Vandenberg Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vandenberg Village 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 2 5% 3 3 3 3 5% 7% 60%	112799
	Night	5% 7% 3 7% 4 4 4 3 5% 7% 50%	115402
Transparency	Day	22% 3 8% 18% 27% 22%	112557
	Night	29% 4 9% 15% 22% 21%	115234
Seeing	Day	8% 10% 26% 31% 19% 7%	16110
	Night	8% 5% 15% 33% 31% 8%	25852

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 2 3 2 4 7% 67%	3943
	11th to 20th	Day	7% 5% 1 4 3 3 3 3 4 6% 62%	4100
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 47%	4510
February	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 6% 54%	1910
	11th to 20th	Day	8% 6% 1 5% 4 3 5% 4 5% 7% 52%	1950
	21st to end	Day	9% 6% 1 4 4 4 4 5% 5% 6% 53%	1650
March	1st to 10th	Day	10% 6% 3 7% 5% 4 4 3 5% 9% 44%	3327
	11th to 20th	Day	6% 4 1 4 4 3 3 2 4 7% 62%	3600
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 5% 7% 9% 44%	4072
April	1st to 10th	Day	7% 5% 2 4 3 4 3 4 6% 7% 55%	2280
	11th to 20th	Day	5% 5% 2 6% 4 3 3 3 5% 7% 58%	2249
	21st to end	Day	6% 5% 1 4 2 2 3 3 5% 7% 61%	2280
May	1st to 10th	Day	3 5% 2 4 2 2 2 2 3 5% 71%	3800
	11th to 20th	Day	1 5% 2 6% 4 3 3 3 5% 9% 58%	3851
	21st to end	Day	2 5% 2 5% 3 3 3 3 5% 7% 60%	4743
June	1st to 10th	Day	4 6% 2 5% 3 3 4 3 5% 9% 56%	2660
	11th to 20th	Day	1 5% 2 5% 3 3 3 3 4 8% 64%	2660
	21st to end	Day	2 5% 2 5% 3 3 3 3 5% 8% 61%	2660
July	1st to 10th	Day	1 3 2 4 3 3 3 3 4 7% 68%	4390
	11th to 20th	Day	2 3 2 5% 3 3 4 3 5% 8% 62%	4110
	21st to end	Day	1 3 2 5% 4 3 3 3 6% 10% 60%	4455
August	1st to 10th	Day	1 5% 1 5% 3 4 3 3 4 9% 61%	3849
	11th to 20th	Day	1 3 1 4 2 2 3 2 4 6% 71%	3724
	21st to end	Day	1 3 2 5% 2 3 2 3 4 7% 68%	4180
September	1st to 10th	Day	2 3 1 4 3 3 3 3 5% 8% 63%	2280
	11th to 20th	Day	2 6% 2 5% 4 3 3 3 5% 8% 60%	2267
	21st to end	Day	1 4 2 3 3 2 3 3 4 6% 68%	2090
October	1st to 10th	Day	2 1 1 3 2 2 2 3 4 5% 75%	3213
	11th to 20th	Day	2 3 2 5% 3 3 3 2 4 6% 67%	3161
	21st to end	Day	3 3 1 4 2 3 3 3 4 7% 66%	3448
November	1st to 10th	Day	4 4 1 4 3 2 3 3 4 5% 66%	1894
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 6% 65%	1800
	21st to end	Day	7% 5% 2 4 4 2 3 3 5% 7% 58%	1800
December	1st to 10th	Day	5% 3 2 5% 3 4 4 3 5% 6% 60%	2861
	11th to 20th	Day	12% 4 2 6% 4 3 4 4 5% 6% 49%	3028
	21st to end	Day	11% 7% 3 7% 5% 4 5% 3 6% 9% 41%	4004
January	1st to 10th	Night	6% 5% 2 5% 3 3 3 2 4 6% 61%	5999
	11th to 20th	Night	6% 8% 3 7% 3 3 4 2 3 5% 55%	5880
	21st to end	Night	11% 9% 3 6% 4 4 4 3 4 6% 46%	6468
February	1st to 10th	Night	10% 6% 2 6% 4 3 3 3 5% 5% 52%	2487
	11th to 20th	Night	8% 7% 2 5% 4 4 3 4 4 8% 52%	2338
	21st to end	Night	10% 6% 3 6% 4 2 3 3 4 6% 53%	1980
March	1st to 10th	Night	9% 10% 3 6% 5% 4 5% 3 6% 8% 40%	3763
	11th to 20th	Night	5% 7% 2 5% 4 4 4 3 5% 6% 56%	3600
	21st to end	Night	11% 10% 3 7% 4 3 3 2 5% 6% 45%	3717
April	1st to 10th	Night	6% 6% 3 6% 6% 5% 4 4 4 7% 50%	1900
	11th to 20th	Night	5% 8% 3 6% 4 4 3 3 3 6% 54%	1879
	21st to end	Night	4 9% 3 5% 3 3 4 3 4 9% 52%	1900
May	1st to 10th	Night	2 5% 2 6% 3 3 3 2 4 6% 64%	3180
	11th to 20th	Night	2 14% 8% 12% 5% 3 3 3 5% 7% 36%	3056
	21st to end	Night	2 14% 4 12% 3 3 3 2 3 4 50%	2829
June	1st to 10th	Night	2 9% 4 9% 6% 5% 5% 3 6% 10% 41%	1520
	11th to 20th	Night	2 7% 3 9% 5% 4 4 3 5% 6% 51%	1520
	21st to end	Night	1 7% 3 9% 6% 5% 5% 5% 6% 10% 43%	1520
July	1st to 10th	Night	1 3 4 9% 6% 4 4 3 5% 7% 55%	2565
	11th to 20th	Night	1 4 5% 13% 6% 6% 5% 4 6% 8% 43%	2860
	21st to end	Night	1 7% 8% 20% 6% 5% 4 4 5% 7% 32%	3109
August	1st to 10th	Night	1 5% 4 16% 8% 6% 5% 4 5% 7% 38%	3093
	11th to 20th	Night	5% 3 10% 6% 5% 3 4 5% 6% 52%	3126
	21st to end	Night	7% 6% 10% 6% 4 3 3 5% 6% 50%	3498
September	1st to 10th	Night	2 6% 2 6% 6% 4 4 2 6% 8% 55%	1900
	11th to 20th	Night	3 9% 3 7% 5% 5% 3 3 6% 8% 48%	1911
	21st to end	Night	2 5% 2 5% 4 2 3 2 4 6% 63%	2090
October	1st to 10th	Night	2 3 1 4 3 2 3 3 5% 6% 68%	3762
	11th to 20th	Night	3 11% 6% 7% 5% 4 3 2 4 5% 49%	3777
	21st to end	Night	3 9% 2 4 3 2 2 2 3 6% 63%	4121
November	1st to 10th	Night	5% 5% 1 5% 4 4 4 3 5% 6% 58%	2404
	11th to 20th	Night	3 4 2 5% 4 3 3 2 6% 6% 62%	2600
	21st to end	Night	5% 6% 2 5% 3 4 4 3 6% 7% 55%	2600
December	1st to 10th	Night	5% 4 2 5% 3 3 4 3 5% 7% 58%	4322
	11th to 20th	Night	10% 6% 2 5% 4 4 5% 5% 6% 7% 45%	5176
	21st to end	Night	10% 12% 5% 9% 5% 5% 5% 4 5% 7% 33%	6952

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	19% 2 6% 31% 26% 15%	3943
	11th to 20th	Day	25% 4 7% 12% 24% 28%	4100
	21st to end	Day	32% 4 7% 18% 22% 17%	4510
February	1st to 10th	Day	31% 3 6% 20% 20% 19%	1910
	11th to 20th	Day	29% 5% 9% 22% 24% 11%	1960
	21st to end	Day	29% 4 11% 21% 25% 10%	1650
March	1st to 10th	Day	34% 5% 13% 22% 18% 7%	3327
	11th to 20th	Day	22% 4 13% 30% 18% 13%	3600
	21st to end	Day	31% 8% 14% 26% 16% 4	4072
April	1st to 10th	Day	26% 4 12% 27% 22% 9%	2280
	11th to 20th	Day	24% 3 12% 26% 26% 10%	2252
	21st to end	Day	21% 4 11% 27% 30% 8%	2280
May	1st to 10th	Day	16% 3 7% 22% 37% 15%	3800
	11th to 20th	Day	21% 5% 9% 23% 33% 10%	3854
	21st to end	Day	16% 3 14% 29% 33% 6%	4743
June	1st to 10th	Day	23% 5% 10% 22% 29% 10%	2660
	11th to 20th	Day	18% 3 8% 14% 36% 21%	2660
	21st to end	Day	18% 2 7% 9% 30% 33%	2660
July	1st to 10th	Day	14% 1 4 7% 16% 58%	4321
	11th to 20th	Day	19% 2 4 9% 20% 46%	4041
	21st to end	Day	18% 3 5% 13% 28% 34%	4315
August	1st to 10th	Day	19% 1 4 14% 32% 28%	3834
	11th to 20th	Day	14% 1 4 8% 31% 43%	3760
	21st to end	Day	16% 1 4 12% 35% 32%	4179
September	1st to 10th	Day	17% 3 6% 9% 28% 37%	2280
	11th to 20th	Day	20% 2 5% 16% 34% 23%	2267
	21st to end	Day	16% 2 5% 15% 35% 27%	2090
October	1st to 10th	Day	12% 2 4 14% 27% 41%	3213
	11th to 20th	Day	19% 2 5% 18% 33% 22%	3161
	21st to end	Day	19% 3 3 14% 34% 28%	3448
November	1st to 10th	Day	21% 2 6% 18% 29% 24%	1894
	11th to 20th	Day	20% 4 7% 19% 27% 23%	1800
	21st to end	Day	27% 3 7% 15% 26% 23%	1800
December	1st to 10th	Day	24% 3 5% 17% 30% 21%	2861
	11th to 20th	Day	36% 4 8% 19% 23% 11%	3028
	21st to end	Day	38% 5% 11% 24% 15% 7%	4004
January	1st to 10th	Night	24% 4 6% 24% 27% 16%	5999
	11th to 20th	Night	28% 6% 7% 12% 20% 28%	5880
	21st to end	Night	37% 4 5% 13% 21% 19%	6468
February	1st to 10th	Night	33% 2 8% 15% 23% 19%	2487
	11th to 20th	Night	30% 4 9% 21% 22% 16%	2339
	21st to end	Night	31% 4 7% 19% 25% 14%	1980
March	1st to 10th	Night	36% 6% 13% 20% 17% 8%	3763
	11th to 20th	Night	25% 5% 12% 24% 23% 11%	3600
	21st to end	Night	33% 5% 16% 22% 19% 5%	3717
April	1st to 10th	Night	29% 6% 13% 23% 19% 10%	1900
	11th to 20th	Night	28% 4 11% 23% 24% 11%	1879
	21st to end	Night	25% 5% 11% 21% 29% 9%	1900
May	1st to 10th	Night	15% 4 12% 20% 28% 20%	3180
	11th to 20th	Night	29% 2 20% 15% 18% 15%	3058
	21st to end	Night	23% 3 22% 17% 28% 8%	2829
June	1st to 10th	Night	28% 7% 14% 17% 24% 11%	1520
	11th to 20th	Night	24% 4 10% 11% 27% 23%	1520
	21st to end	Night	22% 3 11% 12% 21% 31%	1520
July	1st to 10th	Night	21% 2 5% 10% 11% 51%	2525
	11th to 20th	Night	32% 2 8% 9% 13% 37%	2806
	21st to end	Night	44% 3 7% 10% 19% 18%	3011
August	1st to 10th	Night	38% 3 5% 10% 17% 27%	3084
	11th to 20th	Night	26% 2 6% 7% 17% 41%	3156
	21st to end	Night	28% 2 5% 11% 24% 31%	3498
September	1st to 10th	Night	20% 2 8% 10% 19% 41%	1900
	11th to 20th	Night	25% 2 9% 14% 26% 24%	1911
	21st to end	Night	18% 2 8% 12% 30% 30%	2090
October	1st to 10th	Night	14% 2 4 12% 23% 44%	3762
	11th to 20th	Night	35% 3 5% 12% 19% 26%	3777
	21st to end	Night	22% 3 4 10% 32% 29%	4121
November	1st to 10th	Night	23% 3 7% 16% 26% 25%	2404
	11th to 20th	Night	22% 4 7% 15% 26% 26%	2600
	21st to end	Night	27% 3 8% 16% 21% 25%	2600
December	1st to 10th	Night	25% 3 5% 16% 29% 22%	4322
	11th to 20th	Night	36% 5% 11% 14% 23% 12%	5176
	21st to end	Night	47% 5% 9% 20% 14% 6%	6952

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	19% 15% 27% 23% 14% 2	335
	11th to 20th	Day	10% 13% 31% 26% 17% 3	400
	21st to end	Day	12% 13% 31% 24% 15% 5%	440
February	1st to 10th	Day	13% 14% 27% 22% 18% 6%	455
	11th to 20th	Day	12% 17% 29% 25% 14% 3	495
	21st to end	Day	10% 15% 31% 28% 12% 3	414
March	1st to 10th	Day	16% 17% 31% 25% 10% 2	500
	11th to 20th	Day	14% 15% 32% 27% 10% 2	500
	21st to end	Day	11% 20% 36% 21% 9% 3	531
April	1st to 10th	Day	11% 14% 36% 19% 14% 6%	460
	11th to 20th	Day	9% 19% 34% 24% 10% 4	452
	21st to end	Day	5% 19% 35% 24% 12% 5%	460
May	1st to 10th	Day	9% 13% 35% 26% 13% 4	463
	11th to 20th	Day	5% 11% 35% 31% 15% 3	488
	21st to end	Day	9% 14% 30% 31% 12% 5%	529
June	1st to 10th	Day	6% 7% 28% 33% 20% 6%	490
	11th to 20th	Day	3 7% 28% 36% 20% 6%	490
	21st to end	Day	5% 3 23% 39% 22% 8%	490
July	1st to 10th	Day	4 1 17% 39% 30% 9%	486
	11th to 20th	Day	4 1 11% 44% 28% 13%	484
	21st to end	Day	2 2 12% 44% 29% 11%	531
August	1st to 10th	Day	6% 2 17% 47% 21% 7%	487
	11th to 20th	Day	4 2 14% 39% 29% 11%	477
	21st to end	Day	4 2 17% 42% 25% 9%	539
September	1st to 10th	Day	4 2 16% 40% 25% 12%	490
	11th to 20th	Day	5% 7% 27% 38% 17% 7%	490
	21st to end	Day	3 6% 22% 32% 28% 9%	490
October	1st to 10th	Day	2 9% 22% 35% 21% 11%	490
	11th to 20th	Day	4 8% 25% 32% 23% 7%	490
	21st to end	Day	5% 6% 29% 29% 22% 9%	539
November	1st to 10th	Day	6% 8% 23% 31% 23% 8%	430
	11th to 20th	Day	8% 8% 20% 30% 23% 12%	300
	21st to end	Day	9% 9% 19% 28% 27% 8%	300
December	1st to 10th	Day	10% 8% 26% 28% 22% 6%	275
	11th to 20th	Day	10% 13% 20% 27% 24% 8%	200
	21st to end	Day	19% 12% 26% 24% 15% 4	220
January	1st to 10th	Night	13% 6% 19% 33% 21% 9%	800
	11th to 20th	Night	9% 4 19% 39% 23% 7%	800
	21st to end	Night	14% 6% 17% 38% 21% 4	880
February	1st to 10th	Night	15% 6% 16% 34% 23% 7%	800
	11th to 20th	Night	11% 9% 20% 32% 22% 6%	784
	21st to end	Night	12% 6% 23% 38% 18% 3	660
March	1st to 10th	Night	13% 7% 18% 40% 19% 3	800
	11th to 20th	Night	12% 6% 17% 38% 22% 5%	800
	21st to end	Night	10% 7% 24% 35% 20% 3	862
April	1st to 10th	Night	7% 8% 25% 34% 23% 3	760
	11th to 20th	Night	8% 12% 21% 32% 23% 5%	751
	21st to end	Night	8% 8% 25% 29% 23% 7%	760
May	1st to 10th	Night	6% 6% 21% 34% 27% 6%	760
	11th to 20th	Night	6% 5% 20% 35% 26% 7%	692
	21st to end	Night	8% 10% 17% 33% 28% 4	453
June	1st to 10th	Night	4 5% 12% 33% 40% 5%	380
	11th to 20th	Night	5% 3 11% 37% 39% 5%	380
	21st to end	Night	5% 1 7% 33% 48% 5%	380
July	1st to 10th	Night	2 2 8% 25% 53% 11%	382
	11th to 20th	Night	4 1 4 16% 53% 23%	552
	21st to end	Night	2 1 8% 17% 51% 21%	624
August	1st to 10th	Night	3 1 12% 31% 41% 12%	708
	11th to 20th	Night	2 1 6% 28% 49% 14%	752
	21st to end	Night	3 1 6% 26% 49% 15%	836
September	1st to 10th	Night	4 2 5% 24% 53% 12%	760
	11th to 20th	Night	6% 4 12% 33% 38% 8%	760
	21st to end	Night	3 3 8% 29% 46% 10%	760
October	1st to 10th	Night	5% 3 12% 33% 40% 7%	760
	11th to 20th	Night	7% 3 12% 34% 34% 9%	760
	21st to end	Night	8% 4 11% 33% 33% 11%	836
November	1st to 10th	Night	8% 3 12% 36% 30% 11%	780
	11th to 20th	Night	6% 4 15% 38% 30% 8%	800
	21st to end	Night	8% 4 15% 42% 25% 7%	800
December	1st to 10th	Night	11% 4 15% 39% 25% 7%	800
	11th to 20th	Night	13% 5% 17% 38% 22% 5%	800
	21st to end	Night	11% 9% 20% 35% 20% 5%	880

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

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