Ajax
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ajax clear sky chart from 2005-11-05 to 2018-01-12.

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
38%
15267
14%
48410
10%
15232
44%
15232
19%
33647

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
17%
763
9%
2651
3%
761
24%
761
9%
2085
January16th to endNight
22%
768
11%
2496
5%
768
29%
768
11%
1939
February1st to 15thNight
17%
702
10%
2287
3%
701
27%
701
11%
1773
February16th to endNight
24%
631
13%
2020
6%
631
33%
631
14%
1484
March1st to 15thNight
25%
720
14%
1980
6%
720
33%
720
17%
1485
March16th to endNight
35%
768
20%
2112
10%
768
43%
768
25%
1441
April1st to 15thNight
34%
718
15%
1805
5%
718
39%
718
24%
1310
April16th to endNight
44%
579
20%
1659
9%
579
50%
579
28%
1093
May1st to 15thNight
49%
469
16%
1549
12%
469
55%
469
23%
1011
May16th to endNight
58%
374
17%
1497
20%
374
64%
374
27%
820
June1st to 15thNight
51%
360
12%
1440
13%
360
58%
360
21%
863
June16th to endNight
56%
360
12%
1440
18%
360
60%
360
23%
843
July1st to 15thNight
71%
340
16%
1360
25%
340
73%
340
34%
688
July16th to endNight
67%
463
16%
1498
18%
434
68%
434
31%
857
August1st to 15thNight
68%
539
17%
1609
14%
536
70%
536
35%
943
August16th to endNight
64%
636
23%
1782
15%
636
67%
636
37%
1062
September1st to 15thNight
58%
720
20%
1800
10%
720
62%
720
34%
1186
September16th to endNight
57%
717
23%
2005
17%
717
60%
717
33%
1244
October1st to 15thNight
41%
720
17%
2160
16%
720
46%
720
22%
1483
October16th to endNight
29%
768
14%
2304
8%
768
36%
768
16%
1700
November1st to 15thNight
37%
760
17%
2584
15%
760
44%
760
18%
1770
November16th to endNight
27%
780
11%
2730
7%
780
34%
780
12%
2034
December1st to 15thNight
17%
780
7%
2730
3%
780
21%
780
9%
2164
December16th to endNight
14%
832
7%
2912
1%
832
20%
832
7%
2369

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%7%36%5%35%5%5%7%35%
48926
Night
15%7%36%5%3445%6%35%
48588
Cloud CoverDay
14%7%36%5%35%45%7%35%
48936
Night
15%8%36%5%3445%6%35%
48593
TransparencyDay
46%8%13%20%10%1
48622
Night
48%7%12%20%11%1
48410
SeeingDay
16%5%24%28%18%6%
5694
Night
19%7%27%29%14%2
15272

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
17%11%5%8%6%35%45%6%25%
1529
16th to endDay
14%13%6%10%10%46%5%47%18%
1728
February1st to 15thDay
15%12%5%10%8%46%445%22%
1575
16th to endDay
17%10%5%7%6%44446%28%
1452
March1st to 15thDay
16%8%37%6%36%5%5%7%29%
1969
16th to endDay
15%7%35%5%34346%38%
2112
April1st to 15thDay
20%7%35%5%2446%7%31%
2142
16th to endDay
16%6%345%3435%6%40%
2310
May1st to 15thDay
14%6%25%6%35%45%8%37%
2400
16th to endDay
11%425%5%25%5%6%7%43%
2618
June1st to 15thDay
14%5%25%5%35%5%6%9%37%
2520
16th to endDay
11%325%435%47%10%40%
2520
July1st to 15thDay
7%324436%6%7%9%44%
2520
16th to endDay
9%423447%6%7%9%41%
2565
August1st to 15thDay
7%4245%35%5%6%9%43%
2340
16th to endDay
8%424435%5%6%8%45%
2408
September1st to 15thDay
13%5%14435%5%5%8%43%
2160
16th to endDay
11%5%245%3345%8%45%
1953
October1st to 15thDay
18%6%36%5%34446%36%
1800
16th to endDay
21%8%46%6%3445%6%27%
1920
November1st to 15thDay
15%7%37%6%3445%8%31%
1601
16th to endDay
17%10%47%6%36%45%8%25%
1560
December1st to 15thDay
18%12%5%8%6%45%45%7%19%
1560
16th to endDay
20%11%6%8%7%345%5%7%19%
1664
January1st to 15thNight
21%13%5%7%5%3445%5%23%
2651
16th to endNight
15%12%5%8%7%45%45%6%23%
2496
February1st to 15thNight
14%13%6%8%7%3445%6%24%
2285
16th to endNight
16%9%47%7%445%46%29%
2020
March1st to 15thNight
18%9%47%7%34336%31%
1968
16th to endNight
15%6%36%42443443%
2112
April1st to 15thNight
19%6%35%5%2445%6%36%
1805
16th to endNight
12%6%25%43445%7%43%
1659
May1st to 15thNight
15%325%5%445%5%8%38%
1549
16th to endNight
11%31442435%7%49%
1495
June1st to 15thNight
12%425%5%35%46%8%41%
1440
16th to endNight
11%4146%35%46%9%42%
1440
July1st to 15thNight
5%31442345%8%55%
1440
16th to endNight
8%3144245%6%9%48%
1601
August1st to 15thNight
7%41443446%8%50%
1620
16th to endNight
7%41443445%6%52%
1782
September1st to 15thNight
12%42333445%6%48%
1800
16th to endNight
12%5%243235%46%49%
2005
October1st to 15thNight
18%6%26%5%2345%6%38%
2160
16th to endNight
21%8%36%4345%5%6%30%
2304
November1st to 15thNight
17%6%26%5%3445%6%35%
2584
16th to endNight
21%8%36%5%35%45%7%27%
2730
December1st to 15thNight
20%13%47%6%36%446%22%
2730
16th to endNight
21%12%48%7%45%46%6%18%
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
18%11%5%8%7%3435%6%25%
1529
16th to endDay
14%12%7%10%9%46%5%47%18%
1728
February1st to 15thDay
15%12%6%10%8%5%5%445%22%
1575
16th to endDay
17%10%5%7%6%3445%5%29%
1452
March1st to 15thDay
16%8%37%6%36%5%47%29%
1980
16th to endDay
15%8%35%434446%38%
2111
April1st to 15thDay
20%7%45%5%2446%7%31%
2142
16th to endDay
17%6%25%5%3445%5%40%
2310
May1st to 15thDay
14%6%35%6%35%5%5%7%37%
2400
16th to endDay
11%425%5%25%5%7%7%42%
2618
June1st to 15thDay
14%5%345%35%5%6%9%36%
2520
16th to endDay
12%424426%5%7%10%40%
2520
July1st to 15thDay
7%4235%36%6%7%9%44%
2520
16th to endDay
9%424437%6%7%10%40%
2565
August1st to 15thDay
7%425%5%35%5%6%9%42%
2340
16th to endDay
8%5%14435%5%8%8%44%
2408
September1st to 15thDay
13%424335%6%5%8%42%
2160
16th to endDay
11%5%245%34447%45%
1953
October1st to 15thDay
18%7%36%5%3445%5%35%
1800
16th to endDay
22%8%46%6%3446%6%27%
1920
November1st to 15thDay
15%8%37%7%35%45%7%31%
1601
16th to endDay
17%10%48%6%36%448%25%
1560
December1st to 15thDay
17%13%5%8%6%45%45%7%20%
1560
16th to endDay
20%11%6%8%7%34446%20%
1664
January1st to 15thNight
21%13%48%5%34445%24%
2651
16th to endNight
15%11%6%8%7%45%5%5%6%23%
2496
February1st to 15thNight
14%13%6%7%7%34446%25%
2278
16th to endNight
15%9%47%6%445%5%5%30%
2020
March1st to 15thNight
19%9%46%6%35%335%31%
1980
16th to endNight
15%6%36%5%2433443%
2112
April1st to 15thNight
19%6%25%5%24446%36%
1805
16th to endNight
12%6%25%43445%6%44%
1659
May1st to 15thNight
15%415%6%345%6%6%39%
1549
16th to endNight
11%31442445%8%49%
1495
June1st to 15thNight
12%325%5%35%46%7%41%
1440
16th to endNight
11%4246%3446%9%42%
1440
July1st to 15thNight
5%325%32445%8%55%
1440
16th to endNight
8%3134246%6%9%48%
1601
August1st to 15thNight
7%41442446%9%50%
1620
16th to endNight
7%414434446%52%
1782
September1st to 15thNight
12%5%24425%45%6%48%
1800
16th to endNight
12%5%2432345%6%48%
2005
October1st to 15thNight
18%6%25%5%2345%6%38%
2160
16th to endNight
21%7%36%435%5%5%6%30%
2304
November1st to 15thNight
17%7%26%5%345%5%6%35%
2584
16th to endNight
21%9%36%4345%5%7%27%
2730
December1st to 15thNight
20%12%48%6%35%45%5%22%
2730
16th to endNight
21%11%5%8%6%45%45%6%19%
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
60%8%12%13%5%
1530
16th to endDay
64%8%10%9%5%
1728
February1st to 15thDay
63%7%9%15%2
1577
16th to endDay
55%7%12%16%6%
1452
March1st to 15thDay
54%7%12%16%7%
1980
16th to endDay
46%6%10%19%15%1
2112
April1st to 15thDay
51%5%12%17%11%
2142
16th to endDay
44%6%11%21%14%2
2310
May1st to 15thDay
44%7%11%21%13%1
2400
16th to endDay
38%8%14%23%13%1
2622
June1st to 15thDay
42%8%12%22%12%
2520
16th to endDay
36%9%17%22%12%
2520
July1st to 15thDay
31%9%14%26%16%1
2371
16th to endDay
36%10%14%24%11%1
2405
August1st to 15thDay
34%10%17%22%13%1
2327
16th to endDay
33%8%16%29%11%1
2408
September1st to 15thDay
37%9%14%25%11%1
2160
16th to endDay
37%8%12%28%11%
1953
October1st to 15thDay
49%6%12%20%8%1
1800
16th to endDay
55%7%16%13%4
1920
November1st to 15thDay
50%8%14%17%7%1
1601
16th to endDay
57%7%15%14%4
1560
December1st to 15thDay
61%10%15%9%2
1560
16th to endDay
64%8%11%11%3
1664
January1st to 15thNight
61%7%11%12%5%
2651
16th to endNight
60%7%12%14%4
2496
February1st to 15thNight
59%8%10%17%4
2287
16th to endNight
54%7%11%18%7%
2020
March1st to 15thNight
55%412%19%7%
1980
16th to endNight
44%48%23%16%2
2112
April1st to 15thNight
49%5%10%19%15%
1805
16th to endNight
40%6%11%20%17%3
1659
May1st to 15thNight
42%7%11%21%14%2
1549
16th to endNight
33%5%14%25%16%2
1497
June1st to 15thNight
40%6%11%24%15%1
1440
16th to endNight
37%6%12%24%17%1
1440
July1st to 15thNight
26%6%13%26%24%2
1360
16th to endNight
30%8%13%27%16%3
1498
August1st to 15thNight
29%8%18%28%13%1
1609
16th to endNight
31%6%12%32%16%1
1782
September1st to 15thNight
35%7%13%26%15%1
1800
16th to endNight
35%6%12%30%14%
2005
October1st to 15thNight
46%5%10%22%13%
2160
16th to endNight
53%7%13%17%7%
2304
November1st to 15thNight
47%7%12%18%12%1
2584
16th to endNight
54%9%15%15%5%
2730
December1st to 15thNight
62%8%12%12%3
2730
16th to endNight
65%8%11%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
20%20%31%20%6%1
83
16th to endDay
29%12%31%23%3
96
February1st to 15thDay
23%15%44%15%1
90
16th to endDay
21%12%38%21%5%
105
March1st to 15thDay
23%10%34%23%8%
270
16th to endDay
22%6%30%29%8%1
288
April1st to 15thDay
21%5%29%32%9%1
270
16th to endDay
19%431%25%15%4
270
May1st to 15thDay
18%223%31%15%7%
288
16th to endDay
14%120%35%22%5%
331
June1st to 15thDay
17%223%33%20%2
315
16th to endDay
13%120%35%23%5%
315
July1st to 15thDay
9%113%32%33%9%
305
16th to endDay
8%19%35%25%9%
326
August1st to 15thDay
9%114%31%30%12%
313
16th to endDay
12%115%25%26%17%
332
September1st to 15thDay
10%314%27%27%15%
315
16th to endDay
13%217%27%21%17%
314
October1st to 15thDay
20%326%27%16%5%
315
16th to endDay
25%10%31%22%10%
336
November1st to 15thDay
19%7%26%29%14%1
141
16th to endDay
18%10%41%21%7%1
90
December1st to 15thDay
14%17%33%26%6%1
90
16th to endDay
26%15%41%16%
96
January1st to 15thNight
27%14%34%18%4
765
16th to endNight
20%9%35%27%5%
768
February1st to 15thNight
20%13%38%22%4
704
16th to endNight
21%9%36%25%7%
631
March1st to 15thNight
24%8%33%28%4
720
16th to endNight
18%6%32%28%13%1
768
April1st to 15thNight
21%6%31%32%8%
718
16th to endNight
15%5%30%34%12%1
579
May1st to 15thNight
17%124%33%20%1
469
16th to endNight
12%120%40%23%2
375
June1st to 15thNight
13%323%38%19%2
360
16th to endNight
11%117%43%25%1
360
July1st to 15thNight
7%113%47%27%3
340
16th to endNight
8%114%43%28%3
463
August1st to 15thNight
8%11%41%32%5%
539
16th to endNight
8%116%36%31%5%
636
September1st to 15thNight
13%419%29%26%6%
720
16th to endNight
14%317%27%26%9%
717
October1st to 15thNight
21%5%24%29%16%2
720
16th to endNight
24%9%28%28%7%
768
November1st to 15thNight
21%7%25%31%11%2
760
16th to endNight
23%11%28%25%9%1
780
December1st to 15thNight
29%11%35%20%3
780
16th to endNight
26%10%37%21%2
832
Page generated at 2018-01-12 22:01:31. Version ac04

Copyright 2018 A. Danko


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