Livermore
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Livermore clear sky chart from 2005-11-06 to 2024-01-16.

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	5% 3 2 3 3 2 3 4 4 7% 63%	74733
	Night	6% 4 2 3 4 2 4 4 5% 7% 59%	75075
Transparency	Day	22% 4 7% 18% 26% 22%	74450
	Night	25% 6% 7% 17% 22% 22%	74879
Seeing	Day	8% 12% 27% 32% 17% 4	14233
	Night	8% 6% 13% 36% 29% 7%	23693

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	15% 7% 3 5% 7% 4 4 7% 6% 8% 35%	1585
	11th to 20th	Day	9% 4 2 6% 6% 3 5% 4 4 8% 48%	1666
	21st to end	Day	11% 6% 3 6% 6% 3 5% 5% 5% 7% 41%	1782
February	1st to 10th	Day	12% 6% 3 5% 4 3 4 4 6% 8% 46%	1620
	11th to 20th	Day	9% 6% 2 5% 5% 4 5% 5% 4 8% 47%	1677
	21st to end	Day	11% 5% 3 5% 4 3 4 4 4 7% 49%	1480
March	1st to 10th	Day	11% 7% 4 5% 7% 4 4 6% 6% 8% 38%	1913
	11th to 20th	Day	11% 6% 3 6% 7% 3 5% 6% 6% 8% 39%	1980
	21st to end	Day	9% 5% 3 5% 5% 3 4 5% 6% 8% 47%	2227
April	1st to 10th	Day	10% 6% 2 5% 5% 4 4 5% 5% 7% 46%	2160
	11th to 20th	Day	7% 3 2 5% 3 2 4 4 5% 7% 59%	2129
	21st to end	Day	4 4 2 2 3 2 4 3 6% 8% 63%	2160
May	1st to 10th	Day	4 3 2 2 4 2 3 4 5% 8% 64%	2197
	11th to 20th	Day	3 3 1 3 3 2 2 3 4 6% 70%	2384
	21st to end	Day	3 2 1 3 3 2 3 3 5% 8% 67%	2723
June	1st to 10th	Day	3 3 1 3 3 1 4 4 4 8% 67%	2520
	11th to 20th	Day	1 1 1 1 2 3 4 6% 81%	2520
	21st to end	Day	2 1 1 1 1 1 2 2 3 4 83%	2520
July	1st to 10th	Day	1 1 1 1 2 5% 87%	2520
	11th to 20th	Day	1 1 1 1 2 2 2 4 85%	2398
	21st to end	Day	1 1 1 1 2 2 3 5% 84%	2546
August	1st to 10th	Day	1 1 1 2 2 1 2 2 3 5% 81%	2328
	11th to 20th	Day	1 1 1 1 2 3 5% 86%	2165
	21st to end	Day	1 1 1 2 2 3 5% 85%	2376
September	1st to 10th	Day	1 1 1 2 1 1 2 2 3 87%	2160
	11th to 20th	Day	1 1 2 3 1 3 3 4 8% 75%	2160
	21st to end	Day	2 1 1 1 2 1 2 2 3 6% 79%	1925
October	1st to 10th	Day	1 1 1 2 4 2 3 2 4 6% 73%	1800
	11th to 20th	Day	3 2 1 3 3 2 2 3 4 6% 71%	1800
	21st to end	Day	5% 3 1 2 3 2 3 3 5% 8% 66%	1980
November	1st to 10th	Day	5% 3 3 5% 4 2 4 5% 5% 8% 55%	1793
	11th to 20th	Day	6% 4 2 5% 6% 3 4 6% 6% 7% 52%	1710
	21st to end	Day	10% 5% 3 4 4 2 2 4 5% 7% 54%	1587
December	1st to 10th	Day	9% 6% 2 6% 6% 3 4 5% 5% 7% 47%	1520
	11th to 20th	Day	17% 9% 4 6% 5% 5% 5% 6% 6% 6% 30%	1928
	21st to end	Day	12% 9% 4 7% 6% 3 5% 5% 6% 8% 35%	2794
January	1st to 10th	Night	12% 6% 2 5% 6% 3 5% 5% 7% 9% 39%	2575
	11th to 20th	Night	10% 5% 3 5% 5% 4 5% 5% 5% 7% 45%	2405
	21st to end	Night	11% 6% 3 4 5% 3 5% 5% 5% 7% 46%	2574
February	1st to 10th	Night	12% 5% 3 4 4 2 4 4 4 6% 52%	2340
	11th to 20th	Night	7% 4 2 5% 6% 3 5% 7% 6% 8% 48%	2169
	21st to end	Night	9% 5% 3 4 5% 2 5% 4 6% 6% 52%	1776
March	1st to 10th	Night	12% 7% 3 5% 5% 3 5% 5% 5% 7% 43%	2044
	11th to 20th	Night	10% 6% 3 6% 5% 4 4 5% 5% 8% 45%	1980
	21st to end	Night	10% 5% 2 5% 4 3 4 5% 5% 7% 51%	2129
April	1st to 10th	Night	7% 4 3 5% 5% 3 5% 5% 7% 9% 49%	1800
	11th to 20th	Night	5% 3 2 3 4 3 4 4 6% 6% 58%	1779
	21st to end	Night	4 2 1 2 2 2 4 4 5% 10% 64%	1800
May	1st to 10th	Night	4 2 1 3 3 3 4 3 6% 7% 63%	1760
	11th to 20th	Night	2 1 1 2 3 2 3 4 6% 10% 64%	1506
	21st to end	Night	2 1 1 2 3 2 4 4 5% 11% 65%	1552
June	1st to 10th	Night	2 3 1 3 3 2 3 4 5% 8% 67%	1440
	11th to 20th	Night	1 1 1 1 1 3 2 4 6% 79%	1440
	21st to end	Night	1 1 1 1 1 2 2 3 6% 82%	1440
July	1st to 10th	Night	1 1 1 2 2 3 5% 86%	1440
	11th to 20th	Night	1 1 1 2 1 2 2 3 6% 82%	1557
	21st to end	Night	1 1 1 1 2 2 2 3 5% 9% 73%	1773
August	1st to 10th	Night	1 1 1 2 2 2 3 3 5% 7% 73%	1611
	11th to 20th	Night	1 1 1 2 2 5% 7% 79%	1736
	21st to end	Night	1 1 1 2 2 2 3 3 5% 80%	1980
September	1st to 10th	Night	1 1 1 2 3 3 6% 83%	1800
	11th to 20th	Night	1 1 1 2 2 2 2 3 4 8% 75%	1800
	21st to end	Night	1 1 2 2 2 2 2 3 6% 80%	2032
October	1st to 10th	Night	3 2 1 2 2 2 3 3 4 6% 72%	2160
	11th to 20th	Night	3 2 1 2 3 2 3 4 5% 7% 67%	2160
	21st to end	Night	4 2 1 3 2 2 3 3 4 7% 68%	2376
November	1st to 10th	Night	6% 3 1 3 3 2 4 5% 6% 8% 58%	2284
	11th to 20th	Night	6% 5% 2 4 4 2 5% 5% 6% 8% 54%	2470
	21st to end	Night	7% 4 2 3 4 2 3 4 4 7% 57%	2589
December	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 6% 6% 49%	2660
	11th to 20th	Night	17% 7% 3 6% 6% 3 5% 5% 7% 8% 33%	3276
	21st to end	Night	12% 7% 3 7% 7% 4 6% 6% 6% 7% 35%	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	45% 6% 11% 23% 12% 4	1585
	11th to 20th	Day	36% 5% 11% 19% 19% 11%	1666
	21st to end	Day	42% 6% 9% 14% 22% 7%	1782
February	1st to 10th	Day	38% 5% 6% 22% 20% 10%	1620
	11th to 20th	Day	36% 6% 9% 18% 23% 8%	1686
	21st to end	Day	37% 6% 7% 24% 20% 6%	1480
March	1st to 10th	Day	43% 8% 9% 19% 18% 4	1913
	11th to 20th	Day	43% 7% 7% 21% 17% 6%	1980
	21st to end	Day	37% 7% 13% 20% 19% 4	2227
April	1st to 10th	Day	38% 6% 11% 20% 20% 5%	2160
	11th to 20th	Day	27% 5% 13% 24% 25% 7%	2132
	21st to end	Day	20% 6% 11% 29% 29% 6%	2160
May	1st to 10th	Day	19% 6% 9% 25% 33% 8%	2197
	11th to 20th	Day	17% 4 7% 26% 34% 11%	2387
	21st to end	Day	17% 6% 11% 32% 28% 6%	2724
June	1st to 10th	Day	18% 4 9% 24% 30% 15%	2520
	11th to 20th	Day	7% 3 6% 20% 36% 27%	2520
	21st to end	Day	8% 2 2 11% 28% 48%	2520
July	1st to 10th	Day	4 2 2 7% 23% 62%	2451
	11th to 20th	Day	6% 2 3 11% 22% 55%	2325
	21st to end	Day	5% 2 1 6% 28% 58%	2405
August	1st to 10th	Day	8% 3 2 9% 28% 50%	2312
	11th to 20th	Day	4 2 1 10% 34% 49%	2165
	21st to end	Day	4 2 2 9% 36% 47%	2376
September	1st to 10th	Day	6% 2 2 8% 28% 55%	2160
	11th to 20th	Day	8% 6% 3 20% 37% 26%	2160
	21st to end	Day	10% 3 3 20% 38% 27%	1925
October	1st to 10th	Day	15% 4 5% 18% 30% 28%	1800
	11th to 20th	Day	15% 5% 7% 21% 24% 28%	1800
	21st to end	Day	20% 3 6% 21% 28% 22%	1980
November	1st to 10th	Day	29% 6% 7% 22% 23% 13%	1793
	11th to 20th	Day	29% 5% 9% 23% 26% 7%	1710
	21st to end	Day	29% 6% 9% 19% 29% 10%	1587
December	1st to 10th	Day	35% 7% 10% 18% 19% 10%	1520
	11th to 20th	Day	53% 5% 9% 14% 13% 6%	1928
	21st to end	Day	48% 5% 12% 20% 12% 3	2794
January	1st to 10th	Night	39% 7% 11% 23% 14% 5%	2575
	11th to 20th	Night	38% 6% 10% 17% 15% 13%	2405
	21st to end	Night	39% 6% 11% 13% 21% 11%	2574
February	1st to 10th	Night	34% 6% 6% 20% 22% 13%	2340
	11th to 20th	Night	32% 7% 8% 19% 24% 10%	2171
	21st to end	Night	31% 8% 9% 26% 19% 6%	1776
March	1st to 10th	Night	40% 9% 10% 18% 17% 6%	2044
	11th to 20th	Night	38% 7% 7% 21% 19% 8%	1980
	21st to end	Night	33% 9% 11% 20% 19% 8%	2129
April	1st to 10th	Night	33% 7% 13% 19% 20% 8%	1800
	11th to 20th	Night	27% 7% 10% 26% 19% 12%	1779
	21st to end	Night	17% 9% 9% 28% 29% 8%	1800
May	1st to 10th	Night	18% 8% 6% 22% 31% 15%	1760
	11th to 20th	Night	15% 7% 6% 22% 35% 15%	1506
	21st to end	Night	12% 9% 11% 27% 31% 10%	1552
June	1st to 10th	Night	18% 5% 8% 20% 29% 21%	1440
	11th to 20th	Night	8% 3 7% 14% 31% 38%	1440
	21st to end	Night	7% 4 1 10% 24% 53%	1440
July	1st to 10th	Night	4 4 1 5% 17% 69%	1400
	11th to 20th	Night	5% 4 3 8% 17% 64%	1507
	21st to end	Night	7% 4 2 6% 17% 63%	1674
August	1st to 10th	Night	9% 6% 2 8% 20% 55%	1602
	11th to 20th	Night	5% 3 2 8% 28% 55%	1736
	21st to end	Night	5% 3 3 7% 30% 52%	1980
September	1st to 10th	Night	4 3 2 7% 21% 62%	1800
	11th to 20th	Night	8% 7% 2 18% 31% 34%	1800
	21st to end	Night	9% 4 2 18% 35% 33%	2032
October	1st to 10th	Night	15% 4 7% 17% 25% 33%	2160
	11th to 20th	Night	16% 6% 5% 17% 24% 32%	2160
	21st to end	Night	17% 5% 4 17% 30% 27%	2376
November	1st to 10th	Night	23% 8% 8% 22% 21% 18%	2284
	11th to 20th	Night	27% 6% 8% 22% 27% 10%	2470
	21st to end	Night	27% 5% 8% 20% 26% 14%	2589
December	1st to 10th	Night	36% 5% 8% 18% 18% 14%	2660
	11th to 20th	Night	50% 7% 9% 13% 17% 5%	3276
	21st to end	Night	48% 7% 12% 16% 12% 4	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	23% 20% 26% 21% 10% 1	246
	11th to 20th	Day	16% 13% 25% 31% 12% 2	356
	21st to end	Day	15% 13% 25% 28% 17% 2	374
February	1st to 10th	Day	16% 18% 24% 26% 15% 1	340
	11th to 20th	Day	17% 20% 27% 28% 7% 1	381
	21st to end	Day	15% 19% 32% 23% 10% 1	346
March	1st to 10th	Day	20% 20% 29% 23% 7% 1	420
	11th to 20th	Day	17% 21% 25% 21% 12% 3	420
	21st to end	Day	16% 20% 32% 23% 8% 1	462
April	1st to 10th	Day	17% 20% 28% 22% 12% 1	420
	11th to 20th	Day	13% 23% 32% 22% 8% 3	412
	21st to end	Day	6% 23% 27% 28% 12% 4	420
May	1st to 10th	Day	8% 17% 35% 28% 10% 2	423
	11th to 20th	Day	6% 19% 33% 27% 12% 3	448
	21st to end	Day	5% 14% 31% 32% 15% 3	485
June	1st to 10th	Day	5% 14% 31% 30% 17% 4	450
	11th to 20th	Day	3 12% 31% 36% 15% 3	450
	21st to end	Day	2 7% 30% 37% 20% 5%	450
July	1st to 10th	Day	1 4 27% 45% 21% 3	446
	11th to 20th	Day	1 24% 47% 22% 5%	444
	21st to end	Day	2 22% 46% 22% 8%	487
August	1st to 10th	Day	2 6% 27% 41% 19% 5%	447
	11th to 20th	Day	4 26% 38% 22% 9%	437
	21st to end	Day	1 3 19% 45% 25% 8%	495
September	1st to 10th	Day	1 5% 21% 40% 26% 7%	450
	11th to 20th	Day	2 10% 25% 40% 18% 4	450
	21st to end	Day	2 9% 24% 40% 20% 5%	450
October	1st to 10th	Day	3 10% 29% 31% 23% 4	450
	11th to 20th	Day	6% 11% 19% 33% 27% 4	450
	21st to end	Day	7% 9% 25% 33% 23% 3	495
November	1st to 10th	Day	8% 11% 21% 30% 27% 3	389
	11th to 20th	Day	6% 11% 20% 31% 25% 6%	270
	21st to end	Day	9% 11% 30% 31% 18% 1	212
December	1st to 10th	Day	13% 13% 22% 28% 19% 4	180
	11th to 20th	Day	13% 13% 26% 27% 18% 2	180
	21st to end	Day	19% 14% 31% 21% 14% 2	198
January	1st to 10th	Night	17% 7% 14% 33% 22% 8%	760
	11th to 20th	Night	13% 7% 13% 36% 24% 7%	740
	21st to end	Night	17% 7% 12% 33% 25% 7%	792
February	1st to 10th	Night	15% 8% 11% 36% 25% 5%	720
	11th to 20th	Night	11% 9% 15% 36% 21% 7%	704
	21st to end	Night	14% 9% 17% 38% 19% 3	592
March	1st to 10th	Night	16% 13% 16% 30% 21% 4	720
	11th to 20th	Night	15% 8% 17% 31% 23% 5%	720
	21st to end	Night	13% 9% 21% 34% 20% 3	792
April	1st to 10th	Night	11% 8% 19% 36% 22% 4	720
	11th to 20th	Night	8% 13% 20% 34% 20% 6%	711
	21st to end	Night	6% 8% 21% 34% 24% 7%	720
May	1st to 10th	Night	6% 5% 20% 39% 23% 7%	680
	11th to 20th	Night	4 4 12% 42% 34% 4	444
	21st to end	Night	3 4 17% 43% 29% 4	389
June	1st to 10th	Night	3 5% 17% 43% 29% 4	360
	11th to 20th	Night	1 3 14% 48% 31% 3	360
	21st to end	Night	1 1 13% 46% 36% 4	360
July	1st to 10th	Night	1 9% 45% 40% 5%	350
	11th to 20th	Night	1 3 39% 46% 11%	463
	21st to end	Night	1 5% 37% 46% 11%	591
August	1st to 10th	Night	2 1 8% 38% 42% 9%	537
	11th to 20th	Night	1 7% 41% 42% 8%	668
	21st to end	Night	1 1 6% 36% 46% 10%	792
September	1st to 10th	Night	1 1 7% 37% 44% 10%	720
	11th to 20th	Night	3 1 11% 37% 39% 8%	720
	21st to end	Night	2 2 11% 34% 38% 13%	720
October	1st to 10th	Night	4 3 9% 39% 33% 11%	720
	11th to 20th	Night	6% 4 8% 36% 37% 9%	720
	21st to end	Night	5% 4 11% 35% 29% 15%	792
November	1st to 10th	Night	7% 6% 11% 35% 32% 9%	740
	11th to 20th	Night	8% 4 13% 34% 31% 8%	760
	21st to end	Night	11% 4 12% 38% 27% 8%	760
December	1st to 10th	Night	13% 8% 13% 35% 24% 7%	760
	11th to 20th	Night	18% 7% 13% 36% 21% 6%	760
	21st to end	Night	17% 11% 18% 32% 19% 3	836

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