Alberta Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alberta Star Party clear sky chart from 2005-11-05 to 2018-02-22.

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
44%
15947
12%
48963
9%
15920
47%
15920
20%
34197

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
37%
970
9%
2910
6%
970
39%
970
14%
2234
January16th to endNight
42%
939
17%
3019
12%
939
48%
939
18%
2148
February1st to 15thNight
42%
758
12%
2600
12%
756
46%
756
16%
1852
February16th to endNight
46%
660
12%
2104
12%
660
49%
660
18%
1500
March1st to 15thNight
42%
720
13%
2095
9%
720
46%
720
19%
1534
March16th to endNight
37%
768
9%
2109
4%
767
40%
767
16%
1645
April1st to 15thNight
37%
599
9%
1685
3%
599
40%
599
17%
1259
April16th to endNight
40%
540
13%
1620
10%
540
44%
540
21%
1139
May1st to 15thNight
44%
440
11%
1391
10%
440
47%
440
22%
938
May16th to endNight
40%
374
5%
1309
2%
374
42%
374
16%
927
June1st to 15thNight
39%
360
0%
1260
0%
360
39%
360
14%
906
June16th to endNight
47%
360
0%
1260
0%
360
47%
360
18%
861
July1st to 15thNight
60%
340
0%
1190
0%
340
60%
340
24%
742
July16th to endNight
59%
376
7%
1239
6%
354
61%
354
30%
703
August1st to 15thNight
62%
417
9%
1478
11%
415
63%
415
24%
902
August16th to endNight
62%
573
17%
1719
14%
573
64%
573
36%
973
September1st to 15thNight
57%
624
16%
1794
13%
624
59%
624
31%
1109
September16th to endNight
56%
716
21%
1980
15%
716
61%
716
35%
1229
October1st to 15thNight
44%
720
15%
2122
9%
720
50%
720
23%
1444
October16th to endNight
43%
768
16%
2496
10%
768
51%
768
22%
1645
November1st to 15thNight
37%
935
16%
2645
10%
935
42%
935
21%
1879
November16th to endNight
36%
975
11%
2893
7%
975
39%
975
17%
2137
December1st to 15thNight
37%
975
11%
2925
7%
975
39%
975
14%
2226
December16th to endNight
41%
1040
14%
3120
9%
1040
46%
1040
18%
2265

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%33%
49331
Night
8%9%48%6%35%5%6%8%32%
49112
TransparencyDay
46%8%16%20%6%
48981
Night
47%7%15%20%7%1
48966
SeeingDay
14%5%23%31%18%5%
6468
Night
13%425%37%16%2
15959

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
6%13%5%7%8%5%7%5%7%6%24%
1358
16th to endDay
6%11%5%9%7%446%6%8%27%
1567
February1st to 15thDay
10%12%5%8%7%5%45%6%8%25%
1593
16th to endDay
5%12%6%11%10%46%6%5%6%23%
1513
March1st to 15thDay
7%10%6%12%9%5%6%46%6%24%
1865
16th to endDay
11%13%6%10%6%36%5%6%7%22%
2111
April1st to 15thDay
12%12%46%5%45%46%8%28%
2263
16th to endDay
16%8%26%6%445%5%8%31%
2340
May1st to 15thDay
11%8%35%5%35%6%6%8%35%
2559
16th to endDay
19%7%36%6%35%5%5%7%30%
2802
June1st to 15thDay
16%7%36%6%35%5%7%8%28%
2700
16th to endDay
13%435%5%36%6%6%9%35%
2700
July1st to 15thDay
9%5%25%435%5%7%9%41%
2700
16th to endDay
7%424425%5%6%10%47%
2846
August1st to 15thDay
11%5%245%3446%9%43%
2473
16th to endDay
8%3144346%6%9%48%
2483
September1st to 15thDay
13%6%15%42435%6%44%
2165
16th to endDay
9%6%2442445%8%46%
1980
October1st to 15thDay
13%8%47%5%34447%35%
1837
16th to endDay
7%10%36%6%35%6%5%7%36%
1728
November1st to 15thDay
8%14%6%9%7%35%448%27%
1531
16th to endDay
7%12%5%10%9%35%36%8%27%
1396
December1st to 15thDay
8%15%7%9%9%47%446%22%
1365
16th to endDay
412%6%12%8%5%6%7%6%7%22%
1456
January1st to 15thNight
7%10%6%9%8%5%7%7%7%8%21%
2910
16th to endNight
5%11%5%9%7%46%5%6%7%30%
3019
February1st to 15thNight
7%10%5%10%8%45%45%7%29%
2589
16th to endNight
5%10%6%10%8%345%6%9%28%
2104
March1st to 15thNight
5%10%5%8%8%46%6%7%9%28%
2095
16th to endNight
9%12%5%8%7%48%6%6%7%23%
2109
April1st to 15thNight
13%9%48%7%36%5%6%8%26%
1685
16th to endNight
11%10%48%5%25%5%6%7%33%
1620
May1st to 15thNight
11%8%26%5%35%6%5%7%35%
1390
16th to endNight
19%8%25%5%25%46%7%31%
1309
June1st to 15thNight
14%8%37%7%5%6%5%6%6%28%
1260
16th to endNight
11%6%37%7%345%6%7%34%
1260
July1st to 15thNight
8%3246%35%6%6%12%39%
1260
16th to endNight
7%3135%25%47%10%47%
1323
August1st to 15thNight
8%5%15%4445%6%8%44%
1485
16th to endNight
6%4243235%5%9%50%
1719
September1st to 15thNight
13%5%2332345%7%47%
1794
16th to endNight
8%5%25%42345%8%48%
1980
October1st to 15thNight
11%8%36%5%345%5%7%36%
2122
16th to endNight
8%8%35%5%35%5%7%9%36%
2496
November1st to 15thNight
8%9%5%7%7%35%5%5%7%33%
2645
16th to endNight
6%11%5%10%7%46%5%5%8%29%
2893
December1st to 15thNight
6%13%6%11%7%45%45%8%25%
2925
16th to endNight
411%5%11%7%5%5%6%6%9%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
56%6%14%17%4
1358
16th to endDay
50%6%14%17%8%1
1567
February1st to 15thDay
55%6%15%15%6%
1593
16th to endDay
57%7%13%15%5%
1513
March1st to 15thDay
57%8%14%14%5%
1865
16th to endDay
58%8%13%15%4
2112
April1st to 15thDay
52%8%16%16%6%
2263
16th to endDay
50%9%13%18%7%1
2340
May1st to 15thDay
44%7%15%22%9%
2559
16th to endDay
50%7%16%18%6%
2807
June1st to 15thDay
50%9%15%18%5%
2700
16th to endDay
43%10%18%23%4
2700
July1st to 15thDay
37%9%22%24%5%
2541
16th to endDay
32%10%21%26%8%
2667
August1st to 15thDay
36%8%25%21%6%
2455
16th to endDay
30%8%22%27%9%1
2483
September1st to 15thDay
38%7%14%24%11%3
2165
16th to endDay
34%8%15%28%9%3
1980
October1st to 15thDay
47%6%15%21%8%
1837
16th to endDay
43%9%15%22%8%
1728
November1st to 15thDay
55%6%14%17%5%1
1531
16th to endDay
53%7%15%15%7%
1396
December1st to 15thDay
63%6%11%14%3
1365
16th to endDay
56%8%13%15%5%
1456
January1st to 15thNight
56%8%14%13%41
2910
16th to endNight
49%7%12%18%9%2
3019
February1st to 15thNight
52%6%13%19%8%
2600
16th to endNight
51%6%15%16%10%
2104
March1st to 15thNight
48%9%17%18%5%
2095
16th to endNight
58%6%12%17%4
2112
April1st to 15thNight
54%6%15%15%6%
1685
16th to endNight
47%7%11%23%7%2
1620
May1st to 15thNight
46%5%10%24%11%
1391
16th to endNight
49%8%11%19%8%1
1309
June1st to 15thNight
52%8%12%18%7%
1260
16th to endNight
45%10%17%19%6%
1260
July1st to 15thNight
35%10%25%21%6%
1190
16th to endNight
30%9%23%26%8%1
1239
August1st to 15thNight
34%10%21%24%6%
1478
16th to endNight
28%6%19%31%10%2
1719
September1st to 15thNight
35%6%14%23%14%5%
1794
16th to endNight
32%7%16%26%14%2
1980
October1st to 15thNight
44%6%16%22%8%1
2122
16th to endNight
42%8%18%24%6%
2496
November1st to 15thNight
47%7%14%21%7%1
2645
16th to endNight
52%8%16%15%6%1
2893
December1st to 15thNight
56%7%12%18%4
2925
16th to endNight
52%6%14%19%7%
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%314%33%22%13%
90
16th to endDay
9%123%33%20%11%
96
February1st to 15thDay
17%5%23%33%14%5%
108
16th to endDay
15%223%30%23%4
136
March1st to 15thDay
13%233%40%8%1
270
16th to endDay
11%6%35%28%15%1
288
April1st to 15thDay
17%11%28%29%10%2
269
16th to endDay
22%6%25%27%13%3
270
May1st to 15thDay
11%9%23%30%21%3
417
16th to endDay
20%5%20%28%20%5%
517
June1st to 15thDay
17%5%24%34%15%3
495
16th to endDay
14%5%24%30%19%6%
495
July1st to 15thDay
11%317%34%24%8%
475
16th to endDay
11%223%31%24%6%
515
August1st to 15thDay
12%216%33%26%8%
325
16th to endDay
9%6%20%33%24%6%
332
September1st to 15thDay
20%326%26%18%4
315
16th to endDay
13%9%24%29%17%5%
315
October1st to 15thDay
19%5%26%28%14%5%
178
16th to endDay
17%9%23%31%15%2
144
November1st to 15thDay
20%225%34%14%2
135
16th to endDay
14%6%29%25%13%10%
97
December1st to 15thDay
8%331%32%18%5%
90
16th to endDay
11%321%39%19%4
96
January1st to 15thNight
12%6%28%34%15%2
975
16th to endNight
11%6%25%41%13%1
939
February1st to 15thNight
12%5%22%36%19%2
764
16th to endNight
10%321%41%20%4
660
March1st to 15thNight
9%429%40%15%2
720
16th to endNight
15%326%38%15%1
768
April1st to 15thNight
18%6%27%28%16%2
599
16th to endNight
17%5%27%35%12%1
540
May1st to 15thNight
16%5%24%36%15%1
440
16th to endNight
23%425%24%21%1
375
June1st to 15thNight
21%5%23%33%16%
360
16th to endNight
13%423%36%21%1
360
July1st to 15thNight
10%118%42%25%1
340
16th to endNight
9%124%42%21%1
376
August1st to 15thNight
10%415%38%28%2
417
16th to endNight
8%319%42%26%
573
September1st to 15thNight
17%317%39%20%2
624
16th to endNight
11%422%41%17%2
716
October1st to 15thNight
15%426%33%17%3
720
16th to endNight
13%5%28%39%12%
768
November1st to 15thNight
12%6%32%34%12%2
935
16th to endNight
11%5%32%35%12%1
975
December1st to 15thNight
13%6%26%34%16%2
975
16th to endNight
9%328%38%15%3
1040
Page generated at 2018-02-23 09:21:32. Version ac04

Copyright 2018 A. Danko


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