Eastridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eastridge Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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
43%
24305
26%
79499
17%
24200
53%
24200
32%
44772

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
30%
941
27%
4002
10%
926
42%
926
22%
2298
January11th to 20thNight
25%
949
26%
3984
8%
930
37%
930
22%
2082
January21st to endNight
31%
1037
21%
4472
11%
1023
44%
1023
21%
2711
February1st to 10thNight
25%
950
22%
2470
6%
950
35%
950
28%
1606
February11th to 20thNight
21%
760
22%
2190
6%
756
32%
756
25%
1382
February21st to endNight
22%
532
28%
1716
9%
532
38%
532
22%
1047
March1st to 10thNight
30%
540
24%
1980
15%
540
42%
540
24%
1138
March11th to 20thNight
26%
540
22%
1980
12%
540
40%
540
23%
1168
March21st to endNight
26%
594
23%
2178
12%
594
41%
594
23%
1285
April1st to 10thNight
27%
540
23%
1980
13%
540
43%
540
25%
1108
April11th to 20thNight
31%
533
25%
1777
16%
533
46%
533
29%
1011
April21st to endNight
31%
540
23%
1702
13%
540
47%
540
29%
1021
May1st to 10thNight
37%
540
23%
1620
16%
540
50%
540
32%
967
May11th to 20thNight
43%
531
21%
1594
16%
531
53%
531
30%
970
May21st to endNight
48%
584
22%
1746
16%
582
59%
582
33%
1034
June1st to 10thNight
66%
540
23%
1620
22%
540
72%
540
45%
849
June11th to 20thNight
63%
540
25%
1620
23%
540
68%
540
48%
825
June21st to endNight
72%
540
28%
1620
27%
540
77%
540
54%
763
July1st to 10thNight
75%
525
22%
1575
22%
525
78%
525
40%
857
July11th to 20thNight
81%
522
30%
1566
33%
522
85%
522
60%
711
July21st to endNight
82%
591
30%
1673
36%
558
84%
558
52%
819
August1st to 10thNight
80%
537
29%
1601
33%
534
82%
534
49%
809
August11th to 20thNight
76%
534
33%
1600
37%
534
78%
534
45%
853
August21st to endNight
81%
594
26%
1937
31%
594
81%
594
45%
958
September1st to 10thNight
72%
540
28%
1948
32%
540
74%
540
39%
973
September11th to 20thNight
66%
540
27%
1980
27%
540
71%
540
31%
1073
September21st to endNight
66%
540
36%
1980
33%
540
73%
540
44%
902
October1st to 10thNight
57%
636
34%
2076
26%
636
65%
636
42%
1058
October11th to 20thNight
44%
720
33%
2160
16%
720
56%
720
40%
1170
October21st to endNight
39%
792
31%
2376
17%
792
50%
792
34%
1360
November1st to 10thNight
42%
740
32%
2220
17%
740
55%
740
40%
1198
November11th to 20thNight
37%
874
29%
2394
13%
874
49%
874
38%
1379
November21st to endNight
31%
950
29%
2470
12%
950
42%
950
34%
1512
December1st to 10thNight
33%
950
28%
2470
11%
950
44%
950
34%
1523
December11th to 20thNight
26%
949
28%
2869
11%
948
37%
948
24%
1804
December21st to endNight
27%
1040
17%
4353
9%
1026
40%
1026
20%
2548

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
11%5%25%43445%7%49%
78782
Night
10%5%2442445%7%54%
80353
TransparencyDay
35%6%11%23%20%5%
78507
Night
31%5%10%23%23%7%
80148
SeeingDay
12%11%26%28%18%4
14282
Night
12%10%30%31%15%1
24329

By Month

Percentage Cloud Cover SE (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
12%10%45%423345%47%
2847
11th to 20thDay
8%6%24323345%59%
2850
21st to endDay
20%11%34322335%45%
3135
February1st to 10thDay
16%9%46%6%33435%42%
1710
11th to 20thDay
13%7%37%5%345%36%44%
1765
21st to endDay
20%8%35%423345%43%
1538
March1st to 10thDay
13%6%35%424446%48%
1980
11th to 20thDay
16%9%36%43433444%
1980
21st to endDay
16%8%35%4345%5%7%41%
2178
April1st to 10thDay
11%5%25%435%5%5%7%48%
1980
11th to 20thDay
15%5%244345%5%6%47%
2130
21st to endDay
16%6%36%5%25%446%42%
2254
May1st to 10thDay
14%6%36%5%3445%6%45%
2340
11th to 20thDay
14%5%345%25%5%6%8%42%
2302
21st to endDay
11%5%35%6%46%6%6%9%39%
2531
June1st to 10thDay
9%424435%46%10%48%
2340
11th to 20thDay
7%4245%35%5%6%10%50%
2340
21st to endDay
421442446%9%59%
2340
July1st to 10thDay
7%425%6%47%7%7%10%41%
2340
11th to 20thDay
4213435%5%5%10%57%
2340
21st to endDay
6%2235%36%7%7%10%50%
2546
August1st to 10thDay
42245%36%6%7%10%51%
2328
11th to 20thDay
9%4245%345%6%8%51%
2301
21st to endDay
5%3246%35%6%7%10%50%
2417
September1st to 10thDay
11%32443445%7%53%
2008
11th to 20thDay
12%425%445%45%6%48%
1980
21st to endDay
8%21333446%6%59%
1980
October1st to 10thDay
6%4245%35%446%57%
1864
11th to 20thDay
11%425%32333462%
1800
21st to endDay
17%6%24323345%52%
1980
November1st to 10thDay
10%41442435%7%55%
1858
11th to 20thDay
8%5%34424246%60%
1784
21st to endDay
14%5%24333347%53%
1710
December1st to 10thDay
13%6%25%423447%49%
1710
11th to 20thDay
14%7%45%5%34446%44%
2161
21st to endDay
14%9%36%5%45%5%5%6%39%
3135
January1st to 10thNight
12%9%36%5%23446%48%
4108
11th to 20thNight
8%5%2443445%5%57%
4120
21st to endNight
21%8%23313345%47%
4532
February1st to 10thNight
13%8%35%423446%47%
2470
11th to 20thNight
14%7%35%434336%47%
2190
21st to endNight
13%9%36%423336%49%
1716
March1st to 10thNight
14%6%25%42336%6%49%
1980
11th to 20thNight
16%6%2442335%450%
1980
21st to endNight
12%6%345%25%45%6%49%
2178
April1st to 10thNight
11%43442445%7%51%
1980
11th to 20thNight
12%41442445%6%53%
1777
21st to endNight
13%5%335%3435%7%50%
1702
May1st to 10thNight
10%42442447%10%49%
1620
11th to 20thNight
11%5%24435%5%5%8%49%
1593
21st to endNight
7%415%5%35%5%6%10%49%
1745
June1st to 10thNight
43244235%7%9%59%
1620
11th to 20thNight
5%21332447%8%61%
1620
21st to endNight
311332335%8%68%
1620
July1st to 10thNight
4324435%5%7%12%51%
1620
11th to 20thNight
311222247%12%65%
1620
21st to endNight
32134245%6%12%60%
1772
August1st to 10thNight
21134346%5%10%60%
1611
11th to 20thNight
5%423425%46%9%57%
1600
21st to endNight
32144345%5%10%59%
1937
September1st to 10thNight
8%423323347%60%
1948
11th to 20thNight
11%41444445%7%52%
1980
21st to endNight
6%313333446%64%
1980
October1st to 10thNight
6%32442445%5%61%
2076
11th to 20thNight
12%42332333462%
2160
21st to endNight
17%5%1332323457%
2376
November1st to 10thNight
9%424323345%61%
2220
11th to 20thNight
7%433424445%60%
2394
21st to endNight
13%6%24323446%54%
2470
December1st to 10thNight
13%5%34323346%53%
2470
11th to 20thNight
12%6%37%5%33345%50%
3036
21st to endNight
14%8%3443345%6%48%
4532

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
39%48%23%23%3
2848
11th to 20thDay
28%414%25%26%3
2850
21st to endDay
44%46%17%23%5%
3135
February1st to 10thDay
47%49%16%19%4
1710
11th to 20thDay
43%5%8%21%18%5%
1775
21st to endDay
46%46%14%22%8%
1538
March1st to 10thDay
39%5%8%19%18%12%
1980
11th to 20thDay
47%47%21%16%6%
1980
21st to endDay
45%6%9%21%15%3
2178
April1st to 10thDay
36%6%12%21%18%6%
1980
11th to 20thDay
38%7%11%23%16%5%
2130
21st to endDay
43%6%8%21%19%3
2254
May1st to 10thDay
40%6%11%21%18%3
2340
11th to 20thDay
39%9%14%23%14%1
2306
21st to endDay
42%8%14%21%13%1
2531
June1st to 10thDay
31%8%16%28%14%2
2340
11th to 20thDay
30%8%16%26%18%2
2340
21st to endDay
23%8%14%29%22%4
2340
July1st to 10thDay
34%10%20%22%14%1
2276
11th to 20thDay
22%7%15%31%22%3
2271
21st to endDay
25%9%18%34%14%
2405
August1st to 10thDay
26%10%16%26%20%2
2314
11th to 20thDay
31%7%14%25%21%2
2301
21st to endDay
27%8%17%29%16%4
2417
September1st to 10thDay
31%6%9%23%22%9%
2008
11th to 20thDay
36%6%12%19%19%8%
1980
21st to endDay
24%6%11%22%28%9%
1980
October1st to 10thDay
28%6%12%19%25%11%
1864
11th to 20thDay
30%46%16%31%14%
1800
21st to endDay
36%5%8%20%22%9%
1980
November1st to 10thDay
29%5%9%24%25%7%
1858
11th to 20thDay
28%410%24%26%8%
1784
21st to endDay
35%5%7%21%26%7%
1710
December1st to 10thDay
36%5%10%25%20%5%
1710
11th to 20thDay
41%46%19%23%6%
2159
21st to endDay
44%6%9%17%21%3
3135
January1st to 10thNight
38%48%19%27%4
4108
11th to 20thNight
28%8%12%18%27%6%
4120
21st to endNight
41%47%18%24%6%
4532
February1st to 10thNight
39%5%11%20%18%7%
2470
11th to 20thNight
40%46%22%21%6%
2190
21st to endNight
40%37%17%23%10%
1716
March1st to 10thNight
37%49%17%20%13%
1980
11th to 20thNight
39%5%10%19%20%7%
1980
21st to endNight
37%7%9%24%19%4
2178
April1st to 10thNight
34%6%10%20%19%11%
1980
11th to 20thNight
32%6%10%24%18%10%
1777
21st to endNight
35%6%10%24%22%2
1702
May1st to 10thNight
32%6%13%23%18%7%
1620
11th to 20thNight
34%8%13%28%15%2
1594
21st to endNight
30%8%17%26%16%3
1746
June1st to 10thNight
21%7%17%32%20%3
1620
11th to 20thNight
20%6%15%32%23%4
1620
21st to endNight
15%6%15%28%28%7%
1620
July1st to 10thNight
23%9%18%27%21%2
1575
11th to 20thNight
12%6%14%36%27%5%
1566
21st to endNight
17%6%17%34%24%1
1673
August1st to 10thNight
18%8%15%31%23%4
1601
11th to 20thNight
23%6%13%27%27%4
1600
21st to endNight
21%6%15%31%22%5%
1937
September1st to 10thNight
25%5%10%26%24%10%
1948
11th to 20thNight
31%6%10%20%23%10%
1980
21st to endNight
20%48%24%32%11%
1980
October1st to 10thNight
24%5%11%23%23%13%
2076
11th to 20thNight
28%47%15%30%17%
2160
21st to endNight
33%36%20%25%12%
2376
November1st to 10thNight
27%38%25%26%10%
2220
11th to 20thNight
28%48%22%28%10%
2394
21st to endNight
34%37%20%28%8%
2470
December1st to 10thNight
33%411%22%22%8%
2470
11th to 20thNight
39%46%18%26%8%
3037
21st to endNight
38%5%9%22%20%6%
4532

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
21%21%33%19%5%
270
11th to 20thDay
21%29%32%14%31
270
21st to endDay
20%24%33%18%6%
297
February1st to 10thDay
24%19%41%13%3
270
11th to 20thDay
26%26%34%12%2
252
21st to endDay
29%28%31%10%3
198
March1st to 10thDay
18%29%32%19%2
240
11th to 20thDay
25%25%30%15%5%
240
21st to endDay
22%28%35%11%3
264
April1st to 10thDay
15%26%39%15%41
240
11th to 20thDay
20%21%34%20%5%
408
21st to endDay
20%19%36%18%5%2
514
May1st to 10thDay
14%13%43%25%5%
603
11th to 20thDay
15%11%33%28%12%2
625
21st to endDay
12%8%33%25%17%4
679
June1st to 10thDay
9%5%19%36%23%7%
630
11th to 20thDay
6%324%42%19%5%
630
21st to endDay
2325%36%28%6%
630
July1st to 10thDay
5%114%37%32%11%
621
11th to 20thDay
3112%39%38%7%
618
21st to endDay
418%38%38%12%
684
August1st to 10thDay
4210%45%34%5%
626
11th to 20thDay
9%212%39%33%5%
615
21st to endDay
5%19%32%39%14%
536
September1st to 10thDay
7%19%29%40%13%
298
11th to 20thDay
5%411%39%32%8%
270
21st to endDay
11%319%34%28%6%
270
October1st to 10thDay
5%6%36%31%17%5%
270
11th to 20thDay
13%13%35%27%11%
270
21st to endDay
30%11%27%24%8%
297
November1st to 10thDay
11%13%43%22%9%3
270
11th to 20thDay
12%19%39%24%5%2
270
21st to endDay
19%23%36%17%4
270
December1st to 10thDay
16%22%32%23%7%
270
11th to 20thDay
22%17%39%18%4
270
21st to endDay
19%24%36%16%4
297
January1st to 10thNight
15%15%37%27%6%
950
11th to 20thNight
15%19%37%24%4
950
21st to endNight
15%14%37%30%5%
1045
February1st to 10thNight
17%18%37%24%3
950
11th to 20thNight
19%19%38%21%3
760
21st to endNight
19%20%37%22%2
532
March1st to 10thNight
18%17%32%29%4
540
11th to 20thNight
20%13%38%24%5%
540
21st to endNight
16%15%40%24%5%
594
April1st to 10thNight
13%18%40%24%5%
540
11th to 20thNight
14%14%38%28%7%
533
21st to endNight
15%12%40%24%8%1
540
May1st to 10thNight
10%10%39%32%8%1
540
11th to 20thNight
12%7%34%31%15%1
531
21st to endNight
8%433%33%20%2
584
June1st to 10thNight
4319%43%28%3
540
11th to 20thNight
5%325%48%19%1
540
21st to endNight
2120%45%27%4
540
July1st to 10thNight
5%110%45%34%5%
525
11th to 20thNight
3111%45%37%4
522
21st to endNight
318%43%40%5%
591
August1st to 10thNight
2111%49%35%2
537
11th to 20thNight
5%29%44%37%4
534
21st to endNight
327%42%41%5%
594
September1st to 10thNight
9%110%41%37%2
540
11th to 20thNight
12%113%36%34%4
540
21st to endNight
7%221%36%31%4
540
October1st to 10thNight
8%5%26%33%25%3
636
11th to 20thNight
13%7%32%34%13%1
720
21st to endNight
20%9%30%28%13%1
792
November1st to 10thNight
11%9%35%32%11%1
740
11th to 20thNight
10%15%35%31%10%
874
21st to endNight
18%14%35%24%8%
950
December1st to 10thNight
15%15%34%29%6%
950
11th to 20thNight
18%14%37%25%5%
950
21st to endNight
16%17%37%25%5%
1045
Page generated at 2024-02-12 05:35:32. Version ac07

Copyright 2024 Attilla Danko


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