Douglas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Douglas clear sky chart from 2005-11-05 to 2017-10-06.

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
73%
15505
35%
47090
29%
15467
79%
15467
50%
22967

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%
716
34%
2327
34%
716
79%
716
52%
1060
January16th to endNight
64%
768
35%
2496
32%
768
74%
768
44%
1242
February1st to 15thNight
71%
698
35%
2253
33%
696
78%
696
51%
1033
February16th to endNight
63%
632
42%
1760
33%
632
72%
632
55%
877
March1st to 15thNight
65%
720
41%
1980
31%
720
74%
720
59%
959
March16th to endNight
69%
768
40%
2112
26%
768
79%
768
64%
981
April1st to 15thNight
61%
637
38%
1896
25%
637
74%
637
57%
871
April16th to endNight
60%
540
44%
1800
33%
540
79%
540
66%
684
May1st to 15thNight
66%
539
37%
1727
30%
539
77%
539
67%
685
May16th to endNight
75%
561
43%
1684
36%
561
81%
561
71%
681
June1st to 15thNight
80%
540
34%
1620
29%
540
83%
540
64%
697
June16th to endNight
80%
540
27%
1620
24%
540
81%
540
48%
801
July1st to 15thNight
81%
510
13%
1530
11%
510
81%
510
29%
952
July16th to endNight
70%
564
11%
1593
11%
531
70%
531
21%
1107
August1st to 15thNight
79%
539
18%
1628
18%
536
79%
536
29%
1015
August16th to endNight
78%
573
21%
1910
23%
573
78%
573
28%
1143
September1st to 15thNight
75%
648
23%
1908
21%
648
77%
648
34%
1164
September16th to endNight
83%
716
41%
1980
31%
716
87%
716
60%
969
October1st to 15thNight
80%
684
36%
2031
29%
684
85%
684
58%
956
October16th to endNight
85%
704
42%
2112
36%
704
88%
704
68%
896
November1st to 15thNight
81%
700
43%
2100
37%
700
86%
700
70%
868
November16th to endNight
73%
720
42%
2187
35%
720
79%
720
53%
1045
December1st to 15thNight
73%
720
39%
2340
38%
720
78%
720
53%
1066
December16th to endNight
65%
768
36%
2496
34%
768
71%
768
46%
1215

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
3212323446%63%
48095
Night
3212323346%64%
47295
TransparencyDay
20%35%14%27%28%
47790
Night
19%36%14%27%27%
47101
SeeingDay
6%7%17%27%26%14%
5380
Night
4213%41%33%4
15518

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
332313446%65%
1611
16th to endDay
7%413313445%59%
1728
February1st to 15thDay
3212212336%69%
1599
16th to endDay
431322233467%
1714
March1st to 15thDay
3212212236%70%
1980
16th to endDay
2211112325%73%
2112
April1st to 15thDay
3211111345%73%
2051
16th to endDay
1111122382%
2160
May1st to 15thDay
1111112225%78%
2220
16th to endDay
11111212480%
2429
June1st to 15thDay
111213235%74%
2340
16th to endDay
221232445%7%62%
2340
July1st to 15thDay
5%425%6%47%7%8%11%36%
2340
16th to endDay
8%5%27%8%5%7%7%9%10%26%
2467
August1st to 15thDay
5%425%6%48%7%7%10%36%
2322
16th to endDay
44145%47%7%8%9%41%
2292
September1st to 15thDay
6%3245%35%6%6%9%46%
2049
16th to endDay
411223233470%
1980
October1st to 15thDay
122322336%71%
1724
16th to endDay
11111323477%
1760
November1st to 15thDay
111112336%76%
1759
16th to endDay
431221333469%
1770
December1st to 15thDay
5%32213336%66%
1620
16th to endDay
5%413213246%62%
1728
January1st to 15thNight
4213313345%66%
2327
16th to endNight
7%313323345%60%
2496
February1st to 15thNight
2312323335%68%
2251
16th to endNight
331232323470%
1760
March1st to 15thNight
332222236%69%
1980
16th to endNight
221221123475%
2112
April1st to 15thNight
221231233472%
1896
16th to endNight
1111112481%
1800
May1st to 15thNight
11112236%77%
1727
16th to endNight
1121213382%
1684
June1st to 15thNight
211112335%75%
1620
16th to endNight
22133245%49%60%
1620
July1st to 15thNight
33135%48%9%9%15%33%
1620
16th to endNight
4427%8%5%9%7%9%14%26%
1701
August1st to 15thNight
33246%46%8%9%13%37%
1637
16th to endNight
5%4245%37%6%8%12%41%
1910
September1st to 15thNight
6%4144246%8%10%44%
1908
16th to endNight
322212335%72%
1980
October1st to 15thNight
21222334471%
2031
16th to endNight
11111223477%
2112
November1st to 15thNight
211212235%78%
2100
16th to endNight
5%312211235%69%
2187
December1st to 15thNight
5%212212346%67%
2340
16th to endNight
6%323322335%63%
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
19%25%16%35%19%
1612
16th to endDay
24%2217%32%19%
1728
February1st to 15thDay
17%1215%32%30%
1599
16th to endDay
21%2114%33%27%
1714
March1st to 15thDay
15%1110%37%32%
1980
16th to endDay
15%1110%36%35%
2112
April1st to 15thDay
13%118%35%39%
2051
16th to endDay
9%116%26%55%
2160
May1st to 15thDay
10%115%27%53%
2220
16th to endDay
9%117%28%51%
2432
June1st to 15thDay
13%115%22%56%
2340
16th to endDay
20%349%23%37%
2340
July1st to 15thDay
36%9%16%16%11%9%
2201
16th to endDay
46%11%19%15%6%
2312
August1st to 15thDay
38%9%14%20%13%3
2307
16th to endDay
31%8%16%19%14%9%
2292
September1st to 15thDay
31%6%11%18%22%9%
2049
16th to endDay
17%2314%37%23%
1980
October1st to 15thDay
15%2418%27%30%
1724
16th to endDay
11%2216%30%36%
1760
November1st to 15thDay
10%1216%37%31%
1759
16th to endDay
19%1216%31%29%
1770
December1st to 15thDay
19%2223%34%16%
1620
16th to endDay
22%27%21%34%12%
1728
January1st to 15thNight
19%25%15%33%24%
2327
16th to endNight
25%2318%32%18%
2496
February1st to 15thNight
19%2314%29%31%
2262
16th to endNight
19%1114%32%30%
1760
March1st to 15thNight
17%1211%31%35%
1980
16th to endNight
14%139%36%34%
2112
April1st to 15thNight
16%1110%36%33%
1896
16th to endNight
10%118%28%50%
1800
May1st to 15thNight
9%228%28%49%
1728
16th to endNight
9%1210%29%46%
1685
June1st to 15thNight
12%226%24%52%
1620
16th to endNight
21%46%11%20%36%
1620
July1st to 15thNight
32%11%25%15%8%6%
1530
16th to endNight
41%12%27%13%41
1593
August1st to 15thNight
30%12%21%20%13%1
1628
16th to endNight
33%9%18%17%11%9%
1910
September1st to 15thNight
31%8%15%17%16%10%
1908
16th to endNight
16%2418%36%21%
1980
October1st to 15thNight
16%37%14%26%31%
2031
16th to endNight
11%2315%26%41%
2112
November1st to 15thNight
10%1318%34%31%
2100
16th to endNight
19%1213%30%31%
2187
December1st to 15thNight
19%2422%32%19%
2340
16th to endNight
23%26%20%33%14%
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
7%10%18%38%23%1
90
16th to endDay
9%5%12%41%19%11%
96
February1st to 15thDay
7%7%11%29%34%9%
114
16th to endDay
10%18%28%20%18%4
238
March1st to 15thDay
5%16%24%22%18%11%
270
16th to endDay
419%26%25%15%8%
288
April1st to 15thDay
7%17%25%27%19%3
269
16th to endDay
420%28%23%17%5%
270
May1st to 15thDay
5%16%28%30%12%6%
288
16th to endDay
37%30%37%16%4
330
June1st to 15thDay
4221%34%23%13%
315
16th to endDay
2110%31%35%18%
315
July1st to 15thDay
11%8%34%29%15%
305
16th to endDay
7%7%23%30%29%
327
August1st to 15thDay
6%1222%37%29%
315
16th to endDay
6%25%18%37%30%
332
September1st to 15thDay
8%210%22%40%15%
315
16th to endDay
4416%31%30%13%
315
October1st to 15thDay
115%25%28%28%
126
16th to endDay
410%15%40%29%
96
November1st to 15thDay
38%18%21%37%10%
90
16th to endDay
7%8%25%25%28%3
90
December1st to 15thDay
4314%32%30%15%
90
16th to endDay
12%12%19%33%20%1
96
January1st to 15thNight
5%115%50%25%1
720
16th to endNight
7%218%46%23%1
768
February1st to 15thNight
4416%49%24%1
704
16th to endNight
4325%50%15%
632
March1st to 15thNight
5%321%46%20%2
720
16th to endNight
2220%50%23%
768
April1st to 15thNight
35%25%48%16%
637
16th to endNight
25%29%44%17%
540
May1st to 15thNight
2424%47%19%1
540
16th to endNight
1216%52%25%
563
June1st to 15thNight
2111%49%33%
540
16th to endNight
217%42%44%1
540
July1st to 15thNight
4425%57%7%
510
16th to endNight
6%1117%60%12%
564
August1st to 15thNight
41112%60%20%
539
16th to endNight
6%1118%57%15%
573
September1st to 15thNight
8%423%54%8%
648
16th to endNight
5%6%37%47%3
716
October1st to 15thNight
2112%41%36%5%
684
16th to endNight
216%41%41%5%
704
November1st to 15thNight
2112%42%36%4
700
16th to endNight
7%113%45%28%3
720
December1st to 15thNight
6%213%46%28%2
720
16th to endNight
7%316%48%21%2
768
Page generated at 2017-10-07 11:07:44. Version ac04

Copyright 2017 A. Danko


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