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Duluth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Duluth clear sky chart from 2005-11-05 to 2017-09-23.

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
39%
16210
14%
46662
9%
16163
44%
16163
22%
32157

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
31%
900
11%
2506
6%
895
36%
895
18%
1842
January16th to endNight
25%
960
12%
2631
5%
960
31%
960
16%
2025
February1st to 15thNight
32%
879
14%
2285
4%
875
38%
875
23%
1630
February16th to endNight
38%
738
15%
2000
7%
738
43%
738
23%
1414
March1st to 15thNight
36%
633
14%
2073
12%
633
39%
633
20%
1400
March16th to endNight
36%
576
17%
2061
14%
576
44%
576
19%
1366
April1st to 15thNight
36%
539
13%
1797
12%
539
42%
539
19%
1233
April16th to endNight
39%
540
15%
1667
12%
540
45%
540
20%
1159
May1st to 15thNight
37%
540
14%
1440
7%
540
41%
540
21%
1041
May16th to endNight
49%
563
11%
1498
5%
561
52%
561
27%
1032
June1st to 15thNight
49%
540
9%
1440
5%
540
51%
540
28%
975
June16th to endNight
50%
540
11%
1260
7%
540
51%
540
31%
885
July1st to 15thNight
60%
510
13%
1278
7%
510
62%
510
40%
800
July16th to endNight
63%
564
15%
1417
8%
531
65%
531
40%
841
August1st to 15thNight
65%
539
20%
1530
16%
536
67%
536
38%
877
August16th to endNight
55%
573
21%
1803
19%
573
60%
573
33%
1037
September1st to 15thNight
61%
540
21%
1800
21%
540
67%
540
34%
1005
September16th to endNight
49%
585
14%
1882
12%
585
53%
585
27%
1162
October1st to 15thNight
45%
660
20%
1980
12%
660
52%
660
27%
1246
October16th to endNight
32%
704
12%
2183
7%
704
37%
704
18%
1559
November1st to 15thNight
32%
827
16%
2403
9%
827
39%
827
22%
1657
November16th to endNight
32%
900
15%
2520
9%
900
38%
900
18%
1847
December1st to 15thNight
24%
900
9%
2520
4%
900
29%
900
12%
1967
December16th to endNight
23%
960
9%
2688
3%
960
29%
960
12%
2157

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
13%8%36%5%3445%7%35%
48248
Night
13%9%36%5%3445%7%36%
46831
Cloud CoverDay
11%6%25%5%34446%45%
48259
Night
11%7%25%423446%46%
46835
Cloud CoverDay
13%7%36%5%345%5%7%35%
48257
Night
13%8%36%5%3445%6%36%
46835
TransparencyDay
47%5%15%22%9%
47932
Night
47%5%14%23%9%
46665
SeeingDay
18%423%31%17%4
6212
Night
17%6%26%34%13%1
16211

By Month

Percentage Cloud Cover NE (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
9%12%7%10%5%345%47%28%
1432
16th to endDay
10%11%5%10%8%36%5%7%8%21%
1590
February1st to 15thDay
7%12%48%6%25%45%6%35%
1575
16th to endDay
10%13%47%6%3445%6%32%
1473
March1st to 15thDay
13%10%47%6%345%45%35%
1885
16th to endDay
17%8%37%5%2445%7%32%
2162
April1st to 15thDay
14%8%46%5%44436%35%
2151
16th to endDay
21%9%36%5%25%35%6%30%
2292
May1st to 15thDay
20%7%46%6%35%445%31%
2511
16th to endDay
16%6%25%5%3446%7%37%
2617
June1st to 15thDay
14%5%25%6%35%45%8%37%
2520
16th to endDay
14%5%25%5%35%6%7%8%35%
2694
July1st to 15thDay
8%5%24435%5%49%45%
2601
16th to endDay
6%3245%35%5%6%9%45%
2655
August1st to 15thDay
9%5%26%5%35%5%5%7%42%
2419
16th to endDay
12%5%2442446%9%44%
2399
September1st to 15thDay
9%5%24435%45%7%46%
2160
16th to endDay
15%6%36%5%24446%39%
1903
October1st to 15thDay
14%8%35%5%35%445%38%
1650
16th to endDay
21%10%36%6%34346%30%
1689
November1st to 15thDay
14%10%5%6%6%245%5%5%33%
1454
16th to endDay
17%11%48%5%445%6%7%24%
1440
December1st to 15thDay
14%13%6%8%7%45%5%47%22%
1440
16th to endDay
17%18%7%9%6%34435%18%
1536
January1st to 15thNight
11%9%6%7%6%35%5%5%8%30%
2506
16th to endNight
10%11%6%11%7%44446%27%
2631
February1st to 15thNight
7%12%410%5%35%436%37%
2285
16th to endNight
10%12%47%7%3445%7%34%
2000
March1st to 15thNight
11%10%46%6%34436%37%
2061
16th to endNight
15%9%47%5%24345%37%
2061
April1st to 15thNight
17%9%46%42445%6%34%
1797
16th to endNight
22%9%25%42445%7%31%
1667
May1st to 15thNight
19%6%35%6%33446%34%
1440
16th to endNight
14%4245%346%7%7%36%
1496
June1st to 15thNight
15%5%25%435%5%6%7%37%
1440
16th to endNight
15%7%24435%5%5%8%37%
1260
July1st to 15thNight
7%32432445%8%51%
1356
16th to endNight
6%4134245%8%9%49%
1513
August1st to 15thNight
8%5%23423347%52%
1539
16th to endNight
13%5%23322447%50%
1803
September1st to 15thNight
7%424433447%53%
1800
16th to endNight
13%6%243345%5%7%44%
1882
October1st to 15thNight
14%6%14425%45%6%43%
1980
16th to endNight
20%8%36%5%24346%32%
2183
November1st to 15thNight
14%8%47%434447%36%
2403
16th to endNight
15%9%46%5%35%45%6%32%
2520
December1st to 15thNight
15%13%5%9%6%4445%7%25%
2520
16th to endNight
15%17%5%9%6%25%445%23%
2688

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
6%10%47%5%2346%5%42%
1432
16th to endDay
7%9%410%7%45%5%6%7%32%
1590
February1st to 15thDay
7%11%45%5%2335%5%44%
1575
16th to endDay
7%10%26%43434445%
1473
March1st to 15thDay
10%7%35%423446%47%
1896
16th to endDay
13%7%35%43445%344%
2162
April1st to 15thDay
12%6%25%5%35%33447%
2151
16th to endDay
18%7%25%42343442%
2292
May1st to 15thDay
14%6%26%6%3433443%
2511
16th to endDay
14%5%24423345%48%
2617
June1st to 15thDay
12%4144345%46%47%
2520
16th to endDay
13%5%144345%5%7%44%
2694
July1st to 15thDay
7%313424447%56%
2601
16th to endDay
431442446%7%55%
2655
August1st to 15thDay
7%415%5%345%46%48%
2419
16th to endDay
10%4143135%5%8%51%
2399
September1st to 15thDay
8%41442445%7%51%
2160
16th to endDay
12%5%15%5%24345%47%
1903
October1st to 15thDay
13%7%245%245%45%43%
1650
16th to endDay
18%8%25%5%34345%37%
1689
November1st to 15thDay
12%7%35%5%2344445%
1454
16th to endDay
13%10%37%5%45%5%45%36%
1440
December1st to 15thDay
12%11%38%6%446%45%33%
1440
16th to endDay
14%14%49%6%3443431%
1536
January1st to 15thNight
8%7%46%5%3445%7%41%
2506
16th to endNight
8%10%5%8%6%4345%6%37%
2631
February1st to 15thNight
5%11%48%422335%47%
2278
16th to endNight
6%9%37%5%33345%46%
2000
March1st to 15thNight
7%8%26%5%34435%49%
2073
16th to endNight
12%7%27%42323449%
2061
April1st to 15thNight
13%7%36%423445%44%
1797
16th to endNight
20%8%24323345%41%
1667
May1st to 15thNight
15%6%245%32245%45%
1439
16th to endNight
12%4135%335%6%5%47%
1496
June1st to 15thNight
12%5%14424446%47%
1440
16th to endNight
13%6%1332435%7%48%
1260
July1st to 15thNight
7%31322335%7%57%
1356
16th to endNight
6%333235%47%59%
1513
August1st to 15thNight
7%413323347%57%
1539
16th to endNight
12%5%13312337%56%
1803
September1st to 15thNight
7%314423446%56%
1800
16th to endNight
11%6%1332335%7%50%
1882
October1st to 15thNight
13%6%13424445%48%
1980
16th to endNight
19%6%25%5%33335%39%
2183
November1st to 15thNight
11%8%25%323436%47%
2403
16th to endNight
12%7%26%4235%45%44%
2520
December1st to 15thNight
12%11%37%6%23447%35%
2520
16th to endNight
11%15%48%434436%34%
2688

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
8%12%7%8%7%3446%6%28%
1432
16th to endDay
10%10%5%11%7%46%5%7%8%21%
1590
February1st to 15thDay
8%12%5%8%5%2445%6%35%
1575
16th to endDay
11%11%47%5%35%45%6%32%
1473
March1st to 15thDay
13%9%5%6%5%3345%5%36%
1896
16th to endDay
17%8%36%5%35%446%33%
2160
April1st to 15thDay
14%7%36%6%34346%36%
2151
16th to endDay
21%8%35%5%2445%6%31%
2292
May1st to 15thDay
20%7%37%6%35%445%32%
2511
16th to endDay
17%5%35%4345%5%8%36%
2617
June1st to 15thDay
15%5%245%35%45%8%38%
2520
16th to endDay
14%6%15%5%36%6%6%8%35%
2694
July1st to 15thDay
9%4244345%6%9%45%
2601
16th to endDay
5%3245%35%5%6%9%47%
2655
August1st to 15thDay
9%426%5%35%5%5%7%43%
2419
16th to endDay
11%42442345%9%46%
2399
September1st to 15thDay
8%5%2443446%8%47%
2160
16th to endDay
16%6%25%5%33446%40%
1903
October1st to 15thDay
14%7%345%345%46%38%
1650
16th to endDay
20%10%36%6%34447%29%
1689
November1st to 15thDay
15%9%47%6%3445%5%33%
1454
16th to endDay
16%11%47%6%36%6%5%7%23%
1440
December1st to 15thDay
15%13%5%9%5%46%5%5%6%21%
1440
16th to endDay
17%17%6%9%7%345%3418%
1536
January1st to 15thNight
11%10%5%6%6%45%5%5%7%30%
2506
16th to endNight
10%12%6%8%7%35%46%6%26%
2631
February1st to 15thNight
7%12%5%9%5%34445%37%
2278
16th to endNight
10%10%48%6%3446%6%34%
2000
March1st to 15thNight
12%10%46%5%35%445%38%
2073
16th to endNight
15%9%36%5%24345%37%
2061
April1st to 15thNight
17%9%46%5%3435%5%33%
1797
16th to endNight
22%8%3443345%7%30%
1667
May1st to 15thNight
20%7%25%6%34347%34%
1439
16th to endNight
14%5%245%35%6%7%7%37%
1496
June1st to 15thNight
15%5%345%3447%8%37%
1440
16th to endNight
15%7%23325%46%9%38%
1260
July1st to 15thNight
7%42423446%8%51%
1356
16th to endNight
7%3234246%6%10%49%
1513
August1st to 15thNight
8%41342345%7%53%
1539
16th to endNight
14%414312347%50%
1803
September1st to 15thNight
7%41443435%7%53%
1800
16th to endNight
14%5%2433335%8%44%
1882
October1st to 15thNight
14%5%2443445%6%44%
1980
16th to endNight
21%7%35%6%34436%33%
2183
November1st to 15thNight
15%9%36%425%446%37%
2403
16th to endNight
16%10%36%5%346%46%32%
2520
December1st to 15thNight
15%13%5%8%7%345%5%7%23%
2520
16th to endNight
15%17%6%8%6%245%45%23%
2688

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
54%5%12%19%7%
1433
16th to endDay
58%6%14%15%4
1590
February1st to 15thDay
48%418%18%9%1
1576
16th to endDay
52%415%21%5%
1473
March1st to 15thDay
48%5%18%19%7%
1896
16th to endDay
50%5%17%20%5%1
2162
April1st to 15thDay
50%312%18%13%1
2151
16th to endDay
54%313%18%8%1
2292
May1st to 15thDay
54%412%20%6%1
2511
16th to endDay
45%5%14%22%10%1
2621
June1st to 15thDay
43%5%17%23%9%
2520
16th to endDay
43%6%17%22%9%
2694
July1st to 15thDay
33%414%27%16%1
2450
16th to endDay
32%6%18%28%13%1
2488
August1st to 15thDay
38%5%15%28%10%1
2404
16th to endDay
33%5%19%27%13%
2399
September1st to 15thDay
34%5%18%32%8%
2160
16th to endDay
44%5%16%28%5%
1903
October1st to 15thDay
45%5%16%23%8%
1650
16th to endDay
55%415%17%7%
1689
November1st to 15thDay
51%5%13%19%9%
1454
16th to endDay
59%7%11%15%5%
1440
December1st to 15thDay
62%7%12%14%2
1440
16th to endDay
70%49%11%3
1536
January1st to 15thNight
51%7%14%21%4
2506
16th to endNight
57%5%12%17%5%
2631
February1st to 15thNight
49%314%21%10%
2288
16th to endNight
49%413%23%8%
2000
March1st to 15thNight
47%5%15%20%10%
2073
16th to endNight
48%414%22%8%1
2061
April1st to 15thNight
50%410%18%14%1
1797
16th to endNight
51%311%21%11%
1667
May1st to 15thNight
50%5%12%22%8%1
1440
16th to endNight
43%6%11%24%12%1
1498
June1st to 15thNight
42%5%14%25%10%1
1440
16th to endNight
42%5%13%24%12%1
1260
July1st to 15thNight
30%6%14%28%17%2
1278
16th to endNight
27%7%17%29%15%2
1417
August1st to 15thNight
30%416%32%12%3
1530
16th to endNight
34%314%29%16%2
1803
September1st to 15thNight
30%5%14%38%10%
1800
16th to endNight
37%6%19%29%7%
1882
October1st to 15thNight
39%5%15%29%9%
1980
16th to endNight
53%413%20%7%
2183
November1st to 15thNight
48%314%23%9%
2403
16th to endNight
52%6%15%18%6%1
2520
December1st to 15thNight
59%6%13%17%2
2520
16th to endNight
64%5%13%11%4
2688

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
23%5%24%27%18%
90
16th to endDay
20%329%35%10%1
96
February1st to 15thDay
14%8%40%28%7%
90
16th to endDay
28%227%32%9%
81
March1st to 15thDay
15%6%24%38%13%1
90
16th to endDay
23%7%23%29%11%3
146
April1st to 15thDay
16%7%25%34%14%2
270
16th to endDay
27%6%25%27%9%1
384
May1st to 15thDay
24%5%31%25%9%2
468
16th to endDay
22%5%22%27%16%5%
517
June1st to 15thDay
16%5%25%32%16%3
495
16th to endDay
15%5%26%30%17%3
495
July1st to 15thDay
14%222%28%24%7%
475
16th to endDay
8%322%37%20%7%
515
August1st to 15thDay
13%217%32%30%4
493
16th to endDay
17%316%31%24%7%
439
September1st to 15thDay
9%117%38%26%5%
315
16th to endDay
23%6%22%29%15%1
201
October1st to 15thDay
10%423%35%20%6%
90
16th to endDay
28%428%26%12%1
96
November1st to 15thDay
12%5%35%40%6%
90
16th to endDay
34%8%13%28%13%1
90
December1st to 15thDay
22%6%30%32%8%
90
16th to endDay
33%9%32%20%4
96
January1st to 15thNight
15%7%32%31%10%1
900
16th to endNight
16%6%37%32%6%
960
February1st to 15thNight
14%6%31%36%9%1
880
16th to endNight
15%430%35%13%
738
March1st to 15thNight
17%5%29%35%10%1
633
16th to endNight
18%6%27%32%12%3
576
April1st to 15thNight
22%425%35%11%
539
16th to endNight
28%422%33%10%1
540
May1st to 15thNight
21%5%28%32%9%1
540
16th to endNight
15%419%39%19%1
563
June1st to 15thNight
17%320%42%15%1
540
16th to endNight
18%418%39%17%1
540
July1st to 15thNight
10%221%37%26%2
510
16th to endNight
8%119%41%26%1
564
August1st to 15thNight
10%213%42%26%3
539
16th to endNight
15%319%35%23%2
573
September1st to 15thNight
8%418%38%25%4
540
16th to endNight
17%423%32%20%1
585
October1st to 15thNight
19%5%25%35%12%
660
16th to endNight
25%8%28%28%9%
704
November1st to 15thNight
18%8%31%30%9%
827
16th to endNight
20%11%29%29%9%
900
December1st to 15thNight
20%11%30%29%7%
900
16th to endNight
24%7%29%26%8%2
960
Page generated at 2017-09-24 08:15:58. Version ac04

Copyright 2017 A. Danko


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