Drumheller
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Drumheller clear sky chart from 2005-11-05 to 2017-08-12.

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
43%
15123
11%
46430
8%
15098
47%
15098
20%
32298

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
36%
895
9%
2685
6%
895
38%
895
14%
2059
January16th to endNight
42%
869
16%
2789
11%
869
48%
869
19%
1969
February1st to 15thNight
43%
696
11%
2387
11%
696
47%
696
17%
1673
February16th to endNight
45%
632
11%
2017
12%
632
47%
632
18%
1434
March1st to 15thNight
42%
720
12%
2091
8%
720
46%
720
20%
1523
March16th to endNight
39%
768
9%
2110
4%
767
42%
767
17%
1630
April1st to 15thNight
35%
596
8%
1688
4%
596
39%
596
17%
1261
April16th to endNight
40%
540
13%
1620
10%
540
44%
540
22%
1124
May1st to 15thNight
43%
449
12%
1398
10%
449
46%
449
22%
929
May16th to endNight
40%
374
5%
1309
2%
374
42%
374
16%
932
June1st to 15thNight
40%
360
0%
1260
0%
360
40%
360
16%
896
June16th to endNight
48%
360
0%
1260
0%
360
48%
360
19%
839
July1st to 15thNight
60%
340
0%
1190
0%
340
60%
340
24%
741
July16th to endNight
60%
376
8%
1239
7%
354
63%
354
30%
688
August1st to 15thNight
61%
414
9%
1451
12%
412
62%
412
26%
878
August16th to endNight
62%
525
17%
1575
14%
525
64%
525
38%
884
September1st to 15thNight
55%
566
17%
1642
13%
566
58%
566
29%
1049
September16th to endNight
54%
656
20%
1815
14%
656
59%
656
37%
1113
October1st to 15thNight
43%
660
16%
1943
9%
660
49%
660
23%
1335
October16th to endNight
44%
704
15%
2285
10%
704
50%
704
22%
1492
November1st to 15thNight
37%
863
17%
2438
11%
863
43%
863
22%
1672
November16th to endNight
34%
900
11%
2658
7%
900
37%
900
17%
1971
December1st to 15thNight
35%
900
9%
2700
6%
900
37%
900
13%
2111
December16th to endNight
39%
960
13%
2880
8%
960
44%
960
18%
2095

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
10%8%37%6%35%5%6%8%34%
47576
Night
8%8%47%6%35%5%6%8%33%
46578
TransparencyDay
46%8%16%20%7%
47226
Night
46%7%16%20%7%1
46432
SeeingDay
14%6%24%30%18%4
5918
Night
12%5%27%36%16%2
15138

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
7%12%5%7%7%5%5%7%6%8%25%
1253
16th to endDay
7%11%5%9%7%36%5%7%8%27%
1446
February1st to 15thDay
8%12%5%9%9%45%5%5%7%25%
1476
16th to endDay
411%8%12%9%47%7%46%23%
1455
March1st to 15thDay
7%9%5%11%9%47%5%6%6%25%
1869
16th to endDay
10%12%7%8%7%35%5%7%8%23%
2111
April1st to 15thDay
12%11%47%6%35%5%5%8%28%
2257
16th to endDay
14%8%37%6%35%5%5%7%31%
2340
May1st to 15thDay
12%6%26%6%35%6%6%9%34%
2550
16th to endDay
19%6%36%5%25%5%5%8%30%
2802
June1st to 15thDay
15%7%36%6%35%5%7%8%29%
2700
16th to endDay
13%5%25%5%36%6%7%8%35%
2700
July1st to 15thDay
8%5%15%436%5%6%9%42%
2700
16th to endDay
7%213425%5%7%10%47%
2846
August1st to 15thDay
10%6%25%42446%9%43%
2416
16th to endDay
8%4145%245%6%8%47%
2275
September1st to 15thDay
13%7%24334346%45%
1984
16th to endDay
9%5%244245%6%9%46%
1815
October1st to 15thDay
12%9%36%6%33448%37%
1686
16th to endDay
7%9%45%5%36%6%5%7%38%
1584
November1st to 15thDay
9%12%5%10%6%35%447%31%
1408
16th to endDay
7%11%6%10%8%46%45%7%28%
1299
December1st to 15thDay
7%15%6%10%10%47%5%45%20%
1260
16th to endDay
412%411%8%5%7%7%7%7%23%
1344
January1st to 15thNight
7%11%5%9%9%46%8%6%7%22%
2685
16th to endNight
6%11%5%9%6%35%6%6%7%31%
2789
February1st to 15thNight
6%10%5%10%8%45%46%8%29%
2376
16th to endNight
6%9%6%10%7%35%5%6%8%29%
2017
March1st to 15thNight
5%8%48%8%5%6%7%6%9%29%
2091
16th to endNight
7%11%5%8%7%6%7%6%6%8%23%
2109
April1st to 15thNight
11%9%48%7%5%5%5%5%7%27%
1688
16th to endNight
9%10%46%6%35%5%5%7%33%
1620
May1st to 15thNight
10%8%38%5%35%447%38%
1397
16th to endNight
20%6%25%5%35%5%6%7%31%
1309
June1st to 15thNight
13%8%27%7%37%5%6%7%29%
1260
16th to endNight
9%7%36%6%36%5%7%8%35%
1260
July1st to 15thNight
7%315%5%37%7%8%10%38%
1260
16th to endNight
5%223426%5%6%8%51%
1323
August1st to 15thNight
8%315%5%25%5%6%10%44%
1458
16th to endNight
7%41342336%11%50%
1575
September1st to 15thNight
13%5%14434445%47%
1642
16th to endNight
8%5%2342346%8%49%
1815
October1st to 15thNight
10%7%37%6%35%6%6%7%36%
1943
16th to endNight
7%8%37%6%35%5%6%9%36%
2285
November1st to 15thNight
8%8%46%6%45%5%5%7%36%
2438
16th to endNight
6%10%5%10%8%35%6%5%7%28%
2658
December1st to 15thNight
6%14%7%11%8%5%6%5%48%22%
2700
16th to endNight
410%5%10%8%46%6%5%9%27%
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
54%8%13%17%4
1253
16th to endDay
50%7%16%16%7%2
1446
February1st to 15thDay
55%7%13%15%6%
1476
16th to endDay
59%5%13%15%5%
1455
March1st to 15thDay
56%9%15%13%5%
1869
16th to endDay
57%8%14%15%3
2112
April1st to 15thDay
52%8%15%16%7%
2257
16th to endDay
49%8%13%18%7%1
2340
May1st to 15thDay
44%8%16%19%10%
2550
16th to endDay
50%9%16%17%6%
2807
June1st to 15thDay
50%9%14%18%5%
2700
16th to endDay
42%10%19%22%4
2700
July1st to 15thDay
37%9%22%25%5%
2541
16th to endDay
30%10%20%27%9%
2667
August1st to 15thDay
36%9%24%22%6%
2398
16th to endDay
32%8%21%27%9%1
2275
September1st to 15thDay
39%7%14%24%12%1
1984
16th to endDay
33%8%16%29%9%3
1815
October1st to 15thDay
46%5%16%22%8%
1686
16th to endDay
42%8%16%22%9%
1584
November1st to 15thDay
53%6%15%17%6%1
1408
16th to endDay
53%7%15%15%7%
1299
December1st to 15thDay
64%6%11%13%3
1260
16th to endDay
55%7%16%15%4
1344
January1st to 15thNight
55%8%15%13%41
2685
16th to endNight
48%7%13%19%8%2
2789
February1st to 15thNight
51%5%15%18%8%
2387
16th to endNight
50%7%14%16%10%
2017
March1st to 15thNight
47%10%19%17%5%
2091
16th to endNight
55%8%13%17%4
2112
April1st to 15thNight
54%6%16%15%6%
1688
16th to endNight
47%6%13%23%7%2
1620
May1st to 15thNight
45%6%11%24%10%1
1398
16th to endNight
50%8%13%17%8%1
1309
June1st to 15thNight
50%8%14%18%7%
1260
16th to endNight
42%11%18%20%6%
1260
July1st to 15thNight
34%12%25%20%6%
1190
16th to endNight
28%9%24%26%9%1
1239
August1st to 15thNight
33%11%23%24%6%
1451
16th to endNight
28%6%19%32%10%3
1575
September1st to 15thNight
37%7%13%22%14%5%
1642
16th to endNight
30%7%17%27%14%3
1815
October1st to 15thNight
44%7%16%21%8%1
1943
16th to endNight
41%8%18%24%6%
2285
November1st to 15thNight
45%6%15%22%8%1
2438
16th to endNight
52%8%16%14%6%1
2658
December1st to 15thNight
59%7%13%16%2
2700
16th to endNight
51%7%15%19%5%
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
11%5%11%33%23%15%
60
16th to endDay
14%123%21%28%10%
64
February1st to 15thDay
21%415%38%17%2
73
16th to endDay
14%6%20%35%23%
114
March1st to 15thDay
12%6%35%35%8%
270
16th to endDay
9%8%38%27%14%1
288
April1st to 15thDay
15%14%27%28%10%2
269
16th to endDay
21%7%26%25%15%3
270
May1st to 15thDay
11%10%23%30%20%3
420
16th to endDay
20%5%19%28%20%5%
517
June1st to 15thDay
17%7%24%32%14%3
495
16th to endDay
15%5%27%27%18%5%
495
July1st to 15thDay
10%218%35%24%8%
475
16th to endDay
9%323%32%23%6%
515
August1st to 15thDay
13%217%32%25%8%
312
16th to endDay
9%7%25%35%19%2
268
September1st to 15thDay
21%7%23%25%17%4
255
16th to endDay
11%11%27%27%17%4
255
October1st to 15thDay
19%7%23%32%15%3
126
16th to endDay
14%418%41%18%2
96
November1st to 15thDay
23%5%25%36%8%
90
16th to endDay
8%11%29%22%11%14%
67
December1st to 15thDay
11%140%25%18%3
60
16th to endDay
14%323%25%28%6%
64
January1st to 15thNight
13%8%28%33%14%2
900
16th to endNight
10%5%27%40%13%1
869
February1st to 15thNight
10%6%23%36%19%3
704
16th to endNight
10%323%38%19%3
632
March1st to 15thNight
8%432%37%14%2
720
16th to endNight
12%5%30%36%13%1
768
April1st to 15thNight
15%5%32%29%15%1
596
16th to endNight
15%6%28%36%12%1
540
May1st to 15thNight
14%6%25%34%17%1
450
16th to endNight
22%425%26%19%1
375
June1st to 15thNight
20%5%24%31%15%2
360
16th to endNight
12%325%36%21%1
360
July1st to 15thNight
10%118%45%23%1
340
16th to endNight
7%322%43%21%1
376
August1st to 15thNight
10%117%37%28%3
414
16th to endNight
9%320%43%22%
525
September1st to 15thNight
16%418%38%21%2
566
16th to endNight
10%5%25%40%14%3
656
October1st to 15thNight
14%329%34%15%2
660
16th to endNight
13%5%28%39%13%
704
November1st to 15thNight
11%7%34%33%10%2
863
16th to endNight
11%6%34%33%12%2
900
December1st to 15thNight
12%6%28%33%17%2
900
16th to endNight
9%329%36%16%3
960
Page generated at 2017-08-13 12:16:42. Version ac04

Copyright 2017 A. Danko


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