Sorel-Tracy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sorel-Tracy clear sky chart from 2005-11-05 to 2017-12-20.

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
35%
14975
13%
48041
9%
14943
41%
14943
17%
34343

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
25%
720
10%
2506
7%
716
30%
716
10%
1925
January16th to endNight
30%
768
11%
2688
8%
768
36%
768
12%
2037
February1st to 15thNight
26%
704
10%
2328
7%
701
32%
701
12%
1789
February16th to endNight
29%
631
12%
1893
9%
631
35%
631
15%
1434
March1st to 15thNight
30%
720
15%
2159
12%
720
35%
720
16%
1617
March16th to endNight
38%
768
19%
2004
10%
768
44%
768
25%
1415
April1st to 15thNight
31%
718
16%
1796
6%
718
36%
718
20%
1356
April16th to endNight
30%
598
16%
1678
5%
598
38%
598
21%
1188
May1st to 15thNight
33%
405
15%
1485
14%
405
40%
405
17%
1020
May16th to endNight
35%
375
12%
1497
11%
374
44%
374
16%
1001
June1st to 15thNight
35%
360
8%
1440
7%
360
43%
360
15%
986
June16th to endNight
46%
360
8%
1440
10%
360
49%
360
16%
962
July1st to 15thNight
55%
340
11%
1360
16%
340
60%
340
23%
829
July16th to endNight
56%
376
12%
1418
16%
354
59%
354
22%
869
August1st to 15thNight
59%
373
15%
1444
17%
371
61%
371
20%
922
August16th to endNight
55%
726
19%
1872
11%
726
57%
726
33%
1225
September1st to 15thNight
51%
720
14%
1805
8%
720
52%
720
29%
1246
September16th to endNight
51%
717
22%
1980
16%
717
55%
717
32%
1267
October1st to 15thNight
37%
720
19%
2100
11%
720
46%
720
23%
1428
October16th to endNight
29%
768
12%
2484
8%
768
35%
768
15%
1814
November1st to 15thNight
30%
760
16%
2472
11%
760
38%
760
17%
1770
November16th to endNight
26%
780
13%
2707
9%
780
32%
780
13%
2010
December1st to 15thNight
24%
780
9%
2730
4%
780
30%
780
11%
2074
December16th to endNight
20%
788
11%
2755
6%
788
27%
788
10%
2159

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%8%36%5%3445%6%34%
48808
Night
19%9%36%5%24445%32%
48211
TransparencyDay
49%6%12%20%9%1
48495
Night
52%5%10%19%10%1
48042
SeeingDay
21%5%24%26%16%4
5871
Night
24%426%31%11%
14975

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
21%14%47%6%35%44325%
1432
16th to endDay
14%14%47%5%45%35%6%28%
1536
February1st to 15thDay
13%15%48%7%4444428%
1531
16th to endDay
18%12%49%5%34345%27%
1580
March1st to 15thDay
17%10%47%5%3435%5%30%
1790
16th to endDay
16%8%35%5%24345%39%
2220
April1st to 15thDay
22%7%35%5%24446%33%
2152
16th to endDay
21%6%25%4345%35%38%
2280
May1st to 15thDay
21%6%36%5%33447%33%
2475
16th to endDay
20%6%26%5%3445%7%33%
2618
June1st to 15thDay
22%6%244345%6%8%31%
2520
16th to endDay
17%6%36%6%25%5%6%9%30%
2520
July1st to 15thDay
13%4246%36%5%6%9%36%
2520
16th to endDay
12%5%25%5%36%7%6%9%35%
2654
August1st to 15thDay
12%5%26%6%36%7%7%8%32%
2493
16th to endDay
9%423435%5%6%8%46%
2328
September1st to 15thDay
17%4245%245%5%6%41%
2154
16th to endDay
13%41432345%5%49%
1980
October1st to 15thDay
22%6%25%5%2445%5%35%
1858
16th to endDay
22%9%45%6%34445%30%
1740
November1st to 15thDay
17%10%26%6%34447%33%
1716
16th to endDay
22%10%35%5%2345%5%31%
1583
December1st to 15thDay
26%11%36%5%34335%25%
1560
16th to endDay
26%14%5%6%32334424%
1568
January1st to 15thNight
19%15%5%8%5%3444424%
2506
16th to endNight
14%13%5%7%8%46%445%25%
2688
February1st to 15thNight
12%13%5%11%8%35%44423%
2326
16th to endNight
17%12%5%8%5%35%435%28%
1893
March1st to 15thNight
20%12%46%5%3434430%
2147
16th to endNight
16%9%45%32443439%
2004
April1st to 15thNight
24%8%36%424445%30%
1796
16th to endNight
23%7%34323346%36%
1678
May1st to 15thNight
23%8%35%5%24445%34%
1485
16th to endNight
21%6%35%425%45%6%33%
1495
June1st to 15thNight
25%7%25%433447%31%
1440
16th to endNight
18%5%15%425%6%6%8%33%
1440
July1st to 15thNight
11%425%4346%5%9%40%
1440
16th to endNight
11%5%245%35%5%7%8%40%
1514
August1st to 15thNight
13%5%245%36%5%6%8%38%
1454
16th to endNight
13%4144245%6%7%45%
1872
September1st to 15thNight
17%425%5%23446%42%
1805
16th to endNight
17%423423446%47%
1980
October1st to 15thNight
18%5%26%5%33345%40%
2100
16th to endNight
26%8%35%5%23446%30%
2484
November1st to 15thNight
20%9%35%5%34445%33%
2472
16th to endNight
25%10%37%5%2433429%
2707
December1st to 15thNight
23%12%5%8%5%1433426%
2730
16th to endNight
24%16%5%7%5%23335%23%
2755

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
63%5%10%13%6%
1433
16th to endDay
56%411%19%7%
1536
February1st to 15thDay
59%5%10%18%5%
1533
16th to endDay
59%48%16%9%1
1580
March1st to 15thDay
55%5%11%15%10%1
1800
16th to endDay
47%411%20%13%3
2220
April1st to 15thDay
51%49%20%10%3
2152
16th to endDay
48%49%19%14%3
2280
May1st to 15thDay
51%5%9%18%13%1
2475
16th to endDay
50%6%11%18%10%2
2622
June1st to 15thDay
50%6%13%17%10%1
2520
16th to endDay
49%9%10%21%8%
2520
July1st to 15thDay
40%10%13%23%11%
2371
16th to endDay
42%10%17%21%8%
2487
August1st to 15thDay
45%10%15%22%5%
2479
16th to endDay
33%9%19%26%11%
2328
September1st to 15thDay
41%6%12%25%12%
2154
16th to endDay
35%7%13%30%12%
1980
October1st to 15thDay
50%412%22%9%
1858
16th to endDay
56%5%13%18%6%
1740
November1st to 15thDay
51%5%13%19%9%
1716
16th to endDay
55%5%12%17%8%
1583
December1st to 15thDay
62%412%15%5%
1560
16th to endDay
64%410%11%9%
1568
January1st to 15thNight
62%410%15%5%
2506
16th to endNight
60%5%9%16%6%1
2688
February1st to 15thNight
61%5%10%15%6%
2328
16th to endNight
59%49%15%10%
1893
March1st to 15thNight
57%48%16%10%1
2160
16th to endNight
48%410%17%16%3
2004
April1st to 15thNight
54%46%17%15%2
1796
16th to endNight
49%5%7%17%15%4
1678
May1st to 15thNight
52%49%15%15%3
1485
16th to endNight
49%6%10%19%11%2
1497
June1st to 15thNight
53%411%18%11%1
1440
16th to endNight
47%8%9%20%13%1
1440
July1st to 15thNight
38%8%13%24%13%1
1360
16th to endNight
40%7%17%21%12%
1418
August1st to 15thNight
41%8%14%25%9%
1444
16th to endNight
36%6%14%28%12%
1872
September1st to 15thNight
42%6%12%25%12%
1805
16th to endNight
36%6%11%31%13%
1980
October1st to 15thNight
45%5%10%24%12%
2100
16th to endNight
54%6%11%18%8%
2484
November1st to 15thNight
52%6%12%17%8%1
2472
16th to endNight
59%310%18%7%
2707
December1st to 15thNight
61%412%15%5%
2730
16th to endNight
65%49%13%6%
2755

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
28%10%20%30%11%
60
16th to endDay
26%9%25%25%7%6%
64
February1st to 15thDay
26%10%26%29%7%
95
16th to endDay
27%427%30%10%
239
March1st to 15thDay
24%6%29%30%8%
270
16th to endDay
21%326%28%15%3
288
April1st to 15thDay
24%8%25%27%10%3
270
16th to endDay
21%7%28%24%15%2
270
May1st to 15thDay
27%5%26%24%13%2
288
16th to endDay
22%6%31%18%18%3
331
June1st to 15thDay
28%5%20%26%13%3
315
16th to endDay
16%424%32%17%3
315
July1st to 15thDay
15%226%27%20%7%
305
16th to endDay
16%214%34%28%4
326
August1st to 15thDay
15%118%31%23%8%
313
16th to endDay
11%319%27%22%15%
332
September1st to 15thDay
15%420%25%23%11%
315
16th to endDay
15%421%24%24%9%
314
October1st to 15thDay
22%5%24%26%17%3
315
16th to endDay
29%7%25%21%15%1
291
November1st to 15thDay
23%6%27%26%13%1
280
16th to endDay
30%7%29%19%12%1
113
December1st to 15thDay
32%428%22%8%3
90
16th to endDay
37%6%40%13%1
72
January1st to 15thNight
26%8%27%28%8%
720
16th to endNight
22%5%29%33%7%1
768
February1st to 15thNight
19%5%32%32%9%
704
16th to endNight
23%430%34%6%
631
March1st to 15thNight
27%5%29%32%5%
720
16th to endNight
21%330%33%10%1
768
April1st to 15thNight
27%5%28%30%7%
718
16th to endNight
27%7%29%25%9%
598
May1st to 15thNight
27%427%31%7%1
405
16th to endNight
25%328%34%8%
375
June1st to 15thNight
27%225%31%12%
360
16th to endNight
21%124%38%13%
360
July1st to 15thNight
12%222%40%20%1
340
16th to endNight
14%119%47%16%1
376
August1st to 15thNight
15%15%43%23%2
373
16th to endNight
16%120%35%23%1
726
September1st to 15thNight
20%220%38%17%1
720
16th to endNight
17%422%31%20%2
717
October1st to 15thNight
21%328%32%13%1
720
16th to endNight
31%6%27%27%7%
768
November1st to 15thNight
25%5%29%26%11%
760
16th to endNight
30%6%28%23%8%1
780
December1st to 15thNight
29%6%27%29%6%
780
16th to endNight
31%7%28%23%7%1
788
Page generated at 2017-12-21 07:04:56. Version ac04

Copyright 2017 A. Danko


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