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St.John's
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St.John's clear sky chart from 2005-11-05 to 2022-11-11.

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%
21756
8%
66765
3%
21708
26%
21708
10%
54013

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
8%
1115
5%
3751
1%
1115
14%
1115
4%
3246
January16th to endNight
11%
1187
8%
3760
2%
1187
17%
1187
6%
3166
February1st to 15thNight
9%
1088
5%
3225
0%
1085
13%
1085
6%
2737
February16th to endNight
10%
929
7%
2765
1%
929
15%
929
8%
2321
March1st to 15thNight
16%
897
10%
2929
4%
897
23%
897
9%
2346
March16th to endNight
17%
811
8%
2980
4%
811
23%
811
7%
2414
April1st to 15thNight
18%
759
10%
2436
4%
758
26%
758
9%
1933
April16th to endNight
19%
751
8%
2252
4%
751
24%
751
10%
1822
May1st to 15thNight
25%
756
7%
2225
3%
756
28%
756
11%
1822
May16th to endNight
32%
780
8%
1842
2%
779
34%
779
15%
1509
June1st to 15thNight
25%
761
4%
1782
2%
760
26%
760
10%
1560
June16th to endNight
36%
758
5%
1776
3%
758
37%
758
17%
1439
July1st to 15thNight
37%
729
7%
1704
3%
729
39%
729
18%
1353
July16th to endNight
39%
795
7%
1921
3%
759
40%
759
14%
1576
August1st to 15thNight
37%
737
8%
2196
5%
733
39%
733
14%
1712
August16th to endNight
40%
807
11%
2426
9%
807
44%
807
17%
1800
September1st to 15thNight
36%
762
11%
2620
8%
761
42%
761
14%
1896
September16th to endNight
31%
756
12%
2788
8%
756
38%
756
14%
1978
October1st to 15thNight
28%
852
12%
2977
6%
852
36%
852
12%
2224
October16th to endNight
20%
1134
9%
3441
4%
1133
25%
1133
9%
2812
November1st to 15thNight
22%
1156
7%
3526
3%
1156
25%
1156
11%
2801
November16th to endNight
14%
1118
8%
3557
2%
1118
19%
1118
8%
2890
December1st to 15thNight
11%
1122
6%
3818
1%
1122
17%
1122
6%
3150
December16th to endNight
12%
1196
3%
4068
2%
1196
15%
1196
5%
3506

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%11%48%7%45%5%5%6%21%
68171
Night
20%12%48%6%35%5%5%6%21%
66926
TransparencyDay
61%8%11%12%5%
67841
Night
63%8%10%12%4
66774
SeeingDay
25%12%29%24%7%
15259
Night
27%13%29%22%6%
21764

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
19%13%7%9%8%46%5%6%6%13%
1801
16th to endDay
18%13%6%10%8%5%5%45%7%13%
2144
February1st to 15thDay
18%10%411%8%5%6%5%6%8%14%
2200
16th to endDay
15%12%7%11%8%46%5%5%6%14%
2126
March1st to 15thDay
16%12%6%9%8%45%5%5%6%18%
2637
16th to endDay
21%11%6%10%8%4445%5%17%
2978
April1st to 15thDay
20%11%5%8%7%46%5%45%19%
3124
16th to endDay
26%11%47%5%3434421%
3252
May1st to 15thDay
19%13%48%6%35%5%5%5%21%
3315
16th to endDay
18%11%48%7%35%45%7%23%
3859
June1st to 15thDay
23%15%48%8%35%445%15%
3818
16th to endDay
20%10%48%6%445%5%7%24%
3798
July1st to 15thDay
16%8%27%6%345%6%8%29%
3812
16th to endDay
17%8%37%6%46%5%6%8%25%
3815
August1st to 15thDay
22%9%37%6%3445%7%25%
3222
16th to endDay
18%7%37%7%46%5%6%8%25%
3509
September1st to 15thDay
17%7%36%5%345%5%7%31%
2968
16th to endDay
18%8%25%5%3445%8%32%
2789
October1st to 15thDay
19%9%38%6%345%5%6%27%
2596
16th to endDay
21%15%48%7%45%5%46%17%
2512
November1st to 15thDay
18%10%37%7%46%45%8%23%
2207
16th to endDay
22%15%6%9%6%34336%18%
2006
December1st to 15thDay
19%14%5%8%8%44446%17%
1782
16th to endDay
19%15%6%12%8%35%446%12%
1901
January1st to 15thNight
20%13%6%10%8%36%5%5%5%13%
3751
16th to endNight
17%13%5%10%8%45%5%5%7%15%
3759
February1st to 15thNight
18%10%411%9%46%5%6%6%14%
3225
16th to endNight
15%13%7%10%7%5%5%5%46%16%
2763
March1st to 15thNight
16%10%5%9%8%5%6%5%5%6%20%
2907
16th to endNight
23%11%5%10%7%44445%18%
2980
April1st to 15thNight
22%13%6%9%5%34346%21%
2440
16th to endNight
27%14%47%6%2333423%
2252
May1st to 15thNight
24%13%5%6%6%35%446%19%
2226
16th to endNight
22%9%47%6%235%6%6%24%
1840
June1st to 15thNight
25%14%47%7%35%5%6%5%15%
1782
16th to endNight
21%11%46%6%3445%6%26%
1776
July1st to 15thNight
18%10%36%5%3446%9%26%
1779
16th to endNight
18%8%46%6%35%6%6%9%23%
2017
August1st to 15thNight
21%10%47%5%3445%6%26%
2206
16th to endNight
20%8%26%5%245%5%7%30%
2426
September1st to 15thNight
20%8%35%5%3445%8%30%
2621
16th to endNight
20%8%36%6%4345%6%31%
2789
October1st to 15thNight
20%9%37%6%45%5%5%6%26%
2976
16th to endNight
23%14%37%6%4345%6%19%
3444
November1st to 15thNight
19%11%36%6%35%46%7%24%
3526
16th to endNight
19%14%5%8%6%45%45%6%19%
3554
December1st to 15thNight
19%14%5%9%7%35%5%47%17%
3818
16th to endNight
19%17%6%9%7%35%5%5%6%13%
4069

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%8%10%6%2
1803
16th to endDay
70%6%9%8%4
2145
February1st to 15thDay
67%9%9%7%5%
2200
16th to endDay
70%5%10%7%4
2125
March1st to 15thDay
64%7%11%11%4
2658
16th to endDay
68%6%9%9%41
2977
April1st to 15thDay
64%7%9%10%6%
3124
16th to endDay
65%6%8%10%9%
3252
May1st to 15thDay
61%8%10%12%6%
3311
16th to endDay
58%9%11%14%5%
3861
June1st to 15thDay
70%8%8%9%3
3816
16th to endDay
59%9%11%14%5%
3804
July1st to 15thDay
51%11%12%16%8%
3645
16th to endDay
55%11%13%15%3
3635
August1st to 15thDay
57%9%10%17%5%
3213
16th to endDay
53%10%15%15%4
3508
September1st to 15thDay
50%8%12%20%8%
2968
16th to endDay
48%8%15%17%8%
2788
October1st to 15thDay
56%6%13%16%7%
2598
16th to endDay
66%8%8%10%5%
2512
November1st to 15thDay
58%9%15%13%3
2207
16th to endDay
68%5%10%9%5%
2008
December1st to 15thDay
66%9%9%9%4
1782
16th to endDay
75%5%7%8%2
1901
January1st to 15thNight
72%7%8%7%3
3751
16th to endNight
68%8%8%9%4
3760
February1st to 15thNight
70%7%10%8%3
3226
16th to endNight
68%7%9%9%4
2765
March1st to 15thNight
63%6%11%11%4
2929
16th to endNight
67%6%8%10%5%
2980
April1st to 15thNight
64%5%9%12%7%
2436
16th to endNight
66%5%7%11%8%
2252
May1st to 15thNight
64%7%8%13%5%
2229
16th to endNight
58%10%11%13%5%
1842
June1st to 15thNight
69%8%8%9%3
1782
16th to endNight
58%8%12%14%5%
1776
July1st to 15thNight
54%10%11%17%6%
1705
16th to endNight
57%12%11%15%3
1921
August1st to 15thNight
58%8%12%16%4
2198
16th to endNight
51%9%14%18%5%
2426
September1st to 15thNight
50%10%12%18%7%
2620
16th to endNight
53%6%12%19%8%
2789
October1st to 15thNight
56%7%12%16%5%
2977
16th to endNight
65%7%10%11%4
3441
November1st to 15thNight
59%9%14%11%4
3526
16th to endNight
64%7%11%11%4
3557
December1st to 15thNight
66%7%9%10%4
3818
16th to endNight
72%7%9%7%2
4068

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
25%20%35%14%3
462
16th to endDay
24%21%33%15%4
491
February1st to 15thDay
24%22%36%14%1
457
16th to endDay
20%22%37%16%2
408
March1st to 15thDay
23%21%35%15%31
464
16th to endDay
25%16%31%20%41
495
April1st to 15thDay
27%15%27%20%7%
685
16th to endDay
30%10%30%21%5%
800
May1st to 15thDay
26%10%32%21%7%1
837
16th to endDay
24%8%28%28%9%
882
June1st to 15thDay
32%7%28%23%6%
865
16th to endDay
25%423%32%11%2
857
July1st to 15thDay
24%5%27%29%10%1
848
16th to endDay
23%424%35%11%
903
August1st to 15thDay
23%324%33%12%1
831
16th to endDay
23%5%22%31%16%1
921
September1st to 15thDay
21%7%27%31%10%1
629
16th to endDay
23%10%30%25%9%
491
October1st to 15thDay
22%11%33%23%8%1
493
16th to endDay
28%16%27%21%5%1
527
November1st to 15thDay
23%20%30%20%5%
492
16th to endDay
31%17%33%16%1
463
December1st to 15thDay
28%22%31%12%4
463
16th to endDay
23%23%31%16%4
495
January1st to 15thNight
29%19%34%12%3
1115
16th to endNight
24%21%35%16%2
1187
February1st to 15thNight
25%24%35%12%1
1089
16th to endNight
24%16%39%14%3
929
March1st to 15thNight
21%18%34%19%4
897
16th to endNight
29%16%28%20%4
811
April1st to 15thNight
27%15%28%20%7%
759
16th to endNight
36%7%28%19%7%
752
May1st to 15thNight
31%6%26%26%7%1
757
16th to endNight
27%6%26%28%9%
780
June1st to 15thNight
34%6%24%26%7%
761
16th to endNight
27%5%21%29%14%1
759
July1st to 15thNight
24%5%25%33%9%1
729
16th to endNight
22%425%36%10%
797
August1st to 15thNight
27%321%35%9%1
737
16th to endNight
25%322%36%11%
808
September1st to 15thNight
24%6%27%32%8%1
762
16th to endNight
25%7%29%27%8%
757
October1st to 15thNight
26%11%29%23%8%
852
16th to endNight
32%14%27%19%5%
1134
November1st to 15thNight
26%17%29%20%6%
1156
16th to endNight
27%20%32%17%3
1118
December1st to 15thNight
28%21%31%13%3
1122
16th to endNight
27%21%29%17%4
1196
Page generated at 2022-11-12 15:12:32. Version ac05

Copyright 2022 A. Danko


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