Wilson Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilson Hill Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
58%
15099
25%
46945
21%
15062
64%
15062
33%
26959

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
50%
718
17%
2491
14%
716
56%
716
22%
1581
January16th to endNight
46%
768
25%
2496
20%
768
54%
768
24%
1587
February1st to 15thNight
44%
697
21%
2287
18%
696
51%
696
20%
1501
February16th to endNight
43%
632
20%
1927
16%
632
51%
632
21%
1306
March1st to 15thNight
40%
720
12%
2040
8%
720
44%
720
18%
1488
March16th to endNight
41%
768
17%
2073
11%
768
46%
768
23%
1441
April1st to 15thNight
42%
719
18%
1799
8%
719
47%
719
25%
1260
April16th to endNight
52%
720
23%
1800
10%
720
57%
720
38%
1093
May1st to 15thNight
55%
480
25%
1560
18%
480
63%
480
38%
819
May16th to endNight
61%
375
20%
1496
21%
374
66%
374
27%
809
June1st to 15thNight
65%
360
22%
1440
26%
360
72%
360
32%
716
June16th to endNight
75%
360
31%
1440
43%
360
80%
360
50%
558
July1st to 15thNight
90%
340
32%
1360
45%
340
91%
340
65%
455
July16th to endNight
90%
477
39%
1509
41%
447
93%
447
73%
552
August1st to 15thNight
90%
538
38%
1611
32%
535
91%
535
71%
657
August16th to endNight
89%
747
44%
1893
29%
747
91%
747
81%
836
September1st to 15thNight
87%
720
42%
1800
28%
720
89%
720
79%
817
September16th to endNight
75%
688
39%
1875
31%
688
80%
688
60%
887
October1st to 15thNight
66%
660
30%
1980
28%
660
74%
660
45%
1001
October16th to endNight
63%
704
30%
2112
29%
704
69%
704
38%
1170
November1st to 15thNight
57%
700
23%
2251
20%
700
63%
700
27%
1393
November16th to endNight
50%
720
19%
2497
18%
720
55%
720
23%
1546
December1st to 15thNight
44%
720
18%
2520
14%
720
52%
720
20%
1642
December16th to endNight
35%
768
20%
2688
15%
768
44%
768
17%
1844

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
11%412212335%59%
47973
Night
13%413213345%56%
47127
TransparencyDay
28%5%7%17%23%17%
47653
Night
31%5%7%18%21%15%
46947
SeeingDay
14%13%26%29%12%3
5849
Night
15%6%15%29%28%5%
15109

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
18%6%23324446%42%
1447
16th to endDay
20%7%24213345%45%
1728
February1st to 15thDay
20%6%25%313436%42%
1576
16th to endDay
20%9%34412446%38%
1547
March1st to 15thDay
25%8%14423446%32%
1919
16th to endDay
21%6%23423349%37%
2151
April1st to 15thDay
18%8%34323447%39%
2149
16th to endDay
11%422323345%54%
2160
May1st to 15thDay
7%313313347%60%
2388
16th to endDay
9%413324445%56%
2615
June1st to 15thDay
8%313323245%60%
2520
16th to endDay
41111122379%
2520
July1st to 15thDay
11111122284%
2520
16th to endDay
111289%
2553
August1st to 15thDay
111112384%
2340
16th to endDay
111112286%
2309
September1st to 15thDay
1111113482%
2160
16th to endDay
421212236%72%
1918
October1st to 15thDay
8%31222225%5%64%
1650
16th to endDay
12%413312336%56%
1760
November1st to 15thDay
14%31342445%7%46%
1606
16th to endDay
17%6%2433233446%
1461
December1st to 15thDay
22%5%15%3235%46%39%
1440
16th to endDay
28%6%23212336%37%
1536
January1st to 15thNight
16%6%24324447%43%
2491
16th to endNight
20%6%2322334446%
2496
February1st to 15thNight
20%6%24423436%41%
2276
16th to endNight
19%9%24413346%39%
1927
March1st to 15thNight
24%7%23424447%33%
2040
16th to endNight
18%6%2432345%6%41%
2073
April1st to 15thNight
15%6%345%2345%8%41%
1799
16th to endNight
13%312312347%56%
1800
May1st to 15thNight
9%22224446%61%
1560
16th to endNight
7%424425%346%55%
1496
June1st to 15thNight
8%43313347%58%
1440
16th to endNight
411211123376%
1440
July1st to 15thNight
1111212381%
1440
16th to endNight
1111112286%
1613
August1st to 15thNight
1111122382%
1620
16th to endNight
1122386%
1893
September1st to 15thNight
11112485%
1800
16th to endNight
31121123476%
1875
October1st to 15thNight
7%212212235%67%
1980
16th to endNight
10%4322335%5%58%
2112
November1st to 15thNight
14%333236%5%6%48%
2251
16th to endNight
18%5%2322345%6%45%
2497
December1st to 15thNight
24%5%23223346%41%
2520
16th to endNight
28%6%13323335%37%
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
42%7%9%18%16%6%
1447
16th to endDay
42%5%7%15%16%11%
1728
February1st to 15thDay
44%6%9%16%19%4
1576
16th to endDay
47%7%7%24%10%2
1547
March1st to 15thDay
52%6%6%14%14%4
1919
16th to endDay
45%7%12%17%12%4
2151
April1st to 15thDay
45%8%10%17%17%1
2149
16th to endDay
31%6%10%24%20%5%
2160
May1st to 15thDay
23%6%10%24%26%9%
2388
16th to endDay
30%7%9%24%21%6%
2619
June1st to 15thDay
27%5%9%17%23%17%
2520
16th to endDay
12%3415%37%26%
2520
July1st to 15thDay
8%2312%33%39%
2371
16th to endDay
6%1212%26%50%
2394
August1st to 15thDay
7%2318%30%37%
2324
16th to endDay
6%1313%35%38%
2309
September1st to 15thDay
8%2312%33%39%
2160
16th to endDay
14%37%22%31%20%
1918
October1st to 15thDay
22%5%7%21%28%13%
1650
16th to endDay
31%49%17%24%12%
1760
November1st to 15thDay
37%6%10%22%13%8%
1606
16th to endDay
42%5%8%18%16%8%
1461
December1st to 15thDay
45%7%8%15%17%5%
1440
16th to endDay
49%5%7%13%16%7%
1536
January1st to 15thNight
40%7%10%16%16%7%
2491
16th to endNight
42%5%5%15%18%13%
2496
February1st to 15thNight
45%5%7%17%16%7%
2288
16th to endNight
45%6%8%20%14%3
1927
March1st to 15thNight
51%7%9%12%12%6%
2040
16th to endNight
43%8%11%18%13%4
2073
April1st to 15thNight
41%9%13%19%13%3
1799
16th to endNight
28%6%11%28%21%4
1800
May1st to 15thNight
24%6%8%25%25%9%
1561
16th to endNight
30%8%11%25%17%6%
1496
June1st to 15thNight
26%6%10%21%23%12%
1440
16th to endNight
13%45%16%33%25%
1440
July1st to 15thNight
9%1312%28%44%
1360
16th to endNight
7%239%22%54%
1509
August1st to 15thNight
9%1415%30%37%
1611
16th to endNight
5%2215%33%39%
1893
September1st to 15thNight
6%2412%31%43%
1800
16th to endNight
12%46%20%30%25%
1875
October1st to 15thNight
21%46%21%29%16%
1980
16th to endNight
26%6%8%21%22%13%
2112
November1st to 15thNight
33%11%10%24%12%8%
2251
16th to endNight
38%7%8%19%17%8%
2497
December1st to 15thNight
45%5%7%14%22%4
2520
16th to endNight
50%5%5%11%19%6%
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
37%12%28%14%8%
75
16th to endDay
27%16%19%17%14%3
256
February1st to 15thDay
27%15%22%24%9%
236
16th to endDay
26%13%30%18%10%
233
March1st to 15thDay
35%17%21%14%10%1
270
16th to endDay
25%24%24%18%7%
288
April1st to 15thDay
26%22%25%18%41
269
16th to endDay
14%24%36%15%8%1
270
May1st to 15thDay
14%19%35%22%6%2
288
16th to endDay
13%13%26%26%14%6%
330
June1st to 15thDay
10%17%28%30%10%3
315
16th to endDay
39%31%39%11%5%
315
July1st to 15thDay
1429%43%12%8%
305
16th to endDay
325%48%15%7%
327
August1st to 15thDay
15%28%42%14%7%
315
16th to endDay
429%39%15%9%
332
September1st to 15thDay
25%27%39%20%5%
315
16th to endDay
415%24%36%15%2
284
October1st to 15thDay
12%14%23%27%18%3
255
16th to endDay
20%12%25%27%14%
272
November1st to 15thDay
19%8%11%28%25%5%
112
16th to endDay
22%15%26%22%11%1
63
December1st to 15thDay
51%6%25%13%3
60
16th to endDay
21%7%20%31%18%
64
January1st to 15thNight
20%5%17%34%18%3
720
16th to endNight
24%6%19%26%18%4
768
February1st to 15thNight
24%9%15%31%17%1
704
16th to endNight
25%8%17%30%15%3
632
March1st to 15thNight
28%9%17%23%18%3
720
16th to endNight
23%10%19%24%18%2
768
April1st to 15thNight
17%12%20%30%16%1
719
16th to endNight
14%9%19%32%18%5%
720
May1st to 15thNight
10%7%23%31%24%2
481
16th to endNight
10%5%16%29%34%4
375
June1st to 15thNight
9%5%15%34%32%2
360
16th to endNight
5%213%36%39%3
360
July1st to 15thNight
15%25%63%4
340
16th to endNight
1424%61%7%
477
August1st to 15thNight
2324%58%9%
538
16th to endNight
16%31%51%7%
747
September1st to 15thNight
117%32%45%10%
720
16th to endNight
36%11%29%34%13%
688
October1st to 15thNight
8%7%14%32%28%8%
660
16th to endNight
13%6%13%30%27%8%
704
November1st to 15thNight
16%417%29%24%6%
700
16th to endNight
20%8%16%28%21%4
720
December1st to 15thNight
28%6%15%29%17%3
720
16th to endNight
31%7%22%24%13%1
768
Page generated at 2017-09-24 06:15:47. Version ac04

Copyright 2017 A. Danko


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