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 2024-11-25.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	101524
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 42%	97949
Transparency	Day	43% 4 12% 23% 16% 2	105056
	Night	42% 4 12% 24% 16% 2	102506
Seeing	Day	22% 14% 30% 21% 10% 3	15028
	Night	21% 11% 31% 28% 9% 1	24184

By Month

Percentage Cloud Cover NE (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% 6% 2 5% 3 4 4 3 5% 6% 47%	2517
	11th to 20th	Day	16% 8% 3 7% 6% 7% 5% 3 5% 6% 35%	2520
	21st to end	Day	22% 12% 4 8% 4 3 4 3 4 5% 32%	3025
February	1st to 10th	Day	17% 8% 3 7% 4 4 4 4 5% 7% 37%	1710
	11th to 20th	Day	14% 8% 2 6% 4 3 4 4 4 6% 43%	1838
	21st to end	Day	20% 9% 2 5% 4 5% 5% 3 5% 5% 37%	1570
March	1st to 10th	Day	26% 7% 3 6% 4 4 4 2 4 5% 35%	3116
	11th to 20th	Day	10% 4 2 6% 6% 5% 5% 4 7% 8% 43%	3352
	21st to end	Day	21% 8% 2 6% 3 3 3 3 4 5% 43%	4124
April	1st to 10th	Day	18% 9% 2 6% 4 4 4 3 5% 6% 39%	2280
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 3 5% 6% 41%	2254
	21st to end	Day	19% 7% 2 6% 4 4 4 3 6% 6% 39%	2294
May	1st to 10th	Day	29% 8% 2 5% 4 3 4 3 5% 6% 30%	4123
	11th to 20th	Day	24% 8% 2 8% 5% 4 4 3 6% 6% 30%	4398
	21st to end	Day	14% 5% 2 5% 3 4 5% 3 6% 9% 44%	4837
June	1st to 10th	Day	16% 6% 2 6% 5% 5% 5% 5% 7% 9% 35%	2660
	11th to 20th	Day	16% 6% 3 6% 5% 5% 6% 4 6% 9% 35%	2660
	21st to end	Day	12% 5% 3 7% 5% 5% 5% 5% 6% 9% 39%	2660
July	1st to 10th	Day	10% 7% 2 8% 6% 5% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	11% 6% 3 6% 4 5% 6% 5% 8% 10% 38%	4440
	21st to end	Day	15% 7% 3 8% 6% 6% 5% 4 6% 7% 32%	4814
August	1st to 10th	Day	21% 5% 3 7% 5% 5% 5% 4 6% 7% 31%	4184
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 4 6% 8% 42%	3730
	21st to end	Day	12% 6% 2 5% 3 4 4 3 5% 8% 48%	4180
September	1st to 10th	Day	15% 5% 2 6% 5% 4 5% 4 5% 6% 43%	2280
	11th to 20th	Day	13% 6% 2 4 3 4 4 3 4 7% 50%	2208
	21st to end	Day	19% 5% 3 7% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Day	20% 6% 2 5% 4 4 3 3 5% 6% 42%	1967
	11th to 20th	Day	15% 5% 1 5% 3 4 4 4 5% 6% 47%	1900
	21st to end	Day	21% 5% 2 4 3 3 4 4 4 7% 42%	1947
November	1st to 10th	Day	14% 6% 3 5% 2 3 3 3 4 6% 53%	1761
	11th to 20th	Day	18% 6% 2 3 3 3 3 3 5% 7% 47%	1800
	21st to end	Day	17% 6% 2 4 3 3 4 5% 5% 7% 44%	1647
December	1st to 10th	Day	20% 8% 2 6% 4 4 3 3 6% 6% 38%	1520
	11th to 20th	Day	22% 5% 2 4 3 3 3 3 5% 7% 44%	1906
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 4 5% 6% 47%	4429
	11th to 20th	Night	15% 8% 3 8% 4 3 4 3 4 6% 41%	4440
	21st to end	Night	24% 11% 2 5% 3 3 3 3 5% 6% 35%	4628
February	1st to 10th	Night	17% 9% 2 5% 4 3 4 3 5% 6% 42%	2470
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 6% 5% 42%	2226
	21st to end	Night	19% 7% 3 6% 4 4 3 3 4 5% 42%	1884
March	1st to 10th	Night	24% 9% 2 6% 4 4 3 2 4 6% 37%	3724
	11th to 20th	Night	11% 7% 2 5% 4 4 4 3 5% 7% 48%	3589
	21st to end	Night	18% 10% 3 6% 3 3 3 3 4 5% 43%	3508
April	1st to 10th	Night	18% 9% 2 5% 4 4 4 4 4 7% 38%	1900
	11th to 20th	Night	19% 6% 2 6% 3 4 4 3 5% 7% 40%	1875
	21st to end	Night	20% 7% 1 6% 3 4 3 3 5% 6% 42%	1883
May	1st to 10th	Night	26% 9% 4 7% 4 3 3 3 4 6% 29%	2834
	11th to 20th	Night	25% 8% 3 7% 4 4 4 3 4 5% 34%	2507
	21st to end	Night	16% 6% 2 6% 4 3 4 3 5% 9% 42%	2738
June	1st to 10th	Night	17% 5% 2 4 4 4 4 4 5% 8% 43%	1520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 5% 6% 10% 40%	1520
	21st to end	Night	12% 4 2 6% 5% 4 4 4 6% 9% 44%	1520
July	1st to 10th	Night	10% 5% 2 6% 5% 5% 6% 5% 6% 9% 41%	2520
	11th to 20th	Night	13% 5% 2 6% 4 4 5% 5% 7% 10% 38%	2520
	21st to end	Night	18% 7% 2 5% 4 3 4 4 7% 8% 38%	2739
August	1st to 10th	Night	22% 5% 2 7% 4 5% 5% 3 5% 8% 33%	2708
	11th to 20th	Night	14% 7% 2 7% 5% 5% 5% 4 5% 6% 39%	3097
	21st to end	Night	11% 5% 2 4 3 3 3 3 5% 7% 53%	3476
September	1st to 10th	Night	15% 6% 2 7% 4 4 3 4 5% 6% 45%	1900
	11th to 20th	Night	14% 5% 2 5% 3 2 3 3 4 7% 52%	1971
	21st to end	Night	19% 6% 2 5% 4 3 3 3 4 6% 45%	2090
October	1st to 10th	Night	20% 8% 2 5% 3 3 3 3 4 6% 42%	2209
	11th to 20th	Night	16% 5% 2 4 3 3 3 2 5% 6% 50%	2280
	21st to end	Night	21% 7% 2 5% 2 2 3 2 4 6% 45%	2650
November	1st to 10th	Night	12% 5% 2 5% 3 3 4 4 5% 6% 51%	2537
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 4 5% 48%	2600
	21st to end	Night	15% 5% 2 6% 4 4 4 4 5% 7% 46%	2625
December	1st to 10th	Night	19% 7% 2 5% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	19% 7% 2 5% 3 4 4 3 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 6% 4 4 4 4 4 6% 36%	4884

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	38% 4 10% 33% 12% 3	2518
	11th to 20th	Day	50% 4 11% 22% 12% 2	2520
	21st to end	Day	55% 3 9% 21% 11% 2	3025
February	1st to 10th	Day	46% 4 13% 22% 13% 2	1710
	11th to 20th	Day	42% 4 10% 25% 16% 3	1847
	21st to end	Day	47% 4 10% 23% 13% 4	1570
March	1st to 10th	Day	53% 3 10% 23% 10% 2	3119
	11th to 20th	Day	37% 4 12% 30% 14% 2	3352
	21st to end	Day	45% 2 7% 17% 24% 5%	4124
April	1st to 10th	Day	46% 3 10% 21% 16% 5%	2280
	11th to 20th	Day	43% 4 11% 22% 17% 4	2254
	21st to end	Day	44% 3 10% 22% 17% 4	2294
May	1st to 10th	Day	54% 4 13% 16% 12% 2	4137
	11th to 20th	Day	54% 4 13% 19% 9% 2	4402
	21st to end	Day	36% 5% 12% 27% 19% 2	4837
June	1st to 10th	Day	42% 6% 14% 21% 15% 1	2660
	11th to 20th	Day	44% 6% 13% 23% 11% 2	2660
	21st to end	Day	40% 6% 14% 23% 16% 1	2660
July	1st to 10th	Day	43% 8% 11% 22% 14% 2	4370
	11th to 20th	Day	39% 6% 16% 23% 14% 1	4365
	21st to end	Day	49% 6% 10% 17% 16% 2	4661
August	1st to 10th	Day	50% 6% 13% 21% 10%	4170
	11th to 20th	Day	38% 4 14% 29% 13% 1	3766
	21st to end	Day	35% 5% 9% 29% 19% 2	4180
September	1st to 10th	Day	41% 6% 9% 22% 19% 3	2280
	11th to 20th	Day	35% 4 11% 23% 25% 3	2208
	21st to end	Day	44% 5% 9% 19% 18% 3	2090
October	1st to 10th	Day	39% 5% 8% 19% 24% 6%	3266
	11th to 20th	Day	27% 3 10% 25% 31% 4	3140
	21st to end	Day	27% 3 14% 25% 26% 4	3185
November	1st to 10th	Day	35% 3 11% 25% 23% 3	1761
	11th to 20th	Day	38% 4 10% 25% 20% 3	1800
	21st to end	Day	40% 3 14% 29% 12% 2	1647
December	1st to 10th	Day	46% 3 15% 21% 13% 1	1520
	11th to 20th	Day	42% 3 16% 24% 12% 2	1906
	21st to end	Day	53% 4 12% 22% 8%	2772
January	1st to 10th	Night	39% 3 13% 30% 12% 4	4429
	11th to 20th	Night	46% 3 12% 24% 13% 2	4440
	21st to end	Night	52% 3 9% 22% 12% 2	4628
February	1st to 10th	Night	44% 4 13% 24% 13% 2	2470
	11th to 20th	Night	44% 4 10% 20% 18% 5%	2228
	21st to end	Night	46% 3 6% 25% 17% 4	1884
March	1st to 10th	Night	51% 3 10% 22% 11% 3	3734
	11th to 20th	Night	37% 3 14% 26% 17% 3	3590
	21st to end	Night	45% 3 7% 17% 22% 7%	3508
April	1st to 10th	Night	46% 4 10% 22% 15% 4	1900
	11th to 20th	Night	44% 5% 9% 21% 20% 2	1875
	21st to end	Night	44% 4 9% 22% 18% 4	1883
May	1st to 10th	Night	55% 6% 10% 17% 10% 1	2840
	11th to 20th	Night	54% 4 15% 15% 11% 2	2508
	21st to end	Night	40% 5% 15% 24% 13% 3	2739
June	1st to 10th	Night	40% 6% 11% 23% 20% 2	1520
	11th to 20th	Night	39% 6% 16% 27% 12% 1	1520
	21st to end	Night	34% 8% 14% 26% 16% 1	1520
July	1st to 10th	Night	39% 8% 16% 20% 15% 3	2480
	11th to 20th	Night	41% 8% 14% 24% 13% 1	2472
	21st to end	Night	43% 6% 14% 15% 19% 2	2651
August	1st to 10th	Night	50% 6% 16% 18% 9% 1	2698
	11th to 20th	Night	43% 6% 12% 27% 10% 1	3127
	21st to end	Night	32% 5% 10% 32% 20% 1	3476
September	1st to 10th	Night	40% 5% 9% 25% 19% 1	1900
	11th to 20th	Night	34% 4 10% 24% 25% 3	1971
	21st to end	Night	41% 4 9% 22% 22% 2	2090
October	1st to 10th	Night	39% 4 11% 23% 21% 2	3690
	11th to 20th	Night	25% 4 9% 29% 29% 4	3779
	21st to end	Night	31% 3 12% 32% 21% 2	4362
November	1st to 10th	Night	34% 4 11% 24% 22% 4	2537
	11th to 20th	Night	40% 3 8% 24% 20% 4	2600
	21st to end	Night	38% 4 14% 29% 14% 1	2625
December	1st to 10th	Night	45% 4 13% 24% 13% 1	2660
	11th to 20th	Night	44% 4 13% 20% 16% 4	3288
	21st to end	Night	50% 4 12% 22% 11% 1	4884

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	24% 26% 32% 16% 2	180
	11th to 20th	Day	32% 23% 34% 9% 2	180
	21st to end	Day	22% 24% 36% 12% 4 1	269
February	1st to 10th	Day	30% 21% 37% 10% 1	270
	11th to 20th	Day	27% 20% 38% 14% 2	446
	21st to end	Day	27% 20% 35% 15% 3	382
March	1st to 10th	Day	27% 20% 31% 17% 5%	460
	11th to 20th	Day	24% 23% 33% 15% 5% 1	460
	21st to end	Day	28% 22% 28% 15% 6% 1	506
April	1st to 10th	Day	28% 21% 31% 13% 6% 1	460
	11th to 20th	Day	24% 21% 33% 14% 6% 2	452
	21st to end	Day	31% 16% 32% 15% 4 2	460
May	1st to 10th	Day	34% 16% 28% 14% 6% 2	463
	11th to 20th	Day	23% 15% 32% 20% 8% 1	487
	21st to end	Day	21% 8% 27% 29% 12% 2	529
June	1st to 10th	Day	19% 10% 33% 23% 12% 2	490
	11th to 20th	Day	19% 12% 30% 27% 11% 1	490
	21st to end	Day	14% 12% 33% 26% 13% 2	490
July	1st to 10th	Day	14% 7% 26% 30% 18% 5%	485
	11th to 20th	Day	11% 6% 27% 35% 19% 3	484
	21st to end	Day	14% 8% 29% 32% 15% 2	532
August	1st to 10th	Day	15% 5% 24% 33% 15% 8%	486
	11th to 20th	Day	16% 5% 23% 32% 19% 5%	479
	21st to end	Day	14% 9% 27% 27% 16% 7%	539
September	1st to 10th	Day	18% 11% 25% 24% 16% 7%	490
	11th to 20th	Day	17% 6% 28% 23% 14% 12%	490
	21st to end	Day	22% 9% 30% 23% 10% 5%	490
October	1st to 10th	Day	26% 9% 27% 21% 13% 5%	490
	11th to 20th	Day	18% 17% 31% 22% 11% 2	490
	21st to end	Day	26% 12% 31% 19% 11% 1	463
November	1st to 10th	Day	19% 13% 32% 24% 9% 3	395
	11th to 20th	Day	26% 16% 31% 22% 4 1	400
	21st to end	Day	23% 19% 34% 18% 4 2	283
December	1st to 10th	Day	26% 23% 31% 15% 6%	180
	11th to 20th	Day	33% 19% 32% 13% 3	180
	21st to end	Day	29% 16% 36% 15% 4 1	198
January	1st to 10th	Night	21% 16% 39% 20% 3	760
	11th to 20th	Night	25% 16% 33% 23% 4	760
	21st to end	Night	21% 18% 36% 22% 3	836
February	1st to 10th	Night	23% 12% 38% 24% 2	760
	11th to 20th	Night	22% 18% 40% 18% 1	743
	21st to end	Night	26% 17% 34% 20% 4	628
March	1st to 10th	Night	24% 15% 37% 19% 4	760
	11th to 20th	Night	23% 17% 35% 21% 3 1	760
	21st to end	Night	22% 17% 36% 20% 5%	836
April	1st to 10th	Night	23% 17% 35% 20% 4	760
	11th to 20th	Night	22% 15% 34% 23% 5%	751
	21st to end	Night	23% 14% 33% 24% 5%	743
May	1st to 10th	Night	26% 12% 34% 20% 7%	570
	11th to 20th	Night	22% 13% 30% 29% 6%	386
	21st to end	Night	20% 5% 22% 37% 14% 1	411
June	1st to 10th	Night	18% 5% 28% 35% 12% 1	380
	11th to 20th	Night	16% 5% 28% 38% 13%	380
	21st to end	Night	12% 4 27% 46% 11%	380
July	1st to 10th	Night	12% 5% 24% 37% 21% 1	370
	11th to 20th	Night	12% 5% 21% 43% 19% 1	368
	21st to end	Night	14% 4 20% 44% 15% 1	416
August	1st to 10th	Night	13% 2 21% 41% 21% 2	489
	11th to 20th	Night	14% 3 20% 38% 23% 1	750
	21st to end	Night	15% 5% 18% 39% 21% 2	836
September	1st to 10th	Night	17% 4 24% 36% 17% 2	760
	11th to 20th	Night	18% 5% 19% 35% 20% 4	760
	21st to end	Night	21% 4 25% 33% 14% 2	760
October	1st to 10th	Night	25% 7% 27% 24% 15% 3	760
	11th to 20th	Night	20% 11% 27% 31% 10% 1	760
	21st to end	Night	25% 11% 33% 24% 8%	836
November	1st to 10th	Night	16% 11% 31% 29% 12% 1	780
	11th to 20th	Night	23% 12% 32% 25% 7% 1	800
	21st to end	Night	19% 15% 34% 26% 6% 1	779
December	1st to 10th	Night	24% 14% 31% 25% 5% 1	760
	11th to 20th	Night	23% 13% 35% 26% 3	760
	21st to end	Night	25% 13% 34% 25% 2	836

Page generated at 2024-11-22 08:02:27. Version ac07

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