Lookout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Observatory clear sky chart from 2005-11-06 to 2024-03-08.

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
46%
24231
18%
79994
13%
24133
52%
24133
21%
51835

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 10thNight
25%
755
17%
4037
8%
737
37%
737
11%
2366
January11th to 20thNight
27%
756
24%
3980
10%
740
38%
740
11%
2299
January21st to endNight
26%
831
14%
4467
11%
814
40%
814
10%
2891
February1st to 10thNight
31%
760
21%
2385
12%
760
41%
760
23%
1527
February11th to 20thNight
21%
741
17%
2219
7%
740
31%
740
17%
1524
February21st to endNight
22%
628
20%
1884
8%
628
33%
628
18%
1301
March1st to 10thNight
30%
751
22%
2113
13%
751
38%
751
21%
1423
March11th to 20thNight
28%
720
15%
1980
8%
720
34%
720
20%
1384
March21st to endNight
29%
792
15%
2178
7%
792
35%
792
20%
1508
April1st to 10thNight
35%
720
20%
1980
11%
720
43%
720
27%
1258
April11th to 20thNight
40%
619
22%
1769
13%
619
47%
619
27%
1109
April21st to endNight
50%
540
23%
1620
16%
540
57%
540
28%
1012
May1st to 10thNight
50%
540
16%
1620
8%
540
54%
540
25%
1046
May11th to 20thNight
50%
531
12%
1593
8%
531
53%
531
21%
1107
May21st to endNight
65%
582
14%
1745
11%
582
66%
582
26%
1151
June1st to 10thNight
65%
540
12%
1620
10%
540
66%
540
25%
1083
June11th to 20thNight
68%
540
11%
1620
9%
540
70%
540
31%
1018
June21st to endNight
71%
540
15%
1620
13%
540
72%
540
29%
1031
July1st to 10thNight
69%
525
11%
1575
10%
525
70%
525
23%
1105
July11th to 20thNight
70%
522
10%
1566
9%
522
71%
522
22%
1096
July21st to endNight
71%
591
12%
1672
11%
558
72%
558
23%
1153
August1st to 10thNight
70%
537
10%
1600
9%
534
70%
534
22%
1127
August11th to 20thNight
64%
534
15%
1598
14%
534
65%
534
21%
1146
August21st to endNight
65%
638
14%
1940
13%
638
66%
638
21%
1341
September1st to 10thNight
62%
720
18%
1980
16%
720
63%
720
24%
1366
September11th to 20thNight
56%
720
18%
1980
15%
720
58%
720
22%
1401
September21st to endNight
58%
720
23%
1980
19%
720
60%
720
28%
1292
October1st to 10thNight
52%
720
23%
2010
19%
720
57%
720
29%
1283
October11th to 20thNight
48%
720
24%
2160
20%
720
55%
720
28%
1332
October21st to endNight
48%
792
30%
2376
22%
792
59%
792
30%
1401
November1st to 10thNight
54%
740
25%
2306
21%
740
61%
740
29%
1383
November11th to 20thNight
45%
760
26%
2470
20%
760
55%
760
27%
1483
November21st to endNight
42%
760
24%
2470
17%
760
52%
760
24%
1490
December1st to 10thNight
31%
760
18%
2470
11%
760
40%
760
16%
1719
December11th to 20thNight
34%
759
21%
2987
16%
759
45%
759
18%
1884
December21st to endNight
30%
827
12%
4424
11%
817
39%
817
10%
2795

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
10%7%36%6%46%6%6%8%37%
78930
Night
10%7%37%6%45%5%6%8%39%
80640
TransparencyDay
41%9%13%18%15%3
78653
Night
39%10%13%19%16%3
80436
SeeingDay
18%13%21%22%17%9%
14082
Night
16%11%19%30%20%4
24259

By Month

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 10thDay
11%6%36%6%35%5%6%10%40%
2836
11th to 20thDay
10%6%46%6%47%7%5%6%41%
2840
21st to endDay
14%13%48%5%2445%5%36%
3124
February1st to 10thDay
12%7%36%6%35%5%6%7%38%
1790
11th to 20thDay
13%8%49%5%345%5%7%37%
1848
21st to endDay
13%8%37%6%35%5%5%6%38%
1570
March1st to 10thDay
12%6%35%5%345%6%8%43%
2006
11th to 20thDay
15%8%48%5%46%5%5%6%34%
1980
21st to endDay
12%10%46%6%35%5%6%7%35%
2178
April1st to 10thDay
9%5%35%5%46%5%6%9%42%
1980
11th to 20thDay
13%6%45%5%245%5%9%41%
2153
21st to endDay
11%7%36%5%445%6%7%43%
2340
May1st to 10thDay
9%6%47%6%46%6%6%8%38%
2340
11th to 20thDay
12%6%37%7%46%7%7%8%32%
2301
21st to endDay
9%6%46%7%47%7%7%11%33%
2531
June1st to 10thDay
9%6%36%8%6%7%7%7%10%32%
2340
11th to 20thDay
6%6%36%8%6%7%8%7%10%33%
2340
21st to endDay
7%5%36%8%5%8%8%8%9%33%
2340
July1st to 10thDay
8%7%48%9%6%9%8%7%10%26%
2340
11th to 20thDay
10%6%38%8%6%8%8%8%9%26%
2340
21st to endDay
8%5%37%9%5%8%9%9%10%27%
2547
August1st to 10thDay
10%6%37%9%5%8%8%9%10%24%
2327
11th to 20thDay
10%6%38%8%5%8%7%8%9%27%
2303
21st to endDay
9%7%37%7%5%7%8%8%9%31%
2393
September1st to 10thDay
10%5%47%7%46%7%7%8%35%
1980
11th to 20thDay
13%7%26%7%37%6%7%9%32%
1980
21st to endDay
11%6%27%6%47%5%6%8%39%
1980
October1st to 10thDay
10%6%36%5%35%45%6%47%
1949
11th to 20thDay
9%6%35%6%35%436%52%
1800
21st to endDay
11%7%34434436%51%
1980
November1st to 10thDay
8%6%25%433346%56%
1767
11th to 20thDay
9%6%36%5%345%5%6%49%
1710
21st to endDay
11%7%45%42445%7%46%
1710
December1st to 10thDay
14%8%48%6%46%5%6%5%35%
1710
11th to 20thDay
11%7%46%5%26%5%6%8%40%
2153
21st to endDay
10%9%48%7%46%5%5%7%35%
3124
January1st to 10thNight
12%8%48%9%46%5%6%7%31%
4109
11th to 20thNight
12%8%37%6%35%5%6%7%37%
4120
21st to endNight
14%12%48%6%35%45%5%34%
4532
February1st to 10thNight
11%8%47%5%35%5%7%7%39%
2385
11th to 20thNight
15%8%46%6%45%5%5%6%37%
2218
21st to endNight
13%7%48%6%5%5%5%6%6%36%
1884
March1st to 10thNight
11%7%46%6%346%6%7%41%
2113
11th to 20thNight
12%8%47%7%45%5%6%8%35%
1980
21st to endNight
10%9%46%6%45%5%5%9%37%
2178
April1st to 10thNight
10%6%345%345%6%8%45%
1980
11th to 20thNight
8%7%36%5%345%5%8%45%
1769
21st to endNight
9%5%36%6%3445%7%47%
1620
May1st to 10thNight
8%6%35%5%45%6%7%9%41%
1620
11th to 20thNight
9%6%37%8%36%7%7%7%37%
1592
21st to endNight
6%6%36%6%46%7%7%11%38%
1744
June1st to 10thNight
7%5%36%5%48%7%8%14%35%
1620
11th to 20thNight
5%6%35%5%35%6%10%11%41%
1620
21st to endNight
5%5%35%5%46%5%9%11%42%
1620
July1st to 10thNight
8%6%37%6%5%7%6%7%11%35%
1620
11th to 20thNight
7%5%36%7%47%7%10%12%33%
1620
21st to endNight
5%5%37%7%5%8%8%8%11%33%
1771
August1st to 10thNight
7%5%36%6%47%7%7%13%35%
1611
11th to 20thNight
8%6%37%7%46%8%7%9%34%
1598
21st to endNight
7%7%37%7%46%8%7%10%35%
1940
September1st to 10thNight
9%5%36%7%5%6%6%6%8%40%
1980
11th to 20thNight
11%9%36%7%45%46%7%38%
1980
21st to endNight
8%6%37%6%25%5%46%47%
1980
October1st to 10thNight
13%6%35%43445%6%47%
2010
11th to 20thNight
9%6%35%6%3446%6%47%
2160
21st to endNight
9%6%36%42445%5%52%
2376
November1st to 10thNight
10%6%244345%5%6%50%
2306
11th to 20thNight
10%7%36%5%2445%6%48%
2470
21st to endNight
11%6%26%6%35%5%6%6%45%
2470
December1st to 10thNight
14%8%47%7%35%5%6%7%33%
2470
11th to 20thNight
13%9%48%5%345%5%6%38%
3042
21st to endNight
11%9%48%7%46%6%7%7%30%
4532

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 10thDay
33%9%12%22%22%3
2837
11th to 20thDay
37%10%10%13%26%3
2840
21st to endDay
44%8%9%16%20%2
3124
February1st to 10thDay
44%6%11%18%18%3
1790
11th to 20thDay
45%8%10%17%17%4
1858
21st to endDay
45%6%10%15%17%6%
1570
March1st to 10thDay
37%7%9%21%20%6%
2006
11th to 20thDay
48%7%12%15%15%4
1980
21st to endDay
46%8%12%19%12%2
2178
April1st to 10thDay
36%7%13%23%18%4
1980
11th to 20thDay
40%6%10%19%21%6%
2153
21st to endDay
38%7%14%24%15%2
2340
May1st to 10thDay
40%10%15%20%14%2
2340
11th to 20thDay
47%11%15%16%10%1
2305
21st to endDay
42%11%15%22%10%1
2531
June1st to 10thDay
44%12%19%17%8%1
2340
11th to 20thDay
43%11%18%15%12%1
2340
21st to endDay
43%10%16%18%11%2
2340
July1st to 10thDay
49%12%16%14%8%1
2275
11th to 20thDay
48%12%19%11%9%2
2271
21st to endDay
44%14%19%16%7%1
2405
August1st to 10thDay
49%14%17%16%4
2314
11th to 20thDay
48%13%16%15%7%1
2303
21st to endDay
44%13%15%17%7%3
2393
September1st to 10thDay
42%10%15%16%13%3
1980
11th to 20thDay
44%9%12%18%14%2
1980
21st to endDay
42%7%13%18%16%5%
1980
October1st to 10thDay
35%8%12%18%22%5%
1949
11th to 20thDay
32%7%10%23%21%8%
1800
21st to endDay
34%5%7%23%24%7%
1980
November1st to 10thDay
30%5%9%21%27%9%
1767
11th to 20thDay
34%6%8%21%26%6%
1710
21st to endDay
36%6%9%22%22%5%
1710
December1st to 10thDay
48%7%8%18%15%4
1710
11th to 20thDay
36%6%14%17%23%5%
2150
21st to endDay
41%8%12%21%15%2
3124
January1st to 10thNight
38%12%15%16%18%2
4109
11th to 20thNight
37%11%12%14%22%4
4120
21st to endNight
48%7%9%14%21%2
4532
February1st to 10thNight
41%6%13%20%17%3
2385
11th to 20thNight
46%7%9%18%16%4
2219
21st to endNight
46%7%11%16%16%4
1884
March1st to 10thNight
41%8%9%16%20%5%
2113
11th to 20thNight
44%8%13%19%13%3
1980
21st to endNight
44%8%13%21%13%2
2178
April1st to 10thNight
35%7%14%23%18%2
1980
11th to 20thNight
35%7%12%22%19%5%
1769
21st to endNight
35%8%14%26%16%1
1620
May1st to 10thNight
37%10%16%25%10%2
1620
11th to 20thNight
41%13%15%21%9%1
1593
21st to endNight
37%12%18%24%8%1
1745
June1st to 10thNight
37%13%22%20%7%1
1620
11th to 20thNight
32%11%27%20%10%
1620
21st to endNight
33%11%21%20%11%2
1620
July1st to 10thNight
40%14%18%18%9%1
1575
11th to 20thNight
38%16%23%15%6%2
1566
21st to endNight
38%15%21%19%7%1
1672
August1st to 10thNight
36%19%22%16%6%
1600
11th to 20thNight
40%16%18%15%10%1
1598
21st to endNight
40%14%19%19%7%1
1940
September1st to 10thNight
39%13%14%20%12%3
1980
11th to 20thNight
44%10%13%17%15%1
1980
21st to endNight
36%9%11%23%17%3
1980
October1st to 10thNight
37%7%12%19%23%3
2010
11th to 20thNight
35%8%11%22%19%5%
2160
21st to endNight
32%7%7%22%25%7%
2376
November1st to 10thNight
33%7%10%21%22%7%
2306
11th to 20thNight
36%6%7%20%24%8%
2470
21st to endNight
37%5%9%24%20%4
2470
December1st to 10thNight
46%10%11%16%13%4
2470
11th to 20thNight
40%8%11%17%20%3
3044
21st to endNight
44%10%12%20%13%1
4532

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 10thDay
29%27%30%11%21
270
11th to 20thDay
35%22%21%17%4
270
21st to endDay
26%32%26%12%4
297
February1st to 10thDay
27%26%29%14%4
270
11th to 20thDay
38%29%23%10%
270
21st to endDay
38%28%22%9%2
225
March1st to 10thDay
25%20%26%21%7%1
397
11th to 20thDay
29%21%24%20%6%1
420
21st to endDay
27%21%26%19%6%
462
April1st to 10thDay
23%19%24%21%11%2
420
11th to 20thDay
20%18%25%20%13%4
412
21st to endDay
20%15%25%20%15%5%
420
May1st to 10thDay
16%20%23%22%14%6%
423
11th to 20thDay
17%10%19%27%16%10%
447
21st to endDay
11%7%20%27%20%15%
485
June1st to 10thDay
12%6%22%27%21%13%
450
11th to 20thDay
9%6%20%22%25%17%
450
21st to endDay
10%6%27%23%19%15%
450
July1st to 10thDay
9%313%22%31%21%
445
11th to 20thDay
8%410%26%27%25%
444
21st to endDay
7%313%23%31%23%
488
August1st to 10thDay
16%415%23%20%23%
446
11th to 20thDay
9%5%11%29%27%20%
439
21st to endDay
12%313%25%27%20%
495
September1st to 10thDay
10%313%26%32%16%
450
11th to 20thDay
15%6%13%22%30%15%
450
21st to endDay
14%6%18%29%26%8%
450
October1st to 10thDay
16%9%19%25%23%8%
450
11th to 20thDay
13%14%22%26%20%5%
450
21st to endDay
19%15%21%26%17%3
495
November1st to 10thDay
17%10%27%27%15%4
365
11th to 20thDay
19%21%33%17%9%1
270
21st to endDay
17%22%32%18%10%1
270
December1st to 10thDay
28%26%27%14%4
270
11th to 20thDay
23%20%30%19%8%1
270
21st to endDay
23%22%31%15%6%2
297
January1st to 10thNight
25%18%28%24%6%
760
11th to 20thNight
22%17%27%28%6%
760
21st to endNight
21%20%27%28%3
836
February1st to 10thNight
19%15%31%30%4
760
11th to 20thNight
25%22%28%23%1
743
21st to endNight
23%23%30%21%3
628
March1st to 10thNight
18%19%29%29%4
751
11th to 20thNight
22%15%29%24%9%1
720
21st to endNight
17%18%30%26%8%
792
April1st to 10thNight
19%17%24%30%9%
720
11th to 20thNight
17%13%24%32%12%1
619
21st to endNight
14%11%19%40%15%1
540
May1st to 10thNight
14%9%22%37%17%1
540
11th to 20thNight
13%5%18%36%24%3
531
21st to endNight
8%312%34%37%6%
584
June1st to 10thNight
8%214%35%34%7%
540
11th to 20thNight
6%211%33%36%12%
540
21st to endNight
6%29%36%40%7%
540
July1st to 10thNight
9%36%27%47%9%
525
11th to 20thNight
9%3424%46%14%
522
21st to endNight
7%2324%49%14%
591
August1st to 10thNight
8%17%29%43%11%
537
11th to 20thNight
10%46%28%43%9%
534
21st to endNight
10%2428%44%11%
638
September1st to 10thNight
9%410%30%41%7%
720
11th to 20thNight
14%410%29%37%7%
720
21st to endNight
13%5%15%32%31%4
720
October1st to 10thNight
15%9%17%26%26%6%
720
11th to 20thNight
14%9%21%35%18%2
720
21st to endNight
15%12%19%35%16%2
792
November1st to 10thNight
16%8%17%39%18%3
740
11th to 20thNight
18%12%20%36%13%1
760
21st to endNight
18%14%22%33%13%1
760
December1st to 10thNight
22%17%23%31%7%
760
11th to 20thNight
18%14%27%32%8%1
760
21st to endNight
22%17%24%31%5%
836
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