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Mt. Lemmon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Lemmon Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
69%
15527
35%
46826
29%
15489
75%
15489
49%
23053

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
64%
718
31%
2327
29%
716
70%
716
45%
1130
January16th to endNight
60%
768
34%
2496
31%
768
69%
768
38%
1307
February1st to 15thNight
65%
700
35%
2215
31%
700
75%
700
47%
1063
February16th to endNight
57%
632
37%
1829
31%
632
66%
632
44%
969
March1st to 15thNight
58%
720
38%
1980
28%
720
67%
720
50%
1031
March16th to endNight
66%
768
37%
2112
25%
768
75%
768
56%
1034
April1st to 15thNight
58%
677
34%
1936
22%
677
69%
677
52%
948
April16th to endNight
66%
540
45%
1791
36%
540
80%
540
66%
673
May1st to 15thNight
67%
539
39%
1619
27%
539
78%
539
67%
666
May16th to endNight
68%
561
41%
1684
31%
561
75%
561
68%
694
June1st to 15thNight
79%
540
35%
1620
29%
540
81%
540
68%
677
June16th to endNight
82%
540
30%
1620
26%
540
82%
540
58%
737
July1st to 15thNight
80%
510
20%
1530
18%
510
80%
510
37%
876
July16th to endNight
73%
564
17%
1593
15%
531
73%
531
27%
1034
August1st to 15thNight
84%
539
24%
1611
23%
536
84%
536
39%
907
August16th to endNight
80%
583
30%
1864
31%
583
80%
583
38%
1006
September1st to 15thNight
73%
700
28%
1925
25%
700
74%
700
40%
1151
September16th to endNight
78%
656
40%
1815
30%
656
82%
656
62%
862
October1st to 15thNight
72%
660
39%
1922
30%
660
78%
660
60%
887
October16th to endNight
79%
704
42%
2112
36%
704
85%
704
65%
923
November1st to 15thNight
74%
700
41%
2100
35%
700
80%
700
62%
923
November16th to endNight
65%
720
37%
2289
33%
720
72%
720
49%
1086
December1st to 15thNight
63%
720
35%
2340
34%
720
69%
720
45%
1137
December16th to endNight
57%
768
33%
2496
31%
768
64%
768
36%
1332

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
4313324345%61%
47797
Night
4313323345%63%
47022
TransparencyDay
22%35%11%26%30%
47492
Night
20%35%13%26%30%
46828
SeeingDay
7%12%28%32%15%3
5368
Night
5%414%35%33%7%
15536

By Month

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
6%424323245%60%
1611
16th to endDay
9%414323235%57%
1728
February1st to 15thDay
7%41221333463%
1646
16th to endDay
7%425%423345%57%
1643
March1st to 15thDay
5%423323245%62%
1980
16th to endDay
331221323470%
2112
April1st to 15thDay
3313223345%66%
2012
16th to endDay
22121213477%
2166
May1st to 15thDay
211121322474%
2331
16th to endDay
12121212378%
2429
June1st to 15thDay
221121123476%
2340
16th to endDay
2112324346%68%
2340
July1st to 15thDay
5%3247%37%7%8%9%42%
2340
16th to endDay
8%5%37%7%5%7%7%8%9%28%
2467
August1st to 15thDay
7%4245%46%6%7%8%40%
2340
16th to endDay
4335%6%35%6%6%9%43%
2331
September1st to 15thDay
7%5%145%46%6%5%7%45%
1922
16th to endDay
42321434466%
1815
October1st to 15thDay
321221333470%
1708
16th to endDay
221221233373%
1760
November1st to 15thDay
1212113345%71%
1759
16th to endDay
441331233466%
1669
December1st to 15thDay
7%413412345%60%
1620
16th to endDay
6%5%14324446%56%
1728
January1st to 15thNight
5%5%24313335%61%
2327
16th to endNight
8%4243245%4455%
2496
February1st to 15thNight
4423313245%63%
2204
16th to endNight
6%414324345%58%
1829
March1st to 15thNight
5%32332333365%
1980
16th to endNight
4213213336%67%
2112
April1st to 15thNight
331332333466%
1936
16th to endNight
11111122382%
1791
May1st to 15thNight
11113345%74%
1619
16th to endNight
21121122381%
1684
June1st to 15thNight
22121222477%
1620
16th to endNight
2112423335%70%
1620
July1st to 15thNight
33135%45%7%7%10%44%
1620
16th to endNight
45%25%6%48%7%10%14%30%
1701
August1st to 15thNight
33125%26%7%7%10%48%
1620
16th to endNight
32246%35%6%7%10%47%
1864
September1st to 15thNight
6%4145%2445%7%50%
1925
16th to endNight
33221233372%
1815
October1st to 15thNight
221221233472%
1922
16th to endNight
221221212476%
2112
November1st to 15thNight
121331233473%
2100
16th to endNight
5%31432332465%
2289
December1st to 15thNight
7%412322346%59%
2340
16th to endNight
7%6%25%42333456%
2496

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
25%2411%29%26%
1612
16th to endDay
27%2413%26%25%
1728
February1st to 15thDay
22%2413%26%31%
1646
16th to endDay
26%2412%30%24%
1643
March1st to 15thDay
22%226%33%32%
1980
16th to endDay
17%239%35%32%
2112
April1st to 15thDay
17%136%39%31%
2012
16th to endDay
11%128%28%47%
2166
May1st to 15thDay
13%137%27%47%
2331
16th to endDay
11%127%30%46%
2432
June1st to 15thDay
12%12422%56%
2340
16th to endDay
15%25%7%19%50%
2340
July1st to 15thDay
30%10%11%14%14%17%
2201
16th to endDay
43%11%16%18%7%2
2312
August1st to 15thDay
35%9%9%16%18%10%
2325
16th to endDay
33%7%10%16%19%12%
2331
September1st to 15thDay
33%6%9%17%15%16%
1922
16th to endDay
19%3310%32%30%
1815
October1st to 15thDay
16%3412%27%35%
1708
16th to endDay
13%249%29%41%
1760
November1st to 15thDay
13%1311%36%33%
1759
16th to endDay
20%2210%27%36%
1669
December1st to 15thDay
23%25%15%31%20%
1620
16th to endDay
25%46%18%31%13%
1728
January1st to 15thNight
23%2411%29%27%
2327
16th to endNight
28%2414%28%21%
2496
February1st to 15thNight
21%2414%26%30%
2215
16th to endNight
25%2312%32%22%
1829
March1st to 15thNight
21%238%30%33%
1980
16th to endNight
17%2311%35%30%
2112
April1st to 15thNight
19%138%39%27%
1936
16th to endNight
8%1110%30%47%
1791
May1st to 15thNight
9%149%31%42%
1620
16th to endNight
9%128%27%50%
1685
June1st to 15thNight
11%125%20%58%
1620
16th to endNight
16%145%18%54%
1620
July1st to 15thNight
27%8%15%16%15%16%
1530
16th to endNight
34%11%20%21%8%2
1593
August1st to 15thNight
24%9%13%20%19%12%
1611
16th to endNight
26%6%14%19%19%13%
1864
September1st to 15thNight
29%5%8%21%19%14%
1925
16th to endNight
15%1412%33%31%
1815
October1st to 15thNight
14%2414%27%35%
1922
16th to endNight
13%1312%24%45%
2112
November1st to 15thNight
14%1413%34%32%
2100
16th to endNight
21%1411%23%37%
2289
December1st to 15thNight
23%2415%31%22%
2340
16th to endNight
29%35%16%26%17%
2496

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%14%31%28%10%
90
16th to endDay
12%10%31%23%17%4
96
February1st to 15thDay
11%12%27%35%11%1
161
16th to endDay
10%26%34%21%5%
238
March1st to 15thDay
10%22%32%20%11%2
270
16th to endDay
7%25%32%22%9%2
288
April1st to 15thDay
10%23%35%20%7%2
269
16th to endDay
8%27%36%18%6%1
270
May1st to 15thDay
5%21%41%19%8%2
288
16th to endDay
414%41%31%7%
330
June1st to 15thDay
5%9%43%28%10%3
315
16th to endDay
5%232%37%19%2
315
July1st to 15thDay
5%15%51%22%3
305
16th to endDay
7%14%40%26%9%
327
August1st to 15thDay
8%27%45%26%10%
315
16th to endDay
5%111%43%31%7%
332
September1st to 15thDay
11%318%43%17%5%
294
16th to endDay
8%9%29%36%11%4
255
October1st to 15thDay
6%11%31%30%15%4
148
16th to endDay
6%221%38%30%1
96
November1st to 15thDay
5%16%21%35%18%2
90
16th to endDay
217%36%33%10%
90
December1st to 15thDay
111%21%43%22%1
90
16th to endDay
10%18%31%32%6%1
96
January1st to 15thNight
6%318%43%23%4
720
16th to endNight
8%6%16%39%23%4
768
February1st to 15thNight
5%5%17%37%28%4
704
16th to endNight
6%8%21%41%18%2
632
March1st to 15thNight
6%8%22%33%24%5%
720
16th to endNight
36%18%37%28%5%
768
April1st to 15thNight
5%7%22%41%21%1
677
16th to endNight
28%20%40%24%3
540
May1st to 15thNight
16%22%37%28%3
540
16th to endNight
25%20%40%27%4
563
June1st to 15thNight
2113%42%36%4
540
16th to endNight
317%36%44%7%
540
July1st to 15thNight
4425%54%11%
510
16th to endNight
6%318%54%17%
564
August1st to 15thNight
4115%59%19%
539
16th to endNight
4218%55%18%
583
September1st to 15thNight
6%7%26%44%15%
700
16th to endNight
4110%33%36%13%
656
October1st to 15thNight
2215%38%33%7%
660
16th to endNight
2110%37%35%11%
704
November1st to 15thNight
25%14%40%31%6%
700
16th to endNight
6%418%36%27%5%
720
December1st to 15thNight
8%5%15%37%28%4
720
16th to endNight
8%6%18%40%21%5%
768
Page generated at 2017-09-11 16:35:33. Version ac04

Copyright 2017 A. Danko


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