Maxwell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maxwell Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
48%
23707
22%
79664
16%
23599
55%
23599
24%
49626

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
23%
754
21%
4020
9%
737
37%
737
12%
2486
January11th to 20thNight
25%
759
24%
3964
9%
740
37%
740
11%
2374
January21st to endNight
27%
833
18%
4142
12%
814
41%
814
13%
2756
February1st to 10thNight
31%
760
22%
2280
12%
760
41%
760
23%
1499
February11th to 20thNight
25%
743
18%
2218
8%
739
34%
739
19%
1515
February21st to endNight
24%
611
19%
1831
9%
611
32%
611
18%
1289
March1st to 10thNight
32%
720
22%
2160
13%
720
40%
720
24%
1382
March11th to 20thNight
33%
720
17%
2034
9%
720
39%
720
22%
1395
March21st to endNight
35%
749
21%
2135
11%
749
42%
749
25%
1404
April1st to 10thNight
42%
540
26%
1800
17%
540
53%
540
29%
1023
April11th to 20thNight
40%
533
27%
1775
19%
533
53%
533
29%
1035
April21st to endNight
49%
540
26%
1764
20%
540
58%
540
31%
1011
May1st to 10thNight
53%
540
23%
1620
15%
540
60%
540
34%
963
May11th to 20thNight
55%
531
18%
1592
13%
531
60%
531
27%
1026
May21st to endNight
70%
582
20%
1744
18%
582
72%
582
32%
1057
June1st to 10thNight
65%
540
18%
1620
16%
540
67%
540
29%
1034
June11th to 20thNight
77%
540
20%
1620
17%
540
79%
540
43%
889
June21st to endNight
73%
540
17%
1620
15%
540
74%
540
34%
973
July1st to 10thNight
68%
525
13%
1575
12%
525
69%
525
27%
1020
July11th to 20thNight
76%
522
17%
1566
16%
522
77%
522
32%
976
July21st to endNight
72%
591
17%
1672
16%
558
73%
558
26%
1109
August1st to 10thNight
77%
537
18%
1717
19%
534
78%
534
30%
1034
August11th to 20thNight
67%
534
16%
1776
18%
534
68%
534
26%
1124
August21st to endNight
68%
594
21%
1980
26%
594
68%
594
24%
1273
September1st to 10thNight
70%
589
21%
1849
23%
589
71%
589
31%
1129
September11th to 20thNight
65%
720
22%
1980
19%
720
66%
720
32%
1256
September21st to endNight
61%
720
29%
1980
21%
720
66%
720
37%
1188
October1st to 10thNight
61%
720
33%
1980
27%
720
66%
720
41%
1115
October11th to 20thNight
47%
720
31%
1980
21%
720
56%
720
33%
1224
October21st to endNight
49%
792
29%
2519
26%
792
57%
792
31%
1478
November1st to 10thNight
52%
740
27%
2406
25%
740
60%
740
33%
1349
November11th to 20thNight
42%
760
29%
2470
20%
760
55%
760
32%
1398
November21st to endNight
39%
760
25%
2470
19%
760
49%
760
25%
1521
December1st to 10thNight
30%
760
22%
2470
14%
760
42%
760
19%
1658
December11th to 20thNight
35%
759
25%
2911
17%
758
44%
758
20%
1749
December21st to endNight
29%
829
13%
4424
13%
817
37%
817
10%
2914

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
14%6%35%5%35%5%6%8%40%
78893
Night
14%6%35%5%3445%7%44%
80418
TransparencyDay
41%7%11%20%17%4
78616
Night
39%6%10%20%19%5%
80214
SeeingDay
16%11%22%22%19%9%
13609
Night
16%9%21%29%21%4
23727

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
19%12%35%4245%5%6%35%
2836
11th to 20thDay
21%7%48%43333440%
2840
21st to endDay
25%9%24423335%39%
3448
February1st to 10thDay
19%9%46%4235%37%38%
1900
11th to 20thDay
23%8%35%5%34435%37%
1848
21st to endDay
23%7%36%6%33345%38%
1520
March1st to 10thDay
16%6%36%44445%7%41%
1800
11th to 20thDay
20%8%45%5%345%5%6%35%
1926
21st to endDay
15%6%36%6%36%5%6%8%36%
2235
April1st to 10thDay
13%6%345%35%5%5%7%44%
2160
11th to 20thDay
14%6%25%5%24447%46%
2134
21st to endDay
11%426%5%445%6%8%45%
2196
May1st to 10thDay
13%424435%46%7%46%
2340
11th to 20thDay
11%7%46%7%35%5%6%7%39%
2301
21st to endDay
10%6%25%5%37%6%6%10%40%
2531
June1st to 10thDay
10%6%36%5%46%7%7%11%35%
2340
11th to 20thDay
5%325%5%36%7%9%11%45%
2340
21st to endDay
6%5%26%6%46%6%7%10%42%
2340
July1st to 10thDay
10%5%37%7%5%8%7%8%11%30%
2340
11th to 20thDay
9%5%36%6%5%7%7%10%11%32%
2340
21st to endDay
7%5%26%8%48%7%9%11%32%
2547
August1st to 10thDay
8%5%25%7%5%8%8%9%11%33%
2205
11th to 20thDay
10%5%26%7%47%7%8%10%34%
2125
21st to endDay
13%5%36%6%46%7%7%8%34%
2376
September1st to 10thDay
10%5%35%6%36%6%7%10%40%
2093
11th to 20thDay
12%5%15%5%46%5%7%8%42%
1980
21st to endDay
11%5%25%43445%6%50%
1980
October1st to 10thDay
12%4245%24335%56%
1980
11th to 20thDay
11%5%15%43435%7%53%
1980
21st to endDay
15%6%24433445%52%
1833
November1st to 10thDay
13%5%2442344455%
1672
11th to 20thDay
13%5%245%35%346%51%
1710
21st to endDay
18%6%25%42445%6%44%
1710
December1st to 10thDay
22%8%35%5%345%5%5%35%
1710
11th to 20thDay
18%7%36%6%34435%41%
2153
21st to endDay
19%9%5%6%6%35%45%6%32%
3124
January1st to 10thNight
20%10%25%5%34345%39%
4109
11th to 20thNight
21%7%36%5%23345%41%
4120
21st to endNight
23%13%34433335%37%
4203
February1st to 10thNight
18%10%34424346%42%
2280
11th to 20thNight
22%7%36%43334440%
2218
21st to endNight
24%6%344445%46%36%
1831
March1st to 10thNight
16%7%25%43445%7%43%
2160
11th to 20thNight
17%8%35%5%35%46%8%38%
2034
21st to endNight
15%7%25%5%35%45%6%43%
2135
April1st to 10thNight
12%5%244345%5%8%48%
1800
11th to 20thNight
14%5%24423347%50%
1775
21st to endNight
11%4245%3445%7%50%
1764
May1st to 10thNight
10%4245%2446%7%52%
1620
11th to 20thNight
10%5%26%5%36%5%7%9%43%
1592
21st to endNight
7%425%5%446%6%10%46%
1744
June1st to 10thNight
7%5%35%7%46%5%7%10%41%
1620
11th to 20thNight
5%214425%5%7%11%54%
1620
21st to endNight
6%425%5%35%6%7%11%46%
1620
July1st to 10thNight
8%6%36%7%35%7%8%11%37%
1620
11th to 20thNight
8%3245%45%6%8%12%42%
1620
21st to endNight
6%435%6%48%7%8%10%38%
1771
August1st to 10thNight
5%425%6%46%6%9%13%42%
1728
11th to 20thNight
10%435%6%35%6%7%10%41%
1776
21st to endNight
11%6%26%5%45%5%6%9%41%
1980
September1st to 10thNight
8%5%25%5%35%6%6%8%48%
1849
11th to 20thNight
10%6%25%425%6%6%10%44%
1980
21st to endNight
9%426%5%3445%6%53%
1980
October1st to 10thNight
10%424323346%60%
1980
11th to 20thNight
13%5%26%434446%51%
1980
21st to endNight
14%6%24333445%51%
2519
November1st to 10thNight
12%424433446%53%
2406
11th to 20thNight
13%6%24323446%52%
2470
21st to endNight
17%6%35%433446%45%
2470
December1st to 10thNight
20%7%26%5%345%5%7%37%
2470
11th to 20thNight
18%6%24434445%46%
3042
21st to endNight
19%9%47%5%45%5%6%7%30%
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
49%46%18%21%2
2837
11th to 20thDay
49%36%18%22%2
2840
21st to endDay
49%47%20%18%3
3448
February1st to 10thDay
48%46%20%19%3
1900
11th to 20thDay
50%45%19%16%5%
1858
21st to endDay
49%5%7%14%19%6%
1520
March1st to 10thDay
43%5%7%15%22%7%
1800
11th to 20thDay
49%6%9%14%17%4
1926
21st to endDay
44%7%12%22%13%2
2235
April1st to 10thDay
38%7%11%23%17%6%
2160
11th to 20thDay
39%5%7%20%24%5%
2134
21st to endDay
36%6%9%29%17%2
2196
May1st to 10thDay
36%6%12%25%16%4
2340
11th to 20thDay
42%8%13%22%14%1
2305
21st to endDay
37%9%13%24%15%2
2531
June1st to 10thDay
41%9%14%21%14%1
2340
11th to 20thDay
29%11%19%24%15%2
2340
21st to endDay
36%11%16%21%13%4
2340
July1st to 10thDay
42%12%16%19%9%2
2275
11th to 20thDay
39%14%18%18%9%2
2271
21st to endDay
39%13%18%20%8%1
2405
August1st to 10thDay
39%13%18%21%8%1
2192
11th to 20thDay
41%11%15%20%13%1
2125
21st to endDay
44%10%14%18%11%3
2376
September1st to 10thDay
38%9%15%18%15%5%
2093
11th to 20thDay
38%9%11%20%20%3
1980
21st to endDay
35%5%11%20%21%7%
1980
October1st to 10thDay
32%5%7%21%27%8%
1980
11th to 20thDay
31%49%22%24%9%
1980
21st to endDay
35%45%19%29%8%
1833
November1st to 10thDay
33%47%18%30%8%
1672
11th to 20thDay
36%46%22%25%8%
1710
21st to endDay
41%46%19%25%5%
1710
December1st to 10thDay
51%47%16%19%4
1710
11th to 20thDay
47%46%20%19%5%
2150
21st to endDay
51%5%8%19%14%2
3124
January1st to 10thNight
48%46%18%22%2
4109
11th to 20thNight
47%37%20%17%6%
4120
21st to endNight
51%45%18%19%3
4203
February1st to 10thNight
45%48%19%20%5%
2280
11th to 20thNight
49%46%18%16%7%
2219
21st to endNight
50%5%6%15%17%7%
1831
March1st to 10thNight
42%48%17%20%9%
2160
11th to 20thNight
45%7%10%18%17%4
2034
21st to endNight
43%5%9%24%17%3
2135
April1st to 10thNight
33%6%13%24%20%5%
1800
11th to 20thNight
35%5%6%21%22%11%
1775
21st to endNight
33%5%12%27%19%4
1764
May1st to 10thNight
30%7%12%22%25%3
1620
11th to 20thNight
36%10%15%22%16%1
1593
21st to endNight
31%10%15%24%17%3
1745
June1st to 10thNight
36%10%14%22%17%2
1620
11th to 20thNight
22%9%19%30%17%3
1620
21st to endNight
30%10%18%22%16%4
1620
July1st to 10thNight
37%10%21%18%12%3
1575
11th to 20thNight
29%13%21%21%12%3
1566
21st to endNight
36%13%18%23%10%1
1672
August1st to 10thNight
29%13%21%25%11%1
1717
11th to 20thNight
35%11%19%18%14%3
1776
21st to endNight
39%10%14%22%12%3
1980
September1st to 10thNight
32%10%18%19%17%4
1849
11th to 20thNight
34%9%14%17%23%3
1980
21st to endNight
31%6%9%22%23%9%
1980
October1st to 10thNight
28%47%25%27%9%
1980
11th to 20thNight
35%5%7%20%22%10%
1980
21st to endNight
36%45%19%28%9%
2519
November1st to 10thNight
32%48%21%24%10%
2406
11th to 20thNight
34%37%19%28%10%
2470
21st to endNight
41%46%20%24%6%
2470
December1st to 10thNight
48%5%7%19%18%3
2470
11th to 20thNight
41%46%18%27%4
3044
21st to endNight
51%6%8%20%14%2
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
24%27%32%14%3
270
11th to 20thDay
26%26%30%13%5%
270
21st to endDay
21%27%36%12%4
297
February1st to 10thDay
26%23%33%15%3
270
11th to 20thDay
39%20%30%10%11
270
21st to endDay
36%24%31%7%2
210
March1st to 10thDay
23%20%38%14%32
240
11th to 20thDay
25%22%28%18%5%2
366
21st to endDay
23%18%32%18%8%1
462
April1st to 10thDay
19%17%27%22%14%2
420
11th to 20thDay
16%19%27%24%12%1
412
21st to endDay
16%13%32%24%14%1
420
May1st to 10thDay
16%11%30%26%12%6%
423
11th to 20thDay
10%6%27%28%18%11%
447
21st to endDay
13%6%16%29%22%15%
485
June1st to 10thDay
12%5%16%28%25%14%
450
11th to 20thDay
5%317%26%27%22%
450
21st to endDay
10%316%23%30%17%
450
July1st to 10thDay
9%210%25%33%21%
445
11th to 20thDay
8%111%23%31%26%
444
21st to endDay
9%110%21%34%25%
488
August1st to 10thDay
11%310%24%34%19%
446
11th to 20thDay
10%212%27%35%14%
439
21st to endDay
16%29%21%34%17%
495
September1st to 10thDay
11%312%25%34%15%
450
11th to 20thDay
14%215%21%32%17%
450
21st to endDay
14%414%28%31%9%
450
October1st to 10thDay
13%423%27%23%10%
450
11th to 20thDay
13%10%27%29%20%2
450
21st to endDay
20%11%24%28%14%3
343
November1st to 10thDay
20%10%29%26%13%3
270
11th to 20thDay
14%20%36%24%7%
270
21st to endDay
17%17%33%20%11%2
270
December1st to 10thDay
31%20%25%17%6%1
270
11th to 20thDay
25%21%31%16%6%1
270
21st to endDay
29%19%33%15%4
297
January1st to 10thNight
25%17%30%22%5%
760
11th to 20thNight
23%19%28%23%7%
760
21st to endNight
21%17%33%26%3
836
February1st to 10thNight
23%13%29%31%4
760
11th to 20thNight
27%18%28%25%3
743
21st to endNight
29%15%29%25%2
611
March1st to 10thNight
20%15%29%31%5%
720
11th to 20thNight
22%12%29%28%9%1
720
21st to endNight
18%14%30%28%11%
749
April1st to 10thNight
14%12%28%32%14%
540
11th to 20thNight
16%11%29%29%14%1
533
21st to endNight
12%8%26%37%17%1
540
May1st to 10thNight
11%7%24%33%22%3
540
11th to 20thNight
11%421%31%26%6%
531
21st to endNight
8%310%37%35%7%
584
June1st to 10thNight
9%313%31%37%7%
540
11th to 20thNight
5%19%31%39%14%
540
21st to endNight
7%19%31%40%11%
540
July1st to 10thNight
10%27%24%41%16%
525
11th to 20thNight
9%16%23%41%19%
522
21st to endNight
8%17%24%46%14%
591
August1st to 10thNight
6%15%26%48%14%
537
11th to 20thNight
10%210%23%45%9%
534
21st to endNight
12%27%27%42%10%
594
September1st to 10thNight
9%210%25%44%10%
589
11th to 20thNight
13%213%28%37%7%
720
21st to endNight
9%315%31%39%3
720
October1st to 10thNight
12%417%31%29%7%
720
11th to 20thNight
14%8%23%33%21%1
720
21st to endNight
18%9%20%32%19%2
792
November1st to 10thNight
14%8%21%33%20%3
740
11th to 20thNight
16%11%29%30%14%1
760
21st to endNight
21%10%25%31%13%1
760
December1st to 10thNight
24%13%28%26%9%
760
11th to 20thNight
23%11%26%30%9%
760
21st to endNight
26%14%26%28%6%
836
Page generated at 2024-02-22 05:05:43. Version ac07

Copyright 2024 Attilla Danko


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