Sea Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sea Ranch clear sky chart from 2005-11-06 to 2024-01-12.

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	10% 4 2 4 3 2 3 3 5% 8% 56%	74648
	Night	13% 5% 2 4 3 2 3 4 4 7% 53%	75078
Transparency	Day	28% 4 8% 21% 24% 15%	74371
	Night	32% 4 8% 19% 22% 15%	74877
Seeing	Day	13% 9% 25% 27% 19% 6%	14273
	Night	15% 6% 17% 28% 26% 8%	23590

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	22% 7% 4 7% 5% 2 4 4 6% 6% 33%	1670
	11th to 20th	Day	20% 6% 3 4 4 2 3 3 4 7% 43%	1633
	21st to end	Day	17% 6% 2 5% 3 3 5% 4 6% 7% 41%	1782
February	1st to 10th	Day	20% 6% 3 5% 5% 2 3 4 4 5% 43%	1620
	11th to 20th	Day	16% 5% 1 5% 5% 3 3 4 6% 9% 42%	1575
	21st to end	Day	19% 6% 2 4 4 2 4 4 4 6% 44%	1503
March	1st to 10th	Day	22% 7% 4 6% 5% 3 4 4 5% 7% 34%	1980
	11th to 20th	Day	20% 6% 3 5% 4 3 5% 4 6% 8% 36%	1980
	21st to end	Day	16% 6% 2 4 4 3 4 5% 5% 8% 43%	2178
April	1st to 10th	Day	17% 6% 2 4 5% 2 4 5% 6% 8% 39%	2135
	11th to 20th	Day	10% 5% 2 4 4 3 4 4 5% 8% 49%	2129
	21st to end	Day	8% 3 2 3 4 2 4 4 6% 10% 54%	2186
May	1st to 10th	Day	7% 3 2 3 3 2 3 4 5% 9% 60%	2340
	11th to 20th	Day	8% 3 1 3 3 2 3 3 6% 9% 59%	2300
	21st to end	Day	6% 4 1 4 3 2 3 3 6% 9% 59%	2710
June	1st to 10th	Day	6% 5% 2 3 3 2 4 3 5% 10% 57%	2520
	11th to 20th	Day	2 2 1 2 2 1 2 3 6% 6% 73%	2520
	21st to end	Day	3 1 1 1 2 1 2 3 3 6% 76%	2520
July	1st to 10th	Day	1 1 1 2 2 2 2 3 3 6% 76%	2471
	11th to 20th	Day	1 1 1 2 2 2 3 3 3 8% 74%	2340
	21st to end	Day	1 2 1 2 3 2 3 3 5% 9% 70%	2546
August	1st to 10th	Day	1 2 1 2 2 2 2 3 5% 8% 71%	2328
	11th to 20th	Day	1 2 1 2 2 1 3 3 5% 8% 73%	2280
	21st to end	Day	1 3 2 3 3 2 3 3 5% 9% 67%	2376
September	1st to 10th	Day	1 1 1 2 1 1 2 3 2 8% 78%	2160
	11th to 20th	Day	4 3 2 3 3 2 3 3 5% 8% 65%	2093
	21st to end	Day	4 2 1 2 2 1 3 2 4 7% 71%	1930
October	1st to 10th	Day	7% 3 1 3 3 1 2 3 4 5% 69%	1800
	11th to 20th	Day	11% 3 1 4 3 1 4 3 6% 7% 58%	1800
	21st to end	Day	11% 3 2 4 3 1 4 3 5% 8% 55%	1980
November	1st to 10th	Day	11% 5% 2 4 4 3 4 5% 6% 8% 49%	1859
	11th to 20th	Day	14% 6% 2 5% 3 2 5% 3 5% 7% 47%	1642
	21st to end	Day	12% 4 1 4 4 2 4 4 5% 8% 50%	1520
December	1st to 10th	Day	20% 7% 2 4 3 3 5% 4 5% 8% 41%	1520
	11th to 20th	Day	33% 9% 2 5% 4 3 3 4 5% 5% 27%	1928
	21st to end	Day	26% 8% 4 5% 4 2 4 4 5% 7% 31%	2794
January	1st to 10th	Night	22% 7% 2 5% 4 3 4 5% 6% 8% 34%	2493
	11th to 20th	Night	20% 7% 3 4 5% 2 3 4 4 6% 41%	2366
	21st to end	Night	18% 5% 3 5% 4 2 3 5% 5% 8% 43%	2574
February	1st to 10th	Night	19% 5% 2 3 4 2 4 4 5% 6% 45%	2340
	11th to 20th	Night	16% 7% 2 4 3 3 4 5% 6% 7% 42%	2272
	21st to end	Night	17% 5% 1 4 3 2 4 3 5% 6% 49%	1747
March	1st to 10th	Night	22% 9% 3 6% 4 3 5% 5% 4 5% 34%	1980
	11th to 20th	Night	20% 6% 2 6% 5% 2 4 4 4 6% 39%	1980
	21st to end	Night	18% 5% 2 5% 3 2 4 3 4 6% 47%	2178
April	1st to 10th	Night	14% 7% 3 5% 4 3 4 4 4 8% 44%	1823
	11th to 20th	Night	10% 6% 2 4 4 3 4 4 5% 6% 52%	1779
	21st to end	Night	7% 3 2 3 3 2 3 4 4 8% 61%	1769
May	1st to 10th	Night	5% 5% 1 3 3 2 3 4 4 8% 61%	1620
	11th to 20th	Night	4 4 2 5% 3 2 3 3 5% 10% 59%	1593
	21st to end	Night	6% 3 2 4 3 2 3 3 5% 7% 61%	1561
June	1st to 10th	Night	5% 8% 2 3 3 3 4 4 4 9% 56%	1440
	11th to 20th	Night	3 1 1 2 2 2 2 3 4 6% 73%	1440
	21st to end	Night	3 3 1 2 2 2 3 3 3 4 75%	1440
July	1st to 10th	Night	2 2 1 2 2 2 2 2 3 5% 77%	1484
	11th to 20th	Night	2 2 1 2 2 1 3 2 3 5% 77%	1620
	21st to end	Night	1 2 1 3 3 1 3 4 3 9% 70%	1773
August	1st to 10th	Night	1 3 2 3 2 2 2 3 4 6% 73%	1611
	11th to 20th	Night	1 2 1 4 2 1 3 2 6% 7% 71%	1619
	21st to end	Night	2 3 2 3 2 2 3 3 3 5% 73%	1980
September	1st to 10th	Night	1 1 1 2 2 1 2 3 3 6% 78%	1800
	11th to 20th	Night	5% 4 2 3 3 1 2 3 4 6% 66%	1862
	21st to end	Night	4 3 1 3 3 2 2 2 4 6% 70%	2029
October	1st to 10th	Night	5% 4 2 3 3 2 2 2 3 5% 69%	2160
	11th to 20th	Night	7% 4 1 3 4 2 3 3 4 7% 61%	2160
	21st to end	Night	12% 3 1 2 2 2 3 3 4 7% 60%	2376
November	1st to 10th	Night	13% 5% 2 3 3 2 4 5% 5% 8% 50%	2220
	11th to 20th	Night	16% 5% 1 4 4 2 5% 5% 6% 8% 44%	2531
	21st to end	Night	12% 5% 2 4 3 2 3 4 4 7% 52%	2660
December	1st to 10th	Night	22% 7% 2 4 3 2 3 3 5% 7% 42%	2660
	11th to 20th	Night	34% 7% 2 4 3 2 3 4 4 7% 30%	3276
	21st to end	Night	26% 8% 3 6% 5% 2 4 3 4 6% 34%	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	51% 4 11% 20% 9% 5%	1670
	11th to 20th	Day	44% 3 9% 16% 15% 13%	1633
	21st to end	Day	41% 4 8% 18% 20% 8%	1782
February	1st to 10th	Day	44% 3 8% 17% 20% 8%	1620
	11th to 20th	Day	38% 4 10% 21% 21% 6%	1584
	21st to end	Day	40% 4 11% 24% 15% 5%	1503
March	1st to 10th	Day	50% 4 12% 16% 15% 2	1980
	11th to 20th	Day	46% 4 9% 21% 15% 5%	1980
	21st to end	Day	41% 3 14% 21% 17% 3	2178
April	1st to 10th	Day	42% 4 14% 23% 13% 3	2135
	11th to 20th	Day	33% 4 16% 24% 18% 5%	2132
	21st to end	Day	25% 4 14% 29% 22% 5%	2186
May	1st to 10th	Day	24% 3 11% 30% 25% 7%	2340
	11th to 20th	Day	23% 3 12% 29% 25% 8%	2303
	21st to end	Day	24% 4 14% 34% 21% 2	2711
June	1st to 10th	Day	25% 4 11% 28% 27% 6%	2520
	11th to 20th	Day	13% 3 9% 22% 37% 16%	2520
	21st to end	Day	11% 4 4 16% 38% 28%	2520
July	1st to 10th	Day	10% 5% 3 13% 32% 37%	2404
	11th to 20th	Day	11% 5% 4 14% 31% 36%	2271
	21st to end	Day	12% 5% 3 11% 29% 40%	2405
August	1st to 10th	Day	14% 4 4 20% 28% 30%	2312
	11th to 20th	Day	10% 6% 3 15% 37% 30%	2280
	21st to end	Day	14% 7% 3 16% 33% 26%	2376
September	1st to 10th	Day	9% 3 2 14% 34% 39%	2160
	11th to 20th	Day	20% 4 4 28% 34% 11%	2093
	21st to end	Day	15% 3 4 25% 30% 24%	1930
October	1st to 10th	Day	21% 3 4 22% 28% 23%	1800
	11th to 20th	Day	25% 4 8% 20% 26% 17%	1800
	21st to end	Day	28% 3 9% 22% 23% 16%	1980
November	1st to 10th	Day	32% 4 8% 29% 18% 9%	1859
	11th to 20th	Day	38% 3 12% 23% 15% 8%	1642
	21st to end	Day	33% 4 13% 20% 20% 11%	1520
December	1st to 10th	Day	42% 5% 9% 18% 16% 10%	1520
	11th to 20th	Day	60% 3 7% 16% 11% 4	1928
	21st to end	Day	53% 3 11% 21% 9% 3	2794
January	1st to 10th	Night	47% 4 13% 19% 11% 5%	2493
	11th to 20th	Night	46% 3 10% 17% 12% 12%	2366
	21st to end	Night	40% 3 10% 17% 20% 10%	2574
February	1st to 10th	Night	39% 3 8% 20% 19% 10%	2340
	11th to 20th	Night	39% 5% 8% 21% 20% 7%	2274
	21st to end	Night	36% 3 13% 25% 19% 5%	1747
March	1st to 10th	Night	51% 5% 9% 14% 18% 3	1980
	11th to 20th	Night	46% 3 9% 21% 17% 5%	1980
	21st to end	Night	40% 4 14% 24% 15% 4	2178
April	1st to 10th	Night	40% 4 12% 23% 17% 4	1823
	11th to 20th	Night	33% 5% 12% 25% 19% 6%	1779
	21st to end	Night	24% 4 10% 34% 21% 7%	1769
May	1st to 10th	Night	22% 6% 7% 25% 33% 8%	1620
	11th to 20th	Night	23% 5% 12% 28% 23% 10%	1594
	21st to end	Night	23% 4 14% 34% 22% 3	1561
June	1st to 10th	Night	27% 6% 9% 22% 28% 9%	1440
	11th to 20th	Night	14% 4 8% 22% 36% 17%	1440
	21st to end	Night	14% 4 4 12% 33% 33%	1440
July	1st to 10th	Night	11% 6% 2 9% 31% 43%	1442
	11th to 20th	Night	10% 4 4 10% 28% 43%	1566
	21st to end	Night	14% 6% 1 8% 25% 47%	1674
August	1st to 10th	Night	13% 4 2 14% 33% 34%	1602
	11th to 20th	Night	13% 7% 3 11% 28% 39%	1619
	21st to end	Night	16% 5% 2 13% 29% 35%	1980
September	1st to 10th	Night	9% 4 1 13% 29% 43%	1800
	11th to 20th	Night	19% 4 5% 19% 37% 17%	1862
	21st to end	Night	18% 3 3 20% 26% 30%	2029
October	1st to 10th	Night	21% 3 5% 19% 28% 26%	2160
	11th to 20th	Night	24% 4 6% 19% 28% 20%	2160
	21st to end	Night	26% 3 6% 21% 26% 18%	2376
November	1st to 10th	Night	33% 5% 11% 22% 17% 11%	2220
	11th to 20th	Night	37% 4 13% 22% 18% 6%	2531
	21st to end	Night	33% 3 10% 21% 21% 12%	2660
December	1st to 10th	Night	43% 3 7% 20% 17% 10%	2660
	11th to 20th	Night	55% 3 9% 15% 14% 4	3276
	21st to end	Night	53% 2 11% 21% 10% 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	32% 16% 21% 14% 13% 3	331
	11th to 20th	Day	29% 10% 21% 19% 16% 4	345
	21st to end	Day	24% 10% 18% 29% 17% 3	374
February	1st to 10th	Day	24% 11% 21% 21% 19% 5%	340
	11th to 20th	Day	26% 13% 24% 19% 15% 2	335
	21st to end	Day	22% 15% 28% 20% 11% 4	341
March	1st to 10th	Day	30% 13% 27% 19% 10% 1	420
	11th to 20th	Day	29% 11% 28% 19% 10% 3	420
	21st to end	Day	21% 17% 32% 21% 6% 3	462
April	1st to 10th	Day	24% 15% 29% 20% 9% 2	420
	11th to 20th	Day	17% 17% 33% 20% 9% 4	412
	21st to end	Day	13% 18% 33% 19% 12% 5%	420
May	1st to 10th	Day	10% 14% 33% 26% 13% 4	423
	11th to 20th	Day	16% 14% 28% 26% 12% 3	448
	21st to end	Day	12% 13% 27% 29% 14% 5%	485
June	1st to 10th	Day	10% 11% 31% 29% 15% 4	450
	11th to 20th	Day	6% 13% 34% 29% 16% 2	450
	21st to end	Day	1 4 28% 37% 24% 5%	450
July	1st to 10th	Day	3 6% 26% 41% 19% 5%	446
	11th to 20th	Day	2 25% 40% 27% 7%	444
	21st to end	Day	1 2 17% 43% 30% 8%	487
August	1st to 10th	Day	2 3 26% 38% 24% 6%	447
	11th to 20th	Day	2 3 21% 35% 31% 9%	437
	21st to end	Day	2 4 19% 36% 31% 9%	495
September	1st to 10th	Day	3 4 20% 34% 30% 9%	450
	11th to 20th	Day	5% 7% 21% 33% 25% 8%	450
	21st to end	Day	6% 7% 23% 27% 29% 8%	450
October	1st to 10th	Day	8% 8% 23% 23% 27% 11%	450
	11th to 20th	Day	11% 6% 17% 23% 28% 14%	450
	21st to end	Day	13% 5% 20% 28% 26% 8%	495
November	1st to 10th	Day	16% 9% 19% 25% 23% 8%	455
	11th to 20th	Day	16% 8% 15% 24% 26% 11%	253
	21st to end	Day	16% 4 22% 23% 23% 12%	180
December	1st to 10th	Day	24% 10% 20% 19% 16% 11%	180
	11th to 20th	Day	30% 8% 17% 21% 13% 11%	180
	21st to end	Day	28% 9% 21% 18% 15% 9%	198
January	1st to 10th	Night	25% 7% 16% 26% 20% 6%	760
	11th to 20th	Night	24% 7% 15% 28% 20% 7%	728
	21st to end	Night	21% 7% 13% 28% 25% 6%	792
February	1st to 10th	Night	23% 6% 16% 26% 24% 4	720
	11th to 20th	Night	23% 8% 19% 24% 19% 7%	704
	21st to end	Night	22% 10% 20% 29% 16% 3	592
March	1st to 10th	Night	27% 10% 16% 25% 18% 4	720
	11th to 20th	Night	24% 7% 16% 29% 19% 4	720
	21st to end	Night	22% 9% 25% 26% 15% 3	792
April	1st to 10th	Night	18% 10% 24% 26% 17% 5%	720
	11th to 20th	Night	15% 12% 25% 27% 15% 6%	711
	21st to end	Night	12% 12% 30% 22% 19% 5%	689
May	1st to 10th	Night	7% 10% 28% 28% 20% 7%	540
	11th to 20th	Night	8% 5% 23% 37% 22% 6%	531
	21st to end	Night	9% 10% 24% 29% 23% 5%	398
June	1st to 10th	Night	9% 8% 28% 30% 22% 3	360
	11th to 20th	Night	3 11% 25% 38% 21% 2	360
	21st to end	Night	4 2 21% 42% 26% 5%	360
July	1st to 10th	Night	2 3 20% 34% 32% 9%	392
	11th to 20th	Night	2 1 14% 32% 39% 13%	522
	21st to end	Night	2 1 10% 30% 39% 18%	591
August	1st to 10th	Night	2 2 13% 34% 36% 13%	537
	11th to 20th	Night	1 1 12% 31% 38% 16%	551
	21st to end	Night	3 2 10% 28% 45% 13%	792
September	1st to 10th	Night	1 3 15% 26% 39% 16%	720
	11th to 20th	Night	6% 4 12% 31% 36% 10%	720
	21st to end	Night	6% 6% 13% 27% 35% 13%	720
October	1st to 10th	Night	7% 7% 14% 28% 32% 13%	720
	11th to 20th	Night	9% 5% 11% 25% 37% 13%	720
	21st to end	Night	15% 4 11% 25% 33% 13%	792
November	1st to 10th	Night	15% 6% 15% 23% 31% 10%	740
	11th to 20th	Night	19% 5% 13% 28% 29% 7%	760
	21st to end	Night	16% 6% 16% 29% 26% 7%	760
December	1st to 10th	Night	27% 4 12% 27% 21% 8%	760
	11th to 20th	Night	29% 6% 15% 26% 19% 4	760
	21st to end	Night	26% 8% 19% 26% 17% 4	836

Page generated at 2024-01-09 13:24:28. Version ac07

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