Concordia College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Concordia College Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
33%
16201
14%
46779
8%
16154
39%
16154
20%
32294

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
27%
900
9%
2667
6%
895
31%
895
13%
2073
January16th to endNight
24%
960
11%
2649
4%
960
29%
960
13%
2053
February1st to 15thNight
31%
880
9%
2288
4%
876
34%
876
16%
1744
February16th to endNight
32%
731
13%
1993
7%
731
37%
731
16%
1517
March1st to 15thNight
28%
609
13%
2049
7%
609
34%
609
16%
1456
March16th to endNight
30%
576
14%
2112
11%
576
37%
576
16%
1426
April1st to 15thNight
29%
539
16%
1760
10%
539
40%
539
21%
1115
April16th to endNight
25%
540
16%
1620
7%
540
36%
540
15%
1167
May1st to 15thNight
29%
540
12%
1573
5%
540
33%
540
17%
1108
May16th to endNight
35%
563
13%
1397
3%
561
39%
561
27%
920
June1st to 15thNight
40%
540
13%
1260
5%
540
44%
540
29%
833
June16th to endNight
47%
540
13%
1260
6%
540
51%
540
35%
788
July1st to 15thNight
55%
510
16%
1190
7%
510
58%
510
44%
725
July16th to endNight
52%
564
19%
1359
8%
531
58%
531
43%
771
August1st to 15thNight
59%
539
21%
1610
14%
536
64%
536
37%
887
August16th to endNight
52%
573
22%
1719
20%
573
59%
573
36%
967
September1st to 15thNight
51%
540
22%
1846
20%
540
60%
540
34%
973
September16th to endNight
45%
498
24%
1837
18%
498
57%
498
30%
993
October1st to 15thNight
33%
627
21%
1947
13%
627
42%
627
22%
1239
October16th to endNight
28%
797
15%
2205
7%
797
34%
797
21%
1551
November1st to 15thNight
29%
875
18%
2389
7%
875
36%
875
21%
1689
November16th to endNight
25%
900
13%
2520
7%
900
30%
900
17%
1850
December1st to 15thNight
23%
900
7%
2649
4%
900
25%
900
11%
2091
December16th to endNight
16%
960
9%
2880
3%
960
22%
960
9%
2358

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%36%5%3445%7%37%
48015
Night
11%8%36%5%3445%6%38%
46937
Cloud CoverDay
13%7%36%5%3445%7%37%
48025
Night
12%8%36%5%3445%6%38%
46940
Cloud CoverDay
13%7%36%6%3445%7%37%
48026
Night
11%8%36%5%35%45%6%38%
46941
Cloud CoverDay
13%8%36%5%3445%7%37%
48024
Night
11%8%36%5%35%45%6%38%
46941
TransparencyDay
46%7%14%22%8%
47690
Night
45%6%13%22%9%1
46780
SeeingDay
14%14%26%27%14%2
6187
Night
13%20%26%29%10%
16201

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
8%11%6%10%9%36%47%5%26%
1271
16th to endDay
9%14%6%11%10%5%5%5%5%7%19%
1575
February1st to 15thDay
8%11%6%8%7%5%6%5%6%5%27%
1575
16th to endDay
10%12%5%9%9%6%6%6%7%8%17%
1491
March1st to 15thDay
15%9%5%7%7%35%446%28%
1900
16th to endDay
13%11%48%7%25%5%5%7%27%
2112
April1st to 15thDay
13%8%27%5%3445%8%37%
2184
16th to endDay
22%10%35%43435%6%31%
2340
May1st to 15thDay
20%8%25%6%24445%33%
2376
16th to endDay
16%6%25%5%3445%7%37%
2716
June1st to 15thDay
18%425%5%25%46%8%36%
2700
16th to endDay
10%3145%345%6%9%44%
2700
July1st to 15thDay
8%3144245%5%8%52%
2700
16th to endDay
5%3134245%7%9%51%
2712
August1st to 15thDay
9%424435%5%6%9%44%
2340
16th to endDay
11%413423445%53%
2483
September1st to 15thDay
11%324424447%50%
2110
16th to endDay
14%424413447%48%
1828
October1st to 15thDay
16%7%25%5%24345%42%
1672
16th to endDay
22%10%35%423345%33%
1667
November1st to 15thDay
12%9%48%424435%39%
1469
16th to endDay
12%13%5%8%8%3344430%
1440
December1st to 15thDay
12%14%6%9%8%46%5%6%421%
1310
16th to endDay
13%16%5%10%8%35%445%21%
1344
January1st to 15thNight
8%10%6%10%9%47%7%6%5%24%
2667
16th to endNight
11%11%5%9%6%46%6%6%6%24%
2649
February1st to 15thNight
8%10%49%6%46%5%5%6%30%
2285
16th to endNight
8%9%49%8%47%6%6%6%28%
1993
March1st to 15thNight
13%9%5%8%6%44447%32%
2037
16th to endNight
14%8%47%5%24446%36%
2112
April1st to 15thNight
15%6%35%42445%7%42%
1760
16th to endNight
21%9%35%423345%35%
1620
May1st to 15thNight
18%7%26%6%24346%37%
1573
16th to endNight
10%425%425%6%6%8%44%
1396
June1st to 15thNight
11%315%42445%10%45%
1260
16th to endNight
6%123425%5%5%9%52%
1260
July1st to 15thNight
5%21332445%8%60%
1260
16th to endNight
421332336%8%58%
1453
August1st to 15thNight
7%31432345%7%56%
1620
16th to endNight
8%32322445%6%56%
1719
September1st to 15thNight
9%313213446%58%
1846
16th to endNight
11%413313346%55%
1837
October1st to 15thNight
14%5%25%43445%6%43%
1947
16th to endNight
19%9%3432435%6%37%
2205
November1st to 15thNight
11%10%47%425%45%5%37%
2389
16th to endNight
13%9%46%6%35%45%7%32%
2520
December1st to 15thNight
10%15%7%9%8%45%445%24%
2649
16th to endNight
13%18%6%10%8%3434421%
2880

Percentage Cloud Cover NW (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
8%11%5%10%10%35%48%5%26%
1272
16th to endDay
9%13%6%11%9%5%6%45%6%20%
1575
February1st to 15thDay
9%11%6%8%8%46%5%5%6%27%
1575
16th to endDay
11%12%5%9%9%6%5%5%7%8%18%
1491
March1st to 15thDay
15%9%5%7%6%35%446%28%
1911
16th to endDay
14%11%48%7%25%5%5%7%27%
2110
April1st to 15thDay
13%7%36%5%34448%37%
2184
16th to endDay
22%10%45%434346%31%
2340
May1st to 15thDay
21%8%35%6%24345%33%
2376
16th to endDay
17%6%245%3445%7%38%
2716
June1st to 15thDay
19%425%5%35%45%8%36%
2700
16th to endDay
11%3145%245%6%9%44%
2700
July1st to 15thDay
8%3144245%5%8%52%
2700
16th to endDay
5%31342447%10%51%
2712
August1st to 15thDay
9%425%425%5%7%9%44%
2340
16th to endDay
11%413423446%53%
2483
September1st to 15thDay
12%324423447%50%
2110
16th to endDay
14%424413347%48%
1828
October1st to 15thDay
17%7%26%5%23345%42%
1672
16th to endDay
23%10%35%423345%33%
1667
November1st to 15thDay
13%8%48%434335%39%
1469
16th to endDay
12%13%5%9%7%3344430%
1440
December1st to 15thDay
12%14%6%9%8%5%6%5%5%421%
1310
16th to endDay
13%16%6%10%7%45%445%21%
1344
January1st to 15thNight
9%10%6%10%8%37%7%5%5%25%
2667
16th to endNight
11%11%410%6%46%6%6%6%24%
2649
February1st to 15thNight
9%10%5%8%6%46%5%5%5%30%
2278
16th to endNight
8%10%410%7%47%6%6%6%28%
1993
March1st to 15thNight
14%9%5%8%6%34437%32%
2049
16th to endNight
14%8%47%5%34346%36%
2110
April1st to 15thNight
15%6%25%42445%7%42%
1760
16th to endNight
22%9%35%5%24345%35%
1620
May1st to 15thNight
18%8%26%5%24445%37%
1572
16th to endNight
11%415%3346%7%8%44%
1397
June1st to 15thNight
12%3245%2445%10%45%
1260
16th to endNight
7%123425%5%5%9%52%
1260
July1st to 15thNight
5%213224348%60%
1260
16th to endNight
421331445%8%59%
1453
August1st to 15thNight
7%31432335%7%56%
1620
16th to endNight
8%313224446%57%
1719
September1st to 15thNight
9%313213446%58%
1846
16th to endNight
12%413323336%55%
1837
October1st to 15thNight
15%5%2443445%5%44%
1947
16th to endNight
19%9%2442435%5%38%
2205
November1st to 15thNight
11%10%46%42445%5%37%
2389
16th to endNight
14%9%46%6%345%5%6%32%
2520
December1st to 15thNight
11%14%7%9%9%45%44424%
2649
16th to endNight
13%18%6%10%8%3424421%
2880

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
8%11%6%9%10%35%48%5%26%
1271
16th to endDay
9%13%6%11%9%5%6%5%5%6%20%
1575
February1st to 15thDay
8%12%5%8%8%46%5%5%6%27%
1575
16th to endDay
10%12%5%10%9%5%6%6%7%7%17%
1491
March1st to 15thDay
15%9%5%7%6%35%5%46%28%
1911
16th to endDay
13%12%48%7%25%45%7%27%
2112
April1st to 15thDay
13%7%36%6%35%35%8%37%
2184
16th to endDay
22%10%46%43435%6%31%
2340
May1st to 15thDay
20%8%35%6%24346%33%
2376
16th to endDay
17%6%25%5%3445%6%37%
2716
June1st to 15thDay
19%435%5%25%45%8%35%
2700
16th to endDay
10%3145%245%6%10%43%
2700
July1st to 15thDay
8%3144245%5%9%51%
2700
16th to endDay
5%3134345%7%10%50%
2712
August1st to 15thDay
9%415%425%5%6%9%44%
2340
16th to endDay
11%414423436%53%
2483
September1st to 15thDay
11%3245%23447%50%
2110
16th to endDay
14%424423347%47%
1828
October1st to 15thDay
17%6%25%5%23335%42%
1672
16th to endDay
22%10%35%5%23335%33%
1667
November1st to 15thDay
12%9%48%5%34335%38%
1469
16th to endDay
12%13%5%9%8%2444430%
1440
December1st to 15thDay
12%13%6%10%8%46%6%4421%
1310
16th to endDay
13%17%5%10%7%5%5%445%21%
1344
January1st to 15thNight
8%10%6%10%9%37%7%5%5%25%
2667
16th to endNight
11%11%410%6%47%6%6%6%24%
2649
February1st to 15thNight
9%11%5%8%6%46%5%5%5%30%
2278
16th to endNight
8%10%49%7%47%6%5%6%28%
1993
March1st to 15thNight
14%9%5%8%5%34447%32%
2049
16th to endNight
13%9%38%5%34346%36%
2112
April1st to 15thNight
14%6%3442345%7%41%
1760
16th to endNight
22%8%35%5%24335%35%
1620
May1st to 15thNight
17%8%35%6%15%445%37%
1572
16th to endNight
10%425%3246%6%8%44%
1396
June1st to 15thNight
11%31443446%10%45%
1260
16th to endNight
6%223435%5%5%10%51%
1260
July1st to 15thNight
4213224448%60%
1260
16th to endNight
431332345%9%59%
1453
August1st to 15thNight
6%31432445%8%55%
1620
16th to endNight
8%41332445%6%57%
1719
September1st to 15thNight
9%313214347%58%
1846
16th to endNight
12%413323336%55%
1837
October1st to 15thNight
14%6%24434446%43%
1947
16th to endNight
18%9%3442335%5%37%
2205
November1st to 15thNight
11%10%47%425%45%5%37%
2389
16th to endNight
14%9%37%6%45%45%7%32%
2520
December1st to 15thNight
11%14%7%9%9%45%44424%
2649
16th to endNight
13%18%7%10%8%3434421%
2880

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
7%11%7%9%10%35%48%6%25%
1271
16th to endDay
9%14%6%11%9%5%6%5%5%6%19%
1575
February1st to 15thDay
8%12%5%8%7%46%5%5%6%27%
1575
16th to endDay
10%13%5%10%8%5%6%6%7%8%17%
1491
March1st to 15thDay
15%9%5%7%6%35%5%5%6%28%
1911
16th to endDay
13%12%5%8%7%35%45%7%27%
2110
April1st to 15thDay
13%7%26%6%35%45%8%36%
2184
16th to endDay
21%10%36%42435%5%31%
2340
May1st to 15thDay
20%8%36%6%24345%33%
2376
16th to endDay
16%6%345%345%5%7%37%
2716
June1st to 15thDay
18%435%5%25%36%8%35%
2700
16th to endDay
10%3245%25%5%6%10%43%
2700
July1st to 15thDay
8%3144245%5%9%51%
2700
16th to endDay
5%3144245%7%10%50%
2712
August1st to 15thDay
8%5%15%426%5%6%9%43%
2340
16th to endDay
10%413424447%52%
2483
September1st to 15thDay
11%4245%24447%49%
2110
16th to endDay
14%424413447%47%
1828
October1st to 15thDay
16%7%35%423335%42%
1672
16th to endDay
22%11%35%433336%33%
1667
November1st to 15thDay
12%9%48%434435%38%
1469
16th to endDay
12%13%5%9%8%23435%29%
1440
December1st to 15thDay
12%13%6%10%8%5%5%6%5%421%
1310
16th to endDay
13%17%5%11%7%5%5%445%20%
1344
January1st to 15thNight
8%11%6%10%9%37%7%5%5%24%
2667
16th to endNight
11%11%410%6%47%6%6%6%24%
2649
February1st to 15thNight
8%11%5%8%7%37%5%5%5%30%
2278
16th to endNight
8%10%49%8%47%5%5%7%27%
1993
March1st to 15thNight
13%9%49%5%34447%31%
2049
16th to endNight
13%9%38%5%34346%36%
2112
April1st to 15thNight
14%6%35%32345%7%42%
1760
16th to endNight
21%9%35%5%23245%35%
1620
May1st to 15thNight
17%7%35%6%24445%36%
1572
16th to endNight
10%425%4245%7%7%45%
1396
June1st to 15thNight
11%415%42346%9%44%
1260
16th to endNight
6%213426%46%10%51%
1260
July1st to 15thNight
4213324448%60%
1260
16th to endNight
331332346%8%58%
1453
August1st to 15thNight
6%31432346%8%55%
1620
16th to endNight
8%41322435%5%56%
1719
September1st to 15thNight
9%313224347%58%
1846
16th to endNight
11%413323346%55%
1837
October1st to 15thNight
14%6%25%434447%43%
1947
16th to endNight
18%9%34423445%37%
2205
November1st to 15thNight
11%10%46%435%45%5%37%
2389
16th to endNight
14%9%37%6%45%45%6%32%
2520
December1st to 15thNight
11%15%7%8%9%45%445%24%
2649
16th to endNight
13%18%7%10%8%3434421%
2880

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
56%6%13%18%5%
1272
16th to endDay
63%6%14%12%2
1575
February1st to 15thDay
56%6%14%17%4
1576
16th to endDay
61%8%12%13%3
1491
March1st to 15thDay
55%7%14%17%4
1911
16th to endDay
56%7%15%18%3
2112
April1st to 15thDay
44%6%16%21%9%1
2184
16th to endDay
55%5%11%17%10%
2340
May1st to 15thDay
52%5%12%22%6%
2376
16th to endDay
45%6%13%24%9%
2720
June1st to 15thDay
46%7%15%23%7%
2700
16th to endDay
35%8%18%26%11%
2700
July1st to 15thDay
29%7%15%32%13%1
2541
16th to endDay
26%9%20%30%12%1
2543
August1st to 15thDay
33%9%16%28%10%2
2326
16th to endDay
31%6%15%30%13%1
2483
September1st to 15thDay
33%6%15%33%10%
2110
16th to endDay
36%6%16%32%8%
1828
October1st to 15thDay
44%6%14%24%10%
1672
16th to endDay
54%5%13%18%8%
1667
November1st to 15thDay
48%6%15%18%11%
1469
16th to endDay
57%7%13%14%6%
1440
December1st to 15thDay
63%7%11%14%2
1310
16th to endDay
65%7%10%12%4
1344
January1st to 15thNight
58%7%11%16%6%
2667
16th to endNight
57%7%14%15%5%
2649
February1st to 15thNight
52%8%14%18%5%
2288
16th to endNight
54%7%12%17%7%
1993
March1st to 15thNight
51%6%15%19%6%
2049
16th to endNight
48%6%16%22%5%
2112
April1st to 15thNight
41%5%14%25%11%1
1760
16th to endNight
52%5%9%20%10%2
1620
May1st to 15thNight
47%7%11%18%13%2
1573
16th to endNight
35%8%14%26%12%2
1398
June1st to 15thNight
34%6%16%30%10%1
1260
16th to endNight
26%8%19%28%12%3
1260
July1st to 15thNight
23%7%15%32%18%1
1190
16th to endNight
21%7%17%31%18%3
1359
August1st to 15thNight
25%6%14%31%18%3
1610
16th to endNight
27%7%13%30%19%1
1719
September1st to 15thNight
26%6%14%37%14%1
1846
16th to endNight
31%5%13%33%16%
1837
October1st to 15thNight
41%5%13%27%10%2
1947
16th to endNight
46%6%14%23%8%
2205
November1st to 15thNight
46%6%11%22%10%1
2389
16th to endNight
50%7%17%14%8%
2520
December1st to 15thNight
61%6%13%13%4
2649
16th to endNight
67%5%10%12%3
2880

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
11%8%30%36%12%1
90
16th to endDay
23%6%23%34%11%
96
February1st to 15thDay
13%14%41%27%3
90
16th to endDay
19%8%45%20%4
81
March1st to 15thDay
16%15%34%31%11
90
16th to endDay
15%437%25%16%1
96
April1st to 15thDay
15%24%27%20%11%
303
16th to endDay
26%21%23%18%8%2
450
May1st to 15thDay
17%21%28%20%10%1
468
16th to endDay
18%18%22%24%11%3
517
June1st to 15thDay
15%19%25%24%13%1
495
16th to endDay
9%18%28%27%12%3
495
July1st to 15thDay
8%12%21%30%21%6%
475
16th to endDay
415%24%32%18%4
515
August1st to 15thDay
8%9%19%33%23%6%
493
16th to endDay
11%9%23%29%21%4
523
September1st to 15thDay
8%8%30%33%18%1
265
16th to endDay
22%7%30%23%11%4
93
October1st to 15thDay
16%7%36%27%11%
90
16th to endDay
20%16%25%22%13%1
96
November1st to 15thDay
14%5%27%30%18%3
90
16th to endDay
35%13%22%25%3
90
December1st to 15thDay
20%234%30%13%
90
16th to endDay
20%12%34%19%10%2
96
January1st to 15thNight
11%22%29%25%9%1
900
16th to endNight
14%24%28%25%5%
960
February1st to 15thNight
13%23%22%27%10%2
880
16th to endNight
9%22%26%25%13%2
731
March1st to 15thNight
12%21%28%26%10%
609
16th to endNight
14%23%27%23%10%1
576
April1st to 15thNight
14%24%27%26%6%
539
16th to endNight
23%23%22%20%9%
540
May1st to 15thNight
16%22%26%26%6%
540
16th to endNight
10%22%26%28%11%
563
June1st to 15thNight
11%20%23%36%7%
540
16th to endNight
6%19%22%38%12%
540
July1st to 15thNight
6%13%21%40%18%
510
16th to endNight
418%20%39%16%1
564
August1st to 15thNight
7%11%15%43%19%1
539
16th to endNight
8%10%25%32%20%1
573
September1st to 15thNight
8%10%25%40%13%1
540
16th to endNight
9%13%29%33%13%
498
October1st to 15thNight
17%17%26%29%8%
627
16th to endNight
23%13%28%25%8%
797
November1st to 15thNight
14%20%29%26%8%
875
16th to endNight
15%23%29%24%5%1
900
December1st to 15thNight
14%23%28%26%6%
900
16th to endNight
20%22%27%22%6%
960
Page generated at 2017-09-18 07:38:22. Version ac04

Copyright 2017 A. Danko


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