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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 2018-03-11.

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%
15351
13%
49136
8%
15319
37%
15319
16%
35311

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%
780
7%
2716
3%
776
22%
776
7%
2205
January16th to endNight
22%
832
10%
2866
6%
832
28%
832
11%
2161
February1st to 15thNight
19%
764
10%
2482
4%
761
27%
761
11%
1918
February16th to endNight
22%
683
13%
2106
6%
683
32%
683
13%
1585
March1st to 15thNight
19%
764
12%
2234
7%
764
26%
764
14%
1708
March16th to endNight
30%
768
20%
2031
9%
768
37%
768
21%
1412
April1st to 15thNight
26%
718
15%
1796
5%
718
30%
718
20%
1336
April16th to endNight
30%
645
17%
1725
7%
645
36%
645
22%
1220
May1st to 15thNight
35%
360
16%
1440
14%
360
44%
360
16%
952
May16th to endNight
36%
375
12%
1497
10%
374
46%
374
18%
959
June1st to 15thNight
39%
360
9%
1440
9%
360
47%
360
15%
980
June16th to endNight
42%
360
8%
1440
11%
360
47%
360
18%
930
July1st to 15thNight
55%
340
14%
1360
21%
340
59%
340
27%
762
July16th to endNight
57%
376
14%
1418
17%
354
60%
354
25%
816
August1st to 15thNight
53%
437
14%
1508
12%
435
57%
435
23%
951
August16th to endNight
55%
712
19%
1858
10%
712
58%
712
35%
1175
September1st to 15thNight
48%
720
15%
1800
8%
720
50%
720
29%
1243
September16th to endNight
49%
717
23%
1956
15%
717
53%
717
31%
1247
October1st to 15thNight
35%
720
17%
2160
11%
720
44%
720
21%
1488
October16th to endNight
25%
768
12%
2404
6%
768
33%
768
13%
1827
November1st to 15thNight
28%
760
16%
2527
11%
760
36%
760
16%
1794
November16th to endNight
21%
780
10%
2730
6%
780
26%
780
10%
2109
December1st to 15thNight
20%
780
7%
2730
3%
780
24%
780
8%
2202
December16th to endNight
15%
832
10%
2912
3%
832
23%
832
8%
2331

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%
49499
Night
18%9%36%5%34446%32%
49305
Cloud CoverDay
18%8%36%5%3445%6%32%
49508
Night
18%9%36%5%34445%32%
49311
TransparencyDay
50%7%12%19%9%1
49186
Night
52%6%11%19%9%
49136
SeeingDay
21%11%28%22%11%3
5982
Night
22%10%29%26%10%
15351

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%14%5%9%5%345%4420%
1552
16th to endDay
14%15%5%7%7%4435%5%24%
1709
February1st to 15thDay
13%13%5%10%7%45%445%25%
1710
16th to endDay
17%13%47%6%35%45%425%
1653
March1st to 15thDay
17%10%48%6%46%44427%
1950
16th to endDay
16%6%45%43345%5%40%
2193
April1st to 15thDay
23%8%35%423345%33%
2152
16th to endDay
20%7%35%5%2434436%
2244
May1st to 15thDay
19%7%36%5%34446%33%
2511
16th to endDay
17%6%26%6%35%45%7%35%
2618
June1st to 15thDay
21%5%36%6%45%448%29%
2520
16th to endDay
18%5%26%5%36%6%6%8%30%
2520
July1st to 15thDay
13%425%435%6%6%9%37%
2520
16th to endDay
12%426%5%45%5%6%9%37%
2654
August1st to 15thDay
11%6%25%6%36%6%6%7%37%
2442
16th to endDay
10%425%5%25%5%5%9%43%
2331
September1st to 15thDay
16%415%5%245%5%6%42%
2160
16th to endDay
14%5%2432435%7%46%
2001
October1st to 15thDay
19%9%26%435%346%34%
1800
16th to endDay
25%7%36%7%44345%27%
1818
November1st to 15thDay
16%9%45%5%35%5%5%6%32%
1657
16th to endDay
23%11%36%6%35%44425%
1560
December1st to 15thDay
21%13%5%8%7%345%5%5%18%
1560
16th to endDay
23%14%5%7%6%4433421%
1664
January1st to 15thNight
19%15%6%9%7%35%34419%
2716
16th to endNight
14%16%5%8%6%34446%25%
2866
February1st to 15thNight
13%12%6%11%7%45%445%24%
2480
16th to endNight
17%11%5%8%6%34445%28%
2106
March1st to 15thNight
19%12%5%8%6%3433428%
2221
16th to endNight
15%8%36%5%2333441%
2031
April1st to 15thNight
23%7%35%324336%35%
1796
16th to endNight
19%7%35%5%24446%37%
1725
May1st to 15thNight
21%7%35%324446%35%
1440
16th to endNight
16%6%35%6%3445%6%38%
1495
June1st to 15thNight
18%5%25%6%35%5%6%6%33%
1440
16th to endNight
16%5%16%5%25%7%6%7%36%
1440
July1st to 15thNight
10%3235%246%6%8%46%
1440
16th to endNight
9%424435%5%5%8%46%
1514
August1st to 15thNight
10%6%25%4245%6%10%40%
1518
16th to endNight
9%32443445%6%49%
1858
September1st to 15thNight
15%426%5%3335%6%43%
1800
16th to endNight
16%415%413335%49%
1956
October1st to 15thNight
20%6%345%33346%37%
2160
16th to endNight
24%8%36%5%34446%27%
2404
November1st to 15thNight
21%7%36%5%33346%33%
2527
16th to endNight
22%11%38%6%34445%25%
2730
December1st to 15thNight
22%15%46%6%34445%21%
2730
16th to endNight
23%15%5%8%6%2434421%
2912

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
21%14%6%9%6%3444420%
1552
16th to endDay
15%14%6%8%6%45%45%5%23%
1709
February1st to 15thDay
14%14%411%7%35%445%24%
1710
16th to endDay
18%13%47%6%4445%426%
1653
March1st to 15thDay
21%9%47%6%45%43427%
1960
16th to endDay
19%6%35%433445%39%
2192
April1st to 15thDay
23%9%35%433345%33%
2152
16th to endDay
20%8%25%5%2434437%
2244
May1st to 15thDay
24%6%36%5%34436%30%
2511
16th to endDay
23%6%246%34447%32%
2618
June1st to 15thDay
21%6%36%5%45%45%7%29%
2520
16th to endDay
17%6%25%6%45%6%6%7%30%
2520
July1st to 15thDay
13%5%345%36%6%6%8%38%
2520
16th to endDay
12%426%5%35%5%7%9%37%
2654
August1st to 15thDay
15%425%5%445%5%6%39%
2442
16th to endDay
13%5%1442445%8%43%
2331
September1st to 15thDay
16%426%42345%7%41%
2160
16th to endDay
14%5%2442335%7%45%
2001
October1st to 15thDay
20%8%26%5%3435%6%34%
1800
16th to endDay
25%8%27%7%34436%26%
1818
November1st to 15thDay
16%8%46%5%345%5%6%32%
1657
16th to endDay
23%11%46%7%3443425%
1560
December1st to 15thDay
21%15%48%7%4445%5%18%
1560
16th to endDay
23%14%47%7%3433421%
1664
January1st to 15thNight
18%15%6%10%6%35%43419%
2716
16th to endNight
14%16%5%8%6%34446%25%
2866
February1st to 15thNight
12%13%5%10%8%35%445%25%
2473
16th to endNight
17%11%48%7%24436%28%
2106
March1st to 15thNight
23%11%46%6%3332428%
2234
16th to endNight
19%7%36%42323441%
2031
April1st to 15thNight
23%9%25%324335%35%
1796
16th to endNight
19%7%25%424346%37%
1725
May1st to 15thNight
23%7%35%424346%34%
1440
16th to endNight
19%6%25%43445%6%37%
1495
June1st to 15thNight
19%6%26%5%45%5%5%6%32%
1440
16th to endNight
16%5%26%4345%6%7%36%
1440
July1st to 15thNight
10%3244346%5%8%45%
1440
16th to endNight
9%424435%5%5%9%45%
1514
August1st to 15thNight
13%5%25%3345%5%9%40%
1518
16th to endNight
12%21443435%6%50%
1858
September1st to 15thNight
14%5%25%434346%42%
1800
16th to endNight
15%5%15%422336%48%
1956
October1st to 15thNight
18%7%35%423346%38%
2160
16th to endNight
23%9%35%6%34445%27%
2404
November1st to 15thNight
21%8%36%5%33345%34%
2527
16th to endNight
21%11%48%6%34335%25%
2730
December1st to 15thNight
22%16%46%6%345%45%21%
2730
16th to endNight
23%14%6%7%7%2434421%
2912

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%
1553
16th to endDay
61%6%12%11%7%
1709
February1st to 15thDay
61%6%11%16%4
1712
16th to endDay
58%5%10%14%8%1
1653
March1st to 15thDay
60%5%11%14%7%
1960
16th to endDay
44%6%10%18%14%5%
2193
April1st to 15thDay
52%47%19%12%2
2152
16th to endDay
49%47%18%15%3
2244
May1st to 15thDay
50%6%8%18%13%2
2511
16th to endDay
47%8%12%18%11%1
2622
June1st to 15thDay
53%7%10%19%8%
2520
16th to endDay
47%9%12%18%9%
2520
July1st to 15thDay
38%8%16%24%11%
2371
16th to endDay
42%9%16%21%9%
2487
August1st to 15thDay
42%9%16%21%9%
2428
16th to endDay
36%7%17%27%9%
2331
September1st to 15thDay
40%7%13%26%11%
2160
16th to endDay
37%6%13%32%9%
2001
October1st to 15thDay
50%6%13%20%8%
1800
16th to endDay
59%7%12%13%6%
1818
November1st to 15thDay
50%7%14%18%7%
1657
16th to endDay
61%6%11%13%5%1
1560
December1st to 15thDay
66%8%11%10%2
1560
16th to endDay
66%5%10%11%5%
1664
January1st to 15thNight
68%5%9%10%4
2716
16th to endNight
60%5%10%15%7%
2866
February1st to 15thNight
62%5%10%15%5%
2482
16th to endNight
57%5%9%17%9%
2106
March1st to 15thNight
59%49%17%7%1
2234
16th to endNight
46%49%19%15%4
2031
April1st to 15thNight
52%47%19%14%1
1796
16th to endNight
47%5%8%18%16%3
1725
May1st to 15thNight
49%48%18%14%4
1440
16th to endNight
44%7%13%19%13%2
1497
June1st to 15thNight
48%8%11%21%9%1
1440
16th to endNight
43%8%13%18%15%
1440
July1st to 15thNight
32%7%14%29%14%
1360
16th to endNight
33%9%15%27%14%
1418
August1st to 15thNight
37%10%17%22%11%
1508
16th to endNight
32%7%16%32%11%
1858
September1st to 15thNight
42%6%11%27%11%
1800
16th to endNight
37%5%11%34%10%
1956
October1st to 15thNight
47%5%11%23%11%
2160
16th to endNight
57%6%12%16%5%
2404
November1st to 15thNight
52%5%13%17%9%
2527
16th to endNight
62%5%11%15%4
2730
December1st to 15thNight
65%7%12%11%3
2730
16th to endNight
67%49%12%6%
2912

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
30%14%27%22%41
90
16th to endDay
30%12%38%14%3
107
February1st to 15thDay
30%22%32%14%
135
16th to endDay
31%24%21%17%4
234
March1st to 15thDay
27%11%35%19%5%
312
16th to endDay
22%16%27%20%11%2
288
April1st to 15thDay
25%20%28%17%7%
270
16th to endDay
24%15%27%17%11%3
270
May1st to 15thDay
26%10%31%18%10%2
288
16th to endDay
18%13%32%21%12%1
331
June1st to 15thDay
24%8%32%23%8%2
315
16th to endDay
19%9%30%25%13%1
315
July1st to 15thDay
14%429%30%15%5%
305
16th to endDay
12%326%32%17%6%
326
August1st to 15thDay
11%6%23%33%18%6%
313
16th to endDay
9%5%27%28%18%11%
332
September1st to 15thDay
18%6%22%20%20%12%
315
16th to endDay
14%8%22%22%19%12%
314
October1st to 15thDay
21%10%27%23%13%3
315
16th to endDay
27%16%25%22%7%
310
November1st to 15thDay
20%12%28%24%11%1
221
16th to endDay
27%23%30%17%1
90
December1st to 15thDay
21%18%36%20%3
90
16th to endDay
37%22%28%11%
96
January1st to 15thNight
24%15%33%20%5%
780
16th to endNight
22%11%35%25%5%
832
February1st to 15thNight
21%11%38%23%4
764
16th to endNight
24%12%33%24%4
683
March1st to 15thNight
24%13%35%22%2
764
16th to endNight
20%15%27%26%10%
768
April1st to 15thNight
27%12%31%24%4
718
16th to endNight
23%13%28%25%8%
645
May1st to 15thNight
23%7%28%30%8%1
360
16th to endNight
19%5%33%28%11%
375
June1st to 15thNight
20%5%28%35%9%
360
16th to endNight
18%329%35%12%1
360
July1st to 15thNight
11%225%44%15%
340
16th to endNight
9%126%43%17%1
376
August1st to 15thNight
15%219%38%21%1
437
16th to endNight
10%422%37%22%2
712
September1st to 15thNight
17%5%24%32%19%1
720
16th to endNight
18%7%20%26%24%2
717
October1st to 15thNight
22%7%28%26%13%1
720
16th to endNight
28%12%26%24%7%
768
November1st to 15thNight
25%9%31%21%11%
760
16th to endNight
29%16%25%20%8%
780
December1st to 15thNight
31%12%31%21%3
780
16th to endNight
32%12%31%18%31
832
Page generated at 2018-03-12 13:28:14. Version ac04

Copyright 2018 A. Danko


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