Thunder Bay Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thunder Bay Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
33%
16930
13%
48957
6%
16883
39%
16883
19%
34660

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
22%
975
13%
2716
4%
970
30%
970
17%
1978
January16th to endNight
19%
1040
13%
2912
2%
1040
28%
1040
13%
2273
February1st to 15thNight
28%
949
15%
2525
4%
945
36%
945
20%
1797
February16th to endNight
31%
684
14%
1946
6%
684
36%
684
16%
1426
March1st to 15thNight
33%
720
15%
2160
10%
720
38%
720
19%
1496
March16th to endNight
37%
579
18%
2001
13%
579
47%
579
19%
1324
April1st to 15thNight
36%
539
13%
1797
10%
539
43%
539
19%
1243
April16th to endNight
38%
540
15%
1634
9%
540
44%
540
20%
1138
May1st to 15thNight
36%
540
11%
1440
5%
540
40%
540
20%
1062
May16th to endNight
41%
563
9%
1498
4%
561
44%
561
22%
1098
June1st to 15thNight
41%
540
6%
1440
3%
540
43%
540
23%
1040
June16th to endNight
44%
540
6%
1440
4%
540
46%
540
23%
1023
July1st to 15thNight
49%
510
8%
1360
4%
510
51%
510
31%
885
July16th to endNight
55%
564
14%
1417
6%
531
56%
531
34%
890
August1st to 15thNight
53%
539
18%
1431
9%
536
59%
536
37%
874
August16th to endNight
48%
573
17%
1822
13%
573
53%
573
28%
1103
September1st to 15thNight
50%
540
18%
1800
14%
540
57%
540
32%
1026
September16th to endNight
42%
672
15%
1938
11%
672
46%
672
24%
1308
October1st to 15thNight
33%
720
17%
2160
10%
720
40%
720
21%
1449
October16th to endNight
29%
768
10%
2469
5%
768
35%
768
15%
1804
November1st to 15thNight
28%
845
12%
2556
6%
845
34%
845
15%
1880
November16th to endNight
22%
975
13%
2730
6%
975
29%
975
13%
2100
December1st to 15thNight
20%
975
12%
2850
3%
975
28%
975
13%
2118
December16th to endNight
18%
1040
13%
2915
4%
1040
27%
1040
11%
2325

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%9%36%5%35%45%7%33%
49109
Night
13%9%46%5%3445%6%34%
49127
Cloud CoverDay
14%8%36%5%3445%7%33%
49119
Night
13%9%46%5%3445%6%35%
49132
Cloud CoverDay
14%8%36%6%3445%7%34%
49117
Night
13%9%46%5%35%45%6%34%
49132
TransparencyDay
48%6%14%20%9%
48794
Night
48%6%12%22%8%
48960
SeeingDay
18%12%33%21%10%3
6650
Night
18%10%28%28%12%1
16931

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%5%44448%31%
1552
16th to endDay
12%11%410%7%45%5%5%9%23%
1664
February1st to 15thDay
8%10%48%6%26%5%5%6%35%
1633
16th to endDay
10%12%5%9%7%34346%30%
1527
March1st to 15thDay
13%10%46%6%34445%37%
1796
16th to endDay
15%10%47%7%345%46%30%
2226
April1st to 15thDay
12%8%48%6%35%5%5%7%32%
2151
16th to endDay
20%11%45%433445%32%
2322
May1st to 15thDay
18%10%37%6%35%445%29%
2511
16th to endDay
17%8%35%43446%6%34%
2617
June1st to 15thDay
16%6%36%42445%7%37%
2520
16th to endDay
15%6%35%5%35%5%6%9%32%
2520
July1st to 15thDay
11%6%25%5%36%5%6%8%38%
2520
16th to endDay
9%5%35%5%35%5%5%9%41%
2655
August1st to 15thDay
9%5%245%46%5%6%9%41%
2520
16th to endDay
12%4144245%7%9%43%
2375
September1st to 15thDay
10%6%27%6%35%46%7%40%
2160
16th to endDay
18%8%25%5%2335%7%36%
2010
October1st to 15thDay
15%11%37%5%345%5%6%32%
1800
16th to endDay
21%12%47%6%34445%25%
1755
November1st to 15thDay
15%11%49%7%345%45%27%
1629
16th to endDay
16%13%5%7%6%25%347%27%
1560
December1st to 15thDay
12%11%48%6%345%5%6%30%
1432
16th to endDay
15%18%6%9%6%4445%5%20%
1654
January1st to 15thNight
12%12%5%7%5%25%446%32%
2716
16th to endNight
11%13%6%10%7%45%5%36%25%
2912
February1st to 15thNight
7%9%38%6%46%6%5%7%34%
2525
16th to endNight
9%10%5%7%7%35%6%6%7%28%
1946
March1st to 15thNight
12%11%36%5%245%45%36%
2147
16th to endNight
12%10%36%5%2445%6%37%
2001
April1st to 15thNight
13%10%36%5%35%45%6%34%
1797
16th to endNight
17%10%45%5%24445%34%
1634
May1st to 15thNight
19%8%46%5%24446%32%
1440
16th to endNight
17%7%36%5%25%45%7%33%
1496
June1st to 15thNight
16%8%36%435%446%35%
1440
16th to endNight
14%7%36%6%245%5%8%36%
1440
July1st to 15thNight
10%5%145%35%45%7%45%
1440
16th to endNight
7%3244246%7%9%47%
1513
August1st to 15thNight
8%313325%5%5%7%51%
1440
16th to endNight
13%42333346%6%48%
1822
September1st to 15thNight
10%32442446%7%49%
1800
16th to endNight
15%6%25%6%2445%7%39%
1938
October1st to 15thNight
15%8%246%33346%40%
2160
16th to endNight
16%10%47%6%34437%29%
2469
November1st to 15thNight
16%11%37%6%3445%6%30%
2556
16th to endNight
16%12%5%8%7%34446%27%
2730
December1st to 15thNight
13%12%6%8%5%33446%29%
2850
16th to endNight
14%16%6%10%6%34345%24%
2915

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%5%7%6%4345%7%31%
1552
16th to endDay
12%11%410%7%45%5%5%8%24%
1664
February1st to 15thDay
8%11%48%6%26%46%6%34%
1633
16th to endDay
10%12%5%8%8%35%346%30%
1527
March1st to 15thDay
13%9%47%44444437%
1806
16th to endDay
16%10%5%6%6%35%446%30%
2226
April1st to 15thDay
12%8%48%7%35%5%5%7%32%
2151
16th to endDay
20%10%35%4335%36%32%
2322
May1st to 15thDay
19%10%37%6%35%435%30%
2511
16th to endDay
18%7%35%43445%7%34%
2617
June1st to 15thDay
16%6%35%42445%7%38%
2520
16th to endDay
15%6%35%5%35%5%6%9%33%
2520
July1st to 15thDay
12%5%25%5%36%5%6%7%38%
2520
16th to endDay
10%5%25%5%35%5%5%9%41%
2655
August1st to 15thDay
9%5%245%35%5%6%8%41%
2520
16th to endDay
12%4143245%7%9%43%
2375
September1st to 15thDay
11%6%26%6%35%45%7%40%
2160
16th to endDay
18%8%345%23447%37%
2010
October1st to 15thDay
15%10%27%5%245%5%7%32%
1800
16th to endDay
21%12%47%5%3435%5%25%
1755
November1st to 15thDay
16%10%49%6%35%5%46%27%
1629
16th to endDay
17%13%47%6%35%337%27%
1560
December1st to 15thDay
11%11%48%6%35%46%5%30%
1432
16th to endDay
16%17%5%8%6%44445%20%
1654
January1st to 15thNight
12%12%6%7%5%25%45%6%32%
2716
16th to endNight
11%13%6%10%7%45%445%25%
2912
February1st to 15thNight
8%8%37%6%46%6%5%6%34%
2518
16th to endNight
9%10%47%7%36%6%5%8%28%
1946
March1st to 15thNight
12%10%37%5%35%5%45%37%
2160
16th to endNight
13%10%36%5%2445%6%37%
2001
April1st to 15thNight
14%10%35%6%35%35%6%35%
1797
16th to endNight
18%9%45%5%245%45%34%
1634
May1st to 15thNight
19%8%45%6%34446%33%
1439
16th to endNight
17%7%35%5%35%45%7%34%
1496
June1st to 15thNight
16%8%35%5%35%446%35%
1440
16th to endNight
14%6%27%5%245%5%9%35%
1440
July1st to 15thNight
10%5%145%35%45%7%45%
1440
16th to endNight
7%2145%245%7%8%48%
1513
August1st to 15thNight
9%313425%5%47%51%
1440
16th to endNight
13%42433345%6%48%
1822
September1st to 15thNight
10%4145%235%5%8%49%
1800
16th to endNight
15%6%25%5%2446%7%39%
1938
October1st to 15thNight
15%8%245%3435%5%40%
2160
16th to endNight
16%11%47%6%345%46%30%
2469
November1st to 15thNight
16%11%37%6%3445%6%29%
2556
16th to endNight
16%12%5%8%6%34446%27%
2730
December1st to 15thNight
13%11%6%8%6%23446%30%
2850
16th to endNight
14%16%5%10%6%34445%24%
2915

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%7%6%3445%8%31%
1552
16th to endDay
12%11%410%7%35%5%5%9%23%
1664
February1st to 15thDay
8%10%48%6%35%5%6%6%34%
1633
16th to endDay
10%13%48%8%35%337%30%
1527
March1st to 15thDay
13%10%36%435%44437%
1806
16th to endDay
16%10%46%7%3445%6%30%
2224
April1st to 15thDay
12%9%38%7%345%5%7%32%
2151
16th to endDay
20%10%35%433446%32%
2322
May1st to 15thDay
19%9%46%6%34445%30%
2511
16th to endDay
17%7%36%5%2345%7%34%
2617
June1st to 15thDay
16%6%25%4335%5%7%38%
2520
16th to endDay
16%5%25%5%25%5%6%9%33%
2520
July1st to 15thDay
12%5%246%35%5%6%8%38%
2520
16th to endDay
10%425%5%35%5%6%8%42%
2655
August1st to 15thDay
10%5%145%35%6%6%8%42%
2520
16th to endDay
12%4144245%7%9%44%
2375
September1st to 15thDay
10%6%26%5%35%45%8%41%
2160
16th to endDay
17%8%35%5%2335%7%36%
2010
October1st to 15thDay
15%10%36%5%235%5%6%32%
1800
16th to endDay
20%12%46%7%345%36%25%
1755
November1st to 15thDay
15%11%49%5%45%45%5%27%
1629
16th to endDay
17%11%5%7%6%34447%27%
1560
December1st to 15thDay
12%11%5%8%6%35%46%6%30%
1432
16th to endDay
16%17%5%9%7%34445%20%
1654
January1st to 15thNight
12%12%5%7%5%34446%32%
2716
16th to endNight
11%13%6%10%7%35%445%25%
2912
February1st to 15thNight
8%8%37%6%47%6%5%7%34%
2518
16th to endNight
9%10%5%7%7%46%5%6%7%28%
1946
March1st to 15thNight
13%10%36%5%35%5%45%36%
2160
16th to endNight
13%10%35%5%3435%6%37%
2001
April1st to 15thNight
14%9%36%6%35%35%6%35%
1797
16th to endNight
17%9%45%5%25%445%34%
1634
May1st to 15thNight
20%8%35%5%25%345%34%
1439
16th to endNight
18%6%35%5%345%6%6%34%
1496
June1st to 15thNight
17%8%26%5%35%447%35%
1440
16th to endNight
14%6%36%5%25%45%9%35%
1440
July1st to 15thNight
10%6%245%35%5%5%8%44%
1440
16th to endNight
7%3244245%7%10%47%
1513
August1st to 15thNight
8%314325%45%7%52%
1440
16th to endNight
13%4243135%5%7%47%
1822
September1st to 15thNight
10%4135%3345%7%49%
1800
16th to endNight
16%5%245%2445%8%39%
1938
October1st to 15thNight
16%8%245%24345%40%
2160
16th to endNight
16%10%37%5%35%446%30%
2469
November1st to 15thNight
16%10%47%6%35%45%6%29%
2556
16th to endNight
17%12%48%7%34446%27%
2730
December1st to 15thNight
13%11%5%9%6%24445%31%
2850
16th to endNight
14%16%6%10%6%3434424%
2915

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%5%11%22%8%
1553
16th to endDay
57%7%9%19%6%
1664
February1st to 15thDay
47%5%14%22%9%
1634
16th to endDay
55%411%19%8%
1527
March1st to 15thDay
48%6%11%19%11%2
1806
16th to endDay
53%6%13%16%8%2
2226
April1st to 15thDay
49%6%11%17%12%2
2151
16th to endDay
52%411%19%11%1
2322
May1st to 15thDay
54%411%18%9%
2511
16th to endDay
47%7%12%21%11%
2621
June1st to 15thDay
43%6%14%20%13%
2520
16th to endDay
45%8%17%20%8%
2520
July1st to 15thDay
38%7%14%24%14%
2371
16th to endDay
37%9%14%28%10%1
2488
August1st to 15thDay
36%8%17%26%9%1
2505
16th to endDay
33%8%19%26%12%
2375
September1st to 15thDay
39%7%17%27%6%
2160
16th to endDay
47%7%18%22%4
2010
October1st to 15thDay
49%6%16%21%5%
1800
16th to endDay
60%6%10%17%5%
1755
November1st to 15thDay
55%6%14%15%7%
1629
16th to endDay
56%7%14%14%7%
1560
December1st to 15thDay
52%7%15%18%5%
1432
16th to endDay
65%5%9%12%6%
1654
January1st to 15thNight
51%6%12%22%7%
2716
16th to endNight
59%5%8%18%6%
2912
February1st to 15thNight
47%6%14%21%9%
2528
16th to endNight
51%8%9%22%7%
1946
March1st to 15thNight
48%5%12%20%11%2
2160
16th to endNight
46%6%13%20%10%3
2001
April1st to 15thNight
49%5%10%19%14%1
1797
16th to endNight
50%48%23%12%1
1634
May1st to 15thNight
51%6%9%20%12%
1440
16th to endNight
47%8%9%21%11%
1498
June1st to 15thNight
49%410%19%14%1
1440
16th to endNight
44%9%14%19%11%1
1440
July1st to 15thNight
36%7%12%29%13%
1360
16th to endNight
30%10%16%28%13%1
1417
August1st to 15thNight
30%7%18%31%10%1
1431
16th to endNight
35%7%16%28%12%
1822
September1st to 15thNight
31%6%18%33%9%
1800
16th to endNight
42%7%16%28%4
1938
October1st to 15thNight
44%6%14%26%7%
2160
16th to endNight
54%6%15%18%5%
2469
November1st to 15thNight
53%6%13%18%7%
2556
16th to endNight
57%6%12%16%6%
2730
December1st to 15thNight
53%7%14%18%5%
2850
16th to endNight
62%5%8%17%5%
2915

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
15%14%36%28%5%
135
16th to endDay
19%16%30%23%8%1
144
February1st to 15thDay
12%18%50%13%4
130
16th to endDay
18%24%34%18%3
81
March1st to 15thDay
13%16%42%17%7%2
90
16th to endDay
22%13%26%20%11%6%
210
April1st to 15thDay
17%12%27%27%13%1
270
16th to endDay
28%13%23%21%9%3
321
May1st to 15thDay
23%15%31%18%7%3
468
16th to endDay
22%11%32%21%8%3
517
June1st to 15thDay
19%13%34%19%7%4
495
16th to endDay
17%14%30%23%11%2
495
July1st to 15thDay
14%9%34%27%9%5%
475
16th to endDay
10%8%40%20%13%6%
515
August1st to 15thDay
14%9%34%22%13%5%
493
16th to endDay
15%10%30%23%14%4
389
September1st to 15thDay
11%7%28%23%21%7%
315
16th to endDay
24%10%31%17%13%3
311
October1st to 15thDay
15%20%34%18%9%
135
16th to endDay
34%11%43%9%1
144
November1st to 15thDay
25%19%35%13%32
135
16th to endDay
36%15%23%16%7%
135
December1st to 15thDay
23%10%40%19%32
105
16th to endDay
16%21%42%14%31
142
January1st to 15thNight
17%15%37%23%5%
975
16th to endNight
17%11%37%24%7%1
1040
February1st to 15thNight
14%12%35%28%8%1
950
16th to endNight
14%11%30%31%10%1
684
March1st to 15thNight
16%15%25%30%10%1
720
16th to endNight
17%10%24%30%14%3
579
April1st to 15thNight
16%10%25%32%13%
539
16th to endNight
21%6%23%32%13%2
540
May1st to 15thNight
23%8%24%30%11%1
540
16th to endNight
19%6%24%33%14%1
563
June1st to 15thNight
20%7%22%33%14%1
540
16th to endNight
16%6%21%37%17%
540
July1st to 15thNight
12%5%25%35%17%1
510
16th to endNight
7%425%35%23%2
564
August1st to 15thNight
11%324%35%22%2
539
16th to endNight
16%426%31%17%3
573
September1st to 15thNight
12%5%27%28%21%4
540
16th to endNight
20%7%22%32%14%2
672
October1st to 15thNight
21%13%27%23%12%1
720
16th to endNight
22%11%28%25%11%
768
November1st to 15thNight
21%12%30%24%9%1
845
16th to endNight
23%17%27%22%8%1
975
December1st to 15thNight
19%15%33%21%8%1
975
16th to endNight
22%12%31%24%7%2
1040
Page generated at 2018-02-15 10:58:38. Version ac04

Copyright 2018 A. Danko


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