Addison Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Addison Oaks Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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%
16315
15%
49109
10%
16277
42%
16277
21%
33933

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
19%
971
10%
2716
4%
970
23%
970
13%
2129
January16th to endNight
21%
913
9%
2785
4%
913
27%
913
12%
2168
February1st to 15thNight
18%
761
9%
2468
2%
761
25%
761
11%
1895
February16th to endNight
22%
683
14%
2049
6%
683
30%
683
15%
1507
March1st to 15thNight
25%
764
14%
2195
9%
764
30%
764
17%
1594
March16th to endNight
34%
768
18%
2112
9%
768
41%
768
21%
1483
April1st to 15thNight
29%
602
14%
1812
7%
602
35%
602
20%
1263
April16th to endNight
37%
540
20%
1620
8%
540
47%
540
26%
1049
May1st to 15thNight
40%
540
15%
1620
9%
540
46%
540
23%
1107
May16th to endNight
51%
562
16%
1684
12%
561
57%
561
29%
1052
June1st to 15thNight
56%
379
17%
1285
16%
379
62%
379
28%
774
June16th to endNight
58%
399
18%
1299
17%
399
64%
399
30%
770
July1st to 15thNight
63%
510
16%
1360
14%
510
66%
510
40%
812
July16th to endNight
67%
564
18%
1510
14%
531
70%
531
40%
877
August1st to 15thNight
63%
539
19%
1609
15%
536
67%
536
35%
949
August16th to endNight
62%
573
23%
1719
17%
573
67%
573
35%
1009
September1st to 15thNight
57%
675
23%
1935
18%
675
60%
675
33%
1174
September16th to endNight
60%
717
25%
1980
19%
717
64%
717
36%
1202
October1st to 15thNight
44%
720
18%
2082
14%
720
50%
720
26%
1369
October16th to endNight
26%
768
15%
2394
10%
768
34%
768
17%
1694
November1st to 15thNight
36%
760
19%
2471
15%
760
43%
760
21%
1628
November16th to endNight
25%
780
15%
2636
9%
780
32%
780
15%
1861
December1st to 15thNight
16%
787
8%
2737
2%
787
23%
787
10%
2072
December16th to endNight
14%
1040
8%
3031
2%
1040
20%
1040
9%
2495

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%47%6%35%5%5%7%32%
49495
Night
14%8%36%5%3445%6%35%
49288
Cloud CoverDay
13%8%47%6%35%5%5%7%32%
49505
Night
14%8%36%5%3445%6%36%
49292
TransparencyDay
49%6%12%19%10%1
49192
Night
47%6%12%20%11%1
49109
SeeingDay
16%8%28%23%15%7%
6349
Night
18%8%29%29%12%1
16323

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
15%15%5%11%8%35%5%5%5%19%
1552
16th to endDay
14%16%8%11%8%45%445%16%
1789
February1st to 15thDay
15%13%5%9%9%5%5%45%5%17%
1722
16th to endDay
13%14%6%10%8%3445%6%22%
1710
March1st to 15thDay
16%11%47%6%35%346%28%
1989
16th to endDay
17%10%5%8%6%34445%28%
2112
April1st to 15thDay
18%10%45%4245%5%7%30%
2147
16th to endDay
16%7%27%6%3435%6%37%
2340
May1st to 15thDay
18%7%36%5%35%5%5%6%33%
2331
16th to endDay
14%6%25%5%3445%7%39%
2431
June1st to 15thDay
10%5%25%5%35%5%6%9%39%
2668
16th to endDay
8%426%6%47%7%7%9%35%
2657
July1st to 15thDay
7%425%5%35%5%7%9%42%
2520
16th to endDay
7%425%6%46%7%8%10%36%
2551
August1st to 15thDay
8%5%26%6%45%6%7%8%37%
2340
16th to endDay
11%425%6%36%5%6%8%39%
2481
September1st to 15thDay
13%425%445%5%5%9%38%
2011
16th to endDay
12%5%25%435%46%9%39%
1980
October1st to 15thDay
13%7%36%5%3445%6%38%
1878
16th to endDay
19%10%36%6%33346%31%
1827
November1st to 15thDay
14%6%37%6%3445%6%35%
1717
16th to endDay
15%12%5%7%7%35%445%28%
1651
December1st to 15thDay
14%12%6%11%7%35%445%23%
1550
16th to endDay
19%15%7%9%8%34446%17%
1541
January1st to 15thNight
20%11%48%6%345%45%25%
2716
16th to endNight
11%12%7%9%8%45%5%46%23%
2785
February1st to 15thNight
14%14%5%8%7%45%445%26%
2466
16th to endNight
16%10%48%7%34446%28%
2049
March1st to 15thNight
16%9%48%5%3435%5%33%
2183
16th to endNight
16%7%35%5%35%45%6%36%
2112
April1st to 15thNight
18%8%26%5%3445%6%34%
1812
16th to endNight
15%6%25%43346%7%40%
1620
May1st to 15thNight
17%5%26%5%2445%8%35%
1620
16th to endNight
11%4345%3445%7%45%
1682
June1st to 15thNight
8%425%5%25%5%6%9%44%
1285
16th to endNight
8%6%1443446%8%45%
1299
July1st to 15thNight
7%424325%347%54%
1440
16th to endNight
5%3134245%6%10%51%
1614
August1st to 15thNight
5%3145%25%5%7%10%47%
1620
16th to endNight
9%423423446%53%
1719
September1st to 15thNight
11%42442435%6%50%
1935
16th to endNight
10%425%42345%6%48%
1980
October1st to 15thNight
16%6%25%433447%41%
2082
16th to endNight
19%7%36%5%35%45%433%
2394
November1st to 15thNight
15%7%36%4345%5%6%39%
2471
16th to endNight
18%10%36%6%35%45%7%29%
2636
December1st to 15thNight
18%12%6%8%6%25%446%24%
2737
16th to endNight
20%16%6%8%5%35%445%19%
3031

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
15%14%6%10%9%35%45%6%19%
1552
16th to endDay
14%16%8%10%8%45%445%17%
1789
February1st to 15thDay
15%13%6%9%9%46%45%6%17%
1722
16th to endDay
13%14%5%10%8%35%5%46%22%
1710
March1st to 15thDay
16%10%5%8%6%34445%28%
2000
16th to endDay
16%11%5%7%6%45%34429%
2111
April1st to 15thDay
18%10%5%5%5%25%447%30%
2147
16th to endDay
16%8%26%5%3435%6%37%
2340
May1st to 15thDay
18%7%36%5%35%446%34%
2331
16th to endDay
13%6%26%435%45%8%39%
2431
June1st to 15thDay
10%5%25%6%35%6%6%9%39%
2668
16th to endDay
8%436%6%46%6%6%10%35%
2657
July1st to 15thDay
6%425%6%45%5%6%9%43%
2520
16th to endDay
6%5%25%5%46%7%7%10%36%
2551
August1st to 15thDay
8%5%26%6%36%6%7%9%37%
2340
16th to endDay
11%425%5%35%46%8%39%
2481
September1st to 15thDay
12%5%25%5%25%5%6%9%39%
2011
16th to endDay
12%5%34435%5%6%9%40%
1980
October1st to 15thDay
13%8%36%435%45%6%38%
1878
16th to endDay
18%10%37%5%34345%32%
1827
November1st to 15thDay
14%7%37%6%35%35%7%36%
1717
16th to endDay
14%12%46%7%35%45%6%28%
1651
December1st to 15thDay
14%12%6%11%7%35%446%23%
1550
16th to endDay
19%15%7%9%7%3345%5%18%
1541
January1st to 15thNight
20%10%5%8%6%34446%25%
2716
16th to endNight
12%11%7%10%8%45%5%5%6%23%
2785
February1st to 15thNight
13%13%5%9%6%35%45%5%27%
2459
16th to endNight
16%11%48%7%3435%6%28%
2049
March1st to 15thNight
16%10%47%5%34445%33%
2195
16th to endNight
15%6%36%435%5%46%36%
2112
April1st to 15thNight
18%8%26%5%3446%5%34%
1812
16th to endNight
15%5%25%43445%7%41%
1620
May1st to 15thNight
16%5%35%5%3446%8%35%
1619
16th to endNight
11%5%25%5%2345%7%45%
1682
June1st to 15thNight
7%5%35%435%5%6%9%44%
1285
16th to endNight
8%6%344345%5%9%44%
1299
July1st to 15thNight
7%32442445%7%54%
1440
16th to endNight
5%31342447%10%51%
1614
August1st to 15thNight
5%3245%35%5%7%9%48%
1620
16th to endNight
9%424423447%52%
1719
September1st to 15thNight
11%326%32445%6%50%
1935
16th to endNight
10%426%42345%7%48%
1980
October1st to 15thNight
16%6%24434446%41%
2082
16th to endNight
19%8%36%5%35%5%5%5%33%
2394
November1st to 15thNight
14%7%25%4245%5%6%38%
2471
16th to endNight
18%9%36%5%25%5%6%7%28%
2636
December1st to 15thNight
18%11%5%8%6%2445%5%24%
2737
16th to endNight
20%15%7%9%5%345%45%19%
3031

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
65%6%10%11%6%
1553
16th to endDay
69%5%10%9%4
1789
February1st to 15thDay
66%5%9%12%5%
1724
16th to endDay
62%5%10%14%6%1
1710
March1st to 15thDay
57%6%11%16%7%
2000
16th to endDay
57%410%18%7%1
2112
April1st to 15thDay
52%5%11%19%10%
2147
16th to endDay
47%414%17%14%2
2340
May1st to 15thDay
51%5%11%19%10%2
2331
16th to endDay
42%6%12%23%12%1
2435
June1st to 15thDay
39%7%14%23%14%1
2668
16th to endDay
41%8%12%20%15%1
2657
July1st to 15thDay
36%7%10%25%18%2
2371
16th to endDay
38%9%15%20%14%2
2392
August1st to 15thDay
40%7%13%23%12%1
2327
16th to endDay
39%8%11%24%14%1
2481
September1st to 15thDay
40%6%13%25%12%
2011
16th to endDay
39%6%13%28%12%
1980
October1st to 15thDay
44%5%13%22%13%1
1878
16th to endDay
53%6%14%17%7%
1827
November1st to 15thDay
47%6%12%22%10%1
1717
16th to endDay
56%5%13%17%6%
1651
December1st to 15thDay
62%5%12%14%5%
1550
16th to endDay
68%412%9%4
1541
January1st to 15thNight
60%5%10%14%7%
2716
16th to endNight
60%6%13%13%4
2785
February1st to 15thNight
59%6%10%14%7%
2468
16th to endNight
56%412%18%7%
2049
March1st to 15thNight
52%5%10%19%10%1
2195
16th to endNight
47%6%11%22%10%1
2112
April1st to 15thNight
48%5%11%20%13%
1812
16th to endNight
41%5%12%19%17%3
1620
May1st to 15thNight
45%5%11%20%13%2
1620
16th to endNight
36%6%12%23%16%3
1684
June1st to 15thNight
35%7%12%27%15%1
1285
16th to endNight
33%7%13%24%19%1
1299
July1st to 15thNight
29%5%9%30%22%2
1360
16th to endNight
26%8%17%24%20%3
1510
August1st to 15thNight
30%7%14%30%14%2
1609
16th to endNight
31%6%12%29%17%2
1719
September1st to 15thNight
33%5%11%28%18%1
1935
16th to endNight
33%412%32%15%
1980
October1st to 15thNight
41%6%11%21%18%1
2082
16th to endNight
51%5%13%21%7%
2394
November1st to 15thNight
43%7%12%23%12%1
2471
16th to endNight
53%5%14%19%6%
2636
December1st to 15thNight
59%5%13%14%6%
2737
16th to endNight
67%5%11%10%4
3031

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
17%18%42%15%4
135
16th to endDay
27%12%43%14%2
144
February1st to 15thDay
25%17%41%14%
135
16th to endDay
25%13%45%12%2
120
March1st to 15thDay
28%12%31%21%6%
216
16th to endDay
25%9%30%23%8%2
288
April1st to 15thDay
20%13%30%22%10%2
270
16th to endDay
21%10%29%17%13%7%
270
May1st to 15thDay
23%6%26%25%13%4
288
16th to endDay
16%7%28%22%16%8%
331
June1st to 15thDay
12%5%33%27%16%4
487
16th to endDay
11%5%33%26%16%5%
495
July1st to 15thDay
9%423%32%19%11%
475
16th to endDay
6%325%30%23%10%
411
August1st to 15thDay
10%217%28%21%19%
313
16th to endDay
14%416%23%22%18%
332
September1st to 15thDay
11%220%20%26%18%
315
16th to endDay
13%416%20%29%15%
314
October1st to 15thDay
17%6%26%22%19%7%
315
16th to endDay
23%10%35%23%41
243
November1st to 15thDay
17%14%29%24%12%1
135
16th to endDay
21%18%41%13%5%
111
December1st to 15thDay
21%22%36%14%5%
90
16th to endDay
22%27%37%9%2
116
January1st to 15thNight
25%12%35%21%41
975
16th to endNight
18%11%36%27%4
913
February1st to 15thNight
20%14%39%23%2
764
16th to endNight
22%12%33%25%4
683
March1st to 15thNight
21%10%35%26%5%
764
16th to endNight
19%10%30%30%9%
768
April1st to 15thNight
22%11%30%29%4
602
16th to endNight
17%8%32%29%10%1
540
May1st to 15thNight
18%6%27%34%11%1
540
16th to endNight
13%323%39%17%2
563
June1st to 15thNight
8%226%48%13%
379
16th to endNight
11%121%48%16%
399
July1st to 15thNight
8%119%40%27%3
510
16th to endNight
5%217%47%23%3
564
August1st to 15thNight
7%18%38%30%4
539
16th to endNight
11%116%32%33%4
573
September1st to 15thNight
12%5%18%31%26%6%
675
16th to endNight
12%317%32%27%6%
717
October1st to 15thNight
19%6%23%30%17%2
720
16th to endNight
23%11%34%25%5%
768
November1st to 15thNight
19%10%28%26%14%
760
16th to endNight
23%13%31%22%7%
780
December1st to 15thNight
24%13%36%20%5%
787
16th to endNight
28%11%36%20%3
1040
Page generated at 2018-03-12 13:28:13. Version ac04

Copyright 2018 A. Danko


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