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 2026-07-31.

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% 8% 60%	146071
	Night	5% 8% 4 8% 4 4 4 3 5% 6% 49%	144539
Transparency	Day	22% 3 7% 19% 28% 21%	141128
	Night	31% 4 8% 15% 22% 20%	140460
Seeing	Day	7% 10% 26% 31% 19% 7%	17957
	Night	8% 5% 15% 34% 31% 8%	27567

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	7% 4 2 5% 3 3 3 3 4 7% 60%	5124
	11th to 20th	Day	5% 4 1 3 3 3 3 3 4 6% 66%	5340
	21st to end	Day	7% 5% 2 5% 4 4 4 4 5% 9% 50%	5843
February	1st to 10th	Day	11% 5% 2 5% 4 3 3 3 4 6% 54%	2006
	11th to 20th	Day	8% 6% 1 6% 4 3 5% 4 5% 7% 51%	2050
	21st to end	Day	8% 6% 1 4 4 4 4 5% 5% 6% 53%	1730
March	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 9% 46%	4746
	11th to 20th	Day	8% 5% 1 5% 4 3 3 2 4 6% 57%	5110
	21st to end	Day	7% 6% 2 6% 4 5% 5% 4 6% 10% 45%	5869
April	1st to 10th	Day	7% 4 2 4 3 4 4 4 6% 8% 55%	2520
	11th to 20th	Day	4 4 2 5% 4 3 3 3 6% 7% 58%	2489
	21st to end	Day	7% 5% 1 4 3 2 3 3 6% 7% 60%	2520
May	1st to 10th	Day	2 3 2 4 3 2 3 2 3 6% 70%	7058
	11th to 20th	Day	1 4 2 5% 3 2 3 2 5% 8% 65%	7195
	21st to end	Day	2 5% 2 6% 3 3 3 3 5% 8% 60%	8870
June	1st to 10th	Day	4 6% 2 6% 3 3 4 3 5% 9% 56%	2940
	11th to 20th	Day	1 4 2 5% 3 3 3 3 4 8% 64%	2940
	21st to end	Day	1 5% 2 5% 3 3 3 3 5% 8% 61%	2940
July	1st to 10th	Day	1 2 2 4 3 2 3 2 3 7% 70%	6415
	11th to 20th	Day	1 2 2 6% 4 3 3 2 5% 9% 62%	6010
	21st to end	Day	1 4 2 6% 4 3 3 3 5% 10% 59%	6533
August	1st to 10th	Day	1 3 1 5% 3 3 3 3 5% 10% 63%	5438
	11th to 20th	Day	1 3 2 4 3 2 3 3 4 8% 67%	5364
	21st to end	Day	1 2 2 5% 2 3 2 3 4 7% 69%	5984
September	1st to 10th	Day	2 3 1 4 3 3 3 3 5% 8% 63%	2400
	11th to 20th	Day	2 6% 2 6% 4 3 3 2 5% 8% 60%	2386
	21st to end	Day	2 4 2 4 3 2 3 3 4 6% 67%	2200
October	1st to 10th	Day	2 2 1 3 2 2 2 3 4 5% 75%	3314
	11th to 20th	Day	2 3 2 5% 3 3 3 2 4 6% 68%	3261
	21st to end	Day	3 3 1 4 2 3 3 3 4 7% 66%	3558
November	1st to 10th	Day	4 4 1 4 3 2 3 3 4 6% 66%	1990
	11th to 20th	Day	6% 3 1 4 3 3 3 4 5% 6% 63%	1890
	21st to end	Day	7% 5% 2 4 4 2 3 3 5% 7% 59%	1890
December	1st to 10th	Day	4 3 2 4 3 4 4 3 5% 6% 60%	2948
	11th to 20th	Day	12% 4 2 6% 4 3 4 4 5% 6% 50%	3108
	21st to end	Day	12% 7% 3 7% 5% 4 5% 3 6% 9% 41%	4092
January	1st to 10th	Night	8% 6% 2 6% 3 3 3 2 4 6% 56%	7774
	11th to 20th	Night	5% 6% 2 6% 3 3 3 2 4 5% 60%	7650
	21st to end	Night	10% 9% 3 6% 4 4 4 3 4 7% 46%	8371
February	1st to 10th	Night	10% 6% 2 6% 4 3 3 3 5% 5% 53%	2611
	11th to 20th	Night	8% 7% 2 5% 4 4 3 4 4 8% 51%	2458
	21st to end	Night	9% 6% 3 6% 4 2 3 3 5% 7% 52%	2076
March	1st to 10th	Night	10% 10% 3 5% 5% 4 4 3 6% 8% 42%	5364
	11th to 20th	Night	8% 8% 2 6% 4 3 4 3 4 6% 53%	5110
	21st to end	Night	10% 10% 3 8% 4 3 3 2 5% 7% 46%	5346
April	1st to 10th	Night	6% 6% 3 7% 5% 5% 4 4 4 6% 50%	2100
	11th to 20th	Night	5% 8% 3 6% 4 4 4 3 3 6% 54%	2079
	21st to end	Night	5% 10% 3 6% 3 3 4 3 4 9% 50%	2100
May	1st to 10th	Night	2 9% 7% 8% 3 3 3 2 4 6% 52%	5919
	11th to 20th	Night	2 12% 5% 9% 4 3 3 3 4 6% 48%	5712
	21st to end	Night	1 15% 7% 12% 4 3 3 2 4 4 45%	5304
June	1st to 10th	Night	2 9% 5% 9% 6% 4 5% 3 6% 9% 41%	1680
	11th to 20th	Night	2 8% 4 8% 5% 4 4 3 5% 6% 50%	1680
	21st to end	Night	1 8% 4 9% 6% 5% 5% 4 6% 9% 43%	1680
July	1st to 10th	Night	3 5% 14% 7% 5% 4 3 4 6% 51%	3760
	11th to 20th	Night	1 6% 7% 23% 6% 5% 4 3 5% 7% 34%	4190
	21st to end	Night	16% 12% 21% 5% 4 4 3 4 6% 24%	4562
August	1st to 10th	Night	4 5% 17% 7% 5% 5% 4 5% 7% 40%	4385
	11th to 20th	Night	7% 5% 14% 7% 5% 3 3 4 6% 45%	4506
	21st to end	Night	6% 5% 12% 6% 4 3 3 5% 6% 51%	5015
September	1st to 10th	Night	2 6% 3 6% 6% 4 4 2 6% 8% 53%	2000
	11th to 20th	Night	3 9% 3 7% 5% 5% 3 3 6% 8% 47%	2012
	21st to end	Night	3 5% 2 6% 5% 2 3 2 5% 6% 61%	2200
October	1st to 10th	Night	2 3 1 4 3 2 3 3 4 6% 67%	3881
	11th to 20th	Night	3 11% 6% 7% 5% 4 3 2 4 5% 50%	3897
	21st to end	Night	3 8% 2 4 3 2 3 2 3 6% 63%	4253
November	1st to 10th	Night	4 5% 1 5% 4 4 4 3 5% 6% 58%	2527
	11th to 20th	Night	4 5% 2 5% 4 3 3 3 5% 6% 60%	2730
	21st to end	Night	5% 6% 2 5% 3 4 4 3 6% 7% 56%	2730
December	1st to 10th	Night	5% 4 2 5% 3 3 4 3 5% 7% 59%	4455
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 7% 46%	5316
	21st to end	Night	10% 12% 5% 9% 5% 5% 5% 4 5% 7% 33%	7106

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	25% 3 8% 28% 24% 13%	5125
	11th to 20th	Day	20% 3 6% 10% 26% 34%	5340
	21st to end	Day	31% 3 6% 18% 23% 19%	5843
February	1st to 10th	Day	31% 3 6% 20% 21% 20%	2006
	11th to 20th	Day	30% 5% 9% 21% 24% 11%	2060
	21st to end	Day	29% 4 12% 21% 25% 10%	1730
March	1st to 10th	Day	33% 5% 12% 18% 25% 7%	4746
	11th to 20th	Day	27% 4 11% 29% 18% 10%	5110
	21st to end	Day	32% 6% 13% 27% 18% 3	5869
April	1st to 10th	Day	26% 4 11% 27% 23% 9%	2520
	11th to 20th	Day	24% 3 11% 27% 26% 9%	2492
	21st to end	Day	22% 4 11% 27% 29% 7%	2520
May	1st to 10th	Day	16% 3 7% 27% 34% 13%	7058
	11th to 20th	Day	17% 4 6% 23% 38% 12%	7198
	21st to end	Day	19% 3 9% 26% 36% 7%	8871
June	1st to 10th	Day	23% 5% 9% 23% 29% 10%	2940
	11th to 20th	Day	17% 3 7% 13% 36% 23%	2940
	21st to end	Day	18% 2 7% 9% 30% 34%	2940
July	1st to 10th	Day	14% 1 3 7% 21% 54%	6347
	11th to 20th	Day	20% 2 3 7% 25% 43%	5941
	21st to end	Day	21% 2 4 17% 28% 27%	6348
August	1st to 10th	Day	19% 2 4 14% 33% 28%	3956
	11th to 20th	Day	14% 1 4 7% 32% 42%	3880
	21st to end	Day	16% 1 4 12% 35% 32%	4311
September	1st to 10th	Day	17% 3 5% 9% 30% 35%	2400
	11th to 20th	Day	21% 2 5% 16% 35% 22%	2386
	21st to end	Day	18% 2 5% 15% 34% 26%	2200
October	1st to 10th	Day	12% 2 4 14% 28% 40%	3314
	11th to 20th	Day	19% 2 5% 18% 34% 22%	3261
	21st to end	Day	18% 3 3 14% 33% 28%	3558
November	1st to 10th	Day	20% 2 6% 18% 29% 24%	1990
	11th to 20th	Day	22% 4 7% 18% 27% 22%	1890
	21st to end	Day	26% 3 7% 16% 26% 23%	1890
December	1st to 10th	Day	24% 3 5% 17% 30% 21%	2948
	11th to 20th	Day	35% 3 8% 19% 23% 11%	3108
	21st to end	Day	39% 5% 11% 23% 15% 7%	4092
January	1st to 10th	Night	29% 4 8% 20% 25% 14%	7774
	11th to 20th	Night	24% 5% 5% 9% 22% 35%	7650
	21st to end	Night	37% 4 5% 14% 22% 19%	8371
February	1st to 10th	Night	32% 2 7% 15% 23% 20%	2611
	11th to 20th	Night	31% 4 9% 20% 22% 15%	2459
	21st to end	Night	31% 4 8% 20% 25% 13%	2076
March	1st to 10th	Night	37% 6% 11% 16% 22% 9%	5364
	11th to 20th	Night	30% 5% 11% 24% 20% 10%	5110
	21st to end	Night	34% 5% 13% 24% 20% 4	5346
April	1st to 10th	Night	30% 6% 12% 22% 19% 10%	2100
	11th to 20th	Night	28% 4 10% 24% 24% 10%	2079
	21st to end	Night	27% 5% 11% 21% 27% 9%	2100
May	1st to 10th	Night	29% 5% 10% 16% 27% 12%	5917
	11th to 20th	Night	26% 4 12% 15% 26% 17%	5714
	21st to end	Night	33% 5% 13% 13% 28% 9%	5305
June	1st to 10th	Night	29% 7% 12% 16% 25% 11%	1680
	11th to 20th	Night	26% 4 9% 10% 26% 24%	1680
	21st to end	Night	25% 3 10% 11% 21% 31%	1680
July	1st to 10th	Night	29% 3 4 7% 16% 42%	3720
	11th to 20th	Night	46% 2 6% 6% 12% 28%	4136
	21st to end	Night	56% 4 5% 8% 15% 13%	4435
August	1st to 10th	Night	38% 3 5% 10% 17% 27%	3182
	11th to 20th	Night	27% 2 6% 7% 16% 41%	3256
	21st to end	Night	28% 2 5% 11% 24% 31%	3608
September	1st to 10th	Night	22% 2 8% 10% 19% 39%	2000
	11th to 20th	Night	26% 2 8% 14% 25% 24%	2012
	21st to end	Night	20% 2 8% 12% 30% 28%	2200
October	1st to 10th	Night	15% 2 4 12% 24% 43%	3881
	11th to 20th	Night	34% 3 5% 12% 20% 26%	3897
	21st to end	Night	22% 3 4 10% 32% 29%	4253
November	1st to 10th	Night	24% 3 7% 15% 26% 25%	2527
	11th to 20th	Night	24% 4 7% 15% 25% 25%	2730
	21st to end	Night	27% 3 7% 16% 22% 25%	2730
December	1st to 10th	Night	24% 3 5% 17% 30% 22%	4455
	11th to 20th	Night	36% 5% 10% 14% 23% 13%	5316
	21st to end	Night	48% 5% 8% 19% 14% 6%	7106

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% 16% 26% 23% 14% 2	362
	11th to 20th	Day	10% 12% 29% 26% 19% 4	430
	21st to end	Day	11% 13% 31% 24% 16% 5%	473
February	1st to 10th	Day	12% 14% 26% 24% 18% 6%	491
	11th to 20th	Day	13% 18% 29% 24% 13% 3	535
	21st to end	Day	10% 14% 32% 28% 13% 3	446
March	1st to 10th	Day	15% 17% 31% 26% 9% 1	540
	11th to 20th	Day	13% 14% 31% 27% 12% 3	540
	21st to end	Day	11% 19% 36% 21% 9% 4	594
April	1st to 10th	Day	10% 14% 35% 20% 14% 6%	540
	11th to 20th	Day	8% 17% 33% 25% 11% 5%	532
	21st to end	Day	6% 20% 33% 24% 12% 5%	540
May	1st to 10th	Day	8% 13% 33% 28% 13% 5%	543
	11th to 20th	Day	5% 11% 35% 30% 15% 4	568
	21st to end	Day	8% 14% 31% 31% 12% 5%	617
June	1st to 10th	Day	6% 7% 29% 34% 18% 6%	570
	11th to 20th	Day	3 7% 29% 36% 20% 6%	570
	21st to end	Day	5% 4 23% 39% 22% 8%	570
July	1st to 10th	Day	3 1 20% 39% 28% 8%	566
	11th to 20th	Day	4 1 12% 43% 27% 15%	564
	21st to end	Day	2 2 14% 43% 29% 10%	616
August	1st to 10th	Day	5% 2 19% 46% 20% 8%	527
	11th to 20th	Day	3 2 15% 39% 30% 11%	517
	21st to end	Day	4 2 18% 41% 25% 10%	583
September	1st to 10th	Day	4 3 18% 40% 25% 12%	530
	11th to 20th	Day	5% 7% 27% 37% 17% 8%	530
	21st to end	Day	4 7% 22% 32% 27% 9%	530
October	1st to 10th	Day	3 8% 23% 34% 21% 11%	530
	11th to 20th	Day	5% 9% 25% 31% 22% 7%	530
	21st to end	Day	5% 6% 30% 29% 21% 9%	583
November	1st to 10th	Day	5% 8% 23% 31% 24% 9%	466
	11th to 20th	Day	11% 8% 20% 28% 22% 11%	330
	21st to end	Day	8% 8% 20% 28% 28% 9%	330
December	1st to 10th	Day	9% 7% 25% 28% 25% 6%	302
	11th to 20th	Day	9% 12% 20% 28% 23% 8%	220
	21st to end	Day	21% 11% 26% 23% 14% 4	242
January	1st to 10th	Night	13% 6% 19% 33% 20% 8%	840
	11th to 20th	Night	8% 4 18% 39% 25% 7%	840
	21st to end	Night	14% 6% 16% 39% 21% 4	924
February	1st to 10th	Night	14% 5% 17% 35% 23% 7%	840
	11th to 20th	Night	12% 9% 21% 32% 21% 5%	824
	21st to end	Night	12% 6% 22% 40% 18% 3	692
March	1st to 10th	Night	13% 7% 19% 40% 19% 3	840
	11th to 20th	Night	11% 5% 16% 38% 24% 5%	840
	21st to end	Night	10% 7% 24% 35% 21% 3	924
April	1st to 10th	Night	8% 8% 24% 36% 22% 3	840
	11th to 20th	Night	8% 11% 22% 32% 23% 4	831
	21st to end	Night	9% 8% 25% 30% 22% 6%	840
May	1st to 10th	Night	6% 6% 20% 35% 27% 6%	840
	11th to 20th	Night	6% 6% 20% 35% 26% 7%	766
	21st to end	Night	8% 9% 17% 33% 28% 4	501
June	1st to 10th	Night	4 5% 12% 34% 40% 5%	420
	11th to 20th	Night	6% 4 10% 36% 38% 6%	420
	21st to end	Night	5% 1 9% 33% 47% 5%	420
July	1st to 10th	Night	1 2 9% 26% 52% 10%	424
	11th to 20th	Night	4 1 4 16% 53% 23%	612
	21st to end	Night	3 1 8% 20% 49% 20%	687
August	1st to 10th	Night	3 1 12% 32% 40% 12%	746
	11th to 20th	Night	2 1 7% 28% 48% 14%	792
	21st to end	Night	3 1 6% 27% 49% 14%	880
September	1st to 10th	Night	5% 2 5% 26% 51% 11%	800
	11th to 20th	Night	6% 4 12% 32% 37% 9%	800
	21st to end	Night	4 3 9% 29% 45% 10%	800
October	1st to 10th	Night	5% 3 12% 33% 39% 7%	800
	11th to 20th	Night	7% 4 12% 35% 33% 9%	800
	21st to end	Night	7% 4 12% 33% 33% 11%	880
November	1st to 10th	Night	8% 3 12% 35% 31% 11%	820
	11th to 20th	Night	7% 4 14% 38% 29% 8%	840
	21st to end	Night	7% 3 15% 42% 25% 7%	840
December	1st to 10th	Night	11% 4 15% 39% 25% 6%	840
	11th to 20th	Night	13% 5% 17% 38% 23% 5%	840
	21st to end	Night	13% 9% 20% 34% 19% 5%	924

Page generated at 2026-07-28 00:25:22. Version ac07

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