Maxwell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maxwell Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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%
15309
23%
46992
17%
15266
56%
15266
28%
29146

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
25%
720
22%
2327
9%
716
39%
716
19%
1506
January16th to endNight
27%
768
23%
2370
11%
768
39%
768
21%
1566
February1st to 15thNight
31%
704
22%
2112
10%
701
42%
701
24%
1337
February16th to endNight
28%
631
23%
1893
11%
631
37%
631
21%
1251
March1st to 15thNight
32%
720
19%
2136
11%
720
38%
720
22%
1422
March16th to endNight
39%
738
21%
2082
13%
738
45%
738
27%
1330
April1st to 15thNight
43%
539
24%
1797
16%
539
54%
539
31%
1009
April16th to endNight
50%
540
26%
1776
20%
540
60%
540
33%
999
May1st to 15thNight
52%
540
21%
1620
14%
540
59%
540
30%
1018
May16th to endNight
69%
561
21%
1682
17%
561
72%
561
33%
1014
June1st to 15thNight
70%
540
19%
1620
16%
540
72%
540
34%
966
June16th to endNight
76%
540
19%
1620
17%
540
77%
540
38%
944
July1st to 15thNight
71%
510
14%
1530
12%
510
73%
510
29%
967
July16th to endNight
77%
564
19%
1595
18%
531
78%
531
31%
1001
August1st to 15thNight
74%
539
19%
1747
22%
536
75%
536
31%
1050
August16th to endNight
69%
573
21%
1910
25%
573
69%
573
25%
1226
September1st to 15thNight
66%
633
19%
1893
18%
633
68%
633
29%
1216
September16th to endNight
63%
677
28%
1870
22%
677
66%
677
34%
1141
October1st to 15thNight
57%
660
35%
1815
27%
660
62%
660
37%
1066
October16th to endNight
50%
704
32%
2145
27%
704
58%
704
34%
1229
November1st to 15thNight
49%
700
28%
2276
24%
700
58%
700
33%
1257
November16th to endNight
37%
720
27%
2340
18%
720
51%
720
27%
1398
December1st to 15thNight
34%
720
22%
2340
15%
720
44%
720
22%
1508
December16th to endNight
30%
768
19%
2496
15%
768
38%
768
17%
1725

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%5%25%5%35%5%5%7%40%
47843
Night
12%5%2442445%7%45%
47191
TransparencyDay
41%6%11%20%16%3
47544
Night
37%5%10%20%19%5%
46994
SeeingDay
15%7%18%22%23%13%
5209
Night
15%8%21%28%22%4
15311

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 15thDay
21%7%24314446%38%
1611
16th to endDay
18%6%2442333444%
1851
February1st to 15thDay
17%8%44323436%40%
1750
16th to endDay
18%6%26%5%34335%39%
1580
March1st to 15thDay
18%8%36%423346%37%
1824
16th to endDay
15%5%345%25%6%6%7%38%
2150
April1st to 15thDay
13%6%244245%47%43%
2151
16th to endDay
12%425%43445%7%44%
2184
May1st to 15thDay
13%5%345%35%46%7%41%
2331
16th to endDay
10%6%25%5%36%46%8%39%
2431
June1st to 15thDay
7%426%5%46%6%8%11%36%
2340
16th to endDay
5%425%5%36%6%6%10%43%
2340
July1st to 15thDay
10%436%5%48%6%8%9%31%
2340
16th to endDay
7%425%7%48%7%9%10%31%
2465
August1st to 15thDay
7%425%7%47%7%8%10%35%
2199
16th to endDay
12%5%36%7%46%6%7%9%30%
2292
September1st to 15thDay
12%5%25%6%36%5%6%9%36%
2055
16th to endDay
12%5%25%5%2446%6%45%
1859
October1st to 15thDay
11%314424336%52%
1815
16th to endDay
12%5%1432223456%
1725
November1st to 15thDay
13%41342343354%
1582
16th to endDay
18%324314345%47%
1620
December1st to 15thDay
19%8%26%423445%37%
1620
16th to endDay
25%7%35%43323435%
1728
January1st to 15thNight
19%5%25%424345%41%
2327
16th to endNight
17%7%35%434335%41%
2370
February1st to 15thNight
16%7%23423236%45%
2103
16th to endNight
17%6%3443344442%
1893
March1st to 15thNight
16%7%245%34447%39%
2136
16th to endNight
13%6%24425%35%6%45%
2082
April1st to 15thNight
12%423323449%49%
1797
16th to endNight
10%31442435%7%52%
1776
May1st to 15thNight
10%4245%25%46%7%46%
1619
16th to endNight
5%315%435%5%6%10%47%
1682
June1st to 15thNight
5%3145%35%5%6%10%46%
1620
16th to endNight
3324425%6%7%11%48%
1620
July1st to 15thNight
8%4245%25%7%6%10%40%
1620
16th to endNight
5%3235%37%6%8%12%40%
1703
August1st to 15thNight
5%3146%45%6%7%10%44%
1758
16th to endNight
8%5%26%6%35%5%6%9%40%
1910
September1st to 15thNight
9%5%25%5%25%6%6%8%43%
1893
16th to endNight
9%415%5%2445%7%49%
1870
October1st to 15thNight
11%414323335%55%
1815
16th to endNight
13%42332233455%
2145
November1st to 15thNight
12%424323445%54%
2276
16th to endNight
15%6%24313345%48%
2340
December1st to 15thNight
17%6%25%424446%40%
2340
16th to endNight
22%7%25%434345%35%
2496

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
48%45%16%20%4
1612
16th to endDay
43%37%21%19%4
1851
February1st to 15thDay
46%47%22%17%3
1752
16th to endDay
47%47%18%18%3
1580
March1st to 15thDay
47%47%16%18%4
1824
16th to endDay
42%6%14%20%13%1
2151
April1st to 15thDay
38%6%10%20%17%5%
2151
16th to endDay
38%5%9%24%18%3
2184
May1st to 15thDay
40%7%11%22%14%3
2331
16th to endDay
40%8%12%24%12%2
2435
June1st to 15thDay
38%10%16%21%12%
2340
16th to endDay
33%9%15%21%16%3
2340
July1st to 15thDay
41%11%16%19%8%3
2201
16th to endDay
41%12%17%19%8%
2310
August1st to 15thDay
39%10%15%19%13%1
2186
16th to endDay
46%9%13%18%9%2
2292
September1st to 15thDay
43%8%13%17%12%4
2055
16th to endDay
38%5%11%19%20%4
1859
October1st to 15thDay
32%48%18%26%8%
1815
16th to endDay
33%25%19%29%9%
1725
November1st to 15thDay
34%3418%29%8%
1582
16th to endDay
38%36%19%26%5%
1620
December1st to 15thDay
48%5%5%19%16%4
1620
16th to endDay
53%38%18%13%3
1728
January1st to 15thNight
45%38%18%20%3
2327
16th to endNight
46%36%19%19%5%
2370
February1st to 15thNight
41%38%20%19%5%
2112
16th to endNight
44%46%21%18%4
1893
March1st to 15thNight
44%5%8%17%16%6%
2136
16th to endNight
39%5%11%24%17%1
2082
April1st to 15thNight
32%5%12%22%20%7%
1797
16th to endNight
31%5%11%24%22%5%
1776
May1st to 15thNight
35%7%12%20%22%2
1620
16th to endNight
30%9%16%24%16%2
1684
June1st to 15thNight
29%9%16%27%15%1
1620
16th to endNight
27%8%18%22%19%4
1620
July1st to 15thNight
33%10%19%20%11%4
1530
16th to endNight
30%11%18%23%13%1
1595
August1st to 15thNight
30%10%17%21%15%3
1747
16th to endNight
38%9%15%21%13%2
1910
September1st to 15thNight
35%9%18%16%15%4
1893
16th to endNight
33%5%8%22%22%7%
1870
October1st to 15thNight
31%47%22%23%10%
1815
16th to endNight
33%2316%30%13%
2145
November1st to 15thNight
32%26%19%26%12%
2276
16th to endNight
38%35%18%26%8%
2340
December1st to 15thNight
44%38%19%18%5%
2340
16th to endNight
51%47%17%15%3
2496

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
21%24%32%16%5%
90
16th to endDay
19%23%40%10%5%
96
February1st to 15thDay
18%30%41%8%1
90
16th to endDay
29%14%37%17%1
81
March1st to 15thDay
21%25%31%14%5%2
114
16th to endDay
21%12%29%22%12%2
288
April1st to 15thDay
15%14%25%24%17%2
270
16th to endDay
14%9%22%28%21%2
270
May1st to 15thDay
13%9%26%24%13%12%
288
16th to endDay
13%418%27%18%17%
331
June1st to 15thDay
10%210%20%30%25%
315
16th to endDay
7%114%22%26%27%
315
July1st to 15thDay
10%110%25%29%22%
305
16th to endDay
10%417%33%33%
326
August1st to 15thDay
12%112%19%34%19%
313
16th to endDay
17%5%23%34%18%
332
September1st to 15thDay
15%211%16%33%20%
315
16th to endDay
18%211%22%33%11%
270
October1st to 15thDay
13%321%27%25%7%
255
16th to endDay
15%5%16%28%27%6%
179
November1st to 15thDay
23%15%21%24%13%2
90
16th to endDay
13%15%33%22%14%1
90
December1st to 15thDay
25%17%33%17%5%
90
16th to endDay
32%18%30%14%4
96
January1st to 15thNight
22%17%31%20%7%
720
16th to endNight
20%15%33%27%3
768
February1st to 15thNight
20%13%31%30%3
704
16th to endNight
22%16%29%27%3
631
March1st to 15thNight
21%12%29%30%6%
720
16th to endNight
15%13%26%27%14%1
738
April1st to 15thNight
14%10%29%29%16%1
539
16th to endNight
11%7%25%35%18%
540
May1st to 15thNight
11%5%23%31%24%4
540
16th to endNight
7%212%36%34%6%
563
June1st to 15thNight
6%12%28%41%10%
540
16th to endNight
48%29%43%13%
540
July1st to 15thNight
9%17%27%39%15%
510
16th to endNight
6%15%22%46%18%
564
August1st to 15thNight
7%8%23%48%11%
539
16th to endNight
10%16%26%44%9%
573
September1st to 15thNight
12%210%25%39%9%
633
16th to endNight
10%213%31%38%3
677
October1st to 15thNight
13%419%28%28%5%
660
16th to endNight
15%7%20%28%25%2
704
November1st to 15thNight
13%9%24%29%20%3
700
16th to endNight
18%11%27%25%15%
720
December1st to 15thNight
21%11%27%28%10%
720
16th to endNight
27%13%24%27%6%
768
Page generated at 2017-09-21 06:18:23. Version ac04

Copyright 2017 A. Danko


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