Johnson Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Johnson Ranch clear sky chart from 2005-11-06 to 2024-01-15.

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
76%
24042
36%
74374
33%
23993
81%
23993
54%
34853

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
73%
760
33%
2457
33%
756
78%
756
49%
1169
January11th to 20thNight
69%
736
37%
2392
36%
736
76%
736
50%
1119
January21st to endNight
63%
792
36%
2574
33%
792
71%
792
44%
1296
February1st to 10thNight
70%
720
37%
2277
36%
720
77%
720
54%
1038
February11th to 20thNight
64%
700
34%
2098
31%
700
71%
700
47%
1070
February21st to endNight
62%
592
36%
1736
32%
592
70%
592
49%
889
March1st to 10thNight
65%
720
38%
1980
29%
720
74%
720
56%
985
March11th to 20thNight
70%
720
38%
1980
30%
720
77%
720
60%
957
March21st to endNight
70%
792
38%
2178
28%
792
78%
792
60%
1058
April1st to 10thNight
75%
720
37%
1980
27%
720
81%
720
65%
917
April11th to 20thNight
69%
597
40%
1841
31%
597
79%
597
66%
758
April21st to endNight
73%
540
47%
1686
38%
540
83%
540
73%
650
May1st to 10thNight
76%
540
43%
1620
35%
540
83%
540
72%
661
May11th to 20thNight
79%
531
41%
1594
35%
531
83%
531
70%
660
May21st to endNight
82%
582
42%
1746
35%
582
85%
582
79%
670
June1st to 10thNight
86%
540
37%
1620
32%
540
87%
540
71%
663
June11th to 20thNight
90%
540
41%
1620
34%
540
92%
540
87%
591
June21st to endNight
87%
540
32%
1620
28%
540
87%
540
64%
710
July1st to 10thNight
83%
525
25%
1575
21%
525
84%
525
49%
799
July11th to 20thNight
86%
522
26%
1566
22%
522
86%
522
44%
826
July21st to endNight
79%
591
23%
1674
20%
558
80%
558
35%
1000
August1st to 10thNight
87%
537
28%
1602
26%
534
87%
534
49%
812
August11th to 20thNight
82%
534
33%
1602
31%
534
82%
534
42%
876
August21st to endNight
85%
675
32%
2005
30%
675
85%
675
45%
1064
September1st to 10thNight
81%
720
33%
1980
30%
720
82%
720
48%
1076
September11th to 20thNight
84%
720
41%
1980
35%
720
86%
720
64%
931
September21st to endNight
83%
720
39%
1980
31%
720
87%
720
64%
934
October1st to 10thNight
79%
720
39%
2026
31%
720
83%
720
62%
956
October11th to 20thNight
83%
720
44%
2160
39%
720
88%
720
75%
860
October21st to endNight
80%
792
46%
2376
38%
792
86%
792
74%
953
November1st to 10thNight
80%
740
43%
2220
39%
740
84%
740
65%
961
November11th to 20thNight
79%
760
42%
2388
39%
760
85%
760
62%
1021
November21st to endNight
69%
760
38%
2470
36%
760
77%
760
51%
1148
December1st to 10thNight
71%
760
38%
2470
38%
760
76%
760
48%
1175
December11th to 20thNight
67%
760
33%
2947
36%
758
73%
758
34%
1555
December21st to endNight
67%
824
23%
4354
36%
817
72%
817
27%
2045

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
3213323346%69%
74968
Night
4213323446%67%
74842
TransparencyDay
17%35%11%24%41%
74695
Night
18%35%11%23%41%
74637
SeeingDay
4315%31%33%14%
13829
Night
4213%44%34%4
24060

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 10thDay
5%324432346%64%
1708
11th to 20thDay
6%323413336%66%
1656
21st to endDay
6%413423246%65%
1782
February1st to 10thDay
3313322446%69%
1680
11th to 20thDay
7%424423446%61%
1750
21st to endDay
6%423323446%65%
1517
March1st to 10thDay
5%31432445%7%63%
1980
11th to 20thDay
422343245%5%67%
1980
21st to endDay
3323324335%70%
2178
April1st to 10thDay
2112313347%74%
1980
11th to 20thDay
2211222235%79%
2066
21st to endDay
2111112245%80%
2270
May1st to 10thDay
111222233481%
2340
11th to 20thDay
11222323479%
2301
21st to endDay
12111122286%
2530
June1st to 10thDay
111212335%80%
2340
11th to 20thDay
11111112288%
2340
21st to endDay
2112213235%78%
2340
July1st to 10thDay
22233235%7%7%64%
2340
11th to 20thDay
2314436%7%8%11%51%
2340
21st to endDay
5%3246%46%5%8%12%44%
2545
August1st to 10thDay
33144245%6%9%58%
2328
11th to 20thDay
3223425%5%7%10%55%
2299
21st to endDay
22144345%6%9%60%
2343
September1st to 10thDay
432432335%8%63%
1980
11th to 20thDay
2212212345%77%
1980
21st to endDay
2212322335%75%
1980
October1st to 10thDay
3212323346%73%
1932
11th to 20thDay
11121123484%
1800
21st to endDay
11221223480%
1980
November1st to 10thDay
2112212347%76%
1859
11th to 20thDay
221232334474%
1789
21st to endDay
5%313324347%65%
1710
December1st to 10thDay
6%313434445%63%
1710
11th to 20thDay
6%5%25%5%235%6%8%54%
2169
21st to endDay
9%5%25%423447%55%
3146
January1st to 10thNight
6%22343446%7%60%
2457
11th to 20thNight
6%314323335%67%
2392
21st to endNight
9%424323345%61%
2574
February1st to 10thNight
4314322247%68%
2277
11th to 20thNight
7%414323347%61%
2098
21st to endNight
6%314423346%64%
1736
March1st to 10thNight
5%31232345%7%65%
1980
11th to 20thNight
6%212323346%69%
1980
21st to endNight
4323322348%67%
2178
April1st to 10thNight
221221345%6%71%
1980
11th to 20thNight
211232223478%
1841
21st to endNight
2111112225%82%
1686
May1st to 10thNight
2112112346%77%
1620
11th to 20thNight
211222234479%
1594
21st to endNight
21111122387%
1746
June1st to 10thNight
2112222236%78%
1620
11th to 20thNight
111212487%
1620
21st to endNight
2112322236%74%
1620
July1st to 10thNight
33144345%6%9%58%
1620
11th to 20thNight
1213436%8%11%12%49%
1620
21st to endNight
34246%5%7%7%8%14%39%
1773
August1st to 10thNight
2214435%5%7%10%56%
1611
11th to 20thNight
23246%45%6%7%7%54%
1602
21st to endNight
22145%45%6%7%9%55%
2005
September1st to 10thNight
43234345%6%9%58%
1980
11th to 20thNight
2212323345%74%
1980
21st to endNight
2213333336%72%
1980
October1st to 10thNight
321232345%5%71%
2026
11th to 20thNight
221121123482%
2160
21st to endNight
111121222482%
2376
November1st to 10thNight
3212212335%75%
2220
11th to 20thNight
2113312335%76%
2388
21st to endNight
5%214323347%66%
2470
December1st to 10thNight
6%31332345%6%64%
2470
11th to 20thNight
8%5%25%5%3345%6%54%
3041
21st to endNight
9%4144345%45%57%
4521

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
23%26%16%29%24%
1709
11th to 20thDay
22%25%10%30%31%
1656
21st to endDay
22%25%15%28%29%
1782
February1st to 10thDay
18%25%14%25%37%
1680
11th to 20thDay
26%25%11%25%31%
1760
21st to endDay
22%2411%30%32%
1517
March1st to 10thDay
21%249%28%35%
1980
11th to 20thDay
19%25%10%24%40%
1980
21st to endDay
18%248%32%36%
2178
April1st to 10thDay
13%127%34%44%
1980
11th to 20thDay
12%126%25%54%
2069
21st to endDay
8%137%24%57%
2270
May1st to 10thDay
10%238%20%58%
2340
11th to 20thDay
9%247%22%57%
2304
21st to endDay
7%12419%68%
2530
June1st to 10thDay
9%12317%67%
2340
11th to 20thDay
6%118%82%
2340
21st to endDay
11%236%13%65%
2340
July1st to 10thDay
18%5%6%10%18%44%
2276
11th to 20thDay
24%7%14%21%21%13%
2271
21st to endDay
30%7%15%21%17%11%
2404
August1st to 10thDay
22%410%17%17%30%
2313
11th to 20thDay
22%7%9%19%21%22%
2299
21st to endDay
19%6%8%16%27%24%
2343
September1st to 10thDay
21%47%13%24%31%
1980
11th to 20thDay
11%247%28%48%
1980
21st to endDay
13%25%6%22%52%
1980
October1st to 10thDay
14%25%11%24%44%
1932
11th to 20thDay
7%236%24%58%
1800
21st to endDay
10%238%26%51%
1980
November1st to 10thDay
10%2311%34%41%
1859
11th to 20thDay
15%229%27%44%
1789
21st to endDay
21%2411%25%37%
1710
December1st to 10thDay
23%35%14%26%29%
1710
11th to 20thDay
28%37%17%24%20%
2168
21st to endDay
29%36%19%29%14%
3146
January1st to 10thNight
21%37%14%30%25%
2457
11th to 20thNight
21%2411%28%34%
2392
21st to endNight
26%2412%27%29%
2574
February1st to 10thNight
19%2412%24%40%
2277
11th to 20thNight
24%3414%24%32%
2099
21st to endNight
23%249%27%34%
1736
March1st to 10thNight
19%3410%26%40%
1980
11th to 20thNight
17%2310%24%44%
1980
21st to endNight
17%249%31%37%
2178
April1st to 10thNight
14%238%26%47%
1980
11th to 20thNight
12%125%24%55%
1841
21st to endNight
9%126%21%60%
1686
May1st to 10thNight
10%137%23%56%
1620
11th to 20thNight
11%236%19%60%
1595
21st to endNight
7%12416%71%
1746
June1st to 10thNight
11%13316%67%
1620
11th to 20thNight
412310%79%
1620
21st to endNight
13%25%5%8%67%
1620
July1st to 10thNight
22%38%11%15%41%
1575
11th to 20thNight
21%8%12%21%23%14%
1566
21st to endNight
30%8%14%19%16%12%
1674
August1st to 10thNight
20%6%10%19%15%30%
1602
11th to 20thNight
25%6%10%18%18%23%
1602
21st to endNight
23%6%7%15%24%26%
2005
September1st to 10thNight
23%5%7%17%19%29%
1980
11th to 20thNight
14%247%23%49%
1980
21st to endNight
14%347%21%51%
1980
October1st to 10thNight
15%25%12%20%45%
2026
11th to 20thNight
9%137%20%60%
2160
21st to endNight
9%139%22%56%
2376
November1st to 10thNight
13%138%27%47%
2220
11th to 20thNight
14%2310%25%47%
2388
21st to endNight
20%249%27%37%
2470
December1st to 10thNight
21%3416%23%33%
2470
11th to 20thNight
31%26%14%25%22%
3041
21st to endNight
28%5%6%16%26%19%
4521

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
10%416%41%24%6%
270
11th to 20thDay
11%313%38%27%8%
252
21st to endDay
5%417%44%22%8%
264
February1st to 10thDay
4321%36%29%8%
300
11th to 20thDay
10%8%25%33%22%2
415
21st to endDay
8%10%26%37%17%2
346
March1st to 10thDay
5%9%27%38%18%4
420
11th to 20thDay
7%7%24%28%25%9%
420
21st to endDay
5%9%25%37%19%5%
462
April1st to 10thDay
37%22%34%25%9%
420
11th to 20thDay
29%25%35%23%6%
412
21st to endDay
27%23%33%25%9%
420
May1st to 10thDay
26%23%32%25%12%
423
11th to 20thDay
1319%35%31%11%
448
21st to endDay
15%19%34%34%7%
485
June1st to 10thDay
3212%30%38%14%
450
11th to 20thDay
2213%33%34%17%
450
21st to endDay
117%34%42%14%
450
July1st to 10thDay
2426%44%24%
446
11th to 20thDay
4318%44%31%
444
21st to endDay
31217%44%33%
487
August1st to 10thDay
3118%44%34%
447
11th to 20thDay
21318%42%34%
437
21st to endDay
216%46%36%
495
September1st to 10thDay
5%17%26%41%20%
450
11th to 20thDay
318%24%46%17%
450
21st to endDay
4213%31%33%18%
450
October1st to 10thDay
3215%33%35%11%
402
11th to 20thDay
3114%26%41%14%
270
21st to endDay
2115%34%32%15%
297
November1st to 10thDay
4216%35%33%10%
270
11th to 20thDay
3113%38%37%7%
270
21st to endDay
5%121%36%30%7%
270
December1st to 10thDay
7%115%40%33%4
270
11th to 20thDay
6%218%44%26%5%
270
21st to endDay
11%5%24%33%22%5%
297
January1st to 10thNight
7%114%53%22%2
760
11th to 20thNight
7%216%48%25%3
736
21st to endNight
9%319%48%19%3
792
February1st to 10thNight
5%217%47%26%2
720
11th to 20thNight
8%321%49%19%1
704
21st to endNight
8%322%47%19%1
592
March1st to 10thNight
5%323%51%17%2
720
11th to 20thNight
7%316%41%28%6%
720
21st to endNight
4318%45%28%3
792
April1st to 10thNight
3317%51%25%2
720
11th to 20thNight
3223%49%22%1
597
21st to endNight
3221%47%24%3
540
May1st to 10thNight
2218%51%26%2
540
11th to 20thNight
2115%50%31%2
531
21st to endNight
2113%52%29%2
584
June1st to 10thNight
118%50%39%1
540
11th to 20thNight
8%54%37%1
540
21st to endNight
117%39%50%2
540
July1st to 10thNight
215%34%54%4
525
11th to 20thNight
21422%65%7%
522
21st to endNight
41316%66%9%
591
August1st to 10thNight
2120%66%10%
537
11th to 20thNight
21426%60%7%
534
21st to endNight
31324%61%9%
675
September1st to 10thNight
5%16%31%51%7%
720
11th to 20thNight
218%38%47%5%
720
21st to endNight
219%43%40%4
720
October1st to 10thNight
3112%48%33%3
720
11th to 20thNight
2112%48%35%3
720
21st to endNight
2114%43%33%7%
792
November1st to 10thNight
4111%48%31%4
740
11th to 20thNight
2114%50%31%3
760
21st to endNight
5%218%46%26%3
760
December1st to 10thNight
7%214%46%29%2
760
11th to 20thNight
10%313%49%23%2
760
21st to endNight
8%315%49%22%3
836
Page generated at 2024-01-11 20:33:45. Version ac07

Copyright 2024 Attilla Danko


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