Churchill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Churchill clear sky chart from 2005-11-05 to 2017-09-19.

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
35%
14787
14%
46647
9%
14752
41%
14752
18%
32900

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
16%
718
8%
2485
3%
716
23%
716
8%
2022
January16th to endNight
22%
768
10%
2496
4%
768
28%
768
9%
2034
February1st to 15thNight
20%
701
9%
2287
3%
701
26%
701
10%
1796
February16th to endNight
25%
631
12%
2024
5%
631
33%
631
13%
1505
March1st to 15thNight
23%
720
13%
1980
7%
720
30%
720
16%
1486
March16th to endNight
34%
768
21%
2112
11%
768
41%
768
25%
1429
April1st to 15thNight
29%
718
15%
1820
6%
718
34%
718
22%
1320
April16th to endNight
40%
550
19%
1630
10%
550
46%
550
25%
1089
May1st to 15thNight
47%
483
16%
1563
11%
483
53%
483
24%
999
May16th to endNight
50%
374
17%
1497
15%
374
60%
374
27%
805
June1st to 15thNight
46%
360
12%
1440
12%
360
54%
360
21%
848
June16th to endNight
55%
360
14%
1262
15%
360
59%
360
26%
745
July1st to 15thNight
65%
340
17%
1267
22%
340
69%
340
33%
665
July16th to endNight
60%
477
16%
1511
17%
447
62%
447
31%
868
August1st to 15thNight
67%
539
17%
1609
13%
536
70%
536
37%
917
August16th to endNight
63%
615
22%
1761
14%
615
66%
615
36%
1046
September1st to 15thNight
53%
720
19%
1812
10%
720
57%
720
35%
1165
September16th to endNight
56%
673
21%
1877
16%
673
59%
673
31%
1189
October1st to 15thNight
39%
660
16%
1980
14%
660
44%
660
21%
1370
October16th to endNight
24%
704
10%
2112
6%
704
29%
704
13%
1657
November1st to 15thNight
33%
700
17%
2394
14%
700
39%
700
17%
1655
November16th to endNight
24%
720
10%
2520
7%
720
30%
720
11%
1938
December1st to 15thNight
15%
720
5%
2520
2%
720
19%
720
7%
2069
December16th to endNight
11%
768
5%
2688
1%
768
15%
768
6%
2283

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
15%8%37%6%35%5%5%7%31%
48164
Night
15%9%47%6%35%45%6%32%
46823
Cloud CoverDay
14%8%37%6%35%5%5%7%32%
48174
Night
14%9%47%6%35%45%6%32%
46827
TransparencyDay
50%5%13%19%10%
47858
Night
51%5%12%19%9%
46647
SeeingDay
18%5%24%26%17%7%
5593
Night
19%7%28%30%13%1
14793

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
16%13%6%9%8%45%5%6%5%17%
1450
16th to endDay
12%15%7%10%10%5%5%5%45%15%
1728
February1st to 15thDay
11%14%6%13%9%46%45%5%17%
1575
16th to endDay
15%14%5%10%6%45%5%45%23%
1449
March1st to 15thDay
14%9%48%8%36%445%28%
1969
16th to endDay
14%7%5%7%5%33445%37%
2112
April1st to 15thDay
19%10%35%6%3445%5%30%
2128
16th to endDay
17%7%35%5%23347%38%
2340
May1st to 15thDay
16%6%36%5%345%5%6%36%
2388
16th to endDay
12%5%25%5%245%6%7%41%
2618
June1st to 15thDay
17%6%344245%5%8%37%
2520
16th to endDay
13%5%245%45%5%6%8%37%
2694
July1st to 15thDay
9%4147%36%5%6%8%41%
2613
16th to endDay
9%5%26%6%35%6%6%9%38%
2552
August1st to 15thDay
9%425%6%35%6%6%9%40%
2340
16th to endDay
11%5%25%435%5%7%8%39%
2428
September1st to 15thDay
15%7%25%5%34447%37%
2145
16th to endDay
15%5%27%5%35%45%7%38%
1828
October1st to 15thDay
18%8%37%7%3445%5%31%
1650
16th to endDay
26%12%38%6%34445%19%
1760
November1st to 15thDay
16%11%35%6%445%7%6%27%
1461
16th to endDay
18%15%5%9%8%45%45%6%17%
1440
December1st to 15thDay
17%16%8%11%7%445%46%12%
1440
16th to endDay
20%13%7%10%8%36%5%45%13%
1536
January1st to 15thNight
17%14%6%8%9%45%5%5%5%17%
2485
16th to endNight
13%13%7%11%10%5%6%5%45%15%
2496
February1st to 15thNight
12%16%6%10%9%36%5%46%19%
2285
16th to endNight
14%12%5%9%7%45%45%6%24%
2024
March1st to 15thNight
16%10%5%7%8%45%23431%
1968
16th to endNight
14%8%46%424345%41%
2112
April1st to 15thNight
19%8%35%5%25%446%34%
1820
16th to endNight
14%7%46%5%24436%40%
1630
May1st to 15thNight
16%435%5%2437%8%38%
1563
16th to endNight
11%5%24325%5%5%7%48%
1495
June1st to 15thNight
14%3245%35%5%5%8%40%
1440
16th to endNight
10%425%5%35%5%47%44%
1262
July1st to 15thNight
6%335%423446%54%
1344
16th to endNight
7%324436%5%6%8%46%
1615
August1st to 15thNight
7%3144345%7%9%48%
1620
16th to endNight
9%42343445%7%50%
1761
September1st to 15thNight
14%42342336%6%46%
1812
16th to endNight
14%5%25%5%22346%46%
1877
October1st to 15thNight
18%6%35%5%3445%6%35%
1980
16th to endNight
22%11%36%7%345%5%5%22%
2112
November1st to 15thNight
17%8%46%5%3445%7%31%
2394
16th to endNight
18%13%5%7%6%445%5%6%22%
2520
December1st to 15thNight
18%15%6%11%7%46%435%16%
2520
16th to endNight
20%14%7%12%9%35%445%11%
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
16%13%6%9%9%45%6%5%6%17%
1450
16th to endDay
12%15%6%11%10%46%5%5%6%15%
1728
February1st to 15thDay
11%13%7%13%9%5%6%445%18%
1575
16th to endDay
14%13%5%10%6%36%445%23%
1449
March1st to 15thDay
14%9%48%8%36%5%45%28%
1980
16th to endDay
14%8%47%434445%38%
2111
April1st to 15thDay
19%10%35%5%345%5%5%30%
2128
16th to endDay
16%7%25%5%23447%39%
2340
May1st to 15thDay
15%6%36%4345%6%6%36%
2388
16th to endDay
12%5%25%5%245%6%6%42%
2618
June1st to 15thDay
16%6%25%5%25%46%8%36%
2520
16th to endDay
13%5%245%37%5%5%8%37%
2694
July1st to 15thDay
8%425%5%46%6%5%8%41%
2613
16th to endDay
9%435%6%35%5%7%9%37%
2552
August1st to 15thDay
9%5%25%6%35%5%6%9%39%
2340
16th to endDay
10%5%15%5%35%6%6%9%40%
2428
September1st to 15thDay
16%6%25%5%3445%8%37%
2145
16th to endDay
14%6%26%6%35%45%7%39%
1828
October1st to 15thDay
18%8%37%6%2445%6%31%
1650
16th to endDay
26%12%48%6%335%45%20%
1760
November1st to 15thDay
15%12%37%435%5%6%6%28%
1461
16th to endDay
18%15%6%9%7%35%5%5%6%17%
1440
December1st to 15thDay
16%16%7%11%8%35%5%46%13%
1440
16th to endDay
19%13%7%10%8%45%5%46%13%
1536
January1st to 15thNight
17%15%5%9%8%46%5%5%5%17%
2485
16th to endNight
13%13%6%11%10%5%7%5%5%5%15%
2496
February1st to 15thNight
11%15%6%9%9%45%5%46%19%
2278
16th to endNight
14%12%49%7%45%46%5%25%
2024
March1st to 15thNight
15%10%5%7%7%4433431%
1980
16th to endNight
14%7%36%424445%41%
2112
April1st to 15thNight
19%8%46%5%24346%34%
1820
16th to endNight
14%8%36%5%23437%40%
1630
May1st to 15thNight
14%6%25%6%3446%9%37%
1562
16th to endNight
11%5%24225%5%47%49%
1495
June1st to 15thNight
13%425%5%345%5%8%40%
1440
16th to endNight
9%5%246%45%5%5%7%44%
1262
July1st to 15thNight
6%325%424447%54%
1344
16th to endNight
7%424425%5%7%8%45%
1615
August1st to 15thNight
7%3134345%7%9%48%
1620
16th to endNight
8%5%235%245%5%7%50%
1761
September1st to 15thNight
14%5%2442345%7%45%
1812
16th to endNight
14%6%24424346%46%
1877
October1st to 15thNight
17%7%35%5%34445%36%
1980
16th to endNight
22%10%46%7%35%5%5%6%22%
2112
November1st to 15thNight
17%9%36%43445%7%31%
2394
16th to endNight
19%13%5%8%5%35%45%6%22%
2520
December1st to 15thNight
18%15%6%11%8%45%445%16%
2520
16th to endNight
20%14%6%12%9%35%445%12%
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%6%11%12%4
1451
16th to endDay
68%5%9%11%4
1728
February1st to 15thDay
68%49%13%3
1577
16th to endDay
62%310%15%7%
1449
March1st to 15thDay
56%414%16%6%
1980
16th to endDay
48%310%19%16%1
2112
April1st to 15thDay
54%49%20%11%
2128
16th to endDay
45%311%22%15%2
2340
May1st to 15thDay
46%411%21%14%1
2388
16th to endDay
39%5%14%24%14%2
2622
June1st to 15thDay
43%5%14%24%13%
2520
16th to endDay
42%6%13%23%13%
2694
July1st to 15thDay
37%5%13%25%15%1
2461
16th to endDay
41%6%14%24%11%1
2393
August1st to 15thDay
39%5%17%22%13%1
2327
16th to endDay
38%6%16%27%9%1
2428
September1st to 15thDay
45%5%14%23%10%
2145
16th to endDay
44%5%14%25%9%
1828
October1st to 15thDay
53%311%20%9%
1650
16th to endDay
65%5%14%10%3
1760
November1st to 15thDay
53%6%15%16%7%
1461
16th to endDay
66%6%12%11%3
1440
December1st to 15thDay
72%413%8%
1440
16th to endDay
71%411%10%1
1536
January1st to 15thNight
65%7%10%10%4
2485
16th to endNight
68%5%10%12%2
2496
February1st to 15thNight
64%5%10%15%4
2287
16th to endNight
58%413%15%6%
2024
March1st to 15thNight
57%311%19%6%
1980
16th to endNight
45%310%22%15%1
2112
April1st to 15thNight
51%310%20%13%
1820
16th to endNight
45%310%20%17%2
1630
May1st to 15thNight
42%412%21%16%2
1563
16th to endNight
34%416%27%15%2
1497
June1st to 15thNight
40%5%12%25%15%
1440
16th to endNight
37%6%14%26%15%
1262
July1st to 15thNight
29%5%10%31%21%1
1267
16th to endNight
33%6%13%29%15%1
1511
August1st to 15thNight
28%7%21%28%13%
1609
16th to endNight
31%5%14%29%16%1
1761
September1st to 15thNight
35%5%16%27%12%1
1812
16th to endNight
38%413%30%13%
1877
October1st to 15thNight
47%6%10%22%11%
1980
16th to endNight
60%6%12%13%6%
2112
November1st to 15thNight
50%5%13%20%9%1
2394
16th to endNight
61%5%14%14%3
2520
December1st to 15thNight
69%5%12%9%2
2520
16th to endNight
73%411%8%2
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
17%11%42%15%11%1
63
16th to endDay
28%9%33%28%1
96
February1st to 15thDay
21%10%42%26%
90
16th to endDay
19%15%40%22%2
84
March1st to 15thDay
20%9%34%25%10%
270
16th to endDay
22%5%31%25%12%2
288
April1st to 15thDay
25%7%33%18%11%3
270
16th to endDay
20%8%24%24%16%5%
270
May1st to 15thDay
21%5%21%24%19%8%
288
16th to endDay
16%323%31%18%6%
331
June1st to 15thDay
20%5%18%29%22%3
315
16th to endDay
16%424%32%16%4
489
July1st to 15thDay
11%218%34%23%8%
395
16th to endDay
7%118%37%22%11%
326
August1st to 15thDay
10%15%26%27%18%
313
16th to endDay
13%216%23%26%17%
332
September1st to 15thDay
15%117%20%28%16%
315
16th to endDay
13%216%28%24%13%
266
October1st to 15thDay
18%6%28%23%14%8%
255
16th to endDay
31%11%27%22%7%
272
November1st to 15thDay
19%11%25%22%18%2
81
16th to endDay
31%13%31%15%8%
60
December1st to 15thDay
25%10%36%20%6%1
60
16th to endDay
28%12%51%7%
64
January1st to 15thNight
23%11%37%20%5%
720
16th to endNight
19%10%32%28%8%1
768
February1st to 15thNight
20%10%37%26%5%
704
16th to endNight
22%9%31%30%6%
631
March1st to 15thNight
22%9%35%27%5%
720
16th to endNight
18%8%29%28%13%
768
April1st to 15thNight
22%8%32%29%6%
718
16th to endNight
17%6%29%34%11%1
550
May1st to 15thNight
17%322%37%16%2
483
16th to endNight
12%327%39%17%
375
June1st to 15thNight
14%5%23%40%16%
360
16th to endNight
10%121%43%21%1
360
July1st to 15thNight
6%315%47%23%2
340
16th to endNight
10%219%41%25%1
477
August1st to 15thNight
9%113%42%29%3
539
16th to endNight
11%117%35%30%4
615
September1st to 15thNight
15%320%30%22%7%
720
16th to endNight
16%5%15%33%23%5%
673
October1st to 15thNight
20%427%29%15%1
660
16th to endNight
29%7%31%22%7%
704
November1st to 15thNight
22%8%28%26%12%1
700
16th to endNight
25%13%28%25%7%
720
December1st to 15thNight
27%12%36%19%4
720
16th to endNight
27%10%36%21%4
768
Page generated at 2017-09-20 04:49:52. Version ac04

Copyright 2017 A. Danko


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