Grand Marais
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Marais clear sky chart from 2005-11-05 to 2018-01-20.

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
27%
16791
13%
48502
6%
16744
34%
16744
17%
34069

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
15%
975
11%
2716
3%
970
23%
970
14%
1987
January16th to endNight
9%
985
13%
2757
1%
985
19%
985
10%
2146
February1st to 15thNight
17%
880
13%
2308
1%
876
25%
876
14%
1658
February16th to endNight
26%
699
15%
1961
5%
699
34%
699
16%
1416
March1st to 15thNight
25%
696
15%
2136
7%
696
32%
696
16%
1468
March16th to endNight
31%
576
16%
2018
9%
576
43%
576
16%
1346
April1st to 15thNight
27%
539
12%
1797
7%
539
35%
539
15%
1257
April16th to endNight
27%
540
14%
1645
7%
540
35%
540
15%
1153
May1st to 15thNight
29%
540
12%
1440
4%
540
34%
540
16%
1077
May16th to endNight
36%
563
10%
1498
3%
561
41%
561
20%
1070
June1st to 15thNight
36%
540
6%
1440
4%
540
39%
540
21%
1006
June16th to endNight
38%
540
7%
1440
4%
540
40%
540
22%
992
July1st to 15thNight
45%
510
9%
1360
4%
510
47%
510
29%
858
July16th to endNight
43%
564
15%
1417
6%
531
50%
531
33%
871
August1st to 15thNight
49%
539
20%
1441
11%
536
54%
536
33%
869
August16th to endNight
47%
573
18%
1839
14%
573
55%
573
29%
1066
September1st to 15thNight
48%
540
19%
1800
16%
540
55%
540
29%
1018
September16th to endNight
42%
654
14%
1944
11%
654
46%
654
22%
1274
October1st to 15thNight
31%
720
17%
2160
10%
720
38%
720
20%
1458
October16th to endNight
23%
768
11%
2442
3%
768
30%
768
13%
1786
November1st to 15thNight
21%
860
11%
2571
5%
860
29%
860
13%
1860
November16th to endNight
19%
975
14%
2730
4%
975
27%
975
12%
2047
December1st to 15thNight
12%
975
11%
2730
2%
975
20%
975
10%
2073
December16th to endNight
13%
1040
12%
2912
3%
1040
22%
1040
10%
2313

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
14%8%36%5%3445%7%36%
49038
Night
14%9%35%5%3445%7%36%
48670
Cloud CoverDay
14%7%36%5%3445%7%36%
49048
Night
14%8%36%5%3445%7%35%
48675
Cloud CoverDay
13%7%36%5%35%45%7%35%
49046
Night
14%9%36%5%3445%7%35%
48675
TransparencyDay
47%8%14%20%8%
48723
Night
47%7%13%21%9%
48503
SeeingDay
19%18%30%21%8%2
6591
Night
16%24%25%22%9%1
16791

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
11%11%5%8%6%34446%32%
1552
16th to endDay
11%10%6%11%8%4446%7%22%
1571
February1st to 15thDay
9%10%46%5%35%35%8%34%
1554
16th to endDay
11%13%5%11%6%2445%6%29%
1512
March1st to 15thDay
13%7%47%44444440%
1823
16th to endDay
18%10%35%5%25%446%32%
2205
April1st to 15thDay
12%10%35%5%35%46%6%36%
2151
16th to endDay
21%9%35%434445%33%
2313
May1st to 15thDay
18%7%26%6%35%45%7%33%
2511
16th to endDay
18%5%25%5%25%45%8%35%
2617
June1st to 15thDay
15%425%4245%5%9%38%
2520
16th to endDay
17%5%25%435%5%6%8%35%
2520
July1st to 15thDay
10%314425%46%10%44%
2520
16th to endDay
9%4145%35%5%5%9%46%
2655
August1st to 15thDay
8%415%425%5%6%10%44%
2508
16th to endDay
12%31332445%9%47%
2363
September1st to 15thDay
9%5%245%3446%8%45%
2160
16th to endDay
17%5%24434447%39%
2001
October1st to 15thDay
16%7%35%4345%6%8%34%
1800
16th to endDay
21%11%46%5%33435%30%
1782
November1st to 15thDay
16%10%46%5%35%445%32%
1616
16th to endDay
16%11%5%6%6%3345%6%30%
1560
December1st to 15thDay
13%12%7%8%5%36%46%7%25%
1560
16th to endDay
15%17%6%10%6%3445%5%20%
1664
January1st to 15thNight
12%10%6%7%6%335%5%7%31%
2716
16th to endNight
11%13%5%8%8%45%46%7%23%
2757
February1st to 15thNight
8%9%46%6%36%46%8%33%
2306
16th to endNight
9%12%48%5%3346%9%30%
1961
March1st to 15thNight
12%9%26%5%35%445%39%
2123
16th to endNight
12%9%45%4345%46%38%
2018
April1st to 15thNight
16%9%26%5%3445%5%35%
1797
16th to endNight
20%9%3442445%5%34%
1645
May1st to 15thNight
23%6%35%5%24445%33%
1440
16th to endNight
16%5%245%4445%7%37%
1496
June1st to 15thNight
16%6%25%425%5%5%7%38%
1440
16th to endNight
16%5%2433446%8%39%
1440
July1st to 15thNight
10%3235%25%45%7%48%
1440
16th to endNight
8%323425%5%6%8%49%
1513
August1st to 15thNight
7%325%433446%54%
1450
16th to endNight
12%32331345%7%51%
1839
September1st to 15thNight
9%32432345%7%52%
1800
16th to endNight
15%5%2443445%6%43%
1944
October1st to 15thNight
15%7%25%5%34345%42%
2160
16th to endNight
19%8%35%5%3445%6%32%
2442
November1st to 15thNight
16%10%25%6%3436%6%33%
2571
16th to endNight
18%10%35%5%34446%33%
2730
December1st to 15thNight
14%14%5%8%5%2335%8%26%
2730
16th to endNight
16%16%6%8%5%33345%24%
2912

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
11%12%5%9%6%35%35%8%27%
1552
16th to endDay
11%11%7%11%9%45%5%7%5%21%
1571
February1st to 15thDay
9%10%48%6%35%47%9%32%
1554
16th to endDay
10%13%5%9%6%3446%5%30%
1512
March1st to 15thDay
12%7%46%434445%40%
1833
16th to endDay
17%9%36%5%25%45%6%33%
2205
April1st to 15thDay
12%8%45%6%345%6%7%35%
2151
16th to endDay
21%8%35%434445%34%
2313
May1st to 15thDay
17%7%26%5%3445%7%33%
2511
16th to endDay
18%6%25%425%5%5%9%35%
2617
June1st to 15thDay
15%5%25%4245%6%8%37%
2520
16th to endDay
16%5%35%5%35%5%6%8%35%
2520
July1st to 15thDay
10%3144245%6%10%45%
2520
16th to endDay
9%3244245%6%8%46%
2655
August1st to 15thDay
8%325%425%6%7%9%45%
2508
16th to endDay
11%3143245%5%9%47%
2363
September1st to 15thDay
8%5%15%5%3446%8%46%
2160
16th to endDay
17%5%25%42435%7%39%
2001
October1st to 15thDay
15%7%26%5%25%5%6%7%35%
1800
16th to endDay
21%10%47%5%24435%31%
1782
November1st to 15thDay
16%10%46%5%35%346%32%
1616
16th to endDay
16%11%5%6%5%35%5%46%29%
1560
December1st to 15thDay
13%12%6%8%5%35%5%7%8%22%
1560
16th to endDay
15%17%6%9%7%3445%5%18%
1664
January1st to 15thNight
12%11%5%7%6%345%8%11%23%
2716
16th to endNight
12%13%5%9%8%45%48%7%21%
2757
February1st to 15thNight
8%9%47%7%45%5%7%10%29%
2299
16th to endNight
9%12%5%8%5%3437%8%31%
1961
March1st to 15thNight
13%8%35%5%25%45%439%
2136
16th to endNight
12%8%45%4346%46%38%
2018
April1st to 15thNight
16%9%36%5%3445%5%35%
1797
16th to endNight
20%9%35%42445%5%33%
1645
May1st to 15thNight
23%7%35%5%2445%5%33%
1439
16th to endNight
16%6%246%345%5%7%37%
1496
June1st to 15thNight
16%6%25%4245%5%7%38%
1440
16th to endNight
17%3244245%6%9%39%
1440
July1st to 15thNight
9%424435%5%5%6%48%
1440
16th to endNight
7%3234245%6%8%49%
1513
August1st to 15thNight
7%3245%2445%6%54%
1450
16th to endNight
12%42331445%7%51%
1839
September1st to 15thNight
9%32442345%7%52%
1800
16th to endNight
14%5%2442346%7%43%
1944
October1st to 15thNight
15%7%35%433436%42%
2160
16th to endNight
19%8%35%5%345%46%32%
2442
November1st to 15thNight
17%9%36%5%35%45%6%33%
2571
16th to endNight
18%10%46%5%34347%31%
2730
December1st to 15thNight
14%14%5%8%5%235%7%9%22%
2730
16th to endNight
17%16%7%8%5%3445%7%19%
2912

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
11%11%5%9%6%2445%8%29%
1552
16th to endDay
10%11%6%11%9%345%7%7%21%
1571
February1st to 15thDay
9%10%48%5%45%37%7%34%
1554
16th to endDay
10%13%49%7%35%45%5%30%
1512
March1st to 15thDay
12%7%46%5%35%45%5%40%
1833
16th to endDay
17%9%45%5%25%346%33%
2203
April1st to 15thDay
11%9%46%6%25%46%7%35%
2151
16th to endDay
21%9%35%334346%33%
2313
May1st to 15thDay
17%7%36%6%3445%7%32%
2511
16th to endDay
17%6%25%435%45%8%35%
2617
June1st to 15thDay
15%5%24425%5%6%9%37%
2520
16th to endDay
16%5%25%5%36%5%6%7%35%
2520
July1st to 15thDay
10%3244345%6%10%44%
2520
16th to endDay
8%4134245%7%9%46%
2655
August1st to 15thDay
8%315%5%25%5%7%9%44%
2508
16th to endDay
10%41432445%10%47%
2363
September1st to 15thDay
8%425%6%2445%8%46%
2160
16th to endDay
17%5%25%435%45%7%39%
2001
October1st to 15thDay
15%7%36%5%245%6%7%34%
1800
16th to endDay
21%10%38%5%24345%30%
1782
November1st to 15thDay
16%10%46%5%35%445%32%
1616
16th to endDay
16%11%5%6%5%35%5%46%29%
1560
December1st to 15thDay
13%12%7%8%5%35%5%6%8%24%
1560
16th to endDay
15%17%6%10%7%3445%6%18%
1664
January1st to 15thNight
12%11%5%7%6%235%6%11%26%
2716
16th to endNight
11%13%5%9%8%45%47%7%22%
2757
February1st to 15thNight
8%9%47%7%36%5%7%8%32%
2299
16th to endNight
9%13%48%6%3446%8%31%
1961
March1st to 15thNight
12%8%26%6%25%5%45%39%
2136
16th to endNight
12%9%45%5%345%46%38%
2018
April1st to 15thNight
16%9%26%5%3445%5%35%
1797
16th to endNight
20%10%2443445%5%33%
1645
May1st to 15thNight
23%6%35%43445%5%33%
1439
16th to endNight
16%6%246%345%5%7%37%
1496
June1st to 15thNight
16%5%26%4245%5%7%38%
1440
16th to endNight
16%4244345%5%9%39%
1440
July1st to 15thNight
9%424425%5%46%49%
1440
16th to endNight
7%32442446%9%49%
1513
August1st to 15thNight
7%425%5%24446%53%
1450
16th to endNight
11%42332335%7%51%
1839
September1st to 15thNight
9%42432336%7%52%
1800
16th to endNight
14%6%245%2346%7%43%
1944
October1st to 15thNight
15%6%25%433436%42%
2160
16th to endNight
19%8%35%6%3445%6%32%
2442
November1st to 15thNight
16%10%36%5%3445%6%33%
2571
16th to endNight
17%11%36%5%34346%32%
2730
December1st to 15thNight
13%14%6%9%43346%9%24%
2730
16th to endNight
16%16%7%8%5%3445%7%21%
2912

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
51%6%12%21%7%
1553
16th to endDay
58%7%11%16%5%
1571
February1st to 15thDay
47%7%15%18%10%1
1555
16th to endDay
55%5%13%17%7%
1512
March1st to 15thDay
46%5%16%17%12%1
1833
16th to endDay
53%7%12%15%9%1
2205
April1st to 15thDay
48%7%13%16%12%2
2151
16th to endDay
53%5%10%17%11%1
2313
May1st to 15thDay
52%7%12%18%8%
2511
16th to endDay
47%7%12%21%9%
2621
June1st to 15thDay
42%9%15%21%10%
2520
16th to endDay
45%9%16%21%6%
2520
July1st to 15thDay
34%9%13%27%14%
2371
16th to endDay
34%9%16%26%11%1
2488
August1st to 15thDay
34%10%17%26%8%1
2493
16th to endDay
34%9%19%24%12%
2363
September1st to 15thDay
38%8%18%28%6%
2160
16th to endDay
46%8%19%21%4
2001
October1st to 15thDay
48%9%13%20%7%
1800
16th to endDay
58%7%10%17%5%
1782
November1st to 15thDay
54%7%14%15%7%
1616
16th to endDay
55%8%14%14%7%
1560
December1st to 15thDay
56%8%13%16%5%
1560
16th to endDay
65%7%9%12%5%
1664
January1st to 15thNight
50%7%14%19%7%
2716
16th to endNight
58%6%10%18%6%
2757
February1st to 15thNight
45%9%15%18%10%1
2309
16th to endNight
49%7%11%21%8%1
1961
March1st to 15thNight
47%5%12%17%13%2
2136
16th to endNight
45%7%14%19%10%2
2018
April1st to 15thNight
50%6%10%17%14%
1797
16th to endNight
50%5%9%21%11%
1645
May1st to 15thNight
52%6%9%19%11%
1440
16th to endNight
44%8%10%21%13%
1498
June1st to 15thNight
43%7%11%21%14%
1440
16th to endNight
40%8%16%23%9%1
1440
July1st to 15thNight
34%7%12%30%14%
1360
16th to endNight
29%8%17%29%12%1
1417
August1st to 15thNight
30%7%15%32%12%2
1441
16th to endNight
31%7%19%27%14%
1839
September1st to 15thNight
29%7%18%36%8%
1800
16th to endNight
40%8%19%26%5%
1944
October1st to 15thNight
43%7%13%26%8%
2160
16th to endNight
53%7%15%18%5%
2442
November1st to 15thNight
50%8%15%17%8%
2571
16th to endNight
52%8%12%17%7%
2730
December1st to 15thNight
55%7%13%18%4
2730
16th to endNight
61%6%10%14%6%
2912

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
20%17%37%22%2
135
16th to endDay
24%15%33%18%7%
109
February1st to 15thDay
21%23%46%6%11
90
16th to endDay
30%17%32%14%4
81
March1st to 15thDay
14%16%47%11%10%
90
16th to endDay
24%20%28%14%9%2
189
April1st to 15thDay
17%21%23%29%7%
270
16th to endDay
28%22%23%17%6%1
339
May1st to 15thDay
20%22%33%16%42
468
16th to endDay
23%20%27%19%6%2
517
June1st to 15thDay
16%25%29%18%6%2
495
16th to endDay
19%21%27%21%7%3
495
July1st to 15thDay
13%13%31%26%10%3
475
16th to endDay
10%18%32%25%8%4
515
August1st to 15thDay
12%13%27%29%13%3
493
16th to endDay
16%11%27%28%12%2
403
September1st to 15thDay
13%11%28%26%16%3
315
16th to endDay
21%13%29%21%11%1
284
October1st to 15thDay
20%15%34%20%8%
135
16th to endDay
34%14%31%19%
144
November1st to 15thDay
22%22%34%13%5%1
135
16th to endDay
30%20%27%15%5%
135
December1st to 15thDay
26%14%41%13%3
135
16th to endDay
18%23%39%16%1
144
January1st to 15thNight
14%30%33%17%3
975
16th to endNight
15%31%33%15%3
985
February1st to 15thNight
13%31%30%17%5%
880
16th to endNight
14%26%24%26%7%
699
March1st to 15thNight
13%27%27%23%6%1
696
16th to endNight
14%23%23%24%10%2
576
April1st to 15thNight
16%23%24%26%8%
539
16th to endNight
23%24%21%20%9%1
540
May1st to 15thNight
21%25%19%23%7%2
540
16th to endNight
17%22%18%28%10%2
563
June1st to 15thNight
18%21%19%28%9%2
540
16th to endNight
18%19%18%28%12%1
540
July1st to 15thNight
10%14%23%32%15%2
510
16th to endNight
8%17%23%30%16%2
564
August1st to 15thNight
10%11%20%30%24%2
539
16th to endNight
14%11%21%29%19%2
573
September1st to 15thNight
12%12%23%30%18%3
540
16th to endNight
16%15%20%31%12%2
654
October1st to 15thNight
20%17%27%24%9%
720
16th to endNight
22%20%28%19%7%
768
November1st to 15thNight
19%25%27%19%6%1
860
16th to endNight
19%30%25%17%6%
975
December1st to 15thNight
17%35%27%14%4
975
16th to endNight
20%27%28%17%41
1040
Page generated at 2018-01-21 11:19:24. Version ac04

Copyright 2018 A. Danko


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