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 2017-09-18.

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
28%
16223
13%
46860
6%
16176
34%
16176
17%
32917

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%
900
11%
2506
3%
895
23%
895
14%
1855
January16th to endNight
10%
960
12%
2688
1%
960
19%
960
10%
2099
February1st to 15thNight
18%
880
13%
2308
1%
876
26%
876
14%
1658
February16th to endNight
27%
699
15%
1961
5%
699
34%
699
16%
1416
March1st to 15thNight
25%
696
15%
2136
7%
696
33%
696
16%
1468
March16th to endNight
31%
576
16%
2018
9%
576
43%
576
16%
1346
April1st to 15thNight
27%
539
12%
1797
8%
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
40%
561
20%
1070
June1st to 15thNight
37%
540
6%
1440
4%
540
39%
540
21%
1006
June16th to endNight
39%
540
7%
1440
4%
540
41%
540
22%
992
July1st to 15thNight
45%
510
9%
1360
4%
510
48%
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
48%
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
41%
608
13%
1812
10%
608
45%
608
22%
1189
October1st to 15thNight
32%
660
18%
1980
10%
660
39%
660
19%
1348
October16th to endNight
23%
704
10%
2238
3%
704
30%
704
13%
1633
November1st to 15thNight
22%
792
12%
2368
5%
792
30%
792
13%
1700
November16th to endNight
20%
900
14%
2520
5%
900
28%
900
12%
1890
December1st to 15thNight
12%
900
11%
2520
2%
900
20%
900
10%
1915
December16th to endNight
13%
960
12%
2688
3%
960
22%
960
9%
2163

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%
47948
Night
14%9%35%5%3445%7%36%
47028
Cloud CoverDay
14%7%36%5%3445%7%36%
47958
Night
14%8%36%5%3445%7%35%
47033
Cloud CoverDay
13%7%36%5%35%45%7%36%
47956
Night
14%9%36%5%3445%7%35%
47033
TransparencyDay
47%8%14%20%8%
47633
Night
47%7%13%21%9%
46861
SeeingDay
19%18%29%21%8%2
6208
Night
16%24%25%23%9%1
16223

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%12%5%8%6%34447%31%
1432
16th to endDay
11%11%6%11%8%3446%7%23%
1536
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%2443445%7%40%
1859
October1st to 15thDay
15%8%35%5%345%6%8%34%
1650
16th to endDay
21%11%46%5%34435%30%
1634
November1st to 15thDay
16%10%46%436%445%33%
1489
16th to endDay
16%11%5%6%5%3445%5%29%
1440
December1st to 15thDay
13%12%7%8%5%36%46%7%25%
1440
16th to endDay
16%18%6%10%5%3345%5%20%
1536
January1st to 15thNight
12%10%6%8%6%335%6%7%29%
2506
16th to endNight
11%13%5%8%8%45%46%7%23%
2688
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%5%44%
1812
October1st to 15thNight
14%7%25%5%34446%41%
1980
16th to endNight
19%8%25%5%345%5%6%33%
2238
November1st to 15thNight
16%9%25%5%3436%6%34%
2368
16th to endNight
19%11%45%5%34346%32%
2520
December1st to 15thNight
14%13%5%8%5%2336%8%26%
2520
16th to endNight
17%17%6%8%5%33345%24%
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
11%12%5%8%6%35%36%8%27%
1432
16th to endDay
11%11%7%11%9%35%5%7%5%21%
1536
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%41%
1859
October1st to 15thDay
14%7%26%6%25%5%6%7%34%
1650
16th to endDay
20%10%47%5%24435%31%
1634
November1st to 15thDay
16%9%46%5%35%446%33%
1489
16th to endDay
16%12%5%7%5%245%46%28%
1440
December1st to 15thDay
13%12%7%9%5%35%5%7%8%22%
1440
16th to endDay
17%17%6%9%7%2445%5%18%
1536
January1st to 15thNight
12%11%5%8%6%345%7%10%23%
2506
16th to endNight
12%13%6%9%8%45%48%7%21%
2688
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
15%6%2442346%6%43%
1812
October1st to 15thNight
15%7%25%433437%41%
1980
16th to endNight
19%7%25%5%345%5%6%33%
2238
November1st to 15thNight
16%8%36%5%35%45%6%34%
2368
16th to endNight
19%11%45%5%34347%31%
2520
December1st to 15thNight
14%14%5%8%5%235%8%9%22%
2520
16th to endNight
18%16%7%8%5%3445%6%20%
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
11%11%5%9%6%25%45%8%28%
1432
16th to endDay
11%11%6%11%9%345%7%7%21%
1536
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%43435%7%40%
1859
October1st to 15thDay
15%7%36%5%245%6%7%34%
1650
16th to endDay
21%9%38%5%24345%30%
1634
November1st to 15thDay
15%10%46%5%35%446%33%
1489
16th to endDay
16%12%5%7%5%345%46%29%
1440
December1st to 15thDay
13%11%7%8%5%35%5%6%8%24%
1440
16th to endDay
16%17%6%10%7%2345%5%19%
1536
January1st to 15thNight
12%11%5%7%7%235%6%10%26%
2506
16th to endNight
12%13%5%9%8%45%47%7%22%
2688
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%6%43%
1812
October1st to 15thNight
15%6%25%5%33446%41%
1980
16th to endNight
19%8%25%6%3445%6%33%
2238
November1st to 15thNight
16%9%36%5%3445%7%34%
2368
16th to endNight
18%11%35%5%34346%32%
2520
December1st to 15thNight
13%13%6%9%43346%9%24%
2520
16th to endNight
18%16%7%8%5%3335%6%21%
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
51%7%13%21%6%
1433
16th to endDay
58%7%11%16%5%
1536
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%7%19%21%4
1859
October1st to 15thDay
48%9%14%20%7%
1650
16th to endDay
58%7%11%16%6%
1634
November1st to 15thDay
53%7%14%15%8%
1489
16th to endDay
56%8%13%13%7%
1440
December1st to 15thDay
55%8%13%16%5%
1440
16th to endDay
65%7%9%12%41
1536
January1st to 15thNight
51%7%14%19%6%
2506
16th to endNight
58%6%10%17%6%
2688
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%18%27%4
1812
October1st to 15thNight
44%7%13%26%7%
1980
16th to endNight
52%7%15%19%5%
2238
November1st to 15thNight
49%8%15%17%7%
2368
16th to endNight
53%7%12%17%8%
2520
December1st to 15thNight
55%7%14%18%4
2520
16th to endNight
63%6%10%13%5%
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
20%15%38%22%3
90
16th to endDay
27%14%30%18%8%1
96
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%15%28%20%12%2
235
October1st to 15thDay
17%13%35%21%11%1
90
16th to endDay
34%13%30%21%
96
November1st to 15thDay
21%23%35%13%6%
90
16th to endDay
36%13%20%22%6%1
90
December1st to 15thDay
28%12%43%13%2
90
16th to endDay
26%23%35%12%2
96
January1st to 15thNight
14%31%33%17%3
900
16th to endNight
15%31%33%15%3
960
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
17%16%19%30%12%2
608
October1st to 15thNight
19%19%25%25%9%
660
16th to endNight
22%20%28%19%7%
704
November1st to 15thNight
18%26%27%19%6%1
792
16th to endNight
20%29%24%18%7%
900
December1st to 15thNight
16%36%27%14%4
900
16th to endNight
21%28%26%17%5%1
960
Page generated at 2017-09-19 06:32:20. Version ac04

Copyright 2017 A. Danko


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