Poole's Resort Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Poole's Resort Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
25%
14752
13%
46926
7%
14721
32%
14721
14%
33853

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
11%
720
6%
2506
2%
716
15%
716
5%
2051
January16th to endNight
15%
768
9%
2616
4%
768
21%
768
8%
2024
February1st to 15thNight
11%
704
8%
2287
4%
701
17%
701
7%
1850
February16th to endNight
17%
631
11%
1940
4%
631
26%
631
10%
1493
March1st to 15thNight
16%
720
13%
2091
6%
720
24%
720
12%
1558
March16th to endNight
22%
768
18%
2037
7%
768
31%
768
18%
1441
April1st to 15thNight
19%
718
16%
1796
5%
718
25%
718
19%
1314
April16th to endNight
23%
678
16%
1758
4%
678
31%
678
19%
1228
May1st to 15thNight
28%
360
17%
1440
13%
360
39%
360
13%
941
May16th to endNight
29%
374
14%
1497
9%
374
41%
374
15%
935
June1st to 15thNight
29%
360
11%
1440
9%
360
40%
360
13%
953
June16th to endNight
36%
360
10%
1440
10%
360
46%
360
17%
891
July1st to 15thNight
41%
340
14%
1360
17%
340
49%
340
23%
763
July16th to endNight
45%
376
14%
1418
13%
354
56%
354
23%
808
August1st to 15thNight
46%
470
14%
1541
11%
468
50%
468
21%
969
August16th to endNight
51%
720
21%
1866
11%
720
55%
720
34%
1165
September1st to 15thNight
45%
720
17%
1800
9%
720
48%
720
30%
1200
September16th to endNight
46%
693
23%
1886
15%
693
50%
693
30%
1220
October1st to 15thNight
29%
660
16%
1980
12%
660
36%
660
18%
1411
October16th to endNight
19%
704
8%
2186
3%
704
25%
704
10%
1715
November1st to 15thNight
25%
700
15%
2313
12%
700
31%
700
14%
1617
November16th to endNight
17%
720
12%
2520
6%
720
25%
720
8%
1963
December1st to 15thNight
10%
720
5%
2520
2%
720
15%
720
5%
2087
December16th to endNight
10%
768
6%
2688
3%
768
13%
768
5%
2256

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
17%8%36%5%3445%6%33%
48010
Night
18%9%36%5%34446%32%
47095
Cloud CoverDay
18%8%36%5%34446%33%
48019
Night
19%10%37%5%34446%31%
47101
TransparencyDay
51%5%12%19%9%1
47697
Night
53%5%11%18%9%1
46926
SeeingDay
21%19%26%18%10%3
5539
Night
21%23%24%20%8%
14753

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
22%14%47%7%35%435%21%
1432
16th to endDay
16%14%6%9%8%445%45%20%
1608
February1st to 15thDay
14%14%5%12%8%36%445%19%
1575
16th to endDay
18%14%5%8%7%44335%24%
1532
March1st to 15thDay
18%11%5%9%7%4434425%
1856
16th to endDay
18%9%36%5%2323439%
2186
April1st to 15thDay
22%9%46%5%23335%33%
2152
16th to endDay
19%8%35%5%23445%37%
2208
May1st to 15thDay
19%6%35%5%3445%7%33%
2511
16th to endDay
15%7%25%435%45%9%37%
2618
June1st to 15thDay
21%6%25%5%25%447%33%
2520
16th to endDay
16%6%25%5%25%5%6%8%35%
2520
July1st to 15thDay
12%5%25%425%5%6%9%40%
2520
16th to endDay
11%5%245%35%5%7%8%39%
2654
August1st to 15thDay
10%6%26%6%35%5%6%8%38%
2406
16th to endDay
11%415%5%345%6%9%42%
2324
September1st to 15thDay
15%6%25%423448%42%
2160
16th to endDay
14%6%25%423346%45%
1931
October1st to 15thDay
21%8%245%24346%35%
1650
16th to endDay
26%10%37%6%35%34425%
1686
November1st to 15thDay
13%8%37%6%45%5%6%7%32%
1545
16th to endDay
21%12%48%5%24445%24%
1440
December1st to 15thDay
24%15%5%8%6%24345%18%
1440
16th to endDay
26%15%5%7%6%3443417%
1536
January1st to 15thNight
20%16%5%9%6%3444418%
2506
16th to endNight
15%16%6%9%6%34345%23%
2616
February1st to 15thNight
16%14%6%11%8%35%43421%
2285
16th to endNight
17%12%5%8%7%34445%26%
1940
March1st to 15thNight
20%12%5%6%5%2333431%
2078
16th to endNight
18%8%46%422325%39%
2037
April1st to 15thNight
23%8%34323445%34%
1796
16th to endNight
18%6%36%5%33347%38%
1758
May1st to 15thNight
20%7%25%4245%47%36%
1440
16th to endNight
13%6%25%435%5%5%7%40%
1495
June1st to 15thNight
19%7%35%5%3445%8%32%
1440
16th to endNight
15%415%426%6%6%9%36%
1440
July1st to 15thNight
9%5%24435%47%8%44%
1440
16th to endNight
9%414425%37%9%45%
1514
August1st to 15thNight
10%5%345%35%6%6%9%39%
1551
16th to endNight
10%42432346%8%49%
1866
September1st to 15thNight
13%5%25%43345%7%44%
1800
16th to endNight
14%42442335%7%45%
1886
October1st to 15thNight
21%7%26%42446%5%34%
1980
16th to endNight
26%9%37%6%24445%25%
2186
November1st to 15thNight
18%9%25%5%3445%7%32%
2313
16th to endNight
22%11%46%5%35%445%24%
2520
December1st to 15thNight
22%15%5%9%6%33335%20%
2520
16th to endNight
25%14%5%9%6%3443417%
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
23%14%5%7%7%35%34420%
1432
16th to endDay
16%15%6%9%8%45%44420%
1608
February1st to 15thDay
16%15%6%10%8%45%5%45%18%
1575
16th to endDay
18%15%48%6%3443425%
1532
March1st to 15thDay
18%12%6%10%6%3433425%
1866
16th to endDay
20%8%37%323335%39%
2185
April1st to 15thDay
22%10%45%42333433%
2152
16th to endDay
19%9%245%24445%37%
2208
May1st to 15thDay
19%6%26%42446%7%35%
2511
16th to endDay
16%5%35%4345%5%8%37%
2618
June1st to 15thDay
22%6%35%435%446%33%
2520
16th to endDay
17%6%244245%5%8%36%
2520
July1st to 15thDay
12%425%425%6%5%9%40%
2520
16th to endDay
12%4245%346%6%10%38%
2654
August1st to 15thDay
12%5%26%5%35%5%6%7%39%
2406
16th to endDay
12%4144345%6%8%44%
2324
September1st to 15thDay
16%5%24433437%42%
2160
16th to endDay
16%5%24423436%46%
1931
October1st to 15thDay
21%6%25%424438%34%
1650
16th to endDay
26%10%37%6%3343425%
1686
November1st to 15thDay
13%8%36%6%45%45%7%32%
1545
16th to endDay
21%12%5%8%5%245%45%23%
1440
December1st to 15thDay
24%16%5%9%6%34345%17%
1440
16th to endDay
26%17%5%7%6%4434415%
1536
January1st to 15thNight
20%18%5%10%6%24445%17%
2506
16th to endNight
15%16%5%9%6%34445%23%
2616
February1st to 15thNight
17%15%6%13%6%25%43320%
2278
16th to endNight
18%11%49%7%34446%25%
1940
March1st to 15thNight
21%12%46%5%2434430%
2091
16th to endNight
19%9%5%6%41223439%
2037
April1st to 15thNight
24%7%3442345%5%34%
1796
16th to endNight
19%7%34424445%39%
1758
May1st to 15thNight
21%7%25%3245%46%36%
1440
16th to endNight
13%6%25%5%26%447%40%
1495
June1st to 15thNight
19%7%35%5%3435%8%32%
1440
16th to endNight
15%415%5%35%5%5%9%37%
1440
July1st to 15thNight
10%325%435%46%8%44%
1440
16th to endNight
10%4243346%7%8%44%
1514
August1st to 15thNight
11%5%25%435%6%6%8%39%
1551
16th to endNight
10%425%42345%7%49%
1866
September1st to 15thNight
15%5%25%413347%45%
1800
16th to endNight
15%42342435%7%46%
1886
October1st to 15thNight
22%7%25%424446%34%
1980
16th to endNight
27%10%37%5%34345%24%
2186
November1st to 15thNight
19%8%25%5%345%46%32%
2313
16th to endNight
23%11%47%5%3444424%
2520
December1st to 15thNight
23%16%5%9%6%3434318%
2520
16th to endNight
25%17%5%8%6%3433416%
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
66%5%9%13%4
1433
16th to endDay
66%411%9%6%
1608
February1st to 15thDay
69%38%14%3
1577
16th to endDay
63%6%9%11%8%
1532
March1st to 15thDay
63%310%14%6%1
1866
16th to endDay
49%29%18%15%4
2186
April1st to 15thDay
53%37%19%12%2
2152
16th to endDay
49%49%19%14%3
2208
May1st to 15thDay
47%6%9%20%13%1
2511
16th to endDay
44%6%14%21%11%1
2622
June1st to 15thDay
51%6%12%20%9%
2520
16th to endDay
44%6%15%20%11%
2520
July1st to 15thDay
37%7%13%27%12%
2371
16th to endDay
40%7%18%23%9%
2487
August1st to 15thDay
42%8%15%22%10%
2392
16th to endDay
36%7%16%28%11%
2324
September1st to 15thDay
42%5%12%26%12%
2160
16th to endDay
40%5%11%28%13%
1931
October1st to 15thDay
50%5%12%20%10%
1650
16th to endDay
61%6%11%15%5%
1686
November1st to 15thDay
49%7%14%19%7%1
1545
16th to endDay
62%5%11%12%6%
1440
December1st to 15thDay
68%7%11%10%2
1440
16th to endDay
72%5%8%9%3
1536
January1st to 15thNight
69%5%10%10%3
2506
16th to endNight
63%410%14%6%
2616
February1st to 15thNight
68%49%12%4
2287
16th to endNight
60%5%11%15%7%
1940
March1st to 15thNight
57%311%19%7%
2091
16th to endNight
50%39%18%15%3
2037
April1st to 15thNight
51%48%19%14%1
1796
16th to endNight
46%5%10%18%16%2
1758
May1st to 15thNight
48%5%8%18%14%4
1440
16th to endNight
43%6%13%20%13%2
1497
June1st to 15thNight
48%6%13%21%9%
1440
16th to endNight
42%6%15%21%14%
1440
July1st to 15thNight
34%6%12%29%15%1
1360
16th to endNight
35%6%16%26%13%1
1418
August1st to 15thNight
40%7%16%22%12%
1541
16th to endNight
33%5%14%32%13%
1866
September1st to 15thNight
39%5%13%28%11%1
1800
16th to endNight
37%5%10%31%14%
1886
October1st to 15thNight
51%411%21%10%
1980
16th to endNight
62%5%13%12%5%
2186
November1st to 15thNight
51%5%15%15%9%2
2313
16th to endNight
61%6%9%15%5%
2520
December1st to 15thNight
70%5%11%11%2
2520
16th to endNight
72%5%10%8%3
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
25%25%28%10%11%
60
16th to endDay
42%13%26%14%3
76
February1st to 15thDay
31%33%31%4
90
16th to endDay
35%24%25%12%2
191
March1st to 15thDay
27%27%21%18%4
270
16th to endDay
26%24%27%13%5%2
288
April1st to 15thDay
27%28%25%10%7%
270
16th to endDay
21%27%25%12%8%4
270
May1st to 15thDay
27%20%23%17%8%1
288
16th to endDay
16%25%29%17%9%2
331
June1st to 15thDay
26%18%28%19%6%1
315
16th to endDay
20%20%27%19%11%1
315
July1st to 15thDay
14%12%28%25%13%4
305
16th to endDay
11%16%30%25%12%2
326
August1st to 15thDay
13%12%25%27%15%6%
313
16th to endDay
11%11%25%24%16%10%
332
September1st to 15thDay
16%13%24%20%13%11%
315
16th to endDay
17%12%19%20%19%9%
287
October1st to 15thDay
20%19%24%19%12%3
255
16th to endDay
31%20%27%16%3
259
November1st to 15thDay
17%20%30%19%10%2
199
16th to endDay
40%5%21%26%6%
60
December1st to 15thDay
28%21%31%11%6%
60
16th to endDay
43%28%25%3
64
January1st to 15thNight
26%30%25%13%4
720
16th to endNight
23%30%24%17%4
768
February1st to 15thNight
22%31%29%15%2
704
16th to endNight
23%25%28%18%4
631
March1st to 15thNight
26%28%24%17%3
720
16th to endNight
21%25%25%18%7%
768
April1st to 15thNight
23%27%28%17%3
718
16th to endNight
19%26%26%17%8%
678
May1st to 15thNight
23%22%19%26%8%
360
16th to endNight
10%24%31%25%6%
375
June1st to 15thNight
17%24%23%27%7%
360
16th to endNight
14%20%22%27%13%
360
July1st to 15thNight
10%14%26%32%16%
340
16th to endNight
9%18%22%34%14%1
376
August1st to 15thNight
13%12%20%32%18%1
470
16th to endNight
11%11%21%32%20%2
720
September1st to 15thNight
16%12%20%29%18%2
720
16th to endNight
16%14%20%23%20%4
693
October1st to 15thNight
24%19%22%20%12%
660
16th to endNight
29%20%25%20%4
704
November1st to 15thNight
19%24%26%18%10%
700
16th to endNight
28%29%20%13%7%
720
December1st to 15thNight
30%30%23%12%2
720
16th to endNight
28%28%26%14%11
768
Page generated at 2017-09-25 09:02:26. Version ac04

Copyright 2017 A. Danko


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