Lookum Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookum Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
28%
15899
10%
46905
6%
15854
32%
15854
15%
35262

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
12%
900
4%
2506
0%
895
14%
895
8%
2142
January16th to endNight
13%
960
5%
2688
1%
960
16%
960
8%
2268
February1st to 15thNight
19%
830
4%
2345
3%
827
20%
827
9%
1945
February16th to endNight
19%
631
7%
1893
4%
631
22%
631
10%
1534
March1st to 15thNight
24%
720
11%
2160
7%
720
27%
720
15%
1608
March16th to endNight
28%
677
14%
2030
9%
677
34%
677
15%
1503
April1st to 15thNight
27%
539
10%
1797
7%
539
31%
539
13%
1315
April16th to endNight
31%
540
15%
1635
8%
540
38%
540
20%
1124
May1st to 15thNight
33%
540
12%
1530
9%
540
37%
540
18%
1115
May16th to endNight
41%
562
13%
1498
7%
561
44%
561
27%
1022
June1st to 15thNight
44%
408
11%
1308
8%
408
47%
408
23%
854
June16th to endNight
42%
409
10%
1309
7%
409
45%
409
23%
870
July1st to 15thNight
51%
510
13%
1360
7%
510
53%
510
34%
844
July16th to endNight
57%
564
14%
1417
10%
531
58%
531
37%
865
August1st to 15thNight
61%
539
18%
1482
12%
536
65%
536
37%
898
August16th to endNight
53%
573
17%
1811
13%
573
58%
573
31%
1078
September1st to 15thNight
47%
567
14%
1827
12%
567
50%
567
24%
1171
September16th to endNight
42%
669
14%
1848
11%
669
45%
669
25%
1260
October1st to 15thNight
30%
660
12%
1907
6%
660
36%
660
20%
1363
October16th to endNight
23%
704
6%
2288
5%
704
25%
704
9%
1879
November1st to 15thNight
18%
700
11%
2276
5%
700
26%
700
11%
1764
November16th to endNight
16%
837
7%
2503
4%
837
19%
837
7%
2129
December1st to 15thNight
10%
900
4%
2700
1%
900
12%
900
6%
2282
December16th to endNight
11%
960
5%
2787
1%
960
15%
960
6%
2429

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
16%10%47%5%3445%6%30%
47886
Night
15%11%5%8%6%34446%28%
47073
Cloud CoverDay
15%10%47%5%3445%6%30%
47895
Night
15%11%5%8%6%34446%28%
47078
TransparencyDay
53%7%13%17%7%
47572
Night
55%6%13%16%6%
46905
SeeingDay
21%11%31%23%9%3
6083
Night
21%11%30%25%9%1
15900

By Month

Percentage Cloud Cover NE (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
13%16%9%12%10%4433414%
1432
16th to endDay
12%15%8%14%10%5%5%445%14%
1536
February1st to 15thDay
11%14%7%13%13%5%7%45%312%
1516
16th to endDay
11%14%8%15%10%46%445%15%
1580
March1st to 15thDay
13%11%7%12%8%35%445%22%
1790
16th to endDay
15%13%6%9%6%2435%5%27%
2205
April1st to 15thDay
18%12%5%6%42335%6%31%
2151
16th to endDay
18%11%46%424447%32%
2325
May1st to 15thDay
18%11%35%42435%6%33%
2418
16th to endDay
12%7%26%42446%7%40%
2617
June1st to 15thDay
14%6%35%4245%5%8%37%
2646
16th to endDay
16%6%25%425%5%6%8%35%
2646
July1st to 15thDay
12%42443446%8%44%
2520
16th to endDay
11%5%233245%5%8%47%
2655
August1st to 15thDay
11%4245%34447%46%
2467
16th to endDay
17%42432445%9%41%
2390
September1st to 15thDay
18%6%25%33445%7%38%
2121
16th to endDay
18%6%35%43446%9%32%
1837
October1st to 15thDay
22%8%37%434446%29%
1722
16th to endDay
28%20%47%5%2444413%
1584
November1st to 15thDay
19%17%5%7%424345%24%
1582
16th to endDay
19%20%10%8%5%22345%15%
1452
December1st to 15thDay
15%17%10%14%8%3333415%
1260
16th to endDay
15%22%10%11%7%2344411%
1434
January1st to 15thNight
15%15%9%12%8%44345%15%
2506
16th to endNight
12%13%8%14%11%45%45%5%14%
2688
February1st to 15thNight
9%13%8%12%12%5%6%44417%
2343
16th to endNight
12%14%7%12%8%5%5%5%5%5%17%
1893
March1st to 15thNight
12%9%6%10%9%34435%30%
2147
16th to endNight
14%10%7%8%6%34446%28%
2030
April1st to 15thNight
19%10%46%5%35%45%5%27%
1797
16th to endNight
18%9%45%424346%36%
1635
May1st to 15thNight
19%7%36%5%25%45%7%31%
1530
16th to endNight
13%6%25%5%245%5%8%39%
1496
June1st to 15thNight
14%7%245%3445%6%40%
1308
16th to endNight
13%6%246%25%5%6%7%37%
1309
July1st to 15thNight
12%5%2332435%9%46%
1440
16th to endNight
8%41432446%9%48%
1513
August1st to 15thNight
8%323425%46%8%49%
1491
16th to endNight
12%5%25%323347%48%
1811
September1st to 15thNight
16%6%24433446%42%
1827
16th to endNight
18%5%25%42446%6%39%
1848
October1st to 15thNight
20%8%34434447%34%
1907
16th to endNight
24%16%47%5%3444419%
2288
November1st to 15thNight
20%18%35%5%24346%25%
2276
16th to endNight
17%18%9%10%7%3443417%
2503
December1st to 15thNight
15%17%8%12%6%35%445%16%
2700
16th to endNight
17%18%9%12%7%3433414%
2787

Percentage Cloud Cover SE (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
12%17%9%11%12%45%33415%
1432
16th to endDay
13%14%9%13%10%45%44414%
1536
February1st to 15thDay
11%13%7%13%13%5%7%45%411%
1516
16th to endDay
11%14%7%15%10%5%5%44414%
1580
March1st to 15thDay
13%12%6%12%8%45%345%22%
1800
16th to endDay
15%13%6%9%5%3444427%
2204
April1st to 15thDay
18%13%5%6%424345%31%
2151
16th to endDay
17%11%46%334446%32%
2325
May1st to 15thDay
18%11%35%434446%33%
2418
16th to endDay
12%8%26%42446%7%39%
2617
June1st to 15thDay
14%6%36%4345%5%8%37%
2646
16th to endDay
16%7%25%425%5%7%8%35%
2646
July1st to 15thDay
11%4145%3445%8%45%
2520
16th to endDay
11%5%14325%5%6%8%46%
2655
August1st to 15thDay
11%425%5%335%5%6%46%
2467
16th to endDay
17%5%2432436%8%40%
2390
September1st to 15thDay
17%7%25%33445%7%38%
2121
16th to endDay
18%6%35%5%3445%9%32%
1837
October1st to 15thDay
21%9%37%5%3435%6%29%
1722
16th to endDay
27%19%5%7%5%2444413%
1584
November1st to 15thDay
19%16%6%7%43344424%
1582
16th to endDay
19%21%10%8%6%22345%15%
1452
December1st to 15thDay
15%17%10%13%8%3432415%
1260
16th to endDay
16%21%9%12%7%3435%411%
1434
January1st to 15thNight
15%14%9%13%8%45%445%15%
2506
16th to endNight
11%13%7%14%11%46%5%5%5%14%
2688
February1st to 15thNight
9%13%9%12%12%5%7%34417%
2336
16th to endNight
12%14%6%13%8%46%45%5%17%
1893
March1st to 15thNight
12%10%6%9%8%44435%30%
2160
16th to endNight
14%10%6%9%6%34447%28%
2030
April1st to 15thNight
19%10%46%5%35%45%6%27%
1797
16th to endNight
17%9%45%425%246%36%
1635
May1st to 15thNight
18%7%36%5%35%5%47%31%
1529
16th to endNight
12%6%25%425%6%5%8%39%
1496
June1st to 15thNight
15%7%26%42435%7%40%
1308
16th to endNight
12%6%345%35%5%6%8%37%
1309
July1st to 15thNight
12%6%1342435%9%46%
1440
16th to endNight
8%5%2332446%9%48%
1513
August1st to 15thNight
7%32432447%8%49%
1491
16th to endNight
12%5%25%423347%49%
1811
September1st to 15thNight
15%6%34424446%42%
1827
16th to endNight
18%5%3432445%6%39%
1848
October1st to 15thNight
19%9%344335%46%35%
1907
16th to endNight
23%17%48%5%3444418%
2288
November1st to 15thNight
19%18%45%424346%25%
2276
16th to endNight
17%17%9%11%7%3343417%
2503
December1st to 15thNight
15%17%9%11%7%35%44417%
2700
16th to endNight
17%18%9%13%7%3343414%
2787

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
72%6%7%10%1
1433
16th to endDay
70%6%12%8%1
1536
February1st to 15thDay
72%7%13%41
1518
16th to endDay
70%7%9%7%4
1580
March1st to 15thDay
63%7%11%11%6%1
1800
16th to endDay
58%414%16%41
2205
April1st to 15thDay
55%5%10%20%7%
2151
16th to endDay
51%6%9%18%11%2
2325
May1st to 15thDay
51%6%11%16%11%2
2418
16th to endDay
41%7%13%24%12%
2621
June1st to 15thDay
43%8%13%21%11%
2646
16th to endDay
44%8%16%21%8%
2646
July1st to 15thDay
36%7%15%26%12%1
2371
16th to endDay
35%8%16%25%14%
2488
August1st to 15thDay
35%7%15%29%11%
2452
16th to endDay
40%7%18%23%9%
2390
September1st to 15thDay
43%8%15%23%8%
2121
16th to endDay
47%7%17%21%5%
1837
October1st to 15thDay
55%6%14%18%5%
1722
16th to endDay
72%5%12%6%2
1584
November1st to 15thDay
62%5%10%15%5%
1582
16th to endDay
70%7%12%6%2
1452
December1st to 15thDay
74%6%11%5%2
1260
16th to endDay
75%7%9%6%1
1434
January1st to 15thNight
69%7%13%7%1
2506
16th to endNight
68%7%15%7%1
2688
February1st to 15thNight
67%6%13%10%2
2345
16th to endNight
64%6%13%10%3
1893
March1st to 15thNight
54%6%14%16%7%
2160
16th to endNight
54%6%12%18%7%
2030
April1st to 15thNight
55%6%10%18%7%1
1797
16th to endNight
48%412%18%12%2
1635
May1st to 15thNight
51%7%11%16%11%2
1530
16th to endNight
40%8%13%23%13%
1498
June1st to 15thNight
43%6%11%24%12%
1308
16th to endNight
42%8%13%23%11%1
1309
July1st to 15thNight
32%7%13%31%13%1
1360
16th to endNight
31%6%16%28%15%2
1417
August1st to 15thNight
29%8%18%30%11%1
1482
16th to endNight
34%5%16%28%13%1
1811
September1st to 15thNight
42%5%15%24%11%
1827
16th to endNight
42%7%16%24%8%
1848
October1st to 15thNight
48%7%16%19%7%1
1907
16th to endNight
66%7%11%10%3
2288
November1st to 15thNight
60%6%12%13%6%
2276
16th to endNight
71%6%11%8%2
2503
December1st to 15thNight
69%7%12%8%1
2700
16th to endNight
74%6%10%7%1
2787

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
20%11%51%17%
90
16th to endDay
27%11%39%16%41
96
February1st to 15thDay
25%28%33%10%2
90
16th to endDay
25%22%35%14%1
81
March1st to 15thDay
26%22%31%16%3
90
16th to endDay
29%11%27%20%8%2
279
April1st to 15thDay
25%10%30%26%6%1
270
16th to endDay
28%12%28%16%9%3
270
May1st to 15thDay
24%16%31%16%8%2
375
16th to endDay
20%11%32%24%8%2
517
June1st to 15thDay
18%12%34%22%8%2
495
16th to endDay
19%9%32%27%8%2
495
July1st to 15thDay
14%7%32%29%13%3
475
16th to endDay
11%5%36%27%13%4
515
August1st to 15thDay
13%328%32%16%5%
440
16th to endDay
22%6%23%23%17%6%
332
September1st to 15thDay
17%8%23%26%15%8%
315
16th to endDay
19%8%29%26%10%4
262
October1st to 15thDay
25%12%29%22%7%2
189
16th to endDay
40%17%28%11%2
96
November1st to 15thDay
16%16%42%16%7%
90
16th to endDay
37%24%15%19%2
82
December1st to 15thDay
45%16%20%13%5%
60
16th to endDay
21%32%37%7%
79
January1st to 15thNight
22%19%35%19%3
900
16th to endNight
18%15%40%19%5%1
960
February1st to 15thNight
15%16%36%24%6%
830
16th to endNight
19%11%36%25%6%
631
March1st to 15thNight
17%15%35%22%8%
720
16th to endNight
18%14%31%25%8%1
677
April1st to 15thNight
23%13%30%25%5%
539
16th to endNight
24%9%29%25%10%1
540
May1st to 15thNight
22%10%26%28%10%1
540
16th to endNight
17%7%30%30%13%1
563
June1st to 15thNight
18%6%24%36%13%
408
16th to endNight
15%6%30%33%12%1
409
July1st to 15thNight
14%226%36%18%1
510
16th to endNight
10%323%40%18%2
564
August1st to 15thNight
10%121%40%24%2
539
16th to endNight
15%323%36%19%2
573
September1st to 15thNight
19%423%29%20%3
567
16th to endNight
20%6%25%31%14%1
669
October1st to 15thNight
25%10%29%23%11%
660
16th to endNight
35%13%23%20%6%
704
November1st to 15thNight
32%11%33%17%6%
700
16th to endNight
28%16%30%19%5%
837
December1st to 15thNight
24%19%37%15%3
900
16th to endNight
25%16%33%19%31
960
Page generated at 2017-09-19 07:32:22. Version ac04

Copyright 2017 A. Danko


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