Four Winds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Winds Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
33%
16094
11%
47210
7%
16052
36%
16052
15%
36135

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
12%
900
2%
2506
1%
895
13%
895
4%
2314
January16th to endNight
13%
960
3%
2688
1%
960
14%
960
4%
2476
February1st to 15thNight
17%
770
4%
2292
1%
770
19%
770
6%
2015
February16th to endNight
22%
631
7%
1893
4%
631
25%
631
8%
1594
March1st to 15thNight
31%
720
13%
2145
8%
720
35%
720
16%
1601
March16th to endNight
36%
712
17%
2056
13%
712
40%
712
20%
1474
April1st to 15thNight
31%
539
13%
1797
9%
539
37%
539
16%
1272
April16th to endNight
38%
540
19%
1626
12%
540
45%
540
23%
1108
May1st to 15thNight
41%
540
13%
1605
9%
540
45%
540
19%
1141
May16th to endNight
51%
562
14%
1498
9%
561
56%
561
31%
975
June1st to 15thNight
50%
502
12%
1402
8%
502
53%
502
25%
946
June16th to endNight
56%
511
12%
1411
8%
511
59%
511
29%
917
July1st to 15thNight
64%
510
15%
1360
9%
510
67%
510
39%
814
July16th to endNight
60%
564
16%
1417
11%
531
62%
531
37%
873
August1st to 15thNight
67%
539
19%
1539
15%
536
69%
536
36%
910
August16th to endNight
58%
573
17%
1800
15%
573
61%
573
28%
1108
September1st to 15thNight
56%
594
16%
1854
14%
594
58%
594
27%
1166
September16th to endNight
53%
717
18%
1980
15%
717
55%
717
28%
1299
October1st to 15thNight
38%
684
15%
1944
11%
684
42%
684
19%
1423
October16th to endNight
25%
704
8%
2288
6%
704
29%
704
10%
1850
November1st to 15thNight
27%
700
13%
2276
11%
700
31%
700
12%
1737
November16th to endNight
17%
762
6%
2394
4%
762
19%
762
6%
2090
December1st to 15thNight
8%
900
1%
2700
1%
900
9%
900
3%
2518
December16th to endNight
10%
960
3%
2739
0%
960
12%
960
4%
2514

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%9%47%6%34446%33%
47933
Night
15%11%5%9%7%34345%28%
47378
Cloud CoverDay
14%9%47%6%34446%33%
47942
Night
15%11%5%9%7%34345%28%
47383
TransparencyDay
51%6%12%19%9%
47619
Night
57%6%10%15%7%
47210
SeeingDay
16%6%26%29%16%4
6103
Night
19%9%27%29%12%1
16098

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
16%18%10%16%11%5%32337%
1432
16th to endDay
13%15%12%17%13%5%5%4325%
1536
February1st to 15thDay
13%15%8%14%14%46%335%11%
1570
16th to endDay
13%15%8%11%11%46%43415%
1580
March1st to 15thDay
12%10%411%8%35%445%29%
1805
16th to endDay
15%8%5%7%6%3345%6%33%
2178
April1st to 15thDay
19%11%35%42335%5%33%
2151
16th to endDay
17%9%36%434446%35%
2334
May1st to 15thDay
14%7%26%6%24445%39%
2343
16th to endDay
10%5%24425%45%7%46%
2617
June1st to 15thDay
12%425%43446%9%42%
2525
16th to endDay
11%4144346%5%7%45%
2522
July1st to 15thDay
9%3134345%5%7%51%
2520
16th to endDay
8%3134135%6%9%51%
2655
August1st to 15thDay
8%41442446%9%50%
2409
16th to endDay
14%5%34423347%47%
2400
September1st to 15thDay
14%5%245%2445%6%43%
2094
16th to endDay
15%4235%35%5%6%7%41%
1980
October1st to 15thDay
22%8%36%5%34436%30%
1814
16th to endDay
27%14%47%6%34435%17%
1584
November1st to 15thDay
18%18%37%5%24346%24%
1582
16th to endDay
19%24%8%11%5%2433313%
1560
December1st to 15thDay
19%20%15%15%10%122126%
1260
16th to endDay
22%22%11%11%7%332228%
1482
January1st to 15thNight
18%17%9%14%12%4422210%
2506
16th to endNight
12%17%10%16%13%5%43339%
2688
February1st to 15thNight
13%14%9%13%15%5%432314%
2290
16th to endNight
16%14%6%14%8%35%345%17%
1893
March1st to 15thNight
12%10%49%6%345%45%32%
2132
16th to endNight
13%10%47%6%34446%34%
2056
April1st to 15thNight
21%10%26%5%33445%33%
1797
16th to endNight
16%7%26%5%34335%39%
1626
May1st to 15thNight
15%6%46%6%36%5%5%6%33%
1605
16th to endNight
10%5%344245%7%7%43%
1496
June1st to 15thNight
14%5%25%445%45%6%41%
1402
16th to endNight
9%6%245%3445%9%43%
1411
July1st to 15thNight
9%42433346%7%51%
1440
16th to endNight
8%32442345%8%51%
1513
August1st to 15thNight
6%4245%2445%9%50%
1548
16th to endNight
14%424433347%47%
1800
September1st to 15thNight
13%5%24424445%46%
1854
16th to endNight
16%5%25%42345%8%42%
1980
October1st to 15thNight
24%8%37%423346%32%
1944
16th to endNight
24%11%47%7%3444422%
2288
November1st to 15thNight
18%16%5%5%6%24346%26%
2276
16th to endNight
20%21%6%11%7%3333413%
2394
December1st to 15thNight
18%22%11%16%9%332227%
2700
16th to endNight
18%23%10%13%7%232338%
2739

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
16%17%10%17%10%5%42337%
1432
16th to endDay
12%16%11%19%12%5%44326%
1536
February1st to 15thDay
13%14%8%14%15%46%235%11%
1570
16th to endDay
13%16%8%12%10%45%44414%
1580
March1st to 15thDay
12%9%411%8%35%446%28%
1815
16th to endDay
15%8%5%7%6%3345%6%32%
2177
April1st to 15thDay
19%11%35%32345%6%33%
2151
16th to endDay
16%10%35%42435%6%35%
2334
May1st to 15thDay
15%7%35%6%24445%39%
2343
16th to endDay
10%5%24425%45%7%45%
2617
June1st to 15thDay
12%425%43446%8%42%
2525
16th to endDay
11%5%145%245%5%7%44%
2522
July1st to 15thDay
10%3134245%5%8%51%
2520
16th to endDay
8%3134145%6%9%50%
2655
August1st to 15thDay
8%32442446%9%49%
2409
16th to endDay
14%5%24423346%46%
2400
September1st to 15thDay
14%5%25%434447%43%
2094
16th to endDay
14%5%244345%6%7%41%
1980
October1st to 15thDay
20%9%37%5%44447%30%
1814
16th to endDay
25%15%48%7%35%43418%
1584
November1st to 15thDay
16%17%47%6%2335%6%24%
1582
16th to endDay
19%23%8%12%6%2333413%
1560
December1st to 15thDay
18%20%14%17%10%222216%
1260
16th to endDay
21%22%11%11%7%342238%
1482
January1st to 15thNight
18%16%9%15%11%5%432210%
2506
16th to endNight
12%17%9%16%13%5%43339%
2688
February1st to 15thNight
12%14%9%13%14%5%432315%
2283
16th to endNight
15%14%7%13%9%35%345%17%
1893
March1st to 15thNight
13%9%5%8%7%345%45%32%
2145
16th to endNight
14%10%47%6%34346%34%
2056
April1st to 15thNight
21%9%36%5%2435%5%32%
1797
16th to endNight
17%7%26%433436%39%
1626
May1st to 15thNight
15%6%36%5%47%45%7%33%
1604
16th to endNight
10%5%25%4245%7%7%43%
1496
June1st to 15thNight
14%5%245%4445%6%41%
1402
16th to endNight
9%6%245%35%46%9%43%
1411
July1st to 15thNight
9%4143345%5%7%51%
1440
16th to endNight
7%33442345%7%51%
1513
August1st to 15thNight
6%4245%3446%8%51%
1548
16th to endNight
13%5%24433446%47%
1800
September1st to 15thNight
12%6%24425%445%47%
1854
16th to endNight
16%426%423448%43%
1980
October1st to 15thNight
21%10%36%433346%33%
1944
16th to endNight
22%12%49%6%35%445%22%
2288
November1st to 15thNight
17%15%5%6%5%34346%26%
2276
16th to endNight
19%20%6%12%7%4433413%
2394
December1st to 15thNight
17%21%11%15%10%333228%
2700
16th to endNight
17%23%10%14%7%233349%
2739

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
83%6%44
1433
16th to endDay
84%6%33
1536
February1st to 15thDay
78%5%7%7%
1572
16th to endDay
73%6%7%9%2
1580
March1st to 15thDay
57%7%13%16%5%
1815
16th to endDay
52%6%13%20%41
2178
April1st to 15thDay
51%5%11%20%10%
2151
16th to endDay
48%5%11%15%15%2
2334
May1st to 15thDay
46%5%11%23%10%3
2343
16th to endDay
36%7%14%25%14%2
2621
June1st to 15thDay
38%7%13%26%12%
2525
16th to endDay
36%8%16%23%13%
2522
July1st to 15thDay
30%6%13%31%16%1
2371
16th to endDay
30%7%16%27%17%1
2488
August1st to 15thDay
31%6%18%30%11%
2394
16th to endDay
38%6%14%25%14%1
2400
September1st to 15thDay
39%7%15%25%11%
2094
16th to endDay
39%7%16%26%9%
1980
October1st to 15thDay
53%6%11%20%7%
1814
16th to endDay
69%7%11%10%2
1584
November1st to 15thDay
59%6%11%14%7%
1582
16th to endDay
75%6%10%6%1
1560
December1st to 15thDay
86%444
1260
16th to endDay
82%5%7%3
1482
January1st to 15thNight
81%5%5%5%
2506
16th to endNight
80%6%6%4
2688
February1st to 15thNight
76%5%7%9%1
2292
16th to endNight
69%6%10%9%2
1893
March1st to 15thNight
53%8%12%17%8%
2145
16th to endNight
50%6%12%21%9%
2056
April1st to 15thNight
52%5%9%20%10%1
1797
16th to endNight
46%5%9%19%15%3
1626
May1st to 15thNight
48%7%10%18%10%3
1605
16th to endNight
37%6%14%24%14%2
1498
June1st to 15thNight
41%8%11%23%14%1
1402
16th to endNight
36%8%14%24%14%1
1411
July1st to 15thNight
29%6%14%28%19%2
1360
16th to endNight
31%6%14%28%17%1
1417
August1st to 15thNight
29%7%18%31%11%
1539
16th to endNight
37%6%15%23%15%1
1800
September1st to 15thNight
38%6%14%23%16%
1854
16th to endNight
39%6%16%26%9%
1980
October1st to 15thNight
52%5%9%21%10%
1944
16th to endNight
63%8%11%12%3
2288
November1st to 15thNight
59%6%12%14%6%
2276
16th to endNight
75%5%9%6%1
2394
December1st to 15thNight
84%5%44
2700
16th to endNight
80%6%7%31
2739

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%14%33%26%4
90
16th to endDay
29%434%26%6%
96
February1st to 15thDay
18%20%40%17%3
90
16th to endDay
19%11%41%17%9%
81
March1st to 15thDay
20%12%31%23%11%
105
16th to endDay
23%5%27%29%12%1
288
April1st to 15thDay
28%5%26%26%9%2
270
16th to endDay
21%8%30%23%12%3
270
May1st to 15thDay
18%8%29%28%12%3
300
16th to endDay
14%7%29%29%15%4
517
June1st to 15thDay
15%330%29%16%4
495
16th to endDay
11%428%36%14%4
495
July1st to 15thDay
10%5%21%34%22%5%
475
16th to endDay
8%224%36%21%6%
515
August1st to 15thDay
10%115%38%25%8%
382
16th to endDay
19%417%26%24%7%
332
September1st to 15thDay
14%421%23%22%13%
315
16th to endDay
12%6%17%33%24%5%
314
October1st to 15thDay
21%9%25%27%13%1
253
16th to endDay
26%6%41%21%4
96
November1st to 15thDay
17%8%26%30%15%1
90
16th to endDay
24%25%25%19%5%
87
December1st to 15thDay
31%25%28%11%11
60
16th to endDay
29%21%39%8%1
87
January1st to 15thNight
24%16%31%21%5%
900
16th to endNight
19%14%37%22%6%
960
February1st to 15thNight
18%13%35%25%6%
773
16th to endNight
22%12%28%29%7%
631
March1st to 15thNight
17%9%34%28%9%
720
16th to endNight
17%9%27%33%10%1
712
April1st to 15thNight
24%7%30%28%7%1
539
16th to endNight
19%6%30%32%10%1
540
May1st to 15thNight
18%429%34%12%
540
16th to endNight
12%425%37%18%1
563
June1st to 15thNight
16%322%38%17%
502
16th to endNight
10%220%42%20%1
511
July1st to 15thNight
10%215%40%27%2
510
16th to endNight
8%121%37%27%2
564
August1st to 15thNight
6%115%43%28%2
539
16th to endNight
15%315%40%22%3
573
September1st to 15thNight
16%419%31%23%6%
594
16th to endNight
17%5%18%31%22%4
717
October1st to 15thNight
25%7%22%30%12%1
684
16th to endNight
27%13%28%23%5%
704
November1st to 15thNight
25%13%27%26%6%
700
16th to endNight
29%17%28%20%4
762
December1st to 15thNight
25%22%32%15%3
900
16th to endNight
26%13%36%19%21
960
Page generated at 2017-10-07 14:07:55. Version ac04

Copyright 2017 A. Danko


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