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 2017-09-18.

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%
15021
5%
46584
4%
14989
38%
14989
9%
37549

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
35%
898
6%
3043
6%
895
37%
895
8%
2494
January16th to endNight
37%
960
7%
2924
4%
960
41%
960
10%
2342
February1st to 15thNight
43%
876
8%
2580
6%
876
44%
876
12%
1993
February16th to endNight
42%
789
8%
2051
4%
789
44%
789
11%
1694
March1st to 15thNight
46%
726
10%
2166
8%
726
48%
726
15%
1632
March16th to endNight
48%
576
12%
2067
11%
576
56%
576
12%
1467
April1st to 15thNight
44%
539
13%
1663
8%
539
47%
539
16%
1206
April16th to endNight
46%
540
8%
1469
5%
540
48%
540
19%
1051
May1st to 15thNight
31%
495
0%
1215
0%
495
31%
495
12%
1000
May16th to endNight
36%
344
0%
1094
0%
344
36%
344
12%
823
June1st to 15thNight
41%
180
0%
900
0%
180
41%
180
9%
625
June16th to endNight
52%
180
0%
900
0%
180
52%
180
13%
557
July1st to 15thNight
51%
170
0%
850
0%
170
51%
170
11%
578
July16th to endNight
47%
382
0%
1064
0%
356
51%
356
20%
734
August1st to 15thNight
50%
539
1%
1253
1%
536
50%
536
23%
944
August16th to endNight
43%
573
6%
1628
4%
573
44%
573
15%
1245
September1st to 15thNight
30%
540
4%
1732
3%
540
31%
540
9%
1382
September16th to endNight
25%
542
7%
1845
5%
542
28%
542
8%
1494
October1st to 15thNight
18%
660
5%
1980
4%
660
20%
660
5%
1764
October16th to endNight
15%
877
1%
2445
1%
877
15%
877
2%
2312
November1st to 15thNight
21%
875
3%
2595
2%
875
22%
875
3%
2402
November16th to endNight
33%
900
4%
2880
2%
900
34%
900
4%
2547
December1st to 15thNight
36%
900
3%
2976
2%
900
37%
900
6%
2554
December16th to endNight
35%
960
8%
3264
7%
960
38%
960
7%
2709

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%11%48%6%46%6%6%7%23%
48269
Night
13%12%5%8%8%47%7%7%6%17%
46700
Cloud CoverDay
14%11%48%7%46%6%6%7%23%
48278
Night
13%12%5%8%8%47%7%8%6%17%
46703
TransparencyDay
57%7%13%17%3
47902
Night
63%7%11%13%3
46584
SeeingDay
18%10%10%26%24%9%
6273
Night
17%16%13%26%19%5%
15028

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
7%12%5%9%7%7%10%9%9%8%11%
895
16th to endDay
6%13%6%11%9%49%8%12%10%7%
1296
February1st to 15thDay
48%46%9%6%13%11%10%9%15%
1283
16th to endDay
6%9%5%8%7%6%9%11%12%11%10%
1422
March1st to 15thDay
8%10%5%8%7%47%8%10%11%17%
1795
16th to endDay
6%7%48%7%5%10%9%9%7%22%
2157
April1st to 15thDay
9%10%39%9%5%9%8%6%5%20%
2282
16th to endDay
6%8%311%11%6%7%5%5%8%24%
2490
May1st to 15thDay
19%13%6%10%8%3334421%
2736
16th to endDay
14%11%5%7%6%245%5%7%28%
3017
June1st to 15thDay
17%10%45%5%35%446%33%
3060
16th to endDay
11%5%35%5%25%5%6%8%41%
3060
July1st to 15thDay
17%8%36%435%5%6%8%30%
3060
16th to endDay
14%6%26%5%25%5%5%7%38%
3026
August1st to 15thDay
19%5%245%345%5%7%36%
2700
16th to endDay
23%7%36%5%245%5%8%28%
2572
September1st to 15thDay
24%13%36%6%34445%24%
2227
16th to endDay
26%19%47%6%2443416%
1828
October1st to 15thDay
33%21%47%43423412%
1650
16th to endDay
28%22%6%14%7%222337%
1426
November1st to 15thDay
17%16%7%14%10%46%35%210%
1263
16th to endDay
8%16%8%10%7%6%7%8%7%6%12%
1080
December1st to 15thDay
7%12%5%11%10%6%9%8%10%7%10%
984
16th to endDay
8%14%6%10%9%6%9%8%7%7%10%
960
January1st to 15thNight
7%10%5%12%11%6%8%8%12%7%8%
3043
16th to endNight
7%13%5%8%9%5%10%10%14%7%7%
2924
February1st to 15thNight
38%47%11%6%11%10%13%10%11%
2577
16th to endNight
5%8%5%12%10%6%9%11%10%8%10%
2051
March1st to 15thNight
8%9%5%7%6%49%10%9%8%20%
2154
16th to endNight
7%8%36%6%6%10%10%7%7%24%
2067
April1st to 15thNight
10%9%37%6%39%7%7%7%27%
1663
16th to endNight
8%7%6%8%9%45%45%7%33%
1469
May1st to 15thNight
20%13%5%11%7%34345%20%
1215
16th to endNight
15%13%7%8%5%3445%6%26%
1093
June1st to 15thNight
15%9%5%8%6%15%45%7%29%
900
16th to endNight
12%6%345%45%6%6%5%38%
900
July1st to 15thNight
15%8%36%436%47%7%32%
900
16th to endNight
14%8%25%6%25%46%7%35%
1139
August1st to 15thNight
21%5%25%5%2446%7%33%
1260
16th to endNight
19%8%27%6%36%5%5%5%28%
1628
September1st to 15thNight
24%10%35%6%35%45%6%23%
1732
16th to endNight
25%16%46%434335%22%
1845
October1st to 15thNight
34%19%36%42333315%
1980
16th to endNight
32%20%6%10%6%332328%
2445
November1st to 15thNight
17%18%8%12%9%35%5%4310%
2595
16th to endNight
8%14%6%10%7%5%9%8%7%8%12%
2880
December1st to 15thNight
7%10%5%10%10%6%9%7%11%9%9%
2976
16th to endNight
9%14%6%10%8%5%9%9%6%7%11%
3264

Percentage Cloud Cover NW (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
6%12%6%9%7%7%10%9%10%9%10%
895
16th to endDay
6%12%5%11%9%5%9%9%12%10%6%
1296
February1st to 15thDay
38%5%6%9%6%14%11%10%9%14%
1283
16th to endDay
6%10%49%7%5%9%11%13%10%9%
1422
March1st to 15thDay
8%10%5%8%7%47%8%10%11%16%
1806
16th to endDay
6%7%48%7%5%11%9%9%7%22%
2155
April1st to 15thDay
9%11%39%9%6%10%8%6%6%19%
2282
16th to endDay
6%8%410%10%7%7%6%5%7%24%
2490
May1st to 15thDay
19%13%6%10%8%3334421%
2736
16th to endDay
13%12%5%7%6%245%5%6%28%
3017
June1st to 15thDay
16%10%45%5%34446%32%
3060
16th to endDay
10%5%35%5%25%5%6%7%41%
3060
July1st to 15thDay
16%8%46%436%5%5%8%30%
3060
16th to endDay
13%6%25%5%35%5%5%7%38%
3026
August1st to 15thDay
19%5%25%5%345%5%8%35%
2700
16th to endDay
22%8%26%5%245%5%7%28%
2572
September1st to 15thDay
23%13%37%6%24445%23%
2227
16th to endDay
26%20%47%6%3333415%
1828
October1st to 15thDay
32%21%5%7%5%3322412%
1650
16th to endDay
28%22%8%13%7%222326%
1426
November1st to 15thDay
17%17%7%14%10%45%4438%
1263
16th to endDay
8%16%9%10%7%7%8%9%6%412%
1080
December1st to 15thDay
6%11%6%11%10%6%9%9%10%6%9%
984
16th to endDay
8%15%7%10%8%7%8%8%7%8%10%
960
January1st to 15thNight
7%10%5%12%11%6%8%9%13%6%7%
3043
16th to endNight
6%13%6%8%9%5%10%10%15%7%7%
2924
February1st to 15thNight
39%47%11%6%11%10%13%10%11%
2570
16th to endNight
5%7%5%11%10%6%9%12%11%8%10%
2051
March1st to 15thNight
8%10%5%6%6%49%10%9%9%18%
2166
16th to endNight
7%7%35%7%6%10%10%8%7%24%
2065
April1st to 15thNight
10%9%37%6%39%7%7%7%26%
1663
16th to endNight
8%7%5%8%9%45%45%7%32%
1469
May1st to 15thNight
19%12%5%12%8%24345%20%
1214
16th to endNight
15%12%6%9%6%34446%26%
1094
June1st to 15thNight
15%10%5%8%5%25%45%9%28%
900
16th to endNight
12%6%35%5%36%6%6%6%36%
900
July1st to 15thNight
15%8%36%436%5%6%7%31%
900
16th to endNight
13%8%35%6%245%6%7%36%
1139
August1st to 15thNight
21%6%246%2345%6%34%
1260
16th to endNight
18%8%37%7%36%6%5%6%27%
1628
September1st to 15thNight
23%10%46%6%45%45%5%23%
1732
16th to endNight
24%16%45%5%34335%21%
1845
October1st to 15thNight
34%19%46%5%2323314%
1980
16th to endNight
32%20%7%10%7%232227%
2445
November1st to 15thNight
17%18%8%13%9%36%5%3310%
2595
16th to endNight
8%14%7%10%8%5%9%9%8%6%11%
2880
December1st to 15thNight
7%10%5%11%11%6%10%8%11%8%8%
2976
16th to endNight
9%14%6%10%8%5%9%9%7%7%11%
3264

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
63%8%14%11%2
895
16th to endDay
63%5%10%14%5%
1296
February1st to 15thDay
56%7%13%19%3
1284
16th to endDay
58%8%11%14%6%
1422
March1st to 15thDay
53%7%11%21%6%
1806
16th to endDay
53%6%11%19%7%
2157
April1st to 15thDay
59%7%11%14%6%
2282
16th to endDay
54%7%15%18%4
2490
May1st to 15thDay
64%5%10%14%4
2736
16th to endDay
53%6%14%20%4
3021
June1st to 15thDay
51%6%14%23%4
3060
16th to endDay
40%6%15%29%8%
3060
July1st to 15thDay
49%7%17%22%3
2881
16th to endDay
43%8%19%25%2
2839
August1st to 15thDay
45%7%22%21%3
2683
16th to endDay
52%9%18%17%1
2572
September1st to 15thDay
62%8%13%13%1
2227
16th to endDay
71%5%10%9%1
1828
October1st to 15thDay
80%5%6%6%1
1650
16th to endDay
87%45%2
1426
November1st to 15thDay
84%6%5%3
1263
16th to endDay
74%10%8%5%
1080
December1st to 15thDay
69%9%10%9%1
984
16th to endDay
66%8%11%12%
960
January1st to 15thNight
66%7%11%12%2
3043
16th to endNight
62%7%11%14%3
2924
February1st to 15thNight
56%9%13%15%4
2580
16th to endNight
60%10%9%12%7%
2051
March1st to 15thNight
54%7%14%17%4
2166
16th to endNight
51%8%12%18%8%1
2067
April1st to 15thNight
51%6%11%20%8%1
1663
16th to endNight
50%5%13%22%8%
1469
May1st to 15thNight
64%48%16%4
1215
16th to endNight
58%5%10%17%7%
1094
June1st to 15thNight
52%8%11%22%4
900
16th to endNight
44%8%12%26%8%
900
July1st to 15thNight
49%9%15%22%2
850
16th to endNight
44%8%16%26%4
1064
August1st to 15thNight
49%6%17%21%3
1253
16th to endNight
54%8%16%19%1
1628
September1st to 15thNight
62%7%16%10%2
1732
16th to endNight
66%6%12%11%3
1845
October1st to 15thNight
79%47%6%2
1980
16th to endNight
87%45%2
2445
November1st to 15thNight
83%45%4
2595
16th to endNight
73%10%9%6%
2880
December1st to 15thNight
67%12%12%7%
2976
16th to endNight
68%7%9%13%
3264

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
326%10%46%13%
30
16th to endDay
26%10%30%29%3
88
February1st to 15thDay
8%122%33%23%11%
90
16th to endDay
18%114%25%25%13%
81
March1st to 15thDay
23%113%18%26%16%
90
16th to endDay
9%7%8%28%26%19%
141
April1st to 15thDay
12%14%13%32%21%5%
401
16th to endDay
414%13%28%28%10%
450
May1st to 15thDay
21%13%11%25%21%6%
468
16th to endDay
13%13%13%26%25%7%
517
June1st to 15thDay
22%13%7%24%25%8%
495
16th to endDay
10%12%7%28%29%11%
495
July1st to 15thDay
16%9%7%26%26%12%
475
16th to endDay
18%12%422%30%11%
515
August1st to 15thDay
19%7%7%23%28%13%
493
16th to endDay
23%7%8%27%22%9%
523
September1st to 15thDay
35%10%14%20%13%4
382
16th to endDay
41%412%22%17%1
139
October1st to 15thDay
42%416%20%15%1
90
16th to endDay
33%425%25%11%1
96
November1st to 15thDay
26%333%26%7%1
78
16th to endDay
23%18%40%23%3
60
December1st to 15thDay
25%15%31%25%2
44
16th to endDay
12%18%21%34%12%
32
January1st to 15thNight
8%17%16%27%20%8%
900
16th to endNight
9%21%14%30%19%4
960
February1st to 15thNight
6%17%15%31%23%5%
880
16th to endNight
6%17%13%31%22%7%
789
March1st to 15thNight
7%18%14%28%23%6%
726
16th to endNight
7%19%11%30%24%7%
576
April1st to 15thNight
12%18%13%30%19%5%
539
16th to endNight
8%17%12%29%27%5%
540
May1st to 15thNight
20%17%11%24%21%4
495
16th to endNight
16%18%12%30%19%3
345
June1st to 15thNight
17%16%6%31%23%3
180
16th to endNight
15%17%5%30%26%5%
180
July1st to 15thNight
18%12%5%32%25%4
170
16th to endNight
15%18%6%20%28%10%
382
August1st to 15thNight
21%10%5%21%30%9%
539
16th to endNight
23%10%9%28%22%4
573
September1st to 15thNight
33%10%16%22%13%3
540
16th to endNight
37%13%18%19%10%1
542
October1st to 15thNight
45%13%12%18%8%1
660
16th to endNight
41%13%14%15%11%3
877
November1st to 15thNight
23%18%17%23%12%3
875
16th to endNight
14%19%16%28%16%5%
900
December1st to 15thNight
10%18%17%30%18%5%
900
16th to endNight
13%18%12%29%21%6%
960
Page generated at 2017-09-19 06:32:21. Version ac04

Copyright 2017 A. Danko


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