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 2024-12-24.

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	7% 6% 2 5% 3 3 3 3 5% 7% 56%	105454
	Night	9% 8% 3 7% 4 4 4 3 5% 6% 47%	103422
Transparency	Day	28% 4 8% 19% 23% 18%	105214
	Night	36% 5% 8% 17% 19% 14%	103252
Seeing	Day	10% 11% 29% 32% 14% 3	15533
	Night	12% 6% 14% 36% 27% 5%	24915

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	16% 9% 3 6% 3 4 4 3 5% 8% 38%	2707
	11th to 20th	Day	18% 9% 3 10% 5% 5% 4 3 5% 5% 33%	2860
	21st to end	Day	21% 10% 3 8% 5% 5% 4 3 5% 6% 30%	3146
February	1st to 10th	Day	17% 7% 2 5% 3 3 4 3 5% 6% 45%	1710
	11th to 20th	Day	13% 8% 2 6% 5% 4 3 3 6% 8% 42%	1741
	21st to end	Day	13% 6% 2 6% 4 4 4 3 4 6% 48%	1570
March	1st to 10th	Day	13% 11% 5% 10% 7% 5% 5% 3 6% 6% 29%	3399
	11th to 20th	Day	10% 6% 2 5% 4 3 3 3 5% 7% 53%	3490
	21st to end	Day	12% 8% 3 6% 5% 6% 5% 5% 7% 9% 35%	3876
April	1st to 10th	Day	13% 7% 2 6% 5% 3 3 4 5% 8% 45%	2280
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 6% 55%	2249
	21st to end	Day	6% 4 1 4 3 3 3 3 6% 10% 57%	2280
May	1st to 10th	Day	6% 4 1 3 1 2 2 2 3 5% 72%	3946
	11th to 20th	Day	3 3 1 3 3 2 3 2 4 7% 68%	4156
	21st to end	Day	3 6% 2 4 2 3 3 3 4 6% 65%	4813
June	1st to 10th	Day	5% 6% 2 4 3 3 3 4 6% 8% 58%	2660
	11th to 20th	Day	1 3 1 3 2 2 2 3 5% 8% 69%	2660
	21st to end	Day	3 4 2 4 3 3 3 3 4 6% 66%	2660
July	1st to 10th	Day	1 3 1 3 2 2 2 2 3 5% 77%	4420
	11th to 20th	Day	1 3 2 4 3 3 3 3 5% 7% 67%	4123
	21st to end	Day	6% 2 4 2 3 3 3 5% 8% 64%	4455
August	1st to 10th	Day	2 4 2 7% 5% 3 4 4 7% 10% 52%	4091
	11th to 20th	Day	1 4 2 4 3 2 3 3 5% 7% 67%	3846
	21st to end	Day	2 4 2 4 3 3 3 3 5% 7% 64%	4180
September	1st to 10th	Day	2 3 1 4 2 2 3 2 4 6% 71%	2280
	11th to 20th	Day	4 6% 3 5% 3 3 3 3 6% 8% 57%	2280
	21st to end	Day	3 3 1 3 2 2 2 2 4 6% 71%	2010
October	1st to 10th	Day	2 3 1 3 2 2 3 3 4 6% 70%	3180
	11th to 20th	Day	4 6% 3 4 2 3 3 3 4 6% 61%	3161
	21st to end	Day	6% 5% 2 4 3 3 3 3 6% 7% 58%	3448
November	1st to 10th	Day	8% 6% 1 4 3 3 3 3 5% 9% 56%	1926
	11th to 20th	Day	11% 8% 3 6% 5% 4 3 3 4 8% 47%	1800
	21st to end	Day	12% 6% 2 4 3 3 3 3 6% 6% 53%	1625
December	1st to 10th	Day	13% 8% 2 5% 3 4 4 4 5% 6% 46%	1600
	11th to 20th	Day	25% 10% 3 6% 3 4 4 3 5% 6% 31%	2008
	21st to end	Day	17% 12% 3 7% 4 4 4 3 5% 8% 33%	2818
January	1st to 10th	Night	14% 8% 2 5% 4 3 4 4 4 7% 44%	4240
	11th to 20th	Night	19% 8% 3 7% 6% 5% 5% 4 5% 6% 32%	4110
	21st to end	Night	22% 13% 4 8% 5% 4 4 3 4 6% 30%	4521
February	1st to 10th	Night	16% 7% 2 4 3 3 3 3 5% 6% 47%	2470
	11th to 20th	Night	12% 7% 3 7% 4 3 4 3 5% 8% 43%	2326
	21st to end	Night	12% 6% 2 5% 4 3 3 3 5% 7% 50%	1884
March	1st to 10th	Night	16% 12% 3 8% 5% 5% 4 3 5% 6% 33%	3471
	11th to 20th	Night	13% 6% 3 5% 3 3 3 3 5% 6% 51%	3490
	21st to end	Night	14% 13% 3 7% 4 4 4 3 4 6% 38%	3777
April	1st to 10th	Night	9% 8% 3 7% 4 3 2 4 5% 7% 47%	1900
	11th to 20th	Night	10% 8% 2 4 3 2 3 3 4 7% 54%	1879
	21st to end	Night	5% 5% 2 4 3 4 3 3 5% 8% 57%	1900
May	1st to 10th	Night	5% 5% 2 4 2 2 2 2 3 5% 68%	3024
	11th to 20th	Night	2 7% 5% 11% 4 4 3 4 6% 6% 49%	2743
	21st to end	Night	3 8% 4 5% 3 2 3 4 4 4 59%	2762
June	1st to 10th	Night	5% 8% 3 6% 4 3 4 5% 6% 8% 49%	1520
	11th to 20th	Night	1 5% 2 6% 3 3 3 3 4 8% 62%	1520
	21st to end	Night	2 8% 4 8% 4 3 4 3 3 6% 56%	1520
July	1st to 10th	Night	1 5% 4 5% 3 3 3 2 5% 6% 65%	2540
	11th to 20th	Night	1 6% 5% 9% 4 4 4 3 7% 8% 49%	2843
	21st to end	Night	1 19% 7% 9% 5% 4 5% 4 6% 6% 35%	3109
August	1st to 10th	Night	3 10% 9% 23% 6% 5% 4 4 5% 7% 25%	2848
	11th to 20th	Night	1 9% 5% 6% 3 5% 5% 4 5% 7% 50%	2997
	21st to end	Night	2 8% 4 11% 5% 4 4 3 5% 7% 47%	3498
September	1st to 10th	Night	1 4 2 7% 4 4 3 4 5% 8% 58%	1900
	11th to 20th	Night	5% 10% 5% 8% 3 3 4 4 4 7% 47%	1900
	21st to end	Night	3 4 2 5% 4 3 3 2 4 7% 63%	2166
October	1st to 10th	Night	3 3 2 4 2 2 3 3 5% 6% 67%	3800
	11th to 20th	Night	4 12% 4 6% 3 4 3 3 4 4 51%	3777
	21st to end	Night	8% 4 2 4 4 4 5% 3 5% 5% 57%	4121
November	1st to 10th	Night	8% 6% 2 5% 4 3 4 2 5% 8% 53%	2370
	11th to 20th	Night	10% 8% 2 5% 3 3 4 3 5% 8% 50%	2600
	21st to end	Night	11% 5% 1 4 4 3 4 3 5% 7% 54%	2770
December	1st to 10th	Night	15% 7% 2 6% 3 3 3 3 5% 6% 47%	2800
	11th to 20th	Night	28% 9% 3 5% 3 3 3 4 5% 6% 31%	3416
	21st to end	Night	18% 8% 3 7% 4 4 5% 4 6% 6% 34%	4910

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	44% 7% 12% 27% 8% 3	2707
	11th to 20th	Day	54% 5% 11% 13% 10% 7%	2860
	21st to end	Day	55% 6% 9% 15% 12% 4	3146
February	1st to 10th	Day	39% 5% 8% 19% 21% 8%	1710
	11th to 20th	Day	40% 5% 9% 19% 21% 6%	1750
	21st to end	Day	37% 5% 8% 24% 19% 7%	1570
March	1st to 10th	Day	54% 6% 10% 16% 13% 3	3399
	11th to 20th	Day	31% 4 13% 28% 13% 11%	3490
	21st to end	Day	41% 10% 15% 21% 11% 2	3876
April	1st to 10th	Day	38% 5% 13% 20% 19% 4	2280
	11th to 20th	Day	30% 5% 15% 23% 21% 6%	2252
	21st to end	Day	24% 4 13% 30% 25% 4	2280
May	1st to 10th	Day	18% 3 10% 30% 23% 16%	3946
	11th to 20th	Day	17% 3 6% 27% 35% 12%	4159
	21st to end	Day	20% 5% 9% 29% 32% 3	4814
June	1st to 10th	Day	26% 5% 10% 27% 25% 8%	2660
	11th to 20th	Day	15% 3 9% 22% 35% 16%	2660
	21st to end	Day	20% 2 3 14% 30% 30%	2660
July	1st to 10th	Day	12% 1 2 6% 15% 63%	4351
	11th to 20th	Day	16% 3 4 9% 15% 53%	4053
	21st to end	Day	16% 4 3 10% 28% 38%	4315
August	1st to 10th	Day	22% 6% 4 12% 27% 29%	4076
	11th to 20th	Day	15% 3 4 11% 40% 27%	3885
	21st to end	Day	18% 4 4 14% 33% 27%	4179
September	1st to 10th	Day	15% 3 2 11% 30% 39%	2280
	11th to 20th	Day	26% 3 5% 22% 28% 15%	2280
	21st to end	Day	15% 3 5% 22% 33% 23%	2010
October	1st to 10th	Day	16% 2 4 12% 27% 38%	3180
	11th to 20th	Day	23% 4 7% 21% 26% 19%	3161
	21st to end	Day	24% 4 8% 22% 27% 14%	3448
November	1st to 10th	Day	27% 5% 10% 27% 20% 12%	1926
	11th to 20th	Day	37% 4 9% 23% 20% 7%	1800
	21st to end	Day	32% 4 10% 19% 25% 11%	1625
December	1st to 10th	Day	38% 5% 9% 20% 19% 8%	1600
	11th to 20th	Day	54% 4 8% 13% 16% 4	2008
	21st to end	Day	49% 6% 12% 20% 11% 3	2818
January	1st to 10th	Night	40% 6% 19% 23% 9% 3	4240
	11th to 20th	Night	54% 5% 13% 12% 9% 7%	4110
	21st to end	Night	58% 3 9% 12% 11% 6%	4521
February	1st to 10th	Night	38% 4 9% 19% 19% 11%	2470
	11th to 20th	Night	40% 5% 9% 18% 20% 8%	2328
	21st to end	Night	34% 5% 11% 28% 18% 5%	1884
March	1st to 10th	Night	50% 9% 11% 14% 14% 3	3471
	11th to 20th	Night	34% 6% 9% 23% 18% 11%	3490
	21st to end	Night	47% 7% 12% 20% 10% 3	3777
April	1st to 10th	Night	37% 5% 13% 21% 19% 5%	1900
	11th to 20th	Night	32% 5% 11% 25% 19% 8%	1879
	21st to end	Night	25% 5% 12% 30% 22% 6%	1900
May	1st to 10th	Night	21% 4 8% 27% 26% 13%	3024
	11th to 20th	Night	32% 9% 5% 17% 24% 13%	2744
	21st to end	Night	24% 11% 7% 28% 28% 2	2762
June	1st to 10th	Night	30% 7% 8% 21% 26% 7%	1520
	11th to 20th	Night	22% 4 6% 20% 33% 15%	1520
	21st to end	Night	28% 5% 3 13% 26% 27%	1520
July	1st to 10th	Night	20% 3 1 7% 15% 54%	2500
	11th to 20th	Night	29% 4 4 11% 11% 42%	2790
	21st to end	Night	43% 3 4 9% 15% 26%	3011
August	1st to 10th	Night	51% 8% 4 8% 16% 13%	2839
	11th to 20th	Night	28% 3 4 10% 34% 20%	3024
	21st to end	Night	31% 7% 5% 11% 27% 21%	3498
September	1st to 10th	Night	22% 7% 2 7% 27% 35%	1900
	11th to 20th	Night	35% 6% 4 19% 22% 15%	1900
	21st to end	Night	21% 4 4 20% 28% 23%	2166
October	1st to 10th	Night	18% 3 5% 11% 21% 42%	3800
	11th to 20th	Night	32% 6% 6% 16% 17% 22%	3777
	21st to end	Night	27% 5% 5% 20% 24% 19%	4121
November	1st to 10th	Night	31% 5% 8% 26% 17% 13%	2370
	11th to 20th	Night	33% 4 10% 26% 19% 8%	2600
	21st to end	Night	30% 5% 9% 21% 23% 13%	2770
December	1st to 10th	Night	39% 5% 9% 18% 18% 11%	2800
	11th to 20th	Night	54% 4 9% 14% 16% 3	3416
	21st to end	Night	49% 6% 14% 16% 11% 4	4910

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% 24% 30% 13% 1	370
	21st to end	Day	17% 9% 28% 28% 16% 2	407
February	1st to 10th	Day	20% 11% 23% 27% 16% 2	370
	11th to 20th	Day	21% 17% 27% 24% 9% 1	401
	21st to end	Day	15% 15% 29% 28% 12% 1	382
March	1st to 10th	Day	23% 18% 29% 20% 8% 2	460
	11th to 20th	Day	19% 17% 27% 22% 12% 3	460
	21st to end	Day	17% 20% 32% 23% 8% 1	506
April	1st to 10th	Day	17% 17% 32% 21% 9% 3	460
	11th to 20th	Day	16% 18% 32% 23% 7% 4	452
	21st to end	Day	8% 22% 30% 26% 9% 5%	460
May	1st to 10th	Day	12% 16% 35% 27% 9% 1	463
	11th to 20th	Day	10% 16% 33% 28% 11% 1	488
	21st to end	Day	10% 15% 32% 29% 11% 2	529
June	1st to 10th	Day	9% 9% 34% 33% 12% 3	490
	11th to 20th	Day	4 12% 37% 37% 8% 2	490
	21st to end	Day	3 8% 36% 39% 12% 2	490
July	1st to 10th	Day	4 5% 31% 43% 15% 1	486
	11th to 20th	Day	1 2 28% 50% 16% 3	484
	21st to end	Day	2 3 30% 47% 15% 5%	531
August	1st to 10th	Day	3 6% 30% 44% 13% 3	487
	11th to 20th	Day	2 6% 31% 40% 15% 6%	477
	21st to end	Day	3 3 27% 43% 19% 5%	539
September	1st to 10th	Day	3 5% 23% 42% 19% 7%	490
	11th to 20th	Day	5% 13% 27% 35% 15% 5%	490
	21st to end	Day	3 9% 25% 34% 24% 4	490
October	1st to 10th	Day	5% 8% 28% 31% 19% 9%	490
	11th to 20th	Day	8% 9% 23% 32% 21% 7%	490
	21st to end	Day	10% 8% 26% 29% 21% 6%	539
November	1st to 10th	Day	10% 12% 21% 26% 25% 6%	462
	11th to 20th	Day	10% 10% 20% 34% 20% 6%	300
	21st to end	Day	15% 9% 26% 31% 17% 1	213
December	1st to 10th	Day	16% 12% 22% 29% 18% 4	200
	11th to 20th	Day	18% 13% 24% 26% 19% 1	200
	21st to end	Day	22% 13% 29% 22% 13% 1	204
January	1st to 10th	Night	20% 6% 14% 32% 22% 6%	760
	11th to 20th	Night	16% 7% 14% 36% 23% 5%	760
	21st to end	Night	20% 5% 13% 35% 23% 4	836
February	1st to 10th	Night	20% 6% 12% 35% 23% 4	760
	11th to 20th	Night	15% 10% 16% 35% 19% 5%	744
	21st to end	Night	15% 9% 19% 34% 20% 3	628
March	1st to 10th	Night	21% 9% 17% 29% 21% 3	760
	11th to 20th	Night	19% 8% 14% 33% 23% 3	760
	21st to end	Night	17% 10% 20% 35% 17% 2	836
April	1st to 10th	Night	13% 9% 21% 37% 18% 2	760
	11th to 20th	Night	15% 10% 19% 33% 20% 3	751
	21st to end	Night	8% 8% 23% 36% 21% 5%	760
May	1st to 10th	Night	9% 5% 19% 41% 22% 4	669
	11th to 20th	Night	8% 5% 14% 41% 27% 5%	510
	21st to end	Night	13% 9% 17% 37% 20% 4	411
June	1st to 10th	Night	8% 6% 17% 44% 23% 3	380
	11th to 20th	Night	3 3 17% 54% 21% 2	380
	21st to end	Night	6% 3 14% 41% 34% 2	380
July	1st to 10th	Night	4 3 11% 43% 38% 2	370
	11th to 20th	Night	4 1 11% 41% 34% 9%	536
	21st to end	Night	4 4 11% 35% 39% 7%	624
August	1st to 10th	Night	11% 3 11% 36% 32% 5%	567
	11th to 20th	Night	5% 4 12% 39% 34% 6%	671
	21st to end	Night	6% 1 12% 40% 34% 7%	836
September	1st to 10th	Night	2 2 9% 37% 40% 9%	760
	11th to 20th	Night	8% 4 14% 36% 32% 6%	760
	21st to end	Night	4 4 10% 35% 37% 10%	760
October	1st to 10th	Night	8% 3 11% 36% 34% 8%	760
	11th to 20th	Night	9% 6% 10% 32% 35% 8%	760
	21st to end	Night	10% 5% 11% 32% 31% 11%	836
November	1st to 10th	Night	9% 5% 14% 31% 32% 9%	780
	11th to 20th	Night	12% 5% 13% 35% 28% 7%	800
	21st to end	Night	13% 5% 12% 37% 26% 6%	800
December	1st to 10th	Night	17% 5% 14% 37% 22% 6%	800
	11th to 20th	Night	25% 6% 12% 34% 21% 3	800
	21st to end	Night	21% 10% 19% 30% 19% 2	850

Page generated at 2024-12-21 01:13:53. Version ac07

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