West Wind Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Wind Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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
37%
16191
15%
47862
10%
16149
43%
16149
21%
33466

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
16%
900
10%
2506
4%
895
22%
895
12%
1989
January16th to endNight
19%
870
7%
2598
2%
870
23%
870
10%
2095
February1st to 15thNight
18%
701
9%
2244
4%
701
23%
701
10%
1741
February16th to endNight
25%
631
13%
1893
6%
631
32%
631
15%
1392
March1st to 15thNight
28%
720
14%
2087
8%
720
32%
720
17%
1521
March16th to endNight
32%
768
17%
2112
10%
768
38%
768
21%
1496
April1st to 15thNight
29%
574
13%
1808
7%
574
35%
574
18%
1269
April16th to endNight
35%
540
18%
1620
8%
540
45%
540
24%
1090
May1st to 15thNight
37%
540
13%
1620
8%
540
43%
540
21%
1136
May16th to endNight
50%
562
15%
1667
11%
561
55%
561
28%
1061
June1st to 15thNight
56%
540
14%
1440
11%
540
60%
540
32%
928
June16th to endNight
59%
540
16%
1440
12%
540
63%
540
34%
920
July1st to 15thNight
66%
510
16%
1360
14%
510
68%
510
39%
823
July16th to endNight
68%
564
19%
1492
15%
531
71%
531
40%
874
August1st to 15thNight
67%
539
20%
1609
16%
536
70%
536
33%
965
August16th to endNight
66%
573
21%
1758
18%
573
69%
573
34%
1044
September1st to 15thNight
59%
659
26%
1919
21%
659
63%
659
35%
1126
September16th to endNight
60%
717
24%
1980
18%
717
63%
717
34%
1222
October1st to 15thNight
46%
720
19%
2058
15%
720
50%
720
26%
1369
October16th to endNight
27%
768
16%
2418
10%
768
36%
768
17%
1686
November1st to 15thNight
35%
760
19%
2471
15%
760
41%
760
21%
1620
November16th to endNight
25%
780
14%
2535
9%
780
31%
780
15%
1835
December1st to 15thNight
19%
755
8%
2539
3%
755
23%
755
10%
1990
December16th to endNight
14%
960
7%
2688
1%
960
20%
960
8%
2274

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
14%8%36%6%35%45%7%33%
48569
Night
15%8%36%5%34446%36%
48039
Cloud CoverDay
14%8%36%6%35%45%7%33%
48579
Night
15%8%36%5%34446%35%
48043
TransparencyDay
49%6%12%19%10%1
48264
Night
47%6%12%20%11%1
47862
SeeingDay
16%7%27%24%16%7%
6123
Night
18%7%28%29%13%1
16195

By Month

Percentage Cloud Cover NE (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%15%5%9%8%45%5%35%18%
1432
16th to endDay
16%17%7%8%8%4445%5%15%
1625
February1st to 15thDay
14%14%6%12%7%35%445%20%
1615
16th to endDay
15%13%6%11%8%35%346%20%
1580
March1st to 15thDay
17%11%5%6%5%4435%7%27%
1861
16th to endDay
18%9%48%5%34446%30%
2112
April1st to 15thDay
19%10%35%5%34447%30%
2150
16th to endDay
17%7%36%5%23446%38%
2340
May1st to 15thDay
20%7%35%6%45%45%6%31%
2331
16th to endDay
14%5%25%5%25%45%7%39%
2446
June1st to 15thDay
11%4346%35%5%5%8%39%
2520
16th to endDay
10%425%6%46%6%8%9%35%
2520
July1st to 15thDay
7%4245%25%5%5%9%45%
2520
16th to endDay
8%4346%45%5%7%10%39%
2572
August1st to 15thDay
9%5%26%6%45%5%5%9%39%
2340
16th to endDay
10%5%35%5%35%5%6%9%38%
2441
September1st to 15thDay
12%425%5%445%48%41%
2028
16th to endDay
11%6%25%5%245%6%8%42%
1980
October1st to 15thDay
15%6%26%5%3445%6%38%
1902
16th to endDay
20%8%46%5%34345%32%
1806
November1st to 15thDay
16%8%35%5%44446%37%
1717
16th to endDay
18%12%47%5%3445%5%28%
1755
December1st to 15thDay
15%13%7%9%7%25%445%22%
1440
16th to endDay
20%17%8%11%6%33335%15%
1536
January1st to 15thNight
23%12%5%8%5%33345%23%
2506
16th to endNight
13%12%8%12%7%45%435%21%
2598
February1st to 15thNight
16%13%5%9%6%25%435%26%
2242
16th to endNight
16%9%6%8%6%3435%6%29%
1893
March1st to 15thNight
17%10%45%6%34446%32%
2075
16th to endNight
16%8%35%5%25%45%7%35%
2112
April1st to 15thNight
18%8%35%435%45%6%34%
1808
16th to endNight
15%7%245%34447%38%
1620
May1st to 15thNight
19%6%25%6%35%448%33%
1620
16th to endNight
13%425%5%24449%44%
1665
June1st to 15thNight
10%4145%345%48%46%
1440
16th to endNight
8%325%4236%6%10%43%
1440
July1st to 15thNight
7%31443445%7%53%
1440
16th to endNight
5%3244235%5%10%52%
1594
August1st to 15thNight
5%415%5%345%6%9%48%
1620
16th to endNight
10%4245%33347%51%
1758
September1st to 15thNight
11%42432335%6%51%
1919
16th to endNight
10%5%25%42445%7%48%
1980
October1st to 15thNight
14%6%35%42445%6%41%
2058
16th to endNight
20%8%25%5%2434436%
2418
November1st to 15thNight
15%8%25%43445%6%40%
2471
16th to endNight
20%11%45%5%34345%30%
2535
December1st to 15thNight
20%13%6%9%5%24346%23%
2539
16th to endNight
22%15%6%9%5%35%5%4416%
2688

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
17%15%5%9%8%45%435%18%
1432
16th to endDay
16%16%8%8%8%435%5%5%15%
1625
February1st to 15thDay
14%14%6%12%7%35%35%5%20%
1615
16th to endDay
15%13%6%10%8%45%35%7%20%
1580
March1st to 15thDay
17%11%5%6%5%4445%7%26%
1872
16th to endDay
18%9%48%5%33446%30%
2111
April1st to 15thDay
20%10%35%5%34447%29%
2150
16th to endDay
16%7%36%423446%38%
2340
May1st to 15thDay
19%7%36%6%35%45%6%31%
2331
16th to endDay
13%6%26%5%25%5%5%8%39%
2446
June1st to 15thDay
10%5%35%6%36%46%8%39%
2520
16th to endDay
9%5%25%6%46%6%7%10%34%
2520
July1st to 15thDay
7%425%5%35%46%9%45%
2520
16th to endDay
7%425%6%46%6%7%10%39%
2572
August1st to 15thDay
8%6%26%6%45%5%5%9%39%
2340
16th to endDay
10%6%25%6%35%5%7%8%38%
2441
September1st to 15thDay
12%425%5%3445%8%41%
2028
16th to endDay
11%5%246%246%6%8%41%
1980
October1st to 15thDay
14%6%27%6%345%5%6%38%
1902
16th to endDay
20%9%35%6%34346%32%
1806
November1st to 15thDay
15%8%25%5%34446%37%
1717
16th to endDay
18%11%47%5%35%445%28%
1755
December1st to 15thDay
15%13%7%10%7%25%446%22%
1440
16th to endDay
20%17%8%11%7%23335%15%
1536
January1st to 15thNight
22%13%5%8%5%34345%23%
2506
16th to endNight
13%13%8%11%7%45%445%21%
2598
February1st to 15thNight
14%14%6%9%6%35%345%26%
2235
16th to endNight
15%10%5%8%6%3445%6%29%
1893
March1st to 15thNight
18%9%35%6%3445%6%31%
2087
16th to endNight
15%8%35%5%35%447%35%
2112
April1st to 15thNight
18%8%35%5%35%447%33%
1808
16th to endNight
15%7%245%3445%7%38%
1620
May1st to 15thNight
19%5%25%5%35%35%7%34%
1619
16th to endNight
13%4245%24448%43%
1665
June1st to 15thNight
10%4145%345%48%46%
1440
16th to endNight
8%425%4245%7%10%44%
1440
July1st to 15thNight
7%31433435%7%53%
1440
16th to endNight
5%3244245%5%10%52%
1594
August1st to 15thNight
5%415%5%445%6%9%48%
1620
16th to endNight
9%42442435%7%51%
1758
September1st to 15thNight
10%42432345%7%51%
1919
16th to endNight
10%5%2442445%7%47%
1980
October1st to 15thNight
14%6%35%42445%6%41%
2058
16th to endNight
19%8%35%5%34445%36%
2418
November1st to 15thNight
14%8%25%424446%40%
2471
16th to endNight
19%11%5%5%5%33346%30%
2535
December1st to 15thNight
20%12%5%9%6%25%346%23%
2539
16th to endNight
22%15%6%9%6%35%5%5%416%
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
68%6%10%10%3
1433
16th to endDay
71%5%10%8%3
1625
February1st to 15thDay
65%6%9%11%5%
1617
16th to endDay
63%6%10%13%4
1580
March1st to 15thDay
56%7%11%15%7%1
1872
16th to endDay
53%6%12%19%7%1
2112
April1st to 15thDay
54%410%19%10%
2150
16th to endDay
46%6%12%17%14%2
2340
May1st to 15thDay
51%7%11%17%10%1
2331
16th to endDay
42%7%12%23%11%1
2450
June1st to 15thDay
39%8%13%22%14%1
2520
16th to endDay
40%9%13%19%15%
2520
July1st to 15thDay
35%6%12%23%19%2
2371
16th to endDay
37%8%15%21%14%1
2411
August1st to 15thDay
39%8%13%24%12%1
2327
16th to endDay
40%8%12%21%15%2
2441
September1st to 15thDay
39%7%13%24%13%1
2028
16th to endDay
37%6%11%29%14%
1980
October1st to 15thDay
44%5%11%23%12%1
1902
16th to endDay
52%6%14%18%7%
1806
November1st to 15thDay
47%5%11%21%12%1
1717
16th to endDay
56%5%13%18%5%
1755
December1st to 15thDay
63%5%12%13%4
1440
16th to endDay
71%5%11%8%2
1536
January1st to 15thNight
62%5%10%14%6%
2506
16th to endNight
65%6%13%10%3
2598
February1st to 15thNight
60%7%10%14%5%1
2244
16th to endNight
55%5%13%18%6%1
1893
March1st to 15thNight
52%6%10%18%10%1
2087
16th to endNight
48%6%12%21%10%1
2112
April1st to 15thNight
49%6%10%18%14%
1808
16th to endNight
44%5%12%17%16%2
1620
May1st to 15thNight
48%5%11%20%10%2
1620
16th to endNight
38%7%13%23%14%3
1667
June1st to 15thNight
34%8%12%26%16%1
1440
16th to endNight
32%9%15%24%17%
1440
July1st to 15thNight
29%6%11%28%20%2
1360
16th to endNight
26%8%16%24%20%3
1492
August1st to 15thNight
30%9%13%29%15%2
1609
16th to endNight
32%6%11%26%19%3
1758
September1st to 15thNight
32%410%29%20%1
1919
16th to endNight
33%6%12%28%17%
1980
October1st to 15thNight
41%6%11%22%17%1
2058
16th to endNight
49%5%12%21%9%
2418
November1st to 15thNight
43%6%12%22%12%1
2471
16th to endNight
54%5%14%18%7%
2535
December1st to 15thNight
62%6%11%13%5%
2539
16th to endNight
69%6%10%9%3
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
21%11%42%20%41
90
16th to endDay
27%13%39%15%4
96
February1st to 15thDay
22%18%46%10%2
90
16th to endDay
18%16%40%18%6%
81
March1st to 15thDay
31%10%32%19%6%
162
16th to endDay
23%7%31%26%9%2
288
April1st to 15thDay
22%11%31%23%9%1
270
16th to endDay
20%10%32%18%11%7%
270
May1st to 15thDay
23%8%30%20%12%4
288
16th to endDay
18%8%25%22%16%8%
346
June1st to 15thDay
11%430%31%16%5%
495
16th to endDay
11%6%32%27%16%5%
495
July1st to 15thDay
10%324%27%23%10%
475
16th to endDay
8%321%29%24%12%
432
August1st to 15thDay
12%115%28%22%20%
313
16th to endDay
15%416%18%28%15%
332
September1st to 15thDay
11%319%21%25%19%
315
16th to endDay
15%314%20%30%15%
314
October1st to 15thDay
19%425%28%15%7%
315
16th to endDay
25%9%27%30%6%
222
November1st to 15thDay
18%9%28%27%14%2
135
16th to endDay
18%21%39%14%5%
135
December1st to 15thDay
23%22%30%13%10%
68
16th to endDay
22%30%37%9%
96
January1st to 15thNight
28%13%35%18%4
900
16th to endNight
18%11%38%25%6%
870
February1st to 15thNight
23%12%37%22%3
704
16th to endNight
21%10%35%28%4
631
March1st to 15thNight
22%11%31%26%6%
720
16th to endNight
18%10%33%27%8%1
768
April1st to 15thNight
21%12%32%27%5%
574
16th to endNight
21%5%33%28%9%1
540
May1st to 15thNight
21%430%31%10%1
540
16th to endNight
15%325%34%19%2
563
June1st to 15thNight
11%124%47%15%
540
16th to endNight
8%222%44%21%1
540
July1st to 15thNight
10%115%40%28%3
510
16th to endNight
4117%46%27%2
564
August1st to 15thNight
6%115%46%25%3
539
16th to endNight
10%113%35%34%5%
573
September1st to 15thNight
12%319%31%27%5%
659
16th to endNight
11%416%31%29%5%
717
October1st to 15thNight
17%6%23%32%17%2
720
16th to endNight
23%11%34%23%6%
768
November1st to 15thNight
20%9%30%26%12%1
760
16th to endNight
26%11%32%22%7%
780
December1st to 15thNight
25%12%35%21%4
755
16th to endNight
30%11%35%20%3
960
Page generated at 2017-12-03 11:16:37. Version ac04

Copyright 2017 A. Danko


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