Wes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wes 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
53%
15757
22%
47003
16%
15716
60%
15716
29%
29239

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
35%
717
23%
2327
11%
716
49%
716
24%
1410
January16th to endNight
33%
768
23%
2496
14%
768
45%
768
26%
1525
February1st to 15thNight
37%
704
24%
2112
13%
700
49%
700
28%
1312
February16th to endNight
35%
631
26%
1893
13%
631
47%
631
30%
1153
March1st to 15thNight
43%
720
28%
1983
15%
720
54%
720
36%
1181
March16th to endNight
44%
768
23%
2112
12%
768
52%
768
34%
1285
April1st to 15thNight
45%
718
24%
1976
16%
718
53%
718
36%
1176
April16th to endNight
53%
609
29%
1716
19%
609
62%
609
39%
975
May1st to 15thNight
57%
539
24%
1620
15%
539
64%
539
36%
951
May16th to endNight
69%
561
20%
1683
15%
561
71%
561
30%
1047
June1st to 15thNight
68%
540
13%
1620
10%
540
69%
540
27%
1079
June16th to endNight
74%
540
14%
1620
12%
540
74%
540
25%
1083
July1st to 15thNight
71%
510
14%
1530
12%
510
72%
510
26%
1002
July16th to endNight
75%
564
12%
1595
11%
531
75%
531
24%
1088
August1st to 15thNight
73%
539
12%
1609
12%
536
73%
536
23%
1116
August16th to endNight
62%
644
14%
1927
14%
644
62%
644
20%
1361
September1st to 15thNight
68%
720
16%
1980
15%
720
68%
720
27%
1315
September16th to endNight
58%
693
17%
1914
14%
693
60%
693
24%
1320
October1st to 15thNight
59%
660
29%
1874
25%
660
64%
660
34%
1134
October16th to endNight
59%
704
32%
2112
30%
704
66%
704
38%
1186
November1st to 15thNight
56%
700
29%
2128
26%
700
64%
700
35%
1203
November16th to endNight
45%
720
28%
2340
21%
720
57%
720
31%
1339
December1st to 15thNight
44%
720
22%
2340
18%
720
52%
720
27%
1402
December16th to endNight
42%
768
23%
2496
19%
768
50%
768
23%
1596

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%5%25%5%35%5%5%8%42%
47916
Night
10%5%24425%45%7%45%
47204
TransparencyDay
39%7%11%17%16%6%
47617
Night
35%7%12%18%17%8%
47007
SeeingDay
12%316%21%25%20%
5617
Night
12%421%32%24%3
15763

By Month

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
14%5%24325%5%46%44%
1611
16th to endDay
14%5%25%424346%45%
1728
February1st to 15thDay
14%6%24424447%44%
1744
16th to endDay
14%5%34413236%49%
1580
March1st to 15thDay
10%425%323347%49%
1977
16th to endDay
12%5%25%5%2445%5%47%
2111
April1st to 15thDay
10%424424447%49%
1972
16th to endDay
9%41442345%6%52%
2251
May1st to 15thDay
8%3245%35%5%6%7%47%
2331
16th to endDay
8%435%6%35%6%5%9%40%
2431
June1st to 15thDay
10%4246%46%6%7%11%34%
2340
16th to endDay
5%425%5%47%7%8%10%36%
2340
July1st to 15thDay
8%425%7%49%7%8%11%30%
2340
16th to endDay
7%6%26%6%5%7%8%8%10%29%
2465
August1st to 15thDay
9%5%28%7%5%7%8%8%10%26%
2340
16th to endDay
12%6%37%8%47%5%7%9%26%
2260
September1st to 15thDay
10%6%37%6%36%5%5%8%36%
1980
16th to endDay
16%7%26%5%25%5%5%7%34%
1905
October1st to 15thDay
15%424313245%52%
1755
16th to endDay
9%424323345%57%
1760
November1st to 15thDay
9%313423346%56%
1727
16th to endDay
12%5%14323247%51%
1620
December1st to 15thDay
15%5%25%414445%46%
1620
16th to endDay
17%8%25%425%347%38%
1728
January1st to 15thNight
12%5%345%25%446%45%
2327
16th to endNight
16%5%2442434447%
2496
February1st to 15thNight
13%6%25%323346%47%
2106
16th to endNight
13%424424445%49%
1893
March1st to 15thNight
8%4145%2445%8%51%
1983
16th to endNight
10%424424335%53%
2112
April1st to 15thNight
11%423423347%52%
1976
16th to endNight
7%313325%46%7%53%
1716
May1st to 15thNight
5%42442435%7%53%
1619
16th to endNight
4425%435%6%8%7%45%
1682
June1st to 15thNight
9%425%5%37%7%7%12%36%
1620
16th to endNight
5%415%6%46%7%9%11%36%
1620
July1st to 15thNight
7%435%5%47%7%8%13%33%
1620
16th to endNight
5%436%6%46%7%8%11%35%
1703
August1st to 15thNight
5%426%6%37%7%9%13%31%
1620
16th to endNight
10%6%35%6%37%6%8%10%32%
1927
September1st to 15thNight
10%325%5%35%5%6%11%39%
1980
16th to endNight
12%6%35%5%35%5%6%8%36%
1914
October1st to 15thNight
13%6%13313345%52%
1874
16th to endNight
10%323413345%56%
2112
November1st to 15thNight
10%424323346%54%
2128
16th to endNight
12%424324335%53%
2340
December1st to 15thNight
14%5%25%32435%6%46%
2340
16th to endNight
16%6%25%42445%6%41%
2496

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
38%5%7%15%21%10%
1612
16th to endDay
39%36%17%22%9%
1728
February1st to 15thDay
40%47%14%22%10%
1746
16th to endDay
38%36%17%24%11%
1580
March1st to 15thDay
34%5%7%21%21%10%
1977
16th to endDay
37%5%11%16%20%7%
2112
April1st to 15thDay
34%5%8%20%21%10%
1972
16th to endDay
31%5%10%21%21%10%
2251
May1st to 15thDay
34%7%11%20%21%5%
2331
16th to endDay
38%8%13%23%12%3
2435
June1st to 15thDay
39%11%16%19%11%
2340
16th to endDay
38%11%17%18%12%1
2340
July1st to 15thDay
41%12%21%16%5%2
2201
16th to endDay
43%12%20%17%5%
2310
August1st to 15thDay
47%13%16%15%5%
2327
16th to endDay
49%12%16%13%6%
2260
September1st to 15thDay
45%9%14%12%13%3
1980
16th to endDay
47%7%10%15%13%4
1905
October1st to 15thDay
35%37%18%22%11%
1755
16th to endDay
29%36%17%28%15%
1760
November1st to 15thDay
29%37%18%24%16%
1727
16th to endDay
34%38%16%23%13%
1620
December1st to 15thDay
39%49%18%17%9%
1620
16th to endDay
45%49%18%13%8%
1728
January1st to 15thNight
39%48%15%22%9%
2327
16th to endNight
39%37%12%24%12%
2496
February1st to 15thNight
38%46%16%19%15%
2115
16th to endNight
36%46%16%22%13%
1893
March1st to 15thNight
30%5%11%19%21%11%
1983
16th to endNight
33%410%18%21%11%
2112
April1st to 15thNight
31%5%7%21%21%12%
1976
16th to endNight
26%7%11%22%20%11%
1716
May1st to 15thNight
29%7%12%20%22%7%
1620
16th to endNight
31%10%13%25%14%3
1684
June1st to 15thNight
37%11%20%20%10%
1620
16th to endNight
36%13%18%20%10%1
1620
July1st to 15thNight
35%12%21%24%5%1
1530
16th to endNight
37%14%21%19%6%
1595
August1st to 15thNight
37%15%22%17%6%
1609
16th to endNight
42%13%19%16%7%
1927
September1st to 15thNight
36%11%19%16%12%3
1980
16th to endNight
42%9%16%13%14%3
1914
October1st to 15thNight
34%5%9%17%21%12%
1874
16th to endNight
31%36%16%23%19%
2112
November1st to 15thNight
32%37%15%25%16%
2128
16th to endNight
32%5%6%16%21%16%
2340
December1st to 15thNight
38%412%17%18%8%
2340
16th to endNight
43%48%19%16%7%
2496

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
14%10%37%20%8%8%
90
16th to endDay
12%15%47%12%10%1
96
February1st to 15thDay
13%20%28%32%5%
90
16th to endDay
12%6%46%29%4
81
March1st to 15thDay
11%9%28%33%15%
267
16th to endDay
12%5%28%30%17%4
288
April1st to 15thDay
13%10%24%22%23%5%
270
16th to endDay
8%419%27%26%14%
270
May1st to 15thDay
9%5%21%27%19%16%
288
16th to endDay
9%19%19%32%26%
331
June1st to 15thDay
12%7%16%27%34%
315
16th to endDay
8%5%17%33%34%
315
July1st to 15thDay
6%315%29%44%
305
16th to endDay
8%412%34%39%
326
August1st to 15thDay
13%415%32%33%
313
16th to endDay
12%7%14%26%38%
332
September1st to 15thDay
15%11%17%31%23%
315
16th to endDay
18%18%23%28%19%
287
October1st to 15thDay
20%315%26%25%9%
255
16th to endDay
10%218%27%30%9%
272
November1st to 15thDay
14%423%26%26%5%
235
16th to endDay
6%11%24%31%21%5%
90
December1st to 15thDay
18%6%34%24%11%4
90
16th to endDay
29%8%20%19%19%2
96
January1st to 15thNight
13%9%35%30%9%
720
16th to endNight
17%10%35%29%7%
768
February1st to 15thNight
15%10%31%34%7%
704
16th to endNight
15%8%36%36%3
631
March1st to 15thNight
10%9%31%39%8%
720
16th to endNight
13%7%30%33%15%
768
April1st to 15thNight
13%5%31%33%15%1
718
16th to endNight
10%427%37%19%
609
May1st to 15thNight
7%325%38%21%2
540
16th to endNight
5%113%39%35%4
563
June1st to 15thNight
10%17%35%36%7%
540
16th to endNight
6%5%32%43%10%
540
July1st to 15thNight
9%6%25%45%12%
510
16th to endNight
5%5%27%51%8%
564
August1st to 15thNight
8%225%50%11%
539
16th to endNight
12%7%23%42%13%
644
September1st to 15thNight
11%16%28%44%8%
720
16th to endNight
15%112%32%35%2
693
October1st to 15thNight
15%216%33%27%4
660
16th to endNight
12%318%36%26%2
704
November1st to 15thNight
12%5%18%38%22%2
700
16th to endNight
13%6%29%31%17%1
720
December1st to 15thNight
17%6%26%32%15%1
720
16th to endNight
18%7%25%34%13%
768
Page generated at 2017-09-25 09:02:20. Version ac04

Copyright 2017 A. Danko


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