Aurora Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aurora Center clear sky chart from 2005-11-05 to 2017-12-01.

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
40%
16403
20%
47783
11%
16358
48%
16358
31%
29386

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
33%
900
15%
2506
8%
895
39%
895
25%
1680
January16th to endNight
30%
960
18%
2624
7%
960
38%
960
25%
1782
February1st to 15thNight
29%
874
12%
2283
4%
870
34%
870
22%
1639
February16th to endNight
35%
632
21%
1894
9%
632
45%
632
27%
1193
March1st to 15thNight
33%
642
18%
2082
10%
642
41%
642
25%
1310
March16th to endNight
30%
576
17%
2112
12%
576
40%
576
21%
1319
April1st to 15thNight
32%
539
19%
1795
11%
539
46%
539
27%
1077
April16th to endNight
33%
540
18%
1620
13%
540
43%
540
23%
1083
May1st to 15thNight
37%
540
19%
1620
10%
540
46%
540
30%
984
May16th to endNight
40%
561
14%
1632
6%
561
45%
561
28%
1042
June1st to 15thNight
47%
540
16%
1260
4%
540
50%
540
38%
830
June16th to endNight
57%
540
21%
1275
8%
540
61%
540
56%
721
July1st to 15thNight
60%
510
16%
1360
6%
510
63%
510
45%
774
July16th to endNight
65%
564
25%
1468
15%
531
68%
531
51%
767
August1st to 15thNight
64%
539
20%
1610
17%
536
68%
536
43%
874
August16th to endNight
57%
573
27%
1728
23%
573
67%
573
44%
913
September1st to 15thNight
52%
540
24%
1920
20%
540
63%
540
36%
980
September16th to endNight
46%
537
29%
1980
22%
537
60%
537
36%
979
October1st to 15thNight
36%
621
27%
2061
18%
621
46%
621
28%
1194
October16th to endNight
41%
885
27%
2421
14%
885
48%
885
36%
1444
November1st to 15thNight
40%
950
26%
2470
11%
950
48%
950
37%
1484
November16th to endNight
38%
975
25%
2646
14%
975
45%
975
34%
1635
December1st to 15thNight
29%
905
15%
2602
7%
905
37%
905
23%
1757
December16th to endNight
31%
960
17%
2814
8%
960
41%
960
22%
1925

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%6%25%42445%7%46%
48634
Night
9%6%2442445%7%48%
47956
Cloud CoverDay
11%6%25%42445%7%46%
48644
Night
9%6%24424447%48%
47959
Cloud CoverDay
11%6%25%42445%7%45%
48645
Night
9%6%25%42445%7%48%
47960
Cloud CoverDay
10%6%25%42445%7%45%
48643
Night
9%6%25%42445%7%48%
47960
TransparencyDay
37%5%15%26%13%1
48325
Night
35%5%14%25%16%2
47783
SeeingDay
13%7%31%31%14%1
6298
Night
12%8%34%34%10%
16406

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
6%9%5%6%6%35%35%7%40%
1432
16th to endDay
8%10%48%6%34447%37%
1599
February1st to 15thDay
11%9%38%6%36%447%34%
1589
16th to endDay
8%8%37%6%245%48%39%
1580
March1st to 15thDay
12%7%37%5%33337%42%
1867
16th to endDay
16%9%47%6%34345%34%
2112
April1st to 15thDay
16%43432445%7%43%
2152
16th to endDay
21%8%35%425%446%34%
2340
May1st to 15thDay
15%5%25%43445%6%43%
2331
16th to endDay
14%5%35%42435%8%40%
2481
June1st to 15thDay
14%5%25%42445%7%44%
2697
16th to endDay
6%3133235%6%7%55%
2682
July1st to 15thDay
6%32342346%8%55%
2520
16th to endDay
42133245%5%8%57%
2599
August1st to 15thDay
7%4145%35%5%6%8%44%
2340
16th to endDay
7%31332435%7%55%
2471
September1st to 15thDay
11%5%14423346%52%
2040
16th to endDay
9%313312346%60%
1980
October1st to 15thDay
14%6%14322335%51%
1887
16th to endDay
12%5%2432335%6%50%
1800
November1st to 15thDay
5%6%2442345%7%51%
1718
16th to endDay
8%6%37%4235%5%7%45%
1641
December1st to 15thDay
10%12%37%6%245%47%34%
1369
16th to endDay
10%10%5%10%6%25%35%6%33%
1407
January1st to 15thNight
6%7%37%6%35%5%5%8%39%
2506
16th to endNight
6%10%36%5%3446%7%39%
2624
February1st to 15thNight
12%9%46%5%35%446%37%
2280
16th to endNight
8%6%25%5%25%5%5%5%47%
1894
March1st to 15thNight
12%6%25%5%2435%7%44%
2070
16th to endNight
12%7%35%5%2345%7%41%
2112
April1st to 15thNight
14%6%1432435%8%45%
1795
16th to endNight
17%6%245%24438%39%
1620
May1st to 15thNight
13%5%24324446%49%
1620
16th to endNight
13%6%144235%5%6%45%
1630
June1st to 15thNight
9%42442445%8%49%
1260
16th to endNight
5%112313347%64%
1275
July1st to 15thNight
5%21342445%7%57%
1440
16th to endNight
31133235%5%8%61%
1568
August1st to 15thNight
3213425%5%8%9%53%
1620
16th to endNight
5%31332345%7%59%
1728
September1st to 15thNight
9%312423346%58%
1920
16th to endNight
8%312423345%60%
1980
October1st to 15thNight
15%42432334451%
2061
16th to endNight
12%414423346%53%
2421
November1st to 15thNight
7%5%2432335%7%53%
2470
16th to endNight
6%6%2442445%8%49%
2646
December1st to 15thNight
9%9%46%5%35%446%40%
2602
16th to endNight
10%9%5%7%6%24436%39%
2814

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
5%11%46%6%45%35%6%41%
1433
16th to endDay
7%10%38%6%3445%6%37%
1599
February1st to 15thDay
11%8%38%6%35%447%34%
1589
16th to endDay
8%7%47%6%2445%9%39%
1580
March1st to 15thDay
11%8%47%5%24247%42%
1878
16th to endDay
15%10%46%6%2435%5%34%
2110
April1st to 15thDay
16%5%3432445%6%44%
2152
16th to endDay
21%7%36%334446%35%
2340
May1st to 15thDay
14%5%25%43345%7%43%
2331
16th to endDay
15%5%25%5%2345%7%41%
2481
June1st to 15thDay
14%42442445%7%44%
2697
16th to endDay
7%21332445%7%56%
2682
July1st to 15thDay
6%31342345%7%55%
2520
16th to endDay
421332446%8%57%
2599
August1st to 15thDay
7%4246%25%6%6%7%45%
2340
16th to endDay
8%314423447%56%
2471
September1st to 15thDay
11%413423346%53%
2040
16th to endDay
9%31332346%60%
1980
October1st to 15thDay
15%5%2432333452%
1887
16th to endDay
12%6%24313347%50%
1800
November1st to 15thDay
6%6%2442346%6%51%
1718
16th to endDay
8%7%27%4235%5%7%45%
1641
December1st to 15thDay
10%12%46%6%25%5%5%6%34%
1369
16th to endDay
10%9%5%9%6%25%35%5%34%
1407
January1st to 15thNight
6%7%37%6%345%5%8%40%
2506
16th to endNight
6%9%36%6%245%5%8%40%
2624
February1st to 15thNight
12%9%46%5%35%445%38%
2273
16th to endNight
8%6%25%5%25%5%5%6%47%
1894
March1st to 15thNight
12%6%245%2435%7%44%
2082
16th to endNight
12%8%35%42345%7%41%
2110
April1st to 15thNight
13%7%14333347%46%
1795
16th to endNight
17%7%245%33448%40%
1620
May1st to 15thNight
13%5%2332345%5%49%
1619
16th to endNight
14%5%24423446%46%
1631
June1st to 15thNight
10%42343445%8%49%
1260
16th to endNight
5%112323338%64%
1275
July1st to 15thNight
5%1134245%5%8%57%
1440
16th to endNight
311332346%7%61%
1568
August1st to 15thNight
32134245%7%10%53%
1620
16th to endNight
5%31331345%7%60%
1728
September1st to 15thNight
9%213423346%58%
1920
16th to endNight
8%213422345%61%
1980
October1st to 15thNight
15%424323335%51%
2061
16th to endNight
11%413314345%54%
2421
November1st to 15thNight
7%5%24324347%53%
2470
16th to endNight
7%6%34424448%49%
2646
December1st to 15thNight
9%9%5%6%5%35%446%40%
2602
16th to endNight
11%9%5%7%5%33346%39%
2814

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
5%10%5%6%7%34347%40%
1432
16th to endDay
8%10%48%6%25%447%36%
1599
February1st to 15thDay
11%9%48%6%36%347%34%
1589
16th to endDay
8%8%47%5%245%5%8%38%
1580
March1st to 15thDay
12%7%37%5%23337%42%
1878
16th to endDay
16%8%47%6%3445%5%35%
2112
April1st to 15thDay
16%425%3245%47%43%
2152
16th to endDay
21%8%35%43445%6%33%
2340
May1st to 15thDay
15%5%25%43435%6%43%
2331
16th to endDay
15%6%25%42445%8%40%
2481
June1st to 15thDay
14%5%2442345%7%44%
2697
16th to endDay
6%3133235%6%8%55%
2682
July1st to 15thDay
6%2234235%5%7%55%
2520
16th to endDay
42133245%5%8%57%
2599
August1st to 15thDay
7%4245%35%6%6%7%45%
2340
16th to endDay
7%31342335%7%55%
2471
September1st to 15thDay
11%423423336%52%
2040
16th to endDay
9%32232346%60%
1980
October1st to 15thDay
15%6%14322335%51%
1887
16th to endDay
12%6%24323346%49%
1800
November1st to 15thDay
5%6%2442445%7%51%
1718
16th to endDay
8%6%36%4245%5%7%45%
1641
December1st to 15thDay
10%12%46%6%345%5%6%34%
1369
16th to endDay
10%10%5%10%5%35%25%6%33%
1407
January1st to 15thNight
6%7%37%6%35%6%5%8%39%
2506
16th to endNight
6%10%37%5%345%6%7%39%
2624
February1st to 15thNight
12%9%46%5%35%445%38%
2273
16th to endNight
8%6%26%5%246%45%47%
1894
March1st to 15thNight
11%7%345%2435%7%43%
2082
16th to endNight
12%8%35%42346%7%40%
2112
April1st to 15thNight
14%6%1432435%7%45%
1795
16th to endNight
16%7%25%424447%40%
1620
May1st to 15thNight
13%5%242245%36%49%
1619
16th to endNight
13%6%2442345%6%45%
1630
June1st to 15thNight
9%5%144245%5%9%48%
1260
16th to endNight
5%212313247%64%
1275
July1st to 15thNight
5%213425%45%8%57%
1440
16th to endNight
311331445%7%61%
1568
August1st to 15thNight
3213325%5%8%9%54%
1620
16th to endNight
5%31331435%7%59%
1728
September1st to 15thNight
8%312423346%58%
1920
16th to endNight
7%322313345%60%
1980
October1st to 15thNight
15%414323345%51%
2061
16th to endNight
12%414323346%53%
2421
November1st to 15thNight
7%6%2432345%7%52%
2470
16th to endNight
6%6%244345%47%49%
2646
December1st to 15thNight
9%9%46%6%35%446%40%
2602
16th to endNight
11%9%47%6%24446%39%
2814

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
5%10%5%6%7%4435%7%39%
1432
16th to endDay
8%10%49%5%345%5%7%36%
1599
February1st to 15thDay
11%9%38%6%35%447%33%
1589
16th to endDay
7%8%47%5%245%5%8%38%
1580
March1st to 15thDay
12%7%37%6%22347%42%
1878
16th to endDay
16%9%47%6%34445%34%
2110
April1st to 15thDay
16%5%25%42445%6%43%
2152
16th to endDay
21%8%35%42445%6%33%
2340
May1st to 15thDay
15%5%2443435%7%43%
2331
16th to endDay
14%6%25%42445%8%40%
2481
June1st to 15thDay
14%5%2442345%8%43%
2697
16th to endDay
7%21332445%8%55%
2682
July1st to 15thDay
6%2144235%5%8%55%
2520
16th to endDay
4212325%46%8%57%
2599
August1st to 15thDay
7%4245%35%6%7%6%45%
2340
16th to endDay
7%31342335%7%55%
2471
September1st to 15thDay
11%424423435%52%
2040
16th to endDay
9%323212336%60%
1980
October1st to 15thDay
15%6%2332233452%
1887
16th to endDay
12%5%2432245%6%50%
1800
November1st to 15thDay
5%6%243245%5%6%51%
1718
16th to endDay
8%6%36%4235%5%7%45%
1641
December1st to 15thDay
10%12%46%6%345%5%6%34%
1369
16th to endDay
10%10%5%10%5%35%25%6%33%
1407
January1st to 15thNight
5%7%37%5%35%6%5%7%39%
2506
16th to endNight
6%10%37%5%345%6%7%38%
2624
February1st to 15thNight
12%9%47%435%445%37%
2273
16th to endNight
7%6%36%5%245%5%5%46%
1894
March1st to 15thNight
11%7%345%24447%43%
2082
16th to endNight
12%8%35%42446%7%40%
2112
April1st to 15thNight
14%6%2432435%7%45%
1795
16th to endNight
17%7%24434446%40%
1620
May1st to 15thNight
13%5%24224445%49%
1619
16th to endNight
13%6%2442345%6%45%
1630
June1st to 15thNight
9%5%14425%5%49%48%
1260
16th to endNight
5%212214248%64%
1275
July1st to 15thNight
4213425%5%47%57%
1440
16th to endNight
22123135%5%8%61%
1568
August1st to 15thNight
33133345%7%10%53%
1620
16th to endNight
5%31332335%7%59%
1728
September1st to 15thNight
8%313423346%58%
1920
16th to endNight
8%213323445%60%
1980
October1st to 15thNight
14%5%14323345%51%
2061
16th to endNight
11%414323336%53%
2421
November1st to 15thNight
7%6%1442345%7%52%
2470
16th to endNight
7%6%245%2445%7%49%
2646
December1st to 15thNight
9%9%47%5%35%346%40%
2602
16th to endNight
11%9%47%6%24346%39%
2814

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
44%5%17%22%10%
1433
16th to endDay
46%7%16%21%7%
1599
February1st to 15thDay
49%5%17%18%7%
1590
16th to endDay
42%8%16%20%10%1
1580
March1st to 15thDay
43%5%14%25%10%1
1878
16th to endDay
51%6%14%20%6%
2112
April1st to 15thDay
40%5%13%29%9%
2152
16th to endDay
50%5%13%20%9%
2340
May1st to 15thDay
41%6%13%23%14%
2331
16th to endDay
41%6%16%23%11%
2485
June1st to 15thDay
38%6%16%26%10%1
2697
16th to endDay
25%7%17%29%17%2
2682
July1st to 15thDay
27%6%15%29%16%4
2371
16th to endDay
23%5%14%29%21%5%
2436
August1st to 15thDay
34%7%15%27%12%2
2326
16th to endDay
27%5%15%31%15%4
2471
September1st to 15thDay
33%412%29%17%3
2040
16th to endDay
26%5%12%35%19%1
1980
October1st to 15thDay
36%410%27%19%2
1887
16th to endDay
35%414%29%14%2
1800
November1st to 15thDay
31%5%17%26%15%2
1718
16th to endDay
36%5%17%26%12%1
1641
December1st to 15thDay
48%5%16%19%10%
1369
16th to endDay
52%413%20%7%1
1407
January1st to 15thNight
42%6%17%20%12%1
2506
16th to endNight
42%6%17%21%11%
2624
February1st to 15thNight
48%5%15%19%9%1
2283
16th to endNight
36%6%15%25%11%3
1894
March1st to 15thNight
40%5%15%23%13%1
2082
16th to endNight
41%6%14%25%10%1
2112
April1st to 15thNight
38%413%28%13%1
1795
16th to endNight
43%6%12%23%12%1
1620
May1st to 15thNight
35%5%12%24%20%2
1620
16th to endNight
38%6%17%23%12%
1632
June1st to 15thNight
33%6%16%25%16%2
1260
16th to endNight
20%414%33%22%4
1275
July1st to 15thNight
24%5%13%28%18%8%
1360
16th to endNight
19%6%13%29%25%6%
1468
August1st to 15thNight
23%7%18%30%17%3
1610
16th to endNight
23%5%14%29%21%5%
1728
September1st to 15thNight
26%5%11%29%23%4
1920
16th to endNight
26%411%29%25%2
1980
October1st to 15thNight
35%49%24%22%3
2061
16th to endNight
31%414%26%20%3
2421
November1st to 15thNight
30%414%25%21%3
2470
16th to endNight
33%5%15%26%16%1
2646
December1st to 15thNight
44%5%15%24%8%1
2602
16th to endNight
46%414%21%10%1
2814

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
12%10%38%30%8%
90
16th to endDay
19%9%38%19%10%2
96
February1st to 15thDay
16%7%45%23%6%
90
16th to endDay
16%14%34%25%7%1
81
March1st to 15thDay
14%13%35%25%11%
90
16th to endDay
25%7%28%22%14%2
96
April1st to 15thDay
19%8%40%25%4
271
16th to endDay
28%11%27%23%7%1
450
May1st to 15thDay
17%11%35%23%11%
468
16th to endDay
17%6%35%28%8%2
517
June1st to 15thDay
15%7%28%29%16%2
495
16th to endDay
7%5%31%36%17%2
495
July1st to 15thDay
7%228%40%19%2
475
16th to endDay
4227%47%17%
515
August1st to 15thDay
6%226%39%23%2
493
16th to endDay
9%226%35%22%2
511
September1st to 15thDay
12%7%29%29%14%6%
195
16th to endDay
17%5%30%27%17%1
135
October1st to 15thDay
20%437%27%10%
135
16th to endDay
10%16%33%25%12%2
144
November1st to 15thDay
7%6%32%34%15%3
135
16th to endDay
23%14%35%20%5%
135
December1st to 15thDay
32%15%35%8%5%2
90
16th to endDay
15%20%33%26%4
96
January1st to 15thNight
9%11%37%32%8%
900
16th to endNight
12%10%39%32%5%
960
February1st to 15thNight
16%10%37%29%5%
875
16th to endNight
11%9%36%27%12%1
632
March1st to 15thNight
14%9%35%34%5%
642
16th to endNight
16%8%40%27%7%
576
April1st to 15thNight
15%9%39%28%6%
539
16th to endNight
19%10%33%27%8%
540
May1st to 15thNight
15%8%35%28%10%
540
16th to endNight
15%6%31%36%8%
563
June1st to 15thNight
12%431%37%12%
540
16th to endNight
5%229%50%11%
540
July1st to 15thNight
5%326%42%21%
510
16th to endNight
3125%53%15%
564
August1st to 15thNight
5%124%47%20%
539
16th to endNight
5%327%42%20%
573
September1st to 15thNight
10%230%38%15%2
540
16th to endNight
8%7%34%32%16%1
537
October1st to 15thNight
18%9%32%29%9%1
621
16th to endNight
14%8%30%34%11%
885
November1st to 15thNight
11%9%34%33%9%1
950
16th to endNight
9%9%38%32%9%
975
December1st to 15thNight
13%12%38%29%6%
905
16th to endNight
16%9%32%31%9%
960
Page generated at 2017-12-02 08:14:24. Version ac04

Copyright 2017 A. Danko


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