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 2024-11-06.

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 4 3 2 3 3 4 7% 65%	105024
	Night	5% 5% 2 5% 3 3 3 3 5% 7% 58%	102837
Transparency	Day	21% 1 5% 19% 28% 25%	104788
	Night	27% 2 5% 18% 25% 22%	102663
Seeing	Day	5% 6% 21% 37% 25% 7%	15654
	Night	6% 2 11% 33% 37% 10%	25489

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	5% 3 1 3 2 3 3 3 4 5% 67%	2539
	11th to 20th	Day	8% 5% 2 5% 3 3 4 3 6% 9% 54%	2832
	21st to end	Day	13% 5% 2 4 3 3 3 3 4 7% 53%	3471
February	1st to 10th	Day	9% 5% 2 4 3 2 3 3 4 5% 62%	1900
	11th to 20th	Day	7% 3 1 4 3 2 4 3 6% 6% 62%	1850
	21st to end	Day	7% 4 1 5% 3 3 3 3 5% 7% 59%	1570
March	1st to 10th	Day	7% 4 2 5% 4 4 4 5% 7% 7% 51%	3138
	11th to 20th	Day	4 4 1 4 2 3 3 3 6% 9% 63%	3289
	21st to end	Day	8% 5% 2 4 4 4 5% 4 7% 8% 50%	4165
April	1st to 10th	Day	4 4 1 4 4 3 4 4 5% 8% 59%	2280
	11th to 20th	Day	3 4 1 3 3 3 2 3 5% 7% 66%	2249
	21st to end	Day	2 4 1 3 3 2 2 4 3 8% 68%	2280
May	1st to 10th	Day	1 4 1 4 2 2 2 2 4 6% 70%	3854
	11th to 20th	Day	3 9% 3 7% 3 2 2 2 4 7% 58%	4071
	21st to end	Day	3 6% 2 6% 3 2 3 3 4 8% 60%	4477
June	1st to 10th	Day	4 7% 2 5% 3 2 3 2 5% 8% 59%	2515
	11th to 20th	Day	3 5% 2 4 2 2 2 2 4 8% 67%	2660
	21st to end	Day	2 5% 2 3 3 2 3 2 4 6% 69%	2660
July	1st to 10th	Day	2 2 1 3 2 2 2 2 3 6% 74%	4420
	11th to 20th	Day	1 2 1 4 3 3 3 2 4 6% 70%	4398
	21st to end	Day	1 2 1 2 2 2 2 2 4 7% 77%	4119
August	1st to 10th	Day	1 2 1 2 1 2 2 2 3 7% 78%	3783
	11th to 20th	Day	1 2 1 2 1 1 2 1 3 6% 80%	3724
	21st to end	Day	1 2 1 3 2 2 2 2 3 5% 76%	4180
September	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 74%	2280
	11th to 20th	Day	2 2 1 3 2 2 3 2 3 6% 74%	2156
	21st to end	Day	1 3 1 3 3 2 2 3 4 6% 72%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 7% 74%	3490
	11th to 20th	Day	2 3 1 4 2 2 2 2 5% 8% 69%	3228
	21st to end	Day	2 3 1 3 3 2 3 3 5% 7% 67%	3420
November	1st to 10th	Day	2 3 1 3 2 3 3 2 5% 7% 68%	1719
	11th to 20th	Day	4 3 1 3 3 2 2 3 5% 6% 68%	1710
	21st to end	Day	4 3 1 4 3 3 3 3 5% 9% 62%	1710
December	1st to 10th	Day	7% 4 2 4 3 3 5% 3 5% 6% 57%	1710
	11th to 20th	Day	14% 6% 2 6% 4 4 3 2 6% 7% 46%	2169
	21st to end	Day	12% 6% 2 6% 5% 4 4 4 6% 6% 45%	2918
January	1st to 10th	Night	6% 4 2 3 2 2 3 3 4 6% 65%	4406
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 4 7% 54%	4132
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 7% 51%	4200
February	1st to 10th	Night	8% 5% 2 5% 3 2 3 3 3 6% 60%	2280
	11th to 20th	Night	9% 5% 2 5% 4 3 3 3 3 6% 59%	2218
	21st to end	Night	9% 5% 2 6% 4 3 4 2 3 6% 57%	1884
March	1st to 10th	Night	7% 6% 2 6% 4 3 4 4 6% 9% 50%	3736
	11th to 20th	Night	5% 4 1 5% 4 3 4 4 5% 7% 57%	3685
	21st to end	Night	8% 6% 3 5% 3 4 4 4 5% 6% 51%	3488
April	1st to 10th	Night	6% 6% 2 5% 3 3 3 3 5% 6% 56%	1900
	11th to 20th	Night	4 5% 2 5% 2 3 2 3 4 6% 64%	1879
	21st to end	Night	3 7% 2 5% 4 3 4 3 5% 8% 57%	1900
May	1st to 10th	Night	3 7% 2 5% 3 3 3 3 4 6% 62%	3121
	11th to 20th	Night	3 15% 5% 7% 4 2 3 3 4 6% 48%	2834
	21st to end	Night	2 9% 3 5% 3 2 3 3 4 6% 59%	3110
June	1st to 10th	Night	2 10% 3 6% 5% 3 5% 3 7% 6% 50%	1659
	11th to 20th	Night	2 8% 3 5% 3 3 3 4 5% 8% 56%	1520
	21st to end	Night	1 8% 2 6% 5% 4 4 5% 5% 8% 52%	1520
July	1st to 10th	Night	1 5% 2 6% 3 3 3 3 5% 7% 62%	2540
	11th to 20th	Night	1 3 2 5% 4 3 4 4 6% 10% 58%	2558
	21st to end	Night	2 3 2 4 3 3 3 3 4 8% 66%	3452
August	1st to 10th	Night	1 3 1 4 3 3 3 3 6% 8% 65%	3166
	11th to 20th	Night	1 3 1 4 3 2 3 2 5% 8% 66%	3126
	21st to end	Night	1 4 2 5% 4 3 4 3 5% 7% 63%	3498
September	1st to 10th	Night	3 5% 2 4 3 3 3 3 5% 6% 64%	1900
	11th to 20th	Night	2 4 1 4 2 2 3 3 4 7% 67%	2023
	21st to end	Night	1 4 2 5% 3 2 3 3 4 6% 67%	2090
October	1st to 10th	Night	2 3 1 6% 3 4 4 3 7% 8% 59%	3490
	11th to 20th	Night	2 12% 3 5% 3 3 4 3 5% 6% 54%	3705
	21st to end	Night	2 3 1 4 2 3 2 2 4 6% 71%	4146
November	1st to 10th	Night	2 5% 2 4 2 3 4 3 4 7% 65%	2482
	11th to 20th	Night	3 4 3 4 2 2 3 3 4 6% 66%	2470
	21st to end	Night	4 4 1 4 3 3 4 3 5% 6% 61%	2470
December	1st to 10th	Night	6% 5% 2 6% 3 3 3 2 4 7% 57%	2470
	11th to 20th	Night	15% 7% 3 6% 3 3 3 3 4 7% 47%	3041
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 5% 6% 45%	4738

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	21% 1 4 26% 30% 19%	2539
	11th to 20th	Day	30% 2 15% 20% 17% 17%	2832
	21st to end	Day	34% 1 4 21% 23% 16%	3471
February	1st to 10th	Day	26% 2 4 15% 27% 25%	1900
	11th to 20th	Day	23% 2 5% 20% 27% 23%	1860
	21st to end	Day	26% 2 7% 22% 25% 18%	1570
March	1st to 10th	Day	32% 1 7% 27% 18% 15%	3138
	11th to 20th	Day	21% 1 12% 34% 17% 15%	3289
	21st to end	Day	32% 1 11% 31% 16% 9%	4165
April	1st to 10th	Day	23% 3 11% 26% 24% 13%	2280
	11th to 20th	Day	19% 1 6% 27% 29% 18%	2252
	21st to end	Day	18% 2 8% 29% 31% 12%	2280
May	1st to 10th	Day	18% 1 7% 20% 43% 11%	3854
	11th to 20th	Day	28% 1 5% 24% 35% 7%	4074
	21st to end	Day	27% 1 5% 31% 32% 4	4477
June	1st to 10th	Day	26% 2 8% 23% 30% 11%	2515
	11th to 20th	Day	19% 1 5% 16% 35% 24%	2660
	21st to end	Day	19% 1 2 10% 32% 34%	2660
July	1st to 10th	Day	12% 1 1 7% 16% 62%	4351
	11th to 20th	Day	16% 2 4 13% 30% 35%	4323
	21st to end	Day	10% 1 5% 21% 31% 33%	3990
August	1st to 10th	Day	11% 1 2 16% 40% 30%	3770
	11th to 20th	Day	9% 1 1 14% 32% 44%	3760
	21st to end	Day	12% 2 2 10% 32% 43%	4179
September	1st to 10th	Day	13% 2 2 11% 34% 38%	2280
	11th to 20th	Day	15% 2 1 15% 34% 32%	2156
	21st to end	Day	15% 1 1 17% 36% 29%	2090
October	1st to 10th	Day	12% 1 3 15% 21% 49%	3490
	11th to 20th	Day	15% 1 4 18% 36% 26%	3228
	21st to end	Day	17% 2 3 12% 30% 36%	3420
November	1st to 10th	Day	17% 2 4 18% 25% 32%	1719
	11th to 20th	Day	19% 2 5% 17% 20% 37%	1710
	21st to end	Day	22% 2 7% 14% 26% 30%	1710
December	1st to 10th	Day	28% 2 6% 17% 22% 25%	1710
	11th to 20th	Day	38% 2 7% 15% 22% 16%	2168
	21st to end	Day	41% 1 6% 25% 15% 12%	2918
January	1st to 10th	Night	23% 1 6% 18% 32% 20%	4406
	11th to 20th	Night	32% 2 11% 23% 16% 17%	4132
	21st to end	Night	36% 1 5% 21% 20% 17%	4200
February	1st to 10th	Night	29% 2 5% 14% 25% 26%	2280
	11th to 20th	Night	29% 2 5% 17% 24% 24%	2219
	21st to end	Night	32% 2 6% 17% 23% 20%	1884
March	1st to 10th	Night	32% 1 7% 26% 22% 12%	3736
	11th to 20th	Night	28% 2 11% 28% 17% 14%	3685
	21st to end	Night	34% 2 12% 24% 21% 8%	3488
April	1st to 10th	Night	30% 2 9% 25% 20% 14%	1900
	11th to 20th	Night	25% 1 6% 25% 26% 17%	1879
	21st to end	Night	27% 2 8% 25% 27% 12%	1900
May	1st to 10th	Night	26% 2 7% 20% 35% 11%	3121
	11th to 20th	Night	38% 1 5% 24% 25% 7%	2835
	21st to end	Night	31% 1 5% 33% 26% 4	3110
June	1st to 10th	Night	32% 3 11% 21% 24% 9%	1659
	11th to 20th	Night	25% 3 6% 15% 35% 17%	1520
	21st to end	Night	30% 2 3 8% 29% 27%	1520
July	1st to 10th	Night	19% 3 1 8% 18% 50%	2500
	11th to 20th	Night	18% 5% 4 14% 31% 27%	2510
	21st to end	Night	19% 2 4 23% 27% 25%	3344
August	1st to 10th	Night	16% 2 3 19% 37% 23%	3156
	11th to 20th	Night	17% 2 2 14% 32% 33%	3156
	21st to end	Night	20% 3 2 10% 35% 31%	3498
September	1st to 10th	Night	23% 2 3 7% 32% 34%	1900
	11th to 20th	Night	19% 2 2 13% 34% 31%	2023
	21st to end	Night	20% 2 1 16% 33% 28%	2090
October	1st to 10th	Night	17% 4 4 18% 18% 39%	3490
	11th to 20th	Night	27% 5% 4 16% 24% 25%	3705
	21st to end	Night	17% 2 3 11% 30% 38%	4146
November	1st to 10th	Night	21% 3 4 17% 22% 33%	2482
	11th to 20th	Night	21% 1 5% 14% 20% 38%	2470
	21st to end	Night	24% 2 6% 18% 21% 30%	2470
December	1st to 10th	Night	29% 2 6% 14% 21% 28%	2470
	11th to 20th	Night	40% 2 6% 15% 21% 16%	3041
	21st to end	Night	42% 1 7% 22% 16% 12%	4738

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	15% 6% 22% 37% 19% 2	180
	11th to 20th	Day	10% 6% 28% 36% 18% 2	355
	21st to end	Day	9% 10% 27% 37% 14% 2	500
February	1st to 10th	Day	12% 7% 29% 31% 17% 5%	460
	11th to 20th	Day	10% 12% 30% 32% 14% 3	455
	21st to end	Day	8% 12% 34% 35% 10% 1	382
March	1st to 10th	Day	10% 14% 33% 28% 14% 1	460
	11th to 20th	Day	10% 13% 31% 28% 16% 2	460
	21st to end	Day	8% 16% 32% 32% 11% 2	506
April	1st to 10th	Day	8% 10% 28% 32% 17% 5%	460
	11th to 20th	Day	4 12% 36% 33% 12% 4	452
	21st to end	Day	3 10% 30% 33% 17% 6%	460
May	1st to 10th	Day	4 10% 30% 38% 15% 3	463
	11th to 20th	Day	5% 6% 24% 40% 22% 4	488
	21st to end	Day	5% 6% 27% 39% 19% 5%	529
June	1st to 10th	Day	5% 2 19% 37% 31% 5%	490
	11th to 20th	Day	4 3 19% 40% 27% 7%	490
	21st to end	Day	3 1 14% 40% 33% 9%	490
July	1st to 10th	Day	2 6% 40% 40% 12%	486
	11th to 20th	Day	2 1 4 30% 46% 17%	484
	21st to end	Day	1 4 38% 39% 18%	531
August	1st to 10th	Day	2 1 7% 41% 35% 13%	487
	11th to 20th	Day	2 1 6% 37% 42% 12%	477
	21st to end	Day	2 1 9% 39% 37% 13%	539
September	1st to 10th	Day	4 1 11% 44% 29% 11%	490
	11th to 20th	Day	2 3 18% 43% 26% 7%	490
	21st to end	Day	2 2 20% 42% 25% 9%	490
October	1st to 10th	Day	2 4 21% 41% 27% 6%	490
	11th to 20th	Day	3 3 23% 42% 22% 7%	490
	21st to end	Day	4 6% 23% 36% 24% 8%	523
November	1st to 10th	Day	4 6% 15% 36% 32% 8%	285
	11th to 20th	Day	6% 3 19% 38% 27% 8%	270
	21st to end	Day	6% 4 21% 32% 31% 7%	270
December	1st to 10th	Day	9% 4 18% 40% 27% 3	270
	11th to 20th	Day	6% 8% 15% 36% 27% 7%	270
	21st to end	Day	13% 13% 20% 36% 16% 3	232
January	1st to 10th	Night	11% 2 14% 42% 24% 6%	760
	11th to 20th	Night	8% 3 17% 40% 27% 5%	760
	21st to end	Night	11% 4 17% 40% 26% 3	836
February	1st to 10th	Night	10% 4 14% 37% 28% 8%	760
	11th to 20th	Night	9% 4 17% 38% 26% 6%	744
	21st to end	Night	10% 5% 19% 40% 23% 4	628
March	1st to 10th	Night	9% 5% 18% 43% 22% 4	760
	11th to 20th	Night	9% 4 14% 38% 29% 6%	760
	21st to end	Night	8% 5% 18% 40% 25% 4	836
April	1st to 10th	Night	9% 3 14% 41% 29% 4	760
	11th to 20th	Night	6% 4 16% 37% 32% 4	751
	21st to end	Night	4 4 16% 35% 33% 7%	760
May	1st to 10th	Night	8% 3 11% 40% 33% 5%	727
	11th to 20th	Night	7% 1 13% 37% 36% 6%	561
	21st to end	Night	4 1 17% 35% 37% 5%	617
June	1st to 10th	Night	3 2 13% 34% 43% 6%	519
	11th to 20th	Night	4 1 4 29% 52% 9%	380
	21st to end	Night	4 1 4 26% 55% 10%	380
July	1st to 10th	Night	4 1 12% 64% 19%	370
	11th to 20th	Night	2 1 7% 65% 25%	373
	21st to end	Night	3 3 15% 56% 23%	827
August	1st to 10th	Night	4 1 2 21% 54% 19%	756
	11th to 20th	Night	4 1 3 14% 56% 22%	752
	21st to end	Night	2 2 17% 57% 21%	836
September	1st to 10th	Night	6% 1 3 21% 50% 19%	760
	11th to 20th	Night	4 4 29% 51% 12%	760
	21st to end	Night	2 1 5% 29% 50% 12%	760
October	1st to 10th	Night	4 1 6% 34% 47% 7%	760
	11th to 20th	Night	5% 2 9% 31% 42% 11%	760
	21st to end	Night	4 2 10% 32% 38% 13%	836
November	1st to 10th	Night	3 3 10% 35% 36% 12%	764
	11th to 20th	Night	5% 1 8% 38% 36% 12%	760
	21st to end	Night	6% 2 13% 40% 32% 7%	760
December	1st to 10th	Night	8% 3 14% 38% 31% 6%	760
	11th to 20th	Night	13% 4 12% 41% 25% 5%	760
	21st to end	Night	11% 5% 17% 41% 21% 5%	836

Page generated at 2024-11-03 10:19:02. Version ac07

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