Lethbridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lethbridge clear sky chart from 2005-11-05 to 2018-03-21.

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
33%
16086
15%
49263
8%
16054
41%
16054
22%
32026

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
22%
975
11%
2910
4%
970
29%
970
16%
2067
January16th to endNight
25%
881
17%
2961
9%
881
37%
881
17%
1950
February1st to 15thNight
27%
758
13%
2557
8%
756
35%
756
16%
1759
February16th to endNight
28%
684
13%
2158
7%
684
37%
684
16%
1538
March1st to 15thNight
28%
780
14%
2260
6%
780
36%
780
21%
1542
March16th to endNight
27%
792
11%
2178
2%
792
34%
792
17%
1583
April1st to 15thNight
24%
610
13%
1711
4%
610
31%
610
19%
1197
April16th to endNight
33%
540
15%
1620
9%
540
39%
540
19%
1114
May1st to 15thNight
40%
495
13%
1489
10%
495
44%
495
25%
967
May16th to endNight
40%
375
9%
1309
8%
374
44%
374
17%
886
June1st to 15thNight
36%
360
5%
1260
2%
360
39%
360
22%
767
June16th to endNight
45%
360
6%
1260
2%
360
47%
360
26%
744
July1st to 15thNight
58%
340
7%
1190
4%
340
61%
340
37%
605
July16th to endNight
59%
376
17%
1283
16%
354
66%
354
41%
602
August1st to 15thNight
64%
458
17%
1531
17%
456
69%
456
34%
844
August16th to endNight
56%
573
27%
1719
18%
573
62%
573
44%
891
September1st to 15thNight
52%
636
21%
1818
14%
636
56%
636
38%
1041
September16th to endNight
45%
716
23%
1980
13%
716
54%
716
36%
1181
October1st to 15thNight
33%
720
18%
2109
7%
720
44%
720
24%
1383
October16th to endNight
31%
768
21%
2478
9%
768
45%
768
25%
1501
November1st to 15thNight
21%
899
17%
2609
5%
899
33%
899
23%
1717
November16th to endNight
25%
975
15%
2828
5%
975
34%
975
22%
1848
December1st to 15thNight
26%
975
13%
2925
6%
975
33%
975
17%
2072
December16th to endNight
23%
1040
13%
3120
5%
1040
31%
1040
17%
2227

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%7%35%5%3445%8%41%
49621
Night
7%8%36%5%3445%8%41%
49414
Cloud CoverDay
10%7%35%5%3445%7%41%
49622
Night
8%8%36%5%35%45%7%40%
49417
TransparencyDay
39%7%15%24%11%2
49276
Night
40%7%16%22%11%1
49263
SeeingDay
12%12%29%25%15%3
6527
Night
12%11%34%28%11%1
16093

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%11%5%7%5%25%5%48%36%
1358
16th to endDay
5%12%47%6%36%6%6%8%31%
1625
February1st to 15thDay
10%11%36%6%45%6%6%9%30%
1635
16th to endDay
5%12%5%8%7%25%5%5%8%31%
1601
March1st to 15thDay
411%47%6%3446%9%36%
2029
16th to endDay
10%11%5%6%5%36%5%6%7%31%
2172
April1st to 15thDay
10%11%46%6%36%5%5%8%31%
2236
16th to endDay
13%9%35%5%35%5%5%7%35%
2340
May1st to 15thDay
11%7%345%345%5%7%42%
2458
16th to endDay
21%6%25%5%35%5%5%7%31%
2802
June1st to 15thDay
14%5%25%5%35%5%6%7%37%
2700
16th to endDay
10%414435%46%8%44%
2700
July1st to 15thDay
5%31342346%9%54%
2700
16th to endDay
421232345%8%60%
2798
August1st to 15thDay
8%31332346%8%53%
2419
16th to endDay
7%31332345%7%57%
2483
September1st to 15thDay
13%413322236%56%
2139
16th to endDay
11%414323348%53%
1980
October1st to 15thDay
12%9%36%5%34347%38%
1850
16th to endDay
7%7%26%5%35%6%8%8%38%
1746
November1st to 15thDay
9%8%35%5%35%5%7%7%36%
1567
16th to endDay
6%10%5%6%5%2435%9%39%
1462
December1st to 15thDay
5%11%5%8%6%47%5%5%7%32%
1365
16th to endDay
5%12%5%7%8%35%6%6%8%30%
1456
January1st to 15thNight
6%11%5%9%5%35%5%6%9%31%
2910
16th to endNight
5%11%46%5%35%5%5%7%38%
2961
February1st to 15thNight
8%11%37%6%3446%6%35%
2546
16th to endNight
413%5%9%7%35%45%7%32%
2158
March1st to 15thNight
48%38%6%36%5%6%9%35%
2260
16th to endNight
9%10%47%6%35%5%7%9%30%
2175
April1st to 15thNight
11%10%35%6%35%45%7%35%
1711
16th to endNight
12%9%36%5%3445%5%37%
1620
May1st to 15thNight
8%7%47%5%2435%7%42%
1488
16th to endNight
19%5%25%4245%6%8%35%
1309
June1st to 15thNight
13%425%42336%8%44%
1260
16th to endNight
10%424435%46%9%45%
1260
July1st to 15thNight
5%313225%36%7%56%
1260
16th to endNight
221332345%6%62%
1371
August1st to 15thNight
6%213435%5%5%8%53%
1539
16th to endNight
5%31332345%7%59%
1719
September1st to 15thNight
11%414312345%56%
1818
16th to endNight
10%313423448%52%
1980
October1st to 15thNight
12%6%25%6%2345%8%41%
2109
16th to endNight
8%5%25%5%245%5%7%46%
2478
November1st to 15thNight
5%9%45%5%345%6%6%43%
2609
16th to endNight
5%9%47%4345%6%9%39%
2828
December1st to 15thNight
410%6%8%7%45%6%6%8%33%
2925
16th to endNight
5%13%5%9%7%35%5%6%7%31%
3120

Percentage Cloud Cover SW (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%11%5%7%6%25%45%7%35%
1358
16th to endDay
6%11%47%6%35%7%7%9%30%
1625
February1st to 15thDay
10%10%46%5%46%6%6%7%31%
1635
16th to endDay
6%11%5%9%7%345%5%8%31%
1601
March1st to 15thDay
5%11%47%6%25%5%5%8%36%
2029
16th to endDay
10%12%47%6%36%5%5%7%30%
2173
April1st to 15thDay
11%10%47%6%46%5%5%7%31%
2236
16th to endDay
13%9%45%5%345%5%6%34%
2340
May1st to 15thDay
12%7%345%3445%7%42%
2458
16th to endDay
21%6%35%5%35%45%7%31%
2802
June1st to 15thDay
15%5%245%3446%8%37%
2700
16th to endDay
11%424435%5%6%8%44%
2700
July1st to 15thDay
5%31432446%9%53%
2700
16th to endDay
5%21332345%8%60%
2798
August1st to 15thDay
8%31332346%7%53%
2419
16th to endDay
8%21232435%7%58%
2483
September1st to 15thDay
13%413322235%56%
2139
16th to endDay
11%423323347%53%
1980
October1st to 15thDay
12%9%27%5%24446%38%
1850
16th to endDay
7%7%26%5%35%5%7%8%38%
1746
November1st to 15thDay
10%9%35%5%35%6%6%8%35%
1567
16th to endDay
6%10%47%43346%9%39%
1462
December1st to 15thDay
5%12%48%7%46%5%5%6%32%
1365
16th to endDay
6%11%5%8%8%36%5%5%8%29%
1456
January1st to 15thNight
6%11%5%8%5%35%5%6%9%31%
2910
16th to endNight
6%11%37%5%35%6%5%7%37%
2961
February1st to 15thNight
9%11%47%6%35%45%6%35%
2546
16th to endNight
5%14%6%9%6%35%45%6%31%
2158
March1st to 15thNight
5%8%48%6%45%6%7%9%34%
2260
16th to endNight
10%9%47%6%36%5%6%8%30%
2178
April1st to 15thNight
11%9%47%436%35%7%35%
1711
16th to endNight
12%9%35%6%35%5%46%37%
1620
May1st to 15thNight
9%7%36%5%35%346%42%
1488
16th to endNight
19%426%5%35%45%7%35%
1309
June1st to 15thNight
14%42442445%8%43%
1260
16th to endNight
9%4245%345%6%9%44%
1260
July1st to 15thNight
5%22333445%7%56%
1260
16th to endNight
32133245%47%61%
1371
August1st to 15thNight
7%213325%45%8%53%
1539
16th to endNight
5%32332335%7%59%
1719
September1st to 15thNight
11%414312346%55%
1818
16th to endNight
9%3135%2345%6%52%
1980
October1st to 15thNight
12%6%26%5%2445%8%40%
2109
16th to endNight
8%5%25%435%46%6%46%
2478
November1st to 15thNight
6%9%35%5%3446%7%42%
2609
16th to endNight
6%10%46%4245%6%9%39%
2828
December1st to 15thNight
5%11%5%8%6%46%5%5%8%33%
2925
16th to endNight
5%13%5%9%7%35%46%7%31%
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
45%9%16%21%42
1358
16th to endDay
46%8%15%19%7%2
1625
February1st to 15thDay
47%8%16%19%6%1
1635
16th to endDay
49%8%15%21%5%
1601
March1st to 15thDay
42%8%20%20%6%
2029
16th to endDay
50%8%15%19%6%
2173
April1st to 15thDay
50%6%13%18%8%1
2236
16th to endDay
47%7%12%22%8%1
2340
May1st to 15thDay
40%6%13%26%12%
2458
16th to endDay
51%8%13%18%8%
2807
June1st to 15thDay
43%8%15%20%10%1
2700
16th to endDay
35%9%14%28%10%1
2700
July1st to 15thDay
25%8%15%31%15%3
2541
16th to endDay
21%7%15%29%22%4
2623
August1st to 15thDay
26%7%16%31%14%2
2402
16th to endDay
24%6%12%32%20%3
2483
September1st to 15thDay
31%410%26%18%7%
2139
16th to endDay
30%6%11%31%15%4
1980
October1st to 15thDay
45%7%15%21%9%
1850
16th to endDay
39%9%16%24%9%
1746
November1st to 15thDay
44%8%16%22%8%
1567
16th to endDay
41%5%20%21%8%1
1462
December1st to 15thDay
48%8%15%20%5%
1365
16th to endDay
50%6%16%19%7%
1456
January1st to 15thNight
47%8%18%17%5%1
2910
16th to endNight
44%7%16%19%10%1
2961
February1st to 15thNight
46%8%14%19%9%
2557
16th to endNight
50%7%13%19%7%
2158
March1st to 15thNight
42%8%20%22%5%
2260
16th to endNight
47%9%16%19%6%
2178
April1st to 15thNight
46%7%15%21%9%
1711
16th to endNight
46%7%12%23%9%1
1620
May1st to 15thNight
41%5%13%25%12%1
1489
16th to endNight
46%8%14%20%8%1
1309
June1st to 15thNight
37%8%16%26%10%1
1260
16th to endNight
34%7%14%27%14%1
1260
July1st to 15thNight
24%7%15%30%17%5%
1190
16th to endNight
20%6%15%26%23%7%
1283
August1st to 15thNight
26%9%14%28%17%3
1531
16th to endNight
23%411%29%24%6%
1719
September1st to 15thNight
29%5%10%26%20%8%
1818
16th to endNight
30%5%14%27%17%4
1980
October1st to 15thNight
40%6%16%23%10%1
2109
16th to endNight
34%8%17%26%12%
2478
November1st to 15thNight
39%8%18%21%12%
2609
16th to endNight
39%7%24%17%9%1
2828
December1st to 15thNight
47%8%15%21%6%
2925
16th to endNight
50%6%17%19%5%
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
15%5%24%26%14%13%
90
16th to endDay
12%13%46%16%5%5%
96
February1st to 15thDay
17%19%32%21%5%3
118
16th to endDay
12%14%37%21%12%1
182
March1st to 15thDay
8%24%40%14%6%5%
330
16th to endDay
13%24%33%21%6%
311
April1st to 15thDay
14%24%30%21%8%
269
16th to endDay
22%14%29%23%9%1
270
May1st to 15thDay
13%12%31%24%15%2
373
16th to endDay
23%423%26%18%3
517
June1st to 15thDay
12%13%29%25%16%2
495
16th to endDay
10%9%30%28%17%3
495
July1st to 15thDay
7%425%34%25%3
475
16th to endDay
5%8%31%32%19%3
467
August1st to 15thDay
8%424%30%26%5%
315
16th to endDay
8%9%24%29%21%6%
332
September1st to 15thDay
18%9%26%24%14%5%
315
16th to endDay
9%14%29%24%15%6%
315
October1st to 15thDay
17%17%24%24%14%1
185
16th to endDay
9%20%29%25%11%3
144
November1st to 15thDay
15%18%31%22%12%
135
16th to endDay
8%24%41%15%8%3
112
December1st to 15thDay
11%21%32%24%11%
90
16th to endDay
17%15%37%20%7%1
96
January1st to 15thNight
11%19%38%22%7%
975
16th to endNight
12%16%38%24%6%1
881
February1st to 15thNight
14%13%33%24%10%2
764
16th to endNight
11%12%37%27%11%1
684
March1st to 15thNight
8%12%40%26%10%1
780
16th to endNight
14%13%35%28%6%1
792
April1st to 15thNight
15%13%38%22%9%
610
16th to endNight
16%9%32%31%10%
540
May1st to 15thNight
12%8%29%33%15%1
496
16th to endNight
20%428%26%18%1
375
June1st to 15thNight
15%7%34%28%13%1
360
16th to endNight
12%6%30%33%16%1
360
July1st to 15thNight
7%224%43%20%
340
16th to endNight
3229%45%18%
376
August1st to 15thNight
6%219%43%24%2
458
16th to endNight
6%427%39%21%1
573
September1st to 15thNight
14%423%34%20%1
636
16th to endNight
11%8%29%33%16%2
716
October1st to 15thNight
16%9%31%27%13%1
720
16th to endNight
11%12%38%28%9%
768
November1st to 15thNight
12%17%44%20%5%1
899
16th to endNight
10%17%41%24%5%
975
December1st to 15thNight
9%14%39%25%9%1
975
16th to endNight
13%14%37%24%8%1
1040
Page generated at 2018-03-22 09:34:20. Version ac04

Copyright 2018 A. Danko


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