Observatoire Plourde
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Plourde clear sky chart from 2005-11-05 to 2017-09-17.

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
25%
15018
9%
46736
6%
14985
29%
14985
12%
36966

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%
900
7%
2685
4%
895
19%
895
6%
2328
January16th to endNight
24%
885
7%
2742
3%
885
28%
885
7%
2313
February1st to 15thNight
27%
704
9%
2287
6%
701
32%
701
9%
1866
February16th to endNight
21%
631
7%
2051
4%
631
25%
631
8%
1707
March1st to 15thNight
24%
720
11%
2031
9%
720
27%
720
12%
1631
March16th to endNight
29%
768
16%
2103
9%
768
34%
768
17%
1562
April1st to 15thNight
23%
682
12%
1760
5%
682
28%
682
16%
1371
April16th to endNight
29%
540
16%
1620
10%
540
36%
540
19%
1165
May1st to 15thNight
31%
360
13%
1440
14%
360
37%
360
13%
1022
May16th to endNight
31%
375
8%
1418
7%
374
37%
374
14%
1001
June1st to 15thNight
33%
360
6%
1260
3%
360
35%
360
16%
873
June16th to endNight
39%
360
6%
1260
3%
360
40%
360
21%
815
July1st to 15thNight
39%
340
5%
1190
4%
340
40%
340
19%
821
July16th to endNight
46%
376
9%
1292
10%
354
48%
354
18%
862
August1st to 15thNight
41%
473
8%
1544
6%
471
45%
471
18%
1111
August16th to endNight
39%
582
14%
1728
10%
582
42%
582
22%
1215
September1st to 15thNight
32%
720
10%
1800
4%
720
34%
720
21%
1345
September16th to endNight
34%
665
14%
1851
8%
665
38%
665
22%
1320
October1st to 15thNight
22%
660
10%
1980
7%
660
27%
660
12%
1557
October16th to endNight
20%
704
7%
2209
6%
704
22%
704
6%
1941
November1st to 15thNight
14%
700
6%
2452
4%
700
18%
700
6%
2081
November16th to endNight
11%
720
5%
2520
2%
720
14%
720
5%
2193
December1st to 15thNight
13%
833
3%
2633
0%
833
15%
833
5%
2314
December16th to endNight
17%
960
5%
2880
3%
960
19%
960
5%
2552

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
20%13%47%6%35%445%23%
48066
Night
18%14%5%8%6%35%5%45%22%
46889
TransparencyDay
61%5%9%16%6%
47736
Night
63%5%9%14%6%
46737
SeeingDay
27%11%28%20%8%2
5935
Night
25%9%30%24%8%1
15018

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
19%18%5%10%8%46%6%6%39%
1253
16th to endDay
12%18%7%9%8%36%7%8%6%10%
1482
February1st to 15thDay
8%14%6%10%10%6%7%7%6%7%14%
1575
16th to endDay
10%18%7%10%9%36%5%5%5%15%
1422
March1st to 15thDay
14%12%5%8%8%45%44425%
1917
16th to endDay
13%14%48%6%45%445%29%
2121
April1st to 15thDay
21%14%6%7%5%2334425%
2199
16th to endDay
18%12%5%7%42444431%
2340
May1st to 15thDay
21%10%37%6%25%5%45%27%
2511
16th to endDay
25%10%25%424446%28%
2693
June1st to 15thDay
21%9%36%5%3445%7%28%
2700
16th to endDay
20%8%36%5%245%6%6%30%
2700
July1st to 15thDay
21%7%36%5%45%46%7%26%
2700
16th to endDay
18%8%37%7%36%45%6%28%
2787
August1st to 15thDay
22%10%36%6%35%5%5%7%22%
2405
16th to endDay
18%8%37%6%35%5%5%7%27%
2461
September1st to 15thDay
24%8%36%5%24446%28%
2160
16th to endDay
24%8%27%424336%30%
1812
October1st to 15thDay
28%14%35%422235%26%
1650
16th to endDay
33%22%46%5%2323312%
1662
November1st to 15thDay
25%23%6%7%5%2323414%
1406
16th to endDay
25%20%8%10%7%3322311%
1440
December1st to 15thDay
18%22%8%11%6%3344410%
1326
16th to endDay
17%22%7%11%8%46%3449%
1344
January1st to 15thNight
18%17%8%10%8%46%5%4410%
2685
16th to endNight
12%17%7%11%8%5%7%8%6%5%9%
2742
February1st to 15thNight
8%14%6%11%10%5%9%5%5%7%14%
2285
16th to endNight
13%18%6%10%8%46%5%5%5%15%
2051
March1st to 15thNight
14%13%5%10%7%5%6%44422%
2019
16th to endNight
11%12%48%6%35%5%5%5%30%
2103
April1st to 15thNight
21%13%47%43433428%
1760
16th to endNight
20%9%5%6%5%23345%33%
1620
May1st to 15thNight
17%12%36%6%345%45%30%
1440
16th to endNight
22%7%35%435%45%7%30%
1417
June1st to 15thNight
19%9%25%6%2446%5%32%
1260
16th to endNight
14%5%25%6%35%45%8%38%
1260
July1st to 15thNight
16%6%35%6%45%5%7%8%31%
1260
16th to endNight
15%5%45%5%345%6%8%34%
1380
August1st to 15thNight
15%8%47%7%246%5%6%31%
1554
16th to endNight
15%7%26%5%25%5%6%7%35%
1728
September1st to 15thNight
19%8%36%6%34447%32%
1800
16th to endNight
23%7%24432335%37%
1851
October1st to 15thNight
23%12%46%5%34446%23%
1980
16th to endNight
27%21%5%7%6%2343313%
2209
November1st to 15thNight
24%19%8%8%5%2333316%
2452
16th to endNight
23%20%7%9%7%3432313%
2520
December1st to 15thNight
18%20%8%10%8%45%43310%
2633
16th to endNight
19%19%8%10%8%46%5%338%
2880

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
74%5%6%11%1
1254
16th to endDay
68%6%7%11%6%
1482
February1st to 15thDay
65%5%8%13%6%
1577
16th to endDay
68%6%6%15%3
1422
March1st to 15thDay
61%47%14%11%
1928
16th to endDay
56%46%21%9%1
2121
April1st to 15thDay
62%5%6%15%9%
2199
16th to endDay
54%5%9%15%13%1
2340
May1st to 15thDay
57%6%7%17%10%1
2511
16th to endDay
56%6%9%18%9%
2697
June1st to 15thDay
54%49%20%9%
2700
16th to endDay
51%6%10%20%10%
2700
July1st to 15thDay
52%6%13%19%7%
2541
16th to endDay
55%6%12%20%4
2612
August1st to 15thDay
59%8%13%16%1
2391
16th to endDay
54%7%14%17%4
2461
September1st to 15thDay
55%7%12%17%6%
2160
16th to endDay
55%6%11%22%4
1812
October1st to 15thDay
61%410%15%8%
1650
16th to endDay
78%45%8%2
1662
November1st to 15thDay
75%38%7%4
1406
16th to endDay
81%36%7%2
1440
December1st to 15thDay
76%46%10%2
1326
16th to endDay
78%36%6%3
1344
January1st to 15thNight
74%5%6%10%1
2685
16th to endNight
70%6%6%10%5%
2742
February1st to 15thNight
67%5%8%10%7%
2287
16th to endNight
69%6%6%12%4
2051
March1st to 15thNight
64%47%12%9%1
2031
16th to endNight
54%5%7%18%12%2
2103
April1st to 15thNight
59%46%16%11%2
1760
16th to endNight
53%47%18%15%1
1620
May1st to 15thNight
53%7%7%17%12%1
1440
16th to endNight
52%7%9%19%10%
1419
June1st to 15thNight
51%6%10%16%13%1
1260
16th to endNight
43%6%11%26%10%1
1260
July1st to 15thNight
46%8%12%23%7%
1190
16th to endNight
45%8%15%25%5%
1292
August1st to 15thNight
50%8%14%22%4
1544
16th to endNight
45%8%17%22%5%
1728
September1st to 15thNight
52%5%15%18%7%
1800
16th to endNight
48%6%14%24%5%
1851
October1st to 15thNight
61%6%11%14%5%
1980
16th to endNight
76%5%5%10%2
2209
November1st to 15thNight
74%39%8%2
2452
16th to endNight
77%5%7%8%1
2520
December1st to 15thNight
77%5%7%8%1
2633
16th to endNight
78%46%6%3
2880

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
26%15%38%15%31
60
16th to endDay
29%14%36%17%2
75
February1st to 15thDay
14%11%43%31%
90
16th to endDay
29%12%44%12%1
81
March1st to 15thDay
23%12%33%21%6%1
252
16th to endDay
19%15%36%19%8%1
288
April1st to 15thDay
24%17%31%16%8%2
270
16th to endDay
24%14%30%20%7%2
270
May1st to 15thDay
33%10%22%22%9%2
288
16th to endDay
34%11%26%17%7%1
406
June1st to 15thDay
29%13%23%23%8%1
495
16th to endDay
22%10%31%24%8%2
495
July1st to 15thDay
24%10%31%22%9%2
475
16th to endDay
21%9%27%28%9%2
458
August1st to 15thDay
29%7%23%21%13%5%
313
16th to endDay
30%5%25%20%13%5%
332
September1st to 15thDay
24%11%26%22%13%2
315
16th to endDay
28%8%29%19%10%3
259
October1st to 15thDay
32%12%29%15%7%1
255
16th to endDay
41%16%21%13%6%1
214
November1st to 15thDay
38%18%31%10%1
60
16th to endDay
45%20%21%10%3
60
December1st to 15thDay
38%10%31%11%6%1
60
16th to endDay
32%14%39%12%1
64
January1st to 15thNight
28%11%31%21%5%1
900
16th to endNight
21%9%32%24%10%1
885
February1st to 15thNight
15%9%34%29%10%
704
16th to endNight
23%9%34%24%8%
631
March1st to 15thNight
22%13%32%25%5%
720
16th to endNight
19%11%33%25%8%1
768
April1st to 15thNight
30%11%29%21%6%
682
16th to endNight
24%7%33%26%6%1
540
May1st to 15thNight
25%8%30%26%9%
360
16th to endNight
26%8%28%29%6%
375
June1st to 15thNight
24%8%28%28%9%1
360
16th to endNight
14%6%32%34%10%1
360
July1st to 15thNight
18%5%32%31%10%1
340
16th to endNight
16%5%25%37%14%1
376
August1st to 15thNight
20%424%28%19%2
473
16th to endNight
23%427%29%14%1
582
September1st to 15thNight
25%9%28%22%13%1
720
16th to endNight
27%6%26%26%10%2
665
October1st to 15thNight
31%10%28%20%8%
660
16th to endNight
38%11%21%19%6%2
704
November1st to 15thNight
31%14%30%17%5%1
700
16th to endNight
35%9%30%20%4
720
December1st to 15thNight
29%10%35%18%5%
833
16th to endNight
29%9%28%20%7%2
960
Page generated at 2017-09-18 08:38:26. Version ac04

Copyright 2017 A. Danko


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