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 2018-02-22.

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
37%
15502
14%
48963
10%
15466
43%
15466
19%
33826

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
15%
776
10%
2648
4%
776
24%
776
9%
2054
January16th to endNight
16%
832
10%
2704
3%
832
24%
832
10%
2064
February1st to 15thNight
15%
761
8%
2482
2%
761
23%
761
10%
1913
February16th to endNight
24%
659
12%
2092
5%
659
32%
659
14%
1536
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
37%
718
23%
1329
April16th to endNight
43%
555
21%
1635
10%
555
51%
555
26%
1061
May1st to 15thNight
46%
520
17%
1600
11%
520
52%
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
13%
1440
18%
360
64%
360
24%
838
July1st to 15thNight
66%
340
17%
1360
24%
340
69%
340
35%
680
July16th to endNight
66%
524
15%
1555
16%
491
67%
491
33%
898
August1st to 15thNight
71%
539
17%
1609
15%
536
72%
536
36%
954
August16th to endNight
65%
619
23%
1765
15%
619
68%
619
36%
1045
September1st to 15thNight
57%
720
21%
1827
12%
720
62%
720
34%
1192
September16th to endNight
58%
717
23%
1994
17%
717
61%
717
33%
1248
October1st to 15thNight
43%
720
18%
2160
15%
720
48%
720
24%
1435
October16th to endNight
27%
768
15%
2304
9%
768
35%
768
17%
1671
November1st to 15thNight
36%
760
18%
2556
15%
760
43%
760
20%
1693
November16th to endNight
26%
780
12%
2730
7%
780
33%
780
12%
1963
December1st to 15thNight
17%
780
7%
2730
2%
780
23%
780
10%
2111
December16th to endNight
12%
832
6%
2912
1%
832
20%
832
7%
2397

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%33%
49278
Night
14%8%36%5%35%45%7%35%
49145
Cloud CoverDay
13%7%36%6%35%5%5%7%33%
49288
Night
14%8%36%5%35%45%7%35%
49149
TransparencyDay
47%7%13%19%10%1
48978
Night
48%6%12%20%10%1
48963
SeeingDay
16%6%23%26%18%8%
5803
Night
18%7%28%28%14%2
15510

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%12%5%9%6%46%6%5%6%21%
1618
16th to endDay
11%13%7%11%9%5%6%6%5%5%17%
1872
February1st to 15thDay
14%14%5%10%7%36%5%46%18%
1710
16th to endDay
16%12%5%10%7%45%445%22%
1525
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%
2340
16th to endDay
10%5%344345%5%9%41%
2424
September1st to 15thDay
11%5%35%6%35%5%5%7%39%
2130
16th to endDay
12%5%35%5%345%5%7%41%
1965
October1st to 15thDay
17%7%36%6%35%45%6%34%
1800
16th to endDay
21%9%27%6%345%46%26%
1920
November1st to 15thDay
10%8%38%6%35%46%9%33%
1629
16th to endDay
15%12%46%6%45%5%6%7%24%
1560
December1st to 15thDay
14%13%5%9%7%36%45%6%22%
1560
16th to endDay
18%14%5%10%8%46%5%5%5%15%
1664
January1st to 15thNight
17%13%49%7%45%445%23%
2648
16th to endNight
12%11%7%9%7%36%45%7%22%
2704
February1st to 15thNight
14%13%5%10%6%35%45%5%25%
2480
16th to endNight
14%11%5%8%7%35%45%5%28%
2092
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%47%
1620
16th to endNight
6%4245%3345%6%51%
1765
September1st to 15thNight
12%4245%3445%7%46%
1827
16th to endNight
9%5%25%43446%6%46%
1994
October1st to 15thNight
16%6%25%5%2435%7%40%
2160
16th to endNight
20%8%45%43446%5%31%
2304
November1st to 15thNight
15%6%25%435%45%8%38%
2556
16th to endNight
17%9%46%6%35%46%7%28%
2730
December1st to 15thNight
18%13%48%6%4445%6%23%
2730
16th to endNight
18%12%7%10%7%35%5%6%5%17%
2912

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%
1618
16th to endDay
11%14%6%11%9%5%6%6%5%7%16%
1872
February1st to 15thDay
14%15%5%9%7%46%5%5%7%18%
1710
16th to endDay
16%12%5%8%8%45%5%46%23%
1525
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%425%6%36%6%7%10%40%
2340
16th to endDay
10%5%24435%5%5%8%43%
2424
September1st to 15thDay
11%436%6%345%5%7%41%
2130
16th to endDay
12%5%25%4345%5%7%42%
1965
October1st to 15thDay
17%7%26%6%34447%35%
1800
16th to endDay
21%8%37%6%35%46%5%27%
1920
November1st to 15thDay
11%7%47%7%345%6%8%33%
1629
16th to endDay
16%12%37%5%36%5%5%8%25%
1560
December1st to 15thDay
14%13%5%8%7%46%5%46%23%
1560
16th to endDay
19%12%6%10%8%45%6%6%6%14%
1664
January1st to 15thNight
17%13%5%8%7%35%46%5%22%
2648
16th to endNight
12%12%6%8%8%46%5%5%7%22%
2704
February1st to 15thNight
14%13%6%9%6%36%45%6%24%
2473
16th to endNight
14%10%5%8%6%345%5%6%29%
2092
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%48%
1620
16th to endNight
7%4245%2445%6%51%
1765
September1st to 15thNight
11%4145%2445%7%46%
1827
16th to endNight
9%5%25%43446%6%47%
1994
October1st to 15thNight
17%5%25%42445%6%40%
2160
16th to endNight
20%8%35%6%345%5%6%31%
2304
November1st to 15thNight
15%6%34435%5%5%8%37%
2556
16th to endNight
17%9%46%6%3446%7%28%
2730
December1st to 15thNight
18%13%48%6%3445%6%24%
2730
16th to endNight
19%12%7%9%7%45%5%5%6%16%
2912

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
62%6%10%14%4
1619
16th to endDay
65%7%11%10%4
1872
February1st to 15thDay
64%6%10%14%3
1712
16th to endDay
61%6%12%13%41
1525
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
2327
16th to endDay
35%8%14%27%12%1
2424
September1st to 15thDay
39%8%15%23%12%
2130
16th to endDay
39%6%15%26%10%
1965
October1st to 15thDay
49%5%13%20%10%1
1800
16th to endDay
56%6%15%14%5%
1920
November1st to 15thDay
45%9%17%19%7%
1629
16th to endDay
55%7%15%13%6%
1560
December1st to 15thDay
59%8%16%12%2
1560
16th to endDay
68%7%10%9%2
1664
January1st to 15thNight
62%6%11%13%6%
2648
16th to endNight
59%7%13%14%5%
2704
February1st to 15thNight
60%6%12%15%4
2482
16th to endNight
55%6%14%17%6%
2092
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
1609
16th to endNight
31%5%13%30%16%2
1765
September1st to 15thNight
37%5%13%27%15%1
1827
16th to endNight
36%412%30%14%
1994
October1st to 15thNight
44%5%11%23%14%
2160
16th to endNight
52%6%14%19%7%
2304
November1st to 15thNight
44%7%14%21%11%
2556
16th to endNight
54%6%15%17%6%
2730
December1st to 15thNight
60%7%14%12%4
2730
16th to endNight
67%7%10%9%4
2912

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%15%41%14%12%
106
16th to endDay
26%12%36%20%4
144
February1st to 15thDay
22%8%48%16%3
135
16th to endDay
25%15%28%26%2
104
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
8%115%26%27%19%
313
16th to endDay
12%216%21%27%20%
332
September1st to 15thDay
12%214%25%29%16%
315
16th to endDay
15%314%23%23%20%
314
October1st to 15thDay
20%7%20%25%17%9%
315
16th to endDay
24%9%29%24%12%
336
November1st to 15thDay
11%11%30%30%11%4
135
16th to endDay
21%11%31%22%14%
90
December1st to 15thDay
13%24%31%22%8%
90
16th to endDay
26%17%43%10%2
96
January1st to 15thNight
22%15%36%20%4
780
16th to endNight
18%12%39%22%6%
832
February1st to 15thNight
22%13%39%20%4
764
16th to endNight
20%9%34%28%5%
659
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%42%32%5%
539
16th to endNight
9%114%34%35%4
619
September1st to 15thNight
14%317%30%26%8%
720
16th to endNight
12%317%26%30%9%
717
October1st to 15thNight
21%5%23%25%21%3
720
16th to endNight
24%9%30%28%6%
768
November1st to 15thNight
19%8%30%26%13%1
760
16th to endNight
22%11%32%22%9%1
780
December1st to 15thNight
27%14%32%19%5%
780
16th to endNight
26%12%36%20%3
832
Page generated at 2018-02-23 11:21:39. Version ac04

Copyright 2018 A. Danko


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