Lookout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
48%
15435
23%
47161
16%
15392
56%
15392
29%
28760

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
26%
720
23%
2327
10%
716
41%
716
20%
1485
January16th to endNight
24%
768
25%
2400
11%
768
39%
768
21%
1560
February1st to 15thNight
27%
704
24%
2112
9%
701
43%
701
26%
1308
February16th to endNight
24%
631
23%
1893
9%
631
37%
631
22%
1231
March1st to 15thNight
30%
720
22%
2112
12%
720
38%
720
24%
1363
March16th to endNight
37%
768
21%
2112
13%
768
44%
768
28%
1349
April1st to 15thNight
43%
550
25%
1808
16%
550
54%
550
32%
989
April16th to endNight
52%
540
28%
1749
20%
540
62%
540
33%
985
May1st to 15thNight
50%
540
21%
1620
13%
540
57%
540
31%
978
May16th to endNight
65%
561
21%
1682
15%
561
69%
561
32%
1016
June1st to 15thNight
70%
540
18%
1620
15%
540
71%
540
36%
941
June16th to endNight
75%
540
19%
1620
16%
540
77%
540
41%
911
July1st to 15thNight
71%
510
16%
1530
13%
510
73%
510
32%
936
July16th to endNight
72%
564
18%
1595
16%
531
74%
531
32%
975
August1st to 15thNight
71%
539
20%
1709
21%
536
72%
536
31%
1020
August16th to endNight
66%
573
20%
1910
22%
573
68%
573
26%
1202
September1st to 15thNight
64%
654
19%
1914
18%
654
65%
654
28%
1243
September16th to endNight
60%
717
29%
1980
22%
717
65%
717
36%
1195
October1st to 15thNight
57%
684
33%
1881
27%
684
63%
684
40%
1089
October16th to endNight
50%
704
33%
2135
26%
704
60%
704
36%
1194
November1st to 15thNight
48%
700
30%
2276
23%
700
60%
700
34%
1229
November16th to endNight
38%
720
28%
2340
18%
720
52%
720
26%
1372
December1st to 15thNight
33%
720
23%
2340
14%
720
45%
720
22%
1493
December16th to endNight
29%
768
20%
2496
13%
768
39%
768
18%
1696

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
13%5%25%5%35%5%5%7%39%
48032
Night
12%5%2442445%7%45%
47360
TransparencyDay
41%5%11%20%16%4
47733
Night
37%411%21%19%5%
47163
SeeingDay
17%7%19%21%21%13%
5332
Night
15%8%20%28%21%4
15437

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 15thDay
20%7%34323445%40%
1611
16th to endDay
17%5%2442443444%
1821
February1st to 15thDay
16%7%345%24446%40%
1750
16th to endDay
18%5%25%5%3344441%
1580
March1st to 15thDay
18%6%25%5%34446%37%
1847
16th to endDay
15%6%25%5%345%5%7%38%
2111
April1st to 15thDay
12%6%25%5%2445%7%43%
2150
16th to endDay
12%425%5%35%446%44%
2211
May1st to 15thDay
13%5%25%5%3445%6%43%
2331
16th to endDay
11%5%25%5%35%5%6%9%38%
2431
June1st to 15thDay
8%5%36%6%46%6%7%9%34%
2340
16th to endDay
6%4246%46%7%8%11%39%
2340
July1st to 15thDay
10%436%6%46%7%7%10%29%
2340
16th to endDay
7%5%36%8%5%9%7%7%10%27%
2465
August1st to 15thDay
8%5%25%6%37%8%8%11%31%
2238
16th to endDay
15%6%27%7%46%6%6%8%28%
2292
September1st to 15thDay
13%6%37%6%45%5%5%8%33%
2032
16th to endDay
15%4145%2445%6%44%
1980
October1st to 15thDay
13%42442433453%
1877
16th to endDay
12%42431323456%
1735
November1st to 15thDay
12%322423346%53%
1582
16th to endDay
18%41331425%6%46%
1620
December1st to 15thDay
19%7%26%425%245%38%
1620
16th to endDay
25%7%35%5%13335%34%
1728
January1st to 15thNight
19%5%24424345%41%
2327
16th to endNight
16%6%35%435%44441%
2400
February1st to 15thNight
15%5%25%423346%46%
2103
16th to endNight
16%5%35%43445%5%41%
1893
March1st to 15thNight
14%6%25%5%24446%42%
2112
16th to endNight
12%6%25%42445%6%45%
2112
April1st to 15thNight
12%313414448%50%
1808
16th to endNight
10%32332445%7%52%
1749
May1st to 15thNight
10%5%25%5%2346%7%46%
1619
16th to endNight
8%4135%35%6%5%9%46%
1682
June1st to 15thNight
5%3245%345%6%10%47%
1620
16th to endNight
33244245%8%13%47%
1620
July1st to 15thNight
8%435%5%35%5%7%11%40%
1620
16th to endNight
5%3246%36%6%7%11%40%
1703
August1st to 15thNight
7%424435%5%7%11%42%
1720
16th to endNight
12%5%2343447%10%40%
1910
September1st to 15thNight
9%5%25%5%36%5%7%8%40%
1914
16th to endNight
11%314333447%49%
1980
October1st to 15thNight
11%413313345%56%
1881
16th to endNight
11%41341333458%
2135
November1st to 15thNight
13%323213247%55%
2276
16th to endNight
16%5%24313345%48%
2340
December1st to 15thNight
17%5%35%5%33336%41%
2340
16th to endNight
23%7%26%424345%35%
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
45%37%17%21%4
1612
16th to endDay
41%37%21%19%6%
1821
February1st to 15thDay
44%37%22%18%2
1752
16th to endDay
45%26%21%19%3
1580
March1st to 15thDay
47%47%17%19%3
1847
16th to endDay
43%5%12%22%13%2
2112
April1st to 15thDay
39%5%9%21%18%4
2150
16th to endDay
39%48%24%18%4
2211
May1st to 15thDay
40%412%24%14%3
2331
16th to endDay
40%6%14%22%13%2
2435
June1st to 15thDay
41%8%15%23%11%
2340
16th to endDay
33%7%16%24%14%3
2340
July1st to 15thDay
41%9%17%19%8%2
2201
16th to endDay
45%9%17%18%8%
2310
August1st to 15thDay
40%9%16%21%10%1
2225
16th to endDay
49%7%13%15%10%2
2292
September1st to 15thDay
46%7%13%15%11%4
2032
16th to endDay
38%5%10%20%19%5%
1980
October1st to 15thDay
34%46%18%27%8%
1877
16th to endDay
32%2420%29%9%
1735
November1st to 15thDay
32%3419%30%9%
1582
16th to endDay
38%45%19%26%6%
1620
December1st to 15thDay
47%36%20%17%5%
1620
16th to endDay
52%38%17%14%3
1728
January1st to 15thNight
44%37%18%21%4
2327
16th to endNight
44%35%20%20%5%
2400
February1st to 15thNight
39%27%22%20%6%
2112
16th to endNight
44%35%24%19%3
1893
March1st to 15thNight
42%37%20%18%7%
2112
16th to endNight
38%411%26%17%2
2112
April1st to 15thNight
31%312%24%21%6%
1808
16th to endNight
31%49%27%21%6%
1749
May1st to 15thNight
35%5%14%20%21%2
1620
16th to endNight
32%8%16%25%14%3
1684
June1st to 15thNight
30%6%20%27%13%1
1620
16th to endNight
26%6%20%25%17%4
1620
July1st to 15thNight
34%6%19%24%11%3
1530
16th to endNight
32%8%21%23%11%2
1595
August1st to 15thNight
33%7%19%22%14%2
1709
16th to endNight
38%7%19%18%13%2
1910
September1st to 15thNight
38%7%18%17%14%3
1914
16th to endNight
33%410%25%21%5%
1980
October1st to 15thNight
29%47%24%23%9%
1881
16th to endNight
31%2318%30%13%
2135
November1st to 15thNight
30%25%19%28%12%
2276
16th to endNight
37%25%20%25%8%
2340
December1st to 15thNight
44%38%19%19%5%
2340
16th to endNight
49%38%17%16%4
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
27%18%32%16%31
90
16th to endDay
17%32%41%5%3
96
February1st to 15thDay
23%26%40%7%2
90
16th to endDay
33%12%46%7%
81
March1st to 15thDay
23%17%32%20%32
137
16th to endDay
18%14%31%21%12%1
288
April1st to 15thDay
18%11%30%19%18%1
270
16th to endDay
17%8%24%25%19%5%
270
May1st to 15thDay
17%8%25%22%12%13%
288
16th to endDay
19%415%22%20%17%
331
June1st to 15thDay
13%38%24%22%26%
315
16th to endDay
10%116%22%22%26%
315
July1st to 15thDay
10%10%25%27%24%
305
16th to endDay
7%26%17%32%32%
326
August1st to 15thDay
18%18%24%24%22%
313
16th to endDay
21%15%23%31%17%
332
September1st to 15thDay
15%211%21%32%16%
315
16th to endDay
16%211%26%34%8%
314
October1st to 15thDay
16%320%27%24%6%
278
16th to endDay
15%6%23%25%25%5%
212
November1st to 15thDay
25%20%20%22%10%2
90
16th to endDay
17%22%31%18%8%1
90
December1st to 15thDay
25%23%35%13%11
90
16th to endDay
34%14%35%11%4
96
January1st to 15thNight
23%15%29%25%5%
720
16th to endNight
20%15%34%25%3
768
February1st to 15thNight
19%15%33%28%2
704
16th to endNight
19%17%35%23%3
631
March1st to 15thNight
20%13%31%28%5%
720
16th to endNight
17%13%26%27%14%
768
April1st to 15thNight
14%11%27%30%14%1
550
16th to endNight
12%8%22%36%19%1
540
May1st to 15thNight
11%5%24%31%23%4
540
16th to endNight
10%212%32%36%6%
563
June1st to 15thNight
6%10%32%39%9%
540
16th to endNight
417%29%43%13%
540
July1st to 15thNight
8%17%24%43%14%
510
16th to endNight
6%16%21%50%13%
564
August1st to 15thNight
9%15%23%47%12%
539
16th to endNight
15%26%27%41%7%
573
September1st to 15thNight
12%28%28%37%10%
654
16th to endNight
14%213%29%36%4
717
October1st to 15thNight
14%418%33%24%4
684
16th to endNight
13%8%21%33%19%4
704
November1st to 15thNight
15%9%22%29%19%3
700
16th to endNight
19%12%24%30%12%
720
December1st to 15thNight
21%12%26%30%8%
720
16th to endNight
25%13%26%26%7%
768
Page generated at 2017-10-07 13:07:52. Version ac04

Copyright 2017 A. Danko


Lookout Observatory Clear Sky Chart | Charts Home