Alliston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alliston clear sky chart from 2005-11-06 to 2024-02-05.

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
28%
22864
12%
79940
8%
22763
34%
22763
14%
58357

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 10thNight
12%
754
5%
4420
2%
737
18%
737
3%
3461
January11th to 20thNight
13%
758
4%
4178
2%
740
17%
740
3%
3610
January21st to endNight
18%
833
5%
4529
4%
814
23%
814
5%
3809
February1st to 10thNight
11%
739
8%
2399
2%
739
18%
739
8%
1898
February11th to 20thNight
13%
700
10%
2275
2%
700
23%
700
9%
1770
February21st to endNight
14%
592
11%
1870
3%
592
23%
592
10%
1404
March1st to 10thNight
16%
720
14%
1985
5%
720
24%
720
15%
1472
March11th to 20thNight
20%
720
17%
1979
7%
720
29%
720
16%
1426
March21st to endNight
25%
792
17%
2178
7%
792
32%
792
20%
1522
April1st to 10thNight
18%
720
14%
1847
3%
720
24%
720
17%
1383
April11th to 20thNight
26%
625
18%
1689
7%
625
33%
625
22%
1172
April21st to endNight
28%
540
15%
1620
7%
540
35%
540
19%
1145
May1st to 10thNight
37%
540
15%
1620
8%
540
44%
540
24%
1086
May11th to 20thNight
37%
377
21%
1439
16%
377
50%
377
22%
848
May21st to endNight
46%
388
17%
1551
13%
388
60%
388
28%
833
June1st to 10thNight
35%
360
14%
1440
11%
360
48%
360
21%
870
June11th to 20thNight
44%
360
17%
1325
17%
360
53%
360
25%
767
June21st to endNight
45%
360
16%
1260
16%
360
51%
360
25%
746
July1st to 10thNight
56%
350
18%
1231
20%
350
63%
350
35%
641
July11th to 20thNight
50%
348
18%
1392
22%
348
59%
348
27%
768
July21st to endNight
53%
569
17%
1652
13%
538
57%
538
33%
974
August1st to 10thNight
55%
537
18%
1600
12%
534
59%
534
34%
936
August11th to 20thNight
61%
534
22%
1598
15%
534
66%
534
34%
921
August21st to endNight
46%
648
20%
1836
10%
648
52%
648
30%
1150
September1st to 10thNight
47%
720
15%
1800
7%
720
50%
720
34%
1167
September11th to 20thNight
49%
720
25%
1926
14%
720
55%
720
36%
1160
September21st to endNight
42%
720
18%
2002
14%
720
46%
720
25%
1356
October1st to 10thNight
33%
720
14%
2160
11%
720
38%
720
19%
1515
October11th to 20thNight
25%
720
12%
2160
7%
720
32%
720
15%
1571
October21st to endNight
17%
792
12%
2376
6%
792
25%
792
11%
1867
November1st to 10thNight
26%
740
15%
2491
10%
740
33%
740
16%
1717
November11th to 20thNight
18%
760
12%
2660
7%
760
27%
760
10%
1996
November21st to endNight
17%
760
7%
2660
5%
760
21%
760
8%
2135
December1st to 10thNight
11%
760
5%
2660
2%
760
16%
760
6%
2208
December11th to 20thNight
12%
760
4%
3262
1%
758
17%
758
5%
2678
December21st to endNight
9%
828
2%
4870
1%
817
13%
817
2%
4375

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%48%7%45%5%5%7%30%
78648
Night
15%10%5%8%7%45%5%5%6%30%
80176
TransparencyDay
52%8%12%17%9%1
78360
Night
53%8%13%17%9%1
80000
SeeingDay
19%18%31%20%9%3
13778
Night
19%16%32%23%9%1
22887

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 10thDay
16%13%6%11%10%5%5%5%5%6%19%
2517
11th to 20thDay
10%18%7%15%13%46%445%12%
2758
21st to endDay
19%22%7%10%7%34445%15%
3124
February1st to 10thDay
13%15%5%12%11%47%6%5%5%18%
1656
11th to 20thDay
11%14%7%11%9%5%5%5%5%7%21%
1573
21st to endDay
17%16%5%9%7%35%5%5%424%
1382
March1st to 10thDay
13%11%5%10%8%46%5%5%5%28%
1972
11th to 20thDay
12%13%6%9%6%46%445%31%
1980
21st to endDay
17%12%47%6%25%445%33%
2178
April1st to 10thDay
15%13%5%8%7%45%45%5%30%
2111
11th to 20thDay
18%11%35%43445%7%36%
2235
21st to endDay
19%9%47%6%3445%6%34%
2340
May1st to 10thDay
17%8%37%6%345%5%7%35%
2340
11th to 20thDay
15%8%36%435%5%5%7%39%
2451
21st to endDay
11%5%25%6%35%5%6%8%43%
2725
June1st to 10thDay
15%7%345%35%6%6%9%37%
2520
11th to 20thDay
12%6%245%36%6%6%9%42%
2628
21st to endDay
13%6%25%5%46%5%5%9%40%
2700
July1st to 10thDay
9%425%5%35%6%6%9%45%
2689
11th to 20thDay
10%6%35%6%45%6%6%9%40%
2520
21st to endDay
10%6%36%7%37%6%7%9%36%
2565
August1st to 10thDay
10%6%25%5%46%6%7%10%39%
2327
11th to 20thDay
7%5%37%6%5%5%7%8%10%37%
2303
21st to endDay
13%6%25%5%46%5%6%8%39%
2502
September1st to 10thDay
14%6%36%6%45%5%5%7%39%
2160
11th to 20thDay
13%5%25%6%3446%7%43%
2031
21st to endDay
13%7%47%8%46%46%9%34%
1958
October1st to 10thDay
19%9%26%6%35%45%7%33%
1800
11th to 20thDay
19%10%49%7%45%5%5%6%26%
1800
21st to endDay
25%15%48%6%35%446%20%
1980
November1st to 10thDay
13%12%5%8%7%45%5%5%8%28%
1585
11th to 20thDay
11%14%6%9%8%5%7%6%6%6%22%
1520
21st to endDay
17%17%6%11%7%45%6%5%6%16%
1520
December1st to 10thDay
15%17%8%13%10%47%5%5%6%11%
1520
11th to 20thDay
16%14%7%12%7%46%5%6%6%16%
1906
21st to endDay
26%19%8%13%7%444349%
2772
January1st to 10thNight
16%15%7%12%9%45%45%5%18%
4429
11th to 20thNight
12%14%6%13%14%6%6%6%6%5%12%
4185
21st to endNight
18%14%8%10%12%46%5%5%5%13%
4532
February1st to 10thNight
12%15%6%11%9%46%45%6%21%
2399
11th to 20thNight
11%14%7%11%8%46%5%5%6%23%
2273
21st to endNight
13%12%5%11%8%46%5%6%7%25%
1870
March1st to 10thNight
12%10%5%9%7%46%45%5%33%
1975
11th to 20thNight
14%11%5%8%7%34445%35%
1979
21st to endNight
16%9%46%5%35%5%5%6%37%
2178
April1st to 10thNight
17%10%47%6%35%5%5%6%32%
1847
11th to 20thNight
16%8%26%5%3446%7%38%
1689
21st to endNight
15%10%47%6%35%5%46%36%
1620
May1st to 10thNight
16%6%35%6%35%46%8%39%
1620
11th to 20thNight
14%5%25%335%45%7%46%
1438
21st to endNight
9%3243345%5%9%52%
1550
June1st to 10thNight
13%435%6%37%5%5%8%43%
1440
11th to 20thNight
9%425%5%25%7%7%9%45%
1325
21st to endNight
11%5%25%436%5%6%7%48%
1260
July1st to 10thNight
6%3245%24447%57%
1266
11th to 20thNight
9%5%24435%5%5%8%50%
1440
21st to endNight
7%4245%35%5%6%7%51%
1749
August1st to 10thNight
8%325%435%5%6%9%51%
1611
11th to 20thNight
6%4244345%7%9%52%
1598
21st to endNight
11%5%245%245%5%7%48%
1836
September1st to 10thNight
10%5%25%5%345%7%8%46%
1800
11th to 20thNight
11%5%2442346%7%53%
1926
21st to endNight
16%6%36%5%34446%42%
2002
October1st to 10thNight
18%6%36%6%345%6%6%37%
2160
11th to 20thNight
18%9%47%5%45%5%6%6%31%
2160
21st to endNight
22%13%37%8%35%5%5%6%24%
2376
November1st to 10thNight
16%9%35%5%45%5%6%7%34%
2491
11th to 20thNight
15%13%5%8%6%45%5%7%6%27%
2660
21st to endNight
16%14%6%9%7%46%6%5%6%21%
2660
December1st to 10thNight
18%14%7%10%9%45%6%5%6%16%
2660
11th to 20thNight
15%16%6%11%7%46%6%5%6%17%
3288
21st to endNight
25%19%8%13%7%444449%
4884

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 10thDay
62%10%14%11%3
2518
11th to 20thDay
75%8%8%6%2
2758
21st to endDay
72%8%10%8%2
3124
February1st to 10thDay
68%8%9%12%3
1656
11th to 20thDay
63%7%11%13%5%1
1582
21st to endDay
64%5%10%14%7%1
1382
March1st to 10thDay
56%8%12%14%9%
1975
11th to 20thDay
55%7%10%16%11%2
1980
21st to endDay
54%6%9%15%14%2
2178
April1st to 10thDay
56%7%11%17%9%1
2111
11th to 20thDay
48%6%10%21%15%1
2235
21st to endDay
51%6%11%18%11%2
2340
May1st to 10thDay
48%7%9%20%14%1
2340
11th to 20thDay
43%8%11%23%13%1
2455
21st to endDay
38%9%15%22%14%2
2725
June1st to 10thDay
40%9%14%21%15%1
2520
11th to 20thDay
38%9%12%23%17%1
2628
21st to endDay
40%8%15%23%14%1
2700
July1st to 10thDay
34%10%14%23%17%2
2615
11th to 20thDay
38%9%15%27%10%1
2445
21st to endDay
41%10%15%20%12%1
2422
August1st to 10thDay
37%10%18%22%11%2
2314
11th to 20thDay
38%12%19%22%10%
2303
21st to endDay
41%9%15%23%11%1
2502
September1st to 10thDay
43%8%14%23%10%2
2160
11th to 20thDay
39%7%15%27%11%
2031
21st to endDay
47%9%13%24%7%1
1958
October1st to 10thDay
52%7%13%17%10%1
1800
11th to 20thDay
57%8%13%16%6%1
1800
21st to endDay
66%8%12%10%5%
1980
November1st to 10thDay
52%9%15%16%6%
1585
11th to 20thDay
58%11%13%11%6%1
1520
21st to endDay
67%9%13%9%2
1520
December1st to 10thDay
73%8%11%6%1
1520
11th to 20thDay
67%11%11%9%2
1906
21st to endDay
80%6%6%7%1
2772
January1st to 10thNight
65%9%15%9%2
4429
11th to 20thNight
72%11%9%7%2
4185
21st to endNight
70%9%11%7%2
4532
February1st to 10thNight
62%8%13%14%3
2399
11th to 20thNight
60%8%11%16%5%
2275
21st to endNight
57%7%13%15%8%
1870
March1st to 10thNight
54%5%12%19%8%1
1985
11th to 20thNight
51%6%11%20%11%2
1980
21st to endNight
47%6%10%21%14%2
2178
April1st to 10thNight
53%6%10%18%12%1
1847
11th to 20thNight
45%6%11%20%16%2
1689
21st to endNight
49%7%11%16%15%2
1620
May1st to 10thNight
43%7%11%20%16%3
1620
11th to 20thNight
39%6%10%24%18%3
1439
21st to endNight
29%8%17%26%17%4
1551
June1st to 10thNight
39%8%12%23%17%2
1440
11th to 20thNight
33%9%13%24%19%1
1325
21st to endNight
35%8%14%27%15%1
1260
July1st to 10thNight
26%7%12%29%23%3
1231
11th to 20thNight
30%9%13%31%16%1
1392
21st to endNight
30%9%15%29%15%2
1652
August1st to 10thNight
29%9%18%30%13%1
1600
11th to 20thNight
27%10%17%31%15%1
1598
21st to endNight
34%8%15%27%14%1
1836
September1st to 10thNight
33%9%19%26%13%1
1800
11th to 20thNight
30%7%14%32%16%1
1926
21st to endNight
43%6%13%27%9%
2002
October1st to 10thNight
47%9%11%19%13%1
2160
11th to 20thNight
51%9%14%19%7%
2160
21st to endNight
60%7%12%13%8%
2376
November1st to 10thNight
47%9%15%20%8%1
2491
11th to 20thNight
55%10%14%14%7%1
2660
21st to endNight
61%11%15%11%11
2660
December1st to 10thNight
67%9%14%8%2
2660
11th to 20thNight
66%10%12%10%2
3288
21st to endNight
80%7%7%6%1
4884

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 10thDay
19%24%34%17%5%1
180
11th to 20thDay
24%26%35%11%41
249
21st to endDay
24%24%35%14%2
297
February1st to 10thDay
27%33%28%9%3
252
11th to 20thDay
21%34%37%7%1
240
21st to endDay
32%36%24%7%
198
March1st to 10thDay
21%25%36%16%3
415
11th to 20thDay
20%22%38%14%5%
420
21st to endDay
31%19%28%16%5%1
462
April1st to 10thDay
23%23%34%13%6%1
420
11th to 20thDay
28%21%25%15%7%3
412
21st to endDay
27%18%31%16%7%2
420
May1st to 10thDay
21%16%33%17%10%2
423
11th to 20thDay
19%13%32%22%10%3
447
21st to endDay
15%13%29%25%13%5%
485
June1st to 10thDay
16%15%32%26%10%2
450
11th to 20thDay
14%14%31%27%13%2
558
21st to endDay
15%13%35%25%8%3
630
July1st to 10thDay
10%9%31%30%15%4
610
11th to 20thDay
12%9%30%29%13%8%
444
21st to endDay
9%9%33%32%12%5%
488
August1st to 10thDay
8%9%28%30%17%9%
446
11th to 20thDay
7%6%29%28%22%8%
439
21st to endDay
14%11%28%25%16%6%
495
September1st to 10thDay
13%12%29%24%15%7%
450
11th to 20thDay
10%12%25%25%18%11%
450
21st to endDay
14%15%28%22%15%5%
450
October1st to 10thDay
22%17%25%20%13%4
450
11th to 20thDay
21%25%33%16%41
450
21st to endDay
32%23%26%15%3
495
November1st to 10thDay
24%26%29%17%41
235
11th to 20thDay
23%23%36%13%41
180
21st to endDay
28%23%39%8%1
180
December1st to 10thDay
27%29%30%13%2
180
11th to 20thDay
26%31%28%13%11
180
21st to endDay
25%29%35%10%2
198
January1st to 10thNight
22%26%32%16%4
760
11th to 20thNight
22%23%31%20%3
760
21st to endNight
18%18%37%21%6%
836
February1st to 10thNight
22%24%37%16%1
739
11th to 20thNight
19%22%40%16%3
703
21st to endNight
20%24%36%17%2
592
March1st to 10thNight
20%21%36%19%3
720
11th to 20thNight
21%24%32%18%5%
720
21st to endNight
21%16%34%22%7%
792
April1st to 10thNight
23%19%35%21%2
720
11th to 20thNight
19%18%34%19%9%1
625
21st to endNight
21%14%33%25%8%
540
May1st to 10thNight
18%9%30%31%11%1
540
11th to 20thNight
16%7%35%31%10%1
377
21st to endNight
9%9%33%37%13%
389
June1st to 10thNight
13%7%36%33%10%1
360
11th to 20thNight
12%7%32%36%13%
360
21st to endNight
12%7%31%35%15%1
360
July1st to 10thNight
6%6%25%42%20%1
350
11th to 20thNight
9%8%29%34%18%1
348
21st to endNight
8%5%29%39%18%1
569
August1st to 10thNight
9%425%37%24%1
537
11th to 20thNight
6%5%20%40%26%2
534
21st to endNight
13%6%29%29%22%1
648
September1st to 10thNight
12%6%28%30%19%4
720
11th to 20thNight
12%8%26%29%19%5%
720
21st to endNight
18%11%23%28%17%3
720
October1st to 10thNight
20%10%32%22%14%2
720
11th to 20thNight
24%16%32%21%7%1
720
21st to endNight
30%17%31%18%4
792
November1st to 10thNight
22%17%31%21%8%1
740
11th to 20thNight
21%24%31%18%5%1
760
21st to endNight
23%22%33%17%4
760
December1st to 10thNight
26%22%36%13%3
760
11th to 20thNight
20%25%35%16%3
760
21st to endNight
30%19%34%16%2
836
Page generated at 2024-02-02 05:20:27. Version ac07

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