Maxwell Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maxwell Point clear sky chart from 2005-11-06 to 2024-01-12.

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
47%
24271
21%
74347
14%
24219
54%
24219
26%
46719

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
28%
759
23%
2459
9%
757
45%
757
22%
1501
January11th to 20thNight
32%
725
24%
2354
12%
725
48%
725
22%
1457
January21st to endNight
27%
792
27%
2574
13%
792
45%
792
24%
1549
February1st to 10thNight
32%
720
21%
2307
12%
720
44%
720
23%
1443
February11th to 20thNight
24%
702
22%
2099
9%
700
39%
700
24%
1356
February21st to endNight
27%
592
25%
1735
10%
592
42%
592
24%
1122
March1st to 10thNight
35%
720
26%
1980
14%
720
45%
720
31%
1237
March11th to 20thNight
31%
720
22%
1980
10%
720
41%
720
26%
1292
March21st to endNight
31%
792
21%
2178
8%
792
42%
792
26%
1411
April1st to 10thNight
38%
720
24%
1980
13%
720
47%
720
32%
1185
April11th to 20thNight
41%
711
24%
1811
11%
711
49%
711
35%
1130
April21st to endNight
46%
604
30%
1684
17%
604
55%
604
37%
978
May1st to 10thNight
46%
540
21%
1620
10%
540
54%
540
33%
940
May11th to 20thNight
49%
531
15%
1593
9%
531
53%
531
25%
1064
May21st to endNight
63%
582
19%
1744
15%
582
65%
582
29%
1104
June1st to 10thNight
56%
540
14%
1620
11%
540
57%
540
23%
1103
June11th to 20thNight
64%
540
14%
1620
11%
540
65%
540
27%
1052
June21st to endNight
63%
540
13%
1620
10%
540
64%
540
24%
1088
July1st to 10thNight
67%
525
12%
1575
10%
525
67%
525
23%
1075
July11th to 20thNight
69%
522
10%
1566
9%
522
69%
522
23%
1072
July21st to endNight
66%
591
12%
1672
9%
558
68%
558
24%
1164
August1st to 10thNight
65%
537
11%
1600
11%
534
65%
534
22%
1133
August11th to 20thNight
63%
534
15%
1598
13%
534
63%
534
21%
1116
August21st to endNight
61%
733
13%
1948
10%
733
61%
733
23%
1390
September1st to 10thNight
67%
720
19%
1980
16%
720
68%
720
30%
1284
September11th to 20thNight
59%
720
20%
1980
17%
720
61%
720
27%
1346
September21st to endNight
56%
720
19%
1980
16%
720
59%
720
27%
1331
October1st to 10thNight
55%
720
26%
2065
23%
720
61%
720
33%
1256
October11th to 20thNight
52%
720
30%
2160
25%
720
62%
720
35%
1237
October21st to endNight
53%
792
32%
2376
24%
792
64%
792
36%
1340
November1st to 10thNight
50%
740
29%
2221
22%
740
60%
740
34%
1263
November11th to 20thNight
43%
760
28%
2400
20%
760
54%
760
30%
1395
November21st to endNight
46%
760
26%
2470
20%
760
55%
760
28%
1455
December1st to 10thNight
38%
760
24%
2470
14%
760
50%
760
21%
1590
December11th to 20thNight
40%
759
28%
2916
20%
758
51%
758
24%
1647
December21st to endNight
33%
828
15%
4412
14%
817
44%
817
13%
2613

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%5%25%5%35%5%6%8%44%
74917
Night
13%5%35%5%345%5%8%44%
74800
TransparencyDay
37%8%12%19%18%5%
74640
Night
37%7%11%18%19%7%
74596
SeeingDay
15%9%24%25%19%8%
14155
Night
15%8%23%32%19%3
24284

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%6%25%5%3445%6%47%
1706
11th to 20thDay
16%6%35%5%34445%45%
1629
21st to endDay
16%6%245%23445%48%
1782
February1st to 10thDay
15%6%25%6%35%5%5%7%41%
1651
11th to 20thDay
19%5%25%42445%6%45%
1748
21st to endDay
18%6%25%434446%43%
1520
March1st to 10thDay
14%5%23434435%53%
1980
11th to 20thDay
15%6%35%5%35%47%6%43%
1980
21st to endDay
14%6%35%4345%6%7%42%
2178
April1st to 10thDay
10%324425%5%6%7%52%
1980
11th to 20thDay
10%5%25%5%345%6%8%47%
2096
21st to endDay
8%424435%5%6%9%52%
2290
May1st to 10thDay
7%5%244345%6%9%51%
2340
11th to 20thDay
12%5%36%5%45%6%6%8%41%
2301
21st to endDay
10%5%26%6%35%6%7%9%41%
2531
June1st to 10thDay
9%5%36%6%36%7%8%11%37%
2340
11th to 20thDay
7%325%5%37%6%7%12%43%
2340
21st to endDay
4426%6%37%7%7%13%41%
2340
July1st to 10thDay
7%6%26%7%47%7%8%10%34%
2340
11th to 20thDay
7%436%7%5%7%7%9%12%34%
2340
21st to endDay
7%426%6%5%7%7%8%13%35%
2547
August1st to 10thDay
9%5%36%7%47%6%9%12%32%
2327
11th to 20thDay
14%5%36%6%46%6%8%10%32%
2303
21st to endDay
12%6%36%7%46%6%8%11%31%
2382
September1st to 10thDay
7%5%26%7%45%5%7%11%42%
1980
11th to 20thDay
13%6%25%6%445%6%8%42%
1980
21st to endDay
16%6%35%5%2435%7%43%
1980
October1st to 10thDay
14%5%34423346%52%
1895
11th to 20thDay
12%424424346%57%
1800
21st to endDay
11%5%25%323435%57%
1980
November1st to 10thDay
12%5%25%5%24335%55%
1857
11th to 20thDay
14%5%2432335%5%54%
1777
21st to endDay
14%5%25%5%24446%49%
1710
December1st to 10thDay
17%8%35%5%3446%6%38%
1710
11th to 20thDay
16%5%23323446%51%
2153
21st to endDay
19%6%25%423447%43%
3124
January1st to 10thNight
16%6%35%424436%47%
2459
11th to 20thNight
14%6%35%435%446%45%
2354
21st to endNight
16%6%35%323445%48%
2574
February1st to 10thNight
17%5%246%3445%6%44%
2307
11th to 20thNight
18%6%34424446%45%
2098
21st to endNight
16%5%26%43445%7%44%
1735
March1st to 10thNight
14%5%35%434446%49%
1980
11th to 20thNight
15%425%5%35%447%45%
1980
21st to endNight
12%6%35%5%35%5%6%8%44%
2178
April1st to 10thNight
10%5%23425%45%7%52%
1980
11th to 20thNight
11%3345%34446%52%
1811
21st to endNight
8%4245%3345%7%55%
1684
May1st to 10thNight
8%5%24435%5%7%9%48%
1620
11th to 20thNight
10%5%25%5%5%6%6%6%10%39%
1592
21st to endNight
8%426%6%446%7%9%43%
1744
June1st to 10thNight
11%6%46%6%46%6%8%10%34%
1620
11th to 20thNight
8%5%25%6%36%6%7%11%40%
1620
21st to endNight
6%5%37%7%46%7%9%14%33%
1620
July1st to 10thNight
7%6%36%7%46%7%9%11%34%
1620
11th to 20thNight
8%5%26%7%46%7%9%13%34%
1620
21st to endNight
6%5%36%8%47%7%9%11%34%
1771
August1st to 10thNight
8%5%36%8%46%7%9%12%31%
1611
11th to 20thNight
11%7%36%6%46%6%8%11%32%
1598
21st to endNight
10%5%37%7%5%6%7%6%12%32%
1948
September1st to 10thNight
8%436%6%45%6%7%11%42%
1980
11th to 20thNight
11%5%37%7%445%5%8%40%
1980
21st to endNight
16%5%35%4345%6%7%42%
1980
October1st to 10thNight
14%435%423346%52%
2065
11th to 20thNight
14%425%323446%54%
2160
21st to endNight
11%424334445%56%
2376
November1st to 10thNight
12%5%25%323335%56%
2221
11th to 20thNight
14%5%24323336%53%
2400
21st to endNight
14%42443446%6%48%
2470
December1st to 10thNight
17%6%35%5%445%5%5%43%
2470
11th to 20thNight
17%6%24422346%51%
3042
21st to endNight
19%7%25%5%3445%6%40%
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
38%6%9%19%22%6%
1707
11th to 20thDay
42%5%9%16%21%6%
1629
21st to endDay
39%46%20%24%7%
1782
February1st to 10thDay
42%5%10%19%18%6%
1651
11th to 20thDay
40%6%6%19%24%6%
1758
21st to endDay
43%5%10%15%19%9%
1520
March1st to 10thDay
36%47%21%22%10%
1980
11th to 20thDay
40%7%11%18%17%7%
1980
21st to endDay
40%7%11%18%19%5%
2178
April1st to 10thDay
32%5%11%19%26%7%
1980
11th to 20thDay
34%6%11%19%20%10%
2096
21st to endDay
28%8%11%26%22%5%
2290
May1st to 10thDay
31%8%15%22%21%4
2340
11th to 20thDay
39%10%16%17%17%1
2305
21st to endDay
37%11%13%23%15%1
2531
June1st to 10thDay
38%11%17%22%10%2
2340
11th to 20thDay
32%10%19%25%12%1
2340
21st to endDay
33%12%19%20%13%2
2340
July1st to 10thDay
38%14%19%16%9%3
2275
11th to 20thDay
38%15%23%17%6%1
2271
21st to endDay
36%15%21%20%7%1
2405
August1st to 10thDay
40%15%17%19%8%1
2314
11th to 20thDay
44%14%17%16%9%1
2303
21st to endDay
44%12%18%16%8%2
2382
September1st to 10thDay
35%11%15%17%18%4
1980
11th to 20thDay
40%8%11%17%20%4
1980
21st to endDay
41%7%9%20%16%7%
1980
October1st to 10thDay
34%6%7%21%24%8%
1895
11th to 20thDay
31%48%25%25%8%
1800
21st to endDay
31%5%6%18%30%12%
1980
November1st to 10thDay
33%47%17%27%12%
1857
11th to 20thDay
33%48%20%25%11%
1777
21st to endDay
37%5%8%19%22%9%
1710
December1st to 10thDay
45%6%9%18%16%6%
1710
11th to 20thDay
35%5%7%21%23%10%
2150
21st to endDay
41%5%8%20%23%3
3124
January1st to 10thNight
40%48%17%24%6%
2459
11th to 20thNight
40%5%8%17%21%8%
2354
21st to endNight
39%45%20%24%9%
2574
February1st to 10thNight
41%5%8%19%19%9%
2307
11th to 20thNight
42%5%7%18%20%8%
2099
21st to endNight
40%6%9%17%18%10%
1735
March1st to 10thNight
37%48%16%22%12%
1980
11th to 20thNight
39%6%12%16%20%7%
1980
21st to endNight
38%7%11%19%19%6%
2178
April1st to 10thNight
32%5%12%19%23%8%
1980
11th to 20thNight
33%5%9%20%21%11%
1811
21st to endNight
29%6%11%26%24%5%
1684
May1st to 10thNight
31%7%14%24%19%5%
1620
11th to 20thNight
39%11%15%18%16%1
1593
21st to endNight
33%12%14%24%15%3
1745
June1st to 10thNight
40%12%16%20%11%1
1620
11th to 20thNight
36%11%18%23%10%2
1620
21st to endNight
36%15%18%18%11%2
1620
July1st to 10thNight
38%14%21%14%9%3
1575
11th to 20thNight
37%15%24%15%6%2
1566
21st to endNight
38%15%22%17%8%1
1672
August1st to 10thNight
41%14%22%16%6%1
1600
11th to 20thNight
42%12%20%17%8%1
1598
21st to endNight
42%13%18%17%9%2
1948
September1st to 10thNight
35%10%16%19%15%5%
1980
11th to 20thNight
40%9%12%17%18%4
1980
21st to endNight
40%8%12%17%18%5%
1980
October1st to 10thNight
34%6%9%17%28%6%
2065
11th to 20thNight
31%5%9%22%23%11%
2160
21st to endNight
30%5%6%19%27%13%
2376
November1st to 10thNight
32%48%15%27%14%
2221
11th to 20thNight
34%5%6%17%24%14%
2400
21st to endNight
35%5%8%18%24%10%
2470
December1st to 10thNight
43%6%9%18%18%6%
2470
11th to 20thNight
36%37%18%26%9%
3044
21st to endNight
43%5%8%20%20%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%20%46%13%3
270
11th to 20thDay
20%21%34%20%4
243
21st to endDay
21%27%34%15%3
264
February1st to 10thDay
20%23%35%17%5%
240
11th to 20thDay
32%19%37%11%1
240
21st to endDay
23%16%40%16%4
238
March1st to 10thDay
19%17%34%24%7%
420
11th to 20thDay
21%15%39%19%5%
420
21st to endDay
19%17%35%19%9%1
462
April1st to 10thDay
17%16%30%24%13%
420
11th to 20thDay
13%15%30%24%15%4
412
21st to endDay
12%11%29%26%17%5%
420
May1st to 10thDay
9%12%35%25%15%4
423
11th to 20thDay
15%420%32%21%9%
447
21st to endDay
13%5%14%27%24%16%
485
June1st to 10thDay
12%214%32%29%10%
450
11th to 20thDay
10%419%23%28%16%
450
21st to endDay
7%313%35%28%14%
450
July1st to 10thDay
10%28%23%32%25%
445
11th to 20thDay
8%312%23%36%18%
444
21st to endDay
6%110%32%35%15%
488
August1st to 10thDay
14%313%24%28%18%
446
11th to 20thDay
15%410%23%31%17%
439
21st to endDay
14%39%27%30%17%
495
September1st to 10thDay
9%311%28%33%15%
450
11th to 20thDay
16%214%25%30%13%
450
21st to endDay
18%316%29%24%9%
450
October1st to 10thDay
16%5%21%30%21%8%
450
11th to 20thDay
12%7%23%30%21%7%
450
21st to endDay
14%8%26%28%19%6%
495
November1st to 10thDay
17%7%25%27%17%6%
455
11th to 20thDay
18%12%34%27%7%2
337
21st to endDay
10%15%37%27%10%1
270
December1st to 10thDay
26%14%35%21%4
270
11th to 20thDay
23%11%38%21%6%1
270
21st to endDay
28%14%35%15%5%3
297
January1st to 10thNight
21%15%30%26%8%
760
11th to 20thNight
20%13%32%30%7%
725
21st to endNight
19%14%36%26%4
792
February1st to 10thNight
20%13%32%30%5%
720
11th to 20thNight
22%13%37%26%2
703
21st to endNight
19%15%34%28%5%
592
March1st to 10thNight
17%10%34%34%5%
720
11th to 20thNight
19%11%36%27%8%
720
21st to endNight
16%12%36%28%8%
792
April1st to 10thNight
13%15%31%32%9%
720
11th to 20thNight
13%11%32%30%14%
711
21st to endNight
12%7%30%37%13%
604
May1st to 10thNight
10%8%30%37%15%1
540
11th to 20thNight
12%326%37%19%3
531
21st to endNight
11%214%40%30%4
584
June1st to 10thNight
13%414%39%26%5%
540
11th to 20thNight
11%214%34%31%9%
540
21st to endNight
7%313%39%30%7%
540
July1st to 10thNight
9%28%36%36%8%
525
11th to 20thNight
10%9%31%42%8%
522
21st to endNight
7%29%34%41%7%
591
August1st to 10thNight
11%110%29%41%8%
537
11th to 20thNight
14%29%31%38%6%
534
21st to endNight
13%29%30%40%7%
733
September1st to 10thNight
10%29%32%40%6%
720
11th to 20thNight
14%114%28%38%5%
720
21st to endNight
18%313%34%28%4
720
October1st to 10thNight
16%418%31%26%5%
720
11th to 20thNight
16%6%22%32%23%3
720
21st to endNight
13%6%23%32%23%2
792
November1st to 10thNight
15%6%24%34%19%3
740
11th to 20thNight
16%10%27%33%13%1
760
21st to endNight
15%9%25%35%15%1
760
December1st to 10thNight
19%12%27%33%9%1
760
11th to 20thNight
20%9%25%34%11%1
760
21st to endNight
25%13%24%31%8%
836
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