Logan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Logan Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
58%
15537
32%
47385
22%
15495
69%
15495
44%
23411

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
58%
719
32%
2327
27%
716
67%
716
43%
1132
January16th to endNight
53%
768
34%
2496
26%
768
69%
768
41%
1218
February1st to 15thNight
52%
700
32%
2284
24%
698
65%
698
45%
1061
February16th to endNight
39%
632
40%
1812
21%
632
60%
632
45%
854
March1st to 15thNight
48%
720
37%
1980
20%
720
62%
720
47%
986
March16th to endNight
46%
768
37%
2112
18%
768
62%
768
50%
1045
April1st to 15thNight
39%
608
34%
1867
14%
608
59%
608
40%
868
April16th to endNight
45%
540
39%
1800
22%
540
67%
540
48%
750
May1st to 15thNight
54%
539
34%
1661
21%
539
68%
539
54%
734
May16th to endNight
53%
562
34%
1684
20%
561
66%
561
54%
757
June1st to 15thNight
63%
540
32%
1620
23%
540
70%
540
61%
706
June16th to endNight
75%
540
25%
1620
21%
540
76%
540
49%
777
July1st to 15thNight
72%
510
14%
1530
13%
510
73%
510
27%
949
July16th to endNight
76%
564
8%
1593
8%
531
76%
531
23%
1054
August1st to 15thNight
73%
539
16%
1611
15%
536
74%
536
26%
1021
August16th to endNight
76%
573
24%
1893
24%
573
77%
573
28%
1149
September1st to 15thNight
73%
603
25%
1863
23%
603
76%
603
34%
1091
September16th to endNight
67%
716
40%
1980
25%
716
76%
716
57%
953
October1st to 15thNight
60%
720
36%
2155
22%
720
70%
720
57%
965
October16th to endNight
67%
768
43%
2304
29%
768
78%
768
61%
1000
November1st to 15thNight
61%
700
40%
2100
26%
700
73%
700
57%
924
November16th to endNight
56%
720
39%
2257
29%
720
68%
720
48%
1011
December1st to 15thNight
57%
720
35%
2340
25%
720
70%
720
44%
1097
December16th to endNight
43%
768
31%
2496
22%
768
56%
768
33%
1309

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
3324424446%57%
48355
Night
121332345%7%64%
47585
TransparencyDay
27%5%8%16%26%15%
48050
Night
19%5%10%19%29%16%
47391
SeeingDay
9%15%25%26%16%6%
5387
Night
311%21%30%25%7%
15544

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
1322314447%65%
1611
16th to endDay
231321335%5%65%
1728
February1st to 15thDay
1314313335%66%
1575
16th to endDay
31332346%6%63%
1658
March1st to 15thDay
131332445%7%62%
1980
16th to endDay
1323223347%63%
2112
April1st to 15thDay
121222345%7%66%
2078
16th to endDay
2413323345%66%
2160
May1st to 15thDay
2313424345%65%
2286
16th to endDay
3323323435%65%
2429
June1st to 15thDay
2213323336%68%
2340
16th to endDay
33135%245%5%6%57%
2340
July1st to 15thDay
8%5%37%8%5%7%7%7%6%33%
2340
16th to endDay
10%6%39%10%5%8%8%7%7%22%
2467
August1st to 15thDay
9%6%49%9%6%7%6%6%7%25%
2340
16th to endDay
9%5%28%8%46%7%6%8%32%
2308
September1st to 15thDay
8%7%38%7%45%5%5%6%36%
2094
16th to endDay
3324334235%63%
1980
October1st to 15thDay
2212212335%71%
1803
16th to endDay
2212312135%74%
1918
November1st to 15thDay
212212336%72%
1759
16th to endDay
313221235%70%
1701
December1st to 15thDay
1212224447%65%
1620
16th to endDay
3145%34347%60%
1728
January1st to 15thNight
31331346%6%64%
2327
16th to endNight
3133245%5%6%63%
2496
February1st to 15thNight
1312313347%67%
2277
16th to endNight
1222345%8%67%
1812
March1st to 15thNight
1213223345%69%
1980
16th to endNight
1112213247%69%
2112
April1st to 15thNight
111232445%6%67%
1867
16th to endNight
21122235%76%
1800
May1st to 15thNight
112213246%72%
1661
16th to endNight
1112213235%74%
1684
June1st to 15thNight
1111212335%75%
1620
16th to endNight
11123245%5%6%65%
1620
July1st to 15thNight
4315%5%47%8%8%10%40%
1620
16th to endNight
4315%5%47%8%11%14%32%
1701
August1st to 15thNight
3425%5%46%6%8%10%43%
1620
16th to endNight
4325%5%35%7%7%9%44%
1893
September1st to 15thNight
3325%5%35%6%6%8%50%
1863
16th to endNight
212212335%72%
1980
October1st to 15thNight
11111233476%
2155
16th to endNight
111111223477%
2304
November1st to 15thNight
112213346%73%
2100
16th to endNight
1212212336%72%
2257
December1st to 15thNight
31222345%8%66%
2340
16th to endNight
42432445%8%59%
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
19%48%20%31%14%
1612
16th to endDay
21%47%18%34%13%
1728
February1st to 15thDay
21%28%23%22%20%
1575
16th to endDay
20%5%5%20%33%13%
1658
March1st to 15thDay
21%46%15%36%15%
1980
16th to endDay
21%36%17%36%14%
2112
April1st to 15thDay
18%35%19%35%16%
2078
16th to endDay
21%25%18%34%17%
2160
May1st to 15thDay
21%36%16%31%19%
2286
16th to endDay
22%45%13%34%19%
2432
June1st to 15thDay
19%25%11%27%33%
2340
16th to endDay
27%46%9%23%28%
2340
July1st to 15thDay
45%9%12%12%10%9%
2201
16th to endDay
55%12%18%10%2
2312
August1st to 15thDay
54%9%10%11%9%3
2325
16th to endDay
48%7%12%14%13%3
2308
September1st to 15thDay
46%6%9%15%16%5%
2094
16th to endDay
24%36%18%29%17%
1980
October1st to 15thDay
17%36%16%31%23%
1803
16th to endDay
15%25%16%40%18%
1918
November1st to 15thDay
13%26%23%31%21%
1759
16th to endDay
18%3416%33%23%
1701
December1st to 15thDay
19%5%9%26%24%15%
1620
16th to endDay
24%6%11%19%28%9%
1728
January1st to 15thNight
20%47%22%32%12%
2327
16th to endNight
21%410%17%33%12%
2496
February1st to 15thNight
18%39%22%26%18%
2288
16th to endNight
15%39%23%34%13%
1812
March1st to 15thNight
17%36%16%41%14%
1980
16th to endNight
16%35%22%36%15%
2112
April1st to 15thNight
16%5%7%23%35%12%
1867
16th to endNight
12%35%23%37%17%
1800
May1st to 15thNight
13%38%20%37%17%
1662
16th to endNight
14%36%18%36%19%
1685
June1st to 15thNight
12%2410%33%35%
1620
16th to endNight
17%5%8%12%24%30%
1620
July1st to 15thNight
33%11%16%14%13%10%
1530
16th to endNight
34%16%33%11%31
1593
August1st to 15thNight
31%14%19%15%14%4
1611
16th to endNight
31%11%17%18%16%4
1893
September1st to 15thNight
30%7%17%18%19%6%
1863
16th to endNight
15%35%25%29%20%
1980
October1st to 15thNight
12%37%22%31%22%
2155
16th to endNight
12%25%19%38%21%
2304
November1st to 15thNight
13%26%22%35%19%
2100
16th to endNight
15%36%18%31%25%
2257
December1st to 15thNight
18%49%23%26%17%
2340
16th to endNight
23%7%13%20%26%9%
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
5%26%44%12%5%5%
90
16th to endDay
8%17%25%25%16%7%
96
February1st to 15thDay
211%28%34%17%5%
90
16th to endDay
10%37%25%18%7%
209
March1st to 15thDay
11%23%31%24%8%1
270
16th to endDay
10%29%30%21%5%1
288
April1st to 15thDay
8%28%33%18%7%3
269
16th to endDay
15%29%36%12%31
270
May1st to 15thDay
7%24%36%23%6%1
288
16th to endDay
8%21%32%25%10%1
330
June1st to 15thDay
315%34%26%14%4
315
16th to endDay
6%5%18%39%23%6%
315
July1st to 15thDay
12%312%37%24%9%
305
16th to endDay
14%28%28%26%19%
327
August1st to 15thDay
13%28%30%33%12%
315
16th to endDay
10%312%31%27%14%
332
September1st to 15thDay
16%316%30%26%6%
315
16th to endDay
5%13%29%31%17%2
315
October1st to 15thDay
214%31%23%21%6%
138
16th to endDay
36%31%22%25%9%
144
November1st to 15thDay
6%13%27%27%17%6%
90
16th to endDay
6%40%22%21%10%
90
December1st to 15thDay
416%33%23%18%3
90
16th to endDay
13%26%19%33%7%
96
January1st to 15thNight
213%20%35%18%9%
720
16th to endNight
314%24%30%19%6%
768
February1st to 15thNight
315%25%32%18%4
704
16th to endNight
322%33%26%11%1
632
March1st to 15thNight
5%18%25%31%15%3
720
16th to endNight
316%30%29%17%3
768
April1st to 15thNight
323%31%28%11%1
608
16th to endNight
119%31%29%14%3
540
May1st to 15thNight
210%29%36%17%3
540
16th to endNight
210%30%33%20%3
563
June1st to 15thNight
2426%43%20%2
540
16th to endNight
2213%44%31%5%
540
July1st to 15thNight
6%6%30%44%11%
510
16th to endNight
5%322%47%19%
564
August1st to 15thNight
5%5%18%49%20%
539
16th to endNight
5%6%23%49%15%
573
September1st to 15thNight
410%28%46%9%
603
16th to endNight
16%18%30%31%10%
716
October1st to 15thNight
29%25%33%22%6%
720
16th to endNight
26%21%30%28%10%
768
November1st to 15thNight
111%24%30%23%8%
700
16th to endNight
417%18%26%23%8%
720
December1st to 15thNight
415%19%32%22%5%
720
16th to endNight
5%22%25%27%13%4
768
Page generated at 2017-11-01 14:23:39. Version ac04

Copyright 2017 A. Danko


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