Wes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wes Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
52%
24199
21%
74418
15%
24146
59%
24146
28%
46274

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 10thNight
31%
757
23%
2459
10%
757
48%
757
24%
1494
January11th to 20thNight
38%
736
27%
2391
17%
736
52%
736
27%
1410
January21st to endNight
28%
792
23%
2574
11%
792
44%
792
24%
1600
February1st to 10thNight
36%
720
23%
2164
13%
720
46%
720
27%
1364
February11th to 20thNight
32%
703
23%
2098
9%
699
46%
699
27%
1325
February21st to endNight
34%
592
25%
1776
14%
592
45%
592
28%
1091
March1st to 10thNight
42%
720
30%
1983
17%
720
52%
720
36%
1187
March11th to 20thNight
40%
720
24%
1980
11%
720
50%
720
32%
1221
March21st to endNight
38%
792
23%
2178
10%
792
48%
792
33%
1340
April1st to 10thNight
43%
720
24%
1980
15%
720
50%
720
34%
1197
April11th to 20thNight
46%
711
25%
1906
14%
711
53%
711
37%
1143
April21st to endNight
56%
554
32%
1634
23%
554
64%
554
40%
904
May1st to 10thNight
57%
540
27%
1620
16%
540
64%
540
40%
886
May11th to 20thNight
61%
531
18%
1592
12%
531
65%
531
32%
983
May21st to endNight
69%
582
19%
1745
14%
582
71%
582
29%
1103
June1st to 10thNight
66%
540
13%
1620
11%
540
67%
540
25%
1091
June11th to 20thNight
71%
540
14%
1620
11%
540
72%
540
30%
1022
June21st to endNight
72%
540
12%
1620
10%
540
73%
540
24%
1109
July1st to 10thNight
71%
525
12%
1575
10%
525
73%
525
25%
1060
July11th to 20thNight
70%
522
10%
1566
8%
522
71%
522
24%
1067
July21st to endNight
76%
591
14%
1672
12%
558
76%
558
27%
1101
August1st to 10thNight
74%
537
10%
1600
9%
534
74%
534
23%
1101
August11th to 20thNight
69%
534
11%
1604
11%
534
69%
534
21%
1120
August21st to endNight
61%
700
13%
2086
12%
700
61%
700
20%
1486
September1st to 10thNight
67%
720
16%
1980
15%
720
67%
720
27%
1326
September11th to 20thNight
64%
720
15%
1980
14%
720
65%
720
26%
1338
September21st to endNight
60%
720
20%
1980
17%
720
63%
720
27%
1321
October1st to 10thNight
61%
720
27%
1986
22%
720
65%
720
35%
1218
October11th to 20thNight
57%
720
30%
2160
27%
720
65%
720
36%
1232
October21st to endNight
56%
792
31%
2376
28%
792
64%
792
35%
1364
November1st to 10thNight
54%
740
28%
2221
23%
740
61%
740
35%
1268
November11th to 20thNight
45%
760
27%
2417
21%
760
56%
760
31%
1419
November21st to endNight
45%
760
26%
2470
20%
760
55%
760
28%
1457
December1st to 10thNight
42%
760
25%
2470
17%
760
53%
760
26%
1496
December11th to 20thNight
41%
759
24%
2920
18%
758
49%
758
22%
1702
December21st to endNight
38%
829
15%
4415
17%
817
47%
817
14%
2728

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%6%8%43%
74901
Night
11%5%25%5%35%5%6%8%45%
74865
TransparencyDay
38%8%13%18%17%6%
74624
Night
36%8%13%18%18%8%
74661
SeeingDay
12%7%20%24%23%15%
14097
Night
13%6%22%33%23%4
24212

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 10thDay
13%6%25%435%6%5%7%46%
1706
11th to 20thDay
13%5%25%325%347%49%
1647
21st to endDay
15%7%36%5%34446%44%
1782
February1st to 10thDay
16%7%25%6%245%5%8%39%
1792
11th to 20thDay
17%5%3442345%7%47%
1748
21st to endDay
15%7%35%5%3435%7%44%
1480
March1st to 10thDay
10%5%25%32435%7%53%
1975
11th to 20thDay
12%5%35%6%35%5%5%7%44%
1980
21st to endDay
12%5%25%5%345%5%7%47%
2178
April1st to 10thDay
10%435%5%35%45%7%49%
1980
11th to 20thDay
14%5%245%34447%48%
2000
21st to endDay
6%42443446%7%56%
2340
May1st to 10thDay
6%3245%35%5%6%8%53%
2340
11th to 20thDay
10%425%6%446%6%9%44%
2301
21st to endDay
9%436%7%46%6%6%10%39%
2531
June1st to 10thDay
11%5%26%7%5%6%7%7%11%34%
2340
11th to 20thDay
6%4245%47%7%8%11%42%
2340
21st to endDay
6%5%36%6%5%7%8%9%11%33%
2340
July1st to 10thDay
7%5%26%8%5%9%7%8%12%31%
2340
11th to 20thDay
7%5%36%7%5%8%8%9%11%32%
2340
21st to endDay
7%5%26%7%5%8%7%8%12%32%
2547
August1st to 10thDay
8%5%38%7%6%7%8%9%11%28%
2327
11th to 20thDay
10%5%37%7%5%8%7%8%12%28%
2293
21st to endDay
12%7%49%8%46%6%7%10%26%
2250
September1st to 10thDay
9%6%37%7%48%6%7%8%34%
1980
11th to 20thDay
13%6%26%8%35%5%6%8%38%
1980
21st to endDay
13%6%35%5%35%6%5%7%40%
1980
October1st to 10thDay
12%5%35%43445%6%50%
1972
11th to 20thDay
11%31442345%7%56%
1800
21st to endDay
9%5%24324347%56%
1980
November1st to 10thDay
10%5%24424446%54%
1857
11th to 20thDay
12%6%24323347%54%
1758
21st to endDay
14%6%245%33347%48%
1710
December1st to 10thDay
15%5%25%5%25%5%6%6%45%
1710
11th to 20thDay
16%6%24424447%46%
2153
21st to endDay
17%9%36%5%34345%42%
3124
January1st to 10thNight
14%5%35%5%35%5%5%6%45%
2459
11th to 20thNight
12%6%25%5%34346%49%
2391
21st to endNight
17%6%25%42445%5%45%
2574
February1st to 10thNight
14%6%36%5%34447%45%
2164
11th to 20thNight
16%6%25%424445%48%
2098
21st to endNight
14%5%245%25%45%7%47%
1776
March1st to 10thNight
9%5%245%3445%7%53%
1983
11th to 20thNight
11%5%15%435%5%5%7%48%
1980
21st to endNight
10%5%245%34448%50%
2178
April1st to 10thNight
11%4245%24448%51%
1980
11th to 20thNight
10%4244345%6%7%51%
1906
21st to endNight
7%324435%45%8%56%
1634
May1st to 10thNight
7%32442445%7%58%
1620
11th to 20thNight
5%5%35%5%35%6%7%9%46%
1592
21st to endNight
8%5%25%5%36%6%8%7%45%
1744
June1st to 10thNight
10%5%25%6%47%8%7%12%34%
1620
11th to 20thNight
7%425%5%46%7%7%11%42%
1620
21st to endNight
6%425%7%5%7%8%10%11%34%
1620
July1st to 10thNight
7%5%25%5%5%8%7%8%13%34%
1620
11th to 20thNight
7%5%36%7%45%7%8%14%33%
1620
21st to endNight
5%436%6%46%7%9%11%39%
1771
August1st to 10thNight
5%427%7%47%7%10%14%33%
1611
11th to 20thNight
8%6%36%6%5%6%6%9%12%33%
1604
21st to endNight
11%6%36%7%5%7%6%8%9%32%
2086
September1st to 10thNight
11%5%26%5%45%6%7%12%38%
1980
11th to 20thNight
10%5%36%6%35%5%6%9%41%
1980
21st to endNight
12%6%35%6%36%5%6%8%40%
1980
October1st to 10thNight
11%6%2443445%6%51%
1986
11th to 20thNight
13%5%2342334457%
2160
21st to endNight
10%4245%34446%54%
2376
November1st to 10thNight
12%5%2432445%5%54%
2221
11th to 20thNight
13%5%25%434346%51%
2417
21st to endNight
13%5%3442435%6%49%
2470
December1st to 10thNight
13%5%26%4345%5%7%45%
2470
11th to 20thNight
17%6%24424345%49%
3042
21st to endNight
17%8%25%6%345%5%6%38%
4532

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 10thDay
37%5%8%19%23%8%
1707
11th to 20thDay
35%5%9%20%23%8%
1647
21st to endDay
42%46%17%23%9%
1782
February1st to 10thDay
44%49%15%19%8%
1792
11th to 20thDay
37%48%14%27%9%
1758
21st to endDay
41%47%18%18%12%
1480
March1st to 10thDay
32%5%8%19%23%14%
1975
11th to 20thDay
38%7%11%18%16%10%
1980
21st to endDay
36%6%11%18%20%8%
2178
April1st to 10thDay
34%6%9%20%19%11%
1980
11th to 20thDay
36%5%8%18%21%11%
2000
21st to endDay
26%6%11%25%26%7%
2340
May1st to 10thDay
28%6%11%24%25%6%
2340
11th to 20thDay
36%8%15%22%15%3
2305
21st to endDay
39%9%12%21%16%3
2531
June1st to 10thDay
40%12%17%18%13%1
2340
11th to 20thDay
32%12%18%24%14%1
2340
21st to endDay
39%14%20%16%9%2
2340
July1st to 10thDay
39%16%21%16%6%2
2275
11th to 20thDay
41%13%25%15%5%1
2271
21st to endDay
39%14%23%19%5%1
2405
August1st to 10thDay
44%14%20%18%4
2314
11th to 20thDay
44%16%21%14%5%
2293
21st to endDay
50%13%18%11%6%1
2250
September1st to 10thDay
44%11%15%14%11%4
1980
11th to 20thDay
44%8%12%15%16%5%
1980
21st to endDay
42%7%10%17%18%6%
1980
October1st to 10thDay
35%5%9%18%22%11%
1972
11th to 20thDay
28%5%9%21%28%9%
1800
21st to endDay
29%47%17%27%16%
1980
November1st to 10thDay
31%5%8%17%24%15%
1857
11th to 20thDay
32%48%18%24%14%
1758
21st to endDay
36%49%20%21%10%
1710
December1st to 10thDay
39%7%11%17%17%8%
1710
11th to 20thDay
39%47%16%27%7%
2150
21st to endDay
46%46%15%23%5%
3124
January1st to 10thNight
38%6%8%17%22%9%
2459
11th to 20thNight
37%47%15%27%9%
2391
21st to endNight
41%47%14%24%10%
2574
February1st to 10thNight
39%5%8%17%20%10%
2164
11th to 20thNight
39%47%15%21%13%
2099
21st to endNight
36%6%9%18%17%14%
1776
March1st to 10thNight
31%6%9%18%23%13%
1983
11th to 20thNight
34%6%13%18%16%12%
1980
21st to endNight
33%6%12%18%21%10%
2178
April1st to 10thNight
32%7%11%18%19%13%
1980
11th to 20thNight
30%7%8%22%21%12%
1906
21st to endNight
25%7%12%26%22%8%
1634
May1st to 10thNight
26%6%12%23%25%9%
1620
11th to 20thNight
31%11%18%20%17%4
1593
21st to endNight
34%11%13%24%16%3
1745
June1st to 10thNight
38%13%20%19%10%
1620
11th to 20thNight
33%11%21%25%10%
1620
21st to endNight
36%15%21%17%9%1
1620
July1st to 10thNight
36%14%23%19%6%1
1575
11th to 20thNight
37%14%26%16%5%1
1566
21st to endNight
33%15%24%22%5%1
1672
August1st to 10thNight
35%17%27%16%4
1600
11th to 20thNight
41%13%25%15%5%
1604
21st to endNight
43%14%19%16%7%1
2086
September1st to 10thNight
37%11%20%16%12%3
1980
11th to 20thNight
37%12%17%16%15%3
1980
21st to endNight
40%8%15%14%19%4
1980
October1st to 10thNight
33%7%11%18%21%10%
1986
11th to 20thNight
32%47%19%28%10%
2160
21st to endNight
32%46%16%23%18%
2376
November1st to 10thNight
33%310%13%25%16%
2221
11th to 20thNight
35%46%16%24%15%
2417
21st to endNight
36%5%8%20%20%12%
2470
December1st to 10thNight
38%6%13%16%21%6%
2470
11th to 20thNight
39%48%15%26%9%
3044
21st to endNight
46%5%7%17%21%4
4532

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 10thDay
10%16%50%19%5%1
270
11th to 20thDay
14%14%33%23%12%3
249
21st to endDay
22%18%41%14%31
264
February1st to 10thDay
18%18%33%23%8%
240
11th to 20thDay
24%11%34%27%5%
240
21st to endDay
15%17%40%23%42
198
March1st to 10thDay
12%14%30%30%13%1
415
11th to 20thDay
14%11%35%29%10%1
420
21st to endDay
15%10%34%29%10%2
462
April1st to 10thDay
15%14%26%25%17%3
420
11th to 20thDay
13%8%29%24%19%8%
412
21st to endDay
8%8%21%33%21%10%
420
May1st to 10thDay
5%9%24%28%23%11%
423
11th to 20thDay
11%114%25%29%19%
447
21st to endDay
10%211%20%31%26%
485
June1st to 10thDay
10%211%23%28%25%
450
11th to 20thDay
8%310%21%26%32%
450
21st to endDay
6%29%24%31%28%
450
July1st to 10thDay
5%2416%34%39%
445
11th to 20thDay
7%314%31%45%
444
21st to endDay
6%16%17%38%32%
488
August1st to 10thDay
11%28%18%33%30%
446
11th to 20thDay
9%2311%34%40%
439
21st to endDay
13%29%19%29%27%
495
September1st to 10thDay
10%39%22%33%24%
450
11th to 20thDay
13%212%28%31%14%
450
21st to endDay
14%210%25%33%16%
450
October1st to 10thDay
12%424%28%24%9%
450
11th to 20thDay
10%5%20%30%24%11%
450
21st to endDay
11%6%22%30%25%5%
495
November1st to 10thDay
16%5%24%27%23%5%
455
11th to 20thDay
14%10%36%27%13%2
318
21st to endDay
11%15%24%33%16%1
270
December1st to 10thDay
18%14%33%20%13%2
270
11th to 20thDay
19%13%33%22%11%1
270
21st to endDay
24%8%33%20%13%1
297
January1st to 10thNight
16%11%36%30%6%1
760
11th to 20thNight
14%10%32%33%11%
736
21st to endNight
19%9%39%26%6%
792
February1st to 10thNight
16%9%34%33%7%
720
11th to 20thNight
19%11%34%32%4
703
21st to endNight
14%11%34%36%4
592
March1st to 10thNight
11%11%32%40%6%
720
11th to 20thNight
14%9%33%33%11%1
720
21st to endNight
12%9%35%32%11%
792
April1st to 10thNight
12%7%33%34%13%1
720
11th to 20thNight
12%8%30%33%16%1
711
21st to endNight
8%5%26%43%18%
554
May1st to 10thNight
8%5%26%41%19%1
540
11th to 20thNight
8%319%42%25%3
531
21st to endNight
8%111%39%36%5%
584
June1st to 10thNight
11%19%37%36%5%
540
11th to 20thNight
9%111%34%36%10%
540
21st to endNight
6%27%36%38%11%
540
July1st to 10thNight
8%15%27%47%12%
525
11th to 20thNight
9%15%21%51%13%
522
21st to endNight
5%15%29%53%7%
591
August1st to 10thNight
7%1427%48%12%
537
11th to 20thNight
10%1423%51%11%
534
21st to endNight
11%27%25%42%12%
700
September1st to 10thNight
11%27%28%43%10%
720
11th to 20thNight
11%29%34%40%4
720
21st to endNight
14%212%31%36%5%
720
October1st to 10thNight
13%318%35%27%5%
720
11th to 20thNight
15%418%33%27%3
720
21st to endNight
11%422%37%24%2
792
November1st to 10thNight
13%6%21%36%22%3
740
11th to 20thNight
14%9%27%35%14%1
760
21st to endNight
15%7%27%34%16%1
760
December1st to 10thNight
16%7%29%34%13%1
760
11th to 20thNight
18%7%27%33%13%1
760
21st to endNight
21%9%27%33%10%
836
Page generated at 2024-01-11 13:32:03. Version ac07

Copyright 2024 Attilla Danko


Wes Observatory Clear Sky Chart |Charts Home