Viking Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Viking 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
38%
15955
19%
46874
11%
15911
45%
15911
25%
30561

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
22%
900
15%
2506
5%
895
31%
895
20%
1769
January16th to endNight
21%
960
14%
2545
4%
960
29%
960
20%
1855
February1st to 15thNight
25%
868
13%
2279
3%
867
32%
867
20%
1639
February16th to endNight
24%
631
21%
1893
7%
631
36%
631
23%
1230
March1st to 15thNight
28%
666
18%
2106
10%
666
36%
666
20%
1401
March16th to endNight
28%
576
13%
2031
9%
576
35%
576
16%
1416
April1st to 15thNight
29%
539
17%
1797
12%
539
39%
539
22%
1176
April16th to endNight
35%
540
18%
1800
13%
540
44%
540
20%
1200
May1st to 15thNight
35%
540
17%
1543
9%
540
42%
540
23%
1076
May16th to endNight
46%
563
19%
1497
10%
561
51%
561
32%
976
June1st to 15thNight
56%
540
17%
1440
11%
540
59%
540
35%
896
June16th to endNight
49%
540
17%
1440
9%
540
54%
540
34%
919
July1st to 15thNight
66%
510
18%
1360
12%
510
68%
510
39%
825
July16th to endNight
72%
564
24%
1423
17%
531
76%
531
43%
818
August1st to 15thNight
71%
539
22%
1631
22%
536
73%
536
39%
890
August16th to endNight
69%
573
22%
1910
24%
573
74%
573
34%
1069
September1st to 15thNight
62%
540
28%
1800
29%
540
66%
540
38%
950
September16th to endNight
57%
611
27%
1800
20%
611
64%
611
36%
1033
October1st to 15thNight
47%
660
27%
1980
20%
660
53%
660
34%
1151
October16th to endNight
33%
704
19%
2158
11%
704
42%
704
26%
1352
November1st to 15thNight
33%
700
25%
2276
16%
700
45%
700
28%
1349
November16th to endNight
25%
831
19%
2451
9%
831
36%
831
23%
1617
December1st to 15thNight
21%
900
14%
2520
5%
900
29%
900
19%
1850
December16th to endNight
20%
960
13%
2688
4%
960
27%
960
14%
2104

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%7%35%5%3445%7%38%
47927
Night
13%7%35%424446%42%
47043
Cloud CoverDay
13%7%35%5%3445%7%38%
47935
Night
13%7%35%424446%42%
47048
TransparencyDay
44%6%12%21%12%1
47613
Night
41%5%12%23%14%2
46875
SeeingDay
14%7%25%27%19%5%
5979
Night
16%8%30%30%12%1
15957

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%13%48%7%45%436%28%
1432
16th to endDay
14%14%6%10%6%44345%25%
1677
February1st to 15thDay
15%10%6%6%5%36%435%32%
1582
16th to endDay
13%9%5%7%6%34347%33%
1580
March1st to 15thDay
15%9%46%5%34347%34%
1854
16th to endDay
17%11%46%6%2445%7%28%
2193
April1st to 15thDay
16%9%45%424346%36%
2151
16th to endDay
21%7%26%6%34345%33%
2160
May1st to 15thDay
19%8%35%6%3445%7%31%
2406
16th to endDay
15%6%25%5%3446%7%36%
2617
June1st to 15thDay
11%6%26%5%245%5%7%41%
2520
16th to endDay
10%4245%35%5%5%9%42%
2520
July1st to 15thDay
7%3145%35%5%7%9%44%
2520
16th to endDay
5%4245%35%6%7%10%44%
2646
August1st to 15thDay
7%4236%35%5%7%10%41%
2319
16th to endDay
9%426%4335%5%8%45%
2292
September1st to 15thDay
12%313424347%50%
2160
16th to endDay
9%425%435%5%5%8%45%
1871
October1st to 15thDay
15%5%14323446%48%
1650
16th to endDay
17%6%35%32345%6%41%
1713
November1st to 15thDay
14%8%244245%46%42%
1582
16th to endDay
17%8%46%424436%37%
1506
December1st to 15thDay
19%11%5%8%5%3445%427%
1440
16th to endDay
18%15%6%7%5%2335%5%26%
1536
January1st to 15thNight
13%9%47%6%34345%36%
2506
16th to endNight
11%10%6%8%6%35%336%33%
2545
February1st to 15thNight
15%9%45%5%35%447%34%
2276
16th to endNight
14%8%36%423346%41%
1893
March1st to 15thNight
16%9%36%423345%40%
2093
16th to endNight
16%9%47%5%35%35%5%32%
2031
April1st to 15thNight
14%9%36%424336%40%
1797
16th to endNight
18%6%26%5%2435%5%38%
1800
May1st to 15thNight
17%6%36%5%24446%37%
1543
16th to endNight
9%5%26%445%36%10%42%
1496
June1st to 15thNight
10%42442445%7%48%
1440
16th to endNight
7%425%6%35%46%8%45%
1440
July1st to 15thNight
6%3134245%6%9%52%
1440
16th to endNight
5%2134345%7%9%51%
1519
August1st to 15thNight
421443445%8%55%
1641
16th to endNight
9%22431445%7%53%
1910
September1st to 15thNight
11%313322337%56%
1800
16th to endNight
7%325%3345%6%6%50%
1800
October1st to 15thNight
10%6%14423345%52%
1980
16th to endNight
16%6%24423446%44%
2158
November1st to 15thNight
13%7%24322246%50%
2276
16th to endNight
17%7%3442245%6%40%
2451
December1st to 15thNight
18%10%5%7%424345%33%
2520
16th to endNight
21%14%5%8%5%2333427%
2688

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
13%14%48%6%5%5%436%28%
1432
16th to endDay
14%14%6%9%7%34345%25%
1677
February1st to 15thDay
14%10%5%7%6%35%436%31%
1582
16th to endDay
13%9%5%6%6%34347%33%
1580
March1st to 15thDay
15%10%46%5%33447%34%
1864
16th to endDay
18%10%47%5%2445%6%29%
2191
April1st to 15thDay
17%10%45%5%23346%36%
2151
16th to endDay
20%7%27%6%24445%34%
2160
May1st to 15thDay
19%8%345%35%45%6%31%
2406
16th to endDay
15%6%25%5%35%5%6%7%36%
2617
June1st to 15thDay
11%5%36%5%245%5%7%41%
2520
16th to endDay
10%425%5%35%5%5%9%42%
2520
July1st to 15thDay
7%325%5%35%5%7%9%44%
2520
16th to endDay
6%4245%35%6%7%10%44%
2646
August1st to 15thDay
6%4245%35%6%6%10%41%
2319
16th to endDay
9%426%43445%8%45%
2292
September1st to 15thDay
12%413424447%50%
2160
16th to endDay
10%4244345%5%8%46%
1871
October1st to 15thDay
15%5%23323336%49%
1650
16th to endDay
17%7%34324347%41%
1713
November1st to 15thDay
14%8%24424446%42%
1582
16th to endDay
17%9%45%424346%37%
1506
December1st to 15thDay
18%12%48%5%25%45%427%
1440
16th to endDay
19%14%6%6%6%24345%26%
1536
January1st to 15thNight
13%9%46%6%34345%36%
2506
16th to endNight
11%11%6%8%6%35%346%32%
2545
February1st to 15thNight
15%9%46%5%35%447%34%
2269
16th to endNight
13%8%45%423346%40%
1893
March1st to 15thNight
15%9%45%423335%40%
2106
16th to endNight
16%9%46%5%4445%5%32%
2031
April1st to 15thNight
15%8%36%433346%40%
1797
16th to endNight
18%6%26%5%14445%38%
1800
May1st to 15thNight
17%6%45%6%34446%37%
1542
16th to endNight
9%425%5%3446%9%43%
1496
June1st to 15thNight
11%42442445%8%48%
1440
16th to endNight
7%4245%35%5%5%9%45%
1440
July1st to 15thNight
6%3134246%5%9%52%
1440
16th to endNight
4214335%5%6%9%52%
1519
August1st to 15thNight
42143435%5%8%56%
1641
16th to endNight
8%32342445%7%53%
1910
September1st to 15thNight
11%313323246%57%
1800
16th to endNight
7%325%4245%6%7%50%
1800
October1st to 15thNight
10%5%25%423345%52%
1980
16th to endNight
16%6%24423446%44%
2158
November1st to 15thNight
13%7%24322246%50%
2276
16th to endNight
17%7%35%42345%6%40%
2451
December1st to 15thNight
18%10%5%7%424345%33%
2520
16th to endNight
20%14%5%8%5%2334327%
2688

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
57%5%10%15%10%
1433
16th to endDay
60%412%15%7%
1677
February1st to 15thDay
53%5%16%18%5%
1583
16th to endDay
50%5%14%20%9%
1580
March1st to 15thDay
49%6%14%21%7%
1864
16th to endDay
53%5%14%19%5%
2193
April1st to 15thDay
49%411%22%11%
2151
16th to endDay
51%5%9%18%12%1
2160
May1st to 15thDay
51%6%11%21%8%
2406
16th to endDay
45%8%12%17%14%1
2621
June1st to 15thDay
39%8%11%23%15%1
2520
16th to endDay
36%8%13%22%16%2
2520
July1st to 15thDay
34%8%14%24%13%3
2371
16th to endDay
32%9%17%25%13%2
2479
August1st to 15thDay
33%9%14%24%16%1
2305
16th to endDay
35%6%12%24%16%3
2292
September1st to 15thDay
32%5%10%25%20%5%
2160
16th to endDay
34%5%11%27%19%1
1871
October1st to 15thDay
37%49%27%19%1
1650
16th to endDay
42%412%24%12%2
1713
November1st to 15thDay
41%5%11%24%14%2
1582
16th to endDay
48%315%22%8%1
1506
December1st to 15thDay
58%413%17%6%
1440
16th to endDay
59%5%11%14%8%1
1536
January1st to 15thNight
49%412%19%13%
2506
16th to endNight
51%415%18%9%
2545
February1st to 15thNight
49%5%13%20%10%
2279
16th to endNight
43%412%26%11%1
1893
March1st to 15thNight
46%412%23%10%1
2106
16th to endNight
52%5%13%20%7%1
2031
April1st to 15thNight
44%48%24%13%2
1797
16th to endNight
46%5%10%18%14%3
1800
May1st to 15thNight
47%5%12%20%13%
1543
16th to endNight
36%7%15%19%18%2
1498
June1st to 15thNight
33%6%12%25%18%3
1440
16th to endNight
34%7%13%20%21%4
1440
July1st to 15thNight
28%7%13%28%17%3
1360
16th to endNight
25%7%16%29%19%2
1423
August1st to 15thNight
25%7%15%30%17%3
1631
16th to endNight
29%7%11%26%19%6%
1910
September1st to 15thNight
29%310%27%23%5%
1800
16th to endNight
29%5%11%27%21%2
1800
October1st to 15thNight
33%410%25%23%4
1980
16th to endNight
39%5%11%24%17%1
2158
November1st to 15thNight
36%410%24%19%4
2276
16th to endNight
44%412%25%12%
2451
December1st to 15thNight
53%411%21%7%
2520
16th to endNight
60%410%15%7%
2688

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
26%16%34%18%3
90
16th to endDay
20%15%38%13%10%1
96
February1st to 15thDay
17%14%43%16%7%
90
16th to endDay
18%17%34%19%7%2
81
March1st to 15thDay
22%20%37%16%3
90
16th to endDay
27%13%27%19%10%1
177
April1st to 15thDay
20%14%30%22%12%
270
16th to endDay
24%6%27%24%13%3
270
May1st to 15thDay
20%10%30%24%10%2
396
16th to endDay
17%8%29%25%14%4
517
June1st to 15thDay
11%428%29%20%5%
495
16th to endDay
10%6%30%29%16%5%
495
July1st to 15thDay
12%122%33%20%9%
475
16th to endDay
7%18%34%30%8%
515
August1st to 15thDay
6%118%34%28%9%
472
16th to endDay
8%314%31%29%12%
332
September1st to 15thDay
9%313%32%33%8%
315
16th to endDay
6%419%30%29%7%
251
October1st to 15thDay
12%426%27%18%10%
90
16th to endDay
18%10%31%29%10%
96
November1st to 15thDay
211%31%28%18%7%
90
16th to endDay
44%12%28%8%41
90
December1st to 15thDay
26%16%28%18%7%1
90
16th to endDay
30%16%45%6%1
96
January1st to 15thNight
17%14%40%20%6%
900
16th to endNight
16%13%39%27%3
960
February1st to 15thNight
20%11%37%24%5%
870
16th to endNight
18%11%41%23%4
631
March1st to 15thNight
21%10%35%26%6%
666
16th to endNight
22%12%30%26%6%
576
April1st to 15thNight
19%12%35%27%5%
539
16th to endNight
20%10%28%32%7%
540
May1st to 15thNight
19%6%31%31%9%1
540
16th to endNight
11%331%37%15%
563
June1st to 15thNight
12%421%44%16%
540
16th to endNight
9%331%37%17%
540
July1st to 15thNight
9%116%42%28%2
510
16th to endNight
5%113%44%31%3
564
August1st to 15thNight
5%13%42%31%5%
539
16th to endNight
9%12%40%32%3
573
September1st to 15thNight
12%414%36%27%4
540
16th to endNight
9%421%32%27%3
611
October1st to 15thNight
13%6%28%30%19%2
660
16th to endNight
20%10%33%26%8%
704
November1st to 15thNight
16%10%35%26%9%1
700
16th to endNight
21%11%36%22%7%
831
December1st to 15thNight
23%11%37%22%5%
900
16th to endNight
26%12%33%22%4
960
Page generated at 2017-09-19 06:32:23. Version ac04

Copyright 2017 A. Danko


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