Fountain Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fountain Valley clear sky chart from 2005-11-05 to 2017-09-18.

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
75%
15975
30%
46655
28%
15930
77%
15930
45%
24793

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
71%
716
29%
2296
29%
716
76%
716
40%
1198
January16th to endNight
66%
768
32%
2304
29%
768
72%
768
39%
1275
February1st to 15thNight
72%
697
33%
2103
33%
697
76%
697
44%
1109
February16th to endNight
63%
632
26%
1895
28%
632
66%
632
32%
1153
March1st to 15thNight
71%
720
28%
2160
31%
720
75%
720
43%
1152
March16th to endNight
75%
768
27%
2012
23%
768
76%
768
45%
1154
April1st to 15thNight
70%
719
27%
1799
18%
719
72%
719
44%
1073
April16th to endNight
75%
720
29%
1800
18%
720
77%
720
50%
1016
May1st to 15thNight
72%
614
25%
1694
18%
614
73%
614
40%
990
May16th to endNight
74%
561
24%
1685
19%
561
75%
561
41%
948
June1st to 15thNight
73%
537
20%
1617
18%
537
74%
537
36%
974
June16th to endNight
80%
360
28%
1440
33%
360
80%
360
40%
643
July1st to 15thNight
80%
355
27%
1375
30%
355
80%
355
42%
626
July16th to endNight
82%
668
24%
1689
18%
627
81%
627
48%
948
August1st to 15thNight
82%
717
30%
1790
19%
713
82%
713
56%
963
August16th to endNight
88%
764
37%
1910
25%
764
88%
764
64%
966
September1st to 15thNight
84%
720
33%
1839
28%
720
84%
720
59%
954
September16th to endNight
85%
667
39%
1847
39%
667
86%
667
61%
879
October1st to 15thNight
80%
660
35%
1815
34%
660
82%
660
54%
928
October16th to endNight
80%
704
37%
2134
39%
704
81%
704
49%
1053
November1st to 15thNight
80%
700
34%
2275
38%
700
83%
700
52%
1042
November16th to endNight
75%
720
34%
2340
37%
720
78%
720
45%
1151
December1st to 15thNight
68%
720
31%
2340
31%
720
73%
720
37%
1262
December16th to endNight
61%
768
32%
2496
29%
768
68%
768
36%
1336

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
4312213347%64%
48121
Night
5%423323347%59%
46859
TransparencyDay
20%47%18%26%23%
47817
Night
24%37%16%23%23%
46665
SeeingDay
5%5%20%40%23%5%
5978
Night
6%16%30%40%13%
15989

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
7%5%13322346%59%
1641
16th to endDay
9%5%13322336%57%
1920
February1st to 15thDay
7%313313447%60%
1751
16th to endDay
10%42332345%7%51%
1579
March1st to 15thDay
431231346%9%58%
1800
16th to endDay
341322335%9%57%
2208
April1st to 15thDay
5%312323447%61%
2149
16th to endDay
4312212236%68%
2160
May1st to 15thDay
3413312348%62%
2256
16th to endDay
4412312248%63%
2429
June1st to 15thDay
7%5%13312238%59%
2340
16th to endDay
1211213225%75%
2517
July1st to 15thDay
2313313446%65%
2499
16th to endDay
2212213347%67%
2360
August1st to 15thDay
12222226%75%
2160
16th to endDay
111212346%74%
2292
September1st to 15thDay
112222335%74%
2119
16th to endDay
112112235%75%
1838
October1st to 15thDay
5%313223336%65%
1815
16th to endDay
4213322345%66%
1736
November1st to 15thDay
3212313235%69%
1584
16th to endDay
421332325%7%63%
1620
December1st to 15thDay
6%41332445%8%56%
1620
16th to endDay
10%323323346%57%
1728
January1st to 15thNight
5%314323346%60%
2296
16th to endNight
9%314213235%58%
2304
February1st to 15thNight
6%423313335%62%
2101
16th to endNight
11%5%24424445%50%
1895
March1st to 15thNight
5%5%2322235%8%58%
2160
16th to endNight
442332435%9%54%
2012
April1st to 15thNight
6%5%23313246%58%
1799
16th to endNight
4422223337%63%
1800
May1st to 15thNight
5%5%33324349%54%
1694
16th to endNight
46%23323448%56%
1684
June1st to 15thNight
48%35%423447%50%
1617
16th to endNight
26%23425%45%8%53%
1440
July1st to 15thNight
25%2442446%10%51%
1456
16th to endNight
332443446%9%52%
1805
August1st to 15thNight
3424223448%60%
1800
16th to endNight
312224447%65%
1910
September1st to 15thNight
2313323436%64%
1839
16th to endNight
2213212226%70%
1847
October1st to 15thNight
3213223236%67%
1815
16th to endNight
4413213236%66%
2134
November1st to 15thNight
2313212235%69%
2275
16th to endNight
4313313337%63%
2340
December1st to 15thNight
7%324423346%57%
2340
16th to endNight
10%423213235%59%
2496

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
26%37%14%21%26%
1642
16th to endDay
29%47%15%16%27%
1920
February1st to 15thDay
24%45%17%24%23%
1751
16th to endDay
32%5%7%19%26%9%
1579
March1st to 15thDay
22%410%20%21%20%
1800
16th to endDay
23%5%14%24%19%13%
2208
April1st to 15thDay
24%5%10%26%22%10%
2149
16th to endDay
18%411%25%24%16%
2160
May1st to 15thDay
22%5%9%22%24%15%
2256
16th to endDay
21%5%9%29%26%7%
2432
June1st to 15thDay
25%38%16%31%15%
2340
16th to endDay
11%2410%31%39%
2517
July1st to 15thDay
17%45%12%27%33%
2351
16th to endDay
16%48%22%29%17%
2214
August1st to 15thDay
11%1315%38%28%
2146
16th to endDay
10%3415%38%27%
2292
September1st to 15thDay
12%35%13%35%30%
2119
16th to endDay
11%25%15%34%31%
1838
October1st to 15thDay
22%25%21%23%23%
1815
16th to endDay
20%45%14%20%34%
1736
November1st to 15thDay
18%27%17%19%33%
1584
16th to endDay
20%48%14%21%31%
1620
December1st to 15thDay
25%6%10%17%17%23%
1620
16th to endDay
28%5%8%16%20%20%
1728
January1st to 15thNight
26%47%12%21%29%
2296
16th to endNight
30%27%13%13%31%
2304
February1st to 15thNight
24%36%15%22%26%
2112
16th to endNight
35%5%6%13%22%16%
1895
March1st to 15thNight
25%47%20%20%21%
2160
16th to endNight
25%5%12%20%21%14%
2012
April1st to 15thNight
29%39%23%20%13%
1799
16th to endNight
22%410%22%21%17%
1800
May1st to 15thNight
29%5%10%19%21%14%
1695
16th to endNight
27%5%10%24%21%10%
1685
June1st to 15thNight
32%5%10%13%24%12%
1617
16th to endNight
20%5%413%25%29%
1440
July1st to 15thNight
23%25%14%25%28%
1375
16th to endNight
24%410%18%25%15%
1689
August1st to 15thNight
20%35%13%36%21%
1790
16th to endNight
15%25%13%34%28%
1910
September1st to 15thNight
17%36%12%31%29%
1839
16th to endNight
15%2312%32%33%
1847
October1st to 15thNight
19%36%18%28%22%
1815
16th to endNight
21%3313%22%35%
2134
November1st to 15thNight
19%25%16%19%36%
2275
16th to endNight
22%37%16%18%31%
2340
December1st to 15thNight
28%48%14%20%23%
2340
16th to endNight
28%39%14%22%21%
2496

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
18%8%20%39%13%
120
16th to endDay
13%10%26%36%11%1
288
February1st to 15thDay
9%5%27%37%18%1
266
16th to endDay
13%10%28%33%13%1
238
March1st to 15thDay
8%9%28%32%16%4
270
16th to endDay
5%12%27%39%13%2
288
April1st to 15thDay
5%11%36%32%10%3
269
16th to endDay
213%38%33%9%3
270
May1st to 15thDay
5%8%31%38%12%4
288
16th to endDay
5%9%25%37%18%3
330
June1st to 15thDay
7%222%40%24%3
315
16th to endDay
19%44%34%9%
315
July1st to 15thDay
216%40%40%9%
305
16th to endDay
2441%40%10%
327
August1st to 15thDay
36%48%34%6%
315
16th to endDay
5%43%39%10%
332
September1st to 15thDay
212%54%24%5%
315
16th to endDay
2117%49%21%7%
264
October1st to 15thDay
5%428%41%18%1
255
16th to endDay
5%123%40%23%5%
242
November1st to 15thDay
6%10%33%34%15%
90
16th to endDay
311%22%31%28%3
90
December1st to 15thDay
45%15%31%37%5%
90
16th to endDay
12%7%17%36%22%3
96
January1st to 15thNight
7%310%39%28%11%
720
16th to endNight
12%310%33%30%10%
768
February1st to 15thNight
8%28%38%30%11%
704
16th to endNight
14%210%36%29%7%
632
March1st to 15thNight
7%210%39%31%9%
720
16th to endNight
5%28%35%39%8%
768
April1st to 15thNight
7%39%40%31%6%
719
16th to endNight
5%48%38%34%9%
720
May1st to 15thNight
7%110%34%38%7%
615
16th to endNight
5%10%34%42%6%
563
June1st to 15thNight
6%16%38%41%5%
537
16th to endNight
3219%65%8%
360
July1st to 15thNight
5%19%63%19%
355
16th to endNight
3212%58%23%
668
August1st to 15thNight
4115%58%20%
717
16th to endNight
211%56%28%
764
September1st to 15thNight
4116%56%21%
720
16th to endNight
4224%50%17%
667
October1st to 15thNight
36%35%41%12%
660
16th to endNight
7%1428%40%18%
704
November1st to 15thNight
47%32%39%16%
700
16th to endNight
5%18%33%34%16%
720
December1st to 15thNight
9%38%35%33%9%
720
16th to endNight
14%5%11%33%27%8%
768
Page generated at 2017-09-19 04:32:28. Version ac04

Copyright 2017 A. Danko


Fountain Valley Clear Sky Chart | Charts Home