Oakland/Lyons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakland/Lyons Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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% 7% 3 7% 4 4 4 4 5% 7% 44%	131535
	Night	9% 7% 3 7% 4 4 4 3 5% 7% 47%	129912
Transparency	Day	38% 7% 13% 25% 15% 2	135161
	Night	36% 6% 13% 26% 17% 2	134352
Seeing	Day	14% 10% 32% 29% 13% 2	17587
	Night	13% 9% 35% 33% 10%	27634

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	9% 13% 4 16% 8% 6% 4 3 4 5% 29%	5289
	11th to 20th	Day	5% 10% 4 10% 6% 5% 6% 4 6% 7% 37%	5310
	21st to end	Day	5% 9% 4 11% 6% 6% 6% 4 6% 6% 38%	5812
February	1st to 10th	Day	9% 12% 6% 10% 6% 6% 4 4 6% 6% 31%	1890
	11th to 20th	Day	9% 10% 5% 8% 5% 3 4 4 5% 6% 42%	1881
	21st to end	Day	10% 9% 3 8% 4 5% 4 3 4 7% 42%	1730
March	1st to 10th	Day	12% 9% 3 6% 3 3 3 2 4 4 51%	4844
	11th to 20th	Day	10% 8% 2 5% 3 3 3 3 4 7% 50%	4980
	21st to end	Day	20% 11% 4 10% 4 5% 5% 3 6% 7% 26%	5462
April	1st to 10th	Day	13% 10% 3 7% 4 4 3 3 5% 7% 41%	2250
	11th to 20th	Day	17% 9% 3 6% 4 2 3 3 5% 7% 40%	2527
	21st to end	Day	21% 8% 2 6% 4 4 4 3 5% 6% 38%	2600
May	1st to 10th	Day	13% 7% 3 7% 4 4 4 4 5% 6% 44%	5862
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 50%	5862
	21st to end	Day	17% 8% 3 7% 4 4 5% 4 5% 7% 35%	6699
June	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 7% 49%	2800
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 6% 8% 46%	2832
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 8% 49%	3000
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 47%	6331
	11th to 20th	Day	8% 4 2 6% 4 4 4 4 6% 7% 50%	5900
	21st to end	Day	5% 5% 2 5% 4 4 5% 5% 8% 9% 48%	6422
August	1st to 10th	Day	7% 5% 2 7% 5% 4 5% 4 7% 9% 46%	4234
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 6% 8% 40%	4171
	21st to end	Day	8% 5% 2 6% 4 4 4 3 6% 8% 51%	4642
September	1st to 10th	Day	12% 6% 2 4 4 4 4 3 4 6% 52%	2310
	11th to 20th	Day	9% 5% 2 6% 4 4 3 3 5% 7% 53%	2200
	21st to end	Day	10% 4 1 4 3 3 3 3 5% 7% 57%	2200
October	1st to 10th	Day	13% 5% 2 6% 3 3 3 2 4 5% 52%	2057
	11th to 20th	Day	10% 6% 2 5% 3 4 4 2 4 5% 56%	2000
	21st to end	Day	14% 7% 3 6% 4 3 3 3 4 6% 47%	2180
November	1st to 10th	Day	9% 7% 2 6% 4 4 4 3 5% 5% 52%	1853
	11th to 20th	Day	9% 8% 2 8% 4 3 4 4 6% 6% 46%	1806
	21st to end	Day	12% 9% 3 6% 3 4 3 3 6% 7% 44%	1680
December	1st to 10th	Day	6% 5% 3 6% 6% 5% 5% 3 4 6% 51%	2690
	11th to 20th	Day	9% 9% 4 9% 5% 4 4 5% 6% 6% 39%	3088
	21st to end	Day	15% 10% 4 14% 5% 4 4 3 4 5% 32%	4141
January	1st to 10th	Night	9% 10% 4 14% 8% 5% 5% 4 5% 6% 29%	7634
	11th to 20th	Night	4 7% 3 9% 7% 5% 7% 4 7% 6% 40%	7680
	21st to end	Night	5% 9% 5% 12% 5% 4 3 3 5% 6% 42%	8402
February	1st to 10th	Night	10% 10% 4 9% 5% 5% 3 4 4 6% 39%	2730
	11th to 20th	Night	8% 10% 4 7% 4 4 4 4 5% 7% 42%	2642
	21st to end	Night	8% 6% 3 7% 4 4 4 3 5% 5% 50%	2076
March	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 5% 5% 52%	5059
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 5% 6% 53%	4980
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 5% 7% 35%	5467
April	1st to 10th	Night	12% 8% 3 6% 5% 3 4 3 5% 7% 44%	2148
	11th to 20th	Night	12% 8% 3 6% 5% 4 4 3 5% 5% 46%	1818
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 5% 8% 40%	1800
May	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 52%	4053
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 7% 53%	4053
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 7% 42%	4175
June	1st to 10th	Night	8% 3 2 3 3 4 3 3 6% 9% 55%	1600
	11th to 20th	Night	7% 5% 2 5% 3 4 4 4 6% 8% 52%	1557
	21st to end	Night	5% 4 1 4 4 3 4 4 6% 8% 58%	1400
July	1st to 10th	Night	7% 5% 2 5% 3 3 3 3 5% 7% 55%	3619
	11th to 20th	Night	8% 4 2 5% 4 3 4 3 5% 8% 55%	4077
	21st to end	Night	4 4 2 4 4 3 4 4 6% 10% 55%	4449
August	1st to 10th	Night	4 4 1 6% 4 4 4 5% 6% 10% 52%	2926
	11th to 20th	Night	11% 6% 2 5% 4 3 3 3 6% 8% 50%	2888
	21st to end	Night	6% 4 2 5% 4 3 5% 3 6% 8% 54%	3266
September	1st to 10th	Night	8% 4 2 4 3 3 4 3 5% 6% 59%	2086
	11th to 20th	Night	8% 4 2 3 3 3 4 3 5% 7% 58%	2200
	21st to end	Night	8% 5% 2 5% 4 3 3 3 4 5% 60%	2200
October	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 5% 6% 51%	2322
	11th to 20th	Night	12% 7% 2 5% 3 2 3 2 4 5% 55%	2400
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 5% 52%	2655
November	1st to 10th	Night	8% 5% 2 5% 3 3 4 3 5% 7% 55%	2665
	11th to 20th	Night	9% 7% 2 6% 3 3 4 3 4 6% 52%	2811
	21st to end	Night	10% 8% 3 6% 3 3 3 3 5% 6% 49%	2940
December	1st to 10th	Night	5% 7% 3 8% 4 4 4 3 6% 6% 49%	4720
	11th to 20th	Night	10% 8% 3 8% 5% 4 4 4 5% 7% 42%	5339
	21st to end	Night	14% 13% 5% 11% 5% 3 4 3 4 5% 33%	7075

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	57% 6% 13% 15% 9% 1	5290
	11th to 20th	Day	45% 5% 12% 20% 15% 2	5310
	21st to end	Day	44% 8% 17% 22% 10% 1	5812
February	1st to 10th	Day	52% 7% 14% 17% 10% 1	1890
	11th to 20th	Day	44% 5% 13% 22% 14% 2	1890
	21st to end	Day	41% 6% 13% 24% 13% 3	1730
March	1st to 10th	Day	37% 5% 8% 28% 18% 4	4844
	11th to 20th	Day	34% 5% 8% 28% 22% 3	4980
	21st to end	Day	55% 9% 16% 15% 3 2	5464
April	1st to 10th	Day	43% 5% 12% 27% 11% 2	2250
	11th to 20th	Day	43% 6% 13% 22% 13% 3	2527
	21st to end	Day	46% 6% 12% 24% 12%	2600
May	1st to 10th	Day	39% 7% 11% 25% 17% 1	5900
	11th to 20th	Day	34% 6% 10% 24% 21% 5%	5866
	21st to end	Day	44% 8% 12% 21% 14% 1	6713
June	1st to 10th	Day	31% 9% 16% 29% 13% 3	2800
	11th to 20th	Day	34% 7% 14% 26% 16% 2	2832
	21st to end	Day	31% 7% 14% 29% 14% 4	3000
July	1st to 10th	Day	33% 8% 13% 33% 13% 1	6266
	11th to 20th	Day	31% 8% 13% 31% 16% 2	5831
	21st to end	Day	28% 9% 18% 27% 16% 2	6240
August	1st to 10th	Day	33% 7% 14% 28% 16% 2	4220
	11th to 20th	Day	41% 7% 12% 26% 13% 1	4210
	21st to end	Day	31% 7% 15% 23% 20% 4	4641
September	1st to 10th	Day	33% 6% 11% 29% 18% 4	2310
	11th to 20th	Day	31% 6% 13% 32% 17% 1	2200
	21st to end	Day	27% 5% 11% 30% 24% 2	2200
October	1st to 10th	Day	22% 3 6% 23% 42% 3	3343
	11th to 20th	Day	23% 4 14% 29% 24% 6%	3240
	21st to end	Day	36% 4 11% 26% 19% 3	3507
November	1st to 10th	Day	33% 6% 16% 25% 19% 2	1853
	11th to 20th	Day	38% 6% 14% 24% 16% 1	1806
	21st to end	Day	40% 5% 14% 26% 13% 1	1680
December	1st to 10th	Day	34% 5% 18% 27% 15% 1	2690
	11th to 20th	Day	44% 6% 18% 23% 9%	3085
	21st to end	Day	54% 6% 12% 20% 8% 1	4141
January	1st to 10th	Night	54% 7% 12% 16% 10% 1	7635
	11th to 20th	Night	40% 6% 14% 23% 16% 1	7680
	21st to end	Night	42% 6% 15% 21% 15% 1	8402
February	1st to 10th	Night	46% 6% 14% 21% 12% 2	2730
	11th to 20th	Night	41% 6% 13% 22% 14% 3	2643
	21st to end	Night	36% 4 13% 25% 18% 4	2076
March	1st to 10th	Night	35% 4 8% 29% 22% 2	5059
	11th to 20th	Night	31% 5% 6% 28% 24% 5%	4980
	21st to end	Night	47% 9% 16% 22% 5% 1	5467
April	1st to 10th	Night	39% 7% 11% 25% 17% 1	2148
	11th to 20th	Night	40% 6% 10% 25% 17% 3	1818
	21st to end	Night	41% 6% 14% 23% 14% 2	1800
May	1st to 10th	Night	32% 6% 11% 27% 22% 1	4080
	11th to 20th	Night	30% 7% 12% 18% 26% 7%	4054
	21st to end	Night	41% 7% 13% 23% 14% 2	4183
June	1st to 10th	Night	24% 8% 15% 34% 15% 4	1600
	11th to 20th	Night	28% 7% 14% 26% 20% 5%	1557
	21st to end	Night	22% 8% 17% 32% 19% 3	1400
July	1st to 10th	Night	28% 7% 14% 33% 16% 2	3578
	11th to 20th	Night	27% 6% 14% 33% 17% 2	4026
	21st to end	Night	22% 8% 20% 29% 18% 2	4320
August	1st to 10th	Night	25% 7% 15% 32% 17% 3	2916
	11th to 20th	Night	32% 7% 14% 28% 17% 2	2915
	21st to end	Night	28% 7% 14% 25% 17% 8%	3266
September	1st to 10th	Night	25% 6% 11% 31% 22% 5%	2086
	11th to 20th	Night	24% 7% 13% 33% 21% 2	2200
	21st to end	Night	27% 5% 9% 29% 25% 4	2200
October	1st to 10th	Night	21% 3 7% 17% 48% 4	3803
	11th to 20th	Night	23% 4 10% 30% 27% 6%	3899
	21st to end	Night	34% 3 11% 32% 18% 1	4279
November	1st to 10th	Night	28% 5% 17% 26% 21% 4	2665
	11th to 20th	Night	33% 5% 14% 28% 17% 3	2811
	21st to end	Night	36% 6% 12% 29% 16% 2	2940
December	1st to 10th	Night	34% 5% 14% 32% 14% 1	4720
	11th to 20th	Night	41% 6% 15% 28% 9%	5341
	21st to end	Night	53% 5% 11% 23% 7%	7075

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	17% 14% 34% 26% 10%	330
	11th to 20th	Day	16% 15% 38% 27% 3 1	330
	21st to end	Day	14% 9% 46% 24% 7% 1	363
February	1st to 10th	Day	17% 17% 41% 22% 4	330
	11th to 20th	Day	16% 14% 39% 25% 5% 1	330
	21st to end	Day	16% 18% 38% 22% 5%	273
March	1st to 10th	Day	16% 15% 43% 20% 4 1	306
	11th to 20th	Day	22% 16% 36% 19% 7% 1	300
	21st to end	Day	32% 13% 35% 16% 4 1	330
April	1st to 10th	Day	20% 17% 41% 18% 4	350
	11th to 20th	Day	21% 16% 35% 22% 6%	645
	21st to end	Day	25% 14% 32% 20% 9% 1	700
May	1st to 10th	Day	18% 15% 31% 23% 11% 2	703
	11th to 20th	Day	18% 11% 29% 25% 14% 3	725
	21st to end	Day	18% 10% 29% 28% 13% 3	789
June	1st to 10th	Day	7% 9% 27% 35% 19% 4	730
	11th to 20th	Day	9% 5% 35% 32% 16% 3	730
	21st to end	Day	9% 10% 30% 34% 15% 2	730
July	1st to 10th	Day	8% 4 21% 36% 24% 7%	721
	11th to 20th	Day	7% 4 25% 39% 19% 7%	718
	21st to end	Day	6% 3 23% 42% 23% 4	794
August	1st to 10th	Day	9% 3 23% 38% 23% 3	726
	11th to 20th	Day	10% 4 23% 37% 23% 3	715
	21st to end	Day	9% 4 25% 37% 22% 3	783
September	1st to 10th	Day	14% 6% 26% 36% 15% 3	440
	11th to 20th	Day	8% 6% 35% 32% 15% 5%	330
	21st to end	Day	11% 9% 29% 32% 15% 4	330
October	1st to 10th	Day	16% 9% 32% 25% 13% 5%	330
	11th to 20th	Day	12% 16% 40% 23% 7% 2	330
	21st to end	Day	18% 15% 36% 23% 8%	363
November	1st to 10th	Day	18% 14% 38% 19% 8% 2	330
	11th to 20th	Day	14% 15% 46% 20% 6%	330
	21st to end	Day	22% 15% 29% 27% 7%	330
December	1st to 10th	Day	10% 16% 41% 23% 9% 1	330
	11th to 20th	Day	16% 14% 41% 22% 8%	330
	21st to end	Day	22% 15% 39% 20% 4	363
January	1st to 10th	Night	12% 13% 36% 33% 6%	1050
	11th to 20th	Night	13% 14% 39% 28% 6%	1050
	21st to end	Night	14% 9% 44% 27% 5%	1155
February	1st to 10th	Night	15% 11% 41% 29% 4	1050
	11th to 20th	Night	13% 12% 43% 28% 4	1008
	21st to end	Night	12% 11% 45% 26% 6%	692
March	1st to 10th	Night	13% 13% 40% 28% 6% 1	663
	11th to 20th	Night	20% 11% 38% 26% 6%	600
	21st to end	Night	21% 12% 38% 25% 4	660
April	1st to 10th	Night	17% 15% 41% 25% 3	600
	11th to 20th	Night	17% 13% 39% 27% 4 1	593
	21st to end	Night	21% 9% 35% 28% 7%	600
May	1st to 10th	Night	16% 9% 31% 35% 9%	600
	11th to 20th	Night	13% 10% 30% 37% 10%	591
	21st to end	Night	16% 5% 33% 34% 11% 1	650
June	1st to 10th	Night	8% 4 26% 47% 15% 1	600
	11th to 20th	Night	9% 6% 31% 40% 13%	600
	21st to end	Night	6% 4 34% 43% 13%	600
July	1st to 10th	Night	8% 2 21% 42% 26% 1	585
	11th to 20th	Night	4 1 22% 49% 22% 1	582
	21st to end	Night	5% 2 16% 56% 21%	657
August	1st to 10th	Night	6% 2 22% 45% 23% 1	597
	11th to 20th	Night	9% 4 19% 46% 23% 1	594
	21st to end	Night	7% 2 26% 43% 20% 2	660
September	1st to 10th	Night	9% 6% 26% 39% 19% 1	600
	11th to 20th	Night	10% 2 32% 43% 13% 1	600
	21st to end	Night	9% 7% 34% 33% 16% 1	600
October	1st to 10th	Night	16% 10% 31% 31% 11% 1	722
	11th to 20th	Night	14% 14% 37% 30% 6%	800
	21st to end	Night	17% 13% 30% 30% 10%	895
November	1st to 10th	Night	11% 10% 39% 33% 7% 1	1025
	11th to 20th	Night	12% 12% 42% 28% 6%	1050
	21st to end	Night	14% 12% 38% 26% 9%	1050
December	1st to 10th	Night	14% 11% 41% 29% 5%	1050
	11th to 20th	Night	14% 12% 37% 30% 6%	1050
	21st to end	Night	18% 12% 37% 27% 5%	1155

Page generated at 2026-02-28 00:40:20. Version ac07

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