Lethbridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lethbridge clear sky chart from 2005-11-06 to 2024-01-11.

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
32%
23565
15%
74591
8%
23522
41%
23522
22%
46949

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 10thNight
21%
950
13%
2836
4%
946
28%
946
15%
1963
January11th to 20thNight
22%
883
16%
2691
6%
883
33%
883
17%
1846
January21st to endNight
23%
792
19%
2772
7%
792
40%
792
17%
1775
February1st to 10thNight
24%
720
13%
2442
7%
720
33%
720
15%
1679
February11th to 20thNight
24%
702
12%
2273
6%
700
33%
700
15%
1589
February21st to endNight
28%
592
15%
1836
8%
592
38%
592
16%
1282
March1st to 10thNight
28%
720
13%
2139
6%
720
36%
720
20%
1465
March11th to 20thNight
28%
720
18%
1980
7%
720
39%
720
22%
1348
March21st to endNight
30%
792
12%
2178
3%
792
37%
792
18%
1549
April1st to 10thNight
25%
647
16%
1759
4%
647
34%
647
21%
1202
April11th to 20thNight
27%
533
16%
1601
7%
533
33%
533
18%
1101
April21st to endNight
33%
540
13%
1620
8%
540
39%
540
19%
1107
May1st to 10thNight
39%
540
10%
1581
7%
540
42%
540
22%
1069
May11th to 20thNight
46%
379
16%
1264
16%
379
51%
379
26%
764
May21st to endNight
40%
389
8%
1358
6%
388
44%
388
16%
928
June1st to 10thNight
35%
360
7%
1260
2%
360
39%
360
21%
776
June11th to 20thNight
31%
360
6%
1260
1%
360
35%
360
20%
803
June21st to endNight
52%
360
7%
1260
3%
360
54%
360
34%
667
July1st to 10thNight
58%
350
8%
1225
5%
350
60%
350
36%
627
July11th to 20thNight
52%
348
12%
1218
10%
348
59%
348
37%
611
July21st to endNight
61%
394
22%
1370
23%
372
70%
372
46%
597
August1st to 10thNight
61%
415
19%
1481
20%
413
69%
413
34%
771
August11th to 20thNight
56%
534
22%
1602
17%
534
63%
534
41%
869
August21st to endNight
52%
594
27%
1782
17%
594
59%
594
40%
953
September1st to 10thNight
46%
594
22%
1736
13%
594
53%
594
35%
991
September11th to 20thNight
50%
720
21%
1980
14%
720
55%
720
36%
1184
September21st to endNight
39%
720
23%
1980
12%
720
49%
720
33%
1197
October1st to 10thNight
41%
720
21%
2084
10%
720
51%
720
28%
1310
October11th to 20thNight
33%
720
22%
2220
9%
720
46%
720
26%
1346
October21st to endNight
24%
792
18%
2574
6%
792
37%
792
20%
1631
November1st to 10thNight
22%
848
16%
2513
6%
848
32%
848
19%
1725
November11th to 20thNight
19%
950
19%
2660
4%
950
34%
950
23%
1704
November21st to endNight
23%
950
15%
2802
5%
950
33%
950
22%
1760
December1st to 10thNight
23%
950
15%
2850
6%
950
31%
950
18%
1958
December11th to 20thNight
23%
949
13%
3458
5%
949
31%
949
15%
2195
December21st to endNight
21%
1038
10%
4946
4%
1026
30%
1026
13%
2607

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
9%8%36%5%35%5%6%8%43%
74624
Night
7%8%37%6%35%5%6%8%42%
75075
TransparencyDay
38%7%15%25%13%3
74310
Night
39%7%16%23%12%2
74908
SeeingDay
13%14%29%25%15%3
14233
Night
12%14%34%28%11%1
23575

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 10thDay
5%10%6%8%6%46%6%6%10%34%
1329
11th to 20thDay
6%12%45%6%38%5%6%8%36%
1296
21st to endDay
5%11%49%7%45%7%7%9%32%
1584
February1st to 10thDay
8%11%5%8%8%46%6%7%9%29%
1516
11th to 20thDay
6%12%47%7%5%5%7%7%9%30%
1575
21st to endDay
5%11%6%9%8%25%5%6%7%35%
1417
March1st to 10thDay
412%5%9%7%345%7%9%36%
1820
11th to 20thDay
6%10%6%7%5%445%6%9%40%
1979
21st to endDay
8%11%47%6%46%6%7%8%33%
2178
April1st to 10thDay
8%12%5%8%7%47%5%5%8%32%
2199
11th to 20thDay
11%12%48%6%45%45%7%34%
2310
21st to endDay
12%10%36%6%36%6%6%7%36%
2340
May1st to 10thDay
12%9%45%5%45%6%6%8%35%
2377
11th to 20thDay
12%7%25%6%35%5%6%8%41%
2626
21st to endDay
21%7%35%5%35%5%5%7%34%
2917
June1st to 10thDay
13%7%35%5%35%5%7%9%38%
2700
11th to 20thDay
15%6%36%5%46%5%7%8%35%
2700
21st to endDay
7%424435%5%7%9%52%
2700
July1st to 10thDay
6%3234245%6%9%55%
2700
11th to 20thDay
5%3244345%6%9%57%
2700
21st to endDay
321332345%7%66%
2866
August1st to 10thDay
8%31332446%8%58%
2449
11th to 20thDay
7%32432346%8%58%
2299
21st to endDay
9%3244235%5%7%57%
2574
September1st to 10thDay
11%424422347%57%
2220
11th to 20thDay
13%5%2432335%8%52%
1980
21st to endDay
11%6%25%43435%8%50%
1980
October1st to 10thDay
12%8%26%5%35%45%7%42%
1876
11th to 20thDay
7%9%37%6%45%5%5%7%43%
1738
21st to endDay
8%9%36%6%36%5%8%7%39%
1782
November1st to 10thDay
13%12%36%435%47%7%35%
1547
11th to 20thDay
6%9%37%5%46%5%6%9%40%
1520
21st to endDay
5%9%6%8%5%35%46%10%39%
1376
December1st to 10thDay
5%12%5%8%6%45%5%5%7%38%
1330
11th to 20thDay
410%5%9%7%46%7%6%10%32%
1682
21st to endDay
48%36%6%35%5%5%8%45%
2442
January1st to 10thNight
5%10%5%10%7%35%6%6%9%34%
2836
11th to 20thNight
5%11%49%6%45%6%6%8%36%
2691
21st to endNight
5%9%48%6%46%6%7%8%36%
2772
February1st to 10thNight
6%11%5%9%8%45%5%6%7%34%
2442
11th to 20thNight
7%13%5%8%7%5%6%5%6%8%31%
2272
21st to endNight
411%5%10%9%46%5%5%7%34%
1836
March1st to 10thNight
5%10%5%9%7%36%6%6%8%36%
2139
11th to 20thNight
6%8%48%6%46%5%7%9%36%
1980
21st to endNight
8%10%48%6%35%7%7%10%33%
2178
April1st to 10thNight
8%13%47%6%35%45%8%38%
1759
11th to 20thNight
10%11%47%7%345%6%7%35%
1601
21st to endNight
12%9%37%6%45%5%5%6%38%
1620
May1st to 10thNight
9%9%48%7%35%5%7%7%37%
1581
11th to 20thNight
11%6%26%5%25%45%9%46%
1264
21st to endNight
20%6%35%5%446%6%7%34%
1358
June1st to 10thNight
13%5%36%4345%7%8%42%
1260
11th to 20thNight
18%5%35%6%345%6%9%37%
1260
21st to endNight
6%423425%46%9%54%
1260
July1st to 10thNight
6%324435%46%8%56%
1260
11th to 20thNight
7%41433445%8%56%
1260
21st to endNight
221332346%6%66%
1450
August1st to 10thNight
6%2135%36%5%5%8%56%
1489
11th to 20thNight
6%4243335%5%9%56%
1602
21st to endNight
7%3244245%6%8%57%
1782
September1st to 10thNight
10%42442346%6%54%
1736
11th to 20thNight
11%5%1343345%7%53%
1980
21st to endNight
10%5%2443446%7%51%
1980
October1st to 10thNight
12%5%35%5%2446%8%46%
2084
11th to 20thNight
9%7%26%5%345%5%8%47%
2220
21st to endNight
9%7%35%7%45%5%6%7%43%
2574
November1st to 10thNight
10%11%45%5%346%6%7%38%
2513
11th to 20thNight
5%8%46%6%45%5%6%8%44%
2660
21st to endNight
410%5%7%5%3447%10%41%
2802
December1st to 10thNight
5%11%6%8%7%45%6%6%7%37%
2850
11th to 20thNight
38%49%7%46%6%6%10%37%
3510
21st to endNight
49%36%5%35%5%6%8%46%
5214

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 10thDay
43%10%15%24%7%2
1329
11th to 20thDay
45%9%17%20%7%2
1296
21st to endDay
45%8%16%21%8%1
1584
February1st to 10thDay
50%8%15%20%6%2
1516
11th to 20thDay
47%9%17%20%7%1
1584
21st to endDay
48%7%12%20%10%2
1417
March1st to 10thDay
45%7%17%21%10%
1820
11th to 20thDay
40%7%19%24%9%2
1980
21st to endDay
46%10%17%20%7%
2178
April1st to 10thDay
50%6%14%22%7%1
2199
11th to 20thDay
49%5%12%22%9%2
2310
21st to endDay
46%7%13%23%10%1
2340
May1st to 10thDay
44%8%14%23%10%
2377
11th to 20thDay
39%8%14%27%12%1
2630
21st to endDay
49%7%12%21%10%
2918
June1st to 10thDay
42%8%16%23%9%2
2700
11th to 20thDay
45%9%12%21%12%1
2700
21st to endDay
27%9%16%32%13%3
2700
July1st to 10thDay
24%7%16%31%16%5%
2626
11th to 20thDay
23%8%15%27%22%5%
2619
21st to endDay
18%6%13%30%28%6%
2707
August1st to 10thDay
23%7%14%30%20%5%
2432
11th to 20thDay
24%6%16%34%16%5%
2299
21st to endDay
25%6%13%30%21%5%
2574
September1st to 10thDay
29%5%12%27%18%9%
2220
11th to 20thDay
32%7%13%27%17%4
1980
21st to endDay
33%6%12%32%14%3
1980
October1st to 10thDay
41%8%15%24%11%1
1876
11th to 20thDay
40%6%17%24%10%2
1738
21st to endDay
40%9%15%24%10%1
1782
November1st to 10thDay
47%8%13%23%9%1
1547
11th to 20thDay
39%8%19%24%9%1
1520
21st to endDay
41%6%20%21%10%2
1376
December1st to 10thDay
45%7%17%19%9%3
1330
11th to 20thDay
46%9%18%23%41
1684
21st to endDay
35%6%16%23%19%1
2442
January1st to 10thNight
46%8%17%19%9%2
2836
11th to 20thNight
45%8%17%21%7%2
2691
21st to endNight
43%7%17%21%12%1
2772
February1st to 10thNight
47%8%15%17%11%2
2442
11th to 20thNight
49%7%16%20%8%
2273
21st to endNight
48%7%14%20%9%2
1836
March1st to 10thNight
44%8%19%21%8%1
2139
11th to 20thNight
41%8%17%23%10%1
1980
21st to endNight
44%11%18%20%7%1
2178
April1st to 10thNight
44%6%15%24%10%1
1759
11th to 20thNight
47%7%12%22%10%1
1601
21st to endNight
45%8%12%25%9%1
1620
May1st to 10thNight
43%8%14%24%9%1
1581
11th to 20thNight
35%8%13%28%14%2
1264
21st to endNight
48%8%14%20%9%1
1358
June1st to 10thNight
38%9%16%25%11%1
1260
11th to 20thNight
42%7%15%23%12%1
1260
21st to endNight
27%7%17%31%15%3
1260
July1st to 10thNight
24%8%16%31%18%4
1225
11th to 20thNight
25%6%17%22%22%8%
1218
21st to endNight
16%7%13%26%28%11%
1370
August1st to 10thNight
25%9%14%26%20%6%
1481
11th to 20thNight
24%8%13%29%22%5%
1602
21st to endNight
25%6%11%26%26%6%
1782
September1st to 10thNight
29%6%12%27%18%7%
1736
11th to 20thNight
30%6%13%27%18%6%
1980
21st to endNight
32%5%14%28%16%3
1980
October1st to 10thNight
36%8%16%25%15%2
2084
11th to 20thNight
35%7%15%26%14%3
2220
21st to endNight
39%8%17%25%11%1
2574
November1st to 10thNight
44%8%15%22%10%1
2513
11th to 20thNight
36%7%21%21%14%1
2660
21st to endNight
38%6%22%21%11%2
2802
December1st to 10thNight
45%8%16%20%10%2
2850
11th to 20thNight
41%8%23%22%5%1
3507
21st to endNight
36%6%16%24%14%4
5214

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 10thDay
10%19%35%19%8%8%
180
11th to 20thDay
17%16%28%26%12%1
160
21st to endDay
14%20%40%18%5%3
176
February1st to 10thDay
20%22%30%21%6%2
194
11th to 20thDay
15%21%36%20%8%1
240
21st to endDay
14%17%34%25%8%1
283
March1st to 10thDay
11%23%34%21%10%2
420
11th to 20thDay
11%21%28%26%9%5%
420
21st to endDay
11%21%37%21%8%2
462
April1st to 10thDay
15%21%33%23%8%
420
11th to 20thDay
18%18%29%24%11%1
412
21st to endDay
18%20%27%23%11%2
420
May1st to 10thDay
13%13%30%24%16%4
460
11th to 20thDay
17%6%26%27%21%4
625
21st to endDay
21%8%22%27%18%5%
679
June1st to 10thDay
15%13%28%24%18%2
630
11th to 20thDay
16%17%29%23%13%2
630
21st to endDay
7%8%26%32%21%4
630
July1st to 10thDay
7%6%24%34%24%5%
621
11th to 20thDay
7%6%30%34%20%2
618
21st to endDay
38%28%35%21%5%
612
August1st to 10thDay
9%6%25%34%23%4
447
11th to 20thDay
6%7%25%30%25%7%
437
21st to endDay
10%11%24%28%21%6%
495
September1st to 10thDay
12%14%29%24%18%2
450
11th to 20thDay
13%12%29%27%15%4
450
21st to endDay
16%18%30%22%11%4
450
October1st to 10thDay
16%11%26%25%19%3
346
11th to 20thDay
12%21%26%23%13%4
270
21st to endDay
20%25%30%18%6%2
297
November1st to 10thDay
25%21%28%19%7%
270
11th to 20thDay
17%17%44%17%4
270
21st to endDay
11%27%33%13%13%2
201
December1st to 10thDay
16%26%31%21%6%1
180
11th to 20thDay
12%26%39%14%8%1
180
21st to endDay
15%19%31%21%12%3
198
January1st to 10thNight
10%24%36%22%7%1
950
11th to 20thNight
13%18%39%22%7%1
883
21st to endNight
11%20%37%23%7%1
792
February1st to 10thNight
14%16%34%24%10%2
720
11th to 20thNight
15%16%34%27%8%1
704
21st to endNight
11%15%34%26%13%2
592
March1st to 10thNight
10%14%37%28%11%1
720
11th to 20thNight
11%15%37%26%9%2
720
21st to endNight
13%14%33%28%10%2
792
April1st to 10thNight
13%16%36%25%10%
647
11th to 20thNight
16%11%39%26%8%
533
21st to endNight
16%12%31%32%9%
540
May1st to 10thNight
13%10%28%31%16%1
540
11th to 20thNight
14%6%28%34%17%1
379
21st to endNight
20%6%26%29%17%2
389
June1st to 10thNight
14%10%32%29%13%1
360
11th to 20thNight
19%9%35%27%10%
360
21st to endNight
8%6%30%38%17%2
360
July1st to 10thNight
6%7%21%45%20%
350
11th to 20thNight
8%5%28%43%14%1
348
21st to endNight
4427%45%20%1
394
August1st to 10thNight
6%5%21%45%21%1
415
11th to 20thNight
7%327%39%21%2
534
21st to endNight
7%6%28%41%18%1
594
September1st to 10thNight
13%7%27%36%16%1
594
11th to 20thNight
14%5%25%37%19%1
720
21st to endNight
12%11%34%31%11%2
720
October1st to 10thNight
16%8%28%32%15%1
720
11th to 20thNight
13%13%34%28%11%1
720
21st to endNight
13%17%39%22%8%
792
November1st to 10thNight
18%18%38%21%5%
848
11th to 20thNight
13%21%43%18%41
950
21st to endNight
11%20%39%24%6%1
950
December1st to 10thNight
11%18%39%22%9%2
950
11th to 20thNight
8%22%37%26%8%
950
21st to endNight
13%18%38%22%9%1
1045
Page generated at 2024-01-08 09:14:17. Version ac07

Copyright 2024 Attilla Danko


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