Hamilton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hamilton clear sky chart from 2005-11-05 to 2017-08-12.

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%
14738
14%
46547
9%
14702
43%
14702
19%
32207

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
14%
716
10%
2443
4%
716
22%
716
9%
1910
January16th to endNight
16%
768
11%
2496
3%
768
25%
768
10%
1918
February1st to 15thNight
16%
701
8%
2287
2%
701
24%
701
10%
1762
February16th to endNight
25%
631
11%
2002
5%
631
33%
631
15%
1465
March1st to 15thNight
26%
720
12%
1980
7%
720
31%
720
16%
1511
March16th to endNight
34%
768
20%
2112
10%
768
42%
768
23%
1459
April1st to 15thNight
32%
718
15%
1831
6%
718
38%
718
23%
1329
April16th to endNight
44%
555
21%
1635
10%
555
52%
555
26%
1061
May1st to 15thNight
48%
520
17%
1600
12%
520
54%
520
25%
1050
May16th to endNight
51%
374
17%
1497
17%
374
59%
374
25%
860
June1st to 15thNight
51%
360
13%
1440
14%
360
59%
360
21%
864
June16th to endNight
59%
360
14%
1440
18%
360
64%
360
24%
838
July1st to 15thNight
67%
340
17%
1360
24%
340
70%
340
35%
680
July16th to endNight
66%
524
15%
1555
16%
491
67%
491
33%
898
August1st to 15thNight
70%
527
17%
1575
15%
524
72%
524
36%
931
August16th to endNight
64%
567
21%
1617
14%
567
67%
567
35%
968
September1st to 15thNight
56%
660
22%
1675
12%
660
61%
660
33%
1102
September16th to endNight
57%
657
20%
1828
15%
657
60%
657
32%
1159
October1st to 15thNight
43%
660
19%
1980
16%
660
49%
660
24%
1312
October16th to endNight
26%
704
13%
2112
7%
704
34%
704
16%
1555
November1st to 15thNight
37%
700
18%
2354
15%
700
44%
700
21%
1537
November16th to endNight
26%
720
12%
2520
8%
720
33%
720
12%
1839
December1st to 15thNight
17%
720
7%
2520
2%
720
22%
720
9%
1972
December16th to endNight
13%
768
6%
2688
1%
768
19%
768
7%
2227

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
13%8%36%6%35%5%5%7%32%
47415
Night
14%8%36%5%35%45%7%35%
46729
Cloud CoverDay
13%7%36%6%35%5%5%7%33%
47425
Night
14%8%36%5%35%45%7%35%
46733
TransparencyDay
47%7%13%19%10%1
47115
Night
48%6%12%20%10%1
46547
SeeingDay
16%5%23%27%18%8%
5202
Night
18%7%28%28%14%1
14746

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
15%12%5%9%6%46%6%5%6%20%
1493
16th to endDay
11%14%7%11%9%5%6%6%5%5%16%
1728
February1st to 15thDay
14%14%5%11%7%36%5%46%18%
1575
16th to endDay
15%12%5%10%7%45%446%22%
1468
March1st to 15thDay
14%11%5%8%8%46%446%25%
1969
16th to endDay
14%9%46%5%25%45%7%33%
2112
April1st to 15thDay
18%8%37%6%4445%6%30%
2116
16th to endDay
16%7%36%6%23345%40%
2334
May1st to 15thDay
13%7%36%6%35%5%5%7%35%
2349
16th to endDay
11%5%35%5%35%45%8%42%
2618
June1st to 15thDay
12%5%25%6%35%5%5%8%38%
2520
16th to endDay
11%4245%45%6%6%10%38%
2520
July1st to 15thDay
7%4245%36%6%6%10%42%
2520
16th to endDay
8%425%6%36%6%8%9%37%
2503
August1st to 15thDay
7%425%6%36%5%7%10%38%
2288
16th to endDay
10%5%35%4345%5%9%41%
2221
September1st to 15thDay
12%5%35%6%345%5%7%38%
1953
16th to endDay
13%5%35%5%345%5%7%40%
1801
October1st to 15thDay
16%7%36%6%35%45%5%35%
1650
16th to endDay
22%10%37%6%35%5%46%25%
1760
November1st to 15thDay
10%7%38%5%35%5%6%9%33%
1501
16th to endDay
15%13%46%6%45%5%5%8%23%
1440
December1st to 15thDay
15%13%5%10%7%36%446%21%
1440
16th to endDay
18%14%5%9%8%46%5%5%5%14%
1536
January1st to 15thNight
17%13%49%7%34445%22%
2443
16th to endNight
12%12%7%10%7%36%45%7%21%
2496
February1st to 15thNight
14%13%5%10%6%35%45%5%25%
2285
16th to endNight
14%11%5%8%7%35%45%5%29%
2002
March1st to 15thNight
18%9%37%6%35%5%5%6%27%
1968
16th to endNight
14%8%47%424335%40%
2112
April1st to 15thNight
17%8%25%6%33446%35%
1831
16th to endNight
10%6%35%6%24446%42%
1635
May1st to 15thNight
15%6%35%5%34448%38%
1600
16th to endNight
12%315%5%2435%7%46%
1495
June1st to 15thNight
12%4246%45%5%6%7%40%
1440
16th to endNight
9%425%436%5%6%8%44%
1440
July1st to 15thNight
5%323325%45%10%54%
1440
16th to endNight
7%4243245%6%9%49%
1662
August1st to 15thNight
6%33435%6%6%10%48%
1586
16th to endNight
6%425%5%3345%6%51%
1617
September1st to 15thNight
12%4245%34447%46%
1675
16th to endNight
10%5%25%43445%6%45%
1828
October1st to 15thNight
16%5%25%5%2445%7%39%
1980
16th to endNight
20%8%46%5%35%5%6%5%29%
2112
November1st to 15thNight
14%6%25%435%45%9%38%
2354
16th to endNight
17%9%46%6%35%45%6%27%
2520
December1st to 15thNight
19%13%5%8%5%4445%6%23%
2520
16th to endNight
19%12%8%10%7%35%5%6%5%16%
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
15%12%5%9%7%46%5%5%7%20%
1493
16th to endDay
11%14%6%11%9%5%5%6%5%7%15%
1728
February1st to 15thDay
13%15%6%9%7%46%5%5%7%18%
1575
16th to endDay
15%12%5%8%8%45%5%46%23%
1468
March1st to 15thDay
14%11%6%7%8%36%445%26%
1980
16th to endDay
14%8%46%5%3445%7%35%
2111
April1st to 15thDay
18%7%37%6%35%45%6%31%
2116
16th to endDay
16%7%26%5%34345%41%
2334
May1st to 15thDay
13%6%27%6%445%5%7%36%
2349
16th to endDay
10%5%25%5%35%45%8%42%
2618
June1st to 15thDay
12%5%15%5%35%6%5%7%40%
2520
16th to endDay
11%325%5%36%6%5%10%40%
2520
July1st to 15thDay
7%423436%6%6%9%44%
2520
16th to endDay
8%325%5%46%6%8%9%38%
2503
August1st to 15thDay
7%4246%36%6%7%10%40%
2288
16th to endDay
10%424435%5%6%8%43%
2221
September1st to 15thDay
12%436%6%345%5%7%39%
1953
16th to endDay
13%5%26%4345%5%7%40%
1801
October1st to 15thDay
16%7%26%6%34447%36%
1650
16th to endDay
21%8%38%6%35%46%5%25%
1760
November1st to 15thDay
11%6%36%7%346%6%8%34%
1501
16th to endDay
16%12%37%5%37%5%5%8%23%
1440
December1st to 15thDay
15%13%5%8%7%46%5%46%22%
1440
16th to endDay
19%12%6%9%8%45%6%6%6%14%
1536
January1st to 15thNight
18%13%5%8%7%35%45%5%21%
2443
16th to endNight
12%12%6%9%8%45%5%5%7%21%
2496
February1st to 15thNight
14%13%6%9%6%36%45%6%25%
2278
16th to endNight
14%11%5%8%6%345%5%6%29%
2002
March1st to 15thNight
18%9%47%6%35%5%47%27%
1980
16th to endNight
14%9%36%5%34335%40%
2112
April1st to 15thNight
17%7%35%5%34346%36%
1831
16th to endNight
11%6%35%5%3445%5%43%
1635
May1st to 15thNight
15%6%25%5%3345%9%38%
1599
16th to endNight
12%325%5%34447%46%
1495
June1st to 15thNight
12%4145%36%5%6%8%40%
1440
16th to endNight
9%414436%5%6%8%44%
1440
July1st to 15thNight
5%314325%35%10%54%
1440
16th to endNight
8%3234245%6%9%49%
1662
August1st to 15thNight
6%313435%6%6%9%49%
1586
16th to endNight
7%4245%2445%6%50%
1617
September1st to 15thNight
11%5%145%2445%7%46%
1675
16th to endNight
10%5%25%43446%5%45%
1828
October1st to 15thNight
17%5%25%42445%6%40%
1980
16th to endNight
20%9%35%6%345%5%5%30%
2112
November1st to 15thNight
14%5%34435%45%8%38%
2354
16th to endNight
18%9%46%6%3446%6%27%
2520
December1st to 15thNight
19%13%5%8%5%4445%6%23%
2520
16th to endNight
19%13%7%9%6%45%5%5%6%15%
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
63%7%11%13%4
1494
16th to endDay
66%7%11%9%4
1728
February1st to 15thDay
64%6%11%14%2
1577
16th to endDay
60%6%12%13%5%
1468
March1st to 15thDay
58%7%12%15%6%
1980
16th to endDay
48%6%12%20%11%1
2112
April1st to 15thDay
51%6%12%18%11%
2116
16th to endDay
45%411%20%15%2
2334
May1st to 15thDay
45%7%11%22%11%
2349
16th to endDay
39%7%13%23%14%1
2622
June1st to 15thDay
40%7%13%24%12%1
2520
16th to endDay
37%8%15%24%14%
2520
July1st to 15thDay
32%8%14%24%18%1
2371
16th to endDay
38%9%16%21%12%2
2347
August1st to 15thDay
35%10%17%21%13%2
2275
16th to endDay
35%8%14%27%12%1
2221
September1st to 15thDay
40%8%15%22%11%
1953
16th to endDay
41%6%15%25%9%
1801
October1st to 15thDay
48%5%14%19%10%1
1650
16th to endDay
58%6%15%14%3
1760
November1st to 15thDay
44%9%18%19%8%
1501
16th to endDay
56%7%15%13%6%
1440
December1st to 15thDay
60%9%16%11%2
1440
16th to endDay
68%8%10%10%1
1536
January1st to 15thNight
63%6%11%13%5%
2443
16th to endNight
60%7%12%13%5%
2496
February1st to 15thNight
60%6%13%15%4
2287
16th to endNight
54%5%14%17%6%
2002
March1st to 15thNight
55%6%12%19%5%
1980
16th to endNight
46%48%22%14%1
2112
April1st to 15thNight
49%5%9%21%12%
1831
16th to endNight
41%5%9%22%17%3
1635
May1st to 15thNight
43%5%11%24%13%2
1600
16th to endNight
36%6%13%25%16%2
1497
June1st to 15thNight
39%7%12%22%16%1
1440
16th to endNight
36%7%13%24%16%1
1440
July1st to 15thNight
26%6%12%26%25%3
1360
16th to endNight
30%7%16%25%17%3
1555
August1st to 15thNight
28%8%18%28%13%2
1575
16th to endNight
32%5%12%30%16%2
1617
September1st to 15thNight
37%5%13%27%14%1
1675
16th to endNight
38%413%29%13%
1828
October1st to 15thNight
43%5%12%24%13%
1980
16th to endNight
54%6%14%18%7%
2112
November1st to 15thNight
42%7%14%21%12%
2354
16th to endNight
55%6%14%17%6%
2520
December1st to 15thNight
61%8%14%12%3
2520
16th to endNight
68%7%11%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
16%18%40%11%11%1
71
16th to endDay
30%13%34%19%2
96
February1st to 15thDay
15%10%52%17%4
90
16th to endDay
23%14%28%30%3
85
March1st to 15thDay
21%8%32%27%9%
270
16th to endDay
22%6%28%31%9%2
288
April1st to 15thDay
20%9%28%28%9%3
270
16th to endDay
16%7%27%27%14%6%
270
May1st to 15thDay
17%422%27%21%7%
288
16th to endDay
13%224%30%19%9%
331
June1st to 15thDay
14%323%32%22%4
315
16th to endDay
14%220%30%23%8%
315
July1st to 15thDay
9%312%33%25%15%
305
16th to endDay
9%116%31%24%15%
326
August1st to 15thDay
7%216%26%27%19%
297
16th to endDay
12%214%22%26%22%
268
September1st to 15thDay
13%213%24%29%16%
255
16th to endDay
18%314%25%24%12%
254
October1st to 15thDay
18%6%21%25%19%8%
255
16th to endDay
26%7%31%25%9%
272
November1st to 15thDay
10%14%27%29%12%5%
97
16th to endDay
21%13%25%21%18%
60
December1st to 15thDay
15%25%33%20%6%
60
16th to endDay
25%20%45%9%
64
January1st to 15thNight
23%15%36%19%4
720
16th to endNight
18%12%39%22%6%
768
February1st to 15thNight
21%14%37%20%4
704
16th to endNight
20%10%34%29%5%
631
March1st to 15thNight
24%9%32%25%8%
720
16th to endNight
18%7%30%30%11%1
768
April1st to 15thNight
21%8%31%30%8%
718
16th to endNight
14%427%36%14%1
555
May1st to 15thNight
17%222%34%20%2
520
16th to endNight
13%425%32%23%1
375
June1st to 15thNight
15%121%39%19%1
360
16th to endNight
10%120%44%22%1
360
July1st to 15thNight
5%19%45%25%3
340
16th to endNight
10%113%45%26%2
524
August1st to 15thNight
7%11%41%32%5%
527
16th to endNight
9%115%34%34%4
567
September1st to 15thNight
14%317%30%26%8%
660
16th to endNight
13%318%27%30%6%
657
October1st to 15thNight
20%5%23%24%21%3
660
16th to endNight
25%8%32%27%5%
704
November1st to 15thNight
18%8%31%26%13%2
700
16th to endNight
23%11%31%22%9%1
720
December1st to 15thNight
28%14%32%19%5%
720
16th to endNight
26%12%36%20%4
768
Page generated at 2017-08-13 14:16:56. Version ac04

Copyright 2017 A. Danko


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