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 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	12% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	109232
	Night	12% 9% 3 7% 5% 4 4 4 6% 7% 38%	109778
Transparency	Day	45% 7% 11% 19% 14% 4	113026
	Night	43% 7% 12% 18% 15% 4	114123
Seeing	Day	19% 14% 25% 22% 14% 6%	15289
	Night	18% 11% 22% 28% 17% 3	25436

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% 15% 6% 9% 4 3 3 3 6% 5% 32%	4056
	11th to 20th	Day	9% 12% 6% 9% 5% 5% 5% 3 4 5% 38%	4060
	21st to end	Day	14% 13% 5% 8% 5% 3 3 3 5% 6% 36%	4466
February	1st to 10th	Day	14% 13% 4 8% 5% 5% 4 3 5% 5% 32%	1965
	11th to 20th	Day	17% 13% 4 11% 4 4 3 3 4 6% 31%	1948
	21st to end	Day	17% 11% 4 7% 5% 4 4 3 5% 5% 36%	1650
March	1st to 10th	Day	18% 11% 5% 7% 4 4 4 4 4 6% 34%	3366
	11th to 20th	Day	13% 10% 3 6% 4 3 4 3 4 5% 47%	3491
	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%	1928
	21st to end	Day	13% 6% 2 4 4 3 4 3 5% 5% 50%	2090
November	1st to 10th	Day	11% 7% 1 6% 4 3 3 3 5% 7% 52%	1776
	11th to 20th	Day	10% 10% 2 6% 4 3 4 4 6% 6% 46%	1800
	21st to end	Day	10% 10% 3 8% 4 4 4 4 5% 6% 43%	1800
December	1st to 10th	Day	10% 9% 3 9% 5% 4 5% 4 5% 5% 40%	2930
	11th to 20th	Day	13% 13% 5% 8% 6% 5% 6% 4 5% 6% 29%	3373
	21st to end	Day	8% 10% 6% 9% 6% 5% 5% 4 6% 7% 35%	4466
January	1st to 10th	Night	11% 16% 5% 10% 5% 4 4 3 4 5% 32%	5889
	11th to 20th	Night	14% 12% 4 10% 6% 5% 3 3 4 5% 34%	5900
	21st to end	Night	13% 11% 4 8% 5% 4 5% 3 4 5% 38%	6490
February	1st to 10th	Night	14% 12% 3 8% 4 4 4 4 6% 6% 35%	2430
	11th to 20th	Night	18% 13% 4 9% 5% 4 4 3 4 4 31%	2338
	21st to end	Night	17% 11% 3 7% 5% 4 4 4 6% 6% 33%	1980
March	1st to 10th	Night	19% 14% 4 8% 4 4 3 3 4 7% 30%	3705
	11th to 20th	Night	13% 8% 3 6% 4 3 4 3 5% 7% 44%	3498
	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%	2251
	21st to end	Night	13% 6% 2 4 3 3 3 3 5% 7% 50%	2508
November	1st to 10th	Night	13% 7% 3 6% 3 3 3 3 4 6% 50%	2520
	11th to 20th	Night	12% 10% 3 6% 3 3 3 3 5% 6% 45%	2600
	21st to end	Night	12% 10% 3 6% 4 3 4 4 5% 6% 44%	2600
December	1st to 10th	Night	11% 15% 5% 9% 4 3 4 3 5% 5% 37%	4250
	11th to 20th	Night	16% 12% 5% 10% 5% 4 4 3 4 5% 31%	4822
	21st to end	Night	10% 12% 6% 8% 5% 4 5% 4 6% 8% 32%	6490

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	47% 7% 5% 16% 22% 3	4057
	11th to 20th	Day	45% 6% 5% 14% 24% 6%	4060
	21st to end	Day	49% 5% 6% 18% 17% 5%	4466
February	1st to 10th	Day	52% 6% 8% 16% 15% 2	1965
	11th to 20th	Day	55% 6% 6% 16% 14% 3	1958
	21st to end	Day	50% 4 9% 13% 18% 6%	1650
March	1st to 10th	Day	49% 6% 9% 15% 14% 6%	3366
	11th to 20th	Day	38% 8% 8% 21% 18% 8%	3491
	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	30% 4 6% 19% 29% 12%	3480
	11th to 20th	Day	26% 3 6% 22% 24% 19%	3181
	21st to end	Day	25% 3 9% 31% 21% 11%	3428
November	1st to 10th	Day	34% 4 9% 20% 27% 7%	1776
	11th to 20th	Day	39% 5% 6% 20% 23% 6%	1800
	21st to end	Day	41% 6% 7% 20% 21% 4	1800
December	1st to 10th	Day	43% 5% 8% 18% 21% 5%	2930
	11th to 20th	Day	52% 6% 10% 15% 14% 3	3370
	21st to end	Day	46% 6% 13% 23% 10% 2	4466
January	1st to 10th	Night	50% 7% 7% 16% 17% 3	5889
	11th to 20th	Night	49% 7% 5% 11% 20% 8%	5900
	21st to end	Night	50% 4 6% 13% 21% 6%	6490
February	1st to 10th	Night	50% 5% 9% 16% 16% 3	2430
	11th to 20th	Night	57% 5% 7% 14% 13% 3	2339
	21st to end	Night	53% 6% 7% 14% 15% 4	1980
March	1st to 10th	Night	53% 7% 11% 12% 13% 3	3705
	11th to 20th	Night	38% 6% 10% 22% 16% 8%	3498
	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	30% 4 7% 22% 26% 12%	3480
	11th to 20th	Night	29% 3 6% 21% 21% 20%	3737
	21st to end	Night	25% 3 6% 27% 25% 14%	4120
November	1st to 10th	Night	37% 5% 8% 21% 23% 6%	2520
	11th to 20th	Night	39% 5% 7% 19% 22% 8%	2600
	21st to end	Night	42% 6% 7% 22% 19% 4	2600
December	1st to 10th	Night	51% 4 7% 14% 20% 4	4250
	11th to 20th	Night	52% 7% 8% 15% 16% 3	4824
	21st to end	Night	48% 8% 13% 16% 14% 1	6490

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	28% 30% 29% 11% 1	300
	11th to 20th	Day	35% 27% 24% 12% 2	300
	21st to end	Day	27% 32% 31% 9% 2	330
February	1st to 10th	Day	27% 25% 36% 10% 1	300
	11th to 20th	Day	41% 30% 23% 5%	300
	21st to end	Day	40% 28% 26% 6%	249
March	1st to 10th	Day	30% 21% 30% 15% 3	381
	11th to 20th	Day	25% 24% 33% 13% 3 1	464
	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% 14% 2	490
	21st to end	Day	20% 10% 29% 27% 12% 2	539
November	1st to 10th	Day	18% 17% 31% 24% 9% 1	314
	11th to 20th	Day	20% 21% 33% 22% 4	300
	21st to end	Day	19% 20% 34% 22% 5%	300
December	1st to 10th	Day	30% 24% 32% 13% 1	300
	11th to 20th	Day	27% 19% 33% 18% 3	300
	21st to end	Day	26% 19% 38% 12% 5%	330
January	1st to 10th	Night	24% 19% 29% 24% 4	800
	11th to 20th	Night	26% 21% 29% 20% 4	800
	21st to end	Night	21% 21% 33% 23% 2	880
February	1st to 10th	Night	24% 15% 29% 29% 3	800
	11th to 20th	Night	29% 20% 33% 17% 1	783
	21st to end	Night	28% 22% 30% 18% 2	660
March	1st to 10th	Night	24% 18% 30% 24% 4	800
	11th to 20th	Night	21% 19% 29% 24% 6% 1	767
	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% 29% 18% 2	760
	21st to end	Night	17% 10% 24% 34% 14% 2	836
November	1st to 10th	Night	17% 10% 19% 33% 17% 3	780
	11th to 20th	Night	17% 16% 24% 31% 11% 1	800
	21st to end	Night	20% 12% 24% 31% 12% 1	800
December	1st to 10th	Night	24% 18% 26% 25% 6%	800
	11th to 20th	Night	20% 17% 27% 28% 7% 1	800
	21st to end	Night	23% 18% 27% 28% 4	880

Page generated at 2025-03-09 08:08:48. Version ac07

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