Whiskey Bay Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whiskey Bay Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
34%
15526
12%
46867
7%
15483
39%
15483
17%
34163

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
19%
898
6%
2553
2%
895
23%
895
8%
2140
January16th to endNight
21%
960
8%
2688
3%
960
26%
960
11%
2191
February1st to 15thNight
20%
728
9%
2311
3%
725
26%
725
11%
1809
February16th to endNight
28%
631
11%
1901
4%
631
34%
631
12%
1479
March1st to 15thNight
29%
720
14%
2100
7%
720
35%
720
21%
1461
March16th to endNight
35%
768
18%
2112
9%
768
43%
768
25%
1438
April1st to 15thNight
35%
548
15%
1751
11%
548
40%
548
20%
1195
April16th to endNight
37%
540
18%
1620
10%
540
44%
540
23%
1098
May1st to 15thNight
38%
540
12%
1620
9%
540
43%
540
19%
1156
May16th to endNight
48%
442
14%
1404
10%
441
55%
441
25%
881
June1st to 15thNight
48%
360
11%
1260
10%
360
52%
360
24%
787
June16th to endNight
56%
360
11%
1260
10%
360
59%
360
26%
756
July1st to 15thNight
60%
384
13%
1234
11%
384
62%
384
32%
728
July16th to endNight
62%
564
15%
1417
12%
531
62%
531
34%
893
August1st to 15thNight
61%
539
17%
1581
14%
536
65%
536
34%
935
August16th to endNight
60%
573
18%
1719
13%
573
63%
573
31%
1052
September1st to 15thNight
52%
636
13%
1887
11%
636
55%
636
26%
1232
September16th to endNight
49%
685
15%
1892
11%
685
52%
685
27%
1288
October1st to 15thNight
39%
660
15%
1906
10%
660
44%
660
21%
1346
October16th to endNight
24%
704
8%
2260
4%
704
28%
704
10%
1814
November1st to 15thNight
26%
700
12%
2285
8%
700
32%
700
12%
1735
November16th to endNight
17%
726
7%
2526
4%
726
21%
726
7%
2069
December1st to 15thNight
14%
900
6%
2700
2%
900
17%
900
8%
2241
December16th to endNight
15%
960
6%
2880
2%
960
20%
960
8%
2439

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%5%3445%7%36%
48027
Night
16%10%46%5%3445%6%31%
47029
Cloud CoverDay
14%8%36%5%3445%7%36%
48036
Night
16%10%46%6%34446%32%
47034
TransparencyDay
47%7%13%21%9%1
47707
Night
52%6%12%18%8%
46867
SeeingDay
18%5%26%31%15%3
6002
Night
20%7%28%29%12%1
15529

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
14%14%5%11%9%45%45%6%16%
1384
16th to endDay
13%14%7%9%8%45%436%22%
1536
February1st to 15thDay
10%14%5%10%8%46%5%5%6%23%
1550
16th to endDay
13%10%6%6%7%45%46%6%29%
1569
March1st to 15thDay
13%8%47%5%34247%38%
1850
16th to endDay
13%7%34434336%43%
2114
April1st to 15thDay
18%9%35%42445%6%35%
2205
16th to endDay
17%7%35%43445%7%35%
2340
May1st to 15thDay
17%7%25%5%3445%6%36%
2331
16th to endDay
13%5%13435%5%5%6%43%
2709
June1st to 15thDay
14%5%25%4245%6%8%39%
2700
16th to endDay
12%6%24435%5%6%8%39%
2700
July1st to 15thDay
9%5%2442445%8%47%
2649
16th to endDay
9%3244245%6%9%47%
2655
August1st to 15thDay
10%5%145%3445%8%47%
2370
16th to endDay
12%5%245%2345%7%45%
2483
September1st to 15thDay
13%5%2442445%8%43%
2060
16th to endDay
14%5%35%5%2445%8%40%
1881
October1st to 15thDay
21%6%36%6%34445%33%
1724
16th to endDay
23%9%46%6%446%5%7%20%
1609
November1st to 15thDay
19%12%5%7%6%3445%7%24%
1573
16th to endDay
22%16%6%8%6%44345%16%
1431
December1st to 15thDay
18%16%5%9%6%43445%20%
1260
16th to endDay
20%16%49%7%35%435%18%
1344
January1st to 15thNight
18%15%5%9%6%45%45%5%19%
2553
16th to endNight
15%14%6%9%8%45%446%21%
2688
February1st to 15thNight
11%13%5%9%7%46%5%5%6%22%
2309
16th to endNight
13%12%48%8%46%6%45%25%
1901
March1st to 15thNight
15%8%46%5%3445%5%36%
2087
16th to endNight
12%8%35%5%2445%5%40%
2112
April1st to 15thNight
18%6%46%5%34446%35%
1751
16th to endNight
18%7%35%42445%6%38%
1620
May1st to 15thNight
15%8%47%6%445%46%32%
1620
16th to endNight
14%5%25%4145%5%7%42%
1402
June1st to 15thNight
13%5%4442446%9%39%
1260
16th to endNight
9%6%25%425%47%9%42%
1260
July1st to 15thNight
9%425%426%45%7%47%
1308
16th to endNight
6%415%5%345%5%9%48%
1513
August1st to 15thNight
7%3145%3335%7%52%
1590
16th to endNight
10%5%25%433446%49%
1719
September1st to 15thNight
15%5%24434446%44%
1887
16th to endNight
15%7%35%42445%6%40%
1892
October1st to 15thNight
19%6%35%5%2335%8%35%
1906
16th to endNight
26%11%36%6%3445%6%22%
2260
November1st to 15thNight
18%10%37%7%35%45%6%26%
2285
16th to endNight
22%17%5%7%6%34445%19%
2526
December1st to 15thNight
20%16%5%8%6%25%45%5%19%
2700
16th to endNight
21%16%6%9%6%34335%18%
2880

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
15%14%5%12%7%5%5%45%6%16%
1384
16th to endDay
14%13%7%9%7%45%447%22%
1536
February1st to 15thDay
10%14%5%10%7%46%5%5%7%23%
1550
16th to endDay
13%10%5%7%7%45%46%5%29%
1569
March1st to 15thDay
13%8%47%5%24346%38%
1860
16th to endDay
13%7%34434336%43%
2113
April1st to 15thDay
18%8%35%4135%46%36%
2205
16th to endDay
17%7%25%5%3445%7%36%
2340
May1st to 15thDay
18%7%35%434447%36%
2331
16th to endDay
13%6%144245%5%7%44%
2709
June1st to 15thDay
14%5%25%425%46%8%41%
2700
16th to endDay
12%6%245%25%5%5%8%41%
2700
July1st to 15thDay
9%5%243245%5%8%47%
2649
16th to endDay
9%32442445%9%47%
2655
August1st to 15thDay
10%5%235%2436%8%47%
2370
16th to endDay
12%5%245%2346%8%45%
2483
September1st to 15thDay
13%5%24424448%43%
2060
16th to endDay
14%5%35%42445%7%41%
1881
October1st to 15thDay
21%7%36%5%2445%5%33%
1724
16th to endDay
23%9%37%5%36%46%6%21%
1609
November1st to 15thDay
18%13%47%6%34447%24%
1573
16th to endDay
21%16%6%9%6%3444417%
1431
December1st to 15thDay
18%16%6%8%6%345%35%20%
1260
16th to endDay
20%16%6%9%6%3434419%
1344
January1st to 15thNight
18%15%5%9%7%35%445%19%
2553
16th to endNight
15%14%5%9%9%44346%21%
2688
February1st to 15thNight
11%14%5%9%7%46%5%5%5%23%
2302
16th to endNight
13%12%5%8%8%46%5%5%426%
1901
March1st to 15thNight
16%8%46%5%2445%6%36%
2100
16th to endNight
13%8%35%5%24445%41%
2112
April1st to 15thNight
18%7%36%5%34447%34%
1751
16th to endNight
18%6%35%424446%39%
1620
May1st to 15thNight
15%8%47%6%445%47%31%
1619
16th to endNight
13%6%244245%5%7%42%
1402
June1st to 15thNight
13%6%35%5%2445%8%40%
1260
16th to endNight
10%5%245%25%5%6%8%43%
1260
July1st to 15thNight
9%424435%5%47%47%
1308
16th to endNight
7%4244345%5%9%47%
1513
August1st to 15thNight
7%4145%24447%52%
1590
16th to endNight
10%5%25%433446%49%
1719
September1st to 15thNight
15%5%24424347%43%
1887
16th to endNight
15%7%35%42345%6%40%
1892
October1st to 15thNight
19%6%35%5%2335%7%35%
1906
16th to endNight
28%10%37%5%34445%22%
2260
November1st to 15thNight
19%11%46%7%34446%26%
2285
16th to endNight
22%17%5%7%5%33345%20%
2526
December1st to 15thNight
21%16%5%8%6%2445%5%19%
2700
16th to endNight
21%15%6%10%6%34335%19%
2880

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
67%9%10%9%2
1385
16th to endDay
63%6%10%12%6%
1536
February1st to 15thDay
60%8%13%13%4
1552
16th to endDay
55%5%13%18%7%
1569
March1st to 15thDay
46%5%14%20%11%1
1860
16th to endDay
42%5%12%24%11%3
2114
April1st to 15thDay
47%6%11%20%12%
2205
16th to endDay
46%6%9%20%14%3
2340
May1st to 15thDay
46%6%10%20%12%3
2331
16th to endDay
38%7%14%25%13%
2713
June1st to 15thDay
39%7%14%25%12%1
2700
16th to endDay
40%7%14%25%11%
2700
July1st to 15thDay
33%6%14%30%13%
2494
16th to endDay
32%7%16%28%13%
2488
August1st to 15thDay
33%7%18%27%12%1
2355
16th to endDay
36%7%18%27%9%
2483
September1st to 15thDay
39%7%17%26%8%
2060
16th to endDay
40%9%16%25%7%
1881
October1st to 15thDay
51%7%12%20%8%
1724
16th to endDay
61%10%13%9%5%
1609
November1st to 15thDay
59%6%12%15%5%
1573
16th to endDay
69%7%11%6%3
1431
December1st to 15thDay
66%7%11%8%4
1260
16th to endDay
68%7%11%9%2
1344
January1st to 15thNight
67%7%10%9%4
2553
16th to endNight
64%7%10%12%5%
2688
February1st to 15thNight
60%7%12%14%4
2311
16th to endNight
59%7%10%15%6%
1901
March1st to 15thNight
48%5%13%20%10%
2100
16th to endNight
43%6%12%21%13%3
2112
April1st to 15thNight
49%49%23%12%
1751
16th to endNight
46%5%8%19%16%3
1620
May1st to 15thNight
51%5%9%17%12%3
1620
16th to endNight
40%5%13%24%14%1
1404
June1st to 15thNight
39%7%13%22%15%1
1260
16th to endNight
36%7%16%26%11%1
1260
July1st to 15thNight
33%5%14%26%16%1
1234
16th to endNight
33%7%13%28%15%
1417
August1st to 15thNight
31%6%16%32%10%2
1581
16th to endNight
35%6%16%28%11%
1719
September1st to 15thNight
40%7%16%23%10%
1887
16th to endNight
42%6%16%26%7%
1892
October1st to 15thNight
47%6%14%21%8%
1906
16th to endNight
63%7%12%11%3
2260
November1st to 15thNight
56%8%12%16%5%
2285
16th to endNight
67%7%12%8%4
2526
December1st to 15thNight
66%8%12%11%1
2700
16th to endNight
70%6%9%10%3
2880

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%6%39%26%6%
82
16th to endDay
32%5%22%28%10%1
96
February1st to 15thDay
22%13%41%21%2
90
16th to endDay
22%17%30%23%6%
81
March1st to 15thDay
16%16%34%21%11%
150
16th to endDay
23%5%26%28%11%3
288
April1st to 15thDay
23%7%26%27%13%1
270
16th to endDay
23%5%31%22%12%4
270
May1st to 15thDay
22%5%30%25%13%3
288
16th to endDay
17%427%34%12%3
490
June1st to 15thDay
15%434%31%11%2
495
16th to endDay
15%425%39%11%3
495
July1st to 15thDay
11%226%37%18%3
475
16th to endDay
10%322%37%21%3
515
August1st to 15thDay
14%116%36%24%6%
343
16th to endDay
15%419%32%23%4
332
September1st to 15thDay
14%221%25%26%9%
315
16th to endDay
19%419%36%15%5%
278
October1st to 15thDay
21%6%26%30%12%2
255
16th to endDay
27%11%35%19%6%
121
November1st to 15thDay
16%10%38%26%6%1
89
16th to endDay
30%13%33%21%1
60
December1st to 15thDay
35%20%28%11%5%
60
16th to endDay
32%26%31%9%
64
January1st to 15thNight
25%13%30%24%6%
900
16th to endNight
21%9%31%28%7%
960
February1st to 15thNight
17%8%40%25%7%
728
16th to endNight
17%8%34%30%9%
631
March1st to 15thNight
18%8%36%27%7%
720
16th to endNight
19%6%30%31%11%1
768
April1st to 15thNight
20%6%29%33%7%1
548
16th to endNight
21%5%31%26%14%1
540
May1st to 15thNight
17%5%25%34%14%2
540
16th to endNight
14%5%24%35%18%1
443
June1st to 15thNight
15%423%38%16%1
360
16th to endNight
13%122%40%20%1
360
July1st to 15thNight
11%118%42%23%2
384
16th to endNight
9%117%42%26%3
564
August1st to 15thNight
10%218%40%25%3
539
16th to endNight
13%216%37%27%3
573
September1st to 15thNight
16%322%29%21%7%
636
16th to endNight
18%322%30%19%6%
685
October1st to 15thNight
20%8%24%31%13%1
660
16th to endNight
32%10%26%22%6%1
704
November1st to 15thNight
22%12%32%23%9%
700
16th to endNight
31%14%27%20%4
726
December1st to 15thNight
27%15%33%17%5%
900
16th to endNight
29%10%31%19%6%1
960
Page generated at 2017-09-23 06:43:37. Version ac04

Copyright 2017 A. Danko


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