Port Colborne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Colborne clear sky chart from 2005-11-06 to 2024-01-22.

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%
22967
7%
74984
6%
22920
37%
22920
8%
62295

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 10thNight
14%
757
2%
2649
1%
757
16%
757
2%
2439
January11th to 20thNight
14%
760
1%
2485
1%
760
15%
760
2%
2317
January21st to endNight
18%
800
3%
2599
2%
800
20%
800
4%
2331
February1st to 10thNight
13%
720
4%
2340
1%
720
16%
720
4%
2084
February11th to 20thNight
17%
703
4%
2275
1%
700
21%
700
5%
2003
February21st to endNight
17%
592
5%
1848
2%
592
21%
592
6%
1626
March1st to 10thNight
24%
720
7%
1980
3%
720
28%
720
8%
1690
March11th to 20thNight
26%
720
11%
1980
5%
720
31%
720
9%
1657
March21st to endNight
30%
792
11%
2178
6%
792
34%
792
11%
1803
April1st to 10thNight
27%
720
9%
1832
3%
720
30%
720
12%
1523
April11th to 20thNight
35%
690
11%
1754
5%
690
38%
690
13%
1432
April21st to endNight
39%
540
10%
1620
5%
540
42%
540
11%
1322
May1st to 10thNight
43%
540
10%
1620
8%
540
46%
540
12%
1290
May11th to 20thNight
47%
392
15%
1454
13%
392
52%
392
12%
1080
May21st to endNight
54%
388
12%
1551
15%
388
58%
388
13%
1111
June1st to 10thNight
46%
360
9%
1440
9%
360
53%
360
10%
1100
June11th to 20thNight
52%
360
11%
1440
14%
360
56%
360
11%
1069
June21st to endNight
53%
360
9%
1440
12%
360
56%
360
11%
1073
July1st to 10thNight
64%
350
12%
1400
17%
350
67%
350
14%
989
July11th to 20thNight
57%
353
11%
1397
16%
353
60%
353
13%
1012
July21st to endNight
61%
591
10%
1672
8%
558
62%
558
16%
1254
August1st to 10thNight
67%
537
10%
1600
9%
534
68%
534
15%
1216
August11th to 20thNight
62%
534
12%
1598
9%
534
64%
534
17%
1178
August21st to endNight
62%
692
12%
1880
7%
692
63%
692
17%
1437
September1st to 10thNight
55%
720
10%
1800
5%
720
57%
720
15%
1437
September11th to 20thNight
61%
720
17%
1894
11%
720
64%
720
20%
1420
September21st to endNight
47%
720
9%
2022
8%
720
48%
720
12%
1633
October1st to 10thNight
43%
720
10%
2160
8%
720
46%
720
12%
1720
October11th to 20thNight
31%
720
5%
2160
4%
720
33%
720
7%
1829
October21st to endNight
26%
792
7%
2376
5%
792
29%
792
7%
2041
November1st to 10thNight
35%
740
11%
2414
10%
740
37%
740
10%
1896
November11th to 20thNight
23%
760
10%
2660
6%
760
29%
760
7%
2222
November21st to endNight
22%
760
5%
2660
4%
760
24%
760
5%
2302
December1st to 10thNight
17%
760
1%
2660
0%
760
18%
760
2%
2450
December11th to 20thNight
14%
759
3%
3281
0%
759
17%
759
3%
2900
December21st to endNight
13%
825
0%
4865
0%
817
14%
817
1%
4409

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
15%10%47%6%35%5%6%7%32%
74733
Night
17%10%47%6%35%5%5%6%31%
75193
TransparencyDay
33%39%10%12%6%1
74450
Night
37%39%8%10%5%1
75010
SeeingDay
19%11%26%24%14%5%
13409
Night
21%9%27%28%13%2
22983

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 10thDay
18%15%6%12%9%45%46%5%15%
1517
11th to 20thDay
19%18%6%11%8%45%5%5%6%14%
1692
21st to endDay
14%16%7%14%10%5%6%5%5%413%
1791
February1st to 10thDay
20%16%5%13%8%46%445%15%
1620
11th to 20thDay
15%15%7%12%8%445%5%5%20%
1573
21st to endDay
22%12%5%11%8%35%45%421%
1404
March1st to 10thDay
16%13%5%9%8%45%5%5%5%26%
1977
11th to 20thDay
14%14%6%8%6%35%446%30%
1980
21st to endDay
20%11%47%6%35%45%6%29%
2178
April1st to 10thDay
18%12%47%5%35%45%6%31%
2128
11th to 20thDay
18%9%36%5%4445%7%36%
2169
21st to endDay
19%9%37%6%35%446%34%
2340
May1st to 10thDay
16%9%26%6%45%5%5%8%34%
2340
11th to 20thDay
14%7%36%6%35%5%6%6%38%
2437
21st to endDay
11%5%25%5%35%5%6%9%45%
2725
June1st to 10thDay
14%7%25%5%345%7%8%40%
2520
11th to 20thDay
11%5%25%6%35%6%6%10%41%
2520
21st to endDay
13%5%25%4335%6%8%45%
2520
July1st to 10thDay
8%4244346%7%9%49%
2520
11th to 20thDay
11%6%35%5%35%6%7%11%39%
2512
21st to endDay
9%5%35%6%46%6%6%10%40%
2547
August1st to 10thDay
8%435%5%36%6%8%10%43%
2327
11th to 20thDay
10%425%6%45%6%7%11%39%
2303
21st to endDay
11%5%25%435%5%6%9%45%
2457
September1st to 10thDay
13%6%25%435%6%6%7%42%
2160
11th to 20thDay
11%5%245%35%5%7%8%47%
2062
21st to endDay
14%6%37%6%45%6%6%7%35%
1937
October1st to 10thDay
19%7%36%6%35%45%6%36%
1800
11th to 20thDay
19%10%47%7%36%5%5%7%29%
1800
21st to endDay
24%11%49%7%45%446%22%
1980
November1st to 10thDay
15%9%48%6%45%5%47%34%
1659
11th to 20thDay
16%11%47%7%35%5%5%8%30%
1520
21st to endDay
22%13%48%5%345%5%8%23%
1520
December1st to 10thDay
20%17%5%10%8%445%46%17%
1520
11th to 20thDay
20%17%6%10%7%35%5%5%6%17%
1906
21st to endDay
28%21%6%10%6%3344411%
2772
January1st to 10thNight
19%16%6%9%7%5%5%5%45%19%
2649
11th to 20thNight
21%17%6%10%8%445%5%5%15%
2485
21st to endNight
15%16%6%10%9%5%6%5%45%19%
2599
February1st to 10thNight
19%17%7%9%8%45%435%19%
2340
11th to 20thNight
18%14%6%9%7%45%6%5%6%21%
2273
21st to endNight
20%13%5%9%7%5%45%46%22%
1848
March1st to 10thNight
16%11%5%7%8%46%5%46%30%
1970
11th to 20thNight
19%11%47%434446%33%
1979
21st to endNight
17%10%48%5%34446%34%
2178
April1st to 10thNight
21%9%47%6%345%45%32%
1832
11th to 20thNight
18%8%36%5%35%5%5%7%36%
1754
21st to endNight
16%9%35%6%36%5%5%5%35%
1620
May1st to 10thNight
16%9%37%5%36%46%7%35%
1620
11th to 20thNight
13%5%25%6%47%7%5%7%40%
1453
21st to endNight
12%5%25%5%446%5%7%45%
1550
June1st to 10thNight
11%7%37%6%46%7%7%7%37%
1440
11th to 20thNight
10%5%26%6%36%46%8%43%
1440
21st to endNight
13%5%25%6%35%5%6%7%43%
1440
July1st to 10thNight
6%425%5%3445%9%52%
1440
11th to 20thNight
11%425%5%35%6%6%8%45%
1445
21st to endNight
10%435%6%35%6%7%8%45%
1771
August1st to 10thNight
8%5%25%436%6%6%9%46%
1611
11th to 20thNight
9%6%35%435%6%6%9%45%
1598
21st to endNight
9%4346%36%6%6%7%46%
1880
September1st to 10thNight
14%6%26%5%345%5%7%44%
1800
11th to 20thNight
13%414324447%52%
1894
21st to endNight
15%6%36%7%35%47%6%38%
2022
October1st to 10thNight
17%6%26%5%346%47%39%
2160
11th to 20thNight
21%9%36%7%45%6%5%6%30%
2160
21st to endNight
24%8%47%5%45%5%5%6%27%
2376
November1st to 10thNight
17%7%46%5%345%47%39%
2414
11th to 20thNight
16%11%47%6%45%5%5%8%30%
2660
21st to endNight
20%12%47%5%35%5%5%7%25%
2660
December1st to 10thNight
23%17%5%8%5%35%45%6%19%
2660
11th to 20thNight
17%20%7%9%7%35%435%20%
3288
21st to endNight
30%16%6%8%6%35%5%5%5%12%
4884

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 10thDay
48%42%6%41
1518
11th to 20thDay
48%42%6%31
1692
21st to endDay
49%38%8%41
1791
February1st to 10thDay
47%38%8%6%1
1620
11th to 20thDay
45%39%7%6%2
1582
21st to endDay
46%38%8%5%2
1404
March1st to 10thDay
38%39%10%10%31
1980
11th to 20thDay
35%39%9%11%6%1
1980
21st to endDay
36%39%7%13%5%1
2178
April1st to 10thDay
31%38%10%12%8%
2128
11th to 20thDay
30%37%10%13%9%1
2169
21st to endDay
34%37%7%13%9%1
2340
May1st to 10thDay
31%38%8%13%8%2
2340
11th to 20thDay
28%39%8%13%11%2
2441
21st to endDay
23%39%12%15%9%2
2725
June1st to 10thDay
26%39%11%14%9%
2520
11th to 20thDay
24%39%10%18%8%1
2520
21st to endDay
24%40%11%17%7%1
2520
July1st to 10thDay
20%41%10%17%10%1
2450
11th to 20thDay
24%40%13%15%8%
2437
21st to endDay
23%41%14%15%7%
2405
August1st to 10thDay
23%40%13%17%7%
2314
11th to 20thDay
22%39%14%16%8%1
2303
21st to endDay
24%38%11%17%9%1
2457
September1st to 10thDay
27%39%9%16%8%1
2160
11th to 20thDay
24%39%10%19%8%
2062
21st to endDay
33%39%11%12%5%1
1937
October1st to 10thDay
32%38%11%11%7%1
1800
11th to 20thDay
38%39%11%9%2
1800
21st to endDay
42%38%8%8%31
1980
November1st to 10thDay
29%44%7%12%6%1
1659
11th to 20thDay
34%44%10%8%41
1520
21st to endDay
41%42%8%7%2
1520
December1st to 10thDay
45%42%8%4
1520
11th to 20thDay
50%35%8%5%2
1906
21st to endDay
62%27%7%4
2772
January1st to 10thNight
47%42%6%41
2649
11th to 20thNight
48%42%6%21
2485
21st to endNight
47%38%8%6%1
2599
February1st to 10thNight
47%37%7%7%2
2340
11th to 20thNight
44%39%9%6%3
2275
21st to endNight
43%39%7%8%3
1848
March1st to 10thNight
38%39%10%10%31
1980
11th to 20thNight
37%38%7%12%6%1
1980
21st to endNight
35%38%6%13%6%2
2178
April1st to 10thNight
33%38%7%12%8%1
1832
11th to 20thNight
33%37%7%13%10%1
1754
21st to endNight
33%39%7%10%9%2
1620
May1st to 10thNight
32%38%6%13%9%3
1620
11th to 20thNight
26%39%8%14%11%3
1454
21st to endNight
23%39%10%14%12%2
1551
June1st to 10thNight
28%40%8%14%10%1
1440
11th to 20thNight
25%40%9%13%12%1
1440
21st to endNight
27%39%10%15%8%1
1440
July1st to 10thNight
21%40%8%17%13%2
1400
11th to 20thNight
23%39%10%16%10%1
1397
21st to endNight
21%41%11%15%10%1
1672
August1st to 10thNight
25%39%11%16%7%1
1600
11th to 20thNight
23%38%12%18%9%
1598
21st to endNight
23%40%8%18%9%2
1880
September1st to 10thNight
29%38%8%14%10%1
1800
11th to 20thNight
22%37%9%21%10%
1894
21st to endNight
31%39%9%12%7%1
2022
October1st to 10thNight
31%38%8%14%8%1
2160
11th to 20thNight
38%39%9%10%4
2160
21st to endNight
39%39%7%9%41
2376
November1st to 10thNight
26%43%8%15%6%1
2414
11th to 20thNight
34%43%9%9%5%1
2660
21st to endNight
39%43%10%7%2
2660
December1st to 10thNight
46%43%6%41
2660
11th to 20thNight
48%36%9%5%1
3288
21st to endNight
61%28%8%3
4884

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 10thDay
23%18%32%18%7%2
180
11th to 20thDay
27%19%34%13%6%1
262
21st to endDay
24%18%30%20%8%1
267
February1st to 10thDay
28%17%39%14%2
240
11th to 20thDay
23%24%37%15%1
240
21st to endDay
29%21%32%16%2
234
March1st to 10thDay
22%15%35%21%6%
420
11th to 20thDay
23%14%34%23%6%1
420
21st to endDay
28%10%30%22%8%2
462
April1st to 10thDay
22%13%30%25%9%2
420
11th to 20thDay
25%14%27%18%12%4
412
21st to endDay
24%10%31%23%10%3
420
May1st to 10thDay
24%11%24%26%9%5%
423
11th to 20thDay
17%9%22%29%18%5%
447
21st to endDay
13%6%24%28%22%8%
485
June1st to 10thDay
15%8%29%32%14%2
450
11th to 20thDay
13%8%24%30%20%5%
450
21st to endDay
17%5%26%32%16%4
450
July1st to 10thDay
8%5%17%30%31%10%
445
11th to 20thDay
15%5%19%28%22%11%
444
21st to endDay
10%5%24%32%22%6%
488
August1st to 10thDay
8%5%19%30%25%13%
446
11th to 20thDay
13%416%30%25%13%
439
21st to endDay
12%5%20%29%22%12%
495
September1st to 10thDay
15%7%17%28%22%10%
450
11th to 20thDay
11%5%16%26%26%16%
450
21st to endDay
16%11%23%23%19%9%
450
October1st to 10thDay
22%9%24%18%18%8%
450
11th to 20thDay
24%15%28%23%8%2
450
21st to endDay
33%14%24%20%9%
495
November1st to 10thDay
22%15%29%22%9%3
307
11th to 20thDay
26%19%24%23%6%2
180
21st to endDay
31%17%36%13%3
180
December1st to 10thDay
24%21%33%16%6%1
180
11th to 20thDay
28%22%31%13%6%1
180
21st to endDay
26%23%35%14%31
198
January1st to 10thNight
28%17%32%16%7%
760
11th to 20thNight
30%16%30%20%4
760
21st to endNight
23%11%35%26%6%
800
February1st to 10thNight
28%16%33%20%3
720
11th to 20thNight
24%14%35%22%4
703
21st to endNight
28%11%36%23%2
592
March1st to 10thNight
21%11%35%27%6%
720
11th to 20thNight
25%11%31%24%8%
720
21st to endNight
21%7%32%27%11%1
792
April1st to 10thNight
23%10%32%30%5%
720
11th to 20thNight
21%9%31%29%9%2
690
21st to endNight
22%6%26%34%11%
540
May1st to 10thNight
20%424%34%14%3
540
11th to 20thNight
15%426%42%13%1
392
21st to endNight
14%422%35%23%2
389
June1st to 10thNight
13%428%36%18%1
360
11th to 20thNight
12%425%40%18%1
360
21st to endNight
13%5%22%43%17%
360
July1st to 10thNight
7%317%43%28%2
350
11th to 20thNight
11%320%37%26%3
353
21st to endNight
11%217%45%22%2
591
August1st to 10thNight
9%412%41%31%4
537
11th to 20thNight
9%216%33%36%4
534
21st to endNight
11%216%40%27%4
692
September1st to 10thNight
15%418%34%24%5%
720
11th to 20thNight
14%416%31%28%7%
720
21st to endNight
17%6%21%31%21%5%
720
October1st to 10thNight
19%6%23%29%20%3
720
11th to 20thNight
27%11%25%26%9%1
720
21st to endNight
30%10%28%27%5%
792
November1st to 10thNight
21%10%27%29%11%2
740
11th to 20thNight
21%14%35%18%10%2
760
21st to endNight
26%12%35%20%7%
760
December1st to 10thNight
33%15%28%19%5%
760
11th to 20thNight
25%18%33%19%5%
760
21st to endNight
32%13%32%21%3
836
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