Pool Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pool Observatory clear sky chart from 2005-11-05 to 2017-04-26.

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
68%
15422
26%
45655
23%
15384
71%
15384
41%
25247

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
66%
762
22%
2372
23%
761
67%
761
36%
1344
January16th to endNight
64%
768
25%
2496
27%
768
65%
768
33%
1417
February1st to 15thNight
61%
700
18%
2288
19%
699
63%
699
30%
1356
February16th to endNight
56%
632
27%
1938
22%
632
63%
632
36%
1117
March1st to 15thNight
66%
720
29%
1980
23%
720
71%
720
45%
1102
March16th to endNight
60%
768
25%
2112
19%
768
65%
768
39%
1255
April1st to 15thNight
56%
542
22%
1801
21%
542
61%
542
34%
990
April16th to endNight
55%
528
25%
1758
23%
528
62%
528
33%
965
May1st to 15thNight
64%
494
25%
1484
20%
494
68%
494
37%
832
May16th to endNight
65%
513
23%
1404
17%
513
69%
513
44%
784
June1st to 15thNight
73%
495
31%
1320
24%
495
77%
495
60%
638
June16th to endNight
85%
495
31%
1320
27%
495
86%
495
66%
627
July1st to 15thNight
85%
465
21%
1289
19%
465
86%
465
45%
715
July16th to endNight
85%
522
20%
1467
19%
489
85%
489
42%
794
August1st to 15thNight
82%
494
23%
1476
23%
491
82%
491
43%
797
August16th to endNight
85%
525
29%
1718
31%
525
86%
525
42%
887
September1st to 15thNight
79%
495
32%
1650
36%
495
81%
495
42%
825
September16th to endNight
79%
620
36%
1820
31%
620
81%
620
54%
883
October1st to 15thNight
73%
660
33%
1980
28%
660
77%
660
50%
1006
October16th to endNight
74%
704
35%
2112
29%
704
77%
704
50%
1045
November1st to 15thNight
71%
760
31%
2160
26%
760
74%
760
48%
1140
November16th to endNight
66%
900
29%
2502
24%
900
69%
900
48%
1332
December1st to 15thNight
61%
900
17%
2520
13%
900
63%
900
33%
1567
December16th to endNight
55%
960
17%
2688
14%
960
56%
960
26%
1829

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
33234245%6%8%55%
45999
Night
441432445%7%56%
45845
TransparencyDay
25%7%12%22%21%10%
45689
Night
25%6%13%23%20%9%
45657
SeeingDay
6%9%22%33%23%5%
5076
Night
5%316%42%28%3
15433

By Month

Percentage Cloud Cover SW (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
25%245%36%5%7%9%46%
1576
16th to endDay
35%245%2445%8%53%
1728
February1st to 15thDay
3435%5%35%449%49%
1575
16th to endDay
36%345%46%6%6%6%46%
1532
March1st to 15thDay
2425%41445%7%57%
1980
16th to endDay
2324425%5%5%9%55%
2112
April1st to 15thDay
3325%4246%6%7%52%
2146
16th to endDay
3315%3246%6%8%53%
2111
May1st to 15thDay
4323435%5%7%7%52%
2136
16th to endDay
22133245%6%8%58%
2355
June1st to 15thDay
221232445%7%63%
2310
16th to endDay
112212346%71%
2310
July1st to 15thDay
3213435%5%7%10%53%
2254
16th to endDay
3213436%6%7%11%47%
2285
August1st to 15thDay
4313436%6%7%9%46%
2145
16th to endDay
21124347%8%10%52%
2132
September1st to 15thDay
6%3123346%5%7%56%
1980
16th to endDay
3212212346%69%
1807
October1st to 15thDay
6%32232235%7%61%
1650
16th to endDay
4312324345%65%
1760
November1st to 15thDay
221331345%7%63%
1684
16th to endDay
231332345%7%61%
1455
December1st to 15thDay
46%37%6%445%5%8%43%
1440
16th to endDay
310%47%6%46%5%6%7%37%
1536
January1st to 15thNight
36%25%5%2445%9%50%
2372
16th to endNight
6%7%25%424347%51%
2496
February1st to 15thNight
45%26%425%35%7%51%
2277
16th to endNight
46%35%42345%7%51%
1938
March1st to 15thNight
33232245%5%7%58%
1980
16th to endNight
3424425%45%7%53%
2112
April1st to 15thNight
5%4144245%6%7%52%
1801
16th to endNight
6%42442446%5%55%
1758
May1st to 15thNight
6%3133245%7%9%53%
1484
16th to endNight
421233446%8%58%
1404
June1st to 15thNight
111221245%6%71%
1320
16th to endNight
112213347%72%
1320
July1st to 15thNight
312326%5%7%10%54%
1373
16th to endNight
2113435%7%7%12%51%
1575
August1st to 15thNight
321432447%10%55%
1485
16th to endNight
21123245%5%11%56%
1718
September1st to 15thNight
321242445%10%58%
1650
16th to endNight
422313335%69%
1820
October1st to 15thNight
3313323447%64%
1980
16th to endNight
4312212336%67%
2112
November1st to 15thNight
332332335%5%64%
2160
16th to endNight
4413212346%64%
2502
December1st to 15thNight
5%7%35%5%24337%51%
2520
16th to endNight
410%46%6%35%6%48%39%
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
28%8%22%30%9%
1577
16th to endDay
27%7%19%31%12%1
1728
February1st to 15thDay
32%7%20%26%10%2
1575
16th to endDay
32%9%11%28%16%1
1532
March1st to 15thDay
27%6%11%31%20%2
1980
16th to endDay
24%8%11%30%20%4
2112
April1st to 15thDay
27%7%12%22%21%8%
2146
16th to endDay
26%7%11%24%22%6%
2111
May1st to 15thDay
27%8%10%22%24%6%
2136
16th to endDay
21%7%11%18%28%11%
2358
June1st to 15thDay
18%47%14%26%28%
2310
16th to endDay
13%35%11%26%40%
2310
July1st to 15thDay
24%7%13%14%17%23%
2110
16th to endDay
27%10%14%19%13%14%
2130
August1st to 15thDay
29%11%13%15%12%17%
2130
16th to endDay
22%9%14%19%22%13%
2132
September1st to 15thDay
23%8%10%14%25%17%
1980
16th to endDay
16%5%9%18%38%12%
1807
October1st to 15thDay
23%410%26%30%5%
1650
16th to endDay
20%5%9%27%33%3
1760
November1st to 15thDay
18%5%11%27%27%7%
1684
16th to endDay
22%413%36%20%2
1455
December1st to 15thDay
36%8%16%30%8%
1440
16th to endDay
43%8%20%20%6%
1536
January1st to 15thNight
28%7%20%30%12%
2372
16th to endNight
32%416%29%14%2
2496
February1st to 15thNight
32%8%18%26%12%1
2288
16th to endNight
29%6%11%29%20%2
1938
March1st to 15thNight
23%7%11%34%21%2
1980
16th to endNight
29%6%9%25%25%3
2112
April1st to 15thNight
29%6%12%19%21%11%
1801
16th to endNight
28%7%8%23%22%9%
1758
May1st to 15thNight
26%7%12%19%27%5%
1485
16th to endNight
23%6%13%19%25%10%
1405
June1st to 15thNight
13%48%16%25%31%
1320
16th to endNight
11%46%13%22%42%
1320
July1st to 15thNight
21%8%12%15%14%26%
1289
16th to endNight
22%9%18%17%16%15%
1467
August1st to 15thNight
21%8%17%19%13%18%
1476
16th to endNight
21%8%12%17%22%17%
1718
September1st to 15thNight
21%7%13%15%19%22%
1650
16th to endNight
17%37%17%32%19%
1820
October1st to 15thNight
19%5%9%23%29%12%
1980
16th to endNight
19%47%25%35%7%
2112
November1st to 15thNight
21%5%11%26%27%7%
2160
16th to endNight
21%5%11%31%25%4
2502
December1st to 15thNight
33%7%17%26%15%
2520
16th to endNight
40%9%19%22%7%
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%8%13%27%20%12%
90
16th to endDay
8%111%48%21%8%
96
February1st to 15thDay
10%5%8%50%25%
90
16th to endDay
9%10%17%34%19%9%
87
March1st to 15thDay
5%19%26%27%18%2
270
16th to endDay
7%23%31%24%11%1
288
April1st to 15thDay
7%21%33%17%13%5%
269
16th to endDay
10%18%37%24%7%1
254
May1st to 15thDay
8%21%31%28%10%
228
16th to endDay
311%24%31%23%6%
400
June1st to 15thDay
49%25%31%25%4
420
16th to endDay
3316%36%35%6%
420
July1st to 15thDay
4213%36%36%7%
349
16th to endDay
6%115%44%28%4
271
August1st to 15thDay
7%219%35%28%7%
255
16th to endDay
1216%38%33%7%
268
September1st to 15thDay
6%324%44%17%3
255
16th to endDay
6%6%19%31%26%9%
214
October1st to 15thDay
35%13%27%32%17%
90
16th to endDay
7%6%16%30%32%7%
96
November1st to 15thDay
3218%24%32%18%
90
16th to endDay
6%8%30%40%11%3
90
December1st to 15thDay
10%427%45%12%
90
16th to endDay
7%7%13%43%23%4
96
January1st to 15thNight
5%316%45%25%3
766
16th to endNight
8%416%42%24%3
768
February1st to 15thNight
7%221%47%18%1
704
16th to endNight
5%426%49%12%
632
March1st to 15thNight
4322%45%22%1
720
16th to endNight
4424%43%21%1
768
April1st to 15thNight
5%428%44%14%1
542
16th to endNight
8%5%27%36%20%2
528
May1st to 15thNight
8%320%47%19%1
495
16th to endNight
45%20%36%28%4
515
June1st to 15thNight
1317%46%28%2
495
16th to endNight
118%44%40%3
495
July1st to 15thNight
3336%52%3
465
16th to endNight
2429%57%6%
522
August1st to 15thNight
45%33%50%5%
494
16th to endNight
35%33%48%8%
525
September1st to 15thNight
48%43%40%3
495
16th to endNight
5%19%32%43%7%
620
October1st to 15thNight
4215%43%30%3
660
16th to endNight
5%113%40%32%5%
704
November1st to 15thNight
5%314%42%30%3
760
16th to endNight
6%419%41%23%3
900
December1st to 15thNight
8%418%48%19%1
900
16th to endNight
8%6%21%42%19%2
960
Page generated at 2017-04-27 15:48:47. Version ac04

Copyright 2017 A. Danko


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