Drayton Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Drayton Valley 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
39%
15180
10%
46644
7%
15155
42%
15155
17%
34031

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
31%
895
8%
2685
5%
895
34%
895
12%
2142
January16th to endNight
29%
857
15%
2777
9%
857
37%
857
14%
2038
February1st to 15thNight
34%
699
9%
2464
8%
699
38%
699
13%
1809
February16th to endNight
41%
632
11%
1983
10%
632
44%
632
18%
1416
March1st to 15thNight
36%
720
14%
2142
9%
720
42%
720
18%
1575
March16th to endNight
35%
768
9%
2049
4%
767
37%
767
16%
1608
April1st to 15thNight
31%
631
10%
1711
4%
631
35%
631
14%
1347
April16th to endNight
35%
523
9%
1603
8%
523
38%
523
16%
1182
May1st to 15thNight
42%
359
6%
1329
5%
359
45%
359
16%
936
May16th to endNight
42%
374
1%
1309
0%
374
42%
374
13%
969
June1st to 15thNight
39%
360
0%
1194
0%
360
39%
360
12%
925
June16th to endNight
46%
360
0%
1080
0%
360
46%
360
17%
793
July1st to 15thNight
56%
340
0%
1081
0%
340
56%
340
20%
759
July16th to endNight
55%
376
2%
1245
1%
354
55%
354
17%
846
August1st to 15thNight
62%
360
6%
1432
9%
358
63%
358
18%
914
August16th to endNight
56%
553
12%
1699
11%
553
58%
553
25%
1094
September1st to 15thNight
59%
670
15%
1789
11%
670
60%
670
30%
1192
September16th to endNight
50%
716
19%
1980
11%
716
54%
716
32%
1253
October1st to 15thNight
39%
684
14%
2044
9%
684
43%
684
19%
1467
October16th to endNight
40%
704
14%
2288
10%
704
46%
704
18%
1604
November1st to 15thNight
30%
839
13%
2480
8%
839
36%
839
16%
1847
November16th to endNight
29%
900
10%
2700
5%
900
34%
900
15%
2070
December1st to 15thNight
30%
900
11%
2700
8%
900
33%
900
13%
2104
December16th to endNight
35%
960
13%
2880
7%
960
40%
960
16%
2141

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
12%9%37%6%35%5%6%7%31%
48596
Night
11%10%47%6%35%5%5%7%30%
46788
TransparencyDay
49%8%17%18%5%
48242
Night
51%8%14%18%6%
46647
SeeingDay
15%7%24%29%17%4
6495
Night
15%5%27%33%15%1
15192

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
8%12%5%11%7%35%45%7%26%
1253
16th to endDay
8%14%6%7%7%35%45%6%29%
1458
February1st to 15thDay
10%11%5%9%8%45%5%5%7%27%
1400
16th to endDay
6%14%7%10%6%36%7%47%25%
1489
March1st to 15thDay
8%12%48%8%46%5%6%5%27%
1818
16th to endDay
10%14%5%5%5%45%6%6%7%25%
2168
April1st to 15thDay
11%12%47%6%36%5%6%7%26%
2236
16th to endDay
15%10%46%6%45%46%8%27%
2355
May1st to 15thDay
12%8%36%6%36%5%6%7%33%
2622
16th to endDay
21%5%26%5%35%5%5%7%30%
2802
June1st to 15thDay
18%7%36%6%36%5%6%9%26%
2763
16th to endDay
14%5%26%6%46%6%7%8%30%
2880
July1st to 15thDay
14%425%6%46%5%6%8%36%
2813
16th to endDay
10%425%6%36%6%6%9%38%
2840
August1st to 15thDay
12%415%6%35%6%6%10%35%
2520
16th to endDay
9%5%25%6%35%6%6%9%38%
2503
September1st to 15thDay
15%5%244345%5%7%39%
2169
16th to endDay
13%6%25%6%3345%7%42%
1980
October1st to 15thDay
14%10%37%5%2445%6%33%
1712
16th to endDay
10%13%36%6%3445%6%34%
1584
November1st to 15thDay
12%11%5%7%7%445%6%6%28%
1367
16th to endDay
8%12%49%6%5%5%446%30%
1260
December1st to 15thDay
10%15%7%12%7%35%336%23%
1260
16th to endDay
7%14%6%7%7%45%5%6%7%27%
1344
January1st to 15thNight
8%15%6%10%9%46%5%45%24%
2685
16th to endNight
9%14%5%8%6%35%45%6%30%
2777
February1st to 15thNight
10%12%5%9%8%45%5%5%6%26%
2452
16th to endNight
8%14%5%7%6%35%45%7%31%
1983
March1st to 15thNight
8%9%5%9%7%46%6%6%6%29%
2142
16th to endNight
9%14%7%9%6%45%5%6%8%23%
2049
April1st to 15thNight
13%13%46%7%46%5%6%7%24%
1711
16th to endNight
14%11%37%6%35%6%47%28%
1603
May1st to 15thNight
15%8%36%6%36%6%6%7%31%
1328
16th to endNight
22%6%46%6%45%5%5%6%28%
1309
June1st to 15thNight
22%9%36%6%35%5%6%7%23%
1194
16th to endNight
15%5%26%8%5%5%5%7%9%28%
1080
July1st to 15thNight
11%5%25%6%36%6%7%9%34%
1146
16th to endNight
11%326%5%5%8%6%6%7%35%
1329
August1st to 15thNight
11%325%6%45%5%6%9%37%
1440
16th to endNight
11%5%25%435%5%6%11%38%
1699
September1st to 15thNight
13%5%25%5%345%46%44%
1789
16th to endNight
12%5%235%3345%8%46%
1980
October1st to 15thNight
15%9%27%6%34446%33%
2044
16th to endNight
12%9%47%5%35%45%8%32%
2288
November1st to 15thNight
15%11%5%7%6%25%45%7%28%
2480
16th to endNight
11%13%6%8%8%35%45%6%27%
2700
December1st to 15thNight
10%14%6%8%7%44446%27%
2700
16th to endNight
6%13%5%10%8%46%45%7%26%
2880

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%8%11%16%5%1
1253
16th to endDay
54%6%12%15%7%2
1458
February1st to 15thDay
52%8%16%13%7%1
1400
16th to endDay
57%6%13%15%6%
1489
March1st to 15thDay
55%7%14%16%5%
1818
16th to endDay
54%8%15%16%4
2169
April1st to 15thDay
55%9%13%16%5%
2236
16th to endDay
53%8%15%15%6%1
2355
May1st to 15thDay
47%8%15%20%8%
2622
16th to endDay
52%9%14%17%6%
2807
June1st to 15thDay
52%10%18%15%2
2763
16th to endDay
46%10%19%18%4
2880
July1st to 15thDay
44%10%21%20%3
2649
16th to endDay
41%11%25%19%2
2661
August1st to 15thDay
41%13%25%17%2
2503
16th to endDay
39%11%25%17%6%
2503
September1st to 15thDay
43%7%18%22%7%
2169
16th to endDay
41%8%14%26%7%1
1980
October1st to 15thDay
49%8%15%20%6%
1712
16th to endDay
49%7%13%24%4
1584
November1st to 15thDay
54%7%15%16%5%
1367
16th to endDay
54%7%13%14%6%2
1260
December1st to 15thDay
63%6%12%14%3
1260
16th to endDay
53%6%16%15%6%1
1344
January1st to 15thNight
60%8%11%13%32
2685
16th to endNight
54%6%10%17%8%2
2777
February1st to 15thNight
56%6%13%16%5%1
2464
16th to endNight
51%6%14%16%9%1
1983
March1st to 15thNight
51%8%13%18%7%
2142
16th to endNight
56%8%13%15%4
2052
April1st to 15thNight
57%8%12%14%5%1
1711
16th to endNight
53%7%13%18%5%
1603
May1st to 15thNight
50%7%13%16%10%
1329
16th to endNight
55%8%12%15%6%1
1309
June1st to 15thNight
56%10%13%16%3
1194
16th to endNight
49%10%17%18%2
1080
July1st to 15thNight
43%12%19%18%5%
1081
16th to endNight
41%14%23%16%3
1245
August1st to 15thNight
39%12%23%20%3
1432
16th to endNight
38%9%21%23%7%
1699
September1st to 15thNight
39%6%16%25%9%1
1789
16th to endNight
35%6%16%26%11%2
1980
October1st to 15thNight
50%6%11%21%8%
2044
16th to endNight
49%7%15%22%4
2288
November1st to 15thNight
55%6%11%19%6%
2480
16th to endNight
57%6%13%14%5%2
2700
December1st to 15thNight
59%7%11%16%4
2700
16th to endNight
54%7%13%17%6%
2880

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
10%5%28%25%18%13%
60
16th to endDay
9%320%31%28%7%
64
February1st to 15thDay
16%8%28%33%8%5%
60
16th to endDay
13%9%23%33%17%2
152
March1st to 15thDay
14%10%36%27%9%
270
16th to endDay
18%9%36%23%11%1
288
April1st to 15thDay
20%13%31%28%5%
269
16th to endDay
21%14%25%27%9%1
270
May1st to 15thDay
13%10%22%30%18%3
399
16th to endDay
20%6%21%26%20%5%
517
June1st to 15thDay
18%7%22%31%16%4
558
16th to endDay
14%5%26%28%19%5%
675
July1st to 15thDay
14%222%33%21%4
583
16th to endDay
11%5%23%30%24%5%
509
August1st to 15thDay
9%318%32%22%13%
315
16th to endDay
11%6%25%35%18%3
332
September1st to 15thDay
22%5%20%26%20%4
315
16th to endDay
13%9%25%26%19%6%
315
October1st to 15thDay
25%7%20%25%16%3
185
16th to endDay
19%320%36%15%4
96
November1st to 15thDay
21%332%31%8%1
79
16th to endDay
18%5%26%28%11%10%
60
December1st to 15thDay
13%8%30%20%23%5%
60
16th to endDay
15%325%25%21%9%
64
January1st to 15thNight
15%7%30%31%12%2
900
16th to endNight
14%11%30%32%10%1
857
February1st to 15thNight
16%7%25%32%16%2
704
16th to endNight
14%427%34%17%2
632
March1st to 15thNight
11%5%34%35%11%1
720
16th to endNight
14%328%38%11%2
768
April1st to 15thNight
18%6%32%30%11%
631
16th to endNight
19%5%31%31%11%
523
May1st to 15thNight
16%7%24%33%16%
360
16th to endNight
21%323%34%15%1
375
June1st to 15thNight
23%323%31%15%3
360
16th to endNight
16%320%33%24%1
360
July1st to 15thNight
13%117%44%20%1
340
16th to endNight
11%219%40%23%1
376
August1st to 15thNight
12%113%37%30%4
360
16th to endNight
13%218%41%23%
553
September1st to 15thNight
14%116%41%23%1
670
16th to endNight
13%327%35%17%1
716
October1st to 15thNight
18%427%31%16%1
684
16th to endNight
16%5%26%37%12%
704
November1st to 15thNight
18%7%32%29%10%1
839
16th to endNight
15%8%34%28%10%2
900
December1st to 15thNight
17%9%29%28%12%1
900
16th to endNight
12%5%29%33%16%2
960
Page generated at 2017-10-07 12:07:56. Version ac04

Copyright 2017 A. Danko


Drayton Valley Clear Sky Chart | Charts Home