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 2017-10-31.

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
69%
16023
26%
47432
23%
15985
72%
15985
41%
26091

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%
540
26%
1798
23%
540
62%
540
33%
992
May1st to 15thNight
65%
539
24%
1619
19%
539
69%
539
38%
901
May16th to endNight
65%
561
24%
1535
18%
561
69%
561
44%
857
June1st to 15thNight
73%
540
29%
1440
22%
540
76%
540
61%
695
June16th to endNight
85%
540
33%
1440
30%
540
87%
540
68%
674
July1st to 15thNight
86%
510
20%
1414
18%
510
86%
510
46%
777
July16th to endNight
84%
564
20%
1593
18%
531
85%
531
41%
872
August1st to 15thNight
83%
539
22%
1611
22%
536
83%
536
44%
864
August16th to endNight
86%
573
31%
1875
33%
573
87%
573
43%
954
September1st to 15thNight
80%
540
31%
1800
35%
540
82%
540
44%
884
September16th to endNight
77%
677
38%
1986
32%
677
81%
677
54%
959
October1st to 15thNight
74%
720
32%
2160
27%
720
77%
720
51%
1086
October16th to endNight
76%
768
37%
2304
32%
768
78%
768
51%
1127
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
33134245%6%8%55%
48313
Night
441432445%7%57%
47622
TransparencyDay
24%7%12%22%21%11%
48003
Night
25%6%13%23%21%10%
47434
SeeingDay
5%8%21%32%24%6%
5838
Night
5%316%41%29%3
16034

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
3415%3245%6%8%53%
2160
May1st to 15thDay
4323435%5%7%7%52%
2331
16th to endDay
22133245%6%8%58%
2576
June1st to 15thDay
221231445%7%64%
2520
16th to endDay
111212346%72%
2520
July1st to 15thDay
3213425%5%7%10%53%
2459
16th to endDay
3213436%6%8%12%46%
2467
August1st to 15thDay
4313436%6%8%10%46%
2340
16th to endDay
21124347%7%10%54%
2327
September1st to 15thDay
5%3123245%5%7%57%
2160
16th to endDay
4212212246%68%
1971
October1st to 15thDay
6%322322347%62%
1800
16th to endDay
3212223345%66%
1918
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%
1798
May1st to 15thNight
5%3133245%6%9%54%
1619
16th to endNight
421333435%8%58%
1535
June1st to 15thNight
111221235%6%71%
1440
16th to endNight
112113347%73%
1440
July1st to 15thNight
312325%5%7%9%55%
1498
16th to endNight
2113435%6%7%12%50%
1701
August1st to 15thNight
22143245%7%10%55%
1620
16th to endNight
21123245%5%11%57%
1875
September1st to 15thNight
321232446%9%59%
1800
16th to endNight
42231333470%
1986
October1st to 15thNight
3312323347%65%
2160
16th to endNight
3312212235%68%
2304
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%
2160
May1st to 15thDay
27%8%11%22%24%6%
2331
16th to endDay
21%7%11%19%28%11%
2579
June1st to 15thDay
17%47%14%26%28%
2520
16th to endDay
12%35%10%26%41%
2520
July1st to 15thDay
23%7%13%14%17%23%
2315
16th to endDay
26%11%15%19%13%13%
2312
August1st to 15thDay
28%11%13%16%13%15%
2325
16th to endDay
21%8%13%19%23%14%
2327
September1st to 15thDay
23%8%10%15%25%17%
2160
16th to endDay
16%5%9%19%36%12%
1971
October1st to 15thDay
22%49%25%30%7%
1800
16th to endDay
19%49%27%33%4
1918
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%23%9%
1798
May1st to 15thNight
26%7%13%20%26%6%
1620
16th to endNight
23%6%13%19%26%10%
1536
June1st to 15thNight
13%47%15%25%33%
1440
16th to endNight
10%35%12%22%44%
1440
July1st to 15thNight
21%7%12%15%15%26%
1414
16th to endNight
22%9%19%17%16%14%
1593
August1st to 15thNight
21%8%17%21%13%17%
1611
16th to endNight
20%7%11%17%23%18%
1875
September1st to 15thNight
20%6%13%17%20%22%
1800
16th to endNight
17%37%18%32%18%
1986
October1st to 15thNight
19%49%22%30%13%
2160
16th to endNight
19%47%25%35%8%
2304
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%19%36%25%7%1
270
May1st to 15thDay
7%18%31%27%12%1
288
16th to endDay
310%24%29%24%6%
477
June1st to 15thDay
48%24%30%26%4
495
16th to endDay
2317%35%34%6%
495
July1st to 15thDay
4112%33%37%10%
419
16th to endDay
6%113%39%32%7%
327
August1st to 15thDay
5%218%36%30%7%
315
16th to endDay
2214%36%36%8%
332
September1st to 15thDay
5%321%39%21%8%
315
16th to endDay
6%10%22%30%23%8%
270
October1st to 15thDay
5%8%17%28%25%14%
135
16th to endDay
45%15%30%32%11%
144
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
540
May1st to 15thNight
7%320%47%20%1
540
16th to endNight
4420%36%29%4
563
June1st to 15thNight
1317%44%29%3
540
16th to endNight
118%43%41%3
540
July1st to 15thNight
3335%53%4
510
16th to endNight
3328%57%7%
564
August1st to 15thNight
45%33%51%4
539
16th to endNight
2432%50%8%
573
September1st to 15thNight
38%40%42%5%
540
16th to endNight
5%110%33%41%7%
677
October1st to 15thNight
3216%45%28%3
720
16th to endNight
5%112%40%33%6%
768
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 2017-11-01 15:23:38. Version ac04

Copyright 2017 A. Danko


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