Shadowlands Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shadowlands 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
52%
15756
26%
47091
19%
15709
59%
15709
35%
27328

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
37%
900
29%
2327
13%
895
47%
895
36%
1423
January16th to endNight
37%
960
31%
2496
13%
960
48%
960
38%
1492
February1st to 15thNight
34%
880
22%
2288
8%
876
42%
876
32%
1448
February16th to endNight
30%
585
28%
1847
11%
585
45%
585
32%
1051
March1st to 15thNight
38%
540
23%
1980
16%
540
47%
540
23%
1211
March16th to endNight
39%
576
20%
2112
18%
576
45%
576
23%
1300
April1st to 15thNight
38%
539
23%
1850
15%
539
51%
539
29%
1043
April16th to endNight
40%
540
23%
1800
16%
540
53%
540
29%
1058
May1st to 15thNight
49%
539
21%
1650
19%
539
56%
539
29%
1035
May16th to endNight
59%
563
20%
1684
19%
561
64%
561
34%
1004
June1st to 15thNight
77%
540
23%
1620
23%
540
80%
540
48%
831
June16th to endNight
79%
540
25%
1620
25%
540
81%
540
47%
830
July1st to 15thNight
76%
510
18%
1530
20%
510
77%
510
39%
861
July16th to endNight
85%
564
27%
1594
32%
531
85%
531
45%
846
August1st to 15thNight
80%
539
25%
1610
28%
536
81%
536
41%
878
August16th to endNight
77%
573
25%
1887
31%
573
78%
573
35%
1060
September1st to 15thNight
72%
540
28%
1833
32%
540
73%
540
37%
979
September16th to endNight
71%
546
33%
1989
34%
546
75%
546
36%
1016
October1st to 15thNight
60%
684
29%
2052
24%
684
62%
684
38%
1147
October16th to endNight
56%
704
35%
2112
24%
704
64%
704
43%
1104
November1st to 15thNight
53%
700
31%
2100
22%
700
61%
700
37%
1162
November16th to endNight
41%
834
30%
2274
17%
834
50%
834
34%
1388
December1st to 15thNight
42%
900
24%
2340
12%
900
49%
900
33%
1505
December16th to endNight
38%
960
25%
2496
12%
960
45%
960
29%
1656

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
11%5%2442445%6%45%
48100
Night
10%424423347%51%
47287
TransparencyDay
37%5%10%23%18%4
47800
Night
32%410%24%22%6%
47092
SeeingDay
11%5%17%27%28%9%
5790
Night
13%6%22%35%20%2
15757

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
16%5%2432322451%
1611
16th to endDay
13%6%2441234451%
1728
February1st to 15thDay
15%8%3431323448%
1575
16th to endDay
15%8%25%5%2234445%
1634
March1st to 15thDay
17%7%23423345%45%
1980
16th to endDay
18%7%36%5%23335%40%
2110
April1st to 15thDay
13%6%35%424336%47%
2097
16th to endDay
15%7%36%5%24345%41%
2160
May1st to 15thDay
16%6%35%5%3445%5%39%
2298
16th to endDay
11%5%35%6%36%5%5%8%39%
2430
June1st to 15thDay
6%426%5%45%5%5%10%43%
2340
16th to endDay
5%224436%6%7%9%46%
2340
July1st to 15thDay
8%425%6%36%7%7%11%36%
2340
16th to endDay
43145%37%6%8%11%43%
2466
August1st to 15thDay
6%215%6%26%7%8%9%42%
2340
16th to endDay
7%4146%36%6%7%8%42%
2313
September1st to 15thDay
13%5%2433445%6%47%
2124
16th to endDay
8%313435%446%54%
1959
October1st to 15thDay
12%5%25%323445%50%
1706
16th to endDay
12%31321334458%
1760
November1st to 15thDay
10%413423336%56%
1758
16th to endDay
15%6%2431223453%
1683
December1st to 15thDay
15%6%34322345%47%
1620
16th to endDay
17%7%25%31333446%
1728
January1st to 15thNight
15%42331223455%
2327
16th to endNight
11%5%2441223456%
2496
February1st to 15thNight
14%6%24412345%48%
2278
16th to endNight
11%5%34412347%51%
1847
March1st to 15thNight
17%425%423346%45%
1980
16th to endNight
16%5%3442433445%
2112
April1st to 15thNight
10%435%232446%50%
1850
16th to endNight
11%5%35%423447%48%
1800
May1st to 15thNight
12%5%245%2445%6%46%
1649
16th to endNight
7%425%43446%11%45%
1683
June1st to 15thNight
332231336%8%60%
1620
16th to endNight
421321446%10%59%
1620
July1st to 15thNight
44135%25%5%7%11%47%
1620
16th to endNight
31133345%5%11%55%
1702
August1st to 15thNight
32135%345%6%9%53%
1620
16th to endNight
43145%35%5%7%10%46%
1887
September1st to 15thNight
9%31442335%8%53%
1833
16th to endNight
6%3144245%6%7%54%
1989
October1st to 15thNight
10%423323347%54%
2052
16th to endNight
12%21221123463%
2112
November1st to 15thNight
8%423323346%56%
2100
16th to endNight
17%5%2331332452%
2274
December1st to 15thNight
16%5%24323336%48%
2340
16th to endNight
15%7%35%42323445%
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
37%36%25%20%5%
1612
16th to endDay
36%27%29%21%3
1728
February1st to 15thDay
40%210%24%17%4
1576
16th to endDay
42%38%22%17%5%
1634
March1st to 15thDay
42%39%21%16%7%
1980
16th to endDay
48%38%24%13%2
2112
April1st to 15thDay
39%310%21%20%4
2097
16th to endDay
46%47%20%18%3
2160
May1st to 15thDay
45%410%18%18%2
2298
16th to endDay
41%7%12%23%14%
2434
June1st to 15thDay
35%6%13%25%17%
2340
16th to endDay
31%6%14%25%19%2
2340
July1st to 15thDay
38%8%13%27%10%1
2201
16th to endDay
30%10%15%27%15%1
2311
August1st to 15thDay
33%9%13%25%15%3
2326
16th to endDay
34%9%14%22%15%3
2313
September1st to 15thDay
36%5%10%22%16%8%
2124
16th to endDay
30%5%9%24%23%6%
1959
October1st to 15thDay
35%49%21%21%7%
1706
16th to endDay
28%37%22%28%8%
1760
November1st to 15thDay
30%28%28%21%8%
1758
16th to endDay
36%36%21%24%6%
1683
December1st to 15thDay
38%49%23%19%3
1620
16th to endDay
42%37%25%17%4
1728
January1st to 15thNight
34%27%23%27%4
2327
16th to endNight
32%27%26%24%5%
2496
February1st to 15thNight
37%38%27%18%5%
2288
16th to endNight
32%39%28%18%6%
1847
March1st to 15thNight
41%310%17%20%6%
1980
16th to endNight
42%48%23%17%3
2112
April1st to 15thNight
33%412%19%21%8%
1850
16th to endNight
34%5%9%22%24%3
1800
May1st to 15thNight
37%5%11%19%19%5%
1650
16th to endNight
32%6%18%25%15%1
1685
June1st to 15thNight
20%5%14%32%23%3
1620
16th to endNight
20%6%13%28%26%4
1620
July1st to 15thNight
27%6%16%28%19%1
1530
16th to endNight
21%7%14%33%20%2
1594
August1st to 15thNight
25%6%14%29%20%3
1610
16th to endNight
30%6%14%25%20%3
1887
September1st to 15thNight
29%49%25%21%9%
1833
16th to endNight
26%5%8%25%26%7%
1989
October1st to 15thNight
29%312%19%22%11%
2052
16th to endNight
26%16%22%29%12%
2112
November1st to 15thNight
29%37%25%23%11%
2100
16th to endNight
35%27%20%27%6%
2274
December1st to 15thNight
38%310%22%19%5%
2340
16th to endNight
42%28%21%18%5%
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
23%11%28%26%8%1
90
16th to endDay
11%20%38%15%11%2
96
February1st to 15thDay
12%17%44%21%31
90
16th to endDay
20%22%30%19%41
81
March1st to 15thDay
22%18%35%18%4
90
16th to endDay
21%15%28%23%10%
96
April1st to 15thDay
15%15%27%27%12%
216
16th to endDay
19%9%28%24%14%2
270
May1st to 15thDay
17%8%28%29%14%1
435
16th to endDay
14%5%25%31%18%4
517
June1st to 15thDay
7%212%31%33%11%
495
16th to endDay
5%311%34%34%11%
495
July1st to 15thDay
8%10%32%37%11%
475
16th to endDay
35%20%43%27%
515
August1st to 15thDay
8%17%25%41%15%
493
16th to endDay
8%6%24%45%14%
353
September1st to 15thDay
10%15%20%44%17%
279
16th to endDay
5%8%36%29%19%
135
October1st to 15thDay
6%218%39%28%4
107
16th to endDay
13%7%17%36%18%6%
96
November1st to 15thDay
12%218%38%24%3
90
16th to endDay
28%17%22%16%14%
90
December1st to 15thDay
16%11%34%17%14%5%
90
16th to endDay
22%9%36%25%6%
96
January1st to 15thNight
18%10%31%32%7%
900
16th to endNight
14%9%35%35%5%
960
February1st to 15thNight
18%10%32%33%4
880
16th to endNight
14%10%40%30%4
585
March1st to 15thNight
19%9%30%35%5%
540
16th to endNight
17%6%32%32%9%
576
April1st to 15thNight
12%7%36%33%8%
539
16th to endNight
13%6%34%34%11%
540
May1st to 15thNight
14%5%25%39%13%1
540
16th to endNight
9%322%39%23%2
563
June1st to 15thNight
5%110%43%37%2
540
16th to endNight
418%37%42%5%
540
July1st to 15thNight
6%6%40%40%5%
510
16th to endNight
4130%52%10%
564
August1st to 15thNight
46%33%46%8%
539
16th to endNight
7%435%45%6%
573
September1st to 15thNight
11%5%32%45%4
540
16th to endNight
8%12%37%36%5%
546
October1st to 15thNight
12%219%33%27%3
684
16th to endNight
13%6%20%37%20%1
704
November1st to 15thNight
9%8%23%40%16%
700
16th to endNight
19%9%26%30%13%
834
December1st to 15thNight
20%8%26%35%8%
900
16th to endNight
20%10%26%37%5%
960
Page generated at 2017-10-07 13:07:49. Version ac04

Copyright 2017 A. Danko


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