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 2024-02-15.

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	6% 5% 2 4 4 2 4 4 5% 8% 57%	78530
	Night	7% 7% 3 6% 5% 3 4 4 5% 7% 49%	80563
Transparency	Day	25% 4 8% 19% 26% 18%	78251
	Night	30% 4 9% 17% 22% 19%	80364
Seeing	Day	8% 10% 25% 32% 19% 6%	14603
	Night	8% 5% 15% 33% 31% 8%	24353

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 4 4 2 3 4 4 7% 59%	2745
	11th to 20th	Day	10% 7% 2 5% 5% 4 4 5% 5% 8% 46%	2860
	21st to end	Day	12% 6% 3 5% 5% 3 5% 6% 6% 9% 42%	3146
February	1st to 10th	Day	12% 5% 2 4 4 2 3 3 4 6% 55%	1814
	11th to 20th	Day	8% 5% 2 4 4 2 5% 5% 5% 7% 53%	1791
	21st to end	Day	9% 5% 2 4 4 3 4 5% 4 5% 54%	1480
March	1st to 10th	Day	9% 6% 3 6% 5% 2 5% 4 5% 9% 45%	1847
	11th to 20th	Day	10% 6% 2 4 7% 3 4 3 5% 9% 47%	1980
	21st to end	Day	6% 4 2 4 4 3 4 5% 5% 7% 56%	2279
April	1st to 10th	Day	7% 4 2 4 4 3 3 4 7% 8% 54%	2160
	11th to 20th	Day	4 4 2 5% 4 2 3 3 5% 7% 58%	2129
	21st to end	Day	7% 5% 2 4 3 1 3 4 5% 7% 62%	2160
May	1st to 10th	Day	5% 6% 2 4 3 2 3 4 5% 9% 57%	2160
	11th to 20th	Day	2 5% 2 4 4 2 4 3 5% 8% 62%	2172
	21st to end	Day	4 7% 3 4 4 2 3 4 5% 7% 56%	2679
June	1st to 10th	Day	4 5% 2 5% 4 2 4 4 5% 8% 57%	2520
	11th to 20th	Day	1 4 2 4 3 2 3 4 4 7% 64%	2520
	21st to end	Day	2 5% 2 4 4 2 3 4 5% 8% 61%	2520
July	1st to 10th	Day	1 5% 3 4 4 2 4 4 5% 11% 56%	2503
	11th to 20th	Day	3 4 2 3 4 3 4 4 6% 8% 59%	2340
	21st to end	Day	2 4 2 5% 5% 3 5% 4 6% 11% 53%	2546
August	1st to 10th	Day	3 7% 2 5% 4 3 5% 4 5% 10% 53%	2190
	11th to 20th	Day	2 5% 2 5% 3 2 4 4 5% 8% 60%	2122
	21st to end	Day	2 5% 2 5% 3 3 4 4 4 8% 60%	2376
September	1st to 10th	Day	3 3 2 3 4 2 4 4 5% 8% 63%	2160
	11th to 20th	Day	2 5% 2 4 5% 2 3 3 4 8% 61%	2148
	21st to end	Day	2 4 2 3 3 2 3 3 4 6% 68%	1980
October	1st to 10th	Day	3 2 1 3 3 2 3 4 5% 6% 68%	1820
	11th to 20th	Day	3 4 1 3 3 2 3 3 4 6% 68%	1800
	21st to end	Day	3 3 2 4 3 2 3 4 4 7% 65%	1980
November	1st to 10th	Day	5% 3 2 4 3 2 3 4 4 6% 65%	1798
	11th to 20th	Day	5% 3 1 4 4 2 3 4 4 6% 64%	1710
	21st to end	Day	7% 4 2 4 4 2 2 3 5% 8% 60%	1710
December	1st to 10th	Day	8% 4 3 5% 4 3 4 3 5% 6% 55%	1663
	11th to 20th	Day	16% 6% 3 7% 6% 3 4 4 5% 6% 40%	1928
	21st to end	Day	12% 7% 3 5% 6% 3 4 4 6% 7% 42%	2794
January	1st to 10th	Night	8% 6% 2 5% 4 2 3 3 4 6% 56%	4190
	11th to 20th	Night	9% 11% 4 7% 6% 3 4 4 5% 6% 41%	4110
	21st to end	Night	15% 10% 3 5% 5% 2 4 4 4 7% 41%	4521
February	1st to 10th	Night	10% 5% 2 5% 5% 2 4 3 4 6% 53%	2363
	11th to 20th	Night	7% 6% 3 4 4 3 4 4 4 7% 55%	2151
	21st to end	Night	11% 6% 2 6% 5% 2 3 3 4 6% 52%	1776
March	1st to 10th	Night	9% 8% 4 4 6% 3 5% 4 6% 9% 43%	2109
	11th to 20th	Night	9% 7% 3 6% 6% 3 6% 5% 6% 8% 42%	1980
	21st to end	Night	8% 7% 2 5% 4 3 4 3 5% 7% 51%	2075
April	1st to 10th	Night	6% 5% 3 5% 6% 4 5% 5% 4 7% 50%	1800
	11th to 20th	Night	6% 8% 3 6% 5% 2 4 4 3 6% 54%	1779
	21st to end	Night	5% 7% 3 5% 4 3 4 4 4 9% 53%	1800
May	1st to 10th	Night	3 7% 3 6% 5% 3 4 4 6% 10% 49%	1800
	11th to 20th	Night	4 9% 4 8% 6% 2 4 4 6% 10% 42%	1718
	21st to end	Night	4 11% 4 8% 5% 3 4 4 5% 7% 45%	1591
June	1st to 10th	Night	3 8% 5% 8% 7% 3 5% 4 6% 10% 43%	1440
	11th to 20th	Night	3 6% 4 8% 6% 3 4 4 5% 6% 50%	1440
	21st to end	Night	1 7% 4 7% 7% 3 5% 5% 6% 10% 44%	1440
July	1st to 10th	Night	1 6% 6% 9% 7% 4 6% 5% 6% 11% 39%	1451
	11th to 20th	Night	1 6% 3 7% 7% 4 6% 5% 7% 10% 44%	1620
	21st to end	Night	1 5% 5% 12% 8% 5% 6% 6% 6% 10% 37%	1773
August	1st to 10th	Night	1 8% 7% 10% 9% 3 5% 5% 6% 9% 36%	1744
	11th to 20th	Night	1 6% 3 7% 7% 4 4 6% 6% 10% 45%	1780
	21st to end	Night	1 6% 5% 8% 7% 3 4 3 5% 8% 49%	1980
September	1st to 10th	Night	2 5% 2 5% 6% 3 4 4 6% 8% 54%	1800
	11th to 20th	Night	3 7% 2 6% 6% 3 4 4 6% 9% 50%	1810
	21st to end	Night	2 4 2 4 5% 2 3 3 4 6% 64%	1980
October	1st to 10th	Night	3 4 2 4 5% 2 3 4 5% 7% 60%	2135
	11th to 20th	Night	5% 8% 3 5% 6% 3 3 3 4 6% 54%	2160
	21st to end	Night	4 7% 2 4 4 1 3 3 3 6% 61%	2376
November	1st to 10th	Night	5% 5% 2 4 5% 3 4 4 5% 7% 56%	2280
	11th to 20th	Night	3 4 2 5% 4 2 4 3 5% 7% 61%	2470
	21st to end	Night	5% 5% 2 4 4 2 4 4 5% 7% 57%	2470
December	1st to 10th	Night	8% 5% 3 5% 5% 2 4 4 5% 7% 52%	2513
	11th to 20th	Night	15% 8% 3 6% 5% 3 5% 5% 5% 6% 38%	3276
	21st to end	Night	13% 9% 3 6% 6% 3 4 4 4 6% 41%	4862

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	24% 3 8% 34% 24% 6%	2745
	11th to 20th	Day	35% 5% 11% 17% 20% 11%	2860
	21st to end	Day	37% 4 8% 24% 14% 12%	3146
February	1st to 10th	Day	31% 3 6% 20% 20% 20%	1814
	11th to 20th	Day	28% 5% 8% 21% 26% 12%	1801
	21st to end	Day	30% 4 11% 21% 25% 10%	1480
March	1st to 10th	Day	35% 5% 10% 20% 20% 11%	1847
	11th to 20th	Day	34% 4 13% 19% 20% 10%	1980
	21st to end	Day	26% 5% 11% 28% 22% 8%	2279
April	1st to 10th	Day	27% 4 12% 27% 21% 9%	2160
	11th to 20th	Day	24% 3 12% 26% 25% 10%	2132
	21st to end	Day	21% 4 10% 27% 29% 8%	2160
May	1st to 10th	Day	23% 4 11% 22% 31% 10%	2160
	11th to 20th	Day	20% 5% 8% 28% 29% 10%	2175
	21st to end	Day	24% 4 12% 30% 25% 4	2679
June	1st to 10th	Day	23% 5% 10% 21% 30% 11%	2520
	11th to 20th	Day	18% 4 8% 13% 36% 21%	2520
	21st to end	Day	19% 2 8% 9% 30% 32%	2520
July	1st to 10th	Day	19% 2 7% 12% 26% 34%	2434
	11th to 20th	Day	20% 3 7% 15% 31% 24%	2271
	21st to end	Day	23% 4 9% 15% 30% 20%	2405
August	1st to 10th	Day	25% 2 7% 11% 27% 27%	2174
	11th to 20th	Day	19% 2 7% 12% 33% 28%	2122
	21st to end	Day	19% 2 6% 12% 33% 28%	2376
September	1st to 10th	Day	17% 3 6% 10% 29% 36%	2160
	11th to 20th	Day	19% 2 5% 16% 34% 24%	2148
	21st to end	Day	16% 2 5% 16% 36% 25%	1980
October	1st to 10th	Day	15% 3 8% 19% 27% 28%	1820
	11th to 20th	Day	19% 2 6% 17% 28% 29%	1800
	21st to end	Day	19% 4 5% 14% 28% 30%	1980
November	1st to 10th	Day	21% 2 6% 17% 29% 25%	1798
	11th to 20th	Day	21% 4 7% 17% 27% 24%	1710
	21st to end	Day	25% 3 7% 15% 26% 24%	1710
December	1st to 10th	Day	30% 4 8% 16% 25% 17%	1663
	11th to 20th	Day	45% 4 8% 15% 17% 10%	1928
	21st to end	Day	39% 6% 9% 22% 16% 8%	2794
January	1st to 10th	Night	28% 4 8% 25% 25% 10%	4190
	11th to 20th	Night	38% 6% 9% 16% 17% 13%	4110
	21st to end	Night	41% 4 8% 15% 19% 12%	4521
February	1st to 10th	Night	32% 2 7% 15% 24% 20%	2363
	11th to 20th	Night	28% 3 9% 19% 24% 17%	2152
	21st to end	Night	32% 4 7% 18% 25% 13%	1776
March	1st to 10th	Night	36% 5% 11% 20% 17% 11%	2109
	11th to 20th	Night	36% 5% 10% 15% 22% 12%	1980
	21st to end	Night	29% 4 13% 20% 25% 10%	2075
April	1st to 10th	Night	29% 6% 13% 23% 18% 10%	1800
	11th to 20th	Night	28% 3 11% 24% 23% 11%	1779
	21st to end	Night	25% 5% 11% 22% 29% 10%	1800
May	1st to 10th	Night	25% 6% 11% 21% 24% 13%	1800
	11th to 20th	Night	30% 3 12% 20% 23% 12%	1720
	21st to end	Night	30% 5% 14% 23% 22% 7%	1591
June	1st to 10th	Night	28% 7% 12% 16% 25% 12%	1440
	11th to 20th	Night	25% 4 10% 11% 27% 23%	1440
	21st to end	Night	22% 3 12% 12% 22% 30%	1440
July	1st to 10th	Night	24% 2 8% 18% 18% 30%	1411
	11th to 20th	Night	25% 2 11% 15% 20% 28%	1566
	21st to end	Night	30% 3 11% 16% 21% 19%	1674
August	1st to 10th	Night	33% 2 7% 12% 16% 30%	1735
	11th to 20th	Night	22% 2 9% 13% 24% 30%	1780
	21st to end	Night	22% 1 8% 13% 27% 30%	1980
September	1st to 10th	Night	20% 2 8% 11% 19% 39%	1800
	11th to 20th	Night	23% 2 9% 14% 26% 26%	1810
	21st to end	Night	16% 2 8% 13% 31% 30%	1980
October	1st to 10th	Night	18% 2 7% 19% 23% 30%	2135
	11th to 20th	Night	27% 2 8% 13% 22% 28%	2160
	21st to end	Night	21% 2 7% 11% 27% 31%	2376
November	1st to 10th	Night	24% 3 7% 15% 24% 26%	2280
	11th to 20th	Night	23% 4 7% 15% 25% 27%	2470
	21st to end	Night	26% 3 8% 16% 21% 26%	2470
December	1st to 10th	Night	31% 3 8% 16% 23% 19%	2513
	11th to 20th	Night	45% 6% 8% 14% 18% 10%	3276
	21st to end	Night	41% 5% 9% 19% 18% 8%	4862

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	21% 14% 27% 23% 14% 2	308
	11th to 20th	Day	11% 14% 30% 25% 18% 2	370
	21st to end	Day	12% 13% 31% 24% 15% 4	407
February	1st to 10th	Day	12% 13% 26% 23% 19% 7%	419
	11th to 20th	Day	11% 16% 27% 26% 16% 4	432
	21st to end	Day	12% 16% 29% 27% 12% 3	346
March	1st to 10th	Day	14% 17% 30% 26% 11% 2	420
	11th to 20th	Day	14% 15% 30% 29% 10% 2	420
	21st to end	Day	11% 21% 36% 21% 9% 3	462
April	1st to 10th	Day	11% 14% 36% 19% 15% 5%	420
	11th to 20th	Day	9% 19% 35% 24% 9% 4	412
	21st to end	Day	5% 20% 35% 22% 12% 5%	420
May	1st to 10th	Day	9% 13% 33% 27% 13% 4	423
	11th to 20th	Day	5% 12% 36% 31% 13% 3	448
	21st to end	Day	9% 15% 31% 30% 11% 4	485
June	1st to 10th	Day	7% 7% 28% 32% 20% 6%	450
	11th to 20th	Day	3 7% 26% 37% 21% 6%	450
	21st to end	Day	5% 3 24% 38% 23% 7%	450
July	1st to 10th	Day	4 2 17% 40% 30% 8%	446
	11th to 20th	Day	4 1 9% 44% 29% 13%	444
	21st to end	Day	2 2 12% 43% 30% 10%	487
August	1st to 10th	Day	6% 2 18% 48% 20% 6%	447
	11th to 20th	Day	4 2 12% 40% 30% 11%	437
	21st to end	Day	5% 2 16% 43% 26% 8%	495
September	1st to 10th	Day	4 3 16% 40% 26% 11%	450
	11th to 20th	Day	4 5% 26% 39% 18% 8%	450
	21st to end	Day	3 6% 21% 33% 28% 9%	450
October	1st to 10th	Day	2 10% 23% 34% 20% 11%	450
	11th to 20th	Day	4 8% 25% 33% 22% 7%	450
	21st to end	Day	5% 5% 29% 31% 22% 8%	495
November	1st to 10th	Day	6% 7% 23% 32% 25% 7%	394
	11th to 20th	Day	7% 7% 20% 30% 23% 13%	270
	21st to end	Day	8% 8% 19% 27% 29% 9%	270
December	1st to 10th	Day	11% 8% 29% 28% 19% 4	248
	11th to 20th	Day	9% 13% 20% 26% 23% 9%	180
	21st to end	Day	19% 11% 25% 26% 15% 5%	198
January	1st to 10th	Night	13% 6% 18% 32% 22% 9%	760
	11th to 20th	Night	9% 4 18% 38% 24% 8%	760
	21st to end	Night	15% 6% 17% 37% 20% 4	836
February	1st to 10th	Night	14% 5% 16% 33% 24% 8%	760
	11th to 20th	Night	10% 9% 19% 32% 24% 6%	722
	21st to end	Night	13% 7% 23% 36% 18% 3	592
March	1st to 10th	Night	13% 6% 17% 41% 20% 3	720
	11th to 20th	Night	12% 5% 17% 38% 24% 5%	720
	21st to end	Night	10% 6% 24% 35% 20% 4	792
April	1st to 10th	Night	8% 7% 24% 34% 23% 3	720
	11th to 20th	Night	8% 11% 22% 31% 22% 5%	711
	21st to end	Night	8% 8% 26% 29% 23% 7%	720
May	1st to 10th	Night	6% 7% 21% 32% 28% 6%	720
	11th to 20th	Night	6% 5% 21% 34% 26% 7%	655
	21st to end	Night	7% 10% 18% 33% 28% 4	429
June	1st to 10th	Night	4 6% 13% 33% 39% 5%	360
	11th to 20th	Night	5% 3 9% 36% 41% 5%	360
	21st to end	Night	5% 1 7% 34% 48% 5%	360
July	1st to 10th	Night	2 2 8% 25% 52% 10%	361
	11th to 20th	Night	4 1 4 15% 52% 23%	522
	21st to end	Night	2 1 7% 17% 52% 21%	591
August	1st to 10th	Night	3 1 12% 32% 39% 11%	670
	11th to 20th	Night	2 1 5% 28% 49% 15%	712
	21st to end	Night	3 1 6% 26% 50% 15%	792
September	1st to 10th	Night	5% 2 5% 24% 53% 12%	720
	11th to 20th	Night	5% 4 10% 34% 39% 9%	720
	21st to end	Night	4 3 8% 28% 46% 11%	720
October	1st to 10th	Night	5% 3 13% 33% 38% 7%	720
	11th to 20th	Night	7% 4 11% 34% 34% 10%	720
	21st to end	Night	7% 3 12% 32% 33% 12%	792
November	1st to 10th	Night	8% 3 11% 36% 30% 11%	740
	11th to 20th	Night	5% 3 14% 38% 31% 8%	760
	21st to end	Night	7% 4 16% 41% 26% 7%	760
December	1st to 10th	Night	12% 4 16% 38% 25% 6%	760
	11th to 20th	Night	14% 5% 17% 37% 22% 5%	760
	21st to end	Night	11% 9% 19% 35% 21% 5%	836

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