Port Mouton Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Mouton Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
26%
15183
12%
46685
6%
15140
33%
15140
14%
34478

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
16%
743
9%
2467
3%
739
24%
739
8%
1905
January16th to endNight
16%
768
10%
2496
2%
768
24%
768
8%
1968
February1st to 15thNight
14%
702
8%
2286
1%
701
22%
701
8%
1811
February16th to endNight
18%
631
10%
2015
3%
631
27%
631
12%
1504
March1st to 15thNight
19%
720
15%
1980
6%
720
27%
720
15%
1501
March16th to endNight
22%
768
16%
2112
7%
768
31%
768
16%
1522
April1st to 15thNight
20%
571
15%
1822
6%
571
30%
571
14%
1312
April16th to endNight
29%
540
15%
1620
7%
540
36%
540
17%
1150
May1st to 15thNight
25%
540
11%
1581
6%
540
30%
540
14%
1213
May16th to endNight
31%
561
11%
1496
6%
560
35%
560
17%
1123
June1st to 15thNight
29%
540
7%
1440
4%
540
32%
540
16%
1136
June16th to endNight
31%
370
7%
1270
3%
370
35%
370
11%
947
July1st to 15thNight
45%
423
10%
1273
10%
423
47%
423
17%
922
July16th to endNight
38%
565
8%
1530
6%
532
42%
532
15%
1173
August1st to 15thNight
46%
539
14%
1608
10%
535
49%
535
20%
1114
August16th to endNight
50%
573
17%
1770
12%
573
55%
573
21%
1169
September1st to 15thNight
45%
564
19%
1824
16%
564
50%
564
21%
1197
September16th to endNight
42%
681
22%
1894
15%
681
48%
681
24%
1267
October1st to 15thNight
30%
660
18%
1980
9%
660
38%
660
20%
1351
October16th to endNight
23%
704
16%
2112
6%
704
31%
704
18%
1469
November1st to 15thNight
30%
720
13%
2381
8%
720
36%
720
14%
1715
November16th to endNight
19%
750
11%
2520
4%
750
27%
750
10%
1883
December1st to 15thNight
16%
750
10%
2520
3%
750
26%
750
9%
1956
December16th to endNight
11%
800
8%
2688
1%
800
19%
800
6%
2170

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
20%9%35%5%3445%7%30%
48167
Night
20%8%35%5%3445%7%31%
46865
TransparencyDay
52%7%11%18%9%1
47865
Night
54%6%10%18%8%
46685
SeeingDay
23%17%24%24%9%1
7418
Night
22%21%23%23%8%
15185

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
16%12%5%6%7%35%5%7%7%21%
1471
16th to endDay
18%10%5%6%6%3447%8%24%
1728
February1st to 15thDay
18%10%5%8%7%46%6%5%6%20%
1575
16th to endDay
14%11%5%7%7%36%5%5%6%27%
1455
March1st to 15thDay
21%10%45%5%34346%28%
1968
16th to endDay
16%10%6%6%6%25%345%31%
2112
April1st to 15thDay
20%11%46%5%34346%28%
2123
16th to endDay
23%8%35%423337%34%
2340
May1st to 15thDay
26%9%36%5%33346%27%
2371
16th to endDay
23%8%3442445%7%31%
2618
June1st to 15thDay
28%9%45%5%24345%26%
2520
16th to endDay
21%8%26%4345%5%8%29%
2696
July1st to 15thDay
18%9%35%423349%34%
2595
16th to endDay
19%9%47%5%35%45%7%28%
2530
August1st to 15thDay
17%7%35%425%5%6%7%34%
2340
16th to endDay
13%6%244245%5%7%42%
2432
September1st to 15thDay
15%6%2442335%6%44%
2135
16th to endDay
16%7%24323446%43%
1859
October1st to 15thDay
23%5%24414446%39%
1650
16th to endDay
21%8%35%6%36%35%5%30%
1760
November1st to 15thDay
22%8%45%5%235%46%30%
1473
16th to endDay
22%9%36%6%25%45%6%26%
1440
December1st to 15thDay
23%9%37%6%46%6%6%8%19%
1440
16th to endDay
25%8%47%6%35%5%5%7%19%
1536
January1st to 15thNight
16%9%47%6%35%5%6%8%25%
2467
16th to endNight
18%10%47%5%36%5%6%8%23%
2496
February1st to 15thNight
18%8%48%6%46%5%6%7%22%
2285
16th to endNight
14%10%46%7%45%5%5%6%29%
2015
March1st to 15thNight
20%11%35%435%446%30%
1968
16th to endNight
17%9%37%5%34345%35%
2112
April1st to 15thNight
25%9%25%423446%30%
1822
16th to endNight
24%8%235%33447%32%
1620
May1st to 15thNight
26%10%46%5%22346%27%
1581
16th to endNight
22%8%36%43445%6%30%
1494
June1st to 15thNight
29%9%35%42426%6%24%
1440
16th to endNight
24%8%46%5%34346%29%
1270
July1st to 15thNight
17%9%35%42445%8%34%
1350
16th to endNight
22%8%35%5%335%5%7%28%
1636
August1st to 15thNight
16%7%36%433345%41%
1620
16th to endNight
15%6%15%433447%42%
1770
September1st to 15thNight
16%6%24424447%41%
1824
16th to endNight
19%5%24423346%44%
1894
October1st to 15thNight
22%6%23423347%39%
1980
16th to endNight
21%6%244235%5%7%36%
2112
November1st to 15thNight
21%6%35%43445%7%33%
2381
16th to endNight
20%7%35%5%45%45%7%30%
2520
December1st to 15thNight
22%8%46%5%2446%8%24%
2520
16th to endNight
24%10%35%5%35%5%5%7%22%
2688

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
60%8%12%13%4
1472
16th to endDay
57%8%10%18%5%
1728
February1st to 15thDay
61%7%12%13%4
1578
16th to endDay
53%7%14%17%5%
1455
March1st to 15thDay
55%410%18%8%1
1979
16th to endDay
47%6%12%20%11%2
2112
April1st to 15thDay
53%410%17%12%1
2123
16th to endDay
50%412%19%11%1
2340
May1st to 15thDay
58%410%16%8%1
2371
16th to endDay
52%6%12%19%7%
2622
June1st to 15thDay
59%6%10%15%7%1
2520
16th to endDay
54%7%10%15%10%1
2696
July1st to 15thDay
49%10%10%18%9%1
2444
16th to endDay
56%10%9%16%5%1
2373
August1st to 15thDay
46%9%11%19%11%1
2327
16th to endDay
38%9%13%23%13%
2432
September1st to 15thDay
40%6%11%22%17%1
2135
16th to endDay
41%5%9%25%16%
1859
October1st to 15thDay
44%5%11%23%13%1
1650
16th to endDay
53%6%12%17%9%
1760
November1st to 15thDay
52%6%13%18%8%
1473
16th to endDay
58%7%11%15%6%
1440
December1st to 15thDay
62%10%10%12%4
1440
16th to endDay
65%8%8%11%5%
1536
January1st to 15thNight
56%10%13%14%4
2467
16th to endNight
60%8%11%15%3
2496
February1st to 15thNight
61%8%10%14%4
2286
16th to endNight
54%8%14%16%6%
2015
March1st to 15thNight
56%5%10%17%9%1
1980
16th to endNight
50%5%10%18%13%1
2112
April1st to 15thNight
54%49%16%12%2
1822
16th to endNight
51%5%9%20%10%2
1620
May1st to 15thNight
60%38%18%8%
1581
16th to endNight
54%5%11%18%8%
1496
June1st to 15thNight
60%410%17%6%
1440
16th to endNight
58%6%10%13%11%
1270
July1st to 15thNight
49%9%9%21%9%1
1273
16th to endNight
56%7%10%17%6%
1530
August1st to 15thNight
46%7%10%24%10%
1608
16th to endNight
42%7%11%22%14%
1770
September1st to 15thNight
44%5%7%25%14%2
1824
16th to endNight
43%5%6%27%17%
1894
October1st to 15thNight
46%5%11%22%11%2
1980
16th to endNight
48%6%11%22%10%
2112
November1st to 15thNight
52%7%12%19%7%
2381
16th to endNight
55%8%12%16%6%
2520
December1st to 15thNight
59%8%11%16%3
2520
16th to endNight
65%7%9%12%4
2688

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%28%30%19%3
240
16th to endDay
22%23%38%13%2
256
February1st to 15thDay
22%26%27%21%2
236
16th to endDay
15%22%35%21%4
218
March1st to 15thDay
23%21%32%16%5%
270
16th to endDay
23%23%25%20%5%
288
April1st to 15thDay
25%18%30%19%5%
270
16th to endDay
20%15%27%27%7%
270
May1st to 15thDay
25%18%25%20%8%1
327
16th to endDay
28%15%22%24%7%1
519
June1st to 15thDay
27%14%18%31%7%
495
16th to endDay
23%16%20%26%12%1
495
July1st to 15thDay
25%11%14%32%14%1
475
16th to endDay
23%14%16%29%15%1
391
August1st to 15thDay
22%9%16%31%18%2
313
16th to endDay
19%7%20%26%22%3
332
September1st to 15thDay
18%8%21%33%14%2
315
16th to endDay
21%9%22%29%14%2
272
October1st to 15thDay
22%11%23%28%12%2
225
16th to endDay
20%18%33%19%7%
240
November1st to 15thDay
21%21%20%22%12%
235
16th to endDay
25%25%22%21%4
240
December1st to 15thDay
28%23%27%18%2
240
16th to endDay
28%25%30%13%2
256
January1st to 15thNight
18%28%30%18%4
743
16th to endNight
20%28%29%18%3
768
February1st to 15thNight
24%27%28%17%1
704
16th to endNight
18%25%33%18%4
631
March1st to 15thNight
23%23%29%18%4
720
16th to endNight
20%26%25%21%4
768
April1st to 15thNight
24%20%27%21%5%
571
16th to endNight
22%20%22%24%8%1
540
May1st to 15thNight
26%19%20%22%7%2
540
16th to endNight
25%19%16%27%9%2
561
June1st to 15thNight
27%19%16%26%10%
540
16th to endNight
26%18%15%25%12%
370
July1st to 15thNight
21%14%12%35%15%
423
16th to endNight
21%18%13%33%12%
565
August1st to 15thNight
20%12%11%32%20%1
539
16th to endNight
15%10%16%34%19%2
573
September1st to 15thNight
19%11%17%35%12%3
564
16th to endNight
20%12%18%28%17%3
681
October1st to 15thNight
24%15%25%24%9%1
660
16th to endNight
22%18%31%21%4
704
November1st to 15thNight
21%20%23%23%10%1
720
16th to endNight
21%26%28%15%6%
750
December1st to 15thNight
24%28%25%17%3
750
16th to endNight
29%28%26%12%2
800
Page generated at 2017-09-22 08:35:36. Version ac04

Copyright 2017 A. Danko


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