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 2018-02-14.

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%
15926
12%
48853
9%
15901
47%
15901
20%
33910

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
38%
970
9%
2910
7%
970
40%
970
15%
2219
January16th to endNight
42%
941
16%
3021
12%
941
48%
941
19%
2132
February1st to 15thNight
44%
752
12%
2577
12%
752
47%
752
17%
1812
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%
426
9%
1487
12%
424
62%
424
26%
901
August16th to endNight
61%
573
18%
1719
15%
573
64%
573
38%
966
September1st to 15thNight
55%
618
16%
1792
12%
618
57%
618
31%
1126
September16th to endNight
54%
716
21%
1980
15%
716
59%
716
36%
1227
October1st to 15thNight
43%
720
15%
2120
8%
720
49%
720
24%
1449
October16th to endNight
42%
768
16%
2493
10%
768
49%
768
22%
1625
November1st to 15thNight
36%
937
16%
2647
10%
937
41%
937
21%
1851
November16th to endNight
35%
975
11%
2880
7%
975
38%
975
18%
2118
December1st to 15thNight
37%
975
10%
2925
7%
975
39%
975
14%
2219
December16th to endNight
40%
1040
14%
3120
9%
1040
45%
1040
18%
2268

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%
49257
Night
8%8%47%6%35%5%6%8%33%
49001
TransparencyDay
46%8%16%20%7%
48907
Night
46%7%16%20%7%1
48855
SeeingDay
14%6%24%30%18%5%
6447
Night
12%5%27%36%16%2
15941

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%8%8%5%5%7%6%7%25%
1358
16th to endDay
6%10%5%10%7%36%5%7%8%27%
1567
February1st to 15thDay
8%12%5%9%9%46%6%5%7%25%
1586
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%8%44%
2466
16th to endDay
7%3145%2446%8%50%
2483
September1st to 15thDay
12%7%24334346%46%
2164
16th to endDay
8%5%2442445%9%46%
1980
October1st to 15thDay
13%9%36%6%33448%36%
1839
16th to endDay
7%9%45%5%35%6%5%7%38%
1728
November1st to 15thDay
8%13%5%11%7%35%446%29%
1528
16th to endDay
6%11%5%10%8%36%45%6%29%
1407
December1st to 15thDay
7%14%6%9%10%47%5%45%23%
1365
16th to endDay
312%5%12%8%5%7%7%7%7%22%
1456
January1st to 15thNight
7%10%5%9%9%47%8%6%8%22%
2910
16th to endNight
5%10%5%9%6%35%6%6%7%31%
3021
February1st to 15thNight
6%10%5%10%8%445%6%8%28%
2566
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%9%44%
1494
16th to endNight
7%41342336%11%50%
1719
September1st to 15thNight
13%5%14433445%49%
1792
16th to endNight
8%5%2342346%8%49%
1980
October1st to 15thNight
10%7%27%6%35%6%5%7%36%
2120
16th to endNight
7%8%37%5%35%5%6%9%36%
2493
November1st to 15thNight
7%9%47%7%45%5%5%7%34%
2647
16th to endNight
6%10%5%9%8%45%6%5%7%30%
2880
December1st to 15thNight
6%13%6%10%8%45%5%48%25%
2925
16th to endNight
410%5%10%8%46%6%5%10%26%
3120

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
1358
16th to endDay
49%7%15%17%7%1
1567
February1st to 15thDay
56%7%13%15%6%
1586
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
35%9%24%22%7%
2448
16th to endDay
30%8%21%28%10%1
2483
September1st to 15thDay
37%7%14%24%13%3
2164
16th to endDay
33%8%16%28%9%3
1980
October1st to 15thDay
46%5%15%22%8%
1839
16th to endDay
42%8%15%22%9%
1728
November1st to 15thDay
55%6%14%16%5%
1528
16th to endDay
52%7%15%16%7%
1407
December1st to 15thDay
61%6%11%15%4
1365
16th to endDay
56%7%15%14%6%
1456
January1st to 15thNight
54%9%15%13%41
2910
16th to endNight
48%7%13%18%9%2
3021
February1st to 15thNight
51%6%14%18%8%
2577
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%22%23%7%
1487
16th to endNight
28%6%19%31%11%2
1719
September1st to 15thNight
36%6%13%23%14%6%
1792
16th to endNight
31%7%16%26%14%2
1980
October1st to 15thNight
44%7%16%21%9%1
2120
16th to endNight
41%8%18%24%6%
2493
November1st to 15thNight
48%5%14%22%7%1
2647
16th to endNight
51%8%17%15%6%1
2880
December1st to 15thNight
56%7%13%18%3
2925
16th to endNight
51%7%14%19%6%
3120

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
13%411%35%22%13%
90
16th to endDay
9%123%29%25%11%
96
February1st to 15thDay
20%219%38%16%3
105
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%26%8%
327
16th to endDay
8%6%22%34%22%6%
332
September1st to 15thDay
18%6%24%27%18%4
315
16th to endDay
10%10%26%27%19%5%
315
October1st to 15thDay
20%5%24%28%16%4
174
16th to endDay
15%7%26%35%13%1
144
November1st to 15thDay
20%5%25%30%14%2
135
16th to endDay
10%12%30%25%13%10%
100
December1st to 15thDay
8%5%33%26%20%5%
90
16th to endDay
11%5%22%36%19%4
96
January1st to 15thNight
12%7%27%35%15%2
975
16th to endNight
10%5%28%40%13%1
941
February1st to 15thNight
10%6%22%37%19%3
760
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%217%38%28%3
426
16th to endNight
8%320%42%22%1
573
September1st to 15thNight
15%419%38%20%2
618
16th to endNight
11%5%24%40%15%3
716
October1st to 15thNight
14%230%33%16%3
720
16th to endNight
12%6%29%38%12%
768
November1st to 15thNight
12%7%33%33%10%2
937
16th to endNight
11%6%34%34%12%2
975
December1st to 15thNight
11%6%27%33%17%2
975
16th to endNight
9%329%37%16%3
1040
Page generated at 2018-02-15 08:58:46. Version ac04

Copyright 2018 A. Danko


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