Simi Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Simi Valley clear sky chart from 2005-11-05 to

2017-09-12
.

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%
15783
35%
46782
30%
15734
80%
15734
53%
22611

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
58%
720
29%
2443
25%
716
68%
716
39%
1215
January16th to endNight
54%
768
35%
2418
26%
768
68%
768
40%
1256
February1st to 15thNight
65%
697
36%
2101
31%
696
75%
696
47%
1073
February16th to endNight
61%
632
29%
1895
30%
632
65%
632
36%
1076
March1st to 15thNight
68%
720
29%
2160
28%
720
75%
720
47%
1084
March16th to endNight
73%
768
31%
1989
25%
768
77%
768
49%
1097
April1st to 15thNight
68%
719
32%
1799
20%
719
72%
719
51%
1004
April16th to endNight
75%
720
33%
1800
18%
720
79%
720
60%
924
May1st to 15thNight
77%
650
30%
1730
21%
650
78%
650
52%
921
May16th to endNight
81%
561
31%
1685
25%
561
83%
561
58%
785
June1st to 15thNight
90%
401
33%
1481
36%
401
91%
401
54%
614
June16th to endNight
95%
360
40%
1440
50%
360
95%
360
67%
488
July1st to 15thNight
92%
340
35%
1360
43%
340
92%
340
60%
491
July16th to endNight
89%
612
35%
1634
29%
572
90%
572
63%
749
August1st to 15thNight
92%
717
37%
1790
24%
713
92%
713
72%
849
August16th to endNight
94%
764
45%
1910
30%
764
94%
764
77%
874
September1st to 15thNight
90%
706
41%
1770
33%
706
90%
706
71%
848
September16th to endNight
91%
656
45%
1815
43%
656
93%
656
75%
773
October1st to 15thNight
80%
660
37%
1864
36%
660
83%
660
56%
908
October16th to endNight
76%
704
41%
2112
43%
704
80%
704
56%
985
November1st to 15thNight
76%
700
36%
2272
37%
700
83%
700
57%
991
November16th to endNight
70%
720
38%
2340
36%
720
77%
720
51%
1071
December1st to 15thNight
65%
720
35%
2340
31%
720
74%
720
40%
1183
December16th to endNight
56%
768
32%
2634
27%
768
68%
768
35%
1352

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
4212212346%67%
47854
Night
4212212335%68%
46985
TransparencyDay
19%25%17%28%25%
47545
Night
19%35%17%27%27%
46794
SeeingDay
5%7%24%37%19%5%
5944
Night
5%29%32%38%10%
15793

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%323323235%62%
1492
16th to endDay
11%5%22312335%58%
1803
February1st to 15thDay
7%413212345%61%
1751
16th to endDay
11%314423346%54%
1579
March1st to 15thDay
5%313214447%60%
1800
16th to endDay
5%31342345%9%56%
2232
April1st to 15thDay
5%413313347%60%
2149
16th to endDay
4212211336%69%
2160
May1st to 15thDay
4313213337%65%
2217
16th to endDay
3212212247%68%
2429
June1st to 15thDay
4313212249%62%
2476
16th to endDay
1121225%80%
2520
July1st to 15thDay
1112312346%72%
2520
16th to endDay
211222345%73%
2414
August1st to 15thDay
11211113478%
2160
16th to endDay
111123481%
2292
September1st to 15thDay
11111123480%
2109
16th to endDay
11121113380%
1815
October1st to 15thDay
5%212222345%68%
1763
16th to endDay
221321233470%
1760
November1st to 15thDay
3112322335%69%
1586
16th to endDay
4313413246%64%
1620
December1st to 15thDay
6%31232335%8%56%
1620
16th to endDay
10%314322346%56%
1587
January1st to 15thNight
6%423322446%59%
2443
16th to endNight
10%414212236%60%
2418
February1st to 15thNight
6%32331225%6%61%
2101
16th to endNight
13%323323345%54%
1895
March1st to 15thNight
442221345%7%61%
2160
16th to endNight
43332445%6%61%
1989
April1st to 15thNight
6%413212237%64%
1799
16th to endNight
3211212247%70%
1800
May1st to 15thNight
4312312346%65%
1730
16th to endNight
1212212235%73%
1684
June1st to 15thNight
1211212438%70%
1481
16th to endNight
11212484%
1440
July1st to 15thNight
111212235%76%
1440
16th to endNight
2111212245%73%
1748
August1st to 15thNight
121112235%78%
1800
16th to endNight
11223481%
1910
September1st to 15thNight
211211112478%
1770
16th to endNight
112112384%
1815
October1st to 15thNight
32221334470%
1864
16th to endNight
431211223471%
2112
November1st to 15thNight
321221223473%
2272
16th to endNight
4212313336%67%
2340
December1st to 15thNight
7%224223346%59%
2340
16th to endNight
12%412212236%59%
2634

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
25%26%13%25%26%
1492
16th to endDay
29%26%17%17%27%
1803
February1st to 15thDay
25%2415%27%24%
1751
16th to endDay
32%26%20%27%11%
1579
March1st to 15thDay
24%38%20%22%21%
1800
16th to endDay
24%310%24%20%15%
2232
April1st to 15thDay
24%310%25%24%12%
2149
16th to endDay
17%29%22%29%17%
2160
May1st to 15thDay
21%38%21%26%19%
2217
16th to endDay
16%39%28%30%10%
2432
June1st to 15thDay
21%37%18%31%17%
2476
16th to endDay
10%139%36%38%
2520
July1st to 15thDay
14%2211%30%37%
2371
16th to endDay
14%25%20%31%24%
2265
August1st to 15thDay
12%112%39%33%
2146
16th to endDay
8%1112%42%33%
2292
September1st to 15thDay
9%2213%31%40%
2109
16th to endDay
11%1113%35%36%
1815
October1st to 15thDay
18%2421%26%26%
1763
16th to endDay
17%3313%25%36%
1760
November1st to 15thDay
18%3414%25%33%
1586
16th to endDay
21%35%14%22%32%
1620
December1st to 15thDay
25%37%17%23%22%
1620
16th to endDay
29%46%18%21%19%
1587
January1st to 15thNight
25%35%13%25%25%
2443
16th to endNight
27%26%14%16%32%
2418
February1st to 15thNight
23%2417%24%27%
2112
16th to endNight
32%36%16%26%15%
1895
March1st to 15thNight
21%37%20%26%20%
2160
16th to endNight
22%48%23%23%17%
1989
April1st to 15thNight
23%38%26%25%13%
1799
16th to endNight
15%47%25%27%19%
1800
May1st to 15thNight
20%48%20%28%17%
1731
16th to endNight
15%39%28%29%13%
1685
June1st to 15thNight
14%410%18%34%17%
1481
16th to endNight
8%2211%36%38%
1440
July1st to 15thNight
11%2313%25%43%
1360
16th to endNight
13%25%21%28%26%
1634
August1st to 15thNight
10%229%38%35%
1790
16th to endNight
7%219%42%36%
1910
September1st to 15thNight
11%139%31%40%
1770
16th to endNight
8%115%33%40%
1815
October1st to 15thNight
17%3318%28%29%
1864
16th to endNight
16%2313%24%39%
2112
November1st to 15thNight
16%15%13%26%35%
2272
16th to endNight
19%25%17%21%33%
2340
December1st to 15thNight
25%36%16%21%26%
2340
16th to endNight
28%36%16%24%20%
2634

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
16%10%44%25%4
120
16th to endDay
15%17%34%24%7%1
269
February1st to 15thDay
10%9%36%32%9%2
266
16th to endDay
13%14%33%26%10%
238
March1st to 15thDay
7%16%32%27%14%2
270
16th to endDay
6%9%39%32%7%4
288
April1st to 15thDay
9%13%35%28%7%5%
269
16th to endDay
415%39%31%7%2
270
May1st to 15thDay
8%8%30%34%13%3
288
16th to endDay
5%8%27%39%15%3
330
June1st to 15thDay
8%423%38%20%4
315
16th to endDay
11%39%34%12%
315
July1st to 15thDay
19%43%34%11%
305
16th to endDay
31437%37%15%
327
August1st to 15thDay
27%53%27%8%
315
16th to endDay
8%47%32%11%
332
September1st to 15thDay
118%49%24%5%
300
16th to endDay
1222%47%17%7%
255
October1st to 15thDay
38%32%35%16%2
255
16th to endDay
5%7%26%40%17%1
272
November1st to 15thDay
4414%36%25%15%
92
16th to endDay
312%25%37%20%1
90
December1st to 15thDay
38%23%32%30%2
90
16th to endDay
8%12%32%31%13%1
73
January1st to 15thNight
7%421%40%20%5%
720
16th to endNight
13%5%18%37%21%3
768
February1st to 15thNight
7%315%41%26%5%
704
16th to endNight
14%313%40%23%4
632
March1st to 15thNight
6%314%42%27%5%
720
16th to endNight
5%310%40%34%4
768
April1st to 15thNight
7%412%42%30%4
719
16th to endNight
3312%38%34%7%
720
May1st to 15thNight
6%28%37%39%5%
651
16th to endNight
119%36%42%7%
563
June1st to 15thNight
236%49%9%
401
16th to endNight
22%65%11%
360
July1st to 15thNight
26%71%19%
340
16th to endNight
26%63%25%
612
August1st to 15thNight
1113%64%17%
717
16th to endNight
9%59%28%
764
September1st to 15thNight
2218%53%22%
706
16th to endNight
1226%51%16%
656
October1st to 15thNight
5%17%37%41%7%
660
16th to endNight
5%110%34%35%12%
704
November1st to 15thNight
4111%42%29%10%
700
16th to endNight
6%116%36%30%8%
720
December1st to 15thNight
8%413%41%26%5%
720
16th to endNight
14%6%16%38%20%3
768
Page generated at 2017-09-13 04:39:24. Version ac04

Copyright 2017 A. Danko


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