 5% 7% 11% 38%	3079
June	1st to 10th	Night	8% 5% 2 6% 5% 5% 7% 6% 8% 10% 37%	1710
	11th to 20th	Night	4 4 2 5% 4 5% 6% 5% 10% 12% 42%	1710
	21st to end	Night	7% 6% 3 6% 6% 6% 5% 5% 7% 10% 39%	1710
July	1st to 10th	Night	10% 5% 3 6% 5% 7% 7% 7% 8% 11% 33%	2840
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 5% 8% 11% 41%	2840
	21st to end	Night	10% 10% 4 10% 7% 8% 7% 6% 8% 9% 21%	3087
August	1st to 10th	Night	8% 7% 2 7% 5% 5% 6% 5% 7% 11% 38%	2825
	11th to 20th	Night	11% 7% 2 7% 4 5% 5% 5% 7% 9% 39%	2815
	21st to end	Night	6% 4 2 6% 4 4 5% 5% 7% 10% 46%	3476
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 6% 3 6% 7% 42%	2076
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 4 5% 7% 41%	2090
	21st to end	Night	11% 6% 3 6% 4 4 5% 4 5% 6% 46%	2090
October	1st to 10th	Night	14% 6% 2 5% 3 2 2 2 4 6% 53%	2090
	11th to 20th	Night	16% 6% 2 4 3 4 3 3 4 5% 50%	2246
	21st to end	Night	13% 7% 2 4 4 3 3 3 5% 7% 49%	2376
November	1st to 10th	Night	13% 7% 3 5% 3 3 3 3 4 5% 50%	2390
	11th to 20th	Night	12% 9% 3 6% 3 3 3 3 5% 6% 46%	2470
	21st to end	Night	12% 9% 3 6% 4 3 4 4 5% 6% 44%	2470
December	1st to 10th	Night	15% 14% 4 9% 5% 4 4 4 6% 6% 31%	2470
	11th to 20th	Night	15% 13% 4 10% 4 3 3 3 4 5% 36%	3042
	21st to end	Night	12% 13% 6% 8% 5% 5% 5% 4 7% 7% 27%	4532

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	48% 10% 7% 14% 17% 4	2837
	11th to 20th	Day	52% 9% 6% 12% 18% 3	2840
	21st to end	Day	51% 7% 7% 16% 17% 2	3124
February	1st to 10th	Day	53% 6% 8% 15% 16% 3	1866
	11th to 20th	Day	54% 6% 7% 16% 15% 3	1858
	21st to end	Day	52% 5% 10% 13% 16% 6%	1570
March	1st to 10th	Day	49% 7% 9% 15% 14% 6%	3262
	11th to 20th	Day	38% 8% 8% 21% 18% 7%	3480
	21st to end	Day	47% 6% 9% 25% 10% 3	3815
April	1st to 10th	Day	42% 8% 11% 21% 16% 2	2118
	11th to 20th	Day	43% 6% 9% 18% 21% 3	2288
	21st to end	Day	45% 6% 10% 24% 13% 2	2470
May	1st to 10th	Day	50% 9% 11% 20% 9% 1	4120
	11th to 20th	Day	52% 10% 11% 20% 7% 1	4085
	21st to end	Day	39% 12% 14% 20% 14% 1	4489
June	1st to 10th	Day	47% 11% 15% 18% 8% 1	2470
	11th to 20th	Day	44% 11% 18% 17% 10% 1	2470
	21st to end	Day	44% 11% 16% 17% 11% 3	2470
July	1st to 10th	Day	44% 12% 20% 18% 6%	4055
	11th to 20th	Day	48% 7% 21% 17% 5% 1	4051
	21st to end	Day	67% 9% 11% 10% 3	4324
August	1st to 10th	Day	46% 8% 18% 23% 5%	4091
	11th to 20th	Day	44% 8% 22% 16% 10%	4036
	21st to end	Day	40% 7% 15% 31% 7% 1	4160
September	1st to 10th	Day	45% 8% 12% 16% 16% 3	2090
	11th to 20th	Day	47% 8% 10% 19% 15% 1	2090
	21st to end	Day	41% 8% 12% 19% 15% 5%	2090
October	1st to 10th	Day	36% 5% 10% 21% 22% 6%	2090
	11th to 20th	Day	35% 5% 9% 22% 22% 8%	1918
	21st to end	Day	35% 5% 8% 23% 22% 6%	1980
November	1st to 10th	Day	34% 4 8% 19% 28% 7%	1686
	11th to 20th	Day	39% 5% 7% 21% 23% 6%	1710
	21st to end	Day	41% 6% 7% 20% 21% 5%	1710
December	1st to 10th	Day	52% 8% 7% 17% 13% 3	1710
	11th to 20th	Day	44% 9% 10% 14% 19% 4	2150
	21st to end	Day	49% 8% 9% 21% 12% 1	3124
January	1st to 10th	Night	51% 9% 7% 14% 15% 4	4109
	11th to 20th	Night	50% 9% 6% 11% 19% 5%	4120
	21st to end	Night	55% 5% 7% 11% 19% 3	4532
February	1st to 10th	Night	50% 5% 9% 16% 16% 3	2309
	11th to 20th	Night	56% 5% 7% 15% 14% 4	2219
	21st to end	Night	55% 6% 8% 13% 14% 4	1884
March	1st to 10th	Night	54% 7% 12% 12% 12% 3	3589
	11th to 20th	Night	38% 6% 10% 22% 16% 8%	3480
	21st to end	Night	44% 7% 11% 21% 14% 3	3817
April	1st to 10th	Night	42% 6% 12% 21% 17% 3	2078
	11th to 20th	Night	41% 5% 10% 19% 20% 4	1839
	21st to end	Night	41% 7% 12% 27% 12% 1	1710
May	1st to 10th	Night	48% 10% 14% 20% 8% 1	2840
	11th to 20th	Night	47% 10% 15% 20% 7%	2813
	21st to end	Night	34% 15% 19% 22% 9% 1	3087
June	1st to 10th	Night	41% 13% 18% 20% 9% 1	1710
	11th to 20th	Night	31% 14% 22% 24% 9% 1	1710
	21st to end	Night	40% 9% 17% 21% 10% 3	1710
July	1st to 10th	Night	43% 11% 22% 18% 6%	2795
	11th to 20th	Night	37% 10% 27% 20% 4 2	2786
	21st to end	Night	55% 12% 18% 11% 4	2988
August	1st to 10th	Night	39% 7% 23% 23% 7%	2814
	11th to 20th	Night	40% 9% 25% 17% 9%	2842
	21st to end	Night	32% 8% 20% 32% 8% 1	3476
September	1st to 10th	Night	40% 9% 15% 19% 14% 3	2076
	11th to 20th	Night	41% 10% 14% 19% 17%	2090
	21st to end	Night	38% 7% 13% 20% 18% 3	2090
October	1st to 10th	Night	33% 6% 11% 20% 24% 6%	2090
	11th to 20th	Night	38% 5% 9% 22% 19% 7%	2246
	21st to end	Night	35% 5% 7% 22% 23% 7%	2376
November	1st to 10th	Night	37% 5% 7% 20% 24% 6%	2390
	11th to 20th	Night	39% 5% 7% 19% 22% 7%	2470
	21st to end	Night	41% 6% 7% 22% 19% 4	2470
December	1st to 10th	Night	55% 7% 9% 14% 12% 4	2470
	11th to 20th	Night	48% 8% 7% 13% 20% 4	3044
	21st to end	Night	52% 9% 10% 15% 11% 1	4532

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	27% 30% 30% 13% 1	270
	11th to 20th	Day	34% 27% 24% 13% 1	270
	21st to end	Day	24% 31% 33% 10% 2	297
February	1st to 10th	Day	28% 23% 36% 11% 1	270
	11th to 20th	Day	39% 31% 24% 6%	270
	21st to end	Day	40% 29% 25% 6%	225
March	1st to 10th	Day	28% 21% 31% 16% 4	347
	11th to 20th	Day	26% 24% 33% 13% 3 1	460
	21st to end	Day	25% 22% 30% 18% 5%	506
April	1st to 10th	Day	26% 20% 26% 20% 8% 1	460
	11th to 20th	Day	22% 22% 27% 19% 8% 2	452
	21st to end	Day	24% 15% 27% 20% 10% 3	460
May	1st to 10th	Day	19% 20% 27% 21% 8% 5%	463
	11th to 20th	Day	16% 11% 27% 26% 13% 7%	487
	21st to end	Day	15% 8% 25% 26% 15% 11%	529
June	1st to 10th	Day	12% 8% 25% 30% 17% 8%	490
	11th to 20th	Day	8% 6% 23% 30% 22% 11%	490
	21st to end	Day	13% 5% 26% 28% 17% 11%	490
July	1st to 10th	Day	12% 6% 17% 27% 25% 13%	485
	11th to 20th	Day	12% 5% 18% 27% 23% 14%	484
	21st to end	Day	12% 3 18% 28% 27% 12%	532
August	1st to 10th	Day	16% 7% 19% 24% 21% 13%	486
	11th to 20th	Day	11% 6% 19% 30% 24% 9%	479
	21st to end	Day	12% 4 14% 27% 29% 14%	539
September	1st to 10th	Day	11% 5% 15% 29% 31% 10%	490
	11th to 20th	Day	16% 7% 14% 26% 27% 10%	490
	21st to end	Day	18% 8% 17% 32% 20% 5%	490
October	1st to 10th	Day	15% 7% 27% 26% 18% 6%	490
	11th to 20th	Day	18% 11% 28% 26% 15% 2	486
	21st to end	Day	21% 11% 26% 27% 13% 2	495
November	1st to 10th	Day	18% 17% 29% 26% 10% 1	284
	11th to 20th	Day	19% 21% 34% 23% 4	270
	21st to end	Day	18% 19% 33% 25% 5%	270
December	1st to 10th	Day	28% 22% 34% 14% 1	270
	11th to 20th	Day	24% 19% 33% 20% 3	270
	21st to end	Day	25% 20% 39% 12% 4	297
January	1st to 10th	Night	23% 19% 28% 25% 5%	760
	11th to 20th	Night	25% 21% 29% 21% 5%	760
	21st to end	Night	21% 20% 33% 24% 2	836
February	1st to 10th	Night	22% 15% 30% 30% 3	760
	11th to 20th	Night	28% 19% 34% 18% 1	743
	21st to end	Night	29% 21% 29% 19% 2	628
March	1st to 10th	Night	22% 18% 30% 26% 4	760
	11th to 20th	Night	21% 19% 29% 24% 6% 1	760
	21st to end	Night	22% 15% 31% 24% 8%	836
April	1st to 10th	Night	21% 17% 28% 25% 9% 1	748
	11th to 20th	Night	20% 13% 29% 24% 13% 1	563
	21st to end	Night	18% 10% 26% 32% 13% 1	570
May	1st to 10th	Night	15% 12% 25% 32% 13% 2	570
	11th to 20th	Night	15% 8% 21% 33% 21% 2	561
	21st to end	Night	12% 3 15% 34% 31% 5%	617
June	1st to 10th	Night	9% 5% 16% 36% 30% 4	570
	11th to 20th	Night	5% 3 15% 35% 33% 9%	570
	21st to end	Night	9% 2 14% 36% 33% 5%	570
July	1st to 10th	Night	12% 1 8% 31% 42% 5%	555
	11th to 20th	Night	9% 2 8% 31% 38% 11%	552
	21st to end	Night	8% 2 10% 29% 42% 9%	624
August	1st to 10th	Night	10% 3 7% 33% 39% 8%	567
	11th to 20th	Night	12% 4 9% 34% 37% 5%	564
	21st to end	Night	11% 3 8% 30% 39% 9%	627
September	1st to 10th	Night	12% 4 10% 30% 36% 8%	746
	11th to 20th	Night	17% 3 12% 32% 30% 6%	760
	21st to end	Night	15% 4 18% 32% 28% 2	760
October	1st to 10th	Night	16% 6% 18% 24% 28% 8%	760
	11th to 20th	Night	19% 8% 24% 30% 18% 2	759
	21st to end	Night	17% 10% 22% 34% 14% 2	792
November	1st to 10th	Night	18% 8% 19% 34% 18% 3	740
	11th to 20th	Night	17% 16% 23% 32% 11% 1	760
	21st to end	Night	20% 11% 24% 32% 13% 1	760
December	1st to 10th	Night	23% 17% 26% 27% 6%	760
	11th to 20th	Night	20% 16% 26% 30% 7% 1	760
	21st to end	Night	24% 17% 27% 29% 4	836

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