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 2018-03-21.

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%
16545
35%
49138
31%
16496
80%
16496
53%
23746

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
59%
780
29%
2648
26%
776
68%
776
38%
1340
January16th to endNight
56%
832
36%
2619
27%
832
69%
832
41%
1336
February1st to 15thNight
67%
757
37%
2281
32%
756
76%
756
48%
1146
February16th to endNight
62%
684
31%
2051
31%
684
67%
684
38%
1140
March1st to 15thNight
68%
780
28%
2340
27%
780
74%
780
44%
1212
March16th to endNight
72%
792
31%
2055
25%
792
76%
792
48%
1139
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%
720
41%
1806
32%
720
90%
720
70%
872
September16th to endNight
91%
716
47%
1980
45%
716
93%
716
75%
842
October1st to 15thNight
81%
720
36%
2034
35%
720
84%
720
58%
978
October16th to endNight
77%
768
43%
2304
45%
768
81%
768
57%
1070
November1st to 15thNight
76%
760
35%
2467
35%
760
82%
760
54%
1104
November16th to endNight
70%
780
39%
2535
38%
780
77%
780
51%
1164
December1st to 15thNight
65%
780
35%
2535
31%
780
74%
780
41%
1255
December16th to endNight
57%
832
33%
2854
28%
832
69%
832
36%
1449

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%
49686
Night
4212212335%68%
49341
TransparencyDay
19%25%17%28%26%
49377
Night
19%35%16%27%27%
49150
SeeingDay
5%7%24%37%19%5%
6598
Night
5%29%33%38%10%
16555

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%323423345%60%
1617
16th to endDay
10%5%22312335%59%
1953
February1st to 15thDay
7%31321235%5%62%
1901
16th to endDay
10%314423345%56%
1709
March1st to 15thDay
6%414314446%58%
1950
16th to endDay
5%31342445%9%56%
2292
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
11111123479%
2154
16th to endDay
11121113380%
1980
October1st to 15thDay
411222233470%
1923
16th to endDay
221331244470%
1920
November1st to 15thDay
3212323346%66%
1721
16th to endDay
4313423247%63%
1755
December1st to 15thDay
6%31232235%9%58%
1755
16th to endDay
9%314322347%56%
1719
January1st to 15thNight
6%423322446%57%
2648
16th to endNight
9%414211236%61%
2619
February1st to 15thNight
5%32331225%6%62%
2281
16th to endNight
12%313323345%56%
2051
March1st to 15thNight
5%42322345%7%58%
2340
16th to endNight
43332445%6%60%
2055
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
211211123478%
1806
16th to endNight
1111112384%
1980
October1st to 15thNight
322213345%71%
2034
16th to endNight
331211223471%
2304
November1st to 15thNight
321221224470%
2467
16th to endNight
4212313336%67%
2535
December1st to 15thNight
6%223223346%60%
2535
16th to endNight
11%312212335%60%
2854

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%13%24%24%
1617
16th to endDay
28%26%18%18%26%
1953
February1st to 15thDay
24%2314%26%27%
1901
16th to endDay
30%25%20%27%13%
1709
March1st to 15thDay
26%38%20%20%20%
1950
16th to endDay
25%311%24%19%15%
2292
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%
2154
16th to endDay
11%1114%35%35%
1980
October1st to 15thDay
16%2419%26%30%
1923
16th to endDay
17%3313%24%37%
1920
November1st to 15thDay
19%35%16%24%30%
1721
16th to endDay
21%35%13%22%33%
1755
December1st to 15thDay
23%37%16%22%26%
1755
16th to endDay
27%46%17%22%20%
1719
January1st to 15thNight
26%35%14%25%24%
2648
16th to endNight
26%26%15%17%31%
2619
February1st to 15thNight
22%25%16%25%28%
2292
16th to endNight
30%25%16%27%16%
2051
March1st to 15thNight
23%47%19%25%18%
2340
16th to endNight
23%48%23%23%16%
2055
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
12%139%31%40%
1806
16th to endNight
8%2115%34%39%
1980
October1st to 15thNight
16%3317%27%31%
2034
16th to endNight
16%2312%22%41%
2304
November1st to 15thNight
17%26%14%25%32%
2467
16th to endNight
19%25%16%22%33%
2535
December1st to 15thNight
24%36%15%20%29%
2535
16th to endNight
27%36%15%25%22%
2854

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%8%37%25%12%
155
16th to endDay
13%15%34%24%11%1
323
February1st to 15thDay
8%8%33%30%12%6%
326
16th to endDay
11%16%30%29%11%1
290
March1st to 15thDay
9%15%32%29%12%1
330
16th to endDay
8%9%37%32%7%4
311
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
218%48%24%5%
315
16th to endDay
1221%46%20%6%
315
October1st to 15thDay
37%32%36%17%2
315
16th to endDay
46%26%39%17%5%
336
November1st to 15thDay
5%414%41%24%10%
137
16th to endDay
38%22%34%24%5%
135
December1st to 15thDay
49%23%28%30%2
135
16th to endDay
6%14%22%30%22%3
109
January1st to 15thNight
8%420%41%21%4
780
16th to endNight
12%5%18%37%22%3
832
February1st to 15thNight
7%214%40%28%6%
764
16th to endNight
13%313%40%23%4
684
March1st to 15thNight
7%313%43%26%5%
780
16th to endNight
6%310%41%33%4
792
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
3218%53%21%
720
16th to endNight
1227%51%16%
716
October1st to 15thNight
416%37%41%7%
720
16th to endNight
5%110%34%36%12%
768
November1st to 15thNight
4111%43%29%9%
760
16th to endNight
6%115%36%32%8%
780
December1st to 15thNight
8%5%13%40%26%5%
780
16th to endNight
13%6%15%37%22%4
832
Page generated at 2018-03-22 08:34:27. Version ac04

Copyright 2018 A. Danko


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