St-Placide
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St-Placide clear sky chart from 2005-11-05 to 2017-09-24.

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
32%
14662
13%
46913
8%
14631
38%
14631
17%
33637

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
8%
2506
5%
716
22%
716
9%
1975
January16th to endNight
22%
768
10%
2688
5%
768
28%
768
11%
2028
February1st to 15thNight
22%
704
9%
2296
5%
701
27%
701
10%
1788
February16th to endNight
24%
631
13%
1904
6%
631
32%
631
14%
1433
March1st to 15thNight
22%
720
13%
2157
8%
720
29%
720
14%
1648
March16th to endNight
33%
768
20%
1992
10%
768
40%
768
24%
1397
April1st to 15thNight
30%
718
16%
1796
6%
718
35%
718
21%
1342
April16th to endNight
30%
636
16%
1716
6%
636
37%
636
21%
1230
May1st to 15thNight
32%
375
16%
1455
13%
375
43%
375
16%
987
May16th to endNight
35%
374
13%
1497
12%
374
46%
374
17%
983
June1st to 15thNight
35%
360
8%
1440
8%
360
43%
360
14%
1012
June16th to endNight
45%
360
9%
1440
12%
360
50%
360
17%
926
July1st to 15thNight
50%
340
14%
1360
19%
340
56%
340
25%
788
July16th to endNight
55%
376
12%
1418
16%
354
58%
354
24%
827
August1st to 15thNight
54%
374
14%
1445
15%
372
58%
372
22%
878
August16th to endNight
54%
753
19%
1899
10%
753
57%
753
35%
1233
September1st to 15thNight
49%
720
15%
1800
8%
720
51%
720
28%
1271
September16th to endNight
50%
693
22%
1892
15%
693
54%
693
31%
1201
October1st to 15thNight
33%
660
18%
1960
10%
660
43%
660
20%
1352
October16th to endNight
26%
704
10%
2244
8%
704
32%
704
14%
1672
November1st to 15thNight
28%
700
16%
2280
10%
700
37%
700
16%
1632
November16th to endNight
22%
720
12%
2520
8%
720
29%
720
11%
1889
December1st to 15thNight
19%
720
8%
2520
4%
720
25%
720
9%
1996
December16th to endNight
13%
768
10%
2688
3%
768
21%
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
18%8%36%5%3445%6%33%
48021
Night
18%9%36%5%34446%33%
47082
Cloud CoverDay
17%8%36%5%3445%6%33%
48030
Night
18%9%36%5%34446%32%
47088
TransparencyDay
49%6%12%19%10%1
47708
Night
51%6%11%19%10%1
46913
SeeingDay
21%8%26%25%13%4
5583
Night
23%8%29%27%10%
14663

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%39%6%3434422%
1432
16th to endDay
13%15%5%8%5%35%436%26%
1536
February1st to 15thDay
14%13%5%8%8%35%45%5%24%
1563
16th to endDay
18%11%5%8%7%34345%27%
1569
March1st to 15thDay
18%12%48%8%25%44428%
1790
16th to endDay
18%7%36%5%23345%38%
2230
April1st to 15thDay
22%9%35%6%3334433%
2152
16th to endDay
20%7%35%5%34345%37%
2243
May1st to 15thDay
20%7%35%6%3445%6%32%
2505
16th to endDay
19%6%25%435%45%7%34%
2618
June1st to 15thDay
21%6%25%5%3445%7%31%
2520
16th to endDay
17%5%36%6%35%5%6%8%31%
2520
July1st to 15thDay
12%5%25%436%6%5%8%39%
2520
16th to endDay
12%4246%36%5%7%10%35%
2654
August1st to 15thDay
12%5%36%6%45%5%6%8%36%
2500
16th to endDay
10%424435%5%6%8%46%
2292
September1st to 15thDay
15%5%2443445%7%41%
2160
16th to endDay
14%424422347%48%
1927
October1st to 15thDay
21%6%25%5%25%435%36%
1669
16th to endDay
24%9%37%6%3345%5%25%
1628
November1st to 15thDay
16%8%36%5%345%6%7%32%
1577
16th to endDay
24%8%36%5%34445%28%
1440
December1st to 15thDay
26%12%47%425%5%5%5%20%
1440
16th to endDay
26%14%47%6%3443421%
1536
January1st to 15thNight
19%15%6%8%6%3445%421%
2506
16th to endNight
13%13%5%9%7%45%345%26%
2688
February1st to 15thNight
14%12%5%10%7%45%5%46%23%
2294
16th to endNight
15%12%5%8%6%3445%428%
1904
March1st to 15thNight
19%11%37%6%3444428%
2144
16th to endNight
16%10%35%42324440%
1992
April1st to 15thNight
26%7%24434335%33%
1796
16th to endNight
22%6%245%23346%36%
1716
May1st to 15thNight
21%7%45%5%33345%35%
1455
16th to endNight
19%5%345%25%446%37%
1495
June1st to 15thNight
23%6%25%435%5%5%7%30%
1440
16th to endNight
16%5%25%5%26%5%6%8%37%
1440
July1st to 15thNight
10%3235%35%5%6%8%44%
1440
16th to endNight
10%4245%35%5%6%8%42%
1514
August1st to 15thNight
11%5%244335%6%9%40%
1455
16th to endNight
13%31442445%7%48%
1899
September1st to 15thNight
15%6%35%5%34447%40%
1800
16th to endNight
17%413323346%49%
1892
October1st to 15thNight
18%6%35%424447%37%
1960
16th to endNight
24%8%37%6%24345%29%
2244
November1st to 15thNight
20%6%35%6%35%5%36%33%
2280
16th to endNight
23%10%47%5%34335%28%
2520
December1st to 15thNight
23%15%46%43444423%
2520
16th to endNight
24%16%5%6%6%3334422%
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
21%14%39%6%4444422%
1432
16th to endDay
12%15%5%9%5%35%347%26%
1536
February1st to 15thDay
14%13%49%7%45%5%45%23%
1563
16th to endDay
18%11%6%8%6%3434427%
1569
March1st to 15thDay
18%11%5%8%8%25%44427%
1800
16th to endDay
17%8%36%5%23346%37%
2229
April1st to 15thDay
21%9%35%5%24345%33%
2152
16th to endDay
19%7%25%5%3435%5%37%
2243
May1st to 15thDay
19%7%36%5%25%446%32%
2505
16th to endDay
18%6%25%5%35%5%5%7%34%
2618
June1st to 15thDay
20%7%25%5%345%5%7%31%
2520
16th to endDay
16%6%26%6%35%6%6%8%30%
2520
July1st to 15thDay
11%5%35%5%35%6%5%8%39%
2520
16th to endDay
12%4245%46%6%7%9%35%
2654
August1st to 15thDay
11%6%26%7%45%5%6%8%35%
2500
16th to endDay
9%3244346%6%8%46%
2292
September1st to 15thDay
15%5%3442445%8%40%
2160
16th to endDay
14%424422347%48%
1927
October1st to 15thDay
20%7%26%434445%35%
1669
16th to endDay
23%10%37%6%3445%6%25%
1628
November1st to 15thDay
15%9%35%5%35%5%6%7%31%
1577
16th to endDay
23%8%36%5%345%45%28%
1440
December1st to 15thDay
25%12%48%5%346%46%20%
1440
16th to endDay
25%13%5%6%7%3444420%
1536
January1st to 15thNight
18%15%6%8%6%35%445%20%
2506
16th to endNight
13%13%5%10%7%45%445%26%
2688
February1st to 15thNight
13%12%5%10%7%46%5%5%6%22%
2287
16th to endNight
15%12%49%6%35%5%4428%
1904
March1st to 15thNight
20%11%47%6%35%445%28%
2157
16th to endNight
16%10%35%42334440%
1992
April1st to 15thNight
25%7%35%5%24346%32%
1796
16th to endNight
21%6%25%5%24346%36%
1716
May1st to 15thNight
21%8%45%5%33445%34%
1455
16th to endNight
19%6%34434447%36%
1495
June1st to 15thNight
23%6%25%5%345%6%6%29%
1440
16th to endNight
15%5%25%436%5%6%7%36%
1440
July1st to 15thNight
10%4226%345%6%9%43%
1440
16th to endNight
9%5%25%435%5%7%10%41%
1514
August1st to 15thNight
10%6%35%5%2445%11%39%
1455
16th to endNight
12%42443345%7%48%
1899
September1st to 15thNight
14%6%36%5%25%45%7%40%
1800
16th to endNight
16%413413346%48%
1892
October1st to 15thNight
17%6%35%43445%7%36%
1960
16th to endNight
24%8%37%5%34345%29%
2244
November1st to 15thNight
19%7%36%5%34446%32%
2280
16th to endNight
21%11%47%5%24345%27%
2520
December1st to 15thNight
23%15%47%5%2444423%
2520
16th to endNight
24%16%5%6%5%2334422%
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
64%5%9%13%5%
1433
16th to endDay
57%5%12%14%8%
1536
February1st to 15thDay
61%6%9%18%3
1565
16th to endDay
59%410%14%8%1
1569
March1st to 15thDay
59%5%11%14%7%1
1800
16th to endDay
48%410%17%15%4
2230
April1st to 15thDay
53%37%19%12%2
2152
16th to endDay
48%48%18%14%3
2243
May1st to 15thDay
51%5%9%17%13%2
2505
16th to endDay
47%6%11%19%12%1
2622
June1st to 15thDay
51%7%10%19%10%
2520
16th to endDay
48%9%11%20%9%1
2520
July1st to 15thDay
38%9%14%25%12%
2371
16th to endDay
41%9%18%22%9%
2487
August1st to 15thDay
43%9%16%22%7%
2486
16th to endDay
32%8%17%28%12%
2292
September1st to 15thDay
40%7%13%25%12%
2160
16th to endDay
36%5%12%33%11%
1927
October1st to 15thDay
50%5%10%22%9%
1669
16th to endDay
58%6%13%14%6%
1628
November1st to 15thDay
48%7%15%18%9%
1577
16th to endDay
57%7%11%17%6%
1440
December1st to 15thDay
64%8%12%11%2
1440
16th to endDay
66%6%9%11%6%
1536
January1st to 15thNight
64%6%10%14%4
2506
16th to endNight
60%5%10%15%7%1
2688
February1st to 15thNight
60%8%11%15%4
2296
16th to endNight
56%6%9%16%10%
1904
March1st to 15thNight
58%6%8%16%8%1
2157
16th to endNight
47%49%19%15%4
1992
April1st to 15thNight
53%46%18%15%1
1796
16th to endNight
49%5%7%17%16%4
1716
May1st to 15thNight
51%47%16%15%4
1455
16th to endNight
46%7%9%20%13%1
1497
June1st to 15thNight
52%6%11%18%9%
1440
16th to endNight
43%8%12%19%14%
1440
July1st to 15thNight
34%8%12%28%15%
1360
16th to endNight
36%8%17%24%12%
1418
August1st to 15thNight
38%8%18%23%11%
1445
16th to endNight
34%7%15%29%12%
1899
September1st to 15thNight
42%7%10%24%14%
1800
16th to endNight
36%6%10%32%14%
1892
October1st to 15thNight
47%5%10%24%11%
1960
16th to endNight
57%5%12%17%6%
2244
November1st to 15thNight
52%6%12%17%8%2
2280
16th to endNight
58%6%11%17%5%
2520
December1st to 15thNight
63%7%11%14%3
2520
16th to endNight
65%6%9%12%6%
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
18%25%20%28%6%1
60
16th to endDay
28%15%28%21%33
64
February1st to 15thDay
35%13%35%14%1
88
16th to endDay
28%7%31%28%4
228
March1st to 15thDay
21%13%33%27%4
270
16th to endDay
25%8%28%24%11%2
288
April1st to 15thDay
30%12%28%15%10%2
270
16th to endDay
21%12%29%21%11%3
270
May1st to 15thDay
27%9%27%22%10%3
288
16th to endDay
23%8%30%21%12%3
331
June1st to 15thDay
27%8%23%26%11%2
315
16th to endDay
22%423%32%14%1
315
July1st to 15thDay
14%5%26%30%17%5%
305
16th to endDay
15%219%38%20%4
326
August1st to 15thDay
14%320%34%20%6%
313
16th to endDay
9%424%28%18%13%
332
September1st to 15thDay
16%7%21%22%20%11%
315
16th to endDay
17%7%21%20%22%11%
287
October1st to 15thDay
21%7%23%26%17%3
255
16th to endDay
28%12%29%21%8%
248
November1st to 15thDay
23%11%29%24%9%1
231
16th to endDay
33%11%23%25%6%
60
December1st to 15thDay
31%6%28%28%5%
60
16th to endDay
40%14%37%7%
64
January1st to 15thNight
25%13%31%24%4
720
16th to endNight
20%12%35%22%8%
768
February1st to 15thNight
20%11%35%25%6%
704
16th to endNight
22%8%36%26%6%
631
March1st to 15thNight
26%10%31%25%4
720
16th to endNight
21%9%30%29%8%
768
April1st to 15thNight
27%8%27%31%5%
718
16th to endNight
25%9%29%25%10%
636
May1st to 15thNight
24%332%27%9%2
375
16th to endNight
20%5%32%32%8%
375
June1st to 15thNight
28%326%30%10%
360
16th to endNight
18%227%37%13%1
360
July1st to 15thNight
10%327%36%20%1
340
16th to endNight
12%124%41%18%1
376
August1st to 15thNight
13%219%39%22%1
374
16th to endNight
14%223%33%24%2
753
September1st to 15thNight
17%421%39%15%1
720
16th to endNight
18%5%22%26%24%2
693
October1st to 15thNight
21%7%31%27%11%
660
16th to endNight
29%9%28%26%6%
704
November1st to 15thNight
25%10%29%24%10%
700
16th to endNight
26%14%29%19%10%
720
December1st to 15thNight
32%12%28%21%4
720
16th to endNight
33%11%32%16%4
768
Page generated at 2017-09-25 09:02:25. Version ac04

Copyright 2017 A. Danko


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