Torrance
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Torrance clear sky chart from 2005-11-06 to 2026-10-29.

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	4 4 2 5% 3 3 3 3 4 6% 63%	157517
	Night	5% 6% 2 6% 5% 4 4 3 4 6% 56%	152218
Transparency	Day	16% 32% 5% 12% 19% 16%	152608
	Night	19% 33% 6% 12% 17% 14%	148102
Seeing	Day	6% 7% 23% 36% 22% 8%	18388
	Night	7% 3 10% 33% 37% 11%	28209

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	9% 3 2 3 2 2 3 2 4 5% 64%	4722
	11th to 20th	Day	5% 3 1 3 2 2 2 2 4 6% 69%	5374
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 8% 52%	6500
February	1st to 10th	Day	9% 5% 2 4 4 3 3 3 4 6% 59%	2100
	11th to 20th	Day	9% 3 2 3 3 3 3 3 6% 8% 58%	2050
	21st to end	Day	6% 5% 1 4 3 3 3 3 5% 7% 59%	1730
March	1st to 10th	Day	8% 4 2 4 4 4 4 4 5% 7% 54%	4618
	11th to 20th	Day	7% 4 1 4 3 3 3 3 5% 8% 58%	4821
	21st to end	Day	8% 5% 2 4 3 3 4 4 5% 7% 53%	6101
April	1st to 10th	Day	5% 5% 2 4 3 3 3 3 5% 8% 60%	2520
	11th to 20th	Day	4 4 1 4 3 3 3 3 4 7% 65%	2489
	21st to end	Day	3 4 1 4 3 2 3 2 4 7% 66%	2520
May	1st to 10th	Day	3 5% 2 5% 3 3 3 3 4 7% 62%	7164
	11th to 20th	Day	4 8% 2 6% 3 3 3 2 4 6% 59%	7596
	21st to end	Day	3 7% 2 6% 4 3 3 2 4 6% 59%	8370
June	1st to 10th	Day	6% 7% 2 5% 3 2 2 3 4 8% 56%	2744
	11th to 20th	Day	3 6% 2 4 2 2 2 2 4 7% 66%	2940
	21st to end	Day	2 5% 2 5% 3 3 2 2 3 5% 68%	2940
July	1st to 10th	Day	2 3 2 6% 3 3 2 2 3 5% 70%	8219
	11th to 20th	Day	1 4 2 5% 4 3 3 2 4 6% 65%	8081
	21st to end	Day	1 3 1 4 2 3 2 2 3 6% 72%	7686
August	1st to 10th	Day	1 2 2 4 2 3 2 2 3 6% 75%	6986
	11th to 20th	Day	1 3 2 5% 3 2 2 2 3 6% 71%	7001
	21st to end	Day	1 2 1 4 2 2 3 2 4 6% 71%	7750
September	1st to 10th	Day	3 2 1 3 3 2 2 2 4 6% 72%	2520
	11th to 20th	Day	3 4 2 4 2 2 3 2 4 6% 69%	2375
	21st to end	Day	2 4 2 4 2 2 2 2 4 7% 69%	2310
October	1st to 10th	Day	2 2 1 4 3 3 2 2 4 5% 71%	3710
	11th to 20th	Day	4 4 2 4 3 2 3 2 3 7% 66%	3444
	21st to end	Day	2 3 1 4 2 3 3 3 5% 6% 66%	3607
November	1st to 10th	Day	2 4 2 4 3 2 3 3 4 7% 67%	1854
	11th to 20th	Day	6% 3 1 4 2 2 3 3 5% 5% 66%	1890
	21st to end	Day	5% 3 1 4 4 4 3 3 5% 8% 59%	1890
December	1st to 10th	Day	4 4 2 4 3 3 3 4 5% 7% 61%	3040
	11th to 20th	Day	9% 4 2 4 4 3 4 4 6% 8% 53%	3499
	21st to end	Day	9% 7% 4 7% 5% 5% 4 3 6% 8% 42%	4356
January	1st to 10th	Night	9% 6% 2 5% 3 3 3 2 3 5% 60%	8172
	11th to 20th	Night	5% 5% 1 3 2 3 2 2 4 7% 66%	7581
	21st to end	Night	9% 7% 2 5% 4 4 4 3 5% 6% 51%	7747
February	1st to 10th	Night	8% 6% 2 6% 4 3 3 2 4 6% 56%	2520
	11th to 20th	Night	8% 6% 2 5% 4 3 4 3 4 6% 56%	2458
	21st to end	Night	8% 5% 2 6% 3 3 3 2 5% 5% 58%	2076
March	1st to 10th	Night	7% 6% 2 5% 3 4 4 3 6% 8% 52%	5496
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 3 5% 6% 52%	5393
	21st to end	Night	8% 8% 2 5% 4 3 4 3 5% 8% 50%	5116
April	1st to 10th	Night	7% 6% 2 5% 3 3 3 3 5% 7% 55%	2100
	11th to 20th	Night	5% 7% 2 4 3 2 3 3 4 7% 61%	2079
	21st to end	Night	4 8% 3 5% 4 3 3 3 4 6% 56%	2100
May	1st to 10th	Night	4 12% 2 6% 5% 4 3 2 4 6% 52%	5806
	11th to 20th	Night	3 11% 2 5% 4 3 3 2 3 5% 58%	5296
	21st to end	Night	4 8% 2 5% 4 4 4 2 4 5% 59%	5837
June	1st to 10th	Night	4 12% 3 6% 4 4 4 3 5% 7% 49%	1868
	11th to 20th	Night	3 8% 2 4 4 3 3 3 4 8% 57%	1680
	21st to end	Night	3 8% 3 5% 5% 3 5% 4 5% 8% 51%	1680
July	1st to 10th	Night	2 5% 2 6% 8% 4 3 2 3 6% 59%	4740
	11th to 20th	Night	1 7% 3 6% 5% 4 4 3 4 7% 56%	4851
	21st to end	Night	2 5% 2 5% 5% 4 3 2 3 5% 62%	6458
August	1st to 10th	Night	1 2 2 7% 8% 5% 4 2 4 7% 58%	5866
	11th to 20th	Night	1 6% 2 7% 7% 4 3 2 5% 8% 55%	5886
	21st to end	Night	1 4 2 6% 6% 5% 5% 3 3 7% 60%	6499
September	1st to 10th	Night	3 5% 2 5% 4 3 3 3 4 8% 59%	2100
	11th to 20th	Night	3 4 2 6% 3 3 3 2 4 8% 62%	2243
	21st to end	Night	2 6% 3 6% 4 2 3 2 4 7% 63%	2310
October	1st to 10th	Night	2 3 3 9% 8% 5% 3 2 3 6% 58%	3710
	11th to 20th	Night	4 11% 3 6% 5% 3 3 3 4 5% 53%	3917
	21st to end	Night	2 4 2 4 3 4 3 3 4 7% 65%	4378
November	1st to 10th	Night	3 5% 3 5% 3 2 3 2 4 7% 63%	2665
	11th to 20th	Night	4 5% 2 5% 3 2 2 3 4 7% 63%	2730
	21st to end	Night	5% 5% 2 5% 4 3 3 3 7% 7% 56%	2730
December	1st to 10th	Night	4 5% 2 6% 4 4 4 3 4 7% 56%	4370
	11th to 20th	Night	10% 6% 2 6% 4 3 4 4 5% 7% 50%	4941
	21st to end	Night	10% 8% 4 9% 6% 5% 5% 3 5% 7% 38%	6819

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	18% 21% 6% 15% 21% 19%	4723
	11th to 20th	Day	14% 20% 8% 10% 13% 35%	5374
	21st to end	Day	25% 22% 4 12% 17% 20%	6500
February	1st to 10th	Day	14% 59% 3 7% 10% 8%	2100
	11th to 20th	Day	12% 58% 3 8% 9% 11%	2060
	21st to end	Day	9% 58% 4 10% 10% 8%	1730
March	1st to 10th	Day	20% 30% 9% 13% 16% 11%	4618
	11th to 20th	Day	18% 29% 8% 20% 16% 9%	4821
	21st to end	Day	21% 30% 8% 24% 13% 4	6101
April	1st to 10th	Day	9% 59% 3 9% 13% 6%	2520
	11th to 20th	Day	9% 59% 2 9% 13% 8%	2492
	21st to end	Day	8% 59% 5% 13% 10% 4	2520
May	1st to 10th	Day	18% 24% 7% 17% 26% 8%	7164
	11th to 20th	Day	23% 24% 5% 15% 23% 10%	7599
	21st to end	Day	22% 25% 5% 22% 19% 7%	8371
June	1st to 10th	Day	13% 59% 3 9% 12% 4	2744
	11th to 20th	Day	9% 58% 2 6% 13% 12%	2940
	21st to end	Day	10% 57% 2 5% 13% 13%	2940
July	1st to 10th	Day	16% 19% 3 4 16% 42%	8151
	11th to 20th	Day	17% 20% 5% 10% 29% 19%	8006
	21st to end	Day	12% 19% 3 15% 27% 23%	7516
August	1st to 10th	Day	10% 25% 4 16% 30% 16%	5530
	11th to 20th	Day	13% 25% 4 13% 22% 23%	5517
	21st to end	Day	13% 26% 3 11% 22% 25%	6077
September	1st to 10th	Day	8% 54% 2 6% 17% 13%	2520
	11th to 20th	Day	10% 54% 2 6% 17% 11%	2375
	21st to end	Day	9% 54% 2 7% 16% 11%	2310
October	1st to 10th	Day	10% 33% 2 5% 13% 36%	3710
	11th to 20th	Day	14% 35% 2 8% 25% 15%	3444
	21st to end	Day	12% 34% 3 6% 24% 20%	3607
November	1st to 10th	Day	5% 54% 3 6% 13% 19%	1854
	11th to 20th	Day	13% 55% 4 7% 8% 14%	1890
	21st to end	Day	12% 54% 4 8% 9% 13%	1890
December	1st to 10th	Day	13% 34% 3 15% 14% 21%	3040
	11th to 20th	Day	21% 30% 5% 11% 21% 13%	3498
	21st to end	Day	32% 28% 10% 15% 11% 5%	4356
January	1st to 10th	Night	23% 22% 5% 11% 21% 18%	8172
	11th to 20th	Night	17% 20% 7% 11% 12% 33%	7581
	21st to end	Night	28% 23% 4 9% 18% 19%	7747
February	1st to 10th	Night	15% 59% 3 7% 9% 8%	2520
	11th to 20th	Night	13% 58% 2 8% 8% 10%	2459
	21st to end	Night	11% 59% 2 8% 11% 8%	2076
March	1st to 10th	Night	17% 32% 8% 13% 21% 9%	5496
	11th to 20th	Night	21% 29% 8% 21% 11% 10%	5393
	21st to end	Night	21% 31% 12% 19% 15% 2	5116
April	1st to 10th	Night	11% 60% 4 9% 10% 6%	2100
	11th to 20th	Night	9% 59% 3 9% 13% 7%	2079
	21st to end	Night	8% 59% 6% 13% 9% 4	2100
May	1st to 10th	Night	25% 25% 6% 16% 23% 6%	5804
	11th to 20th	Night	22% 24% 8% 19% 21% 7%	5297
	21st to end	Night	19% 23% 7% 24% 21% 5%	5838
June	1st to 10th	Night	14% 60% 5% 9% 9% 3	1868
	11th to 20th	Night	9% 59% 3 5% 14% 9%	1680
	21st to end	Night	14% 57% 2 5% 11% 11%	1680
July	1st to 10th	Night	17% 19% 4 10% 13% 36%	4700
	11th to 20th	Night	20% 19% 8% 11% 26% 16%	4803
	21st to end	Night	16% 19% 6% 17% 26% 16%	6316
August	1st to 10th	Night	16% 25% 7% 14% 25% 13%	4636
	11th to 20th	Night	18% 25% 5% 15% 22% 14%	4636
	21st to end	Night	19% 25% 6% 11% 22% 18%	5092
September	1st to 10th	Night	10% 54% 3 5% 16% 12%	2100
	11th to 20th	Night	11% 54% 3 7% 16% 10%	2243
	21st to end	Night	10% 54% 3 7% 17% 10%	2310
October	1st to 10th	Night	21% 34% 3 6% 10% 27%	3710
	11th to 20th	Night	23% 35% 4 7% 17% 15%	3917
	21st to end	Night	13% 34% 4 6% 19% 24%	4378
November	1st to 10th	Night	7% 53% 3 7% 11% 19%	2665
	11th to 20th	Night	12% 54% 4 7% 9% 14%	2730
	21st to end	Night	13% 55% 5% 7% 10% 11%	2730
December	1st to 10th	Night	18% 34% 4 9% 16% 19%	4370
	11th to 20th	Night	24% 31% 6% 7% 16% 16%	4941
	21st to end	Night	35% 29% 8% 16% 7% 5%	6819

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	13% 5% 19% 39% 20% 5%	220
	11th to 20th	Day	9% 6% 27% 33% 20% 5%	428
	21st to end	Day	9% 9% 27% 34% 19% 4	594
February	1st to 10th	Day	11% 6% 28% 30% 18% 5%	540
	11th to 20th	Day	11% 12% 29% 29% 16% 3	535
	21st to end	Day	8% 11% 31% 33% 14% 2	446
March	1st to 10th	Day	12% 14% 32% 29% 13% 2	540
	11th to 20th	Day	10% 12% 28% 29% 15% 6%	540
	21st to end	Day	9% 15% 31% 30% 12% 4	594
April	1st to 10th	Day	6% 12% 31% 29% 16% 7%	540
	11th to 20th	Day	5% 14% 35% 29% 12% 5%	532
	21st to end	Day	4 12% 33% 31% 15% 5%	540
May	1st to 10th	Day	5% 12% 31% 34% 13% 4	543
	11th to 20th	Day	5% 8% 28% 39% 16% 4	568
	21st to end	Day	5% 8% 31% 37% 16% 3	617
June	1st to 10th	Day	7% 5% 22% 39% 23% 5%	570
	11th to 20th	Day	5% 3 24% 40% 21% 7%	570
	21st to end	Day	3 3 18% 43% 26% 8%	570
July	1st to 10th	Day	3 1 12% 43% 31% 10%	566
	11th to 20th	Day	2 1 8% 41% 33% 15%	564
	21st to end	Day	2 10% 42% 32% 15%	619
August	1st to 10th	Day	2 1 10% 44% 28% 15%	567
	11th to 20th	Day	4 1 11% 41% 29% 14%	557
	21st to end	Day	2 2 14% 40% 29% 13%	627
September	1st to 10th	Day	3 2 19% 39% 25% 12%	570
	11th to 20th	Day	4 4 24% 41% 19% 8%	570
	21st to end	Day	2 6% 24% 37% 22% 9%	570
October	1st to 10th	Day	3 5% 25% 33% 25% 9%	570
	11th to 20th	Day	5% 5% 27% 36% 18% 10%	570
	21st to end	Day	4 8% 20% 33% 25% 11%	596
November	1st to 10th	Day	4 5% 13% 33% 31% 14%	330
	11th to 20th	Day	7% 4 15% 36% 29% 8%	330
	21st to end	Day	4 4 18% 35% 31% 8%	330
December	1st to 10th	Day	7% 3 16% 36% 28% 10%	330
	11th to 20th	Day	5% 5% 13% 38% 27% 12%	330
	21st to end	Day	13% 10% 21% 31% 22% 3	305
January	1st to 10th	Night	11% 3 13% 41% 26% 6%	840
	11th to 20th	Night	8% 2 13% 41% 30% 6%	840
	21st to end	Night	11% 3 14% 41% 27% 4	924
February	1st to 10th	Night	11% 3 13% 36% 30% 6%	840
	11th to 20th	Night	10% 5% 16% 37% 27% 5%	824
	21st to end	Night	10% 4 17% 42% 24% 4	692
March	1st to 10th	Night	8% 5% 20% 42% 21% 4	840
	11th to 20th	Night	9% 4 13% 38% 28% 8%	840
	21st to end	Night	8% 5% 16% 38% 28% 5%	924
April	1st to 10th	Night	8% 5% 14% 38% 29% 5%	840
	11th to 20th	Night	7% 4 15% 35% 34% 5%	831
	21st to end	Night	6% 5% 14% 37% 32% 6%	840
May	1st to 10th	Night	9% 3 13% 36% 33% 7%	803
	11th to 20th	Night	6% 3 16% 33% 36% 6%	621
	21st to end	Night	5% 2 16% 36% 35% 6%	683
June	1st to 10th	Night	6% 3 13% 34% 37% 7%	608
	11th to 20th	Night	5% 1 6% 24% 50% 14%	420
	21st to end	Night	6% 2 5% 24% 52% 12%	420
July	1st to 10th	Night	4 3 10% 60% 22%	410
	11th to 20th	Night	3 1 2 11% 54% 29%	441
	21st to end	Night	5% 1 3 19% 47% 25%	920
August	1st to 10th	Night	4 4 20% 48% 24%	836
	11th to 20th	Night	6% 1 3 15% 49% 26%	832
	21st to end	Night	4 3 17% 52% 24%	924
September	1st to 10th	Night	5% 1 5% 22% 46% 20%	840
	11th to 20th	Night	6% 1 6% 27% 48% 12%	840
	21st to end	Night	4 2 6% 29% 47% 13%	840
October	1st to 10th	Night	4 1 6% 33% 48% 8%	840
	11th to 20th	Night	7% 3 6% 33% 40% 11%	840
	21st to end	Night	4 2 8% 33% 39% 13%	912
November	1st to 10th	Night	4 2 10% 32% 41% 11%	820
	11th to 20th	Night	5% 2 8% 37% 37% 12%	840
	21st to end	Night	6% 2 12% 41% 32% 7%	840
December	1st to 10th	Night	8% 2 10% 42% 32% 6%	840
	11th to 20th	Night	12% 3 12% 39% 29% 6%	840
	21st to end	Night	10% 6% 15% 41% 22% 5%	924

Page generated at 2026-10-26 01:37:49. Version ac07

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