Oakland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakland 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	8% 6% 2 4 4 2 3 4 5% 7% 55%	74720
	Night	10% 7% 3 5% 4 3 4 4 5% 7% 47%	75102
Transparency	Day	30% 4 8% 20% 23% 15%	74440
	Night	36% 5% 8% 18% 20% 13%	74904
Seeing	Day	10% 11% 29% 32% 14% 4	14272
	Night	12% 6% 14% 36% 27% 6%	23700

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	19% 8% 4 6% 4 3 4 4 5% 9% 34%	1622
	11th to 20th	Day	14% 4 2 6% 5% 3 4 4 4 6% 47%	1669
	21st to end	Day	14% 7% 2 6% 5% 3 4 5% 5% 6% 42%	1782
February	1st to 10th	Day	17% 7% 2 4 4 3 3 4 5% 6% 46%	1620
	11th to 20th	Day	13% 8% 2 5% 5% 3 4 4 6% 8% 44%	1647
	21st to end	Day	14% 6% 3 5% 4 3 4 4 4 6% 49%	1480
March	1st to 10th	Day	15% 8% 3 6% 5% 2 5% 4 6% 8% 38%	1948
	11th to 20th	Day	15% 8% 3 6% 6% 3 4 5% 6% 7% 38%	1980
	21st to end	Day	12% 5% 2 4 5% 4 4 5% 5% 9% 44%	2204
April	1st to 10th	Day	13% 6% 3 5% 5% 3 3 4 5% 8% 44%	2160
	11th to 20th	Day	9% 5% 2 4 3 2 4 4 5% 6% 56%	2129
	21st to end	Day	6% 4 1 3 4 3 3 3 6% 10% 57%	2160
May	1st to 10th	Day	5% 6% 2 4 3 2 3 4 5% 7% 60%	2241
	11th to 20th	Day	6% 5% 2 4 3 2 4 3 5% 8% 59%	2347
	21st to end	Day	6% 7% 3 5% 4 2 3 4 5% 7% 55%	2723
June	1st to 10th	Day	5% 6% 2 4 3 2 4 5% 5% 8% 57%	2520
	11th to 20th	Day	1 3 2 3 2 1 3 3 5% 8% 69%	2520
	21st to end	Day	3 4 2 4 3 2 3 4 4 6% 66%	2520
July	1st to 10th	Day	1 5% 2 3 3 2 3 3 5% 7% 65%	2520
	11th to 20th	Day	1 4 3 4 3 2 4 5% 6% 8% 62%	2353
	21st to end	Day	1 4 2 3 3 2 3 4 4 8% 66%	2546
August	1st to 10th	Day	2 6% 3 4 4 2 3 4 5% 9% 58%	2328
	11th to 20th	Day	1 4 2 4 3 2 4 3 5% 7% 66%	2196
	21st to end	Day	2 5% 2 3 3 2 3 3 5% 7% 65%	2376
September	1st to 10th	Day	2 3 2 3 3 2 2 3 4 6% 71%	2160
	11th to 20th	Day	4 5% 3 4 4 2 3 4 6% 8% 58%	2160
	21st to end	Day	3 3 1 3 3 1 2 3 4 6% 71%	1905
October	1st to 10th	Day	4 3 1 3 3 2 3 3 3 5% 68%	1800
	11th to 20th	Day	6% 4 2 4 3 3 3 4 4 6% 61%	1800
	21st to end	Day	8% 5% 2 3 3 2 4 3 4 7% 60%	1980
November	1st to 10th	Day	8% 5% 2 4 3 2 4 4 5% 9% 54%	1828
	11th to 20th	Day	11% 7% 3 5% 5% 3 4 4 4 8% 48%	1710
	21st to end	Day	11% 5% 2 4 4 2 3 4 5% 6% 54%	1544
December	1st to 10th	Day	14% 7% 3 4 4 3 4 5% 5% 6% 45%	1520
	11th to 20th	Day	25% 9% 3 5% 4 3 3 4 5% 6% 32%	1928
	21st to end	Day	17% 11% 3 6% 5% 3 5% 4 5% 8% 34%	2794
January	1st to 10th	Night	17% 8% 2 5% 4 2 5% 5% 5% 8% 38%	2540
	11th to 20th	Night	13% 6% 3 6% 5% 3 4 4 5% 7% 43%	2418
	21st to end	Night	16% 7% 3 5% 4 3 4 4 4 7% 44%	2574
February	1st to 10th	Night	16% 7% 2 4 4 2 4 3 4 6% 49%	2340
	11th to 20th	Night	12% 6% 3 6% 4 3 4 4 5% 8% 44%	2200
	21st to end	Night	13% 5% 2 4 4 3 3 4 5% 7% 50%	1776
March	1st to 10th	Night	19% 8% 3 5% 4 3 4 4 4 6% 39%	2008
	11th to 20th	Night	17% 7% 3 5% 4 3 4 4 6% 8% 40%	1980
	21st to end	Night	14% 8% 3 4 4 2 3 3 3 6% 49%	2152
April	1st to 10th	Night	10% 7% 4 6% 4 3 3 4 6% 7% 47%	1800
	11th to 20th	Night	11% 7% 2 3 3 2 3 3 4 7% 55%	1779
	21st to end	Night	6% 4 2 4 3 2 4 4 5% 8% 57%	1800
May	1st to 10th	Night	5% 8% 3 6% 4 2 3 3 5% 6% 55%	1714
	11th to 20th	Night	4 8% 4 7% 4 3 4 4 5% 8% 49%	1545
	21st to end	Night	6% 12% 4 5% 5% 2 3 3 4 6% 49%	1552
June	1st to 10th	Night	5% 7% 3 5% 5% 3 3 6% 5% 8% 49%	1440
	11th to 20th	Night	2 5% 2 5% 4 2 3 4 4 8% 61%	1440
	21st to end	Night	3 8% 4 7% 5% 2 4 4 3 6% 56%	1440
July	1st to 10th	Night	1 8% 5% 5% 5% 3 4 4 4 9% 53%	1440
	11th to 20th	Night	2 6% 4 7% 5% 3 5% 5% 7% 11% 44%	1603
	21st to end	Night	2 10% 6% 10% 8% 3 7% 5% 6% 7% 35%	1773
August	1st to 10th	Night	3 14% 6% 9% 6% 3 4 6% 5% 9% 35%	1611
	11th to 20th	Night	1 9% 4 8% 5% 4 7% 6% 6% 10% 41%	1703
	21st to end	Night	2 10% 5% 8% 6% 3 4 5% 5% 9% 44%	1980
September	1st to 10th	Night	1 4 3 6% 6% 2 3 5% 5% 8% 58%	1800
	11th to 20th	Night	5% 9% 5% 7% 4 3 4 5% 4 7% 48%	1800
	21st to end	Night	3 4 2 4 4 2 3 3 4 7% 64%	2051
October	1st to 10th	Night	5% 5% 3 4 4 2 3 4 4 5% 61%	2160
	11th to 20th	Night	7% 6% 3 5% 4 3 3 3 4 6% 56%	2160
	21st to end	Night	7% 5% 2 5% 4 2 4 4 4 6% 56%	2376
November	1st to 10th	Night	9% 6% 2 5% 4 2 4 3 4 8% 53%	2248
	11th to 20th	Night	10% 7% 3 4 4 2 4 4 5% 7% 50%	2470
	21st to end	Night	10% 4 1 4 4 3 4 3 4 7% 56%	2631
December	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 4 6% 47%	2660
	11th to 20th	Night	29% 8% 3 4 3 3 3 4 4 6% 32%	3276
	21st to end	Night	18% 8% 3 6% 6% 3 5% 5% 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	47% 7% 12% 19% 10% 5%	1622
	11th to 20th	Day	40% 4 11% 16% 17% 12%	1669
	21st to end	Day	42% 6% 10% 14% 21% 7%	1782
February	1st to 10th	Day	39% 4 8% 19% 21% 8%	1620
	11th to 20th	Day	39% 5% 9% 19% 22% 6%	1656
	21st to end	Day	37% 5% 8% 24% 20% 7%	1480
March	1st to 10th	Day	44% 5% 11% 20% 15% 4	1948
	11th to 20th	Day	45% 5% 9% 21% 15% 4	1980
	21st to end	Day	37% 8% 12% 21% 18% 4	2204
April	1st to 10th	Day	40% 5% 14% 18% 19% 4	2160
	11th to 20th	Day	30% 5% 14% 24% 21% 6%	2132
	21st to end	Day	25% 4 13% 29% 25% 4	2160
May	1st to 10th	Day	25% 4 10% 27% 28% 7%	2241
	11th to 20th	Day	25% 4 9% 31% 23% 8%	2350
	21st to end	Day	29% 4 14% 26% 23% 4	2724
June	1st to 10th	Day	26% 5% 9% 26% 24% 9%	2520
	11th to 20th	Day	15% 3 9% 22% 34% 16%	2520
	21st to end	Day	21% 2 4 14% 31% 28%	2520
July	1st to 10th	Day	20% 2 3 11% 26% 39%	2451
	11th to 20th	Day	21% 3 5% 13% 22% 36%	2283
	21st to end	Day	18% 2 3 13% 28% 37%	2405
August	1st to 10th	Day	25% 3 4 14% 29% 25%	2312
	11th to 20th	Day	19% 1 3 14% 31% 31%	2196
	21st to end	Day	21% 1 3 17% 32% 26%	2376
September	1st to 10th	Day	16% 2 2 11% 30% 39%	2160
	11th to 20th	Day	26% 3 5% 23% 28% 16%	2160
	21st to end	Day	16% 3 5% 22% 32% 23%	1905
October	1st to 10th	Day	21% 2 6% 17% 30% 23%	1800
	11th to 20th	Day	25% 3 8% 19% 22% 23%	1800
	21st to end	Day	26% 3 9% 20% 23% 19%	1980
November	1st to 10th	Day	28% 5% 10% 26% 19% 12%	1828
	11th to 20th	Day	37% 4 9% 22% 21% 7%	1710
	21st to end	Day	31% 4 10% 19% 25% 11%	1544
December	1st to 10th	Day	40% 5% 10% 19% 18% 9%	1520
	11th to 20th	Day	55% 4 8% 13% 15% 4	1928
	21st to end	Day	48% 6% 12% 20% 11% 3	2794
January	1st to 10th	Night	43% 6% 13% 21% 12% 6%	2540
	11th to 20th	Night	40% 5% 12% 16% 14% 13%	2418
	21st to end	Night	42% 4 10% 14% 19% 11%	2574
February	1st to 10th	Night	38% 3 9% 19% 20% 11%	2340
	11th to 20th	Night	38% 5% 9% 18% 21% 9%	2202
	21st to end	Night	34% 5% 10% 27% 19% 5%	1776
March	1st to 10th	Night	45% 6% 10% 18% 16% 5%	2008
	11th to 20th	Night	43% 4 7% 22% 18% 6%	1980
	21st to end	Night	39% 5% 12% 22% 18% 5%	2152
April	1st to 10th	Night	38% 4 13% 20% 19% 5%	1800
	11th to 20th	Night	31% 5% 12% 24% 19% 8%	1779
	21st to end	Night	25% 5% 12% 30% 21% 7%	1800
May	1st to 10th	Night	30% 5% 6% 25% 24% 10%	1714
	11th to 20th	Night	34% 5% 7% 24% 23% 7%	1546
	21st to end	Night	37% 6% 11% 22% 21% 4	1552
June	1st to 10th	Night	31% 7% 8% 20% 26% 7%	1440
	11th to 20th	Night	23% 4 7% 19% 32% 16%	1440
	21st to end	Night	29% 5% 3 13% 26% 25%	1440
July	1st to 10th	Night	29% 4 1 7% 25% 34%	1400
	11th to 20th	Night	30% 5% 5% 13% 17% 31%	1550
	21st to end	Night	43% 3 3 9% 16% 26%	1674
August	1st to 10th	Night	44% 5% 3 9% 21% 18%	1602
	11th to 20th	Night	35% 4 3 11% 23% 25%	1703
	21st to end	Night	35% 5% 2 11% 24% 22%	1980
September	1st to 10th	Night	22% 6% 2 7% 27% 35%	1800
	11th to 20th	Night	34% 7% 3 19% 22% 15%	1800
	21st to end	Night	21% 3 4 21% 29% 23%	2051
October	1st to 10th	Night	24% 4 7% 17% 24% 24%	2160
	11th to 20th	Night	30% 3 6% 18% 19% 24%	2160
	21st to end	Night	30% 4 5% 20% 21% 20%	2376
November	1st to 10th	Night	31% 5% 8% 26% 16% 14%	2248
	11th to 20th	Night	33% 4 9% 25% 19% 8%	2470
	21st to end	Night	29% 4 9% 21% 24% 13%	2631
December	1st to 10th	Night	39% 5% 9% 18% 17% 12%	2660
	11th to 20th	Night	54% 4 9% 14% 16% 4	3276
	21st to end	Night	48% 6% 14% 17% 11% 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	26% 12% 28% 20% 13% 1	283
	11th to 20th	Day	19% 12% 23% 31% 14% 1	357
	21st to end	Day	16% 9% 28% 29% 16% 2	374
February	1st to 10th	Day	20% 10% 23% 27% 17% 2	340
	11th to 20th	Day	20% 17% 28% 25% 10% 1	367
	21st to end	Day	15% 15% 29% 28% 13% 1	346
March	1st to 10th	Day	22% 16% 30% 21% 8% 2	420
	11th to 20th	Day	19% 17% 28% 21% 11% 4	420
	21st to end	Day	16% 19% 32% 24% 8% 1	462
April	1st to 10th	Day	18% 18% 32% 21% 9% 2	420
	11th to 20th	Day	16% 18% 33% 23% 6% 3	412
	21st to end	Day	7% 23% 30% 26% 10% 5%	420
May	1st to 10th	Day	12% 16% 35% 27% 9% 1	423
	11th to 20th	Day	11% 17% 34% 26% 10% 1	448
	21st to end	Day	10% 15% 33% 29% 11% 3	485
June	1st to 10th	Day	9% 10% 33% 33% 12% 3	450
	11th to 20th	Day	4 13% 36% 37% 8% 2	450
	21st to end	Day	3 9% 34% 40% 12% 3	450
July	1st to 10th	Day	4 5% 33% 42% 14% 1	446
	11th to 20th	Day	1 2 27% 51% 16% 3	444
	21st to end	Day	2 1 29% 48% 15% 5%	487
August	1st to 10th	Day	4 6% 30% 44% 13% 4	447
	11th to 20th	Day	2 4 29% 43% 16% 6%	437
	21st to end	Day	3 3 27% 44% 19% 4	495
September	1st to 10th	Day	4 4 22% 43% 19% 8%	450
	11th to 20th	Day	5% 11% 27% 37% 15% 6%	450
	21st to end	Day	4 9% 25% 33% 24% 4	450
October	1st to 10th	Day	5% 9% 29% 30% 18% 9%	450
	11th to 20th	Day	8% 9% 22% 33% 22% 7%	450
	21st to end	Day	11% 7% 25% 29% 21% 6%	495
November	1st to 10th	Day	11% 11% 21% 26% 26% 5%	424
	11th to 20th	Day	8% 10% 18% 35% 22% 7%	270
	21st to end	Day	13% 7% 27% 33% 19% 2	192
December	1st to 10th	Day	18% 13% 23% 27% 16% 4	180
	11th to 20th	Day	17% 13% 25% 24% 19% 1	180
	21st to end	Day	21% 12% 30% 22% 14% 1	198
January	1st to 10th	Night	20% 6% 14% 32% 22% 6%	760
	11th to 20th	Night	15% 7% 14% 36% 24% 5%	744
	21st to end	Night	19% 5% 13% 35% 24% 4	792
February	1st to 10th	Night	19% 6% 12% 35% 24% 4	720
	11th to 20th	Night	13% 10% 17% 35% 20% 5%	704
	21st to end	Night	16% 9% 19% 33% 21% 3	592
March	1st to 10th	Night	21% 8% 18% 29% 22% 3	720
	11th to 20th	Night	18% 8% 14% 33% 23% 3	720
	21st to end	Night	17% 10% 19% 35% 18% 2	792
April	1st to 10th	Night	13% 9% 20% 38% 18% 2	720
	11th to 20th	Night	15% 11% 20% 31% 20% 3	711
	21st to end	Night	8% 8% 23% 35% 21% 5%	720
May	1st to 10th	Night	9% 5% 19% 41% 22% 4	634
	11th to 20th	Night	9% 5% 13% 40% 28% 5%	483
	21st to end	Night	14% 9% 17% 37% 20% 4	389
June	1st to 10th	Night	8% 6% 16% 44% 23% 3	360
	11th to 20th	Night	3 3 17% 53% 23% 2	360
	21st to end	Night	6% 3 14% 40% 34% 3	360
July	1st to 10th	Night	4 3 11% 43% 37% 2	350
	11th to 20th	Night	5% 11% 41% 35% 9%	506
	21st to end	Night	5% 3 9% 36% 39% 8%	591
August	1st to 10th	Night	12% 4 12% 34% 33% 5%	537
	11th to 20th	Night	5% 3 11% 39% 35% 6%	635
	21st to end	Night	6% 1 11% 40% 35% 7%	792
September	1st to 10th	Night	3 2 9% 37% 40% 10%	720
	11th to 20th	Night	8% 3 12% 37% 33% 6%	720
	21st to end	Night	5% 3 9% 35% 37% 11%	720
October	1st to 10th	Night	9% 3 11% 36% 33% 8%	720
	11th to 20th	Night	9% 6% 9% 32% 36% 8%	720
	21st to end	Night	10% 5% 10% 31% 32% 12%	792
November	1st to 10th	Night	10% 4 13% 32% 32% 9%	740
	11th to 20th	Night	12% 4 12% 34% 30% 8%	760
	21st to end	Night	12% 6% 12% 38% 27% 6%	760
December	1st to 10th	Night	18% 5% 14% 36% 21% 6%	760
	11th to 20th	Night	25% 6% 12% 33% 21% 4	760
	21st to end	Night	20% 10% 19% 31% 19% 2	836

Page generated at 2024-01-13 16:28:34. Version ac07

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