Tillsonburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tillsonburg clear sky chart from 2005-11-06 to 2024-01-27.

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
34%
23060
15%
74701
10%
23012
41%
23012
18%
52225

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
15%
758
11%
2557
5%
757
23%
757
9%
1997
January11th to 20thNight
15%
760
6%
2470
3%
760
19%
760
7%
2025
January21st to endNight
20%
820
10%
2664
4%
820
27%
820
10%
2089
February1st to 10thNight
15%
720
8%
2340
3%
720
22%
720
9%
1840
February11th to 20thNight
19%
700
10%
2274
4%
699
27%
699
12%
1724
February21st to endNight
18%
592
11%
1802
3%
592
26%
592
12%
1389
March1st to 10thNight
26%
720
17%
2008
8%
720
34%
720
19%
1427
March11th to 20thNight
26%
720
19%
1980
8%
720
35%
720
20%
1413
March21st to endNight
30%
792
18%
2178
9%
792
36%
792
19%
1567
April1st to 10thNight
27%
720
14%
1894
6%
720
33%
720
20%
1373
April11th to 20thNight
30%
600
19%
1664
8%
600
37%
600
23%
1150
April21st to endNight
34%
540
18%
1620
7%
540
43%
540
22%
1106
May1st to 10thNight
38%
540
15%
1620
10%
540
43%
540
22%
1101
May11th to 20thNight
43%
496
18%
1558
12%
496
51%
496
24%
1005
May21st to endNight
52%
388
18%
1551
18%
388
60%
388
28%
839
June1st to 10thNight
48%
360
15%
1440
17%
360
56%
360
25%
828
June11th to 20thNight
48%
360
16%
1379
17%
360
56%
360
24%
791
June21st to endNight
51%
360
20%
1260
19%
360
61%
360
28%
732
July1st to 10thNight
64%
350
19%
1270
23%
350
69%
350
36%
652
July11th to 20thNight
60%
475
18%
1519
17%
475
64%
475
33%
876
July21st to endNight
63%
591
16%
1672
14%
558
65%
558
33%
990
August1st to 10thNight
68%
537
19%
1600
16%
534
70%
534
35%
945
August11th to 20thNight
65%
534
22%
1598
16%
534
69%
534
36%
926
August21st to endNight
59%
630
23%
1818
15%
630
63%
630
35%
1089
September1st to 10thNight
54%
720
18%
1813
10%
720
57%
720
32%
1201
September11th to 20thNight
63%
720
27%
1980
19%
720
66%
720
38%
1178
September21st to endNight
49%
720
20%
1980
14%
720
53%
720
27%
1316
October1st to 10thNight
45%
720
19%
2142
16%
720
49%
720
25%
1397
October11th to 20thNight
33%
720
16%
2160
10%
720
41%
720
20%
1506
October21st to endNight
27%
792
17%
2376
10%
792
36%
792
16%
1746
November1st to 10thNight
37%
740
21%
2404
16%
740
46%
740
23%
1503
November11th to 20thNight
23%
760
15%
2651
8%
760
34%
760
15%
1856
November21st to endNight
23%
760
10%
2660
6%
760
27%
760
12%
1989
December1st to 10thNight
16%
760
8%
2660
3%
760
22%
760
9%
2061
December11th to 20thNight
15%
760
7%
3261
2%
758
23%
758
7%
2476
December21st to endNight
14%
825
4%
4878
1%
817
20%
817
4%
4122

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%9%47%6%45%5%6%8%32%
75106
Night
16%9%47%6%35%5%5%7%33%
74918
TransparencyDay
50%7%13%19%10%1
74825
Night
50%6%12%20%11%1
74735
SeeingDay
18%11%28%24%13%5%
13734
Night
19%10%29%29%12%1
23077

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
15%15%5%9%8%5%7%6%5%7%19%
1607
11th to 20thDay
16%16%8%12%7%445%5%5%16%
1710
21st to endDay
15%18%7%11%10%5%6%44417%
1836
February1st to 10thDay
17%17%5%10%9%5%5%5%5%5%18%
1620
11th to 20thDay
14%14%8%12%8%45%5%46%20%
1573
21st to endDay
18%14%5%10%7%45%447%22%
1452
March1st to 10thDay
16%12%49%7%45%45%6%26%
1948
11th to 20thDay
14%13%6%10%6%3335%7%30%
1980
21st to endDay
20%11%48%6%44345%30%
2178
April1st to 10thDay
17%10%5%7%6%35%5%5%8%28%
2065
11th to 20thDay
17%10%38%6%3435%8%33%
2262
21st to endDay
21%9%45%5%34447%33%
2340
May1st to 10thDay
17%7%37%6%35%6%5%8%33%
2340
11th to 20thDay
17%7%36%5%3445%8%37%
2331
21st to endDay
11%5%35%5%35%6%7%9%42%
2725
June1st to 10thDay
12%5%36%5%35%5%6%8%40%
2520
11th to 20thDay
12%6%26%5%35%6%6%9%39%
2574
21st to endDay
12%5%25%435%5%7%11%41%
2700
July1st to 10thDay
8%4345%345%7%10%45%
2646
11th to 20thDay
11%5%36%6%45%5%7%11%37%
2386
21st to endDay
10%5%36%7%45%6%7%10%37%
2547
August1st to 10thDay
9%5%25%5%46%7%8%10%40%
2327
11th to 20thDay
10%5%26%7%45%7%7%10%36%
2303
21st to endDay
11%6%35%5%35%6%6%9%41%
2520
September1st to 10thDay
12%6%36%5%46%6%6%8%39%
2142
11th to 20thDay
10%6%345%35%5%6%9%45%
1980
21st to endDay
14%7%35%5%35%6%6%9%36%
1980
October1st to 10thDay
16%8%46%6%45%5%5%5%36%
1818
11th to 20thDay
18%10%37%7%36%5%5%7%29%
1800
21st to endDay
23%10%38%7%445%6%6%23%
1980
November1st to 10thDay
15%9%37%6%36%5%5%8%34%
1672
11th to 20thDay
16%11%47%7%345%6%8%30%
1526
21st to endDay
21%12%6%8%7%45%5%5%5%22%
1520
December1st to 10thDay
17%15%5%12%5%45%45%6%22%
1520
11th to 20thDay
20%15%7%10%6%46%5%45%18%
1906
21st to endDay
29%18%6%9%8%3445%410%
2772
January1st to 10thNight
17%12%6%10%8%45%5%5%5%22%
2557
11th to 20thNight
19%17%6%10%8%45%46%6%17%
2470
21st to endNight
14%13%8%11%7%45%45%6%23%
2664
February1st to 10thNight
17%15%5%10%8%446%5%5%21%
2340
11th to 20thNight
16%12%5%9%7%5%6%5%5%5%25%
2273
21st to endNight
18%12%6%9%7%35%5%5%6%23%
1802
March1st to 10thNight
14%9%47%6%45%5%6%8%32%
1998
11th to 20thNight
16%9%47%6%35%45%7%35%
1979
21st to endNight
18%10%46%6%4345%5%34%
2178
April1st to 10thNight
18%8%45%6%36%5%5%6%33%
1894
11th to 20thNight
17%8%36%5%25%5%5%7%37%
1664
21st to endNight
15%6%37%6%45%6%6%8%34%
1620
May1st to 10thNight
18%7%35%5%35%5%6%8%35%
1620
11th to 20thNight
13%6%37%6%35%6%5%6%41%
1557
21st to endNight
10%5%244245%5%8%51%
1550
June1st to 10thNight
11%425%6%25%47%8%44%
1440
11th to 20thNight
9%5%25%5%35%6%6%11%43%
1379
21st to endNight
11%5%25%5%245%6%8%47%
1260
July1st to 10thNight
6%4245%2345%10%55%
1307
11th to 20thNight
10%4245%3445%9%48%
1570
21st to endNight
7%5%345%46%5%6%8%48%
1771
August1st to 10thNight
6%6%25%446%5%6%10%47%
1611
11th to 20thNight
8%4245%245%7%10%48%
1598
21st to endNight
8%435%5%35%46%9%49%
1818
September1st to 10thNight
12%6%36%5%445%46%44%
1813
11th to 20thNight
10%42443347%6%54%
1980
21st to endNight
16%5%25%6%35%5%6%7%41%
1980
October1st to 10thNight
15%6%35%5%25%5%46%43%
2142
11th to 20thNight
17%8%48%5%3445%7%35%
2160
21st to endNight
22%9%37%5%35%45%6%30%
2376
November1st to 10thNight
15%7%35%43446%8%41%
2404
11th to 20thNight
15%10%37%6%35%6%5%8%31%
2651
21st to endNight
21%12%47%6%35%5%5%7%25%
2660
December1st to 10thNight
19%14%6%9%6%345%5%7%22%
2660
11th to 20thNight
15%16%6%9%7%345%5%6%24%
3288
21st to endNight
28%18%6%9%6%34445%13%
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
64%7%12%13%5%
1608
11th to 20thDay
70%6%10%9%41
1710
21st to endDay
71%5%8%11%5%1
1836
February1st to 10thDay
69%6%10%11%4
1620
11th to 20thDay
66%5%9%13%7%
1582
21st to endDay
63%6%11%13%6%1
1452
March1st to 10thDay
57%7%13%16%6%1
1951
11th to 20thDay
55%5%11%18%10%2
1980
21st to endDay
57%49%18%11%1
2178
April1st to 10thDay
54%6%12%18%11%1
2065
11th to 20thDay
51%412%20%12%1
2262
21st to endDay
51%5%12%19%11%2
2340
May1st to 10thDay
48%7%12%20%11%2
2340
11th to 20thDay
47%6%13%20%13%2
2335
21st to endDay
37%9%15%22%15%2
2725
June1st to 10thDay
39%7%14%25%13%2
2520
11th to 20thDay
40%8%14%22%15%2
2574
21st to endDay
36%7%15%25%15%1
2700
July1st to 10thDay
32%7%14%26%16%4
2575
11th to 20thDay
38%7%16%24%13%1
2314
21st to endDay
38%9%14%23%14%2
2405
August1st to 10thDay
36%9%16%26%12%1
2314
11th to 20thDay
40%9%17%23%10%1
2303
21st to endDay
38%8%14%26%13%2
2520
September1st to 10thDay
40%9%15%23%12%1
2142
11th to 20thDay
34%7%15%29%14%
1980
21st to endDay
42%8%14%24%11%1
1980
October1st to 10thDay
49%5%14%19%12%1
1818
11th to 20thDay
53%7%14%17%9%1
1800
21st to endDay
59%6%13%15%6%1
1980
November1st to 10thDay
48%6%11%24%7%2
1672
11th to 20thDay
51%6%18%15%9%1
1526
21st to endDay
62%6%14%13%3
1520
December1st to 10thDay
63%7%15%12%3
1520
11th to 20thDay
67%7%11%9%5%
1906
21st to endDay
76%7%10%6%1
2772
January1st to 10thNight
62%7%10%13%7%
2557
11th to 20thNight
68%6%11%10%5%
2470
21st to endNight
63%6%10%15%5%1
2664
February1st to 10thNight
63%6%11%14%5%
2340
11th to 20thNight
60%5%12%15%7%
2275
21st to endNight
60%5%12%15%7%1
1802
March1st to 10thNight
49%6%13%21%10%1
2008
11th to 20thNight
50%6%9%21%12%2
1980
21st to endNight
52%5%9%19%13%3
2178
April1st to 10thNight
50%6%9%20%13%2
1894
11th to 20thNight
46%5%9%20%17%2
1664
21st to endNight
45%7%10%20%15%3
1620
May1st to 10thNight
46%6%9%22%14%3
1620
11th to 20thNight
42%6%11%23%14%4
1558
21st to endNight
32%6%14%26%19%3
1551
June1st to 10thNight
36%7%12%27%16%3
1440
11th to 20thNight
35%8%13%24%18%2
1379
21st to endNight
33%8%14%25%19%1
1260
July1st to 10thNight
27%6%12%28%23%4
1270
11th to 20thNight
33%5%13%28%18%3
1519
21st to endNight
31%8%15%24%18%3
1672
August1st to 10thNight
32%6%16%31%14%1
1600
11th to 20thNight
30%7%17%31%14%2
1598
21st to endNight
31%8%14%30%16%2
1818
September1st to 10thNight
39%5%13%24%16%3
1813
11th to 20thNight
30%7%11%33%18%1
1980
21st to endNight
41%7%12%26%14%1
1980
October1st to 10thNight
42%6%10%24%16%1
2142
11th to 20thNight
48%6%13%21%11%
2160
21st to endNight
55%5%10%19%10%1
2376
November1st to 10thNight
41%6%13%26%13%1
2404
11th to 20thNight
51%7%14%19%9%1
2651
21st to endNight
58%7%16%14%5%1
2660
December1st to 10thNight
62%7%14%14%4
2660
11th to 20thNight
60%7%14%14%5%
3288
21st to endNight
74%6%11%7%2
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
23%21%32%16%8%2
222
11th to 20thDay
24%18%40%12%5%1
270
21st to endDay
26%19%35%15%5%1
282
February1st to 10thDay
28%18%43%11%1
240
11th to 20thDay
25%24%36%14%1
240
21st to endDay
29%26%34%11%1
198
March1st to 10thDay
23%15%36%20%5%1
391
11th to 20thDay
23%15%37%18%6%1
420
21st to endDay
30%14%29%19%7%
462
April1st to 10thDay
20%17%32%21%8%1
420
11th to 20thDay
24%16%28%18%10%4
412
21st to endDay
25%12%31%21%8%3
420
May1st to 10thDay
24%12%29%20%11%4
423
11th to 20thDay
18%11%28%25%14%4
447
21st to endDay
12%8%23%30%19%8%
485
June1st to 10thDay
13%5%33%32%14%3
450
11th to 20thDay
15%9%25%31%16%5%
504
21st to endDay
12%7%30%32%15%4
630
July1st to 10thDay
9%322%30%26%9%
570
11th to 20thDay
12%5%24%29%19%11%
444
21st to endDay
9%423%34%22%8%
488
August1st to 10thDay
8%221%32%21%15%
446
11th to 20thDay
11%419%30%22%13%
439
21st to endDay
11%421%30%23%11%
495
September1st to 10thDay
12%5%23%29%20%11%
450
11th to 20thDay
7%6%17%29%27%13%
450
21st to endDay
16%9%25%26%16%8%
450
October1st to 10thDay
20%8%26%22%18%6%
450
11th to 20thDay
20%16%31%23%7%2
450
21st to endDay
28%12%32%21%6%1
495
November1st to 10thDay
16%23%34%17%6%3
270
11th to 20thDay
23%23%28%16%7%2
183
21st to endDay
26%21%31%19%3
180
December1st to 10thDay
26%24%29%14%5%1
180
11th to 20thDay
27%24%32%14%4
180
21st to endDay
31%21%31%13%5%
198
January1st to 10thNight
22%18%36%16%7%1
760
11th to 20thNight
28%17%31%22%3
760
21st to endNight
20%13%36%25%5%
820
February1st to 10thNight
25%16%37%20%2
720
11th to 20thNight
23%15%35%23%5%
703
21st to endNight
25%17%34%21%3
592
March1st to 10thNight
18%14%35%27%6%
720
11th to 20thNight
21%11%36%25%7%
720
21st to endNight
23%12%30%26%9%1
792
April1st to 10thNight
22%13%32%27%5%
720
11th to 20thNight
21%11%32%26%9%1
600
21st to endNight
18%8%34%31%9%
540
May1st to 10thNight
20%9%26%30%14%1
540
11th to 20thNight
16%428%38%13%2
496
21st to endNight
11%5%28%37%19%1
389
June1st to 10thNight
13%428%41%14%1
360
11th to 20thNight
10%5%31%41%13%
360
21st to endNight
12%5%24%44%14%
360
July1st to 10thNight
6%221%44%24%3
350
11th to 20thNight
11%418%39%25%3
475
21st to endNight
9%218%47%23%1
591
August1st to 10thNight
7%413%44%30%3
537
11th to 20thNight
10%215%35%34%4
534
21st to endNight
8%321%37%29%3
630
September1st to 10thNight
13%5%18%35%24%4
720
11th to 20thNight
11%316%38%29%4
720
21st to endNight
17%6%21%32%19%6%
720
October1st to 10thNight
17%6%24%32%17%3
720
11th to 20thNight
20%13%30%27%10%1
720
21st to endNight
26%10%31%28%5%
792
November1st to 10thNight
19%10%29%29%11%1
740
11th to 20thNight
21%16%33%21%8%1
760
21st to endNight
27%11%32%22%7%
760
December1st to 10thNight
28%16%33%17%5%1
760
11th to 20thNight
23%17%38%19%4
760
21st to endNight
29%13%33%22%2
836
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