Johnson Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Johnson Ranch clear sky chart from 2005-11-05 to 2017-09-24.

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
78%
15651
37%
46988
33%
15612
82%
15612
56%
21993

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
73%
719
32%
2327
34%
716
77%
716
50%
1091
January16th to endNight
68%
768
36%
2496
35%
768
75%
768
44%
1245
February1st to 15thNight
73%
699
36%
2189
36%
699
79%
699
53%
1007
February16th to endNight
68%
632
37%
1868
37%
632
73%
632
48%
962
March1st to 15thNight
70%
720
40%
1980
33%
720
77%
720
61%
951
March16th to endNight
77%
768
40%
2112
31%
768
83%
768
65%
979
April1st to 15thNight
73%
701
34%
1960
25%
701
79%
701
60%
935
April16th to endNight
73%
540
46%
1722
38%
540
83%
540
76%
640
May1st to 15thNight
77%
539
40%
1619
33%
539
83%
539
72%
663
May16th to endNight
80%
561
41%
1684
33%
561
84%
561
73%
677
June1st to 15thNight
87%
540
35%
1620
31%
540
88%
540
73%
654
June16th to endNight
91%
540
35%
1620
30%
540
92%
540
73%
659
July1st to 15thNight
83%
510
24%
1530
21%
510
83%
510
47%
780
July16th to endNight
83%
564
26%
1593
22%
531
84%
531
39%
910
August1st to 15thNight
84%
539
29%
1611
26%
536
84%
536
44%
843
August16th to endNight
85%
627
33%
1869
31%
627
85%
627
43%
1025
September1st to 15thNight
80%
720
32%
1980
28%
720
81%
720
49%
1063
September16th to endNight
84%
692
43%
1914
35%
692
87%
692
69%
866
October1st to 15thNight
80%
660
41%
1898
34%
660
84%
660
65%
855
October16th to endNight
86%
704
44%
2112
40%
704
90%
704
71%
875
November1st to 15thNight
82%
700
42%
2108
39%
700
86%
700
66%
900
November16th to endNight
76%
720
40%
2340
38%
720
82%
720
56%
1031
December1st to 15thNight
74%
720
38%
2340
41%
720
77%
720
49%
1107
December16th to endNight
70%
768
36%
2496
37%
768
74%
768
42%
1275

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
3212213346%69%
47934
Night
3212213346%68%
47185
TransparencyDay
16%2410%24%40%
47629
Night
17%2410%23%41%
46991
SeeingDay
4314%30%34%12%
5468
Night
4111%41%37%4
15660

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
5%312322335%65%
1611
16th to endDay
7%312213236%64%
1728
February1st to 15thDay
3313312346%67%
1670
16th to endDay
6%312322346%62%
1603
March1st to 15thDay
4212223345%68%
1980
16th to endDay
2213312335%70%
2112
April1st to 15thDay
212212247%72%
1988
16th to endDay
11111112481%
2234
May1st to 15thDay
111223480%
2331
16th to endDay
1111122382%
2429
June1st to 15thDay
11111122481%
2340
16th to endDay
111212481%
2340
July1st to 15thDay
22143245%7%8%56%
2340
16th to endDay
43245%37%5%8%12%42%
2467
August1st to 15thDay
33144245%6%10%54%
2340
16th to endDay
21134245%6%9%58%
2329
September1st to 15thDay
321332336%7%62%
1980
16th to endDay
21111123478%
1904
October1st to 15thDay
111213245%74%
1730
16th to endDay
11121113479%
1760
November1st to 15thDay
11222246%75%
1750
16th to endDay
3213213135%72%
1620
December1st to 15thDay
6%312223335%63%
1620
16th to endDay
7%323322337%61%
1728
January1st to 15thNight
5%213323345%64%
2327
16th to endNight
8%31331233462%
2496
February1st to 15thNight
4313212237%67%
2179
16th to endNight
6%313424436%61%
1868
March1st to 15thNight
4212112346%70%
1980
16th to endNight
3112212236%73%
2112
April1st to 15thNight
3212212345%70%
1960
16th to endNight
111122383%
1722
May1st to 15thNight
111111345%77%
1619
16th to endNight
21111122283%
1684
June1st to 15thNight
1111222480%
1620
16th to endNight
1212225%80%
1620
July1st to 15thNight
1244246%7%11%54%
1620
16th to endNight
32135%35%7%9%14%43%
1701
August1st to 15thNight
12135%35%5%6%9%54%
1620
16th to endNight
12135%45%6%7%8%53%
1869
September1st to 15thNight
221242445%9%58%
1980
16th to endNight
11221223475%
1914
October1st to 15thNight
212212245%74%
1898
16th to endNight
11112222380%
2112
November1st to 15thNight
21121222476%
2108
16th to endNight
4112212235%71%
2340
December1st to 15thNight
7%312322335%65%
2340
16th to endNight
8%314322345%59%
2496

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
21%25%13%26%29%
1612
16th to endDay
22%2315%25%30%
1728
February1st to 15thDay
19%2415%28%30%
1670
16th to endDay
23%1313%31%26%
1603
March1st to 15thDay
17%226%29%41%
1980
16th to endDay
16%137%30%40%
2112
April1st to 15thDay
13%125%35%40%
1988
16th to endDay
8%26%23%57%
2234
May1st to 15thDay
8%137%21%56%
2331
16th to endDay
9%12420%61%
2432
June1st to 15thDay
8%12214%71%
2340
16th to endDay
9%125%9%71%
2340
July1st to 15thDay
21%6%9%14%17%30%
2201
16th to endDay
30%6%14%22%18%7%
2312
August1st to 15thDay
24%48%17%16%26%
2325
16th to endDay
21%5%7%17%24%23%
2329
September1st to 15thDay
20%47%13%24%29%
1980
16th to endDay
11%13425%53%
1904
October1st to 15thDay
12%247%25%47%
1730
16th to endDay
10%238%25%50%
1760
November1st to 15thDay
10%129%33%42%
1750
16th to endDay
16%229%26%42%
1620
December1st to 15thDay
22%2415%30%24%
1620
16th to endDay
23%35%19%31%16%
1728
January1st to 15thNight
20%26%11%25%32%
2327
16th to endNight
25%2312%26%29%
2496
February1st to 15thNight
18%2414%25%34%
2190
16th to endNight
23%2212%27%30%
1868
March1st to 15thNight
16%227%24%46%
1980
16th to endNight
14%128%30%42%
2112
April1st to 15thNight
16%125%31%42%
1960
16th to endNight
7%25%20%62%
1722
May1st to 15thNight
9%135%24%55%
1620
16th to endNight
9%116%16%64%
1685
June1st to 15thNight
9%1313%70%
1620
16th to endNight
8%1347%73%
1620
July1st to 15thNight
21%5%11%16%15%30%
1530
16th to endNight
26%8%13%20%21%10%
1593
August1st to 15thNight
23%5%10%18%14%27%
1611
16th to endNight
24%6%7%15%22%23%
1869
September1st to 15thNight
21%5%7%17%21%26%
1980
16th to endNight
11%135%24%53%
1914
October1st to 15thNight
13%1410%21%48%
1898
16th to endNight
10%128%20%56%
2112
November1st to 15thNight
12%129%26%47%
2108
16th to endNight
17%138%23%45%
2340
December1st to 15thNight
21%2413%28%30%
2340
16th to endNight
26%3416%28%20%
2496

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
15%215%42%22%2
90
16th to endDay
7%312%36%25%15%
96
February1st to 15thDay
5%214%38%35%3
185
16th to endDay
8%7%23%34%23%3
238
March1st to 15thDay
5%7%22%31%21%12%
270
16th to endDay
29%23%27%26%10%
288
April1st to 15thDay
47%26%32%20%8%
269
16th to endDay
210%30%32%21%2
270
May1st to 15thDay
16%31%28%23%7%
288
16th to endDay
2421%32%33%6%
330
June1st to 15thDay
3216%34%31%11%
315
16th to endDay
3436%40%14%
315
July1st to 15thDay
26%28%44%17%
305
16th to endDay
3417%46%27%
327
August1st to 15thDay
3220%46%26%
315
16th to endDay
119%50%26%
332
September1st to 15thDay
7%6%30%39%14%
315
16th to endDay
5%115%34%34%8%
288
October1st to 15thDay
2315%31%33%13%
170
16th to endDay
4423%48%18%
96
November1st to 15thDay
2217%31%35%11%
90
16th to endDay
7%312%43%30%3
90
December1st to 15thDay
47%24%57%5%
90
16th to endDay
14%320%32%27%2
96
January1st to 15thNight
7%13%53%21%3
720
16th to endNight
9%214%46%24%2
768
February1st to 15thNight
5%113%48%27%2
704
16th to endNight
8%15%50%23%1
632
March1st to 15thNight
6%119%40%28%4
720
16th to endNight
3213%43%32%4
768
April1st to 15thNight
4215%49%26%1
701
16th to endNight
2220%46%25%3
540
May1st to 15thNight
1216%44%31%3
540
16th to endNight
3113%44%34%2
563
June1st to 15thNight
17%51%37%1
540
16th to endNight
436%56%2
540
July1st to 15thNight
3428%55%6%
510
16th to endNight
5%213%67%10%
564
August1st to 15thNight
3119%63%11%
539
16th to endNight
3322%60%10%
627
September1st to 15thNight
38%30%50%7%
720
16th to endNight
217%39%43%5%
692
October1st to 15thNight
310%44%37%3
660
16th to endNight
28%44%38%6%
704
November1st to 15thNight
410%45%34%4
700
16th to endNight
414%47%30%2
720
December1st to 15thNight
8%10%46%31%2
720
16th to endNight
9%110%50%25%2
768
Page generated at 2017-09-25 06:02:19. Version ac04

Copyright 2017 A. Danko


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