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 2018-10-27.

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%
16753
23%
51297
18%
16707
60%
16707
30%
31090

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
34%
975
24%
2522
10%
970
44%
970
29%
1669
January16th to endNight
33%
1027
25%
2691
10%
1027
41%
1027
29%
1754
February1st to 15thNight
35%
764
25%
2290
11%
761
45%
761
27%
1452
February16th to endNight
30%
683
23%
2049
10%
683
40%
683
25%
1301
March1st to 15thNight
38%
592
25%
2152
17%
592
49%
592
24%
1284
March16th to endNight
45%
624
24%
2256
18%
624
54%
624
30%
1237
April1st to 15thNight
43%
584
24%
1947
17%
584
55%
584
29%
1136
April16th to endNight
51%
579
26%
1928
21%
579
62%
579
32%
1067
May1st to 15thNight
59%
584
23%
1949
21%
584
66%
584
35%
1068
May16th to endNight
70%
611
22%
2029
24%
609
74%
609
36%
1108
June1st to 15thNight
80%
585
16%
1771
17%
585
81%
585
34%
1054
June16th to endNight
74%
585
14%
1755
15%
585
75%
585
29%
1106
July1st to 15thNight
81%
555
15%
1665
18%
555
81%
555
31%
1034
July16th to endNight
74%
612
12%
1782
15%
579
75%
579
26%
1163
August1st to 15thNight
81%
575
12%
1906
16%
572
81%
572
32%
1121
August16th to endNight
73%
621
14%
2070
17%
621
73%
621
23%
1359
September1st to 15thNight
74%
585
18%
1950
21%
585
74%
585
27%
1221
September16th to endNight
71%
696
27%
2078
25%
696
72%
696
31%
1287
October1st to 15thNight
68%
780
31%
2340
25%
780
71%
780
44%
1223
October16th to endNight
55%
816
34%
2448
27%
816
61%
816
37%
1370
November1st to 15thNight
55%
760
32%
2280
25%
760
62%
760
36%
1294
November16th to endNight
49%
780
34%
2360
24%
780
59%
780
36%
1323
December1st to 15thNight
40%
780
26%
2415
18%
780
48%
780
26%
1526
December16th to endNight
33%
1000
18%
2664
10%
1000
38%
1000
21%
1933

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%5%25%6%45%5%6%7%38%
52206
Night
10%42442445%8%46%
51503
TransparencyDay
42%7%10%16%16%5%
51912
Night
34%6%12%19%17%8%
51302
SeeingDay
12%415%22%27%17%
6845
Night
12%5%20%30%24%6%
16754

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
16%6%35%423345%43%
1746
16th to endDay
21%6%2442423343%
1882
February1st to 15thDay
16%7%25%434445%41%
1900
16th to endDay
17%7%35%5%2435%6%39%
1713
March1st to 15thDay
18%6%25%5%33347%40%
2145
16th to endDay
10%7%35%5%44446%42%
2318
April1st to 15thDay
11%6%25%5%3445%7%41%
2331
16th to endDay
10%6%245%35%6%6%8%39%
2307
May1st to 15thDay
10%6%35%5%35%5%6%8%37%
2331
16th to endDay
7%5%35%6%46%6%7%8%37%
2436
June1st to 15thDay
6%427%7%5%7%9%9%9%28%
2515
16th to endDay
5%437%9%5%9%8%8%9%27%
2535
July1st to 15thDay
8%5%38%8%5%7%8%8%9%26%
2535
16th to endDay
8%6%47%9%6%8%6%7%9%25%
2625
August1st to 15thDay
7%428%8%5%8%7%7%10%29%
2295
16th to endDay
14%5%26%7%5%7%6%7%8%28%
2484
September1st to 15thDay
11%5%26%6%47%6%7%7%34%
2340
16th to endDay
9%6%25%6%35%45%7%42%
2195
October1st to 15thDay
7%3245%3445%7%52%
1950
16th to endDay
10%313313436%56%
2033
November1st to 15thDay
8%42443436%8%49%
1908
16th to endDay
11%4245%22346%52%
1915
December1st to 15thDay
17%8%35%434445%39%
1859
16th to endDay
21%8%25%6%34345%33%
1908
January1st to 15thNight
16%6%24423445%45%
2522
16th to endNight
18%6%24323346%44%
2691
February1st to 15thNight
15%5%35%424447%43%
2283
16th to endNight
18%6%24422346%43%
2049
March1st to 15thNight
15%5%25%423347%43%
2152
16th to endNight
10%425%32335%7%51%
2256
April1st to 15thNight
11%5%25%424448%47%
1947
16th to endNight
8%414324438%52%
1928
May1st to 15thNight
8%31331446%10%49%
1949
16th to endNight
5%223425%46%10%51%
2029
June1st to 15thNight
3224435%5%9%12%46%
1771
16th to endNight
43246%37%7%10%10%38%
1755
July1st to 15thNight
3314436%6%8%12%43%
1755
16th to endNight
6%326%7%36%6%7%12%37%
1893
August1st to 15thNight
4324435%6%7%14%43%
1918
16th to endNight
8%425%5%45%6%8%12%37%
2070
September1st to 15thNight
9%5%244246%7%10%42%
1950
16th to endNight
7%425%5%35%5%6%7%46%
2078
October1st to 15thNight
5%31432335%6%60%
2340
16th to endNight
10%424423235%57%
2448
November1st to 15thNight
9%424323346%55%
2280
16th to endNight
12%413422235%57%
2360
December1st to 15thNight
15%6%26%42245%6%44%
2415
16th to endNight
22%8%36%433345%34%
2664

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%
1747
16th to endDay
46%2313%23%10%
1882
February1st to 15thDay
44%5%7%13%20%8%
1902
16th to endDay
45%5%6%17%18%7%
1713
March1st to 15thDay
44%47%17%18%6%
2145
16th to endDay
41%5%8%17%23%5%
2320
April1st to 15thDay
41%5%8%17%18%8%
2331
16th to endDay
39%5%11%20%19%4
2307
May1st to 15thDay
41%5%12%18%15%6%
2331
16th to endDay
40%8%13%21%14%1
2440
June1st to 15thDay
45%10%12%17%12%
2515
16th to endDay
47%14%13%17%6%
2535
July1st to 15thDay
48%12%17%14%6%1
2396
16th to endDay
49%11%17%16%4
2473
August1st to 15thDay
46%12%18%15%7%
2283
16th to endDay
48%12%16%12%7%1
2484
September1st to 15thDay
43%10%16%14%11%4
2340
16th to endDay
41%7%10%17%17%5%
2195
October1st to 15thDay
30%6%9%20%21%12%
1950
16th to endDay
28%45%12%30%17%
2033
November1st to 15thDay
32%49%19%26%8%
1908
16th to endDay
33%46%13%27%15%
1915
December1st to 15thDay
46%48%16%15%7%
1859
16th to endDay
52%46%15%15%4
1908
January1st to 15thNight
40%46%14%22%11%
2522
16th to endNight
40%37%15%22%11%
2691
February1st to 15thNight
40%47%17%19%10%
2292
16th to endNight
41%36%18%18%10%
2049
March1st to 15thNight
39%49%17%19%8%
2152
16th to endNight
31%5%12%21%21%7%
2256
April1st to 15thNight
34%5%9%21%18%10%
1947
16th to endNight
29%7%11%21%22%8%
1928
May1st to 15thNight
28%6%14%24%19%7%
1950
16th to endNight
26%7%17%29%17%1
2031
June1st to 15thNight
27%11%18%27%14%1
1771
16th to endNight
32%11%21%23%10%
1755
July1st to 15thNight
28%14%27%21%7%1
1665
16th to endNight
34%13%25%20%5%
1782
August1st to 15thNight
26%12%31%19%8%
1906
16th to endNight
36%13%23%15%8%2
2070
September1st to 15thNight
34%11%18%19%11%5%
1950
16th to endNight
34%8%12%20%16%7%
2078
October1st to 15thNight
23%5%10%22%23%14%
2340
16th to endNight
30%35%13%25%22%
2448
November1st to 15thNight
31%39%17%26%11%
2280
16th to endNight
31%35%16%23%19%
2360
December1st to 15thNight
40%48%20%18%7%
2415
16th to endNight
52%36%15%14%7%
2664

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
22%16%28%20%9%1
135
16th to endDay
18%22%40%13%4
144
February1st to 15thDay
21%14%36%22%5%
135
16th to endDay
15%16%41%22%3
120
March1st to 15thDay
24%13%42%17%2
135
16th to endDay
18%15%22%30%12%1
176
April1st to 15thDay
16%13%25%27%15%
330
16th to endDay
11%5%25%33%21%2
319
May1st to 15thDay
10%5%22%30%24%6%
348
16th to endDay
9%214%28%28%16%
395
June1st to 15thDay
8%8%28%35%18%
550
16th to endDay
8%17%22%34%24%
570
July1st to 15thDay
6%15%18%42%27%
550
16th to endDay
8%16%14%37%30%
546
August1st to 15thDay
8%312%35%39%
358
16th to endDay
13%413%31%36%
396
September1st to 15thDay
11%18%17%35%25%
375
16th to endDay
8%17%21%37%23%
356
October1st to 15thDay
3217%30%28%18%
180
16th to endDay
16%8%19%28%19%7%
178
November1st to 15thDay
15%23%42%14%4
135
16th to endDay
10%9%33%22%20%3
135
December1st to 15thDay
27%6%30%18%13%3
135
16th to endDay
34%8%27%23%5%
144
January1st to 15thNight
19%10%32%29%8%
975
16th to endNight
22%8%31%28%8%
1027
February1st to 15thNight
18%10%32%31%7%
764
16th to endNight
20%12%32%29%4
683
March1st to 15thNight
17%8%30%37%6%
592
16th to endNight
12%6%32%34%14%
624
April1st to 15thNight
13%7%31%31%13%
584
16th to endNight
11%429%37%16%1
579
May1st to 15thNight
9%224%40%22%1
585
16th to endNight
7%13%39%32%6%
611
June1st to 15thNight
45%35%47%7%
585
16th to endNight
415%28%42%17%
585
July1st to 15thNight
2318%49%25%
555
16th to endNight
4316%51%23%
612
August1st to 15thNight
4315%50%26%
575
16th to endNight
8%318%46%22%
621
September1st to 15thNight
10%1424%42%16%
585
16th to endNight
9%7%28%44%9%
696
October1st to 15thNight
6%117%31%38%5%
780
16th to endNight
12%5%21%31%25%3
816
November1st to 15thNight
10%5%22%35%21%3
760
16th to endNight
13%7%26%33%18%1
780
December1st to 15thNight
18%9%26%31%13%
780
16th to endNight
25%8%27%29%9%
1000
Page generated at 2018-10-28 07:41:01. Version ac04

Copyright 2018 A. Danko


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