Bowen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bowen Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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%
15826
31%
47421
28%
15788
75%
15788
47%
24192

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
64%
716
25%
2372
25%
716
68%
716
36%
1282
January16th to endNight
63%
768
27%
2496
28%
768
66%
768
33%
1413
February1st to 15thNight
66%
698
29%
2189
30%
696
70%
696
37%
1214
February16th to endNight
58%
632
25%
1895
25%
632
62%
632
33%
1127
March1st to 15thNight
64%
720
23%
2055
22%
720
68%
720
41%
1168
March16th to endNight
63%
768
23%
2052
18%
768
66%
768
39%
1224
April1st to 15thNight
61%
719
27%
1799
17%
719
64%
719
44%
1062
April16th to endNight
61%
720
30%
1800
14%
720
66%
720
53%
969
May1st to 15thNight
72%
719
23%
1799
14%
719
73%
719
52%
998
May16th to endNight
70%
433
29%
1557
25%
433
75%
433
48%
681
June1st to 15thNight
77%
360
30%
1440
35%
360
80%
360
47%
589
June16th to endNight
90%
360
37%
1440
47%
360
91%
360
68%
470
July1st to 15thNight
91%
393
32%
1413
35%
393
91%
393
67%
512
July16th to endNight
85%
564
35%
1593
31%
531
86%
531
60%
707
August1st to 15thNight
86%
660
34%
1734
24%
657
86%
657
69%
805
August16th to endNight
89%
764
40%
1910
26%
764
89%
764
76%
895
September1st to 15thNight
86%
720
41%
1800
32%
720
87%
720
66%
901
September16th to endNight
86%
716
43%
1921
40%
716
88%
716
74%
848
October1st to 15thNight
76%
720
31%
2160
34%
720
79%
720
52%
1051
October16th to endNight
75%
768
38%
2304
40%
768
79%
768
50%
1144
November1st to 15thNight
75%
700
34%
2198
35%
700
80%
700
51%
1040
November16th to endNight
72%
720
31%
2340
31%
720
77%
720
43%
1172
December1st to 15thNight
64%
720
29%
2466
29%
720
69%
720
32%
1387
December16th to endNight
55%
768
26%
2688
25%
768
63%
768
29%
1533

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
6%312212346%63%
48321
Night
7%413313347%61%
47613
TransparencyDay
21%38%21%26%19%
48010
Night
23%39%21%24%18%
47426
SeeingDay
7%6%21%38%22%4
6233
Night
7%210%31%37%10%
15838

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
11%313424346%54%
1564
16th to endDay
13%413323336%53%
1728
February1st to 15thDay
15%324212345%54%
1669
16th to endDay
18%413323346%47%
1579
March1st to 15thDay
9%41342435%10%50%
1902
16th to endDay
11%413324348%51%
2172
April1st to 15thDay
11%423313337%55%
2149
16th to endDay
8%32212345%64%
2160
May1st to 15thDay
4312212247%67%
2151
16th to endDay
4313212237%67%
2551
June1st to 15thDay
2312212347%66%
2520
16th to endDay
1111227%77%
2520
July1st to 15thDay
221212348%70%
2459
16th to endDay
111221245%7%68%
2468
August1st to 15thDay
1312112347%69%
2217
16th to endDay
121221336%74%
2292
September1st to 15thDay
221212338%72%
2160
16th to endDay
2211111246%74%
2035
October1st to 15thDay
6%21221223470%
1800
16th to endDay
3212312335%68%
1918
November1st to 15thDay
8%21231224466%
1660
16th to endDay
8%213313246%62%
1620
December1st to 15thDay
13%433323446%50%
1491
16th to endDay
17%413323235%52%
1536
January1st to 15thNight
11%413323335%56%
2372
16th to endNight
13%42332334454%
2496
February1st to 15thNight
11%413323345%55%
2182
16th to endNight
16%423322236%52%
1895
March1st to 15thNight
9%5%2231345%7%55%
2055
16th to endNight
9%41431335%7%53%
2052
April1st to 15thNight
9%414412336%59%
1799
16th to endNight
6%411212326%66%
1800
May1st to 15thNight
3423423348%59%
1799
16th to endNight
46%22212348%60%
1555
June1st to 15thNight
3323314448%60%
1440
16th to endNight
111111347%73%
1440
July1st to 15thNight
21221345%8%66%
1497
16th to endNight
11124235%5%11%58%
1701
August1st to 15thNight
1322225%6%11%60%
1743
16th to endNight
21221245%9%67%
1910
September1st to 15thNight
2212212337%69%
1800
16th to endNight
21212236%76%
1921
October1st to 15thNight
5%41221133468%
2160
16th to endNight
5%31331333465%
2304
November1st to 15thNight
5%322212236%67%
2198
16th to endNight
4413214446%62%
2340
December1st to 15thNight
11%41432335%6%53%
2466
16th to endNight
15%413223346%52%
2688

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
31%47%21%21%12%
1564
16th to endDay
34%311%14%18%17%
1728
February1st to 15thDay
33%37%21%22%12%
1669
16th to endDay
38%5%11%23%17%4
1579
March1st to 15thDay
30%5%13%21%18%10%
1902
16th to endDay
32%414%23%18%6%
2172
April1st to 15thDay
31%411%26%21%5%
2149
16th to endDay
21%5%12%24%26%9%
2160
May1st to 15thDay
18%211%25%29%11%
2151
16th to endDay
17%313%29%29%7%
2555
June1st to 15thDay
15%49%24%28%17%
2520
16th to endDay
7%15%17%33%34%
2520
July1st to 15thDay
10%2417%25%39%
2315
16th to endDay
12%36%17%27%31%
2313
August1st to 15thDay
12%15%20%29%31%
2201
16th to endDay
10%1417%36%28%
2292
September1st to 15thDay
11%15%21%28%32%
2160
16th to endDay
10%16%20%36%23%
2035
October1st to 15thDay
19%36%20%25%24%
1800
16th to endDay
18%47%18%26%24%
1918
November1st to 15thDay
23%38%19%30%14%
1660
16th to endDay
25%37%19%27%15%
1620
December1st to 15thDay
34%5%9%17%21%11%
1491
16th to endDay
35%49%21%19%9%
1536
January1st to 15thNight
30%38%19%23%13%
2372
16th to endNight
33%310%11%20%19%
2496
February1st to 15thNight
30%38%21%24%10%
2193
16th to endNight
35%38%24%21%6%
1895
March1st to 15thNight
28%414%24%18%10%
2055
16th to endNight
29%5%16%19%21%8%
2052
April1st to 15thNight
28%312%27%21%7%
1799
16th to endNight
20%312%28%25%10%
1800
May1st to 15thNight
21%413%22%25%13%
1800
16th to endNight
19%215%26%26%9%
1557
June1st to 15thNight
17%310%25%26%16%
1440
16th to endNight
9%7%16%30%35%
1440
July1st to 15thNight
10%1322%24%37%
1413
16th to endNight
15%26%21%26%28%
1593
August1st to 15thNight
13%425%29%26%
1734
16th to endNight
10%421%31%31%
1910
September1st to 15thNight
14%2319%23%37%
1800
16th to endNight
9%17%19%34%27%
1921
October1st to 15thNight
19%35%21%23%25%
2160
16th to endNight
21%28%17%27%22%
2304
November1st to 15thNight
20%29%22%27%18%
2198
16th to endNight
22%5%10%19%24%17%
2340
December1st to 15thNight
32%5%7%17%21%14%
2466
16th to endNight
34%410%20%19%10%
2688

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
20%7%24%30%16%1
192
16th to endDay
14%10%25%28%19%1
256
February1st to 15thDay
15%7%27%26%17%3
253
16th to endDay
19%11%28%26%10%2
238
March1st to 15thDay
8%13%33%34%10%
270
16th to endDay
10%15%26%36%10%1
288
April1st to 15thDay
15%13%31%28%8%2
269
16th to endDay
7%16%35%28%10%1
270
May1st to 15thDay
6%7%32%42%9%2
288
16th to endDay
5%10%25%38%16%3
330
June1st to 15thDay
36%20%44%21%3
315
16th to endDay
16%40%32%8%
315
July1st to 15thDay
17%45%35%8%
305
16th to endDay
15%38%42%11%
327
August1st to 15thDay
211%49%31%4
315
16th to endDay
1444%38%9%
332
September1st to 15thDay
3210%42%32%7%
315
16th to endDay
1415%43%31%3
315
October1st to 15thDay
46%29%40%17%1
315
16th to endDay
46%22%40%23%2
336
November1st to 15thDay
7%6%11%32%34%7%
166
16th to endDay
10%11%25%36%14%2
90
December1st to 15thDay
17%7%24%42%8%
69
16th to endDay
18%7%21%35%15%
64
January1st to 15thNight
12%312%36%28%6%
720
16th to endNight
14%212%38%24%7%
768
February1st to 15thNight
13%310%36%29%6%
704
16th to endNight
16%413%37%23%4
632
March1st to 15thNight
10%216%38%24%7%
720
16th to endNight
10%314%35%30%4
768
April1st to 15thNight
9%5%15%38%27%4
719
16th to endNight
7%320%26%32%9%
720
May1st to 15thNight
4210%36%36%9%
720
16th to endNight
5%213%31%36%9%
434
June1st to 15thNight
47%35%43%8%
360
16th to endNight
1227%55%13%
360
July1st to 15thNight
113%60%24%
393
16th to endNight
118%58%30%
564
August1st to 15thNight
1122%57%16%
660
16th to endNight
18%59%19%
764
September1st to 15thNight
2222%55%18%
720
16th to endNight
5%28%48%15%
716
October1st to 15thNight
6%18%32%40%10%
720
16th to endNight
6%18%34%37%12%
768
November1st to 15thNight
6%111%40%34%6%
700
16th to endNight
5%310%37%33%8%
720
December1st to 15thNight
12%311%37%29%5%
720
16th to endNight
16%417%37%19%4
768
Page generated at 2017-11-01 14:23:40. Version ac04

Copyright 2017 A. Danko


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