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 2024-11-08.

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 1 4 3 3 3 3 5% 7% 58%	105109
	Night	12% 6% 2 4 3 3 3 3 4 6% 54%	102745
Transparency	Day	15% 45% 4 12% 12% 11%	104872
	Night	18% 45% 4 10% 11% 11%	102572
Seeing	Day	13% 9% 25% 27% 19% 6%	15435
	Night	14% 6% 17% 28% 26% 8%	24631

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	20% 8% 3 7% 4 3 4 3 6% 6% 37%	2794
	11th to 20th	Day	29% 9% 4 7% 5% 3 3 3 4 5% 28%	2860
	21st to end	Day	26% 9% 2 7% 3 3 4 4 6% 6% 30%	3146
February	1st to 10th	Day	20% 7% 2 6% 4 3 3 3 4 4 43%	1710
	11th to 20th	Day	17% 6% 1 6% 4 3 3 4 6% 9% 40%	1665
	21st to end	Day	19% 6% 2 5% 3 3 4 3 5% 6% 43%	1594
March	1st to 10th	Day	25% 13% 3 6% 4 3 3 3 4 5% 30%	3442
	11th to 20th	Day	13% 4 2 4 3 3 3 3 5% 8% 53%	3490
	21st to end	Day	21% 10% 2 5% 4 4 5% 4 6% 7% 32%	3825
April	1st to 10th	Day	16% 7% 2 5% 5% 3 4 4 6% 8% 40%	2254
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 6% 8% 48%	2249
	21st to end	Day	8% 3 1 4 3 3 4 4 7% 10% 54%	2308
May	1st to 10th	Day	6% 2 1 3 2 2 3 2 5% 6% 68%	4110
	11th to 20th	Day	4 2 1 2 2 2 3 2 5% 7% 69%	4070
	21st to end	Day	4 2 1 2 2 1 2 2 4 7% 74%	4800
June	1st to 10th	Day	6% 6% 1 3 3 3 3 3 5% 9% 58%	2660
	11th to 20th	Day	2 2 1 2 2 2 2 3 5% 6% 73%	2660
	21st to end	Day	3 1 1 2 2 2 2 2 4 5% 77%	2660
July	1st to 10th	Day	1 1 1 2 1 1 2 2 3 5% 83%	4332
	11th to 20th	Day	1 2 1 3 2 2 3 2 4 7% 74%	4110
	21st to end	Day	1 2 2 2 2 2 4 7% 77%	4455
August	1st to 10th	Day	1 2 1 2 2 3 3 3 6% 8% 70%	4091
	11th to 20th	Day	2 2 1 2 1 1 2 1 3 6% 79%	3995
	21st to end	Day	1 3 1 3 2 2 4 3 5% 7% 68%	4180
September	1st to 10th	Day	1 1 2 1 2 2 3 3 8% 77%	2280
	11th to 20th	Day	4 3 1 3 3 3 3 3 5% 8% 65%	2209
	21st to end	Day	4 2 1 2 1 2 3 2 4 7% 72%	2037
October	1st to 10th	Day	4 2 1 3 2 2 2 2 4 5% 74%	3180
	11th to 20th	Day	10% 2 1 3 2 2 3 3 5% 7% 62%	3161
	21st to end	Day	8% 5% 2 5% 3 3 4 4 6% 9% 51%	3448
November	1st to 10th	Day	11% 5% 2 4 3 3 4 4 6% 8% 50%	1930
	11th to 20th	Day	14% 6% 2 6% 3 3 4 3 6% 7% 47%	1642
	21st to end	Day	12% 4 1 4 4 4 3 4 5% 8% 50%	1520
December	1st to 10th	Day	20% 7% 1 5% 3 3 5% 3 5% 8% 41%	1520
	11th to 20th	Day	33% 10% 2 5% 4 3 3 3 5% 5% 27%	1928
	21st to end	Day	26% 9% 3 5% 3 4 3 3 5% 7% 31%	2794
January	1st to 10th	Night	19% 8% 2 6% 4 4 4 4 6% 8% 36%	4157
	11th to 20th	Night	24% 10% 4 7% 5% 4 4 3 4 5% 29%	4110
	21st to end	Night	29% 10% 4 7% 4 3 4 3 4 6% 27%	4521
February	1st to 10th	Night	19% 6% 2 4 3 3 3 3 5% 6% 45%	2470
	11th to 20th	Night	17% 8% 2 5% 4 4 4 4 6% 7% 40%	2402
	21st to end	Night	16% 7% 1 4 2 3 4 2 5% 6% 49%	1853
March	1st to 10th	Night	23% 14% 3 7% 4 4 4 3 4 5% 29%	3432
	11th to 20th	Night	15% 4 1 4 3 2 3 2 3 6% 55%	3490
	21st to end	Night	17% 12% 3 8% 5% 4 5% 3 5% 6% 32%	3828
April	1st to 10th	Night	13% 7% 2 5% 4 4 3 3 5% 8% 45%	1924
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 52%	1879
	21st to end	Night	7% 4 1 3 3 3 3 3 5% 8% 61%	1867
May	1st to 10th	Night	6% 3 1 3 2 2 2 2 3 6% 70%	2860
	11th to 20th	Night	2 2 1 4 2 2 3 2 4 7% 70%	2833
	21st to end	Night	3 2 1 2 2 1 2 2 3 4 77%	2771
June	1st to 10th	Night	5% 7% 2 4 2 4 3 3 5% 8% 56%	1520
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 6% 74%	1520
	21st to end	Night	3 3 1 2 2 2 2 2 3 3 76%	1520
July	1st to 10th	Night	1 1 2 1 2 2 1 3 4 84%	2626
	11th to 20th	Night	1 2 2 5% 3 3 3 2 3 4 72%	2860
	21st to end	Night	1 1 1 2 2 1 3 3 3 7% 77%	3109
August	1st to 10th	Night	1 3 1 3 2 2 3 2 5% 7% 71%	2848
	11th to 20th	Night	1 1 3 1 2 2 2 4 5% 79%	2843
	21st to end	Night	3 3 1 3 2 3 4 3 4 4 70%	3498
September	1st to 10th	Night	1 1 1 2 2 2 2 3 3 7% 77%	1900
	11th to 20th	Night	4 4 2 4 2 2 2 3 4 7% 66%	1966
	21st to end	Night	4 3 1 3 3 2 2 2 4 6% 71%	2142
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 75%	3800
	11th to 20th	Night	7% 6% 2 4 2 2 2 2 4 6% 64%	3777
	21st to end	Night	12% 3 1 3 2 3 3 3 5% 7% 57%	4121
November	1st to 10th	Night	13% 5% 2 4 3 3 4 4 5% 8% 50%	2309
	11th to 20th	Night	15% 5% 1 4 4 4 4 4 6% 8% 44%	2531
	21st to end	Night	12% 5% 2 5% 3 3 3 3 4 7% 52%	2660
December	1st to 10th	Night	22% 7% 2 5% 3 3 3 2 5% 7% 42%	2660
	11th to 20th	Night	33% 7% 2 4 3 3 3 3 4 7% 30%	3276
	21st to end	Night	26% 8% 3 6% 4 3 3 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	30% 36% 11% 17% 4 1	2794
	11th to 20th	Day	48% 36% 7% 5% 2 2	2860
	21st to end	Day	39% 38% 6% 11% 4 2	3146
February	1st to 10th	Day	20% 64% 3 7% 5% 1	1710
	11th to 20th	Day	19% 63% 3 7% 6% 2	1674
	21st to end	Day	14% 64% 4 11% 5% 2	1594
March	1st to 10th	Day	40% 39% 4 10% 7%	3442
	11th to 20th	Day	13% 39% 7% 18% 12% 11%	3490
	21st to end	Day	33% 40% 10% 13% 4 1	3825
April	1st to 10th	Day	16% 64% 4 11% 5% 1	2254
	11th to 20th	Day	12% 65% 6% 10% 6% 1	2252
	21st to end	Day	9% 65% 6% 11% 7% 1	2308
May	1st to 10th	Day	9% 39% 12% 18% 12% 10%	4110
	11th to 20th	Day	8% 41% 2 12% 24% 12%	4073
	21st to end	Day	5% 38% 5% 30% 22% 1	4801
June	1st to 10th	Day	6% 64% 3 12% 11% 4	2660
	11th to 20th	Day	4 64% 3 10% 15% 4	2660
	21st to end	Day	3 63% 1 5% 17% 12%	2660
July	1st to 10th	Day	3 36% 1 4 6% 49%	4265
	11th to 20th	Day	6% 36% 2 7% 11% 39%	4041
	21st to end	Day	3 35% 1 7% 23% 32%	4315
August	1st to 10th	Day	9% 36% 1 6% 17% 30%	4076
	11th to 20th	Day	7% 37% 1 15% 27% 14%	4034
	21st to end	Day	9% 37% 3 15% 19% 16%	4179
September	1st to 10th	Day	4 59% 1 8% 17% 11%	2280
	11th to 20th	Day	7% 59% 3 14% 14% 3	2209
	21st to end	Day	8% 59% 2 9% 16% 6%	2037
October	1st to 10th	Day	7% 35% 1 8% 13% 35%	3180
	11th to 20th	Day	15% 37% 5% 16% 20% 7%	3161
	21st to end	Day	21% 37% 6% 14% 16% 6%	3448
November	1st to 10th	Day	10% 57% 3 16% 11% 3	1930
	11th to 20th	Day	16% 59% 5% 12% 7% 2	1642
	21st to end	Day	14% 60% 4 9% 8% 5%	1520
December	1st to 10th	Day	21% 60% 4 8% 3 4	1520
	11th to 20th	Day	34% 47% 3 7% 6% 3	1928
	21st to end	Day	32% 36% 7% 17% 6% 2	2794
January	1st to 10th	Night	30% 37% 16% 11% 6% 1	4157
	11th to 20th	Night	46% 37% 7% 6% 2 2	4110
	21st to end	Night	45% 39% 4 7% 3 2	4521
February	1st to 10th	Night	20% 64% 3 6% 5% 2	2470
	11th to 20th	Night	19% 63% 3 6% 6% 3	2404
	21st to end	Night	11% 64% 4 12% 6% 3	1853
March	1st to 10th	Night	40% 40% 5% 10% 5%	3432
	11th to 20th	Night	14% 39% 5% 16% 16% 10%	3490
	21st to end	Night	36% 40% 8% 12% 3 1	3828
April	1st to 10th	Night	16% 64% 3 9% 6% 1	1924
	11th to 20th	Night	11% 66% 4 11% 7% 1	1879
	21st to end	Night	10% 65% 5% 12% 7% 1	1867
May	1st to 10th	Night	10% 39% 5% 21% 14% 11%	2860
	11th to 20th	Night	7% 40% 3 9% 22% 18%	2834
	21st to end	Night	5% 38% 4 29% 22% 3	2771
June	1st to 10th	Night	9% 64% 2 9% 11% 5%	1520
	11th to 20th	Night	4 64% 3 9% 15% 5%	1520
	21st to end	Night	5% 62% 2 2 13% 17%	1520
July	1st to 10th	Night	3 35% 1 3 7% 51%	2584
	11th to 20th	Night	12% 36% 2 4 10% 37%	2806
	21st to end	Night	4 35% 1 5% 18% 38%	3011
August	1st to 10th	Night	10% 37% 1 4 15% 34%	2839
	11th to 20th	Night	5% 37% 1 9% 32% 16%	2870
	21st to end	Night	11% 37% 1 10% 21% 19%	3498
September	1st to 10th	Night	5% 59% 1 6% 16% 12%	1900
	11th to 20th	Night	8% 59% 3 10% 15% 6%	1966
	21st to end	Night	9% 59% 1 9% 11% 10%	2142
October	1st to 10th	Night	8% 36% 1 4 14% 38%	3800
	11th to 20th	Night	15% 37% 3 15% 20% 10%	3777
	21st to end	Night	18% 36% 3 15% 17% 9%	4121
November	1st to 10th	Night	12% 57% 5% 12% 10% 5%	2309
	11th to 20th	Night	17% 59% 5% 10% 7% 2	2531
	21st to end	Night	15% 60% 3 9% 7% 5%	2660
December	1st to 10th	Night	22% 59% 4 7% 4 3	2660
	11th to 20th	Night	33% 49% 3 6% 7% 3	3276
	21st to end	Night	32% 36% 8% 17% 6% 2	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	31% 10% 21% 20% 15% 4	370
	21st to end	Day	25% 10% 19% 28% 15% 3	407
February	1st to 10th	Day	24% 12% 22% 20% 18% 5%	370
	11th to 20th	Day	27% 14% 24% 20% 14% 2	365
	21st to end	Day	21% 14% 27% 23% 11% 4	376
March	1st to 10th	Day	30% 13% 27% 19% 9% 1	460
	11th to 20th	Day	26% 11% 29% 20% 11% 3	460
	21st to end	Day	23% 17% 32% 20% 6% 3	506
April	1st to 10th	Day	23% 15% 29% 21% 9% 3	460
	11th to 20th	Day	17% 17% 32% 21% 10% 4	452
	21st to end	Day	13% 18% 32% 21% 12% 4	460
May	1st to 10th	Day	10% 14% 34% 26% 12% 3	463
	11th to 20th	Day	15% 14% 27% 26% 16% 3	488
	21st to end	Day	11% 12% 28% 29% 14% 5%	529
June	1st to 10th	Day	9% 11% 33% 28% 14% 4	490
	11th to 20th	Day	6% 13% 35% 29% 16% 1	490
	21st to end	Day	1 4 29% 36% 23% 5%	490
July	1st to 10th	Day	3 6% 24% 42% 20% 6%	486
	11th to 20th	Day	2 25% 40% 26% 6%	484
	21st to end	Day	1 2 16% 44% 29% 8%	531
August	1st to 10th	Day	2 3 26% 39% 23% 7%	487
	11th to 20th	Day	3 4 23% 33% 29% 8%	477
	21st to end	Day	1 4 19% 36% 30% 9%	539
September	1st to 10th	Day	2 4 22% 34% 30% 8%	490
	11th to 20th	Day	5% 8% 21% 33% 24% 8%	490
	21st to end	Day	6% 7% 23% 28% 29% 8%	490
October	1st to 10th	Day	8% 7% 23% 24% 28% 10%	490
	11th to 20th	Day	12% 7% 18% 24% 27% 13%	490
	21st to end	Day	13% 6% 22% 27% 25% 7%	539
November	1st to 10th	Day	15% 9% 21% 25% 22% 8%	484
	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% 8% 16% 26% 20% 6%	760
	11th to 20th	Night	24% 7% 15% 28% 20% 6%	760
	21st to end	Night	23% 7% 13% 28% 24% 6%	836
February	1st to 10th	Night	23% 7% 16% 26% 23% 4	760
	11th to 20th	Night	23% 9% 18% 24% 19% 7%	744
	21st to end	Night	21% 11% 20% 30% 16% 3	628
March	1st to 10th	Night	28% 10% 17% 24% 17% 4	760
	11th to 20th	Night	24% 7% 17% 29% 19% 4	760
	21st to end	Night	22% 10% 25% 26% 15% 3	836
April	1st to 10th	Night	18% 10% 25% 26% 17% 5%	760
	11th to 20th	Night	15% 12% 25% 27% 16% 6%	751
	21st to end	Night	11% 12% 31% 22% 18% 5%	727
May	1st to 10th	Night	8% 10% 29% 29% 19% 6%	570
	11th to 20th	Night	7% 5% 22% 35% 24% 6%	561
	21st to end	Night	8% 10% 26% 29% 23% 5%	420
June	1st to 10th	Night	9% 8% 30% 29% 21% 3	380
	11th to 20th	Night	3 11% 26% 38% 21% 2	380
	21st to end	Night	4 3 20% 42% 27% 4	380
July	1st to 10th	Night	2 3 19% 33% 33% 9%	415
	11th to 20th	Night	1 1 13% 33% 39% 13%	552
	21st to end	Night	2 1 10% 30% 40% 17%	624
August	1st to 10th	Night	2 2 13% 34% 37% 13%	567
	11th to 20th	Night	1 1 13% 33% 37% 15%	582
	21st to end	Night	3 2 10% 27% 45% 12%	836
September	1st to 10th	Night	1 3 14% 28% 39% 15%	760
	11th to 20th	Night	6% 4 13% 32% 35% 10%	760
	21st to end	Night	5% 6% 12% 28% 36% 13%	760
October	1st to 10th	Night	6% 7% 14% 29% 32% 12%	760
	11th to 20th	Night	10% 5% 12% 25% 37% 13%	760
	21st to end	Night	14% 4 13% 26% 31% 12%	836
November	1st to 10th	Night	15% 6% 16% 23% 30% 9%	770
	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 2024-11-05 05:15:48. Version ac07

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