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 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	11% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	137836
	Night	12% 9% 3 8% 5% 4 5% 4 6% 7% 37%	134845
Transparency	Day	46% 7% 12% 19% 13% 4	141586
	Night	44% 7% 12% 18% 14% 4	139167
Seeing	Day	21% 15% 25% 22% 13% 5%	17127
	Night	18% 12% 23% 28% 17% 3	27156

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% 14% 5% 9% 4 4 3 4 6% 6% 34%	5258
	11th to 20th	Day	7% 11% 5% 10% 5% 5% 4 3 4 4 42%	5280
	21st to end	Day	13% 13% 5% 9% 6% 4 3 3 4 5% 34%	5780
February	1st to 10th	Day	14% 13% 5% 8% 5% 5% 4 3 5% 5% 32%	2063
	11th to 20th	Day	17% 12% 4 11% 4 4 3 4 4 6% 31%	2048
	21st to end	Day	16% 10% 4 8% 5% 4 4 4 5% 5% 35%	1730
March	1st to 10th	Day	16% 11% 5% 7% 4 4 4 4 5% 6% 35%	4782
	11th to 20th	Day	10% 9% 4 7% 4 4 4 3 5% 6% 46%	5090
	21st to end	Day	14% 9% 2 7% 4 4 4 3 5% 6% 41%	5586
April	1st to 10th	Day	10% 9% 3 6% 5% 5% 5% 4 7% 7% 40%	2341
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 5% 7% 43%	2532
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 6% 6% 39%	2730
May	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 5% 6% 8% 31%	7616
	11th to 20th	Day	11% 7% 3 9% 6% 6% 6% 5% 7% 7% 32%	7626
	21st to end	Day	13% 10% 3 11% 6% 7% 6% 5% 7% 8% 24%	8391
June	1st to 10th	Day	9% 6% 3 7% 7% 7% 6% 5% 7% 10% 33%	2730
	11th to 20th	Day	5% 5% 3 8% 7% 6% 7% 6% 10% 11% 33%	2730
	21st to end	Day	9% 6% 3 6% 6% 6% 6% 6% 8% 11% 33%	2730
July	1st to 10th	Day	6% 5% 2 6% 6% 5% 6% 6% 9% 13% 36%	6030
	11th to 20th	Day	9% 7% 3 8% 6% 6% 7% 6% 8% 10% 29%	5965
	21st to end	Day	10% 8% 4 10% 8% 8% 8% 6% 8% 9% 19%	6424
August	1st to 10th	Day	10% 6% 3 8% 6% 6% 7% 6% 8% 11% 31%	4234
	11th to 20th	Day	9% 7% 2 8% 5% 6% 6% 5% 8% 11% 33%	4126
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 7% 7% 45%	4291
September	1st to 10th	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 8% 38%	2200
	11th to 20th	Day	14% 7% 2 7% 5% 6% 5% 4 6% 8% 37%	2200
	21st to end	Day	14% 5% 2 6% 5% 5% 5% 5% 7% 7% 40%	2200
October	1st to 10th	Day	11% 5% 2 5% 4 4 5% 3 6% 5% 51%	2200
	11th to 20th	Day	13% 7% 2 4 3 2 3 3 4 6% 53%	2029
	21st to end	Day	13% 6% 2 5% 4 3 4 3 5% 5% 49%	2200
November	1st to 10th	Day	10% 7% 2 6% 4 3 3 3 4 7% 52%	1866
	11th to 20th	Day	9% 9% 2 6% 4 3 4 4 6% 6% 46%	1890
	21st to end	Day	11% 10% 3 8% 4 4 4 4 5% 6% 42%	1890
December	1st to 10th	Day	10% 9% 3 9% 5% 4 5% 4 5% 5% 40%	3020
	11th to 20th	Day	13% 13% 5% 8% 6% 5% 6% 4 5% 6% 30%	3463
	21st to end	Day	8% 10% 6% 9% 6% 5% 5% 4 6% 7% 35%	4565
January	1st to 10th	Night	12% 14% 5% 10% 5% 4 3 3 4 6% 34%	7635
	11th to 20th	Night	12% 11% 4 9% 5% 5% 3 2 4 5% 39%	7680
	21st to end	Night	13% 13% 5% 9% 5% 4 4 3 4 5% 35%	8401
February	1st to 10th	Night	14% 12% 3 8% 4 4 4 4 6% 6% 35%	2551
	11th to 20th	Night	18% 13% 4 9% 5% 4 4 3 4 4 32%	2458
	21st to end	Night	17% 12% 3 8% 5% 4 4 4 5% 5% 32%	2076
March	1st to 10th	Night	16% 14% 4 8% 4 4 4 3 4 7% 33%	5289
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 6% 8% 48%	5090
	21st to end	Night	11% 8% 3 7% 5% 5% 5% 4 5% 6% 42%	5588
April	1st to 10th	Night	13% 9% 2 4 4 4 4 3 6% 8% 43%	2296
	11th to 20th	Night	12% 8% 3 6% 5% 3 3 3 5% 7% 46%	2035
	21st to end	Night	14% 6% 2 6% 5% 4 4 4 6% 7% 42%	1890
May	1st to 10th	Night	13% 8% 3 8% 6% 5% 6% 5% 7% 9% 30%	5237
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 5% 6% 8% 34%	5234
	21st to end	Night	14% 9% 3 9% 6% 6% 7% 5% 6% 9% 26%	5761
June	1st to 10th	Night	8% 5% 3 6% 6% 5% 7% 6% 8% 10% 37%	1890
	11th to 20th	Night	5% 5% 2 5% 4 5% 5% 5% 10% 12% 41%	1890
	21st to end	Night	7% 6% 2 6% 6% 5% 5% 5% 8% 10% 40%	1890
July	1st to 10th	Night	9% 5% 3 6% 5% 6% 6% 6% 8% 12% 34%	4148
	11th to 20th	Night	7% 6% 3 7% 5% 5% 5% 5% 9% 12% 35%	4102
	21st to end	Night	9% 9% 4 10% 6% 7% 7% 6% 9% 11% 23%	4427
August	1st to 10th	Night	8% 7% 2 7% 5% 5% 6% 5% 7% 10% 37%	2915
	11th to 20th	Night	11% 7% 2 7% 4 5% 5% 5% 7% 9% 39%	2906
	21st to end	Night	6% 4 2 6% 4 5% 5% 5% 7% 10% 46%	3586
September	1st to 10th	Night	11% 6% 2 7% 5% 5% 6% 3 6% 7% 42%	2186
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 4 5% 7% 42%	2200
	21st to end	Night	11% 6% 3 7% 4 4 5% 4 5% 6% 46%	2200
October	1st to 10th	Night	14% 6% 2 5% 3 2 3 2 4 6% 52%	2200
	11th to 20th	Night	15% 6% 2 4 3 4 3 3 4 5% 51%	2370
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 6% 50%	2640
November	1st to 10th	Night	12% 7% 3 6% 3 3 3 3 4 5% 50%	2649
	11th to 20th	Night	12% 9% 3 6% 3 3 3 4 5% 6% 46%	2730
	21st to end	Night	12% 10% 3 6% 4 3 4 4 5% 6% 43%	2730
December	1st to 10th	Night	11% 15% 5% 9% 4 3 4 3 5% 5% 36%	4380
	11th to 20th	Night	16% 12% 5% 10% 5% 4 4 3 4 6% 32%	4952
	21st to end	Night	10% 12% 6% 9% 5% 4 5% 4 6% 8% 32%	6633

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% 6% 9% 19% 17% 2	5259
	11th to 20th	Day	42% 5% 4 13% 27% 8%	5280
	21st to end	Day	51% 4 6% 17% 16% 5%	5780
February	1st to 10th	Day	52% 5% 8% 16% 15% 2	2063
	11th to 20th	Day	55% 5% 7% 16% 14% 3	2058
	21st to end	Day	51% 4 9% 13% 17% 5%	1730
March	1st to 10th	Day	49% 5% 7% 14% 15% 9%	4782
	11th to 20th	Day	38% 6% 6% 17% 19% 14%	5090
	21st to end	Day	44% 5% 9% 27% 12% 3	5586
April	1st to 10th	Day	41% 7% 12% 22% 15% 2	2341
	11th to 20th	Day	42% 5% 9% 20% 20% 3	2532
	21st to end	Day	45% 6% 10% 25% 12% 2	2730
May	1st to 10th	Day	50% 6% 12% 21% 10% 1	7651
	11th to 20th	Day	49% 6% 15% 21% 8%	7630
	21st to end	Day	55% 9% 11% 14% 9% 1	8405
June	1st to 10th	Day	46% 10% 15% 19% 8% 1	2730
	11th to 20th	Day	43% 10% 18% 17% 10% 1	2730
	21st to end	Day	44% 11% 17% 17% 10% 2	2730
July	1st to 10th	Day	41% 10% 20% 20% 9%	5965
	11th to 20th	Day	52% 7% 24% 13% 3 1	5896
	21st to end	Day	61% 9% 16% 11% 3	6240
August	1st to 10th	Day	46% 8% 18% 22% 5%	4221
	11th to 20th	Day	44% 8% 23% 15% 9%	4165
	21st to end	Day	40% 7% 14% 31% 7% 1	4291
September	1st to 10th	Day	45% 8% 12% 17% 16% 3	2200
	11th to 20th	Day	46% 8% 11% 20% 14% 1	2200
	21st to end	Day	42% 8% 13% 19% 14% 4	2200
October	1st to 10th	Day	30% 4 6% 20% 28% 12%	3590
	11th to 20th	Day	26% 3 5% 22% 25% 19%	3282
	21st to end	Day	26% 3 9% 31% 21% 10%	3538
November	1st to 10th	Day	34% 4 9% 20% 27% 7%	1866
	11th to 20th	Day	38% 5% 7% 22% 23% 6%	1890
	21st to end	Day	42% 6% 7% 21% 20% 4	1890
December	1st to 10th	Day	44% 5% 8% 18% 21% 5%	3020
	11th to 20th	Day	51% 6% 10% 15% 15% 3	3460
	21st to end	Day	45% 6% 13% 23% 10% 2	4565
January	1st to 10th	Night	49% 5% 11% 19% 14% 2	7636
	11th to 20th	Night	47% 5% 4 12% 23% 9%	7680
	21st to end	Night	53% 3 6% 12% 18% 7%	8401
February	1st to 10th	Night	50% 5% 9% 17% 16% 3	2551
	11th to 20th	Night	57% 5% 7% 15% 14% 3	2459
	21st to end	Night	55% 5% 7% 14% 15% 4	2076
March	1st to 10th	Night	51% 6% 9% 14% 15% 5%	5289
	11th to 20th	Night	34% 5% 9% 20% 18% 14%	5090
	21st to end	Night	43% 5% 14% 23% 12% 3	5588
April	1st to 10th	Night	41% 5% 13% 22% 17% 2	2296
	11th to 20th	Night	39% 5% 10% 22% 20% 4	2035
	21st to end	Night	42% 7% 12% 27% 12% 1	1890
May	1st to 10th	Night	50% 7% 14% 21% 7% 1	5264
	11th to 20th	Night	47% 7% 17% 20% 9%	5235
	21st to end	Night	51% 11% 15% 15% 7%	5771
June	1st to 10th	Night	41% 12% 18% 19% 10% 1	1890
	11th to 20th	Night	32% 13% 22% 24% 8% 1	1890
	21st to end	Night	39% 9% 17% 22% 10% 3	1890
July	1st to 10th	Night	40% 10% 22% 21% 6%	4105
	11th to 20th	Night	40% 10% 31% 15% 3 1	4051
	21st to end	Night	50% 12% 21% 13% 4	4297
August	1st to 10th	Night	40% 7% 23% 23% 7%	2904
	11th to 20th	Night	40% 9% 26% 17% 8%	2933
	21st to end	Night	32% 8% 19% 31% 9% 1	3586
September	1st to 10th	Night	40% 9% 15% 19% 14% 3	2186
	11th to 20th	Night	40% 10% 14% 20% 16%	2200
	21st to end	Night	39% 7% 13% 20% 18% 3	2200
October	1st to 10th	Night	30% 4 7% 22% 26% 11%	3590
	11th to 20th	Night	29% 3 6% 21% 22% 20%	3856
	21st to end	Night	25% 3 6% 26% 25% 14%	4252
November	1st to 10th	Night	37% 5% 7% 22% 23% 6%	2649
	11th to 20th	Night	39% 5% 7% 20% 22% 7%	2730
	21st to end	Night	42% 5% 7% 22% 19% 4	2730
December	1st to 10th	Night	51% 4 7% 14% 20% 4	4380
	11th to 20th	Night	51% 6% 9% 15% 16% 3	4954
	21st to end	Night	49% 8% 13% 16% 14% 1	6633

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% 31% 28% 11% 1	330
	11th to 20th	Day	37% 27% 23% 12% 2	330
	21st to end	Day	29% 31% 30% 9% 1	363
February	1st to 10th	Day	29% 26% 34% 9% 1	330
	11th to 20th	Day	42% 31% 22% 5%	330
	21st to end	Day	40% 29% 25% 7%	273
March	1st to 10th	Day	31% 22% 30% 14% 3	415
	11th to 20th	Day	29% 25% 31% 11% 3 1	540
	21st to end	Day	27% 22% 31% 16% 4	594
April	1st to 10th	Day	26% 21% 26% 19% 7% 1	540
	11th to 20th	Day	23% 23% 29% 17% 7% 2	532
	21st to end	Day	25% 15% 29% 20% 9% 3	540
May	1st to 10th	Day	24% 20% 26% 18% 7% 4	543
	11th to 20th	Day	17% 12% 29% 24% 12% 6%	567
	21st to end	Day	19% 10% 25% 24% 13% 9%	617
June	1st to 10th	Day	12% 10% 26% 29% 15% 7%	570
	11th to 20th	Day	9% 8% 25% 29% 19% 10%	570
	21st to end	Day	13% 6% 26% 28% 17% 10%	570
July	1st to 10th	Day	12% 5% 18% 28% 24% 12%	565
	11th to 20th	Day	13% 6% 17% 28% 22% 13%	544
	21st to end	Day	12% 3 17% 29% 26% 12%	576
August	1st to 10th	Day	17% 7% 19% 25% 19% 13%	526
	11th to 20th	Day	11% 6% 19% 31% 23% 9%	519
	21st to end	Day	13% 5% 15% 26% 28% 13%	583
September	1st to 10th	Day	12% 5% 17% 28% 29% 9%	530
	11th to 20th	Day	15% 8% 15% 28% 26% 9%	530
	21st to end	Day	17% 9% 18% 32% 19% 4	530
October	1st to 10th	Day	15% 7% 28% 27% 18% 6%	530
	11th to 20th	Day	17% 11% 30% 26% 14% 2	530
	21st to end	Day	23% 11% 28% 25% 11% 2	583
November	1st to 10th	Day	19% 18% 32% 22% 8% 1	344
	11th to 20th	Day	20% 24% 32% 21% 3	330
	21st to end	Day	22% 19% 34% 20% 4	330
December	1st to 10th	Day	31% 25% 31% 12% 1	330
	11th to 20th	Day	28% 20% 33% 16% 2	330
	21st to end	Day	28% 20% 37% 11% 4	363
January	1st to 10th	Night	25% 19% 29% 23% 4	840
	11th to 20th	Night	26% 22% 29% 19% 4	840
	21st to end	Night	22% 21% 33% 22% 2	924
February	1st to 10th	Night	24% 17% 30% 27% 3	840
	11th to 20th	Night	30% 20% 33% 16% 1	823
	21st to end	Night	29% 22% 29% 18% 2	692
March	1st to 10th	Night	23% 18% 31% 23% 4	840
	11th to 20th	Night	23% 20% 29% 22% 5% 1	840
	21st to end	Night	22% 17% 32% 22% 7%	924
April	1st to 10th	Night	21% 17% 29% 24% 8% 1	826
	11th to 20th	Night	19% 13% 33% 22% 12% 1	623
	21st to end	Night	18% 10% 28% 31% 12% 1	630
May	1st to 10th	Night	16% 14% 26% 30% 12% 2	630
	11th to 20th	Night	17% 8% 23% 30% 19% 2	621
	21st to end	Night	14% 4 18% 31% 28% 4	683
June	1st to 10th	Night	10% 5% 19% 36% 28% 3	630
	11th to 20th	Night	7% 3 18% 35% 30% 8%	630
	21st to end	Night	9% 3 16% 37% 31% 5%	630
July	1st to 10th	Night	12% 1 8% 33% 40% 5%	615
	11th to 20th	Night	10% 2 8% 32% 37% 10%	597
	21st to end	Night	8% 2 10% 30% 42% 8%	657
August	1st to 10th	Night	11% 4 8% 33% 37% 7%	597
	11th to 20th	Night	12% 4 9% 34% 37% 4	594
	21st to end	Night	11% 3 10% 30% 37% 9%	660
September	1st to 10th	Night	12% 4 11% 30% 35% 7%	786
	11th to 20th	Night	16% 3 12% 34% 29% 6%	800
	21st to end	Night	15% 5% 19% 32% 27% 2	800
October	1st to 10th	Night	16% 6% 18% 25% 27% 7%	800
	11th to 20th	Night	18% 8% 25% 30% 17% 2	800
	21st to end	Night	18% 10% 24% 33% 13% 2	880
November	1st to 10th	Night	17% 10% 21% 32% 16% 3	820
	11th to 20th	Night	18% 16% 25% 29% 10% 1	840
	21st to end	Night	21% 13% 25% 30% 12%	840
December	1st to 10th	Night	25% 18% 27% 24% 6%	840
	11th to 20th	Night	21% 18% 27% 27% 6% 1	840
	21st to end	Night	23% 19% 27% 27% 4	924

Page generated at 2026-07-13 03:14:51. Version ac07

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