Fairmont
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fairmont clear sky chart from 2005-11-05 to 2017-10-06.

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
36%
16147
17%
47113
9%
16100
43%
16100
26%
30791

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
27%
900
13%
2470
5%
895
33%
895
20%
1782
January16th to endNight
24%
960
14%
2496
5%
960
31%
960
18%
1852
February1st to 15thNight
26%
879
11%
2288
2%
875
32%
875
20%
1682
February16th to endNight
28%
762
16%
2024
5%
762
36%
762
24%
1391
March1st to 15thNight
33%
540
17%
1980
12%
540
42%
540
22%
1214
March16th to endNight
27%
576
13%
2112
10%
576
35%
576
15%
1474
April1st to 15thNight
29%
539
16%
1818
11%
539
39%
539
20%
1195
April16th to endNight
25%
540
18%
1644
11%
540
36%
540
19%
1174
May1st to 15thNight
36%
540
15%
1572
9%
540
42%
540
26%
1028
May16th to endNight
41%
563
15%
1498
6%
561
47%
561
29%
1002
June1st to 15thNight
49%
540
14%
1440
5%
540
53%
540
33%
934
June16th to endNight
56%
540
19%
1440
7%
540
60%
540
45%
812
July1st to 15thNight
62%
510
18%
1360
8%
510
65%
510
50%
728
July16th to endNight
68%
564
23%
1523
16%
531
69%
531
48%
799
August1st to 15thNight
64%
539
23%
1610
21%
536
68%
536
41%
883
August16th to endNight
62%
573
23%
1773
23%
573
67%
573
39%
977
September1st to 15thNight
57%
540
25%
1809
21%
540
67%
540
40%
938
September16th to endNight
45%
549
24%
1992
17%
549
57%
549
31%
1081
October1st to 15thNight
35%
684
24%
2052
13%
684
44%
684
30%
1241
October16th to endNight
36%
704
18%
2112
10%
704
42%
704
25%
1369
November1st to 15thNight
32%
845
23%
2372
10%
845
42%
845
29%
1505
November16th to endNight
27%
900
16%
2520
8%
900
34%
900
22%
1747
December1st to 15thNight
22%
900
11%
2520
4%
900
29%
900
17%
1896
December16th to endNight
20%
960
13%
2688
5%
960
28%
960
14%
2087

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
13%7%36%5%3445%7%38%
48077
Night
12%7%35%5%24446%42%
47291
Cloud CoverDay
13%7%36%5%3445%7%38%
48088
Night
12%7%35%5%24446%42%
47295
Cloud CoverDay
14%7%36%5%3445%7%38%
48086
Night
12%7%35%5%24446%43%
47295
TransparencyDay
44%6%14%22%10%1
47774
Night
41%5%14%23%13%1
47113
SeeingDay
16%7%29%28%14%3
6147
Night
15%8%33%30%11%1
16148

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
8%11%6%9%8%35%5%6%6%27%
1465
16th to endDay
10%13%6%10%7%35%5%5%5%25%
1728
February1st to 15thDay
9%14%6%9%7%5%5%45%6%25%
1575
16th to endDay
12%8%39%7%35%5%5%8%29%
1458
March1st to 15thDay
16%10%5%9%5%23337%32%
1969
16th to endDay
18%10%46%6%245%5%5%29%
2112
April1st to 15thDay
17%6%37%4245%6%6%34%
2128
16th to endDay
26%11%35%413346%28%
2313
May1st to 15thDay
21%7%25%5%24446%33%
2379
16th to endDay
15%6%25%6%35%45%6%37%
2617
June1st to 15thDay
15%425%5%3445%8%40%
2520
16th to endDay
8%4245%345%6%9%45%
2520
July1st to 15thDay
5%313435%6%6%10%50%
2520
16th to endDay
5%414425%5%7%9%48%
2537
August1st to 15thDay
8%5%26%6%35%5%6%8%42%
2340
16th to endDay
10%5%25%43445%7%45%
2429
September1st to 15thDay
11%5%2332445%7%49%
2148
16th to endDay
12%5%14414347%49%
1955
October1st to 15thDay
14%6%245%23345%46%
1706
16th to endDay
16%8%25%5%24335%41%
1760
November1st to 15thDay
11%6%25%42335%7%46%
1482
16th to endDay
14%8%37%5%24348%37%
1440
December1st to 15thDay
17%10%5%10%9%45%336%24%
1440
16th to endDay
17%16%5%9%7%24446%23%
1536
January1st to 15thNight
7%9%5%8%7%36%6%5%7%32%
2470
16th to endNight
11%11%5%7%7%35%5%5%7%30%
2496
February1st to 15thNight
12%11%47%6%35%45%5%33%
2285
16th to endNight
10%7%36%8%3445%6%38%
2024
March1st to 15thNight
12%8%35%42335%6%43%
1968
16th to endNight
17%9%47%5%24446%33%
2112
April1st to 15thNight
16%7%35%425%446%39%
1818
16th to endNight
22%9%36%5%2333436%
1644
May1st to 15thNight
15%5%25%42336%6%43%
1572
16th to endNight
13%5%15%5%245%5%9%42%
1496
June1st to 15thNight
10%325%5%25%46%10%43%
1440
16th to endNight
6%212324449%57%
1440
July1st to 15thNight
321333346%8%61%
1440
16th to endNight
221332445%10%59%
1628
August1st to 15thNight
5%31342336%8%55%
1620
16th to endNight
8%413423336%58%
1773
September1st to 15thNight
10%31322235%6%57%
1809
16th to endNight
9%5%23324447%53%
1992
October1st to 15thNight
14%6%2431333451%
2052
16th to endNight
16%7%24423345%44%
2112
November1st to 15thNight
12%6%25%42345%5%47%
2372
16th to endNight
11%9%47%5%24446%40%
2520
December1st to 15thNight
13%10%5%7%8%35%445%29%
2520
16th to endNight
19%12%5%8%7%24445%26%
2688

Percentage Cloud Cover SW (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
8%11%6%9%8%445%6%6%27%
1465
16th to endDay
10%13%6%9%8%36%5%46%25%
1728
February1st to 15thDay
10%13%6%10%7%46%36%6%25%
1575
16th to endDay
12%8%49%7%35%5%5%7%30%
1458
March1st to 15thDay
16%10%5%9%6%23337%32%
1980
16th to endDay
18%11%47%5%245%5%5%29%
2112
April1st to 15thDay
17%7%37%42445%6%34%
2128
16th to endDay
26%11%35%423346%28%
2313
May1st to 15thDay
21%7%25%5%24445%34%
2379
16th to endDay
15%6%26%5%35%45%6%37%
2617
June1st to 15thDay
16%425%5%3445%7%40%
2520
16th to endDay
8%4245%3446%9%45%
2520
July1st to 15thDay
5%223435%5%6%9%51%
2520
16th to endDay
5%3134346%6%10%49%
2537
August1st to 15thDay
8%5%26%6%35%5%6%8%42%
2340
16th to endDay
11%5%25%43345%7%46%
2429
September1st to 15thDay
10%5%23324448%49%
2148
16th to endDay
12%5%24324347%49%
1955
October1st to 15thDay
15%6%25%423345%45%
1706
16th to endDay
16%8%25%423335%41%
1760
November1st to 15thDay
11%6%25%42335%6%47%
1482
16th to endDay
13%8%27%5%24348%37%
1440
December1st to 15thDay
16%10%5%10%8%45%335%24%
1440
16th to endDay
17%15%6%8%6%23446%23%
1536
January1st to 15thNight
8%8%5%7%8%35%6%5%8%32%
2470
16th to endNight
10%11%5%7%6%35%5%5%7%30%
2496
February1st to 15thNight
11%11%5%7%6%25%445%34%
2278
16th to endNight
10%7%37%7%35%45%6%38%
2024
March1st to 15thNight
12%8%35%42335%6%43%
1980
16th to endNight
17%9%37%5%24446%33%
2112
April1st to 15thNight
16%7%35%425%446%39%
1818
16th to endNight
21%9%26%5%2423436%
1644
May1st to 15thNight
15%5%25%42335%7%43%
1571
16th to endNight
13%5%25%5%235%49%42%
1496
June1st to 15thNight
9%4245%25%5%5%9%44%
1440
16th to endNight
6%212323448%58%
1440
July1st to 15thNight
321342435%8%61%
1440
16th to endNight
221322446%9%59%
1628
August1st to 15thNight
5%41343336%8%56%
1620
16th to endNight
8%323313336%58%
1773
September1st to 15thNight
10%31222235%6%57%
1809
16th to endNight
9%5%23414447%52%
1992
October1st to 15thNight
14%6%15%31333450%
2052
16th to endNight
16%8%24423345%44%
2112
November1st to 15thNight
11%6%25%42445%447%
2372
16th to endNight
11%9%37%5%24436%40%
2520
December1st to 15thNight
13%10%6%7%8%35%445%30%
2520
16th to endNight
18%12%5%8%6%33445%26%
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
8%11%6%9%8%35%5%6%6%27%
1465
16th to endDay
10%13%6%8%8%45%5%5%5%25%
1728
February1st to 15thDay
9%13%7%9%7%46%45%6%25%
1575
16th to endDay
12%8%48%7%35%5%5%7%30%
1458
March1st to 15thDay
16%9%5%9%5%23337%32%
1980
16th to endDay
18%11%36%5%345%5%5%30%
2110
April1st to 15thDay
18%6%37%42445%7%34%
2128
16th to endDay
27%10%35%423346%28%
2313
May1st to 15thDay
22%6%245%24446%34%
2379
16th to endDay
15%5%35%5%25%45%7%37%
2617
June1st to 15thDay
16%4245%34448%40%
2520
16th to endDay
9%424435%46%9%46%
2520
July1st to 15thDay
6%313435%5%6%10%51%
2520
16th to endDay
6%3134246%7%9%49%
2537
August1st to 15thDay
9%426%6%25%5%6%8%42%
2340
16th to endDay
11%5%2443345%7%46%
2429
September1st to 15thDay
11%42432445%7%49%
2148
16th to endDay
12%5%14414337%49%
1955
October1st to 15thDay
15%5%25%423345%46%
1706
16th to endDay
17%8%25%433335%42%
1760
November1st to 15thDay
11%6%25%42335%6%47%
1482
16th to endDay
14%7%37%6%24348%37%
1440
December1st to 15thDay
16%10%5%10%8%45%435%25%
1440
16th to endDay
18%16%5%8%7%23436%23%
1536
January1st to 15thNight
8%8%6%7%7%36%6%5%7%32%
2470
16th to endNight
11%10%5%7%7%35%45%7%30%
2496
February1st to 15thNight
11%11%5%7%5%3435%5%34%
2278
16th to endNight
9%8%36%7%3445%6%38%
2024
March1st to 15thNight
13%8%35%413347%43%
1980
16th to endNight
18%9%36%5%34446%33%
2112
April1st to 15thNight
16%7%25%425%5%46%39%
1818
16th to endNight
22%9%26%5%2333436%
1644
May1st to 15thNight
15%6%15%42335%6%44%
1571
16th to endNight
13%5%244245%48%43%
1496
June1st to 15thNight
10%325%4345%5%10%44%
1440
16th to endNight
6%212323448%58%
1440
July1st to 15thNight
321342345%8%60%
1440
16th to endNight
3213315%36%8%60%
1628
August1st to 15thNight
6%31342336%8%56%
1620
16th to endNight
9%313323336%58%
1773
September1st to 15thNight
10%31332235%6%58%
1809
16th to endNight
10%413313447%53%
1992
October1st to 15thNight
15%5%2432343451%
2052
16th to endNight
16%7%24423345%44%
2112
November1st to 15thNight
12%6%25%42345%447%
2372
16th to endNight
11%8%47%5%24446%40%
2520
December1st to 15thNight
14%10%5%7%8%345%46%29%
2520
16th to endNight
18%13%5%8%7%34345%26%
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
53%6%15%15%8%
1466
16th to endDay
57%6%15%16%4
1728
February1st to 15thDay
58%413%15%6%
1576
16th to endDay
51%6%13%18%7%1
1458
March1st to 15thDay
53%5%14%19%6%
1980
16th to endDay
54%8%14%18%4
2112
April1st to 15thDay
47%7%13%21%8%1
2128
16th to endDay
57%6%11%17%6%
2313
May1st to 15thDay
50%6%13%20%9%
2379
16th to endDay
45%7%12%21%11%1
2621
June1st to 15thDay
41%7%15%23%11%
2520
16th to endDay
33%7%15%27%13%1
2520
July1st to 15thDay
27%9%16%29%13%3
2371
16th to endDay
28%8%17%27%16%1
2380
August1st to 15thDay
36%9%14%25%11%1
2326
16th to endDay
36%6%13%27%13%2
2429
September1st to 15thDay
32%6%16%27%16%
2148
16th to endDay
34%6%12%32%12%
1955
October1st to 15thDay
39%5%12%24%17%1
1706
16th to endDay
44%413%24%11%
1760
November1st to 15thDay
36%5%13%23%18%1
1482
16th to endDay
46%5%19%19%9%
1440
December1st to 15thDay
62%5%12%11%7%1
1440
16th to endDay
62%5%11%14%5%
1536
January1st to 15thNight
48%7%14%19%9%
2470
16th to endNight
52%6%16%18%7%
2496
February1st to 15thNight
51%5%13%20%8%
2288
16th to endNight
44%5%15%21%10%2
2024
March1st to 15thNight
40%5%16%24%10%1
1980
16th to endNight
52%6%12%21%6%
2112
April1st to 15thNight
44%6%10%24%12%1
1818
16th to endNight
53%38%18%13%2
1644
May1st to 15thNight
40%6%15%21%13%1
1572
16th to endNight
37%8%14%23%13%2
1498
June1st to 15thNight
35%6%17%25%13%1
1440
16th to endNight
24%5%15%30%21%2
1440
July1st to 15thNight
20%5%17%33%17%4
1360
16th to endNight
20%6%16%32%20%4
1523
August1st to 15thNight
25%6%13%31%19%2
1610
16th to endNight
27%5%14%30%17%4
1773
September1st to 15thNight
25%5%14%30%21%1
1809
16th to endNight
30%5%13%31%16%1
1992
October1st to 15thNight
37%311%24%20%2
2052
16th to endNight
41%5%14%23%14%1
2112
November1st to 15thNight
37%412%23%19%1
2372
16th to endNight
45%6%16%20%9%1
2520
December1st to 15thNight
54%6%12%19%6%
2520
16th to endNight
59%5%11%14%8%
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
21%6%36%27%6%1
90
16th to endDay
23%10%28%31%5%1
96
February1st to 15thDay
14%22%40%18%4
90
16th to endDay
20%12%32%22%12%
81
March1st to 15thDay
23%10%36%30%
90
16th to endDay
41%8%23%19%6%
96
April1st to 15thDay
23%8%35%25%7%
247
16th to endDay
34%12%24%18%8%1
423
May1st to 15thDay
22%13%30%24%7%2
468
16th to endDay
19%8%29%27%12%2
517
June1st to 15thDay
14%431%30%14%3
495
16th to endDay
8%7%35%30%15%3
495
July1st to 15thDay
6%229%35%19%6%
475
16th to endDay
7%327%34%22%4
515
August1st to 15thDay
8%220%38%25%3
493
16th to endDay
14%5%22%29%22%5%
469
September1st to 15thDay
11%426%33%18%5%
303
16th to endDay
18%8%30%27%9%5%
135
October1st to 15thDay
13%12%37%18%14%3
107
16th to endDay
17%12%37%16%14%1
96
November1st to 15thDay
36%34%40%12%3
90
16th to endDay
36%11%26%18%6%
90
December1st to 15thDay
23%15%36%17%6%
90
16th to endDay
35%17%32%10%4
96
January1st to 15thNight
11%13%39%27%7%1
900
16th to endNight
17%12%36%27%6%
960
February1st to 15thNight
18%10%37%26%6%1
880
16th to endNight
12%11%39%25%8%2
762
March1st to 15thNight
15%8%38%26%10%
540
16th to endNight
21%8%35%25%8%
576
April1st to 15thNight
19%10%34%28%6%
539
16th to endNight
27%9%32%21%8%1
540
May1st to 15thNight
17%8%33%29%9%1
540
16th to endNight
15%6%32%32%12%
563
June1st to 15thNight
10%5%30%40%13%
540
16th to endNight
7%229%44%15%
540
July1st to 15thNight
3127%41%23%2
510
16th to endNight
2122%47%24%2
564
August1st to 15thNight
6%120%42%26%2
539
16th to endNight
12%118%39%23%4
573
September1st to 15thNight
12%125%37%20%2
540
16th to endNight
10%9%31%32%14%1
549
October1st to 15thNight
16%8%34%26%12%1
684
16th to endNight
20%9%29%31%8%
704
November1st to 15thNight
15%11%37%24%10%
845
16th to endNight
15%14%37%24%8%
900
December1st to 15thNight
18%9%38%27%4
900
16th to endNight
23%10%34%24%6%
960
Page generated at 2017-10-07 13:07:56. Version ac04

Copyright 2017 A. Danko


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