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 2017-09-16.

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%
15300
30%
46892
24%
15261
72%
15261
45%
23959

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%
719
20%
2414
17%
716
62%
716
31%
1393
January16th to endNight
57%
768
26%
2496
23%
768
63%
768
29%
1485
February1st to 15thNight
56%
697
24%
2288
22%
697
64%
697
27%
1386
February16th to endNight
55%
632
26%
1903
21%
632
63%
632
33%
1129
March1st to 15thNight
55%
720
19%
2017
16%
720
59%
720
31%
1280
March16th to endNight
51%
768
23%
2082
15%
768
58%
768
35%
1265
April1st to 15thNight
54%
719
25%
1799
12%
719
61%
719
40%
1110
April16th to endNight
58%
720
28%
1800
12%
720
64%
720
54%
969
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%
660
43%
1808
36%
660
86%
660
71%
796
October1st to 15thNight
72%
660
34%
1980
32%
660
79%
660
56%
906
October16th to endNight
70%
704
35%
2112
34%
704
77%
704
51%
1035
November1st to 15thNight
69%
700
30%
2205
27%
700
76%
700
45%
1115
November16th to endNight
62%
720
26%
2445
26%
720
67%
720
35%
1302
December1st to 15thNight
54%
720
21%
2520
17%
720
62%
720
25%
1529
December16th to endNight
47%
768
21%
2688
16%
768
56%
768
24%
1635

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%212223346%63%
47868
Night
7%312213348%60%
47077
TransparencyDay
22%38%20%25%18%
47552
Night
23%39%20%24%18%
46893
SeeingDay
7%5%21%31%24%8%
5957
Night
8%316%39%27%4
15310

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%33445%45%
1522
16th to endDay
15%5%24434445%44%
1728
February1st to 15thDay
15%5%25%32435%5%44%
1576
16th to endDay
15%5%244245%5%7%42%
1571
March1st to 15thDay
11%5%25%5%45%45%8%40%
1941
16th to endDay
10%4245%3446%8%44%
2141
April1st to 15thDay
11%5%343245%6%7%44%
2149
16th to endDay
4212223347%63%
2160
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%75%
1838
October1st to 15thDay
4112314336%68%
1650
16th to endDay
6%323423237%60%
1760
November1st to 15thDay
6%31332446%7%55%
1652
16th to endDay
11%5%24334345%50%
1512
December1st to 15thDay
17%6%25%43334443%
1440
16th to endDay
17%6%24423347%41%
1536
January1st to 15thNight
12%6%13423449%47%
2414
16th to endNight
14%5%14323447%48%
2496
February1st to 15thNight
14%414435%447%44%
2276
16th to endNight
13%414423348%48%
1903
March1st to 15thNight
13%42443445%7%44%
2017
16th to endNight
12%314333446%51%
2082
April1st to 15thNight
8%322425%45%7%52%
1799
16th to endNight
6%212312346%65%
1800
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
11112328%75%
1808
October1st to 15thNight
41221235%8%66%
1980
16th to endNight
43321335%8%62%
2112
November1st to 15thNight
6%312223349%59%
2205
16th to endNight
8%423323446%56%
2445
December1st to 15thNight
17%42442335%6%45%
2520
16th to endNight
17%5%24323345%46%
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
41%5%12%15%20%4
1522
16th to endDay
41%48%15%20%9%
1728
February1st to 15thDay
41%5%9%20%18%3
1576
16th to endDay
39%5%12%26%12%4
1571
March1st to 15thDay
41%5%12%20%14%4
1941
16th to endDay
37%6%16%17%18%3
2141
April1st to 15thDay
36%6%12%21%19%3
2149
16th to endDay
20%314%27%25%8%
2160
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%2422%35%22%
1838
October1st to 15thDay
18%38%22%28%18%
1650
16th to endDay
25%38%23%27%12%
1760
November1st to 15thDay
26%414%30%16%6%
1652
16th to endDay
36%5%9%22%20%5%
1512
December1st to 15thDay
43%410%20%17%3
1440
16th to endDay
42%5%10%20%16%5%
1536
January1st to 15thNight
35%413%22%16%8%
2414
16th to endNight
36%5%9%16%18%14%
2496
February1st to 15thNight
39%39%21%17%8%
2288
16th to endNight
34%411%27%18%3
1903
March1st to 15thNight
38%412%20%17%6%
2017
16th to endNight
33%311%23%19%7%
2082
April1st to 15thNight
30%5%14%23%18%7%
1799
16th to endNight
19%214%24%27%10%
1800
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
10%1420%36%26%
1808
October1st to 15thNight
16%29%22%27%21%
1980
16th to endNight
20%28%23%26%18%
2112
November1st to 15thNight
23%413%30%18%10%
2205
16th to endNight
29%39%23%24%9%
2445
December1st to 15thNight
39%411%18%19%6%
2520
16th to endNight
39%411%16%20%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
26%5%19%22%20%6%
150
16th to endDay
16%5%18%23%25%10%
256
February1st to 15thDay
17%9%21%20%22%8%
236
16th to endDay
20%6%19%24%18%9%
237
March1st to 15thDay
16%8%24%21%17%11%
270
16th to endDay
11%12%25%23%20%4
288
April1st to 15thDay
12%13%30%23%12%8%
269
16th to endDay
5%15%30%24%18%5%
270
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
2418%27%22%23%
258
October1st to 15thDay
5%6%20%27%23%16%
255
16th to endDay
9%421%28%22%13%
272
November1st to 15thDay
8%315%22%33%16%
158
16th to endDay
16%9%16%27%29%
72
December1st to 15thDay
30%13%11%30%13%1
60
16th to endDay
14%132%20%29%1
64
January1st to 15thNight
14%315%33%26%5%
720
16th to endNight
16%413%33%25%6%
768
February1st to 15thNight
15%413%35%25%4
704
16th to endNight
15%418%35%22%3
632
March1st to 15thNight
14%417%32%28%2
720
16th to endNight
13%5%21%36%21%1
768
April1st to 15thNight
10%5%23%38%19%2
719
16th to endNight
6%5%25%35%23%3
720
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
1113%38%37%7%
660
October1st to 15thNight
5%314%40%30%6%
660
16th to endNight
6%215%34%32%8%
704
November1st to 15thNight
7%316%32%35%6%
700
16th to endNight
11%414%38%24%7%
720
December1st to 15thNight
17%5%12%35%21%6%
720
16th to endNight
19%6%19%30%22%1
768
Page generated at 2017-09-17 09:05:47. Version ac04

Copyright 2017 A. Danko


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