McGill's Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McGill's Island clear sky chart from 2005-11-05 to 2017-10-16.

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
22%
15203
12%
46873
5%
15161
29%
15161
14%
34516

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
15%
739
9%
2443
3%
735
23%
735
9%
1914
January16th to endNight
13%
768
8%
2496
2%
768
20%
768
8%
1984
February1st to 15thNight
12%
701
7%
2286
1%
701
19%
701
7%
1843
February16th to endNight
15%
631
10%
1994
3%
631
24%
631
10%
1532
March1st to 15thNight
17%
720
14%
1998
5%
720
25%
720
13%
1535
March16th to endNight
18%
768
15%
2112
4%
768
29%
768
17%
1527
April1st to 15thNight
16%
587
14%
1814
4%
587
26%
587
13%
1336
April16th to endNight
19%
540
14%
1620
5%
540
27%
540
17%
1159
May1st to 15thNight
17%
540
11%
1605
3%
540
24%
540
13%
1220
May16th to endNight
22%
561
10%
1496
4%
560
27%
560
17%
1135
June1st to 15thNight
20%
491
8%
1391
3%
491
24%
491
13%
1088
June16th to endNight
26%
360
9%
1260
4%
360
33%
360
15%
895
July1st to 15thNight
32%
371
10%
1221
7%
371
37%
371
19%
847
July16th to endNight
26%
565
9%
1558
7%
532
30%
532
17%
1173
August1st to 15thNight
37%
539
13%
1608
9%
535
40%
535
21%
1110
August16th to endNight
34%
573
18%
1755
10%
573
41%
573
23%
1160
September1st to 15thNight
32%
588
18%
1848
10%
588
41%
588
22%
1215
September16th to endNight
37%
717
23%
1980
14%
717
45%
717
26%
1303
October1st to 15thNight
29%
720
17%
2160
8%
720
38%
720
20%
1472
October16th to endNight
22%
708
16%
2127
5%
708
31%
708
17%
1487
November1st to 15thNight
29%
716
14%
2373
7%
716
37%
716
17%
1654
November16th to endNight
22%
750
11%
2520
5%
750
30%
750
12%
1850
December1st to 15thNight
16%
750
9%
2520
3%
750
25%
750
10%
1943
December16th to endNight
13%
800
8%
2688
2%
800
21%
800
7%
2134

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
22%9%46%5%24346%30%
48498
Night
21%9%36%5%3445%6%28%
47049
TransparencyDay
54%5%11%18%9%1
48192
Night
54%6%11%18%8%
46873
SeeingDay
29%15%29%17%6%1
7411
Night
27%13%31%21%5%
15206

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%8%7%5%5%45%5%15%
1448
16th to endDay
20%13%5%9%7%45%45%5%19%
1728
February1st to 15thDay
16%16%7%9%8%46%446%14%
1575
16th to endDay
15%14%7%10%7%34345%22%
1476
March1st to 15thDay
22%13%46%6%3432427%
1951
16th to endDay
19%11%6%7%5%22345%30%
2112
April1st to 15thDay
22%13%36%424435%30%
2132
16th to endDay
25%7%24323345%35%
2340
May1st to 15thDay
28%9%46%323245%29%
2346
16th to endDay
26%8%35%424347%30%
2618
June1st to 15thDay
30%7%26%5%24235%27%
2577
16th to endDay
25%6%2443445%6%33%
2700
July1st to 15thDay
23%6%33323449%33%
2654
16th to endDay
23%8%35%4245%46%30%
2500
August1st to 15thDay
20%6%35%4345%5%6%35%
2340
16th to endDay
17%6%24324447%42%
2447
September1st to 15thDay
19%6%33323237%43%
2110
16th to endDay
19%6%24423336%42%
1980
October1st to 15thDay
21%6%34424336%40%
1800
16th to endDay
24%7%46%5%3435%5%28%
1763
November1st to 15thDay
23%11%46%5%24345%28%
1485
16th to endDay
23%10%5%8%5%35%445%21%
1440
December1st to 15thDay
26%12%5%6%6%45%345%18%
1440
16th to endDay
25%14%6%9%6%25%335%17%
1536
January1st to 15thNight
18%11%48%7%45%5%6%7%19%
2443
16th to endNight
18%13%5%9%7%5%5%5%5%7%16%
2496
February1st to 15thNight
18%13%6%10%8%47%5%5%5%16%
2285
16th to endNight
13%13%5%8%8%46%5%5%7%21%
1994
March1st to 15thNight
21%10%36%6%35%445%27%
1986
16th to endNight
18%9%5%6%5%35%346%32%
2112
April1st to 15thNight
26%9%36%424436%29%
1814
16th to endNight
24%8%245%33446%31%
1620
May1st to 15thNight
26%10%36%424435%27%
1605
16th to endNight
25%7%26%42446%5%30%
1494
June1st to 15thNight
29%9%36%43335%6%24%
1391
16th to endNight
25%7%35%334347%31%
1260
July1st to 15thNight
22%7%2342345%10%31%
1293
16th to endNight
23%7%36%425%45%8%27%
1665
August1st to 15thNight
18%7%36%322447%37%
1620
16th to endNight
16%6%35%42345%7%41%
1755
September1st to 15thNight
20%5%24324346%41%
1848
16th to endNight
20%5%24323445%43%
1980
October1st to 15thNight
21%7%24423446%38%
2160
16th to endNight
23%8%25%423446%34%
2127
November1st to 15thNight
21%7%35%5%3446%8%29%
2373
16th to endNight
21%10%46%43445%6%28%
2520
December1st to 15thNight
24%11%47%5%34448%20%
2520
16th to endNight
25%12%5%8%6%2445%5%19%
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%7%13%11%3
1449
16th to endDay
63%6%10%16%3
1728
February1st to 15thDay
67%8%11%9%3
1578
16th to endDay
61%6%11%14%5%
1476
March1st to 15thDay
59%49%16%8%1
1962
16th to endDay
56%49%17%9%2
2112
April1st to 15thDay
57%48%16%12%1
2132
16th to endDay
50%411%19%12%1
2340
May1st to 15thDay
58%5%8%16%10%1
2346
16th to endDay
53%6%11%19%7%
2622
June1st to 15thDay
59%49%15%8%1
2577
16th to endDay
51%7%11%18%10%1
2700
July1st to 15thDay
46%6%14%20%10%1
2498
16th to endDay
52%7%11%20%6%
2344
August1st to 15thDay
47%7%11%19%12%1
2327
16th to endDay
40%6%13%24%14%
2447
September1st to 15thDay
41%5%10%22%17%1
2110
16th to endDay
43%47%26%16%1
1980
October1st to 15thDay
47%310%23%13%1
1800
16th to endDay
55%5%12%16%9%
1763
November1st to 15thDay
57%410%17%8%1
1485
16th to endDay
61%6%13%13%4
1440
December1st to 15thDay
64%6%11%13%3
1440
16th to endDay
68%49%12%4
1536
January1st to 15thNight
59%8%14%13%3
2443
16th to endNight
61%8%13%13%2
2496
February1st to 15thNight
64%6%11%13%3
2286
16th to endNight
58%7%12%14%6%
1994
March1st to 15thNight
57%5%11%15%8%1
1998
16th to endNight
51%411%17%13%1
2112
April1st to 15thNight
56%310%15%10%2
1814
16th to endNight
52%5%11%19%10%2
1620
May1st to 15thNight
58%5%8%18%8%
1605
16th to endNight
54%6%12%17%8%
1496
June1st to 15thNight
60%5%9%17%6%
1391
16th to endNight
53%6%12%16%10%
1260
July1st to 15thNight
46%9%14%19%9%
1221
16th to endNight
52%9%11%19%5%1
1558
August1st to 15thNight
46%6%12%23%10%
1608
16th to endNight
41%8%11%24%13%
1755
September1st to 15thNight
44%5%8%26%13%1
1848
16th to endNight
41%47%27%18%1
1980
October1st to 15thNight
46%5%10%21%13%1
2160
16th to endNight
49%5%11%22%10%
2127
November1st to 15thNight
49%6%15%19%7%
2373
16th to endNight
54%7%14%16%6%
2520
December1st to 15thNight
60%6%14%15%3
2520
16th to endNight
63%7%12%12%4
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
26%19%32%18%3
194
16th to endDay
27%21%36%11%2
256
February1st to 15thDay
26%19%33%17%2
236
16th to endDay
21%19%36%18%3
222
March1st to 15thDay
32%24%25%11%5%
270
16th to endDay
30%21%27%10%7%1
288
April1st to 15thDay
31%23%28%12%4
270
16th to endDay
26%20%33%12%5%1
270
May1st to 15thDay
35%17%30%11%31
302
16th to endDay
35%13%27%16%41
519
June1st to 15thDay
32%15%30%16%5%
495
16th to endDay
34%11%24%21%6%1
495
July1st to 15thDay
28%8%30%21%9%1
475
16th to endDay
28%9%28%24%8%1
361
August1st to 15thDay
23%9%31%24%7%1
313
16th to endDay
23%10%27%22%13%2
332
September1st to 15thDay
22%11%35%21%6%2
315
16th to endDay
25%12%29%17%9%4
314
October1st to 15thDay
27%10%32%16%10%3
270
16th to endDay
26%21%27%16%6%
243
November1st to 15thDay
26%16%27%17%11%
235
16th to endDay
33%16%23%18%5%1
240
December1st to 15thDay
37%20%25%13%2
240
16th to endDay
36%18%27%14%2
256
January1st to 15thNight
27%18%32%18%3
739
16th to endNight
29%17%31%17%2
768
February1st to 15thNight
28%17%32%19%1
704
16th to endNight
25%17%34%17%4
631
March1st to 15thNight
27%19%30%19%3
720
16th to endNight
24%17%34%16%6%
768
April1st to 15thNight
30%16%32%17%3
587
16th to endNight
28%12%34%17%5%
540
May1st to 15thNight
32%13%32%16%4
540
16th to endNight
27%10%36%19%5%1
561
June1st to 15thNight
31%9%33%21%3
491
16th to endNight
30%5%33%22%8%
360
July1st to 15thNight
23%6%34%28%7%
371
16th to endNight
24%5%37%27%4
565
August1st to 15thNight
22%6%26%33%10%
539
16th to endNight
19%6%33%28%9%1
573
September1st to 15thNight
21%9%34%24%9%1
588
16th to endNight
23%9%25%24%14%2
717
October1st to 15thNight
26%11%28%22%10%1
720
16th to endNight
29%15%29%20%5%
708
November1st to 15thNight
23%13%28%24%8%1
716
16th to endNight
27%17%27%19%7%
750
December1st to 15thNight
33%16%28%18%3
750
16th to endNight
34%19%27%17%2
800
Page generated at 2017-10-17 17:35:23. Version ac04

Copyright 2017 A. Danko


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