Fountain Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fountain Valley clear sky chart from 2005-11-06 to 2024-01-13.

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
72%
24553
30%
74069
28%
24501
75%
24501
42%
40041

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
68%
757
29%
2457
29%
756
71%
756
39%
1294
January11th to 20thNight
70%
728
36%
2228
31%
728
76%
728
42%
1166
January21st to endNight
61%
792
36%
2376
29%
792
70%
792
41%
1283
February1st to 10thNight
68%
720
35%
2160
33%
720
73%
720
43%
1138
February11th to 20thNight
65%
700
32%
2098
30%
700
71%
700
42%
1127
February21st to endNight
61%
592
28%
1776
28%
592
66%
592
34%
1037
March1st to 10thNight
63%
720
24%
2160
25%
720
67%
720
34%
1264
March11th to 20thNight
65%
720
24%
2120
25%
720
68%
720
38%
1214
March21st to endNight
67%
792
29%
1980
21%
792
72%
792
44%
1182
April1st to 10thNight
68%
720
26%
1800
19%
720
69%
720
41%
1115
April11th to 20thNight
66%
711
31%
1779
19%
711
70%
711
46%
1032
April21st to endNight
71%
720
27%
1800
17%
720
72%
720
44%
1072
May1st to 10thNight
69%
653
23%
1733
15%
653
69%
653
40%
1044
May11th to 20thNight
68%
531
23%
1595
18%
531
69%
531
35%
955
May21st to endNight
69%
582
24%
1746
19%
582
70%
582
39%
1011
June1st to 10thNight
66%
540
19%
1620
16%
540
67%
540
32%
1032
June11th to 20thNight
74%
446
28%
1526
27%
446
75%
446
38%
793
June21st to endNight
73%
360
27%
1440
32%
360
73%
360
35%
695
July1st to 10thNight
77%
350
29%
1400
32%
350
77%
350
41%
619
July11th to 20thNight
84%
458
28%
1502
26%
458
84%
458
47%
740
July21st to endNight
79%
748
26%
1823
18%
707
79%
707
50%
1020
August1st to 10thNight
83%
716
29%
1780
19%
712
83%
712
57%
954
August11th to 20thNight
83%
712
34%
1780
22%
712
83%
712
60%
934
August21st to endNight
85%
792
35%
1980
24%
792
85%
792
61%
1025
September1st to 10thNight
81%
720
35%
1800
28%
720
81%
720
56%
972
September11th to 20thNight
85%
720
38%
1948
36%
720
85%
720
62%
938
September21st to endNight
83%
720
38%
1980
38%
720
84%
720
59%
969
October1st to 10thNight
80%
720
35%
1980
34%
720
82%
720
54%
1009
October11th to 20thNight
76%
720
37%
2056
37%
720
78%
720
51%
1047
October21st to endNight
79%
792
39%
2424
40%
792
82%
792
52%
1158
November1st to 10thNight
76%
740
34%
2405
37%
740
80%
740
50%
1110
November11th to 20thNight
79%
760
37%
2470
40%
760
82%
760
50%
1162
November21st to endNight
70%
760
32%
2470
34%
760
73%
760
40%
1281
December1st to 10thNight
68%
760
30%
2470
29%
760
72%
760
38%
1313
December11th to 20thNight
62%
758
29%
2962
31%
758
67%
758
26%
1772
December21st to endNight
61%
823
19%
4445
29%
817
68%
817
20%
2564

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
5%42332345%7%63%
75324
Night
5%5%2442445%7%58%
74430
TransparencyDay
21%5%8%18%26%23%
75052
Night
26%5%8%16%22%23%
74225
SeeingDay
6%5%20%38%24%7%
14653
Night
7%210%31%38%11%
24577

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
9%5%1433446%8%54%
1708
11th to 20thDay
7%4233235%46%60%
1773
21st to endDay
9%5%24423336%59%
1980
February1st to 10thDay
8%324324437%61%
1800
11th to 20thDay
7%31342345%8%60%
1750
21st to endDay
8%413434447%57%
1480
March1st to 10thDay
7%5%234346%6%9%51%
1800
11th to 20thDay
7%32432346%10%56%
1840
21st to endDay
441333446%8%59%
2371
April1st to 10thDay
5%42333446%8%59%
2160
11th to 20thDay
3423313445%66%
2129
21st to endDay
4413223347%66%
2160
May1st to 10thDay
45%2433445%9%58%
2226
11th to 20thDay
35%2442335%8%63%
2301
21st to endDay
5%5%2432335%8%60%
2530
June1st to 10thDay
5%5%24423349%58%
2340
11th to 20thDay
4423313337%67%
2426
21st to endDay
1413324335%69%
2520
July1st to 10thDay
2314323446%68%
2520
11th to 20thDay
231231445%7%68%
2399
21st to endDay
221332346%7%67%
2384
August1st to 10thDay
2313223235%74%
2149
11th to 20thDay
1212212247%76%
2122
21st to endDay
121232345%5%74%
2376
September1st to 10thDay
2212223346%74%
2160
11th to 20thDay
2213222336%74%
2010
21st to endDay
1213212346%75%
1980
October1st to 10thDay
4412323346%68%
1980
11th to 20thDay
5%323323325%69%
1900
21st to endDay
431232235%6%69%
1931
November1st to 10thDay
3323323247%68%
1674
11th to 20thDay
4313323346%68%
1710
21st to endDay
43235%2336%9%60%
1710
December1st to 10thDay
7%5%2432435%7%57%
1710
11th to 20thDay
11%5%35%435%5%6%9%45%
2169
21st to endDay
10%7%37%6%45%5%7%7%40%
3146
January1st to 10thNight
8%42442445%7%57%
2457
11th to 20thNight
5%41432345%7%60%
2228
21st to endNight
9%424324336%60%
2376
February1st to 10thNight
6%424422345%62%
2160
11th to 20thNight
7%5%23423446%60%
2098
21st to endNight
10%5%14434446%55%
1776
March1st to 10thNight
7%6%35%4345%6%8%50%
2160
11th to 20thNight
8%8%2442445%8%52%
2120
21st to endNight
6%5%3433436%8%55%
1980
April1st to 10thNight
8%5%4442336%8%53%
1800
11th to 20thNight
5%8%24313346%62%
1779
21st to endNight
5%6%34424447%55%
1800
May1st to 10thNight
5%7%44424448%53%
1733
11th to 20thNight
48%45%43445%9%50%
1594
21st to endNight
48%45%423448%55%
1746
June1st to 10thNight
5%10%5%8%5%345%47%45%
1620
11th to 20thNight
38%345%335%5%8%54%
1526
21st to endNight
37%36%6%35%5%6%9%48%
1440
July1st to 10thNight
27%45%4245%6%10%51%
1440
11th to 20thNight
2425%5%35%47%9%55%
1552
21st to endNight
3436%43446%9%54%
1930
August1st to 10thNight
35%2422345%8%63%
1790
11th to 20thNight
242442345%7%63%
1780
21st to endNight
142332445%8%62%
1980
September1st to 10thNight
342442445%6%62%
1800
11th to 20thNight
2313323336%71%
1948
21st to endNight
2324223236%70%
1980
October1st to 10thNight
3323323346%67%
1980
11th to 20thNight
5%424323235%67%
2056
21st to endNight
3413323346%68%
2424
November1st to 10thNight
341332335%7%65%
2405
11th to 20thNight
3323323346%69%
2470
21st to endNight
5%5%2443445%8%56%
2470
December1st to 10thNight
7%4345%24448%56%
2470
11th to 20thNight
12%8%35%434446%47%
3041
21st to endNight
11%6%36%5%35%5%5%6%46%
4521

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
29%47%20%20%19%
1709
11th to 20thDay
25%5%8%13%23%26%
1773
21st to endDay
29%37%17%16%28%
1980
February1st to 10thDay
26%45%15%24%26%
1800
11th to 20thDay
23%5%6%17%26%22%
1760
21st to endDay
28%6%8%17%24%17%
1480
March1st to 10thDay
30%6%9%18%17%20%
1800
11th to 20thDay
24%5%12%21%23%14%
1840
21st to endDay
23%6%13%23%21%14%
2371
April1st to 10thDay
24%7%12%27%20%11%
2160
11th to 20thDay
21%5%8%22%26%18%
2132
21st to endDay
18%5%10%28%27%12%
2160
May1st to 10thDay
24%6%12%21%24%13%
2226
11th to 20thDay
22%6%8%26%27%12%
2304
21st to endDay
24%6%10%28%25%6%
2530
June1st to 10thDay
24%5%11%20%28%13%
2340
11th to 20thDay
17%37%14%32%26%
2426
21st to endDay
16%3411%29%37%
2520
July1st to 10thDay
14%47%10%27%38%
2451
11th to 20thDay
14%5%7%21%30%23%
2326
21st to endDay
15%5%10%25%31%15%
2252
August1st to 10thDay
13%2415%35%32%
2135
11th to 20thDay
10%15%19%36%29%
2122
21st to endDay
12%45%13%36%31%
2376
September1st to 10thDay
11%36%11%36%33%
2160
11th to 20thDay
12%35%14%34%33%
2010
21st to endDay
12%35%16%36%28%
1980
October1st to 10thDay
19%36%20%24%28%
1980
11th to 20thDay
19%3417%25%31%
1900
21st to endDay
17%45%14%21%39%
1931
November1st to 10thDay
18%37%18%23%31%
1674
11th to 20thDay
18%38%16%19%36%
1710
21st to endDay
22%5%8%14%22%28%
1710
December1st to 10thDay
26%5%8%17%20%24%
1710
11th to 20thDay
36%7%9%15%18%15%
2168
21st to endDay
40%8%10%18%14%11%
3146
January1st to 10thNight
27%49%14%24%21%
2457
11th to 20thNight
25%47%14%20%29%
2228
21st to endNight
28%38%15%15%31%
2376
February1st to 10thNight
26%36%14%22%29%
2160
11th to 20thNight
26%47%15%22%26%
2099
21st to endNight
32%6%5%13%22%22%
1776
March1st to 10thNight
32%6%8%19%16%19%
2160
11th to 20thNight
30%5%9%17%22%16%
2120
21st to endNight
27%6%9%22%23%13%
1980
April1st to 10thNight
30%6%10%23%18%13%
1800
11th to 20thNight
24%6%8%20%23%18%
1779
21st to endNight
26%6%12%21%22%12%
1800
May1st to 10thNight
29%7%12%19%19%14%
1733
11th to 20thNight
32%6%10%22%19%11%
1595
21st to endNight
29%6%11%25%21%8%
1746
June1st to 10thNight
35%7%12%14%21%11%
1620
11th to 20thNight
25%6%8%15%25%20%
1526
21st to endNight
25%6%6%14%24%26%
1440
July1st to 10thNight
22%47%14%22%31%
1400
11th to 20thNight
22%48%19%25%22%
1502
21st to endNight
23%412%22%25%14%
1823
August1st to 10thNight
19%37%14%31%26%
1780
11th to 20thNight
18%36%13%33%27%
1780
21st to endNight
17%36%14%31%28%
1980
September1st to 10thNight
20%35%11%29%30%
1800
11th to 20thNight
15%36%12%28%36%
1948
21st to endNight
16%4413%34%30%
1980
October1st to 10thNight
18%5%6%19%23%29%
1980
11th to 20thNight
22%35%15%24%31%
2056
21st to endNight
18%4412%22%40%
2424
November1st to 10thNight
19%45%18%20%35%
2405
11th to 20thNight
19%45%16%18%38%
2470
21st to endNight
26%48%15%18%29%
2470
December1st to 10thNight
28%5%8%14%19%26%
2470
11th to 20thNight
37%6%8%14%20%16%
3041
21st to endNight
36%8%11%18%14%13%
4521

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
12%8%17%40%20%3
270
11th to 20thDay
12%7%21%39%18%3
381
21st to endDay
8%12%26%35%17%3
462
February1st to 10thDay
11%7%24%32%21%5%
420
11th to 20thDay
9%9%29%35%16%2
415
21st to endDay
10%13%27%37%13%1
346
March1st to 10thDay
12%11%32%30%11%2
420
11th to 20thDay
11%8%31%30%18%2
420
21st to endDay
7%13%31%36%10%2
462
April1st to 10thDay
6%8%31%33%18%4
420
11th to 20thDay
312%34%36%10%3
412
21st to endDay
49%29%38%17%5%
420
May1st to 10thDay
39%31%36%16%5%
423
11th to 20thDay
6%5%26%41%19%4
448
21st to endDay
8%8%25%39%16%4
485
June1st to 10thDay
5%418%38%31%4
450
11th to 20thDay
4219%40%27%8%
450
21st to endDay
2114%44%31%8%
450
July1st to 10thDay
36%42%40%9%
446
11th to 20thDay
2335%43%17%
444
21st to endDay
1441%39%15%
487
August1st to 10thDay
318%41%36%11%
447
11th to 20thDay
26%41%37%14%
437
21st to endDay
27%40%38%12%
495
September1st to 10thDay
3112%46%28%10%
450
11th to 20thDay
2118%46%26%7%
450
21st to endDay
2220%40%28%8%
450
October1st to 10thDay
3322%42%24%5%
450
11th to 20thDay
6%223%41%22%6%
450
21st to endDay
45%21%35%27%8%
446
November1st to 10thDay
46%16%36%30%8%
270
11th to 20thDay
4420%36%28%9%
270
21st to endDay
48%20%35%24%9%
270
December1st to 10thDay
10%5%15%36%30%3
270
11th to 20thDay
6%5%20%35%26%9%
270
21st to endDay
13%10%20%35%18%4
297
January1st to 10thNight
9%5%11%39%27%8%
760
11th to 20thNight
8%313%37%32%7%
728
21st to endNight
11%417%35%28%5%
792
February1st to 10thNight
9%214%36%30%9%
720
11th to 20thNight
9%316%36%29%7%
704
21st to endNight
12%416%39%25%5%
592
March1st to 10thNight
9%315%43%25%5%
720
11th to 20thNight
9%316%34%30%9%
720
21st to endNight
8%314%37%33%5%
792
April1st to 10thNight
10%311%40%31%6%
720
11th to 20thNight
6%5%15%35%31%8%
711
21st to endNight
8%411%35%35%8%
720
May1st to 10thNight
8%413%34%36%6%
653
11th to 20thNight
7%113%33%37%8%
531
21st to endNight
6%214%37%35%6%
584
June1st to 10thNight
9%112%36%37%5%
540
11th to 20thNight
6%110%26%49%9%
446
21st to endNight
7%6%22%52%13%
360
July1st to 10thNight
7%39%60%20%
350
11th to 20thNight
3214%54%26%
458
21st to endNight
35%15%54%23%
748
August1st to 10thNight
5%319%52%21%
716
11th to 20thNight
41313%52%27%
712
21st to endNight
4214%55%25%
792
September1st to 10thNight
6%1418%52%20%
720
11th to 20thNight
31423%55%14%
720
21st to endNight
315%28%48%15%
720
October1st to 10thNight
417%35%43%10%
720
11th to 20thNight
7%29%29%41%12%
720
21st to endNight
5%29%31%38%15%
792
November1st to 10thNight
5%39%32%39%13%
740
11th to 20thNight
418%38%36%14%
760
21st to endNight
6%312%39%32%8%
760
December1st to 10thNight
9%411%40%31%6%
760
11th to 20thNight
12%414%37%27%6%
760
21st to endNight
11%6%16%36%26%7%
836
Page generated at 2024-01-09 22:25:00. Version ac07

Copyright 2024 Attilla Danko


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