Woodland Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodland Hills clear sky chart from 2005-11-06 to 2026-09-29.

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 3 1 3 2 2 2 2 4 6% 70%	156993
	Night	5% 4 2 4 3 2 3 2 4 6% 66%	152104
Transparency	Day	17% 4 7% 18% 28% 27%	152082
	Night	20% 4 7% 17% 26% 26%	147990
Seeing	Day	6% 6% 20% 34% 26% 8%	18192
	Night	6% 3 11% 35% 37% 8%	27962

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 1 3 2 2 3 2 4 5% 65%	4722
	11th to 20th	Day	4 3 1 3 2 2 2 2 4 6% 71%	5318
	21st to end	Day	8% 5% 1 4 3 3 3 3 5% 8% 56%	6334
February	1st to 10th	Day	9% 5% 1 4 2 2 2 3 4 6% 61%	2100
	11th to 20th	Day	10% 3 1 2 2 2 3 3 5% 7% 60%	2050
	21st to end	Day	7% 4 1 4 3 3 3 3 5% 7% 60%	1730
March	1st to 10th	Day	10% 4 1 5% 3 3 4 4 4 6% 55%	4618
	11th to 20th	Day	8% 4 1 4 2 3 3 3 4 6% 61%	4834
	21st to end	Day	10% 5% 2 3 3 4 4 4 6% 7% 51%	6101
April	1st to 10th	Day	5% 4 1 4 3 3 3 3 4 8% 62%	2520
	11th to 20th	Day	4 3 1 4 2 3 3 3 4 6% 65%	2489
	21st to end	Day	4 5% 1 4 2 2 3 3 4 6% 67%	2520
May	1st to 10th	Day	3 6% 2 4 2 2 2 3 4 6% 67%	7129
	11th to 20th	Day	2 7% 3 5% 2 2 2 2 3 5% 65%	7596
	21st to end	Day	2 7% 2 5% 2 2 2 2 3 6% 67%	8370
June	1st to 10th	Day	3 6% 2 4 2 2 3 3 5% 8% 62%	2826
	11th to 20th	Day	3 4 1 3 2 2 2 2 4 6% 72%	2940
	21st to end	Day	1 4 1 2 2 2 2 2 3 4 77%	2940
July	1st to 10th	Day	2 1 2 1 1 1 1 2 3 85%	8219
	11th to 20th	Day	1 1 1 3 2 2 2 2 4 5% 77%	8149
	21st to end	Day	1 2 1 1 1 1 2 2 4 84%	7783
August	1st to 10th	Day	1 1 1 1 1 1 1 2 4 86%	6986
	11th to 20th	Day	1 1 1 2 1 1 2 1 3 5% 83%	7001
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 82%	7750
September	1st to 10th	Day	3 2 1 2 1 2 1 2 3 5% 79%	2520
	11th to 20th	Day	2 3 1 3 1 2 2 2 2 4 78%	2394
	21st to end	Day	2 2 1 2 2 2 2 1 3 5% 78%	2289
October	1st to 10th	Day	2 2 1 1 1 2 1 1 3 4 82%	3600
	11th to 20th	Day	2 3 2 3 2 2 2 2 4 7% 72%	3297
	21st to end	Day	2 3 1 3 3 2 3 3 5% 5% 69%	3538
November	1st to 10th	Day	3 3 1 3 2 3 2 2 3 5% 73%	1854
	11th to 20th	Day	5% 3 1 3 2 3 3 2 4 6% 67%	1890
	21st to end	Day	5% 3 1 4 3 3 3 3 5% 7% 62%	1890
December	1st to 10th	Day	4 2 1 3 3 3 4 3 5% 7% 65%	3040
	11th to 20th	Day	10% 4 1 4 3 3 4 4 6% 7% 54%	3499
	21st to end	Day	11% 4 2 4 5% 4 4 3 6% 8% 49%	4157
January	1st to 10th	Night	10% 5% 1 3 3 2 2 2 3 4 63%	8172
	11th to 20th	Night	5% 3 2 4 2 2 2 2 4 6% 69%	7667
	21st to end	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	7888
February	1st to 10th	Night	8% 5% 2 4 3 2 2 2 4 6% 62%	2520
	11th to 20th	Night	9% 4 2 5% 3 2 3 2 4 6% 60%	2458
	21st to end	Night	9% 4 1 3 3 4 3 3 4 5% 60%	2076
March	1st to 10th	Night	7% 7% 2 4 3 3 3 3 5% 8% 56%	5496
	11th to 20th	Night	7% 6% 1 3 3 3 4 3 4 6% 59%	5368
	21st to end	Night	10% 5% 3 5% 2 3 3 3 4 7% 55%	5116
April	1st to 10th	Night	6% 6% 1 4 3 3 2 3 3 7% 62%	2100
	11th to 20th	Night	5% 4 2 4 2 2 3 3 3 6% 66%	2079
	21st to end	Night	4 5% 1 4 2 2 3 3 5% 7% 63%	2100
May	1st to 10th	Night	3 9% 3 8% 4 3 2 2 3 5% 58%	5842
	11th to 20th	Night	1 7% 4 10% 4 2 2 2 3 6% 59%	5296
	21st to end	Night	1 7% 3 8% 3 1 2 1 3 5% 65%	5837
June	1st to 10th	Night	2 6% 2 5% 4 2 3 3 4 8% 61%	1787
	11th to 20th	Night	2 4 2 3 2 2 2 2 5% 7% 69%	1680
	21st to end	Night	2 4 1 4 3 2 2 2 3 6% 72%	1680
July	1st to 10th	Night	1 1 3 3 1 2 1 2 4 80%	4740
	11th to 20th	Night	1 1 1 5% 3 4 3 2 3 5% 72%	4796
	21st to end	Night	1 2 2 3 3 2 2 2 3 5% 76%	6340
August	1st to 10th	Night	1 1 1 2 2 2 2 3 5% 81%	5866
	11th to 20th	Night	1 2 2 5% 3 2 2 1 3 5% 75%	5886
	21st to end	Night	1 1 1 3 2 2 2 2 3 4 79%	6499
September	1st to 10th	Night	3 3 1 3 2 2 2 2 3 5% 75%	2100
	11th to 20th	Night	2 3 2 2 2 1 2 1 3 4 77%	2226
	21st to end	Night	2 2 1 3 1 2 3 2 3 4 77%	2288
October	1st to 10th	Night	2 2 1 3 2 2 2 1 2 3 82%	3600
	11th to 20th	Night	3 5% 4 7% 2 2 2 2 3 5% 65%	3857
	21st to end	Night	2 3 1 3 2 2 2 2 3 4 76%	4269
November	1st to 10th	Night	3 2 1 2 2 2 4 2 4 6% 72%	2665
	11th to 20th	Night	5% 3 1 4 2 2 3 2 3 6% 69%	2730
	21st to end	Night	5% 3 1 4 3 3 4 3 6% 7% 62%	2730
December	1st to 10th	Night	5% 3 1 4 2 3 3 3 4 6% 67%	4370
	11th to 20th	Night	11% 4 1 3 3 3 3 4 6% 8% 54%	4941
	21st to end	Night	10% 5% 1 4 4 4 5% 4 7% 9% 47%	7039

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	23% 3 7% 15% 29% 24%	4723
	11th to 20th	Day	15% 5% 6% 12% 19% 43%	5318
	21st to end	Day	27% 4 4 16% 22% 27%	6334
February	1st to 10th	Day	25% 3 6% 15% 25% 26%	2100
	11th to 20th	Day	23% 5% 9% 18% 24% 22%	2060
	21st to end	Day	23% 6% 9% 18% 23% 20%	1730
March	1st to 10th	Day	26% 7% 9% 17% 21% 20%	4618
	11th to 20th	Day	23% 5% 10% 27% 22% 13%	4834
	21st to end	Day	25% 9% 14% 26% 18% 8%	6101
April	1st to 10th	Day	21% 6% 13% 23% 23% 14%	2520
	11th to 20th	Day	18% 5% 9% 23% 28% 17%	2492
	21st to end	Day	16% 6% 11% 26% 29% 11%	2520
May	1st to 10th	Day	18% 5% 9% 21% 33% 15%	7129
	11th to 20th	Day	20% 5% 7% 24% 28% 15%	7599
	21st to end	Day	18% 6% 10% 30% 29% 8%	8371
June	1st to 10th	Day	20% 6% 11% 22% 28% 12%	2826
	11th to 20th	Day	14% 4 7% 16% 32% 27%	2940
	21st to end	Day	14% 2 5% 11% 33% 35%	2940
July	1st to 10th	Day	8% 2 2 7% 22% 59%	8151
	11th to 20th	Day	12% 2 4 14% 36% 31%	8074
	21st to end	Day	7% 2 4 18% 39% 30%	7611
August	1st to 10th	Day	6% 1 2 17% 42% 30%	5530
	11th to 20th	Day	7% 1 4 18% 36% 34%	5517
	21st to end	Day	10% 1 3 15% 32% 39%	6077
September	1st to 10th	Day	10% 3 4 13% 31% 38%	2520
	11th to 20th	Day	12% 3 5% 15% 32% 33%	2394
	21st to end	Day	11% 3 5% 18% 33% 31%	2289
October	1st to 10th	Day	9% 2 5% 12% 18% 54%	3600
	11th to 20th	Day	14% 4 4 14% 35% 29%	3297
	21st to end	Day	16% 4 4 10% 30% 37%	3538
November	1st to 10th	Day	16% 3 6% 16% 25% 34%	1854
	11th to 20th	Day	19% 4 6% 14% 20% 36%	1890
	21st to end	Day	22% 4 9% 12% 23% 30%	1890
December	1st to 10th	Day	19% 5% 4 14% 24% 35%	3040
	11th to 20th	Day	28% 4 7% 14% 25% 21%	3498
	21st to end	Day	30% 7% 10% 21% 23% 9%	4157
January	1st to 10th	Night	26% 3 6% 11% 30% 24%	8172
	11th to 20th	Night	18% 4 5% 14% 15% 44%	7667
	21st to end	Night	29% 5% 5% 13% 22% 27%	7888
February	1st to 10th	Night	25% 3 7% 14% 23% 27%	2520
	11th to 20th	Night	26% 3 8% 18% 22% 23%	2459
	21st to end	Night	26% 5% 7% 17% 22% 24%	2076
March	1st to 10th	Night	24% 8% 10% 16% 24% 18%	5496
	11th to 20th	Night	24% 6% 12% 26% 17% 15%	5368
	21st to end	Night	26% 6% 15% 24% 22% 7%	5116
April	1st to 10th	Night	24% 5% 11% 23% 22% 15%	2100
	11th to 20th	Night	19% 5% 10% 23% 25% 18%	2079
	21st to end	Night	20% 5% 13% 25% 26% 11%	2100
May	1st to 10th	Night	27% 7% 9% 19% 27% 12%	5840
	11th to 20th	Night	20% 9% 8% 23% 26% 13%	5297
	21st to end	Night	19% 6% 9% 31% 27% 8%	5838
June	1st to 10th	Night	21% 7% 15% 21% 24% 12%	1787
	11th to 20th	Night	15% 4 9% 17% 31% 23%	1680
	21st to end	Night	18% 3 6% 13% 30% 31%	1680
July	1st to 10th	Night	11% 1 2 8% 25% 52%	4700
	11th to 20th	Night	17% 2 5% 16% 30% 30%	4748
	21st to end	Night	14% 2 5% 20% 33% 27%	6200
August	1st to 10th	Night	9% 1 4 19% 40% 26%	4636
	11th to 20th	Night	11% 1 4 17% 37% 29%	4636
	21st to end	Night	12% 1 3 15% 37% 32%	5092
September	1st to 10th	Night	14% 3 5% 10% 29% 39%	2100
	11th to 20th	Night	13% 3 4 14% 32% 33%	2226
	21st to end	Night	12% 3 6% 14% 33% 32%	2288
October	1st to 10th	Night	11% 2 4 10% 16% 57%	3600
	11th to 20th	Night	23% 3 5% 12% 26% 30%	3857
	21st to end	Night	14% 2 3 9% 27% 44%	4269
November	1st to 10th	Night	14% 4 7% 16% 23% 35%	2665
	11th to 20th	Night	18% 3 7% 13% 22% 37%	2730
	21st to end	Night	21% 5% 8% 16% 20% 31%	2730
December	1st to 10th	Night	19% 3 4 14% 21% 38%	4370
	11th to 20th	Night	29% 3 8% 15% 21% 24%	4941
	21st to end	Night	29% 8% 11% 22% 20% 9%	7039

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	18% 8% 25% 33% 15% 1	220
	11th to 20th	Day	10% 10% 31% 32% 17% 1	421
	21st to end	Day	9% 12% 31% 33% 14% 1	562
February	1st to 10th	Day	12% 10% 30% 30% 15% 4	540
	11th to 20th	Day	12% 13% 30% 33% 10% 2	535
	21st to end	Day	7% 12% 36% 33% 10% 1	446
March	1st to 10th	Day	12% 15% 31% 26% 14% 1	540
	11th to 20th	Day	9% 14% 29% 30% 16% 3	540
	21st to end	Day	8% 13% 32% 30% 13% 3	594
April	1st to 10th	Day	8% 9% 27% 33% 17% 6%	540
	11th to 20th	Day	5% 10% 35% 32% 14% 5%	532
	21st to end	Day	4 10% 31% 31% 17% 7%	540
May	1st to 10th	Day	5% 9% 27% 38% 16% 5%	543
	11th to 20th	Day	5% 5% 25% 38% 23% 4	568
	21st to end	Day	5% 6% 24% 38% 22% 6%	617
June	1st to 10th	Day	5% 2 18% 34% 32% 7%	570
	11th to 20th	Day	4 1 15% 37% 32% 11%	570
	21st to end	Day	4 1 12% 35% 36% 12%	570
July	1st to 10th	Day	2 1 5% 34% 41% 17%	566
	11th to 20th	Day	1 5% 25% 47% 22%	564
	21st to end	Day	1 3 30% 44% 21%	619
August	1st to 10th	Day	2 1 5% 34% 40% 18%	567
	11th to 20th	Day	2 1 4 32% 45% 17%	557
	21st to end	Day	1 7% 39% 37% 15%	627
September	1st to 10th	Day	4 1 10% 37% 34% 14%	570
	11th to 20th	Day	4 2 18% 39% 30% 8%	570
	21st to end	Day	2 3 19% 36% 31% 10%	563
October	1st to 10th	Day	2 4 18% 38% 30% 8%	530
	11th to 20th	Day	3 4 22% 40% 25% 6%	530
	21st to end	Day	4 6% 22% 36% 26% 7%	575
November	1st to 10th	Day	4 6% 16% 32% 33% 9%	330
	11th to 20th	Day	8% 7% 23% 38% 19% 5%	330
	21st to end	Day	7% 7% 24% 33% 25% 4	330
December	1st to 10th	Day	8% 4 23% 37% 25% 3	330
	11th to 20th	Day	5% 6% 21% 35% 28% 5%	330
	21st to end	Day	16% 14% 22% 32% 16% 1	256
January	1st to 10th	Night	12% 5% 16% 42% 19% 5%	840
	11th to 20th	Night	8% 3 20% 44% 21% 4	840
	21st to end	Night	13% 4 21% 40% 21% 2	924
February	1st to 10th	Night	10% 4 17% 40% 24% 5%	840
	11th to 20th	Night	10% 4 18% 39% 23% 6%	824
	21st to end	Night	11% 4 22% 41% 19% 3	692
March	1st to 10th	Night	9% 6% 18% 43% 21% 3	840
	11th to 20th	Night	8% 3 16% 39% 29% 5%	840
	21st to end	Night	8% 4 17% 43% 25% 4	924
April	1st to 10th	Night	8% 3 14% 43% 28% 4	840
	11th to 20th	Night	6% 3 16% 42% 31% 3	831
	21st to end	Night	5% 5% 14% 39% 30% 7%	840
May	1st to 10th	Night	7% 2 10% 41% 33% 6%	814
	11th to 20th	Night	5% 1 14% 37% 38% 5%	621
	21st to end	Night	4 1 14% 37% 40% 5%	683
June	1st to 10th	Night	2 1 9% 35% 47% 6%	527
	11th to 20th	Night	3 1 3 32% 54% 8%	420
	21st to end	Night	4 2 27% 58% 8%	420
July	1st to 10th	Night	2 1 11% 72% 13%	410
	11th to 20th	Night	2 9% 68% 21%	425
	21st to end	Night	2 2 13% 64% 19%	879
August	1st to 10th	Night	3 1 17% 61% 18%	836
	11th to 20th	Night	2 1 15% 62% 19%	832
	21st to end	Night	2 1 1 19% 59% 18%	924
September	1st to 10th	Night	4 1 3 25% 50% 17%	840
	11th to 20th	Night	4 3 29% 52% 12%	840
	21st to end	Night	2 5% 33% 48% 12%	832
October	1st to 10th	Night	4 1 7% 39% 44% 6%	800
	11th to 20th	Night	6% 2 9% 33% 41% 9%	800
	21st to end	Night	4 2 11% 37% 35% 12%	880
November	1st to 10th	Night	2 4 11% 40% 34% 9%	820
	11th to 20th	Night	6% 3 11% 41% 32% 8%	840
	21st to end	Night	7% 2 16% 43% 27% 6%	840
December	1st to 10th	Night	8% 4 17% 40% 26% 5%	840
	11th to 20th	Night	12% 4 16% 42% 23% 4	840
	21st to end	Night	12% 5% 21% 41% 18% 4	924

Page generated at 2026-09-26 01:18:42. Version ac07

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