Rideau Ferry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rideau Ferry Observatory clear sky chart from 2005-11-06 to 2024-01-10.

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
27%
22616
14%
74710
8%
22578
35%
22578
16%
52654

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%
760
9%
2647
3%
757
22%
757
8%
2086
January11th to 20thNight
16%
720
9%
2520
4%
720
23%
720
8%
1984
January21st to endNight
20%
792
13%
2664
7%
792
27%
792
11%
1965
February1st to 10thNight
12%
720
10%
2340
2%
720
21%
720
9%
1818
February11th to 20thNight
15%
700
14%
2275
4%
700
28%
700
13%
1659
February21st to endNight
18%
592
15%
1776
6%
592
29%
592
13%
1331
March1st to 10thNight
20%
720
15%
2138
8%
720
28%
720
15%
1569
March11th to 20thNight
20%
720
17%
1979
6%
720
31%
720
17%
1420
March21st to endNight
25%
792
20%
2075
8%
792
34%
792
20%
1477
April1st to 10thNight
20%
720
16%
1800
4%
720
27%
720
20%
1304
April11th to 20thNight
22%
711
18%
1775
5%
711
29%
711
20%
1269
April21st to endNight
28%
635
16%
1715
7%
635
33%
635
19%
1268
May1st to 10thNight
33%
360
17%
1440
13%
360
42%
360
17%
941
May11th to 20thNight
32%
354
22%
1416
16%
354
49%
354
19%
861
May21st to endNight
33%
388
15%
1551
11%
388
46%
388
24%
885
June1st to 10thNight
37%
360
11%
1440
9%
360
47%
360
17%
936
June11th to 20thNight
38%
360
14%
1440
15%
360
48%
360
21%
856
June21st to endNight
42%
360
12%
1440
14%
360
48%
360
18%
921
July1st to 10thNight
46%
350
15%
1400
18%
350
54%
350
26%
766
July11th to 20thNight
50%
348
17%
1392
21%
348
57%
348
25%
798
July21st to endNight
50%
394
16%
1486
16%
372
56%
372
26%
838
August1st to 10thNight
48%
432
17%
1496
13%
430
55%
430
26%
889
August11th to 20thNight
52%
537
18%
1601
13%
537
56%
537
31%
985
August21st to endNight
44%
792
19%
1980
7%
792
49%
792
33%
1293
September1st to 10thNight
42%
720
18%
1800
7%
720
47%
720
32%
1211
September11th to 20thNight
49%
720
23%
1800
12%
720
54%
720
37%
1139
September21st to endNight
40%
720
23%
2042
16%
720
46%
720
27%
1328
October1st to 10thNight
33%
720
17%
2160
11%
720
41%
720
19%
1491
October11th to 20thNight
25%
720
14%
2160
7%
720
33%
720
16%
1556
October21st to endNight
22%
792
13%
2494
6%
792
33%
792
14%
1838
November1st to 10thNight
25%
740
18%
2407
9%
740
36%
740
17%
1628
November11th to 20thNight
20%
760
17%
2650
9%
760
33%
760
14%
1830
November21st to endNight
18%
760
11%
2660
6%
760
26%
760
10%
2023
December1st to 10thNight
13%
760
7%
2660
3%
760
20%
760
7%
2136
December11th to 20thNight
17%
760
11%
3244
5%
759
25%
759
8%
2415
December21st to endNight
12%
827
5%
4847
2%
817
18%
817
4%
3940

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
18%9%47%6%35%45%7%33%
74704
Night
18%10%47%6%3445%6%33%
74963
TransparencyDay
52%411%21%11%1
74409
Night
53%411%20%11%1
74792
SeeingDay
23%16%30%19%8%3
13376
Night
23%14%30%24%9%1
22629

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
16%17%7%9%8%4444324%
1509
11th to 20thDay
19%16%6%8%7%35%44424%
1440
21st to endDay
14%13%5%10%10%46%5%46%23%
1688
February1st to 10thDay
18%13%5%12%7%46%45%6%22%
1620
11th to 20thDay
13%15%6%8%7%45%346%29%
1573
21st to endDay
21%14%5%8%6%45%45%5%23%
1479
March1st to 10thDay
15%12%6%10%8%45%44429%
1816
11th to 20thDay
17%12%47%7%36%35%5%31%
1980
21st to endDay
20%11%46%433345%38%
2280
April1st to 10thDay
20%11%5%6%5%34446%32%
2160
11th to 20thDay
21%8%37%443445%37%
2134
21st to endDay
23%9%36%6%3445%6%32%
2258
May1st to 10thDay
19%8%37%5%345%5%6%34%
2520
11th to 20thDay
16%7%46%5%35%348%39%
2478
21st to endDay
14%5%35%6%45%6%6%7%39%
2725
June1st to 10thDay
22%7%36%5%35%5%5%7%30%
2520
11th to 20thDay
16%5%36%5%36%5%5%9%38%
2520
21st to endDay
17%8%36%6%46%5%5%7%33%
2520
July1st to 10thDay
11%5%36%6%26%5%6%9%41%
2520
11th to 20thDay
13%5%36%5%35%5%6%10%38%
2520
21st to endDay
12%5%35%6%36%6%8%9%37%
2744
August1st to 10thDay
13%6%35%7%45%5%6%8%39%
2430
11th to 20thDay
13%5%25%6%35%5%6%10%39%
2281
21st to endDay
14%5%25%7%35%5%6%8%41%
2376
September1st to 10thDay
14%5%25%5%35%6%6%8%41%
2160
11th to 20thDay
13%5%25%6%3446%7%46%
2160
21st to endDay
18%6%25%6%345%5%6%40%
1916
October1st to 10thDay
21%8%37%5%33446%37%
1800
11th to 20thDay
21%9%37%6%35%5%5%7%28%
1800
21st to endDay
27%11%36%7%33445%26%
1861
November1st to 10thDay
15%8%36%7%46%5%5%6%34%
1671
11th to 20thDay
18%12%48%7%3445%6%29%
1527
21st to endDay
21%15%48%7%45%45%5%22%
1520
December1st to 10thDay
23%16%5%9%7%35%45%6%17%
1520
11th to 20thDay
21%14%5%8%6%35%445%25%
1906
21st to endDay
27%16%6%10%6%3333320%
2772
January1st to 10thNight
18%16%6%10%8%44445%21%
2647
11th to 20thNight
19%16%5%10%8%35%445%22%
2520
21st to endNight
13%12%6%11%8%5%5%446%28%
2664
February1st to 10thNight
16%15%6%10%7%445%6%6%21%
2340
11th to 20thNight
14%14%6%8%7%34445%29%
2273
21st to endNight
16%13%6%7%7%4445%6%29%
1776
March1st to 10thNight
16%12%5%9%6%35%45%430%
2128
11th to 20thNight
18%13%5%6%5%33445%34%
1979
21st to endNight
18%9%37%5%23445%38%
2075
April1st to 10thNight
21%8%5%6%6%3345%5%34%
1800
11th to 20thNight
20%8%37%6%33445%38%
1775
21st to endNight
21%11%36%6%3445%6%32%
1715
May1st to 10thNight
22%7%26%5%35%5%46%36%
1440
11th to 20thNight
15%7%36%6%3445%6%41%
1415
21st to endNight
13%6%35%425%45%9%45%
1550
June1st to 10thNight
18%5%36%6%36%5%6%8%35%
1440
11th to 20thNight
15%6%35%5%345%6%7%42%
1440
21st to endNight
16%6%36%5%45%6%5%9%36%
1440
July1st to 10thNight
9%5%25%6%45%46%8%45%
1440
11th to 20thNight
12%5%25%5%35%6%7%8%42%
1440
21st to endNight
10%425%5%36%6%6%9%46%
1574
August1st to 10thNight
9%5%27%5%35%5%8%8%43%
1506
11th to 20thNight
10%6%35%5%3447%8%44%
1601
21st to endNight
11%5%35%435%5%6%8%45%
1980
September1st to 10thNight
12%5%36%6%33447%46%
1800
11th to 20thNight
14%5%2342345%7%50%
1800
21st to endNight
17%6%25%5%3445%7%43%
2042
October1st to 10thNight
18%8%46%5%35%45%8%36%
2160
11th to 20thNight
23%8%36%6%345%5%7%31%
2160
21st to endNight
24%10%37%5%3445%6%28%
2494
November1st to 10thNight
19%10%35%4345%45%36%
2407
11th to 20thNight
18%11%47%6%35%45%5%33%
2650
21st to endNight
21%13%47%7%3445%7%25%
2660
December1st to 10thNight
20%18%6%10%6%35%44419%
2660
11th to 20thNight
22%14%48%6%3433427%
3288
21st to endNight
30%16%410%6%3443416%
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
65%312%14%6%1
1510
11th to 20thDay
65%48%12%10%1
1440
21st to endDay
63%5%9%14%8%1
1688
February1st to 10thDay
64%48%18%5%1
1620
11th to 20thDay
58%310%17%10%1
1582
21st to endDay
65%39%11%9%1
1479
March1st to 10thDay
60%38%17%10%1
1819
11th to 20thDay
57%410%16%12%3
1980
21st to endDay
51%37%19%14%6%
2280
April1st to 10thDay
54%46%19%13%3
2160
11th to 20thDay
50%27%21%17%2
2134
21st to endDay
55%39%16%14%4
2258
May1st to 10thDay
50%49%18%16%3
2520
11th to 20thDay
45%49%24%15%2
2482
21st to endDay
43%6%14%21%13%2
2725
June1st to 10thDay
53%49%19%13%1
2520
11th to 20thDay
43%411%26%13%2
2520
21st to endDay
49%5%13%20%11%1
2520
July1st to 10thDay
38%6%11%29%15%1
2450
11th to 20thDay
40%6%16%28%11%
2445
21st to endDay
42%7%15%25%11%
2591
August1st to 10thDay
43%5%15%26%11%
2416
11th to 20thDay
40%5%16%26%12%1
2281
21st to endDay
41%414%27%13%1
2376
September1st to 10thDay
41%5%13%27%13%1
2160
11th to 20thDay
37%5%12%31%15%1
2160
21st to endDay
45%5%13%27%10%
1916
October1st to 10thDay
50%311%23%12%1
1800
11th to 20thDay
55%414%19%7%1
1800
21st to endDay
60%411%17%8%1
1861
November1st to 10thDay
50%415%22%9%1
1671
11th to 20thDay
56%412%16%10%1
1527
21st to endDay
65%5%12%11%7%
1520
December1st to 10thDay
69%412%11%4
1520
11th to 20thDay
65%413%13%4
1906
21st to endDay
72%37%14%4
2772
January1st to 10thNight
67%410%14%5%
2647
11th to 20thNight
66%49%12%8%1
2520
21st to endNight
59%48%17%10%1
2664
February1st to 10thNight
64%49%16%6%1
2340
11th to 20thNight
58%39%21%8%
2275
21st to endNight
58%48%18%11%1
1776
March1st to 10thNight
57%312%16%11%1
2138
11th to 20thNight
53%311%19%12%2
1980
21st to endNight
49%47%20%16%4
2075
April1st to 10thNight
52%37%22%14%2
1800
11th to 20thNight
50%38%20%18%2
1775
21st to endNight
54%47%16%15%3
1715
May1st to 10thNight
49%47%19%16%5%
1440
11th to 20thNight
44%47%24%18%3
1416
21st to endNight
37%5%17%20%18%3
1551
June1st to 10thNight
47%6%13%22%12%1
1440
11th to 20thNight
42%412%22%18%2
1440
21st to endNight
45%7%13%22%12%1
1440
July1st to 10thNight
34%6%11%27%18%3
1400
11th to 20thNight
37%5%13%31%14%
1392
21st to endNight
35%7%16%28%14%1
1486
August1st to 10thNight
38%5%17%27%13%1
1496
11th to 20thNight
38%415%29%13%1
1601
21st to endNight
37%5%14%29%13%1
1980
September1st to 10thNight
38%6%11%30%14%1
1800
11th to 20thNight
34%414%34%12%1
1800
21st to endNight
41%411%32%10%1
2042
October1st to 10thNight
48%5%9%23%13%1
2160
11th to 20thNight
54%412%20%9%1
2160
21st to endNight
57%413%16%9%
2494
November1st to 10thNight
49%5%13%22%11%1
2407
11th to 20thNight
53%412%20%10%2
2650
21st to endNight
61%5%11%17%5%
2660
December1st to 10thNight
69%410%13%4
2660
11th to 20thNight
62%311%16%8%1
3288
21st to endNight
73%39%13%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
27%22%33%14%41
178
11th to 20thDay
36%16%30%16%31
160
21st to endDay
25%20%33%17%5%
222
February1st to 10thDay
37%23%32%8%
240
11th to 20thDay
31%28%34%5%1
240
21st to endDay
34%20%33%10%2
345
March1st to 10thDay
25%20%35%15%5%
420
11th to 20thDay
30%18%33%14%4
420
21st to endDay
32%21%27%12%8%
462
April1st to 10thDay
30%21%29%14%7%
420
11th to 20thDay
31%20%22%16%8%3
412
21st to endDay
29%19%31%13%6%2
420
May1st to 10thDay
25%18%30%19%6%3
423
11th to 20thDay
19%17%35%19%7%2
447
21st to endDay
19%14%32%23%10%2
485
June1st to 10thDay
24%13%32%21%7%2
450
11th to 20thDay
16%17%30%23%11%2
450
21st to endDay
20%12%30%23%11%4
450
July1st to 10thDay
13%7%29%32%15%3
445
11th to 20thDay
14%12%29%26%15%4
444
21st to endDay
14%9%33%30%11%4
488
August1st to 10thDay
15%9%28%30%14%4
446
11th to 20thDay
14%6%28%30%15%7%
439
21st to endDay
16%10%32%24%11%7%
495
September1st to 10thDay
14%11%32%23%12%7%
450
11th to 20thDay
13%10%26%25%16%10%
450
21st to endDay
20%11%28%23%13%4
450
October1st to 10thDay
26%16%25%17%11%4
450
11th to 20thDay
28%20%28%16%5%2
450
21st to endDay
31%20%26%19%4
435
November1st to 10thDay
26%18%29%18%8%
365
11th to 20thDay
28%19%33%13%5%3
187
21st to endDay
29%23%34%11%3
180
December1st to 10thDay
30%24%30%14%2
180
11th to 20thDay
34%24%29%9%31
180
21st to endDay
35%18%32%12%31
198
January1st to 10thNight
29%19%31%18%3
760
11th to 20thNight
30%16%29%20%41
720
21st to endNight
20%16%35%24%5%
792
February1st to 10thNight
26%22%33%17%2
720
11th to 20thNight
23%18%39%17%3
703
21st to endNight
25%19%33%19%4
592
March1st to 10thNight
26%16%32%22%4
720
11th to 20thNight
26%19%29%20%5%1
720
21st to endNight
23%16%31%22%8%1
792
April1st to 10thNight
27%15%31%23%3
720
11th to 20thNight
26%19%29%18%7%1
711
21st to endNight
26%13%27%25%9%
635
May1st to 10thNight
25%9%26%26%11%2
360
11th to 20thNight
16%11%34%32%7%
354
21st to endNight
13%10%39%26%12%1
389
June1st to 10thNight
16%9%29%35%10%1
360
11th to 20thNight
17%9%29%31%13%1
360
21st to endNight
18%5%28%34%14%1
360
July1st to 10thNight
9%7%31%37%16%1
350
11th to 20thNight
13%5%28%36%17%1
348
21st to endNight
11%429%42%13%1
394
August1st to 10thNight
12%6%26%36%19%1
432
11th to 20thNight
11%5%22%36%24%2
537
21st to endNight
12%8%31%31%16%3
792
September1st to 10thNight
14%7%31%29%17%1
720
11th to 20thNight
17%7%22%29%20%4
720
21st to endNight
19%10%25%24%19%2
720
October1st to 10thNight
23%13%26%21%14%2
720
11th to 20thNight
27%12%31%22%7%1
720
21st to endNight
30%13%27%23%6%
792
November1st to 10thNight
27%14%30%21%8%
740
11th to 20thNight
26%18%31%17%9%
760
21st to endNight
29%17%28%19%6%
760
December1st to 10thNight
31%18%30%18%3
760
11th to 20thNight
28%19%31%19%31
760
21st to endNight
34%17%29%18%2
836
Page generated at 2024-01-07 10:06:56. Version ac07

Copyright 2024 Attilla Danko


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