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 2005-11-05 to

2017-09-12
.

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
28%
14672
14%
46807
8%
14644
35%
14644
17%
32880

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
14%
720
7%
2506
2%
716
20%
716
7%
1997
January16th to endNight
19%
768
12%
2616
6%
768
26%
768
11%
1953
February1st to 15thNight
16%
701
9%
2287
4%
701
23%
701
10%
1758
February16th to endNight
19%
631
14%
1952
6%
631
30%
631
13%
1448
March1st to 15thNight
19%
720
14%
2085
6%
720
27%
720
16%
1515
March16th to endNight
29%
768
20%
2043
9%
768
37%
768
23%
1407
April1st to 15thNight
21%
718
16%
1796
5%
718
27%
718
19%
1297
April16th to endNight
29%
662
18%
1742
8%
662
35%
662
22%
1220
May1st to 15thNight
35%
360
17%
1440
16%
360
45%
360
18%
937
May16th to endNight
32%
374
14%
1497
10%
374
45%
374
20%
911
June1st to 15thNight
35%
360
10%
1440
9%
360
45%
360
16%
951
June16th to endNight
41%
360
10%
1440
12%
360
46%
360
19%
909
July1st to 15thNight
48%
340
15%
1360
21%
340
54%
340
28%
732
July16th to endNight
55%
376
14%
1418
17%
354
60%
354
28%
791
August1st to 15thNight
48%
470
16%
1541
12%
468
54%
468
27%
929
August16th to endNight
51%
708
22%
1854
11%
708
57%
708
39%
1114
September1st to 15thNight
44%
707
18%
1768
8%
707
48%
707
32%
1187
September16th to endNight
45%
657
22%
1799
14%
657
50%
657
31%
1143
October1st to 15thNight
32%
660
18%
1980
11%
660
41%
660
19%
1387
October16th to endNight
22%
704
10%
2184
4%
704
30%
704
13%
1653
November1st to 15thNight
24%
700
18%
2331
12%
700
34%
700
17%
1596
November16th to endNight
20%
720
13%
2520
7%
720
28%
720
10%
1913
December1st to 15thNight
15%
720
6%
2520
2%
720
19%
720
8%
1983
December16th to endNight
13%
768
9%
2688
4%
768
18%
768
8%
2149

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%9%36%5%34446%32%
47861
Night
17%9%46%5%34446%33%
46976
Cloud CoverDay
18%9%36%6%34446%32%
47870
Night
17%9%46%5%34446%32%
46982
TransparencyDay
51%411%20%10%1
47548
Night
52%411%20%10%1
46807
SeeingDay
23%12%29%20%10%4
5458
Night
23%12%29%24%9%
14676

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
20%16%5%7%7%4334323%
1432
16th to endDay
13%14%5%9%10%35%435%22%
1605
February1st to 15thDay
14%13%5%12%7%36%345%22%
1575
16th to endDay
19%14%5%6%6%45%335%25%
1520
March1st to 15thDay
17%11%5%8%9%46%33326%
1863
16th to endDay
16%8%35%42434440%
2181
April1st to 15thDay
22%10%45%323345%33%
2152
16th to endDay
19%8%26%423346%36%
2226
May1st to 15thDay
19%7%36%5%2345%6%33%
2511
16th to endDay
15%5%35%5%345%5%7%36%
2618
June1st to 15thDay
22%6%26%435%45%8%31%
2520
16th to endDay
17%6%25%5%36%5%48%33%
2520
July1st to 15thDay
11%5%36%426%5%6%9%38%
2520
16th to endDay
12%5%25%6%36%5%7%9%34%
2654
August1st to 15thDay
12%6%26%7%345%5%7%37%
2408
16th to endDay
12%4146%35%5%5%8%42%
2336
September1st to 15thDay
17%5%25%424447%41%
2112
16th to endDay
16%5%245%2335%5%44%
1830
October1st to 15thDay
20%8%26%5%33446%34%
1650
16th to endDay
27%10%46%7%2333425%
1686
November1st to 15thDay
14%8%37%7%45%5%46%33%
1526
16th to endDay
22%13%47%5%3345%5%25%
1440
December1st to 15thDay
23%14%5%8%6%34445%19%
1440
16th to endDay
24%15%5%6%5%35%43321%
1536
January1st to 15thNight
19%15%5%9%8%34335%20%
2506
16th to endNight
14%13%6%9%6%44436%25%
2616
February1st to 15thNight
14%14%6%9%6%445%5%5%22%
2285
16th to endNight
16%13%5%7%6%34345%28%
1952
March1st to 15thNight
19%11%5%7%5%2344432%
2072
16th to endNight
16%8%46%42335%5%40%
2043
April1st to 15thNight
23%8%35%5%2343434%
1796
16th to endNight
18%8%25%5%23446%38%
1742
May1st to 15thNight
20%8%26%424435%36%
1440
16th to endNight
14%6%35%42446%7%39%
1495
June1st to 15thNight
19%6%35%5%35%35%6%34%
1440
16th to endNight
14%6%25%5%36%5%6%7%37%
1440
July1st to 15thNight
9%5%245%35%45%8%46%
1440
16th to endNight
9%314425%6%6%9%45%
1514
August1st to 15thNight
9%5%26%4345%7%8%41%
1551
16th to endNight
9%32432445%8%50%
1854
September1st to 15thNight
15%425%5%33345%44%
1768
16th to endNight
16%5%24323346%48%
1799
October1st to 15thNight
20%6%35%42435%6%34%
1980
16th to endNight
26%10%36%5%23446%26%
2184
November1st to 15thNight
18%11%35%424445%34%
2331
16th to endNight
22%12%5%7%6%34345%25%
2520
December1st to 15thNight
20%17%5%9%6%2434421%
2520
16th to endNight
24%15%5%8%6%24435%19%
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
20%17%48%7%3443422%
1432
16th to endDay
13%15%5%9%9%35%445%22%
1605
February1st to 15thDay
15%13%5%12%8%35%436%22%
1575
16th to endDay
19%14%5%7%6%34435%24%
1520
March1st to 15thDay
19%11%49%8%45%33425%
1873
16th to endDay
17%8%46%42333440%
2180
April1st to 15thDay
21%11%45%323335%33%
2152
16th to endDay
19%8%36%5%23446%36%
2226
May1st to 15thDay
19%7%36%6%24446%33%
2511
16th to endDay
16%6%26%5%25%45%8%37%
2618
June1st to 15thDay
22%6%35%5%25%45%7%30%
2520
16th to endDay
17%6%25%6%35%5%5%7%33%
2520
July1st to 15thDay
12%5%25%5%345%6%8%39%
2520
16th to endDay
12%5%25%5%45%6%7%8%35%
2654
August1st to 15thDay
12%6%36%7%35%45%8%37%
2408
16th to endDay
12%4146%345%5%8%42%
2336
September1st to 15thDay
17%5%25%5%23447%40%
2112
16th to endDay
17%5%24423346%43%
1830
October1st to 15thDay
21%7%25%5%33346%35%
1650
16th to endDay
27%10%46%5%24235%25%
1686
November1st to 15thDay
14%8%36%7%45%446%33%
1526
16th to endDay
21%12%5%8%5%2344426%
1440
December1st to 15thDay
24%14%48%6%335%35%19%
1440
16th to endDay
24%16%5%7%6%3433320%
1536
January1st to 15thNight
19%14%5%10%7%35%33420%
2506
16th to endNight
14%14%6%9%7%44446%24%
2616
February1st to 15thNight
14%14%7%9%7%35%445%23%
2278
16th to endNight
16%13%48%6%44345%27%
1952
March1st to 15thNight
20%12%5%6%5%3333431%
2085
16th to endNight
16%8%46%423345%40%
2043
April1st to 15thNight
22%9%35%423335%34%
1796
16th to endNight
19%7%35%423446%38%
1742
May1st to 15thNight
21%7%34414445%37%
1440
16th to endNight
14%6%36%5%2345%7%39%
1495
June1st to 15thNight
19%7%346%2445%6%34%
1440
16th to endNight
14%6%245%36%5%6%7%36%
1440
July1st to 15thNight
10%425%5%245%5%9%45%
1440
16th to endNight
8%4144246%8%8%45%
1514
August1st to 15thNight
9%5%16%5%35%46%9%40%
1551
16th to endNight
10%31442445%8%50%
1854
September1st to 15thNight
15%5%245%2345%5%44%
1768
16th to endNight
16%6%23323346%47%
1799
October1st to 15thNight
20%5%26%5%3445%6%35%
1980
16th to endNight
27%9%36%5%33345%26%
2184
November1st to 15thNight
18%10%35%5%24446%34%
2331
16th to endNight
22%11%48%5%35%345%25%
2520
December1st to 15thNight
20%17%6%8%5%2434422%
2520
16th to endNight
24%14%6%8%6%2433419%
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
65%310%13%6%1
1433
16th to endDay
63%48%13%8%
1605
February1st to 15thDay
63%39%18%4
1577
16th to endDay
62%310%12%10%1
1520
March1st to 15thDay
63%39%15%7%1
1873
16th to endDay
47%39%19%15%5%
2181
April1st to 15thDay
53%37%18%14%2
2152
16th to endDay
49%37%20%16%3
2226
May1st to 15thDay
50%49%19%14%2
2511
16th to endDay
45%5%13%22%11%2
2622
June1st to 15thDay
51%5%11%20%10%
2520
16th to endDay
48%5%12%21%11%
2520
July1st to 15thDay
38%6%13%30%11%
2371
16th to endDay
43%7%14%24%10%
2487
August1st to 15thDay
44%5%16%22%10%
2394
16th to endDay
38%415%29%12%
2336
September1st to 15thDay
42%411%26%13%
2112
16th to endDay
41%410%31%12%
1830
October1st to 15thDay
50%214%22%10%
1650
16th to endDay
62%410%16%5%
1686
November1st to 15thDay
51%315%19%9%
1526
16th to endDay
60%411%14%7%
1440
December1st to 15thDay
67%412%12%2
1440
16th to endDay
68%5%9%11%5%
1536
January1st to 15thNight
67%410%12%5%
2506
16th to endNight
61%39%16%7%
2616
February1st to 15thNight
62%411%15%5%
2287
16th to endNight
58%39%19%9%
1952
March1st to 15thNight
55%212%19%8%
2085
16th to endNight
46%310%19%16%3
2043
April1st to 15thNight
52%27%21%14%1
1796
16th to endNight
46%48%19%18%3
1742
May1st to 15thNight
48%48%19%14%4
1440
16th to endNight
42%5%13%20%15%2
1497
June1st to 15thNight
48%5%13%19%11%1
1440
16th to endNight
43%6%12%22%13%
1440
July1st to 15thNight
33%5%12%30%17%1
1360
16th to endNight
32%7%16%26%15%
1418
August1st to 15thNight
38%5%16%25%13%
1541
16th to endNight
31%416%33%13%
1854
September1st to 15thNight
39%411%31%11%1
1768
16th to endNight
37%411%33%11%1
1799
October1st to 15thNight
50%49%22%12%
1980
16th to endNight
60%312%16%6%
2184
November1st to 15thNight
50%413%18%11%1
2331
16th to endNight
61%410%17%5%
2520
December1st to 15thNight
65%313%13%3
2520
16th to endNight
68%410%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
30%25%21%15%8%
60
16th to endDay
42%10%30%12%4
75
February1st to 15thDay
37%24%30%7%
90
16th to endDay
34%19%27%12%5%
179
March1st to 15thDay
25%16%31%20%5%
270
16th to endDay
25%17%31%15%10%1
288
April1st to 15thDay
28%22%27%11%9%
270
16th to endDay
22%18%28%17%7%5%
270
May1st to 15thDay
29%13%27%19%6%4
288
16th to endDay
20%15%32%18%9%3
331
June1st to 15thDay
26%9%29%23%8%2
315
16th to endDay
21%9%30%23%12%2
315
July1st to 15thDay
15%7%29%27%14%5%
305
16th to endDay
13%6%30%28%14%6%
326
August1st to 15thDay
14%5%29%30%13%6%
313
16th to endDay
15%6%26%25%13%12%
332
September1st to 15thDay
17%8%28%21%12%12%
299
16th to endDay
22%6%30%19%14%6%
254
October1st to 15thDay
27%12%27%20%9%3
255
16th to endDay
33%16%25%18%5%
259
November1st to 15thDay
18%14%31%23%10%2
180
16th to endDay
28%11%36%11%11%
60
December1st to 15thDay
31%21%30%10%6%
60
16th to endDay
46%26%26%
64
January1st to 15thNight
30%17%30%17%3
720
16th to endNight
22%15%34%22%5%
768
February1st to 15thNight
22%20%34%19%2
704
16th to endNight
23%16%35%19%5%
631
March1st to 15thNight
28%15%31%21%2
720
16th to endNight
21%17%26%23%9%
768
April1st to 15thNight
27%15%30%21%4
718
16th to endNight
24%14%28%21%9%1
662
May1st to 15thNight
24%7%26%30%8%1
360
16th to endNight
14%9%38%26%10%
375
June1st to 15thNight
20%9%26%31%10%
360
16th to endNight
16%330%33%14%
360
July1st to 15thNight
10%5%28%38%16%
340
16th to endNight
9%227%41%17%1
376
August1st to 15thNight
13%424%34%20%1
470
16th to endNight
10%6%25%34%20%2
708
September1st to 15thNight
18%426%28%19%1
707
16th to endNight
19%8%23%26%20%2
657
October1st to 15thNight
25%11%25%23%12%1
660
16th to endNight
33%12%25%22%6%
704
November1st to 15thNight
26%11%30%19%11%
700
16th to endNight
31%16%25%18%8%
720
December1st to 15thNight
31%19%28%16%3
720
16th to endNight
34%14%30%17%21
768
Page generated at 2017-09-13 07:39:17. Version ac04

Copyright 2017 A. Danko


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