South Plymouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Plymouth clear sky chart from 2005-11-05 to 2017-08-12.

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
34%
14826
17%
46441
9%
14791
43%
14791
21%
31131

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
19%
720
16%
2506
5%
716
33%
716
17%
1643
January16th to endNight
17%
768
17%
2672
5%
768
33%
768
15%
1784
February1st to 15thNight
18%
704
15%
2171
4%
701
33%
701
17%
1508
February16th to endNight
19%
631
22%
1893
5%
631
38%
631
22%
1249
March1st to 15thNight
25%
720
17%
2133
8%
720
36%
720
20%
1465
March16th to endNight
27%
768
20%
2066
8%
768
38%
768
23%
1421
April1st to 15thNight
31%
718
17%
1796
5%
718
37%
718
24%
1292
April16th to endNight
35%
574
17%
1654
6%
574
42%
574
22%
1151
May1st to 15thNight
33%
540
14%
1620
7%
540
39%
540
19%
1159
May16th to endNight
40%
474
10%
1596
9%
473
44%
473
16%
1142
June1st to 15thNight
40%
360
11%
1440
13%
360
45%
360
14%
1002
June16th to endNight
57%
360
11%
1440
16%
360
60%
360
21%
885
July1st to 15thNight
55%
340
11%
1360
16%
340
57%
340
20%
835
July16th to endNight
53%
392
13%
1433
17%
369
56%
369
19%
925
August1st to 15thNight
59%
528
15%
1575
11%
524
61%
524
29%
995
August16th to endNight
60%
640
19%
1690
12%
640
62%
640
32%
1105
September1st to 15thNight
55%
660
20%
1730
12%
660
58%
660
32%
1138
September16th to endNight
52%
657
23%
1815
18%
657
57%
657
31%
1167
October1st to 15thNight
39%
660
20%
1837
11%
660
48%
660
24%
1238
October16th to endNight
30%
704
16%
2271
8%
704
41%
704
21%
1489
November1st to 15thNight
33%
700
15%
2277
10%
700
41%
700
19%
1531
November16th to endNight
29%
720
19%
2340
8%
720
41%
720
19%
1509
December1st to 15thNight
22%
720
17%
2438
6%
720
36%
720
17%
1637
December16th to endNight
16%
768
17%
2688
5%
768
31%
768
14%
1861

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
16%6%2442445%7%40%
47535
Night
17%7%25%424446%39%
46614
Cloud CoverDay
17%6%2442445%7%40%
47545
Night
17%7%25%424446%38%
46619
TransparencyDay
43%6%12%21%14%1
47226
Night
45%5%12%20%13%1
46441
SeeingDay
20%5%25%28%16%4
5856
Night
20%8%30%28%11%1
14826

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%9%35%32345%6%40%
1432
16th to endDay
16%7%35%424445%41%
1551
February1st to 15thDay
18%7%25%434446%38%
1687
16th to endDay
15%8%35%424446%41%
1580
March1st to 15thDay
19%8%245%23337%37%
1817
16th to endDay
16%7%34424346%42%
2157
April1st to 15thDay
18%8%25%324346%39%
2152
16th to endDay
18%5%24424446%43%
2304
May1st to 15thDay
24%8%26%422346%34%
2332
16th to endDay
16%6%24424447%41%
2527
June1st to 15thDay
24%6%2332445%7%34%
2520
16th to endDay
12%5%24425%5%5%9%40%
2520
July1st to 15thDay
12%6%2443446%9%40%
2520
16th to endDay
13%5%245%245%7%10%39%
2624
August1st to 15thDay
11%42443446%8%43%
2288
16th to endDay
11%5%1442445%8%46%
2159
September1st to 15thDay
14%424324447%45%
1900
16th to endDay
14%42432435%6%48%
1815
October1st to 15thDay
19%6%13413346%44%
1793
16th to endDay
17%424423346%45%
1599
November1st to 15thDay
23%7%24422435%39%
1581
16th to endDay
17%6%2442446%7%39%
1620
December1st to 15thDay
18%6%36%5%23336%39%
1521
16th to endDay
22%10%25%5%24335%32%
1536
January1st to 15thNight
17%9%35%424446%38%
2506
16th to endNight
18%10%35%42434438%
2672
February1st to 15thNight
15%9%36%433445%38%
2170
16th to endNight
15%7%35%5%23345%41%
1893
March1st to 15thNight
18%8%25%5%23446%38%
2120
16th to endNight
16%8%35%434335%41%
2066
April1st to 15thNight
17%8%35%5%24446%36%
1796
16th to endNight
20%6%345%34345%38%
1654
May1st to 15thNight
20%9%37%5%24347%32%
1620
16th to endNight
18%8%36%5%35%5%5%6%31%
1594
June1st to 15thNight
22%6%35%5%34447%32%
1440
16th to endNight
16%6%23425%349%40%
1440
July1st to 15thNight
13%7%25%43446%8%38%
1440
16th to endNight
12%6%35%6%36%6%7%8%33%
1530
August1st to 15thNight
9%5%25%435%6%9%7%41%
1587
16th to endNight
12%6%244335%6%7%44%
1690
September1st to 15thNight
13%425%5%2445%6%45%
1730
16th to endNight
13%5%15%423445%48%
1815
October1st to 15thNight
19%5%24424345%41%
1837
16th to endNight
17%6%2442445%5%41%
2271
November1st to 15thNight
20%7%25%5%2434440%
2277
16th to endNight
17%6%25%42435%6%41%
2340
December1st to 15thNight
19%6%25%5%23345%38%
2438
16th to endNight
18%9%35%42445%6%35%
2688

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
17%9%35%323346%39%
1432
16th to endDay
16%6%345%24346%41%
1551
February1st to 15thDay
17%8%25%434447%37%
1687
16th to endDay
15%8%25%3245%45%41%
1580
March1st to 15thDay
20%8%34423347%37%
1827
16th to endDay
16%8%35%324336%42%
2157
April1st to 15thDay
18%7%34324436%39%
2152
16th to endDay
17%5%14424346%43%
2304
May1st to 15thDay
24%7%35%422346%33%
2332
16th to endDay
16%5%24434448%40%
2527
June1st to 15thDay
23%6%2432445%8%33%
2520
16th to endDay
12%6%24435%5%6%9%40%
2520
July1st to 15thDay
12%6%144245%6%9%40%
2520
16th to endDay
13%5%244245%7%9%39%
2624
August1st to 15thDay
12%42443446%8%44%
2288
16th to endDay
11%5%2442445%8%46%
2159
September1st to 15thDay
14%5%24424447%44%
1900
16th to endDay
14%42431435%6%48%
1815
October1st to 15thDay
19%6%13413337%43%
1793
16th to endDay
17%5%24414445%45%
1599
November1st to 15thDay
23%7%34323345%38%
1581
16th to endDay
17%6%25%42445%7%38%
1620
December1st to 15thDay
18%6%36%423346%38%
1521
16th to endDay
21%11%345%33336%32%
1536
January1st to 15thNight
17%9%25%423446%38%
2506
16th to endNight
18%10%35%42433438%
2672
February1st to 15thNight
15%8%46%5%33445%38%
2163
16th to endNight
15%7%35%5%33345%41%
1893
March1st to 15thNight
18%8%35%423446%38%
2133
16th to endNight
16%8%35%424336%40%
2065
April1st to 15thNight
18%8%35%5%24446%36%
1796
16th to endNight
20%6%25%5%34436%37%
1654
May1st to 15thNight
20%8%36%5%23347%32%
1620
16th to endNight
18%9%26%5%35%5%5%6%31%
1594
June1st to 15thNight
23%6%35%6%23446%32%
1440
16th to endNight
17%6%22326%45%9%39%
1440
July1st to 15thNight
13%7%35%5%25%36%8%39%
1440
16th to endNight
13%6%36%5%36%6%7%9%33%
1530
August1st to 15thNight
9%425%5%346%8%8%41%
1587
16th to endNight
12%6%25%4235%6%6%44%
1690
September1st to 15thNight
13%425%5%3445%7%44%
1730
16th to endNight
13%6%15%423345%48%
1815
October1st to 15thNight
19%5%24424446%41%
1837
16th to endNight
17%7%24423446%41%
2271
November1st to 15thNight
20%7%25%424335%39%
2277
16th to endNight
17%6%25%424346%41%
2340
December1st to 15thNight
19%6%25%5%23446%38%
2438
16th to endNight
19%9%35%43445%6%34%
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
45%5%12%22%10%3
1433
16th to endDay
44%6%11%24%12%1
1551
February1st to 15thDay
46%6%14%19%12%1
1690
16th to endDay
43%5%14%21%13%1
1580
March1st to 15thDay
48%414%20%9%2
1827
16th to endDay
43%5%11%21%14%3
2157
April1st to 15thDay
45%49%21%16%2
2152
16th to endDay
42%5%9%21%16%3
2304
May1st to 15thDay
51%5%9%16%14%2
2332
16th to endDay
42%6%14%22%11%1
2531
June1st to 15thDay
49%6%13%19%10%
2520
16th to endDay
39%6%14%22%15%1
2520
July1st to 15thDay
39%8%13%22%14%1
2371
16th to endDay
38%8%14%23%11%2
2459
August1st to 15thDay
36%7%16%23%14%1
2275
16th to endDay
34%7%11%26%18%1
2159
September1st to 15thDay
37%6%12%20%22%
1900
16th to endDay
36%5%9%25%20%3
1815
October1st to 15thDay
41%6%11%23%15%2
1793
16th to endDay
40%5%14%22%15%2
1599
November1st to 15thDay
48%413%18%12%2
1581
16th to endDay
44%7%12%22%11%1
1620
December1st to 15thDay
47%5%16%15%14%
1521
16th to endDay
54%5%13%16%8%1
1536
January1st to 15thNight
46%5%15%19%11%1
2506
16th to endNight
48%5%11%20%12%1
2672
February1st to 15thNight
48%6%12%21%10%1
2171
16th to endNight
45%313%20%15%1
1893
March1st to 15thNight
47%5%12%18%13%2
2133
16th to endNight
45%49%18%17%4
2066
April1st to 15thNight
48%5%8%18%16%2
1796
16th to endNight
47%5%8%19%14%4
1654
May1st to 15thNight
52%5%10%15%13%2
1620
16th to endNight
52%7%11%18%8%2
1596
June1st to 15thNight
53%5%9%17%12%
1440
16th to endNight
41%7%12%22%15%1
1440
July1st to 15thNight
42%6%13%23%13%
1360
16th to endNight
44%7%13%23%7%2
1433
August1st to 15thNight
37%7%14%24%14%1
1575
16th to endNight
37%6%11%27%15%1
1690
September1st to 15thNight
38%5%12%24%18%
1730
16th to endNight
38%5%6%22%25%1
1815
October1st to 15thNight
44%411%21%14%2
1837
16th to endNight
43%6%14%20%13%1
2271
November1st to 15thNight
48%412%18%13%2
2277
16th to endNight
44%412%22%12%2
2340
December1st to 15thNight
47%5%14%20%12%
2438
16th to endNight
49%6%13%17%11%
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
20%10%43%20%6%
60
16th to endDay
24%8%37%26%2
79
February1st to 15thDay
25%10%38%23%2
255
16th to endDay
14%10%45%22%7%
239
March1st to 15thDay
24%10%37%21%5%
270
16th to endDay
21%10%33%24%9%
288
April1st to 15thDay
22%7%30%29%8%1
270
16th to endDay
24%5%27%28%11%3
270
May1st to 15thDay
33%323%22%11%4
288
16th to endDay
19%122%34%19%2
331
June1st to 15thDay
24%221%30%17%4
315
16th to endDay
14%319%38%20%3
315
July1st to 15thDay
18%11%35%30%3
305
16th to endDay
12%112%37%30%5%
326
August1st to 15thDay
13%110%39%28%6%
297
16th to endDay
13%9%29%31%14%
268
September1st to 15thDay
17%19%24%28%9%
255
16th to endDay
20%118%31%13%14%
254
October1st to 15thDay
24%6%20%23%18%6%
251
16th to endDay
16%5%38%29%9%
240
November1st to 15thDay
25%5%28%23%14%2
235
16th to endDay
17%16%31%21%11%1
240
December1st to 15thDay
21%9%34%24%9%
141
16th to endDay
29%17%35%12%4
64
January1st to 15thNight
21%13%41%19%4
720
16th to endNight
24%16%37%19%2
768
February1st to 15thNight
21%13%40%23%1
704
16th to endNight
18%12%45%19%3
631
March1st to 15thNight
23%9%36%25%5%
720
16th to endNight
20%9%37%24%8%
768
April1st to 15thNight
21%6%34%31%5%
718
16th to endNight
21%430%30%11%
574
May1st to 15thNight
25%330%27%11%2
540
16th to endNight
24%321%36%13%1
474
June1st to 15thNight
24%323%32%15%
360
16th to endNight
19%113%45%19%
360
July1st to 15thNight
16%217%44%19%
340
16th to endNight
16%114%43%23%1
392
August1st to 15thNight
10%119%45%21%1
528
16th to endNight
17%112%36%28%4
640
September1st to 15thNight
15%218%40%20%3
660
16th to endNight
16%319%29%25%5%
657
October1st to 15thNight
22%6%25%28%13%3
660
16th to endNight
21%11%33%24%9%
704
November1st to 15thNight
24%9%27%25%11%1
700
16th to endNight
20%13%31%24%9%1
720
December1st to 15thNight
23%12%36%21%5%
720
16th to endNight
23%15%40%18%1
768
Page generated at 2017-08-13 14:16:54. Version ac04

Copyright 2017 A. Danko


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