Maple's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maple's 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
64%
15523
25%
46972
23%
15487
66%
15487
36%
26864

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
63%
716
18%
2372
18%
716
66%
716
30%
1396
January16th to endNight
61%
768
24%
2496
26%
768
63%
768
27%
1543
February1st to 15thNight
59%
700
22%
2261
24%
700
62%
700
26%
1411
February16th to endNight
52%
632
20%
1895
19%
632
55%
632
27%
1215
March1st to 15thNight
56%
720
17%
2019
16%
720
58%
720
28%
1321
March16th to endNight
55%
768
19%
2078
16%
768
57%
768
29%
1354
April1st to 15thNight
52%
719
21%
1799
13%
719
54%
719
31%
1206
April16th to endNight
58%
720
22%
1800
11%
720
61%
720
42%
1082
May1st to 15thNight
61%
668
22%
1748
14%
668
62%
668
41%
1036
May16th to endNight
53%
402
21%
1525
19%
402
59%
402
28%
840
June1st to 15thNight
62%
360
22%
1440
25%
360
65%
360
31%
747
June16th to endNight
78%
360
31%
1440
40%
360
80%
360
55%
540
July1st to 15thNight
74%
395
25%
1415
30%
395
74%
395
49%
605
July16th to endNight
66%
564
27%
1593
24%
531
68%
531
44%
825
August1st to 15thNight
63%
592
24%
1665
18%
589
63%
589
43%
905
August16th to endNight
75%
764
31%
1910
21%
764
75%
764
57%
1033
September1st to 15thNight
80%
720
36%
1800
27%
720
81%
720
60%
947
September16th to endNight
75%
683
38%
1856
35%
683
77%
683
56%
939
October1st to 15thNight
72%
660
28%
1980
31%
660
74%
660
43%
1055
October16th to endNight
70%
704
31%
2112
35%
704
72%
704
42%
1137
November1st to 15thNight
68%
700
29%
2181
30%
700
70%
700
37%
1199
November16th to endNight
68%
720
25%
2379
28%
720
71%
720
35%
1291
December1st to 15thNight
59%
720
22%
2520
22%
720
64%
720
26%
1536
December16th to endNight
52%
768
20%
2688
20%
768
56%
768
22%
1701

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
7%6%24323347%54%
47908
Night
8%7%24423347%50%
47162
TransparencyDay
27%49%18%23%15%
47597
Night
31%5%9%17%21%14%
46973
SeeingDay
8%7%24%37%17%4
6063
Night
10%212%29%33%10%
15533

By Month

Percentage Cloud Cover SW (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
12%5%24423347%48%
1566
16th to endDay
14%7%25%42443446%
1728
February1st to 15thDay
14%8%33323445%45%
1602
16th to endDay
16%8%35%5%34446%39%
1579
March1st to 15thDay
11%6%25%4345%6%10%39%
1938
16th to endDay
12%6%35%6%3445%7%41%
2145
April1st to 15thDay
12%8%245%3335%6%44%
2149
16th to endDay
8%6%24322345%54%
2160
May1st to 15thDay
5%5%243224410%55%
2200
16th to endDay
8%9%24423348%48%
2587
June1st to 15thDay
5%5%24424448%53%
2520
16th to endDay
2412212247%67%
2520
July1st to 15thDay
1423223338%63%
2457
16th to endDay
2312223249%63%
2468
August1st to 15thDay
26%233123410%58%
2286
16th to endDay
413313348%64%
2292
September1st to 15thDay
2312212239%68%
2160
16th to endDay
45%11212336%67%
1912
October1st to 15thDay
6%313312446%61%
1650
16th to endDay
6%5%14323336%59%
1760
November1st to 15thDay
8%5%24423436%53%
1675
16th to endDay
10%6%2422345%6%52%
1578
December1st to 15thDay
13%8%25%5%34346%42%
1440
16th to endDay
15%6%34423347%44%
1536
January1st to 15thNight
11%5%24423348%47%
2372
16th to endNight
13%6%24423345%48%
2496
February1st to 15thNight
12%7%2442445%6%43%
2250
16th to endNight
14%7%35%423346%44%
1895
March1st to 15thNight
12%7%34424347%44%
2019
16th to endNight
11%8%25%424347%44%
2078
April1st to 15thNight
11%6%2442445%6%46%
1799
16th to endNight
8%5%24214246%57%
1800
May1st to 15thNight
38%25%423346%53%
1748
16th to endNight
8%9%36%322346%48%
1524
June1st to 15thNight
5%9%35%5%2335%7%48%
1440
16th to endNight
25%13323246%63%
1440
July1st to 15thNight
17%3442435%8%54%
1500
16th to endNight
112%35%43446%9%41%
1701
August1st to 15thNight
213%47%7%235%47%41%
1674
16th to endNight
18%35%5%33449%51%
1910
September1st to 15thNight
341332335%7%60%
1800
16th to endNight
35%13312336%64%
1856
October1st to 15thNight
6%424323336%58%
1980
16th to endNight
6%5%24433346%55%
2112
November1st to 15thNight
8%6%24223246%57%
2181
16th to endNight
8%5%23323347%54%
2379
December1st to 15thNight
13%6%24423445%46%
2520
16th to endNight
16%6%24424335%45%
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
36%5%10%21%16%9%
1566
16th to endDay
40%5%7%12%20%12%
1728
February1st to 15thDay
40%48%18%20%6%
1602
16th to endDay
45%7%8%22%13%3
1579
March1st to 15thDay
39%8%12%17%15%6%
1938
16th to endDay
41%7%15%17%15%2
2145
April1st to 15thDay
40%6%12%24%14%2
2149
16th to endDay
30%5%12%25%19%6%
2160
May1st to 15thDay
22%412%28%25%6%
2200
16th to endDay
31%5%12%25%20%4
2591
June1st to 15thDay
25%6%11%19%25%11%
2520
16th to endDay
12%17%17%34%26%
2520
July1st to 15thDay
13%15%9%26%42%
2313
16th to endDay
12%26%11%31%35%
2313
August1st to 15thDay
16%16%13%29%32%
2270
16th to endDay
13%15%16%34%28%
2292
September1st to 15thDay
12%25%16%30%32%
2160
16th to endDay
17%27%23%31%18%
1912
October1st to 15thDay
22%410%22%24%16%
1650
16th to endDay
24%49%22%22%16%
1760
November1st to 15thDay
30%5%9%21%26%6%
1675
16th to endDay
32%411%17%26%7%
1578
December1st to 15thDay
42%6%10%13%19%7%
1440
16th to endDay
41%5%13%17%16%6%
1536
January1st to 15thNight
35%412%18%19%9%
2372
16th to endNight
38%6%9%12%17%15%
2496
February1st to 15thNight
40%5%9%17%18%8%
2261
16th to endNight
41%413%23%13%3
1895
March1st to 15thNight
38%7%13%17%16%7%
2019
16th to endNight
36%8%14%18%16%5%
2078
April1st to 15thNight
38%5%12%24%14%3
1799
16th to endNight
27%6%15%23%20%7%
1800
May1st to 15thNight
28%5%9%19%26%9%
1749
16th to endNight
33%5%12%22%21%5%
1525
June1st to 15thNight
29%5%11%16%19%17%
1440
16th to endNight
14%26%12%31%32%
1440
July1st to 15thNight
19%25%7%23%42%
1415
16th to endNight
25%38%9%22%30%
1593
August1st to 15thNight
28%15%12%22%29%
1665
16th to endNight
21%1413%29%28%
1910
September1st to 15thNight
17%3312%28%34%
1800
16th to endNight
18%3419%33%20%
1856
October1st to 15thNight
25%48%22%22%17%
1980
16th to endNight
26%47%22%23%16%
2112
November1st to 15thNight
28%5%10%21%25%8%
2181
16th to endNight
29%5%11%19%24%9%
2379
December1st to 15thNight
38%6%10%14%20%8%
2520
16th to endNight
41%6%11%17%15%7%
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
18%9%26%26%15%2
194
16th to endDay
16%9%25%29%16%3
256
February1st to 15thDay
13%10%26%24%22%2
241
16th to endDay
16%13%28%29%10%1
238
March1st to 15thDay
13%10%32%24%14%3
270
16th to endDay
9%14%39%25%9%1
288
April1st to 15thDay
15%18%33%23%8%1
269
16th to endDay
6%21%34%28%7%1
270
May1st to 15thDay
10%13%32%33%7%2
288
16th to endDay
13%12%26%33%11%3
330
June1st to 15thDay
47%37%36%10%3
315
16th to endDay
1222%45%24%3
315
July1st to 15thDay
315%50%25%5%
305
16th to endDay
210%52%25%8%
327
August1st to 15thDay
5%16%52%19%5%
315
16th to endDay
112%53%25%6%
332
September1st to 15thDay
4117%47%21%8%
315
16th to endDay
47%16%39%25%6%
280
October1st to 15thDay
5%7%26%40%16%3
255
16th to endDay
11%327%36%19%2
272
November1st to 15thDay
6%7%19%26%30%9%
181
16th to endDay
8%8%19%40%21%1
83
December1st to 15thDay
21%6%26%33%11%
60
16th to endDay
14%9%10%32%28%4
64
January1st to 15thNight
12%312%32%29%9%
720
16th to endNight
15%413%29%28%9%
768
February1st to 15thNight
14%413%30%28%7%
704
16th to endNight
18%5%16%31%22%4
632
March1st to 15thNight
14%414%31%26%7%
720
16th to endNight
11%5%19%33%26%4
768
April1st to 15thNight
12%5%20%33%23%4
719
16th to endNight
9%420%29%26%9%
720
May1st to 15thNight
8%215%37%28%8%
669
16th to endNight
13%315%27%30%9%
403
June1st to 15thNight
8%115%34%32%6%
360
16th to endNight
5%6%29%49%8%
360
July1st to 15thNight
5%422%50%17%
395
16th to endNight
4421%45%23%
564
August1st to 15thNight
7%5%27%45%12%
592
16th to endNight
5%427%48%14%
764
September1st to 15thNight
5%422%50%17%
720
16th to endNight
5%9%23%41%19%
683
October1st to 15thNight
8%19%30%35%15%
660
16th to endNight
9%19%27%32%19%
704
November1st to 15thNight
9%211%30%34%12%
700
16th to endNight
10%111%31%33%10%
720
December1st to 15thNight
14%313%32%27%6%
720
16th to endNight
18%5%17%31%22%4
768
Page generated at 2017-09-23 03:43:42. Version ac04

Copyright 2017 A. Danko


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