Sonoma State University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sonoma State University Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
61%
15304
26%
46861
22%
15268
66%
15268
35%
26635

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%
716
19%
2377
18%
716
62%
716
27%
1448
January16th to endNight
55%
768
25%
2496
24%
768
59%
768
28%
1515
February1st to 15thNight
52%
698
23%
2288
22%
698
57%
698
24%
1443
February16th to endNight
47%
632
22%
1927
16%
632
55%
632
27%
1217
March1st to 15thNight
50%
720
16%
1986
12%
720
53%
720
25%
1356
March16th to endNight
44%
768
21%
2104
14%
768
51%
768
30%
1354
April1st to 15thNight
45%
719
24%
1799
11%
719
51%
719
32%
1154
April16th to endNight
51%
720
27%
1800
12%
720
57%
720
42%
1041
May1st to 15thNight
61%
568
27%
1648
17%
568
66%
568
45%
859
May16th to endNight
61%
402
27%
1525
23%
402
70%
402
35%
724
June1st to 15thNight
64%
360
25%
1440
25%
360
72%
360
36%
669
June16th to endNight
78%
360
33%
1440
42%
360
83%
360
51%
563
July1st to 15thNight
85%
387
30%
1407
34%
387
86%
387
52%
579
July16th to endNight
78%
564
31%
1593
29%
531
79%
531
40%
835
August1st to 15thNight
76%
538
29%
1611
24%
535
77%
535
37%
868
August16th to endNight
77%
750
33%
1896
21%
750
79%
750
48%
1086
September1st to 15thNight
83%
706
37%
1765
25%
706
85%
706
56%
939
September16th to endNight
76%
656
37%
1812
32%
656
80%
656
53%
929
October1st to 15thNight
66%
660
30%
1980
28%
660
73%
660
43%
1042
October16th to endNight
68%
704
31%
2112
32%
704
73%
704
39%
1179
November1st to 15thNight
65%
700
27%
2172
27%
700
69%
700
38%
1197
November16th to endNight
59%
720
23%
2475
25%
720
63%
720
30%
1387
December1st to 15thNight
50%
720
20%
2520
19%
720
56%
720
22%
1600
December16th to endNight
48%
768
21%
2688
20%
768
54%
768
24%
1651

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
10%423313346%56%
47795
Night
11%413323347%53%
47049
TransparencyDay
30%28%21%23%13%
47483
Night
32%38%19%22%13%
46862
SeeingDay
12%9%23%31%17%5%
6001
Night
12%412%30%31%7%
15316

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
20%5%24323245%45%
1558
16th to endDay
17%7%2442423443%
1728
February1st to 15thDay
19%6%24424335%42%
1576
16th to endDay
20%7%23423447%38%
1545
March1st to 15thDay
20%6%35%42435%7%35%
1972
16th to endDay
19%5%2442445%7%39%
2118
April1st to 15thDay
16%5%344345%46%40%
2149
16th to endDay
9%42321235%8%56%
2160
May1st to 15thDay
7%41311235%7%61%
2301
16th to endDay
7%6%1322235%8%56%
2584
June1st to 15thDay
7%5%12212346%61%
2520
16th to endDay
3211112235%75%
2520
July1st to 15thDay
1211111246%74%
2466
16th to endDay
1313111236%73%
2468
August1st to 15thDay
1312122337%69%
2340
16th to endDay
1412112238%69%
2306
September1st to 15thDay
121222237%71%
2114
16th to endDay
6%211111246%69%
1815
October1st to 15thDay
9%312312346%60%
1650
16th to endDay
11%413323346%56%
1760
November1st to 15thDay
10%22441335%8%51%
1687
16th to endDay
16%6%2442344447%
1482
December1st to 15thDay
22%8%2332242442%
1440
16th to endDay
24%7%33323346%39%
1536
January1st to 15thNight
17%5%1442435%8%42%
2377
16th to endNight
20%6%23213346%47%
2496
February1st to 15thNight
18%6%24334346%41%
2276
16th to endNight
17%6%24323347%43%
1927
March1st to 15thNight
17%6%25%425%446%40%
1986
16th to endNight
18%7%24312336%46%
2104
April1st to 15thNight
13%5%2432445%6%48%
1799
16th to endNight
9%313323236%59%
1800
May1st to 15thNight
4424423247%61%
1648
16th to endNight
5%413223347%60%
1524
June1st to 15thNight
4313213447%60%
1440
16th to endNight
31221213474%
1440
July1st to 15thNight
212213236%73%
1491
16th to endNight
2413324349%59%
1701
August1st to 15thNight
15%14224449%57%
1620
16th to endNight
6%23324248%60%
1896
September1st to 15thNight
133214338%67%
1765
16th to endNight
4312122245%68%
1812
October1st to 15thNight
7%423312335%62%
1980
16th to endNight
9%413323346%55%
2112
November1st to 15thNight
10%42331235%8%54%
2172
16th to endNight
14%424313346%51%
2475
December1st to 15thNight
23%5%23323346%40%
2520
16th to endNight
22%413423346%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
42%312%18%14%8%
1558
16th to endDay
44%37%14%18%11%
1728
February1st to 15thDay
44%38%21%18%4
1576
16th to endDay
47%29%25%11%3
1545
March1st to 15thDay
47%412%18%13%4
1972
16th to endDay
43%412%21%15%2
2118
April1st to 15thDay
42%313%22%15%2
2149
16th to endDay
27%314%28%21%5%
2160
May1st to 15thDay
23%27%33%25%6%
2301
16th to endDay
28%214%28%21%5%
2588
June1st to 15thDay
25%311%23%24%12%
2520
16th to endDay
14%15%18%38%21%
2520
July1st to 15thDay
15%1311%31%36%
2321
16th to endDay
18%1310%29%36%
2313
August1st to 15thDay
20%2215%32%26%
2324
16th to endDay
20%1117%37%21%
2306
September1st to 15thDay
18%1216%33%27%
2114
16th to endDay
19%1326%29%18%
1815
October1st to 15thDay
26%27%21%27%14%
1650
16th to endDay
31%27%26%22%9%
1760
November1st to 15thDay
33%310%31%13%7%
1687
16th to endDay
41%29%20%18%6%
1482
December1st to 15thDay
46%39%17%19%3
1440
16th to endDay
47%39%17%14%6%
1536
January1st to 15thNight
40%312%20%14%8%
2377
16th to endNight
39%39%15%17%15%
2496
February1st to 15thNight
44%28%20%17%7%
2288
16th to endNight
40%412%23%15%3
1927
March1st to 15thNight
45%413%16%16%4
1986
16th to endNight
40%311%21%18%4
2104
April1st to 15thNight
35%414%22%18%4
1799
16th to endNight
27%210%28%21%8%
1800
May1st to 15thNight
25%26%24%30%11%
1649
16th to endNight
26%210%30%22%7%
1525
June1st to 15thNight
24%410%22%24%14%
1440
16th to endNight
16%2315%36%25%
1440
July1st to 15thNight
17%218%32%38%
1407
16th to endNight
28%228%25%31%
1593
August1st to 15thNight
30%2112%25%26%
1611
16th to endNight
27%2212%29%26%
1896
September1st to 15thNight
21%1213%31%30%
1765
16th to endNight
21%1222%30%21%
1812
October1st to 15thNight
26%26%21%25%17%
1980
16th to endNight
30%25%23%25%12%
2112
November1st to 15thNight
29%313%30%14%7%
2172
16th to endNight
35%29%23%20%8%
2475
December1st to 15thNight
45%28%17%19%5%
2520
16th to endNight
42%310%17%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
29%9%20%22%15%2
186
16th to endDay
18%11%22%26%17%3
256
February1st to 15thDay
20%7%26%22%20%2
236
16th to endDay
21%15%24%24%12%1
233
March1st to 15thDay
25%14%25%18%11%4
270
16th to endDay
19%14%33%22%6%2
288
April1st to 15thDay
17%22%29%20%5%3
269
16th to endDay
14%23%27%23%8%2
270
May1st to 15thDay
10%16%29%29%12%1
288
16th to endDay
12%11%21%27%19%6%
330
June1st to 15thDay
9%13%28%34%10%4
315
16th to endDay
2328%36%21%6%
315
July1st to 15thDay
2216%44%23%9%
305
16th to endDay
114%51%21%10%
327
August1st to 15thDay
3420%42%22%6%
315
16th to endDay
2322%38%24%8%
332
September1st to 15thDay
5%321%39%21%9%
300
16th to endDay
6%7%21%29%24%10%
255
October1st to 15thDay
10%7%26%31%16%7%
255
16th to endDay
15%9%22%31%16%4
272
November1st to 15thDay
9%8%19%23%29%9%
193
16th to endDay
13%11%26%25%20%1
67
December1st to 15thDay
41%10%20%15%13%
60
16th to endDay
18%15%10%29%21%3
64
January1st to 15thNight
18%39%35%26%7%
720
16th to endNight
20%5%10%30%25%7%
768
February1st to 15thNight
19%5%10%32%26%4
704
16th to endNight
19%6%17%31%19%5%
632
March1st to 15thNight
18%7%13%29%25%4
720
16th to endNight
18%7%19%31%20%2
768
April1st to 15thNight
13%11%20%31%19%4
719
16th to endNight
10%10%22%25%24%6%
720
May1st to 15thNight
6%418%33%32%5%
569
16th to endNight
7%6%17%30%30%7%
403
June1st to 15thNight
6%418%36%31%2
360
16th to endNight
4111%40%38%3
360
July1st to 15thNight
3427%54%10%
387
16th to endNight
42323%51%14%
564
August1st to 15thNight
5%15%27%47%12%
538
16th to endNight
5%25%29%46%10%
750
September1st to 15thNight
31429%48%12%
706
16th to endNight
6%28%30%38%13%
656
October1st to 15thNight
8%5%10%31%33%10%
660
16th to endNight
11%28%31%31%14%
704
November1st to 15thNight
11%311%31%32%9%
700
16th to endNight
14%5%12%30%29%8%
720
December1st to 15thNight
24%410%31%22%6%
720
16th to endNight
22%6%15%34%18%2
768
Page generated at 2017-09-13 04:39:11. Version ac04

Copyright 2017 A. Danko


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