UBC Liquid-Mirror Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UBC Liquid-Mirror Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
30%
14496
8%
46786
6%
14468
33%
14468
13%
35935

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
17%
750
10%
2686
5%
746
23%
746
8%
2188
January16th to endNight
19%
777
8%
2738
5%
777
24%
777
9%
2192
February1st to 15thNight
15%
700
6%
2288
3%
700
20%
700
7%
1908
February16th to endNight
20%
632
13%
2034
5%
632
29%
632
11%
1578
March1st to 15thNight
16%
720
4%
2073
2%
720
17%
720
8%
1788
March16th to endNight
17%
768
5%
2064
1%
768
19%
768
8%
1792
April1st to 15thNight
25%
719
6%
1799
2%
719
26%
719
11%
1512
April16th to endNight
25%
501
6%
1581
4%
501
27%
501
11%
1287
May1st to 15thNight
42%
359
10%
1439
14%
359
45%
359
15%
985
May16th to endNight
46%
374
5%
1475
7%
374
47%
374
13%
1063
June1st to 15thNight
41%
360
2%
1260
1%
360
42%
360
14%
933
June16th to endNight
46%
360
4%
1260
2%
360
46%
360
15%
914
July1st to 15thNight
67%
340
9%
1190
8%
340
68%
340
31%
675
July16th to endNight
72%
376
14%
1340
20%
354
74%
354
34%
685
August1st to 15thNight
76%
415
15%
1487
20%
413
77%
413
36%
750
August16th to endNight
65%
620
17%
1766
15%
620
65%
620
33%
1078
September1st to 15thNight
60%
720
19%
1800
10%
720
62%
720
39%
1112
September16th to endNight
42%
692
15%
1899
11%
692
44%
692
19%
1413
October1st to 15thNight
32%
660
10%
1980
8%
660
35%
660
17%
1466
October16th to endNight
24%
704
5%
2203
3%
704
26%
704
9%
1830
November1st to 15thNight
10%
700
4%
2450
1%
700
15%
700
5%
2147
November16th to endNight
15%
720
5%
2520
2%
720
19%
720
8%
2063
December1st to 15thNight
14%
729
9%
2574
2%
729
22%
729
7%
2093
December16th to endNight
7%
800
6%
2880
0%
800
14%
800
5%
2483

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
32%8%25%42333428%
48169
Night
33%8%24423335%29%
46941
Cloud CoverDay
33%9%35%42333426%
48169
Night
34%8%2442333427%
46944
TransparencyDay
62%5%10%14%6%1
47827
Night
61%411%14%6%1
46787
SeeingDay
34%10%20%24%8%2
6116
Night
38%5%19%21%13%1
14502

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
47%8%25%32322219%
1253
16th to endDay
41%10%2421433321%
1482
February1st to 15thDay
42%10%26%43333416%
1576
16th to endDay
31%14%35%5%2332323%
1439
March1st to 15thDay
48%10%3432422312%
1887
16th to endDay
40%12%37%5%2333314%
2159
April1st to 15thDay
36%10%47%6%3344414%
2149
16th to endDay
34%10%36%6%3444417%
2376
May1st to 15thDay
29%7%25%5%24336%29%
2511
16th to endDay
30%8%46%5%24445%23%
2633
June1st to 15thDay
33%9%35%5%23335%24%
2700
16th to endDay
29%9%34434345%26%
2700
July1st to 15thDay
16%414413345%49%
2700
16th to endDay
16%5%13313345%51%
2735
August1st to 15thDay
16%422322346%50%
2463
16th to endDay
17%5%23323347%45%
2435
September1st to 15thDay
17%6%24322225%49%
2160
16th to endDay
31%9%35%41233430%
1917
October1st to 15thDay
34%6%24323345%28%
1650
16th to endDay
45%7%24322235%18%
1669
November1st to 15thDay
55%8%3431312311%
1408
16th to endDay
45%9%2442233319%
1440
December1st to 15thDay
39%11%3422332222%
1383
16th to endDay
47%12%35%31212315%
1344
January1st to 15thNight
45%8%2421223421%
2686
16th to endNight
39%11%34312335%21%
2738
February1st to 15thNight
39%9%34423335%18%
2276
16th to endNight
32%9%25%42233427%
2034
March1st to 15thNight
45%10%25%32423317%
2073
16th to endNight
40%11%25%5%2423317%
2060
April1st to 15thNight
30%9%37%5%34346%21%
1799
16th to endNight
32%9%26%5%24345%22%
1581
May1st to 15thNight
22%6%36%42435%5%36%
1439
16th to endNight
21%6%35%4345%5%6%31%
1475
June1st to 15thNight
24%7%346%34435%31%
1260
16th to endNight
22%7%36%424445%33%
1260
July1st to 15thNight
9%214433345%57%
1260
16th to endNight
9%312313345%61%
1433
August1st to 15thNight
10%213212247%61%
1495
16th to endNight
11%31432345%9%50%
1766
September1st to 15thNight
11%313323235%59%
1800
16th to endNight
28%6%245%23345%33%
1899
October1st to 15thNight
28%6%2442333435%
1980
16th to endNight
40%7%2443333421%
2203
November1st to 15thNight
51%7%345%2222314%
2450
16th to endNight
41%9%245%1322422%
2520
December1st to 15thNight
40%10%2432223422%
2574
16th to endNight
47%12%2431322217%
2880

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
47%9%3332233218%
1253
16th to endDay
41%11%2432233420%
1482
February1st to 15thDay
43%11%36%42322316%
1576
16th to endDay
32%16%46%5%2232420%
1439
March1st to 15thDay
49%12%35%42431211%
1887
16th to endDay
41%15%36%42332211%
2159
April1st to 15thDay
37%13%47%5%2443313%
2149
16th to endDay
36%11%37%6%3443314%
2376
May1st to 15thDay
30%7%36%424445%25%
2511
16th to endDay
32%9%46%5%24335%20%
2633
June1st to 15thDay
36%9%35%423335%21%
2700
16th to endDay
33%8%45%43443423%
2700
July1st to 15thDay
17%424324345%47%
2700
16th to endDay
18%5%24323335%48%
2735
August1st to 15thDay
17%5%24323436%46%
2463
16th to endDay
19%6%1442345%6%42%
2435
September1st to 15thDay
18%7%25%313335%47%
2160
16th to endDay
34%7%25%42233429%
1917
October1st to 15thDay
35%7%3432344427%
1650
16th to endDay
45%7%25%422235%17%
1669
November1st to 15thDay
57%8%2432222310%
1408
16th to endDay
45%9%2442223318%
1440
December1st to 15thDay
39%13%3431232222%
1383
16th to endDay
47%16%25%41211213%
1344
January1st to 15thNight
46%8%2431123320%
2685
16th to endNight
39%12%35%312235%20%
2738
February1st to 15thNight
40%10%35%42333417%
2276
16th to endNight
32%12%35%42233326%
2034
March1st to 15thNight
44%12%3432322315%
2073
16th to endNight
40%13%35%42332315%
2064
April1st to 15thNight
32%11%46%5%34436%17%
1799
16th to endNight
35%8%37%5%24435%20%
1581
May1st to 15thNight
24%5%35%4245%47%32%
1439
16th to endNight
25%8%25%425%5%5%6%29%
1475
June1st to 15thNight
27%8%36%5%43346%27%
1260
16th to endNight
25%6%36%4335%5%430%
1260
July1st to 15thNight
10%4245%2325%5%54%
1260
16th to endNight
10%213313446%57%
1433
August1st to 15thNight
11%3221245%6%58%
1495
16th to endNight
12%4233245%6%7%47%
1766
September1st to 15thNight
12%314413335%56%
1800
16th to endNight
29%7%245%13336%32%
1899
October1st to 15thNight
30%6%25%43423432%
1980
16th to endNight
42%8%25%423335%18%
2203
November1st to 15thNight
53%7%3432232312%
2450
16th to endNight
42%9%25%42323321%
2520
December1st to 15thNight
40%11%3431322321%
2574
16th to endNight
48%13%2331222215%
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
73%46%8%6%1
1253
16th to endDay
69%38%12%32
1482
February1st to 15thDay
75%37%6%5%1
1576
16th to endDay
69%36%13%6%
1439
March1st to 15thDay
81%35%7%1
1887
16th to endDay
79%36%9%1
2159
April1st to 15thDay
75%6%7%9%1
2149
16th to endDay
72%6%9%7%3
2376
May1st to 15thDay
59%6%11%15%6%
2511
16th to endDay
65%6%13%12%2
2637
June1st to 15thDay
66%5%12%10%31
2700
16th to endDay
63%6%11%13%4
2700
July1st to 15thDay
39%6%13%25%12%2
2541
16th to endDay
37%6%16%28%10%1
2565
August1st to 15thDay
38%7%15%27%9%1
2446
16th to endDay
41%6%17%24%7%1
2435
September1st to 15thDay
41%5%11%21%16%3
2160
16th to endDay
60%5%9%15%7%1
1917
October1st to 15thDay
59%5%11%13%9%
1650
16th to endDay
69%410%10%4
1669
November1st to 15thDay
81%346%11
1408
16th to endDay
71%45%8%8%1
1440
December1st to 15thDay
70%36%10%7%1
1383
16th to endDay
79%438%31
1344
January1st to 15thNight
70%35%13%6%1
2686
16th to endNight
68%37%12%5%2
2738
February1st to 15thNight
71%48%9%22
2288
16th to endNight
63%48%15%6%1
2034
March1st to 15thNight
74%49%9%2
2073
16th to endNight
75%310%8%1
2064
April1st to 15thNight
68%5%11%11%2
1799
16th to endNight
66%5%11%12%3
1581
May1st to 15thNight
50%6%16%16%7%1
1440
16th to endNight
54%7%20%13%3
1475
June1st to 15thNight
58%419%10%5%1
1260
16th to endNight
54%7%14%16%41
1260
July1st to 15thNight
33%5%14%28%16%2
1190
16th to endNight
25%7%16%33%13%3
1340
August1st to 15thNight
25%6%21%30%12%3
1487
16th to endNight
32%7%20%25%10%3
1766
September1st to 15thNight
31%5%16%22%20%4
1800
16th to endNight
54%411%18%7%2
1899
October1st to 15thNight
56%411%16%9%1
1980
16th to endNight
69%5%10%10%4
2203
November1st to 15thNight
78%46%6%22
2450
16th to endNight
70%49%7%8%1
2520
December1st to 15thNight
69%47%10%6%1
2574
16th to endNight
76%35%7%5%1
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
21%15%16%26%13%6%
60
16th to endDay
62%412%15%4
64
February1st to 15thDay
50%11%14%16%5%1
236
16th to endDay
45%8%21%16%7%
215
March1st to 15thDay
61%11%13%12%1
270
16th to endDay
53%12%17%11%3
288
April1st to 15thDay
42%12%19%16%8%1
269
16th to endDay
36%16%24%16%41
270
May1st to 15thDay
32%12%24%23%41
288
16th to endDay
33%10%17%22%10%4
348
June1st to 15thDay
30%14%20%23%9%1
495
16th to endDay
29%11%26%23%7%1
495
July1st to 15thDay
16%9%25%36%10%1
475
16th to endDay
15%10%21%38%10%3
404
August1st to 15thDay
18%5%22%34%14%4
315
16th to endDay
18%6%23%35%13%2
332
September1st to 15thDay
22%9%21%30%13%1
315
16th to endDay
32%5%20%25%11%4
288
October1st to 15thDay
40%8%20%21%8%
255
16th to endDay
47%421%16%7%1
190
November1st to 15thDay
70%8%20%1
60
16th to endDay
53%6%11%6%11%10%
60
December1st to 15thDay
65%11%10%13%
60
16th to endDay
56%418%15%31
64
January1st to 15thNight
50%7%21%16%3
750
16th to endNight
47%5%22%20%3
777
February1st to 15thNight
45%8%24%17%3
704
16th to endNight
40%8%25%17%6%
632
March1st to 15thNight
50%8%20%14%5%
720
16th to endNight
48%6%21%17%6%
768
April1st to 15thNight
39%5%21%22%9%
719
16th to endNight
41%322%22%8%
501
May1st to 15thNight
26%417%30%20%
360
16th to endNight
28%213%30%24%1
375
June1st to 15thNight
28%316%27%21%2
360
16th to endNight
26%5%13%32%21%1
360
July1st to 15thNight
12%310%33%35%5%
340
16th to endNight
11%19%26%44%6%
376
August1st to 15thNight
12%15%26%47%7%
415
16th to endNight
15%210%31%37%3
620
September1st to 15thNight
14%116%33%31%2
720
16th to endNight
32%5%12%30%17%1
692
October1st to 15thNight
33%5%23%24%11%1
660
16th to endNight
47%419%21%6%
704
November1st to 15thNight
57%8%21%10%3
700
16th to endNight
49%7%21%15%5%
720
December1st to 15thNight
47%8%26%15%1
729
16th to endNight
56%10%24%8%1
800
Page generated at 2017-09-25 06:02:26. Version ac04

Copyright 2017 A. Danko


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