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 2005-11-06 to 2024-02-10.

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	6% 3 1 3 3 2 3 3 4 6% 65%	78481
	Night	7% 5% 2 3 3 2 3 3 4 6% 62%	80526
Transparency	Day	21% 4 7% 20% 27% 21%	78201
	Night	24% 5% 7% 19% 25% 21%	80328
Seeing	Day	8% 9% 24% 34% 19% 5%	14497
	Night	8% 4 13% 33% 34% 9%	24202

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 4 4 3 5% 4 5% 7% 53%	2699
	11th to 20th	Day	13% 7% 2 4 4 3 4 5% 6% 8% 44%	2860
	21st to end	Day	14% 6% 3 6% 6% 3 5% 5% 6% 9% 38%	3146
February	1st to 10th	Day	15% 6% 2 3 3 1 2 3 4 5% 54%	1781
	11th to 20th	Day	10% 5% 3 4 4 2 3 4 5% 8% 53%	1750
	21st to end	Day	14% 5% 2 4 5% 2 3 4 5% 6% 51%	1480
March	1st to 10th	Day	13% 6% 2 6% 6% 3 5% 4 5% 9% 41%	1843
	11th to 20th	Day	12% 5% 2 4 6% 3 5% 5% 5% 7% 46%	1980
	21st to end	Day	9% 5% 2 3 4 3 5% 5% 4 8% 54%	2280
April	1st to 10th	Day	10% 5% 2 4 4 2 4 3 4 7% 55%	2160
	11th to 20th	Day	7% 4 2 3 3 1 3 4 5% 6% 60%	2129
	21st to end	Day	6% 3 1 2 2 2 3 4 5% 7% 65%	2160
May	1st to 10th	Day	4 3 1 3 2 2 3 3 4 6% 69%	2160
	11th to 20th	Day	3 2 1 2 2 2 3 3 5% 6% 71%	2202
	21st to end	Day	4 3 1 3 3 2 2 3 4 7% 69%	2716
June	1st to 10th	Day	3 2 1 2 2 1 2 3 5% 7% 70%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 5% 84%	2520
	21st to end	Day	1 1 1 1 2 2 2 2 4 85%	2520
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 5% 84%	2520
	11th to 20th	Day	2 1 1 2 1 2 2 3 5% 79%	2368
	21st to end	Day	1 1 1 2 2 1 3 3 4 6% 76%	2546
August	1st to 10th	Day	1 1 1 2 2 2 2 2 3 4 80%	2217
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 86%	2122
	21st to end	Day	1 1 1 2 1 1 2 3 4 84%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 2 4 85%	2160
	11th to 20th	Day	2 1 1 1 2 1 2 2 2 3 83%	2152
	21st to end	Day	2 1 1 2 2 1 2 3 3 6% 78%	1980
October	1st to 10th	Day	4 2 1 2 2 1 3 3 4 5% 73%	1814
	11th to 20th	Day	3 2 1 3 3 2 3 4 3 5% 72%	1800
	21st to end	Day	3 3 1 3 3 2 2 3 3 7% 69%	1980
November	1st to 10th	Day	6% 3 2 3 2 2 3 4 4 5% 66%	1776
	11th to 20th	Day	6% 4 1 2 4 2 4 3 4 5% 66%	1710
	21st to end	Day	8% 4 2 4 3 2 4 4 4 6% 58%	1710
December	1st to 10th	Day	9% 4 3 5% 4 3 3 4 5% 8% 52%	1622
	11th to 20th	Day	23% 8% 2 5% 5% 2 3 4 4 5% 38%	1928
	21st to end	Day	14% 7% 3 5% 5% 3 3 5% 5% 8% 42%	2794
January	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 4 5% 54%	4248
	11th to 20th	Night	11% 8% 3 6% 4 3 4 4 5% 7% 44%	4110
	21st to end	Night	16% 10% 2 5% 4 3 4 4 5% 6% 42%	4521
February	1st to 10th	Night	12% 6% 2 4 3 2 3 3 4 5% 55%	2381
	11th to 20th	Night	9% 4 1 3 3 2 4 4 5% 7% 58%	2098
	21st to end	Night	11% 8% 3 4 4 2 2 3 4 4 56%	1776
March	1st to 10th	Night	11% 8% 3 5% 4 3 3 5% 5% 8% 46%	2114
	11th to 20th	Night	9% 7% 2 5% 4 3 5% 5% 5% 7% 49%	1980
	21st to end	Night	10% 5% 2 3 3 2 4 4 4 7% 56%	2075
April	1st to 10th	Night	7% 5% 2 4 3 2 3 3 4 6% 60%	1800
	11th to 20th	Night	6% 4 1 3 3 2 3 3 2 6% 66%	1779
	21st to end	Night	4 5% 3 3 3 1 3 4 4 6% 65%	1800
May	1st to 10th	Night	4 4 1 3 2 2 3 3 4 7% 68%	1800
	11th to 20th	Night	3 2 1 4 2 2 2 3 4 7% 69%	1688
	21st to end	Night	3 3 1 3 4 2 3 3 5% 8% 64%	1554
June	1st to 10th	Night	2 2 1 3 2 2 3 4 4 7% 70%	1440
	11th to 20th	Night	1 2 1 1 1 1 2 2 4 6% 79%	1440
	21st to end	Night	1 1 2 2 1 1 2 2 4 84%	1440
July	1st to 10th	Night	1 1 2 1 2 2 3 7% 81%	1440
	11th to 20th	Night	1 2 2 2 1 2 2 4 5% 80%	1588
	21st to end	Night	1 1 1 1 3 1 3 3 4 5% 76%	1773
August	1st to 10th	Night	1 2 1 2 3 1 2 2 3 3 82%	1722
	11th to 20th	Night	1 1 1 2 2 2 3 5% 83%	1780
	21st to end	Night	1 1 2 1 2 2 3 4 84%	1980
September	1st to 10th	Night	2 1 1 1 2 1 2 2 3 3 82%	1800
	11th to 20th	Night	2 2 1 3 1 1 2 2 1 4 81%	1808
	21st to end	Night	1 1 1 2 2 1 2 2 2 3 83%	1980
October	1st to 10th	Night	3 3 1 2 3 1 2 2 4 5% 74%	2142
	11th to 20th	Night	3 2 2 3 3 2 3 3 3 5% 71%	2160
	21st to end	Night	4 3 1 3 2 1 3 3 2 5% 72%	2376
November	1st to 10th	Night	4 3 1 3 2 2 3 3 4 6% 67%	2300
	11th to 20th	Night	3 3 2 3 3 2 4 4 4 6% 66%	2470
	21st to end	Night	5% 4 2 3 4 3 4 4 5% 6% 59%	2470
December	1st to 10th	Night	11% 5% 2 4 3 2 3 4 5% 7% 54%	2555
	11th to 20th	Night	22% 7% 2 5% 4 3 4 4 5% 5% 39%	3276
	21st to end	Night	13% 7% 3 6% 6% 3 5% 5% 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% 18% 22% 18%	1781
	11th to 20th	Day	30% 4 7% 22% 26% 11%	1760
	21st to end	Day	34% 4 9% 20% 25% 8%	1480
March	1st to 10th	Day	39% 5% 10% 16% 19% 9%	1843
	11th to 20th	Day	35% 5% 10% 21% 20% 9%	1980
	21st to end	Day	29% 6% 11% 28% 19% 8%	2280
April	1st to 10th	Day	30% 4 12% 25% 20% 9%	2160
	11th to 20th	Day	24% 4 12% 26% 25% 9%	2132
	21st to end	Day	20% 5% 10% 27% 29% 8%	2160
May	1st to 10th	Day	18% 3 10% 26% 32% 11%	2160
	11th to 20th	Day	14% 5% 7% 30% 33% 11%	2205
	21st to end	Day	17% 4 10% 32% 30% 6%	2717
June	1st to 10th	Day	15% 5% 9% 24% 31% 16%	2520
	11th to 20th	Day	8% 3 5% 15% 41% 27%	2520
	21st to end	Day	8% 3 3 12% 34% 41%	2520
July	1st to 10th	Day	7% 2 2 10% 34% 45%	2451
	11th to 20th	Day	10% 3 4 11% 34% 38%	2297
	21st to end	Day	10% 4 4 15% 34% 33%	2405
August	1st to 10th	Day	11% 3 2 12% 31% 42%	2201
	11th to 20th	Day	6% 3 2 13% 39% 38%	2122
	21st to end	Day	7% 3 1 11% 40% 37%	2376
September	1st to 10th	Day	8% 3 2 12% 31% 45%	2160
	11th to 20th	Day	9% 3 2 20% 40% 26%	2152
	21st to end	Day	10% 3 3 19% 36% 29%	1980
October	1st to 10th	Day	14% 4 6% 21% 23% 32%	1814
	11th to 20th	Day	16% 5% 5% 17% 31% 28%	1800
	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 6% 18% 25% 17%	2381
	11th to 20th	Night	25% 5% 7% 22% 26% 15%	2099
	21st to end	Night	32% 3 7% 22% 25% 10%	1776
March	1st to 10th	Night	37% 4 11% 22% 16% 10%	2114
	11th to 20th	Night	32% 6% 9% 20% 23% 9%	1980
	21st to end	Night	28% 5% 13% 23% 23% 8%	2075
April	1st to 10th	Night	26% 5% 13% 27% 18% 11%	1800
	11th to 20th	Night	21% 4 9% 29% 26% 10%	1779
	21st to end	Night	20% 5% 9% 26% 31% 9%	1800
May	1st to 10th	Night	18% 4 11% 23% 30% 14%	1800
	11th to 20th	Night	17% 5% 8% 27% 31% 12%	1689
	21st to end	Night	18% 8% 8% 27% 30% 9%	1554
June	1st to 10th	Night	14% 7% 10% 20% 30% 20%	1440
	11th to 20th	Night	10% 4 4 17% 35% 30%	1440
	21st to end	Night	8% 4 2 10% 32% 44%	1440
July	1st to 10th	Night	7% 6% 1 9% 29% 49%	1400
	11th to 20th	Night	9% 4 3 12% 28% 44%	1536
	21st to end	Night	11% 5% 2 12% 33% 38%	1674
August	1st to 10th	Night	10% 3 1 9% 29% 46%	1713
	11th to 20th	Night	6% 4 1 8% 36% 45%	1780
	21st to end	Night	7% 3 1 9% 35% 46%	1980
September	1st to 10th	Night	9% 4 2 9% 26% 52%	1800
	11th to 20th	Night	10% 4 3 14% 34% 35%	1808
	21st to end	Night	9% 2 3 16% 39% 31%	1980
October	1st to 10th	Night	15% 3 4 21% 25% 33%	2142
	11th to 20th	Night	17% 4 5% 17% 27% 29%	2160
	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	405
	11th to 20th	Day	15% 16% 31% 25% 11% 2	415
	21st to end	Day	12% 20% 33% 25% 7% 3	346
March	1st to 10th	Day	19% 17% 34% 24% 6%	420
	11th to 20th	Day	17% 17% 30% 27% 8% 1	420
	21st to end	Day	17% 19% 31% 26% 7% 1	462
April	1st to 10th	Day	15% 13% 34% 25% 11% 2	420
	11th to 20th	Day	12% 15% 33% 27% 10% 2	412
	21st to end	Day	7% 13% 36% 26% 13% 5%	420
May	1st to 10th	Day	11% 10% 33% 29% 11% 5%	423
	11th to 20th	Day	5% 12% 28% 36% 16% 4	448
	21st to end	Day	8% 12% 24% 37% 15% 4	485
June	1st to 10th	Day	4 7% 21% 39% 23% 6%	450
	11th to 20th	Day	2 6% 25% 39% 23% 5%	450
	21st to end	Day	3 20% 40% 28% 9%	450
July	1st to 10th	Day	1 13% 47% 30% 10%	446
	11th to 20th	Day	2 6% 45% 34% 12%	444
	21st to end	Day	1 8% 46% 33% 12%	487
August	1st to 10th	Day	2 2 15% 43% 29% 9%	447
	11th to 20th	Day	2 1 9% 43% 33% 13%	437
	21st to end	Day	1 1 9% 44% 34% 11%	495
September	1st to 10th	Day	3 3 13% 46% 28% 8%	450
	11th to 20th	Day	3 5% 21% 44% 22% 5%	450
	21st to end	Day	1 8% 21% 39% 28% 4	450
October	1st to 10th	Day	2 10% 25% 42% 18% 4	450
	11th to 20th	Day	3 8% 28% 38% 20% 3	450
	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%	758
	11th to 20th	Night	10% 8% 18% 35% 23% 5%	704
	21st to end	Night	15% 7% 19% 39% 17% 3	592
March	1st to 10th	Night	14% 6% 18% 41% 18% 4	720
	11th to 20th	Night	12% 5% 17% 35% 24% 7%	720
	21st to end	Night	12% 7% 18% 34% 25% 3	792
April	1st to 10th	Night	9% 6% 17% 38% 26% 4	720
	11th to 20th	Night	7% 8% 20% 32% 27% 6%	711
	21st to end	Night	6% 6% 20% 32% 27% 9%	720
May	1st to 10th	Night	6% 4 12% 37% 32% 8%	720
	11th to 20th	Night	4 4 10% 36% 37% 8%	625
	21st to end	Night	4 4 10% 38% 36% 9%	391
June	1st to 10th	Night	4 3 7% 35% 45% 8%	360
	11th to 20th	Night	1 2 9% 31% 48% 9%	360
	21st to end	Night	1 1 3 31% 52% 13%	360
July	1st to 10th	Night	1 19% 65% 14%	350
	11th to 20th	Night	2 1 9% 61% 26%	492
	21st to end	Night	1 1 2 12% 59% 27%	591
August	1st to 10th	Night	1 1 2 25% 55% 16%	648
	11th to 20th	Night	1 1 19% 63% 15%	712
	21st to end	Night	1 2 21% 61% 16%	792
September	1st to 10th	Night	2 1 3 24% 56% 15%	720
	11th to 20th	Night	3 1 5% 36% 44% 11%	720
	21st to end	Night	1 2 7% 33% 46% 10%	720
October	1st to 10th	Night	5% 1 8% 39% 39% 7%	720
	11th to 20th	Night	6% 3 9% 38% 36% 8%	720
	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 2024-02-07 03:11:58. Version ac07

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