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 2024-01-14.

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	16% 6% 3 5% 5% 3 5% 5% 5% 7% 40%	74766
	Night	17% 6% 2 5% 4 3 4 4 5% 7% 43%	74976
Transparency	Day	43% 5% 12% 23% 15% 3	74471
	Night	42% 5% 12% 23% 16% 3	74805
Seeing	Day	22% 14% 30% 21% 10% 3	13835
	Night	21% 11% 31% 28% 9% 1	23108

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	13% 6% 3 4 5% 4 5% 5% 5% 7% 43%	1517
	11th to 20th	Day	16% 7% 3 6% 6% 4 6% 5% 5% 6% 36%	1464
	21st to end	Day	13% 7% 3 6% 5% 2 4 5% 6% 7% 42%	1725
February	1st to 10th	Day	18% 8% 3 6% 5% 3 5% 4 5% 7% 36%	1620
	11th to 20th	Day	15% 8% 2 6% 5% 3 4 5% 4 6% 42%	1739
	21st to end	Day	20% 8% 2 5% 4 4 5% 4 5% 6% 38%	1480
March	1st to 10th	Day	14% 7% 3 5% 5% 3 5% 3 5% 7% 43%	1797
	11th to 20th	Day	15% 6% 3 5% 7% 3 5% 4 6% 8% 38%	1908
	21st to end	Day	19% 8% 3 6% 4 2 4 4 4 6% 39%	2348
April	1st to 10th	Day	18% 8% 3 6% 5% 3 3 4 5% 6% 40%	2160
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 4 4 7% 42%	2134
	21st to end	Day	20% 6% 2 5% 4 3 5% 4 5% 7% 39%	2173
May	1st to 10th	Day	24% 8% 2 4 5% 3 5% 5% 4 7% 34%	2343
	11th to 20th	Day	20% 6% 2 5% 6% 4 5% 5% 6% 7% 35%	2478
	21st to end	Day	15% 6% 2 6% 4 3 6% 4 5% 8% 40%	2725
June	1st to 10th	Day	17% 5% 2 5% 5% 3 5% 6% 7% 9% 35%	2520
	11th to 20th	Day	17% 5% 3 5% 6% 3 6% 6% 5% 9% 34%	2520
	21st to end	Day	12% 5% 3 6% 6% 4 5% 6% 6% 9% 39%	2520
July	1st to 10th	Day	12% 6% 3 6% 6% 3 6% 5% 6% 8% 39%	2520
	11th to 20th	Day	10% 5% 3 5% 4 3 6% 6% 8% 10% 39%	2520
	21st to end	Day	12% 5% 3 6% 6% 4 6% 6% 7% 8% 37%	2744
August	1st to 10th	Day	11% 5% 3 6% 7% 4 6% 6% 7% 9% 36%	2378
	11th to 20th	Day	13% 6% 3 5% 7% 5% 5% 6% 6% 7% 37%	2126
	21st to end	Day	15% 5% 2 5% 4 4 5% 5% 5% 8% 40%	2376
September	1st to 10th	Day	15% 5% 2 6% 5% 3 5% 5% 5% 6% 41%	2160
	11th to 20th	Day	13% 6% 2 4 4 3 3 4 4 7% 50%	2092
	21st to end	Day	18% 5% 3 6% 5% 3 4 4 5% 6% 41%	1980
October	1st to 10th	Day	21% 6% 2 4 4 3 3 4 5% 6% 41%	1864
	11th to 20th	Day	16% 5% 2 4 3 3 4 5% 5% 6% 46%	1800
	21st to end	Day	22% 6% 2 4 4 3 4 5% 4 7% 40%	1845
November	1st to 10th	Day	14% 6% 3 4 3 2 3 3 3 6% 52%	1671
	11th to 20th	Day	19% 6% 2 3 3 3 3 4 4 7% 47%	1710
	21st to end	Day	16% 5% 2 4 3 2 4 6% 5% 7% 44%	1611
December	1st to 10th	Day	20% 7% 3 5% 5% 3 4 4 6% 6% 38%	1520
	11th to 20th	Day	22% 5% 2 4 3 2 3 3 5% 7% 44%	1906
	21st to end	Day	18% 8% 4 7% 6% 4 5% 5% 6% 8% 30%	2772
January	1st to 10th	Night	16% 6% 2 4 3 2 4 4 5% 7% 45%	2649
	11th to 20th	Night	19% 7% 3 5% 5% 3 4 5% 5% 7% 38%	2569
	21st to end	Night	14% 9% 3 4 4 3 4 4 4 8% 44%	2628
February	1st to 10th	Night	18% 8% 3 5% 4 3 4 3 5% 6% 40%	2340
	11th to 20th	Night	17% 7% 2 5% 5% 3 5% 5% 5% 6% 41%	2105
	21st to end	Night	19% 6% 3 6% 4 3 4 4 3 5% 42%	1776
March	1st to 10th	Night	16% 6% 2 4 4 3 4 4 4 7% 46%	2150
	11th to 20th	Night	17% 8% 2 5% 4 3 4 4 5% 6% 43%	2047
	21st to end	Night	17% 7% 3 5% 4 2 4 5% 5% 7% 41%	2008
April	1st to 10th	Night	18% 8% 3 5% 4 3 4 4 4 7% 39%	1800
	11th to 20th	Night	19% 5% 2 5% 4 3 5% 4 4 7% 41%	1775
	21st to end	Night	21% 7% 2 5% 4 3 3 3 4 7% 41%	1784
May	1st to 10th	Night	22% 7% 3 7% 6% 3 4 4 5% 5% 35%	1620
	11th to 20th	Night	19% 7% 4 5% 4 3 5% 4 4 6% 39%	1427
	21st to end	Night	17% 5% 2 5% 4 3 4 5% 5% 9% 41%	1550
June	1st to 10th	Night	17% 4 3 4 4 3 5% 5% 5% 8% 42%	1440
	11th to 20th	Night	14% 6% 2 5% 4 3 4 6% 6% 10% 39%	1440
	21st to end	Night	12% 3 2 5% 5% 3 4 5% 6% 9% 45%	1440
July	1st to 10th	Night	12% 4 2 5% 7% 3 5% 6% 6% 9% 41%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 3 6% 6% 7% 10% 39%	1440
	21st to end	Night	12% 4 2 4 5% 3 5% 6% 7% 10% 43%	1574
August	1st to 10th	Night	10% 5% 2 5% 5% 4 6% 6% 5% 9% 44%	1536
	11th to 20th	Night	12% 6% 3 7% 7% 4 5% 7% 5% 8% 37%	1774
	21st to end	Night	15% 5% 3 5% 5% 3 4 4 6% 7% 44%	1980
September	1st to 10th	Night	16% 5% 2 5% 5% 3 4 4 5% 6% 44%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 3 3 3 7% 52%	1867
	21st to end	Night	18% 5% 2 4 5% 2 3 4 4 6% 47%	1980
October	1st to 10th	Night	21% 7% 3 5% 4 3 3 3 4 6% 42%	2092
	11th to 20th	Night	17% 5% 2 3 4 3 3 3 5% 6% 48%	2160
	21st to end	Night	22% 7% 2 5% 3 2 3 3 4 5% 44%	2510
November	1st to 10th	Night	13% 5% 2 4 4 2 4 5% 4 6% 50%	2407
	11th to 20th	Night	20% 6% 2 4 3 2 3 3 4 5% 48%	2470
	21st to end	Night	15% 4 2 5% 4 3 5% 4 5% 7% 47%	2566
December	1st to 10th	Night	19% 7% 2 5% 5% 3 4 4 5% 6% 40%	2660
	11th to 20th	Night	19% 6% 2 5% 4 3 4 4 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 6% 5% 3 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	41% 4 11% 28% 13% 4	1518
	11th to 20th	Day	48% 4 14% 19% 12% 3	1464
	21st to end	Day	41% 3 11% 26% 16% 3	1725
February	1st to 10th	Day	47% 4 13% 22% 12% 2	1620
	11th to 20th	Day	43% 4 10% 24% 15% 3	1748
	21st to end	Day	47% 3 9% 23% 14% 4	1480
March	1st to 10th	Day	42% 3 13% 24% 15% 3	1800
	11th to 20th	Day	44% 5% 10% 24% 15% 2	1908
	21st to end	Day	47% 3 8% 19% 18% 5%	2348
April	1st to 10th	Day	45% 3 10% 21% 16% 5%	2160
	11th to 20th	Day	42% 4 11% 22% 17% 4	2134
	21st to end	Day	45% 3 10% 22% 16% 4	2173
May	1st to 10th	Day	50% 4 9% 19% 16% 3	2343
	11th to 20th	Day	46% 4 11% 21% 15% 3	2482
	21st to end	Day	42% 5% 15% 22% 14% 2	2725
June	1st to 10th	Day	43% 6% 14% 21% 15% 1	2520
	11th to 20th	Day	46% 6% 12% 22% 11% 2	2520
	21st to end	Day	40% 6% 14% 24% 16% 1	2520
July	1st to 10th	Day	42% 6% 11% 23% 15% 2	2450
	11th to 20th	Day	37% 6% 15% 26% 14% 2	2445
	21st to end	Day	43% 6% 12% 19% 17% 3	2591
August	1st to 10th	Day	41% 7% 14% 23% 14% 1	2364
	11th to 20th	Day	43% 5% 14% 24% 13% 1	2126
	21st to end	Day	41% 6% 10% 23% 18% 3	2376
September	1st to 10th	Day	42% 6% 9% 22% 18% 3	2160
	11th to 20th	Day	35% 4 11% 22% 25% 3	2092
	21st to end	Day	43% 5% 9% 20% 19% 3	1980
October	1st to 10th	Day	44% 5% 10% 22% 16% 3	1864
	11th to 20th	Day	38% 4 12% 26% 19% 1	1800
	21st to end	Day	44% 4 10% 24% 16% 2	1845
November	1st to 10th	Day	36% 3 11% 26% 21% 3	1671
	11th to 20th	Day	39% 4 11% 24% 20% 3	1710
	21st to end	Day	39% 3 14% 29% 12% 2	1611
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	40% 3 12% 25% 16% 4	2649
	11th to 20th	Night	46% 5% 14% 23% 11% 2	2569
	21st to end	Night	40% 4 10% 24% 20% 3	2628
February	1st to 10th	Night	45% 4 13% 24% 13% 2	2340
	11th to 20th	Night	44% 4 10% 20% 17% 5%	2107
	21st to end	Night	46% 3 6% 26% 17% 3	1776
March	1st to 10th	Night	41% 3 12% 25% 14% 4	2160
	11th to 20th	Night	43% 4 10% 22% 18% 3	2048
	21st to end	Night	42% 4 9% 19% 19% 6%	2008
April	1st to 10th	Night	45% 4 10% 22% 16% 4	1800
	11th to 20th	Night	44% 5% 9% 21% 20% 2	1775
	21st to end	Night	44% 4 9% 21% 17% 4	1784
May	1st to 10th	Night	52% 4 9% 18% 15% 2	1620
	11th to 20th	Night	46% 5% 10% 17% 19% 3	1428
	21st to end	Night	40% 7% 16% 22% 12% 3	1551
June	1st to 10th	Night	41% 5% 11% 22% 19% 2	1440
	11th to 20th	Night	40% 6% 15% 26% 12% 1	1440
	21st to end	Night	33% 9% 15% 27% 16% 1	1440
July	1st to 10th	Night	40% 6% 14% 21% 16% 3	1400
	11th to 20th	Night	39% 7% 14% 26% 12% 2	1392
	21st to end	Night	33% 8% 18% 22% 16% 3	1486
August	1st to 10th	Night	37% 7% 15% 24% 16% 2	1526
	11th to 20th	Night	44% 8% 14% 23% 11% 1	1774
	21st to end	Night	40% 6% 12% 20% 20% 2	1980
September	1st to 10th	Night	41% 6% 10% 25% 18% 1	1800
	11th to 20th	Night	34% 4 10% 23% 25% 3	1867
	21st to end	Night	40% 4 9% 23% 24% 2	1980
October	1st to 10th	Night	45% 4 10% 23% 15% 3	2092
	11th to 20th	Night	37% 4 13% 28% 16% 2	2160
	21st to end	Night	43% 4 10% 25% 16% 2	2510
November	1st to 10th	Night	35% 4 11% 24% 22% 4	2407
	11th to 20th	Night	41% 3 9% 25% 19% 4	2470
	21st to end	Night	38% 4 14% 29% 14% 1	2566
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% 20% 36% 10% 2	166
	21st to end	Day	21% 26% 36% 12% 4 2	239
February	1st to 10th	Day	33% 22% 35% 9% 2	240
	11th to 20th	Day	28% 19% 37% 14% 1	407
	21st to end	Day	29% 19% 34% 15% 2	346
March	1st to 10th	Day	26% 21% 32% 17% 4	420
	11th to 20th	Day	24% 23% 33% 15% 5% 1	420
	21st to end	Day	28% 23% 28% 15% 6% 1	462
April	1st to 10th	Day	27% 21% 31% 14% 6% 1	420
	11th to 20th	Day	23% 20% 33% 14% 7% 2	412
	21st to end	Day	34% 16% 32% 13% 4 2	420
May	1st to 10th	Day	34% 17% 29% 13% 6% 2	423
	11th to 20th	Day	22% 16% 34% 19% 8% 1	447
	21st to end	Day	22% 7% 26% 29% 13% 3	485
June	1st to 10th	Day	19% 10% 33% 23% 13% 3	450
	11th to 20th	Day	21% 13% 31% 25% 10% 1	450
	21st to end	Day	13% 12% 33% 26% 13% 3	450
July	1st to 10th	Day	15% 7% 25% 31% 18% 5%	445
	11th to 20th	Day	11% 5% 28% 34% 19% 3	444
	21st to end	Day	14% 7% 30% 33% 15% 2	488
August	1st to 10th	Day	13% 5% 24% 34% 15% 8%	446
	11th to 20th	Day	17% 5% 22% 32% 19% 5%	439
	21st to end	Day	14% 8% 28% 26% 17% 7%	495
September	1st to 10th	Day	19% 11% 24% 24% 15% 7%	450
	11th to 20th	Day	17% 7% 29% 23% 13% 12%	450
	21st to end	Day	20% 10% 32% 22% 11% 5%	450
October	1st to 10th	Day	28% 8% 26% 20% 13% 4	450
	11th to 20th	Day	18% 16% 30% 23% 11% 1	450
	21st to end	Day	28% 13% 32% 17% 10% 1	427
November	1st to 10th	Day	19% 13% 31% 24% 10% 3	365
	11th to 20th	Day	27% 16% 30% 22% 4 1	370
	21st to end	Day	21% 18% 35% 19% 4 2	271
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% 15% 32% 24% 4	735
	21st to end	Night	20% 19% 37% 22% 3	792
February	1st to 10th	Night	24% 13% 38% 23% 2	720
	11th to 20th	Night	23% 18% 38% 19% 1	703
	21st to end	Night	25% 17% 35% 19% 3	592
March	1st to 10th	Night	24% 16% 38% 19% 4	720
	11th to 20th	Night	24% 16% 35% 22% 3 1	720
	21st to end	Night	21% 17% 36% 20% 5% 1	792
April	1st to 10th	Night	23% 18% 35% 20% 5%	720
	11th to 20th	Night	22% 15% 34% 23% 5%	711
	21st to end	Night	24% 14% 32% 24% 5%	704
May	1st to 10th	Night	26% 12% 34% 20% 7%	540
	11th to 20th	Night	22% 13% 30% 29% 5%	366
	21st to end	Night	21% 6% 21% 37% 14% 1	389
June	1st to 10th	Night	19% 5% 28% 34% 13% 1	360
	11th to 20th	Night	16% 5% 28% 37% 13%	360
	21st to end	Night	11% 3 28% 46% 12%	360
July	1st to 10th	Night	12% 5% 25% 36% 21% 1	350
	11th to 20th	Night	12% 4 21% 43% 19% 1	348
	21st to end	Night	14% 4 20% 44% 16% 2	394
August	1st to 10th	Night	11% 2 21% 42% 21% 2	462
	11th to 20th	Night	14% 3 19% 39% 24% 2	710
	21st to end	Night	15% 5% 18% 39% 21% 2	792
September	1st to 10th	Night	18% 4 23% 37% 17% 2	720
	11th to 20th	Night	18% 5% 20% 34% 19% 4	720
	21st to end	Night	20% 4 25% 33% 14% 2	720
October	1st to 10th	Night	26% 7% 27% 24% 14% 3	720
	11th to 20th	Night	21% 11% 26% 31% 10%	720
	21st to end	Night	26% 11% 33% 22% 7%	792
November	1st to 10th	Night	17% 11% 31% 29% 12% 1	740
	11th to 20th	Night	24% 12% 32% 25% 7% 1	760
	21st to end	Night	18% 15% 34% 26% 6% 1	760
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 2024-01-11 04:22:43. Version ac07

Copyright 2024 Attilla Danko