MAC-Johnson Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MAC-Johnson Site clear sky chart from 2005-11-06 to 2024-01-13.

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
49%
24314
22%
74365
15%
24260
57%
24260
27%
46354

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
30%
759
23%
2459
10%
757
46%
757
23%
1516
January11th to 20thNight
35%
732
25%
2378
14%
732
50%
732
25%
1435
January21st to endNight
28%
792
26%
2574
13%
792
46%
792
25%
1567
February1st to 10thNight
35%
720
21%
2300
13%
720
46%
720
24%
1438
February11th to 20thNight
28%
703
23%
2098
10%
699
42%
699
25%
1327
February21st to endNight
29%
592
25%
1722
11%
592
43%
592
26%
1093
March1st to 10thNight
38%
720
28%
1980
16%
720
47%
720
33%
1223
March11th to 20thNight
33%
720
21%
1980
10%
720
43%
720
28%
1271
March21st to endNight
35%
792
23%
2178
11%
792
45%
792
28%
1383
April1st to 10thNight
41%
720
24%
1980
14%
720
49%
720
33%
1188
April11th to 20thNight
45%
711
25%
1812
13%
711
51%
711
37%
1112
April21st to endNight
50%
626
29%
1706
16%
626
57%
626
39%
992
May1st to 10thNight
49%
540
22%
1620
12%
540
55%
540
34%
938
May11th to 20thNight
53%
531
15%
1592
8%
531
58%
531
26%
1036
May21st to endNight
67%
582
19%
1744
14%
582
69%
582
28%
1102
June1st to 10thNight
61%
540
15%
1620
12%
540
62%
540
25%
1065
June11th to 20thNight
67%
540
14%
1620
12%
540
68%
540
29%
1036
June21st to endNight
67%
540
14%
1620
11%
540
69%
540
25%
1083
July1st to 10thNight
67%
525
12%
1575
10%
525
68%
525
24%
1057
July11th to 20thNight
70%
522
11%
1566
9%
522
70%
522
23%
1059
July21st to endNight
70%
591
13%
1672
11%
558
72%
558
25%
1118
August1st to 10thNight
69%
537
12%
1600
11%
534
69%
534
21%
1141
August11th to 20thNight
66%
534
13%
1598
12%
534
66%
534
21%
1127
August21st to endNight
62%
746
14%
1964
11%
746
62%
746
23%
1402
September1st to 10thNight
70%
720
18%
1980
15%
720
70%
720
29%
1284
September11th to 20thNight
61%
720
20%
1980
18%
720
63%
720
26%
1349
September21st to endNight
57%
720
18%
1980
15%
720
60%
720
26%
1356
October1st to 10thNight
58%
720
27%
2066
24%
720
63%
720
34%
1242
October11th to 20thNight
57%
720
31%
2160
28%
720
64%
720
39%
1201
October21st to endNight
55%
792
32%
2376
26%
792
65%
792
38%
1330
November1st to 10thNight
54%
740
29%
2221
24%
740
62%
740
37%
1240
November11th to 20thNight
45%
760
29%
2375
21%
760
55%
760
31%
1383
November21st to endNight
46%
760
26%
2470
20%
760
57%
760
30%
1442
December1st to 10thNight
41%
760
24%
2470
16%
760
54%
760
24%
1550
December11th to 20thNight
40%
759
27%
2921
19%
758
52%
758
25%
1656
December21st to endNight
36%
828
16%
4408
16%
817
46%
817
14%
2612

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
12%6%25%5%35%5%6%8%43%
74930
Night
12%6%25%5%35%5%6%8%45%
74819
TransparencyDay
38%7%12%20%18%5%
74653
Night
38%6%11%19%19%7%
74615
SeeingDay
13%6%21%25%21%13%
14196
Night
14%6%22%33%21%3
24326

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
15%6%35%43436%7%46%
1706
11th to 20thDay
15%7%25%5%2445%7%45%
1644
21st to endDay
17%7%34433336%47%
1782
February1st to 10thDay
14%7%35%5%245%6%8%41%
1656
11th to 20thDay
19%6%35%333446%45%
1748
21st to endDay
18%7%245%245%46%43%
1532
March1st to 10thDay
13%6%23434446%51%
1980
11th to 20thDay
14%6%36%5%35%45%7%43%
1980
21st to endDay
14%6%35%5%345%6%6%43%
2178
April1st to 10thDay
9%425%43446%7%51%
1980
11th to 20thDay
11%6%25%5%3445%7%47%
2094
21st to endDay
8%41443446%7%54%
2268
May1st to 10thDay
8%4345%3446%8%52%
2340
11th to 20thDay
11%6%26%6%35%6%6%8%42%
2301
21st to endDay
10%6%35%7%46%6%7%8%39%
2531
June1st to 10thDay
10%6%36%6%45%7%8%10%36%
2340
11th to 20thDay
6%435%5%36%6%8%12%43%
2340
21st to endDay
6%435%6%47%7%8%10%40%
2340
July1st to 10thDay
8%437%6%5%8%6%8%11%34%
2340
11th to 20thDay
8%5%36%8%47%7%7%13%32%
2340
21st to endDay
7%5%35%7%5%8%7%9%12%31%
2547
August1st to 10thDay
8%6%36%7%5%7%8%9%11%30%
2327
11th to 20thDay
10%6%36%7%5%7%8%7%11%30%
2303
21st to endDay
11%7%37%8%46%7%8%10%29%
2366
September1st to 10thDay
7%436%7%46%6%8%9%40%
1980
11th to 20thDay
12%7%26%5%346%6%8%41%
1980
21st to endDay
16%5%25%5%445%5%6%42%
1980
October1st to 10thDay
13%6%245%34346%50%
1892
11th to 20thDay
10%424423346%57%
1800
21st to endDay
11%5%2343343457%
1980
November1st to 10thDay
12%5%24423445%54%
1857
11th to 20thDay
13%7%24322445%53%
1801
21st to endDay
14%6%25%32435%7%48%
1710
December1st to 10thDay
17%7%26%5%2446%7%40%
1710
11th to 20thDay
16%5%2341345%6%51%
2153
21st to endDay
19%7%25%423445%44%
3124
January1st to 10thNight
15%7%25%5%24445%47%
2459
11th to 20thNight
13%7%35%43445%7%45%
2378
21st to endNight
16%6%35%434445%48%
2574
February1st to 10thNight
16%6%25%6%345%5%7%43%
2300
11th to 20thNight
19%6%25%424346%45%
2098
21st to endNight
16%5%27%42446%7%43%
1722
March1st to 10thNight
12%6%2443445%6%50%
1980
11th to 20thNight
14%6%24435%5%5%8%44%
1980
21st to endNight
12%5%35%5%35%45%7%45%
2178
April1st to 10thNight
11%424435%45%8%51%
1980
11th to 20thNight
13%5%24424348%51%
1812
21st to endNight
8%325%43345%7%56%
1706
May1st to 10thNight
7%425%5%35%5%5%8%51%
1620
11th to 20thNight
8%6%36%5%46%6%7%10%39%
1592
21st to endNight
8%6%35%5%46%6%7%8%42%
1744
June1st to 10thNight
12%5%36%436%7%9%10%35%
1620
11th to 20thNight
6%5%36%5%35%6%9%11%40%
1620
21st to endNight
6%6%26%7%47%6%9%12%35%
1620
July1st to 10thNight
8%6%36%5%46%7%8%11%35%
1620
11th to 20thNight
7%6%36%7%46%7%8%12%34%
1620
21st to endNight
6%5%36%7%47%7%10%11%34%
1771
August1st to 10thNight
7%6%28%7%5%8%6%10%10%31%
1611
11th to 20thNight
9%6%37%7%47%7%9%11%30%
1598
21st to endNight
11%6%37%8%46%6%7%11%32%
1964
September1st to 10thNight
7%5%35%5%45%7%7%10%40%
1980
11th to 20thNight
11%6%36%8%45%45%7%41%
1980
21st to endNight
14%7%26%6%45%5%5%7%40%
1980
October1st to 10thNight
13%5%25%5%32346%52%
2066
11th to 20thNight
13%42332335%6%56%
2160
21st to endNight
9%425%423446%56%
2376
November1st to 10thNight
11%5%24323446%57%
2221
11th to 20thNight
14%5%24323446%52%
2375
21st to endNight
13%5%25%42446%6%49%
2470
December1st to 10thNight
16%6%24435%5%5%7%43%
2470
11th to 20thNight
17%5%24423345%51%
3042
21st to endNight
19%7%35%43445%7%39%
4532

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
39%49%21%22%6%
1707
11th to 20thDay
40%48%18%23%6%
1644
21st to endDay
41%3419%25%8%
1782
February1st to 10thDay
42%410%21%17%7%
1656
11th to 20thDay
42%35%20%25%6%
1758
21st to endDay
43%5%7%16%20%10%
1532
March1st to 10thDay
35%48%21%21%12%
1980
11th to 20thDay
43%411%18%17%7%
1980
21st to endDay
41%5%10%19%20%5%
2178
April1st to 10thDay
32%5%10%20%26%7%
1980
11th to 20thDay
36%5%10%19%20%10%
2094
21st to endDay
28%6%11%28%23%4
2268
May1st to 10thDay
30%6%13%25%22%4
2340
11th to 20thDay
40%7%16%19%17%2
2305
21st to endDay
40%8%12%23%16%1
2531
June1st to 10thDay
40%9%17%21%11%1
2340
11th to 20thDay
32%8%20%26%13%1
2340
21st to endDay
35%10%19%22%11%2
2340
July1st to 10thDay
40%11%19%19%8%3
2275
11th to 20thDay
41%11%22%18%7%2
2271
21st to endDay
39%12%21%19%8%1
2405
August1st to 10thDay
43%12%18%22%5%1
2314
11th to 20thDay
44%12%17%19%7%1
2303
21st to endDay
47%11%16%17%8%2
2366
September1st to 10thDay
38%10%16%15%17%4
1980
11th to 20thDay
40%8%12%16%20%4
1980
21st to endDay
42%6%9%19%18%6%
1980
October1st to 10thDay
37%5%6%20%24%8%
1892
11th to 20thDay
29%48%23%27%8%
1800
21st to endDay
31%46%16%31%13%
1980
November1st to 10thDay
33%46%17%26%14%
1857
11th to 20thDay
34%36%20%24%12%
1801
21st to endDay
37%49%20%21%9%
1710
December1st to 10thDay
44%5%10%18%17%7%
1710
11th to 20thDay
35%37%21%25%9%
2150
21st to endDay
43%47%19%24%4
3124
January1st to 10thNight
41%47%18%24%7%
2459
11th to 20thNight
40%48%19%22%8%
2378
21st to endNight
40%4418%23%11%
2574
February1st to 10thNight
41%5%9%18%19%10%
2300
11th to 20thNight
41%46%19%21%9%
2099
21st to endNight
40%5%9%16%18%12%
1722
March1st to 10thNight
36%48%17%23%13%
1980
11th to 20thNight
39%6%12%15%20%8%
1980
21st to endNight
38%5%10%21%19%7%
2178
April1st to 10thNight
32%5%10%20%22%10%
1980
11th to 20thNight
33%48%22%22%11%
1812
21st to endNight
29%5%12%25%23%6%
1706
May1st to 10thNight
32%5%14%24%20%5%
1620
11th to 20thNight
37%10%18%18%16%1
1593
21st to endNight
36%9%13%24%16%3
1745
June1st to 10thNight
39%11%18%20%12%1
1620
11th to 20thNight
35%10%19%25%9%2
1620
21st to endNight
38%12%20%18%10%2
1620
July1st to 10thNight
39%12%22%14%10%3
1575
11th to 20thNight
39%13%23%17%7%1
1566
21st to endNight
37%13%24%19%7%1
1672
August1st to 10thNight
42%14%21%18%5%1
1600
11th to 20thNight
43%12%20%18%7%1
1598
21st to endNight
45%9%19%16%9%1
1964
September1st to 10thNight
35%11%17%20%12%6%
1980
11th to 20thNight
42%8%10%18%18%4
1980
21st to endNight
43%7%12%16%17%5%
1980
October1st to 10thNight
35%49%18%27%7%
2066
11th to 20thNight
29%49%23%24%11%
2160
21st to endNight
30%46%20%27%13%
2376
November1st to 10thNight
30%310%15%27%15%
2221
11th to 20thNight
34%47%16%25%14%
2375
21st to endNight
37%47%19%23%11%
2470
December1st to 10thNight
41%5%10%17%19%7%
2470
11th to 20thNight
37%37%18%27%9%
3044
21st to endNight
45%46%19%22%4
4532

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
18%13%45%19%4
270
11th to 20thDay
20%13%34%25%7%1
248
21st to endDay
22%17%37%18%5%
264
February1st to 10thDay
17%16%40%20%7%
240
11th to 20thDay
28%12%41%17%3
240
21st to endDay
19%16%37%21%6%2
250
March1st to 10thDay
15%14%31%26%13%1
420
11th to 20thDay
16%11%41%24%8%1
420
21st to endDay
16%11%37%25%10%1
462
April1st to 10thDay
13%14%28%29%13%2
420
11th to 20thDay
10%12%25%25%20%7%
412
21st to endDay
10%8%23%29%19%11%
420
May1st to 10thDay
8%9%26%31%19%7%
423
11th to 20thDay
12%216%22%30%17%
447
21st to endDay
13%212%27%21%25%
485
June1st to 10thDay
10%211%27%29%20%
450
11th to 20thDay
9%312%23%28%25%
450
21st to endDay
6%39%29%29%24%
450
July1st to 10thDay
7%27%21%27%36%
445
11th to 20thDay
9%25%16%37%31%
444
21st to endDay
7%27%23%36%26%
488
August1st to 10thDay
11%210%20%33%24%
446
11th to 20thDay
10%28%18%32%30%
439
21st to endDay
14%27%20%32%26%
495
September1st to 10thDay
9%26%26%32%24%
450
11th to 20thDay
16%49%22%35%14%
450
21st to endDay
18%111%26%30%14%
450
October1st to 10thDay
14%320%30%23%10%
450
11th to 20thDay
9%5%20%30%24%11%
450
21st to endDay
13%5%22%27%24%8%
495
November1st to 10thDay
17%424%29%21%6%
455
11th to 20thDay
19%7%32%29%11%2
361
21st to endDay
12%11%30%30%13%3
270
December1st to 10thDay
22%9%33%27%8%1
270
11th to 20thDay
20%11%35%23%9%2
270
21st to endDay
25%10%34%20%8%2
297
January1st to 10thNight
20%11%34%27%8%
760
11th to 20thNight
16%11%32%32%8%
732
21st to endNight
17%11%39%29%4
792
February1st to 10thNight
19%12%30%33%6%
720
11th to 20thNight
21%11%34%31%3
703
21st to endNight
17%14%34%30%4
592
March1st to 10thNight
15%8%35%36%5%
720
11th to 20thNight
16%9%36%30%9%
720
21st to endNight
14%9%35%31%10%
792
April1st to 10thNight
13%13%31%32%12%
720
11th to 20thNight
15%8%27%34%16%1
711
21st to endNight
11%7%27%42%13%
626
May1st to 10thNight
10%429%42%14%1
540
11th to 20thNight
11%323%37%22%3
531
21st to endNight
10%210%41%33%4
584
June1st to 10thNight
14%213%39%26%6%
540
11th to 20thNight
10%211%34%33%11%
540
21st to endNight
6%212%36%38%7%
540
July1st to 10thNight
10%36%31%41%9%
525
11th to 20thNight
9%1332%46%9%
522
21st to endNight
7%26%34%45%6%
591
August1st to 10thNight
9%17%27%45%10%
537
11th to 20thNight
12%26%32%43%5%
534
21st to endNight
14%19%26%42%8%
746
September1st to 10thNight
8%38%29%47%6%
720
11th to 20thNight
13%29%31%39%6%
720
21st to endNight
17%213%32%32%5%
720
October1st to 10thNight
14%415%37%26%5%
720
11th to 20thNight
15%321%32%26%3
720
21st to endNight
11%6%23%35%23%3
792
November1st to 10thNight
13%6%22%35%20%3
740
11th to 20thNight
16%8%27%36%12%1
760
21st to endNight
14%8%27%34%16%1
760
December1st to 10thNight
18%9%26%34%12%1
760
11th to 20thNight
19%7%29%33%12%1
760
21st to endNight
24%11%25%31%9%1
836
Page generated at 2024-01-10 19:35:22. Version ac07

Copyright 2024 Attilla Danko


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