Dunceath Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dunceath Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
54%
15319
23%
46919
18%
15273
60%
15273
30%
28440

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
35%
900
24%
2327
9%
895
44%
895
29%
1533
January16th to endNight
33%
948
24%
2484
10%
948
41%
948
29%
1626
February1st to 15thNight
36%
704
26%
2110
12%
701
47%
701
28%
1313
February16th to endNight
30%
631
23%
1893
11%
631
39%
631
25%
1204
March1st to 15thNight
37%
546
24%
1986
16%
546
48%
546
24%
1204
March16th to endNight
46%
576
24%
2082
19%
576
55%
576
31%
1129
April1st to 15thNight
44%
539
24%
1797
17%
539
56%
539
29%
1043
April16th to endNight
50%
540
26%
1800
21%
540
60%
540
31%
1011
May1st to 15thNight
57%
539
21%
1799
19%
539
65%
539
33%
1009
May16th to endNight
69%
563
22%
1869
24%
561
72%
561
36%
1021
June1st to 15thNight
79%
540
16%
1635
16%
540
80%
540
34%
977
June16th to endNight
73%
540
15%
1620
16%
540
75%
540
28%
1036
July1st to 15thNight
80%
510
15%
1530
18%
510
80%
510
31%
951
July16th to endNight
74%
564
12%
1634
16%
531
74%
531
25%
1087
August1st to 15thNight
80%
539
13%
1788
16%
536
80%
536
31%
1064
August16th to endNight
72%
573
14%
1910
18%
573
72%
573
22%
1270
September1st to 15thNight
74%
540
19%
1800
22%
540
75%
540
28%
1101
September16th to endNight
72%
600
28%
1797
25%
600
73%
600
33%
1091
October1st to 15thNight
68%
660
32%
1980
26%
660
71%
660
45%
1024
October16th to endNight
58%
704
34%
2112
28%
704
63%
704
40%
1141
November1st to 15thNight
54%
700
33%
2100
25%
700
61%
700
35%
1195
November16th to endNight
47%
720
33%
2178
23%
720
57%
720
35%
1237
December1st to 15thNight
40%
720
26%
2229
18%
720
48%
720
25%
1409
December16th to endNight
34%
923
18%
2459
10%
923
39%
923
22%
1764

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
11%6%25%6%45%5%6%7%37%
47849
Night
11%42442445%8%46%
47125
TransparencyDay
43%7%10%16%16%5%
47555
Night
34%6%12%19%18%8%
46924
SeeingDay
11%414%22%28%18%
5412
Night
12%5%20%30%24%6%
15320

By Month

Percentage Cloud Cover SE (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
17%6%35%423345%43%
1611
16th to endDay
21%6%245%2423443%
1737
February1st to 15thDay
15%6%25%434445%43%
1750
16th to endDay
17%7%35%5%23345%40%
1583
March1st to 15thDay
19%6%25%5%34346%38%
1980
16th to endDay
9%6%35%5%45%5%5%6%41%
2140
April1st to 15thDay
11%6%35%5%3445%7%40%
2151
16th to endDay
10%6%25%5%45%6%6%8%37%
2160
May1st to 15thDay
11%6%35%5%45%5%6%8%35%
2151
16th to endDay
8%6%35%6%46%6%7%8%37%
2244
June1st to 15thDay
6%5%27%8%5%8%9%9%9%27%
2322
16th to endDay
5%5%37%9%5%10%8%8%9%26%
2340
July1st to 15thDay
8%5%38%8%5%7%7%8%9%26%
2340
16th to endDay
9%6%47%9%6%8%6%7%9%24%
2421
August1st to 15thDay
7%427%8%5%8%7%7%10%28%
2160
16th to endDay
15%5%26%7%5%7%6%7%8%27%
2292
September1st to 15thDay
11%425%5%47%6%7%8%36%
2160
16th to endDay
9%6%25%5%35%45%7%42%
1894
October1st to 15thDay
8%3245%2445%6%53%
1650
16th to endDay
9%313312437%57%
1760
November1st to 15thDay
8%42442336%8%49%
1758
16th to endDay
12%424422346%51%
1768
December1st to 15thDay
16%8%35%5%34445%38%
1716
16th to endDay
21%7%26%6%34345%34%
1761
January1st to 15thNight
16%6%24423445%45%
2327
16th to endNight
18%6%24323346%44%
2484
February1st to 15thNight
14%5%25%423446%46%
2103
16th to endNight
19%6%24422336%44%
1893
March1st to 15thNight
16%6%25%423347%43%
1986
16th to endNight
10%32432335%7%52%
2082
April1st to 15thNight
11%425%32445%8%47%
1797
16th to endNight
8%424334449%51%
1800
May1st to 15thNight
9%423315%46%10%47%
1799
16th to endNight
6%323425%46%9%51%
1869
June1st to 15thNight
3225%435%5%8%12%45%
1635
16th to endNight
44346%37%7%10%11%37%
1620
July1st to 15thNight
33145%36%6%7%12%43%
1620
16th to endNight
6%326%7%37%6%7%12%36%
1745
August1st to 15thNight
4325%435%6%7%13%43%
1800
16th to endNight
8%425%5%45%7%8%12%35%
1910
September1st to 15thNight
8%5%244345%6%10%44%
1800
16th to endNight
7%4244345%6%8%47%
1797
October1st to 15thNight
5%324223346%61%
1980
16th to endNight
9%314323235%59%
2112
November1st to 15thNight
9%424323345%55%
2100
16th to endNight
12%423422235%56%
2178
December1st to 15thNight
15%6%26%42345%6%43%
2229
16th to endNight
21%8%36%433335%35%
2459

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
42%26%15%22%10%
1612
16th to endDay
47%2413%22%9%
1737
February1st to 15thDay
41%47%14%22%9%
1752
16th to endDay
44%45%17%19%7%
1583
March1st to 15thDay
46%47%18%17%5%
1980
16th to endDay
41%5%7%17%22%5%
2142
April1st to 15thDay
41%5%8%17%18%8%
2151
16th to endDay
40%6%11%19%17%4
2160
May1st to 15thDay
43%6%12%16%14%6%
2151
16th to endDay
40%8%12%21%15%1
2248
June1st to 15thDay
46%10%12%17%11%
2322
16th to endDay
48%14%13%17%5%
2340
July1st to 15thDay
47%12%17%14%6%1
2201
16th to endDay
50%11%17%15%4
2269
August1st to 15thDay
46%12%17%15%7%
2148
16th to endDay
49%12%16%12%7%1
2292
September1st to 15thDay
41%10%16%14%11%4
2160
16th to endDay
40%7%9%17%19%6%
1894
October1st to 15thDay
29%5%8%17%23%14%
1650
16th to endDay
27%4412%32%17%
1760
November1st to 15thDay
32%38%19%27%8%
1758
16th to endDay
33%36%13%26%15%
1768
December1st to 15thDay
46%48%17%15%6%
1716
16th to endDay
51%5%6%16%15%4
1761
January1st to 15thNight
39%46%14%22%11%
2327
16th to endNight
41%37%15%21%11%
2484
February1st to 15thNight
38%36%17%20%11%
2112
16th to endNight
42%35%17%19%11%
1893
March1st to 15thNight
40%49%17%19%7%
1986
16th to endNight
31%412%21%22%8%
2082
April1st to 15thNight
34%5%9%21%18%10%
1797
16th to endNight
30%7%11%20%20%8%
1800
May1st to 15thNight
29%7%14%23%17%7%
1800
16th to endNight
28%6%17%28%18%1
1871
June1st to 15thNight
28%10%18%27%13%1
1635
16th to endNight
33%11%21%21%10%
1620
July1st to 15thNight
28%13%26%22%6%2
1530
16th to endNight
35%14%25%19%4
1634
August1st to 15thNight
27%13%30%19%8%
1788
16th to endNight
38%12%22%13%8%2
1910
September1st to 15thNight
33%9%18%20%12%5%
1800
16th to endNight
32%7%12%19%19%8%
1797
October1st to 15thNight
23%5%9%19%26%16%
1980
16th to endNight
27%35%14%26%22%
2112
November1st to 15thNight
32%37%16%28%11%
2100
16th to endNight
32%35%16%23%19%
2178
December1st to 15thNight
40%47%21%18%5%
2229
16th to endNight
51%36%16%14%7%
2459

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
25%15%26%24%6%1
90
16th to endDay
18%23%39%13%4
96
February1st to 15thDay
12%16%35%27%7%
90
16th to endDay
18%16%34%25%4
81
March1st to 15thDay
32%14%32%17%3
90
16th to endDay
16%12%18%34%16%1
126
April1st to 15thDay
16%12%25%28%16%1
270
16th to endDay
12%6%25%33%19%2
270
May1st to 15thDay
11%6%24%30%21%5%
288
16th to endDay
10%216%28%29%13%
331
June1st to 15thDay
8%9%28%36%16%
477
16th to endDay
9%17%22%34%24%
495
July1st to 15thDay
5%15%18%41%27%
475
16th to endDay
8%15%12%37%34%
470
August1st to 15thDay
8%310%36%39%
313
16th to endDay
15%313%29%36%
332
September1st to 15thDay
10%7%18%36%26%
315
16th to endDay
7%17%23%37%22%
251
October1st to 15thDay
318%31%30%16%
90
16th to endDay
14%7%14%28%21%13%
96
November1st to 15thDay
17%24%40%12%5%
90
16th to endDay
14%11%37%18%14%3
90
December1st to 15thDay
25%6%34%21%8%3
90
16th to endDay
32%12%26%22%6%
96
January1st to 15thNight
19%9%32%29%8%
900
16th to endNight
22%9%31%28%8%
948
February1st to 15thNight
17%10%32%31%7%
704
16th to endNight
21%13%31%29%4
631
March1st to 15thNight
18%8%30%36%6%
546
16th to endNight
12%6%30%34%15%
576
April1st to 15thNight
13%7%30%32%14%
539
16th to endNight
11%429%36%16%1
540
May1st to 15thNight
10%225%40%20%
540
16th to endNight
7%14%41%31%3
563
June1st to 15thNight
45%36%47%6%
540
16th to endNight
416%27%42%18%
540
July1st to 15thNight
2318%50%24%
510
16th to endNight
4316%51%23%
564
August1st to 15thNight
4315%50%25%
539
16th to endNight
9%319%45%22%
573
September1st to 15thNight
10%1425%42%15%
540
16th to endNight
9%7%30%43%9%
600
October1st to 15thNight
6%117%32%38%4
660
16th to endNight
11%420%32%27%3
704
November1st to 15thNight
10%6%23%35%20%4
700
16th to endNight
14%7%26%33%16%1
720
December1st to 15thNight
18%9%26%31%13%
720
16th to endNight
24%9%27%29%9%
923
Page generated at 2017-09-20 03:49:53. Version ac04

Copyright 2017 A. Danko


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