Truro
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Truro clear sky chart from 2005-11-06 to 2024-01-12.

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
19%
23774
11%
74457
4%
23709
26%
23709
12%
56494

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
11%
850
7%
2649
1%
847
17%
847
6%
2193
January11th to 20thNight
13%
806
7%
2535
1%
806
18%
806
7%
2077
January21st to endNight
15%
792
11%
2574
3%
792
24%
792
9%
1961
February1st to 10thNight
12%
720
8%
2340
3%
720
19%
720
8%
1831
February11th to 20thNight
10%
703
9%
2276
1%
700
19%
700
7%
1804
February21st to endNight
16%
592
12%
1878
3%
592
25%
592
11%
1436
March1st to 10thNight
14%
720
13%
2028
4%
720
22%
720
10%
1623
March11th to 20thNight
20%
720
13%
1980
4%
720
27%
720
13%
1525
March21st to endNight
18%
770
12%
2156
4%
770
26%
770
14%
1665
April1st to 10thNight
13%
540
11%
1800
4%
540
21%
540
9%
1384
April11th to 20thNight
18%
534
14%
1737
6%
534
27%
534
13%
1252
April21st to endNight
17%
540
12%
1620
5%
540
24%
540
13%
1232
May1st to 10thNight
16%
540
12%
1512
5%
540
23%
540
12%
1176
May11th to 20thNight
21%
532
13%
1417
5%
532
27%
532
17%
1070
May21st to endNight
14%
583
9%
1551
2%
582
20%
582
17%
1169
June1st to 10thNight
16%
540
8%
1440
3%
540
20%
540
14%
1136
June11th to 20thNight
20%
499
12%
1399
4%
499
26%
499
19%
998
June21st to endNight
25%
360
6%
1260
3%
360
29%
360
12%
941
July1st to 10thNight
30%
431
7%
1306
3%
431
35%
431
21%
929
July11th to 20thNight
30%
522
8%
1392
5%
522
33%
522
20%
1030
July21st to endNight
32%
590
10%
1493
8%
558
34%
558
18%
1134
August1st to 10thNight
35%
538
11%
1600
7%
534
37%
534
23%
1103
August11th to 20thNight
32%
532
11%
1596
7%
532
36%
532
16%
1183
August21st to endNight
38%
594
14%
1898
9%
594
43%
594
22%
1254
September1st to 10thNight
32%
540
15%
1800
9%
540
40%
540
22%
1137
September11th to 20thNight
30%
562
18%
1822
12%
562
38%
562
21%
1191
September21st to endNight
25%
720
16%
2064
8%
720
33%
720
20%
1427
October1st to 10thNight
31%
720
17%
2160
9%
720
37%
720
20%
1478
October11th to 20thNight
23%
720
16%
2160
6%
720
32%
720
18%
1511
October21st to endNight
16%
806
13%
2403
5%
806
23%
806
11%
1852
November1st to 10thNight
18%
830
11%
2529
4%
830
25%
830
12%
1928
November11th to 20thNight
18%
850
12%
2660
5%
850
25%
850
10%
2039
November21st to endNight
14%
850
8%
2660
2%
850
20%
850
9%
2103
December1st to 10thNight
11%
850
8%
2660
1%
850
19%
850
8%
2158
December11th to 20thNight
8%
850
9%
3242
1%
849
16%
849
6%
2668
December21st to endNight
10%
928
4%
4860
1%
907
17%
907
4%
3896

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
22%11%47%6%3445%6%28%
74992
Night
22%11%47%5%34446%28%
74703
TransparencyDay
57%7%12%16%8%1
74696
Night
57%7%12%16%7%1
74534
SeeingDay
31%20%29%15%41
16268
Night
29%16%31%19%4
23781

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
18%20%6%10%7%3435%5%18%
1516
11th to 20thDay
24%17%410%6%44445%18%
1448
21st to endDay
15%12%6%10%8%345%47%25%
1778
February1st to 10thDay
20%15%5%10%8%3344424%
1620
11th to 20thDay
19%14%5%12%7%34435%24%
1573
21st to endDay
12%15%8%8%7%34346%30%
1376
March1st to 10thDay
16%16%6%10%8%44445%25%
1926
11th to 20thDay
16%12%6%10%9%35%435%27%
1980
21st to endDay
19%17%8%8%5%23335%27%
2199
April1st to 10thDay
27%15%5%6%5%3344424%
2160
11th to 20thDay
22%12%35%6%2445%6%31%
2171
21st to endDay
26%13%46%5%2445%5%25%
2340
May1st to 10thDay
30%12%36%5%45%446%22%
2447
11th to 20thDay
24%10%36%5%2335%6%32%
2478
21st to endDay
25%10%46%5%34447%28%
2724
June1st to 10thDay
29%10%36%6%3445%6%23%
2520
11th to 20thDay
24%9%35%5%3445%7%32%
2571
21st to endDay
30%9%45%5%3445%6%26%
2700
July1st to 10thDay
19%7%36%5%345%5%9%35%
2588
11th to 20thDay
19%7%35%5%35%5%7%8%33%
2520
21st to endDay
23%10%37%5%245%5%7%28%
2735
August1st to 10thDay
18%7%26%6%346%7%9%33%
2327
11th to 20thDay
20%8%26%5%35%5%5%8%31%
2304
21st to endDay
16%6%25%5%345%6%8%40%
2456
September1st to 10thDay
19%6%35%5%2436%7%40%
2160
11th to 20thDay
22%7%35%43445%5%38%
2135
21st to endDay
22%7%25%43435%6%39%
1895
October1st to 10thDay
19%8%36%6%3446%7%36%
1800
11th to 20thDay
23%9%36%5%35%5%6%7%29%
1800
21st to endDay
24%12%47%7%34445%27%
1951
November1st to 10thDay
24%12%47%6%45%335%27%
1545
11th to 20thDay
23%14%48%5%34435%27%
1520
21st to endDay
19%16%6%8%7%34435%24%
1520
December1st to 10thDay
25%16%6%9%5%34335%22%
1520
11th to 20thDay
32%15%5%8%5%2334420%
1906
21st to endDay
23%15%11%11%5%24345%16%
2783
January1st to 10thNight
20%16%7%9%7%45%45%5%19%
2649
11th to 20thNight
22%15%6%9%6%44445%21%
2535
21st to endNight
17%12%5%10%8%345%5%6%26%
2574
February1st to 10thNight
20%14%410%7%34346%23%
2340
11th to 20thNight
19%15%5%10%7%33446%23%
2273
21st to endNight
13%13%5%10%8%35%445%29%
1878
March1st to 10thNight
16%15%6%11%7%44445%24%
2019
11th to 20thNight
19%11%6%7%6%35%5%5%6%28%
1979
21st to endNight
19%13%6%9%5%24345%30%
2156
April1st to 10thNight
26%14%47%5%3334427%
1800
11th to 20thNight
23%12%35%425%445%33%
1737
21st to endNight
26%12%36%424446%28%
1620
May1st to 10thNight
29%12%45%5%35%335%27%
1512
11th to 20thNight
25%11%25%5%3445%432%
1416
21st to endNight
20%11%46%5%3445%8%30%
1550
June1st to 10thNight
28%9%36%6%2335%6%27%
1440
11th to 20thNight
23%8%45%32445%7%35%
1399
21st to endNight
27%8%37%5%335%6%6%26%
1260
July1st to 10thNight
18%8%37%5%346%6%9%31%
1345
11th to 20thNight
19%6%25%5%45%7%6%8%33%
1440
21st to endNight
20%7%37%7%445%5%9%30%
1580
August1st to 10thNight
17%7%25%5%35%5%5%8%37%
1612
11th to 20thNight
20%9%27%5%446%6%7%31%
1596
21st to endNight
17%5%35%5%35%6%5%7%40%
1898
September1st to 10thNight
17%6%35%4345%5%8%42%
1800
11th to 20thNight
21%7%35%423447%41%
1822
21st to endNight
21%6%35%5%34346%39%
2064
October1st to 10thNight
21%7%25%5%2445%7%37%
2160
11th to 20thNight
21%8%36%43445%8%35%
2160
21st to endNight
28%11%36%6%33445%27%
2403
November1st to 10thNight
24%11%46%5%35%446%30%
2529
11th to 20thNight
22%13%46%5%3446%5%27%
2660
21st to endNight
23%14%6%7%5%33346%25%
2660
December1st to 10thNight
26%13%49%6%24445%22%
2660
11th to 20thNight
33%14%47%5%2233422%
3293
21st to endNight
27%15%6%11%5%3434420%
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
69%6%10%10%41
1517
11th to 20thDay
69%7%9%9%6%
1448
21st to endDay
60%6%12%13%8%
1778
February1st to 10thDay
65%5%10%12%8%1
1620
11th to 20thDay
65%6%10%13%6%1
1581
21st to endDay
59%410%16%10%2
1376
March1st to 10thDay
63%6%8%15%8%1
1930
11th to 20thDay
62%6%9%14%8%2
1980
21st to endDay
63%49%15%8%2
2199
April1st to 10thDay
65%5%7%13%8%3
2160
11th to 20thDay
54%6%11%17%12%1
2171
21st to endDay
60%7%10%15%7%1
2340
May1st to 10thDay
63%6%9%13%7%1
2447
11th to 20thDay
54%7%11%18%10%
2482
21st to endDay
57%7%12%16%8%
2724
June1st to 10thDay
62%7%10%16%5%1
2520
11th to 20thDay
52%7%13%18%9%1
2571
21st to endDay
61%6%10%13%9%
2700
July1st to 10thDay
45%10%16%21%8%
2518
11th to 20thDay
48%9%15%20%8%1
2444
21st to endDay
55%9%13%17%5%
2582
August1st to 10thDay
48%10%16%19%7%
2314
11th to 20thDay
50%10%15%19%6%
2304
21st to endDay
42%7%16%24%10%1
2456
September1st to 10thDay
44%7%14%23%11%1
2160
11th to 20thDay
48%6%13%21%12%1
2135
21st to endDay
47%6%11%23%13%
1895
October1st to 10thDay
48%7%12%23%10%
1800
11th to 20thDay
54%8%14%18%6%
1800
21st to endDay
60%5%12%17%6%
1951
November1st to 10thDay
60%8%9%16%7%
1545
11th to 20thDay
60%6%14%13%6%1
1520
21st to endDay
63%7%13%12%4
1520
December1st to 10thDay
67%5%11%13%4
1520
11th to 20thDay
70%6%9%11%4
1905
21st to endDay
71%7%11%7%3
2783
January1st to 10thNight
68%7%11%11%3
2649
11th to 20thNight
67%6%10%10%5%1
2535
21st to endNight
60%6%13%15%6%1
2574
February1st to 10thNight
64%5%10%13%7%1
2340
11th to 20thNight
64%6%11%12%6%1
2276
21st to endNight
58%7%10%15%8%1
1878
March1st to 10thNight
63%6%9%14%8%
2028
11th to 20thNight
56%8%11%15%9%2
1980
21st to endNight
58%6%10%16%8%2
2156
April1st to 10thNight
63%5%8%12%9%3
1800
11th to 20thNight
55%6%8%18%12%1
1737
21st to endNight
58%6%11%14%10%1
1620
May1st to 10thNight
59%6%8%17%9%
1512
11th to 20thNight
54%6%10%21%8%1
1417
21st to endNight
52%8%15%18%6%1
1551
June1st to 10thNight
59%7%10%18%6%
1440
11th to 20thNight
50%6%12%20%11%1
1399
21st to endNight
58%7%14%13%7%1
1260
July1st to 10thNight
46%9%19%17%8%
1306
11th to 20thNight
48%11%14%18%9%1
1392
21st to endNight
52%9%15%17%6%
1493
August1st to 10thNight
43%9%17%24%6%
1600
11th to 20thNight
51%11%15%18%5%
1596
21st to endNight
42%8%17%25%8%
1898
September1st to 10thNight
41%7%14%27%11%1
1800
11th to 20thNight
45%5%12%25%12%1
1822
21st to endNight
47%7%12%23%11%1
2064
October1st to 10thNight
46%6%13%23%11%
2160
11th to 20thNight
49%6%14%24%7%
2160
21st to endNight
60%5%11%16%8%
2403
November1st to 10thNight
55%9%12%16%7%
2529
11th to 20thNight
57%9%13%13%7%
2660
21st to endNight
62%7%14%13%3
2660
December1st to 10thNight
65%7%11%13%4
2660
11th to 20thNight
68%5%9%12%6%
3295
21st to endNight
68%7%12%10%4
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
38%19%29%14%1
370
11th to 20thDay
35%23%27%11%4
343
21st to endDay
27%23%34%13%3
374
February1st to 10thDay
35%24%28%11%1
340
11th to 20thDay
39%26%21%13%1
336
21st to endDay
30%21%33%11%41
280
March1st to 10thDay
26%28%33%10%21
398
11th to 20thDay
33%25%27%11%4
420
21st to endDay
35%29%24%9%3
462
April1st to 10thDay
45%25%21%7%2
420
11th to 20thDay
34%27%26%10%2
412
21st to endDay
35%19%30%13%3
420
May1st to 10thDay
39%20%26%9%41
530
11th to 20thDay
30%20%29%16%41
624
21st to endDay
32%20%30%15%2
680
June1st to 10thDay
38%16%28%14%4
630
11th to 20thDay
30%16%32%18%31
630
21st to endDay
35%13%27%19%5%1
630
July1st to 10thDay
23%15%34%22%5%
620
11th to 20thDay
23%10%36%22%8%
618
21st to endDay
29%12%32%21%6%
675
August1st to 10thDay
17%13%39%25%5%1
446
11th to 20thDay
25%15%32%18%10%1
439
21st to endDay
18%17%32%24%8%2
495
September1st to 10thDay
20%17%33%22%6%1
450
11th to 20thDay
29%19%26%20%5%1
450
21st to endDay
24%19%30%16%9%1
408
October1st to 10thDay
23%16%32%19%8%3
360
11th to 20thDay
29%19%28%14%9%1
360
21st to endDay
32%26%25%11%6%1
396
November1st to 10thDay
33%21%26%14%5%1
365
11th to 20thDay
37%21%24%14%41
370
21st to endDay
35%24%28%10%31
370
December1st to 10thDay
38%21%28%12%1
370
11th to 20thDay
44%24%23%9%1
370
21st to endDay
32%25%28%11%31
407
January1st to 10thNight
32%20%31%15%2
850
11th to 20thNight
33%19%30%15%3
806
21st to endNight
27%22%33%15%3
792
February1st to 10thNight
31%19%33%17%1
720
11th to 20thNight
34%27%25%12%2
703
21st to endNight
22%24%33%17%4
592
March1st to 10thNight
25%23%33%17%2
720
11th to 20thNight
26%19%27%22%5%
720
21st to endNight
29%19%30%18%4
770
April1st to 10thNight
36%18%29%15%1
540
11th to 20thNight
30%18%31%16%5%
534
21st to endNight
33%16%32%16%31
540
May1st to 10thNight
34%14%31%16%5%
540
11th to 20thNight
29%13%33%20%31
532
21st to endNight
23%16%43%15%3
583
June1st to 10thNight
35%13%33%16%3
540
11th to 20thNight
27%13%37%21%2
499
21st to endNight
30%8%31%26%5%
360
July1st to 10thNight
23%6%36%30%5%
431
11th to 20thNight
21%7%37%29%6%
522
21st to endNight
23%8%31%32%6%
590
August1st to 10thNight
18%7%34%33%7%1
538
11th to 20thNight
23%8%31%29%8%1
532
21st to endNight
20%7%32%33%8%1
594
September1st to 10thNight
20%8%36%29%7%
540
11th to 20thNight
26%10%29%25%9%
562
21st to endNight
25%13%32%22%6%1
720
October1st to 10thNight
27%12%26%27%8%1
720
11th to 20thNight
25%14%33%19%8%1
720
21st to endNight
35%18%28%16%4
806
November1st to 10thNight
33%15%29%18%5%1
830
11th to 20thNight
30%22%26%18%4
850
21st to endNight
34%22%26%17%2
850
December1st to 10thNight
35%18%30%14%2
850
11th to 20thNight
37%23%27%11%1
850
21st to endNight
33%23%26%15%21
935
Page generated at 2024-01-08 23:31:26. Version ac07

Copyright 2024 Attilla Danko


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