Johnson Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Johnson Valley clear sky chart from 2005-11-05 to 2019-06-19.

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
72%
18528
41%
54031
31%
18489
81%
18489
66%
22932

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
68%
837
36%
2717
31%
836
78%
836
51%
1217
January16th to endNight
66%
896
40%
2747
32%
896
77%
896
54%
1244
February1st to 15thNight
65%
820
41%
2468
33%
819
78%
819
57%
1097
February16th to endNight
61%
736
39%
2207
34%
736
72%
736
54%
1001
March1st to 15thNight
65%
840
37%
2509
31%
840
78%
840
58%
1089
March16th to endNight
61%
896
39%
2397
25%
896
74%
896
63%
1100
April1st to 15thNight
51%
839
41%
2099
15%
839
66%
839
59%
1020
April16th to endNight
57%
830
42%
2078
17%
830
69%
830
68%
921
May1st to 15thNight
63%
630
44%
1889
27%
629
73%
629
73%
712
May16th to endNight
56%
657
38%
1973
21%
657
68%
657
71%
740
June1st to 15thNight
70%
630
38%
1890
27%
630
78%
630
80%
695
June16th to endNight
74%
597
36%
1791
29%
597
79%
597
86%
651
July1st to 15thNight
87%
555
33%
1665
28%
555
89%
555
70%
684
July16th to endNight
88%
612
36%
1737
30%
579
90%
579
64%
753
August1st to 15thNight
91%
761
40%
1907
26%
758
92%
758
81%
855
August16th to endNight
91%
828
43%
2070
30%
828
91%
828
79%
948
September1st to 15thNight
92%
780
44%
2034
34%
780
94%
780
79%
885
September16th to endNight
87%
776
49%
2145
42%
776
93%
776
87%
838
October1st to 15thNight
79%
780
47%
2145
39%
780
87%
780
75%
897
October16th to endNight
82%
832
46%
2526
43%
832
89%
832
73%
989
November1st to 15thNight
80%
820
42%
2665
41%
820
89%
820
71%
1008
November16th to endNight
76%
840
43%
2730
42%
840
85%
840
63%
1097
December1st to 15thNight
69%
840
39%
2730
33%
840
80%
840
53%
1210
December16th to endNight
62%
896
38%
2912
29%
896
75%
896
50%
1281

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
111212346%74%
54681
Night
111112235%77%
54230
TransparencyDay
11%2315%28%37%
54377
Night
10%2416%30%35%
54036
SeeingDay
49%22%35%22%5%
8186
Night
25%16%32%33%9%
18537

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
222214337%68%
1881
16th to endDay
121222335%7%67%
2177
February1st to 15thDay
1111113438%71%
2051
16th to endDay
112222447%68%
1839
March1st to 15thDay
1211212339%70%
2110
16th to endDay
1211235%7%72%
2527
April1st to 15thDay
11222347%73%
2509
16th to endDay
1111236%80%
2485
May1st to 15thDay
111111245%79%
2721
16th to endDay
11112235%79%
2845
June1st to 15thDay
113484%
2730
16th to endDay
11111288%
2577
July1st to 15thDay
1112323446%68%
2535
16th to endDay
21133345%6%7%60%
2675
August1st to 15thDay
11223445%73%
2293
16th to endDay
1121246%6%72%
2484
September1st to 15thDay
11222345%75%
2255
16th to endDay
111122286%
2145
October1st to 15thDay
1121223480%
2145
16th to endDay
111112484%
2047
November1st to 15thDay
11111234478%
1854
16th to endDay
111212347%73%
1890
December1st to 15thDay
1212222448%66%
1890
16th to endDay
1112324347%67%
2016
January1st to 15thNight
122224348%66%
2717
16th to endNight
122313346%69%
2747
February1st to 15thNight
222212345%72%
2461
16th to endNight
111221345%7%67%
2207
March1st to 15thNight
11121235%9%69%
2509
16th to endNight
12112337%74%
2397
April1st to 15thNight
111212246%75%
2099
16th to endNight
11236%82%
2078
May1st to 15thNight
1225%83%
1889
16th to endNight
113486%
1972
June1st to 15thNight
112387%
1890
16th to endNight
11290%
1791
July1st to 15thNight
111112235%78%
1755
16th to endNight
111212236%74%
1845
August1st to 15thNight
1111225%83%
1916
16th to endNight
121212383%
2070
September1st to 15thNight
11222483%
2034
16th to endNight
11291%
2145
October1st to 15thNight
12235%82%
2145
16th to endNight
111122483%
2526
November1st to 15thNight
11234480%
2665
16th to endNight
111212246%75%
2730
December1st to 15thNight
122223348%67%
2730
16th to endNight
2112213248%68%
2912

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
16%26%22%32%18%
1882
16th to endDay
16%36%21%31%19%
2177
February1st to 15thDay
13%25%19%31%26%
2051
16th to endDay
14%35%22%34%19%
1839
March1st to 15thDay
12%1422%34%23%
2110
16th to endDay
11%26%23%33%22%
2527
April1st to 15thDay
12%1417%35%27%
2509
16th to endDay
7%1217%36%34%
2485
May1st to 15thDay
9%1213%35%37%
2721
16th to endDay
9%2214%33%38%
2848
June1st to 15thDay
5%127%21%61%
2730
16th to endDay
6%1310%77%
2577
July1st to 15thDay
15%2210%17%50%
2396
16th to endDay
18%45%16%21%32%
2520
August1st to 15thDay
11%3210%20%52%
2279
16th to endDay
10%3311%24%46%
2484
September1st to 15thDay
11%348%21%51%
2255
16th to endDay
7%15%29%55%
2145
October1st to 15thDay
10%2211%31%42%
2145
16th to endDay
7%1210%32%45%
2047
November1st to 15thDay
11%1317%34%31%
1854
16th to endDay
12%25%20%30%28%
1890
December1st to 15thDay
16%37%22%28%22%
1890
16th to endDay
16%48%24%28%17%
2016
January1st to 15thNight
16%37%22%27%22%
2717
16th to endNight
16%27%21%28%23%
2747
February1st to 15thNight
14%25%20%30%27%
2472
16th to endNight
14%35%22%32%21%
2207
March1st to 15thNight
12%26%23%31%23%
2509
16th to endNight
10%36%20%39%20%
2397
April1st to 15thNight
11%25%20%35%24%
2099
16th to endNight
6%1316%40%32%
2078
May1st to 15thNight
5%1316%39%33%
1890
16th to endNight
5%1418%37%33%
1973
June1st to 15thNight
41110%20%61%
1890
16th to endNight
36%13%75%
1791
July1st to 15thNight
9%238%18%56%
1665
16th to endNight
12%25%17%26%34%
1737
August1st to 15thNight
6%1210%23%55%
1907
16th to endNight
7%129%29%49%
2070
September1st to 15thNight
6%239%22%55%
2034
16th to endNight
36%31%57%
2145
October1st to 15thNight
6%1312%34%40%
2145
16th to endNight
7%138%30%48%
2526
November1st to 15thNight
8%1415%38%31%
2665
16th to endNight
11%1420%32%29%
2730
December1st to 15thNight
16%36%20%28%24%
2730
16th to endNight
15%39%22%30%18%
2912

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
8%7%21%38%19%3
180
16th to endDay
6%9%27%37%15%3
353
February1st to 15thDay
5%15%26%31%15%5%
386
16th to endDay
8%19%26%32%13%
342
March1st to 15thDay
7%16%29%30%14%1
390
16th to endDay
7%12%31%33%12%1
416
April1st to 15thDay
8%19%24%25%17%3
389
16th to endDay
5%25%27%24%12%4
378
May1st to 15thDay
411%27%33%16%5%
408
16th to endDay
413%28%34%14%3
458
June1st to 15thDay
16%24%37%22%6%
435
16th to endDay
1121%37%28%9%
388
July1st to 15thDay
110%39%33%13%
365
16th to endDay
218%42%31%13%
391
August1st to 15thDay
1214%41%28%10%
359
16th to endDay
112%38%34%13%
396
September1st to 15thDay
1218%48%25%3
375
16th to endDay
16%20%41%27%3
375
October1st to 15thDay
29%28%39%18%2
375
16th to endDay
3315%36%31%8%
295
November1st to 15thDay
2418%36%31%6%
180
16th to endDay
5%7%22%28%28%6%
180
December1st to 15thDay
7%7%20%33%28%2
180
16th to endDay
5%10%19%31%25%6%
192
January1st to 15thNight
2419%35%26%11%
840
16th to endNight
37%17%35%28%7%
896
February1st to 15thNight
45%20%35%26%8%
824
16th to endNight
37%24%38%19%6%
736
March1st to 15thNight
28%19%39%23%5%
840
16th to endNight
28%23%31%27%5%
896
April1st to 15thNight
313%27%27%22%5%
839
16th to endNight
314%23%28%24%5%
830
May1st to 15thNight
18%23%35%25%4
630
16th to endNight
111%27%28%26%2
659
June1st to 15thNight
422%37%32%2
630
16th to endNight
122%38%35%2
597
July1st to 15thNight
215%32%50%8%
555
16th to endNight
1229%56%9%
612
August1st to 15thNight
1424%54%15%
761
16th to endNight
1320%53%20%
828
September1st to 15thNight
1327%51%15%
780
16th to endNight
28%28%46%14%
776
October1st to 15thNight
15%12%38%34%8%
780
16th to endNight
1310%28%38%18%
832
November1st to 15thNight
213%36%36%10%
820
16th to endNight
2412%32%33%14%
840
December1st to 15thNight
35%17%35%29%8%
840
16th to endNight
5%8%19%34%24%7%
896
Page generated at 2019-06-20 05:02:28. Version ac04

Copyright 2019 A. Danko


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