Topanga
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Topanga clear sky chart from 2005-11-06 to 2025-03-27.

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 1 3 2 2 2 2 4 6% 69%	113246
	Night	5% 4 1 4 3 3 3 3 4 6% 64%	114949
Transparency	Day	9% 43% 4 10% 15% 18%	113008
	Night	11% 42% 5% 10% 15% 17%	114776
Seeing	Day	5% 6% 20% 34% 26% 8%	16105
	Night	6% 2 11% 35% 37% 8%	26016

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	4 2 1 3 2 2 2 2 4 5% 73%	3639
	11th to 20th	Day	6% 3 1 4 2 2 2 2 4 6% 66%	4082
	21st to end	Day	11% 5% 2 4 3 2 3 3 5% 9% 54%	4899
February	1st to 10th	Day	10% 4 2 3 3 2 2 2 5% 6% 61%	2000
	11th to 20th	Day	9% 3 1 3 2 3 3 3 5% 7% 62%	1950
	21st to end	Day	8% 5% 1 3 3 4 3 2 5% 6% 60%	1650
March	1st to 10th	Day	9% 4 2 5% 3 4 4 4 5% 7% 52%	3238
	11th to 20th	Day	5% 4 1 3 2 2 3 3 5% 7% 65%	3401
	21st to end	Day	8% 5% 2 4 3 4 4 4 6% 8% 51%	4239
April	1st to 10th	Day	5% 5% 1 4 3 3 3 3 5% 8% 61%	2280
	11th to 20th	Day	4 4 1 4 2 3 2 3 4 6% 68%	2249
	21st to end	Day	3 4 1 2 2 2 2 3 4 7% 70%	2280
May	1st to 10th	Day	2 4 1 3 2 2 2 2 3 6% 73%	3831
	11th to 20th	Day	2 11% 3 5% 2 1 2 2 4 6% 61%	4071
	21st to end	Day	3 7% 2 4 2 2 2 2 3 6% 66%	4477
June	1st to 10th	Day	4 7% 2 4 2 2 2 2 4 8% 63%	2549
	11th to 20th	Day	3 5% 1 2 2 2 2 1 4 6% 72%	2660
	21st to end	Day	2 4 1 3 2 1 2 2 3 5% 75%	2660
July	1st to 10th	Day	1 2 1 2 1 1 1 2 2 4 82%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 3 3 5% 76%	4372
	21st to end	Day	1 2 1 1 1 1 2 2 3 5% 83%	4160
August	1st to 10th	Day	2 2 1 2 1 1 1 1 2 4 83%	3783
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 87%	3724
	21st to end	Day	1 2 1 1 1 2 2 1 3 5% 82%	4180
September	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 78%	2280
	11th to 20th	Day	3 3 2 1 2 2 1 2 4 79%	2165
	21st to end	Day	2 2 1 2 2 2 2 2 3 6% 76%	2090
October	1st to 10th	Day	2 2 1 1 1 1 1 2 3 3 82%	3490
	11th to 20th	Day	2 4 1 3 2 1 2 2 4 7% 72%	3197
	21st to end	Day	2 3 1 4 3 2 3 3 5% 6% 68%	3431
November	1st to 10th	Day	3 2 1 3 2 3 3 2 3 5% 72%	1764
	11th to 20th	Day	4 3 1 3 2 2 3 3 4 5% 71%	1800
	21st to end	Day	5% 3 1 4 3 3 4 3 5% 8% 62%	1800
December	1st to 10th	Day	4 2 1 3 3 3 4 4 6% 6% 62%	2950
	11th to 20th	Day	11% 4 1 4 2 3 4 4 6% 7% 53%	3409
	21st to end	Day	10% 4 2 5% 5% 4 4 4 7% 10% 46%	4076
January	1st to 10th	Night	5% 3 1 3 2 2 2 2 3 5% 71%	6306
	11th to 20th	Night	6% 4 2 5% 3 3 3 2 3 5% 65%	5880
	21st to end	Night	11% 5% 1 4 3 3 4 3 5% 6% 56%	6091
February	1st to 10th	Night	9% 6% 1 4 3 2 2 2 4 5% 62%	2400
	11th to 20th	Night	9% 4 2 3 3 3 3 2 4 6% 61%	2338
	21st to end	Night	10% 5% 1 4 3 3 4 2 3 5% 61%	1980
March	1st to 10th	Night	8% 6% 1 5% 3 3 4 3 6% 9% 53%	3856
	11th to 20th	Night	4 5% 1 4 3 3 3 4 5% 7% 61%	3781
	21st to end	Night	10% 5% 2 4 4 4 3 3 4 6% 56%	3552
April	1st to 10th	Night	6% 6% 2 4 3 2 2 2 4 6% 61%	1900
	11th to 20th	Night	4 6% 1 3 3 2 3 3 4 5% 66%	1879
	21st to end	Night	4 4 2 4 2 2 3 3 4 7% 63%	1900
May	1st to 10th	Night	3 6% 2 4 3 3 2 2 4 5% 66%	3132
	11th to 20th	Night	2 10% 4 11% 6% 4 3 2 3 5% 49%	2834
	21st to end	Night	2 8% 2 7% 3 2 2 2 3 5% 65%	3110
June	1st to 10th	Night	2 8% 3 5% 4 3 3 3 5% 7% 58%	1625
	11th to 20th	Night	2 6% 2 4 3 3 2 3 5% 6% 65%	1520
	21st to end	Night	2 7% 2 4 2 2 3 2 4 7% 65%	1520
July	1st to 10th	Night	1 2 1 4 2 3 2 2 4 6% 73%	2540
	11th to 20th	Night	1 2 1 3 2 3 3 4 5% 7% 68%	2586
	21st to end	Night	1 2 1 2 2 2 2 2 3 4 78%	3412
August	1st to 10th	Night	2 2 1 2 2 2 2 2 4 6% 75%	3166
	11th to 20th	Night	1 3 1 2 2 2 2 2 4 6% 76%	3126
	21st to end	Night	1 1 1 3 3 3 3 2 4 5% 73%	3498
September	1st to 10th	Night	4 3 1 4 2 2 2 2 4 5% 72%	1900
	11th to 20th	Night	2 3 1 3 1 2 2 1 3 5% 76%	2014
	21st to end	Night	2 2 1 3 2 2 2 2 3 4 76%	2090
October	1st to 10th	Night	2 2 1 2 2 2 2 1 3 3 80%	3490
	11th to 20th	Night	2 7% 3 5% 2 2 3 3 5% 5% 61%	3736
	21st to end	Night	2 3 1 3 2 2 2 2 3 5% 75%	4137
November	1st to 10th	Night	3 3 1 3 2 2 3 3 4 5% 71%	2535
	11th to 20th	Night	3 3 1 4 2 2 2 2 4 5% 71%	2600
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 7% 62%	2600
December	1st to 10th	Night	5% 3 1 4 3 4 3 3 4 6% 65%	4240
	11th to 20th	Night	11% 4 1 4 3 3 4 4 6% 8% 53%	4811
	21st to end	Night	10% 5% 1 4 3 4 6% 4 7% 9% 46%	6864

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	9% 26% 3 15% 26% 21%	3639
	11th to 20th	Day	14% 29% 6% 14% 12% 25%	4082
	21st to end	Day	20% 29% 3 14% 20% 15%	4899
February	1st to 10th	Day	11% 62% 4 6% 10% 8%	2000
	11th to 20th	Day	10% 60% 2 7% 10% 11%	1960
	21st to end	Day	9% 62% 4 8% 9% 9%	1650
March	1st to 10th	Day	18% 44% 8% 13% 9% 9%	3238
	11th to 20th	Day	8% 41% 10% 22% 8% 11%	3401
	21st to end	Day	14% 45% 12% 18% 8% 3	4239
April	1st to 10th	Day	7% 66% 4 7% 10% 5%	2280
	11th to 20th	Day	6% 65% 3 6% 11% 8%	2252
	21st to end	Day	5% 67% 5% 9% 10% 5%	2280
May	1st to 10th	Day	7% 42% 6% 12% 23% 10%	3831
	11th to 20th	Day	13% 43% 8% 15% 18% 3	4074
	21st to end	Day	11% 43% 10% 20% 15% 1	4477
June	1st to 10th	Day	8% 65% 4 9% 10% 4	2549
	11th to 20th	Day	6% 64% 2 7% 12% 10%	2660
	21st to end	Day	7% 63% 2 5% 11% 12%	2660
July	1st to 10th	Day	4 35% 2 3 6% 50%	4351
	11th to 20th	Day	8% 35% 3 6% 15% 33%	4297
	21st to end	Day	3 34% 2 11% 18% 31%	4029
August	1st to 10th	Day	5% 35% 1 6% 28% 24%	3770
	11th to 20th	Day	2 36% 1 5% 20% 37%	3760
	21st to end	Day	4 35% 1 6% 17% 37%	4179
September	1st to 10th	Day	6% 59% 2 6% 13% 14%	2280
	11th to 20th	Day	7% 60% 2 6% 14% 12%	2165
	21st to end	Day	4 59% 3 7% 15% 12%	2090
October	1st to 10th	Day	2 36% 1 5% 10% 46%	3490
	11th to 20th	Day	8% 37% 2 10% 26% 16%	3197
	21st to end	Day	12% 36% 2 5% 22% 23%	3431
November	1st to 10th	Day	3 55% 2 7% 11% 21%	1764
	11th to 20th	Day	9% 57% 3 6% 8% 16%	1800
	21st to end	Day	11% 56% 5% 6% 9% 13%	1800
December	1st to 10th	Day	11% 36% 2 10% 16% 25%	2950
	11th to 20th	Day	20% 32% 4 9% 17% 18%	3408
	21st to end	Day	22% 29% 8% 17% 18% 5%	4076
January	1st to 10th	Night	11% 27% 4 9% 28% 21%	6306
	11th to 20th	Night	18% 29% 5% 15% 11% 22%	5880
	21st to end	Night	21% 31% 4 10% 20% 14%	6091
February	1st to 10th	Night	12% 62% 3 6% 8% 8%	2400
	11th to 20th	Night	10% 60% 4 6% 10% 11%	2339
	21st to end	Night	10% 62% 3 6% 10% 9%	1980
March	1st to 10th	Night	15% 46% 7% 12% 13% 7%	3856
	11th to 20th	Night	10% 42% 10% 20% 8% 10%	3781
	21st to end	Night	14% 42% 12% 17% 13% 2	3552
April	1st to 10th	Night	9% 65% 3 8% 9% 5%	1900
	11th to 20th	Night	6% 65% 4 7% 12% 7%	1879
	21st to end	Night	5% 64% 6% 9% 10% 5%	1900
May	1st to 10th	Night	8% 43% 6% 11% 21% 11%	3132
	11th to 20th	Night	11% 46% 9% 16% 15% 3	2835
	21st to end	Night	9% 43% 11% 21% 15% 1	3110
June	1st to 10th	Night	10% 64% 6% 7% 9% 4	1625
	11th to 20th	Night	6% 64% 2 8% 12% 9%	1520
	21st to end	Night	10% 62% 2 6% 10% 10%	1520
July	1st to 10th	Night	5% 34% 1 4 11% 45%	2500
	11th to 20th	Night	8% 34% 3 5% 18% 32%	2538
	21st to end	Night	4 34% 3 13% 16% 30%	3305
August	1st to 10th	Night	6% 35% 2 9% 25% 22%	3156
	11th to 20th	Night	5% 35% 1 7% 22% 29%	3156
	21st to end	Night	8% 35% 1 4 24% 27%	3498
September	1st to 10th	Night	8% 59% 2 5% 14% 13%	1900
	11th to 20th	Night	6% 60% 2 6% 14% 12%	2014
	21st to end	Night	4 59% 3 6% 16% 13%	2090
October	1st to 10th	Night	4 35% 1 4 8% 47%	3490
	11th to 20th	Night	16% 37% 3 8% 19% 17%	3736
	21st to end	Night	9% 36% 1 5% 20% 28%	4137
November	1st to 10th	Night	3 55% 3 7% 11% 21%	2535
	11th to 20th	Night	9% 57% 3 6% 9% 16%	2600
	21st to end	Night	10% 57% 5% 8% 8% 12%	2600
December	1st to 10th	Night	11% 35% 3 10% 14% 27%	4240
	11th to 20th	Night	19% 32% 6% 10% 13% 20%	4811
	21st to end	Night	22% 31% 10% 19% 14% 5%	6864

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	17% 8% 23% 36% 17% 1	200
	11th to 20th	Day	10% 10% 30% 32% 17% 1	395
	21st to end	Day	10% 12% 30% 33% 13% 1	525
February	1st to 10th	Day	12% 10% 29% 31% 15% 4	500
	11th to 20th	Day	11% 12% 30% 34% 11% 2	495
	21st to end	Day	8% 12% 36% 32% 10% 1	414
March	1st to 10th	Day	11% 15% 32% 27% 14% 1	500
	11th to 20th	Day	10% 15% 30% 29% 14% 2	500
	21st to end	Day	7% 14% 34% 30% 13% 3	531
April	1st to 10th	Day	8% 9% 28% 33% 17% 5%	460
	11th to 20th	Day	5% 11% 36% 32% 13% 4	452
	21st to end	Day	3 8% 31% 32% 19% 7%	460
May	1st to 10th	Day	4 9% 28% 38% 16% 5%	463
	11th to 20th	Day	5% 5% 23% 39% 24% 4	488
	21st to end	Day	4 6% 24% 38% 23% 5%	529
June	1st to 10th	Day	5% 2 18% 33% 34% 8%	490
	11th to 20th	Day	4 2 15% 36% 32% 10%	490
	21st to end	Day	3 1 10% 35% 39% 12%	490
July	1st to 10th	Day	2 4 32% 45% 17%	486
	11th to 20th	Day	1 3 23% 50% 22%	484
	21st to end	Day	2 2 29% 46% 21%	531
August	1st to 10th	Day	2 1 5% 34% 42% 16%	487
	11th to 20th	Day	1 1 4 31% 47% 16%	477
	21st to end	Day	1 7% 37% 40% 15%	539
September	1st to 10th	Day	3 1 8% 38% 34% 15%	490
	11th to 20th	Day	3 2 16% 40% 30% 8%	490
	21st to end	Day	2 2 17% 38% 32% 10%	490
October	1st to 10th	Day	2 3 18% 39% 31% 7%	490
	11th to 20th	Day	2 4 22% 41% 26% 6%	490
	21st to end	Day	4 6% 21% 37% 26% 6%	534
November	1st to 10th	Day	5% 7% 17% 32% 31% 9%	300
	11th to 20th	Day	5% 6% 24% 40% 20% 5%	300
	21st to end	Day	7% 7% 24% 33% 25% 5%	300
December	1st to 10th	Day	9% 4 21% 39% 24% 3	300
	11th to 20th	Day	5% 7% 22% 35% 27% 4	300
	21st to end	Day	12% 14% 23% 34% 16% 1	235
January	1st to 10th	Night	11% 4 16% 43% 20% 6%	800
	11th to 20th	Night	8% 4 19% 44% 21% 4	800
	21st to end	Night	13% 4 20% 39% 21% 3	880
February	1st to 10th	Night	10% 4 17% 39% 25% 6%	800
	11th to 20th	Night	9% 4 17% 40% 24% 6%	784
	21st to end	Night	11% 4 21% 40% 20% 3	660
March	1st to 10th	Night	10% 5% 18% 43% 22% 3	800
	11th to 20th	Night	9% 3 16% 38% 29% 5%	800
	21st to end	Night	8% 4 17% 43% 24% 4	862
April	1st to 10th	Night	8% 3 13% 44% 28% 4	760
	11th to 20th	Night	5% 3 16% 41% 32% 3	751
	21st to end	Night	5% 4 14% 38% 32% 7%	760
May	1st to 10th	Night	7% 2 10% 42% 34% 5%	738
	11th to 20th	Night	5% 1 13% 38% 39% 5%	561
	21st to end	Night	4 1 13% 36% 40% 5%	617
June	1st to 10th	Night	2 1 9% 34% 49% 5%	485
	11th to 20th	Night	3 1 3 31% 54% 8%	380
	21st to end	Night	4 2 26% 60% 8%	380
July	1st to 10th	Night	2 1 9% 73% 14%	370
	11th to 20th	Night	2 7% 69% 21%	388
	21st to end	Night	2 2 12% 64% 20%	800
August	1st to 10th	Night	4 1 17% 61% 17%	756
	11th to 20th	Night	3 1 13% 63% 20%	752
	21st to end	Night	2 1 17% 59% 20%	836
September	1st to 10th	Night	4 1 3 22% 51% 18%	760
	11th to 20th	Night	3 3 28% 53% 12%	760
	21st to end	Night	2 5% 31% 50% 12%	760
October	1st to 10th	Night	4 1 6% 38% 44% 6%	760
	11th to 20th	Night	6% 1 9% 33% 42% 9%	760
	21st to end	Night	4 2 11% 37% 34% 12%	836
November	1st to 10th	Night	3 4 11% 39% 34% 9%	780
	11th to 20th	Night	5% 3 11% 41% 33% 8%	800
	21st to end	Night	6% 2 15% 43% 27% 6%	800
December	1st to 10th	Night	8% 4 16% 39% 27% 6%	800
	11th to 20th	Night	13% 4 16% 42% 22% 4	800
	21st to end	Night	11% 5% 20% 42% 18% 5%	880

Page generated at 2025-03-24 06:04:28. Version ac07

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