Sonoma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sonoma clear sky chart from 2005-11-05 to 2017-08-12.

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
62%
15183
25%
46546
22%
15145
67%
15145
35%
26313

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
58%
718
18%
2386
17%
716
62%
716
26%
1456
January16th to endNight
55%
768
25%
2496
24%
768
60%
768
27%
1535
February1st to 15thNight
54%
698
22%
2288
22%
698
60%
698
23%
1466
February16th to endNight
50%
632
22%
1919
17%
632
58%
632
27%
1213
March1st to 15thNight
52%
720
16%
1995
13%
720
55%
720
26%
1352
March16th to endNight
46%
768
21%
2097
14%
768
52%
768
30%
1350
April1st to 15thNight
47%
719
23%
1799
11%
719
53%
719
32%
1161
April16th to endNight
54%
720
26%
1800
12%
720
59%
720
44%
1039
May1st to 15thNight
64%
579
26%
1659
18%
579
68%
579
46%
871
May16th to endNight
67%
392
26%
1515
24%
392
74%
392
38%
711
June1st to 15thNight
69%
360
24%
1440
25%
360
77%
360
39%
647
June16th to endNight
83%
360
33%
1440
43%
360
86%
360
52%
556
July1st to 15thNight
89%
376
29%
1396
36%
376
90%
376
53%
564
July16th to endNight
77%
564
30%
1593
28%
531
78%
531
42%
806
August1st to 15thNight
72%
526
28%
1575
23%
523
73%
523
42%
805
August16th to endNight
80%
695
30%
1745
19%
695
81%
695
53%
957
September1st to 15thNight
84%
660
37%
1650
25%
660
85%
660
62%
846
September16th to endNight
77%
656
36%
1808
31%
656
81%
656
55%
916
October1st to 15thNight
67%
660
30%
1980
28%
660
74%
660
43%
1035
October16th to endNight
69%
704
31%
2112
31%
704
73%
704
39%
1182
November1st to 15thNight
65%
700
27%
2181
25%
700
70%
700
40%
1177
November16th to endNight
59%
720
24%
2464
25%
720
63%
720
30%
1382
December1st to 15thNight
51%
720
19%
2520
17%
720
57%
720
22%
1620
December16th to endNight
48%
768
21%
2688
18%
768
55%
768
24%
1666

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
9%423423346%56%
47428
Night
10%413423347%54%
46733
TransparencyDay
29%48%19%23%14%
47115
Night
30%49%18%21%14%
46547
SeeingDay
11%9%24%31%18%4
5861
Night
11%314%32%31%6%
15193

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
18%5%24424335%44%
1549
16th to endDay
16%5%25%5%35%34443%
1728
February1st to 15thDay
19%425%423445%41%
1576
16th to endDay
18%7%245%3345%6%38%
1553
March1st to 15thDay
19%6%35%42445%7%36%
1962
16th to endDay
17%425%5%2445%7%39%
2125
April1st to 15thDay
15%5%345%2445%7%40%
2149
16th to endDay
7%42432225%8%57%
2160
May1st to 15thDay
5%323312347%62%
2289
16th to endDay
5%5%24423247%57%
2596
June1st to 15thDay
6%412422336%60%
2520
16th to endDay
23212246%72%
2520
July1st to 15thDay
212212235%73%
2478
16th to endDay
212322236%72%
2468
August1st to 15thDay
1312322326%69%
2291
16th to endDay
1312322136%71%
2106
September1st to 15thDay
1212322226%72%
1980
16th to endDay
4311212335%70%
1820
October1st to 15thDay
8%312412345%61%
1650
16th to endDay
10%423322245%57%
1760
November1st to 15thDay
10%21442446%7%51%
1678
16th to endDay
15%5%235%3434446%
1494
December1st to 15thDay
20%7%3442332442%
1440
16th to endDay
21%6%24423347%38%
1536
January1st to 15thNight
15%5%2342435%8%43%
2386
16th to endNight
17%5%23313336%47%
2496
February1st to 15thNight
17%5%24425%35%6%42%
2276
16th to endNight
16%425%424447%44%
1919
March1st to 15thNight
16%5%25%5%35%446%41%
1995
16th to endNight
16%4145%22346%47%
2097
April1st to 15thNight
12%32442335%6%49%
1799
16th to endNight
7%412314247%60%
1800
May1st to 15thNight
3224313446%62%
1659
16th to endNight
432331235%8%60%
1514
June1st to 15thNight
321232345%7%63%
1440
16th to endNight
212212236%72%
1440
July1st to 15thNight
1112223437%70%
1479
16th to endNight
121443445%9%57%
1701
August1st to 15thNight
14245%244410%55%
1584
16th to endNight
213423448%62%
1745
September1st to 15thNight
23222348%69%
1650
16th to endNight
2213322336%68%
1808
October1st to 15thNight
6%313323336%62%
1980
16th to endNight
7%413423447%56%
2112
November1st to 15thNight
9%31341335%7%56%
2181
16th to endNight
12%5%14323336%53%
2464
December1st to 15thNight
20%6%24423245%41%
2520
16th to endNight
20%414324245%45%
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
42%5%11%16%15%8%
1549
16th to endDay
44%5%7%12%19%11%
1728
February1st to 15thDay
44%5%7%19%18%3
1576
16th to endDay
45%5%10%22%11%3
1553
March1st to 15thDay
46%6%11%17%13%4
1962
16th to endDay
43%7%12%18%15%3
2125
April1st to 15thDay
42%6%12%18%17%2
2149
16th to endDay
26%5%14%25%22%6%
2160
May1st to 15thDay
22%38%30%27%7%
2289
16th to endDay
26%5%12%27%21%6%
2600
June1st to 15thDay
26%310%22%23%13%
2520
16th to endDay
14%25%17%36%23%
2520
July1st to 15thDay
15%2312%26%39%
2332
16th to endDay
16%25%9%26%40%
2313
August1st to 15thDay
18%2412%32%29%
2275
16th to endDay
17%2415%35%24%
2106
September1st to 15thDay
16%15%12%33%29%
1980
16th to endDay
17%25%22%31%19%
1820
October1st to 15thDay
24%47%19%27%15%
1650
16th to endDay
30%48%23%23%11%
1760
November1st to 15thDay
30%7%12%27%13%7%
1678
16th to endDay
39%5%9%18%19%6%
1494
December1st to 15thDay
45%5%8%17%19%4
1440
16th to endDay
46%5%10%16%14%6%
1536
January1st to 15thNight
39%5%12%18%15%8%
2386
16th to endNight
38%5%9%13%18%14%
2496
February1st to 15thNight
41%6%8%18%16%7%
2288
16th to endNight
38%6%13%22%16%2
1919
March1st to 15thNight
43%5%13%16%16%4
1995
16th to endNight
38%5%11%20%19%5%
2097
April1st to 15thNight
35%6%14%21%18%5%
1799
16th to endNight
25%411%26%21%9%
1800
May1st to 15thNight
21%6%9%21%28%12%
1660
16th to endNight
23%413%29%20%8%
1515
June1st to 15thNight
20%6%12%22%24%14%
1440
16th to endNight
15%2416%34%26%
1440
July1st to 15thNight
16%15%9%26%40%
1396
16th to endNight
26%27%10%17%35%
1593
August1st to 15thNight
27%28%11%24%26%
1575
16th to endNight
22%37%12%28%26%
1745
September1st to 15thNight
16%27%10%31%31%
1650
16th to endNight
19%25%20%30%21%
1808
October1st to 15thNight
24%38%20%25%17%
1980
16th to endNight
28%5%7%21%22%14%
2112
November1st to 15thNight
27%414%29%15%8%
2181
16th to endNight
33%48%22%21%9%
2464
December1st to 15thNight
44%49%16%18%6%
2520
16th to endNight
40%5%11%15%18%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
27%6%27%23%14%1
177
16th to endDay
16%8%25%26%19%2
256
February1st to 15thDay
21%9%22%25%19%1
236
16th to endDay
19%15%21%24%17%1
233
March1st to 15thDay
25%14%24%17%15%3
270
16th to endDay
17%17%30%22%9%2
288
April1st to 15thDay
18%20%27%23%7%2
269
16th to endDay
11%24%27%24%9%2
270
May1st to 15thDay
9%17%31%29%9%2
288
16th to endDay
9%13%24%30%19%3
330
June1st to 15thDay
8%12%31%31%12%3
315
16th to endDay
2325%41%22%4
315
July1st to 15thDay
2315%46%26%5%
305
16th to endDay
2118%48%20%9%
327
August1st to 15thDay
3420%44%23%5%
300
16th to endDay
4122%45%19%6%
268
September1st to 15thDay
3220%42%21%9%
255
16th to endDay
6%5%21%32%24%9%
255
October1st to 15thDay
9%7%27%30%17%7%
255
16th to endDay
14%7%24%29%20%2
272
November1st to 15thDay
10%5%19%21%35%6%
184
16th to endDay
17%10%21%28%21%
69
December1st to 15thDay
31%16%25%11%15%
60
16th to endDay
18%10%20%25%21%3
64
January1st to 15thNight
17%212%34%26%6%
720
16th to endNight
19%314%29%26%6%
768
February1st to 15thNight
18%5%11%33%25%5%
704
16th to endNight
18%418%32%21%4
632
March1st to 15thNight
17%6%16%29%26%4
720
16th to endNight
16%5%23%30%20%2
768
April1st to 15thNight
14%8%22%31%20%3
719
16th to endNight
9%6%24%29%24%5%
720
May1st to 15thNight
5%218%35%33%4
580
16th to endNight
5%416%36%31%6%
393
June1st to 15thNight
3417%39%32%1
360
16th to endNight
29%47%37%1
360
July1st to 15thNight
3333%53%5%
376
16th to endNight
45%29%51%8%
564
August1st to 15thNight
6%15%29%49%7%
526
16th to endNight
37%35%45%6%
695
September1st to 15thNight
26%31%47%11%
660
16th to endNight
4110%30%41%11%
656
October1st to 15thNight
8%314%31%32%9%
660
16th to endNight
10%211%29%32%13%
704
November1st to 15thNight
9%316%28%33%9%
700
16th to endNight
13%413%31%28%8%
720
December1st to 15thNight
22%413%31%20%7%
720
16th to endNight
22%5%16%34%19%2
768
Page generated at 2017-08-13 11:16:30. Version ac04

Copyright 2017 A. Danko


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