Lac des Ilets
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac des Ilets clear sky chart from 2005-11-05 to 2017-10-31.

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
20%
14724
8%
47348
4%
14692
24%
14692
9%
38252

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
12%
726
5%
2541
3%
722
15%
722
4%
2213
January16th to endNight
17%
768
6%
2688
2%
768
23%
768
6%
2256
February1st to 15thNight
17%
704
7%
2402
5%
701
21%
701
8%
1975
February16th to endNight
13%
631
7%
1893
3%
631
18%
631
8%
1600
March1st to 15thNight
18%
720
11%
2160
8%
720
23%
720
10%
1743
March16th to endNight
22%
768
13%
2022
6%
768
27%
768
13%
1604
April1st to 15thNight
20%
703
10%
1781
4%
703
23%
703
12%
1457
April16th to endNight
21%
540
13%
1620
6%
540
28%
540
15%
1189
May1st to 15thNight
24%
421
10%
1501
8%
421
30%
421
12%
1116
May16th to endNight
21%
375
9%
1398
5%
374
30%
374
11%
1040
June1st to 15thNight
28%
360
5%
1260
2%
360
31%
360
11%
944
June16th to endNight
31%
360
4%
1260
3%
360
33%
360
13%
919
July1st to 15thNight
32%
340
4%
1246
3%
340
34%
340
13%
904
July16th to endNight
31%
376
6%
1418
8%
354
33%
354
11%
1037
August1st to 15thNight
38%
389
9%
1460
7%
387
42%
387
12%
1076
August16th to endNight
30%
621
8%
1767
3%
621
33%
621
14%
1370
September1st to 15thNight
30%
720
8%
1842
3%
720
32%
720
19%
1412
September16th to endNight
25%
717
12%
1980
7%
717
29%
717
17%
1491
October1st to 15thNight
20%
720
11%
2106
5%
720
26%
720
12%
1646
October16th to endNight
14%
768
6%
2494
4%
768
17%
768
5%
2134
November1st to 15thNight
15%
700
8%
2277
5%
700
20%
700
6%
1901
November16th to endNight
17%
747
6%
2652
5%
747
20%
747
5%
2236
December1st to 15thNight
10%
750
2%
2700
0%
750
12%
750
3%
2437
December16th to endNight
14%
800
5%
2880
3%
800
17%
800
3%
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
19%12%48%6%35%445%23%
48406
Night
17%12%5%8%7%45%5%45%22%
47513
TransparencyDay
62%7%10%12%5%
48089
Night
63%8%9%12%4
47348
SeeingDay
27%17%28%17%6%1
6313
Night
24%18%30%19%6%
14724

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
9%14%7%11%10%6%9%5%5%6%12%
1394
16th to endDay
8%10%6%13%9%5%9%8%8%413%
1536
February1st to 15thDay
8%10%6%12%11%8%11%7%4414%
1455
16th to endDay
7%19%6%15%9%47%44417%
1580
March1st to 15thDay
13%13%6%10%6%47%6%4421%
1790
16th to endDay
13%15%6%8%6%35%345%26%
2199
April1st to 15thDay
19%16%5%6%5%25%44423%
2167
16th to endDay
20%12%36%6%24446%29%
2340
May1st to 15thDay
23%10%36%424345%31%
2460
16th to endDay
24%9%36%5%35%45%5%26%
2714
June1st to 15thDay
23%8%36%6%345%47%27%
2700
16th to endDay
23%7%36%6%46%5%5%5%24%
2700
July1st to 15thDay
24%7%27%6%4446%8%22%
2636
16th to endDay
21%6%37%6%35%5%5%7%26%
2654
August1st to 15thDay
24%8%37%6%36%5%6%7%20%
2477
16th to endDay
22%8%36%5%35%6%5%7%25%
2433
September1st to 15thDay
23%8%36%5%34335%30%
2118
16th to endDay
21%7%35%5%34445%31%
1980
October1st to 15thDay
22%14%37%5%34445%24%
1854
16th to endDay
22%23%5%6%6%3433416%
1728
November1st to 15thDay
16%21%7%8%6%33345%18%
1581
16th to endDay
18%17%7%11%8%3343417%
1306
December1st to 15thDay
17%19%7%8%10%46%5%3311%
1260
16th to endDay
16%18%7%11%8%5%6%5%3313%
1344
January1st to 15thNight
11%13%6%14%10%6%8%6%5%411%
2541
16th to endNight
9%13%6%10%10%6%9%8%6%413%
2688
February1st to 15thNight
6%10%5%11%11%7%10%7%5%5%17%
2401
16th to endNight
11%19%6%11%9%35%445%17%
1893
March1st to 15thNight
14%14%5%8%8%47%5%4422%
2147
16th to endNight
11%15%6%8%7%34345%27%
2022
April1st to 15thNight
22%15%5%7%6%2433424%
1781
16th to endNight
22%11%345%24345%32%
1620
May1st to 15thNight
25%10%35%5%25%34428%
1501
16th to endNight
24%10%36%434446%27%
1396
June1st to 15thNight
22%7%46%6%35%5%46%28%
1260
16th to endNight
19%7%36%6%35%5%5%8%28%
1260
July1st to 15thNight
19%6%25%6%346%7%9%27%
1321
16th to endNight
17%6%35%6%46%5%6%9%27%
1514
August1st to 15thNight
18%6%36%6%35%6%6%8%27%
1470
16th to endNight
22%6%36%5%445%5%8%27%
1767
September1st to 15thNight
21%7%26%5%24446%33%
1842
16th to endNight
23%8%25%43435%433%
1980
October1st to 15thNight
20%14%26%5%33445%28%
2106
16th to endNight
26%19%46%5%2433417%
2494
November1st to 15thNight
18%16%6%8%6%34445%19%
2277
16th to endNight
16%14%7%12%7%45%445%17%
2652
December1st to 15thNight
16%16%7%11%10%6%6%43311%
2700
16th to endNight
15%15%8%11%11%5%6%6%3310%
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
71%7%9%7%3
1395
16th to endDay
65%10%7%10%5%
1536
February1st to 15thDay
70%8%9%7%4
1458
16th to endDay
69%7%5%11%5%
1580
March1st to 15thDay
63%6%7%13%8%
1800
16th to endDay
61%5%7%15%8%1
2199
April1st to 15thDay
65%48%12%7%1
2167
16th to endDay
57%6%10%12%11%1
2340
May1st to 15thDay
55%6%10%15%10%1
2460
16th to endDay
59%7%7%16%7%
2718
June1st to 15thDay
57%6%10%15%8%1
2700
16th to endDay
61%8%10%13%6%
2700
July1st to 15thDay
58%9%14%13%3
2482
16th to endDay
61%9%10%15%4
2487
August1st to 15thDay
64%10%12%10%2
2463
16th to endDay
57%10%16%13%2
2433
September1st to 15thDay
56%7%13%16%5%
2118
16th to endDay
54%8%13%17%5%
1980
October1st to 15thDay
63%7%9%14%5%
1854
16th to endDay
73%6%9%8%2
1728
November1st to 15thDay
69%7%8%10%2
1581
16th to endDay
71%8%9%8%1
1306
December1st to 15thDay
77%7%6%8%
1260
16th to endDay
75%7%6%45%
1344
January1st to 15thNight
73%8%7%7%2
2541
16th to endNight
68%9%8%10%3
2688
February1st to 15thNight
65%9%9%11%4
2402
16th to endNight
69%7%6%10%5%
1893
March1st to 15thNight
64%6%7%13%6%
2160
16th to endNight
60%6%8%17%6%1
2022
April1st to 15thNight
65%46%13%8%1
1781
16th to endNight
53%6%9%16%12%1
1620
May1st to 15thNight
59%5%8%15%10%
1501
16th to endNight
58%6%10%16%7%
1398
June1st to 15thNight
57%7%10%17%6%
1260
16th to endNight
52%10%13%16%6%1
1260
July1st to 15thNight
50%11%16%17%4
1246
16th to endNight
55%9%13%17%4
1418
August1st to 15thNight
52%11%16%16%2
1460
16th to endNight
53%12%14%16%3
1767
September1st to 15thNight
51%9%14%17%6%
1842
16th to endNight
52%8%14%18%5%
1980
October1st to 15thNight
58%8%9%16%6%
2106
16th to endNight
72%7%7%9%3
2494
November1st to 15thNight
66%9%9%9%4
2277
16th to endNight
70%7%9%9%3
2652
December1st to 15thNight
78%7%6%5%1
2700
16th to endNight
77%6%6%5%2
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
15%33%40%11%
60
16th to endDay
23%20%29%20%6%
64
February1st to 15thDay
19%19%39%14%6%1
98
16th to endDay
24%20%31%18%5%
239
March1st to 15thDay
25%20%28%17%6%
270
16th to endDay
21%19%29%19%7%1
288
April1st to 15thDay
27%21%29%15%41
270
16th to endDay
28%19%31%14%42
270
May1st to 15thDay
30%14%30%17%41
288
16th to endDay
27%18%32%15%41
427
June1st to 15thDay
27%15%25%21%7%1
495
16th to endDay
23%13%32%21%6%1
495
July1st to 15thDay
28%13%28%20%8%
416
16th to endDay
25%12%30%21%9%
326
August1st to 15thDay
27%8%25%23%10%3
313
16th to endDay
25%15%26%19%8%5%
332
September1st to 15thDay
29%13%24%21%6%2
315
16th to endDay
25%16%31%15%8%2
314
October1st to 15thDay
27%22%25%17%5%
301
16th to endDay
39%21%23%10%4
288
November1st to 15thDay
31%28%21%11%5%1
235
16th to endDay
35%25%27%9%2
85
December1st to 15thDay
26%21%41%5%5%
60
16th to endDay
34%35%25%31
64
January1st to 15thNight
20%25%33%15%4
726
16th to endNight
16%22%34%19%6%1
768
February1st to 15thNight
12%19%40%21%5%
704
16th to endNight
23%16%38%14%6%
631
March1st to 15thNight
25%20%31%18%4
720
16th to endNight
20%21%29%22%6%
768
April1st to 15thNight
29%18%27%20%3
703
16th to endNight
28%16%30%19%5%
540
May1st to 15thNight
31%11%28%22%5%
421
16th to endNight
27%15%32%19%5%
375
June1st to 15thNight
23%10%28%30%6%
360
16th to endNight
18%11%32%27%8%1
360
July1st to 15thNight
20%10%32%27%8%
340
16th to endNight
19%8%34%25%10%
376
August1st to 15thNight
20%9%26%29%12%1
389
16th to endNight
24%9%31%23%9%1
621
September1st to 15thNight
25%13%27%24%7%1
720
16th to endNight
27%14%29%20%6%1
717
October1st to 15thNight
30%15%29%17%6%
720
16th to endNight
38%19%23%12%5%
768
November1st to 15thNight
27%26%24%13%7%1
700
16th to endNight
25%24%27%16%5%
747
December1st to 15thNight
25%25%30%14%4
750
16th to endNight
25%21%28%18%5%1
800
Page generated at 2017-11-01 17:23:31. Version ac04

Copyright 2017 A. Danko


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