Thunder Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thunder Bay clear sky chart from 2005-11-05 to 2017-08-12.

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
34%
15981
12%
46570
6%
15934
39%
15934
19%
33252

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
23%
900
10%
2506
3%
895
31%
895
16%
1881
January16th to endNight
20%
960
11%
2688
3%
960
27%
960
13%
2107
February1st to 15thNight
28%
879
13%
2351
3%
875
34%
875
20%
1696
February16th to endNight
33%
678
13%
1940
6%
678
37%
678
17%
1418
March1st to 15thNight
34%
720
15%
2160
10%
720
38%
720
19%
1493
March16th to endNight
37%
591
17%
2007
12%
591
47%
591
19%
1344
April1st to 15thNight
37%
539
13%
1797
10%
539
43%
539
18%
1248
April16th to endNight
40%
540
14%
1633
9%
540
45%
540
21%
1131
May1st to 15thNight
37%
540
11%
1440
6%
540
40%
540
21%
1053
May16th to endNight
43%
563
9%
1498
4%
561
45%
561
23%
1086
June1st to 15thNight
43%
471
5%
1371
4%
471
45%
471
21%
971
June16th to endNight
48%
462
6%
1362
5%
462
49%
462
21%
953
July1st to 15thNight
51%
510
7%
1360
5%
510
53%
510
30%
902
July16th to endNight
58%
564
13%
1417
7%
531
58%
531
34%
907
August1st to 15thNight
57%
527
18%
1400
10%
524
61%
524
36%
869
August16th to endNight
51%
525
15%
1664
12%
525
54%
525
28%
1026
September1st to 15thNight
55%
495
18%
1650
15%
495
61%
495
30%
956
September16th to endNight
43%
621
14%
1779
10%
621
46%
621
24%
1212
October1st to 15thNight
34%
660
17%
1972
10%
660
41%
660
20%
1353
October16th to endNight
29%
704
8%
2271
3%
704
34%
704
14%
1677
November1st to 15thNight
27%
772
12%
2348
6%
772
33%
772
14%
1744
November16th to endNight
23%
900
12%
2520
6%
900
28%
900
13%
1946
December1st to 15thNight
20%
900
6%
2688
2%
900
25%
900
11%
2045
December16th to endNight
18%
960
9%
2748
3%
960
24%
960
10%
2234

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%7%36%5%35%5%5%7%34%
47392
Night
14%9%36%5%35%5%5%7%33%
46740
Cloud CoverDay
14%7%36%5%35%5%5%7%34%
47402
Night
14%9%46%6%35%5%5%7%33%
46745
Cloud CoverDay
13%7%36%6%35%5%5%7%34%
47400
Night
14%9%46%6%35%5%5%7%33%
46745
TransparencyDay
46%8%14%20%8%
47077
Night
49%6%14%20%7%
46573
SeeingDay
18%10%33%23%10%3
6028
Night
18%9%28%28%12%1
15982

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%9%6%445%6%7%26%
1432
16th to endDay
12%10%5%9%8%35%6%5%8%25%
1536
February1st to 15thDay
8%10%47%6%35%5%5%6%35%
1509
16th to endDay
9%10%5%7%8%44446%33%
1533
March1st to 15thDay
13%9%46%33445%5%38%
1790
16th to endDay
15%8%36%6%45%5%5%6%33%
2229
April1st to 15thDay
12%7%36%6%35%5%6%7%35%
2151
16th to endDay
19%8%26%5%24446%34%
2325
May1st to 15thDay
18%7%37%5%3446%5%33%
2511
16th to endDay
16%7%35%5%2445%7%35%
2617
June1st to 15thDay
15%5%25%4345%5%8%38%
2582
16th to endDay
16%6%25%5%35%5%6%8%33%
2590
July1st to 15thDay
11%5%35%5%35%5%6%8%40%
2520
16th to endDay
9%5%25%5%35%5%6%9%41%
2655
August1st to 15thDay
9%324436%5%6%9%44%
2465
16th to endDay
11%3144345%6%8%46%
2183
September1st to 15thDay
10%5%26%6%3445%7%42%
1980
16th to endDay
17%7%345%2445%7%37%
1840
October1st to 15thDay
16%8%26%5%35%5%6%7%32%
1656
16th to endDay
20%9%35%6%45%45%5%26%
1601
November1st to 15thDay
15%8%48%7%35%45%6%29%
1508
16th to endDay
18%11%48%5%35%46%7%24%
1440
December1st to 15thDay
12%10%5%7%7%445%8%11%21%
1269
16th to endDay
17%17%6%11%7%35%35%5%16%
1470
January1st to 15thNight
12%13%46%7%35%5%6%7%27%
2506
16th to endNight
12%13%5%10%8%35%5%5%6%24%
2688
February1st to 15thNight
8%8%47%6%47%5%5%7%32%
2351
16th to endNight
10%10%5%8%7%35%5%5%7%29%
1940
March1st to 15thNight
13%7%46%6%35%445%37%
2147
16th to endNight
13%8%36%6%3445%7%37%
2007
April1st to 15thNight
15%8%25%6%35%5%5%6%34%
1797
16th to endNight
18%10%345%2445%6%34%
1633
May1st to 15thNight
21%7%35%434446%33%
1440
16th to endNight
18%6%36%5%2446%6%34%
1496
June1st to 15thNight
17%7%36%5%34446%35%
1371
16th to endNight
15%7%26%435%5%6%7%34%
1362
July1st to 15thNight
10%6%25%5%35%5%6%7%41%
1440
16th to endNight
8%323435%6%8%8%45%
1513
August1st to 15thNight
8%3135%245%5%7%51%
1409
16th to endNight
12%5%235%2445%7%45%
1664
September1st to 15thNight
10%42342445%7%50%
1650
16th to endNight
15%6%35%3345%5%7%39%
1779
October1st to 15thNight
17%8%25%434445%38%
1972
16th to endNight
17%10%37%5%35%45%7%28%
2271
November1st to 15thNight
17%8%37%6%36%5%5%5%29%
2348
16th to endNight
18%13%47%6%2445%6%25%
2520
December1st to 15thNight
13%11%5%9%6%35%5%7%7%22%
2688
16th to endNight
15%17%6%9%6%3445%6%18%
2748

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%11%49%6%45%5%6%8%27%
1432
16th to endDay
12%9%5%10%8%345%6%8%25%
1536
February1st to 15thDay
9%9%46%7%25%5%6%6%36%
1509
16th to endDay
9%10%5%7%8%45%346%33%
1533
March1st to 15thDay
13%9%46%435%45%5%38%
1800
16th to endDay
15%8%36%6%45%45%6%32%
2229
April1st to 15thDay
12%7%36%5%46%5%5%7%35%
2151
16th to endDay
19%9%26%5%23446%34%
2325
May1st to 15thDay
18%7%36%6%35%45%5%33%
2511
16th to endDay
16%7%35%5%345%5%7%35%
2617
June1st to 15thDay
15%5%25%5%345%6%7%38%
2582
16th to endDay
16%6%25%435%6%6%8%33%
2590
July1st to 15thDay
11%5%35%5%35%46%9%38%
2520
16th to endDay
9%5%246%35%5%6%9%40%
2655
August1st to 15thDay
9%325%5%35%5%6%9%43%
2465
16th to endDay
11%3144246%6%8%45%
2183
September1st to 15thDay
10%426%6%345%5%7%42%
1980
16th to endDay
16%6%36%43445%7%37%
1840
October1st to 15thDay
15%9%36%6%25%5%6%7%32%
1656
16th to endDay
20%9%46%6%45%45%6%26%
1601
November1st to 15thDay
16%7%5%8%7%35%5%47%27%
1508
16th to endDay
18%11%39%5%245%6%6%26%
1440
December1st to 15thDay
11%10%48%6%445%8%12%22%
1269
16th to endDay
17%17%6%11%7%35%446%17%
1470
January1st to 15thNight
12%13%5%7%6%35%46%7%27%
2506
16th to endNight
11%13%5%9%9%445%5%6%24%
2688
February1st to 15thNight
9%8%48%6%47%5%5%7%32%
2344
16th to endNight
9%10%5%8%7%36%5%6%6%30%
1940
March1st to 15thNight
13%8%36%5%35%5%45%37%
2160
16th to endNight
13%8%36%7%3345%6%37%
2007
April1st to 15thNight
15%7%35%5%45%5%5%6%34%
1797
16th to endNight
18%10%35%4335%5%6%34%
1633
May1st to 15thNight
20%7%34425%45%6%33%
1439
16th to endNight
18%6%37%42445%7%34%
1496
June1st to 15thNight
17%7%35%6%34447%35%
1371
16th to endNight
16%5%36%5%35%6%6%7%34%
1362
July1st to 15thNight
10%5%245%35%5%6%8%41%
1440
16th to endNight
8%324425%6%7%7%46%
1513
August1st to 15thNight
8%3135%245%5%8%51%
1409
16th to endNight
13%5%2342445%8%45%
1664
September1st to 15thNight
10%414424448%50%
1650
16th to endNight
16%5%35%5%2346%7%39%
1779
October1st to 15thNight
17%7%25%435%446%38%
1972
16th to endNight
16%11%36%6%35%45%7%28%
2271
November1st to 15thNight
18%8%47%6%36%5%5%5%29%
2348
16th to endNight
18%12%48%6%3445%7%25%
2520
December1st to 15thNight
13%11%5%8%6%345%6%10%23%
2688
16th to endNight
15%16%7%9%6%2445%7%19%
2748

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%49%6%36%46%7%27%
1432
16th to endDay
12%9%5%10%8%345%6%8%24%
1536
February1st to 15thDay
9%9%46%7%25%45%6%36%
1509
16th to endDay
9%10%5%7%8%45%346%33%
1533
March1st to 15thDay
12%9%45%435%45%5%38%
1800
16th to endDay
15%8%36%6%46%45%6%32%
2227
April1st to 15thDay
12%7%36%5%46%5%5%7%35%
2151
16th to endDay
19%8%26%5%23446%34%
2325
May1st to 15thDay
18%7%36%6%45%45%5%33%
2511
16th to endDay
16%7%35%5%345%5%7%34%
2617
June1st to 15thDay
15%5%25%5%345%6%7%38%
2582
16th to endDay
16%6%25%5%35%6%6%8%33%
2590
July1st to 15thDay
11%5%36%5%35%5%6%9%38%
2520
16th to endDay
8%5%246%35%5%6%9%40%
2655
August1st to 15thDay
8%325%5%35%5%6%10%42%
2465
16th to endDay
11%3145%246%6%8%45%
2183
September1st to 15thDay
10%426%6%35%5%5%7%42%
1980
16th to endDay
16%6%26%5%2445%7%36%
1840
October1st to 15thDay
15%9%36%5%25%5%7%6%32%
1656
16th to endDay
20%9%47%6%45%45%6%26%
1601
November1st to 15thDay
15%7%48%7%35%5%47%27%
1508
16th to endDay
17%11%39%5%25%5%5%7%25%
1440
December1st to 15thDay
12%11%48%6%446%7%12%22%
1269
16th to endDay
16%17%6%10%7%35%446%16%
1470
January1st to 15thNight
12%13%5%7%6%35%46%7%27%
2506
16th to endNight
11%13%6%9%9%45%5%5%6%24%
2688
February1st to 15thNight
9%8%48%6%47%5%5%7%32%
2344
16th to endNight
9%10%5%8%7%36%5%6%6%30%
1940
March1st to 15thNight
13%8%36%5%345%45%37%
2160
16th to endNight
12%9%36%7%2345%6%37%
2007
April1st to 15thNight
15%8%35%6%45%5%5%6%34%
1797
16th to endNight
18%10%35%4245%5%7%34%
1633
May1st to 15thNight
20%7%35%42445%7%33%
1439
16th to endNight
17%6%37%43446%7%34%
1496
June1st to 15thNight
17%7%35%6%3445%6%35%
1371
16th to endNight
15%6%26%5%35%5%6%7%34%
1362
July1st to 15thNight
10%6%24445%47%8%41%
1440
16th to endNight
7%424335%6%7%8%45%
1513
August1st to 15thNight
8%4134245%5%7%50%
1409
16th to endNight
12%5%2442445%9%44%
1664
September1st to 15thNight
10%414424448%49%
1650
16th to endNight
15%5%35%5%3446%7%39%
1779
October1st to 15thNight
17%7%25%434446%38%
1972
16th to endNight
16%10%47%6%35%45%7%28%
2271
November1st to 15thNight
17%8%47%6%35%6%5%5%29%
2348
16th to endNight
18%12%47%6%3435%7%25%
2520
December1st to 15thNight
12%12%5%8%7%345%6%10%22%
2688
16th to endNight
15%16%7%9%6%25%45%7%19%
2748

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
55%5%14%20%4
1433
16th to endDay
56%7%11%19%5%
1536
February1st to 15thDay
47%6%16%19%8%
1510
16th to endDay
52%6%13%18%7%
1533
March1st to 15thDay
45%8%13%19%10%2
1800
16th to endDay
49%9%12%17%8%2
2229
April1st to 15thDay
45%9%13%18%11%2
2151
16th to endDay
49%6%11%20%11%1
2325
May1st to 15thDay
50%7%12%19%9%1
2511
16th to endDay
46%7%13%20%11%
2621
June1st to 15thDay
42%8%13%21%14%
2582
16th to endDay
46%7%16%21%7%
2590
July1st to 15thDay
37%9%13%24%14%
2371
16th to endDay
36%9%15%27%9%1
2488
August1st to 15thDay
33%10%18%25%10%1
2450
16th to endDay
33%9%18%27%10%
2183
September1st to 15thDay
38%8%18%28%5%
1980
16th to endDay
46%8%19%20%4
1840
October1st to 15thDay
48%10%16%20%4
1656
16th to endDay
57%8%14%15%4
1601
November1st to 15thDay
54%6%16%15%6%
1508
16th to endDay
57%7%14%14%5%
1440
December1st to 15thDay
54%9%17%16%1
1269
16th to endDay
69%410%10%3
1470
January1st to 15thNight
55%5%15%18%4
2506
16th to endNight
60%6%11%17%4
2688
February1st to 15thNight
50%5%14%20%8%
2354
16th to endNight
51%7%12%20%7%
1940
March1st to 15thNight
48%5%11%20%11%1
2160
16th to endNight
46%6%13%20%10%3
2007
April1st to 15thNight
48%6%10%20%13%1
1797
16th to endNight
48%410%22%12%1
1633
May1st to 15thNight
50%6%11%19%11%
1440
16th to endNight
46%8%10%21%11%1
1498
June1st to 15thNight
48%7%10%17%14%1
1371
16th to endNight
47%7%14%18%10%1
1362
July1st to 15thNight
37%7%12%27%13%
1360
16th to endNight
31%10%17%28%12%1
1417
August1st to 15thNight
30%8%17%30%11%1
1400
16th to endNight
36%7%16%28%10%
1664
September1st to 15thNight
32%7%18%33%9%
1650
16th to endNight
42%8%17%27%3
1779
October1st to 15thNight
46%6%16%24%5%
1972
16th to endNight
55%7%17%15%4
2271
November1st to 15thNight
54%7%14%17%5%
2348
16th to endNight
57%7%13%16%5%
2520
December1st to 15thNight
57%7%18%14%2
2688
16th to endNight
65%5%12%13%2
2748

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
13%10%48%23%4
90
16th to endDay
25%7%32%25%8%2
96
February1st to 15thDay
15%15%51%12%41
90
16th to endDay
18%20%37%20%2
81
March1st to 15thDay
14%14%40%18%10%2
90
16th to endDay
20%13%32%18%11%4
216
April1st to 15thDay
17%13%27%29%12%
270
16th to endDay
27%11%24%24%8%3
314
May1st to 15thDay
19%12%35%20%7%2
468
16th to endDay
21%10%33%22%9%3
517
June1st to 15thDay
18%10%34%22%9%3
495
16th to endDay
19%9%31%23%13%2
495
July1st to 15thDay
13%6%34%30%10%4
475
16th to endDay
12%6%36%25%12%7%
515
August1st to 15thDay
13%6%33%27%13%5%
474
16th to endDay
15%8%29%28%12%5%
315
September1st to 15thDay
10%7%27%21%24%8%
255
16th to endDay
22%11%31%17%12%3
254
October1st to 15thDay
18%10%32%27%10%1
96
16th to endDay
37%9%39%12%1
96
November1st to 15thDay
20%18%33%18%6%2
90
16th to endDay
41%10%14%27%5%1
90
December1st to 15thDay
29%14%39%9%6%
61
16th to endDay
21%23%38%14%11
85
January1st to 15thNight
18%13%36%25%6%
900
16th to endNight
19%9%40%22%6%1
960
February1st to 15thNight
14%11%35%27%9%1
880
16th to endNight
14%8%30%34%10%
678
March1st to 15thNight
16%13%26%32%9%1
720
16th to endNight
15%9%27%29%15%2
591
April1st to 15thNight
18%8%28%30%12%
539
16th to endNight
21%7%24%28%14%2
540
May1st to 15thNight
24%6%26%28%12%2
540
16th to endNight
20%5%22%33%14%2
563
June1st to 15thNight
20%6%20%34%15%1
471
16th to endNight
18%220%37%18%2
462
July1st to 15thNight
13%225%34%21%2
510
16th to endNight
9%222%35%26%3
564
August1st to 15thNight
10%123%37%24%3
527
16th to endNight
14%424%32%19%4
525
September1st to 15thNight
13%6%21%32%22%5%
495
16th to endNight
19%7%23%31%15%2
621
October1st to 15thNight
21%12%27%23%13%1
660
16th to endNight
24%10%26%27%9%1
704
November1st to 15thNight
23%10%31%23%9%1
772
16th to endNight
25%13%28%23%7%
900
December1st to 15thNight
19%17%33%21%6%1
900
16th to endNight
23%13%31%23%6%1
960
Page generated at 2017-08-13 14:16:54. Version ac04

Copyright 2017 A. Danko


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