Mar Vista
Clear Sky Chart
History

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

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 4 3 2 3 3 4 7% 65%	135169
	Night	4 6% 2 5% 3 3 3 3 5% 7% 59%	132439
Transparency	Day	21% 2 5% 19% 28% 25%	130259
	Night	26% 3 6% 19% 25% 22%	128322
Seeing	Day	5% 6% 21% 36% 24% 7%	17005
	Night	6% 3 11% 34% 37% 9%	26818

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 3 2 4 5% 72%	3639
	11th to 20th	Day	6% 4 2 4 2 2 3 2 4 7% 65%	4072
	21st to end	Day	10% 5% 2 4 3 3 3 3 5% 9% 53%	4989
February	1st to 10th	Day	9% 5% 2 4 3 2 3 3 4 5% 61%	2000
	11th to 20th	Day	8% 3 1 4 2 2 4 3 6% 7% 61%	1950
	21st to end	Day	7% 4 1 5% 3 3 3 3 5% 7% 60%	1650
March	1st to 10th	Day	8% 4 2 5% 3 3 4 4 5% 7% 55%	4518
	11th to 20th	Day	8% 4 2 4 3 3 3 3 5% 8% 59%	4721
	21st to end	Day	8% 5% 2 4 3 4 4 4 6% 8% 53%	5969
April	1st to 10th	Day	4 4 1 4 3 3 4 3 5% 8% 61%	2400
	11th to 20th	Day	3 4 1 4 3 3 2 3 5% 7% 65%	2369
	21st to end	Day	3 4 1 3 3 2 2 4 3 8% 67%	2400
May	1st to 10th	Day	2 5% 1 5% 2 3 3 3 5% 6% 64%	5520
	11th to 20th	Day	3 8% 3 7% 3 2 2 2 4 7% 59%	5841
	21st to end	Day	2 6% 2 6% 3 3 3 3 4 7% 60%	6423
June	1st to 10th	Day	4 7% 2 5% 3 2 3 2 5% 8% 58%	2648
	11th to 20th	Day	2 5% 2 4 2 2 2 2 4 8% 67%	2800
	21st to end	Day	2 5% 2 3 3 2 3 2 4 6% 69%	2800
July	1st to 10th	Day	1 2 1 3 2 2 2 2 3 6% 75%	6319
	11th to 20th	Day	1 4 2 4 3 3 3 2 4 6% 69%	6285
	21st to end	Day	1 2 1 3 2 2 2 2 4 6% 75%	5923
August	1st to 10th	Day	1 1 1 2 1 2 2 2 4 7% 78%	5346
	11th to 20th	Day	1 2 1 3 2 1 2 2 3 6% 78%	5364
	21st to end	Day	1 2 1 3 2 2 2 2 3 6% 77%	5984
September	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 74%	2400
	11th to 20th	Day	2 2 1 4 3 2 3 2 3 6% 73%	2269
	21st to end	Day	1 3 1 3 3 2 3 3 4 6% 71%	2200
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 7% 74%	3600
	11th to 20th	Day	2 3 1 4 2 2 2 2 5% 8% 69%	3330
	21st to end	Day	2 3 1 3 3 2 3 3 5% 7% 67%	3529
November	1st to 10th	Day	2 3 1 3 2 3 3 2 5% 6% 69%	1782
	11th to 20th	Day	4 3 1 3 2 2 2 3 4 6% 69%	1800
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 9% 61%	1800
December	1st to 10th	Day	4 3 2 4 3 3 4 3 6% 7% 60%	2950
	11th to 20th	Day	9% 4 2 4 3 3 5% 3 7% 7% 53%	3409
	21st to end	Day	9% 5% 2 6% 5% 5% 4 4 7% 9% 44%	4170
January	1st to 10th	Night	5% 3 2 3 2 2 3 2 4 6% 69%	6306
	11th to 20th	Night	6% 5% 2 5% 3 2 3 2 4 6% 62%	5902
	21st to end	Night	9% 4 2 5% 3 3 4 4 5% 7% 53%	6004
February	1st to 10th	Night	8% 6% 2 5% 3 2 3 3 4 6% 58%	2400
	11th to 20th	Night	9% 5% 2 5% 4 3 3 3 4 6% 58%	2338
	21st to end	Night	9% 4 1 5% 4 3 4 2 3 5% 59%	1980
March	1st to 10th	Night	7% 6% 2 5% 4 3 4 3 5% 8% 54%	5376
	11th to 20th	Night	6% 5% 2 6% 4 4 4 3 4 7% 55%	5273
	21st to end	Night	9% 7% 3 4 3 3 3 3 5% 7% 53%	5006
April	1st to 10th	Night	6% 6% 2 5% 3 3 3 3 5% 6% 58%	2000
	11th to 20th	Night	4 6% 2 5% 2 3 2 3 4 6% 63%	1979
	21st to end	Night	3 7% 2 5% 4 3 4 3 5% 8% 56%	2000
May	1st to 10th	Night	3 10% 3 5% 3 3 4 3 4 6% 56%	4473
	11th to 20th	Night	2 11% 3 5% 3 2 3 2 4 6% 57%	4074
	21st to end	Night	2 8% 3 5% 3 2 3 3 4 6% 63%	4474
June	1st to 10th	Night	3 10% 3 6% 5% 3 5% 3 6% 6% 50%	1746
	11th to 20th	Night	2 8% 2 5% 3 3 3 4 5% 9% 56%	1600
	21st to end	Night	1 8% 2 6% 5% 4 4 5% 5% 8% 53%	1600
July	1st to 10th	Night	1 5% 2 6% 4 3 3 3 4 7% 61%	3640
	11th to 20th	Night	1 7% 3 6% 4 3 4 4 5% 9% 54%	3672
	21st to end	Night	1 4 2 5% 4 4 3 3 4 7% 63%	4969
August	1st to 10th	Night	1 2 2 4 3 3 3 3 6% 9% 64%	4486
	11th to 20th	Night	1 6% 2 5% 4 3 3 2 5% 7% 62%	4506
	21st to end	Night	1 3 2 5% 3 3 4 3 5% 7% 64%	5015
September	1st to 10th	Night	3 4 2 4 3 3 3 3 5% 6% 64%	2000
	11th to 20th	Night	3 4 2 4 2 2 3 3 4 7% 66%	2130
	21st to end	Night	2 4 2 5% 3 3 3 3 4 6% 66%	2200
October	1st to 10th	Night	2 3 1 6% 3 4 3 3 7% 8% 60%	3600
	11th to 20th	Night	2 12% 3 5% 3 3 4 3 5% 6% 55%	3823
	21st to end	Night	2 3 2 4 2 3 2 2 4 6% 70%	4279
November	1st to 10th	Night	2 4 2 4 2 3 4 3 4 7% 65%	2561
	11th to 20th	Night	3 4 2 4 2 2 3 2 4 6% 68%	2600
	21st to end	Night	5% 4 1 4 3 3 4 3 6% 7% 60%	2600
December	1st to 10th	Night	4 5% 2 5% 3 3 4 3 4 6% 61%	4240
	11th to 20th	Night	10% 5% 2 5% 3 3 4 4 5% 8% 52%	4811
	21st to end	Night	10% 5% 2 6% 4 4 6% 5% 7% 8% 43%	6776

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	17% 1 3 22% 30% 27%	3639
	11th to 20th	Day	22% 2 10% 16% 18% 32%	4072
	21st to end	Day	30% 2 3 19% 24% 22%	4989
February	1st to 10th	Day	27% 3 5% 15% 27% 24%	2000
	11th to 20th	Day	23% 2 5% 21% 26% 22%	1960
	21st to end	Day	25% 2 7% 21% 25% 21%	1650
March	1st to 10th	Day	30% 1 7% 22% 23% 17%	4518
	11th to 20th	Day	26% 2 10% 29% 21% 12%	4721
	21st to end	Day	29% 2 11% 31% 19% 8%	5969
April	1st to 10th	Day	22% 2 10% 26% 25% 14%	2400
	11th to 20th	Day	20% 2 7% 26% 29% 17%	2372
	21st to end	Day	18% 2 8% 30% 30% 12%	2400
May	1st to 10th	Day	22% 3 8% 21% 35% 11%	5520
	11th to 20th	Day	28% 2 5% 23% 35% 7%	5844
	21st to end	Day	25% 2 5% 30% 30% 7%	6424
June	1st to 10th	Day	26% 2 8% 23% 30% 11%	2648
	11th to 20th	Day	19% 1 4 16% 34% 25%	2800
	21st to end	Day	19% 1 2 10% 32% 35%	2800
July	1st to 10th	Day	12% 1 2 8% 20% 57%	6251
	11th to 20th	Day	17% 2 3 12% 37% 29%	6210
	21st to end	Day	12% 2 4 18% 36% 29%	5753
August	1st to 10th	Day	11% 1 2 16% 40% 30%	3890
	11th to 20th	Day	9% 1 1 14% 33% 43%	3880
	21st to end	Day	12% 2 2 10% 32% 43%	4311
September	1st to 10th	Day	13% 2 2 11% 35% 37%	2400
	11th to 20th	Day	16% 2 2 15% 34% 32%	2269
	21st to end	Day	16% 2 2 17% 35% 29%	2200
October	1st to 10th	Day	12% 1 3 15% 21% 48%	3600
	11th to 20th	Day	15% 1 4 17% 35% 27%	3330
	21st to end	Day	17% 2 3 12% 30% 36%	3529
November	1st to 10th	Day	17% 2 4 18% 25% 34%	1782
	11th to 20th	Day	18% 2 5% 16% 22% 37%	1800
	21st to end	Day	23% 2 7% 13% 25% 30%	1800
December	1st to 10th	Day	22% 3 5% 17% 21% 32%	2950
	11th to 20th	Day	30% 2 7% 16% 29% 17%	3408
	21st to end	Day	35% 2 10% 26% 19% 8%	4170
January	1st to 10th	Night	19% 1 5% 18% 31% 25%	6306
	11th to 20th	Night	25% 2 8% 19% 17% 29%	5902
	21st to end	Night	32% 3 4 18% 22% 21%	6004
February	1st to 10th	Night	30% 2 5% 14% 24% 25%	2400
	11th to 20th	Night	29% 2 5% 18% 23% 23%	2339
	21st to end	Night	31% 2 5% 16% 24% 22%	1980
March	1st to 10th	Night	30% 2 8% 20% 27% 14%	5376
	11th to 20th	Night	30% 3 10% 28% 16% 13%	5273
	21st to end	Night	33% 2 14% 24% 21% 6%	5006
April	1st to 10th	Night	29% 2 8% 25% 22% 14%	2000
	11th to 20th	Night	25% 1 6% 25% 26% 16%	1979
	21st to end	Night	28% 2 8% 26% 25% 11%	2000
May	1st to 10th	Night	30% 4 8% 19% 30% 8%	4470
	11th to 20th	Night	29% 2 7% 26% 29% 7%	4075
	21st to end	Night	26% 2 6% 33% 27% 7%	4474
June	1st to 10th	Night	32% 3 11% 21% 24% 9%	1746
	11th to 20th	Night	25% 3 6% 15% 34% 18%	1600
	21st to end	Night	30% 2 3 8% 29% 28%	1600
July	1st to 10th	Night	20% 3 3 12% 17% 45%	3600
	11th to 20th	Night	22% 7% 4 13% 30% 23%	3624
	21st to end	Night	21% 3 4 20% 32% 19%	4828
August	1st to 10th	Night	16% 2 3 19% 37% 23%	3256
	11th to 20th	Night	18% 2 2 13% 33% 32%	3256
	21st to end	Night	20% 3 2 10% 34% 31%	3608
September	1st to 10th	Night	22% 2 3 8% 32% 33%	2000
	11th to 20th	Night	20% 2 2 12% 34% 30%	2130
	21st to end	Night	21% 2 2 16% 32% 27%	2200
October	1st to 10th	Night	17% 4 4 18% 19% 38%	3600
	11th to 20th	Night	27% 5% 4 16% 25% 25%	3823
	21st to end	Night	17% 2 3 11% 29% 38%	4279
November	1st to 10th	Night	20% 3 4 17% 22% 34%	2561
	11th to 20th	Night	20% 2 5% 14% 22% 37%	2600
	21st to end	Night	25% 2 6% 17% 20% 29%	2600
December	1st to 10th	Night	25% 3 5% 13% 24% 30%	4240
	11th to 20th	Night	32% 2 8% 14% 24% 19%	4811
	21st to end	Night	36% 4 11% 25% 14% 9%	6776

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	16% 6% 22% 36% 19% 3	200
	11th to 20th	Day	10% 6% 30% 35% 17% 2	385
	21st to end	Day	10% 11% 26% 36% 14% 2	544
February	1st to 10th	Day	12% 7% 30% 31% 16% 4	500
	11th to 20th	Day	11% 12% 30% 31% 13% 3	495
	21st to end	Day	7% 11% 35% 35% 11% 1	414
March	1st to 10th	Day	11% 15% 33% 27% 13% 1	500
	11th to 20th	Day	12% 13% 31% 27% 16% 2	500
	21st to end	Day	8% 15% 32% 32% 11% 2	550
April	1st to 10th	Day	7% 11% 28% 32% 17% 5%	500
	11th to 20th	Day	4 12% 36% 32% 12% 4	492
	21st to end	Day	3 11% 30% 34% 17% 6%	500
May	1st to 10th	Day	5% 10% 30% 37% 15% 3	503
	11th to 20th	Day	6% 6% 25% 38% 20% 4	528
	21st to end	Day	5% 6% 28% 39% 19% 5%	573
June	1st to 10th	Day	5% 4 20% 37% 30% 5%	530
	11th to 20th	Day	4 3 19% 40% 27% 7%	530
	21st to end	Day	3 2 15% 40% 31% 9%	530
July	1st to 10th	Day	2 1 8% 40% 38% 12%	526
	11th to 20th	Day	2 1 4 32% 45% 16%	524
	21st to end	Day	1 5% 38% 38% 17%	575
August	1st to 10th	Day	2 1 7% 42% 34% 14%	527
	11th to 20th	Day	2 1 6% 38% 41% 12%	517
	21st to end	Day	2 1 10% 39% 36% 13%	583
September	1st to 10th	Day	4 1 12% 43% 29% 11%	530
	11th to 20th	Day	2 4 18% 42% 25% 7%	530
	21st to end	Day	2 3 21% 41% 25% 8%	530
October	1st to 10th	Day	2 4 22% 40% 26% 6%	530
	11th to 20th	Day	4 3 24% 41% 21% 7%	530
	21st to end	Day	4 7% 23% 35% 24% 8%	566
November	1st to 10th	Day	4 6% 15% 35% 31% 10%	306
	11th to 20th	Day	5% 5% 19% 38% 26% 7%	300
	21st to end	Day	6% 5% 21% 33% 28% 6%	300
December	1st to 10th	Day	8% 3 17% 41% 27% 4	300
	11th to 20th	Day	6% 7% 16% 36% 28% 8%	300
	21st to end	Day	12% 12% 22% 37% 15% 2	257
January	1st to 10th	Night	11% 3 15% 42% 23% 6%	800
	11th to 20th	Night	8% 3 18% 41% 26% 5%	800
	21st to end	Night	11% 4 16% 41% 25% 3	880
February	1st to 10th	Night	11% 4 14% 38% 26% 7%	800
	11th to 20th	Night	9% 4 18% 38% 25% 6%	784
	21st to end	Night	10% 5% 19% 40% 23% 4	660
March	1st to 10th	Night	9% 6% 19% 43% 21% 3	800
	11th to 20th	Night	9% 5% 15% 38% 28% 6%	800
	21st to end	Night	8% 5% 18% 40% 26% 4	880
April	1st to 10th	Night	9% 4 15% 39% 29% 5%	800
	11th to 20th	Night	6% 4 16% 38% 32% 4	791
	21st to end	Night	5% 4 16% 36% 32% 7%	800
May	1st to 10th	Night	8% 3 11% 40% 33% 5%	765
	11th to 20th	Night	6% 2 14% 37% 35% 6%	591
	21st to end	Night	4 1 16% 36% 37% 5%	650
June	1st to 10th	Night	3 2 13% 34% 42% 5%	546
	11th to 20th	Night	4 1 4 30% 52% 9%	400
	21st to end	Night	5% 1 4 26% 55% 11%	400
July	1st to 10th	Night	3 2 13% 63% 19%	390
	11th to 20th	Night	2 1 7% 64% 25%	394
	21st to end	Night	3 3 16% 55% 22%	871
August	1st to 10th	Night	3 1 2 21% 55% 18%	796
	11th to 20th	Night	4 1 3 16% 56% 21%	792
	21st to end	Night	2 2 19% 57% 20%	880
September	1st to 10th	Night	6% 1 3 22% 50% 19%	800
	11th to 20th	Night	4 4 29% 50% 12%	800
	21st to end	Night	2 1 6% 31% 48% 12%	800
October	1st to 10th	Night	4 1 7% 35% 46% 6%	800
	11th to 20th	Night	6% 2 10% 32% 41% 10%	800
	21st to end	Night	3 2 10% 33% 39% 13%	880
November	1st to 10th	Night	3 3 10% 35% 37% 11%	788
	11th to 20th	Night	5% 2 9% 38% 35% 12%	800
	21st to end	Night	7% 2 13% 42% 30% 7%	800
December	1st to 10th	Night	8% 3 15% 39% 31% 6%	800
	11th to 20th	Night	12% 4 12% 42% 26% 5%	800
	21st to end	Night	10% 5% 17% 42% 20% 5%	880

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