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 2024-11-02.

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
45%
24908
17%
96084
13%
24717
52%
24717
18%
60964

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
25%
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
29%
758
14%
3484
13%
745
37%
745
11%
2616
March11th to 20thNight
28%
754
23%
3412
8%
740
35%
740
16%
1737
March21st to endNight
28%
829
12%
3708
7%
814
35%
814
14%
2193
April1st to 10thNight
35%
760
20%
2090
10%
760
42%
760
26%
1339
April11th to 20thNight
40%
653
22%
1867
13%
653
47%
653
27%
1171
April21st to endNight
50%
570
22%
1710
15%
570
56%
570
28%
1064
May1st to 10thNight
48%
564
16%
2785
8%
559
53%
559
15%
1795
May11th to 20thNight
49%
550
12%
2791
8%
541
53%
541
12%
1872
May21st to endNight
64%
600
13%
3048
11%
593
66%
593
17%
1711
June1st to 10thNight
64%
570
12%
1710
10%
570
65%
570
24%
1150
June11th to 20thNight
67%
570
11%
1710
9%
570
69%
570
31%
1074
June21st to endNight
70%
570
14%
1710
13%
570
71%
570
30%
1085
July1st to 10thNight
68%
540
11%
2727
10%
535
69%
535
14%
1816
July11th to 20thNight
69%
538
9%
2651
10%
533
70%
533
14%
1708
July21st to endNight
69%
609
7%
2978
11%
569
71%
569
11%
2289
August1st to 10thNight
70%
549
9%
2759
9%
544
70%
544
14%
1758
August11th to 20thNight
63%
551
10%
2692
14%
543
65%
543
13%
1793
August21st to endNight
65%
655
14%
2960
13%
652
66%
652
18%
1631
September1st to 10thNight
62%
760
19%
2090
17%
760
63%
760
25%
1437
September11th to 20thNight
55%
760
17%
2090
15%
760
56%
760
22%
1485
September21st to endNight
57%
760
22%
2090
18%
760
59%
760
28%
1366
October1st to 10thNight
53%
760
24%
2122
21%
760
58%
760
30%
1347
October11th to 20thNight
49%
760
23%
2280
20%
760
56%
760
29%
1385
October21st to endNight
49%
836
30%
2508
23%
836
59%
836
31%
1471
November1st to 10thNight
53%
745
25%
2319
21%
745
61%
745
29%
1392
November11th to 20thNight
44%
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
44%
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%38%5%5%6%5%6%8%37%
101101
Night
10%8%38%5%5%5%46%8%38%
97817
TransparencyDay
41%9%14%19%14%3
100914
Night
40%10%14%19%14%3
97674
SeeingDay
18%13%21%22%17%9%
15038
Night
16%11%19%31%20%3
25077

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%26%5%45%46%10%40%
2836
11th to 20thDay
10%7%37%5%5%6%5%5%5%41%
2840
21st to endDay
14%13%49%43435%5%36%
3124
February1st to 10thDay
12%8%37%5%45%46%7%38%
1790
11th to 20thDay
13%9%410%44445%6%37%
1848
21st to endDay
13%8%39%5%46%35%6%38%
1570
March1st to 10thDay
16%10%47%5%44447%37%
3362
11th to 20thDay
10%7%37%444445%49%
3480
21st to endDay
14%9%37%44446%7%39%
3815
April1st to 10thDay
10%6%35%46%5%5%6%9%42%
2090
11th to 20thDay
13%8%36%5%4436%8%41%
2275
21st to endDay
11%7%36%5%45%36%7%44%
2470
May1st to 10thDay
9%8%410%6%6%6%6%6%8%32%
4082
11th to 20thDay
12%8%49%6%6%6%5%7%8%29%
4081
21st to endDay
6%5%37%5%6%6%5%7%11%37%
4476
June1st to 10thDay
9%6%37%7%8%6%6%8%10%31%
2470
11th to 20thDay
5%7%38%6%8%6%7%8%10%33%
2470
21st to endDay
7%6%36%7%6%7%6%8%9%34%
2470
July1st to 10thDay
5%6%39%7%7%7%6%7%10%33%
4120
11th to 20thDay
8%6%38%7%7%7%6%8%9%31%
4120
21st to endDay
12%9%411%9%8%8%6%8%8%17%
4466
August1st to 10thDay
11%7%39%6%6%7%6%10%11%24%
4104
11th to 20thDay
7%5%37%6%6%8%5%9%11%33%
4044
21st to endDay
5%426%5%5%6%5%7%7%47%
4197
September1st to 10thDay
9%6%47%6%5%6%5%7%8%36%
2090
11th to 20thDay
14%7%28%6%5%6%5%7%9%32%
2090
21st to endDay
12%7%28%5%5%6%47%7%37%
2090
October1st to 10thDay
10%7%37%34435%6%48%
2057
11th to 20thDay
8%6%26%5%35%336%53%
1900
21st to endDay
10%7%35%434346%52%
2090
November1st to 10thDay
8%6%26%433346%55%
1777
11th to 20thDay
9%7%36%5%3445%6%49%
1710
21st to endDay
11%7%46%44335%7%46%
1710
December1st to 10thDay
14%8%48%5%5%6%46%5%35%
1710
11th to 20thDay
11%7%46%5%45%46%8%40%
2153
21st to endDay
10%9%49%6%6%6%45%7%35%
3124
January1st to 10thNight
12%9%49%8%6%6%46%7%31%
4109
11th to 20thNight
11%9%38%5%45%46%7%37%
4120
21st to endNight
13%13%49%5%45%35%5%34%
4532
February1st to 10thNight
11%8%37%445%47%7%39%
2385
11th to 20thNight
15%9%37%5%5%445%6%37%
2218
21st to endNight
13%8%49%5%5%5%46%6%36%
1884
March1st to 10thNight
17%13%5%9%6%5%5%45%5%26%
3489
11th to 20thNight
8%7%36%5%45%46%8%45%
3480
21st to endNight
13%7%36%5%4445%8%41%
3817
April1st to 10thNight
10%7%35%5%5%346%8%43%
2090
11th to 20thNight
8%8%37%5%4436%8%44%
1867
21st to endNight
9%6%36%5%4435%7%47%
1710
May1st to 10thNight
9%8%48%5%5%5%47%9%35%
2813
11th to 20thNight
10%8%410%6%5%5%6%6%7%32%
2812
21st to endNight
6%5%38%5%6%5%6%8%12%38%
3079
June1st to 10thNight
7%6%27%46%6%5%9%14%34%
1710
11th to 20thNight
5%7%25%5%5%5%5%10%11%40%
1710
21st to endNight
5%6%26%5%6%5%48%12%42%
1710
July1st to 10thNight
6%6%39%6%8%7%5%8%11%32%
2840
11th to 20thNight
7%5%27%6%5%7%5%9%11%36%
2840
21st to endNight
11%10%5%12%7%7%7%5%7%9%20%
3087
August1st to 10thNight
7%7%38%6%6%7%6%8%12%31%
2825
11th to 20thNight
8%7%410%6%7%6%6%7%9%32%
2785
21st to endNight
6%5%26%445%5%7%10%47%
3422
September1st to 10thNight
9%6%28%5%6%6%46%9%40%
2090
11th to 20thNight
11%9%38%6%5%5%46%7%36%
2090
21st to endNight
9%6%38%435%5%47%46%
2090
October1st to 10thNight
12%6%36%44445%6%47%
2122
11th to 20thNight
8%7%26%45%436%6%48%
2280
21st to endNight
8%7%36%33335%5%52%
2508
November1st to 10thNight
10%6%25%4445%5%6%49%
2319
11th to 20thNight
10%7%36%44345%6%48%
2470
21st to endNight
11%6%27%5%5%5%45%6%45%
2470
December1st to 10thNight
14%9%48%6%5%5%46%7%33%
2470
11th to 20thNight
13%10%39%44445%6%38%
3042
21st to endNight
11%10%49%6%6%6%47%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
42%9%10%16%15%7%
3362
11th to 20thDay
35%7%9%20%21%8%
3480
21st to endDay
42%7%12%22%15%3
3815
April1st to 10thDay
36%8%13%22%18%4
2090
11th to 20thDay
39%6%10%19%20%6%
2275
21st to endDay
38%7%14%24%15%2
2470
May1st to 10thDay
44%11%14%18%12%1
4120
11th to 20thDay
46%13%13%20%7%1
4085
21st to endDay
35%12%17%20%15%1
4489
June1st to 10thDay
44%12%19%17%8%1
2470
11th to 20thDay
41%11%18%17%12%1
2470
21st to endDay
42%10%16%18%12%2
2470
July1st to 10thDay
44%11%19%19%7%
4055
11th to 20thDay
45%10%22%18%5%1
4051
21st to endDay
61%10%14%11%4
4324
August1st to 10thDay
49%9%19%20%3
4091
11th to 20thDay
40%8%24%17%9%2
4083
21st to endDay
33%8%14%33%11%2
4197
September1st to 10thDay
41%10%14%16%15%3
2090
11th to 20thDay
45%8%12%19%14%2
2090
21st to endDay
43%7%14%17%15%4
2090
October1st to 10thDay
34%7%11%19%23%5%
2057
11th to 20thDay
31%7%9%23%20%10%
1900
21st to endDay
33%5%7%23%23%8%
2090
November1st to 10thDay
30%5%9%21%27%9%
1777
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
50%15%9%11%13%3
3489
11th to 20thNight
32%8%13%21%17%9%
3480
21st to endNight
41%6%13%23%14%3
3817
April1st to 10thNight
35%8%14%23%18%3
2090
11th to 20thNight
35%7%12%22%20%4
1867
21st to endNight
35%8%14%26%16%1
1710
May1st to 10thNight
41%12%15%23%8%1
2840
11th to 20thNight
42%16%15%21%7%
2813
21st to endNight
29%16%20%25%10%1
3087
June1st to 10thNight
37%14%21%20%7%1
1710
11th to 20thNight
32%11%26%21%10%
1710
21st to endNight
34%11%21%20%12%2
1710
July1st to 10thNight
43%13%19%19%6%
2795
11th to 20thNight
39%13%25%18%41
2786
21st to endNight
56%11%17%12%4
2988
August1st to 10thNight
42%12%28%15%4
2814
11th to 20thNight
45%10%23%15%7%
2812
21st to endNight
30%9%18%34%8%1
3422
September1st to 10thNight
39%12%13%20%12%3
2090
11th to 20thNight
45%10%13%18%14%1
2090
21st to endNight
37%9%12%23%17%3
2090
October1st to 10thNight
36%6%12%19%23%4
2122
11th to 20thNight
34%7%11%22%19%7%
2280
21st to endNight
32%6%7%22%25%7%
2508
November1st to 10thNight
33%7%10%21%22%7%
2319
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
27%20%25%20%7%1
409
11th to 20thDay
28%21%25%20%6%1
460
21st to endDay
27%21%26%19%6%
506
April1st to 10thDay
25%18%24%20%10%2
460
11th to 20thDay
20%19%25%20%12%4
452
21st to endDay
20%15%26%20%15%4
460
May1st to 10thDay
16%20%23%22%13%6%
463
11th to 20thDay
17%11%19%27%16%9%
487
21st to endDay
11%7%21%27%20%14%
529
June1st to 10thDay
11%6%23%27%20%12%
490
11th to 20thDay
8%6%22%23%25%16%
490
21st to endDay
10%6%27%23%19%15%
490
July1st to 10thDay
9%313%23%32%20%
485
11th to 20thDay
8%410%26%27%25%
484
21st to endDay
8%314%23%30%21%
532
August1st to 10thDay
16%416%23%19%21%
486
11th to 20thDay
9%5%13%30%25%18%
479
21st to endDay
11%312%26%27%21%
539
September1st to 10thDay
9%414%27%31%15%
490
11th to 20thDay
16%6%15%21%29%14%
490
21st to endDay
16%6%17%29%25%7%
490
October1st to 10thDay
15%9%20%26%22%8%
490
11th to 20thDay
13%14%22%27%20%5%
490
21st to endDay
18%14%22%26%17%3
539
November1st to 10thDay
17%10%27%27%15%4
369
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
19%19%29%29%4
760
11th to 20thNight
22%15%29%25%9%1
760
21st to endNight
18%18%30%26%8%
836
April1st to 10thNight
19%18%24%30%9%
760
11th to 20thNight
18%13%24%32%12%1
653
21st to endNight
13%11%21%40%15%1
570
May1st to 10thNight
14%9%21%36%18%1
570
11th to 20thNight
13%6%18%37%24%3
561
21st to endNight
8%312%35%35%6%
617
June1st to 10thNight
9%215%35%33%7%
570
11th to 20thNight
6%211%34%36%11%
570
21st to endNight
6%29%36%40%7%
570
July1st to 10thNight
9%36%27%46%8%
555
11th to 20thNight
9%3424%46%14%
552
21st to endNight
8%2325%47%14%
624
August1st to 10thNight
8%17%31%43%11%
567
11th to 20thNight
10%47%29%41%9%
564
21st to endNight
10%2428%44%11%
674
September1st to 10thNight
9%410%30%40%7%
760
11th to 20thNight
14%5%11%28%35%6%
760
21st to endNight
14%6%15%32%29%4
760
October1st to 10thNight
15%9%16%28%26%6%
760
11th to 20thNight
14%9%21%35%18%2
760
21st to endNight
15%12%19%36%16%2
836
November1st to 10thNight
16%8%17%39%18%3
745
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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