Grande Prairie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grande Prairie clear sky chart from 2005-11-05 to 2017-12-01.

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
39%
15357
9%
47676
6%
15331
42%
15331
16%
34774

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
32%
925
8%
2865
5%
925
35%
925
11%
2256
January16th to endNight
30%
842
11%
2877
7%
842
35%
842
13%
2115
February1st to 15thNight
35%
697
8%
2464
7%
696
38%
696
12%
1825
February16th to endNight
48%
632
10%
2024
11%
632
50%
632
17%
1476
March1st to 15thNight
34%
720
12%
2160
8%
720
39%
720
16%
1605
March16th to endNight
43%
768
12%
2007
7%
767
45%
767
19%
1536
April1st to 15thNight
37%
689
9%
1769
4%
689
40%
689
17%
1370
April16th to endNight
39%
390
9%
1470
11%
390
43%
390
14%
1038
May1st to 15thNight
40%
359
4%
1374
2%
359
42%
359
17%
909
May16th to endNight
45%
374
0%
1173
0%
374
45%
374
20%
810
June1st to 15thNight
45%
360
0%
1080
0%
360
45%
360
19%
771
June16th to endNight
46%
360
0%
1080
0%
360
46%
360
22%
745
July1st to 15thNight
53%
340
0%
1020
0%
340
53%
340
24%
676
July16th to endNight
53%
376
0%
1134
0%
354
54%
354
23%
756
August1st to 15thNight
63%
360
5%
1432
7%
358
65%
358
23%
827
August16th to endNight
47%
477
12%
1623
12%
477
50%
477
21%
1057
September1st to 15thNight
53%
720
12%
1800
7%
720
55%
720
31%
1230
September16th to endNight
45%
716
16%
1946
8%
716
48%
716
24%
1329
October1st to 15thNight
38%
720
12%
2198
7%
720
43%
720
18%
1574
October16th to endNight
32%
768
11%
2514
5%
768
40%
768
14%
1840
November1st to 15thNight
31%
858
11%
2758
7%
858
36%
858
13%
2055
November16th to endNight
30%
979
9%
2941
4%
979
35%
979
12%
2311
December1st to 15thNight
31%
935
10%
2895
6%
935
34%
935
12%
2292
December16th to endNight
35%
992
11%
3072
6%
992
40%
992
13%
2371

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
11%9%47%6%35%5%6%7%31%
48796
Night
10%11%48%7%45%5%5%7%29%
47809
TransparencyDay
49%8%17%18%5%
48430
Night
52%7%15%18%6%
47680
SeeingDay
15%7%22%30%19%5%
7095
Night
15%6%25%33%17%2
15371

By Month

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
9%15%6%9%6%36%5%5%7%24%
1074
16th to endDay
10%13%5%8%7%46%46%5%26%
1356
February1st to 15thDay
9%11%5%9%8%45%5%5%7%26%
1400
16th to endDay
7%15%6%9%8%5%6%5%45%23%
1447
March1st to 15thDay
7%12%6%10%7%36%6%6%5%26%
1800
16th to endDay
9%13%6%9%7%36%5%6%7%24%
2210
April1st to 15thDay
7%10%5%7%7%36%6%6%7%30%
2179
16th to endDay
11%10%38%7%35%6%7%8%27%
2490
May1st to 15thDay
9%7%37%6%47%5%5%6%35%
2575
16th to endDay
16%6%38%6%45%5%6%8%29%
2935
June1st to 15thDay
14%6%47%7%45%6%6%7%29%
2880
16th to endDay
13%7%36%6%35%5%6%7%35%
2880
July1st to 15thDay
13%425%435%5%6%7%38%
2880
16th to endDay
9%435%5%36%6%7%8%40%
2955
August1st to 15thDay
9%5%25%5%46%5%7%9%39%
2520
16th to endDay
10%5%26%6%45%6%6%10%34%
2578
September1st to 15thDay
14%5%26%5%3345%6%41%
2160
16th to endDay
13%5%25%5%35%5%7%8%38%
2011
October1st to 15thDay
12%10%49%6%35%45%7%30%
1761
16th to endDay
14%12%46%5%345%7%6%29%
1707
November1st to 15thDay
13%14%5%8%7%4435%6%25%
1417
16th to endDay
8%13%5%11%9%34446%26%
1349
December1st to 15thDay
14%12%7%8%9%5%7%6%4420%
1080
16th to endDay
8%15%5%10%7%46%6%6%6%22%
1152
January1st to 15thNight
9%13%7%10%9%5%5%446%23%
2865
16th to endNight
11%13%5%8%6%35%45%8%27%
2877
February1st to 15thNight
10%13%48%8%45%45%7%25%
2452
16th to endNight
6%11%5%9%8%46%5%7%7%27%
2024
March1st to 15thNight
8%13%6%9%8%35%45%7%27%
2160
16th to endNight
10%12%5%8%5%46%5%6%7%26%
2006
April1st to 15thNight
8%9%5%9%8%5%7%6%7%7%24%
1769
16th to endNight
12%10%5%7%6%35%45%6%31%
1470
May1st to 15thNight
10%9%36%8%445%5%8%32%
1374
16th to endNight
13%9%36%435%5%7%7%32%
1173
June1st to 15thNight
12%7%48%6%45%5%6%8%31%
1080
16th to endNight
15%6%26%5%25%5%6%9%33%
1080
July1st to 15thNight
10%6%26%5%35%7%6%7%40%
1080
16th to endNight
10%426%6%47%6%7%8%34%
1212
August1st to 15thNight
7%315%5%35%5%7%9%43%
1440
16th to endNight
9%437%7%36%5%6%9%36%
1623
September1st to 15thNight
9%6%26%5%345%6%9%41%
1800
16th to endNight
13%6%25%5%35%46%9%36%
1946
October1st to 15thNight
13%9%47%5%35%45%8%32%
2198
16th to endNight
12%12%48%6%35%5%5%7%28%
2514
November1st to 15thNight
13%13%6%8%6%4445%5%27%
2758
16th to endNight
10%16%5%10%8%44445%24%
2941
December1st to 15thNight
10%14%5%9%8%45%45%6%23%
2895
16th to endNight
7%14%5%10%8%46%6%5%7%22%
3072

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
57%6%16%14%31
1074
16th to endDay
56%7%11%17%6%1
1356
February1st to 15thDay
54%8%15%14%6%
1400
16th to endDay
61%6%14%12%5%
1447
March1st to 15thDay
55%7%14%16%5%
1800
16th to endDay
55%8%17%14%3
2210
April1st to 15thDay
50%9%16%17%6%
2179
16th to endDay
52%8%14%17%6%
2490
May1st to 15thDay
46%7%14%19%11%
2575
16th to endDay
50%8%14%18%8%
2940
June1st to 15thDay
51%9%15%19%5%
2880
16th to endDay
46%7%16%20%8%
2880
July1st to 15thDay
41%9%16%24%7%
2711
16th to endDay
37%10%24%21%6%
2770
August1st to 15thDay
38%11%22%23%4
2503
16th to endDay
43%9%22%20%4
2578
September1st to 15thDay
41%7%23%21%6%
2160
16th to endDay
41%9%17%22%7%
2011
October1st to 15thDay
52%6%18%18%3
1761
16th to endDay
52%7%16%19%3
1707
November1st to 15thDay
59%414%16%5%
1417
16th to endDay
59%6%14%13%41
1349
December1st to 15thDay
64%7%12%11%3
1080
16th to endDay
59%7%14%13%5%
1152
January1st to 15thNight
61%6%13%13%21
2865
16th to endNight
55%7%15%14%5%1
2877
February1st to 15thNight
56%7%15%14%5%
2464
16th to endNight
53%6%17%17%4
2024
March1st to 15thNight
56%5%13%18%6%
2160
16th to endNight
53%8%13%17%7%
2010
April1st to 15thNight
55%7%12%16%7%
1769
16th to endNight
51%8%14%17%7%
1470
May1st to 15thNight
47%6%11%20%12%1
1375
16th to endNight
46%7%16%18%10%
1173
June1st to 15thNight
49%7%16%20%6%
1080
16th to endNight
45%7%16%21%9%
1080
July1st to 15thNight
38%10%15%25%8%
1020
16th to endNight
41%9%23%19%5%
1134
August1st to 15thNight
32%11%21%27%7%
1432
16th to endNight
41%9%20%21%6%
1623
September1st to 15thNight
38%8%20%22%8%
1800
16th to endNight
42%7%17%22%9%
1946
October1st to 15thNight
49%8%16%20%5%
2198
16th to endNight
53%7%15%19%3
2514
November1st to 15thNight
56%6%13%17%5%
2758
16th to endNight
60%8%11%15%31
2941
December1st to 15thNight
61%7%13%13%4
2895
16th to endNight
58%7%12%16%4
3072

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
20%315%30%20%11%
60
16th to endDay
14%320%40%15%6%
64
February1st to 15thDay
6%15%20%33%16%8%
60
16th to endDay
14%6%18%30%26%3
197
March1st to 15thDay
15%6%29%32%13%1
270
16th to endDay
15%320%38%18%3
288
April1st to 15thDay
12%9%24%34%14%4
269
16th to endDay
18%8%24%29%16%2
270
May1st to 15thDay
11%10%24%31%20%1
352
16th to endDay
17%5%19%29%21%6%
651
June1st to 15thDay
15%6%24%27%21%4
675
16th to endDay
16%5%20%28%23%6%
675
July1st to 15thDay
14%423%31%20%5%
645
16th to endDay
9%6%24%32%22%4
623
August1st to 15thDay
11%422%24%26%10%
315
16th to endDay
12%10%27%36%11%1
332
September1st to 15thDay
18%7%25%24%17%6%
315
16th to endDay
15%9%24%26%18%5%
315
October1st to 15thDay
22%13%22%21%13%6%
276
16th to endDay
28%8%20%21%16%4
139
November1st to 15thDay
17%422%32%18%4
90
16th to endDay
15%13%17%32%11%10%
90
December1st to 15thDay
8%318%30%30%10%
60
16th to endDay
18%12%14%34%12%7%
64
January1st to 15thNight
14%7%24%33%15%3
930
16th to endNight
16%10%28%30%13%1
842
February1st to 15thNight
17%7%25%26%18%4
704
16th to endNight
11%318%36%25%3
632
March1st to 15thNight
13%7%30%33%13%1
720
16th to endNight
15%320%38%19%2
768
April1st to 15thNight
12%5%29%35%15%1
689
16th to endNight
16%7%25%27%21%1
390
May1st to 15thNight
14%6%27%35%14%1
360
16th to endNight
16%423%32%22%1
375
June1st to 15thNight
16%321%29%26%1
360
16th to endNight
17%322%32%21%2
360
July1st to 15thNight
13%223%38%19%2
340
16th to endNight
10%320%36%25%2
376
August1st to 15thNight
10%117%31%34%4
360
16th to endNight
12%225%37%19%1
477
September1st to 15thNight
12%321%36%23%2
720
16th to endNight
16%7%24%33%15%2
716
October1st to 15thNight
19%5%28%32%12%1
720
16th to endNight
18%8%29%30%11%1
768
November1st to 15thNight
20%7%28%30%11%2
858
16th to endNight
18%8%25%32%12%3
979
December1st to 15thNight
17%7%24%32%14%2
935
16th to endNight
14%6%23%32%19%3
992
Page generated at 2017-12-02 07:14:15. Version ac04

Copyright 2017 A. Danko


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