Vallejo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vallejo Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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%
15337
26%
46911
22%
15301
65%
15301
37%
26038

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
62%
716
19%
2395
18%
716
66%
716
29%
1413
January16th to endNight
57%
768
25%
2496
26%
768
61%
768
28%
1504
February1st to 15thNight
53%
698
23%
2288
22%
698
60%
698
25%
1408
February16th to endNight
50%
632
23%
1908
18%
632
58%
632
28%
1185
March1st to 15thNight
51%
720
18%
2004
16%
720
55%
720
28%
1306
March16th to endNight
49%
768
21%
2091
15%
768
54%
768
33%
1317
April1st to 15thNight
45%
719
24%
1799
11%
719
51%
719
34%
1136
April16th to endNight
51%
720
26%
1800
11%
720
56%
720
45%
1011
May1st to 15thNight
64%
596
26%
1676
17%
596
68%
596
50%
851
May16th to endNight
57%
385
26%
1507
22%
385
66%
385
41%
665
June1st to 15thNight
58%
360
24%
1440
21%
360
69%
360
37%
659
June16th to endNight
71%
360
34%
1440
38%
360
80%
360
58%
515
July1st to 15thNight
78%
367
29%
1387
31%
367
85%
367
52%
566
July16th to endNight
69%
564
29%
1593
24%
531
72%
531
37%
844
August1st to 15thNight
68%
544
30%
1617
22%
541
71%
541
42%
840
August16th to endNight
69%
764
34%
1910
20%
764
71%
764
51%
1077
September1st to 15thNight
75%
720
36%
1800
24%
720
78%
720
58%
955
September16th to endNight
72%
664
37%
1823
32%
664
77%
664
55%
916
October1st to 15thNight
67%
660
31%
1980
28%
660
75%
660
44%
1031
October16th to endNight
68%
704
33%
2112
33%
704
72%
704
42%
1130
November1st to 15thNight
67%
700
28%
2189
27%
700
72%
700
40%
1163
November16th to endNight
62%
720
25%
2448
27%
720
66%
720
33%
1343
December1st to 15thNight
54%
720
20%
2520
19%
720
59%
720
24%
1561
December16th to endNight
49%
768
21%
2688
19%
768
55%
768
24%
1642

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%423323346%58%
47864
Night
8%424423347%53%
47098
TransparencyDay
26%48%20%24%15%
47550
Night
29%49%20%21%14%
46912
SeeingDay
8%9%27%34%15%4
5992
Night
9%416%36%28%5%
15349

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
17%7%25%323346%43%
1541
16th to endDay
15%6%35%433346%43%
1728
February1st to 15thDay
16%7%25%415%345%42%
1576
16th to endDay
16%6%3442445%8%39%
1565
March1st to 15thDay
14%5%35%5%2446%8%38%
1953
16th to endDay
11%5%25%5%345%5%9%41%
2133
April1st to 15thDay
13%5%25%5%2445%7%43%
2149
16th to endDay
5%323323348%60%
2160
May1st to 15thDay
321221335%7%65%
2271
16th to endDay
4324323347%61%
2604
June1st to 15thDay
3323223446%62%
2520
16th to endDay
1111212246%74%
2520
July1st to 15thDay
112322336%72%
2488
16th to endDay
112312246%72%
2468
August1st to 15thDay
1212323235%71%
2334
16th to endDay
112323235%72%
2292
September1st to 15thDay
1213222235%71%
2160
16th to endDay
2212322236%71%
1838
October1st to 15thDay
4313322346%64%
1650
16th to endDay
8%5%13322346%58%
1760
November1st to 15thDay
8%433413447%53%
1669
16th to endDay
12%7%245%13445%49%
1509
December1st to 15thDay
15%9%35%322445%42%
1440
16th to endDay
18%7%25%424337%40%
1536
January1st to 15thNight
14%5%243235%5%8%44%
2395
16th to endNight
15%6%24313336%47%
2496
February1st to 15thNight
14%6%25%434346%43%
2276
16th to endNight
14%5%2442445%8%43%
1908
March1st to 15thNight
14%5%25%5%23448%42%
2004
16th to endNight
12%5%24424446%48%
2091
April1st to 15thNight
9%42443445%7%49%
1799
16th to endNight
5%314423346%61%
1800
May1st to 15thNight
3214323347%63%
1676
16th to endNight
3123423348%62%
1507
June1st to 15thNight
2114424449%59%
1440
16th to endNight
112212247%73%
1440
July1st to 15thNight
11233445%7%65%
1469
16th to endNight
12136%5%6%45%10%51%
1701
August1st to 15thNight
22236%5%6%45%11%50%
1626
16th to endNight
215%5%34449%57%
1910
September1st to 15thNight
121332445%8%63%
1800
16th to endNight
1214323347%65%
1823
October1st to 15thNight
5%31342335%6%61%
1980
16th to endNight
5%414423347%56%
2112
November1st to 15thNight
7%414314348%56%
2189
16th to endNight
9%5%24323446%53%
2448
December1st to 15thNight
17%6%24423446%42%
2520
16th to endNight
18%5%24313346%45%
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%311%17%18%5%
1541
16th to endDay
42%49%13%20%10%
1728
February1st to 15thDay
44%38%20%20%4
1576
16th to endDay
45%39%24%13%4
1565
March1st to 15thDay
43%312%21%14%4
1953
16th to endDay
39%6%14%19%16%3
2133
April1st to 15thDay
39%414%20%17%3
2149
16th to endDay
23%314%26%23%7%
2160
May1st to 15thDay
17%38%31%28%9%
2271
16th to endDay
23%312%30%23%7%
2608
June1st to 15thDay
20%5%10%23%24%14%
2520
16th to endDay
10%3418%36%26%
2520
July1st to 15thDay
11%4312%26%42%
2341
16th to endDay
11%5%49%25%44%
2313
August1st to 15thDay
13%4213%31%33%
2318
16th to endDay
13%3115%37%27%
2292
September1st to 15thDay
14%3315%32%30%
2160
16th to endDay
16%2225%32%19%
1838
October1st to 15thDay
21%48%22%27%16%
1650
16th to endDay
25%38%24%25%12%
1760
November1st to 15thDay
30%412%30%15%7%
1669
16th to endDay
37%310%21%21%5%
1509
December1st to 15thDay
44%210%19%18%3
1440
16th to endDay
44%411%17%16%5%
1536
January1st to 15thNight
36%412%21%16%8%
2395
16th to endNight
38%49%16%16%14%
2496
February1st to 15thNight
41%39%20%18%6%
2288
16th to endNight
38%5%12%25%15%3
1908
March1st to 15thNight
40%5%12%21%16%4
2004
16th to endNight
36%5%12%21%18%5%
2091
April1st to 15thNight
33%415%22%19%4
1799
16th to endNight
23%313%26%22%9%
1800
May1st to 15thNight
19%410%25%28%12%
1677
16th to endNight
20%414%31%21%7%
1507
June1st to 15thNight
19%8%11%22%24%14%
1440
16th to endNight
11%25%16%37%26%
1440
July1st to 15thNight
14%4210%23%44%
1387
16th to endNight
22%10%39%17%36%
1593
August1st to 15thNight
21%8%213%27%26%
1617
16th to endNight
20%6%212%29%27%
1910
September1st to 15thNight
17%5%312%28%32%
1800
16th to endNight
16%4322%29%22%
1823
October1st to 15thNight
23%46%23%24%17%
1980
16th to endNight
25%47%25%22%14%
2112
November1st to 15thNight
27%413%29%16%8%
2189
16th to endNight
31%39%24%22%8%
2448
December1st to 15thNight
42%310%17%18%6%
2520
16th to endNight
41%312%16%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
23%7%25%24%13%4
169
16th to endDay
15%6%23%32%17%4
256
February1st to 15thDay
20%8%23%25%17%5%
236
16th to endDay
18%11%21%27%15%4
235
March1st to 15thDay
17%14%27%18%14%7%
270
16th to endDay
13%17%31%25%8%3
288
April1st to 15thDay
16%17%33%22%7%2
269
16th to endDay
9%21%28%27%9%2
270
May1st to 15thDay
5%14%36%34%8%
288
16th to endDay
5%11%24%42%12%3
330
June1st to 15thDay
6%13%37%32%9%1
315
16th to endDay
6%30%45%15%1
315
July1st to 15thDay
327%51%16%
305
16th to endDay
129%47%17%3
327
August1st to 15thDay
1329%49%13%2
315
16th to endDay
126%50%18%3
332
September1st to 15thDay
1223%42%24%5%
315
16th to endDay
28%22%33%21%11%
260
October1st to 15thDay
5%9%28%29%17%9%
255
16th to endDay
11%6%29%27%19%5%
272
November1st to 15thDay
7%6%21%22%32%9%
175
16th to endDay
12%9%22%38%15%1
71
December1st to 15thDay
21%13%31%20%11%1
60
16th to endDay
12%12%23%26%21%3
64
January1st to 15thNight
16%29%35%30%5%
720
16th to endNight
16%411%34%26%6%
768
February1st to 15thNight
16%6%11%34%26%4
704
16th to endNight
15%5%18%32%23%4
632
March1st to 15thNight
16%6%15%30%27%4
720
16th to endNight
12%7%23%32%21%1
768
April1st to 15thNight
10%11%24%32%18%2
719
16th to endNight
6%11%25%31%21%4
720
May1st to 15thNight
3321%43%24%2
597
16th to endNight
25%25%42%20%3
386
June1st to 15thNight
2428%45%18%1
360
16th to endNight
121%50%25%
360
July1st to 15thNight
114%49%31%1
367
16th to endNight
2212%41%36%4
564
August1st to 15thNight
315%41%34%4
544
16th to endNight
115%48%28%5%
764
September1st to 15thNight
1112%41%35%7%
720
16th to endNight
2214%36%36%7%
664
October1st to 15thNight
5%5%12%34%34%6%
660
16th to endNight
8%211%30%35%10%
704
November1st to 15thNight
8%313%33%34%7%
700
16th to endNight
11%5%10%34%30%7%
720
December1st to 15thNight
17%5%11%34%24%6%
720
16th to endNight
19%5%15%35%22%1
768
Page generated at 2017-09-18 05:38:20. Version ac04

Copyright 2017 A. Danko


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