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 2017-04-25.

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%
15446
15%
45665
9%
15404
42%
15404
20%
32104

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
24%
701
10%
1741
February16th to endNight
24%
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
36%
574
18%
1269
April16th to endNight
35%
525
19%
1575
8%
525
45%
525
24%
1056
May1st to 15thNight
36%
495
14%
1485
8%
495
43%
495
21%
1047
May16th to endNight
52%
514
14%
1525
11%
513
57%
513
29%
958
June1st to 15thNight
52%
495
15%
1320
11%
495
57%
495
30%
871
June16th to endNight
60%
495
15%
1320
12%
495
64%
495
33%
854
July1st to 15thNight
66%
465
17%
1240
15%
465
69%
465
40%
744
July16th to endNight
68%
522
17%
1373
13%
489
70%
489
38%
816
August1st to 15thNight
66%
494
20%
1474
16%
491
69%
491
33%
886
August16th to endNight
66%
525
20%
1611
17%
525
69%
525
34%
953
September1st to 15thNight
58%
604
27%
1759
22%
604
63%
604
35%
1035
September16th to endNight
59%
657
22%
1815
17%
657
62%
657
33%
1134
October1st to 15thNight
46%
660
20%
1886
16%
660
51%
660
27%
1241
October16th to endNight
26%
704
14%
2216
9%
704
35%
704
17%
1563
November1st to 15thNight
35%
700
20%
2276
16%
700
42%
700
22%
1473
November16th to endNight
25%
720
13%
2340
9%
720
30%
720
14%
1723
December1st to 15thNight
18%
747
8%
2514
3%
747
23%
747
10%
1973
December16th to endNight
15%
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%46%6%35%45%7%32%
45956
Night
15%8%36%5%34446%35%
45842
Cloud CoverDay
14%8%47%6%35%45%7%32%
45966
Night
15%8%36%5%34446%35%
45846
TransparencyDay
49%6%12%18%10%1
45651
Night
48%6%12%19%11%1
45665
SeeingDay
17%7%26%24%16%7%
5238
Night
19%8%29%29%12%1
15450

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
16%7%36%5%23446%39%
2273
May1st to 15thDay
19%7%36%6%45%45%6%30%
2136
16th to endDay
14%5%25%425%45%7%40%
2237
June1st to 15thDay
11%5%35%6%35%5%5%9%37%
2310
16th to endDay
10%425%6%46%6%8%9%35%
2310
July1st to 15thDay
7%4245%25%5%5%9%44%
2310
16th to endDay
8%4346%46%6%7%10%38%
2383
August1st to 15thDay
9%5%26%6%45%5%5%9%40%
2145
16th to endDay
10%5%35%5%35%6%6%9%37%
2237
September1st to 15thDay
13%425%5%445%48%41%
1859
16th to endDay
11%6%25%5%245%6%8%39%
1815
October1st to 15thDay
15%6%26%5%3446%6%38%
1744
16th to endDay
21%8%46%5%34345%32%
1656
November1st to 15thDay
15%7%345%4445%6%38%
1582
16th to endDay
18%12%46%5%35%45%5%27%
1620
December1st to 15thDay
16%13%7%9%7%25%446%22%
1428
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%39%
1575
May1st to 15thNight
19%5%25%6%35%448%32%
1485
16th to endNight
13%4245%24349%45%
1523
June1st to 15thNight
11%4246%345%48%44%
1320
16th to endNight
9%325%4246%7%10%43%
1320
July1st to 15thNight
7%21443435%7%53%
1320
16th to endNight
5%3244245%5%10%50%
1475
August1st to 15thNight
6%415%5%345%6%9%48%
1485
16th to endNight
11%324433247%52%
1611
September1st to 15thNight
12%42432335%6%51%
1759
16th to endNight
11%425%43445%6%46%
1815
October1st to 15thNight
14%6%35%42445%6%42%
1886
16th to endNight
20%8%25%5%2444435%
2216
November1st to 15thNight
14%7%25%435%45%6%41%
2276
16th to endNight
20%11%5%5%5%34345%29%
2340
December1st to 15thNight
20%13%6%8%5%24346%23%
2514
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%
2273
May1st to 15thDay
19%7%36%6%35%45%6%30%
2136
16th to endDay
13%5%26%425%5%5%8%40%
2237
June1st to 15thDay
10%5%35%6%36%46%8%37%
2310
16th to endDay
10%5%25%6%46%6%8%10%35%
2310
July1st to 15thDay
7%425%5%36%46%9%44%
2310
16th to endDay
8%425%6%46%6%7%10%38%
2383
August1st to 15thDay
8%6%26%6%45%5%5%9%39%
2145
16th to endDay
10%6%35%6%35%6%7%8%37%
2237
September1st to 15thDay
13%425%5%3445%8%41%
1859
16th to endDay
11%6%246%246%6%9%39%
1815
October1st to 15thDay
14%6%26%6%3445%6%38%
1744
16th to endDay
20%8%36%6%34346%31%
1656
November1st to 15thDay
14%8%25%5%345%46%38%
1582
16th to endDay
18%11%47%5%35%445%27%
1620
December1st to 15thDay
15%13%7%10%7%25%446%21%
1428
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%25%5%3445%7%39%
1575
May1st to 15thNight
19%5%25%5%35%35%8%33%
1484
16th to endNight
13%4245%24449%45%
1523
June1st to 15thNight
11%5%15%5%345%48%44%
1320
16th to endNight
8%425%4345%7%10%43%
1320
July1st to 15thNight
7%31433435%7%53%
1320
16th to endNight
5%3244245%5%10%50%
1475
August1st to 15thNight
5%415%5%445%6%9%47%
1485
16th to endNight
10%42442435%7%51%
1611
September1st to 15thNight
11%414323347%51%
1759
16th to endNight
11%5%25%5%2445%7%46%
1815
October1st to 15thNight
13%6%35%42445%6%42%
1886
16th to endNight
19%9%35%5%34445%35%
2216
November1st to 15thNight
14%8%25%424447%41%
2276
16th to endNight
20%11%5%6%5%34345%29%
2340
December1st to 15thNight
20%12%5%9%6%25%336%23%
2514
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%5%12%17%14%2
2273
May1st to 15thDay
52%7%12%17%9%
2136
16th to endDay
42%7%12%24%12%2
2241
June1st to 15thDay
41%8%13%21%13%1
2310
16th to endDay
40%9%13%18%15%1
2310
July1st to 15thDay
35%6%12%22%19%2
2161
16th to endDay
37%8%16%21%13%2
2222
August1st to 15thDay
39%8%13%24%12%1
2132
16th to endDay
40%8%12%21%15%2
2237
September1st to 15thDay
40%7%12%23%14%1
1859
16th to endDay
38%6%11%29%13%
1815
October1st to 15thDay
44%6%11%23%12%1
1744
16th to endDay
53%5%14%18%7%
1656
November1st to 15thDay
46%5%11%21%13%1
1582
16th to endDay
58%5%12%18%4
1620
December1st to 15thDay
63%5%12%13%4
1428
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%17%3
1575
May1st to 15thNight
49%6%11%20%10%1
1485
16th to endNight
36%7%13%24%14%3
1525
June1st to 15thNight
37%8%12%25%15%1
1320
16th to endNight
33%9%15%23%17%
1320
July1st to 15thNight
29%6%11%27%22%2
1240
16th to endNight
27%8%16%23%19%3
1373
August1st to 15thNight
30%9%13%27%16%2
1474
16th to endNight
32%6%11%27%18%3
1611
September1st to 15thNight
32%410%28%21%1
1759
16th to endNight
34%6%13%27%17%
1815
October1st to 15thNight
40%6%11%21%18%1
1886
16th to endNight
50%6%13%21%8%
2216
November1st to 15thNight
42%6%12%22%13%1
2276
16th to endNight
56%5%13%17%6%
2340
December1st to 15thNight
62%6%12%13%5%
2514
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
18%8%32%19%12%8%
250
May1st to 15thDay
23%7%30%19%13%6%
228
16th to endDay
17%5%24%22%19%10%
281
June1st to 15thDay
13%5%30%29%14%5%
420
16th to endDay
11%428%30%17%6%
420
July1st to 15thDay
10%323%27%24%10%
400
16th to endDay
8%321%31%23%11%
369
August1st to 15thDay
13%13%30%22%20%
253
16th to endDay
14%416%16%29%17%
268
September1st to 15thDay
13%216%20%27%18%
255
16th to endDay
17%413%23%30%11%
254
October1st to 15thDay
17%423%30%15%7%
255
16th to endDay
27%7%30%27%7%
168
November1st to 15thDay
7%13%27%32%16%2
90
16th to endDay
22%18%37%13%7%
90
December1st to 15thDay
23%23%32%14%6%
64
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%32%28%9%1
525
May1st to 15thNight
21%430%31%10%1
495
16th to endNight
14%324%35%20%2
515
June1st to 15thNight
12%126%45%13%
495
16th to endNight
8%120%44%22%2
495
July1st to 15thNight
9%116%40%29%3
465
16th to endNight
5%117%46%26%2
522
August1st to 15thNight
7%116%46%25%3
494
16th to endNight
11%112%34%34%5%
525
September1st to 15thNight
13%319%30%27%5%
604
16th to endNight
12%416%33%28%4
657
October1st to 15thNight
16%6%23%32%17%2
660
16th to endNight
23%12%34%23%6%
704
November1st to 15thNight
19%9%31%25%13%1
700
16th to endNight
27%11%31%22%7%
720
December1st to 15thNight
26%12%35%21%4
747
16th to endNight
30%11%35%20%3
960
Page generated at 2017-04-26 17:21:40. Version ac04

Copyright 2017 A. Danko


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