Lake Sonoma
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake 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
60%
15156
27%
46556
22%
15119
66%
15119
37%
25628

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
57%
716
18%
2372
16%
716
61%
716
24%
1481
January16th to endNight
54%
768
26%
2496
26%
768
58%
768
28%
1517
February1st to 15thNight
50%
700
22%
2288
21%
700
55%
700
22%
1476
February16th to endNight
44%
632
21%
1939
15%
632
53%
632
26%
1217
March1st to 15thNight
47%
720
14%
1980
10%
720
51%
720
23%
1383
March16th to endNight
41%
768
20%
2112
13%
768
47%
768
27%
1368
April1st to 15thNight
39%
719
22%
1802
10%
719
46%
719
26%
1182
April16th to endNight
48%
720
27%
1800
11%
720
55%
720
41%
1044
May1st to 15thNight
56%
539
29%
1619
17%
539
65%
539
47%
795
May16th to endNight
60%
413
27%
1535
22%
412
70%
412
40%
690
June1st to 15thNight
60%
360
27%
1440
26%
360
71%
360
39%
634
June16th to endNight
71%
360
36%
1440
42%
360
79%
360
60%
506
July1st to 15thNight
86%
395
33%
1415
37%
395
89%
395
73%
487
July16th to endNight
87%
564
39%
1593
35%
531
89%
531
68%
654
August1st to 15thNight
86%
526
38%
1575
30%
523
89%
523
69%
643
August16th to endNight
84%
668
39%
1718
25%
668
86%
668
70%
800
September1st to 15thNight
87%
660
43%
1650
30%
660
89%
660
77%
752
September16th to endNight
76%
656
40%
1820
33%
656
82%
656
65%
830
October1st to 15thNight
66%
660
30%
1980
27%
660
74%
660
45%
1007
October16th to endNight
67%
704
31%
2112
31%
704
73%
704
41%
1141
November1st to 15thNight
62%
700
25%
2160
23%
700
67%
700
34%
1241
November16th to endNight
55%
720
22%
2502
21%
720
59%
720
26%
1463
December1st to 15thNight
50%
720
20%
2520
17%
720
56%
720
21%
1600
December16th to endNight
44%
768
20%
2688
18%
768
51%
768
21%
1717

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%313313346%59%
47410
Night
11%313323346%56%
46745
TransparencyDay
27%48%20%24%15%
47099
Night
29%49%19%22%15%
46557
SeeingDay
12%13%25%28%15%4
5884
Night
12%6%15%29%28%7%
15165

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%435%422345%43%
1564
16th to endDay
18%6%25%323346%43%
1728
February1st to 15thDay
20%5%24424436%42%
1576
16th to endDay
20%6%24324447%37%
1532
March1st to 15thDay
20%8%35%42445%6%33%
1980
16th to endDay
18%5%245%35%35%7%40%
2112
April1st to 15thDay
15%6%24434347%41%
2146
16th to endDay
8%323323349%54%
2160
May1st to 15thDay
6%311212348%64%
2329
16th to endDay
6%323312347%60%
2575
June1st to 15thDay
5%312223336%64%
2520
16th to endDay
3111223479%
2520
July1st to 15thDay
111123383%
2457
16th to endDay
111111235%80%
2468
August1st to 15thDay
1112235%78%
2291
16th to endDay
111235%81%
2129
September1st to 15thDay
11112135%80%
1980
16th to endDay
412112136%74%
1806
October1st to 15thDay
10%212213335%63%
1650
16th to endDay
12%31331235%6%56%
1760
November1st to 15thDay
9%323335%5%5%6%51%
1696
16th to endDay
15%5%33423326%48%
1455
December1st to 15thDay
21%6%35%43332440%
1440
16th to endDay
23%6%35%323446%37%
1536
January1st to 15thNight
16%41343445%8%41%
2372
16th to endNight
19%5%13213347%46%
2496
February1st to 15thNight
18%5%2442435%6%41%
2276
16th to endNight
18%5%2332335%7%44%
1939
March1st to 15thNight
17%5%346%245%5%7%37%
1980
16th to endNight
16%6%24223446%46%
2112
April1st to 15thNight
11%5%35%42346%6%46%
1802
16th to endNight
7%313223445%61%
1800
May1st to 15thNight
3313313247%65%
1619
16th to endNight
3212223347%64%
1534
June1st to 15thNight
3322213447%64%
1440
16th to endNight
22111122380%
1440
July1st to 15thNight
111211483%
1500
16th to endNight
1121237%78%
1701
August1st to 15thNight
111112146%77%
1584
16th to endNight
11212336%75%
1718
September1st to 15thNight
111136%81%
1650
16th to endNight
3111111147%73%
1820
October1st to 15thNight
5%213313346%63%
1980
16th to endNight
9%31331335%7%57%
2112
November1st to 15thNight
11%32332336%8%50%
2160
16th to endNight
15%424412345%49%
2502
December1st to 15thNight
23%5%23323346%41%
2520
16th to endNight
22%5%2332435%6%41%
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%10%18%12%10%
1564
16th to endDay
42%5%6%14%18%12%
1728
February1st to 15thDay
43%49%17%20%4
1576
16th to endDay
45%5%11%22%11%3
1532
March1st to 15thDay
50%6%9%14%14%4
1980
16th to endDay
44%5%12%19%14%3
2112
April1st to 15thDay
42%5%13%22%14%1
2146
16th to endDay
26%6%14%26%19%5%
2160
May1st to 15thDay
19%310%33%25%7%
2329
16th to endDay
23%413%30%22%5%
2579
June1st to 15thDay
22%410%23%25%12%
2520
16th to endDay
10%25%17%40%24%
2520
July1st to 15thDay
7%1313%35%38%
2313
16th to endDay
10%2311%27%43%
2313
August1st to 15thDay
9%2318%33%32%
2275
16th to endDay
9%1419%37%27%
2129
September1st to 15thDay
9%1417%35%31%
1980
16th to endDay
13%16%25%32%20%
1806
October1st to 15thDay
23%47%22%26%15%
1650
16th to endDay
29%49%23%24%10%
1760
November1st to 15thDay
30%7%12%28%12%8%
1696
16th to endDay
39%410%19%17%7%
1455
December1st to 15thDay
48%47%15%20%4
1440
16th to endDay
46%5%9%16%14%7%
1536
January1st to 15thNight
39%6%12%16%15%9%
2372
16th to endNight
38%48%16%18%13%
2496
February1st to 15thNight
43%5%8%18%17%6%
2288
16th to endNight
39%414%22%15%2
1939
March1st to 15thNight
45%7%12%15%14%4
1980
16th to endNight
39%6%12%19%18%4
2112
April1st to 15thNight
36%7%14%21%17%3
1802
16th to endNight
25%49%30%22%6%
1800
May1st to 15thNight
20%37%25%32%9%
1620
16th to endNight
20%412%32%21%9%
1535
June1st to 15thNight
20%49%24%24%16%
1440
16th to endNight
12%1416%35%29%
1440
July1st to 15thNight
7%29%36%42%
1415
16th to endNight
11%1411%22%49%
1593
August1st to 15thNight
11%315%29%38%
1575
16th to endNight
12%416%34%31%
1718
September1st to 15thNight
8%313%36%36%
1650
16th to endNight
13%15%22%31%25%
1820
October1st to 15thNight
22%48%21%26%17%
1980
16th to endNight
26%39%22%24%12%
2112
November1st to 15thNight
30%6%13%26%14%7%
2160
16th to endNight
36%5%9%20%20%8%
2502
December1st to 15thNight
44%48%16%19%5%
2520
16th to endNight
43%5%9%15%18%6%
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
30%14%23%14%16%2
192
16th to endDay
21%15%21%22%16%3
256
February1st to 15thDay
22%15%25%19%15%2
236
16th to endDay
23%22%21%21%10%
229
March1st to 15thDay
28%20%23%15%8%3
270
16th to endDay
21%23%32%16%42
288
April1st to 15thDay
18%28%26%18%5%2
269
16th to endDay
16%26%28%19%7%1
270
May1st to 15thDay
13%23%30%21%8%1
288
16th to endDay
11%14%23%26%18%5%
330
June1st to 15thDay
10%15%33%27%11%2
315
16th to endDay
47%32%33%17%4
315
July1st to 15thDay
2418%43%25%5%
305
16th to endDay
216%49%21%9%
327
August1st to 15thDay
2323%43%20%7%
300
16th to endDay
1226%43%20%4
268
September1st to 15thDay
15%19%43%22%7%
255
16th to endDay
49%20%34%23%7%
255
October1st to 15thDay
10%9%27%25%19%7%
255
16th to endDay
16%10%24%27%18%1
272
November1st to 15thDay
10%13%20%22%29%3
202
16th to endDay
17%14%34%17%7%7%
63
December1st to 15thDay
41%8%26%16%6%
60
16th to endDay
26%14%12%20%20%6%
64
January1st to 15thNight
18%5%11%32%24%7%
720
16th to endNight
22%413%29%22%7%
768
February1st to 15thNight
21%5%14%32%22%4
704
16th to endNight
21%7%20%27%18%4
632
March1st to 15thNight
19%9%17%27%21%4
720
16th to endNight
19%10%24%26%16%2
768
April1st to 15thNight
15%13%23%26%16%4
719
16th to endNight
10%14%23%25%20%5%
720
May1st to 15thNight
5%7%25%32%23%5%
540
16th to endNight
5%8%21%28%30%5%
413
June1st to 15thNight
39%22%35%27%1
360
16th to endNight
4219%40%30%1
360
July1st to 15thNight
218%30%50%6%
395
16th to endNight
11426%52%13%
564
August1st to 15thNight
27%32%44%14%
526
16th to endNight
218%28%50%8%
668
September1st to 15thNight
126%30%44%15%
660
16th to endNight
5%311%30%37%12%
656
October1st to 15thNight
7%414%28%33%11%
660
16th to endNight
11%312%26%33%12%
704
November1st to 15thNight
13%414%32%27%8%
700
16th to endNight
17%7%13%28%23%9%
720
December1st to 15thNight
25%5%13%28%20%7%
720
16th to endNight
24%9%15%29%17%3
768
Page generated at 2017-08-13 11:16:33. Version ac04

Copyright 2017 A. Danko


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