Vacaville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vacaville clear sky chart from 2005-11-05 to 2018-04-23.

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
66%
16168
30%
49558
24%
16129
72%
16129
45%
25358

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
56%
779
19%
2616
17%
776
62%
776
29%
1540
January16th to endNight
58%
832
24%
2704
22%
832
64%
832
29%
1617
February1st to 15thNight
57%
757
26%
2483
23%
757
66%
757
29%
1455
February16th to endNight
55%
684
28%
2059
22%
684
64%
684
35%
1196
March1st to 15thNight
55%
780
19%
2185
16%
780
59%
780
30%
1394
March16th to endNight
51%
832
23%
2256
15%
832
58%
832
36%
1364
April1st to 15thNight
54%
779
26%
1949
12%
779
60%
779
39%
1206
April16th to endNight
59%
744
29%
1860
13%
744
65%
744
55%
995
May1st to 15thNight
68%
593
31%
1673
20%
593
73%
593
64%
764
May16th to endNight
69%
374
31%
1496
28%
374
79%
374
59%
528
June1st to 15thNight
71%
360
29%
1440
29%
360
82%
360
54%
544
June16th to endNight
75%
360
37%
1440
42%
360
85%
360
69%
468
July1st to 15thNight
84%
343
36%
1363
41%
343
91%
343
75%
416
July16th to endNight
86%
564
40%
1593
32%
531
91%
531
79%
610
August1st to 15thNight
82%
547
40%
1620
30%
544
86%
544
75%
645
August16th to endNight
87%
764
45%
1910
28%
764
89%
764
83%
850
September1st to 15thNight
87%
720
43%
1800
29%
720
90%
720
81%
799
September16th to endNight
80%
716
45%
1962
37%
716
86%
716
73%
854
October1st to 15thNight
72%
720
33%
2160
31%
720
80%
720
58%
967
October16th to endNight
72%
768
38%
2304
38%
768
79%
768
53%
1109
November1st to 15thNight
68%
760
29%
2394
26%
760
74%
760
43%
1232
November16th to endNight
62%
780
25%
2649
26%
780
66%
780
34%
1434
December1st to 15thNight
55%
780
22%
2730
19%
780
63%
780
27%
1603
December16th to endNight
47%
832
22%
2912
17%
832
57%
832
24%
1768

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
6%312223346%62%
49960
Night
7%312313347%60%
49743
TransparencyDay
23%38%20%25%18%
49644
Night
24%39%20%24%18%
49559
SeeingDay
8%5%20%31%24%8%
6671
Night
8%316%39%27%4
16178

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%345%33446%42%
1650
16th to endDay
15%6%24434445%43%
1872
February1st to 15thDay
14%425%32435%6%46%
1711
16th to endDay
14%5%244245%5%7%44%
1700
March1st to 15thDay
12%5%25%6%35%45%8%39%
2103
16th to endDay
10%4245%3446%8%44%
2319
April1st to 15thDay
12%4344245%6%7%44%
2329
16th to endDay
4212223347%63%
2214
May1st to 15thDay
321221225%8%69%
2274
16th to endDay
311221335%8%65%
2615
June1st to 15thDay
3212212346%69%
2520
16th to endDay
11145%81%
2520
July1st to 15thDay
1135%83%
2514
16th to endDay
1125%84%
2468
August1st to 15thDay
1111236%80%
2329
16th to endDay
111125%83%
2292
September1st to 15thDay
1112245%79%
2160
16th to endDay
211112235%76%
1995
October1st to 15thDay
3112313346%69%
1800
16th to endDay
6%323423236%62%
1920
November1st to 15thDay
7%31332446%8%54%
1793
16th to endDay
11%6%24334345%49%
1638
December1st to 15thDay
15%6%25%333345%45%
1560
16th to endDay
16%6%25%433347%41%
1664
January1st to 15thNight
13%5%2442345%8%45%
2616
16th to endNight
14%5%2432345%7%47%
2704
February1st to 15thNight
13%414435%447%47%
2471
16th to endNight
13%414322348%51%
2059
March1st to 15thNight
13%42443445%7%43%
2185
16th to endNight
12%313333446%52%
2256
April1st to 15thNight
8%3235%25%45%7%51%
1949
16th to endNight
6%211312346%66%
1860
May1st to 15thNight
212113338%71%
1673
16th to endNight
21111235%10%69%
1496
June1st to 15thNight
211112247%72%
1440
16th to endNight
111225%81%
1440
July1st to 15thNight
1112484%
1443
16th to endNight
1111411%75%
1701
August1st to 15thNight
11112411%73%
1629
16th to endNight
122411%74%
1910
September1st to 15thNight
11239%78%
1800
16th to endNight
11112227%77%
1962
October1st to 15thNight
312212347%69%
2160
16th to endNight
42221335%8%64%
2304
November1st to 15thNight
7%322323349%57%
2394
16th to endNight
9%423423446%54%
2649
December1st to 15thNight
16%31442335%6%47%
2730
16th to endNight
16%5%24423345%46%
2912

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
43%5%12%15%19%4
1650
16th to endDay
42%48%15%19%8%
1872
February1st to 15thDay
39%49%21%20%5%
1711
16th to endDay
37%5%12%25%14%4
1700
March1st to 15thDay
42%5%11%21%13%4
2103
16th to endDay
36%6%16%18%18%3
2319
April1st to 15thDay
36%5%12%22%19%3
2329
16th to endDay
20%313%27%25%8%
2214
May1st to 15thDay
14%28%29%33%12%
2274
16th to endDay
17%312%32%24%9%
2619
June1st to 15thDay
16%410%25%26%17%
2520
16th to endDay
6%1417%38%32%
2520
July1st to 15thDay
5%1211%27%52%
2365
16th to endDay
5%411%25%52%
2313
August1st to 15thDay
7%1315%32%39%
2313
16th to endDay
5%1216%38%35%
2292
September1st to 15thDay
8%1413%36%35%
2160
16th to endDay
12%25%22%36%21%
1995
October1st to 15thDay
16%38%20%27%23%
1800
16th to endDay
24%28%22%26%14%
1920
November1st to 15thDay
27%413%31%16%6%
1793
16th to endDay
36%410%22%20%4
1638
December1st to 15thDay
41%39%19%19%5%
1560
16th to endDay
42%410%20%15%5%
1664
January1st to 15thNight
36%413%22%15%7%
2616
16th to endNight
35%5%11%16%17%13%
2704
February1st to 15thNight
36%38%21%19%9%
2483
16th to endNight
32%411%27%20%4
2059
March1st to 15thNight
39%412%20%17%6%
2185
16th to endNight
33%310%23%21%7%
2256
April1st to 15thNight
31%413%23%19%7%
1949
16th to endNight
19%213%25%28%10%
1860
May1st to 15thNight
13%29%23%33%16%
1674
16th to endNight
11%213%36%23%13%
1496
June1st to 15thNight
13%39%23%29%20%
1440
16th to endNight
7%2314%33%38%
1440
July1st to 15thNight
6%18%25%56%
1363
16th to endNight
7%212%23%53%
1593
August1st to 15thNight
8%1114%29%44%
1620
16th to endNight
5%1212%35%42%
1910
September1st to 15thNight
6%1313%32%42%
1800
16th to endNight
9%1421%36%26%
1962
October1st to 15thNight
15%28%20%26%26%
2160
16th to endNight
19%28%22%27%19%
2304
November1st to 15thNight
24%312%31%17%9%
2394
16th to endNight
30%39%22%23%8%
2649
December1st to 15thNight
37%410%18%20%9%
2730
16th to endNight
39%410%17%20%6%
2912

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
26%418%24%20%5%
188
16th to endDay
16%418%24%26%9%
304
February1st to 15thDay
15%9%22%20%23%9%
281
16th to endDay
17%7%22%25%18%8%
288
March1st to 15thDay
18%8%21%25%16%9%
330
16th to endDay
13%11%25%25%20%4
352
April1st to 15thDay
13%12%27%21%15%8%
329
16th to endDay
6%14%28%23%20%6%
288
May1st to 15thDay
46%32%32%21%2
288
16th to endDay
36%24%32%26%6%
330
June1st to 15thDay
5%7%27%35%19%3
315
16th to endDay
1320%38%31%4
315
July1st to 15thDay
16%46%30%4
305
16th to endDay
15%46%26%9%
327
August1st to 15thDay
1214%46%27%6%
315
16th to endDay
14%40%32%11%
332
September1st to 15thDay
1113%38%31%13%
315
16th to endDay
2419%31%22%19%
315
October1st to 15thDay
48%21%27%23%13%
315
16th to endDay
7%318%26%27%16%
336
November1st to 15thDay
11%315%22%31%14%
209
16th to endDay
16%7%12%34%28%
108
December1st to 15thDay
21%11%11%25%23%7%
90
16th to endDay
11%129%17%35%5%
96
January1st to 15thNight
15%315%33%26%6%
780
16th to endNight
15%313%34%25%6%
832
February1st to 15thNight
14%5%14%35%25%4
764
16th to endNight
14%418%36%22%3
684
March1st to 15thNight
14%417%33%27%2
780
16th to endNight
13%5%22%36%20%1
832
April1st to 15thNight
10%5%23%38%19%2
779
16th to endNight
6%5%24%35%24%3
744
May1st to 15thNight
3223%44%23%2
594
16th to endNight
2222%44%25%1
375
June1st to 15thNight
3220%54%18%
360
16th to endNight
20%52%25%
360
July1st to 15thNight
13%58%27%
343
16th to endNight
19%51%35%3
564
August1st to 15thNight
112%48%34%2
547
16th to endNight
10%50%36%2
764
September1st to 15thNight
18%43%40%4
720
16th to endNight
1114%38%37%7%
716
October1st to 15thNight
4314%40%29%6%
720
16th to endNight
5%214%33%34%9%
768
November1st to 15thNight
7%215%33%34%5%
760
16th to endNight
11%314%38%24%6%
780
December1st to 15thNight
16%5%12%34%23%6%
780
16th to endNight
19%6%18%30%24%1
832
Page generated at 2018-04-24 07:03:00. Version ac04

Copyright 2018 A. Danko


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