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Ottawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ottawa clear sky chart from 2005-11-05 to 2017-03-26.

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
31%
14172
13%
45336
8%
14140
37%
14140
16%
32596

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
17%
720
7%
2506
3%
716
21%
716
7%
2044
January16th to endNight
23%
768
10%
2646
7%
768
29%
768
11%
1989
February1st to 15thNight
20%
704
10%
2287
5%
701
26%
701
10%
1779
February16th to endNight
23%
631
13%
1946
6%
631
32%
631
13%
1470
March1st to 15thNight
20%
720
13%
2103
7%
720
27%
720
15%
1582
March16th to endNight
30%
748
20%
1981
9%
748
38%
748
22%
1372
April1st to 15thNight
25%
658
16%
1646
5%
658
30%
658
20%
1228
April16th to endNight
31%
591
17%
1581
7%
591
37%
591
23%
1105
May1st to 15thNight
37%
330
17%
1320
15%
330
46%
330
18%
844
May16th to endNight
38%
343
13%
1369
11%
342
48%
342
19%
866
June1st to 15thNight
38%
330
9%
1320
9%
330
46%
330
14%
915
June16th to endNight
43%
330
8%
1320
11%
330
48%
330
19%
839
July1st to 15thNight
56%
310
15%
1240
22%
310
60%
310
28%
685
July16th to endNight
56%
348
12%
1306
15%
326
60%
326
25%
757
August1st to 15thNight
52%
400
15%
1381
12%
398
57%
398
24%
859
August16th to endNight
54%
652
18%
1702
9%
652
58%
652
35%
1081
September1st to 15thNight
47%
660
15%
1650
8%
660
49%
660
28%
1143
September16th to endNight
46%
657
21%
1793
14%
657
51%
657
30%
1156
October1st to 15thNight
34%
660
17%
1980
11%
660
43%
660
20%
1386
October16th to endNight
26%
704
11%
2203
6%
704
33%
704
12%
1685
November1st to 15thNight
28%
700
16%
2328
12%
700
36%
700
17%
1653
November16th to endNight
21%
720
10%
2520
6%
720
27%
720
10%
1948
December1st to 15thNight
20%
720
6%
2520
3%
720
24%
720
8%
2039
December16th to endNight
15%
768
9%
2688
4%
768
22%
768
8%
2171

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
17%8%36%5%35%45%6%32%
45646
Night
18%9%46%5%34446%32%
45505
Cloud CoverDay
18%8%36%5%3445%6%32%
45655
Night
18%9%36%5%34445%32%
45511
TransparencyDay
50%7%12%18%9%1
45333
Night
52%6%11%19%9%
45336
SeeingDay
20%10%28%24%12%4
4789
Night
22%10%29%26%9%
14172

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
22%13%6%9%5%3444421%
1432
16th to endDay
14%15%47%7%45%35%5%25%
1577
February1st to 15thDay
13%13%5%11%6%45%445%25%
1575
16th to endDay
16%13%48%6%35%45%426%
1527
March1st to 15thDay
17%9%47%6%46%45%428%
1844
16th to endDay
15%6%45%43345%5%41%
2130
April1st to 15thDay
22%9%36%5%23345%33%
1972
16th to endDay
20%7%35%5%2435%437%
2057
May1st to 15thDay
17%6%36%6%34446%34%
2301
16th to endDay
17%6%26%6%35%45%6%35%
2394
June1st to 15thDay
21%6%36%6%35%45%8%29%
2310
16th to endDay
17%6%26%5%36%6%6%8%31%
2310
July1st to 15thDay
13%425%435%6%7%9%38%
2310
16th to endDay
11%436%5%45%5%7%9%37%
2458
August1st to 15thDay
11%6%25%6%35%6%6%7%37%
2239
16th to endDay
10%425%5%25%5%5%8%42%
2136
September1st to 15thDay
16%425%5%245%5%6%40%
1980
16th to endDay
15%5%2432435%8%44%
1834
October1st to 15thDay
19%9%26%425%35%6%34%
1650
16th to endDay
26%8%36%7%44345%26%
1667
November1st to 15thDay
16%8%45%5%35%5%5%7%33%
1527
16th to endDay
24%11%47%6%3444425%
1440
December1st to 15thDay
23%13%5%9%7%35%45%5%17%
1440
16th to endDay
24%14%5%7%7%4433420%
1536
January1st to 15thNight
19%16%6%9%7%45%34419%
2506
16th to endNight
13%16%5%9%6%34447%25%
2646
February1st to 15thNight
13%11%6%11%7%45%445%24%
2285
16th to endNight
17%11%5%8%6%34445%28%
1946
March1st to 15thNight
19%10%47%6%34335%30%
2090
16th to endNight
14%8%36%5%2333441%
1981
April1st to 15thNight
23%7%35%334336%35%
1646
16th to endNight
19%7%25%5%23346%38%
1581
May1st to 15thNight
19%7%25%424446%37%
1320
16th to endNight
15%6%35%6%3445%6%39%
1367
June1st to 15thNight
19%6%25%6%35%5%6%6%32%
1320
16th to endNight
15%5%16%425%7%5%7%37%
1320
July1st to 15thNight
10%3234246%6%8%46%
1320
16th to endNight
8%324435%5%6%9%45%
1402
August1st to 15thNight
10%6%25%42446%10%40%
1391
16th to endNight
9%32443445%6%49%
1702
September1st to 15thNight
15%5%26%5%3435%6%42%
1650
16th to endNight
17%425%413235%48%
1793
October1st to 15thNight
20%7%345%3335%6%36%
1980
16th to endNight
24%8%36%5%34446%27%
2203
November1st to 15thNight
20%7%46%5%33346%33%
2328
16th to endNight
22%11%47%6%34445%24%
2520
December1st to 15thNight
23%15%46%6%24445%21%
2520
16th to endNight
25%15%5%8%6%2434320%
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
22%14%6%9%6%2434420%
1432
16th to endDay
15%14%5%8%6%45%45%5%24%
1577
February1st to 15thDay
14%13%411%7%35%445%24%
1575
16th to endDay
17%13%48%6%4445%426%
1527
March1st to 15thDay
21%8%47%6%45%44428%
1854
16th to endDay
19%6%35%433445%40%
2129
April1st to 15thDay
22%9%35%433345%33%
1972
16th to endDay
20%7%25%5%2434437%
2057
May1st to 15thDay
22%6%36%5%34437%32%
2301
16th to endDay
23%6%246%34447%32%
2394
June1st to 15thDay
21%6%36%6%45%45%7%29%
2310
16th to endDay
16%6%35%6%35%6%6%7%31%
2310
July1st to 15thDay
12%4345%36%6%6%8%38%
2310
16th to endDay
11%426%5%35%5%7%9%37%
2458
August1st to 15thDay
16%5%25%5%345%5%6%40%
2239
16th to endDay
13%5%1442445%7%43%
2136
September1st to 15thDay
16%426%42345%7%40%
1980
16th to endDay
15%5%25%42335%7%44%
1834
October1st to 15thDay
20%8%25%5%3436%6%33%
1650
16th to endDay
26%9%37%7%33336%25%
1667
November1st to 15thDay
16%8%46%5%345%5%6%33%
1527
16th to endDay
23%11%47%7%2443426%
1440
December1st to 15thDay
22%15%48%6%4445%5%17%
1440
16th to endDay
24%14%5%8%7%3433420%
1536
January1st to 15thNight
18%16%6%10%7%35%43419%
2506
16th to endNight
13%16%6%8%6%34446%25%
2646
February1st to 15thNight
13%13%6%11%7%35%445%24%
2278
16th to endNight
17%12%48%7%24436%28%
1946
March1st to 15thNight
24%10%46%6%3333430%
2103
16th to endNight
18%7%36%5%2323441%
1981
April1st to 15thNight
22%9%25%324335%35%
1646
16th to endNight
19%7%25%423345%39%
1581
May1st to 15thNight
22%6%34425%346%36%
1320
16th to endNight
19%6%25%334445%38%
1367
June1st to 15thNight
19%6%26%5%45%5%6%5%32%
1320
16th to endNight
15%5%26%5%245%6%7%37%
1320
July1st to 15thNight
10%3244346%5%8%46%
1320
16th to endNight
8%424435%5%6%9%44%
1402
August1st to 15thNight
13%5%25%3345%5%9%41%
1391
16th to endNight
13%21442435%6%50%
1702
September1st to 15thNight
15%5%26%5%34346%42%
1650
16th to endNight
16%5%15%322335%48%
1793
October1st to 15thNight
19%8%35%434346%36%
1980
16th to endNight
24%9%36%6%33445%26%
2203
November1st to 15thNight
20%8%36%5%33345%34%
2328
16th to endNight
22%11%48%6%35%435%25%
2520
December1st to 15thNight
23%16%46%6%345%4421%
2520
16th to endNight
25%14%6%7%7%2334420%
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
66%5%9%12%5%
1433
16th to endDay
60%6%12%11%7%
1577
February1st to 15thDay
61%6%11%16%3
1577
16th to endDay
58%6%10%14%8%1
1527
March1st to 15thDay
58%6%11%14%7%
1854
16th to endDay
43%6%10%19%14%5%
2130
April1st to 15thDay
52%5%7%19%12%2
1972
16th to endDay
48%47%18%16%3
2057
May1st to 15thDay
48%6%8%18%14%2
2301
16th to endDay
46%8%11%19%12%2
2398
June1st to 15thDay
53%7%9%19%8%
2310
16th to endDay
47%9%12%19%10%1
2310
July1st to 15thDay
37%8%16%24%11%
2161
16th to endDay
42%10%17%21%9%
2291
August1st to 15thDay
42%9%16%21%10%
2225
16th to endDay
36%7%18%26%10%
2136
September1st to 15thDay
41%7%14%26%10%
1980
16th to endDay
39%7%13%30%9%
1834
October1st to 15thDay
50%6%14%19%8%
1650
16th to endDay
61%7%11%12%6%
1667
November1st to 15thDay
49%7%15%18%7%
1527
16th to endDay
61%6%12%13%5%1
1440
December1st to 15thDay
67%8%11%10%2
1440
16th to endDay
68%5%10%10%5%
1536
January1st to 15thNight
68%6%9%10%4
2506
16th to endNight
60%5%10%15%7%
2646
February1st to 15thNight
62%5%10%15%5%
2287
16th to endNight
58%5%9%17%8%
1946
March1st to 15thNight
57%410%18%7%1
2103
16th to endNight
46%49%19%15%4
1981
April1st to 15thNight
53%37%19%14%1
1646
16th to endNight
46%5%8%18%17%3
1581
May1st to 15thNight
47%49%19%15%4
1320
16th to endNight
43%7%12%20%14%2
1369
June1st to 15thNight
50%8%11%20%8%1
1320
16th to endNight
43%7%13%19%16%
1320
July1st to 15thNight
31%7%14%30%14%
1240
16th to endNight
33%9%15%26%14%
1306
August1st to 15thNight
37%9%17%22%12%
1381
16th to endNight
32%7%15%31%11%
1702
September1st to 15thNight
42%6%11%27%10%
1650
16th to endNight
38%411%34%10%
1793
October1st to 15thNight
49%5%11%22%11%
1980
16th to endNight
58%6%12%16%5%
2203
November1st to 15thNight
52%5%14%17%10%
2328
16th to endNight
62%5%11%15%4
2520
December1st to 15thNight
65%6%12%11%2
2520
16th to endNight
67%5%9%11%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
33%15%21%25%31
60
16th to endDay
32%11%35%15%5%
71
February1st to 15thDay
31%22%32%14%
90
16th to endDay
30%20%22%20%5%
186
March1st to 15thDay
24%12%34%22%5%
270
16th to endDay
19%16%27%21%11%2
267
April1st to 15thDay
23%18%28%20%8%
210
16th to endDay
20%12%27%20%13%4
210
May1st to 15thDay
21%9%33%20%12%3
228
16th to endDay
16%12%32%21%14%1
267
June1st to 15thDay
26%8%29%22%10%2
255
16th to endDay
17%5%30%27%15%2
255
July1st to 15thDay
13%327%31%17%5%
245
16th to endDay
11%325%34%18%6%
270
August1st to 15thDay
12%6%20%35%18%6%
253
16th to endDay
9%227%29%18%11%
268
September1st to 15thDay
18%5%22%18%21%13%
255
16th to endDay
17%9%25%22%15%10%
254
October1st to 15thDay
21%10%26%23%14%3
255
16th to endDay
29%15%26%20%7%
255
November1st to 15thDay
17%11%29%25%12%2
181
16th to endDay
30%16%26%25%1
60
December1st to 15thDay
21%16%36%23%1
60
16th to endDay
40%17%34%7%
64
January1st to 15thNight
24%16%32%21%4
720
16th to endNight
22%10%35%26%5%
768
February1st to 15thNight
21%11%37%24%4
704
16th to endNight
24%12%33%23%5%
631
March1st to 15thNight
24%13%36%23%2
720
16th to endNight
19%15%27%26%10%
748
April1st to 15thNight
25%12%32%24%4
658
16th to endNight
23%12%28%26%8%
591
May1st to 15thNight
21%7%29%30%9%1
330
16th to endNight
18%5%33%29%12%
343
June1st to 15thNight
20%6%28%34%9%
330
16th to endNight
17%329%35%13%1
330
July1st to 15thNight
10%124%44%16%
310
16th to endNight
8%128%42%17%1
348
August1st to 15thNight
16%320%37%20%2
400
16th to endNight
11%323%38%21%1
652
September1st to 15thNight
18%5%24%31%18%1
660
16th to endNight
19%7%22%27%21%1
657
October1st to 15thNight
23%7%28%26%12%1
660
16th to endNight
29%11%25%25%7%
704
November1st to 15thNight
24%9%32%20%12%
700
16th to endNight
29%15%25%20%8%
720
December1st to 15thNight
31%12%30%21%3
720
16th to endNight
33%12%30%18%41
768
Page generated at 2017-03-27 11:15:19. Version ac04

Copyright 2017 A. Danko


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