Oakland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakland clear sky chart from 2005-11-05 to 2017-10-06.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
59%
15453
24%
47132
21%
15417
63%
15417
32%
27730

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
60%
716
18%
2380
17%
716
64%
716
27%
1438
January16th to endNight
56%
768
24%
2496
25%
768
59%
768
26%
1552
February1st to 15thNight
53%
698
22%
2288
21%
698
58%
698
25%
1428
February16th to endNight
49%
632
21%
1906
17%
632
56%
632
26%
1237
March1st to 15thNight
51%
720
17%
1998
14%
720
54%
720
26%
1337
March16th to endNight
49%
768
20%
2094
14%
768
54%
768
28%
1373
April1st to 15thNight
46%
719
22%
1799
11%
719
51%
719
31%
1182
April16th to endNight
54%
720
24%
1800
11%
720
59%
720
41%
1072
May1st to 15thNight
64%
602
24%
1682
17%
602
66%
602
43%
930
May16th to endNight
56%
399
22%
1522
21%
399
62%
399
29%
811
June1st to 15thNight
64%
360
21%
1440
23%
360
69%
360
30%
738
June16th to endNight
75%
360
32%
1440
40%
360
79%
360
46%
600
July1st to 15thNight
77%
384
26%
1404
31%
384
79%
384
41%
661
July16th to endNight
60%
564
24%
1593
23%
531
61%
531
30%
944
August1st to 15thNight
58%
547
23%
1620
20%
544
58%
544
28%
982
August16th to endNight
66%
764
27%
1910
17%
764
66%
764
40%
1191
September1st to 15thNight
71%
720
32%
1800
23%
720
72%
720
47%
1059
September16th to endNight
75%
716
37%
1968
34%
716
78%
716
50%
1027
October1st to 15thNight
67%
684
28%
2052
27%
684
72%
684
43%
1083
October16th to endNight
65%
704
30%
2112
30%
704
69%
704
36%
1212
November1st to 15thNight
66%
700
27%
2178
27%
700
70%
700
36%
1223
November16th to endNight
60%
720
24%
2442
26%
720
64%
720
31%
1373
December1st to 15thNight
54%
720
20%
2520
18%
720
59%
720
22%
1588
December16th to endNight
47%
768
21%
2688
18%
768
54%
768
22%
1689

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 ForecastData
Points
Cloud CoverDay
8%5%24323347%55%
48067
Night
10%6%34423347%48%
47320
TransparencyDay
30%38%19%23%14%
47755
Night
34%48%19%20%12%
47133
SeeingDay
10%11%28%33%13%3
6100
Night
12%5%12%33%30%6%
15465

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%5%34333448%43%
1557
16th to endDay
16%6%26%423336%43%
1728
February1st to 15thDay
18%7%15%323446%42%
1576
16th to endDay
16%8%3442345%7%38%
1568
March1st to 15thDay
15%7%345%2435%8%38%
1959
16th to endDay
13%5%346%3445%6%41%
2130
April1st to 15thDay
13%6%25%42445%7%43%
2149
16th to endDay
7%413323347%57%
2160
May1st to 15thDay
441321335%7%62%
2266
16th to endDay
7%6%24313347%55%
2590
June1st to 15thDay
5%5%2321345%7%58%
2520
16th to endDay
2312212346%69%
2520
July1st to 15thDay
1422313246%66%
2468
16th to endDay
1423213347%66%
2468
August1st to 15thDay
15%23312348%61%
2331
16th to endDay
1423213346%66%
2292
September1st to 15thDay
2413312346%66%
2160
16th to endDay
3312212246%68%
1989
October1st to 15thDay
6%313323335%63%
1705
16th to endDay
9%5%13223336%58%
1760
November1st to 15thDay
9%6%23323347%51%
1680
16th to endDay
13%7%34423346%47%
1515
December1st to 15thDay
18%8%24324445%41%
1440
16th to endDay
19%7%25%323347%41%
1536
January1st to 15thNight
14%6%2432445%8%43%
2380
16th to endNight
17%6%24323336%45%
2496
February1st to 15thNight
16%6%35%424446%42%
2276
16th to endNight
15%6%3432445%8%40%
1906
March1st to 15thNight
17%6%25%434446%41%
1998
16th to endNight
14%7%34423347%45%
2094
April1st to 15thNight
12%6%3432345%7%45%
1799
16th to endNight
7%423323347%57%
1800
May1st to 15thNight
36%3431335%7%55%
1682
16th to endNight
5%9%34312346%52%
1521
June1st to 15thNight
45%344235%48%51%
1440
16th to endNight
25%23313337%63%
1440
July1st to 15thNight
15%3443335%10%52%
1488
16th to endNight
18%49%7%36%5%5%9%37%
1701
August1st to 15thNight
312%48%5%344411%37%
1629
16th to endNight
19%47%5%345%6%10%42%
1910
September1st to 15thNight
26%25%5%13439%54%
1800
16th to endNight
3323313248%62%
1968
October1st to 15thNight
7%433312346%59%
2052
16th to endNight
8%5%24424345%53%
2112
November1st to 15thNight
9%5%23323347%54%
2178
16th to endNight
10%6%24423346%52%
2442
December1st to 15thNight
19%5%24423335%43%
2520
16th to endNight
19%6%24323336%43%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
39%5%12%17%16%8%
1557
16th to endDay
44%49%12%18%11%
1728
February1st to 15thDay
42%49%18%20%3
1576
16th to endDay
44%49%24%13%3
1568
March1st to 15thDay
43%412%19%13%5%
1959
16th to endDay
41%7%12%19%15%3
2130
April1st to 15thDay
40%5%14%19%18%2
2149
16th to endDay
27%413%26%21%6%
2160
May1st to 15thDay
21%39%29%26%8%
2266
16th to endDay
29%412%27%21%5%
2594
June1st to 15thDay
26%5%9%21%22%13%
2520
16th to endDay
17%1319%33%24%
2520
July1st to 15thDay
20%1310%24%39%
2323
16th to endDay
19%1311%25%37%
2313
August1st to 15thDay
23%1313%30%27%
2315
16th to endDay
20%317%35%21%
2292
September1st to 15thDay
20%2315%29%28%
2160
16th to endDay
19%2425%30%18%
1989
October1st to 15thDay
24%27%20%26%18%
1705
16th to endDay
29%38%23%21%12%
1760
November1st to 15thDay
32%411%28%14%7%
1680
16th to endDay
39%48%18%23%5%
1515
December1st to 15thDay
45%39%18%18%4
1440
16th to endDay
43%5%11%18%16%4
1536
January1st to 15thNight
37%5%12%19%15%8%
2380
16th to endNight
41%39%13%16%15%
2496
February1st to 15thNight
42%310%18%17%7%
2288
16th to endNight
41%5%11%23%14%2
1906
March1st to 15thNight
43%411%20%14%5%
1998
16th to endNight
40%5%11%19%18%4
2094
April1st to 15thNight
37%5%14%20%19%3
1799
16th to endNight
27%412%25%20%9%
1800
May1st to 15thNight
27%38%24%24%11%
1683
16th to endNight
33%311%25%19%6%
1522
June1st to 15thNight
29%5%9%19%23%12%
1440
16th to endNight
19%2216%33%24%
1440
July1st to 15thNight
24%219%25%35%
1404
16th to endNight
39%2310%16%27%
1593
August1st to 15thNight
40%229%24%20%
1620
16th to endNight
34%2212%27%21%
1910
September1st to 15thNight
26%4210%27%28%
1800
16th to endNight
22%2324%25%20%
1968
October1st to 15thNight
25%37%20%22%19%
2052
16th to endNight
32%36%22%20%14%
2112
November1st to 15thNight
30%411%29%16%7%
2178
16th to endNight
33%38%23%21%8%
2442
December1st to 15thNight
43%49%16%19%6%
2520
16th to endNight
42%5%11%16%17%7%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
22%8%25%25%17%
185
16th to endDay
17%10%23%29%16%2
256
February1st to 15thDay
21%10%21%29%16%
236
16th to endDay
19%15%25%25%13%1
236
March1st to 15thDay
19%15%28%18%12%4
270
16th to endDay
15%19%33%22%7%1
288
April1st to 15thDay
18%23%28%21%6%1
269
16th to endDay
11%27%27%24%6%2
270
May1st to 15thDay
7%19%38%27%6%
288
16th to endDay
12%15%26%33%9%3
330
June1st to 15thDay
8%14%37%30%6%1
315
16th to endDay
15%32%43%14%3
315
July1st to 15thDay
2225%49%18%
305
16th to endDay
2227%48%13%6%
327
August1st to 15thDay
2328%46%13%4
315
16th to endDay
2125%46%17%6%
332
September1st to 15thDay
4423%42%18%6%
315
16th to endDay
211%24%33%21%6%
315
October1st to 15thDay
7%10%29%33%12%5%
278
16th to endDay
14%8%29%26%18%3
272
November1st to 15thDay
9%9%23%22%31%4
186
16th to endDay
12%17%24%28%16%
73
December1st to 15thDay
25%13%35%16%8%1
60
16th to endDay
10%23%20%26%17%1
64
January1st to 15thNight
17%49%33%27%7%
720
16th to endNight
18%411%32%26%7%
768
February1st to 15thNight
17%6%12%33%25%5%
704
16th to endNight
17%7%17%30%21%5%
632
March1st to 15thNight
17%7%13%28%28%4
720
16th to endNight
16%8%16%33%22%2
768
April1st to 15thNight
13%10%20%33%18%3
719
16th to endNight
9%9%19%31%24%4
720
May1st to 15thNight
6%314%42%28%4
603
16th to endNight
11%6%15%37%24%5%
400
June1st to 15thNight
5%415%45%25%3
360
16th to endNight
419%46%35%2
360
July1st to 15thNight
45%37%45%6%
384
16th to endNight
5%2430%45%11%
564
August1st to 15thNight
10%27%32%40%6%
547
16th to endNight
5%17%37%40%7%
764
September1st to 15thNight
5%7%29%44%11%
720
16th to endNight
427%36%37%11%
716
October1st to 15thNight
9%49%35%33%8%
684
16th to endNight
11%49%28%33%13%
704
November1st to 15thNight
10%312%31%34%8%
700
16th to endNight
12%6%10%31%28%9%
720
December1st to 15thNight
20%5%11%33%21%6%
720
16th to endNight
20%8%15%31%21%2
768
Page generated at 2017-10-07 11:07:43. Version ac04

Copyright 2017 A. Danko


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