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 2026-04-17.

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% 5% 2 5% 3 3 3 3 5% 7% 56%	140303
	Night	9% 8% 3 7% 4 3 4 3 5% 6% 47%	139343
Transparency	Day	27% 5% 8% 19% 24% 17%	135225
	Night	36% 5% 8% 18% 20% 13%	135409
Seeing	Day	10% 11% 29% 32% 14% 3	17239
	Night	12% 6% 15% 36% 26% 5%	26673

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% 7% 2 5% 3 3 4 4 6% 9% 42%	5058
	11th to 20th	Day	10% 5% 2 6% 3 3 3 2 4 6% 56%	5340
	21st to end	Day	14% 9% 3 8% 4 4 3 3 5% 7% 39%	5843
February	1st to 10th	Day	18% 7% 2 5% 3 3 3 3 5% 7% 45%	1890
	11th to 20th	Day	13% 8% 2 7% 5% 4 4 3 6% 8% 39%	1929
	21st to end	Day	13% 7% 3 6% 4 4 4 3 5% 7% 46%	1730
March	1st to 10th	Day	11% 10% 4 9% 6% 4 5% 4 6% 6% 35%	4991
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 6% 8% 48%	5110
	21st to end	Day	11% 7% 3 6% 5% 6% 5% 5% 7% 10% 35%	5685
April	1st to 10th	Day	12% 7% 2 6% 4 3 3 4 5% 8% 45%	2520
	11th to 20th	Day	9% 6% 2 5% 4 3 4 3 5% 6% 54%	2442
	21st to end	Day	6% 5% 2 4 3 3 3 3 6% 10% 56%	2400
May	1st to 10th	Day	4 3 1 2 1 2 2 2 3 5% 74%	5651
	11th to 20th	Day	3 2 1 2 2 2 3 2 4 7% 71%	5965
	21st to end	Day	2 4 2 3 2 2 3 3 4 7% 68%	6902
June	1st to 10th	Day	5% 6% 2 4 3 3 3 4 6% 8% 58%	2800
	11th to 20th	Day	1 3 1 3 2 2 3 3 5% 8% 69%	2800
	21st to end	Day	3 4 2 4 3 3 3 3 4 6% 67%	2800
July	1st to 10th	Day	2 2 4 2 2 2 2 4 5% 75%	6319
	11th to 20th	Day	1 3 2 4 3 3 4 3 4 6% 67%	5893
	21st to end	Day	1 9% 2 5% 4 4 5% 3 5% 8% 53%	6402
August	1st to 10th	Day	1 3 2 5% 4 3 4 4 6% 8% 61%	5777
	11th to 20th	Day	5% 2 4 3 3 3 3 4 7% 66%	5538
	21st to end	Day	1 4 2 5% 3 3 3 3 6% 8% 63%	5984
September	1st to 10th	Day	2 4 2 4 2 2 3 2 4 6% 69%	2400
	11th to 20th	Day	4 6% 3 5% 3 3 3 3 6% 8% 57%	2400
	21st to end	Day	4 3 1 3 2 2 2 2 4 6% 70%	2115
October	1st to 10th	Day	3 3 1 3 2 2 3 3 4 6% 70%	3280
	11th to 20th	Day	4 6% 3 4 2 3 3 2 4 6% 61%	3261
	21st to end	Day	6% 5% 2 4 3 3 4 3 6% 7% 57%	3558
November	1st to 10th	Day	8% 6% 1 4 3 3 3 3 5% 9% 55%	2024
	11th to 20th	Day	11% 8% 3 6% 5% 4 4 3 4 8% 45%	1890
	21st to end	Day	11% 5% 2 4 3 3 3 3 6% 6% 53%	1706
December	1st to 10th	Day	8% 5% 2 4 2 3 3 4 6% 9% 54%	2700
	11th to 20th	Day	22% 8% 3 6% 4 4 5% 4 6% 8% 30%	3108
	21st to end	Day	24% 11% 3 7% 4 4 4 3 5% 7% 28%	4092
January	1st to 10th	Night	16% 7% 3 5% 3 3 4 3 5% 8% 44%	7850
	11th to 20th	Night	10% 5% 3 5% 4 3 4 3 4 7% 52%	7650
	21st to end	Night	14% 10% 4 7% 4 4 4 3 4 7% 39%	8371
February	1st to 10th	Night	17% 7% 2 4 3 3 3 3 5% 6% 47%	2730
	11th to 20th	Night	14% 8% 3 7% 4 3 4 3 5% 7% 42%	2577
	21st to end	Night	12% 6% 2 5% 4 3 3 3 5% 7% 49%	2076
March	1st to 10th	Night	14% 11% 4 8% 4 4 3 3 5% 6% 37%	5106
	11th to 20th	Night	16% 6% 3 5% 3 3 3 3 5% 6% 48%	5110
	21st to end	Night	15% 11% 3 6% 4 4 4 3 4 7% 40%	5532
April	1st to 10th	Night	9% 9% 3 7% 4 4 2 4 5% 7% 47%	2100
	11th to 20th	Night	10% 8% 3 4 3 2 3 3 4 6% 52%	2039
	21st to end	Night	5% 6% 2 4 3 4 3 3 5% 8% 56%	2000
May	1st to 10th	Night	4 5% 2 4 2 2 2 2 4 4 69%	4334
	11th to 20th	Night	2 6% 4 9% 4 4 4 3 5% 6% 52%	3941
	21st to end	Night	2 6% 4 6% 4 2 3 5% 5% 4 58%	3972
June	1st to 10th	Night	5% 8% 4 7% 4 3 4 5% 6% 8% 48%	1600
	11th to 20th	Night	1 5% 2 6% 3 3 3 3 4 7% 63%	1600
	21st to end	Night	2 7% 4 8% 4 3 4 3 3 6% 56%	1600
July	1st to 10th	Night	4 6% 9% 3 3 3 3 6% 6% 57%	3640
	11th to 20th	Night	1 10% 9% 13% 4 3 3 3 6% 7% 40%	4069
	21st to end	Night	2 31% 6% 7% 4 3 4 4 6% 5% 28%	4472
August	1st to 10th	Night	2 9% 6% 17% 5% 5% 4 4 6% 6% 35%	4035
	11th to 20th	Night	12% 5% 9% 3 4 4 4 5% 6% 48%	4321
	21st to end	Night	2 7% 5% 14% 5% 4 4 3 5% 6% 44%	5015
September	1st to 10th	Night	2 5% 3 7% 4 4 3 4 5% 7% 56%	2000
	11th to 20th	Night	5% 10% 5% 8% 3 4 4 4 4 7% 47%	2000
	21st to end	Night	4 5% 2 5% 4 3 3 2 4 7% 62%	2280
October	1st to 10th	Night	3 3 2 4 2 2 3 3 5% 6% 66%	3920
	11th to 20th	Night	5% 12% 4 6% 3 4 3 3 4 4 52%	3897
	21st to end	Night	8% 5% 2 5% 4 4 5% 3 5% 5% 56%	4253
November	1st to 10th	Night	8% 6% 2 5% 4 3 4 2 5% 8% 53%	2492
	11th to 20th	Night	11% 8% 2 5% 3 3 4 3 5% 8% 48%	2730
	21st to end	Night	11% 4 1 4 4 3 4 3 5% 7% 54%	2909
December	1st to 10th	Night	9% 4 2 4 3 3 3 3 5% 6% 58%	4700
	11th to 20th	Night	23% 9% 3 6% 4 4 4 4 6% 7% 30%	5316
	21st to end	Night	25% 9% 3 7% 4 4 4 3 5% 5% 31%	7106

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% 8% 15% 22% 13% 4	5059
	11th to 20th	Day	31% 3 7% 13% 26% 21%	5340
	21st to end	Day	44% 5% 7% 16% 14% 14%	5843
February	1st to 10th	Day	39% 5% 8% 18% 21% 8%	1890
	11th to 20th	Day	42% 5% 10% 18% 19% 5%	1938
	21st to end	Day	38% 5% 9% 23% 18% 7%	1730
March	1st to 10th	Day	46% 6% 9% 19% 18% 2	4991
	11th to 20th	Day	34% 5% 15% 27% 10% 8%	5110
	21st to end	Day	39% 11% 16% 22% 11% 2	5685
April	1st to 10th	Day	38% 5% 13% 20% 20% 4	2520
	11th to 20th	Day	30% 6% 15% 23% 20% 6%	2445
	21st to end	Day	25% 4 13% 30% 24% 4	2400
May	1st to 10th	Day	14% 3 8% 28% 29% 17%	5651
	11th to 20th	Day	13% 3 7% 33% 34% 8%	5968
	21st to end	Day	16% 5% 8% 29% 39% 3	6904
June	1st to 10th	Day	25% 5% 10% 27% 25% 8%	2800
	11th to 20th	Day	14% 3 9% 21% 36% 17%	2800
	21st to end	Day	20% 2 3 14% 31% 30%	2800
July	1st to 10th	Day	12% 3 2 8% 21% 54%	6251
	11th to 20th	Day	15% 4 3 8% 14% 56%	5823
	21st to end	Day	21% 8% 7% 13% 23% 28%	6217
August	1st to 10th	Day	22% 6% 4 12% 28% 28%	4206
	11th to 20th	Day	15% 3 4 11% 40% 27%	4009
	21st to end	Day	18% 4 4 14% 34% 27%	4311
September	1st to 10th	Day	16% 3 3 12% 29% 38%	2400
	11th to 20th	Day	26% 4 5% 22% 28% 14%	2400
	21st to end	Day	16% 3 5% 21% 32% 23%	2115
October	1st to 10th	Day	16% 2 5% 12% 27% 37%	3280
	11th to 20th	Day	23% 4 7% 21% 26% 19%	3261
	21st to end	Day	25% 4 8% 22% 27% 14%	3558
November	1st to 10th	Day	27% 5% 10% 26% 20% 11%	2024
	11th to 20th	Day	38% 5% 9% 22% 20% 6%	1890
	21st to end	Day	31% 4 10% 20% 25% 11%	1706
December	1st to 10th	Day	27% 4 7% 28% 28% 6%	2700
	11th to 20th	Day	50% 6% 9% 15% 16% 4	3108
	21st to end	Day	54% 5% 12% 17% 9% 2	4092
January	1st to 10th	Night	39% 7% 18% 20% 13% 3	7850
	11th to 20th	Night	33% 4 8% 12% 25% 18%	7650
	21st to end	Night	45% 4 7% 14% 18% 13%	8371
February	1st to 10th	Night	39% 4 9% 18% 19% 12%	2730
	11th to 20th	Night	41% 5% 9% 18% 19% 7%	2579
	21st to end	Night	34% 5% 11% 26% 18% 5%	2076
March	1st to 10th	Night	46% 7% 9% 19% 16% 2	5106
	11th to 20th	Night	36% 6% 11% 23% 15% 8%	5110
	21st to end	Night	43% 8% 12% 22% 12% 2	5532
April	1st to 10th	Night	37% 5% 13% 21% 19% 5%	2100
	11th to 20th	Night	34% 5% 11% 24% 18% 8%	2039
	21st to end	Night	26% 6% 12% 30% 21% 6%	2000
May	1st to 10th	Night	19% 4 8% 26% 29% 14%	4331
	11th to 20th	Night	28% 9% 7% 24% 23% 9%	3942
	21st to end	Night	21% 10% 8% 26% 32% 2	3972
June	1st to 10th	Night	31% 7% 8% 21% 26% 7%	1600
	11th to 20th	Night	21% 4 6% 20% 34% 16%	1600
	21st to end	Night	27% 5% 3 13% 26% 26%	1600
July	1st to 10th	Night	23% 4 2 10% 20% 41%	3600
	11th to 20th	Night	39% 4 3 9% 10% 34%	4016
	21st to end	Night	52% 4 5% 8% 13% 18%	4345
August	1st to 10th	Night	50% 8% 4 9% 17% 12%	2929
	11th to 20th	Night	28% 3 4 10% 34% 21%	3120
	21st to end	Night	31% 7% 5% 11% 26% 21%	3608
September	1st to 10th	Night	24% 7% 2 7% 26% 34%	2000
	11th to 20th	Night	35% 6% 4 19% 22% 14%	2000
	21st to end	Night	22% 4 4 20% 28% 22%	2280
October	1st to 10th	Night	18% 3 5% 12% 21% 41%	3920
	11th to 20th	Night	32% 6% 6% 17% 17% 21%	3897
	21st to end	Night	27% 6% 5% 19% 24% 18%	4253
November	1st to 10th	Night	31% 5% 8% 25% 18% 13%	2492
	11th to 20th	Night	35% 5% 9% 25% 18% 8%	2730
	21st to end	Night	29% 5% 9% 22% 22% 12%	2909
December	1st to 10th	Night	27% 4 7% 23% 28% 11%	4700
	11th to 20th	Night	51% 6% 8% 15% 16% 4	5316
	21st to end	Night	54% 6% 12% 16% 9% 3	7106

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	25% 13% 27% 21% 13% 1	335
	11th to 20th	Day	17% 11% 24% 33% 14% 1	430
	21st to end	Day	15% 10% 28% 29% 16% 2	473
February	1st to 10th	Day	21% 11% 23% 28% 15% 2	430
	11th to 20th	Day	21% 19% 27% 24% 9% 1	469
	21st to end	Day	13% 15% 30% 29% 11% 1	446
March	1st to 10th	Day	22% 18% 30% 20% 8% 2	540
	11th to 20th	Day	18% 16% 26% 22% 15% 3	540
	21st to end	Day	16% 18% 32% 23% 10% 1	594
April	1st to 10th	Day	17% 16% 31% 23% 9% 3	540
	11th to 20th	Day	15% 17% 34% 22% 7% 3	517
	21st to end	Day	8% 21% 30% 26% 10% 5%	500
May	1st to 10th	Day	11% 15% 35% 27% 10% 1	503
	11th to 20th	Day	11% 15% 34% 28% 11% 1	528
	21st to end	Day	9% 14% 33% 30% 11% 2	573
June	1st to 10th	Day	8% 9% 36% 33% 12% 2	530
	11th to 20th	Day	4 12% 38% 36% 8% 2	530
	21st to end	Day	3 8% 35% 39% 12% 3	530
July	1st to 10th	Day	4 5% 33% 43% 14% 1	526
	11th to 20th	Day	1 2 28% 50% 16% 3	524
	21st to end	Day	2 4 31% 45% 14% 4	575
August	1st to 10th	Day	3 6% 30% 43% 13% 4	527
	11th to 20th	Day	2 6% 31% 40% 15% 5%	517
	21st to end	Day	3 3 27% 43% 19% 5%	583
September	1st to 10th	Day	4 6% 25% 40% 18% 7%	530
	11th to 20th	Day	5% 13% 27% 34% 15% 5%	530
	21st to end	Day	5% 9% 25% 33% 23% 4	530
October	1st to 10th	Day	5% 8% 28% 30% 19% 9%	530
	11th to 20th	Day	8% 10% 23% 32% 21% 6%	530
	21st to end	Day	11% 8% 26% 29% 21% 6%	583
November	1st to 10th	Day	10% 12% 20% 27% 26% 6%	500
	11th to 20th	Day	11% 11% 21% 33% 18% 6%	330
	21st to end	Day	14% 8% 26% 34% 16% 2	234
December	1st to 10th	Day	15% 10% 22% 30% 19% 4	220
	11th to 20th	Day	18% 13% 21% 25% 21% 1	220
	21st to end	Day	26% 13% 28% 21% 12% 1	242
January	1st to 10th	Night	20% 7% 14% 33% 20% 6%	840
	11th to 20th	Night	14% 6% 14% 36% 25% 5%	840
	21st to end	Night	19% 5% 13% 37% 23% 3	924
February	1st to 10th	Night	20% 6% 13% 36% 22% 3	840
	11th to 20th	Night	16% 10% 17% 35% 18% 5%	824
	21st to end	Night	15% 9% 18% 36% 19% 2	692
March	1st to 10th	Night	20% 9% 18% 29% 20% 2	840
	11th to 20th	Night	19% 8% 13% 34% 23% 3	840
	21st to end	Night	16% 10% 19% 36% 17% 2	924
April	1st to 10th	Night	13% 9% 21% 37% 18% 2	840
	11th to 20th	Night	15% 10% 19% 34% 19% 3	815
	21st to end	Night	8% 8% 22% 36% 21% 4	800
May	1st to 10th	Night	8% 5% 20% 41% 22% 4	704
	11th to 20th	Night	9% 5% 14% 42% 26% 4	537
	21st to end	Night	12% 9% 18% 38% 19% 4	433
June	1st to 10th	Night	7% 6% 18% 44% 23% 3	400
	11th to 20th	Night	3 3 18% 54% 21% 2	400
	21st to end	Night	5% 3 15% 41% 34% 2	400
July	1st to 10th	Night	3 3 12% 43% 37% 2	390
	11th to 20th	Night	4 1 12% 41% 34% 9%	565
	21st to end	Night	5% 5% 12% 34% 37% 7%	657
August	1st to 10th	Night	11% 4 12% 35% 32% 6%	597
	11th to 20th	Night	5% 4 13% 39% 33% 6%	707
	21st to end	Night	5% 1 12% 40% 34% 7%	880
September	1st to 10th	Night	4 2 10% 37% 39% 9%	800
	11th to 20th	Night	9% 4 13% 36% 32% 6%	800
	21st to end	Night	5% 4 10% 35% 36% 10%	800
October	1st to 10th	Night	8% 3 12% 36% 34% 8%	800
	11th to 20th	Night	9% 6% 10% 32% 35% 8%	800
	21st to end	Night	10% 5% 11% 32% 32% 11%	880
November	1st to 10th	Night	9% 5% 13% 30% 33% 9%	820
	11th to 20th	Night	14% 5% 13% 34% 27% 7%	840
	21st to end	Night	13% 5% 12% 38% 26% 6%	840
December	1st to 10th	Night	16% 5% 13% 37% 23% 6%	840
	11th to 20th	Night	24% 6% 12% 34% 21% 3	840
	21st to end	Night	22% 10% 18% 31% 17% 1	924

Page generated at 2026-04-13 23:44:31. Version ac07

Copyright © 2026 Attilla Danko.