Lake Sonoma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Sonoma clear sky chart from 2005-11-06 to 2024-07-08.

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	10% 4 2 4 3 3 3 3 4 6% 59%	89780
	Night	12% 5% 2 4 3 3 3 3 4 6% 54%	89686
Transparency	Day	27% 5% 9% 22% 23% 15%	89501
	Night	31% 5% 9% 20% 21% 15%	89488
Seeing	Day	14% 10% 23% 28% 19% 6%	14896
	Night	14% 6% 16% 31% 27% 6%	24153

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	18% 8% 3 7% 4 3 3 4 5% 6% 39%	2731
	11th to 20th	Day	26% 9% 4 8% 5% 3 3 2 5% 5% 30%	2860
	21st to end	Day	23% 8% 3 7% 4 4 4 3 5% 6% 33%	3146
February	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 3 5% 44%	1710
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 8% 43%	1674
	21st to end	Day	17% 6% 2 6% 3 3 4 3 4 6% 45%	1579
March	1st to 10th	Day	25% 14% 3 7% 4 3 3 3 4 4 29%	3442
	11th to 20th	Day	11% 4 1 4 3 4 4 3 5% 6% 53%	3490
	21st to end	Day	22% 7% 2 6% 4 4 4 4 6% 7% 34%	3825
April	1st to 10th	Day	14% 8% 2 6% 5% 4 4 3 6% 7% 43%	2274
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 5% 8% 51%	2249
	21st to end	Day	6% 4 2 4 3 3 3 3 6% 10% 56%	2280
May	1st to 10th	Day	5% 3 1 3 2 2 3 2 4 6% 70%	4107
	11th to 20th	Day	4 2 1 2 1 1 2 2 3 5% 75%	4121
	21st to end	Day	3 2 1 2 1 2 2 2 3 6% 76%	4813
June	1st to 10th	Day	6% 4 2 3 2 3 3 3 5% 7% 62%	2660
	11th to 20th	Day	2 1 2 2 2 2 2 4 7% 76%	2660
	21st to end	Day	3 1 1 2 2 2 2 2 3 4 81%	2660
July	1st to 10th	Day	2 1 1 2 1 2 2 3 4 82%	2617
	11th to 20th	Day	1 1 2 2 2 2 2 4 5% 80%	2340
	21st to end	Day	1 1 1 3 2 2 2 2 3 5% 79%	2546
August	1st to 10th	Day	1 1 1 2 1 3 2 2 4 6% 76%	2328
	11th to 20th	Day	1 1 1 2 1 1 1 2 4 6% 80%	2260
	21st to end	Day	1 1 1 3 1 1 2 2 4 5% 79%	2376
September	1st to 10th	Day	1 1 1 2 1 2 1 2 3 5% 83%	2160
	11th to 20th	Day	3 2 1 3 2 2 3 2 4 7% 71%	2124
	21st to end	Day	4 1 1 2 1 2 2 2 3 6% 76%	1912
October	1st to 10th	Day	7% 3 1 3 2 2 3 2 3 4 70%	1800
	11th to 20th	Day	9% 2 1 3 3 2 2 3 4 6% 64%	1800
	21st to end	Day	11% 3 2 3 2 2 3 2 6% 6% 60%	1980
November	1st to 10th	Day	11% 4 1 4 4 4 4 4 5% 7% 53%	1855
	11th to 20th	Day	13% 5% 3 6% 4 3 4 4 5% 5% 49%	1639
	21st to end	Day	11% 5% 2 3 4 4 3 3 5% 7% 52%	1520
December	1st to 10th	Day	18% 6% 2 5% 3 4 3 3 4 6% 44%	1520
	11th to 20th	Day	34% 9% 2 5% 3 3 3 3 4 4 30%	1928
	21st to end	Day	24% 8% 2 5% 4 4 4 3 5% 8% 34%	2794
January	1st to 10th	Night	17% 7% 2 5% 4 4 3 4 6% 8% 38%	4217
	11th to 20th	Night	23% 9% 3 8% 6% 4 4 4 4 5% 30%	4110
	21st to end	Night	26% 9% 3 7% 4 4 4 3 5% 6% 30%	4521
February	1st to 10th	Night	17% 6% 2 5% 3 3 3 2 5% 6% 47%	2470
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 7% 43%	2391
	21st to end	Night	14% 6% 1 4 3 3 3 2 5% 6% 53%	1870
March	1st to 10th	Night	22% 13% 3 7% 4 4 4 3 4 6% 31%	3432
	11th to 20th	Night	13% 5% 1 4 2 2 2 2 4 5% 59%	3490
	21st to end	Night	17% 11% 3 7% 4 4 4 3 5% 6% 37%	3828
April	1st to 10th	Night	10% 7% 3 6% 4 3 3 3 6% 7% 49%	1905
	11th to 20th	Night	8% 4 2 4 4 4 3 4 5% 6% 55%	1879
	21st to end	Night	6% 3 1 3 3 2 3 3 5% 7% 63%	1899
May	1st to 10th	Night	4 3 1 4 2 2 2 2 3 5% 71%	2860
	11th to 20th	Night	2 2 1 4 4 2 2 2 4 6% 71%	2778
	21st to end	Night	2 2 1 2 1 2 2 2 3 4 79%	2762
June	1st to 10th	Night	3 4 2 4 3 3 4 4 5% 9% 61%	1520
	11th to 20th	Night	1 2 1 1 1 2 3 2 4 5% 77%	1520
	21st to end	Night	2 3 1 2 2 1 2 2 2 4 78%	1520
July	1st to 10th	Night	1 1 2 1 1 2 2 2 5% 84%	1504
	11th to 20th	Night	1 2 1 2 2 1 2 1 2 4 83%	1619
	21st to end	Night	1 1 2 2 1 2 3 5% 8% 76%	1773
August	1st to 10th	Night	1 1 1 2 2 2 2 1 5% 6% 76%	1611
	11th to 20th	Night	1 3 2 2 3 2 4 7% 76%	1638
	21st to end	Night	1 2 1 3 3 2 2 2 3 6% 75%	1980
September	1st to 10th	Night	1 2 1 1 1 1 4 6% 83%	1800
	11th to 20th	Night	4 3 1 3 2 2 2 3 5% 8% 67%	1831
	21st to end	Night	3 2 1 3 2 2 2 2 4 5% 75%	2047
October	1st to 10th	Night	4 4 1 4 2 2 2 2 4 5% 70%	2160
	11th to 20th	Night	6% 3 1 3 3 3 4 3 5% 6% 64%	2160
	21st to end	Night	9% 3 1 3 2 2 3 3 5% 7% 61%	2376
November	1st to 10th	Night	11% 4 2 5% 4 3 3 3 6% 9% 52%	2221
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 6% 7% 48%	2536
	21st to end	Night	11% 4 2 5% 4 3 3 3 5% 6% 54%	2660
December	1st to 10th	Night	21% 6% 2 4 3 3 3 3 4 6% 44%	2660
	11th to 20th	Night	33% 7% 2 3 3 3 3 3 5% 6% 31%	3276
	21st to end	Night	24% 8% 2 5% 4 4 4 3 5% 6% 35%	4862

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	45% 6% 13% 24% 8% 4	2731
	11th to 20th	Day	56% 6% 9% 12% 9% 8%	2860
	21st to end	Day	52% 6% 8% 17% 12% 5%	3146
February	1st to 10th	Day	43% 4 8% 18% 18% 9%	1710
	11th to 20th	Day	39% 6% 10% 19% 20% 6%	1683
	21st to end	Day	40% 6% 10% 23% 15% 6%	1579
March	1st to 10th	Day	57% 7% 8% 13% 13% 2	3442
	11th to 20th	Day	30% 6% 10% 27% 16% 11%	3490
	21st to end	Day	46% 8% 14% 19% 10% 2	3825
April	1st to 10th	Day	40% 6% 13% 22% 15% 4	2274
	11th to 20th	Day	32% 6% 14% 24% 19% 5%	2252
	21st to end	Day	23% 6% 15% 30% 22% 5%	2280
May	1st to 10th	Day	16% 5% 13% 31% 20% 15%	4107
	11th to 20th	Day	12% 4 7% 27% 36% 15%	4124
	21st to end	Day	13% 3 11% 42% 28% 3	4814
June	1st to 10th	Day	22% 5% 11% 28% 27% 7%	2660
	11th to 20th	Day	10% 4 9% 23% 38% 17%	2660
	21st to end	Day	9% 3 5% 16% 37% 31%	2660
July	1st to 10th	Day	8% 3 3 13% 30% 43%	2548
	11th to 20th	Day	9% 2 5% 14% 32% 38%	2271
	21st to end	Day	10% 3 3 11% 28% 46%	2405
August	1st to 10th	Day	11% 3 5% 20% 30% 31%	2312
	11th to 20th	Day	8% 2 3 15% 39% 33%	2260
	21st to end	Day	9% 3 4 19% 36% 29%	2376
September	1st to 10th	Day	7% 3 3 13% 33% 42%	2160
	11th to 20th	Day	15% 3 7% 27% 35% 13%	2124
	21st to end	Day	12% 3 5% 24% 32% 24%	1912
October	1st to 10th	Day	20% 3 5% 20% 29% 24%	1800
	11th to 20th	Day	22% 5% 8% 19% 25% 22%	1800
	21st to end	Day	25% 4 9% 20% 25% 16%	1980
November	1st to 10th	Day	29% 6% 9% 27% 18% 11%	1855
	11th to 20th	Day	35% 7% 11% 23% 17% 8%	1639
	21st to end	Day	32% 5% 12% 19% 19% 13%	1520
December	1st to 10th	Day	41% 6% 8% 17% 19% 10%	1520
	11th to 20th	Day	59% 3 6% 12% 14% 5%	1928
	21st to end	Day	49% 6% 11% 20% 10% 4	2794
January	1st to 10th	Night	42% 8% 19% 18% 9% 3	4217
	11th to 20th	Night	56% 8% 9% 11% 9% 8%	4110
	21st to end	Night	54% 7% 9% 11% 13% 6%	4521
February	1st to 10th	Night	38% 5% 8% 19% 19% 11%	2470
	11th to 20th	Night	39% 6% 9% 21% 18% 7%	2393
	21st to end	Night	33% 4 14% 24% 21% 4	1870
March	1st to 10th	Night	53% 10% 10% 13% 13% 2	3432
	11th to 20th	Night	29% 4 9% 24% 23% 10%	3490
	21st to end	Night	46% 9% 13% 20% 10% 3	3828
April	1st to 10th	Night	34% 7% 13% 24% 17% 5%	1905
	11th to 20th	Night	28% 6% 13% 26% 19% 8%	1879
	21st to end	Night	22% 5% 10% 34% 24% 6%	1899
May	1st to 10th	Night	17% 4 5% 30% 29% 15%	2860
	11th to 20th	Night	12% 7% 6% 26% 30% 20%	2779
	21st to end	Night	12% 3 8% 40% 32% 5%	2762
June	1st to 10th	Night	22% 4 9% 24% 31% 10%	1520
	11th to 20th	Night	10% 3 8% 22% 36% 21%	1520
	21st to end	Night	12% 2 4 15% 31% 35%	1520
July	1st to 10th	Night	8% 2 2 11% 31% 46%	1464
	11th to 20th	Night	7% 2 4 13% 30% 43%	1566
	21st to end	Night	11% 2 2 13% 23% 49%	1674
August	1st to 10th	Night	12% 2 3 17% 27% 39%	1602
	11th to 20th	Night	10% 2 4 14% 29% 40%	1638
	21st to end	Night	12% 3 3 16% 31% 35%	1980
September	1st to 10th	Night	6% 2 3 14% 32% 44%	1800
	11th to 20th	Night	17% 3 7% 18% 38% 17%	1831
	21st to end	Night	13% 3 4 23% 26% 30%	2047
October	1st to 10th	Night	17% 4 7% 20% 28% 25%	2160
	11th to 20th	Night	20% 6% 8% 19% 25% 23%	2160
	21st to end	Night	23% 4 9% 19% 24% 20%	2376
November	1st to 10th	Night	30% 6% 10% 23% 19% 12%	2221
	11th to 20th	Night	33% 7% 13% 22% 18% 8%	2536
	21st to end	Night	31% 5% 9% 19% 22% 13%	2660
December	1st to 10th	Night	40% 6% 7% 17% 19% 11%	2660
	11th to 20th	Night	54% 5% 8% 14% 15% 5%	3276
	21st to end	Night	50% 6% 12% 17% 11% 3	4862

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	36% 13% 20% 14% 15% 2	294
	11th to 20th	Day	27% 11% 23% 19% 16% 3	370
	21st to end	Day	21% 11% 23% 26% 16% 3	407
February	1st to 10th	Day	22% 12% 22% 21% 18% 4	370
	11th to 20th	Day	28% 14% 22% 24% 11% 1	369
	21st to end	Day	24% 15% 22% 26% 10% 2	382
March	1st to 10th	Day	34% 16% 22% 20% 8% 1	460
	11th to 20th	Day	24% 15% 29% 18% 9% 4	460
	21st to end	Day	23% 20% 29% 19% 6% 2	506
April	1st to 10th	Day	23% 15% 30% 21% 8% 3	460
	11th to 20th	Day	20% 18% 28% 21% 11% 3	452
	21st to end	Day	13% 19% 34% 17% 11% 5%	460
May	1st to 10th	Day	13% 19% 30% 25% 11% 3	463
	11th to 20th	Day	13% 15% 31% 22% 13% 6%	488
	21st to end	Day	10% 12% 26% 27% 19% 6%	529
June	1st to 10th	Day	10% 11% 30% 28% 16% 4	490
	11th to 20th	Day	8% 13% 32% 30% 15% 2	490
	21st to end	Day	2 5% 28% 34% 22% 8%	490
July	1st to 10th	Day	4 3 20% 44% 22% 7%	475
	11th to 20th	Day	1 3 17% 43% 28% 8%	444
	21st to end	Day	1 1 14% 42% 32% 10%	487
August	1st to 10th	Day	2 4 19% 42% 26% 7%	447
	11th to 20th	Day	1 3 20% 38% 29% 9%	437
	21st to end	Day	1 3 18% 41% 28% 9%	495
September	1st to 10th	Day	2 5% 18% 38% 28% 9%	450
	11th to 20th	Day	4 8% 21% 33% 26% 7%	450
	21st to end	Day	6% 8% 22% 33% 23% 9%	450
October	1st to 10th	Day	9% 8% 23% 25% 25% 10%	450
	11th to 20th	Day	11% 7% 18% 24% 29% 12%	450
	21st to end	Day	15% 7% 20% 26% 24% 9%	495
November	1st to 10th	Day	14% 10% 20% 24% 25% 7%	451
	11th to 20th	Day	14% 6% 15% 25% 30% 10%	237
	21st to end	Day	17% 6% 22% 22% 20% 12%	180
December	1st to 10th	Day	26% 7% 18% 22% 17% 9%	180
	11th to 20th	Day	33% 8% 16% 19% 14% 9%	180
	21st to end	Day	28% 10% 20% 21% 16% 5%	198
January	1st to 10th	Night	24% 7% 14% 29% 21% 5%	760
	11th to 20th	Night	23% 5% 14% 33% 19% 5%	760
	21st to end	Night	21% 6% 14% 33% 21% 4	836
February	1st to 10th	Night	21% 6% 16% 32% 21% 4	760
	11th to 20th	Night	21% 9% 17% 32% 17% 5%	744
	21st to end	Night	20% 9% 20% 33% 15% 3	628
March	1st to 10th	Night	26% 8% 17% 29% 15% 3	760
	11th to 20th	Night	21% 8% 18% 31% 18% 3	760
	21st to end	Night	23% 8% 23% 30% 14% 2	836
April	1st to 10th	Night	18% 10% 24% 28% 17% 3	760
	11th to 20th	Night	14% 12% 23% 29% 17% 5%	751
	21st to end	Night	10% 16% 27% 24% 20% 3	759
May	1st to 10th	Night	9% 10% 28% 29% 21% 4	570
	11th to 20th	Night	5% 5% 24% 33% 27% 5%	532
	21st to end	Night	9% 10% 22% 27% 27% 5%	411
June	1st to 10th	Night	7% 10% 23% 33% 24% 2	380
	11th to 20th	Night	3 11% 24% 39% 21% 2	380
	21st to end	Night	3 2 19% 39% 35% 1	380
July	1st to 10th	Night	2 4 16% 36% 39% 5%	366
	11th to 20th	Night	1 1 12% 33% 43% 10%	522
	21st to end	Night	1 1 9% 25% 54% 11%	591
August	1st to 10th	Night	2 13% 33% 40% 12%	537
	11th to 20th	Night	1 1 14% 32% 42% 11%	570
	21st to end	Night	2 2 9% 31% 49% 8%	792
September	1st to 10th	Night	1 3 10% 34% 42% 10%	720
	11th to 20th	Night	6% 4 12% 37% 34% 9%	720
	21st to end	Night	5% 5% 15% 30% 35% 10%	720
October	1st to 10th	Night	7% 5% 15% 33% 32% 8%	720
	11th to 20th	Night	8% 5% 12% 31% 37% 8%	720
	21st to end	Night	13% 3 12% 29% 32% 11%	792
November	1st to 10th	Night	14% 5% 14% 29% 31% 7%	740
	11th to 20th	Night	16% 3 14% 37% 24% 6%	760
	21st to end	Night	13% 7% 16% 34% 23% 7%	760
December	1st to 10th	Night	25% 4 13% 31% 21% 6%	760
	11th to 20th	Night	30% 6% 11% 30% 19% 4	760
	21st to end	Night	25% 7% 17% 32% 16% 3	836

Page generated at 2024-07-05 08:05:41. Version ac07

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