BoonHill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BoonHill Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
32%
16058
12%
46960
8%
16016
36%
16016
17%
35084

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
13%
900
4%
2506
2%
895
15%
895
5%
2243
January16th to endNight
15%
960
5%
2688
2%
960
18%
960
7%
2381
February1st to 15thNight
17%
749
7%
2265
3%
749
21%
749
8%
1909
February16th to endNight
22%
631
8%
1893
3%
631
26%
631
10%
1553
March1st to 15thNight
26%
720
13%
2139
7%
720
31%
720
17%
1577
March16th to endNight
30%
722
17%
2066
11%
722
35%
722
21%
1469
April1st to 15thNight
25%
539
13%
1797
9%
539
32%
539
16%
1282
April16th to endNight
32%
540
19%
1627
9%
540
42%
540
23%
1096
May1st to 15thNight
32%
540
13%
1620
8%
540
37%
540
20%
1137
May16th to endNight
38%
562
15%
1511
6%
561
46%
561
30%
986
June1st to 15thNight
43%
540
13%
1440
8%
540
47%
540
27%
968
June16th to endNight
49%
540
13%
1440
7%
540
53%
540
29%
952
July1st to 15thNight
60%
510
16%
1360
11%
510
63%
510
40%
796
July16th to endNight
58%
564
16%
1417
11%
531
61%
531
37%
885
August1st to 15thNight
63%
539
21%
1562
17%
536
65%
536
37%
908
August16th to endNight
57%
573
19%
1803
17%
573
61%
573
30%
1093
September1st to 15thNight
56%
603
20%
1863
18%
603
59%
603
33%
1095
September16th to endNight
51%
669
19%
1848
14%
669
54%
669
29%
1201
October1st to 15thNight
39%
660
18%
1864
13%
660
44%
660
22%
1314
October16th to endNight
26%
704
10%
2288
7%
704
32%
704
13%
1755
November1st to 15thNight
26%
700
14%
2276
11%
700
32%
700
14%
1702
November16th to endNight
16%
733
6%
2353
4%
733
20%
733
7%
1986
December1st to 15thNight
12%
900
2%
2646
1%
900
13%
900
5%
2398
December16th to endNight
13%
960
5%
2688
1%
960
15%
960
6%
2398

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
15%10%47%6%3445%6%29%
47829
Night
14%11%5%8%6%34445%29%
47128
Cloud CoverDay
14%10%48%6%35%45%6%29%
47838
Night
14%11%5%8%7%34446%29%
47133
TransparencyDay
54%6%10%18%9%
47515
Night
55%5%11%17%8%
46960
SeeingDay
19%10%29%25%11%4
6015
Night
19%9%31%28%9%1
16062

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%16%10%17%10%5%42229%
1432
16th to endDay
11%19%12%16%12%5%5%2227%
1536
February1st to 15thDay
11%15%8%13%15%46%43312%
1596
16th to endDay
11%16%12%12%12%35%43314%
1580
March1st to 15thDay
12%12%5%10%9%35%446%25%
1811
16th to endDay
16%11%5%8%7%3435%5%29%
2169
April1st to 15thDay
19%15%35%423345%29%
2151
16th to endDay
17%11%36%5%24446%32%
2331
May1st to 15thDay
18%8%36%5%34346%33%
2331
16th to endDay
12%5%25%5%246%6%6%40%
2602
June1st to 15thDay
14%6%36%435%45%8%36%
2520
16th to endDay
13%5%25%5%35%5%7%8%36%
2520
July1st to 15thDay
9%5%244345%7%10%41%
2520
16th to endDay
10%5%245%36%5%6%8%40%
2655
August1st to 15thDay
9%6%25%5%45%6%7%8%37%
2388
16th to endDay
15%5%25%5%3445%8%39%
2397
September1st to 15thDay
17%5%145%345%46%41%
2085
16th to endDay
15%5%26%435%45%8%37%
1837
October1st to 15thDay
21%9%26%5%34346%32%
1763
16th to endDay
24%15%47%7%34445%19%
1584
November1st to 15thDay
16%16%6%45%2435%7%27%
1582
16th to endDay
17%22%11%11%5%2333413%
1605
December1st to 15thDay
16%22%11%17%9%122139%
1298
16th to endDay
20%21%11%12%9%332247%
1536
January1st to 15thNight
17%16%8%15%11%5%432312%
2506
16th to endNight
10%16%9%14%11%5%6%34411%
2688
February1st to 15thNight
11%13%8%13%11%6%6%43315%
2263
16th to endNight
13%13%7%12%10%45%435%17%
1893
March1st to 15thNight
13%12%6%8%6%24445%31%
2126
16th to endNight
13%9%5%7%5%35%446%33%
2066
April1st to 15thNight
20%10%46%425%447%30%
1797
16th to endNight
18%7%35%423435%40%
1627
May1st to 15thNight
16%6%25%7%45%5%6%6%33%
1620
16th to endNight
12%6%245%2446%8%41%
1509
June1st to 15thNight
13%6%245%3446%7%39%
1440
16th to endNight
9%5%26%6%25%5%6%8%42%
1440
July1st to 15thNight
9%41342445%8%52%
1440
16th to endNight
7%4244345%6%8%48%
1513
August1st to 15thNight
6%325%42446%9%49%
1571
16th to endNight
11%6%24424445%48%
1803
September1st to 15thNight
14%5%2331335%5%50%
1863
16th to endNight
12%5%26%5%3445%7%42%
1848
October1st to 15thNight
18%10%26%423335%37%
1864
16th to endNight
23%12%36%5%3445%5%25%
2288
November1st to 15thNight
14%16%5%7%5%34346%28%
2276
16th to endNight
18%19%8%11%6%3443416%
2353
December1st to 15thNight
17%19%11%14%9%3432210%
2646
16th to endNight
17%20%11%13%8%2433410%
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
16%15%9%16%11%6%42329%
1432
16th to endDay
10%18%12%16%13%5%5%3327%
1536
February1st to 15thDay
10%15%7%13%13%6%6%43312%
1596
16th to endDay
10%14%12%12%11%5%5%44314%
1580
March1st to 15thDay
12%10%5%9%8%45%5%46%24%
1821
16th to endDay
15%11%49%7%3435%5%29%
2168
April1st to 15thDay
19%14%5%5%42425%6%29%
2151
16th to endDay
17%10%26%5%3445%6%32%
2331
May1st to 15thDay
17%9%36%6%34446%33%
2331
16th to endDay
11%5%35%4346%6%6%41%
2602
June1st to 15thDay
13%7%26%5%35%45%7%36%
2520
16th to endDay
12%5%36%5%35%6%6%8%36%
2520
July1st to 15thDay
8%5%245%35%6%7%10%41%
2520
16th to endDay
9%5%25%5%36%5%7%9%40%
2655
August1st to 15thDay
8%6%25%5%46%5%7%8%37%
2388
16th to endDay
15%5%25%5%3445%8%39%
2397
September1st to 15thDay
16%5%245%34446%41%
2085
16th to endDay
14%6%25%5%25%5%5%8%37%
1837
October1st to 15thDay
20%9%27%434446%32%
1763
16th to endDay
22%15%47%7%34446%18%
1584
November1st to 15thDay
14%15%5%7%5%2435%8%27%
1582
16th to endDay
17%21%10%11%7%3432413%
1605
December1st to 15thDay
16%20%12%15%9%2322310%
1298
16th to endDay
20%21%10%11%9%343247%
1536
January1st to 15thNight
17%16%7%14%11%5%432312%
2506
16th to endNight
10%15%9%15%11%6%6%45%410%
2688
February1st to 15thNight
11%14%6%12%11%5%7%5%4316%
2256
16th to endNight
13%14%7%12%9%36%5%35%17%
1893
March1st to 15thNight
13%12%5%7%6%3445%5%31%
2139
16th to endNight
13%9%5%7%5%35%446%33%
2066
April1st to 15thNight
19%10%5%6%425%45%5%30%
1797
16th to endNight
18%7%25%423345%40%
1627
May1st to 15thNight
15%8%25%7%45%45%7%33%
1619
16th to endNight
11%6%25%5%3446%8%41%
1509
June1st to 15thNight
13%5%25%5%245%6%8%39%
1440
16th to endNight
9%5%26%5%245%6%9%41%
1440
July1st to 15thNight
8%3134245%5%8%52%
1440
16th to endNight
6%425%425%5%5%8%49%
1513
August1st to 15thNight
6%325%43436%10%49%
1571
16th to endNight
10%6%25%424445%49%
1803
September1st to 15thNight
13%41341425%6%50%
1863
16th to endNight
12%5%26%425%45%7%43%
1848
October1st to 15thNight
17%10%45%5%23345%37%
1864
16th to endNight
22%11%47%5%35%45%6%25%
2288
November1st to 15thNight
12%15%48%6%34346%28%
2276
16th to endNight
18%18%7%12%7%3443415%
2353
December1st to 15thNight
17%18%11%14%9%3432310%
2646
16th to endNight
17%19%11%13%8%2433310%
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
82%446%1
1433
16th to endDay
83%45%41
1536
February1st to 15thDay
76%47%10%1
1598
16th to endDay
73%5%7%10%3
1580
March1st to 15thDay
57%7%11%14%7%
1821
16th to endDay
54%5%12%19%5%1
2169
April1st to 15thDay
56%39%19%11%
2151
16th to endDay
51%6%11%12%15%2
2331
May1st to 15thDay
51%49%22%9%2
2331
16th to endDay
39%7%13%24%13%1
2606
June1st to 15thDay
44%6%11%23%14%
2520
16th to endDay
42%7%14%21%13%
2520
July1st to 15thDay
34%7%11%27%17%1
2371
16th to endDay
38%8%12%22%15%2
2488
August1st to 15thDay
40%7%13%26%11%1
2373
16th to endDay
42%6%11%23%14%1
2397
September1st to 15thDay
41%6%11%27%11%1
2085
16th to endDay
43%6%15%22%10%
1837
October1st to 15thDay
52%6%10%21%8%
1763
16th to endDay
66%6%12%11%3
1584
November1st to 15thDay
56%5%11%18%7%
1582
16th to endDay
75%411%6%2
1605
December1st to 15thDay
82%35%6%1
1298
16th to endDay
83%46%41
1536
January1st to 15thNight
79%36%7%2
2506
16th to endNight
75%5%9%6%2
2688
February1st to 15thNight
71%5%7%12%2
2265
16th to endNight
67%5%11%10%4
1893
March1st to 15thNight
53%6%11%17%9%
2139
16th to endNight
49%5%12%22%9%
2066
April1st to 15thNight
53%49%18%11%1
1797
16th to endNight
46%410%20%15%3
1627
May1st to 15thNight
48%6%11%20%10%2
1620
16th to endNight
39%5%12%24%14%2
1511
June1st to 15thNight
40%7%12%23%15%
1440
16th to endNight
37%8%13%23%15%1
1440
July1st to 15thNight
28%5%13%29%21%1
1360
16th to endNight
30%8%15%26%16%1
1417
August1st to 15thNight
29%6%16%32%14%
1562
16th to endNight
37%5%13%26%16%1
1803
September1st to 15thNight
33%5%14%29%15%1
1863
16th to endNight
38%6%14%29%9%
1848
October1st to 15thNight
49%5%9%24%11%
1864
16th to endNight
59%6%13%15%5%
2288
November1st to 15thNight
56%6%11%15%7%1
2276
16th to endNight
72%411%8%2
2353
December1st to 15thNight
80%47%5%1
2646
16th to endNight
78%48%6%2
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
17%15%38%25%2
90
16th to endDay
31%6%33%23%41
96
February1st to 15thDay
15%26%44%11%2
90
16th to endDay
23%20%34%17%3
81
March1st to 15thDay
29%18%23%21%5%
111
16th to endDay
29%7%22%31%7%1
288
April1st to 15thDay
28%9%31%21%6%1
270
16th to endDay
23%12%31%20%7%4
270
May1st to 15thDay
24%18%24%21%8%2
288
16th to endDay
15%13%32%26%7%3
502
June1st to 15thDay
17%10%37%22%10%2
495
16th to endDay
15%9%34%26%9%4
495
July1st to 15thDay
12%7%28%31%16%4
475
16th to endDay
12%7%30%30%13%7%
515
August1st to 15thDay
10%323%29%22%10%
361
16th to endDay
21%419%25%20%7%
332
September1st to 15thDay
15%220%26%20%13%
315
16th to endDay
17%6%22%29%19%4
262
October1st to 15thDay
21%9%24%29%12%2
241
16th to endDay
31%7%45%12%3
96
November1st to 15thDay
22%8%37%18%12%
90
16th to endDay
24%23%30%15%5%1
90
December1st to 15thDay
31%28%27%9%11
66
16th to endDay
31%29%32%7%
96
January1st to 15thNight
26%12%33%20%6%
900
16th to endNight
15%14%39%25%4
960
February1st to 15thNight
18%13%37%26%3
752
16th to endNight
20%13%34%25%5%
631
March1st to 15thNight
17%12%35%25%8%
720
16th to endNight
18%9%35%28%7%1
722
April1st to 15thNight
23%10%35%24%5%
539
16th to endNight
20%9%35%26%7%
540
May1st to 15thNight
19%8%34%29%7%
540
16th to endNight
13%8%33%31%11%
563
June1st to 15thNight
15%5%29%36%12%
540
16th to endNight
12%5%26%40%14%1
540
July1st to 15thNight
12%121%41%20%1
510
16th to endNight
9%123%40%22%1
564
August1st to 15thNight
8%119%47%20%2
539
16th to endNight
14%418%38%23%1
573
September1st to 15thNight
17%219%35%19%5%
603
16th to endNight
14%6%22%33%19%3
669
October1st to 15thNight
23%6%25%33%10%
660
16th to endNight
30%11%27%23%6%
704
November1st to 15thNight
23%10%34%23%7%
700
16th to endNight
27%13%33%20%4
733
December1st to 15thNight
26%14%37%20%2
900
16th to endNight
23%12%36%21%3
960
Page generated at 2017-09-19 07:32:31. Version ac04

Copyright 2017 A. Danko


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