Big Bear Solar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bear Solar Observatory 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
62%
16033
36%
46825
26%
15993
71%
15993
52%
22489

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
50%
716
29%
2327
21%
716
61%
716
38%
1187
January16th to endNight
48%
768
34%
2337
24%
768
61%
768
36%
1274
February1st to 15thNight
50%
700
33%
2108
27%
699
60%
699
42%
1104
February16th to endNight
44%
632
31%
1895
24%
632
57%
632
34%
1061
March1st to 15thNight
48%
720
30%
2159
21%
720
62%
720
40%
1125
March16th to endNight
49%
768
33%
2039
19%
768
61%
768
44%
1112
April1st to 15thNight
40%
719
34%
1799
12%
719
53%
719
45%
966
April16th to endNight
50%
720
37%
1800
14%
720
62%
720
56%
886
May1st to 15thNight
54%
554
38%
1633
21%
553
64%
553
61%
684
May16th to endNight
53%
561
36%
1685
19%
561
65%
561
62%
696
June1st to 15thNight
66%
540
34%
1620
24%
540
73%
540
70%
651
June16th to endNight
71%
468
39%
1548
32%
468
78%
468
79%
543
July1st to 15thNight
87%
456
30%
1476
28%
456
88%
456
61%
619
July16th to endNight
83%
582
32%
1610
26%
548
84%
548
56%
762
August1st to 15thNight
88%
717
37%
1790
24%
713
89%
713
73%
849
August16th to endNight
87%
764
42%
1910
28%
764
88%
764
73%
908
September1st to 15thNight
87%
720
40%
1870
31%
720
90%
720
70%
873
September16th to endNight
81%
656
47%
1816
38%
656
89%
656
81%
735
October1st to 15thNight
65%
660
41%
1815
31%
660
75%
660
61%
857
October16th to endNight
71%
704
42%
2137
36%
704
81%
704
59%
928
November1st to 15thNight
66%
700
35%
2275
31%
700
77%
700
53%
1009
November16th to endNight
63%
720
37%
2340
35%
720
71%
720
46%
1109
December1st to 15thNight
50%
720
31%
2340
24%
720
62%
720
37%
1215
December16th to endNight
46%
768
33%
2496
26%
768
58%
768
32%
1336

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
2213323346%64%
47879
Night
1213323346%66%
47026
TransparencyDay
20%2415%27%29%
47576
Night
18%2414%29%30%
46830
SeeingDay
6%15%32%32%10%2
5857
Night
39%20%29%28%8%
16043

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
14144245%6%6%57%
1611
16th to endDay
35%245%3435%6%54%
1884
February1st to 15thDay
242435%5%346%57%
1751
16th to endDay
2426%5%4445%6%51%
1579
March1st to 15thDay
241332447%9%57%
1800
16th to endDay
1323445%35%9%56%
2182
April1st to 15thDay
23145%32336%62%
2149
16th to endDay
311223348%68%
2160
May1st to 15thDay
121231325%6%69%
2316
16th to endDay
112223246%72%
2429
June1st to 15thDay
2212246%74%
2340
16th to endDay
11111112283%
2396
July1st to 15thDay
3212313447%63%
2380
16th to endDay
3313425%45%8%56%
2446
August1st to 15thDay
212313445%70%
2160
16th to endDay
21233445%6%66%
2292
September1st to 15thDay
212323345%67%
2088
16th to endDay
12221322377%
1816
October1st to 15thDay
1212323236%69%
1815
16th to endDay
11121225%6%73%
1733
November1st to 15thDay
1213323345%67%
1584
16th to endDay
332424446%62%
1620
December1st to 15thDay
23246%35%6%7%7%49%
1620
16th to endDay
35%35%5%35%346%51%
1728
January1st to 15thNight
2335%5%345%5%6%54%
2327
16th to endNight
3425%6%35%346%54%
2337
February1st to 15thNight
25%23435%35%7%55%
2101
16th to endNight
23147%48%5%6%6%49%
1895
March1st to 15thNight
14135%35%45%7%56%
2159
16th to endNight
1213436%45%8%57%
2039
April1st to 15thNight
132232435%7%62%
1799
16th to endNight
1112213347%70%
1800
May1st to 15thNight
1221335%7%71%
1633
16th to endNight
12212236%76%
1684
June1st to 15thNight
11111235%80%
1620
16th to endNight
1111287%
1548
July1st to 15thNight
111221222475%
1566
16th to endNight
2212322445%68%
1719
August1st to 15thNight
11111223480%
1800
16th to endNight
1211122480%
1910
September1st to 15thNight
11221223478%
1870
16th to endNight
122386%
1816
October1st to 15thNight
1113213335%72%
1815
16th to endNight
11223235%74%
2137
November1st to 15thNight
213224345%68%
2275
16th to endNight
22135%2435%8%62%
2340
December1st to 15thNight
3425%5%3447%8%51%
2340
16th to endNight
3435%5%45%46%6%50%
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
23%46%16%29%19%
1612
16th to endDay
29%35%17%23%19%
1884
February1st to 15thDay
26%3319%24%21%
1751
16th to endDay
31%26%18%29%11%
1579
March1st to 15thDay
21%36%19%30%18%
1800
16th to endDay
25%36%22%27%15%
2182
April1st to 15thDay
25%2420%32%15%
2149
16th to endDay
15%26%21%32%20%
2160
May1st to 15thDay
16%25%17%36%22%
2316
16th to endDay
15%1417%40%20%
2432
June1st to 15thDay
12%1311%25%45%
2340
16th to endDay
9%2417%65%
2396
July1st to 15thDay
18%349%19%44%
2241
16th to endDay
23%47%16%20%27%
2292
August1st to 15thDay
15%3410%19%46%
2146
16th to endDay
18%2411%30%33%
2292
September1st to 15thDay
18%348%28%36%
2088
16th to endDay
12%118%31%44%
1816
October1st to 15thDay
17%2214%30%32%
1815
16th to endDay
13%2311%32%35%
1733
November1st to 15thDay
19%2415%32%25%
1584
16th to endDay
22%4415%29%24%
1620
December1st to 15thDay
27%5%8%17%21%18%
1620
16th to endDay
31%36%21%20%16%
1728
January1st to 15thNight
26%35%15%26%22%
2327
16th to endNight
30%26%14%23%23%
2337
February1st to 15thNight
25%35%16%26%23%
2112
16th to endNight
30%35%16%27%17%
1895
March1st to 15thNight
25%35%17%25%22%
2159
16th to endNight
23%25%21%29%16%
2039
April1st to 15thNight
20%35%19%32%18%
1799
16th to endNight
12%25%17%41%20%
1800
May1st to 15thNight
10%15%18%39%24%
1634
16th to endNight
10%1417%40%25%
1685
June1st to 15thNight
9%1311%24%50%
1620
16th to endNight
6%25%18%67%
1548
July1st to 15thNight
13%247%21%51%
1476
16th to endNight
18%27%16%27%27%
1610
August1st to 15thNight
10%2213%24%47%
1790
16th to endNight
10%1210%32%40%
1910
September1st to 15thNight
10%2310%28%44%
1870
16th to endNight
5%19%36%46%
1816
October1st to 15thNight
14%1314%32%33%
1815
16th to endNight
13%238%33%38%
2137
November1st to 15thNight
17%2412%34%28%
2275
16th to endNight
20%3316%28%27%
2340
December1st to 15thNight
27%37%15%24%21%
2340
16th to endNight
30%27%18%22%18%
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
11%25%33%26%21
90
16th to endDay
10%24%33%24%5%1
252
February1st to 15thDay
427%27%30%7%1
266
16th to endDay
11%28%34%21%4
238
March1st to 15thDay
10%20%38%21%8%1
270
16th to endDay
6%29%34%22%6%
288
April1st to 15thDay
12%28%34%16%5%1
269
16th to endDay
8%33%34%19%4
270
May1st to 15thDay
8%20%36%27%43
288
16th to endDay
420%38%28%6%2
330
June1st to 15thDay
314%40%34%5%3
315
16th to endDay
4440%36%10%3
315
July1st to 15thDay
4223%45%19%4
305
16th to endDay
5%19%49%14%9%
327
August1st to 15thDay
3327%44%14%6%
315
16th to endDay
3125%45%18%5%
332
September1st to 15thDay
35%35%42%13%
315
16th to endDay
211%30%41%12%1
256
October1st to 15thDay
5%16%38%30%9%
255
16th to endDay
48%34%33%17%1
195
November1st to 15thDay
312%25%23%28%6%
90
16th to endDay
322%31%32%11%
90
December1st to 15thDay
6%16%31%34%8%2
90
16th to endDay
11%18%28%33%7%1
96
January1st to 15thNight
5%9%25%30%18%9%
720
16th to endNight
6%13%24%26%23%5%
768
February1st to 15thNight
5%10%26%31%19%5%
704
16th to endNight
416%29%25%18%4
632
March1st to 15thNight
414%26%28%19%6%
720
16th to endNight
316%26%27%21%5%
768
April1st to 15thNight
321%29%23%16%5%
719
16th to endNight
218%26%24%21%6%
720
May1st to 15thNight
12%29%33%18%4
554
16th to endNight
111%29%28%25%3
563
June1st to 15thNight
6%25%42%23%2
540
16th to endNight
124%44%26%2
468
July1st to 15thNight
25%35%46%9%
456
16th to endNight
2432%51%8%
582
August1st to 15thNight
15%27%50%14%
717
16th to endNight
26%22%51%16%
764
September1st to 15thNight
15%28%48%14%
720
16th to endNight
1213%27%41%13%
656
October1st to 15thNight
16%21%30%31%7%
660
16th to endNight
15%17%28%30%15%
704
November1st to 15thNight
26%19%31%29%10%
700
16th to endNight
38%20%30%26%11%
720
December1st to 15thNight
5%11%26%28%21%6%
720
16th to endNight
7%15%25%27%17%5%
768
Page generated at 2017-09-16 14:07:02. Version ac04

Copyright 2017 A. Danko


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