Sonoma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sonoma clear sky chart from 2005-11-06 to 2024-02-25.

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 4 2 3 3 4 6% 56%	78576
	Night	12% 5% 2 4 4 2 4 4 4 7% 52%	80749
Transparency	Day	29% 5% 9% 19% 22% 15%	78295
	Night	32% 6% 10% 18% 20% 14%	80552
Seeing	Day	10% 10% 24% 31% 20% 5%	14354
	Night	11% 5% 16% 34% 29% 5%	23780

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 6% 5% 3 4 4 4 6% 40%	2681
	11th to 20th	Day	22% 9% 4 6% 6% 3 4 4 4 5% 34%	2860
	21st to end	Day	22% 7% 3 7% 6% 3 4 5% 4 6% 32%	3146
February	1st to 10th	Day	18% 4 2 6% 4 3 4 4 4 5% 44%	1710
	11th to 20th	Day	15% 7% 2 6% 5% 3 3 4 6% 6% 42%	1718
	21st to end	Day	16% 5% 2 3 5% 3 3 3 5% 6% 47%	1521
March	1st to 10th	Day	17% 8% 3 6% 5% 3 4 4 5% 6% 38%	1954
	11th to 20th	Day	19% 5% 3 5% 4 3 5% 5% 6% 7% 38%	1980
	21st to end	Day	15% 5% 2 5% 5% 3 4 5% 5% 8% 43%	2197
April	1st to 10th	Day	14% 7% 3 5% 5% 3 5% 4 5% 8% 41%	2160
	11th to 20th	Day	9% 4 2 5% 4 2 4 4 5% 7% 53%	2129
	21st to end	Day	6% 4 2 4 3 2 3 3 6% 9% 58%	2160
May	1st to 10th	Day	6% 4 2 4 3 2 3 3 5% 7% 61%	2276
	11th to 20th	Day	6% 3 2 4 3 2 3 4 4 8% 62%	2357
	21st to end	Day	4 4 2 5% 5% 2 4 3 5% 7% 58%	2723
June	1st to 10th	Day	7% 5% 2 3 4 2 3 4 5% 8% 59%	2520
	11th to 20th	Day	1 2 1 2 3 2 3 3 4 7% 73%	2520
	21st to end	Day	2 1 1 4 3 2 2 2 4 6% 73%	2520
July	1st to 10th	Day	1 3 1 3 3 2 3 2 3 5% 75%	2520
	11th to 20th	Day	1 2 1 3 4 2 3 3 4 7% 71%	2369
	21st to end	Day	1 2 1 2 2 2 2 3 4 6% 74%	2546
August	1st to 10th	Day	1 3 2 3 4 2 3 4 3 7% 68%	2328
	11th to 20th	Day	1 2 1 2 3 2 3 3 3 6% 73%	2219
	21st to end	Day	1 4 2 3 3 2 3 2 3 7% 72%	2376
September	1st to 10th	Day	1 2 1 2 2 2 2 2 3 6% 77%	2160
	11th to 20th	Day	3 4 1 4 4 2 2 3 4 6% 66%	2160
	21st to end	Day	4 2 1 2 2 2 2 3 4 4 74%	1900
October	1st to 10th	Day	5% 2 1 2 4 1 3 3 4 6% 69%	1800
	11th to 20th	Day	7% 4 1 3 3 2 3 3 4 5% 66%	1800
	21st to end	Day	10% 3 2 3 3 2 3 3 4 7% 60%	1980
November	1st to 10th	Day	11% 3 1 3 4 3 4 4 5% 7% 55%	1824
	11th to 20th	Day	13% 4 3 5% 5% 3 4 3 4 7% 48%	1700
	21st to end	Day	12% 4 2 3 5% 3 4 5% 5% 5% 53%	1520
December	1st to 10th	Day	17% 7% 2 5% 3 2 4 4 5% 6% 45%	1520
	11th to 20th	Day	31% 8% 4 5% 5% 2 3 3 4 4 32%	1928
	21st to end	Day	24% 7% 2 5% 4 2 4 4 5% 8% 34%	2794
January	1st to 10th	Night	16% 8% 2 4 5% 3 4 4 5% 7% 44%	4251
	11th to 20th	Night	21% 9% 2 6% 5% 3 4 4 5% 6% 34%	4110
	21st to end	Night	23% 8% 3 6% 5% 3 4 4 4 6% 33%	4521
February	1st to 10th	Night	17% 5% 2 4 4 3 4 3 5% 5% 48%	2470
	11th to 20th	Night	13% 6% 3 6% 4 2 4 4 5% 8% 46%	2346
	21st to end	Night	13% 5% 2 4 4 2 4 4 3 6% 53%	1829
March	1st to 10th	Night	17% 7% 3 5% 5% 3 5% 4 4 6% 40%	2003
	11th to 20th	Night	16% 5% 3 4 5% 3 5% 4 5% 8% 43%	1980
	21st to end	Night	16% 5% 2 5% 3 2 2 3 4 6% 51%	2157
April	1st to 10th	Night	12% 5% 2 6% 5% 2 3 4 5% 7% 50%	1800
	11th to 20th	Night	10% 5% 2 3 3 3 3 3 4 6% 58%	1779
	21st to end	Night	6% 3 1 3 3 2 3 3 5% 10% 61%	1800
May	1st to 10th	Night	5% 3 2 4 3 2 4 4 5% 6% 61%	1681
	11th to 20th	Night	4 3 2 4 4 3 3 5% 4 8% 61%	1536
	21st to end	Night	4 4 2 4 4 2 3 3 6% 8% 60%	1552
June	1st to 10th	Night	4 3 2 3 4 3 4 4 5% 8% 61%	1440
	11th to 20th	Night	2 1 1 2 2 2 3 3 5% 8% 73%	1440
	21st to end	Night	2 3 2 3 3 2 2 3 4 6% 70%	1440
July	1st to 10th	Night	3 1 2 3 2 3 3 3 7% 73%	1440
	11th to 20th	Night	1 2 1 4 4 3 3 4 5% 7% 67%	1587
	21st to end	Night	1 3 2 6% 5% 4 4 4 6% 10% 56%	1773
August	1st to 10th	Night	2 4 2 5% 6% 2 5% 4 4 9% 56%	1611
	11th to 20th	Night	1 3 2 4 4 3 3 4 5% 9% 63%	1682
	21st to end	Night	1 3 2 4 5% 2 3 3 4 7% 66%	1980
September	1st to 10th	Night	1 2 1 2 3 2 2 3 4 7% 74%	1800
	11th to 20th	Night	4 4 2 5% 4 3 3 3 4 8% 62%	1800
	21st to end	Night	2 2 2 3 3 2 3 3 3 6% 71%	2057
October	1st to 10th	Night	5% 3 1 3 4 2 3 3 3 5% 69%	2160
	11th to 20th	Night	6% 3 2 4 4 2 3 4 5% 7% 61%	2160
	21st to end	Night	8% 5% 1 3 4 2 2 4 4 7% 61%	2376
November	1st to 10th	Night	9% 4 2 3 4 2 4 3 5% 7% 56%	2253
	11th to 20th	Night	11% 5% 2 5% 4 2 4 3 5% 7% 52%	2477
	21st to end	Night	10% 4 2 4 4 3 3 2 4 6% 58%	2660
December	1st to 10th	Night	18% 6% 2 5% 5% 2 3 3 4 6% 46%	2660
	11th to 20th	Night	32% 6% 2 4 4 2 3 3 6% 5% 32%	3276
	21st to end	Night	23% 6% 2 5% 5% 3 4 4 4 5% 38%	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	44% 8% 14% 25% 7% 3	2681
	11th to 20th	Day	54% 7% 9% 13% 10% 7%	2860
	21st to end	Day	52% 7% 9% 16% 11% 4	3146
February	1st to 10th	Day	40% 6% 8% 19% 19% 8%	1710
	11th to 20th	Day	41% 7% 8% 19% 19% 7%	1727
	21st to end	Day	37% 6% 10% 23% 17% 7%	1521
March	1st to 10th	Day	45% 7% 12% 17% 16% 3	1954
	11th to 20th	Day	44% 6% 10% 21% 13% 5%	1980
	21st to end	Day	37% 9% 14% 20% 17% 4	2197
April	1st to 10th	Day	41% 7% 12% 19% 17% 4	2160
	11th to 20th	Day	30% 7% 15% 23% 20% 6%	2132
	21st to end	Day	23% 6% 14% 29% 23% 4	2160
May	1st to 10th	Day	23% 5% 10% 28% 28% 7%	2276
	11th to 20th	Day	22% 5% 9% 33% 23% 8%	2360
	21st to end	Day	25% 7% 15% 27% 22% 4	2724
June	1st to 10th	Day	25% 5% 11% 28% 25% 7%	2520
	11th to 20th	Day	13% 4 10% 20% 35% 17%	2520
	21st to end	Day	14% 3 5% 15% 35% 28%	2520
July	1st to 10th	Day	14% 3 4 12% 25% 42%	2451
	11th to 20th	Day	16% 3 6% 13% 25% 37%	2298
	21st to end	Day	13% 3 5% 9% 27% 44%	2405
August	1st to 10th	Day	18% 3 6% 14% 31% 28%	2312
	11th to 20th	Day	15% 3 4 11% 35% 32%	2219
	21st to end	Day	16% 3 5% 14% 33% 29%	2376
September	1st to 10th	Day	12% 2 4 11% 31% 41%	2160
	11th to 20th	Day	19% 5% 8% 21% 34% 13%	2160
	21st to end	Day	14% 3 6% 21% 32% 24%	1900
October	1st to 10th	Day	19% 4 6% 17% 31% 23%	1800
	11th to 20th	Day	22% 6% 8% 19% 24% 22%	1800
	21st to end	Day	27% 4 7% 20% 24% 17%	1980
November	1st to 10th	Day	27% 8% 10% 26% 18% 11%	1824
	11th to 20th	Day	36% 6% 10% 22% 18% 7%	1700
	21st to end	Day	32% 6% 11% 19% 21% 12%	1520
December	1st to 10th	Day	39% 7% 9% 19% 18% 8%	1520
	11th to 20th	Day	56% 5% 9% 11% 15% 4	1928
	21st to end	Day	47% 8% 14% 19% 9% 3	2794
January	1st to 10th	Night	39% 9% 19% 22% 7% 3	4251
	11th to 20th	Night	50% 9% 12% 12% 9% 8%	4110
	21st to end	Night	51% 8% 11% 12% 12% 6%	4521
February	1st to 10th	Night	37% 6% 8% 20% 19% 11%	2470
	11th to 20th	Night	36% 7% 11% 19% 19% 8%	2348
	21st to end	Night	32% 5% 11% 26% 21% 6%	1829
March	1st to 10th	Night	45% 7% 12% 15% 17% 4	2003
	11th to 20th	Night	39% 6% 9% 22% 18% 6%	1980
	21st to end	Night	34% 7% 14% 22% 18% 6%	2157
April	1st to 10th	Night	34% 7% 14% 19% 20% 6%	1800
	11th to 20th	Night	28% 5% 12% 26% 18% 11%	1779
	21st to end	Night	21% 5% 13% 30% 25% 6%	1800
May	1st to 10th	Night	22% 7% 9% 21% 29% 11%	1681
	11th to 20th	Night	22% 5% 12% 26% 25% 9%	1537
	21st to end	Night	24% 6% 14% 28% 22% 6%	1552
June	1st to 10th	Night	23% 7% 11% 22% 29% 8%	1440
	11th to 20th	Night	12% 4 10% 21% 34% 18%	1440
	21st to end	Night	16% 5% 4 16% 31% 28%	1440
July	1st to 10th	Night	13% 4 6% 11% 26% 40%	1400
	11th to 20th	Night	18% 4 8% 12% 21% 37%	1535
	21st to end	Night	25% 4 7% 10% 17% 37%	1674
August	1st to 10th	Night	27% 3 8% 13% 23% 26%	1602
	11th to 20th	Night	19% 5% 7% 10% 26% 33%	1682
	21st to end	Night	20% 4 8% 13% 24% 31%	1980
September	1st to 10th	Night	12% 3 6% 10% 30% 39%	1800
	11th to 20th	Night	23% 5% 7% 19% 31% 16%	1800
	21st to end	Night	17% 4 6% 20% 27% 27%	2057
October	1st to 10th	Night	19% 4 8% 17% 27% 24%	2160
	11th to 20th	Night	24% 5% 7% 18% 22% 24%	2160
	21st to end	Night	24% 5% 8% 19% 23% 21%	2376
November	1st to 10th	Night	27% 5% 11% 26% 17% 13%	2253
	11th to 20th	Night	31% 6% 12% 25% 18% 9%	2477
	21st to end	Night	29% 5% 9% 22% 22% 13%	2660
December	1st to 10th	Night	39% 6% 10% 17% 17% 11%	2660
	11th to 20th	Night	52% 6% 10% 13% 15% 4	3276
	21st to end	Night	46% 9% 14% 16% 11% 4	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	31% 11% 26% 17% 13% 2	270
	11th to 20th	Day	21% 11% 24% 27% 14% 3	370
	21st to end	Day	16% 8% 29% 29% 17% 2	407
February	1st to 10th	Day	19% 12% 20% 27% 19% 2	370
	11th to 20th	Day	21% 17% 24% 24% 14% 1	390
	21st to end	Day	15% 17% 25% 27% 16% 1	363
March	1st to 10th	Day	23% 17% 29% 19% 10% 1	420
	11th to 20th	Day	23% 12% 28% 21% 13% 4	420
	21st to end	Day	15% 19% 31% 25% 10% 1	462
April	1st to 10th	Day	17% 15% 32% 23% 11% 3	420
	11th to 20th	Day	13% 20% 29% 22% 12% 4	412
	21st to end	Day	6% 18% 30% 26% 12% 7%	420
May	1st to 10th	Day	9% 17% 29% 27% 14% 4	423
	11th to 20th	Day	9% 15% 30% 25% 17% 3	448
	21st to end	Day	8% 12% 27% 31% 18% 5%	485
June	1st to 10th	Day	10% 10% 27% 31% 17% 6%	450
	11th to 20th	Day	4 11% 30% 38% 15% 3	450
	21st to end	Day	2 4 26% 38% 25% 5%	450
July	1st to 10th	Day	3 4 23% 43% 23% 4	446
	11th to 20th	Day	2 2 16% 40% 32% 9%	444
	21st to end	Day	2 1 16% 47% 27% 8%	487
August	1st to 10th	Day	2 4 19% 43% 26% 6%	447
	11th to 20th	Day	3 3 22% 38% 25% 9%	437
	21st to end	Day	4 1 18% 42% 27% 8%	495
September	1st to 10th	Day	3 3 18% 39% 28% 9%	450
	11th to 20th	Day	6% 7% 23% 36% 22% 8%	450
	21st to end	Day	5% 5% 24% 33% 26% 7%	450
October	1st to 10th	Day	6% 7% 26% 28% 24% 10%	450
	11th to 20th	Day	7% 9% 19% 27% 29% 8%	450
	21st to end	Day	12% 6% 20% 29% 26% 6%	495
November	1st to 10th	Day	13% 7% 19% 23% 31% 7%	420
	11th to 20th	Day	10% 7% 15% 27% 32% 9%	265
	21st to end	Day	13% 7% 22% 30% 23% 5%	180
December	1st to 10th	Day	20% 12% 21% 22% 17% 7%	180
	11th to 20th	Day	22% 13% 19% 24% 16% 6%	180
	21st to end	Day	22% 13% 23% 25% 16% 2	198
January	1st to 10th	Night	21% 6% 15% 31% 23% 6%	760
	11th to 20th	Night	19% 4 17% 35% 21% 4	760
	21st to end	Night	18% 6% 15% 33% 25% 3	836
February	1st to 10th	Night	18% 6% 15% 35% 22% 3	760
	11th to 20th	Night	15% 8% 18% 33% 21% 5%	744
	21st to end	Night	16% 8% 21% 33% 20% 2	610
March	1st to 10th	Night	19% 9% 20% 29% 20% 3	720
	11th to 20th	Night	19% 5% 17% 31% 24% 3	720
	21st to end	Night	16% 7% 26% 32% 17% 2	792
April	1st to 10th	Night	15% 6% 25% 33% 18% 3	720
	11th to 20th	Night	12% 11% 23% 29% 22% 4	711
	21st to end	Night	8% 6% 28% 31% 23% 4	720
May	1st to 10th	Night	6% 6% 22% 35% 26% 4	601
	11th to 20th	Night	5% 3 20% 34% 34% 4	474
	21st to end	Night	5% 6% 21% 34% 29% 5%	389
June	1st to 10th	Night	6% 4 21% 36% 31% 2	360
	11th to 20th	Night	2 5% 17% 48% 26% 2	360
	21st to end	Night	3 2 14% 44% 36% 2	360
July	1st to 10th	Night	2 10% 38% 47% 3	350
	11th to 20th	Night	3 1 4 34% 48% 9%	491
	21st to end	Night	3 1 6% 34% 50% 6%	591
August	1st to 10th	Night	5% 2 8% 30% 46% 7%	537
	11th to 20th	Night	3 1 9% 39% 41% 9%	614
	21st to end	Night	4 1 8% 37% 44% 7%	792
September	1st to 10th	Night	1 1 9% 37% 43% 8%	720
	11th to 20th	Night	5% 3 12% 36% 36% 8%	720
	21st to end	Night	4 3 13% 34% 37% 9%	720
October	1st to 10th	Night	6% 3 16% 33% 32% 10%	720
	11th to 20th	Night	8% 5% 13% 32% 35% 8%	720
	21st to end	Night	10% 3 12% 30% 33% 12%	792
November	1st to 10th	Night	10% 5% 15% 29% 33% 8%	740
	11th to 20th	Night	12% 3 14% 34% 30% 6%	760
	21st to end	Night	11% 5% 16% 36% 26% 6%	760
December	1st to 10th	Night	20% 5% 14% 33% 22% 6%	760
	11th to 20th	Night	25% 5% 15% 32% 20% 4	760
	21st to end	Night	21% 6% 21% 32% 18% 2	836

Page generated at 2024-02-22 03:05:42. Version ac07

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