Santa Margarita Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Margarita Lake clear sky chart from 2005-11-05 to 2024-10-14.

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	5% 3 1 3 2 2 3 2 4 5% 68%	100656
	Night	6% 5% 1 4 3 3 3 3 4 5% 64%	98160
Transparency	Day	18% 4 7% 19% 27% 25%	100413
	Night	22% 5% 7% 18% 24% 25%	97993
Seeing	Day	8% 9% 24% 35% 19% 5%	15485
	Night	7% 4 13% 33% 34% 8%	25058

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	8% 6% 1 5% 4 3 4 3 5% 7% 53%	2699
	11th to 20th	Day	13% 8% 2 5% 3 4 4 4 6% 8% 44%	2860
	21st to end	Day	14% 6% 3 8% 4 4 5% 4 6% 9% 37%	3146
February	1st to 10th	Day	15% 6% 2 4 3 2 2 3 4 5% 54%	1790
	11th to 20th	Day	10% 7% 2 5% 3 3 3 3 5% 8% 52%	1850
	21st to end	Day	13% 6% 2 5% 4 3 3 3 5% 6% 50%	1570
March	1st to 10th	Day	13% 9% 2 7% 4 4 4 3 5% 8% 39%	3220
	11th to 20th	Day	7% 4 1 3 3 3 3 3 4 6% 62%	3490
	21st to end	Day	10% 8% 2 6% 4 5% 6% 5% 5% 7% 42%	4004
April	1st to 10th	Day	10% 5% 2 4 3 3 3 2 4 7% 56%	2280
	11th to 20th	Day	7% 5% 2 4 3 2 3 4 5% 6% 59%	2249
	21st to end	Day	6% 3 1 3 3 3 3 3 5% 6% 64%	2280
May	1st to 10th	Day	3 3 1 2 2 2 2 2 3 4 77%	3800
	11th to 20th	Day	2 2 1 3 2 3 3 2 5% 7% 71%	3907
	21st to end	Day	2 2 1 3 2 2 2 2 3 6% 77%	4806
June	1st to 10th	Day	3 3 1 3 2 2 2 3 5% 8% 70%	2660
	11th to 20th	Day	1 1 1 1 1 2 2 2 5% 84%	2660
	21st to end	Day	1 1 1 1 1 1 2 2 2 4 85%	2660
July	1st to 10th	Day	1 1 1 1 1 2 3 91%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 82%	4151
	21st to end	Day	1 1 1 1 1 2 2 3 4 85%	4455
August	1st to 10th	Day	1 1 1 1 1 1 2 2 3 4 83%	3889
	11th to 20th	Day	1 1 1 1 2 2 92%	3724
	21st to end	Day	1 1 1 1 1 1 2 3 89%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 4 85%	2280
	11th to 20th	Day	2 2 1 2 2 1 2 1 2 4 82%	2271
	21st to end	Day	1 2 2 1 1 2 2 4 5% 79%	2090
October	1st to 10th	Day	3 2 1 2 2 1 3 3 4 5% 74%	1914
	11th to 20th	Day	2 3 1 3 3 2 3 3 3 5% 72%	1831
	21st to end	Day	3 3 1 4 3 3 2 2 3 7% 69%	1980
November	1st to 10th	Day	6% 4 1 4 2 3 3 3 4 5% 66%	1776
	11th to 20th	Day	6% 4 1 3 3 3 3 3 4 5% 65%	1710
	21st to end	Day	8% 4 1 4 3 3 4 4 3 7% 58%	1710
December	1st to 10th	Day	9% 5% 2 6% 4 4 3 3 5% 8% 52%	1622
	11th to 20th	Day	23% 8% 2 5% 4 3 3 3 5% 5% 38%	1928
	21st to end	Day	14% 7% 2 6% 5% 3 4 4 5% 8% 42%	2794
January	1st to 10th	Night	9% 6% 2 6% 3 4 4 3 4 5% 54%	4248
	11th to 20th	Night	11% 8% 3 7% 3 4 4 3 5% 7% 44%	4110
	21st to end	Night	16% 10% 2 5% 4 3 4 3 5% 6% 42%	4521
February	1st to 10th	Night	12% 6% 2 4 3 3 3 2 5% 5% 55%	2388
	11th to 20th	Night	10% 4 1 4 3 3 4 3 5% 7% 57%	2218
	21st to end	Night	10% 8% 2 5% 3 3 2 2 4 5% 55%	1884
March	1st to 10th	Night	12% 12% 3 6% 4 4 4 4 6% 7% 37%	3651
	11th to 20th	Night	5% 5% 2 4 3 3 4 3 4 6% 61%	3490
	21st to end	Night	12% 10% 2 4 3 4 3 3 6% 7% 45%	3648
April	1st to 10th	Night	7% 6% 2 4 3 3 2 3 5% 6% 60%	1900
	11th to 20th	Night	5% 5% 1 4 3 3 3 2 3 6% 66%	1879
	21st to end	Night	4 6% 2 4 2 2 3 3 4 6% 65%	1900
May	1st to 10th	Night	2 3 1 2 2 2 1 2 3 5% 78%	3180
	11th to 20th	Night	2 1 1 9% 5% 4 2 2 4 9% 61%	2998
	21st to end	Night	1 4 2 4 4 3 3 3 5% 7% 64%	2764
June	1st to 10th	Night	2 2 1 3 3 3 3 4 4 6% 70%	1520
	11th to 20th	Night	1 2 1 2 1 1 2 2 4 6% 79%	1520
	21st to end	Night	1 1 2 2 1 2 1 2 4 84%	1520
July	1st to 10th	Night	1 1 1 1 1 2 4 89%	2540
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 84%	2814
	21st to end	Night	1 1 1 1 2 2 2 3 5% 81%	3109
August	1st to 10th	Night	1 2 1 1 2 2 3 3 84%	3057
	11th to 20th	Night	1 1 1 1 1 2 3 90%	3126
	21st to end	Night	1 1 2 1 1 2 3 88%	3498
September	1st to 10th	Night	1 1 2 2 1 2 2 3 3 83%	1900
	11th to 20th	Night	2 3 1 3 2 2 2 2 2 4 80%	1909
	21st to end	Night	1 1 1 2 1 2 1 2 3 3 83%	2090
October	1st to 10th	Night	3 3 1 3 3 2 2 2 4 5% 74%	2262
	11th to 20th	Night	3 2 2 3 2 3 2 2 4 5% 71%	2207
	21st to end	Night	4 3 1 3 2 2 3 2 3 5% 72%	2376
November	1st to 10th	Night	4 4 1 3 2 3 3 3 4 6% 67%	2300
	11th to 20th	Night	3 4 1 4 2 3 3 3 4 6% 66%	2470
	21st to end	Night	5% 5% 2 4 3 4 4 4 5% 6% 58%	2470
December	1st to 10th	Night	10% 6% 2 4 2 3 4 3 5% 7% 54%	2555
	11th to 20th	Night	22% 8% 2 5% 4 3 4 4 5% 5% 39%	3276
	21st to end	Night	13% 8% 3 7% 5% 4 5% 4 6% 6% 40%	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	27% 6% 11% 33% 17% 5%	2699
	11th to 20th	Day	37% 5% 11% 20% 17% 11%	2860
	21st to end	Day	39% 8% 10% 19% 14% 9%	3146
February	1st to 10th	Day	32% 3 6% 19% 22% 18%	1790
	11th to 20th	Day	31% 4 7% 23% 25% 10%	1860
	21st to end	Day	34% 4 9% 21% 24% 8%	1570
March	1st to 10th	Day	39% 7% 13% 19% 16% 6%	3220
	11th to 20th	Day	22% 4 12% 32% 18% 12%	3490
	21st to end	Day	33% 10% 14% 25% 13% 4	4004
April	1st to 10th	Day	29% 4 11% 25% 21% 9%	2280
	11th to 20th	Day	23% 5% 12% 26% 25% 8%	2252
	21st to end	Day	20% 6% 10% 27% 29% 8%	2280
May	1st to 10th	Day	14% 2 8% 27% 35% 15%	3800
	11th to 20th	Day	10% 10% 5% 27% 37% 12%	3910
	21st to end	Day	10% 5% 8% 31% 39% 7%	4807
June	1st to 10th	Day	14% 5% 9% 25% 31% 15%	2660
	11th to 20th	Day	8% 3 5% 15% 42% 27%	2660
	21st to end	Day	7% 2 3 12% 33% 43%	2660
July	1st to 10th	Day	4 1 1 5% 19% 69%	4351
	11th to 20th	Day	9% 2 3 7% 20% 59%	4080
	21st to end	Day	6% 2 2 10% 32% 47%	4315
August	1st to 10th	Day	8% 2 1 10% 35% 43%	3874
	11th to 20th	Day	3 1 1 7% 32% 55%	3760
	21st to end	Day	4 2 1 11% 29% 52%	4179
September	1st to 10th	Day	7% 2 2 12% 30% 47%	2280
	11th to 20th	Day	9% 3 2 21% 40% 25%	2271
	21st to end	Day	10% 3 3 18% 36% 31%	2090
October	1st to 10th	Day	14% 4 5% 20% 23% 34%	1914
	11th to 20th	Day	16% 4 5% 17% 31% 27%	1831
	21st to end	Day	18% 3 4 16% 28% 30%	1980
November	1st to 10th	Day	20% 4 7% 19% 29% 22%	1776
	11th to 20th	Day	21% 4 7% 20% 26% 22%	1710
	21st to end	Day	26% 4 7% 16% 25% 23%	1710
December	1st to 10th	Day	31% 4 9% 17% 21% 18%	1622
	11th to 20th	Day	48% 4 7% 16% 16% 9%	1928
	21st to end	Day	38% 6% 11% 24% 15% 6%	2794
January	1st to 10th	Night	29% 6% 12% 26% 22% 5%	4248
	11th to 20th	Night	37% 6% 10% 24% 12% 11%	4110
	21st to end	Night	41% 5% 11% 17% 15% 10%	4521
February	1st to 10th	Night	31% 4 7% 17% 25% 16%	2388
	11th to 20th	Night	26% 5% 7% 22% 25% 14%	2219
	21st to end	Night	32% 4 7% 22% 25% 9%	1884
March	1st to 10th	Night	41% 7% 10% 21% 16% 6%	3651
	11th to 20th	Night	23% 6% 10% 27% 24% 10%	3490
	21st to end	Night	34% 7% 18% 19% 18% 5%	3648
April	1st to 10th	Night	26% 5% 13% 27% 19% 11%	1900
	11th to 20th	Night	21% 4 9% 29% 27% 10%	1879
	21st to end	Night	20% 5% 10% 26% 31% 9%	1900
May	1st to 10th	Night	11% 3 10% 25% 29% 22%	3180
	11th to 20th	Night	14% 18% 6% 22% 23% 16%	2999
	21st to end	Night	14% 15% 7% 23% 32% 9%	2764
June	1st to 10th	Night	13% 8% 10% 20% 30% 19%	1520
	11th to 20th	Night	10% 4 4 17% 36% 31%	1520
	21st to end	Night	8% 3 2 10% 31% 46%	1520
July	1st to 10th	Night	4 3 1 5% 16% 71%	2500
	11th to 20th	Night	7% 2 2 7% 17% 65%	2762
	21st to end	Night	7% 3 1 8% 34% 47%	3011
August	1st to 10th	Night	8% 2 1 9% 30% 49%	3048
	11th to 20th	Night	4 2 4 25% 64%	3156
	21st to end	Night	5% 2 2 8% 27% 56%	3498
September	1st to 10th	Night	8% 4 2 8% 25% 53%	1900
	11th to 20th	Night	11% 4 3 14% 35% 34%	1909
	21st to end	Night	9% 2 2 16% 38% 33%	2090
October	1st to 10th	Night	14% 3 4 20% 24% 35%	2262
	11th to 20th	Night	17% 4 5% 17% 27% 29%	2207
	21st to end	Night	18% 3 4 15% 29% 32%	2376
November	1st to 10th	Night	19% 3 6% 20% 27% 26%	2300
	11th to 20th	Night	19% 4 10% 18% 26% 23%	2470
	21st to end	Night	25% 4 8% 18% 22% 23%	2470
December	1st to 10th	Night	29% 4 7% 17% 23% 20%	2555
	11th to 20th	Night	46% 4 8% 15% 16% 10%	3276
	21st to end	Night	41% 7% 11% 18% 17% 7%	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	24% 14% 31% 20% 10% 1	275
	11th to 20th	Day	16% 14% 30% 27% 12% 1	370
	21st to end	Day	14% 14% 32% 26% 14% 1	407
February	1st to 10th	Day	19% 13% 28% 25% 13% 2	408
	11th to 20th	Day	16% 16% 30% 25% 11% 2	455
	21st to end	Day	13% 19% 34% 25% 7% 2	382
March	1st to 10th	Day	20% 17% 33% 24% 6%	460
	11th to 20th	Day	16% 17% 32% 27% 9% 1	460
	21st to end	Day	18% 19% 31% 24% 7% 1	506
April	1st to 10th	Day	15% 13% 33% 25% 11% 2	460
	11th to 20th	Day	13% 14% 33% 27% 11% 2	452
	21st to end	Day	7% 13% 37% 28% 13% 4	460
May	1st to 10th	Day	11% 10% 34% 30% 11% 5%	463
	11th to 20th	Day	4 11% 27% 37% 17% 4	488
	21st to end	Day	8% 11% 23% 38% 16% 5%	529
June	1st to 10th	Day	4 6% 20% 41% 23% 6%	490
	11th to 20th	Day	2 6% 27% 38% 23% 5%	490
	21st to end	Day	3 19% 41% 28% 10%	490
July	1st to 10th	Day	1 12% 46% 30% 11%	486
	11th to 20th	Day	3 7% 45% 33% 12%	484
	21st to end	Day	1 8% 44% 34% 13%	531
August	1st to 10th	Day	2 1 15% 42% 29% 10%	487
	11th to 20th	Day	2 1 9% 43% 32% 12%	477
	21st to end	Day	1 1 10% 44% 32% 11%	539
September	1st to 10th	Day	2 3 13% 46% 28% 8%	490
	11th to 20th	Day	3 5% 23% 43% 21% 5%	490
	21st to end	Day	1 8% 20% 40% 27% 4	490
October	1st to 10th	Day	1 9% 23% 41% 21% 4	490
	11th to 20th	Day	3 8% 27% 39% 20% 3	463
	21st to end	Day	5% 7% 26% 36% 22% 3	495
November	1st to 10th	Day	8% 9% 28% 32% 21% 3	372
	11th to 20th	Day	10% 12% 27% 31% 16% 4	270
	21st to end	Day	9% 10% 29% 29% 19% 4	270
December	1st to 10th	Day	12% 14% 31% 31% 11% 1	228
	11th to 20th	Day	15% 14% 25% 28% 15% 3	180
	21st to end	Day	21% 18% 29% 19% 10% 4	198
January	1st to 10th	Night	16% 7% 18% 33% 20% 7%	760
	11th to 20th	Night	11% 5% 19% 41% 20% 5%	760
	21st to end	Night	16% 6% 18% 37% 18% 5%	836
February	1st to 10th	Night	16% 7% 14% 36% 22% 6%	760
	11th to 20th	Night	12% 8% 17% 35% 22% 5%	744
	21st to end	Night	14% 7% 19% 40% 17% 3	628
March	1st to 10th	Night	15% 6% 18% 40% 18% 3	760
	11th to 20th	Night	11% 5% 18% 36% 24% 7%	760
	21st to end	Night	13% 8% 19% 34% 24% 3	836
April	1st to 10th	Night	9% 6% 18% 38% 25% 3	760
	11th to 20th	Night	8% 8% 20% 32% 27% 6%	751
	21st to end	Night	6% 6% 21% 32% 26% 8%	760
May	1st to 10th	Night	5% 4 14% 38% 31% 8%	760
	11th to 20th	Night	4 4 10% 36% 38% 8%	660
	21st to end	Night	4 4 9% 39% 35% 9%	413
June	1st to 10th	Night	3 2 7% 36% 44% 7%	380
	11th to 20th	Night	1 2 10% 32% 46% 8%	380
	21st to end	Night	1 1 2 31% 53% 12%	380
July	1st to 10th	Night	1 18% 65% 15%	370
	11th to 20th	Night	2 1 1 10% 60% 26%	521
	21st to end	Night	1 1 12% 58% 27%	624
August	1st to 10th	Night	1 1 2 24% 56% 16%	685
	11th to 20th	Night	1 1 21% 62% 14%	752
	21st to end	Night	2 21% 60% 16%	836
September	1st to 10th	Night	2 1 3 24% 56% 14%	760
	11th to 20th	Night	3 1 6% 37% 43% 11%	760
	21st to end	Night	1 2 7% 34% 47% 10%	760
October	1st to 10th	Night	4 1 8% 39% 40% 6%	760
	11th to 20th	Night	5% 3 9% 38% 36% 8%	734
	21st to end	Night	6% 2 16% 34% 32% 10%	792
November	1st to 10th	Night	6% 5% 13% 37% 31% 8%	740
	11th to 20th	Night	5% 4 18% 38% 28% 7%	760
	21st to end	Night	6% 7% 18% 40% 24% 5%	760
December	1st to 10th	Night	13% 7% 18% 35% 24% 4	760
	11th to 20th	Night	16% 5% 19% 37% 20% 4	760
	21st to end	Night	15% 7% 21% 36% 18% 4	836

Page generated at 2024-10-11 07:50:02. Version ac07

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