Duncan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Duncan clear sky chart from 2005-11-05 to 2017-09-21.

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
46%
14526
10%
46772
9%
14498
48%
14498
17%
33572

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
29%
749
9%
2686
7%
746
33%
746
8%
2172
January16th to endNight
38%
782
9%
2725
9%
782
39%
782
10%
2149
February1st to 15thNight
32%
696
7%
2288
4%
696
36%
696
9%
1839
February16th to endNight
40%
632
11%
2053
10%
632
43%
632
14%
1528
March1st to 15thNight
31%
720
7%
2038
5%
720
33%
720
10%
1688
March16th to endNight
34%
768
8%
2092
5%
768
36%
768
11%
1691
April1st to 15thNight
42%
699
10%
1779
4%
699
44%
699
18%
1344
April16th to endNight
48%
531
10%
1611
8%
531
50%
531
18%
1159
May1st to 15thNight
58%
359
14%
1439
21%
359
61%
359
20%
887
May16th to endNight
61%
375
7%
1448
10%
374
63%
374
18%
945
June1st to 15thNight
56%
360
4%
1260
3%
360
56%
360
23%
796
June16th to endNight
59%
360
7%
1260
4%
360
59%
360
25%
764
July1st to 15thNight
76%
340
11%
1190
11%
340
78%
340
40%
589
July16th to endNight
82%
376
16%
1315
23%
354
85%
354
47%
574
August1st to 15thNight
81%
465
17%
1539
20%
463
82%
463
40%
770
August16th to endNight
74%
597
22%
1743
18%
597
75%
597
42%
948
September1st to 15thNight
76%
720
23%
1800
14%
720
77%
720
50%
1009
September16th to endNight
55%
680
18%
1883
13%
680
58%
680
26%
1268
October1st to 15thNight
53%
660
11%
1980
10%
660
55%
660
22%
1355
October16th to endNight
39%
704
8%
2192
5%
704
43%
704
13%
1674
November1st to 15thNight
27%
700
7%
2450
5%
700
32%
700
7%
2000
November16th to endNight
33%
720
8%
2520
5%
720
37%
720
10%
1969
December1st to 15thNight
32%
733
5%
2601
4%
733
35%
733
8%
2113
December16th to endNight
24%
800
7%
2880
4%
800
29%
800
8%
2341

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
18%9%37%6%35%45%6%29%
48115
Night
17%8%35%5%35%45%6%34%
46925
Cloud CoverDay
16%9%36%6%35%45%6%31%
48115
Night
17%8%35%5%35%45%6%34%
46928
TransparencyDay
53%9%13%16%5%
47771
Night
50%8%14%17%7%1
46773
SeeingDay
19%10%24%26%16%3
6226
Night
20%6%17%27%22%5%
14536

By Month

Percentage Cloud Cover NW (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
26%13%47%6%46%5%3416%
1253
16th to endDay
22%12%6%9%7%46%445%16%
1495
February1st to 15thDay
27%15%47%6%35%335%16%
1576
16th to endDay
17%13%5%7%7%45%6%5%7%19%
1421
March1st to 15thDay
23%13%49%8%46%45%5%13%
1918
16th to endDay
23%13%49%8%5%443417%
2131
April1st to 15thDay
20%12%49%7%46%5%5%5%17%
2167
16th to endDay
22%11%48%7%35%5%5%6%20%
2348
May1st to 15thDay
17%7%38%6%46%5%5%7%28%
2511
16th to endDay
19%9%47%7%36%5%6%6%22%
2660
June1st to 15thDay
18%7%47%6%46%5%5%7%26%
2700
16th to endDay
17%7%47%7%45%45%6%29%
2700
July1st to 15thDay
10%424433447%49%
2700
16th to endDay
9%323323446%54%
2761
August1st to 15thDay
10%5%14434447%48%
2412
16th to endDay
8%415%6%45%45%8%44%
2458
September1st to 15thDay
10%32442335%8%51%
2160
16th to endDay
19%6%36%6%345%5%6%33%
1867
October1st to 15thDay
21%8%36%6%45%5%45%28%
1650
16th to endDay
24%10%47%6%24447%22%
1679
November1st to 15thDay
28%9%48%7%35%5%3417%
1408
16th to endDay
23%12%48%6%35%45%5%20%
1440
December1st to 15thDay
20%13%6%7%5%45%445%21%
1356
16th to endDay
27%14%26%6%35%6%5%5%17%
1344
January1st to 15thNight
24%11%35%5%35%5%45%23%
2686
16th to endNight
21%11%36%6%45%5%5%6%23%
2725
February1st to 15thNight
24%12%36%5%35%5%5%5%22%
2276
16th to endNight
17%8%36%5%35%36%7%31%
2053
March1st to 15thNight
21%9%46%6%46%6%7%5%21%
2038
16th to endNight
17%10%5%7%5%45%5%6%7%23%
2088
April1st to 15thNight
16%7%45%6%46%46%7%31%
1779
16th to endNight
16%7%35%5%35%5%5%9%32%
1611
May1st to 15thNight
14%325%5%245%5%6%43%
1439
16th to endNight
9%5%26%5%46%5%7%10%37%
1448
June1st to 15thNight
10%7%35%5%35%5%47%42%
1260
16th to endNight
8%434425%6%7%9%43%
1260
July1st to 15thNight
5%213323336%64%
1260
16th to endNight
3112213346%69%
1406
August1st to 15thNight
3312323347%64%
1547
16th to endNight
5%313324447%58%
1743
September1st to 15thNight
5%212323435%64%
1800
16th to endNight
15%5%15%42445%8%39%
1883
October1st to 15thNight
16%6%25%5%35%445%40%
1980
16th to endNight
23%8%37%6%35%45%5%26%
2192
November1st to 15thNight
27%10%26%6%46%5%45%20%
2450
16th to endNight
23%9%47%6%35%445%25%
2520
December1st to 15thNight
20%14%5%7%6%35%5%45%21%
2601
16th to endNight
26%12%46%5%35%445%21%
2880

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
26%14%47%7%35%45%5%16%
1253
16th to endDay
23%14%6%8%8%35%44414%
1495
February1st to 15thDay
27%14%5%6%6%3445%5%17%
1576
16th to endDay
17%12%5%7%7%45%5%5%7%20%
1421
March1st to 15thDay
23%12%6%8%8%5%5%5%4415%
1918
16th to endDay
21%13%5%8%7%36%5%4419%
2131
April1st to 15thDay
18%10%48%7%46%6%6%6%20%
2167
16th to endDay
18%11%46%7%46%46%6%23%
2348
May1st to 15thDay
13%8%36%7%46%5%5%7%32%
2511
16th to endDay
16%9%46%6%36%5%5%8%26%
2660
June1st to 15thDay
14%7%46%7%45%46%7%31%
2700
16th to endDay
14%8%36%7%45%5%5%7%32%
2700
July1st to 15thDay
8%424324346%53%
2700
16th to endDay
6%323223446%58%
2761
August1st to 15thDay
8%31442445%6%53%
2412
16th to endDay
7%414435%5%6%8%48%
2458
September1st to 15thDay
7%42442345%7%53%
2160
16th to endDay
18%6%25%5%3445%7%34%
1867
October1st to 15thDay
21%8%37%5%35%446%28%
1650
16th to endDay
22%12%47%5%3435%7%22%
1679
November1st to 15thDay
28%10%47%5%46%435%18%
1408
16th to endDay
25%11%5%7%6%35%5%46%18%
1440
December1st to 15thDay
22%14%5%7%6%34445%21%
1356
16th to endDay
27%12%37%5%35%5%6%5%16%
1344
January1st to 15thNight
25%11%36%6%35%44423%
2685
16th to endNight
22%11%36%6%35%45%7%23%
2725
February1st to 15thNight
25%12%36%5%35%45%5%22%
2276
16th to endNight
18%8%36%5%35%45%6%31%
2053
March1st to 15thNight
22%10%36%6%36%5%6%6%21%
2038
16th to endNight
18%9%48%7%36%5%5%6%24%
2092
April1st to 15thNight
16%6%36%7%35%5%5%6%31%
1779
16th to endNight
16%8%245%45%5%48%33%
1611
May1st to 15thNight
13%425%435%47%6%43%
1439
16th to endNight
9%435%5%347%7%10%37%
1448
June1st to 15thNight
10%5%36%6%25%45%8%42%
1260
16th to endNight
9%414425%6%6%9%44%
1260
July1st to 15thNight
331332335%5%65%
1260
16th to endNight
4112213146%69%
1406
August1st to 15thNight
3213222446%65%
1547
16th to endNight
5%213323447%60%
1743
September1st to 15thNight
6%21222335%5%65%
1800
16th to endNight
14%5%25%5%2436%8%40%
1883
October1st to 15thNight
16%6%25%43435%5%41%
1980
16th to endNight
24%7%26%6%25%45%6%27%
2192
November1st to 15thNight
28%9%36%6%45%5%45%20%
2450
16th to endNight
23%8%46%7%35%45%5%24%
2520
December1st to 15thNight
21%14%48%6%35%5%5%5%19%
2601
16th to endNight
25%13%36%5%35%44421%
2880

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
71%7%7%9%4
1253
16th to endDay
72%6%9%9%11
1495
February1st to 15thDay
70%7%8%9%4
1576
16th to endDay
62%9%11%12%3
1421
March1st to 15thDay
72%9%9%7%1
1918
16th to endDay
69%9%9%9%1
2131
April1st to 15thDay
63%12%10%11%2
2167
16th to endDay
62%9%12%11%3
2348
May1st to 15thDay
52%9%14%16%5%
2511
16th to endDay
56%12%15%14%1
2664
June1st to 15thDay
52%11%18%12%3
2700
16th to endDay
50%11%17%16%4
2700
July1st to 15thDay
31%10%16%26%11%2
2541
16th to endDay
25%11%19%30%11%1
2589
August1st to 15thDay
32%10%17%28%8%2
2395
16th to endDay
33%11%20%25%7%
2458
September1st to 15thDay
30%9%16%25%16%1
2160
16th to endDay
49%10%13%17%8%1
1867
October1st to 15thDay
56%9%12%14%6%
1650
16th to endDay
62%7%13%11%3
1679
November1st to 15thDay
69%7%8%9%31
1408
16th to endDay
66%8%9%12%3
1440
December1st to 15thDay
66%9%9%10%4
1356
16th to endDay
69%8%8%9%3
1344
January1st to 15thNight
65%7%8%12%5%
2686
16th to endNight
61%8%10%13%42
2725
February1st to 15thNight
63%8%11%12%3
2288
16th to endNight
53%9%14%17%6%
2053
March1st to 15thNight
61%11%10%12%3
2038
16th to endNight
59%10%11%15%3
2092
April1st to 15thNight
51%9%15%18%5%
1779
16th to endNight
48%9%16%18%6%
1611
May1st to 15thNight
40%7%17%21%11%
1440
16th to endNight
39%13%20%22%4
1448
June1st to 15thNight
41%7%23%21%41
1260
16th to endNight
33%11%24%21%6%2
1260
July1st to 15thNight
22%6%18%33%13%4
1190
16th to endNight
15%6%22%34%17%1
1315
August1st to 15thNight
21%8%20%32%13%4
1539
16th to endNight
23%7%23%31%10%3
1743
September1st to 15thNight
20%6%18%26%20%6%
1800
16th to endNight
40%8%16%21%9%2
1883
October1st to 15thNight
45%7%17%18%10%
1980
16th to endNight
57%8%14%13%6%
2192
November1st to 15thNight
65%8%9%11%31
2450
16th to endNight
61%7%11%11%7%
2520
December1st to 15thNight
66%7%11%11%3
2601
16th to endNight
66%7%10%10%4
2880

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
21%6%18%15%28%10%
60
16th to endDay
39%11%20%15%11%
109
February1st to 15thDay
35%18%19%20%5%
236
16th to endDay
25%20%25%18%9%1
211
March1st to 15thDay
36%24%21%14%2
270
16th to endDay
32%18%24%19%31
288
April1st to 15thDay
24%14%27%21%10%1
269
16th to endDay
21%13%34%18%10%1
270
May1st to 15thDay
19%10%28%27%13%1
288
16th to endDay
15%7%22%30%17%5%
375
June1st to 15thDay
12%8%29%30%15%3
495
16th to endDay
13%9%29%27%17%2
495
July1st to 15thDay
8%418%36%27%4
475
16th to endDay
6%221%36%26%5%
430
August1st to 15thDay
9%314%33%28%10%
315
16th to endDay
7%422%35%22%6%
332
September1st to 15thDay
10%328%30%22%4
315
16th to endDay
24%8%25%24%14%3
276
October1st to 15thDay
30%8%25%21%12%1
255
16th to endDay
28%14%24%20%8%3
218
November1st to 15thDay
40%10%28%16%5%
60
16th to endDay
21%11%20%21%10%15%
60
December1st to 15thDay
40%15%15%20%8%1
60
16th to endDay
31%10%26%15%12%3
64
January1st to 15thNight
32%10%18%19%16%2
750
16th to endNight
28%6%16%26%18%3
782
February1st to 15thNight
28%12%17%22%16%2
704
16th to endNight
22%9%18%28%16%3
632
March1st to 15thNight
25%13%23%22%12%2
720
16th to endNight
23%10%20%27%13%3
768
April1st to 15thNight
16%9%20%28%20%4
699
16th to endNight
20%317%38%16%2
531
May1st to 15thNight
14%413%38%24%5%
360
16th to endNight
9%214%37%30%4
375
June1st to 15thNight
10%320%30%31%3
360
16th to endNight
9%5%19%36%24%5%
360
July1st to 15thNight
329%30%47%7%
340
16th to endNight
47%25%49%12%
376
August1st to 15thNight
5%423%50%15%
465
16th to endNight
6%111%24%43%11%
597
September1st to 15thNight
7%18%27%38%16%
720
16th to endNight
18%314%26%27%9%
680
October1st to 15thNight
20%5%13%32%21%6%
660
16th to endNight
27%418%25%17%6%
704
November1st to 15thNight
32%10%21%25%9%1
700
16th to endNight
26%9%20%22%16%5%
720
December1st to 15thNight
27%9%18%28%13%2
733
16th to endNight
31%9%24%24%8%1
800
Page generated at 2017-09-22 04:35:35. Version ac04

Copyright 2017 A. Danko


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