Decorah
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Decorah 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
36%
16064
17%
46883
9%
16017
43%
16017
24%
31136

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%
900
12%
2506
5%
895
33%
895
19%
1806
January16th to endNight
20%
960
13%
2554
3%
960
27%
960
17%
1912
February1st to 15thNight
23%
879
14%
2288
3%
875
30%
875
20%
1657
February16th to endNight
26%
693
19%
1955
6%
693
36%
693
22%
1336
March1st to 15thNight
29%
624
16%
2064
10%
624
36%
624
22%
1323
March16th to endNight
30%
576
13%
2064
8%
576
38%
576
16%
1441
April1st to 15thNight
27%
539
16%
1797
10%
539
38%
539
20%
1203
April16th to endNight
32%
540
18%
1761
11%
540
42%
540
19%
1208
May1st to 15thNight
34%
540
17%
1476
10%
540
41%
540
26%
1023
May16th to endNight
42%
563
16%
1497
6%
561
49%
561
31%
980
June1st to 15thNight
47%
540
13%
1440
6%
540
50%
540
29%
958
June16th to endNight
52%
540
18%
1440
8%
540
56%
540
37%
886
July1st to 15thNight
64%
510
16%
1360
9%
510
66%
510
45%
774
July16th to endNight
67%
564
22%
1419
14%
531
69%
531
45%
806
August1st to 15thNight
66%
539
22%
1610
20%
536
69%
536
38%
919
August16th to endNight
60%
573
21%
1854
22%
573
65%
573
33%
1052
September1st to 15thNight
58%
540
25%
1800
24%
540
65%
540
35%
984
September16th to endNight
50%
578
23%
1826
16%
578
58%
578
32%
1062
October1st to 15thNight
41%
660
23%
1980
15%
660
47%
660
31%
1188
October16th to endNight
34%
704
18%
2146
10%
704
43%
704
23%
1384
November1st to 15thNight
32%
742
23%
2318
13%
742
43%
742
27%
1409
November16th to endNight
21%
900
14%
2520
6%
900
29%
900
20%
1776
December1st to 15thNight
18%
900
11%
2520
3%
900
25%
900
15%
1919
December16th to endNight
18%
960
12%
2688
3%
960
27%
960
12%
2130

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
14%8%36%5%3445%7%36%
47917
Night
12%7%36%5%24446%41%
47053
Cloud CoverDay
26%6%25%423346%32%
47928
Night
25%6%25%423345%36%
47057
Cloud CoverDay
14%8%36%5%3445%7%36%
47926
Night
13%7%36%5%24446%41%
47057
TransparencyDay
45%6%14%21%10%1
47604
Night
42%5%13%23%13%1
46884
SeeingDay
16%8%29%26%13%4
6071
Night
16%8%32%29%11%1
16065

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
9%11%5%9%7%26%46%7%28%
1432
16th to endDay
13%13%5%12%7%3445%6%22%
1668
February1st to 15thDay
10%12%5%7%6%345%7%6%29%
1575
16th to endDay
15%9%36%5%34346%35%
1518
March1st to 15thDay
15%10%45%5%33348%35%
1895
16th to endDay
20%8%46%5%33446%31%
2160
April1st to 15thDay
17%10%47%43445%6%31%
2151
16th to endDay
23%10%36%423345%31%
2198
May1st to 15thDay
20%7%45%5%45%447%29%
2472
16th to endDay
15%6%36%5%35%45%8%35%
2617
June1st to 15thDay
13%6%26%5%2445%7%40%
2520
16th to endDay
10%5%25%6%35%5%6%8%39%
2520
July1st to 15thDay
6%4145%35%6%6%10%46%
2520
16th to endDay
8%425%5%35%6%7%9%40%
2651
August1st to 15thDay
8%5%25%5%4446%9%41%
2340
16th to endDay
12%6%245%245%5%8%41%
2346
September1st to 15thDay
12%5%243235%5%7%47%
2160
16th to endDay
13%6%35%434347%41%
1845
October1st to 15thDay
15%7%25%324335%45%
1650
16th to endDay
16%10%25%5%24336%39%
1724
November1st to 15thDay
11%7%36%5%25%35%7%42%
1539
16th to endDay
13%10%36%5%34347%38%
1440
December1st to 15thDay
16%11%49%6%25%45%7%25%
1440
16th to endDay
20%14%7%8%5%24346%21%
1536
January1st to 15thNight
11%9%5%7%7%35%45%6%32%
2506
16th to endNight
12%11%5%9%6%35%45%7%28%
2554
February1st to 15thNight
9%10%5%9%6%33446%34%
2285
16th to endNight
12%8%45%5%34446%40%
1955
March1st to 15thNight
15%9%35%323346%42%
2052
16th to endNight
16%9%36%5%35%46%5%32%
2064
April1st to 15thNight
16%8%45%5%25%435%38%
1797
16th to endNight
21%8%24423436%37%
1761
May1st to 15thNight
18%5%2342445%6%40%
1476
16th to endNight
11%5%25%42446%8%45%
1496
June1st to 15thNight
10%5%26%5%346%5%8%41%
1440
16th to endNight
8%425%4235%48%51%
1440
July1st to 15thNight
431432445%9%56%
1440
16th to endNight
5%21332446%10%54%
1515
August1st to 15thNight
5%4145%3446%9%50%
1620
16th to endNight
9%424413337%54%
1854
September1st to 15thNight
9%414323345%57%
1800
16th to endNight
8%5%3432335%8%50%
1826
October1st to 15thNight
13%5%23323345%50%
1980
16th to endNight
14%7%25%5%23346%42%
2146
November1st to 15thNight
10%7%35%423336%48%
2318
16th to endNight
15%9%36%5%24345%37%
2520
December1st to 15thNight
15%11%39%7%345%46%27%
2520
16th to endNight
19%14%48%6%34345%24%
2688

Percentage Cloud Cover SW (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
23%8%38%6%35%5%47%24%
1432
16th to endDay
28%10%411%7%2334418%
1668
February1st to 15thDay
24%11%47%5%2345%5%26%
1575
16th to endDay
27%8%25%434335%30%
1518
March1st to 15thDay
29%8%24322247%31%
1906
16th to endDay
31%7%25%5%33436%26%
2160
April1st to 15thDay
31%9%25%323445%26%
2151
16th to endDay
36%10%25%42233424%
2198
May1st to 15thDay
33%6%245%34345%25%
2472
16th to endDay
30%5%25%425%346%29%
2617
June1st to 15thDay
28%5%25%433445%32%
2520
16th to endDay
25%415%5%34446%33%
2520
July1st to 15thDay
22%3133335%5%8%37%
2520
16th to endDay
24%3245%3446%7%33%
2651
August1st to 15thDay
16%5%15%5%3445%9%38%
2340
16th to endDay
19%5%2442445%6%40%
2346
September1st to 15thDay
18%41332345%6%45%
2160
16th to endDay
21%5%14433348%38%
1845
October1st to 15thDay
24%6%14323335%42%
1650
16th to endDay
23%8%24423336%37%
1724
November1st to 15thDay
22%5%25%423346%38%
1539
16th to endDay
27%9%25%42223434%
1440
December1st to 15thDay
30%10%38%5%13436%21%
1440
16th to endDay
33%12%5%8%42233419%
1536
January1st to 15thNight
24%7%36%6%34445%28%
2506
16th to endNight
27%10%37%5%24445%24%
2554
February1st to 15thNight
23%9%47%5%22235%30%
2278
16th to endNight
24%7%35%423436%34%
1955
March1st to 15thNight
28%7%25%32233436%
2064
16th to endNight
28%8%25%4245%5%428%
2064
April1st to 15thNight
29%7%25%42333433%
1797
16th to endNight
34%7%1342233430%
1761
May1st to 15thNight
33%32332334434%
1475
16th to endNight
27%414323347%36%
1496
June1st to 15thNight
26%325%5%245%46%33%
1440
16th to endNight
23%42342335%5%42%
1440
July1st to 15thNight
21%213213347%47%
1440
16th to endNight
21%2222235%8%46%
1515
August1st to 15thNight
14%31343345%8%47%
1620
16th to endNight
16%414412345%51%
1854
September1st to 15thNight
15%314412335%53%
1800
16th to endNight
15%5%14322346%48%
1826
October1st to 15thNight
21%5%13322335%46%
1980
16th to endNight
22%6%24422345%39%
2146
November1st to 15thNight
23%6%24412235%43%
2318
16th to endNight
27%8%26%42333433%
2520
December1st to 15thNight
29%9%38%6%34435%21%
2520
16th to endNight
33%11%37%5%2333420%
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
9%11%6%9%6%37%46%7%28%
1432
16th to endDay
13%13%6%11%7%3445%6%23%
1668
February1st to 15thDay
10%12%5%7%6%245%7%7%29%
1575
16th to endDay
15%9%36%5%34347%35%
1518
March1st to 15thDay
15%10%45%5%3435%8%34%
1906
16th to endDay
20%8%46%5%33446%31%
2158
April1st to 15thDay
18%10%37%434446%31%
2151
16th to endDay
23%10%25%5%32346%31%
2198
May1st to 15thDay
20%7%45%5%35%447%30%
2472
16th to endDay
15%5%26%5%35%45%8%36%
2617
June1st to 15thDay
14%5%36%43446%7%40%
2520
16th to endDay
11%5%25%5%35%5%5%8%39%
2520
July1st to 15thDay
6%4145%35%5%7%10%46%
2520
16th to endDay
8%425%5%35%6%7%10%40%
2651
August1st to 15thDay
8%5%26%5%45%5%6%9%41%
2340
16th to endDay
13%5%2442446%8%42%
2346
September1st to 15thDay
12%5%143235%5%7%47%
2160
16th to endDay
14%5%35%43435%7%42%
1845
October1st to 15thDay
16%7%15%424345%46%
1650
16th to endDay
16%9%35%423436%39%
1724
November1st to 15thDay
11%7%26%424347%42%
1539
16th to endDay
13%9%36%5%24346%38%
1440
December1st to 15thDay
17%11%49%6%3445%7%25%
1440
16th to endDay
20%15%7%8%5%24346%21%
1536
January1st to 15thNight
11%9%47%7%35%45%6%32%
2506
16th to endNight
12%11%5%9%6%25%5%5%6%28%
2554
February1st to 15thNight
9%10%5%9%7%34346%34%
2278
16th to endNight
12%8%45%5%34446%40%
1955
March1st to 15thNight
15%9%35%323346%42%
2064
16th to endNight
16%9%36%5%25%5%6%6%32%
2064
April1st to 15thNight
17%8%45%6%24435%38%
1797
16th to endNight
22%7%24423445%37%
1761
May1st to 15thNight
19%5%2442445%6%40%
1475
16th to endNight
12%425%42446%7%45%
1496
June1st to 15thNight
11%426%5%25%6%6%7%42%
1440
16th to endNight
8%425%42345%7%52%
1440
July1st to 15thNight
5%21422435%9%57%
1440
16th to endNight
5%21232436%10%55%
1515
August1st to 15thNight
5%32343446%9%50%
1620
16th to endNight
9%424422346%54%
1854
September1st to 15thNight
10%41442244457%
1800
16th to endNight
8%5%2432435%6%51%
1826
October1st to 15thNight
13%5%24323346%51%
1980
16th to endNight
15%7%25%5%23346%42%
2146
November1st to 15thNight
10%8%345%23336%48%
2318
16th to endNight
15%9%37%5%34345%37%
2520
December1st to 15thNight
15%11%49%7%34446%27%
2520
16th to endNight
19%14%5%7%6%34345%24%
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
54%5%14%15%9%
1433
16th to endDay
61%5%13%14%5%
1668
February1st to 15thDay
51%6%14%19%7%
1576
16th to endDay
49%6%13%22%8%1
1518
March1st to 15thDay
47%6%15%20%8%
1906
16th to endDay
53%6%14%19%4
2160
April1st to 15thDay
52%6%12%19%8%
2151
16th to endDay
54%413%16%9%1
2198
May1st to 15thDay
53%6%13%18%7%
2472
16th to endDay
45%8%11%21%10%1
2621
June1st to 15thDay
41%7%13%24%12%
2520
16th to endDay
39%8%14%22%13%1
2520
July1st to 15thDay
31%9%17%26%13%2
2371
16th to endDay
36%9%16%21%14%1
2484
August1st to 15thDay
37%7%12%27%12%1
2326
16th to endDay
39%7%13%25%12%1
2346
September1st to 15thDay
33%5%14%29%15%
2160
16th to endDay
41%5%14%27%10%
1845
October1st to 15thDay
40%412%25%16%
1650
16th to endDay
46%414%23%9%
1724
November1st to 15thDay
40%5%13%25%12%1
1539
16th to endDay
47%5%19%20%7%
1440
December1st to 15thDay
57%6%12%16%5%
1440
16th to endDay
64%411%12%6%
1536
January1st to 15thNight
50%5%13%19%10%
2506
16th to endNight
54%5%14%16%8%
2554
February1st to 15thNight
50%413%20%10%
2288
16th to endNight
43%6%12%25%9%1
1955
March1st to 15thNight
42%5%13%25%11%1
2064
16th to endNight
51%6%15%20%6%
2064
April1st to 15thNight
47%410%21%13%1
1797
16th to endNight
47%6%9%21%11%2
1761
May1st to 15thNight
42%7%12%24%12%1
1476
16th to endNight
36%7%15%24%14%1
1498
June1st to 15thNight
38%8%13%24%15%
1440
16th to endNight
31%6%13%24%20%3
1440
July1st to 15thNight
23%6%15%32%18%2
1360
16th to endNight
22%8%18%31%16%3
1419
August1st to 15thNight
28%6%14%29%19%2
1610
16th to endNight
31%6%14%28%15%4
1854
September1st to 15thNight
29%5%10%29%25%
1800
16th to endNight
32%5%11%31%16%1
1826
October1st to 15thNight
34%413%25%19%2
1980
16th to endNight
42%5%14%21%14%
2146
November1st to 15thNight
38%412%24%18%2
2318
16th to endNight
48%5%13%23%6%1
2520
December1st to 15thNight
57%412%17%6%
2520
16th to endNight
62%411%13%6%
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
21%11%37%25%31
90
16th to endDay
23%12%40%18%31
96
February1st to 15thDay
12%25%38%18%4
90
16th to endDay
34%9%25%22%7%
81
March1st to 15thDay
22%17%38%15%5%
90
16th to endDay
33%11%25%20%6%2
144
April1st to 15thDay
21%11%31%22%11%
270
16th to endDay
31%12%25%21%8%1
308
May1st to 15thDay
23%12%31%22%8%2
468
16th to endDay
18%13%30%22%12%3
517
June1st to 15thDay
15%8%29%30%14%2
495
16th to endDay
12%7%35%24%15%3
495
July1st to 15thDay
8%326%32%17%10%
475
16th to endDay
8%426%34%19%7%
515
August1st to 15thDay
8%224%35%21%7%
493
16th to endDay
15%5%22%30%17%9%
386
September1st to 15thDay
11%424%26%22%9%
315
16th to endDay
16%9%29%24%15%4
191
October1st to 15thDay
13%11%27%25%17%4
90
16th to endDay
22%10%31%27%8%
96
November1st to 15thDay
5%12%38%28%7%6%
90
16th to endDay
37%13%32%10%5%1
90
December1st to 15thDay
22%16%44%15%1
90
16th to endDay
34%17%35%10%2
96
January1st to 15thNight
16%14%37%24%7%
900
16th to endNight
18%11%40%24%4
960
February1st to 15thNight
16%11%38%24%7%
880
16th to endNight
16%13%37%25%7%
693
March1st to 15thNight
18%10%35%28%5%1
624
16th to endNight
20%9%33%26%8%1
576
April1st to 15thNight
20%11%36%26%4
539
16th to endNight
25%5%33%27%6%1
540
May1st to 15thNight
19%7%35%29%6%
540
16th to endNight
14%6%30%37%11%1
563
June1st to 15thNight
14%5%26%41%12%
540
16th to endNight
10%328%42%13%
540
July1st to 15thNight
6%123%39%26%2
510
16th to endNight
6%19%45%24%2
564
August1st to 15thNight
7%18%46%24%2
539
16th to endNight
11%220%37%23%4
573
September1st to 15thNight
10%324%34%22%5%
540
16th to endNight
11%6%27%34%19%1
578
October1st to 15thNight
16%7%32%25%16%1
660
16th to endNight
20%8%31%30%8%
704
November1st to 15thNight
13%12%37%26%8%1
742
16th to endNight
19%13%39%19%8%
900
December1st to 15thNight
21%11%39%22%4
900
16th to endNight
26%11%32%23%5%
960
Page generated at 2017-09-19 06:32:22. Version ac04

Copyright 2017 A. Danko


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