Vacaville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vacaville clear sky chart from 2005-11-06 to 2024-01-12.

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
64%
23549
30%
74741
25%
23501
71%
23501
44%
38183

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 10thNight
52%
759
18%
2595
16%
756
57%
756
25%
1594
January11th to 20thNight
54%
724
22%
2353
17%
724
62%
724
28%
1404
January21st to endNight
56%
792
26%
2574
23%
792
63%
792
30%
1501
February1st to 10thNight
55%
720
27%
2340
24%
720
64%
720
30%
1345
February11th to 20thNight
51%
700
27%
2196
20%
700
62%
700
34%
1223
February21st to endNight
53%
592
30%
1776
22%
592
64%
592
37%
989
March1st to 10thNight
49%
720
19%
2035
14%
720
55%
720
29%
1291
March11th to 20thNight
54%
720
26%
1980
21%
720
59%
720
34%
1230
March21st to endNight
50%
792
23%
2135
13%
792
58%
792
38%
1259
April1st to 10thNight
55%
720
26%
1800
12%
720
62%
720
41%
1093
April11th to 20thNight
53%
711
32%
1779
13%
711
61%
711
50%
992
April21st to endNight
61%
720
31%
1800
14%
720
67%
720
60%
927
May1st to 10thNight
62%
635
32%
1715
18%
635
68%
635
60%
835
May11th to 20thNight
69%
431
35%
1493
27%
431
78%
431
59%
596
May21st to endNight
64%
388
31%
1552
26%
388
78%
388
60%
545
June1st to 10thNight
68%
360
29%
1440
27%
360
79%
360
50%
574
June11th to 20thNight
70%
360
38%
1440
38%
360
83%
360
70%
453
June21st to endNight
71%
360
37%
1440
40%
360
83%
360
70%
468
July1st to 10thNight
80%
350
39%
1400
42%
350
90%
350
79%
410
July11th to 20thNight
82%
441
39%
1485
35%
441
89%
441
79%
514
July21st to endNight
81%
591
42%
1674
31%
558
89%
558
78%
638
August1st to 10thNight
77%
537
39%
1602
28%
534
83%
534
72%
649
August11th to 20thNight
82%
637
43%
1705
26%
637
86%
637
81%
717
August21st to endNight
85%
792
45%
1980
27%
792
87%
792
85%
867
September1st to 10thNight
85%
720
46%
1800
30%
720
89%
720
86%
776
September11th to 20thNight
78%
720
46%
1800
31%
720
84%
720
75%
836
September21st to endNight
77%
720
43%
2041
38%
720
84%
720
72%
868
October1st to 10thNight
75%
720
36%
2160
33%
720
83%
720
64%
926
October11th to 20thNight
72%
720
39%
2160
37%
720
81%
720
59%
970
October21st to endNight
69%
792
39%
2376
36%
792
78%
792
55%
1108
November1st to 10thNight
67%
740
32%
2292
28%
740
75%
740
45%
1163
November11th to 20thNight
65%
760
29%
2470
27%
760
72%
760
41%
1278
November21st to endNight
62%
760
29%
2636
29%
760
68%
760
37%
1333
December1st to 10thNight
52%
760
23%
2660
18%
760
61%
760
27%
1547
December11th to 20thNight
51%
759
18%
3235
18%
759
58%
759
17%
2217
December21st to endNight
44%
826
14%
4822
16%
817
54%
817
13%
3047

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
7%313323347%64%
74696
Night
8%313323347%61%
75017
TransparencyDay
22%48%20%26%20%
74412
Night
24%49%20%24%20%
74822
SeeingDay
8%6%21%32%25%9%
14158
Night
9%319%40%26%3
23566

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 10thDay
19%7%46%5%335%47%35%
1566
11th to 20thDay
12%435%6%34346%51%
1630
21st to endDay
13%7%25%5%35%6%6%6%42%
1782
February1st to 10thDay
14%436%43435%6%47%
1620
11th to 20thDay
12%4344345%5%7%49%
1651
21st to endDay
12%5%2443446%7%50%
1480
March1st to 10thDay
11%7%36%5%45%5%6%8%40%
1921
11th to 20thDay
14%5%25%6%35%46%8%41%
1980
21st to endDay
10%4244345%6%8%50%
2219
April1st to 10thDay
11%6%345%345%7%8%45%
2160
11th to 20thDay
8%3233235%5%8%59%
2129
21st to endDay
331333445%9%64%
2160
May1st to 10thDay
431332325%8%67%
2240
11th to 20thDay
321231345%9%68%
2399
21st to endDay
311232335%8%68%
2723
June1st to 10thDay
331222335%9%67%
2520
11th to 20thDay
111112336%82%
2520
21st to endDay
211111245%83%
2520
July1st to 10thDay
11111235%86%
2520
11th to 20thDay
11111236%85%
2422
21st to endDay
111111236%83%
2546
August1st to 10thDay
111212336%80%
2328
11th to 20thDay
11112335%83%
2193
21st to endDay
1111111235%86%
2376
September1st to 10thDay
1111123486%
2160
11th to 20thDay
221221335%7%74%
2160
21st to endDay
2112212235%79%
1916
October1st to 10thDay
2212323335%74%
1800
11th to 20thDay
5%222323346%69%
1800
21st to endDay
6%323323337%66%
1980
November1st to 10thDay
7%41432445%7%59%
1784
11th to 20thDay
9%6%25%44445%7%51%
1710
21st to endDay
9%42333445%6%56%
1539
December1st to 10thDay
13%6%25%3345%5%6%47%
1520
11th to 20thDay
27%10%36%5%33346%32%
1928
21st to endDay
19%8%36%5%3445%8%36%
2794
January1st to 10thNight
15%6%25%5%2445%9%42%
2595
11th to 20thNight
12%5%25%5%4445%7%47%
2353
21st to endNight
13%5%244245%5%8%48%
2574
February1st to 10thNight
14%424434345%52%
2340
11th to 20thNight
10%425%435%45%8%52%
2194
21st to endNight
12%424323348%55%
1776
March1st to 10thNight
13%6%36%44445%6%44%
2035
11th to 20thNight
13%5%24335%5%5%8%47%
1980
21st to endNight
12%424433446%55%
2135
April1st to 10thNight
7%4235%35%45%7%54%
1800
11th to 20thNight
7%32232345%6%64%
1779
21st to endNight
421232245%8%68%
1800
May1st to 10thNight
3212223338%70%
1715
11th to 20thNight
2112222448%71%
1493
21st to endNight
221211235%9%72%
1552
June1st to 10thNight
3212223348%70%
1440
11th to 20thNight
111112236%82%
1440
21st to endNight
1111211235%82%
1440
July1st to 10thNight
11111225%86%
1440
11th to 20thNight
1111111136%83%
1534
21st to endNight
111111125%11%75%
1773
August1st to 10thNight
2111112349%74%
1611
11th to 20thNight
11123410%77%
1705
21st to endNight
11111249%80%
1980
September1st to 10thNight
11111137%84%
1800
11th to 20thNight
2112112348%75%
1800
21st to endNight
111212336%79%
2041
October1st to 10thNight
3212212347%74%
2160
11th to 20thNight
3212223349%70%
2160
21st to endNight
5%21231335%7%68%
2376
November1st to 10thNight
6%32333345%9%60%
2292
11th to 20thNight
8%42332345%8%57%
2470
21st to endNight
8%3244235%46%59%
2636
December1st to 10thNight
14%5%26%5%33346%49%
2660
11th to 20thNight
25%7%35%42446%7%34%
3276
21st to endNight
16%7%36%6%35%46%6%38%
4862

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 10thDay
50%7%12%17%11%3
1566
11th to 20thDay
37%412%18%20%10%
1630
21st to endDay
41%5%11%17%20%7%
1782
February1st to 10thDay
39%48%22%19%8%
1620
11th to 20thDay
35%5%10%21%21%8%
1660
21st to endDay
33%410%25%19%9%
1480
March1st to 10thDay
41%5%12%21%16%4
1921
11th to 20thDay
41%410%23%16%6%
1980
21st to endDay
32%7%16%20%21%5%
2219
April1st to 10thDay
35%6%13%21%19%7%
2160
11th to 20thDay
24%5%13%25%24%9%
2132
21st to endDay
19%413%30%28%7%
2160
May1st to 10thDay
17%310%28%32%11%
2240
11th to 20thDay
15%48%32%30%12%
2402
21st to endDay
15%415%34%25%8%
2724
June1st to 10thDay
16%5%10%29%29%11%
2520
11th to 20thDay
6%28%24%35%24%
2520
21st to endDay
6%1314%37%37%
2520
July1st to 10thDay
41310%27%54%
2451
11th to 20thDay
5%1414%27%49%
2348
21st to endDay
6%2310%27%54%
2405
August1st to 10thDay
8%2316%33%38%
2312
11th to 20thDay
5%2314%35%41%
2193
21st to endDay
5%1214%36%42%
2376
September1st to 10thDay
6%138%33%50%
2160
11th to 20thDay
12%25%22%41%18%
2160
21st to endDay
10%3419%34%29%
1916
October1st to 10thDay
14%36%17%32%28%
1800
11th to 20thDay
18%38%20%24%26%
1800
21st to endDay
22%38%21%27%19%
1980
November1st to 10thDay
24%49%28%22%12%
1784
11th to 20thDay
34%5%10%25%20%6%
1710
21st to endDay
29%411%23%24%10%
1539
December1st to 10thDay
37%5%12%22%17%8%
1520
11th to 20thDay
56%5%9%12%15%4
1928
21st to endDay
47%7%13%19%12%3
2794
January1st to 10thNight
40%5%14%24%12%6%
2595
11th to 20thNight
36%5%12%19%15%12%
2353
21st to endNight
34%5%13%17%22%9%
2574
February1st to 10thNight
35%38%21%22%10%
2340
11th to 20thNight
31%410%23%21%11%
2196
21st to endNight
30%39%27%23%8%
1776
March1st to 10thNight
40%413%18%19%5%
2035
11th to 20thNight
36%47%25%19%8%
1980
21st to endNight
31%412%23%22%7%
2135
April1st to 10thNight
30%5%15%20%22%9%
1800
11th to 20thNight
22%411%28%20%14%
1779
21st to endNight
17%312%30%31%8%
1800
May1st to 10thNight
16%310%22%35%14%
1715
11th to 20thNight
13%39%30%31%14%
1493
21st to endNight
11%315%36%24%11%
1552
June1st to 10thNight
16%410%24%32%15%
1440
11th to 20thNight
7%27%20%36%28%
1440
21st to endNight
7%3312%33%42%
1440
July1st to 10thNight
5%1210%26%57%
1400
11th to 20thNight
6%1311%23%56%
1485
21st to endNight
7%1210%24%56%
1674
August1st to 10thNight
10%1213%30%44%
1602
11th to 20thNight
5%2311%31%48%
1705
21st to endNight
5%1311%31%49%
1980
September1st to 10thNight
5%129%29%55%
1800
11th to 20thNight
10%25%19%38%26%
1800
21st to endNight
9%2419%30%36%
2041
October1st to 10thNight
12%38%19%29%30%
2160
11th to 20thNight
15%38%17%28%29%
2160
21st to endNight
17%37%21%27%25%
2376
November1st to 10thNight
23%410%26%20%16%
2292
11th to 20thNight
27%312%27%22%9%
2470
21st to endNight
27%49%22%25%13%
2636
December1st to 10thNight
37%410%20%18%11%
2660
11th to 20thNight
50%5%11%15%16%3
3276
21st to endNight
45%9%13%17%13%4
4862

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 10thDay
30%5%21%24%16%3
227
11th to 20thDay
16%6%20%31%20%7%
344
21st to endDay
15%6%20%25%27%8%
374
February1st to 10thDay
15%10%20%24%23%7%
340
11th to 20thDay
17%10%24%24%18%7%
369
21st to endDay
14%9%27%29%16%5%
346
March1st to 10thDay
17%10%25%30%12%5%
420
11th to 20thDay
18%7%25%25%18%8%
420
21st to endDay
13%13%26%27%18%3
462
April1st to 10thDay
14%8%28%24%18%7%
420
11th to 20thDay
8%11%32%24%17%8%
412
21st to endDay
310%26%26%24%10%
420
May1st to 10thDay
5%8%30%29%22%5%
423
11th to 20thDay
5%5%30%29%22%10%
448
21st to endDay
27%25%30%26%9%
485
June1st to 10thDay
46%25%35%22%8%
450
11th to 20thDay
18%22%38%26%5%
450
21st to endDay
1322%39%29%6%
450
July1st to 10thDay
1216%46%30%6%
446
11th to 20thDay
113%43%34%9%
444
21st to endDay
113%43%33%10%
487
August1st to 10thDay
2314%44%29%9%
447
11th to 20thDay
1216%38%30%14%
437
21st to endDay
1113%38%33%14%
495
September1st to 10thDay
1210%37%36%15%
450
11th to 20thDay
2418%33%29%14%
450
21st to endDay
2418%33%29%14%
450
October1st to 10thDay
27%20%26%27%18%
450
11th to 20thDay
6%5%18%27%28%17%
450
21st to endDay
8%5%18%27%28%14%
495
November1st to 10thDay
8%5%20%23%31%13%
380
11th to 20thDay
11%6%17%30%27%9%
270
21st to endDay
11%5%18%35%28%3
189
December1st to 10thDay
21%5%19%28%18%9%
180
11th to 20thDay
21%5%19%29%22%5%
180
21st to endDay
21%5%25%24%21%4
198
January1st to 10thNight
18%316%36%21%5%
760
11th to 20thNight
14%5%16%39%21%5%
724
21st to endNight
16%416%34%26%4
792
February1st to 10thNight
17%6%15%37%22%4
720
11th to 20thNight
11%6%24%33%22%4
704
21st to endNight
14%7%21%36%20%2
592
March1st to 10thNight
16%5%20%33%23%2
720
11th to 20thNight
16%419%36%23%2
720
21st to endNight
13%5%25%38%18%1
792
April1st to 10thNight
9%5%24%43%18%2
720
11th to 20thNight
9%6%28%34%20%3
711
21st to endNight
5%427%40%22%2
720
May1st to 10thNight
5%328%39%23%3
635
11th to 20thNight
3223%46%24%2
431
21st to endNight
3427%45%21%
389
June1st to 10thNight
4223%50%21%
360
11th to 20thNight
1225%55%18%
360
21st to endNight
1125%51%22%
360
July1st to 10thNight
1117%59%23%
350
11th to 20thNight
114%55%28%2
441
21st to endNight
1112%54%30%2
591
August1st to 10thNight
218%48%29%3
537
11th to 20thNight
115%50%31%2
637
21st to endNight
113%49%36%1
792
September1st to 10thNight
1111%47%37%3
720
11th to 20thNight
2116%45%31%4
720
21st to endNight
2216%40%36%5%
720
October1st to 10thNight
4314%42%31%6%
720
11th to 20thNight
4317%39%32%5%
720
21st to endNight
6%317%35%31%8%
792
November1st to 10thNight
7%318%32%35%6%
740
11th to 20thNight
9%216%39%28%5%
760
21st to endNight
10%5%16%40%24%5%
760
December1st to 10thNight
16%6%16%35%22%5%
760
11th to 20thNight
22%416%34%22%3
760
21st to endNight
19%7%20%33%20%1
836
Page generated at 2024-01-08 19:31:27. Version ac07

Copyright 2024 Attilla Danko


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