This page made possible by the sponsorship of:
.

Cornwall
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cornwall clear sky chart from 2005-11-05 to 2019-04-11.

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
26%
16728
12%
53381
7%
16697
32%
16697
14%
39487

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
11%
840
7%
2926
2%
836
17%
836
6%
2423
January16th to endNight
15%
896
7%
3114
4%
896
20%
896
7%
2472
February1st to 15thNight
11%
824
8%
2677
2%
821
18%
821
7%
2207
February16th to endNight
17%
735
10%
2229
4%
735
26%
735
11%
1728
March1st to 15thNight
17%
840
11%
2494
6%
840
24%
840
11%
1960
March16th to endNight
27%
896
18%
2342
8%
896
34%
896
20%
1709
April1st to 15thNight
22%
822
15%
2056
5%
822
27%
822
17%
1583
April16th to endNight
26%
706
16%
1862
6%
706
32%
706
20%
1342
May1st to 15thNight
29%
397
17%
1567
13%
397
39%
397
15%
1056
May16th to endNight
31%
406
13%
1625
9%
406
42%
406
16%
1039
June1st to 15thNight
32%
390
9%
1560
9%
390
39%
390
12%
1100
June16th to endNight
36%
390
9%
1560
11%
390
43%
390
19%
977
July1st to 15thNight
47%
370
15%
1480
18%
370
56%
370
27%
819
July16th to endNight
46%
408
13%
1546
14%
386
51%
386
22%
933
August1st to 15thNight
45%
434
14%
1575
12%
432
50%
432
20%
1028
August16th to endNight
46%
809
19%
2051
9%
809
50%
809
33%
1336
September1st to 15thNight
44%
780
17%
1950
8%
780
47%
780
29%
1350
September16th to endNight
43%
777
21%
2109
15%
777
47%
777
28%
1391
October1st to 15thNight
29%
780
16%
2335
10%
780
37%
780
18%
1666
October16th to endNight
20%
832
9%
2629
5%
832
26%
832
11%
2045
November1st to 15thNight
24%
820
14%
2678
10%
820
32%
820
13%
1977
November16th to endNight
19%
840
9%
2940
7%
840
24%
840
8%
2306
December1st to 15thNight
14%
840
6%
2940
2%
840
19%
840
6%
2436
December16th to endNight
12%
896
7%
3136
3%
896
16%
896
6%
2604

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
18%9%36%5%34446%32%
53838
Night
19%10%47%5%34446%30%
53550
Cloud CoverDay
19%9%36%5%34446%31%
53847
Night
19%10%47%5%34445%30%
53556
TransparencyDay
53%6%11%18%9%1
53525
Night
55%6%10%17%9%
53381
SeeingDay
26%15%27%19%8%2
7416
Night
26%13%28%22%8%
16729

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
21%16%6%10%7%35%43417%
1672
16th to endDay
15%16%6%10%7%345%45%20%
1813
February1st to 15thDay
16%13%6%11%7%35%45%419%
1845
16th to endDay
19%15%5%7%7%34335%25%
1816
March1st to 15thDay
20%14%49%6%35%33325%
2114
16th to endDay
19%8%36%423335%38%
2586
April1st to 15thDay
23%9%46%5%33335%30%
2457
16th to endDay
22%9%34433345%35%
2376
May1st to 15thDay
19%6%26%434446%36%
2721
16th to endDay
17%6%35%5%34447%36%
2842
June1st to 15thDay
23%6%36%5%33447%31%
2730
16th to endDay
19%6%245%4446%7%32%
2730
July1st to 15thDay
12%5%244345%5%8%41%
2730
16th to endDay
12%5%25%5%36%6%7%8%36%
2878
August1st to 15thDay
13%6%26%5%36%6%6%6%34%
2627
16th to endDay
11%4245%345%7%7%42%
2490
September1st to 15thDay
17%5%24433446%42%
2340
16th to endDay
15%5%13423446%46%
2181
October1st to 15thDay
22%7%25%6%35%446%32%
1953
16th to endDay
25%10%37%5%2442426%
1945
November1st to 15thDay
18%8%46%5%35%45%7%29%
1840
16th to endDay
23%12%5%7%5%35%345%23%
1680
December1st to 15thDay
22%17%5%9%6%3444416%
1680
16th to endDay
26%16%5%8%6%3424418%
1792
January1st to 15thNight
20%18%6%10%6%3433417%
2926
16th to endNight
15%17%6%8%8%45%345%21%
3114
February1st to 15thNight
15%14%7%13%7%3434420%
2675
16th to endNight
17%13%5%8%7%3444327%
2229
March1st to 15thNight
20%14%47%6%3423427%
2481
16th to endNight
19%10%35%5%2333438%
2342
April1st to 15thNight
25%9%37%5%23335%31%
2056
16th to endNight
21%8%24433336%37%
1862
May1st to 15thNight
20%7%35%5%34445%35%
1567
16th to endNight
18%5%25%4235%5%8%37%
1623
June1st to 15thNight
23%5%26%5%345%5%8%29%
1560
16th to endNight
15%6%25%5%2446%10%36%
1560
July1st to 15thNight
11%214435%47%10%44%
1560
16th to endNight
10%5%24326%5%6%9%42%
1642
August1st to 15thNight
12%6%36%425%5%5%8%38%
1585
16th to endNight
13%3245%3335%7%47%
2051
September1st to 15thNight
16%5%35%43345%7%41%
1950
16th to endNight
16%424423445%46%
2109
October1st to 15thNight
20%7%35%434446%34%
2335
16th to endNight
26%9%36%5%34446%25%
2629
November1st to 15thNight
22%10%36%424435%31%
2678
16th to endNight
23%12%5%7%6%24445%24%
2940
December1st to 15thNight
22%16%5%8%6%4444418%
2940
16th to endNight
24%17%5%8%6%3443418%
3136

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
22%15%6%10%7%45%33317%
1672
16th to endDay
15%17%5%10%7%35%445%19%
1813
February1st to 15thDay
17%13%6%11%8%35%45%419%
1845
16th to endDay
18%16%5%7%6%34335%24%
1816
March1st to 15thDay
19%15%5%9%5%4434325%
2124
16th to endDay
19%9%45%423335%38%
2585
April1st to 15thDay
23%10%36%5%3334430%
2457
16th to endDay
23%8%34324346%34%
2376
May1st to 15thDay
19%6%35%5%34346%35%
2721
16th to endDay
17%6%25%435%448%36%
2842
June1st to 15thDay
23%6%26%5%3445%7%30%
2730
16th to endDay
20%435%5%345%6%8%32%
2730
July1st to 15thDay
12%5%244345%5%7%41%
2730
16th to endDay
12%5%246%36%6%7%8%36%
2878
August1st to 15thDay
13%6%26%6%46%6%6%7%33%
2627
16th to endDay
11%4245%45%5%5%8%42%
2490
September1st to 15thDay
17%5%15%424446%42%
2340
16th to endDay
16%42432345%6%45%
2181
October1st to 15thDay
22%7%35%6%25%346%32%
1953
16th to endDay
26%11%36%5%335%3426%
1945
November1st to 15thDay
19%9%46%444447%29%
1840
16th to endDay
22%15%48%5%2443423%
1680
December1st to 15thDay
23%17%6%8%6%35%44415%
1680
16th to endDay
26%17%5%8%5%34345%16%
1792
January1st to 15thNight
19%18%6%11%6%24335%17%
2926
16th to endNight
15%17%6%8%8%4434421%
3114
February1st to 15thNight
16%14%7%14%8%3434419%
2668
16th to endNight
17%13%5%9%6%3434426%
2229
March1st to 15thNight
21%14%5%7%7%3323426%
2494
16th to endNight
20%10%45%42323436%
2342
April1st to 15thNight
25%9%37%5%24335%30%
2056
16th to endNight
22%7%35%433345%37%
1862
May1st to 15thNight
21%6%25%43435%5%35%
1567
16th to endNight
18%5%25%5%3445%7%37%
1623
June1st to 15thNight
23%6%25%5%4446%7%28%
1560
16th to endNight
16%6%2442445%10%37%
1560
July1st to 15thNight
11%323425%47%9%45%
1560
16th to endNight
10%5%335%246%6%9%41%
1642
August1st to 15thNight
12%6%36%5%345%6%8%38%
1585
16th to endNight
14%3245%3345%7%46%
2051
September1st to 15thNight
16%425%5%3445%6%42%
1950
16th to endNight
16%42442435%5%45%
2109
October1st to 15thNight
21%7%35%5%2435%6%34%
2335
16th to endNight
27%10%36%6%34346%24%
2629
November1st to 15thNight
22%10%35%6%23445%30%
2678
16th to endNight
24%12%47%6%3344423%
2940
December1st to 15thNight
22%17%6%8%5%3443417%
2940
16th to endNight
24%16%5%9%5%3343417%
3136

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
72%47%9%5%
1673
16th to endDay
65%6%11%12%4
1813
February1st to 15thDay
67%6%8%14%3
1847
16th to endDay
63%5%10%11%8%
1816
March1st to 15thDay
64%410%12%7%
2124
16th to endDay
49%49%16%15%3
2586
April1st to 15thDay
57%38%17%11%2
2457
16th to endDay
50%5%8%17%14%3
2376
May1st to 15thDay
48%6%8%19%15%1
2721
16th to endDay
46%7%11%19%12%1
2846
June1st to 15thDay
53%6%11%18%9%
2730
16th to endDay
48%7%12%19%11%1
2730
July1st to 15thDay
38%7%12%28%11%
2581
16th to endDay
41%10%15%23%8%
2711
August1st to 15thDay
46%10%15%20%7%
2613
16th to endDay
37%8%16%25%11%
2490
September1st to 15thDay
41%6%12%25%13%
2340
16th to endDay
38%6%12%30%10%
2181
October1st to 15thDay
53%5%12%19%8%
1953
16th to endDay
61%6%12%14%5%
1945
November1st to 15thDay
54%7%13%17%7%1
1840
16th to endDay
64%5%10%12%6%
1680
December1st to 15thDay
71%6%9%10%2
1680
16th to endDay
71%5%9%8%4
1792
January1st to 15thNight
70%5%10%9%4
2926
16th to endNight
65%5%9%12%5%
3114
February1st to 15thNight
69%5%8%12%3
2677
16th to endNight
61%410%14%8%
2229
March1st to 15thNight
62%49%15%6%
2494
16th to endNight
52%39%17%13%4
2342
April1st to 15thNight
57%48%17%12%
2056
16th to endNight
49%5%8%17%16%3
1862
May1st to 15thNight
48%7%7%16%17%3
1567
16th to endNight
44%8%12%20%13%1
1625
June1st to 15thNight
53%7%12%15%10%
1560
16th to endNight
42%8%14%21%13%
1560
July1st to 15thNight
31%8%14%27%17%
1480
16th to endNight
37%9%13%23%15%
1546
August1st to 15thNight
41%9%17%20%10%
1575
16th to endNight
36%6%14%29%12%
2051
September1st to 15thNight
41%7%11%26%12%
1950
16th to endNight
38%7%10%30%11%
2109
October1st to 15thNight
49%6%11%22%8%
2335
16th to endNight
60%6%12%14%4
2629
November1st to 15thNight
55%6%12%15%8%1
2678
16th to endNight
63%6%10%13%4
2940
December1st to 15thNight
70%5%9%10%2
2940
16th to endNight
70%6%9%9%3
3136

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
35%15%25%17%5%
120
16th to endDay
33%21%31%12%
134
February1st to 15thDay
47%24%25%2
180
16th to endDay
34%20%27%15%2
319
March1st to 15thDay
33%20%28%12%5%
390
16th to endDay
27%23%24%15%8%1
416
April1st to 15thDay
35%18%29%11%5%
372
16th to endDay
33%13%24%15%10%1
319
May1st to 15thDay
27%17%26%16%9%2
348
16th to endDay
21%18%31%17%9%
395
June1st to 15thDay
29%12%30%21%6%1
375
16th to endDay
21%13%33%22%7%1
375
July1st to 15thDay
14%7%30%30%13%2
365
16th to endDay
15%6%32%31%10%3
390
August1st to 15thDay
18%8%28%27%11%5%
358
16th to endDay
12%8%29%28%13%7%
396
September1st to 15thDay
18%7%26%22%15%9%
375
16th to endDay
16%12%26%21%16%6%
374
October1st to 15thDay
25%16%28%15%12%3
375
16th to endDay
36%19%24%16%3
358
November1st to 15thDay
30%15%28%14%10%
314
16th to endDay
40%20%20%15%3
120
December1st to 15thDay
30%22%25%16%3
120
16th to endDay
46%22%17%11%1
128
January1st to 15thNight
32%19%29%15%3
840
16th to endNight
26%20%29%18%4
896
February1st to 15thNight
27%19%32%18%1
824
16th to endNight
27%17%32%21%2
735
March1st to 15thNight
32%16%29%18%3
840
16th to endNight
26%14%25%25%7%
896
April1st to 15thNight
31%14%28%21%4
822
16th to endNight
29%12%28%21%8%
706
May1st to 15thNight
26%9%29%24%9%1
397
16th to endNight
19%10%33%28%8%
407
June1st to 15thNight
25%8%26%31%6%
390
16th to endNight
18%5%32%30%10%1
390
July1st to 15thNight
10%6%30%36%15%
370
16th to endNight
12%5%31%37%12%
408
August1st to 15thNight
15%325%35%18%1
434
16th to endNight
15%427%31%19%1
809
September1st to 15thNight
19%5%25%32%14%2
780
16th to endNight
19%9%23%23%21%2
777
October1st to 15thNight
24%11%28%22%11%
780
16th to endNight
34%14%26%19%5%
832
November1st to 15thNight
29%15%25%20%8%
820
16th to endNight
32%17%23%17%7%
840
December1st to 15thNight
33%19%26%17%3
840
16th to endNight
36%14%30%15%3
896
Page generated at 2019-04-12 19:23:21. Version ac04

Copyright 2019 A. Danko


Cornwall Clear Sky Chart |Charts Home