Granada Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Granada Hills clear sky chart from 2005-11-05 to 2017-09-16.

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
76%
15805
35%
46802
30%
15756
80%
15756
53%
22563

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
63%
718
29%
2456
27%
716
72%
716
43%
1175
January16th to endNight
60%
768
35%
2394
30%
768
69%
768
41%
1234
February1st to 15thNight
68%
697
36%
2101
33%
696
76%
696
48%
1054
February16th to endNight
62%
632
30%
1895
30%
632
67%
632
38%
1068
March1st to 15thNight
67%
720
30%
2160
28%
720
74%
720
47%
1077
March16th to endNight
73%
768
31%
1995
23%
768
78%
768
48%
1095
April1st to 15thNight
67%
719
31%
1799
19%
719
71%
719
51%
1006
April16th to endNight
73%
720
33%
1800
16%
720
78%
720
60%
914
May1st to 15thNight
73%
635
29%
1715
20%
635
75%
635
52%
905
May16th to endNight
77%
561
30%
1685
24%
561
79%
561
57%
795
June1st to 15thNight
83%
423
31%
1503
33%
423
85%
423
55%
629
June16th to endNight
94%
360
40%
1440
50%
360
95%
360
67%
479
July1st to 15thNight
92%
340
35%
1360
43%
340
92%
340
60%
493
July16th to endNight
91%
615
34%
1635
28%
573
91%
573
63%
752
August1st to 15thNight
90%
717
36%
1790
23%
713
90%
713
70%
866
August16th to endNight
93%
764
44%
1910
30%
764
93%
764
75%
892
September1st to 15thNight
89%
720
40%
1815
32%
720
89%
720
68%
886
September16th to endNight
92%
656
44%
1816
43%
656
93%
656
74%
781
October1st to 15thNight
80%
660
36%
1851
35%
660
83%
660
57%
903
October16th to endNight
78%
704
41%
2120
42%
704
82%
704
55%
994
November1st to 15thNight
77%
700
36%
2275
37%
700
83%
700
57%
985
November16th to endNight
75%
720
38%
2340
37%
720
81%
720
52%
1063
December1st to 15thNight
67%
720
35%
2340
31%
720
76%
720
41%
1177
December16th to endNight
59%
768
33%
2607
30%
768
69%
768
36%
1340

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
4212212235%69%
47916
Night
5%212212235%69%
47007
TransparencyDay
18%36%17%28%26%
47609
Night
18%26%17%26%27%
46814
SeeingDay
5%6%22%35%23%5%
5944
Night
6%29%32%38%10%
15817

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%313323225%63%
1480
16th to endDay
12%312222336%58%
1827
February1st to 15thDay
7%22221335%6%62%
1751
16th to endDay
11%413323346%54%
1579
March1st to 15thDay
5%313313447%61%
1800
16th to endDay
5%31232436%8%58%
2226
April1st to 15thDay
6%312323337%62%
2149
16th to endDay
5%21122246%70%
2160
May1st to 15thDay
4312222346%66%
2232
16th to endDay
3213212135%69%
2429
June1st to 15thDay
5%412111237%68%
2453
16th to endDay
1111112383%
2520
July1st to 15thDay
12211323474%
2520
16th to endDay
2212112245%73%
2415
August1st to 15thDay
121111121480%
2160
16th to endDay
111122483%
2292
September1st to 15thDay
1111123381%
2145
16th to endDay
1111212381%
1816
October1st to 15thDay
5%21222346%68%
1777
16th to endDay
321221333471%
1750
November1st to 15thDay
3212222235%70%
1584
16th to endDay
5%312313246%64%
1620
December1st to 15thDay
7%31222435%9%58%
1620
16th to endDay
10%313324345%57%
1611
January1st to 15thNight
7%412312346%61%
2456
16th to endNight
9%413212246%61%
2394
February1st to 15thNight
5%323312336%64%
2101
16th to endNight
13%413323335%55%
1895
March1st to 15thNight
5%322212347%63%
2160
16th to endNight
4212324447%62%
1995
April1st to 15thNight
6%312212236%65%
1799
16th to endNight
322112237%72%
1800
May1st to 15thNight
4412213236%66%
1715
16th to endNight
2322212225%72%
1684
June1st to 15thNight
2211212229%71%
1503
16th to endNight
1111121384%
1440
July1st to 15thNight
11121213478%
1440
16th to endNight
212112236%74%
1751
August1st to 15thNight
22211212478%
1800
16th to endNight
121113481%
1910
September1st to 15thNight
221211122478%
1815
16th to endNight
111112384%
1816
October1st to 15thNight
311221324372%
1851
16th to endNight
431221122373%
2120
November1st to 15thNight
321221223474%
2275
16th to endNight
4211222335%68%
2340
December1st to 15thNight
7%314213347%59%
2340
16th to endNight
11%412212226%61%
2607

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%23%29%
1480
16th to endDay
27%37%15%17%27%
1827
February1st to 15thDay
22%36%14%26%26%
1751
16th to endDay
30%47%17%27%12%
1579
March1st to 15thDay
22%49%21%21%21%
1800
16th to endDay
23%5%10%24%19%16%
2226
April1st to 15thDay
22%411%23%24%13%
2149
16th to endDay
16%39%22%28%18%
2160
May1st to 15thDay
18%49%20%27%19%
2232
16th to endDay
17%38%28%30%10%
2432
June1st to 15thDay
19%29%17%32%19%
2453
16th to endDay
9%1310%36%38%
2520
July1st to 15thDay
14%2211%31%36%
2371
16th to endDay
14%36%20%31%23%
2268
August1st to 15thDay
10%1213%37%34%
2146
16th to endDay
7%1213%41%34%
2292
September1st to 15thDay
9%2313%32%38%
2145
16th to endDay
11%1214%34%35%
1816
October1st to 15thDay
17%35%20%26%27%
1777
16th to endDay
16%4313%23%39%
1750
November1st to 15thDay
18%2414%24%35%
1584
16th to endDay
21%35%14%22%32%
1620
December1st to 15thDay
24%5%8%16%21%23%
1620
16th to endDay
29%47%16%22%20%
1611
January1st to 15thNight
23%26%15%23%28%
2456
16th to endNight
25%27%14%17%32%
2394
February1st to 15thNight
22%26%16%24%28%
2112
16th to endNight
32%26%17%25%15%
1895
March1st to 15thNight
22%28%20%24%22%
2160
16th to endNight
21%5%10%22%22%17%
1995
April1st to 15thNight
23%38%26%23%14%
1799
16th to endNight
14%39%26%26%19%
1800
May1st to 15thNight
20%49%20%28%16%
1716
16th to endNight
15%310%27%28%13%
1685
June1st to 15thNight
13%5%11%18%33%18%
1503
16th to endNight
9%1312%34%38%
1440
July1st to 15thNight
13%1214%27%40%
1360
16th to endNight
14%26%23%28%24%
1635
August1st to 15thNight
13%1211%38%33%
1790
16th to endNight
9%1112%40%34%
1910
September1st to 15thNight
12%239%31%39%
1815
16th to endNight
9%1114%33%38%
1816
October1st to 15thNight
17%3417%27%29%
1851
16th to endNight
16%3312%23%39%
2120
November1st to 15thNight
15%25%14%24%37%
2275
16th to endNight
18%25%16%21%35%
2340
December1st to 15thNight
25%37%15%21%26%
2340
16th to endNight
27%36%14%25%21%
2607

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
13%8%43%25%8%
108
16th to endDay
14%9%37%27%10%1
273
February1st to 15thDay
8%10%32%31%14%2
266
16th to endDay
13%13%34%28%10%
238
March1st to 15thDay
7%15%31%24%18%2
270
16th to endDay
6%11%34%33%10%2
288
April1st to 15thDay
9%11%38%26%9%4
269
16th to endDay
415%40%28%7%2
270
May1st to 15thDay
6%10%29%33%15%3
288
16th to endDay
46%30%36%17%3
330
June1st to 15thDay
7%418%42%20%6%
315
16th to endDay
19%40%34%12%
315
July1st to 15thDay
35%39%39%12%
305
16th to endDay
26%35%42%13%
327
August1st to 15thDay
38%40%40%6%
315
16th to endDay
16%36%43%12%
332
September1st to 15thDay
2114%47%27%6%
315
16th to endDay
119%49%22%6%
256
October1st to 15thDay
36%24%44%17%3
255
16th to endDay
6%424%37%24%1
262
November1st to 15thDay
35%10%31%35%14%
90
16th to endDay
38%27%38%21%
90
December1st to 15thDay
5%6%17%35%33%1
90
16th to endDay
11%15%28%27%16%
77
January1st to 15thNight
8%316%43%22%6%
720
16th to endNight
12%414%38%25%4
768
February1st to 15thNight
7%212%40%29%7%
704
16th to endNight
15%312%38%24%5%
632
March1st to 15thNight
6%5%14%39%28%6%
720
16th to endNight
5%311%41%32%5%
768
April1st to 15thNight
8%313%40%29%4
719
16th to endNight
45%13%38%30%6%
720
May1st to 15thNight
8%111%38%35%5%
636
16th to endNight
4112%38%40%3
563
June1st to 15thNight
27%36%48%4
423
16th to endNight
24%66%6%
360
July1st to 15thNight
219%73%13%
340
16th to endNight
111%66%19%
615
August1st to 15thNight
318%58%17%
717
16th to endNight
111%58%26%
764
September1st to 15thNight
3220%52%20%
720
16th to endNight
1225%53%16%
656
October1st to 15thNight
5%7%36%40%9%
660
16th to endNight
5%28%30%38%14%
704
November1st to 15thNight
4210%37%32%13%
700
16th to endNight
6%210%35%33%11%
720
December1st to 15thNight
9%411%38%29%7%
720
16th to endNight
14%5%14%38%20%5%
768
Page generated at 2017-09-16 14:07:01. Version ac04

Copyright 2017 A. Danko


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