This page made possible by the sponsorship of: Naperville Astronomical Association.

NAA Ransom
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NAA Ransom clear sky chart from 2005-11-06 to 2024-01-16.

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
37%
24568
18%
74702
11%
24515
44%
24515
23%
50310

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 10thNight
21%
950
14%
2648
4%
946
30%
946
18%
1935
January11th to 20thNight
18%
926
12%
2591
5%
926
24%
926
15%
1982
January21st to endNight
20%
990
11%
2673
4%
990
26%
990
16%
2044
February1st to 10thNight
18%
868
11%
2308
3%
868
24%
868
17%
1753
February11th to 20thNight
25%
700
18%
2099
9%
700
33%
700
18%
1463
February21st to endNight
21%
592
16%
1776
4%
592
32%
592
16%
1273
March1st to 10thNight
25%
720
15%
2160
8%
720
31%
720
18%
1513
March11th to 20thNight
31%
674
18%
2110
9%
674
40%
674
22%
1373
March21st to endNight
24%
594
14%
1980
8%
594
33%
594
15%
1454
April1st to 10thNight
27%
540
16%
1800
9%
540
38%
540
20%
1196
April11th to 20thNight
30%
533
20%
1775
13%
533
41%
533
22%
1147
April21st to endNight
30%
540
15%
1742
8%
540
40%
540
20%
1185
May1st to 10thNight
35%
540
15%
1620
9%
540
41%
540
23%
1121
May11th to 20thNight
41%
531
18%
1472
10%
531
47%
531
27%
997
May21st to endNight
47%
583
18%
1552
10%
582
53%
582
28%
1051
June1st to 10thNight
53%
540
18%
1440
11%
540
58%
540
36%
896
June11th to 20thNight
53%
540
20%
1440
14%
540
57%
540
37%
892
June21st to endNight
52%
540
17%
1440
10%
540
57%
540
31%
949
July1st to 10thNight
69%
525
17%
1400
13%
525
70%
525
37%
868
July11th to 20thNight
67%
522
23%
1392
17%
522
70%
522
44%
804
July21st to endNight
70%
591
24%
1487
18%
558
74%
558
42%
872
August1st to 10thNight
71%
537
21%
1509
19%
534
73%
534
39%
879
August11th to 20thNight
71%
534
22%
1776
24%
534
74%
534
34%
986
August21st to endNight
69%
594
24%
1980
25%
594
73%
594
36%
1073
September1st to 10thNight
60%
540
24%
1800
23%
540
65%
540
34%
1002
September11th to 20thNight
64%
620
33%
1880
31%
620
68%
620
38%
1048
September21st to endNight
54%
720
24%
1980
16%
720
59%
720
33%
1224
October1st to 10thNight
52%
720
25%
2046
18%
720
57%
720
34%
1224
October11th to 20thNight
32%
720
24%
2160
12%
720
45%
720
27%
1345
October21st to endNight
26%
792
18%
2551
10%
792
36%
792
19%
1705
November1st to 10thNight
31%
740
26%
2406
17%
740
44%
740
27%
1416
November11th to 20thNight
27%
760
19%
2470
9%
760
39%
760
20%
1615
November21st to endNight
25%
816
19%
2526
11%
816
35%
816
21%
1712
December1st to 10thNight
22%
950
13%
2660
5%
950
28%
950
19%
1928
December11th to 20thNight
24%
950
15%
3193
6%
948
31%
948
15%
2296
December21st to endNight
15%
1036
6%
4860
3%
1026
22%
1026
6%
4089

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%8%46%6%35%5%5%7%37%
74829
Night
14%8%46%5%3445%7%39%
74995
TransparencyDay
45%7%12%22%12%2
74530
Night
45%6%11%22%14%2
74815
SeeingDay
16%9%27%26%16%6%
14606
Night
17%9%30%30%12%1
24581

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 10thDay
14%12%6%8%8%45%45%6%28%
1517
11th to 20thDay
13%16%8%11%8%45%35%6%21%
1480
21st to endDay
15%15%7%10%7%3445%6%23%
1678
February1st to 10thDay
18%12%5%8%7%46%45%6%26%
1652
11th to 20thDay
15%10%5%6%7%45%5%6%6%31%
1748
21st to endDay
16%13%6%10%5%34346%29%
1480
March1st to 10thDay
17%12%5%7%5%3445%6%33%
1800
11th to 20thDay
14%10%48%6%346%6%8%31%
1866
21st to endDay
20%12%5%8%7%345%5%7%24%
2376
April1st to 10thDay
16%11%46%6%3445%6%34%
2160
11th to 20thDay
16%9%36%7%445%37%36%
2134
21st to endDay
20%7%36%5%36%5%5%7%32%
2218
May1st to 10thDay
17%9%46%6%36%5%6%7%31%
2340
11th to 20thDay
19%7%36%6%345%5%7%34%
2419
21st to endDay
14%6%36%6%45%6%6%8%37%
2725
June1st to 10thDay
9%425%6%35%5%7%8%45%
2520
11th to 20thDay
9%5%25%6%36%5%5%9%44%
2520
21st to endDay
10%6%36%6%46%6%6%9%39%
2520
July1st to 10thDay
9%425%5%35%6%7%9%46%
2520
11th to 20thDay
9%325%4346%8%9%46%
2520
21st to endDay
6%425%6%36%6%7%10%44%
2743
August1st to 10thDay
7%425%5%35%5%8%12%44%
2418
11th to 20thDay
8%426%6%345%7%10%45%
2125
21st to endDay
8%4245%35%6%8%9%48%
2376
September1st to 10thDay
12%5%25%435%5%5%7%47%
2160
11th to 20thDay
12%4234245%5%8%51%
2062
21st to endDay
9%6%36%4335%5%7%47%
1980
October1st to 10thDay
12%6%25%5%345%5%6%46%
1911
11th to 20thDay
17%7%26%5%35%5%47%38%
1800
21st to endDay
19%9%36%5%2445%6%37%
1805
November1st to 10thDay
11%7%345%2446%8%47%
1672
11th to 20thDay
16%10%5%5%6%34447%36%
1710
21st to endDay
18%10%5%8%434346%36%
1653
December1st to 10thDay
15%11%5%8%6%5%5%345%33%
1520
11th to 20thDay
13%14%5%8%7%45%5%46%29%
1918
21st to endDay
21%18%9%13%7%3433415%
2783
January1st to 10thNight
14%11%5%8%7%34445%35%
2648
11th to 20thNight
15%14%6%10%6%35%445%28%
2591
21st to endNight
15%13%6%8%7%35%445%28%
2673
February1st to 10thNight
17%14%5%8%6%34346%30%
2308
11th to 20thNight
14%10%37%6%45%45%6%35%
2098
21st to endNight
19%11%5%7%445%445%33%
1776
March1st to 10thNight
16%10%6%6%5%35%45%5%36%
2160
11th to 20thNight
14%7%36%435%45%7%41%
2110
21st to endNight
21%9%5%7%5%35%45%6%30%
1980
April1st to 10thNight
15%8%47%5%345%5%7%39%
1800
11th to 20thNight
18%7%345%3445%6%41%
1775
21st to endNight
19%7%25%5%345%6%7%35%
1742
May1st to 10thNight
16%8%35%6%35%5%6%9%35%
1620
11th to 20thNight
16%5%26%5%35%46%9%39%
1472
21st to endNight
11%6%26%5%46%6%7%9%39%
1551
June1st to 10thNight
10%5%35%43445%7%52%
1440
11th to 20thNight
9%5%25%5%245%6%11%46%
1440
21st to endNight
9%6%346%445%5%10%43%
1440
July1st to 10thNight
7%425%5%35%47%10%49%
1440
11th to 20thNight
7%214435%5%6%8%55%
1440
21st to endNight
4325%425%5%7%9%53%
1575
August1st to 10thNight
6%42343447%11%50%
1518
11th to 20thNight
7%424435%5%7%8%52%
1776
21st to endNight
7%4145%3445%8%55%
1980
September1st to 10thNight
11%5%25%32345%8%53%
1800
11th to 20thNight
9%424434447%55%
1880
21st to endNight
9%5%25%6%46%6%6%8%46%
1980
October1st to 10thNight
11%5%25%33445%6%53%
2046
11th to 20thNight
16%8%35%423346%47%
2160
21st to endNight
20%7%36%5%33446%39%
2551
November1st to 10thNight
11%7%3443445%6%49%
2406
11th to 20thNight
14%8%47%6%35%45%6%39%
2470
21st to endNight
17%9%36%5%34446%39%
2526
December1st to 10thNight
16%10%49%5%44446%34%
2660
11th to 20thNight
14%13%6%8%6%24345%34%
3279
21st to endNight
23%17%7%10%7%45%445%15%
4884

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 10thDay
57%6%10%16%10%1
1518
11th to 20thDay
65%5%11%13%5%1
1480
21st to endDay
62%6%10%14%7%1
1678
February1st to 10thDay
60%412%16%6%2
1652
11th to 20thDay
52%6%12%20%8%1
1758
21st to endDay
57%410%20%7%2
1480
March1st to 10thDay
53%5%13%22%8%1
1800
11th to 20thDay
48%7%14%20%9%1
1866
21st to endDay
59%6%11%18%41
2376
April1st to 10thDay
50%6%12%20%12%
2160
11th to 20thDay
49%6%9%22%11%4
2134
21st to endDay
51%6%12%17%11%2
2218
May1st to 10thDay
51%7%12%21%8%
2340
11th to 20thDay
48%7%11%21%12%1
2423
21st to endDay
44%7%12%19%16%2
2725
June1st to 10thDay
34%8%13%26%16%3
2520
11th to 20thDay
35%8%11%22%21%3
2520
21st to endDay
39%8%15%21%14%2
2520
July1st to 10thDay
32%9%14%28%14%4
2451
11th to 20thDay
31%10%16%27%14%2
2445
21st to endDay
33%10%16%23%16%2
2591
August1st to 10thDay
31%9%17%29%13%2
2403
11th to 20thDay
32%7%16%26%17%2
2125
21st to endDay
29%8%14%26%18%4
2376
September1st to 10thDay
35%7%13%24%17%5%
2160
11th to 20thDay
30%7%11%28%20%4
2062
21st to endDay
34%7%10%26%21%2
1980
October1st to 10thDay
39%5%13%23%18%2
1911
11th to 20thDay
45%5%9%24%15%1
1800
21st to endDay
49%5%11%22%11%2
1805
November1st to 10thDay
35%5%15%25%18%3
1672
11th to 20thDay
49%412%22%12%1
1710
21st to endDay
51%5%11%23%10%
1653
December1st to 10thDay
56%412%20%8%1
1520
11th to 20thDay
56%6%10%21%6%1
1915
21st to endDay
74%5%8%9%4
2783
January1st to 10thNight
52%6%10%18%13%1
2648
11th to 20thNight
58%5%14%14%8%
2591
21st to endNight
57%5%13%16%8%1
2673
February1st to 10thNight
57%411%17%9%2
2308
11th to 20thNight
49%6%11%22%11%1
2099
21st to endNight
53%5%11%18%10%3
1776
March1st to 10thNight
51%5%11%22%11%1
2160
11th to 20thNight
43%6%13%20%15%3
2110
21st to endNight
55%7%10%18%9%1
1980
April1st to 10thNight
45%6%12%21%13%2
1800
11th to 20thNight
44%5%9%22%16%5%
1775
21st to endNight
46%7%12%20%11%4
1742
May1st to 10thNight
45%8%12%24%11%
1620
11th to 20thNight
41%8%14%22%15%1
1473
21st to endNight
39%9%12%19%17%3
1552
June1st to 10thNight
32%7%12%25%19%4
1440
11th to 20thNight
32%7%13%23%22%3
1440
21st to endNight
36%9%16%21%15%4
1440
July1st to 10thNight
30%9%14%28%14%4
1400
11th to 20thNight
25%7%15%28%21%4
1392
21st to endNight
25%9%15%27%20%4
1487
August1st to 10thNight
26%9%18%28%17%2
1509
11th to 20thNight
28%8%14%25%22%3
1776
21st to endNight
27%8%12%27%21%5%
1980
September1st to 10thNight
31%6%12%26%21%5%
1800
11th to 20thNight
28%6%10%28%24%4
1880
21st to endNight
34%7%13%25%19%3
1980
October1st to 10thNight
33%6%10%25%23%3
2046
11th to 20thNight
39%5%7%26%21%2
2160
21st to endNight
47%5%9%23%14%2
2551
November1st to 10thNight
36%5%10%27%18%4
2406
11th to 20thNight
45%5%13%21%14%2
2470
21st to endNight
48%411%24%12%1
2526
December1st to 10thNight
52%5%12%20%9%1
2660
11th to 20thNight
54%5%10%20%10%1
3281
21st to endNight
72%5%8%10%4
4884

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 10thDay
21%12%35%23%8%1
270
11th to 20thDay
25%16%37%15%6%1
255
21st to endDay
18%19%31%25%7%
264
February1st to 10thDay
25%14%39%18%3
240
11th to 20thDay
24%14%37%20%5%
240
21st to endDay
25%17%42%13%4
198
March1st to 10thDay
23%21%33%21%3
240
11th to 20thDay
26%13%35%20%5%
244
21st to endDay
30%13%32%17%7%2
462
April1st to 10thDay
20%13%35%24%7%1
420
11th to 20thDay
19%15%32%19%12%3
412
21st to endDay
24%11%29%26%8%2
420
May1st to 10thDay
22%13%29%23%11%3
423
11th to 20thDay
21%9%27%26%13%4
565
21st to endDay
15%7%29%24%17%9%
679
June1st to 10thDay
9%6%27%31%21%6%
630
11th to 20thDay
12%5%25%31%23%4
630
21st to endDay
11%9%30%30%15%5%
630
July1st to 10thDay
10%217%28%26%17%
621
11th to 20thDay
9%419%32%23%12%
618
21st to endDay
7%319%36%27%8%
684
August1st to 10thDay
5%314%36%27%14%
582
11th to 20thDay
8%5%17%26%29%15%
439
21st to endDay
8%218%30%28%15%
495
September1st to 10thDay
14%5%18%27%27%9%
450
11th to 20thDay
11%314%30%28%14%
450
21st to endDay
10%9%27%24%21%8%
450
October1st to 10thDay
16%6%26%31%16%6%
381
11th to 20thDay
16%21%33%20%9%
270
21st to endDay
31%13%29%21%5%1
297
November1st to 10thDay
14%10%39%22%11%4
270
11th to 20thDay
21%17%34%18%9%1
270
21st to endDay
23%10%35%24%8%
270
December1st to 10thDay
17%16%38%19%8%2
270
11th to 20thDay
16%17%34%26%6%
270
21st to endDay
22%21%37%17%3
297
January1st to 10thNight
19%15%38%22%6%
950
11th to 20thNight
22%15%36%21%5%1
926
21st to endNight
20%13%35%27%4
990
February1st to 10thNight
25%11%39%22%4
868
11th to 20thNight
20%15%34%27%4
703
21st to endNight
23%14%38%21%4
592
March1st to 10thNight
21%15%35%24%5%
720
11th to 20thNight
18%10%37%28%6%1
674
21st to endNight
25%9%37%22%6%1
594
April1st to 10thNight
18%13%38%25%6%
540
11th to 20thNight
22%12%32%27%6%
533
21st to endNight
23%9%33%28%6%
540
May1st to 10thNight
18%9%34%31%8%
540
11th to 20thNight
18%5%31%34%12%1
531
21st to endNight
13%5%28%36%18%1
584
June1st to 10thNight
12%226%45%15%
540
11th to 20thNight
12%423%44%16%1
540
21st to endNight
10%426%42%17%2
540
July1st to 10thNight
9%214%39%32%5%
525
11th to 20thNight
7%119%43%27%3
522
21st to endNight
5%115%49%29%2
591
August1st to 10thNight
7%113%45%30%4
537
11th to 20thNight
7%310%43%33%3
534
21st to endNight
7%217%38%34%3
594
September1st to 10thNight
14%417%36%27%2
540
11th to 20thNight
10%315%37%30%4
620
21st to endNight
10%6%24%34%24%3
720
October1st to 10thNight
13%5%25%35%20%2
720
11th to 20thNight
19%13%31%28%10%
720
21st to endNight
23%12%33%23%8%
792
November1st to 10thNight
15%11%39%24%10%1
740
11th to 20thNight
18%14%35%26%6%
760
21st to endNight
20%12%36%25%6%
816
December1st to 10thNight
21%11%38%24%5%
950
11th to 20thNight
21%12%35%27%5%
950
21st to endNight
27%15%33%22%3
1045
Page generated at 2024-01-13 00:38:09. Version ac07

Copyright 2024 Attilla Danko


NAA Ransom Clear Sky Chart |Charts Home