Douglas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Douglas clear sky chart from 2005-11-06 to 2024-01-16.

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
68%
23760
34%
74270
28%
23715
76%
23715
48%
36365

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 10thNight
66%
757
34%
2457
32%
756
74%
756
49%
1165
January11th to 20thNight
65%
744
38%
2418
33%
744
77%
744
52%
1089
January21st to endNight
57%
792
36%
2574
29%
792
71%
792
43%
1289
February1st to 10thNight
65%
720
36%
2340
32%
720
76%
720
50%
1068
February11th to 20thNight
57%
700
33%
2089
25%
700
68%
700
47%
1055
February21st to endNight
54%
592
42%
1628
28%
592
68%
592
56%
807
March1st to 10thNight
55%
720
39%
1980
24%
720
69%
720
52%
1010
March11th to 20thNight
60%
720
38%
1980
25%
720
70%
720
58%
977
March21st to endNight
61%
792
40%
2178
24%
792
73%
792
59%
1045
April1st to 10thNight
63%
687
40%
1947
25%
687
76%
687
63%
887
April11th to 20thNight
57%
533
42%
1777
30%
533
75%
533
59%
725
April21st to endNight
60%
540
45%
1800
34%
540
78%
540
65%
692
May1st to 10thNight
63%
540
38%
1782
30%
540
76%
540
61%
723
May11th to 20thNight
73%
531
41%
1594
35%
531
80%
531
70%
650
May21st to endNight
75%
582
45%
1746
38%
582
82%
582
75%
686
June1st to 10thNight
78%
540
36%
1620
31%
540
81%
540
60%
721
June11th to 20thNight
78%
540
36%
1620
30%
540
81%
540
64%
694
June21st to endNight
75%
540
25%
1620
22%
540
76%
540
42%
857
July1st to 10thNight
78%
525
17%
1575
15%
525
78%
525
31%
944
July11th to 20thNight
68%
522
10%
1566
10%
522
68%
522
21%
1087
July21st to endNight
67%
591
9%
1674
9%
558
67%
558
18%
1201
August1st to 10thNight
76%
537
14%
1602
14%
534
76%
534
27%
1029
August11th to 20thNight
74%
534
17%
1715
18%
534
74%
534
25%
1094
August21st to endNight
77%
594
19%
1980
20%
594
77%
594
26%
1211
September1st to 10thNight
72%
612
22%
1872
22%
612
73%
612
29%
1170
September11th to 20thNight
80%
720
36%
1980
30%
720
82%
720
51%
1052
September21st to endNight
76%
720
35%
1980
24%
720
81%
720
55%
1011
October1st to 10thNight
79%
720
36%
2128
29%
720
83%
720
55%
1029
October11th to 20thNight
75%
720
39%
2160
28%
720
83%
720
59%
982
October21st to endNight
79%
792
45%
2376
36%
792
85%
792
71%
971
November1st to 10thNight
77%
740
45%
2220
36%
740
84%
740
69%
921
November11th to 20thNight
75%
760
42%
2280
31%
760
83%
760
61%
1021
November21st to endNight
63%
760
40%
2322
31%
760
73%
760
49%
1145
December1st to 10thNight
69%
760
38%
2470
35%
760
75%
760
48%
1186
December11th to 20thNight
64%
758
35%
2910
32%
758
73%
758
40%
1404
December21st to endNight
60%
825
23%
4310
31%
817
68%
817
32%
1767

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
431342445%7%63%
75030
Night
431342445%7%63%
74818
TransparencyDay
21%35%14%27%29%
74757
Night
21%36%14%27%28%
74613
SeeingDay
6%6%17%28%27%16%
13623
Night
5%317%42%29%4
23782

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 10thDay
441342445%7%61%
1708
11th to 20thDay
5%31332445%6%65%
1669
21st to endDay
6%423323445%64%
1782
February1st to 10thDay
5%312313446%68%
1620
11th to 20thDay
6%424334336%63%
1754
21st to endDay
5%31332234470%
1628
March1st to 10thDay
4324323448%63%
1980
11th to 20thDay
4422322235%72%
1980
21st to endDay
3212223447%70%
2178
April1st to 10thDay
221222235%6%72%
2011
11th to 20thDay
321121222381%
2131
21st to endDay
1211112325%81%
2160
May1st to 10thDay
1212212225%79%
2174
11th to 20thDay
2112213225%78%
2301
21st to endDay
211112123483%
2530
June1st to 10thDay
2212313346%72%
2340
11th to 20thDay
1112323346%74%
2340
21st to endDay
33245%35%5%5%8%57%
2340
July1st to 10thDay
4425%7%48%7%8%10%41%
2340
11th to 20thDay
5%426%7%5%7%8%10%13%34%
2340
21st to endDay
9%6%37%8%5%7%8%9%10%28%
2545
August1st to 10thDay
5%425%6%5%8%8%8%12%38%
2328
11th to 20thDay
5%5%25%7%48%7%8%10%37%
2184
21st to endDay
5%4246%47%8%9%10%43%
2376
September1st to 10thDay
7%425%6%35%7%7%9%46%
2084
11th to 20thDay
43144335%6%8%59%
1980
21st to endDay
4212233346%69%
1980
October1st to 10thDay
121232345%7%70%
1830
11th to 20thDay
221232234475%
1800
21st to endDay
2111213335%77%
1980
November1st to 10thDay
1212212347%76%
1859
11th to 20thDay
2312213337%72%
1900
21st to endDay
5%424423346%64%
1853
December1st to 10thDay
7%312323447%63%
1710
11th to 20thDay
5%6%36%42335%7%56%
2169
21st to endDay
432332445%6%64%
3146
January1st to 10thNight
5%31432345%6%63%
2457
11th to 20thNight
6%213322346%69%
2418
21st to endNight
7%424323345%61%
2574
February1st to 10thNight
4312324345%69%
2340
11th to 20thNight
6%413423345%65%
2088
21st to endNight
431332433470%
1628
March1st to 10thNight
441332335%7%63%
1980
11th to 20thNight
3423322335%71%
1980
21st to endNight
321332335%6%70%
2178
April1st to 10thNight
2213313335%75%
1947
11th to 20thNight
2212212335%76%
1777
21st to endNight
221221123481%
1800
May1st to 10thNight
1212312335%77%
1782
11th to 20thNight
112213345%78%
1594
21st to endNight
111111223385%
1746
June1st to 10thNight
321232345%7%70%
1620
11th to 20thNight
2212213336%74%
1620
21st to endNight
3325%435%5%5%10%55%
1620
July1st to 10thNight
44245%48%8%9%12%40%
1620
11th to 20thNight
45%37%9%5%10%8%8%16%26%
1620
21st to endNight
5%6%38%9%6%9%8%10%13%23%
1773
August1st to 10thNight
35%36%7%5%7%9%10%12%35%
1611
11th to 20thNight
7%425%6%5%6%7%9%14%34%
1715
21st to endNight
45%25%6%48%7%8%12%38%
1980
September1st to 10thNight
8%5%25%5%36%6%9%10%40%
1872
11th to 20thNight
441332345%7%64%
1980
21st to endNight
3314323336%68%
1980
October1st to 10thNight
221332345%6%69%
2128
11th to 20thNight
2212222445%74%
2160
21st to endNight
211221223481%
2376
November1st to 10thNight
2111312345%77%
2220
11th to 20thNight
3213222346%73%
2280
21st to endNight
6%423322346%65%
2322
December1st to 10thNight
6%31332335%6%64%
2470
11th to 20thNight
442443435%7%59%
3041
21st to endNight
7%31342345%6%62%
4521

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 10thDay
22%35%17%35%18%
1709
11th to 20thDay
19%3417%35%23%
1669
21st to endDay
23%2316%32%24%
1782
February1st to 10thDay
19%2314%28%35%
1620
11th to 20thDay
25%2315%29%27%
1764
21st to endDay
21%2110%29%38%
1628
March1st to 10thDay
22%2212%31%31%
1980
11th to 20thDay
17%2210%32%37%
1980
21st to endDay
16%229%37%34%
2178
April1st to 10thDay
13%217%35%41%
2011
11th to 20thDay
11%116%28%53%
2134
21st to endDay
9%116%31%51%
2160
May1st to 10thDay
11%116%22%58%
2174
11th to 20thDay
11%138%27%49%
2304
21st to endDay
9%21427%58%
2530
June1st to 10thDay
15%218%25%49%
2340
11th to 20thDay
14%215%20%57%
2340
21st to endDay
26%4411%23%31%
2340
July1st to 10thDay
34%8%12%17%13%16%
2276
11th to 20thDay
38%9%19%20%11%3
2271
21st to endDay
45%11%19%15%9%1
2404
August1st to 10thDay
34%10%16%22%14%4
2313
11th to 20thDay
38%7%17%19%13%6%
2184
21st to endDay
32%8%14%21%17%9%
2376
September1st to 10thDay
33%5%10%17%21%14%
2084
11th to 20thDay
22%5%5%16%29%24%
1980
21st to endDay
17%2417%35%24%
1980
October1st to 10thDay
15%36%19%29%29%
1830
11th to 20thDay
15%2214%31%36%
1800
21st to endDay
12%2215%31%38%
1980
November1st to 10thDay
11%2215%40%29%
1859
11th to 20thDay
15%2319%31%31%
1900
21st to endDay
24%2218%30%24%
1853
December1st to 10thDay
23%3420%32%19%
1710
11th to 20thDay
29%1421%29%16%
2168
21st to endDay
21%2315%44%15%
3146
January1st to 10thNight
22%25%16%35%20%
2457
11th to 20thNight
19%1316%33%27%
2418
21st to endNight
26%2316%31%22%
2574
February1st to 10thNight
19%2313%26%36%
2340
11th to 20thNight
24%2314%29%28%
2089
21st to endNight
19%2210%27%41%
1628
March1st to 10thNight
21%2313%30%31%
1980
11th to 20thNight
19%139%30%39%
1980
21st to endNight
16%239%36%33%
2178
April1st to 10thNight
14%1110%38%36%
1947
11th to 20thNight
14%218%29%46%
1777
21st to endNight
11%118%29%49%
1800
May1st to 10thNight
13%227%23%54%
1782
11th to 20thNight
10%2311%28%47%
1595
21st to endNight
8%117%30%54%
1746
June1st to 10thNight
15%228%28%45%
1620
11th to 20thNight
13%227%22%54%
1620
21st to endNight
26%47%12%20%31%
1620
July1st to 10thNight
33%8%18%17%10%13%
1575
11th to 20thNight
44%10%23%16%5%1
1566
21st to endNight
47%12%24%12%5%1
1674
August1st to 10thNight
35%11%20%20%11%2
1602
11th to 20thNight
37%10%20%16%11%5%
1715
21st to endNight
36%8%17%17%11%10%
1980
September1st to 10thNight
35%9%15%12%17%12%
1872
11th to 20thNight
22%47%20%26%21%
1980
21st to endNight
19%36%18%33%21%
1980
October1st to 10thNight
19%38%14%27%30%
2128
11th to 20thNight
15%3314%26%38%
2160
21st to endNight
9%1314%31%41%
2376
November1st to 10thNight
10%2416%36%32%
2220
11th to 20thNight
15%2317%32%30%
2280
21st to endNight
22%2216%32%25%
2322
December1st to 10thNight
22%3420%29%21%
2470
11th to 20thNight
25%25%22%29%17%
3041
21st to endNight
24%2314%37%19%
4521

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 10thDay
10%7%19%38%21%4
270
11th to 20thDay
11%317%38%26%6%
257
21st to endDay
6%8%21%39%19%8%
264
February1st to 10thDay
7%5%17%35%27%8%
240
11th to 20thDay
13%13%28%32%14%1
366
21st to endDay
14%18%31%25%9%3
346
March1st to 10thDay
11%12%28%29%17%3
420
11th to 20thDay
11%14%23%25%20%7%
420
21st to endDay
6%19%28%27%14%6%
462
April1st to 10thDay
5%12%26%30%21%7%
420
11th to 20thDay
6%12%31%26%19%6%
412
21st to endDay
414%25%30%19%8%
420
May1st to 10thDay
413%26%28%16%13%
423
11th to 20thDay
46%22%34%25%8%
448
21st to endDay
45%26%37%21%7%
485
June1st to 10thDay
4223%28%29%13%
450
11th to 20thDay
2314%30%33%18%
450
21st to endDay
328%30%40%16%
450
July1st to 10thDay
7%2324%37%27%
446
11th to 20thDay
7%2215%40%34%
444
21st to endDay
8%2218%30%39%
487
August1st to 10thDay
6%2113%36%42%
447
11th to 20thDay
7%3319%32%35%
437
21st to endDay
5%25%15%36%39%
495
September1st to 10thDay
8%28%26%36%21%
450
11th to 20thDay
436%26%37%24%
450
21st to endDay
3412%30%31%19%
450
October1st to 10thDay
3412%27%28%26%
300
11th to 20thDay
4313%30%28%22%
270
21st to endDay
2414%26%37%17%
297
November1st to 10thDay
35%18%31%31%11%
270
11th to 20thDay
4217%30%37%10%
270
21st to endDay
9%6%24%31%27%3
270
December1st to 10thDay
9%415%38%28%6%
270
11th to 20thDay
8%423%39%22%4
270
21st to endDay
15%6%19%32%24%4
297
January1st to 10thNight
7%119%49%22%2
760
11th to 20thNight
6%320%48%21%2
744
21st to endNight
10%324%45%17%1
792
February1st to 10thNight
6%422%44%22%3
720
11th to 20thNight
9%5%24%47%14%1
704
21st to endNight
6%5%32%45%12%1
592
March1st to 10thNight
6%6%30%44%13%1
720
11th to 20thNight
6%327%40%22%2
720
21st to endNight
4327%48%18%1
792
April1st to 10thNight
2425%51%17%1
687
11th to 20thNight
35%32%45%14%1
533
21st to endNight
3430%47%14%2
540
May1st to 10thNight
3426%50%15%1
540
11th to 20thNight
2219%51%24%2
531
21st to endNight
1317%54%25%
584
June1st to 10thNight
4111%55%28%1
540
11th to 20thNight
2213%52%30%1
540
21st to endNight
4110%41%41%2
540
July1st to 10thNight
6%2432%51%6%
525
11th to 20thNight
7%2224%57%9%
522
21st to endNight
6%2320%58%11%
591
August1st to 10thNight
41216%59%18%
537
11th to 20thNight
8%1216%60%12%
534
21st to endNight
6%1223%57%11%
594
September1st to 10thNight
10%2329%51%6%
612
11th to 20thNight
6%1432%50%7%
720
21st to endNight
4111%39%40%5%
720
October1st to 10thNight
2112%47%34%5%
720
11th to 20thNight
4216%47%29%3
720
21st to endNight
2214%45%32%5%
792
November1st to 10thNight
2215%44%33%5%
740
11th to 20thNight
4216%48%28%2
760
21st to endNight
9%321%46%19%3
760
December1st to 10thNight
8%117%48%23%3
760
11th to 20thNight
6%321%50%19%2
760
21st to endNight
10%319%47%19%3
836
Page generated at 2024-01-13 17:28:32. Version ac07

Copyright 2024 Attilla Danko


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